Natural gas is a colorless and odorless combustible gas, which is produced in oil and gas fields. Its main component is methane (CH4), accounting for 80 ~ 99%, followed by ethane, propane, total butane, total pentane, carbon dioxide, carbon monoxide, hydrogen sulfide, total sulfur and moisture. In the standard state, the boiling point is-162℃, the density of natural gas is generally 640-750g/m3, and the relative density with air is 0.55-0.62.
2. The working principle of natural gas as fuel
CH4+2o 2——2H2O+CO2+38MJ/m3
3. Main uses of natural gas
Natural gas is an important industrial raw material and fuel, and its main uses are as follows.
1) The main fuel for industrial enterprises such as power plants, heat energy, heating and air conditioning;
2) Catering industry and civil fuel;
3) The main raw materials of chemical industry, which can synthesize or refine a variety of industrial raw materials and semi-finished products;
4) As a clean fuel for motor vehicles that meets the requirements of environmental protection, it is an ideal substitute for gasoline and diesel, and a new technology that has developed rapidly at home and abroad in recent years, and can be used in automobiles, ships, trains and even airplanes.
4. Basic parameters of LNG
The main components of LNG are methane (above 90%), ethane, nitrogen (0.5- 1%) and a small amount of C3-C5 alkanes. Liquefied natural gas is another form of energy converted from natural gas.
1) The main component of LNG is methane, whose chemical name is CH4, and a small amount of ethane C2H6, propane C3H8, nitrogen N2 and other components.
2) The critical temperature is -82.3℃.
3) The boiling point is-162℃ and the ignition point is 650℃.
4) The liquid density is 0.420 ~ 0.46 t/m3, and the gas density is 0.68 ~ 0.75 kg/m3.
5) The gas calorific value is 38MJ/m3, and the liquid calorific value is 50MJ/kg.
6) Explosion range: upper limit 15% and lower limit 5%.
7) Octane number ASTM: 130.
8) Colorless, tasteless, nontoxic and non-corrosive.
9) The volume is about 1/625 of the same volume of gaseous natural gas.
5. Briefly describe the six advantages of LNG.
1) The volume of LNG is 625 times smaller than that of natural gas of the same quality, so LNG can be transported to places without natural gas conveniently by cars and ships.
2)LNG storage efficiency is high, and it occupies less land. With less investment, 10m3LNG storage capacity can supply 10000 households 1 day of domestic gas.
3) As a high-quality vehicle fuel, LNG has higher octane number, better antiknock performance and longer engine life compared with gasoline. The fuel cost is low. Good environmental protection performance and the like. It can reduce 72% hydrocarbons, 39% nitrogen oxides, 90% carbon monoxide and zero sulfur oxides and lead.
4) 4) The latent heat of vaporization of LNG is high, and the cold energy during liquefaction can be recycled.
5) Because the density of liquefied natural gas after vaporization is very low, only about half that of air, it will fly away immediately if it leaks slightly, so as not to cause explosion.
6) LNG is pure in composition, completely burned, and produces carbon dioxide and water after combustion, which is beneficial to protecting the environment and reducing urban pollution. It is a good clean fuel.
6. The main use of liquefied natural gas
1), as a clean fuel, is safe, convenient, fast and less polluting after being vaporized for urban residents.
2) Used as a substitute for automobile fuel. When LNG is used as the fuel of automobile engine, it is only necessary to replace the engine properly, which is not only safe and reliable, but also low in noise and pollution. Especially in today's increasingly stringent emission regulations, the exhaust emissions of vehicles using LNG as fuel have been significantly improved. According to data reports, compared with compressed natural gas (CNG), for medium-sized and heavy-duty vehicles, the fuel cost of LNG vehicles is 20% lower and the weight is 2/3 lighter. At the same time, the cost of fuel supply system is reduced by at least 2/3. It can be proved that liquefied natural gas and its storage in liquid state is the most economical and effective method to popularize its application in transportation fuel.
3) As a cold source, it can be used to produce instant food, crush plastics and rubber at low temperature, and also be used for seawater desalination and cable cooling.
4) As industrial gas fuel, it is used in glass shell factory, craft glass factory and other industries.
7. Mode of transportation of liquefied natural gas
The main modes of LNG transportation are ships, trains and tankers. Within the economic transportation radius of 500 ~ 800 kilometers, the tank car is an ideal way to transport LNG. The tank body of tank car adopts double-wall vacuum powder insulation, and is equipped with operating valve and infusion hose safety system. The manufacturing technology of domestic cryogenic liquid tank car is relatively mature and safe to use. LNG products are stored in cryogenic liquid storage tanks, which are insulated by double-wall vacuum powder. The daily evaporation rate of LNG can be controlled within 0.46%, and the storage period is 4 ~ 7 days.
8. Liquefied natural gas is a clean automobile fuel.
Among all clean fuels, natural gas is regarded as the most suitable alternative fuel for automobiles by many countries and experts in the world because of its mature application technology, safety, reliability and economic feasibility. Compared with gasoline, the automobile uses natural gas as power fuel, and its exhaust emissions are reduced by 72% HC, 39% NOx, 90% CO, and 0 SOx and Pb. The noise is reduced by 40%. Therefore, promoting the use of natural gas fuel will play a positive role in reducing air pollution and improving the environment.