Gas Detector Knowledge Gas Awareness: General Combustible Gases

[Gas]
●Gas is a general term for gaseous fuels. It burns and releases heat for use by urban residents and industrial companies. There are many types of gas, including natural gas, artificial gas, liquefied petroleum gas and biogas.

[Type of gas]
● Gas: It is a mixture of gases. Due to the different raw materials and production processes used to produce gas, the composition of the various gases is also different. It is mainly composed of lower hydrocarbons (methane, ethane, propane, butane, ethylene, propylene, butylene), combustible components such as hydrogen and carbon monoxide, and impurities such as ammonia, sulfides, water vapor, tar, naphthalene, and dust. .
● Oil gas: It can be divided into two types: heavy oil gas and light oil gas. The raw material heavy oil or naphtha is put into an industrial furnace and subjected to pressure, temperature and catalyst. The heavy oil is cracked to generate combustible gas. By-products include crude benzene and alkali slag.
● Gasification of gas: The raw coal or coke is put into an industrial furnace (generation furnace, water gas furnace, etc.) to be burned, and air and water vapor are introduced to generate combustible gas mainly composed of carbon monoxide and hydrogen.
● Retorted gas: The coal is placed in an industrial furnace (a coke oven, a martial arts furnace, etc.) to isolate the air from heating, and the coal undergoes a physical chemical change called a dry distillation. After heating, the flammable gas can be purified to obtain tar, ammonia, crude benzene and other chemical products. The furnace has some coke.
● Biogas: A variety of organic substances are fermented under the condition of being isolated from air, and combustible gases produced by biochemical action under the action of microorganisms are also called biogas. Its components are methane and carbon dioxide, as well as small amounts of nitrogen and carbon monoxide. The calorific value is about 22MJ/Nm3.
● Liquefied petroleum gas: Combustibles obtained from condensate gas, oil associated gas or refinery gas as raw materials. The main components are propane, propylene, butane and butenes. There is also a small amount of pentane and other impurities. The calorific value of gaseous liquefied petroleum gas is about 93 MJ/Nm3; the liquid liquefied petroleum gas calorific value is about 46 MJ/Nm3.
● Pure natural gas: Gas produced from underground gas is pure natural gas.
● LNG: Natural gas undergoes cryogenic liquefaction and becomes liquid LNG at 160°C. It is transported on liquefied methane ships and special-purpose vehicles.
● Compressed natural gas: When the natural gas is compressed and pressurized to 200kg/cm2, the volume of natural gas is reduced by 200 times and stored in a container, which is convenient for automobile transportation. The economic transportation radius is 150 to 200 kilometers. Compressed natural gas can be used for civilian purposes and as a clean fuel for automobiles.
● Condensate gas: gas containing petroleum light fractions. For transport, natural gas can also be processed.
● CBM: Mine gas extracted from underground coal seams.
● Mine gas: mine gas collected when mining coal.
● Associated gas of petroleum: The gas that comes out with the exploitation of oil is called petroleum associated gas.

[Basic characteristics of gas]
Density: The weight per unit volume.
● The gas density of LPG is 2.0-2.5kg/Nm3
● The proportion of gas refers to the density of gas per unit volume, and the ratio of air density under the same state, also called relative density or relative proportion.
Calorific value: The amount of heat released from the complete combustion of gas per unit volume becomes the calorific value of the gas.
● Calorific value is divided into high calorific value and low calorific value.
● High calorific value refers to the total calories released when the unit gas is completely combusted and its flue gas is cooled to the initial temperature, in which the water vapor is discharged in the state of condensed water.
● Low calorific value refers to the total amount of heat released when the unit gas is completely burned and its flue gas is cooled to the initial temperature, in which the water vapor is discharged in the state of vapor.
Theoretical air volume: The minimum amount of air required for a unit gas to burn completely according to the combustion reaction equation.
● The amount of air needed to burn LPG is three times that of natural gas; it is six times that of artificial gas.
Expansion and compression
● The volume of liquid liquefied petroleum gas expands due to an increase in temperature. In a closed container filled with liquefied petroleum gas, as the temperature rises, its volume rapidly expands so that the pressure quickly rises to burst the container. If the volume expansion coefficient of water is set to 1, the volumetric expansion coefficient of liquid liquefied petroleum gas is approximately 16 times that of water.
Saturated vapor pressure
● The saturated vapor pressure of liquid hydrocarbons, abbreviated as vapor pressure, is the absolute pressure expressed by vapor when the liquid and its vapor pressure in a closed container are in dynamic equilibrium at a certain temperature.
● The saturation vapor pressure is independent of the size of the vessel and the amount of liquid, and is related to the composition and temperature of the liquefied petroleum gas. When the temperature rises, the saturated vapor pressure increases; the light components have a higher saturated vapor pressure than the reconstituted components.
Latent heat of vaporization
● The latent heat of vaporization is the heat absorbed by a unit mass (1 KG) of liquid into a vapor that is in equilibrium with it.
• Substances change from a gaseous state to a liquid state, which is called liquefaction. When a gaseous state changes into a liquid state, heat is released. Substances change from liquid to gaseous, called gasification. When the liquid is in a gaseous state, it absorbs heat.
● Liquefied petroleum gas is stored in a liquid state, and all kinds of burning appliances use gaseous liquefied petroleum gas. Therefore, the liquefied petroleum gas undergoes a process of changing from a liquid state to a gaseous state, which is called gasification or evaporation and must absorb heat. When the external temperature is low and the heat required for vaporization or evaporation cannot be supplied, the liquefied petroleum gas absorbs its own heat and lowers the temperature until the gasification is stopped.
Classification of pressure
● The pressure per unit area is called pressure strength, or pressure for short. The pressure is simply referred to as pressure in engineering. The pressure is divided into relative, absolute, and negative pressures.
● Relative pressure: The part of the pressure measured by the meter, also called gauge pressure, positive pressure, and working pressure.
● Absolute pressure: The sum of atmospheric pressure and gauge pressure, called absolute pressure, also called actual pressure.
● Negative pressure: The part of the pressure below the atmospheric pressure is measured by a measuring instrument. At this time, the relative pressure is less than the atmospheric pressure, and the indicated value is positive, which is called negative pressure. Also called vacuum.
Fire temperature
● The lowest temperature at which the fuel can continuously burn, and the ignition temperature. Under normal pressure (atmospheric pressure), the ignition temperature of liquefied petroleum gas is 365-460°C, the ignition temperature of natural gas is 270-540°C, and the ignition temperature of city gas is 270-605°C. Its ignition temperature is much lower than other fuels, so it is also called flammable gas.
Explosion limit
● The concentration range of combustible gas when the combustible gas and air mixture explodes in the event of an open flame is called the explosion limit. The content of combustible gas in this mixture when it is reduced to such an extent that the explosive mixture cannot be formed is called the lower explosion limit of combustible gas; and when the content of combustible gas is increased to such an extent that the explosive mixture cannot be formed, it is said to be The upper limit of the explosion (see table on the following page) The calorific value of combustion ● The combustible components (hydrogen, carbon monoxide, hydrocarbons, hydrogen sulfide) in the gaseous fuel undergo intense oxidation with oxygen under certain conditions, and generate a large amount of heat and light. The physical and chemical reaction process is called burning.
● Three conditions of combustion: combustibles, combustibles (oxygen), and ignition sources are all indispensable.
● The heat released from the complete combustion of a standard cubic meter of gas is called the calorific value of the gas. The unit is KJ/m3.
● Calorific value is divided into high calorific value and low calorific value.
● The low calorific value of general coke oven gas is approximately 160-17,000KJ/m3, natural gas is 36000-46000KJ/m3, and liquefied petroleum gas is 88000-12000KJ/m3.
● Calculated by 1KCAL=4.1868KJ:
● The low calorific value of coke oven gas is approximately 3,800-4,060 KCAL/m3; natural gas is 8,600-11,000 KCAL/m3; liquefied petroleum gas is 21,000-28,600 KCAL/m3.

[Common gas introduction]
natural gas
●Natural gas is colorless, odorless, non-toxic and non-corrosive. The main component is methane.
Natural gas can be generally divided into four types: • Gas field gas or natural gas extracted from gas wells;
● LPG mined with oil, also known as petroleum associated gas;
● Condensate gas field containing petroleum light fractions;
● Coal mine gas extracted from underground coal seams.
liquified natural gas
● When natural gas is cooled to about -162 degrees Celsius under atmospheric pressure, the natural gas is converted into a liquid state, which is called liquefied natural gas.
● LNG is colorless, odorless, non-toxic and non-corrosive. Its volume is about 1/600 of the volume of the same amount of gaseous natural gas, and the weight of LNG is only about 45% of the same volume of water.
Compressed natural gas
● Compressed natural gas is natural gas that is pressurized and stored in a container in a gaseous state. It has the same composition as pipeline natural gas. Can be used as a vehicle fuel.
● Use of natural gas: Mainly used for power generation. Natural gas fueled gas turbine power plants have much lower waste emissions than coal-fired and oil-fired power plants. They also have high power generation efficiency, low construction costs, and fast construction speed. In addition, gas turbines start and stop at a high speed. Strong peak shaving capacity, less water consumption, and land occupation.
● Natural gas can also be used as a chemical raw material. The chemical production equipment using natural gas as raw material has the advantages of low investment, low energy consumption, less land occupation, less personnel, good environmental protection, and low operating costs.
● Natural gas is widely used in civil and commercial gas stoves, water heaters, heating and refrigeration, but also in papermaking, metallurgy, quarrying, ceramics, glass and other industries. It can also be used for waste incineration and dry dehydration.
● The natural gas vehicle's exhaust emission is much lower than that of gasoline and diesel engine cars. It is carbon-free, non-abrasive, and has low operating costs. It is an environmentally friendly car.
Liquefied petroleum gas ● Liquefied petroleum gas is a byproduct of the process of extracting and refining petroleum. Its main component is propane.

[City Gas]
The following gases are seen in daily life:
● Natural gas: A combustible gas naturally occurring in the ground is called natural gas.
● According to the different ways of mining and formation, natural gas can be divided into 5 types:
Pure natural gas: gas from underground is pure natural gas; petroleum associated gas: gas accompanying a piece of oil is called oil-associated gas; mine gas: mine gas collected when coal is extracted; coal bed methane: extracted from underground coal seam Mine gas; Condensate gas: gas containing petroleum light fractions.
● For the convenience of transportation, natural gas can be processed after processing:
Compressed Natural Gas: When natural gas is compressed and pressurized to 200kg/cm2, the volume of natural gas is reduced by 200 times and stored in a container, which facilitates the transportation of automobiles. The economic transportation radius is 150-200km. Compressed natural gas can be used for civilian purposes and as a clean fuel for automobiles; LNG: Natural gas is cryogenic and liquefied and becomes liquid at 1600C to become liquefied natural gas. It is transported on liquefied methane ships and special vehicles.
Artificial gas
● It is a general term for all kinds of artificially produced gas. Coal and heavy oil are its raw materials, which are as follows:
Dry distillation of gas: The coal is placed in an industrial furnace (a coke oven, a martial arts furnace, etc.) to isolate the air from heating, and the coal undergoes a physical chemical change called a dry distillation. The flammable gas, ammonia, crude benzol and other chemical products can be obtained after the heating and the flammable gas is purified. The coke is stored in the furnace; gasification gas: the raw coal or coke is put into an industrial furnace (generating furnace, water gas furnace, etc.) In the combustion, and through the air, water vapor, to generate carbon monoxide and hydrogen as the main combustible gas; heavy oil gas: can also be called oil gas, the raw material heavy oil into the industrial furnace by the pressure, temperature and the role of the catalyst The heavy oil is cracked to produce combustible gas. By-products include crude benzene and alkali slag.
liquefied petroleum gas
• The production of liquefied petroleum gas is mainly produced from refineries in the cracking process of refined petroleum. Liquefied petroleum gas can be obtained in the processes of atmospheric and vacuum distillation, thermal cracking, catalytic cracking, platinum reforming, and delayed coking in petrochemical plants of petroleum refineries. Generally speaking, refining 1 ton of crude oil can produce 3%-5. % of liquefied petroleum gas; liquefied petroleum gas can also be recovered from natural gas. The crude oil and moisture mixture coming out of the oil field is separated by a gas-liquid separator, and the natural gas from the upper part is sent to a gas storage tank and subjected to pressure (16kg/cm2) for fractionation and then absorbed by diesel fuel spray; natural gas (dry gas) From the top of the tower, the rich oil that has absorbed the liquefied gas passes through the fractionation tower and is condensed to a liquid state at a pressure of 16 kg/cm2 to form liquefied petroleum gas.
Alternative natural gas
● Liquefied petroleum gas is heated and volatilized into gaseous state in special equipment. At the same time, some air (about 50%) is mixed in to expand its volume, dilute the concentration, and reduce the calorific value (close to natural gas calorific value and Chinese white index). Can be used as natural gas. When the natural gas long-distance pipeline network arrives, the substitute natural gas will be replaced by natural gas, and the previously-invested gas pipeline network, gas meters, and gas cookers will not be replaced, and the natural gas can be successfully connected to end users.