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Boiling point of propane as a function of pressure. Comparison of liquefied petroleum gas (LPG) and liquefied natural gas (LNG)

Liquefied hydrocarbon gases - propane-butane, hereinafter LPG - mixtures of hydrocarbons, which, when normal conditions are in a gaseous state, and with a slight increase in pressure and a constant temperature or a slight decrease in temperature and atmospheric pressure, they pass from a gaseous state to a liquid state.

LPG is a propane-butane mixture. The composition of liquefied gas also includes in small quantities: propylene, butylene, ethane, ethylene, methane and a liquid non-evaporating residue - pentane, hexane.

The raw materials for the production of LPG are mainly petroleum associated gases, gas condensate deposits and gases obtained in the process of oil refining.

From LPG plants in railway tanks it goes to gas filling stations (GFS) of gas facilities, where it is stored in special tanks until it is released to consumers. LPG is delivered to consumers in cylinders or tank trucks -

Introduction

Liquefied hydrocarbon gases (LHG) - a mixture of light hydrocarbons liquefied under pressure with a boiling point of? 50 to 0 ° C. Designed for use as a fuel. Main components: propane, propylene, isobutane, isobutylene, n-butane and butylene.

It is produced mainly from associated petroleum gas. It is transported and stored in cylinders and gas holders. It is used for cooking, boiling water, heating, used in lighters, as fuel for vehicles.

Liquefied hydrocarbon gases(propane-butane, hereinafter referred to as LPG) - mixtures of hydrocarbons that under normal conditions are in a gaseous state, and with a slight increase in pressure or a slight decrease in temperature, they pass from a gaseous state to a liquid state.

The main components of LPG are propane and butane. Propane-butane (liquefied petroleum gas, LPG, in English - liquifiedpetroleumgas, LPG) is a mixture of two gases. The composition of liquefied gas also includes in small quantities: propylene, butylene, ethane, ethylene, methane and a liquid non-evaporating residue (pentane, hexane).

The raw materials for the production of LPG are mainly petroleum associated gases, gas condensate deposits and gases obtained in the process of oil refining. liquefied hydrocarbon propane refinery

From LPG plants in railway tanks it goes to gas filling stations (GFS) of gas facilities, where it is stored in special tanks until sold (released) to consumers. LPG is delivered to consumers in cylinders or tankers.

In vessels (tanks, tanks, cylinders) for storage and transportation, LPG is simultaneously in 2 phases: liquid and vapor. LPG is stored and transported in liquid form under pressure, which is created by its own gas vapors. This property makes LPG a convenient source of fuel supply for domestic and industrial consumers, because liquefied gas during storage and transportation in the form of a liquid occupies hundreds of times less volume than gas in its natural (gaseous or vaporous) state, and is distributed through gas pipelines and used (burned) in gaseous form.

Liquefied hydrocarbon gases (LHG) consist of simple hydrocarbon compounds, which are organic substances containing in their composition 2 chemical elements - carbon (C) and hydrogen (H). Hydrocarbons differ from each other in the number of carbon and hydrogen atoms in the molecule, as well as the nature of the bonds between them.

Commercial liquefied gas must consist of hydrocarbons, which are gases under normal conditions, and with a relatively small increase in pressure and temperature environment or a slight decrease in temperature at atmospheric pressure, they change from a gaseous state to a liquid state.

The simplest hydrocarbon containing only one carbon atom is methane (CH 4). It is the main component of natural as well as some artificial combustible gases. The next carbon in this series - ethane (C 2 H 6) - has 2 carbon atoms. A hydrocarbon with three carbon atoms is propane (C 3 H 8), and with four - butane (C 4 H 10).

All hydrocarbons of this type have general formula C n H 2n+2 and lead to homologous series saturated hydrocarbons - compounds in which carbon is saturated to the limit with hydrogen atoms. Under normal conditions, only methane, ethane, propane and butane are gases from saturated hydrocarbons.

To obtain liquefied gases, natural gases extracted from the bowels of the Earth are currently widely used, which are a mixture of various hydrocarbons, mainly of the methane series (saturated hydrocarbons). Natural gases from pure gas fields are mostly methane and are lean or dry; heavy hydrocarbons (from propane and above) contain less than 50 g/cm 3 . Associated gases emitted from wells oil fields Together with oil, in addition to methane, they contain a significant amount of heavier hydrocarbons (usually more than 150 g / m 3) and are fatty. Gases that are produced from condensate deposits consist of a mixture of dry gas and condensate vapor. Condensate vapors are a mixture of vapors of heavy hydrocarbons (C3, C4, gasoline, naphtha, kerosene). At gas processing plants, propane-butane fraction is separated from associated gases.

WFLH - a wide fraction of light hydrocarbons, includes mainly a mixture of light hydrocarbons of ethane (C 2) and hexane (C 6) fractions. In general, a typical NGL composition is as follows: ethane from 2 to 5%; liquefied gas fractions C 4 -C 5 40-85%; hexane fraction C 6 from 15 to 30%, the pentane fraction accounts for the remainder.

Given the widespread use of LPG in the gas industry, it is necessary to dwell in more detail on the properties of propane and butane.

Propamn is an organic substance of the alkane class. Contained in natural gas, formed during the cracking of petroleum products. Chemical formula C 3 H 8 (Fig. 1). Colorless, odorless gas, very slightly soluble in water. Boiling point? 42.1C. Forms explosive mixtures with air at vapor concentrations from 2.1 to 9.5%. The self-ignition temperature of propane in air at a pressure of 0.1 MPa (760 mm Hg) is 466 °C.

Propane is used as a fuel, the main component of the so-called liquefied hydrocarbon gases, in the production of monomers for the synthesis of polypropylene. It is the raw material for the production of solvents. In the food industry, propane is registered as a food additive E944, as a propellant.

Butamn (C 4 H 10) is an organic compound of the alkane class. In chemistry, the name is mainly used to refer to n-butane. Chemical formula C4H10 (Fig. 1). The mixture of n-butane and its isomer isobutane CH(CH 3) 3 has the same name. Colourless, flammable gas, odorless, easily liquefied (below 0 °C and normal pressure, or at elevated pressure and normal temperature, a highly volatile liquid). Contained in gas condensate and petroleum gas (up to 12%). It is a product of catalytic and hydrocatalytic cracking of oil fractions.

The production of both liquefied gas and NGLs is carried out at the expense of the following three main sources:

? oil production enterprises - the production of LPG and NGL occurs during the production of crude oil during the processing of associated (bound) gas and the stabilization of crude oil;
? gas production enterprises - obtaining LPG and NGL occurs during the primary processing of well gas or free gas and condensate stabilization;
? oil refineries - the production of liquefied gas and similar NGLs occurs during the processing of crude oil at refineries. In this category, NGL consists of a mixture of butane-hexane fractions (C4-C6) with a small amount of ethane and propane.

The main advantage of LPG is the possibility of their existence at ambient temperature and moderate pressures, both in liquid and gaseous states. In the liquid state they are easily processed, stored and transported, in the gaseous state they have a better combustion characteristic.

The state of hydrocarbon systems is determined by a combination of influences of various factors, therefore, for a complete characterization, it is necessary to know all the parameters. The main parameters that can be directly measured and affect the LPG flow regimes include pressure, temperature, density, viscosity, concentration of components, and phase ratio.

The system is in equilibrium if all parameters remain unchanged. In this state, there are no visible qualitative and quantitative changes in the system. A change in at least one parameter violates the equilibrium state of the system, causing that

or some other process.

During storage and transportation, liquefied gases constantly change their state of aggregation, part of the gas evaporates and turns into a gaseous state, and part condenses, turning into a liquid state. In cases where the amount of evaporated liquid is equal to the amount of condensed vapor, the liquid-gas system reaches equilibrium and the vapor above the liquid becomes saturated, and their pressure is called saturation pressure or vapor pressure.

pressure and temperature. The pressure of a gas is the total result of the collision of molecules against the walls of a vessel occupied by this gas.

The elasticity (pressure) of saturated gas vapor * p p is the most important parameter by which the working pressure in tanks and cylinders is determined. The temperature of the gas determines the degree of its heating, i.e. a measure of the intensity of the movement of its molecules. The pressure and temperature of liquefied gases strictly correspond to each other.

The vapor pressure of LPG - saturated (boiling) liquids - varies in proportion to the temperature of the liquid phase (see Fig. I-1) and is a value strictly defined for a given temperature. All equations relating the physical parameters of a gas or liquid substance include absolute pressure and temperature, and equations for technical calculations (strength of the walls of cylinders, tanks) include excess pressure.

The vapor pressure of LPG increases with increasing temperature and decreases with decreasing temperature.

This property of liquefied gases is one of the determining factors in the design of storage and distribution systems. When a boiling liquid is taken from tanks and transported through a pipeline, part of the liquid evaporates due to pressure losses, a two-phase flow is formed, the vapor pressure of which depends on the flow temperature, which is lower than the temperature in the tank. In the event that the movement of a two-phase liquid through the pipeline stops, the pressure at all points equalizes and becomes equal to the vapor pressure.

Liquefied hydrocarbon gases are transported in railway and road tanks, stored in tanks of various volumes in a state of saturation: boiling liquid is placed in the lower part of the vessels, and dry saturated vapors are in the upper part (Fig. 2). When the temperature in the tanks decreases, part of the vapors will condense, i.e. the mass of the liquid increases and the mass of the vapor decreases, a new equilibrium state occurs. As the temperature rises, the reverse process occurs until the phases are in equilibrium at the new temperature. Thus, evaporation and condensation processes occur in tanks and pipelines, which in two-phase media proceed at constant pressure and temperature, while the evaporation and condensation temperatures are equal.

Figure 2. Phase states of liquefied gases during storage.

IN real conditions Liquefied gases contain some amount of water vapor. Moreover, their amount in gases can increase to saturation, after which moisture from gases precipitates in the form of water and mixes with liquid hydrocarbons to the limiting degree of solubility, and then free water is released, which settles in tanks. The amount of water in LPG depends on their hydrocarbon composition, thermodynamic state and temperature. It has been proven that if the temperature of LPG is reduced by 15-30 0 C, then the solubility of water will decrease by 1.5-2 times and free water will accumulate at the bottom of the tank or fall out in the form of condensate in pipelines. The water accumulated in the tanks must be periodically removed, otherwise it can get to the consumer or lead to equipment failure.

According to the LPG test methods, the presence of only free water is determined, the presence of dissolved water is allowed.

Abroad, there are more stringent requirements for the presence of water in LPG and its amount, through filtration, it is brought to 0.001% by weight. This is justified, since dissolved water in liquefied gases is a pollutant, because even at positive temperatures it forms solid compounds in the form of hydrates.

Density. Mass per unit volume, i.e. the ratio of the mass of a substance at rest to the volume it occupies is called density (notation). The unit of density in the SI system is kilogram per cubic meter (kg / m 3). In general

When moving liquefied gases with a pressure below the vapor pressure, i.e. when moving two-phase flows, to determine the density at a point, you should use the ratio limit:

In numerous calculations, especially in the field of thermodynamics of gases and gas-liquid mixtures, one often has to use the concept of relative density d - the ratio of the density of a given substance to the density of a given substance to the density of a substance, taken as specific or standard c,

For solid and liquid substances, the density of distilled water at a pressure of 760 mm Hg is taken as standard. and a temperature of 3.98ºС (999.973 kg / m 3 1 t / m 3), for gases - the density of dry atmospheric air at a pressure of 760 mm Hg. and a temperature of 0 ºС (1.293 kg / m 3).

Figure I-2 shows the density curves of the saturated liquid and vapor phases of the main components of liquefied gases as a function of temperature. The black dot on each curve indicates the critical density. This point of inflection of the density curve corresponds to the critical temperature at which the density of the vapor phase is equal to the density of the liquid phase. The branch of the curve located above the critical point gives the density of the saturated liquid phase, and below - the saturated vapor. The critical points of saturated hydrocarbons are connected by a solid line, and those of unsaturated hydrocarbons by a dashed line. Density can also be determined from state diagrams. IN general view the dependence of density on temperature is expressed next

T \u003d T0 + (T-T 0) + (T-T 0) 2 + (T-T 0) 2 ±.

The influence of the third and other members of this series on the density value due to small values is insignificant, therefore, with an accuracy quite sufficient for technical calculations, it can be neglected. Then

T \u003d T0 + (T-T 0)

Where = 1.354 for propane, 1.068 for n-butane, 1.145 for isobutane.

The relative change in the volume of a liquid with a change in temperature by one degree is characterized by the temperature coefficient of volumetric expansion, W, which for liquefied gases (propane and butane) is several times greater than for other liquids.

Propane - 3.06 * 10 -3;

Butane - 2.12 * 10 -3;

Kerosene - 0.95 * 10 -3;

Water - 0.19 * 10 -3;

When the pressure increases, the liquid phase of propane and butane is compressed. Its degree of compression is estimated by the coefficient of volumetric compressibility vszh, the dimension of which is inverse to the dimension of pressure.

Specific volume. The volume of a unit mass of a substance is called the specific volume (designation). The unit of specific volume in the SI system is a cubic meter per kilogram (m 3 / kg)

Specific volume and density are reciprocals, i.e.

Unlike most liquids, which slightly change their volume with temperature changes, the liquid phase of liquefied gases increases its volume quite sharply with increasing temperature (15 times more than water). When filling tanks and cylinders, you have to take into account the possible increase in the volume of liquid (Fig. I-3).

Compressibility. Estimated by the coefficient of volumetric compression, m 3 / n,

The reciprocal of p is called the modulus of elasticity and is written as follows:

The compressibility of liquefied gases compared to other liquids is very significant. So, if the compressibility of water (48.310 -9 m 2 / n) is taken as 1, then the compressibility of oil is 1.565, gasoline is 1.92, and propane is 15.05 (respectively 75.5610 -9, 92.7910 -9 and 727, 4410 -9 m 2 / n).

If the liquid phase occupies the entire volume of the reservoir (cylinder), then when the temperature rises, it has nowhere to expand and it begins to shrink. The pressure in the tank in this case increases by an amount, N / m 2,

where t is the temperature difference of the liquid phase, .

The increase in pressure in the tank (cylinder) with an increase in ambient temperature should not exceed the allowable calculated value, otherwise an accident is possible. Therefore, when filling, it is necessary to provide a steam cushion of a certain size, i.e. fill the tank not completely. Hence, it is necessary to know the degree of filling, determined by the relation

If it is necessary to find out what temperature difference is permissible with the existing filling, it can be calculated using the formula:

Critical parameters. Gases can be converted into a liquid state by compression, if the temperature does not exceed a certain value characteristic of each homogeneous gas. The temperature above which a given gas cannot be liquefied by any increase in pressure is called the critical temperature of the gas (T cr). The pressure required to liquefy a gas at a critical temperature is called critical pressure (p cr). The volume of gas corresponding to the critical temperature is called the critical volume (Vcr), and the state of the gas, determined by the critical temperature, pressure and volume, is called the critical state of the gas. The density of the vapor over the liquid in the critical state becomes equal to the density of the liquid.

The principle of corresponding states. Usually, to summarize the experimental data on the study various processes and substances use criterion systems based on the analysis of the equations of motion, heat conduction, etc. To use such similarity equations, tables of physical properties of working media are needed. The inaccuracy in the determination of physical properties or their absence does not make it possible to use the similarity equations. This is especially true for poorly studied working fluids, in particular, for liquefied hydrocarbon gases, on the physical properties of which there are rather contradictory data in the literature, often at random pressures and temperatures. At the same time, there are accurate data on the critical parameters and molecular weight of the substance. This allows, using the given parameters and the law of the corresponding states, which is confirmed by numerous studies and theoretically substantiated by the modern kinetic theory of matter, to determine unknown parameters.

For thermodynamically similar substances, and liquefied hydrocarbon gases are thermodynamically similar, the reduced equations of state, i.e. the equations of state written in dimensionless (reduced) parameters (р pr = р/р cr =) have the same form. At different times, up to fifty equations of state for real substances were proposed by various authors. The most famous and commonly used of them is the van der Waals equation:

where a and b are constants inherent in a given chemical compound;

Having expressed the parameters of the gas in dimensionless reduced quantities, it can be established that for gases there is a general equation of state that does not contain quantities that characterize this gas:

F(r pr, T pr, V pr) = 0.

The laws of the gas state are valid only for an ideal gas, therefore, in technical calculations related to real gases, they are used with real gases within a pressure range of 2-10 kgf / cm 2 and at temperatures exceeding 0. The degree of deviation from the laws of ideal gases is characterized by a coefficient compressibility Z = (Fig. 1-4 - 1-6). It can be used to determine the specific volume if the pressure and temperature are known, or the pressure if the specific volume and temperature are known. Knowing the specific volume, you can determine the density.

Specific gravity. The weight of a unit volume of a substance, i.e. the ratio of the weight (gravity) of a substance to its volume is called the specific gravity (designation. In the general case, where G is the weight (gravity of the substance, V volume, m 3. Unit of specific gravity in SI = newton per cubic meter (n / m 3). Specific gravity depends on the acceleration of gravity at the point of its definition and, therefore, is a parameter of matter.

Heat of combustion. The amount of heat that is released during the complete combustion of a unit mass or volume of gas is called the heat of combustion (notation Q). The unit of heat of combustion in SI is joule per kilogram (j/kg) or joule per cubic meter (j/m3).

Ignition temperature. The minimum temperature to which the gas-air mixture must be heated in order for the combustion process (combustion reaction) to begin is called the ignition temperature. It is not a constant value and depends on many reasons: the content of combustible gas in the gas-air mixture, the degree of homogeneity of the mixture, the size and shape of the vessel in which it is heated, the speed and method of heating the mixture, the pressure under which the mixture is, etc.

Gas flammability limits. Gas-air mixtures can ignite (explode) only if the gas content in the air (or oxygen) is within certain limits, beyond which these mixtures do not burn spontaneously (without a constant influx of heat from the outside). The existence of these limits is explained by the fact that as the content of air or pure gas in the gas-air mixture increases, the flame propagation speed decreases, heat losses increase and combustion stops. As the temperature of the gas-air mixture increases, the flammability limits expand.

Heat capacity. The amount of heat required to change the temperature of a body or system by one degree is called the heat capacity of the body or system (notation C). The unit in SI is joule per degree Kelvin (J/K). 1 j / K - 0.2388 cal / K \u003d 0.2388 * 10 -3 kcal / K.

In practical calculations, the average and true heat capacity are distinguished, depending on the temperature range in which it is determined. The average heat capacity C m is a value determined in a finite temperature range, i.e.

With m \u003d q / (t 2 -t 1).

The true heat capacity is the value determined at a given point (for given p and T or and T), i.e.

There are heat capacities determined at constant pressure (C p) or at constant volume (C v).

Thermal conductivity. The ability of a substance to transmit thermal energy called thermal conductivity. It is determined by the amount of heat Q passing through a wall with an area F of thickness over a period of time at a temperature difference t 2 -t 1, i.e.

where is the thermal conductivity coefficient characterizing the heat-conducting properties of a substance, W / (m * K) or kcal / (m * h * C).

Viscosity- this is the ability of gases or liquids to resist shear forces, due to the forces of adhesion between the molecules of a substance. The force of resistance to slip or shear F, and arising from the movement of two adjacent layers of liquid or gas, is proportional to the change (gradient) of the velocity along the axis normal to the direction of the flow of liquid from gas, i.e.

where - coefficient of proportionality, ns / m 2 (in SI); it is called the coefficient of dynamic viscosity (internal friction) or dynamic viscosity; dw is the velocity gradient in two adjacent layers located at a distance dy.

In many technical calculations, kinematic viscosity is used, which is the ratio of the dynamic viscosity of a liquid or gas to their density, i.e. =/. The unit of kinematic viscosity in SI is square meter per second (m2/sec).

The viscosity of the liquid phase decreases with increasing temperature, while the viscosity of the gas and vapor increases.

Octane number gas fuel is higher than that of gasoline, so the knock resistance of liquefied gas is greater than that of even the highest quality gasoline. The average octane number of liquefied gas - 105 - is unattainable for any brand of gasoline. This allows you to achieve greater efficiency in the use of fuel in a gas boiler.

Diffusion. The gas mixes easily with air and burns more evenly. The gas mixture burns completely, so no soot is formed in the furnaces and on the heating elements.

pressure in the container. In a closed vessel, LPG forms a two-phase system consisting of liquid and vapor phases. The pressure in the vessel depends on the saturated vapor pressure, which in turn depends on the temperature of the liquid phase and percentage propane and butane in it. Saturated vapor pressure characterizes the volatility of LPG. The volatility of propane is higher than that of butane, therefore, its pressure at low temperatures is much higher. Calculations and experiments have established that at low ambient temperatures it is more efficient to use LPG with a high propane content, since this ensures reliable gas evaporation, and hence the sufficiency of gas for gas consumption. In addition, sufficient overpressure in the tank will ensure reliable gas supply to the boiler in severe frosts. At high positive ambient temperatures, it is more efficient to use LPG with a lower propane content, since in this case a significant overpressure will be created in the tank, which can cause the discharge valve to operate. In addition to propane and butane, LPG contains a small amount of methane, ethane and other hydrocarbons that can change the properties of LPG. During the operation of the tank, non-evaporable condensate may form, which adversely affects the operation of gas equipment.

Change in the volume of the liquid phase during heating. Regulations of the United Nations Economic Commission for Europe provide for the installation of an automatic device that limits the filling of the container to 85% of its volume. This requirement is explained by the large volumetric expansion coefficient of the liquid phase, which is 0.003 for propane and 0.002 for butane per 1°C increase in gas temperature. For comparison: the expansion coefficient of propane is 15 times, and butane is 10 times greater than that of water.

Change in the volume of gas during evaporation. When liquefied gas evaporates, about 250 liters are formed. gaseous. Thus, even a minor LPG leak can be dangerous, since the volume of gas during evaporation increases by 250 times. The density of the gas phase is 1.5--2.0 times greater than the density of air. This explains the fact that in case of leaks, the gas is difficult to disperse in the air, especially in indoors. Its vapors can accumulate in natural and artificial recesses, forming an explosive mixture. SNiP 42-01-2002 provides for the mandatory installation of a gas analyzer that gives a signal to the shut-off valve to close in the event of gas accumulation at a concentration of 10% of the explosive concentration.

Odoration. The gas itself practically does not smell, therefore, for safety and timely diagnosis of gas leaks by human olfactory organs, small amounts of strong-smelling substances are added to it. At mass fraction mercaptan sulfur less than 0.001% LPG must be odorized. For odorization, ethyl mercaptan (С2Н5SH) is used, which is an unpleasantly smelling liquid with a density of 0.839 kg/l and a boiling point of 35°C. Odor sensitivity threshold 0.00019 mg/l, maximum allowable concentration in air working area 1 mg/m3. In the case when the toxicity is normal or slightly below the norm, the smell of the odorant is practically not felt and its accumulation in the room is not observed.

Conclusion

Thus, it is possible to summarize and highlight the main properties of propane-butane mixtures that affect the conditions for their storage, transportation and measurement.

1. Liquefied hydrocarbon gases are low-boiling liquids capable of being in a liquid state under saturated vapor pressure.

Boiling temperature:

Propane -42 0 С;

Butane - 0.5 0 C.

2. Under normal conditions, the volume of gaseous propane is 270 times greater than the volume of liquefied propane.
3. Liquefied hydrocarbon gases are characterized by a high coefficient of thermal expansion.
4. LPG is characterized by low density and viscosity compared to light oil products.
5. Instability of the aggregate state of LPG during the flow through pipelines depending on temperature, hydraulic resistance, uneven conditional passages.
6. Transportation, storage and measurement of LPG is possible only through closed (sealed) systems, designed, as a rule, for a working pressure of 1.6 MPa.
7. Pumping, measuring operations require the use of special equipment, materials and technologies.

All over the world, hydrocarbon systems and equipment, as well as the arrangement of technological systems, are subject to uniform requirements and rules.

Liquefied gas is a Newtonian fluid, so the pumping and measurement processes are described by the general laws of hydrodynamics. But the function of hydrocarbon systems is not only to simply move the liquid and measure it, but also to ensure that the influence of “negative” physical and chemical properties SUG.

Fundamentally, systems pumping LPG differ little from systems for water and oil products, and, nevertheless, it is necessary optional equipment, which guarantees the qualitative and quantitative characteristics of the measurement.

Based on this, the technological hydrocarbon system, at a minimum, must include a tank, a pump, a gas separator, a meter, a differential valve, a shut-off or control valve, and safety devices against excess pressure or flow rate.

Features of the use of liquefied petroleum gas (LPG) in the form of a mixture of propane with butane and its counterpart liquefied natural gas (LNG) methane in automobile gas-balloon equipment.

In wide use for cars, two compositions of gas are propane and methane. Which one is better, cheaper, more technologically advanced and more reliable? Let's figure it out so that after reading there is no doubt.

Methane equipment is used in only 25% of cars, propane is used in the remaining 75% of cars. At the same time, methane is often put on commercial vehicles, where the choice is made not by the driver, but by the organization owner vehicle. Let us examine the reasons for this ratio in the HBO market.

The autoblogger analyzes the features of propane and methane in a fifteen-minute video: what is better for a car, the main difference

Features of propane-butane (LPG)

Propane is a carbon gas, a by-product of oil production. It is odorless, transparent and harmless to humans. Odorants are also added to it so that if it leaks, it can be smelled. The chemical formula is C 3 H 8 .

At gas stations we see the inscription "propane-butane". Butane is also a carbon gas that is released under similar conditions. It is mixed with propane in order to achieve the desired octane number. And in different time compositions change: in winter there is more propane, and in summer butane.

It is stored in cylinders in a car in liquefied form. That is, it is liquid, not gaseous - it “flops” in a balloon. Also a big advantage is the working pressure, which is only 14 atmospheres. It requires containers made of lighter metal and the walls of the cylinder are much thinner. Now the most widespread are toroidal cylinders in the form of a donut, which are placed in place of the reserve. At the same time, the cylinder does not take up space in the trunk, but you have to sacrifice the spare wheel.

On average equipment with a full refueling, you can drive 650 ... 850 kilometers, which is four times more than that of the opponent.

Propane consumption is 11 ... 13 liters per 100 km on an average car with a 1.6-liter engine on the 4th generation of HBO.

Equipment costs twice as much. In our experience, nine out of ten installation companies gas equipment specialize in propane.

Lots of refills. Also a big plus is that there are dozens of times more propane gas stations.

The engine power loss is lower, about 5…10%.

Propane Pros:

Cheap equipment.
There are a lot of companies that serve and install.
Low pressure.
Stored in liquefied form.
Lightweight and compact equipment, can be installed in the spare wheel slot.
Greater mileage.
Less power loss is about 5…10%.

Cons of propane:

Propane is more expensive than methane by about 3 rubles per liter. Propap costs 17 rubles against 14 per liter of methane.
More explosive than methane. If the cylinder is damaged, it does not evaporate into the atmosphere so quickly.

Propane, although it costs a little more, has a lot of advantages and the prevalence of gas stations.

Compatibility of LPG and LNG with the latest generations of LPG

And finally, about one more minus of methane - incompatibility with the fifth and sixth generations of HBO. Propane can work with these generations, but methane does not and most likely cannot.

In generations 5 and 6, gas is supplied as a liquid to the fuel injection system and is similar to gasoline. Propane is stored in cylinders in liquid form, and methane in gaseous form. Therefore, methane installation is possible only up to the 4th generation of equipment. The latest generations give an expense approximately equal to the consumption of gasoline. There is virtually no power loss. The engine can be started immediately on gas even at sub-zero temperatures.

Properties of liquefied hydrocarbon gases Features of the operation of hydrocarbon systems. For more than 30 years in our country, liquefied hydrocarbon gases have been used as a car fuel. In a relatively short period of time, a rather difficult path has been passed in organizing the accounting of liquefied gases, a clear understanding of the processes occurring during pumping, measurement, storage, and transportation. It is well known that the extraction and use in Russia has a long history.

However, the technical level of the field gas economy until the 20th century was extremely primitive. Finding no economically justified areas of application, the oil owners not only did not care about the preservation of gas or light fractions of hydrocarbons, but also tried to get rid of them. A negative attitude was also observed towards the gasoline fractions of oil, since they caused an increase in the flash point and the danger of fire and explosions. The separation of the gas industry in 1946 into an independent industry allowed a revolutionary change in the situation and a sharp increase in both the volume of gas production in absolute terms and its share in the country's fuel balance.

The rapid growth of gas production became possible due to the radical intensification of construction work main gas pipelines, connecting the main gas producing regions with gas consumers, large industrial centers and chemical plants. Nevertheless, a thorough approach to the accurate measurement and accounting of liquefied gases in our country began to appear no more than 10 - 15 years ago. For comparison, liquefied gas in England has been produced since the early 30s of the XX century, given that this is a country with a developed market economy, technology for measuring and accounting for liquefied gases, as well as the production of special equipment for these purposes, began to develop almost from the start of production.

So let's take a quick look

So, let's briefly consider (Properties of liquefied hydrocarbon gases Features of the operation of hydrocarbon systems), what are liquefied hydrocarbon gases and how they are produced. Liquefied gases are divided into two groups:

Liquefied hydrocarbon gases ( LPG ) - are a mixture of chemical compounds, consisting mainly of hydrogen and carbon with different molecular structures, i.e. a mixture of hydrocarbons of various molecular weights and different structure. The main components of LPG are propane and butane, as impurities they contain lighter hydrocarbons (methane and ethane) and heavier ones (pentane). All listed components are saturated hydrocarbons. LPG may also contain unsaturated hydrocarbons: ethylene, propylene, butylene. Butane-butylenes may be present as isomeric compounds (isobutane and isobutylene).

NGL - a wide fraction of light hydrocarbons, mainly includes a mixture of light hydrocarbons of ethane (С2) and hexane (С6) fractions.

In general, a typical NGL composition is as follows: ethane from 2 to 5%; liquefied gas fractions C4-C5 40-85%; hexane fraction C6 from 15 to 30%, the pentane fraction accounts for the remainder.

Given the widespread use of LPG in the gas industry, it is necessary to dwell in more detail on the properties of propane and butane.

Propane

Propane is an organic compound of the alkane class. Contained in natural gas, formed during the cracking of petroleum products. Chemical formula C 3 H 8 (Fig. 1). Colorless, odorless gas, very slightly soluble in water. Boiling point -42.1C. Forms explosive mixtures with air at vapor concentrations from 2.1 to 9.5%. The self-ignition temperature of propane in air at a pressure of 0.1 MPa (760 mm Hg) is 466 °C.

Butane(C 4 H 10) - an organic compound of the alkane class. In chemistry, the name is used mainly to refer to n-butane. Chemical formula C 4 H 10 (Fig. 1). The mixture of n-butane and its isomer isobutane CH(CH 3) 3 has the same name. Colourless, flammable gas, odorless, easily liquefied (below 0 °C and normal pressure or at elevated pressure and normal temperature - volatile liquid). Contained in gas condensate and petroleum gas (up to 12%). It is a product of catalytic and hydro-catalytic cracking of oil fractions.

– carbon;
– hydrogen

The production of both liquefied gas and NGLs is carried out at the expense of the following three main sources:

oil production enterprises - obtaining LPG and NGL occurs during the production of crude oil during the processing of associated (bound) gas and the stabilization of crude oil;

gas production enterprises - obtaining LPG and NGL occurs during the primary processing of well gas or free gas and condensate stabilization;

oil refineries - the production of liquefied gas and similar NGLs occurs during the processing of crude oil at refineries. In this category, NGL consists of a mixture of butane-hexane fractions (C4-C6) with a small amount of ethane and propane. The main advantage of LPG is the possibility of their existence at ambient temperature and moderate pressures, both in liquid and gaseous states. In a liquid state, they are easily processed, stored and transported, in a gaseous state they have a better combustion characteristic.

The state of hydrocarbon systems is determined by the totality of the influences of various factors, therefore, for a complete characterization, it is necessary to know all the parameters. The main parameters that can be directly measured and affect the LPG flow regimes include pressure, temperature, density, viscosity, concentration of components, phase ratio.

System

Hydrocarbon systems can be homogeneous or heterogeneous. If the system has homogeneous physical and Chemical properties- it is homogeneous, but if it is heterogeneous or consists of substances in different aggregate states - it is heterogeneous. Two-phase systems are heterogeneous.

A phase is understood as a certain homogeneous part of the system, which has a clear interface with other phases.

During storage and transportation, liquefied gases constantly change their state of aggregation, part of the gas evaporates and turns into a gaseous state, and part condenses, turning into a liquid state. In cases where the amount of evaporated liquid is equal to the amount of condensed vapor, the liquid-gas system reaches equilibrium and the vapor on the liquid becomes saturated, and their pressure is called saturation pressure or vapor pressure.

The vapor pressure of LPG increases with increasing temperature and decreases with decreasing temperature.

Liquefied hydrocarbon gases

Liquefied hydrocarbon gases are transported in railway and road tanks, stored in tanks of various volumes in a state of saturation: boiling liquid is placed in the lower part of the vessels, and dry saturated vapors are in the upper part (Fig. 2). When the temperature in the tanks decreases, part of the vapors will condense, i.e. the mass of the liquid increases and the mass of the vapor decreases, a new equilibrium state sets in. As the temperature rises, the reverse process occurs until the phases are in equilibrium at the new temperature.

Thus, evaporation and condensation processes occur in tanks and pipelines, which in two-phase media proceed at constant pressure and temperature, while the
The evaporation and condensation temperatures are equal.

In real conditions, liquefied gases contain water vapor in one quantity or another. Moreover, their amount in gases can increase to saturation, after which moisture from gases precipitates in the form of water and mixes with liquid hydrocarbons to the limiting degree of solubility, and then free water is released, which settles in tanks. The amount of water in LPG depends on their hydrocarbon composition, thermodynamic state and temperature. It has been proven that if the temperature of LPG is reduced by 15-30 0 C, then the solubility of water will decrease by 1.5-2 times and free water will accumulate at the bottom of the tank or fall out in the form of condensate in pipelines.

The water accumulated in the tanks must be periodically removed, otherwise it can get to the consumer or lead to equipment failure.

1-3 - vapor pressure: 1 - propane, 2 - propane-butane mixtures, 3 - butane; 4-5 - lines of hydrate formation: 4 - propane, 5 - butane.

Figure 3. Hydrate formation and vapor pressure of propane and butane.

According to the LPG test methods, the presence of only free water is determined, the presence of dissolved water is allowed.

Hydrates

Hydrates can be attributed to chemical compounds, since they have a strictly defined composition, but these are compounds of the molecular type, however, hydrates do not have a chemical bond based on electrons. Depending on the molecular characteristics and structural shape of the internal cells, various gases outwardly represent clearly defined transparent crystals of various shapes, and hydrates obtained in a turbulent flow - an amorphous mass in the form of densely compressed snow.

According to the graph presented in Fig. 3, it can be seen that the pressure at which hydrates are formed at a temperature less than 0 0 С, than the vapor pressure of propane, the same zone exists for butane.

The conditions for the formation of hydrates must be known when designing pipelines and systems for transporting gases, equipment for gas pumping stations, gas filling stations, as well as for developing measures to prevent their formation and eliminate hydrate plugs. It has been established that the pressure at which hydrates are formed at a temperature of +5 0 C is lower than the vapor pressure of propane and butane.

In most cases, speaking of liquefied gases, we mean hydrocarbons corresponding to GOST 20448-90 "Liquefied hydrocarbon gases for domestic consumption" and GOST 27578-87 "Liquefied hydrocarbon gases for road transport". They are a mixture consisting mainly of propane, butane and isobutane. Due to the identity of the structure of their molecules, the rule of additivity is approximately observed: the parameters of the mixture are proportional to the concentrations and parameters of the individual components. Therefore, according to some parameters, it is possible to judge the composition of gases.

Relevant mixture parameters

The corresponding mixture parameters are obtained by summing the partial parameters of the individual components:

ycm = ∑yi xi ,

(1)

Where y cm is the mixture parameter; y i – component parameter; x i is the concentration of the component.

In accordance with the rule of additivity and tables 1; 2, any mixture parameter can be calculated. For example, let's take a propane-butane mixture with a concentration of 40% butane and 60% propane. It is necessary to determine the density of the mixture at 10 0 C. According to formula 1, we find:

ρ cm= 516.8 × 0.6 + 586.3 × 0.4 = 310.08 + 234.52 = 544.6

Thus, for these conditions, the density of the mixture will be 544.6 kg/m 3 .

When measuring the amount of LPG and during accounting operations at storage facilities, such concepts as density, thermal expansion and viscosity are important.

Density , kg / m 3 - the ratio of body mass to its volume, depending on the hydrocarbon composition and its state. The vapor phase density of LPG is a complex function of temperature, state and pressure for each component.

The density of the liquid phase of propane-butane mixtures depends on the composition of hydrocarbons and temperature, since the density of the liquid decreases with increasing temperature, which is due to volumetric expansion.

The relative change in the volume of a liquid with a change in temperature by one degree is characterized by the temperature coefficient of volumetric expansion β t, which for liquefied gases (propane and butane) is several times greater than for other liquids.

Propane - 3.06 10 -3; Butane - 2.12 10 -3; Kerosene - 0.95 10 -3; Water - 0.19 10 -3;

When the pressure increases, the liquid phase of propane and butane is compressed. The degree of its compression is estimated by the coefficient of volumetric compressibility β com, the dimension of which is the inverse of the dimension of pressure.

Viscosity - this is the ability of gases or liquids to resist shear forces, due to the forces of adhesion between the molecules of a substance. With relative motion between the layers of the flow, a tangential force arises, which depends on the area of contact between the layers and the velocity gradient. The specific shear stress that occurs between the layers determines the dynamic viscosity of a gas or liquid and is called the dynamic viscosity coefficient. An analysis of experimental studies has shown that the viscosity of LPG depends on temperature, and increases slightly with increasing pressure. Unlike liquids, a gas's viscosity increases with increasing temperature.

	In technical calculations, kinematic viscosity ν is often used, which is the ratio of dynamic viscosity to density:
			ν = η ;	ρ					(2)
	Physical and thermodynamic properties of liquefied gases are given in tables 1 - 2.
	Table1
	Thermodynamic and physical properties of the liquid phase of propane and butane
	0			3	v, 10 -7		Szh,	r,		λ , 10 -3	a 2 , 10-
	T, TO(	WITH)	R, MPa	ρ and, kg/ m	m 2 / With		kJ/(kg	kJ/ kg		Tue/(m	‘ m 2 / With	Rg
					Liquid	propane phase
223	(-50)		0,070	594,3	4,095		2,207	434,94		126,68	0,966	4,24
228	(-45)		0,088	587,9	3,932		2,230	429,50		125,99	0,961	4,09
233	(-40)		0,109	581,4	3,736		2,253	424,02		125,30	0,957	3,90
238	(-35)		0,134	574,9	3,568		2,278	418,32		124,61	0,951	3,75
243	(-30)		0,164	568,5	3,410		2,303	412,62		123,92	0,946	3,60
248	(-25)		0,199	562,0	3,259		2,328	406,685		123,23	0,942	3,46
253	(-20)		0,239	555,5	3,116		2,353	400,75		122,55	0,938	3,32
258	(-15)		0,285	549,1	2,980		2,385	394,58		121,86	0,931	3,20
263	(-10)		0,338	542,6	2,851		2,416	388,41		121,17	0,924	3,09
268	(-5)		0,398	536,2	2,731		2,448	381,76		120,48	0,918	2,97
273	(0)		0,467	529,7	2,613		2,479	375,11		119,79	0,912	2,87
278	(5)		0,544	523,2	2,502		2,519	367,99		119,10	0,904	2 77
283	(10)		0,630	516,8	2,398		2,558	360,87		118,41	0,896	2,68
288	(15)		0,727	510,3	2,300		2,604	353,27		11-7,72	0,886	2,60

293 (20)	0,834	503,9	2,209	2,650	345,67	117,03	0,876	2,52
298 (25)	0,953	497,4	2,120	2,699	337,125	116,35	0,867	2,45
303 (30)	1,084	490,9	2,037	2,747	328,58	115,66	0,858	2,37
308 (35)	1,228	484,5	1,960	2,799	318,84	114,97	0,848	2,31
313 (40)	1,385	478,0	1,887	2,851	309,11	114,28	0,839	2,25
318 (45)	1,558	571,5	1,818	2,916	297,48	113,59	0,826	2,20
323 (50)	1,745	465,1	1,755	2,981	285,84	112,90	0,814	2,16

Butane liquid phase

228 (-45) 0,0126 667,0 4,92 2,125 420,36 132,72 0,9364 5,25

223	(-50)	0,0094	674,3	5,09	2,114	423,96	133,45	0,9362	5,44
233	(-40)	0,0167	659,7	4,76	2,135	416,75	131,59	0,9371	5,08
238	(-35)	0,0218	652,3	4,60	2,152	412,97	131,27	0,9351	4,92
243	(-30)	0,0280	645,0	4,43	2,169	409,19	130,54	0,9331	4,75
248	(-25)	0,0357	637,7	4,28	2,188	405,41	129,82	0,9304	4,60
253	(-20)	0,0449	630,3	4,18	2,207	401,63	129,09	0,9280	4,50
258	(-15)	0,056	616,6	3,98	2,234	397,67	128,37	0,9319	4,27
263	(-10)	0,069	611,5	3,83	2,261	393,70	127,64	0,9232	4,15
268	(-5)	0,085	606,3	3,698	2,270	389,56	126,92	0,9222	4,01
273	(0)	0,103	601,0	3,561	2,307	385,42	126,19	0,9101	3,91
278	(5)	0,123	593,7	3,422	2,334	381,10	125,46	0,9054	3,78
283	(10)	0,147	586,3	3,320	2,361	376,77	124,74	0,9011	3,68
288	(15)	0,175	579,0	3,173	2,392	372,09	124,01	0,8940	3,55
293	(20)	0,206	571,7	3,045	2,424	367,41	123,29	0,8897	3,42
298	(25)	0,242	564,3	2,934	2,460	362,37	122,56	0,8828	3,32
303	(30)	0,282	557,0	2,820	2,495	357,32	121,84	0,8767	3,22
308	(35)	0,327	549,7	2,704	2,535	351,92	121,11	0,8691	3,11
313	(40)	0,377	542,3	2,606	2,575	346,52	120,39	0,8621	3,02
318	(45)	0,432	535,0	2,525	2,625	340,76	119,66	0,8521	2,96
323	(50)	0,494	527,7	2,421	2,680	334,99	118,93	0,8409	2,88

Table2.

		Thermodynamic and physical properties of propane and butane vapor phase
T, TO(		0	WITH)	R, MPa	3	v, 10 -7	WITHn,	r, kJ/ kg	λ , 10 -3	a 2 , 10-
T, TO(			WITH)	R, MPa	ρ n, kg/ m	m 2 / With	kJ/(kg– TO)	r, kJ/ kg	Tue/(mTO)	‘ m 2 / With
						Propane vapor phase
223	(-50)			0,070	1 96	30,28	1,428	434 94	0,92	32,9
228	(-45)			0,088	2 41	25,23	1,454	429,50	0,96	27,4
233	(-40)			0,109	2 92	21,32	1,480	424,02	1,00	23,1
238	(-35)			0,134	3,52	18,09	1,505	418,32	1,04	19,6
243	(-30)			0,164	4,22	15,43	1,535	412,62	1,07	16,5
248	(-25)			0,199	5,02	13,26	1,552	406,685	1,11	14,2
253	(-20)			0,239	5,90	11,52	1,587	400,75	1,15	12,3
258	(-15)			0,285	6 90	10,06	1,610	394,58	1,19	10,7
263	(-10)			0,338	8,03	8,82	1,640	388,41	1,24	9,4
268	(-5)			0,398	9,28	7,78	1,675	381,76	1,28	8 2
273	(0)			0,467	10,67	6,90	1,710	375,11	1,32	7,2
278	(5)			0,544	12 23	6,14	1,750	367,99	1,36	6,4
283	(10)			0,630	13,91	5,50	1,786	360,87	1,41	5,7
288	(15)			0,727	15 75	4,94	1,820	353,27	1,45	5,1
293	(20)			0,834	17,79	4,45	1,855	345,67	1,50	4 5
298	(25)			0,953	19,99	4,03	1,888	337,125	1,54	4,1
303	(30)			1,084	22 36	Z,67	1,916	328,58	1,59	3,7
308	(35)			1,22 8	24,92	3,35	1,940	318,84	1,63	3,4
313	(40)			1,385	27,66	3,06	1,960	309,11	1,68	3,1
318	(45)			1,558	Z0.60	2,81	1,976	297,48	1,73	2,9
323	(50)			1,745	33,76	2,59	1,989	285,84	1,78	2,7
						Vapor phase butane
223	(-50)			0,0094	0,30	168,535	1,440	423,96	0,90	208,3
228	(-45)			0,0126	0,39	132,866	1,463	420,36	0,93	163,0
233	(-40)			0,0167	0,51	104,062	1,480	416,75	0,97	128,5
238	(-35)			0,0218	0,65	83,573	1,505	412,97	1,01	103,2
243	(-30)			0,0280	0,82	67,768	1,520	409,19	1,05	84,2
248	(-25)			0,0357	1,03	55,159	1,540	405,41	1,09	68,7
253	(-20)			0,0449	1,27	45,712	1,560	401,63	1,13	57,0
258	(-15)			0,056	1,55	38,252	1,580	397,67	1,17	47,8
263	(-10)			0,069	1,86	32,540	1,610	393,70	1,21	40,4
268	(-5)			0,085	2,26	27,325	1,632	389,56	1,26	34,2
273	(0)			0,103	2,66	23,677	1,654	385,42	1,30	29,5
278	(5)			0,123	3,18	20,189	1,674	381,10	1,34	25,2
283	(10)			0,147	3,71	17,634	1,694	376,77	1,39	22,1
288	(15)			0,175	4,35	15,318	1,713	372,09	1,43	19,2
293	(20)			0,206	5,05	13,435	1,732	367,41	1,48	16,9
298	(25)			0,242	5,82	11,864	1,751	362,37	1,53	15,0

303 (30)	0,282	6,68	10,517	1,770	357.32′	1,57	13,3
308 (35)	0,327	7,60	9,402	1,791	351,92	1,62	11,9
313 (40)	0,377	8,62	8,428	1,810	346,52	1,67	10,7
318 (45)	0,432	9,72	7,596	1,830	340,755	1,72	9,7
323 (50)	0,494	10,93	6,864	1,848	334,99	1,77	8,8

Thus, it is possible to summarize and highlight the main properties of propane-butane mixtures that affect the conditions for their storage, transportation and measurement.

Liquefied hydrocarbon gases (Properties of liquefied hydrocarbon gases Features of the operation of hydrocarbon systems) are low-boiling liquids that can be in a liquid state under saturated vapor pressure.

Boiling point: Propane -42 0 С; Butane - 0.5 0 C.

Under normal conditions, the volume of gaseous propane is 270 times greater than the volume of liquefied propane.
Liquefied hydrocarbon gases are characterized by a high coefficient of thermal expansion.
LPG is characterized by low density and viscosity compared to light oil products.

Instability of the aggregate state of LPG during the flow through pipelines depending on temperature, hydraulic resistance, uneven conditional passages.
Transportation, storage and measurement of LPG is possible only through closed (sealed) systems, designed, as a rule, for a working pressure of 1.6 MPa.

Pumping, measuring operations require the use of special equipment, materials and technologies.

In the world

All over the world, hydrocarbon systems and equipment, as well as the arrangement of technological systems, are subject to uniform requirements and rules.

Liquefied gas is a Newtonian fluid, so the pumping and measurement processes are described by the general laws of hydrodynamics. But the function of hydrocarbon systems is reduced not only to the simple movement of the liquid and its measurement, but also to ensure that the influence of the "negative" physical and chemical properties of LPG is reduced.

In principle, systems pumping LPG (Properties of liquefied hydrocarbon gases Features of the operation of hydrocarbon systems) differ little from systems for water and oil products, and, nevertheless, additional equipment is needed to guarantee the qualitative and quantitative characteristics of the measurement.

Explanations

storage tank must be equipped with a product loading inlet, a discharge drain line and a vapor phase line that is used for pressure equalization, vapor return from the gas separator or system calibration.

Pump – Provides the pressure needed to move the product through the dispensing system. The pump must be selected according to capacity, performance and pressure.

Meter - includes a product quantity converter and a reading device (indication) which can be electronic or mechanical.

Gas separator – separates the vapor generated during the liquid flow before it reaches the counter and returns it to the vapor space of the tank.

Differential valve - serves to ensure that only a liquid product passes through the meter by creating an excess differential pressure after the meter, which is obviously greater than the vapor pressure in the container.

The system must meet the following requirements:

be airtight and withstand the required design pressure; made of materials intended for work with LPG;

equipped with pressure relief valves for controlled release of the product when the pressure exceeds the working one.

The main design features described above apply to all types of systems used for LPG metering and dispensing. However, these are not the only criteria. The design of the system should reflect various conditions its use for the commercial release of the product (Properties of liquefied hydrocarbon gases Features of the operation of hydrocarbon systems).

Conventionally, measurement systems can be divided into the following groups (types):

implementation of LPG measurement (including filling of tankers) at a relatively high speed flow (400-500 l / min.). As a rule, this is a refinery, GNS.

measuring the amount of LPG when delivering to gas filling stations or end users by tankers (including loading tankers). Productivity in this case fluctuates from 200 to 250 l/min.

Commercial refueling of LPG vehicles. Filling speed usually does not exceed 50 l/min.

The design and type of measurement systems for LPG is determined by the physical properties of the product, especially its dependence on temperature and pressure during tempering.

To ensure accurate measurement, the design of the system must include means to minimize evaporation and eliminate the resulting steam before it enters the meter.

The design of a measuring system depends on its use and on the maximum performance. Measuring installations can be used both stationary and installed on tankers, used in wholesale and retail sales.

Let us consider separately the components that are involved in LPG measurement operations and are mandatory for most accounting systems (Properties of liquefied hydrocarbon gases Features of the operation of hydrocarbon systems).

pressure line – connects the storage tank and the inlet pipe of the measurement unit and has elements that control the flow of liquid and ensure that it is kept in a liquid state. The pressure line, as a rule, consists of the following elements:

Pumps .

Since the liquid-vapor system in the storage tank is in equilibrium and, together with the measurement system, constitute a closed system, the gas cannot flow independently. As a result, a pump must be used to supply the LPG to the distribution line.

There are several typical designs of pumps that are widely used in various cases. These are vane pumps, gear pumps, vortex pumps.

Pump speed can be critical to the accuracy of the measuring system and

performance. If the pump speed is high, the suction line pressure may drop below the vapor pressure and evaporation will occur. This phenomenon is called cavitation. To minimize the effects of cavitation, the length of piping from the tank to the pump should be kept to a minimum. This piping must be straight, to avoid hydraulic resistance, and a size larger than the pressure line piping.

bypass valve .

For short periods of time, the pump may be in operation while no product is being dispensed. To prevent damage, a number of pumps are equipped with bypass valves. When the pressure rises, the valve inside the pump opens and fluid begins to circulate inside the pump. As a rule, such a scheme leads to heating of the product and its boiling, while a vapor cushion is formed that prevents the movement of the liquid. Having carried out repeated experiments with pumps equipped with internal bypass valves, we have come to the conclusion that the optimal solution for liquids such as LPG is the installation of an external bypass valve.

This design allows the product to circulate through the storage tank and continuously supply the pump with unheated gas.

Speed valves .

High-speed valves must be equipped with all branch pipes of the storage tank and dispensing sleeves. The purpose of these valves is to stop the flow of product in the event of a hose rupture or disconnection of the dispensing tap.

Pressure gauges .

Pressure gauges must be installed on the suction and pressure lines of the pump, on the vapor phase of the storage tank, as well as on the system filters (Properties of liquefied petroleum gases Features of the operation of hydrocarbon systems).

Safety valves .

In any place of the technological and measuring systems, where it is possible to contain the volume of liquid between two shut-off devices, it is necessary to install safety valves to prevent possible overpressure.

Gas separator .

Gas Separator - Separates the vapor generated during the liquid flow before it reaches the meter and returns it to the vapor space of the tank.

As a rule, gas separators have a float-operated gas separation system, but some manufacturers refuse such a scheme in favor of using high-speed or check valves and installing expanding pipes (siphons) together with small diameter holes. Such a scheme for LPG is quite effective if we take into account that the gas separator in closed systems plays the role of a gas condenser, i.e. its purpose is to condense the vapor phase, and take part of it into a storage tank.

Filters .

Filters are an important element of the hydraulic system. They are installed in front of the pump and in the measuring block and are designed to protect the pump or meter from solid contaminants that can disable them. The filter elements must be replaceable or be able to be cleaned periodically.

Taps and valves .

Locking devices are an integral part of any technological system for LPG. They are designed to provide convenient and fast Maintenance individual components without degassing and depressurizing the entire system.

Counters and reading devices .

The liquid separated from the vapor, after the gas separator, enters the meter (volume converter) (Properties of liquefied hydrocarbon gases Features of the operation of hydrocarbon systems). In most LPG metering systems, the meters are of the chamber flow meter type, which we believe is the most reliable and highly accurate liquid metering method. There are also other types of flowmeters, such as turbine or mass (Coriolis) flowmeters.

The design of chamber flowmeters is quite complex from a technical point of view, but the principle of their operation is straightforward. There are the following types of flow meters: gear, rotary, ring, disc, vane, bucket, piston, etc.

Due to the simple principle of operation of such measurement devices, the number of factors that cause inaccurate measurement is few.

The first is the presence of a vapor phase in the product stream. Secondly, the inaccuracy of the meter may be caused by contamination of the moving parts. This once again speaks of the important function of applying filters. Thirdly, the accuracy of the measurement devices depends on the wear of moving parts.

Differential valve

Differential valve – serves to ensure that only liquid product passes through the meter by creating an excess differential pressure after the meter, which is obviously greater than the vapor pressure in the container.

Typically, a differential valve names diaphragm or piston design. By means of a diaphragm or piston, the device is divided into two chambers. The upper one is connected with the vapor phase of the tank, and the lower one with the product dispensing line. The valve spring is located in the cavity of the vapor phase and is adjusted to a minimum pressure of 1 kg/cm 2 . When the liquid pressure is less than or equal to the vapor phase pressure, the valve is closed. To open it, it is necessary to create a pressure that exceeds the vapor pressure by at least 0.1 MPa. This ensures that the vapor phase condenses up to the meter and only the liquid product passes through the meter.

The beginning and end of the movement of the product into the filled container is controlled by electric valves. These can be solenoid valves, all kinds of gate valves and valves with electric or pneumatic actuators, control valves, etc. The purpose of a shut-off or control valve is to open the release line on command at the start of filling and close it when the specified release dose is reached. To avoid excessive load on the internal parts of the hydraulic system units, shut-off valves must operate in a mode that excludes the negative effect of hydraulic shocks. In other words, the valves must at least open and
close in two stages - from low to high flow at the beginning and vice versa at the end of refueling.

Vacation line

The release line passes the measured product to the point of issue. To ensure an accurate measurement, the hose must be filled with liquid product at the start of dispensing and at operating pressure. This is called "full sleeve". To do this, the dispense guns have a valve that closes when the dispense valve is released and disconnected.

The properties of liquefied hydrocarbon gases, as well as other liquids that require accounting, imply an individual approach to the choice of equipment

Nevertheless, thanks to many years of world experience and accurate theoretical data on the properties of liquefied gases, the versatility of the equipment takes place, i.e. the configuration of a particular hydraulic unit allows it to be used in any technological system for pumping, measuring and accounting of LPG.

Our company daily faces the challenges of selecting and designing equipment for various technological systems. Thanks to own experience, as well as the experience of world manufacturers, we managed to create devices that in any technological system allow us to eliminate, or at least minimize the negative factors of the thermodynamic properties of LPG.

Thus, summing up what has been said, we can conclude that the choice of equipment should be as easy as possible and be made according to the parameters of performance, accuracy, appearance etc. (fig.4) Others specifications equipment (this is confirmed by world practice) should be provided for by the design itself.

Criteriachoice of technologicalequipment

USE OF FACTORY HYDROCARBON GASES. FUEL AND COMPLEX PROFILE PLANTS

CHAPTER VIII

USE AND PROCESSING OF FACTORY HYDROCARBON GASES

GAS CHARACTERISTICS

All processes of destructive processing of crude oil are accompanied by the formation of hydrocarbon gases. The output of these gases is on average 5-20% of the raw material. With deep processing, a modern oil refinery with a capacity of 12 million tons of oil per year produces approximately 1 million tons (ie, over 8% by weight) of gaseous hydrocarbons. Pyrolysis occupies a special place among the destructive processes in this regard, where a gas rich in light olefins is the target product. In this case, after the extraction of ethylene, propylene, and butylene-butadiene fraction, a saturated part of the gas also remains, which, during the pyrolysis of gases, is mainly recirculated, and, during the pyrolysis of gasoline and other liquid raw materials, leaves the gas fractionation plant.

The gas yields during the main catalytic processes of processing oil feedstock are very significant: catalytic reforming produces 10-20% (mass.) of gas for feedstock (including from 1 to 2% of hydrogen); in catalytic cracking, the gas yield is 12-15% (wt.). In table. 39 gives an approximate composition of the gases formed during the main oil refining processes.

For processes occurring under hydrogen pressure (reforming, isomerization, hydrocracking, hydrotreatment), the gas composition is relatively simple and, like natural and associated gases, is characterized by the absence of unsaturated hydrocarbons. At the same time, all thermal and part of the catalytic processes give gases of a more complex composition, with a greater or lesser content of unsaturated hydrocarbons. The concentration of unsaturated hydrocarbons to some extent depends on the composition of the feedstock, but is mainly determined by the severity of the regime, and for catalytic cracking - and the catalyst used. For example, continuous tar coking in normal mode (530-

540 °C) gives a gas with "30% (wt.) unsaturated hydrocarbons, and an increase in temperature to 600 °C increases the amount of unsaturated hydrocarbons to almost 50%. The transition of catalytic cracking units to zeolite-containing catalysts caused a decrease in the total gas yield.

In addition to the content of unsaturated hydrocarbons, factory gases are also characterized by the concentration of the "fat" part - the C 3 -C 4 fraction. The most valuable hydrocarbons of this fraction are iso-butane and butylenes, which are the raw materials for catalytic alkylation (obtaining a high-octane component of automobile and aviation gasolines). The "dry" part of the gas - hydrogen, methane and the Cr fraction (ethane + ethylene) is of the least interest. Hydrogen and ethylene included in the dry gas are valuable, but hydrogen is extracted only from the reforming gas, since it is formed there in significant quantities and separated in the gas separator high pressure at the reformer itself (the rest of the gas contains only traces of hydrogen). The gases of other processes, when mixed before purification and gas fractionation, contain hydrogen already in a relatively small con-

Table 39. Composition of hydrocarbon gases in the main oil refining processes

Gas composition, % (wt.)

Components	Thermal cracking under pressure	delayed coking		continuous coking in a fluidized bed of coke	catalytic cracking of vacuum gas oil g	catalytic reforming of benzene^	heavy hydrocracking 1 \| distillate raw materials e j
Components	Thermal cracking under pressure	tar®	» ? I R th " 0JG.& §	continuous coking in a fluidized bed of coke	on amorphous catalyst	catalytic reforming of benzene^	heavy hydrocracking 1 \| distillate raw materials e j
Hydrogen
Methane
Ethylene
Ethane
Propylene
Propane
n-Butylene
"n-Butane
Isobutane					15, $
Isobutylene
The amount of unlimited

a Data from A. N. Tarasov. ^Data by A.F. Krasyukov. in Data 3. I. Sunyaeva. d Data by V.N. Erkiya. e Summarized data. f Data by S. P. Rogov.

centering. With deep oil refining, the yield of dry gases reaches 3-4.5% (mass), and their composition is approximately the following (% mass, per gas):

Hydrogen ..... 3.0-3.5 Ethane ..... "30

Methane .......... 26-27 Propane + propylene. . 8.0-8.5

Ethylene ..........27-28 Fraction C* . . . . "5

Of course, the composition of the dry gas varies from plant to plant depending on the profile of the plant and the ratio between the capacities of the individual processes. The complexity of the ethylene and hydrogen extraction technology makes it necessary to abandon it for the time being, and dry gas is usually used at the plant as a process fuel. However, it is possible that provision will be made for the preliminary separation of the most valuable components from dry gas. M, According to the relative concentration of the dry and wet parts of the gas, thermal cracking gas under pressure H and coking gas can be considered “dry”, where the content of fractions up to Cr inclusive B is 35-60% (mass.). On the contrary, catalytic cracking gases contain 60-75% C3-C4 hydrocarbons (see Table 39) - ™ these are "fat" gases.

Resources of refinery gases are, of course, related to the depth of oil refining at the refinery; in deep processing, the rational use of gas is of particular economic importance. The direction of processing of gas fractions l is determined by the profile of the plant, especially taking into account the fact that the plant R is usually a petrochemical complex in which R processes of oil refining are combined with the preparation of monomers R for petrochemical synthesis or are accompanied by the petrochemical processes themselves (obtaining polypropylene, additives I

Some gas components use hydrocarbons directly at the plant: “dry” gas is usually a process fuel, hydrogen-containing reforming gas is needed for hydronization processes (hydrotreatment, hydrocracking). If hydrocracking units are included in the plant layout, the hydrogen demand cannot be met by reforming alone, so a portion of the dry gas (usually methane and ethane) is converted to B to produce hydrogen. AND

Essential for the use of refinery gases;I is the completeness of the selection of the most valuable components from their potential content, i.e., the efficient operation of gas separation units. Most modern refineries have two B gas separation units: for saturated and unsaturated gases. The joint separation of these gases is irrational, since the unsaturated components are more valuable, and it is easier to select them with the greatest completeness from more concentrated mixtures. Gas schemes

Table 40. Some physical constants of gaseous hydrocarbons

Hydrocarbon	T. kip. at 760 mm Hg Art., °С	DENSITY	Density of liquefied gas,* kg/m3	critical temperature,	pressure,

			569.9 (-103.4 °С)

Propylene			609.5 (-47 °С)

Isobutylene			626.8 (-6.8 °С)
a-Butylene
zuigyas-.r-butylene
cys-\|3-Butylene
Isobutane

Acetylene			615.4 (-80.3 °С)
Butadiene

* In parentheses is the temperature at which the density of the liquefied

separation of saturated and unsaturated gases may be similar or somewhat different (depending on the profile of the plant, i.e., on the specific volume of those and other gases).

In table. 40 shows some physical constants for gaseous hydrocarbons. The least volatile are the isomers (5-butylene and n- butane. The critical temperatures of the components of the C4 fraction lie in the range of 134-163 °C, which indicates the possibility of liquefying these hydrocarbons at relatively low pressures and temperatures above 30-40 °C available for water cooling. For example, n-butane at 40 °C has a pressure of 0.4 MPa, and at this temperature can be easily converted into a liquid (even with water cooling at the top of the butane column). On the contrary, ethylene has a critical temperature of only +9.5 °C, i.e., water cooling is unsuitable for its condensation even at a much higher pressure, and special refrigerants must be used.

GAS PREPARATION FOR PROCESSING

The general principles and technological schemes for drying hydrocarbon gases and purifying them from hydrogen sulfide are set out in Part I of the course "Oil and Gas Processing Technology" in relation to natural and associated gases. Only those preparation methods that are specific to plant hydrocarbon gases are mentioned below.

Dehydration of factory gases is not always required. As a matter of fact, it is used in cases where the gas is subjected to subsequent low-temperature distillation (for example, when pure ethylene is isolated) or is sent directly for catalytic processing to a unit with a moisture-sensitive catalyst. At low rectification temperatures (up to -100 ° C), water condensate will fall out even at low gas humidity. For example, for a hydrocarbon gas at 0 MPa "with a water content of 2 g / m 3, the dew point was l; 1 When holding water 0.17 g / m 3 only -20 ° C, i.e. at temperatures below -20 ° C, the gas should have contained less than 0.17 g of moisture 1ag per

1 m 3. An increase in pressure also causes the need for deeper drying, since the pressure increases the dew point; For example, for the same gas, with an increase in absolute pressure from 0.7 to 3.5 MPa, the dew point increased from 14 to 39 14 °C and 3.5 MPa, the maximum allowable moisture content was only 0.5 g/m 3 .

The degree of gas drying is determined not only by the possibility of water condensation, but also by the formation of hydrates. Hydrates! are complex compounds of gas molecules with water. Methane hydrates are known (CH 4 -6H 2 0), ethane (C 2 Hb-7H 2 0)) and D p * In appearance, hydrates are bulky crystalline; formations, depending on the composition, white or transparent, to ice Hydrates are unstable and easily decompose into gas and water when the temperature or pressure changes.

It is characteristic that hydrates can form only at elevated pressures and at temperatures above zero, and heavier hydrocarbons form hydrates more easily than low molecular weight hydrocarbons. Thus, methane is able to form hydrates at 12.5°C and 10 MPa; ethane at the same temperature forms 1 HID rat under a pressure of only 2.5 MPa. Hydrates can exist only in the presence of excess moisture in the gas, i.e., when the partial pressure of water vapor in the gas phase is greater than the vapor pressure hy, Dr. which the pressure of saturated water vapor will be less than the vapor pressure of the hydrate at the temperature of the medium.

Liquid moisture absorbers cannot reduce the dew point below minus 15 ° C, and for reliable operation of the installation that fractionates pyrolysis gases, the dew point should not exceed min^ gg_

minus 70 °С. Therefore, for drying pyrolysis gases, solid absorbers are used - mainly zeolites or zeolites with a. dumo-gel. Drying of gases containing unsaturated hydrocarbons with adsorbents is complicated by the possibility of partial polyimide of Isa. tions of these components. For pyrolysis gas only great importance has a preliminary separation of hydrocarbons C5 and C4, consisting partly of dienes, which are most easily polymerized. The content of 3-5% (wt.) C5 hydrocarbons in the gas leads to a rapid loss of adsorbent activity.

A necessary unit of catalytic reforming units is a dehydration unit for circulating hydrogen-containing gas. In ch. VI it was noted that in order to avoid deactivation of the catalyst (due to washing out of the halogen), the moisture content in the circulating gas is maintained in the range of (14-1.5) 10~3% (vol.).

Preliminary drying of the reforming feedstock is carried out in the stabilization column of the hydrotreating unit. Drying of the circulating gas takes place in one of two or more alternately operating adsorbers filled with acid-resistant (against HC1) zeolites. The time of continuous operation of the adsorber is 24-36 hours, after which the gas supply is switched to another adsorber, and the spent zeolite layer is treated with hot inert gas (up to 350 °C). According to A. D. Sulimov, adsorbers for gas drying can be turned on only for the period when the reformer is brought to operation, as well as during catalyst regeneration.

As a rule, before sending the factory gases to separation, they are subjected to purification. The purpose of purification is most often the removal of sulfur compounds, represented in petroleum gases mainly by hydrogen sulfide. The presence of hydrogen sulfide in the gas is unacceptable due to: 1) the corrosive and toxic properties of hydrogen sulfide and 2) the poisoning effect on many catalysts. Since the concentration of hydrogen sulfide in the gas during the processing of sulfurous raw materials can be very significant, it is necessary not only to remove it from the gas, but also to use it to produce sulfur or sulfuric acid. If heavy gas components are obtained from the process plant in liquid form (under pressure), they are sometimes subjected only to washing with alkali to remove sulfur and acid compounds. To purify hydrocarbons in the gas phase, aqueous solutions of ethanolamines, phenolates and other reagents are used. The most common cleaning ethanolamines:

H 2 N-C 2 H 4 OH HN (C 2 H 4 OH) 2 N (C 2 H 4 OH) 3

monoethaiolamn diethanolamn triethanolamine

Gas purification with ethanolamines is a typical example of a circular sorption process (Fig. 101). In processes of this type, hydrogen sulfide is absorbed from the gas by a reagent solution in one apparatus and is released from the solution as a result of its stripping in another apparatus. The thus regenerated reagent is returned to the absorption of hydrogen sulfide. Gas purification occurs by chemisorption of hydrogen sulfide with a 15-30% aqueous solution of ethanolamine. Sometimes a mixture of ethanolamine with ethylene glycol is used or the gas is treated sequentially with these solvents. For example, at catalytic) reforming plants of an older type (35-5), where the hydrotreatment of raw materials o "ETS at TST was high, it was provided for the purification of circulating gas a with monoethanolamine, followed by washing with water and drying with DIE

lenglicol. T^xno^ LO Giche Purified CepoSodopol What is the factory cleaning scheme

Rice. 101. Technology system gas purification with two-stage supply of monoethanolamine:

1 - absorber; 2 - absorbent refrigerators; 3 - pumps; 4 - heat exchangers; 5 - hydrogen sulfide refrigerator; 6 - desorber; 7 - knucklehead.

gases, in principle, does not differ from that for natural gas.

Of the other amines i, methyl diethanol ^ min ^ N-methylpyrrolidone ((cyclic amine) is used; pos ^ L 0 diy is recommended for ras 30Bj containing, in addition to ^ hydrogen sulfide, a significant amount of carbon dioxide.

The main devices for cleaning gases with liquid reagents are a plate-type or packed-type absorber and a stripping column ha (de-sorber). The absorber is made of carbon steel; it has 10-20 plates or a nozzle from Raschig rings. The stripping columns for hydrogen sulfide stripping are also manufactured! yut ta. ribbed or packed.

The heat required for steaming is introduced through an external boiler, usually heated by water vapor. An important parameter is the temperature at the bottom of the desorber. So, for monoethanolamine, a stripping temperature of no more than 125 ° C is recommended, since with an increase in temperature, the rate of time, laying down of this reagent increases rapidly. Due to the high temperature at the bottom of the stripping column and in the boiler, hydrogen sulfide corrosion is observed, so the tubes of the TIL-nika boiler are made of stainless steel (St. 18-8); The lower part of the column also has a corresponding lining.

GAS SEPARATION INTO COMPONENTS

The composition of factory gases, presented in table. 39 (p. 275), is typical for the entire gas (balance amount) F obtained in this process, i.e. it means that ) g etI . the zine fraction does not contain gaseous components - gasoline is stable. Practical separation of gas from be! NZ ina can be carried out in one or more steps.

Thus, for example, during catalytic reforming and hydrogenation processes, a hydrogen-containing gas is separated in a high-pressure gas separator. The concentration of hydrogen in it is determined by the pressure and separation temperature: the higher the pressure and the lower the temperature, the greater the solubility of the hydrocarbon part of the gas in the catalyzate and the “drier” (lighter) the gas separated from the catalyzate.

In the high-pressure gas separator, placed according to the scheme of the catalytic reforming unit directly behind the heat exchangers and condensers, the pressure is almost the same as in the reactor block, for example, 3 MPa; this ensures that the gas is separated from 70-80% (vol.) hydrogen, and most of the hydrocarbon components remain dissolved in the catalyzate. The compositions of the gas and liquid phases will be determined by the equilibrium relations inherent in a given combination of temperature and pressure. In the next gas separator, a part of the hydrocarbon gas is released from the catalyzate due to the pressure difference, but its heaviest part remains (predominantly) in the catalyzate, which must be stabilized. A similar picture is observed in hydrogenation plants.

In the process of catalytic cracking, which takes place at a pressure close to atmospheric, the low pressure in the gas separator makes it necessary to resort to a compressor, which receives gas. However, in this case, although the gas separator mode favors the separation of heavy components, the latter will partially remain in gasoline, and its stabilization will be required. At the same time, the gas leaving the gas separator captures a light fraction of gasoline, which must then be extracted from it.

Many of the modern schemes combine the separation of gas into components and the stabilization of gasoline.

For a clear separation of gaseous hydrocarbons, fractionation or a combination of rectification with absorption is required. The latter is necessary if there is a lot of "dry" part in the gas, especially methane. In this case, it is advisable to first separate the "dry" part by absorption, followed by separation of the rest of the gas by distillation. At a moderate methane content, the absorption unit can be excluded from the scheme. On fig. 102 shows a scheme of this type, intended for the separation of saturated gases: wet gas and unstable head fraction from atmospheric oil distillation units, as well as catalytic reforming gases.

All gaseous components (hydrocarbon reformer gas, straight run gas) are subjected to compression by a compressor CC-1) followed by cooling in a water cooler XK-1 and ammonia refrigerator HK-2 up to 4 C. To liquefied gas in the collection C-4 attach unstable liquid stabilization distillates from the AT and reforming units and direct the entire stream to the deethanizer column K-1-

Column K-1 operates in the mode of incomplete condensation of the head product - methane-ethane fraction. Ammonia refrigerator-

Rice. 102. Technological scheme of gas fractionation plant (GFU):

CC-1- gas compressor; XK-1- water cooler; XK-2, XK-3- ammonia refrigerators; XK-4, XK-5, XK-6 - air coolers; P-1, P-2, P-3, P-4- separators-collectors of liquid gas; K-1 - deethanizer; K "2 - debutanizer; K-3 - propane column; K-4 - isobutane column; E-1, E-2, E-3, E-4 - irrigation tanks; H-1, H-2- pumps.

Nick HK-3 cools the head strap to 0°C; at the same time, the condensate (heavier part of the dry gas - ethane) circulates in the form of irrigation, and the balance amount of dry gas leaves the top of the tank E-1. De-ethanized residue from the column K-1 enters the further separation in the column K-2. Column K-2 serves to separate the propane-butane fraction from Cs and higher hydrocarbons. Head strap of the column K-2 after condensation and cooling, it partially serves as an irrigation of this column; the rest of the condensate goes to the propane column K-3, where the propane fraction is separated. in a column K-4 separation occurs n- and iso: butane.

Below are the main operating parameters of the columns of the described HFC and the number of plates in the columns:

Installations for gas fractionation by rectification are characterized by some features. The need for complete or partial condensation of the overhead makes it necessary to carry out rectification under pressure, which is higher, the lighter the overhead. However, increased pressure makes separation difficult. For example, for a binary mixture of propane + isobutane, the relative volatility a at 100 ° C and 2 MPa is “1.7, and at the same temperature, but at 1 MPa already a = 1.9, i.e. separation is facilitated.

The subsequent use of gas components requires a fairly clear separation and high selection from the potential, so the HFC columns contain a large number of plates. It is known that the allowable vapor velocity in columns is a function of the density difference between the hot reflux flowing down from the plate and the vapor rising in the same section. Since an increase in pressure to 1–2 MPa increases the vapor density by a factor of 10–20, respectively (against separation conditions at atmospheric pressure), the permissible vapor velocities in HFC columns do not exceed 0.20–0.25 m/s.

The described HFC scheme is of little use if the gas is rich in methane, which is typical, for example, for thermal cracking and coking gases. In this case, in the irrigation tank of the first column (deethanizer), due to the high partial pressure of methane, it is not possible to achieve even partial gas condensation. The column works only as an evaporator, and it is necessary to include a unit for the preliminary absorption separation of the methane-ethane fraction in the gas fractionation scheme, i.e., to separate the gas according to the absorption-rectification scheme (AGFU).

The use of conventional absorption is not effective enough, since absorption alone cannot achieve a clear separation, and if dry gas is selected to 100% of the potential content in the gas mixture, it will inevitably take with it some of the heavier components. If, on the other hand, the Cs fraction is completely absent in the dry gas, a part of the dry gas will leave together with the saturated absorbent and, when the latter is stripped, will fall into the Cs-C 4 fractions.

The most widely used apparatus at present is called a fractionating absorber and combining the processes of absorption of the C3 fraction and desorption of dry gas (therefore, a fractionating absorber is sometimes called an absorber-desorber). The fractionating absorber is a combined column; cold absorbent enters the upper part of it, and heat is communicated to the lower part. Wet gas is fed into the middle part of the apparatus (Fig. 103). Typically, there are 40-50 trays in the apparatus, distributed approximately equally between the absorption and desorption sections. As a result, many

stepwise contact of the gas and liquid phases in the upper h parts of the apparatus absorbed the heaviest part of the gas; flowing down, the saturated absorbent encounters increasingly hot parfas desorbed from the liquid flowing into the lower parts of the column. As a result, from the top of the fractionating absorber leaves

dry a gas containing hydrocarbons Ci-C 2, and from below, together with a lean a&bsorbent, hydrocarbons C 3-3-C 4 are removed.

Rice. 103. Fractionating absorber (deethanizer):

I - column; 2, 4 - refrigerators "absorbent; 3 - pumps; 5 - boiling

The pressure in the fractionating absorber is usually maintained at 1.2 to 2.0 MPa, although in some cases it reaches 3 MPa. With an increase in pressure, the absorption of gas cleaning agents increases, but it should be borne in mind that an increase in pressure in the range of 1.2-2 MPa does not contribute much to the absorption of propane, and at the same time, the non-accumulative absorption of ethane increases significantly (equilibrium constants of hydrocarbons Cu-Cr decrease with increasing pressure to a greater extent than for hydrocarbons Cz-C 4).

Below is a diagram of a unit * for joint gas separation and gasification of catalytic cracked gasoline operated at one of the plants (Fig. 104). The main gaps are the gas-fractionated absorber 3, stabilization column 8, propane column 11 sh butane column 14.

Wet gas from the gas separator through the top of the mist separator / enters the cleaning unit A monuet-nolamine and then by compressors is fed into the gas-fraction-expanding absorber 3; unstable gasoline from the bottom of the tank is pumped there as irrigation 2, as well as (slightly above the gas inlet) the condensate formed as a result of the compression of the wet gas, and the liquid from the mist separator /.

The main absorbent supplied to the top of the absorber 3, serves unstable gasoline from the tank 2\ in addition, stable gasoline (several plates higher) is supplied to absorb the carryover of unstable gasoline. The absorber has a system

three circulating irrigations for removal of absorption heat; circulating streams are cooled in water coolers 4 and return to the overlying plate. Dry gas passes through a gas separator 5, where a certain amount of condensate separates” and goes into the gas network of the plant.

dry gas

1 - drop eliminator; 2, 10 - containers; 3 - gas-fraction absorber; 4 - Refrigerators of circulating irrigation; 5 - gas separator; 6 - tubular furnace (riboiler); 7 - heat exchangers; 8 - stabilizer; 9 - refrigerators-condensers; 11 - propane column; /2-. refrigerators; 13 - riboilers; 14 - butane column; A - gas purification unit with monoethanol» amine; B - compressor room; IN - block for purification and drying of stabilization distillate; G- block of alkalization of stable gasoline.

De-ethanized gasoline with absorbed C 3 -C 4 fractions is heated in the heat exchanger 7 and fed into the stabilization column 8, the purpose of which is debutanization of gasoline. Bake 6 (two-section) is a reboiler for columns 3 to 8. Stable gasoline passes through heat exchanger 7, gives off heat to unstable gasoline and propane column feedstock, cools in the refrigerator 12 and goes to the block G alkalization. The distillate (head) of stabilization is condensed in the refrigerator-condenser 9 and from the container 10 partially pumped out for column irrigation 8\ the balance amount of the distillate is sent sequentially for purification with monoethanolamine and alkali solution and for drying with diethylene glycol. Then the distillate, consisting mainly of Cs-C4 fractions, is sent to the column AND to separate the propane-propylene fraction, which is removed from the installation from the top of this column after condensation and cooling.

The remainder of the column 11 flows into the column 14, where there is a similar separation of the butane-butylene fraction from the heavier residue (mainly the C5 fraction), which through the refrigerator 12 joins the stream of stable gasoline. In view of

Table 41

Absorber3 Column8 ColumnJ1 Column14

Indicators

Diameter, mm

Distance between plates, mm Pressure, MPa Temperature, °C

power supply section

Irrigation frequency

Note. Each column contains 60 double flow valve trays.

the fact that the temperature of the bottom of the columns I and 14 relatively small (Table 41), they are heated by steam reboilers 13.

The described installation has a design capacity of 417 thousand tons per year, including 257 thousand tons of unstable gasoline and 160 thousand tons of wet gas. In the process of operation, the productivity of the installation exceeded the design one. Purity of propane-propylene fraction 96%, butane-butylene 97%; selection from the potential, respectively, 82 and 95%; dry gas contained only 0.3% of the C 4 fraction and almost 90% consisted of fractions up to C 2 (inclusive).

Usually, at the distillation unit for unsaturated gases, separation of fractions C 3 and C 4 is practiced without their subsequent separation into the limiting and unsaturated parts. If the refinery provides for the polymerization of propylene or its use as a component of the alkylation feedstock, propane accompanying propylene does not adversely affect these processes. Since propylene completely reacts, propane is then easily separated from the products. The same can be said about n- butane. If the plant has a catalytic cracker, it is usually accompanied by an olefin isobutane alkylation unit; the ballast fraction in this process is n-butane, which is then isolated from the catalyzate.

USE OF GAS COMPONENTS

Dry gas, propane-propylene and butane-butylene fractions leave the AGFU units of the unsaturated gas separation unit. Typical industrial gases from unsaturated hydrocarbons contain only olefins: ethylene, propylene, butylenes. Hydrocarbons of higher unsaturation - acetylene, butadiene - are found only in pyrolysis gases, and in thermal cracking gases they appear only with a significant tightening of the regime.

Polymerization of gaseous olefins can produce a variety of products - from light gasoline fractions to high molecular weight polymers, the molecular weight of which reaches two to three million.

In the 1930s, the process of selective catalytic polymerization of butylenes was widely used for the purpose of subsequent hydrogenation of the dimer (iso-CgHie) and thus obtaining technical isooctane, a component of aviation gasoline. This process subsequently lost its significance, since it was replaced by catalytic alkylation of isobutane, which is contained in large quantities in catalytic cracking gases, with butylenes. Later, a process for producing polymer-gasoline based on propylene was introduced, which was less scarce. Phosphoric acid supported on quartz is used as a catalyst. Polymerization is carried out at 220-230 °C, 6.5-7.0 MPa and space velocity of feedstock from 1.7 to 2.9 h -1 . Copolymerization of propylenes and butylenes or butylenes and amylenes is also used.

The saturated hydrocarbons contained in the polymerization feedstock do not naturally react, but have a beneficial effect on the thermal balance of the reactor, preventing the reaction from going too deep, which is accompanied by the formation of heavier polymers. The heat of polymerization is "1550 kJ (370 kcal) per 1 kg of propylene. The maximum octane number - about 90 - has a polymerizate obtained from the butylene fraction (dimer); gasoline - a product of the polymerization of propylene - has an octane number of approximately

10 below (80-82 by motor method). According to the chemical composition, polymer-gasoline, of course, consists almost entirely of olefins, which causes its low chemical stability during storage and low injectivity to ethyl liquid; with the addition of 3 ml of TES, the octane number of polymer-gasoline increases by only 3-4 units.

The great need of the petrochemical industry for propylene forced the abandonment of the use of this olefin for the production of polymer gasoline.

Catalytic Alkylation of Isobutane with Olefins

The essence of the process. The alkylation process consists in the addition of an olefin to paraffin with the formation of the corresponding hydrocarbon of a higher molecular weight. From the point of view of the molecular structure, the resulting alkyl paraffin can be considered as the original paraffin, in which one hydrogen atom is replaced by an alkyl group. However, the main reaction is accompanied by a number of side reactions, resulting in a more or less complex hydrocarbon mixture.

Various modifications to the alkylation process have been made in the oil refining industry. The most common installations for the alkylation of isobutane with olefins (mainly butylenes) to obtain a wide gasoline fraction - alkylate. Alkylate, consisting almost entirely of isoparaffins, has a high octane number (90-95 according to the motor method) and is used as a component of automobile and aviation gasolines. For some time, the product of benzene alkylation with propylene, isopropyl benzene (cumene), was also widely used as a high-octane component of aviation gasoline. Due to the continuous reduction in the production of aviation fuel for carburetor engines, cumene has lost its importance as a fuel component, but is used as an intermediate in the production of phenol and acetone. In the years

World War II, another high-octane component, neohexane (2,2-dimethyl-butane), was produced (in limited quantities) by thermal alkylation of isobutane with ethylene.

In 1932, V.N. Ipatiev showed the possibility of the interaction of isobutane, previously considered an "inert" hydrocarbon, with olefins. AlCl was used as a catalyst. This reaction, then developed using other catalysts - sulfuric acid and later hydrogen fluoride - was quickly introduced into industry. The first industrial plants for sulfuric acid alkylation were put into operation at the end of the 1930s, and hydrofluoric alkylation plants in 1942. Initially, the target product was exclusively a high-octane aviation gasoline component, and only in the postwar years did alkylation begin to be used to improve the motor qualities of commercial motor gasoline.

In an industrial alkylation process, it is easier and cheaper to obtain a high-octane component of gasoline than in the previously used process of catalytic polymerization of butylenes with subsequent hydrogenation of the dimer to isooctane. Replacing the selective polymerization of butylenes with catalytic alkylation of isobutane with butylenes provided the following advantages:

1) obtaining gasoline rich in isooctane in one stage instead of a two-stage polymerization - hydrogenation process;

2) half the consumption of valuable olefins to obtain the same amount of high-octane component;

3) no hydrogen consumption for hydrogenation;

4) more complete involvement of olefins contained in plant gases; during alkylation, the olefins react completely, while during polymerization, a less active olefin (for example, n-butylene in the polymerization of a mixture of butylenes) remains partially unreacted.

However, the catalytic alkylation of isobutane began to develop intensively only as a result of the widespread introduction of catalytic cracking units. Catalytic cracking gas, rich in isobutane, provided alkylation plants with one of the feedstock components, and thermal process gases had to be used to produce olefins.

The main factors of the process. As industrial alkylation catalysts, only sulfuric acid and liquid hydrogen fluoride are used. The choice of these substances is due to their good selectivity, ease of handling liquid catalysts, relative cheapness, and long cycles of plant operation due to the possibility of regeneration or continuous replenishment of catalyst activity.

Catalytic alkylation in the presence of sulfuric acid or hydrogen fluoride can only be subjected to isostructure paraffins containing an active tertiary hydrocarbon atom. In this case, the alkylation of isobutane with ethylene is difficult, obviously due to the stability of the resulting intermediate compounds - ethers. Alkylation with propylene and especially with butylenes proceeds quite deeply. The concentration of the acid is decisive. So, for alkylation of isobutane with butylenes, 96-98% sulfuric acid can be used, while for alkylation with propylene, only 98-100% acid is used.

Characteristically, as a result of the main reaction of addition of isobutane to the olefin, simultaneous structural isomerization occurs, which indicates the highest probability of the carbonium-ion chain mechanism. Along with the main alkylation reaction, in which 1 mole of olefin is consumed per 1 mole of isobutane, side reactions occur.

1. Hydrogen transfer, or self-alkylation. So, the interaction of isobutane with propylene partially goes in the following direction:

2iso-C 4 H 10 -j- C 3 H e -> iso-C 8 H 18 -j- C 3 H 8

This reaction is undesirable, as it causes an increased consumption of isoparaffin and the formation of low-value propane.

2. Destructive alkylation. The primary alkylation products are cleaved, and the resulting olefin (different from the original) reacts again with the original paraffin, for example:

2 "zo-C 4 H 10 + SdH, -> iso- C 5 H 12 + iso- C to H 14

3. Polymerization. Acid catalysts cause the polymerization of olefins, therefore, the regime unfavorable for alkylation - a low concentration of isoparaffin, insufficient catalyst activity and elevated temperature - cause the appearance of polymers in the composition of alkylation products.

In the process of alkylation, a gradual deactivation of the catalyst occurs - a drop in the concentration of the acid and its darkening, caused by the interaction of the acid with unsaturated hydrocarbons and moisture. Moisture can be contained in the feedstock, and is also formed as a result of the side interaction of olefins with. acid:

SlN 2P + H a S0 4< - ¦ ? - С Л Н 2Л _2 + 2Н 2 0 -t- so 2

Decreasing the acid concentration weakens the target alkylation reaction and increases the proportion of polymerized olefins. The required acid concentration in the reaction zone is maintained by partial or complete replacement of the spent acid with fresh one.

The alkylation reaction proceeds with a positive thermal effect ("960 kJ, or 230 kcal per 1 kg of alkylate"). To maintain the isothermal regime, the released heat must be continuously removed from the reaction zone.

Thermodynamically, alkylation is a low temperature reaction. Temperature limits for industrial sulfuric acid alkydation from 0 to 10 °С; alkylation in the presence of hydrogen fluoride is carried out at a slightly higher temperature - about 25-30 °C. This difference is explained by the fact that at temperatures above 10-15°C, sulfuric acid begins to intensively oxidize hydrocarbons.

Although lowering the temperature slows down alkylation, it increases its selectivity towards the formation of the primary alkylation product, and therefore the quality of the resulting alkylate improves. A decrease in temperature by 10-11 °C causes an increase in the octane number of the alkylate by about 1. An excessive decrease in temperature is limited by the solidification temperature of the catalyst acid, as well as an increase in the viscosity of the catalyst and, consequently, the difficulty of dispersing it in the reaction mixture. The possibility of carrying out the reaction at a higher temperature is one of the advantages of hydrogen fluoride, since this simplifies the system for removing heat from the reaction mixture.

The pressure in the reactor is chosen so that all or most of the hydrocarbon feedstock is in the liquid phase. The pressure in industrial reactors is on average 0.3-1.2 MPa.

The catalysts used cause the polymerization of olefins, so it is necessary that the concentration of olefins in the reaction mixture was significantly lower than required by the stoichiometric reaction equation. For this purpose, it is practiced

Table 42. Indicators and product yield in the production of alkylate - a component of motor gasoline

Data by O. Iverson and L. Schmerling

* Yield of depentanized total alkylate.

adding raw materials with a stream of isobutane, continuously circulating in the system. The molar ratio of isobutane: olefin in the hydrocarbon mixture entering the alkylation is usually (4-=-10) : 1; the most commonly used is a six- or seven-fold dilution. With an excess of isobutane, the quality of the alkylate increases and not only polymerization is suppressed, but also side reactions of dealkylation. Since the selectivity of the process increases with a large ratio of isobutane, the consumption of olefins per unit amount of isobutane is reduced. Increasing the ratio of isobutane:olefin more than 10:1 is ineffective. It should be taken into account that with an increased expansion rate of isobutane, the operating costs for its circulation and cooling increase, and it is also necessary to increase the size of the main apparatuses.

Of great importance is the intensity of mixing of the hydrocarbon phase and the catalyst, due to the fact that their mutual solubility is very low. Obviously, the reaction takes place in the catalyst phase and at the phase boundary between the isobutane dissolved in the catalyst and the olefin component of the feedstock. In the absence or deficiency of isobutane, the contact of the olefin with the acid causes polymerization of the olefins. Intensive mixing also promotes the separation of the resulting alkylate from the catalyst. The desire to increase the concentration of isobutane at the point of entry of the mixture has led to the development of special mixing and circulation devices that allow increasing the

the ratio of isobutane and olefin in the incoming mixture is up to 100: lH or more. From the data in Table. 42 it can be seen that the ratio between H30 -H butane and olefin in the initial feed mixture should be close to theoretical. The highest octane number of alky-R lata is observed with butylene raw materials. I

The concept of the duration of the reaction is conditional for this process, since, in accordance with the above, And the reaction may not proceed in the entire volume of the catalyst. Conditional In the duration of the reaction. IN

The amount of acid dispersed in the reactor should be taken as the volume of the catalyst, since the rest of it, P falling-B giving into the settling zone or not forming an emulsion and 3 (- due to not-B sufficiently intensive mixing, in fact, will not catalyze the alkylation. However, this volume cannot be taken into account, and in this case the conditional space velocity is expressed by the volumetric amount of olefins supplied per hour per unit of catalyst volume. Insufficient mass exchange causes local overheating of the reaction mixture and a decrease in the quality of the alkylate.The average volumetric feed rate of olefins for sulfuric acid alkylation is 0.1-0.6 h -1.

The completeness of the reaction is ensured when the hydrocarbon phase stays in the reactor for a long time of 5–10 min for hydrofluorofluoric alkylation and 20–30 min for sulfuric acid–B th alkylation. In this case, the volume ratio of catalyst and hydrocarbon is taken equal to 1: 1 (this is established based on i the presence in the reactor of a homogeneous emulsion of hydrocarbons in acid). An increase in the relative volume of acid does not harm the process! su, but increases the viscosity of the mixture and, accordingly, energy consumption! gii for mixing; a decrease in the proportion of acid leads to ! the formation of its emulsion in hydrocarbon, to the deterioration of the Quality I of the alkylate and to an increase in catalyst consumption. Ratio acid-I lot: the hydrocarbon varies somewhat depending on the con-? concentration of acid, its density, quality of raw materials, type of reactor \ etc. The above 1:1 ratio is an average. I Industrial plants for sulfuric acid alkylation. In the oil refining industry, the process of sulfuric acid alkylation is the most common. The released heat is removed in two ways: 1) by cooling the reaction mixture through the heat exchange surface; 2) cooling the mixture by its partial evaporation. Accordingly, there are two types of reactors.

On fig. 105 and 106 are sketches of the reactors of the first type, the so-called contactors.

On fig. 105 shows a vertical contactor (overall height '11.7 m, internal diameter '2 m) of an older type, designed for a small capacity. The reaction mixture is cooled with ammonia or propane circulating through double tubes.

hmdoagent1

cold agent

Products

reactions

Acid

Raw material

Rice. 105. Vertical contactor:

I- frame; 2 - cylindrical casing; 3 - tube bundle; 4 - propeller pump.

Having exited through the open ends of the inner tubes, the liquefied gas passes into the outer annular gap and, evaporating, exits the system. Heat removal is regulated by changing the pressure in the cooling system. The reaction mixture is stirred with a propeller pump; the drive is an electric motor or a steam turbine. The working volume of the reactor is divided by a cylindrical partition; a mixture of hydrocarbons and acid, driven by a propeller pump, continuously circulates in the apparatus, rising along the annular section and descending along the inner cylinder, where heat is removed from it through the surface of the cooling tubes. To streamline the upward flow, vertical ribs are welded to the cylindrical baffle.

In a horizontal contactor (Fig. 106), the introduction of raw materials and a catalyst is more successfully carried out - they immediately fall into the zone of the most intensive mixing. Next, the mixture is pumped through the annular space and at the opposite end of the apparatus turns into the inner cylinder. The horizontal arrangement of the apparatus

Eliminates the need for a gear drive to the actuator and facilitates maintenance of the contactor. An extremely intensive circulation takes place in the apparatus; its multiplicity reaches 200 m 3 per minute at large installations. With such a circulation ratio, the incoming mixture is almost instantly mixed with the emulsion filling the reactor. The isobutane:olefin ratio at the point of entry of the feed stream reaches 500:1 or more. Horizon-

Rice. 106. Horizontal contactor:

1 - tube bundle; 2, 5 - circulation pipe; 3 - frame; 4 - propeller stirrer:

6 - guide blades; 7 - turbine.

tal contactors are structurally simpler. They also differ in that a stream of reaction products is used as a refrigerant. Their capacity is greater than that of vertical apparatuses, but it can only be increased to certain limits, since the use of very large contactors worsens the quality of mixing; therefore, they prefer to install at least three or four contactors.

The power supply system of the devices is of great importance. Experience in the operation of sulfuric acid alkylation plants has shown that it is expedient to feed circulating isobutane and catalyst into the contactor sequentially, and it is better to feed the initial hydrocarbon mixture (isobutane and olefins) in parallel, distributing it into streams according to the number of contactors. In this case, the relative proportion of olefins in the reaction mixture decreases, which makes it possible to increase the selectivity of the process, reduce the consumption of sulfuric acid, and improve the quality of the alkylate.

Such a change in the reactor feed system at one of the alkylation units at the Grozny plant reduced* acid consumption by 35%. Sometimes, with such a scheme of operation of contactors, an additional parallel supply of acid is practiced. For example, in a system of four contactors, circulating isobutane passes in series, the original hydrocarbon

the flow is divided into four parallel ones, and the acid, having passed the first and second reactors, settles from the hydrocarbon phase in the settler and returns to the first reactor again. Similarly, the third reactor receives acid from the sump serving the third and fourth reactors.

In alkylation reactors By Intensity of mixing of the reaction mixture is of great importance. Decrease E 91 temperature increases octa ~

13 p i W P id Temperature°?

Rice. 107. Effect of temperature on the octane number of alkylate.

new alkylate number<§ 30

(Fig. 107). However, it was shown that for a given number J 89 revolutions (320-380 per minute), the temperature should not be lower than 10-11°C, since with a further decrease in the viscosity of the reaction emulsion, it increases so much that a greater number of revolutions of the stirrer is required. Thus, the reaction temperature and the stirrer speed must be in optimal combination - in particular for vertical contactors, 8 °C and 500-520 rpm are recommended with a contact time of 8-10 minutes *.

The cascade reactor most fully corresponds to modern high-power plants (Fig. 108). This is a reactor of the second type, where the mixture is cooled due to its partial evaporation. The cascade reactor is a horizontal cylindrical apparatus with several displacement sections equipped with agitators and a two-section settling zone. Circulating isobutane and sulfuric acid enter the first mixing section; the feedstock - a mixture of isobutane with olefins - is evenly distributed over all sections, due to which a significant excess of isobutane is provided in each zone. The scheme of the mixing section is shown in fig. 109. Above the agitators there are coils for the input of raw materials and vertical perforated pipes for the circulation of the emulsion. The direction of the emulsion flow can be seen in Fig. 109.

The accepted mode of pressure in the reactor is as follows: in the first mixing section 0.15-0.20 MPa, the pressure drop for each section is 0.01-0.02 MPa; the average olefin space velocity is about 0.3 h - 1 . In the last two sections, the acid is separated from the hydrocarbon layer. The temperature and pressure in the reactor provide partial evaporation of the hydrocarbon phase, mainly the lightest component - isobutane. Evaporated-

the gas is sucked off by a compressor and, after cooling and condensation, is returned to the reaction zone. The released heat of reaction is removed by the heat of evaporation of isobutane. The temperature in the reactor is maintained at a given level automatically.

The cascade reactor can have from three to six mixing sections. There are installations with a reactor in which there are six mixing sections (three on each side) and one settling zone located in the middle part of the apparatus. One of the largest plants for sulfuric acid alkylation with a capacity of up to 950 m

Rice. 108. Horizontal cascade type reactors: A- five-section; b- double;

1 , 2, 3, 4, 5 - sections; b - acid settling zone; 7 - alkylate withdrawal zone; 8 - nozobutane capacity.

5-stage reactor with a diameter of "3.5 m and a length of" 22 m.

The presence of cascade reactors operating on the principle of "auto-cooling" simplifies and reduces the cost of alkylation plants, as it makes it possible to abandon the refrigerant (ammonia, propane). A comparison of the specific consumption of sulfuric acid in the reactors of the described designs indicates the advantages of a cascade reactor; for a vertical contactor, this flow rate is

Rice. 109. Mixing section of the cascade reactor:

1, 2 - sections of the reactor; 3 - stirrer; 4 - circulation pipes.

200-250 kg per 1 ton of alkylate, in cascade 60-100 kg/ton. The octane number of the target product (light alkylate) in the first case is 90-91 (according to the motor method), in the second 92-95. However, cascade reactors have some drawbacks: the sections are interconnected, and a violation of the regime in one of them can lead to a disorder in the operation of the apparatus as a whole; as the emulsion moves, the concentration of isobutane decreases.

The basic technological scheme of the sulfuric acid alkylation unit is shown in fig. 110. This scheme is characterized by a complex distillation unit consisting of four distillation columns: propane, isobutane,

butane and alkylate secondary distillation column. The initial hydrocarbon mixture is cooled by evaporating butane in a refrigerator and enters in five parallel streams into the mixing sections of the reactor; circulating isobutane and sulfuric acid are also fed into the first section. Sulfuric acid exits the reactor settling zone (for circulation or for discharge) To a hydrocarbon mixture that is neutralized with alkali and washed with water.

The part of hydrocarbons evaporated in the reactor through the drop breaker enters the compressor intake 2, which feeds it through a refrigerator into a container and a propane column 3. This column serves to separate and remove propane from the system in order to avoid its gradual accumulation in the system. The rest of the propane column - isobutane - partially circulates through the raw cooler and compressor intake 2, and partially joins the total flow of circulating isobutane. The main hydrocarbon stream from the settler 5 is sent to the isobutane column 6 for separation of recirculating isobutane. The head logon of this column - isobutane - is returned to the first mixture -

initial

carbsZoroda

"4 p Yu

Etc-^Heavy

alkylate

Alkali + baud

Rice. 110. Technological scheme of sulfuric acid alkylation of nozobutane with olefins:

1 - reactor; 2 - compressor; 3 - propane column; 4 - irrigation tanks; 5 - sump; 6 - isobutane column; 7 - butane column; 8 - Alknla secondary distillation column; 9 - coalescing apparatus; 10 - separator.

the body section of the reactor. With a certain excess of fresh isobutane in the feedstock, its removal is envisaged. The rest of the iso-butane column enters the butane column 7 for further separation, and the remainder of the butane column goes to the column 8 for the distillation of alkylate. Vapors of the target fraction (light alkylate) leave the top of this column, and heavy alkylate, which boils above 150-170 ° C and is usually used as a component of kerosene, leaves from the bottom.

In table. 43 presents data on distillation columns of a large alkylation plant and their mode of operation. For a clear separation of the products, the columns are equipped with steam ri-boilers and, as can be seen from the table, have a significant number of plates. Instead of a stream of circulating isobutane, it is possible to depropanize the distillation of the isobutane column. The advantage of such a system is a slightly higher concentration of propane in the feed of the propane column, which facilitates the separation of propane.

In many modern sulfuric acid alkylation plants, the hydrocarbon stream leaving the reactor is purified with bauxite and only then neutralized with alkali and washed with water. This purification is needed to separate the esters formed under the action of the catalyst. When treated with alkali, only part of the acidic products is neutralized, and the most persistent of the esters either decompose when heated and cause gradual sludge formation in the distillation system and corrosion, or get into the commercial alkylate and reduce its antiknock performance.

To remove these harmful impurities, the hydrocarbon stream after the reactor is sent sequentially to a coalescer filled with glass wool and to one or two columns filled with bauxite. The purpose of the coalescing apparatus is to remove the smallest droplets of acid contained in the hydrocarbon stream. Bauxite columns work alternately: through 1 kg of bauxite, from 500 to 1500 mA of alkylate can be passed (depending on the degree of its contamination with ethers), after which the hydrocarbon stream is switched to the second column. The removal of traces of sulfuric acid and esters by bauxite is based on the selective adsorption of these polar compounds. The health of bauxite is judged by the beginning of desorption - the release of neutral esters containing sulfur together with alkylate. Contaminated bauxite is blown with water vapor, washed

Table 43. Dimensions and technological parameters of distillation columns at the sulfuric acid alkylation unit

Data by V.P. Sukhanov

water and dried by passing hydrocarbon gas through it. The bauxite-purified hydrocarbon stream is subjected to alkaline and water washing. Due to the fact that bauxite purification is introduced into the alkylation scheme, the duration of the continuous run of the installation increases and exceeds 8 months.

The decisive influence on the formation of esters is exerted by the intensity of mixing of the emulsion in the reactor; at high stirring intensity, the esters decompose. An analysis of the operation of industrial plants showed that the minimum content of esters in the total alkylate was observed at a sulfuric acid concentration of 89–92% (mass) (Fig. 111). The presence of a minimum is explained by the fact that at a higher acid concentration, its interaction with olefins is enhanced, i.e., the formation of esters is also activated. At excessively low acid concentrations, its selectivity as an alkylation catalyst decreases, and the esters leave with the alkylation products.

96 94 92 90 88 8$

Concentration H 2 S0 4,% (wt.)

Rice. 111. Dependence of the content of esters in the total alkylate on the concentration of sulfuric acid:

1 - alkylation of isobutane with butylene; 2 - alkylation of isobutane with propylene.

Of great importance are the purity and lack of moisture in the alkylation feedstock. It was shown that by reducing the moisture content of raw materials from 0.03 to 0.001% (wt.), it is possible to reduce the consumption of sulfuric acid by 16 kg (per 1 ton of alkylate). The combination of settling tanks placed on the cooled feed stream in front of the reactors with adsorption removal of moisture should give a significant economic effect.

As a result of side reactions, the alkylate, as a rule, contains more or less heavy fractions - boiling over above 170 ° C, i.e., above the end point of the boiling point of commercial gasolines. In this regard, an alkylate secondary distillation column is needed. The yield of heavy alkylate under normal conditions does not exceed 5%. The concentration of isobutane in the reaction zone is decisive here. Since the result of the reaction is determined by the composition of the stream leaving the reactor, it is important that a high concentration of isobutane is maintained in this stream.

The presence of inert diluents (n-butane and propane) degrades the quality of the alkylate, and the purity of the isobutane used for circulation plays a very important role. So, with other equal regime indicators, an increase in the concentration of isobutane in

the hydrocarbon stream leaving the reactor from 40 to 70% (vol.) caused an increase in the octane number of the total alkylate from 90 to 92.8; in the first case, the difference between the octane numbers of the total and light alkylate was “0.9, and in the second it was only 0.3, which indicates that the yield of light alkylate was approaching 100%.

The disadvantage of sulfuric acid alkylation is the rather significant consumption of sulfuric acid due to its dilution by reaction by-products. The lowest consumption of acid is observed if pure butylenes are used as olefin raw materials; when using propylene, the consumption of acid increases approximately three times. As shown above, the consumption of acid is also related to the intensity of stirring of the reaction mixture and to the temperature, the increase of which increases the degree of dilution of the acid. Acid consumption also increases in the presence of impurities such as sulfur compounds and moisture in the raw material. Catalyst costs can be reduced by using spent acid for other purposes (for example, for refining oils and other petroleum products), as well as by regenerating it.

Industrial plants for hydrofluoric alkylation. At foreign plants, alkylation units with hydrogen fluoride as a catalyst are quite widespread. Liquid hydrogen fluoride is more active than sulfuric acid and, due to its volatility (bp 20 °C), is more easily regenerated. Another advantage of this catalyst is its lower density (?1.0 versus 1.84 for sulfuric acid). This facilitates the formation of an emulsion of the catalyst with the hydrocarbon phase in the reactor and even eliminates mechanical mixing. The concentration of the catalyst used is 90%, and it has relatively little effect on the yield and quality of the alkylate. However, the catalyst regeneration system is quite complex.

On fig. 112 is a schematic diagram of a hydrofluoric alkylation unit. Feedstock undergoes bauxite drying in columns 1 and enters the reactors 2. Water-cooled tubular-type reactors are used, since the reaction proceeds at 20-40 ° C. At some plants, the reactors are structurally combined with settling tanks. A feature of hydrofluoric alkylation plants is the presence of a catalyst regeneration system. Alkylate, after settling from the main volume of HF, enters regenerator column 4, where the circulating isobutane is separated as a side stream. Regenerator column 4 heated at the bottom by circulating the residue through the furnace 3. At the same time, isobutane, propane and catalyst are stripped from the alkylate. At. heating the residue to 200-205 °C also destroys organic fluorides formed

as side products of the reaction. From the top of the regenerator column 4 propane, hydrogen fluoride and a certain amount of isobutane leave in the gas phase. After condensation, part of this mixture is returned to the reactors, part is fed to the column for irrigation 4, and the rest is sent to the propane column 6, from the top

Rice. 112. Scheme of the plant for alkylation of isobutane with olefins in the presence of hydrogen fluoride:

1 - drying columns; 2 - reactors; 3 - bake; 4 - regenerator column; 5 - sump; 6 - propane column; 7 - steam heater. .

which leaves stripped hydrogen fluoride, and propane from the bottom

with traces of isobutane.

For a more complete recovery of the catalyst, regeneration (in a separate unit) of a part of the acid layer from the sump is also provided. Alkylate from the bottom of the column 4 after cooling, it passes through bauxite columns, where it is freed from the rest of fluorine compounds. As a result of good regeneration, the catalyst consumption does not exceed 1 kg per 1 ton of alkylate.

The use of a hydrofluoric catalyst, due to its toxicity and significant volatility, requires strict precautions to be taken. Continuous automatic monitoring of points of possible leakage of hydrogen fluoride is carried out: in water flows cooling reactors and condensers, in acid refrigerators, etc. The zone where acid pumps and acid-containing devices are located is considered dangerous, and it can only be entered in special costumes and masks. Much attention is paid to the selection of materials and designs of equipment, equipment and pipelines. Special gasket materials are used from substances resistant to HF - organofluorine plastics. In places of greatest corrosion, monel metal is used, and the main equipment is made of carbon steel.

Sulfuric acid alkylation dominates in US refineries, but by the beginning of 1977, the share of hydrofluoric alkylation already reached 40% of the total (by raw material) against 30.6% in 1970. The relatively faster growth in the capacity of alkylation plants with hydrogen fluoride is explained by the improvement of the process scheme . For example, in some plants where only butylenes are used as olefins, the HF and propane stripping columns are excluded from the scheme, and the isobutane column stripping is directly returned to the process. Installations are described where the mixing of raw materials with acid is carried out in a riser (vertical pipes of large diameter connecting the outlet fittings of acid coolers with the inlet fitting of the reactor). At the same time, the reactors themselves are devoid of mixing devices, which eliminates the destruction of the apparatus from the corrosive action of hydrogen fluoride.

Increasing the resources of raw materials for alkylation. Resources of raw materials for alkylation are limited. Isobutane is found in significant concentration only in the gases of catalytic cracking and hydrocracking; it can also be separated from associated gas. Butylenes are contained in the gases of catalytic, thermal cracking and coking and are absent in the gases obtained from hydrogenation processes.

Isobutane resources can be increased by isomerization n- butane on catalysts related to C5-C6 hydrocarbon isomerization catalysts. Isomerization unit n- butane can be combined with an alkylation unit - with total% p isobutane column.

To expand the resources of olefins, the propylene fraction is involved in the alkylation process or subjected to dehydrogenation n- butane. However, on the one hand, an alkylate based on propylene or its mixture with butylenes has a lower octane number: when using only propylene, by about 5 units. On the other hand, propylene is a valuable petrochemical raw material, and the dehydrogenation of m-butane is more often carried out in order to obtain butadiene, a raw material for the production of synthetic rubber. It is possible that the resources of C 3 -C 4 olefins will increase due to the growing trend towards heavier pyrolysis feedstock AND tougher regime of catalytic cracking units.

USE OF HYDROGEN SULFIDE CONTAINED IN PLANT HYDROCARBON GASES

Hydrocarbon gases from sour oil refineries contain hydrogen sulfide. Part of this hydrogen sulfide is formed during thermal or thermal catalytic destruction of the least stable sulfur compounds contained in petroleum feedstock, during its thermal and catalytic cracking and coking. In this case, the sulfur contained in the raw material is distributed among the products of the process. During hydrogenation processes, a deeper destruction of sulfur compounds occurs: most of them turn into hydrogen sulfide and concentrate in the gas.

In table. 44 shows the approximate yield of dry gas and the content of hydrogen sulfide in it during the main destructive processes of processing petroleum feedstocks. It can be seen that there is only one sour crude oil hydrocracking unit with a capacity of 1 million tons per year. will give from 2200 to 7700 tons of hydrogen sulfide per year.

Hydrogen sulfide from process plants is typically used in refineries to produce sulfur and sometimes to produce sulfuric acid. The most common industrial method for obtaining sulfur based on factory and natural gases is the Claus process, carried out in two stages: 2/xS x+ 2H a O

The first reaction proceeds without a catalyst - hydrogen sulfide is burned with a lack of air (to avoid further oxidation of S0 2 to S0 3). The volume of air entering the combustion zone must be strictly dosed dbiTb in order to provide the required ratio of S0 2 and H 2 S for the second stage of the process. The temperature in the H 2 S combustion furnace, depending on the concentration of H 2 S and hydrocarbons in the gas, is 1100- 1300 °C. The furnace is usually a cylindrical horizontal apparatus. So, on a plant designed to receive l; 145 tons of sulfur per day, the reactor furnace had a diameter of 3.66 m and a length of 10.7 m. Gas burners were mounted along the length of the furnace or at one of the ends. Along the axis of the furnace, there is a horizontal lattice saddle wall for better gas mixing.

Sulfur formation begins already in the first reactor. The reaction of the second stage proceeds over the catalyst - aluminum oxide. The setup diagram is shown in fig. 113. Hot gases from the reactor furnace 1 pass through the waste heat boiler 3, Where they cool down

Table 44. Gas output and hydrogen sulfide content V it during the main destructive processes of processing sour and sour oils

Data I. G. Sorkin

	Gas output for raw materials, % (wt.)
Thermal cracking of 40% sulfurous residue

Catalytic cracking of high vacuum gas oil
crude oil
Delayed coking of 28% cracked residue
mixtures of oriental oils
Hydrotreatment of diesel oil from sulphurous

Hydrocracking of fuel oil.sour crude oil
Thermal contact cracking of sour tar
Arlan oil

Note. Gas yield and HaS content are referred to “dry gas*”, i.e., “excluding stabilization distillation. "

up to about 450 ° C, so that sulfur remains in the gas phase (the condensation temperature of sulfur vapor is “300 ° C). Next, the gas is supplemented

Rice. 113. Scheme of sulfur production (Claus process):

I- oven-reactor; 2 - blower; 3 - waste heat boiler; 4 - acid gas heater; $, 8 - reactors with a catalyst; 6 - economizer; 7, 0 - scrubbers; /0 - sulfur collector; it- capacity of commercial sulfur.

thoroughly cooled in a heat exchanger 4 (not lower than up to 340 °C), and the gas mixture enters the reactor 5, containing a catalyst.

The interaction of Hg5 and S0 2 is favored by low temperatures, hence the reaction is exothermic. Therefore, the catalytic part of the process, in turn, is divided into two stages (reactors 5 and 8 ). Reactor inlet temperature 5 about 340 °C, to reactor 8 about 265 °C; the temperature rise in each reactor is about 40 °C; space velocity of gas supply to the catalyst W 850 h -1 .

Hot gases after the reactor 5 a water economizer 6 and a scrubber 7 with a nozzle pass through, where the gases are further cooled and separated from the condensed sulfur, which flows in the form of a melt from the bottom of the scrubber into the collection 10. The gases from scrubber 7 are reheated in the preheater 4 and the reactor 8 and the scrubber pass in a similar way 9, from where liquid sulfur is also poured into the collection 10. Both scrubbers are sprayed with molten sulfur.

The resulting sulfur has a high degree of purity. Most of it is used to produce sulfuric acid. If for this purpose not sulfur, but directly hydrogen sulfide is used as a feedstock, it is more expensive. In addition, sulfur is easily transported to sulfuric acid production sites, which may not coincide with refinery locations. Sulfur is also used in the rubber industry, medicine, for the production of carbon disulfide and in other sectors of the economy.

Boiling point of propane as a function of pressure. Comparison of liquefied petroleum gas (LPG) and liquefied natural gas (LNG)

Features of propane-butane (LPG)

Compatibility of LPG and LNG with the latest generations of LPG

So let's take a quick look

Propane

The production of both liquefied gas and NGLs is carried out at the expense of the following three main sources:

System

Liquefied hydrocarbon gases

Hydrates

Relevant mixture parameters

Thermodynamic and physical properties of the liquid phase of propane and butane

Butane liquid phase

Thermodynamic and physical properties of propane and butane vapor phase

Vapor phase butane

In the world

Explanations

Pumps .

bypass valve .

Speed ​​valves .

Pressure gauges .

Safety valves .

Filters .

Taps and valves .

Counters and reading devices .

Differential valve

Vacation line

Popular

Speed valves .