Physical and chemical properties of gases. Physical properties of natural gases

Any gas fuel is a mixture of various simple combustible and ballast gases. The chemical properties of the gas determine the properties of the mixture, i.e., the gaseous fuel.

Alkanes, i.e. hydrocarbons of the limiting series, are the main components of the combustible part of natural and associated gases. Alkanes are often called paraffins or hydrocarbons of the methane series. The general chemical formula of alkanes is СnН 2n+2. The ancestor of a number of alkanes is methane - CH 4, then, as the number of carbon atoms in the molecule increases, follow: ethane - C 2 H 6, propane - C 3 H 8, butane - C 4 H 10, pentane - C 5 H 12, hexane - C 6 H 14, etc.

Physical and Chemical properties gases of saturated hydrocarbons naturally change as their molecular weight increases.

Under normal conditions, i.e. at a temperature of 0 ° C and a pressure of 760 mm Hg. Art., the first members of the series up to and including butane are gases that do not have color and smell, the subsequent ones are liquids. All alkanes, except methane, have a density greater than that of air.

Under the influence high temperature alkanes are split, turning into simpler and more stable compounds (for example, methane, as well as alkenes), releasing black carbon and hydrogen. The resistance of alkanes to temperature decreases with increasing molecular weight.

Alkanes, like the products of their complete combustion, are not toxic. There is evidence that high-molecular saturated hydrocarbons at high concentrations in the air have a weak narcotic effect.

Alkenes, or olefins, are present in appreciable amounts in artificial gases, especially liquid fuel cracking gases. The ancestor of a number of alkenes is ethylene. The general chemical formula of alkenes is C n H2 n - The first three members of this series are ethylene (ethene) - C 2 H 4, propylene (propene) - C 3 H 6 and butylene (butene) - C 4 H 8.

Alkenes, which are unsaturated hydrocarbons, are valuable raw materials for the chemical industry.

The toxic effect of alkenes is similar to that of alkanes, that is, at high concentrations they have narcotic properties.

Hydrogen H 2 is present in all artificial gases. It is a combustible gas, odorless and colorless, non-toxic. Hydrogen is the lightest of the gases, it is 14.5 times lighter than air, so its lower volumetric heat of combustion is less than that of other gas fuel components.

Hydrogen sulfide H 2 S is found in most artificial and some natural gases. It is a colorless combustible gas heavier than air (density - 1.54 kg / m 3), with a strong odor reminiscent of the smell of rotten eggs. Causes severe corrosion of metals.

Hydrogen sulfide is poisonous. It acts on nervous system, as well as on Airways and eyes. At concentrations of hydrogen sulfide above 1 mg / l, fatal poisoning can occur almost instantly from paralysis of the respiratory centers. Its permissible concentration in indoor air is set to no more than 0.01 mg / l, and in the gas entering the city networks - no more than 2 g per 100 m 3. The high toxicity of hydrogen sulfide and strict requirements for its content make it necessary to purify gas fuel before supplying it to consumers.

Carbon monoxide CO is contained in large quantities in generator gases, being, along with hydrogen, the main combustible component.

Carbon monoxide is a chemically resistant, colorless, combustible gas. The density of CO (1.25 kg / m 3) is slightly lower than the density of air.

Carbon monoxide is a strong poison; its concentration in the air at 1% leads in 1-2 minutes to severe poisoning and death. The maximum concentration of CO in the air of the working area of ​​workshops, according to existing standards, is not more than 0.03 mg/l during long-term operation and not more than 0.05 mg/l when staying in a gassed atmosphere for up to 1 hour.

Carbon monoxide is a product of incomplete combustion of carbon and can be found in the combustion products of any fuel containing carbon or carbon compounds.

Carbon disulphide CS 2 is present in small amounts in gases obtained from the dry distillation of fuels containing sulfur. The boiling point of carbon disulfide is +46 ° C, i.e. under normal conditions it is a liquid. Vapors of carbon disulfide are 2.6 times heavier than air. High concentrations of carbon disulfide vapors in the air lead to poisoning. Maximum allowable concentration in working area 0.01 mg/l.

Hydrogen cyanide HCN - the strongest poison contained in small quantities in the gases of the dry distillation of fuel. Maximum content of HCN in gases used for urban gas supply, Pe above 0.05 mg/l, maximum allowable concentration in air industrial enterprises- 0.0003 mg/l.

In addition to the combustible gases and vapors listed above, artificial gases contain a certain amount of tar, ammonia, and naphthalene. These compounds, which are of great value to the chemical industry, are extracted from gaseous fuels in gas recovery or purification plants.

As ballast impurities in all gases, both natural and artificial, there are nitrogen N 2 , water vapor H 2 O and carbon dioxide CO 2 . Nitrogen and carbon dioxide are non-toxic and non-aggressive, i.e. they do not have corrosive properties. The presence of water vapor can lead to the formation of condensate, increased corrosion of pipelines and the formation of hydrate plugs during long-distance transportation of natural gas. To avoid this, natural and associated gases are dried before being fed into the main pipelines, which simultaneously removes carbon dioxide.

Gas fuels of non-petroleum origin

Gas fuels of petroleum origin

Classification of gas fuels

SUMMARY PLAN

LESSON SUMMARY #10

Discipline - Refueling Vehicle fuels and lubricants

MDK 03.02. Organization of transportation, reception, storage and distribution of petroleum products

Lesson topic. "Features of liquefied gases and their characteristics"

ñ liquefied petroleum gases

ñ compressed companion pairs

ñ compressed natural gas

ñ gas condensate fuel

ñ alcohols

ñ hydrogen

Gas fuels are divided into

ñ low-calorie,

ñ medium-calorie,

ñ high-calorie.

Low-calorie gas fuels include blast-furnace gas (10,000 kJ of heat are obtained from 1 m3).

Medium-calorific gas fuels include coke oven and lighting gases (out of 1 m3 of gas - 10,000 - 20,000 kJ of heat).

High-calorific gas fuels include natural gas (35,000 kJ), associated petroleum (45,000 kJ), liquefied (46,000 kJ), cracked (50,000 kJ).

natural gases have no color, smell or taste.

Heat of combustion- this is the amount of heat that is released during the complete combustion of 1 m3 of gas. It is measured in kcal/m3.

combustion temperature called Maximum temperature, which can be achieved with complete combustion of the gas, if the amount of air required for combustion exactly corresponds to the chemical formulas of combustion, and the initial temperature of the gas and air is equal to Combustion temperature of individual gases is 2000 - 2100ºС.

Ignition temperature - is the minimum initial temperature at which combustion begins. For natural gas, it is 645ºС.

explosive limits. The gas-air mixture in which the gas is:

up to 5% - does not burn;

from 5 to 15% - explodes;

more than 15% - burns when air is supplied.

Flame spread rate for natural gas - 0.67 m/s (methane CH4)

Combustible gases are odorless. To timely determine the presence of them in the air, quickly and accurately determine the places of leakage, the gas is odorized (give a smell). Ethyl mercoptan (C2H5SH) is used for odorization. The odorization rate is 16 g of odorant per 1000 m3 of gas. Odorization is carried out at gas distribution stations (GDS). If there is 1% natural gas in the air, its smell should be felt.

combustible gases, used as a motor fuel for cars, can be divided into three main types according to the conditions of the specifics of the content, which affects the possibility of using it in different classes of cars (cars, trucks, buses):

1. Liquefied petroleum gases (LPG);

2. Compressed (compressed) natural gases (CNG);

3. Liquefied natural gases (LNG);

4. Hydrogen fuel.

The main components of liquefied gases(modern fuel for engines) are C3H8 propane, C4H10 butane and mixtures thereof.

These hydrocarbons are obtained from gases, accompanying oil, when drilling wells and from gaseous fractions formed during various types of processing of petroleum products and coal.

Critical temperatures propane (97°C) and butane (126°C) well above normal temperatures environment, therefore, these hydrocarbons at low pressure (without cooling) pass into a liquid state. At 20 °C, propane liquefies at a pressure of 0.716 MPa, and butane at a pressure of 0.103 MPa, i.e. LPG installations for the production of liquefied natural gas are medium pressure installations.

Store liquefied gases in cylinders with a capacity of 250 liters (162 ... 225 liters of gas provide a vehicle cruising range of up to 500 km), designed for a working pressure of 1.6 MPa. In such conditions, even pure propane is in liquid form, which makes it possible to operate cars on liquefied petroleum gases (LPG) year-round (except in the southern regions in the summer, where the temperature is above 48.5 ° C).

Octane number propane 105, and normal butane and isobutane 94.

Octane number (OC) characterizes the anti-knock properties of the gas and serves as a criterion for establishing the permissible compression ratio of the engine. The OC of gas fuels is in the range of 70–110. The higher the OC of the gas, the less prone it is to detonation combustion and the higher the allowable compression ratio of the engine and, consequently, its efficiency.

Density of liquefied gases is 510 ... 580 kg / m3, i.e. they are almost two times lighter than water. Density (P, kg/m3) is a mass enclosed in a unit volume of gas in its liquid or gaseous phase under certain external conditions (temperature and pressure).

Viscosity of gases very small, which facilitates their transportation through pipelines. The volumetric expansion coefficient of LPG is very high, i.e. when the outside temperature rises, they expand significantly, therefore, when filling the tanks, it is necessary to leave free space (approximately 15% of the capacity). Under normal conditions, LPG is non-toxic and odorless.
LPG is half the price of gasoline and at the same time provides up to 10 ... 20% energy savings, i.e. for a car that consumes 15 liters of high-octane gasoline per 100 km, 13 liters of LPG is enough, and for a car with a consumption of 11 liters of gasoline per 100 km, 9.8 liters of LPG is enough.

GOST 27578 - 87"Liquefied hydrocarbon gases for road transport" establishes the following grades of LPG: PA - automobile propane for use in winter at temperatures from -20° to -30°C; PBA - automotive propane-butane for use at temperatures not lower than -20 °C.
These indicators are interconnected by the ratio:

Cetane Number (CT) characterizes the flammability of the gas: the lower it is, the worse the ignition of the gas occurs and, consequently, the starting properties of the engine on this gas deteriorate.

Octane and cetane numbers are linked by a linear relationship: the higher the octane, the lower the CG.

Gas flammability limits characterize the boundary values ​​of the gas content (as a percentage by volume) in the air, at which ignition of the combustible mixture is still possible. The flammability of a gas mixture is influenced by temperature, pressure and its turbulence (swirl of gas flows). over-poor and over-enriched gas mixtures do not ignite.

Knowledge of these limits is important both for organizing the work process and regulating the fuel supply in engines, and for determining the explosion and fire safety of concentrations and the appropriate arrangement of storage and Maintenance cars.

Critical temperature (Tcr) is the temperature at which the densities of the liquid and its saturated vapor become equal and the interface between them disappears.

Saturated vapor pressure (Rcr) at critical temperature is called critical pressure.

The first indicator is the chemical formula. Methane and liquefied petroleum gas, which includes ethane, propane, butane and pentane, do not have lead in their composition or in impurities, which makes the exhaust when they are burned more environmentally friendly than gasoline.

The molecular weight of gases is lower than that of gasoline, therefore, filling the cylinders with a combustible mixture, other things being equal, will be lower than that of gasoline. This is a minus, as it leads to a decrease in the power of the internal combustion engine.

Relative density of the gas phase in air- the value necessary to calculate the mechanisms of mixture formation of the working fluid (gas-air mixture) and does not directly characterize the advantages or disadvantages of gas fuel over gasoline, but indicates that in case of a leak, methane will go up, and LPG will accumulate below.

Liquid Density- characterizes the volume of the vessel for storing the liquid phase of the fuel. We see that for the same mass, gasoline needs less volume than gas. This is a minus.

critical temperature.Hydrocarbon gases having a critical temperature well above normal ambient temperatures (e.g. 96.8°C for propane and 152.0°C for butane) are readily liquefied and stored in a liquefied state at relatively low pressure. and. They are stored in sufficiently light containers that allow them to be used to power the engines of cars and light trucks.

And methane, whose critical temperature is much lower (minus 82.1 ° C), will be in the gaseous state at any pressure, and for its use as a gas fuel it is contained in cylinders at a pressure of 20 MPa.

Lowest calorific value for all gasesmore than gasoline. This is an advantage of gaseous fuel and compensates for the reduced filling of the cylinders due to the low relative density of the gas.

The stoichiometric coefficient of gases is higher than that of gasoline.

Octane numbergas is much higher than gasoline. This is a great advantage of gas, which allows you to save the engine from detonation, increase its power by increasing the compression ratio and reduce fuel consumption.

Flash point. Not for gas. This will degrade the starting performance of the engine.

Flammability limits and excess air ratio in favor of gaseous fuels. They say that the limits of regulation of internal combustion engines on gas fuel are wider than on gasoline.

Based on the considered physicochemical properties of gaseous fuels, it can be argued that they are definitely superior to gasoline in the following parameters:

–allow to achieve higher power and fuel-economic indicators than similar in the way the workflow is organized gasoline engines. Specially designed gas engines are superior to gasoline engines in terms of specific power indicators, and are close to diesel engines in terms of fuel efficiency;

– in terms of environmental performance, the exhaust is significantly superior to gasoline.

PHYSICO-CHEMICAL PROPERTIES OF NATURAL GASES. Natural gases are colorless, odorless and tasteless.

The main indicators of combustible gases that are used in boiler rooms: composition, calorific value, specific gravity, combustion and ignition temperature, explosive limits and flame propagation speed.

Natural gases of purely gas fields consist mainly of methane (82...98%) and other hydrocarbons. The calorific value is the amount of heat that is released during the complete combustion of 1 m3 of gas. It is measured in kcal/m3. There is a distinction between the higher calorific value Qв, when the heat spent on the condensation of water vapor, which are in the flue gases, and the lower Qн, when this heat is not taken into account, are taken into account - it is used in calculations. In practice, gases with different calorific values ​​are used.

For equalizing characteristics of fuel quality, the so-called reference fuel is used, for which 1 kg of fuel is taken as a unit, having a calorific value Qн = 7000 kcal/m3 (29300 kJ/kg). The combustion temperature is the maximum temperature that can be achieved with complete combustion of the gas, if the amount of air required for combustion exactly corresponds to the chemical formulas of combustion, and the initial temperature of the gas and air is 0. The combustion temperature of individual gases is 2000 - 2100ºС. The actual combustion temperature in the boiler furnaces is lower than the heat output (1100 - 1400ºС) and depends on the combustion conditions.

The ignition temperature is the minimum initial temperature at which combustion begins. For natural gas, it is 645ºС. explosive limits. The gas-air mixture in which the gas is located: up to 5% - does not burn; from 5 to 15% - explodes; more than 15% - burns when air is supplied. Speed ​​of spread of a flame for natural gas - 0,67 m/s (methane CH4) Combustible gases have no smell.

To timely determine the presence of them in the air, quickly and accurately determine the places of leakage, the gas is odorized (give a smell). Ethyl mercoptan (C2H5SH) is used for odorization. The odorization rate is 16 g of odorant per 1000 m3 of gas. Odorization is carried out at gas distribution stations (GDS). If there is 1% natural gas in the air, its smell should be felt.

The presence of more than 20% of the gas in the room causes suffocation, its accumulation in a closed volume from 5 to 15% can lead to an explosion of the gas-air mixture, with incomplete combustion carbon monoxide CO is released, which even at a low concentration (0.15%) is poisonous. 2.3

End of work -

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Composition of natural gas
Physical Properties

Reduced pressures and temperatures

For an objective assessment of bottomhole pressures and the possibility of their comparison, the concept of reduced pressure is introduced. Measured or calculated bottomhole pressures are reduced (recalculated) to a conditional horizontal plane, which can be taken as any plane within the reservoir, the absolute elevation of which is known.

Usually, the reference plane is taken to be the plane passing through the initial oil-water contact, the absolute mark of which is determined during the exploration of the field. If the well bottoms are connected through a permeable formation, then the same reduced static pressures are set in them.

Reduced temperature - the ratio of the thermodynamic temperature of a substance to its critical temperature

1) critical - the limiting temperature of the equilibrium coexistence of two phases (liquid and its vapor), above which these phases are indistinguishable

Physical properties of fluids in reservoir conditions

Water compressibility is a reversible change in the volume of water in reservoir conditions under the influence of pressure. The value of the compressibility coefficient ranges from (3-5)-104. The compressibility of water decreases with increasing salt concentration and increases with increasing dissolved gas content.

Formation water volume factor bv depends on salinity, chemical composition, gas content, reservoir pressure and temperature. For formation waters of oil and gas fields, bv = 0.8-1.2.

The density of water in reservoir conditions depends mainly on its salinity, pressure and temperature. In most cases, due to temperature, the density of water in reservoir conditions is 20% less than in surface conditions.

Formation water viscosity depends primarily on temperature, salinity and chemical composition. In most cases, the viscosity of formation waters of oil and gas fields is 0.2-1.5 mPa-s.

Concepts: oil field, reservoir, deposit, development object

Oil and oil and gas fields are accumulations of hydrocarbons in the earth's crust, confined to one or more localized geological structures, i.e. structures located near the same geographic location.

A reservoir is a natural local single accumulation of oil in one or more interconnected reservoirs, i.e. in rocks capable of containing and releasing oil during development.

A development object is a geological formation (layer, massif, structure, set of layers) artificially identified within the field being developed, containing industrial reserves of hydrocarbons, which are extracted from the subsoil using a certain group of wells or other mining structures.

One, several or all layers of the field can be included in the development object.

The main features of the development object are the presence of industrial oil reserves in it and a certain group of wells inherent in this object, with the help of which it is developed.

Rational oil field development system

Rational is a development system that provides the most complete extraction of fluids from reservoirs at the lowest cost. It provides for compliance with the rules for the protection of subsoil and the environment, takes into account the natural, production and economic features of the region.

Features of the multilayer field development system

There are three systems for developing a multilayer oil field:

The bottom-up development system, in which oil reservoirs (deposits) are introduced into development sequentially: each overlying after the development of the underlying one, and the reservoir from which development begins is called the base or reference horizon (reservoir). The base horizon is selected on the basis of its high productivity and oil grade, and the reservoir must be well studied over a large area and lie in conditions favorable for its rapid drilling

A top-down development system in which layers are introduced into development: each underlying after the development of the overlying. This system was widely used during the period when percussion drilling prevailed. Currently, the "top-down" development system is allowed as an exception in the development of shallow oil reservoirs drilled by light mobile rigs, provided that the upper reservoirs are poorly permeable and when their subsequent wells pass to the underlying reservoirs, the loss of clay mud and the pack of upper reservoirs itself are excluded. reservoirs are developed according to the "bottom-up" system.

The system of simultaneous development of two or more layers (deposits) provides that each of the layers is drilled simultaneously by a separate grid of wells. This system is applied under the condition that the oil reservoirs are highly productive with a well-defined pressure regime, are drilled at a fast pace and are operated while maintaining reservoir pressure.

Production facilities development system

The field development system provides for the solution and implementation of the following activities:

1. Identification of operational facilities (at a multifaceted field) and determination of the procedure for putting them into development. A production facility is a productive formation or a group of formations developed by an independent grid of wells while ensuring control and regulation of the process of their operation.

2. Determination of the number of wells, their placement at the production facility and the procedure for putting wells into operation.

3. Establishment of the operating mode of production (sometimes injection) wells (determination of their debtor or flow rate, bottomhole pressures and changes in these indicators over time).

4. Regulation of the balance of reservoir energy in oil or gas deposits "by influencing the reservoirs as a whole.

Field development systems can be classified according to the nature or order of implementation of these activities as follows.

Theory of enlarged well

The enlarged well theory is most relevant for gas and gas condensate fields, since gas fields are developed in the reservoir energy depletion mode, and most gas condensate fields are also developed without reservoir pressure maintenance, and sooner or later they switch to reservoir energy depletion mode. In the case of oil fields, as a rule, reservoir pressure is maintained. Therefore, the flow of contour water is of subordinate importance. The development of oil fields under natural water drive usually takes place in the case of small initial oil reserves and good reservoir properties of the reservoir.

Basic concepts of the phase state of multicomponent systems

contain more than three components, which can be simple substances and (or) chemical compounds. Multicomponent systems in nature - ores, sea water, minerals, brines of salt lakes, oils, hydrocarbon gases, etc.; in technology - metal alloys, salt mixtures, aqueous solutions salts, mixtures of organic compounds, etc.

In oilfield practice, there are different kinds phase transitions of a substance - evaporation, condensation, melting, etc. Most often, a field engineer has to deal with phase transformations of solutions. In a system undergoing a phase transition, two or more different phases can coexist in thermodynamic equilibrium simultaneously. The conditions for phase equilibrium are the equality of temperatures and pressures in all parts of the system. In addition, at constant temperature and pressure, the chemical potentials of the contacting phases must be equal. In multicomponent systems, phase equilibrium conditions occur when the chemical potentials of a given component in all phases of the system in equilibrium become equal to each other.

All phase transitions are divided into two types - the first and second kind.

The simplest examples of first-order phase transitions are evaporation and melting. During phase transformations of this kind, the volume of the system changes and an amount of heat is absorbed (or released), which is called the latent heat of transition. The existence of a heat of transition indicates a change in the entropy of the system. In the process of evaporation, the substance absorbs heat. Its entropy in the gaseous state at a given pressure and temperature is greater than in the liquid state. Consequently, during a phase transition of the first order, the volume Ii of the entropy of the substance changes. A first-order phase transition (equivalent to the one described above) can be characterized using the Gibbs function

Question 33

Physical properties of natural gases

The significant difference between the physical properties of gas and the physical properties of oil, expressed mainly in its low density, high elasticity, significantly lower viscosity, determines the specifics of the development of gas and gas condensate fields, which consists in the fact that gas is produced mainly by the flowing method. At the same time, the complex and extended gas supply system from deposit to consumption is completely hermetic and is a single whole.

Natural gas is a mineral in its gaseous state. It is widely used as a fuel. But natural gas itself is not used as a fuel, its components are separated from it for separate use.
Composition of natural gas
Up to 98% of natural gas is methane, it also includes methane homologues - ethane, propane and butane. Sometimes carbon dioxide, hydrogen sulfide and helium may be present. This is the composition of natural gas.
Physical Properties
Natural gas is colorless and odorless (if it does not contain hydrogen sulfide), it is lighter than air. Flammable and explosive.
Approximate physical characteristics (depending on the composition; under normal conditions, unless otherwise indicated):

Density: 0.68 to 0.85 kg/m³ relative to air (dry gas); 400 kg/m³ (liquid). Auto-ignition temperature: 650 °C; Explosive concentrations of a mixture of gas with air from 5% to 15% by volume; Specific heat of combustion: 28-46 MJ/m³ (6.7-11.0 Mcal/m³); Octane number when used in internal combustion engines: 120-130. It is 1.8 times lighter than air, therefore, when leaking, it does not collect in the lowlands, but rises up