Composition of liquefied hydrocarbon gases

Liquefied petroleum gas (LPG)- these are hydrocarbons or their mixtures, which at normal pressure and ambient temperature are in a gaseous state, but with an increase in pressure by a relatively small amount, without changing the temperature, they pass into a liquid state.

Liquefied gases are obtained from associated petroleum gases, as well as gas condensate fields. At processing plants, ethane, propane, and also natural gasoline are extracted from them. Propane and butane are of the greatest value to the gas supply industry. Their main advantage is that they can be easily stored and transported as a liquid and used as a gas. In other words, the advantages of the liquid phase are used for the transportation and storage of liquefied gases, and the gaseous phase is used for combustion.

Liquefied hydrocarbon gas has been widely used in many countries of the world, including Russia, for the needs of industry, housing and public utilities, petrochemical industries, and also as an automotive fuel.

A propane molecule is made up of three carbon atoms and eight hydrogen atoms.

Propane

For gas supply systems operated in Russia, the most suitable is the technical propane(C 3 H 8), since it has a high vapor pressure down to minus 35°C (the boiling point of propane at atmospheric pressure is minus 42.1°C). Even at low temperatures, it is easy to take the right amount of the vapor phase from a cylinder or gas tank filled with propane under natural evaporation conditions. This makes it possible to install LPG cylinders outdoors in winter and to extract the vapor phase at low temperatures.

Butane

When a butane molecule is burned, four carbon atoms and ten hydrogen atoms enter into the reaction, which explains its greater calorific value compared to propane

Butane(C 4 H 10) - cheaper gas, but differs from propane in low vapor pressure, therefore it is used only at positive temperatures. The boiling point of butane at atmospheric pressure is minus 0.5°C.

The gas temperature in the tanks of the autonomous gas supply system must be positive, otherwise the evaporation of the butane component of the LPG will be impossible. To ensure gas temperatures above 0°C, geothermal heat is used: a gas tank for a private house is installed underground.

A mixture of propane and butane

In the domestic sector, a mixture of propane and technical butane (SPBT) is used, in everyday life called propane-butane. When the butane content in SPBT is more than 60%, the uninterrupted operation of reservoir units in the climatic conditions of Russia is impossible. In such cases, LPG evaporators are used to force the transfer of the liquid phase to the vapor phase.

Features and properties of LPG

The properties of liquefied gases affect the safety measures, as well as the design and technical features of the equipment in which they are stored, transported and used.

Distinctive features of liquefied gases:

  • high vapor pressure;
  • have no smell. For timely detection of leaks, liquefied gases are given a specific smell - they are odorized with ethyl mercaptan (C 2 H 5 SH);
  • low temperatures and flammability limits. The ignition temperature of butane is 430°C, propane is 504°C. The lower flammability limit of propane is 2.3%, butane is 1.9%;
  • propane, butane and their mixtures heavier than air. In the event of a leak, liquefied gas may accumulate in wells or cellars. It is forbidden to install equipment operating on liquefied gas in basement-type premises;
  • transition to a liquid phase with increasing pressure or decreasing temperature;
  • high calorific value. To burn LPG, a large amount of air is needed (to burn 1 m³ of the gas phase of propane, 24 m³ of air is needed, and butane - 31 m³ of air);
  • high coefficient of volumetric expansion of the liquid phase(the volumetric expansion coefficient of the liquid phase of propane is 16 times greater than that of water). Cylinders and tanks are filled no more than 85% of the geometric volume. Filling more than 85% can lead to their rupture, subsequent rapid outflow and evaporation of gas, as well as ignition of the mixture with air;
  • as a result of evaporation of 1 kg of the liquid phase of LPG at n. y. 450 liters of vapor phase are obtained. In other words, 1 m³ of the vapor phase of the propane-butane mixture has a mass of 2.2 kg;
  • when burning 1 kg of propane-butane mixture, about 11.5 kWh of thermal energy is released;
  • liquefied gas evaporates intensively and, getting on the skin of a person, causes frostbite.


The dependence of the density of the propane-butane mixture on its composition and temperature

Table of densities of a liquefied propane-butane mixture (in t / m³) depending on its composition and temperature

−25 −20 −15 −10 −5 0 5 10 15 20 25
P/B, %
100/0 0,559 0,553 0,548 0,542 0,535 0,528 0,521 0,514 0,507 0,499 0,490
90/10 0,565 0,559 0,554 0,548 0,542 0,535 0,528 0,521 0,514 0,506 0,498
80/20 0,571 0,565 0,561 0,555 0,548 0,541 0,535 0,528 0,521 0,514 0,505
70/30 0,577 0,572 0,567 0,561 0,555 0,548 0,542 0,535 0,529 0,521 0,513
60/40 0,583 0,577 0,572 0,567 0,561 0,555 0,549 0,542 0,536 0,529 0,521
50/50 0,589 0,584 0,579 0,574 0,568 0,564 0,556 0,549 0,543 0,536 0,529
40/60 0,595 0,590 0,586 0,579 0,575 0,568 0,562 0,555 0,550 0,543 0,536
30/70 0,601 0,596 0,592 0,586 0,581 0,575 0,569 0,562 0,557 0,551 0,544
20/80 0,607 0,603 0,598 0,592 0,588 0,582 0,576 0,569 0,565 0,558 0,552
10/90 0,613 0,609 0,605 0,599 0,594 0,588 0,583 0,576 0,572 0,566 0,559
0/100 0,619 0,615 0,611 0,605 0,601 0,595 0,590 0,583 0,579 0,573 0,567

T is the temperature of the gas mixture (average daily air temperature); P / B - the ratio of propane and butane in the mixture,%

Liquefied hydrocarbon gases(propane-butane, hereinafter LPG) - mixtures of hydrocarbons, which under normal conditions (atmospheric pressure and air T = 0 ° C) are in a gaseous state, and with a slight increase in pressure (at a constant temperature) or a slight decrease in temperature (at atmospheric pressure) change 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 - liquified petroleum gas, 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.
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 tank trucks.
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 supplied to settlements must comply with the requirements of GOST 20448-90. For domestic consumption and industrial purposes, the standard provides for the production and sale of LPG of three grades:
PT - technical propane;
SPBT - a mixture of propane and butane technical;
BT - technical butane.

brand Name OKP code
Fri Propane technical 02 7236 0101
SPBT Mixture of propane and butane technical 02 7236 0102
BT Butane technical 02 7236 0103
Name of indicator Norm for the brand Test method
Fri SPBT BT
1. Mass fraction of components, %: According to GOST 10679
sum of methane, ethane and ethylene Not standardized
amount of propane and propylene, not less than 75 Not standardized
sum of butanes and butylenes, not less than Not standardized - 60
no more 60 -
2. Volume fraction of liquid residue at 20 °С, %, According to clause 3.2
no more 0,7 1,6 1,8
3. Saturated vapor pressure, gauge, MPa, at temperature: According to clause 3.3 or GOST 28656
plus 45 °С, no more 1,6 1,6 1,6
minus 20 °С, not less 0,16 - -
4. Mass fraction of hydrogen sulfide and mercaptan sulfur,%, no more 0,013 0,013 0,013 According to GOST 22985
including hydrogen sulfide, no more 0,003 0,003 0,003 According to GOST 22985 or GOST 11382
5. Free water and alkali content Absence According to clause 3.2
6. Odor intensity, points, not less than 3 3 3 According to GOST 22387.5 and clause 3.4 of this standard

The use of LPG by brand is associated with outdoor temperatures, on which the elasticity (pressure) of liquefied gas vapors located in cylinders in the open air or in underground tanks depends.
In winter conditions at low temperatures, in order to create and maintain the necessary pressure in gas supply systems, the composition of liquefied gas should be dominated by the more easily evaporating component of LPG - propane. In summer, the main component in LPG is butane.

The main physical and chemical properties of the components of liquefied hydrocarbon gases and their combustion products:
- boiling point (evaporation) at atmospheric pressure for propane - 42 0 С, for butane - 0.5 0 С;
This means that at a gas temperature above the specified values, gas evaporation occurs, and at a temperature below the specified values, gas vapor condensation occurs, i.e. vapors form liquid (liquefied gas condensate). Because propane and butane are rarely supplied in their pure form, the temperatures given do not always correspond to the boiling and condensing temperatures of the gas used. The gas used in winter usually evaporates normally at ambient temperatures down to minus 20 0 C. If manufacturers supply gas with a high butane content, then condensation of gas vapors can also occur in summer with slight frosts.
- low flash point at atmospheric pressure:
for propane - 504-588 0 С, for butane - 430-569 0 С;
This means that ignition (flash) can occur from heated, but not yet luminous objects, i.e. without open flames.
- low ignition temperature I at a pressure of 0.1 MPa (1 kgf / cm 2)
for propane - 466 0, for butane - 405 0 С;
-high calorific value(the amount of heat that is released during the combustion of 1 m 3 of gas vapor):
for propane 91-99 MJ / m 3 or 22-24 thousand kcal,
for butane 118-128 MJ / m 3 or 28-31 thousand kcal.
- low explosive limits(flammability):
propane mixed with air 2.1-9.5 vol.%,
butane mixed with air 1.5-8.5 vol.%,
mixtures of propane and butane with air 1.5-9.5 vol.%.
This means that gas-air mixtures can ignite (explode) only if the gas content in air or oxygen is within certain limits, beyond which these mixtures do not burn without a constant influx (presence) of heat or fire. 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.
With an increase in the temperature of the gas-air mixture, the limits of explosiveness (flammability) expand.
-gas vapor density(mixtures of propane and butane) - 1.9-2.58 kg / m 3;
LPG vapors are much heavier than air (air density 1.29 kg/m 3) and collect in the lower part of the room, where an explosive gas-air mixture can form with very small gas leaks. When LPG vapor leaks (in the form of a creeping fog or a transparent shimmering cloud) into unventilated basements, sewerage devices, buried rooms, they can remain there for a very long time. Often this happens when gas leaks from underground tanks and gas pipelines. It is especially dangerous that such a leak cannot be detected by external inspection, because. gas does not always come to the surface of the earth, and spreading underground, it can enter sewers or basements at a great distance from the place of leakage.
- density of gas in liquid state- 0.5-0.6 kg/l.
- liquid phase volume expansion coefficient CS G- 16 times more than water. When the gas temperature rises, its volume increases significantly, which can lead to destruction (rupture) of the walls of the vessel with gas.
- for complete combustion of LPG vapors, it is necessary
per 1m 3 propane vapor - 24m 3 air or 5.0 m 3 oxygen
for 1 m 3 of butane vapor - 31 m 3 of air or 6.5 m 3 of oxygen.
- gas vapor volume with 1 kg of propane - 0.51 m 3,
with 1 liter of propane - 0.269m 3,
with 1 kg of butane - 0.386m 3,
with 1 liter of butane - 0.235 m 3.
- maximum flame propagation speed burning propane - 0.821 m / s, butane - 0.826 m / s.
LPG is colorless (invisible) and for the most part does not have a strong odor of its own, therefore, if it leaks, an explosive gas-air mixture can form in the room. In order to timely detect gas leaks, combustible gases are subjected to odorization, that is, they are given a sharp specific smell.
Technical ethyl mercaptan is used as an odorant.

Ethyl mercaptan is a volatile liquid with a pungent, unpleasant odor.

Ethyl mercaptan is a colorless, transparent, mobile, flammable liquid with a sharp, disgusting odor. The smell of ethyl mercaptan is found in very low concentrations (up to 2*10 -9 mg/l). Ethylmercaptan is soluble in most organic solvents, slightly soluble in water. In dilute solutions, ethyl mercaptan exists as a monomer; upon concentration, dimers of predominantly linear structure are formed due to the formation of S-H...S hydrogen bonds. Ethanthiol is easily oxidized. Depending on the oxidation conditions, diethyl sulfoxide (C 2 H 5 ) 2 SO (by the action of oxygen in an alkaline environment), diethyl disulfide (C 2 H 5 )SS(C 2 H 5 ) (by the action of activated MnO 2 or hydrogen peroxide) and other derivatives. In the gas phase at 400°C, ethyl mercaptan decomposes into hydrogen sulfide and ethylene. In nature, ethanethiol is used by some animals to scare off enemies. In particular, it is part of the fluid produced by the skunk.

Receipt.

An industrial method for producing ethyl mercaptan is based on the reaction of ethanol with hydrogen sulfide at 300-350°C in the presence of catalysts.

C 2 H 5 OH + H 2 S --> C 2 H 5 SH + H 2 O

Application.
  • as an odorant for natural gas, propane-butane mixture, as well as other fuel gases. Almost all fuel gases are almost odorless, the addition of ethyl mercaptan allows you to detect gas leaks in time.
  • as an intermediate reagent in the production of certain types of plastics, insecticides, antioxidants.

    • The maximum permissible concentration of ethyl mercaptan in the air of the working area is 1 mg/m 3 . The specific smell of ethyl mercaptan is felt at its negligible concentrations in the air.
    To give a smell at manufacturing plants, ethyl mercaptan is added to LPG in the amount of 42-90 grams per ton of liquid gas, depending on the content of sulfur mercaptan in the gas.
    The smell of LPG with low explosive limits should be felt when they are in the air: PT - 0.5 vol.%, SPBT - 0.4% vol.%, BT - 0.3% vol.%.
    Vapors of LPG have a narcotic effect on the body. Signs of narcotic action are malaise and dizziness, then a state of intoxication occurs, accompanied by unreasonable gaiety, loss of consciousness. LPG is non-toxic, but a person in an atmosphere with a small amount of LPG vapor in the air experiences oxygen starvation, and with significant concentrations of vapor in the air, he can die from suffocation.
    The maximum permissible concentration in the air of the working area (in terms of carbon) of hydrocarbon vapors is from 100 to 300 mg/m 3 . For comparison, it can be noted that such a concentration of gas vapors is approximately 15-18 times lower than the explosive limit.
    When the liquid phase of LPG gets on clothing and skin, due to its instantaneous evaporation, intense absorption of heat from the body occurs, which causes frostbite. By the nature of the impact, frostbite resembles a burn. Contact with the liquid phase in the eyes can lead to loss of vision. When working with the liquid phase of LPG, woolen and cotton gloves should not be worn, as they do not protect against burns (they fit snugly to the body and are impregnated with liquid gas). It is necessary to use leather or canvas gloves, rubberized aprons, glasses.
    With incomplete combustion of LPG vapors, carbon monoxide (CO) is released - carbon monoxide, which is a strong poison that reacts with blood hemoglobin and causes oxygen starvation. The concentration of carbon monoxide in indoor air from 0.5 to 0.8 vol.% is life-threatening even with short-term exposure. The presence of 1vol.% carbon monoxide in the room air causes death in 1-2 minutes. According to sanitary standards, the maximum allowable concentration of carbon monoxide in the air of the working area is 0.03 mg/liter.

    Sources used
    1. Physical and chemical properties of liquefied hydrocarbon gases for domestic consumption according to G0ST 20448-90.

    Liquid or liquefied gas is a mixture of hydrocarbons, which under normal conditions (20 ° C and 760 mm Hg) is gaseous, and with a decrease in temperature or a slight increase in pressure, it turns into a liquid. The volume of the mixture is reduced by more than 200 times, which makes it possible to transport liquid gas to places of consumption in lightweight vessels. These hydrocarbons include: C 3 H 8 propane and C 3 H 3 propylene; butane C 4 H 10 and butylene C 4 H 8 .

    The main sources of obtaining liquid gases are oil refining products and natural "associated" petroleum gas, which contains a significant amount of heavy hydrocarbons (up to 15% or more).

    The production of liquid gas from natural petroleum gases together with gas gasoline consists of two stages. In the first stage, heavy hydrocarbons are released, and in the second, they are separated into hydrocarbons that make up stable gas gasoline and hydrocarbons that make up liquid gases - propane, butane, iso-butane. There are three main methods for separating heavy hydrocarbons from natural petroleum gas.

    1. Compression - based on the compression and cooling of the gas, as a result of which the condensed hydrocarbons are separated.
    2. Absorption - based on the properties of a liquid to absorb (absorb) vapors and gases. This method consists in the fact that natural gas is fed into special apparatus, where it reacts with an absorbent that absorbs heavy hydrocarbons. Hydrocarbons are separated from absorbents in special evaporation columns.
    3. Adsorption - based on the properties of solids to absorb vapors and gases. This method consists in the fact that natural petroleum gas is passed through an adsorber filled with a solid absorber, which adsorbs (absorbs) heavy hydrocarbons from the gas.

    After the absorber is saturated with heavy hydrocarbons, superheated steam is let into the adsorber, with the help of which hydrocarbons evaporate, and the mixture of steam with hydrocarbons is fed into the condenser, where hydrocarbons in liquid form are separated from water.

    From the place of production (gas plants) to distribution stations, liquid gas is usually transported in rail tank cars with a capacity of 50 m 3 or tank trucks with a capacity of 3-5 m 3 . Liquid gas in tanks is under pressure of 16 MPa (16 atm.). Since it expands significantly with increasing temperature, the tanks are only 85% filled.

    Liquid gas distribution stations are usually located outside the city or in sparsely populated areas of the city. At the station, liquid gas is stored in cylindrical tanks, which are installed above ground or underground on a foundation or on a solid pound. The station has workshops for filling cylinders, where a compressor or pumps and a filling ramp with flexible hoses for filling cylinders are located; premises for storage of empty and filled cylinders (balloon park); rooms for repair and testing of cylinders.

    Above-ground tanks, in which liquid gas is stored, are painted with aluminum paint to protect against solar radiation, underground tanks are covered with insulation to protect against corrosion.

    The supply of consumers with liquid gas is carried out in three ways: network, group (centralized), individual. With the network supply method, an evaporation station is arranged, where liquid gas is evaporated by heating with steam, hot water or electric heaters and is fed into the city gas network in pure form or mixed with air.

    With a group (centralized) method of supplying liquid gas, for example, for large apartment buildings, underground tanks with a capacity of 1.8-4 m 3 are installed in the courtyard of the house, filled with liquid gas from a tank truck under pressure up to 1.6 MPa. The tanks have a branch pipe equipped with a pressure reducer, with a safety valve and a pressure gauge for connecting gas supply pipelines to consumers.

    With individual supply of consumers, liquid gas is delivered in cylinders with a capacity of up to 50 liters, having a valve tightly screwed into the neck opening, closed with a steel safety cap. On the cylinders, painted red, the name of the gas is written in large letters. Gas is supplied by two-cylinder and one-cylinder systems.

    With a two-cylinder system, cylinders with a gas supply for 25-40 days will be placed in a metal cabinet installed on a blank wall of the house (without windows). The cabinet must stand on a solid support, securely attached to the wall, have slots for ventilation and be locked. Installation of individual liquefied gas installations is carried out using rubber-fabric sleeves or water and gas pipes. The installation of gas pipelines using rubber-fabric sleeves for low-pressure gas pipelines (after the reducer) is carried out from one piece no more than 10 m long. Only one device can be powered from one cylinder.

    Liquid gas is burned in the same household appliances in which artificial or natural gas is burned. Liquid gas is non-toxic, but in case of incomplete combustion it produces highly toxic carbon monoxide, therefore, when using liquid gas, it is necessary to strictly follow the established operating rules, also taking into account that when gas leaks, its content in the air in the range of 1.8–9.5% can cause an explosion.

    CIS (eng. - L P G - Liquified Petroleum Gas - liquefied petroleum gas) is a mixture of propane (C3H8) and butane (C4H10), used as a fuel, refrigerant in refrigerators and freezers, pressurizing aerosols (less harmful to the ozone layer). It is also used as a fuel for internal combustion engines. LPG components are organic hydrocarbon compounds from the alkanes group, which are colorless, odorless and flammable gases. LPG is stored in the liquid state and used in the gaseous state after the evaporation procedure. After condensation, it increases the density of stored energy, which is very important when used to control the machine (one liter of gas in the liquid state is formed from 260 liters of gas in the volatile phase).

    LPG is compressed and stored in liquid form primarily for ease of storage and transport. Because it does not lose or change its properties over time, that is, it does not weather, does not change its state, etc., it can be stored for a long time without compromising quality and performance. The octane number of LPG is more favorable compared to gasoline and diesel fuel and, depending on the proportion of propane and butane, becomes from 90 to 110 octane. The energy efficiency of LPG is lower than conventional fuels due to the lower energy per unit volume (although the unit weight is higher). This results in a 10-20% increase in combustion compared to gasoline fuel, but the price fluctuates around 50% of the price of gasoline.

    On the plus side, LPG is a natural gas and doesn't need to be "sprayed" into the cylinders like gasoline fuel, so it burns more efficiently and safely in the engine, even when the engine is cold. LPG burns relatively cleanly, with no smoke or ash. This contributes to the formation of a small amount of harmful substances.

    Compared to diesel fuel:

    - 90% less particulate matter
    - 90% less nitrogen oxides
    - 70% less ozone generation potential
    - 60% less carbon dioxide
    — LPG cannot pollute underground sources because it does not dissolve in water.

    Abbreviations that occur

    The abbreviation LPG has nothing to do with the similar sounds of other names that refer to other types of fuel, which are natural gas or biogas. The main component of the latter is methane, which affects some of the abbreviations used, such as:

    CNG - compressed natural gas (CNG)
    CMG - compressed gas methane (CM)
    LNG - Liquified Natural Gas - liquefied natural gas (LNG)
    LBG - - Liquified Biogas - liquefied biogas
    CBG - Compressed Biogas - compressed biogas

    Why is propane mixed with butane?

    The octane number (OC) is responsible for the fuel's resistance to detonation. It is achieved by increasing the content of saturated hydrocarbons (eg propane, n-butane, isobutane). Isobutane, which has the highest value of this parameter, has the greatest influence on the OC. The content of propylene and butene reduces the octane number of LPG. The content of the diene (unsaturated hydrocarbons) also reduces the octane. More importantly, they tend to polymerize, which contributes to the formation of deposits, the so-called soot in the tank, in the fuel system and in the combustion chamber. Thus, the composition of LPG used as automotive fuel must meet certain requirements prescribed in regulatory documents.

    Vapor pressure (mixture volatility) is very important at low ambient temperatures. Keeping it at an appropriate level allows the LPG to exit the tank. Both components of the mixture are gaseous and low-boiling - propane boils at atmospheric pressure already at -42 ° C, butane, under the same temperature conditions at -0.5 ° C.

    For this reason, in winter, the propane content in autogas increases. This is a way to increase the gas vapor pressure (volatility). This norm stipulates the obligation to use a mixture of propane and butane in winter, which provides a minimum vapor pressure of 150 kPa at an ambient temperature of -10 ° C (type A). However, each stick has two ends. In summer, too high vapor pressure can cause gas to evaporate in the line, which also leads to engine malfunction. Thus, filling stations must sell summer gas in summer and winter gas in winter. Most often, problems begin in winter, when summer gas is sold. In summer, the mixture ratio is about 40% propane and 60% butane, while in winter the ratio is the opposite: 60/40.

    Temperature at which the relative elasticity (pressure) of steam is not less than 150 kPa

    In winter, the price of LPG is higher.

    Sometimes in winter we meet with the opinion that at low temperatures, a car with a LPG system does not work well: there is no speed and the engine runs unevenly. Problems are looked for in the incorrectness of the gas installation. However, this often happens due to the poor quality of gas fuel.

    In pursuit of low prices, dishonest sellers, who, fortunately, are becoming less and less, offer cheaper gas with the wrong parameters. The way out of this situation is to stop looking for additional fuel savings by shopping at random LPG gas stations. This problem also applies to a lesser extent to the 4th generation of HBO - when there is a decrease in pressure, the car simply switches to gasoline. On the one hand, this is bad - you will not reach your destination on gas. On the other hand, it will save your engine from premature failure.

    Different European countries use different types of gas, depending on the climate. In countries located in the Far North, the content of propane in the LPG is higher, sometimes it is just pure propane, in southern (warm) countries the butane content is increased, reducing the vapor pressure so that evaporation does not occur in the fuel line.

    How to make CIS?

    Today LPG is produced by 3 different methods.

    Method I (directly from crude oil)

    In order to maximize the use of the gases contained in oil, they are extracted directly to the fields. The oil extracted from the shaft enters a special equipment called a distributor, where, due to a pressure drop, the gases dissolved in it are released. Then the oil enters the tanks, where it is stabilized. During this process, components are released: ethane, propane, butane and partly pentane. These processes also produce gasoline (a mixture of light liquid hydrocarbons), which contains significant amounts of ethane, propane and butane.

    Method II

    The most important in our market is the method of obtaining liquid gas in the processing of oil refineries. Propane-butane in them is formed during the cracking and hydrogenation of crude oil. During these processes, thermal decomposition of hydrocarbons occurs. Cracking is the distribution of large particles from the hydrocarbons contained in crude oil into a large number of small particles. The process is carried out without air and involves heating the oil. Hydrogenation is a process in which oil is enriched with hydrogen at high pressure and temperature. In this way, light hydrocarbons with a higher hydrogen content and a lower boiling point are achieved. The amount of LPG collected during the processing of crude oil (by weight) is approximately 2%.

    Method III

    Liquefied gas is a product of the degasification of natural gas produced in the process of oil refining. It involves the separation of hydrocarbons from gas heavier than ethane, and as a result we get mainly propane and butane. Mixed LPG gases are also found in natural gas fields.

    Why does gas stink?

    For safety reasons, the liquid propane-butane mixture is flavored. The smell of LPG should be unpleasant and perceptible at a concentration of one fifth of the lower explosive limit.

    To aromatize the gas, ethanethiol (ethyl mercaptan, which includes, among others, sulfur compounds) is used. It is an organic compound found in low concentrations in crude oil and is known for its very strong malodorous odour. It can already be felt in the air at a concentration of 0.00035 parts per million (ppm).

    In 2000, in the Guinness Book of Records, this compound was established as the most stinking substance in the world.

    Aromatization of LPG is also associated with a reduction in the sulfur content of the fuel. Achieving the sulfur content in liquid gases with the standard since 2009, in classic motor fuels (10 ppm - 10 sulfur particles per 1 million particles of solution) is very difficult, because the flavor raises the content of this element. The sulfur content after aromatization can be up to 50 mg/kg.

    Liquefied hydrocarbon gases are used as automotive 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 of oil and gas 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 producers not only did not care about the preservation of gas or light fractions of hydrocarbons, but also tried to get rid of them. Negative attitudes were also observed towards the gasoline fractions of oil, since they caused an increase in the flash point and the danger of fires 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 in gas production became possible due to the radical intensification of work on the construction of main gas pipelines that connected 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 has been produced in England since the early 30s of the 20th century, given that this is a country with a developed market economy, the 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 at what liquefied hydrocarbon gases are and how they are produced. Liquefied gases are divided into two groups:

    Liquefied hydrocarbon gases (LHG)- 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 structures. 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 (C2) and hexane (C6) 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 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.

    Butane (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 C 4 H 10 . The mixture of n-butane and its isomer isobutane CH(CH3)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 one or another process.

    Hydrocarbon systems can be homogeneous or heterogeneous. If the system has homogeneous physical and chemical properties, it is homogeneous; if it is heterogeneous or consists of substances in different states of aggregation, 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 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 located in the upper part. When the temperature in the tanks decreases, part of the vapors 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 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.

    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.

    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.

    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.

    Liquefied hydrocarbon gases are low-boiling liquids that can be in a liquid state under saturated vapor pressure.

    1. Boiling point: 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. GOST R 55085-2012
    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 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.

    Fundamentally, systems pumping LPG do not differ much from systems for water and oil products, and, nevertheless, additional equipment is needed to guarantee the qualitative and quantitative characteristics of the measurement.

    Based on this, the technological hydrocarbon system, at a minimum, must include a reservoir, 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.

    The 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 recovery 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 meter 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.

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