Liquefied petroleum gases (LPG)(English) Liquefiedpetroleumgas (LPG)) - a mixture of light hydrocarbons liquefied under pressure with a boiling point from − 50 to 0 °C. Intended for use as fuel. The composition can vary significantly, the main components are: propane, butane, propylene, isobutane, isobutylene, n-butane and butylene.
The raw materials for the production of LPG are mainly associated petroleum gases, gas condensate fields and gases obtained during oil refining. Transported and stored in cylinders and gas holders. It is used for cooking, boiling water, heating, used in lighters, and as fuel in vehicles.
In vessels (cisterns, reservoirs, cylinders) for storage and transportation, LPG is simultaneously in 2 phases: liquid and vapor, with 85% of the volume of the vessel occupied by the liquid phase, 15% by the vapor. LPG is stored and transported in liquid form under pressure created by the gas’s own vapors. This property makes LPG a convenient source of fuel supply for municipal and industrial consumers, because When stored and transported as a liquid, liquefied gas occupies hundreds of times less volume than gas in its natural (gaseous or vapor) state, and is distributed through gas pipelines and used (burned) in gaseous form.
Among commonly used fuels, liquefied petroleum gases (LPG) are the only fuels of their kind that can be transported and stored in liquid form at a certain pressure and temperature. However, when normal pressure and comparatively low temperatures these mixtures evaporate and are used as gases. The transition of liquefied hydrocarbon gases into a gaseous or liquid state depends on three factors:
– pressure;
– temperature;
– volume.
Among commonly used fuels, liquefied petroleum gases are the only fuels of their kind that can be transported and stored in liquid form at a certain pressure and temperature. However, at normal pressure and relatively low temperatures, these mixtures evaporate and are used as gases. The transition of liquefied hydrocarbon gases into a gaseous or liquid state depends on three factors - pressure, temperature and volume.
Main characteristics of LPG:
Liquid carbohydrates, which are part of liquefied gases, are characterized by a high volumetric expansion coefficient, significantly higher than the expansion coefficient of gasoline, kerosene and water, low density, significant vapor elasticity, which increases with increasing liquid temperature.
Gaseous hydrocarbons included in liquefied gases are characterized by different densities, which can be less or greater than the density of air, slow diffusion into the atmosphere, especially in the absence of wind, low ignition temperature, low explosive limits in air, the possibility of condensation formation when the temperature drops to a point dew or increased pressure.
Liquefied gases are flammable and explosive, low-toxic, have a specific characteristic odor, and according to the degree of impact on the body, they are classified as substances of the 4th hazard class GOST 12.1.007.
Liquefied gases form explosive mixtures with air at a concentration of propane vapor from 2.3% to 9.5%, normal butane from 1.8% to 9.1% (by volume), at a pressure of 0.1 MPa (1 atm.) and temperature 15 ÷ 20ºС. The auto-ignition temperature of propane in air is 470ºС, normal butane – 405ºС. Maximum permissible concentration in air working area(in terms of carbon) saturated hydrocarbons (propane, normal butane) - 300 mg/m 3, unsaturated hydrocarbons (propylene, butylene) - 100 mg/m 3.
Liquefied gases entering the human body cause frostbite, reminiscent of a burn. Liquefied gas vapor is heavier than air and can accumulate in low, unventilated places.
To ensure safety when using liquefied gas, as well as correct handling With this product, it is necessary to take into account the basic properties of this gas and special requirements.
Technological parameters of liquefied gas are given in table. 5.1:
Table 5.1
Technological parameters of liquefied gas
Liquefied hydrocarbon gases supplied to settlements, must comply with the requirements of GOST 20448-90. For municipal consumption and industrial purposes, the standard provides for the production and sale of LPG of the following brands:
– PT – technical propane;
– SPBT – technical mixture of propane and butane;
– BT – technical butane.
– SPBTZ (technical winter mixture of propane and butane).
–SPBTL (summer mixture of propane and butane technical).
Cost-effective transportation
To transport liquefied hydrocarbon gases LPG there is no need to lay a wide network of gas pipelines, build supports and electrical networks. LPG is transported in tanks, cylinders and tanks across railway, by water by tankers or vehicles in a liquid state. Since in the liquid state a gas occupies a volume several hundred times less than its original volume, a significant amount of thermal energy is concentrated in a unit volume of this gas. For example, a 50-liter cylinder contains 22 kg of LPG, the evaporation of which produces 11 m 3 of propane-butane vapor with a total calorific value of 240,000 kcal. This cylinder is enough for one family to cook food and heat water for a whole month.
During liquefaction, the volume of natural gas decreases by more than 600 times, which is equivalent to compressing the gas to a pressure of 60 MPa. LPG is almost two times lighter than gasoline, non-toxic, and not chemically active; specific heat combustion (12,000 kcal/kg) by 12%, and the octane number is 15% higher than that of gasoline.
Consumption
Liquefied natural gas and liquefied propane-butane is used for the same purposes as main natural gas:
– obtaining electrical and thermal energy in local energy installations;
– gasification of populated areas and industrial facilities;
– use as motor fuel;
– use as raw material for the chemical industry;
Due to the “dual” nature, on the one hand, liquefied gases have the advantages of liquids during transport and storage (easy transportability, small occupied volume, the possibility of using thinner-walled vessels, relatively simple fittings, etc.), and on the other hand, being in gaseous state, they acquire the advantages characteristic of gases when they are distributed through networks and burned.
Liquefied hydrocarbon gases(propane-butane, hereinafter referred to as LPG) - mixtures of hydrocarbons that, when normal conditions(atmospheric pressure and air temperature = 0 ° C) are in a gaseous state, and with a slight increase in pressure (at constant temperature) or a slight decrease in temperature (with atmospheric pressure) 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 - 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 liquid non-evaporating residue (pentane, hexane).
The raw materials for the production of LPG are mainly associated petroleum gases, gas condensate fields and gases obtained during oil refining.
From factories, LPG is supplied in railway tanks to gas filling stations (GFS) of gas facilities, where it is stored in special tanks until sold (dispensed) to consumers. LPG is delivered to consumers in cylinders or by tanker trucks.
In vessels (tanks, reservoirs, cylinders) for storage and transportation, LPG is simultaneously in 2 phases: liquid and vapor. LPG is stored and transported in liquid form under pressure created by the gas’s own vapors. This property makes LPG a convenient source of fuel supply for municipal and industrial consumers, because When stored and transported as a liquid, liquefied gas occupies hundreds of times less volume than gas in its natural (gaseous or vapor) state, and is distributed through gas pipelines and used (burned) in gaseous form.
Liquefied hydrocarbon gases supplied to populated areas must comply with the requirements of GOST 20448-90.
For municipal consumption and industrial purposes, the standard provides for the production and sale of three brands of LPG:
PT - technical propane;
SPBT - technical mixture of propane and butane;
| BT - technical butane. | Brand | Name |
| OKP code | PT | 02 7236 0101 |
| Technical propane | SPBT | 02 7236 0102 |
| A mixture of propane and butane technical | BT | 02 7236 0103 |
| Technical butane | Indicator name | Standard for the brand | ||
| OKP code | Technical propane | A mixture of propane and butane technical | ||
| 1. Test method Mass fraction | components,%: | |||
| According to GOST 10679 | sum of methane, ethane and ethylene | |||
| Not standardized | 75 | sum of methane, ethane and ethylene | ||
| amount of propane and propylene, not less | sum of methane, ethane and ethylene | - | 60 | |
| sum of butanes and butylenes, not less | 60 | - | ||
| no more | 2. Volume fraction of liquid residue at 20 °C, %, | |||
| sum of butanes and butylenes, not less | 0,7 | 1,6 | 1,8 | |
| According to clause 3.2 | 3. Saturated vapor pressure, excess, MPa, at temperature: | |||
| According to clause 3.3 or GOST 28656 | 1,6 | 1,6 | 1,6 | |
| plus 45 °C, no more | 0,16 | - | - | |
| minus 20 °C, not less | 0,013 | 0,013 | 0,013 | 4. Mass fraction of hydrogen sulfide and mercaptan sulfur, %, no more |
| According to GOST 22985 | 0,003 | 0,003 | 0,003 | including hydrogen sulfide, no more |
| According to GOST 22985 or GOST 11382 | 5. Free water and alkali content | 2. Volume fraction of liquid residue at 20 °C, %, | ||
| 6. Odor intensity, points, not less | 3 | 3 | 3 | According to GOST 22387.5 and clause 3.4 of this standard |
The use of LPG by brand is associated with external temperatures, on which the elasticity (pressure) of liquefied gas vapors contained in cylinders depends on outdoors or in underground tanks.
In winter conditions at low temperatures, in order to create and maintain the required pressure in gas supply systems, the more easily evaporating component of LPG, propane, must predominate in the composition of liquefied gas. In summer, the main component in LPG is butane.
Basic physicochemical properties of components of liquefied hydrocarbon gases and their combustion products:
- boiling point (evaporation) at atmospheric pressure for propane - 42 0 C, for butane - 0.5 0 C;
This means that at a gas temperature above the specified values, gas evaporation occurs, and at a temperature below the specified values, condensation of gas vapor occurs, i.e. a liquid (liquefied gas condensate) is formed from the vapor. Because propane and butane in pure form are rarely supplied, the temperatures given do not always correspond to the boiling and condensation temperatures of the gas used. Used in winter time gas usually evaporates normally at ambient temperatures down to minus 20 0 C. If manufacturing plants supply gas with increased content butane, then condensation of gas vapor can occur in summer time with slight frosts.
- low flash point at atmospheric pressure:
for propane - 504-588 0 C, for butane - 430-569 0 C;
This means that ignition (flash) can occur from heated but not yet luminous objects, i.e. without the presence of open fire.
- low auto-ignition temperature I at a pressure of 0.1 MPa (1 kgf/cm2)
for propane - 466 0, for butane - 405 0 C;
-high calorific value(the amount of heat that is released when 1 m 3 of gas vapor is burned):
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 flow (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 speed of flame propagation decreases and increases heat losses and the combustion stops.
With increasing temperature of the gas-air mixture, the limits of explosion (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/m3) and collect in the lower part of the room, where an explosive gas-air mixture can form with very small gas leaks. When LPG vapors flow (in the form of creeping fog or a transparent shimmering cloud) into unventilated basements, sewage systems, and buried rooms, they can remain there for a very long time. This often occurs due to gas leaks from underground tanks and gas pipelines. What is especially dangerous is that external inspection such a leak cannot be detected, because gas does not always come to the surface of the earth, and as it spreads underground it can end up in sewers or basements at a great distance from the leak site.
- liquid gas density- About 5-0.6 kg/l.
- coefficient of volumetric expansion of the liquid phase of GC G - 16 times more than water. As the temperature of a gas increases, its volume increases significantly, which can lead to destruction (rupture) of the walls of the vessel containing the gas.
- for complete combustion of LPG vapors it is necessary
per 1 m 3 of propane vapor - 24 m 3 of air or 5.0 m 3 of 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 - 0.269m3,
with 1 kg of butane - 0.386 m 3,
with 1 liter of butane - 0.235m3.
- maximum speed flame spread 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 promptly detect gas leaks, flammable gases are subjected to odorization, that is, they are given a sharp, specific odor.
Technical ethyl mercaptan is used as an odorant.
Ethyl mercaptan is a highly volatile liquid with a strong, unpleasant odor.
Ethyl mercaptan is a colorless, transparent, mobile, flammable liquid with a pungent, disgusting odor. The odor of ethyl mercaptan is detected in very low concentrations (up to 2*10 -9 mg/l). Ethyl mercaptan is soluble in most organic solvents and slightly soluble in water. In dilute solutions, ethyl mercaptan exists as a monomer; upon concentration, dimers of a predominantly linear structure are formed due to the formation of S-H...S hydrogen bonds. Ethanethiol is easily oxidized. Depending on the oxidation conditions, diethyl sulfoxide (C 2 H 5 ) 2 SO (by the action of oxygen in 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 repel enemies. In particular, it is part of the fluid produced by the skunk.
Receipt.The 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.The maximum permissible concentration of ethyl mercaptan in the air of the working area is 1 mg/m 3 . The specific odor of ethyl mercaptan is felt at negligible concentrations in the air.
To add an odor, ethyl mercaptan is added to LPG at manufacturing plants in an amount of 42-90 grams per ton of liquid gas, depending on the sulfur content of mercaptan in the gas.
The smell of LPG, which has low explosive limits, should be felt when present in the air: PT - O.5 vol.%, SPBT - 0.4% vol.%, BT - 0.3% vol.%.
LPG vapors have a narcotic effect on the body. Signs of narcotic effects are malaise and dizziness, then a state of intoxication sets in, accompanied by causeless gaiety and loss of consciousness. LPG is non-toxic, but a person in an atmosphere with a small content of LPG vapor in the air experiences oxygen starvation, and with significant concentrations of vapor in the air can die from suffocation.
The maximum permissible concentration of hydrocarbon vapors in the air of the working area (in terms of carbon) is from 100 to 300 mg/m 3 . For comparison, it can be noted that such a concentration of gas vapor is approximately 15-18 times lower than the explosive limit.
When the liquid phase of LPG gets on clothing and skin, due to its instant evaporation, intense absorption of heat from the body occurs, which causes frostbite. The nature of the effect of frostbite resembles a burn. Contact of the liquid phase with the eyes can lead to loss of vision. When working with the liquid phase of LPG, you cannot wear wool and cotton gloves, as they do not protect against burns (they fit tightly to the body and are saturated with liquid gas). It is necessary to use leather or canvas gloves, rubberized aprons, and goggles.
When LPG vapors are incompletely burned, carbon monoxide (CO) is released - carbon monoxide, which is a strong poison that reacts with hemoglobin in the blood and causes oxygen starvation. Concentration carbon monoxide in room air from 0.5 to 0.8 vol.% is life-threatening even with short-term exposure. The presence of 1 vol.% carbon monoxide in the air of a room causes death within 1-2 minutes. According to sanitary standards, the maximum permissible concentration of carbon monoxide in the air of the working area is 0.03 mg/liter.
Sources used
1. Physico-chemical properties of liquefied hydrocarbon gases for municipal and household consumption in accordance with G0ST 20448-90.
PHYSICAL AND CHEMICAL PROPERTIES OF LIQUEFIED HYDROCARBON GASES
The term "liquefied petroleum gases" refers to propane, butane, iso-butane, a mixture of propane and butane. Among the commonly used fuels, liquefied hydrocarbon gases are so far the only types of fuel that, at relatively low pressure and normal temperature can be transported and stored in liquid form. However, at normal pressure and relatively low temperatures, these mixtures are capable of evaporation, in which case they are used as gases. The transition of liquefied hydrocarbon gases into a gaseous or liquid state depends on three factors - pressure, temperature and volume.
Gaseous hydrocarbons that make up liquefied gases have a density that significantly exceeds the density of air and are characterized by slow diffusion into the atmosphere, low ignition temperature, low explosive limits in air, and the possibility of condensation forming when the temperature drops to the dew point or when the pressure increases. In accordance with GOST 20448--80, three grades of liquefied hydrocarbon gases are produced for domestic consumption: SPBTZ, SPBTL - a mixture of propane and technical butane, winter and summer, respectively, BT - technical butane. Pure propane as liquefied gas can be used as fuel without regasification and at temperatures up to 253 K.
Butanes without regasification can be used as fuel only at temperatures exceeding 273 K. At lower temperatures, their vapor pressure is less than atmospheric pressure. At temperatures of 318, 313 and 258 K, the pressure of n-butane is 0.49, 0.42 and 0.06 MPa, respectively.
If liquefied gases are used for high temperatures, then it is desirable to use butanes, since at the same temperature their saturated vapor pressure is approximately three times lower than that of propane. This allows the liquid phase of butanes to be stored at normal temperatures (313 K) in tanks designed for a pressure of 0.7 MPa, and at temperatures up to 353 K - in tanks designed for a pressure of 1.6 MPa.
The density of the liquid phase of liquefied gas at a temperature of 273 K and a pressure of 0.1 MPa, depending on the composition, is equal to 0.58-0.6 of the density of water, i.e., the liquid phase of liquefied gas is approximately two times lighter than water. Consequently, water sedimentation will occur in the lower part of tanks and apparatus.
With intensive extraction of the vapor phase from the reservoir, the temperature of the liquid phase will decrease due to the heat consumption of the liquid for evaporation. The maximum temperature at which the liquid does not evaporate is 231 K for propane and 273 K for butane. For mixtures of propane and butanes, this temperature is variable. It depends on the composition of the mixture.
FEATURES OF LIQUEFIED HYDROCARBON GASES AND THEIR IMPACT ON THE HUMAN BODY
Liquefied hydrocarbon gases are saturated (boiling liquids) in the presence of a free surface of the liquid phase. In this case, a two-phase system (liquid - vapor) always appears. Vapor pressure depends on the temperature of the liquid phase and can reach significant values with temperature changes external environment. This property of liquefied hydrocarbon gases in the event of a rupture of an apparatus or pipelines causes the pressure to be maintained in them for a long time (until complete release from the liquid phase), which creates a significantly greater danger for surrounding objects than in the case of a rupture of an oil or natural gas pipeline, in which the pressure is at the gap quickly decreases to zero.
The density of the vapor phase of liquefied hydrocarbon gases is significantly greater than the density of air. The vapor density of liquefied hydrocarbon gases at a temperature of 273 K and a pressure of 0.1 MPa ranges from 19.6 to 26.46 kg/m 3 . The relative density (in air) of propane is 15.62, iso-butane is 20.64, n-butane is 20.91.
The vapor phase of liquefied hydrocarbon gases does not dissipate in the atmosphere, rising upward (like natural gas). It spreads along the surface of the earth or the floor of a room (like CO 2 and other heavy gases). In this regard, it is necessary to arrange ventilation of premises at floor level, through ventilation of the design bureau (GNS) site at ground level, to avoid recesses and pits both in the premises and on the site itself.
Liquefied hydrocarbon gases at atmospheric pressure do not have a toxic (poisonous) effect on the human body, since they dissolve little in the blood. However, when they enter the air, they mix with it and reduce the oxygen content in the air. A person in such an atmosphere experiences oxygen starvation, and with a significant content of liquefied hydrocarbon gas in the air, he can die from suffocation. Inhaling air containing 1% propane or butane for 10 minutes does not cause any symptoms of poisoning. Inhaling air containing 10% liquefied gases for two minutes causes dizziness. Propylene and butylene have narcotic properties. With a content of 15% propylene in the air, loss of consciousness occurs after 30 minutes, with a content of 24% - after 3 minutes, with a content of 35-40% - after 20 s. In this regard, all components of liquefied hydrocarbon gases are included in the list of substances harmful to the human body. Sanitary standards establish the maximum permissible concentration of liquefied hydrocarbon gases in the air of the working area of industrial premises, equal to 300 mg/m 3 (in terms of carbon). These standards must also be observed in the working area of outdoor installations. This concentration is approximately 15-18 times less than the lower explosive limit.
The dangerous impact on humans of liquefied hydrocarbon gases increases significantly if they contain hydrogen sulfide and other sulfur compounds that are strong poisons. When the hydrogen sulfide content in the air is from 150 to 230 mg/m3, a person develops symptoms after a few hours mild poisoning, at a content of 310 mg/m 3 - after 5-8 minutes, severe irritation of the mucous membrane of the eyes, nose and throat occurs. An increase in concentration from 770 to 1080 mg/m 3 after 1 hour causes serious poisoning, and at a concentration of 1540-4620 mg/m 3 death occurs.
Vapors of liquefied hydrocarbon gases mixed with air form an explosive mixture. At a temperature of 273 K and a pressure of 0.1 MPa, the explosive limit of propane occurs when its volumetric content in air is equal to 2.3 - 9.5%, n-butane - 16, 1.5 - 8.4%, iso -butane--1.8--8.4%. As a result of this, and also because of the very slow dispersion of liquefied hydrocarbon gas vapors in the atmosphere, the mixture of their vapors with air remains explosive and fire hazardous for a long time and at a great distance from the place of evaporation.
Uncontrolled combustion of liquefied hydrocarbon gases indoors or in open areas leads to fires. The fire hazard of these gases is characterized by a heat output that exceeds 2273 K and ensures a flame temperature measured by instruments in the range of 2103-- 2198 K, significant heat released during combustion of the gas-air mixture, low flammability and explosion limits, low auto-ignition temperature, and a high need for air during combustion And big amount the resulting combustion products.
An explosion of a gas-air mixture occurs when it ignites and burns in a confined space (production room, basement, channel, tank, boiler firebox, furnace, etc.). When a gas-air mixture explodes in a room, it forms a large number of heated gases, as a result of an increase in the volume of which the pressure increases (up to 0.858 MPa). Under the influence of such pressure, building structures collapse. The actual volume of the vapor phase of propane during evaporation of its liquid phase at a temperature of 273 K and a pressure of 0.1 MPa is 269 m3, mzo-butane - 229 m3, n-butane - 235 m3.
Introduction
Liquefied hydrocarbon gases (LPG) are a mixture of light hydrocarbons liquefied under pressure with a boiling point from? 50 to 0 ° C. Intended for use as fuel. Main components: propane, propylene, isobutane, isobutylene, n-butane and butylene.
Produced mainly from associated petroleum gas. Transported and stored in cylinders and gas holders. It is used for cooking, boiling water, heating, used in lighters, and as fuel in vehicles.
Liquefied hydrocarbon gases(propane-butane, hereinafter referred to as LPG) are 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 liquid non-evaporating residue (pentane, hexane).
The raw materials for the production of LPG are mainly associated petroleum gases, gas condensate fields and gases obtained during oil refining. liquefied hydrocarbon propane petroleum distillation
From factories, LPG is supplied in railway tanks to gas filling stations (GFS) of gas facilities, where it is stored in special tanks until sold (dispensed) to consumers. LPG is delivered to consumers in cylinders or by tanker trucks.
In vessels (tanks, reservoirs, cylinders) for storage and transportation, LPG is simultaneously in 2 phases: liquid and vapor. LPG is stored and transported in liquid form under pressure created by the gas’s own vapors. This property makes LPG a convenient source of fuel supply for municipal and industrial consumers, because When stored and transported as a liquid, liquefied gas occupies hundreds of times less volume than gas in its natural (gaseous or vapor) state, and is distributed through gas pipelines and used (burned) in gaseous form.
Liquefied petroleum gases (LPG) consist of simple hydrocarbon compounds, which are organic substances containing 2 chemical element- 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 under normal conditions are gases, and at a relatively small increase in pressure and temperature environment or a slight decrease in temperature at atmospheric pressure, they pass 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 With n H 2n+2 and taken to homologous series saturated hydrocarbons - compounds in which carbon is extremely saturated with hydrogen atoms. Under normal conditions, the only saturated hydrocarbon gases are methane, ethane, propane and butane.
To obtain liquefied gases, natural gases extracted from the depths of the Earth, which are a mixture of various hydrocarbons, mainly of the methane series (saturated hydrocarbons), are now widely used. Natural gases are pure gas fields mainly composed of methane and are lean or dry; heavy hydrocarbons (from propane and above) contain less than 50 g/cm3. Associated gases released from oil field wells together with oil, in addition to methane, contain a significant amount of heavier hydrocarbons (usually more than 150 g/m 3) and are fatty. Gases that are extracted from condensate deposits consist of a mixture of dry gas and condensate vapor. Condensate vapor is a mixture of heavy hydrocarbon vapors (C3, C4, gasoline, naphtha, kerosene). At gas processing plants, gas gasoline is separated into the propane-butane fraction from associated gases.
NGLs - a wide fraction of light hydrocarbons, mainly includes a mixture of light hydrocarbons of ethane (C 2) and hexane (C 6) fractions. In general, a typical composition of natural gas liquids looks like in the following way: 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.
Considering the widespread use of LPG in the gas industry, we should dwell in more detail on the properties of propane and butane.
Propamn is organic matter class of alkanes. Contained in natural gas, it is formed during the cracking of petroleum products. Chemical formula C 3 H 8 (Fig. 1). A 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 auto-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 so-called liquefied petroleum gases, in the production of monomers for the synthesis of polypropylene. It is the starting material for the production of solvents. In the food industry, propane is registered as food additives E944 as propellant.
Butamn (C 4 H 10) is an organic compound of the alkanes class. In chemistry, the name is used primarily to refer to n-butane. Chemical formula C4H10 (Fig. 1). The same name is given to a mixture of n-butane and its isomer isobutane CH(CH 3) 3. Colorless flammable gas, odorless, easily liquefied (below 0 °C and normal pressure or at high blood pressure and normal temperature - a highly volatile liquid). Contained in gas condensate and oil gas(up to 12%). It is a product of catalytic and hydrocatalytic cracking of petroleum fractions.
The production of both liquefied gas and natural gas liquids is carried out from the following three main sources:
- ? oil production enterprises - production of LPG and natural gas liquids occurs during crude oil production during processing of associated (associated) gas and stabilization of crude oil;
- ? gas production enterprises - production of LPG and natural gas liquids occurs during the primary processing of well gas or unbound gas and stabilization of condensate;
- ? oil refineries - the production of liquefied gas and similar natural gas liquids 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 temperatures 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 better combustion characteristics.
The state of hydrocarbon systems is determined by a set of influences various factors, therefore for full characteristics you need to know all the parameters. The main parameters that can be directly measured and influence the flow regimes of LPG include pressure, temperature, density, viscosity, concentration of components, and phase relationships.
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 disrupts the equilibrium state of the system, causing it
or 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. Gas pressure is the total result of the collision of molecules with the walls of a container occupied by this gas.
Elasticity (pressure) of saturated gas vapor* p p is the most important parameter used to determine operating pressure in tanks and cylinders. The temperature of the gas determines the degree of its heating, i.e. a measure of the intensity of movement of its molecules. The pressure and temperature of liquefied gases strictly correspond to each other.
The elasticity of LPG vapors - 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 pressure of LPG vapor increases with increasing temperature and decreases with decreasing temperature.
This property of liquefied gases is one of the determining ones in the design of storage and distribution systems. When boiling liquid is taken from reservoirs and transported through a pipeline, part of the liquid evaporates due to pressure loss, a two-phase flow is formed, the vapor pressure of which depends on the temperature of the flow, which is lower than the temperature in the reservoir. If the movement of a two-phase liquid through the pipeline stops, the pressure at all points is equalized 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 liquid is placed in the upper part saturated couples(Fig. 2). When the temperature in the tanks decreases, some of the vapors will condense, i.e. The mass of liquid increases and the mass of vapor decreases, a new equilibrium state occurs. As the temperature increases, the reverse process occurs until phase equilibrium occurs at the new temperature. Thus, evaporation and condensation processes occur in tanks and pipelines, which in two-phase media occur 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 water vapor in varying quantities. Moreover, their amount in gases can increase until saturation, after which moisture from the gases precipitates in the form of water and mixes with liquid hydrocarbons to the maximum degree of solubility, and then free water is released, which settles in tanks. The amount of water in LPG depends on its 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 as condensate in pipelines. Water accumulated in tanks must be periodically removed, otherwise it may reach the consumer or lead to equipment failure.
According to LPG test methods, only the presence of free water is determined; the presence of dissolved water is allowed.
Abroad, more stringent requirements are imposed on the presence of water in LPG and its quantity, which is brought to 0.001% by weight through filtration. 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 SI unit of density is kilogram per cubic meter(kg/m3). In general
When liquefied gases move at a pressure below vapor pressure, i.e. When two-phase flows move, to determine the density at a point, one should use the ratio limit:
In numerous calculations, especially in the field of thermodynamics of gases and gas-liquid mixtures, it is often necessary 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 any substance, taken as specific or standard c,
For hard and liquid substances The density of distilled water at a pressure of 760 mm Hg is taken as standard. and temperature 3.98ºC (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 temperature 0 °C (1.293 kg/m3).
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 inflection point 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 the critical points of unsaturated hydrocarbons by a dashed line. Density can also be determined from phase diagrams. IN general view the dependence of density on temperature is expressed by the series
T = T0 +(T-T 0)+(T-T 0) 2 +(T-T 0) 2 ±.
The influence of the third and other terms 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 = 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;
As pressure increases, the liquid phase of propane and butane contracts. Its degree of compression is estimated by the coefficient of volumetric compressibility VSC, the dimension of which is the inverse of the dimension of pressure.
Specific volume. The volume of a unit mass of a substance is called specific volume (notation). The SI unit of specific volume is cubic meter per kilogram (m 3 /kg)
Specific volume and density are reciprocal quantities, i.e.
Unlike most liquids, which change their volume slightly when 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 possible increase fluid volume (Fig. I-3).
Compressibility. Estimated by volumetric compression ratio, m 3 /n,
The reciprocal of p is called the elastic modulus 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 (balloon), then when the temperature rises, it has nowhere to expand and 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) when the ambient temperature rises should not exceed the permissible design value, otherwise an accident may occur. Therefore, when filling, it is necessary to provide a steam cushion of a certain size, i.e. The tank is not completely filled. This means that it is necessary to know the degree of filling, determined by the relation
If you need 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 gas temperature (Tcr). 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 critical volume (Vcr), and the state of the gas, determined critical temperatures, pressure and volume, - the critical state of the gas. The density of vapor above the liquid at a critical state becomes equal to the density of the liquid.
The principle of corresponding states. Usually, to generalize experimental data on the study of various processes and substances, criterion systems are used based on the analysis of the equations of motion, thermal conductivity, etc. To use such similarity equations, tables of physical properties of working media are needed. Inaccurate determination of physical properties or their absence does not make it possible to use similarity equations. This especially applies to little-studied working fluids, in particular to liquefied hydrocarbon gases, about the physical properties of which there are quite contradictory data in the literature, often at random pressures and temperatures. At the same time, there is accurate data on the critical parameters and molecular weight of the substance. This allows, using the given parameters and the law of corresponding states, which is confirmed by numerous studies and theoretically justified by the modern kinetic theory of matter, to determine unknown parameters.
For thermodynamically similar substances, and liquefied hydrocarbon gases are thermodynamically similar, the given equations of state, i.e. equations of state written in dimensionless (reduced) parameters (r pr = r/r cr =) have the same form. IN different time Various authors have proposed up to fifty equations of state for real substances. The most famous and used of them is the van der Waals equation:
where a and b are constants inherent in a given chemical compound;
By expressing the parameters of a gas in dimensionless reduced quantities, we can establish that for gases there is a general equation of state that does not contain quantities characterizing a given 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 the 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 the coefficient compressibility Z = (Fig. 1-4 - 1-6). From it you can 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 specific gravity (notation. In general, where G is the weight (gravity force of the substance, V volume, m 3. The SI unit of specific gravity = newton per cubic meter (N/m 3). Specific gravity depends on the acceleration of gravity at the point of its determination and, therefore, is a parameter of the substance.
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 (designation Q). The SI dimension of the heat of combustion 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 for the combustion process to begin (combustion reaction) is called the ignition temperature. It is not a constant value and depends on many reasons: the content of flammable 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 located, etc.
Gas flammability limits. 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 spontaneously (without a constant flow 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 speed of flame propagation decreases, heat losses increase and combustion stops. With increasing temperature of the gas-air mixture, 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 (designation C). The SI unit is joule per degree Kelvin (J/K). 1 J/K - 0.2388 cal/K = 0.2388*10 -3 kcal/K.
In practical calculations, a distinction is made between average and true heat capacity depending on the temperature range in which it is determined. The average heat capacity C m is a value determined over a finite temperature range, i.e.
With m = q/(t 2 -t 1).
True heat capacity is a value determined at a given point (for given p and T or and T), i.e.
A distinction is made between heat capacity 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 of area F with 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 the substance, W/(m*K) or kcal/(m*h*C).
Viscosity- this is the ability of gases or liquids to resist shearing forces, due to the forces of adhesion between the molecules of the substance. The force of resistance to sliding or shear F, and, which arises when moving two adjacent layers of liquid or gas, is proportional to the change (gradient) of speed along the axis normal to the direction of flow of liquid and gas, i.e.
where is the proportionality coefficient, nsec/m2 (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 its density, i.e. =/. Unit kinematic viscosity in SI - square meter per second (m 2 /sec).
The viscosity of the liquid phase decreases with increasing temperature, while the viscosity of gas and vapor increases.
Octane number gas fuel is higher than that of gasoline, therefore the detonation resistance of liquefied gas is greater than that of gasoline even of the highest quality. The average octane number of liquefied gas - 105 - is unattainable for any brand of gasoline. This makes it possible to achieve greater fuel efficiency in a gas boiler.
Diffusion. The gas mixes easily with air and burns more evenly. Gas mixture burns completely, so no soot is formed in the fireboxes 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 container depends on the saturated vapor pressure, which in turn depends on the temperature of the liquid phase and the percentage of propane and butane in it. Saturated vapor pressure characterizes the volatility of LPG. The volatility of propane is higher than that of butane, and therefore the pressure at negative temperatures his is much higher. Calculations and experiments have established that at low ambient temperatures it is more effective to use LPG with a high propane content, since this ensures reliable evaporation of gas, and therefore sufficient gas for gas consumption. In addition, sufficient excess pressure in the tank will ensure a reliable supply of gas to the boiler in severe frosts. At high positive ambient temperatures, it is more effective to use LPG with a lower propane content, since this will create significant excess pressure in the tank, which can trigger the release valve. 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 operation of the container, non-evaporating condensate may form, which negatively affects the operation of gas equipment.
Change in the volume of the liquid phase upon heating. The rules of the UN 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 coefficient of volumetric expansion of the liquid phase, which for propane is 0.003, and for butane 0.002 per 1°C increase in gas temperature. For comparison: the coefficient of volumetric expansion of propane is 15 times, and butane is 10 times greater than that of water.
Change in gas volume during evaporation. When liquefied gas evaporates, about 250 liters are formed. gaseous. Thus, even a minor leak of LPG 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 when there is a leak, the gas has difficulty dispersing into the air, especially indoors. Its vapors can accumulate in natural and artificial depressions, forming an explosive mixture. SNiP 42-01-2002 provides for the mandatory installation of a gas analyzer that issues a signal to the shut-off valve to close in the event of gas accumulation in a concentration of 10% of the explosive concentration.
Odoration. The gas itself has practically no odor, therefore, for safety and timely diagnosis of gas leaks by the human olfactory organs, small amounts of strong-smelling substances are added to it. If the mass fraction of mercaptan sulfur is less than 0.001%, LPG must be odorized. For odorization, ethyl mercaptan (C2H5SH) is used, which is an unpleasant-smelling liquid with a density of 0.839 kg/l and a boiling point of 35°C. The odor sensitivity threshold is 0.00019 mg/l, the maximum permissible concentration in the air of the working area is 1 mg/m 3. In cases where toxicity is normal or slightly below normal, the odor of the odorant is practically not felt and its accumulation in the room is not observed.
Conclusion
Thus, we can summarize and highlight the main properties of propane-butane mixtures that affect the conditions of their storage, transportation and measurement.
1. Liquefied hydrocarbon gases are low-boiling liquids that can be in a liquid state under saturated vapor pressure.
Boiling temperature:
Propane -42 0 C;
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 petroleum products.
- 5. Instability of the aggregate state of LPG when flowing through pipelines, depending on temperature, hydraulic resistance, and uneven nominal diameters.
- 6. Transportation, storage and measurement of LPG are possible only through closed (sealed) systems, designed, as a rule, for a working pressure of 1.6 MPa.
- 7. Pumping and measuring operations require the use of special equipment, materials and technologies.
Worldwide, hydrocarbon systems and equipment, as well as device technological systems subject to uniform requirements and rules.
Liquefied gas is a Newtonian liquid, 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 fluid and measure it, but also to ensure that the influence of “negative” factors is reduced physical and chemical properties LPG.
Fundamentally, systems pumping LPG differ little from systems for water and oil products, and, nevertheless, additional equipment is needed to guarantee qualitative and quantitative measurement characteristics.
Based on this, a hydrocarbon process system, at a minimum, must include a reservoir, pump, gas separator, meter, differential valve, shut-off or control valve, safety devices against excess pressure or flow rate.
This term refers to the entire spectrum liquefied hydrocarbon gases of various origins (ethane, propane, butanes and their derivatives - ethylene, propylene, etc.) and mixtures thereof. But most often under LPG understand a mixture of liquefied propane and butanes used as household fuel and. IN Lately the names and abbreviations of SPBF began to be used more often ( liquefied propane-butane fraction), SPBT ( liquefied propane-butane technical), LPG ( liquefied carbon gas), CIS ( liquefied petroleum gas).
The physical properties of LPG are determined physical properties its main components. It can be stored in liquefied form at relatively low pressures up to 1.5 MPa in a wide temperature range, which makes it possible to transport LPG in tanks or cylinders. Depending on the specification, LPG may also contain isobutane and ethane. The volume of LPG is approximately 1/310 of the volume of gas under standard conditions.
The physical properties of propane and n-butane, which determine the method of their transportation in liquefied form in tanks, are presented in the table.
LPG used as household fuel (heating, cooking), and also used as environmentally friendly motor fuel, in particular for public transport V major cities. Liquefied gas is a raw material for the production of olefins (ethylene, propylene), aromatic hydrocarbons (benzene, toluene, xylene, cyclohexane), alkylate (an additive that increases the octane number of gasoline), synthetic motor fuels. In winter, butane is added to gasoline to increase RVP (Reid vapor pressure). In the USA, LPG, after being diluted with nitrogen and/or air (to bring the specific caloric content to the indicators of network gas), is used as an additional source of gas to smooth out peak loads on gas distribution networks.
Natural gas and oil and petroleum associated gases are used as raw materials for the production of LPG. The technology for the production of liquefied gas depends on the industry sector: oil and gas refining and petrochemicals. In the petroleum refining industries, liquefied carbon dioxide is actually an additional product in the production of gasoline. In gas processing, liquefied gas is the main product for final sale or further processing.
Due to the depletion of Cenomanian deposits "dry gas" deposits of the Neocomian-Jurassic horizons, characterized by an increased content of hydrocarbon gases of the C 2+ series, are being transferred to development ( "wet and condensate gas"). In petrochemistry, fat content is understood as the average number of carbon atoms per gas molecule (for methane the fat content is 1, for ethane it is 2, etc.). From the point of view of preparing gas for transportation by pipeline, fat content means the excessive presence of hydrocarbons of the C 3+ series in the gas, leading to their condensation in the gas pipeline during transportation. The fat content of gas increases its value as a feedstock for petrochemicals.
Liquefied petroleum gas produced in Russia is used mainly in three directions: 1) LPG as a raw material in petrochemicals; 2) in the public utility sector; 3) export.
