Speed ​​of sound propane gas liquefied hydrocarbon. Comparison of liquefied petroleum gas (LPG) and liquefied natural gas (LNG). Properties and abilities of liquefied propane, butane and methane

Composition of liquefied hydrocarbon gases

LPG is understood as such individual hydrocarbons or mixtures thereof, which under normal conditions are in a gaseous state, and with a relatively small increase in pressure without a change in temperature or a slight decrease in temperature at atmospheric pressure, it passes into a liquid state.

Under normal conditions, of the saturated hydrocarbons (C n H 2 n +2), only methane, ethane, propane, and butane are gases.

Let's consider what gases pass into a liquid state with a slight increase in pressure at a temperature of O 0 C: ethane condenses into a liquid when the pressure rises to 3 MPa. Propane up to 0.47 MPa, N-butane up to 0.116 MPa, Isobutane up to 0.16 MPa. Most of all meets the required conditions

propane and butane.

Consider which hydrocarbons turn into a liquid state with a relatively small decrease in temperature and atmospheric pressure: the boiling point of methane is 161.5 0 С; ethane - 88.5 0 С; propane - 42.1 0 С; n-butane - 0.5 0 C. The most suitable for practical use are propane and butane.

Along with normal saturated hydrocarbons, there are isomeric compounds that differ in the nature of the arrangement of carbon atoms, as well as in some properties. An isomer of butane is isobutane. Propane has no isomer.

Structure and f-la N-butane CH 3 -CH 2 -CH 2 - CH 3

Isobutane:

In addition to the limiting ones, there are also a group of unsaturates in the composition of LPG. Or unsaturated hydrocarbons, characterized by a double or triple bond between carbon atoms. These are ethylene, propylene, butylene (normal and isomeric). The general formula for unsaturated hydrocarbons with a double bond is C n H 2 n. Ethylene C2H4 CH2=CH2.

To obtain LPG, fatty natural gases are used, i.e. gases from oil and condensate fields containing large amounts of heavy hydrocarbons. At gas processing plants, propane-butane fraction and natural gasoline (С5Н12) are emitted from these gases. Technical propane and butane, as well as their mixtures, are liquefied gas used for gas supply to consumers.

Technical gases differ from pure gases by the content of small amounts of hydrocarbons and the presence of impurities. For technical propane, the content of C3H8 + C3H6 (propylene) should be Not< 93%. Содержание С2Н6 +С2Н4(этилен) не>4%. The content of С4Н10+С4Н8 is not >3%.

For technical butane: С4Н10+С4Н8 d.b. Not< 93%. С3Н8 +С3Н6 не>4%. С5Н12+С5Н10 not >3%.

For a mixture of butane and propane content: С3Н8+С3Н6, С4Н10+С4Н8 d.b. Not< 93%. С2Н6 +С2Н4 не>4%. С5Н12+С5Н10 not >3%.

SUG property.

There are 3 states of liquefied gas in which they are stored and used:

1) As a liquid (liquid phase)

2) Steam (vapor phase), i.e. saturated vapors that are together with a liquid in a tank or cylinder.

3) Gas (when the pressure in the vapor phase is lower than the saturated vapor pressure at a given temperature).

The properties of liquefied gases easily change from one state to another, which makes them a particularly valuable source of gas supply, because. they can be transported and stored in liquid form, and burned in the form of gas. That. liquid phases are mainly used during transportation and storage, and gaseous phases during combustion.

The elasticity of saturated gas vapor is the most important parameter by which the working pressure in cylinders and tanks is determined. It varies in proportion to the temperature of the liquid phase and is a strictly defined value for a given temperature.

All equations relating the physical parameters of a gaseous or liquid substance include absolute pressure and temperature. And in the equations for technical calculations of the strength of the walls of cylinders, reservoirs - excess pressure.

In the gaseous composition, LPG is 1.5-2 times heavier than air. In the liquid state, their density is in the range of 510-580 kg / m 3, i.e. they are almost 2 times lighter than water. The viscosity of LPG is very low, which facilitates their transportation through pipelines and favors leaks.

LPG has low flammable limits in air (2.3% for propane, 1.7% for butane). The difference between the upper and lower limits is insignificant, therefore, when they are compressed, an air-liquefied gas ratio can be used.

Diffusion into the atmosphere is very slow, especially in the absence of wind. They have low ignition t-s compared to most combustible gases (510 0 C for propane and 490 0 C for butane).

Condensation may form when the t-ry drops to the dew point or when the pressure rises. Liquefied gases are characterized by a low boiling point and therefore, during evaporation during a sudden exit from a pipeline or tank into the atmosphere, it cools to a negative t-point. The liquid phase getting on unprotected human skin can lead to frostbite. By the nature of the impact, it resembles a burn.

Unlike most liquids, which slightly change their volume when changing t-ry, the liquid phase of LPG increases its volume quite sharply with increasing t-ry (16 times more than water). Therefore, when filling tanks and cylinders, it is necessary to take into account the possibility of increasing the volume of liquid.

The compressibility of liquefied gases compared to other liquids is very significant. If the compressibility of water is taken as one, then the compressibility of oil is 1.56, and propane is 15. If the liquid phase occupies the entire volume of the reservoir, then with an increase in t-ry it has nowhere to expand and it begins to shrink. The pressure in the tank rises. Pressure increase d.b. not more than the allowable calculated, otherwise an accident is possible. Therefore, when filling tanks and cylinders, it is planned to leave a vapor cushion of a certain size, i.e. fill them out completely. Vapor cushion value Liquefied gases have a higher volumetric calorific value than natural gases (2.5-3.4 times higher).

Liquefied gases are non-toxic. They have no smell, color and taste (both in liquid and gaseous form), which dictates the need for their odorization.

underground tanks is 10%, for above-ground and cylinders 15%.

Determination of LPG properties

With a known composition of liquefied gas, the pressure of the mixture can be calculated using the formulas:

The density of a gas mixture of a given composition is determined by:

Mole fraction of the i-th component of the mixture

- Density of the i-th component of the mixture, kg / m 3

It is in the table or calculated according to Avogadro's law:

Where is the molecular weight of the i-th component, kg/kmol

- Molecular volume of the i-th component, m 3 / kmol

The average density of a liquid mixture with a known mass composition is determined by the formula:

With a known molecular composition:

,

Where is the density of the i-th component included in the liquid mixture in the liquid phase, kg / l

The density of the gas mixture at elevated pressure is found from the equation of state for real gases.

,

Where - absolute pressure (MPa) and t-ra of the mixture.

- gas constant of the mixture, (J / kg K)

z-coefficient of compressibility, which takes into account the deviation of real gases from the z-new ideal gases.

The gas constant of a mixture is calculated from the universal gas constant and from the molecular weight of the mixture.

The compressibility coefficient is determined according to the graph depending on the given parameters (pressure and temperature) of the gas.

The average critical pressure and temperature for a mixture of gases is determined by its composition.

;

The volume of gas, it turns out the evaporation of the LPG mixture, m.b. found by the formula:

is the mass of the i-th component of the mixture, kg

is the molecular weight of the i-th component of the mixture, kg/kmol

V Mi -molecular volume of the i-th component

To calculate the lowest volumetric combustion temperature of the LPG mixture, the following relationship is used

– lower volumetric calorific value of the i-th component, kJ / m 3

Lowest Mass Combustion Temperature

The ignition limits of an LPG mixture that does not contain ballast impurities are determined by:

L cm - the lower or upper limit of ignition of a mixture of gases.

is the lower or upper flammability limit of the i-th component.

Due to the level difference

The use of hydrostatic head is used when filling underground tanks from railway and tank trucks, as well as when spilling LPG into cylinders, if the terrain allows. In order to drain the tanks into the tank, it is necessary to connect their vapor and liquid phases. In communicating vessels, the liquid is set at the same level, so the liquid phase will flow into the lower tank.

To create a sufficient drain rate, at the same temperature and pressure, in the tank and the tank, it is necessary that due to the hydrostatic pressure a pressure difference of at least 0.7-0.1 MPa be created.

The minimum required value of hydrostatic head under these conditions will be 14-20 meters of liquid column.

In winter, the cistern has a lower temperature than the reservoir. When the tank is located underground, the temperature difference can reach 10-15 0 C. The gas pressure in the tank will be much lower than in the tank.

For reliable draining, it is necessary that the level difference compensate for this temperature difference and, accordingly, the pressure difference. The required level difference is:

,

Where is the gas pressure in the tank, Pa

- gas pressure in the tank

- density of the liquid phase of LPG, kg / m 3

Received max. the difference is necessary to start draining. In the future, t inside the tank will begin to decrease due to the flow of cooled liquid from the tank. The pressure in the underground tank will become less and the difference in levels will be required already less. At the initial moment, it is almost impossible to create such a level difference, therefore it is necessary to connect the steam production into tanks and tanks. In this case, the pressure is equalized and the avenue is drained using the full hydrostatic head.

In summer, at the initial moment of draining, the location of tanks below the tank is possible. But here the influence of the temperature in the tank from the warmer liquid from the tank will affect, and the pressure drop will drop to about 0. The drain will stop. Therefore, in the summer, when draining, the vapor phases of the tank truck and the tank do not need to be connected.

"+" of the method: 1. Simplicity of the scheme

2. No mechanical units

3. Reliability of all devices

4. The readiness of the circuit to work at any time, regardless of the presence of an external energy source

5. Low repair and maintenance costs

"-" method:

1. The impossibility of using terrain with mountainous terrain.

2. Long duration of the process.

3. Large losses of gas when sending it back in the form of vapors in drained tanks.

Gas filling stations

HPS are the base for the supply of liquefied gases and are designed to receive, store and supply consumers with liquefied gases supplied by rail, road, water transport, and from enterprises where these gases are produced (gasoline plants).

The volume of gas storage tanks at the station is not more than 8000 m 3 . Usually the gas reserve does not exceed 300-600 tons and the capacity is from 6000 to 24000 tons/year.

The following work is being carried out at the HPS:

Reception of liquefied gases from the supplier

Draining of compressed gases into own storages

Storage of LPG in aboveground, underground or isothermal tanks, in cylinders or underground voids.

Draining of unevaporated residues from the cylinder and compressed gas from cylinders with malfunctions

Spill of liquefied gas into cylinders, mobile tanks and tank trucks

Reception of empty and delivery of filled cylinders

Transportation of compressed gases through the internal pipeline network

Repair of cylinders and their re-examination

Maintenance and repair of equipment at the station

In a number of cases, the STS produces:

Refueling vehicles running on compressed gas from a filling station

LPG regasification

Mixing of gas vapors with air or low-calorie gases

Delivery of compressed gas vapors, gas-air and gas mixtures to urban distribution systems.

To perform these operations, the GNS has the following. departments and workshops:
- drain overpass of a railway line or input of a pipeline with disconnecting devices

LPG storage base, consisting of above-ground or underground pressurized tanks, isothermal tanks or underground storage in voids

Pumping and compressor shop for draining LPG from railway tanks to storage facilities and supplying it for filling cylinders and tankers

Workshop for filling cylinders and draining unevaporated heavy residues from them

Warehouse for daily stock of empty and filled cylinders

Columns for filling tankers

Communications of the liquid and vapor phases, connecting all departments of the HPS and ensuring the movement of liquid and vapor flows.

HPS should be placed outside settlements on the leeward side of the prevailing winds, while maintaining the required distances between the HPS and other structures.

Depending on the volume of storages, the method of installation of tanks, these distances are from 40 to 300 m.

Along the perimeter of the territory, the STS is fenced with a reinforced concrete fence with a height of 3.4 m. With a reservoir capacity of > 200 m 3, the territory of the HPS is divided by a light fence into 2 territories - a working one, including the listed departments and workshops, and an auxiliary one, including administrative and utility rooms, garages, a water tower and a tank for fire-fighting water supply.

A schematic diagram of the supply of LPG consumers is shown in the figure:

Isothermal storage of LPG

The storages are thin-walled tanks of large volume from 5000 to 50000 m 3 of cylindrical shape with a vaulted or conical roof. Their outer surface is thermally insulated. Steel storages can be both above ground and buried. Maintaining a low t (-42⁰С - for propane) can be. carried out by evaporating part of the LPG and discharging vapors into gas networks or special. refrigeration unit. The flow of heat through the walls of the tank is insignificant and causes the evaporation of 0.3-0.5% of the volume of stored liquid per day.

There are 3 main technological schemes isothermal. repositories:

With complex refrigeration unit

With buffer tanks

- with intermediate cooling

The “hot” product entering through tube 1 is throttled in tank 2 with a drop in t and p . Vapors formed due to heat inflow from the outside and the incoming “horizontal” product are supplied by compressor 3 through pipeline 4 to refrigeration unit 5, where it is cooled and condensed. The condensate through the throttle valve 6 enters the isothermal. storage tank.

Power cold. the unit depends on the total heat influx into the reservoir and determines:

- heat input by the filled “mountain” product

Where - speed of LPG drain from the tank kg / h;

Heat capacity of the LPG liquid phase kJ/(kg⁰С);

And - the temperature in the tank and the reservoir.

– influx of the body from the external environment;

where M is the mass of liquefied gas in isothermal. tank, kg;

r is the heat of vaporization of LPG, kJ/kg;

0.005 - 5% evaporates per day.

– unaccounted heat inputs:

b=0.04..0.12

From the formula for determining it can be seen that it is possible to reduce the capacity of the refrigeration unit by reducing the filling rate of the tank. Usually, when draining 3 railway tanks, it comp. 33-35t/h, which requires very powerful refrigeration equipment operating only a few hours a day (when draining). The rest of the time is cold. needed only to liquefy the gas evaporating in the tank, which comp. max 0.5% of stored LPG.

Liquefied gas transport

In the CIS countries, the most widespread transportation of LPG in railway and machine tanks, as well as cylinders. At a distance of up to 300 km, machine transport is used, at a greater distance - railway. The railway tank is designed for operating pressure when transporting propane - 2 MPa, butane - 0.8 MPa.

Have been widely used horizontal cylindrical tanks volume of 50-100 m 3. In the upper part of the tank there is a neck, which serves as a hatch and is intended for inspection and repair of the internal cavity of the tank. The manhole cover is made in the form of a flange, on which fittings are provided: there are devices for filling and draining the liquid phase with high-speed valves, supplying and extracting the vapor phase with high-speed valves, and a safety valve.

For the transportation of LPG on machine roads, tank trucks, capacity from 2 to 5 tons. liquefied gas. A safety valve is installed at the top of the tank. In the center of the rear bottom there is a hatch on the inner cavity of the cover of which there is an instrumentation: a thermometer, a pressure gauge, a level indicator. The level gauge is a glass tube enclosed in a steel tube. There are 6 valves on both sides for filling and draining tanks, 4 hoses up to 3.5 m are provided.

Individual consumers located near the gas pumping station receive LPG in cylinders. Cylinders are delivered by airborne vehicles or special vehicles. Adapted for these purposes (in containers). The container is a welded cage designed for 2 or 3 tier arrangement of cylinders.

Transporting LPG by water has become widespread in Western Europe.

There are 3 types of LPG carriers:

1) Tankers with 1.6 MPa pressure tanks

2) Tankers with thermally insulated reduced pressure tanks. LPG is transported with intermediate cooling from -5 0 C to +5 0 C and reduced pressure (0.3 ... 0.6 MPa)

3) Tankers with thermally insulated tanks under pressure close to atmospheric and at low temperature (-42 0 C for propane, -161 0 C for natural gas)

River transport is widely used to supply the northern regions of Russia. Air transportation is used to supply LPG to consumers in the Arctic and Antarctic.

Film evaporators of LPG.

It is a tube-in-tube heat exchanger. A thin film of LPG is created by spraying it onto the walls of the inner pipe 3 with nozzles 2 . The coolant (hot water or water vapor) enters the annular annulus 4 , providing intensive evaporation of LPG inside the pipe 3 . For uniform temperature distribution along the length of the evaporator, the coolant is supplied to 2 points, and removed in one.

In order to avoid an unacceptable increase in pressure in the evaporator on the pipe 3 safety relief valve installed 5 . Unevaporated condensate is drained through the drain fitting 6 . If it is necessary to increase the productivity of the installation, several evaporators can be connected to the collector 1. The heat transfer coefficient is about 2 times higher than in serpentine and tubular ones, so they are more compact and less metal-intensive.

Gas combustion temperatures.

The main amount of heat released during gas combustion is spent on heating the combustion products to a certain temperature.

The following combustion temperatures are distinguished:

Heating capacity

Calorimetric

theoretical

Valid

Heating capacity - these are t products of complete combustion of combustible gases under adiabatic conditions at α=1 and at the initial t of gas and air = 0 0 С.

Q n \u003d i ave. burn \u003d V ave. burn ∙С r ave. burn ∙t f

i etc. burn - heat content of combustion products kJ / m 3

t w - heat output, 0 C.

t well \u003d Q n / V ave. burn ∙С r ave. burn \u003d Q n / (V co 2 ∙ C r CO2 + V H20 ∙ C r H 20 + V N 2 ∙ C r N 2)

V co 2 V H20 V N 2 - the volume of the constituent parts of the combustion products of 1 m 3 of gas.

С р – average volumetric heat capacity at P=const. components of combustion products.

The formula uses the average heat capacity, since the Cp value is not constant, it increases with increasing temperature.

t well: for methane 2043 0 С; for propane 2110 0 С; for hydrogen 2235 0 C

These data are for combustion in dry air.

Calorimetric- t combustion gas, taking into account the coefficient. Excess air and physical heat of gas and air, i.e. the actual values ​​​​of temperature are taken. in other words, this is t to which the products of complete combustion would be heated if all the heat of the fuel and air went to heat them.

Q n + i g + i in \u003d i ave.

i g i v - enthalpy of gas and air kJ / m 3

By writing the equation in expanded form and solving it for calorimes. temps We get:

T g t in - the initial temperature of gas and air.

T to ≈1900 0 C,

Gas consumption,

The theoretical amount of air required to burn 1 cubic meter. gas.

The physical heat of gas and air should be taken into account if they are heated above 100 0 C before combustion, since at lower t this value is insignificant compared to the calorific value.

Theoretical combustion temperature takes into account heat losses due to chemical incompleteness of combustion and endothermic reactions of dissociation of combustion products.

CO 2 ↔CO + 0.5O 2 -Q

H 2 O↔H 2 +0.5O 2 -Q;

Qx - heat loss due to chemical incompleteness of combustion and dissociation of CO2 and H20.

At t up to 1500 0 C (occurs in the furnaces of boilers and industrial furnaces), the value of Qx can be ignored, since in this case an insignificant fraction of combustion products dissociates. At higher temperatures, it must be taken into account.).

Actual combustion temperature is achieved in real conditions of fuel combustion, it is lower than the theoretical one, since when determining it, heat losses to the environment, the duration of the combustion process, the method of gas combustion and other factors are taken into account.

t d = t t ∙η p

η p - experimental pyrometric coefficient. For most furnaces of boilers and furnaces 0.65. For the most perfect 0.8-0.85

Diffusion burners

In this type of burners, gas and air enter the furnace in separate streams, where mixture formation and combustion take place. The simplest diff. The burner is a treb with holes drilled in it.

Such burners can be straight, round, T- and U-shaped, etc. The gas is supplied inside such burners and exits through the holes in numerous streams, forming separate torches. The number of holes and their diameter depend on the capacity of the burner. The pitch between the holes is chosen so that there is no merging of the torch, and the fluency of fire is ensured when the gas is afterburned on the burner.

Hole diameter d.b. from 0.5 to 5 mm. In this case, the easy clogging of a small diameter hole should be taken into account. For good mixing of gas with air, it is recommended to make no more than two rows of holes in each differential tube. burners. The cross section of the pipe supplying gas d.b. not less than the total cross section of the burner holes.

"+" differential burners:

Easy to manufacture, reliable in operation (flame flashback is excluded),

has large control limits, can operate both at low and medium gas pressure without blast,

Gives a steady luminous torch with high radiation.

"-" differential burners:

· There are small thermal loads;

work with increased α (1.2-1.5). Despite a large excess of air, these burners often work with chem. underburnt.

Long torch length

The need to ensure stable discharge in the furnace volume

Difficulty in automating the gas combustion process (automatic proportioning of gas and air)

Designs have been created for larger differential burners with good performance properties (for example, a burner for heating and industrial boilers). Good mixing of gas with air is achieved due to the multi-jet gas outlet at an angle to the burner axis, which leads to swirling of the flow

1-inner glass

2-outer body

3-tangential nozzle slots

4.5- air chokes

The inner glass is inserted into the body of a larger diameter. Gas passes through the internal space between the body and the glass, flowing through 3 into the furnace. About 50% of the consumed air is supplied through the inner glass. The rest is through the outer annular slot. The movement of air is due to the presence of vacuum in the furnace. The capacity of such a burner is from 30 to 350 m 3 /h. They might. low and medium pressure.

Diff burners are indispensable in high-temperature furnaces (heat-melting, steel-smelting) when air is heated to temperatures significantly higher than the ignition temperature of the gas. Preliminary mixing of gas with air is not feasible, therefore, in such furnaces, gas combustion is not only forced, but also the most justified, because. allows you to get a brightly glowing sooty torch with a high degree of blackness and intense radiation.

Hearth burners

In boiler technology, differential burners can be located on the front or side walls of the furnace, as well as inside it, on the hearth. Burners of the latter type are called hearth burners. They are used when converting heating and industrial boilers with layered furnaces to gaseous fuel. The gas from the burner goes into the furnace, where air enters from under the grate. The gas jets from the hearth burners are directed at an angle to the air flow and are evenly distributed over its cross section.

The mixing process is carried out in cracks formed by the refractory lining. This intensifies the mixing of gas with air, reduces α, and ensures stable ignition in the resulting mixture.

1- Collector

The burner manifold is mounted on bricks located on the grate. Above the collector, the refractory lining forms straight slots into which the gas, not mixed with air, enters. The gas outlet holes are located in 2 rows in a checkerboard pattern, symmetrical with respect to the vertical plane with an angle between the rows from 90 to 180 °. Air is supplied under the grate by a fan or by vacuum in the furnace, supported by draft and passage through the slot, washing the collector from both sides.

As a result of turbulent diffusion, the gas jet mixes with air and begins to burn at a distance of 20–40 mm from the hole. The combustion process ends at a distance of 0.5 - 1 m from the burner. Here, the diffusion principle of gas combustion is implemented. The mixture formation process is activated by the fact that the gas flow is broken into small streams that exit at high speed at an angle to the direct air flow. The refractory walls of the slot act as a flame stabilizer, preventing flame separation, and are indirect emitters.

The maximum temperature on the surface of the slot is from 900 - 1000 ° C. On the surface of the collector from 300 - 500 ° C. The temperature of the grate under the slot is 75 - 80 ° C. Hearth burners provide complete combustion of gas at α from 1.1 to 1.3. Gas pressure from 500 to 5000 Pa (nominal about 1000 Pa). Air pressure from 600 to 1000 Pa. When working without blast in the furnace, d.b. discharge 20 - 30 Pa for boilers of medium productivity (from 2 to 10 tons of steam per hour) and no more than 8 Pa for small heating boilers.

Hearth burners of heating boilers have the following dimensions: hole diameter from 1.3 to 3 mm (max 10 - 20 mm), slot height 130 - 200 mm; the width is determined by calculation and is usually in the range of 80 - 110 mm.

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§ simplicity of design

§ Ability to work at low gas pressure

§ No need for pressurized air supply

§ Complete combustion of gas of various characteristics

§ Stable operation in a wide range of load changes

§ Silent operation, reliable and easy operation

§ High excess air ratio

§ Low productivity (no more than 120 kW with one burner)

§ Due to the design features (burner in the furnace), a significant α cannot be used in high-temperature installations.

Mixing burners.

Forced air mixing burners are widely used. Structurally, they are performed in such a way as to ensure the best movement of gas and air flows, which is supplied to the burner through separate pipes. The manifestation of mixture formation begins in the burner itself and is actively completed in the combustion chamber. As a result, the gas burns with a short and non-luminous flame. Mixing of gas with air is carried out as a result of turbulent diffusion. Therefore, they are called turbulent mixing burners or simply mixers.

To increase the intensity of gas combustion, it is necessary to intensify the mixing of gas with air as much as possible, since mixture formation is an inhibitory link in the entire process. Injection of the mixture formation process is achieved as follows: by swirling the air flow with guide vanes, tangential supply, gas supply in the form of small jets under the air flow, separation of gas and air flows into small flows in which mixture formation occurs.

The positive qualities of the burners are:

1) The possibility of burning a large amount of gas with a relatively small size of the burner.

2) Wide range of burner performance solution.

3) Possibility of heating gas and air to t exceeding t ignition, which is of great importance for high-temperature furnaces.

4) Relatively easy possibility of making mixtures with combined fuel compression, namely: gas-fuel oil or gas-coal dust.

Main disadvantages:

1) Forced air supply

2) Combustion of gas with a lower volumetric thermal stress than with kinetic combustion.

3) Combustion of gas with chemical incompleteness is greater than with kinetic combustion.

There is a performance of 60kW-60MW. Used for heating industrial furnaces and boilers.

Turbulent mixing burner:

1-body, 2-nozzle, 3-nozzle tip, 4-nozzle.

The gas enters the burner through the nozzle and flows out of the nozzle at a certain speed. Air is supplied to the burner under pressure. Before entering the burner nose, it twists. The mixing of gas with air begins inside the burner when the gas exits the nozzle and is injected by a swirling air flow. With multi-jet gas supply, the process of mixture formation occurs faster and the gas burns in a short flame. With a single-jet tip, an elongated torch is created. The advantages of the burner are the simplicity and compactness of the design, the ability to work at low pressures of gas and air, wide limits of capacity regulation.

Multi-jet vortex burners are widely used, based on the principle of splitting gas and air flows into several small flows. Inside them, an injection mixing process takes place, their productivity is 40-940 m 3 / h.

Mixing burners are often combined. They allow you to quickly transfer the unit from one type of fuel to another. In addition, the gas in them can be compressed simultaneously with other types of fuel.

Displacement method.

It is used when storing LPG in underground storage facilities at a depth of 100 to 1200 m (in salt beds).

The selection of liquefied gas is carried out by displacing it with an inert liquid or gaseous medium. The most commonly used brine.

1-central brine column

2-brine pipeline

3-outer column for supplying LPG

4-pipeline liquefied gas

5-underground capacity

7-liquefied gas

Underground tank communicating with the surface 2-column system:

The casing pipe (3) and the central column freely suspended at the wellhead 1.

LPG is supplied and taken from the tank through the annulus.

The central column is lowered to the very bottom of the tank. Since the density of the brine is 2 times greater than the density of LPG, the latter is stored on a brine pad.

To empty the underground tank, it is enough to bring the brine to the mouth of the central column and, under its hydrostatic pressure (1.3 MPa at a depth of 100 m), the LPG will enter the distribution pipeline with excess pressure. It can be transported without the use of pumps.

LPG is pumped into the storage under pressure determined by the backpressure of the brine column and the pressure loss due to friction when the fluid moves through the annular space and the central column.

"+" method:

1. simplicity of design

2. the ability to release gas at 1 time even in the absence of an external energy source

3. reliable operation of all devices

4. energy costs only for the removal of brine when pumping liquefied gas into the storage

5. the need for pumping only high-performance pumps with high efficiency

"-" method:

1. the need for an external source of energy with sufficient power when draining

Liquefied hydrocarbon gases (LHG) are produced from associated petroleum gas. These are pure gases or special mixtures that can be used for home heating, as automotive fuel, and also for the production of petrochemical products.

NGL to HFC

Liquefied hydrocarbon gases are obtained from the wide fraction of light hydrocarbons (NGL), which, in turn, is separated from associated petroleum gas (APG).

Separation of NGL into its constituent components - individual hydrocarbons - takes place at gas fractionation units (GFU). The separation process is similar to the separation of APG. However, in this case, the separation should be more careful. From NGLs in the process of gas fractionation, various products can be obtained. It can be propane or butane, as well as a propane-butane mixture (it is called SPBT, or a technical propane-butane mixture). SPBT is the most common type of liquefied gases - it is in this form that this product is supplied to the population, industrial enterprises and exported. Thus, out of 2.034 million tons of LPG sold by Gazprom Gazenergoset in 2012, propane-butane mixture accounted for 41%, butane - a third of deliveries, propane - about 15%.

Also, by separating NGL, technical butane and technical propane, automobile propane (PA) or a mixture of PBA (propane-butane automobile) are obtained.

There are other components that are isolated by processing NGLs. These are isobutane and isobutylene, pentane, isopentane.

How are liquefied petroleum gases used?

Liquefied hydrocarbon gases can be used in a variety of ways. Probably, everyone is familiar with bright red propane cylinders since Soviet times. They are used for cooking on household stoves or for heating in country houses.

Also, liquefied gas can be used in lighters - either propane or butane is usually pumped there.

Liquefied hydrocarbon gases are also used for heating industrial enterprises and residential buildings in those regions where natural gas has not yet reached through pipelines. LPG in these cases is stored in gas holders - special containers, which can be both ground and underground.

In terms of efficiency, propane-butane ranks second after the main natural gas. At the same time, the use of LPG is more environmentally friendly compared to, for example, diesel fuel or fuel oil.

Gas in motors and packages

Propane, butane and their mixtures, along with natural gas (methane), are used as an alternative fuel for refueling cars.
The use of gas motor fuel is currently very relevant, because every year the domestic vehicle fleet, consisting of more than 34 million vehicles, emits 14 million tons of harmful substances together with exhaust gases. And this is 40% of the total industrial emissions into the atmosphere. Exhaust gases from gas-powered engines are several times less harmful.

The exhaust of gas engines contains 2–3 times less carbon monoxide (CO) and 1.2 times less nitrogen oxide. At the same time, compared to gasoline, the cost of LPG is approximately 30–50% lower.

The gas motor fuel market is actively developing. Currently, there are more than 3,000 gas stations and more than 1 million LPG vehicles in our country.

Finally, liquefied hydrocarbon gases are the raw material for the petrochemical industry. For the production of LPG products, they undergo a complex process that takes place at very high temperatures - pyrolysis. The result is olefins - ethylene and propylene, which are then, as a result of the polymerization process, converted into polymers or plastics - polyethylene, polypropylene and other types of products. That is, plastic bags used by us in daily life, disposable tableware, containers and packaging of many products are made from liquefied gases.

Claims about the excellent performance of fuel mixtures are usually too general and uninformative. We make up for the lack of information - this article provides actual data on liquefied hydrocarbon gases (LHG). They will be useful to everyone who already uses such fuel or is just planning autonomous gasification of their home (commercial facility).

What is LPG and what is their main feature?

The name "liquefied hydrocarbon gases" refers to mixtures of low molecular weight hydrocarbons - propane and butane. Their main difference is the easy transition from the gaseous phase to the liquid and vice versa:

• Under conditions of normal atmospheric pressure and at normal ambient temperature, the components of the mixture are gases.
• With a slight increase in pressure (without a decrease in temperature), LPG hydrocarbons turn into liquids. At the same time, their volume decreases sharply.

Such properties make it easy to transport and store LPG. After all, it is enough to pump the mixture into a closed container under pressure so that it becomes liquid and receives a small volume. And before operation, LPG evaporates, and then it can be used in the same way as ordinary natural gas. At the same time, a mixture of butane and propane has a higher efficiency. The specific heat of combustion of liquefied gas is approximately 25% higher than that of natural gas.

LPG is produced at gas processing plants from associated petroleum gas or natural gas condensate fraction. During processing, raw materials are separated into light and heavy fractions - ethane, methane, natural gasoline, etc. Two of them - propane and butane - are further processed into liquefied gas. They are cleaned of impurities, mixed in the right ratio, liquefied and transported to storage or to the consumer.

Properties of LPG components - propane and butane

Both gases are low molecular weight saturated hydrocarbons:

• Propane (C 3 H 8). A linear molecule contains three carbon atoms and eight hydrogen atoms. The gas is ideal for use in Russian climatic conditions - its boiling point is -42.1 °C. At the same time, up to -35 ° C, propane retains high vapor pressure. That is, it evaporates well in a natural way and is transported through the outdoor pipeline even in the most severe winter. Pure liquefied propane can be used in above-ground gas tanks and cylinders - there will be no failures in the flow of gas during frosts.
• Butane (C 4 H 10). Consists of four carbon atoms and ten hydrogen atoms. The molecule can be linear or branched. Butane has a higher heating value than propane and is cheaper. But he has a serious drawback. The boiling point of butane is only -0.5 °C. This means that at the slightest frost it will remain in a liquid state. The natural evaporation of butane at a temperature below -0.5 ° C stops, and additional heating has to be used to obtain gas.

From the above information, we obtain an important conclusion: the temperature of the liquefied propane-butane mixture in a gas tank or cylinder must always be positive. Otherwise, butane will not evaporate and there will be problems with gas supply. To achieve the desired temperature, gas holders are installed underground (here they are heated by geothermal heat). Another option is to equip the tank with electric heating (evaporator). Filled cylinders are always kept indoors.

What determines the quality of LPG?

So, liquefied gas supplied for autonomous gasification systems is always a mixture. In official documents, it passes as SPBT - a mixture of propane and technical butane. In addition to these two gases, LPG always contains a small amount of impurities - water, alkalis, unsaturated hydrocarbons, etc. The quality of the mixture depends on the ratio of propane and butane in it, as well as on the amount and type of impurities:

1. The more propane in SPBT, the better it will evaporate in the cold season. True, liquefied gases with a high concentration of the propane component are more expensive, so they are usually used only as a winter fuel. In any case, in the conditions of the Russian climate, it is impossible to use a mixture with a butane content of more than 60%. It will only evaporate if there is an evaporator.
2. The more impurities in LPG, the worse for gas equipment. Unsaturated hydrocarbons do not burn out completely, but polymerize and coke. Their residues contaminate the equipment and drastically reduce its service life. Heavy fractions - water and alkalis - also do not benefit technology. Many substances remain in the tank and pipelines as non-evaporable condensate, which reduces the efficiency of the system. In addition, impurities do not produce as much heat as propane and butane, so their increased concentration reduces fuel efficiency.

Useful facts about liquefied gases

• The propane-butane mixture mixes perfectly with air, burns evenly and burns out completely, leaving no soot and deposits on the equipment elements.
• LPG in the gaseous state is heavier than air: propane - 1.5 times, butane - 2 times. When leaking, the mixture sinks down. Therefore, liquefied gas tanks cannot be installed above basements and wells. But the underground gas holder is absolutely safe - even if it is damaged, the gas mixture will go into the lower layers of the soil. There it will not be able to mix with the air and explode or catch fire.
• The liquid phase of LPG has a very high coefficient of thermal expansion (0.003 for propane and 0.002 for butane for each degree of temperature increase). This is about 16 times higher than that of water. Therefore, gas tanks cannot be filled more than 85%. Otherwise, when the temperature rises, the liquid mixture may expand greatly and, at best, occupy the entire volume of the tank. Then there will simply be no room for evaporation and gas will not enter the system. In the worst cases, excessive expansion of the liquid mixture leads to rupture of gas tanks, large leaks and the formation of explosive and flammable mixtures with air.
• When 1 liter of the liquid phase of LPG evaporates, 250 liters of gas are formed. Therefore, tanks with a liquefied mixture installed indoors are so dangerous. Even with a slight leakage of the liquid phase, it instantly evaporates, and the room is filled with a huge amount of gas. The gas-air mixture in this case quickly reaches an explosive ratio.
• Evaporation of the liquid phase in air is very fast. Liquefied gas spilled on human skin causes frostbite.
• Pure propane and butane are odorless gases. Strongly smelling substances - odorants - are specially added to them. As a rule, these are sulfur compounds, most often ethyl mercaptan. They have a very strong and unpleasant smell, which "informs" a person about a gas leak.
• The mixture has a high calorific value. So, when burning 1 cu. m of gaseous propane is used 24 cubic meters. m of air, butane - 31 cubic meters. m of air. As a result of combustion of 1 kg of the mixture, an average of 11.5 kWh of energy is released.

The heat supply system provides residential, administrative, industrial buildings and premises with hot water, gas, heat and electricity. As part of such a system, a complex of gas-using equipment is involved, for the operation of which a sufficient amount of fuel is required.

At the moment, liquefied hydrocarbon gas (LHG) and liquefied natural gas (LNG) are widely used as a stored fuel for autonomous gas supply systems that are not connected to the main gas supply line. In English labeling LPG (liquefied petroleum gas) and LNG (liquefied natural gas), respectively.

LNG- This is a mixture of gases formed in the deep layers of the Earth during the anaerobic decomposition of organic compounds. Production is from reservoirs and from oil fields where gas can be a by-product of oil. In some cases, gas hydrates, a crystalline form of natural gas, may come across.

LPG- this is also a mixture of gases, but obtained from associated petroleum gas or from the condensate fraction of natural gas due to separation using an absorption gas fractionation unit.

LPG and LNG can be interchanged. Liquefied hydrocarbon gas can act as the main type of fuel, as well as a reserve in the gas supply system on liquefied natural gas.

Both gases are similar to each other in several ways:

• scope of application: heat and gas supply;
• ability to evaporate: gas is stored and transported in a liquid phase, which, subject to a certain temperature, is converted into a gaseous state;
• environmental friendliness: during combustion, sulfur compounds are not released into the atmosphere, there is no soot and ash;
• little toxicity.

In its pure form, both gases do not have a pronounced odor, therefore, for the timely detection of a substance in the air, odorants are mixed into the gas - ethanethiol, a mixture of natural mercaptans, etc.

Differences between liquefied gases LPG and LNG

Having a similar structure, parameters and physical and chemical properties, both gases differ from each other, which makes it possible to select the optimal fuel for the technological line of the facility's gas supply systems.

Index	Liquefied petroleum gas LPG	Liquefied natural gas LNG
Compound	Basic substances: propane and butane, the content is not less than 95% Additional substances: pentane, methane, ethane, ethylene, propylene, butylene	Main substance: methane, content 85-95% Additional substances: ethane, propane, butane, nitrogen, hydrogen sulfide, mercaptan sulfur
Storage method	or gas tanks	cryo-tanks in which a reduced temperature is maintained
To generate 1 Gcal, it is necessary to burn normal fuel	99.84 kg*	104.48 kg*
Critical temperature above which gas liquefaction is impossible	96.84°C (propane)	-82.5°C (methane)
Gas phase density at 0°C	0.7168 kg / m 3	2.0037 kg / m 3
Density of the liquid phase at 0°C	416 kg/m3	528 kg/m3
Specific heat of combustion	45.58 MJ/kg	43.56 MJ/kg
Gas concentration required for ignition	propane vapor concentration from 2.3 to 9.5%, normal butane from 1.8 to 9.1% (by volume)	4.4% to 17% (V/V)
* The value is given conditionally, because. the accuracy of the calculation directly depends on the composition of the gas used at the facility

Based on the data in the table above, the key and most important difference is storage temperature. LPG is stored in gas tanks under pressure at a temperature close to the ambient temperature. Insufficient evaporation of the liquid phase can be observed in the Far North, where the air temperature can be below -60°C. To improve the regasification process in such regions, a liquid or electric type is installed.

LNG storage conditions are fundamentally different. Liquefied natural gas may only be stored in fully sealed isothermal tanks (cryotanks) made of materials resistant to product storage temperatures. Inside the container, a low temperature of about -163 ° C should be constantly maintained.

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 owners 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. Colorless, 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 NGL 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 tank, a pump, a gas separator, a meter, a differential valve, a shut-off or control valve, and safety devices against excess pressure or flow rate.

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.