Liquefaction of gases and the use of liquid gases in technology. What is Liquefied Natural Gas (LNG)

GAS. gaseous state called a state of matter in which the forces acting between the molecules are extremely small and the dimensions of the molecules themselves are negligible compared with the gaps between them. Between collisions, gas molecules move in a straight line, evenly and completely randomly. When heated and rarefied, all gases tend to the limiting state of the so-called ideal, or perfect gas.

IN ideal gas the intermolecular forces are zero, and the volume of the molecules themselves is infinitesimal compared to the volume of the intermolecular space. The state of an ideal gas is that limiting diluted state of matter to which all bodies of nature tend at sufficiently high temperatures and sufficiently low pressures; this is the special significance of the state of an ideal gas, which, moreover, is the most easily amenable to research and therefore the most fully studied. A substance that fills in extreme rarefaction interplanetary space, can be considered to be in an ideal gas state.

Gas pressure (p) is determined by the impact of gas molecules on the walls of the vessel. According to the kinetic theory, the average kinetic energy of gas molecules is proportional to the absolute temperature. In the kinetic theory, it is shown that an ideal gas strictly obeys the following equation of state, which relates three state parameters: v, T and p, of which two are independent, and the third is their function:

This equation ( Clapeyron's equation) contains in explicit form three basic laws of the state of an ideal gas:

1) Boyle-Mariotte law. At constant temperature(T) the product (p ∙ v) for a given amount of ideal gas is a constant value (p ∙ v \u003d Const), i.e. the volume of an ideal gas (v) is inversely proportional to its pressure (p): ideal gas isotherms in the coordinate system ( v, p) are isosceles hyperbolas whose asymptotes are the coordinate axes.

2). At a constant (p), the volume of a given amount of ideal gas increases linearly with temperature:

(v 0 - volume at temperature \u003d 0 ° C, α - expansion coefficient of an ideal gas). Change (p) with temperature at v = Const obeys the same law:

(α) in equation (3) - pressure coefficient, numerically equal to the expansion coefficient (α) in equation (2) = 1/273.1 = 0.00367 - a value independent of the nature of the gas and the same for all ideal gases; p 0 - pressure at temperature \u003d 0 ° C. Introducing absolute temperature instead of temperature

we find instead of equations (2) and (3):

3) Avogadro's law. Equation (1) shows that gas constant R \u003d p 0 ∙ v 0 /273.1 is proportional to the normal volume v 0 occupied by a given amount of gas at normal conditions(p 0 \u003d 1 Atm and t 0 \u003d 0 ° C \u003d 273.1 ° K), that is, it is inversely proportional to the gas density under normal conditions D 0. According to Avogadro's law, with the same (p) and (T), all ideal gases contain in equal volumes (for example, equal to v 0) equal number molecules. Vice versa: an equal number of molecules (for example, 1 mol \u003d 1 gram molecule) of any gas in an ideal state occupies the same volume v 0 under normal conditions, regardless of the nature of the gas (1 mole of any substance contains N 0 = 6.06∙10 23 individual molecules - Avogadro's number). Found with great accuracy that normal molar volume any ideal gas (V 0) m is equal to 22.412 liters / mol. From here you can calculate the number of molecules in 1 cm 3 of any ideal gas under normal conditions: n0 \u003d 6.06 ∙ 10 23 / 10 3 ∙ 22.416 \u003d 2.705 ∙ 10 19 cm 3 (Loshmit number). Using equation (1), Avogadro's law is expressed in the fact that the gas constant R when calculated for 1 mole of any gas will be the same, regardless of the nature of the gas. That. R is a universal constant with dimension [ Job]/[weight][temperature] and expresses the work of expansion of 1 mole of an ideal gas when it is heated by 1 ° C at p \u003d Const:

this is the physical meaning of R.

find a numeric value

In other units, the R values ​​(per 1 mole) are:

In addition to the analyzed three laws, from the equation (1) of the state of an ideal gas in conjunction with the two laws of thermodynamics, the following basic laws also follow:

4) Joule's law. One of the general equations of thermodynamics

gives, together with equation (1), the following conditions for the internal energy U of an ideal gas:

i.e., U of an ideal gas is a function of only T (Joule's law); during isothermal expansion of an ideal gas, all absorbed heat is converted into external work, and during isothermal compression, all expended work is converted into heat released.

5) The heat capacities of an ideal gas at constant volume c v and at constant pressure c p are functions of T alone. Thermodynamics gives the general equations

but for an ideal gas (p) and (v) are linearly dependent on (T), according to the Gay-Lussac law (4) and (5); therefore, the right parts of equations (9) turn to 0 and

The heat capacities c p and c v are not independent of each other, but are related for an ideal gas by a simple condition:

arising from gas laws (R has the dimension of heat capacity), i.e., if c p and c v are related to 1 mole of an ideal gas, then they differ from each other by 2 (more precisely, by 1.986) - cal / mol ∙ deg.

In the kinetic theory, it is accepted, according to the principle of uniform distribution of energy, that for each degree of freedom of a gas molecule there is an energy k 0 ∙T / 2, and for 1 mole there is

(k 0 \u003d -R / N 0 is the gas constant calculated for 1 molecule - Boltzmann's constant). The number of degrees of freedom (i) is the number of types of mechanical energy that are independent of each other, which a gas molecule has. Then the energy of 1 mole

(approximately, assuming R = 2, c v = i, c p = i + 2).

In the study of gas important role plays the ratio c p /c v = γ; from equations (11) and (12):

In the simplest case monatomic gas(whose molecule consists of 1 atom, what are the noble gases and vapors of many metals) i is the smallest and equals 3: the entire energy of the molecule is reduced to its kinetic energy translational movements, which can be performed in three independent mutually perpendicular directions; Then

and γ has the largest possible value: γ = 5/3 = 1.667. For diatomic gases(H 2 , O 2 , N 2 , CO and others) can be considered I \u003d 3 + 2 (two rotations around two mutually perpendicular axes perpendicular to the line connecting both atoms); then cv = 4.96 ≈ 5, cр = 6.95 ≈ 7 and γ = 7/5 = 1.40. For triatomic gas(Н 2 O, СO 2, H 2 S, N 2 O) i = 3+3 (rotation around three mutually perpendicular axes) and c v = 5.96 ≈ 6, cр = 7.95 ≈ 7 and γ = 4/ 3 = 1.33.

With further complication of the structure of the molecule, i.e., with an increase in i, c v and c p increase, and γ = 1 + 2/i and tends to 1. Table. 1 shows that everything said is in good agreement with the experimental data, that γ is always >1 and ≤1.667 and cannot be = 1.50 (for i = 4).

For monatomic gases, c v and c p, in accordance with the theory, practically do not change with temperature (for example, for Ar, the values ​​of c v and c p lie in the range from 2.98 to 3.00 between temperatures = 0 ° and 1000 ° C). Changes in c v and c p with temperature are explained in quantum theory. However, the heat capacities of gases that are close to ideal do not practically change over wide temperature ranges. Usually p and y are experimentally determined, and c v is calculated from these data.

real gases. All gases that actually exist are real gases b. or m. deviate from the laws of ideal gases, but the less, the higher the temperature and the lower the pressure. That. the laws of ideal gases are limiting for real gases. At ordinary temperatures, the deviation is least for gases whose critical temperatures are extremely low (the so-called constant gases: He, H 2 , N 2 , O 2 , air); for gases with a relatively high critical temperature and for vapors (a gas at a temperature below the critical temperature is called steam), the deviations are very significant. The reasons for deviations of real gases from gas laws are that: 1) intermolecular forces act in them; therefore, surface molecules are drawn into gases by forces, the resultant of which, calculated per unit surface and directed perpendicular to it, is called molecular (internal) pressure K; 2) not the entire volume of gas (v), but only part of it (v-b) gives freedom for the movements of molecules; part of the volume (b), covolum, as if occupied by the molecules themselves. If the gas were ideal, its pressure would be greater than the observed (p) by the value of K; therefore, the equation of state for a real gas will be written in the form

In this general equation, K and b may depend on T and v.

Van der Waals showed that in the simplest case, K \u003d a / v 2, and b is a constant value equal to four times the volume of the gas molecules themselves. Thus, the van der Waals equation has the form:

a and b, the van der Waals constants, as experience shows, still depend on T and v, and therefore equation (15) is only a first approximation; it reproduces well the qualitative shape of the isotherms of real gases.

In FIG. 1 are shown for CO 2 theoretical isotherms: S-shaped parts of these isotherms correspond to thermodynamically metastable states.

In FIG. Figure 2 shows the experimental isotherms for CO 2 : the S-shaped parts of the curves are replaced by straight parts; to the right of these parts, the curves correspond to gas (unsaturated vapor), to the left - to liquids, and the straight segments themselves - to the equilibrium of vapor and liquid. Equation (15), in full agreement with experience, shows that with increasing temperature, the dimensions of the straight segments on the isotherms become smaller and smaller (Fig. 2) and, finally, at a certain temperature equal to the critical temperature, the length of this segment becomes 0. At a temperature greater than At a critical temperature, a gas cannot turn into a liquid at any pressure: the liquid ceases to exist. That. the van der Waals equation covers two states - gaseous and liquid - and serves as the basis for the doctrine of the continuity of the transition between these two states. Critical temperatures for some gases have the following values: +360°C for H 2 O, +31°C for CO 2, -241°C for H 2 and -254°C for He.

Gas liquefaction. Any gas can be turned into a liquid at the proper pressure, having previously cooled it below the critical temperature. The pressures required to liquefy CO 2 (in Atm) at different temperatures are given in table. 2.

It is clear that these pressures are pressures saturated steam liquid carbon dioxide and the lower, the lower the temperature.

In order to pre-cool the gas for liquefaction, in technical installations they use the Joule-Thomson effect, which consists in the fact that during adiabatic expansion (for example, with a sharp drop in pressure when the gas flows out of the hole), the internal energy of the gas increases by ΔU, and T changes by ΔT, and thermodynamically

In the case of ideal gases, ΔU = 0 and ΔT = 0 [because, according to equation (1), T∙dv/dT – v = 0].

For real gases, ΔТ ≠ 0, i.e. cooling or heating occurs, depending on whether T∙dv/dT – v ≠ 0 (Δp< 0). По уравнению Ван-дер-Ваальса,

(with sufficient approximation). That. at sufficiently high temperatures, all gases heat up during adiabatic expansion (ΔТ > 0, because a/R∙T< b), но с понижением температуры для каждого газа наступает inversion pointТ i determined by the condition

below which gases begin to cool during adiabatic expansion (a/R∙T> b at T< Т i). Для всех газов, кроме Н 2 и Не, Т i лежит выше обычных температур (так, для воздуха Т i соответствует +360°С), и потому газы могут быть сжижены по принципу Линде , без предварительного охлаждения. Для Н 2 инверсионная точка Т i - 80,5°С, а для Не - даже 15°К; поэтому Н 2 и Не для сжижения д. б. предварительно охлаждены ниже этих температур.

Relevant states. Critical temperature T to, pressure p to and volume v to m. b. expressed in terms of the van der Waals constants a, b and R as follows:

If we take critical values ​​for the units of measurement T, p and v, respectively, then instead of T, p and v, the state will be characterized by given values:

If we introduce θ, π, and ϕ into the van der Waals equation (15), then the constants a, b, and R cancel out, and we get reduced equation of state, with numerical coefficients

which does not contain quantities that depend on the nature of the substance. Equation (19) assumes, however, that the van der Waals equation is correct, and therefore deviations from it are often quite significant, especially in the case of associated substances. The doctrine of the corresponding states (the so-called states corresponding to the same θ, π and ϕ) makes it possible to find big number universal dependencies similar to equation (19).

Application of gases. Compressed and liquefied gases are used in technology wherever large quantities of gas are needed in a small volume; so, CO 2 is used for carbonation of waters, Cl 2 and phosgene - in the military chemical business, O 2 - for medical purposes, compressed air - for starting internal combustion engines. Liquefied gases (CO 2 and NH 3) are of particular importance in refrigeration, in refrigeration machines (for example, to obtain artificial ice). Light gases (H 2, lighting gas, in Lately Not) are used to fill balloons. Inert gases (N 2 and noble gases, especially Ar) are used to fill half-watt incandescent lamps. Of particular note is the use of gas for lighting or as a fuel: lighting, power, water gases and others.


Introduction

Gases-state of aggregation of a substance in which its particles are not bound or very weakly bound by interaction forces and move freely, filling the entire volume provided to them. Gases have a number of characteristic properties. Unlike solids and liquids, the volume of a gas depends significantly on pressure and temperature.

Any gas can be turned into a liquid by simple compression if the gas temperature is below the critical one. Those substances that we are used to considering as gases simply have very low critical temperatures, that is, temperatures after which the gas acquires the properties of a liquid, and therefore at a temperature close to to room temperature, they cannot be in a liquid state. On the contrary, for substances that we classify as liquids, the critical temperatures are high.

I was interested in the question of what properties does liquefied gas have, in what areas is it used? The topic of the work is relevant today, since liquefied gases are in demand in many areas of medicine, science and technology. In this regard, I have set myself the following goals and objectives:

Target:-consideration of the nature of the phenomenon and the properties of liquefied gases

Tasks:

* Learn about liquefied gases

* Determine the properties of liquefied gases

ñ Story

The experimental fact of cooling a substance during evaporation has been known for a long time and has even been used in practice (for example, the use of porous vessels to preserve the freshness of water). But the first scientific study of this issue was undertaken by Gian Francesco Cigna and described in the work of 1760 "De frigore ex evaporation" ("On the cold due to evaporation").

The problem of gas liquefaction has a centuries-old history dating back to the second half of the 18th century. It all started with the liquefaction of ammonia by simple cooling, which was produced by van Marum, sulfuric anhydride by Monge and Clouet, chlorine by Northmore (1805) and the liquefaction of ammonia by the compression method proposed by Baccelli (1812).

Charles Cagnard de Latour (1777-1859) and Michael Faraday (1791-1867) simultaneously and independently made decisive contributions to the solution of this problem.

What is liquefied gas and its properties

Liquefaction of gases is the conversion of gases into a liquid state. It can be produced by compressing the gas (increasing pressure) and simultaneously cooling it.

Any gas can be converted into a liquid state, but a prerequisite for this is the preliminary cooling of the gas to a temperature below the "critical" one. Carbon dioxide, for example, can be liquefied at room temperature, since its critical temperature is 31.1 0 C. The same can be said about gases such as ammonia and chlorine.

But there are also gases that cannot be converted to a liquid state at room temperature. These gases include air, hydrogen, and helium, whose critical temperatures are well below room temperature. To liquefy such gases, they must first be cooled to a temperature slightly below the critical temperature, after which the gas can be transferred to a liquid state by increasing the pressure.

Use of liquefied gases

Liquefied gases are widely used in engineering. Nitrogen is used to produce ammonia and nitrogen salts used in agriculture to fertilize the soil. Argon, neon and other inert gases are used to fill electric incandescent lamps, as well as gas lamps. Oxygen is the most widely used. In a mixture with acetylene or hydrogen, it gives a flame very high temperature used for cutting and welding metals. Injection of oxygen (oxygen blast) accelerates metallurgical processes. Oxygen delivered from pharmacies in pillows acts as an anesthetic. Especially important is the use of liquid oxygen as an oxidizing agent for space rocket engines.

Liquid hydrogen is used as fuel in space rockets. For example, 90 tons of liquid hydrogen are required to refuel the American Saturn V rocket.

Liquid ammonia has found wide application in refrigerators - huge warehouses where perishable products are stored. The cooling that occurs during the evaporation of liquefied gases is used in refrigerators when transporting perishable products.

Gases used in industry, medicine, etc., are easier to transport when they are in a liquefied state, since in this case a larger amount of substance is contained in the same volume.

Faraday tube

English physicist - experimenter, chemist .

Discovered electromagnetic induction, which underlies the modern industrial production of electricity and many of its applications. Created the first modelelectric motor. Among his other discoveries is the first transformer , the chemical action of the current,laws of electrolysis, action magnetic field into the world. He was the first to predict electromagnetic waves. Faraday introduced the terms ion into scientific use, cathode, anode, electrolyte , dielectric, diamagnetism, paramagnetism, etc.

Faraday is the founder of the theory of the electromagnetic field, which he then mathematically formalized and developedMaxwell.

At that time, Faraday was only a modest laboratory assistant for Humphry Davy.

Humphry Davy - English chemist, physicist and geologist, one of the founders electrochemistry . Known for the discovery of many chemical elements, as well as patronage of Faraday at the initial stage of his scientific activity.

On his behalf, he studied hydrochloride, a crystalline compound formed by the interaction at low temperatures of water and chlorine. To test how this compound behaves when heated, Faraday placed several crystals of chlorine hydrate in a closed leg of a curved V -shaped tube, after which the other knee was soldered. Next, he heated the crystals, while the free knee remained cold. The crystals melted and gave off greenish-yellow fumes, the fumes condensed in the cold knee to form an oily liquid, which turned out to be liquid chlorine.

1) bent and sealed tube

2) a substance or mixture that, when heated, releases the required gas

3) cooled elbow where liquefied gas is collected

4) water or coolant

Faraday discovered a new method for liquefying gases: it was not necessary to receive gases in one vessel and pump them into another vessel, where liquefaction would take place. It is convenient to transfer gases to a liquid state in the same vessel where they are formed. In this way, during 1823, Faraday managed to convert hydrogen sulfide, sulfur dioxide, carbon dioxide, and nitrous oxide into a liquid state.

conclusions
Any gas can be turned into a liquid by simple compression.
Liquefaction of gases is a complex process that involves many compressions.
Liquefaction can be done by compressing a gas and simultaneously cooling it.
Liquefied gases are widely used
Liquefied gases are used not only in engineering, medicine and agriculture, but also in science.

Bibliography

h ttp://en.wikipedia.org/wiki/Liquefaction_gases

The transformation of any gas into a liquid - the liquefaction of a gas - is possible only at a temperature below the critical one (see § 62). In early attempts to liquefy gases, it turned out that some gases (C1 2, CO 2, NH 3) were easily liquefied by isothermal compression, and a number of gases (O 2 , N2, hz, He) were not amenable to liquefaction. Such unsuccessful attempts were explained by D. I. Mendeleev, who showed that the liquefaction of these gases was carried out at a temperature higher than the critical one, and therefore was doomed to failure in advance. Subsequently, it was possible to obtain liquid oxygen, nitrogen and hydrogen (their critical temperatures are 154.4, 126.1 and 33 K, respectively), and in 1908 the Dutch physicist G. Kamerling-Onnes (1853-1926) achieved the liquefaction of helium, which has the most low critical temperature (5.3 K).

For the liquefaction of gases, two industrial methods are more often used, which are based on either the Joule-Thomson effect or cooling the gas while doing work.

A diagram of one of the installations that uses the Joule-Thomson effect, the Linde machine*, is shown in fig. 95. The air in the compressor (K) is compressed to a pressure of tens of megapascals and cooled in the refrigerator (X) to a temperature below the inversion temperature, as a result of which, with further expansion of the gas, a positive Joule-Thomson effect is observed (cooling of the gas during its expansion). Then the compressed air passes through the inner tube of the heat exchanger (TO) and is passed through the throttle (Dr), while it greatly expands and cools. The expanded air is again sucked in through the outer tube of the heat exchanger, cooling the second portion of the compressed air flowing through the inner tube. Since each subsequent portion of air is pre-cooled and then passed through the throttle, the temperature drops more and more. As a result of a 6-8-hour cycle, part of the air (> 5%), cooling to a temperature below the critical one, liquefies and enters the Dewar vessel (DS) (see § 49), and the rest of it returns to the heat exchanger.

The second method of liquefying gases is based on cooling the gas while doing work. Compressed gas, entering the piston machine (expander), expands and does the work of moving the piston. Since the work is done due to the internal energy of the gas, its temperature decreases.

Academician P. L. Kapitsa suggested using a turbo-expander instead of an expander, in which the gas, compressed to only 500-600 kPa, is cooled, doing the work of rotating the turbine. This method was successfully applied by Kapitsa to liquefy helium, which was pre-cooled liquid nitrogen. Modern powerful refrigeration units operate on the principle of a turboexpander.

For more than 30 years in the USSR, then in Russia, liquefied and compressed gases have been used in national economy. During this time passed enough hard way on the organization of accounting for liquefied gases, the development of technologies for their pumping, measurement, storage, transportation.

From incineration to recognition

Historically, the potential of gas as an energy source has been underestimated in our country. Seeing no economically justified areas of application, oil producers tried to get rid of light fractions of hydrocarbons, burned them to no avail. In 1946, the separation of the gas industry into an independent industry revolutionized the situation. The volume of production of this type of hydrocarbons has increased sharply, as well as the ratio in the fuel balance of Russia.

When scientists and engineers learned how to liquefy gases, it became possible to build gas-liquefying enterprises and deliver blue fuel to remote areas that are not equipped with a gas pipeline, and use it in every home, as a car fuel, in production, and also export it for hard currency.

What are liquefied hydrocarbon gases

They are divided into two groups:

  1. Liquefied hydrocarbon gases (LHG) are a mixture of chemical compounds consisting mainly of hydrogen and carbon with different molecular structures, that is, a mixture of hydrocarbons of various molecular weights and structures.
  2. Broad fractions of light hydrocarbons (NGL) - includes for the most part mixtures of light hydrocarbons of hexane (C6) and ethane (C2) fractions. Their typical composition: ethane 2-5%, liquefied gas fractions C4-C5 40-85%, hexane fraction C6 15-30%, the pentane fraction accounts for the remainder.

Liquefied gas: propane, butane

In the gas industry, it is LPG that is used on an industrial scale. Their main components are propane and butane. They also contain lighter hydrocarbons (methane and ethane) and heavier ones (pentane) as impurities. 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).

Liquefaction technologies

They learned to liquefy gases at the beginning of the 20th century: in 1913, for the liquefaction of helium, Nobel Prize Dutchman K. O. Heike. Some gases are brought to a liquid state by simple cooling without additional conditions. However, most hydrocarbon "industrial" gases (carbon dioxide, ethane, ammonia, butane, propane) are liquefied under pressure.

The production of liquefied gas is carried out at gas liquefaction plants located either near hydrocarbon deposits or on the way of main gas pipelines near large transport hubs. Liquefied (or compressed) natural gas can be easily delivered by road, rail or water transport to the final consumer, where it can be stored, then again converted to a gaseous state and fed into the gas supply network.

Special equipment

Used to liquefy gases special installations. They significantly reduce the amount of blue fuel and increase the energy density. With their help, it is possible to various ways processing of hydrocarbons, depending on the subsequent application, properties of the feedstock and conditions environment.

Liquefaction and compression plants are designed for gas treatment and have a block (modular) design or are fully containerized. Thanks to regasification stations, it becomes possible to provide cheap natural fuel even to the most remote regions. The regasification system also makes it possible to store natural gas and supply it in the required amount depending on the need (for example, during periods of peak consumption).

Most of the various gases in a liquefied state find practical applications:

  • Liquid chlorine is used to disinfect and bleach fabrics, and is used as a chemical weapon.
  • Oxygen - in medical institutions for patients with breathing problems.
  • Nitrogen - in cryosurgery, for freezing organic tissues.
  • Hydrogen is like jet fuel. Recently, hydrogen-powered vehicles have appeared.
  • Argon - in industry for metal cutting and plasma welding.

You can also liquefy hydrocarbon-class gases, the most popular of which are propane and butane (n-butane, isobutane):

  • Propane (C3H8) is a substance of organic origin of the alkane class. It is obtained from natural gas and during the cracking of petroleum products. Colorless, odorless gas, slightly soluble in water. They are used as fuel, for the synthesis of polypropylene, the production of solvents, in Food Industry(additive E944).
  • Butane (C4H10), a class of alkanes. Colourless, odorless, combustible gas, easily liquefied. It is obtained from gas condensate, petroleum gas (up to 12%), during the cracking of petroleum products. Used as a fuel, in the chemical industry, in refrigerators as a refrigerant, in the food industry (additive E943).

Characteristics of LPG

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

The state of hydrocarbon systems is determined by the totality of the influences of various factors, therefore, for complete characteristics you need to know all the parameters. The main ones that can be directly measured and affect the flow regimes are: pressure, temperature, density, viscosity, concentration of components, phase ratio.

The system is in equilibrium if all parameters remain unchanged. In such a state, there are no visible qualitative and quantitative metamorphoses in the system. A change in at least one parameter violates the equilibrium state of the system, causing one or another process.

Properties

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

Instruction

Looks like liquefied natural gas(LNG) is a colorless and odorless liquid, 75-90% composed and possessing very important properties: in the liquid state, it is not combustible, nor is it aggressive, which is extremely important during transportation. The LNG liquefaction process has a character, where each new stage means compression by 5-12 times, followed by cooling and moving to the next stage. LNG becomes liquid upon completion of the last stage of compression.

If gas needs to be transported over very long distances, then it is much more profitable to use special vessels - gas carriers. From the place of gas to the nearest suitable place on sea ​​coast a pipeline is being laid, and a terminal is being built on the shore. There, the gas is highly compressed and cooled, turning it into a liquid state, and pumped into isothermal tanks of tankers (at temperatures of the order of -150 ° C).

This method of transportation has a number of advantages over pipeline transportation. Firstly, one of these in one flight can carry a huge amount of gas, because the density of a substance in a liquid state is much higher. Secondly, the main costs are not for transportation, but for loading and unloading the product. Thirdly, storage and transportation of liquefied gas is much safer than compressed gas. There can be no doubt that the share of natural gas transported in liquefied form will steadily increase compared to pipeline supplies.

Liquefied natural gas in demand in various fields of human activity - in industry, in road transport, in medicine, in agriculture, in science, etc. Liquefied gas We won due to the convenience of their use and transportation, as well as environmental friendliness and low cost.

Instruction

Before liquefying hydrocarbon gas and it must first be cleaned and removed water vapor. Carbonic gas removed using a three-stage molecular filter system. Purified in this way gas in small quantities it is used as a regeneration. Recoverable gas either incinerated or used to generate power in generators.

Drying occurs with the help of 3 molecular filters. One filter absorbs water vapor. Another dries gas, which goes further and passes through the third filter. To lower the temperature gas passed through a water cooler.

The nitrogen method involves the production of liquefied hydrocarbon gas and from any gas new sources. The advantages of this method include the simplicity of technology, the level of safety, flexibility, ease and low cost of operation. The limitations of this method are the need for a power source and high capital costs.

At mixed way production of liquefied gas and a mixture of nitrogen and is used as a refrigerant. receive gas also from any source. This method is distinguished by the flexibility of the production cycle and small variable costs for production. Compared to the nitrogen liquefaction process, capital costs are more significant here. A source of electricity is also needed.

Sources:

  • What is gas liquefaction?
  • Liquefied gas: receipt, storage and transportation
  • what is liquefied gas

Natural gas is extracted from the bowels of the Earth. This mineral consists of a mixture of gaseous hydrocarbons, which is formed as a result of the decomposition of organic matter in sedimentary rocks. earth's crust.

What are the ingredients in natural gas

80-98% natural gas consists of (CH4). It is the physicochemical properties of methane that determine the characteristics of natural gas. Along with methane, natural gas contains compounds of the same structural type - ethane (C2H6), propane (C3H8) and butane (C4H10). In some cases, in small quantities, from 0.5 to 1%, natural gas contains: (С5Н12), (С6Н14), heptane (С7Н16), (С8Н18) and nonane (С9Н20).

Natural gas also includes compounds of hydrogen sulfide (H2S), carbon dioxide (CO2), nitrogen (N2), helium (He), water vapor. The composition of natural gas depends on the characteristics of the fields where it is produced. Natural gas produced in pure gas fields consists mainly of methane.

Characteristics of natural gas constituents

All chemical compounds that make up natural gas have a number of properties that are useful in various industries and in everyday life.

Methane is a colorless, odorless, flammable gas that is lighter than air. It is used in industry and everyday life as a fuel. Ethane is a colorless, odorless, combustible gas that is slightly heavier than air. Basically, ethylene is obtained from. Propane is a poisonous, colorless and odorless gas. Butane is close to him in properties. Propane is used, for example, for welding work, in the processing of scrap metal. Liquefied and butane fill lighters and gas cylinders. Butane is used in refrigeration.

Pentane, hexane, heptane, octane and nonane -. Pentane is present in small amounts motor fuels. Hexane is also used in the extraction of vegetable oils. Heptane, hexane, octane and nonane are good organic solvents.

Hydrogen sulfide is a poisonous colorless heavy gas, rotten eggs. This gas, even in small concentrations, causes paralysis of the olfactory nerve. But due to the fact that hydrogen sulfide has good antiseptic properties, it is used in small doses in medicine for hydrogen sulfide baths.

Carbon dioxide is a non-flammable, colorless, odorless gas with a sour taste. Carbon dioxide is used in the food industry: in the production of carbonated drinks to saturate them with carbon dioxide, to freeze food, to cool cargo during transportation, etc.

Nitrogen is a harmless colorless gas, odorless and tasteless. It is used in the production of mineral fertilizers, used in medicine, etc.

Helium is one of the lightest gases. It is colorless and odorless, non-flammable, non-toxic. Helium is used in various industries - for cooling nuclear reactors, filling stratospheric balloons.

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