L n g
Liquefied natural gas (Liquefied Natural Gas, referred to as LNG), the main component is methane, is recognized as a relatively clean fossil energy on the earth. Colorless, tasteless, non-toxic and non-corrosive, its volume is about 1/625 of the volume of the same amount of gaseous natural gas, and the quality of liquefied natural gas is only about 45% of the same volume of water.
The manufacturing process is to purify the natural gas produced in the gas field, after a series of ultra-low temperature liquefaction, and then transport it by LNG ship. After the combustion of liquefied natural gas, the air pollution is very small, and the heat released is large, so liquefied natural gas is a relatively advanced energy source.
Liquefied natural gas is natural gas after compression, cooling to its freezing point (-161.5 ℃) temperature into liquid, usually liquefied natural gas stored in -161.5 degrees Celsius, about 0.1MPa cryogenic storage tank. Its main component is methane, which is transported by special ship or tank truck and re-gasified when used. Since the 1970 s, the world's liquefied natural gas production and trade volume have increased rapidly. In 2005, the international trade volume of LNG reached 188.81 billion cubic meters. The main exporter is Indonesia, with an export of 31.46 billion cubic meters; the main importer is Japan, 76.32 billion cubic meters.
Natural gas refers to the flammable gas contained in the formation, mainly a mixture of low molecular alkanes, can be divided into dry gas natural gas and wet natural gas, dry gas is mainly methane, wet natural gas in addition to containing a large amount of methane, but also contains more ethane, propane and butane.
The main component of liquefied natural gas (Liquefied Natural Gas) is methane, with small amounts of ethane and propane. Liquefied natural gas is colorless, tasteless, non-toxic and non-corrosive. Natural gas can be liquefied at normal pressure and -162 ℃. The volume of liquefied natural gas is about 1/625 of the gaseous volume.
Under normal pressure, the density of LNG is about 430-470kg/ m (slightly different due to different components), the ignition point is about 650 ℃, the calorific value is 52MMBtu(1MMBtu = 2.52 × 108cal), and the explosion limit (volume) in air is 5%-15%. The storage of liquefied natural gas is one of the natural gas storage methods. LNG storage tanks are usually double-layer metal tanks, the inner layer in contact with LNG is made of low-temperature steel containing 9% Ni, the outer layer is made of carbon steel, the intermediate insulation layer is expanded perlite, and the insulation layer at the bottom of the tank is foam glass.
The world's advanced environmental protection countries are promoting the use of LNG. In addition to being used as fuel for power plants, factories and household users, the methane contained in it can be used as chemical raw materials such as fertilizer, methanol solvent and synthetic acetic acid; in addition, the ethane and propane contained in it can be cracked to generate ethylene and propylene, which are important raw materials for plastic products.
In addition, ultra-low temperature LNG can provide a large amount of cold energy in the process of transforming into normal temperature gaseous state under atmospheric pressure. These cold energy can be recycled and can also be used in 6 low temperature applications: separating air to produce liquid oxygen, liquid nitrogen, liquefied carbon dioxide and dry ice, using cold energy to generate electricity, manufacturing frozen food or used in frozen warehouses, and low temperature crushing of industrial wastes such as rubber, plastics and iron filings, desalination of sea water.
In the face of the increasingly serious situation of ecological environment pollution, in order to optimize the energy consumption structure, improve the atmospheric environment, and realize the economic development strategy of sustainable development, people choose natural gas as a clean, efficient and ecological high-quality energy and fuel. Now, both industrial and civil, have produced a growing dependence on natural gas. Liquefied natural gas (LNG) is the liquid form of natural gas. In some cases, the choice of liquefied natural gas has more advantages than the choice of gaseous natural gas. The application of LNG is actually the application of natural gas, but due to its characteristics, LNG has a wider range of uses than natural gas.
LNG for (I) industry
1. Power generation
The use of LNG is efficient and economical. In power generation, the thermal energy utilization rate of natural gas can reach 55%, which is higher than that of fuel oil and coal. Especially for peak shaving power plants, the advantage of natural gas replacing fuel oil is very obvious. The main industrial use of LNG.
Japan has always been the country that imports the most LNG in the world. More than 75% of its LNG imports are used for power generation, and 20% ~ 23% are used for city gas. South Korea is also a major LNG importer, and its power industry is the largest user of Korea Gas Corporation (Kogas), consuming more than half of the country's total LNG imports.
There have been many gas-steam combined cycle power plants using natural gas or liquefied natural gas as fuel in the world. From 1999 to 2020, about 90% of the new power generation planned in the United States will be natural gas power generation. By then, the proportion of natural gas power generation in the United States will reach 33%. The combined cycle power station, which emerged in the 1980 s, is dominated by gas turbines (accounting for about 2/3 of the total electricity), and the pure efficiency of the power station has reached more than 50%, while the efficiency of conventional coal-fired steam turbine power stations is only 30% ~ 35%. Gas turbine power station and combined cycle power station not only high efficiency, but also good mobility, from the unit start to full load operation time is short, can be used for basic load operation, but also for peak operation. In addition, the combined cycle power plant has low pollution and high reliability.
At present, my country's "West-East Gas Transmission" and other large-scale natural gas transmission and distribution projects have been completed; the first phase of the Guangdong LNG station line project has been officially launched; the total construction scale is 5 million t/year, and the total investment of the first phase of the project exceeds 22 billion yuan. The Fujian LNG project was also officially launched. The commissioning and start-up of these projects provide the necessary material guarantee for the development of natural gas power generation in China, and will play an important role in alleviating the contradiction between energy supply and demand and optimizing the energy structure in China.
2. Ceramic, glass and other industries
Some enterprises with large energy consumption are often far away from cities or natural gas pipelines, or cannot get natural gas transported by pipelines at all. In this case, LNG has more obvious advantages. The most typical one is ceramic factories. Using LNG can improve the product grade and reduce the cost. Used in glass, ceramic manufacturing, petrochemical and building materials industries (alkali-free glass cloth), it can greatly improve the product quality or reduce the cost, thus, due to the change of fuel or raw materials, it has become a new benefit growth point for related enterprises.
LNG for domestic use in small and medium-sized towns in (II)
In recent years, with the improvement of residents' living standards, residents in small and medium-sized towns prefer to use clean energy. LNG as a clean energy source has attracted much attention. The carbon dioxide and nitrogen oxides produced after natural gas combustion are only 50% and 20% of coal, the pollution is 1/4 of liquefied petroleum gas and 1/800 of coal. LNG gasification station has better economy than pipeline gas due to the large investment cost of pipeline laying, in small and medium-sized towns, LNG gasification stations can be used as gas sources for residents to use. In addition, they can also be used for commercial, public institutions and heating of users.
(III) LNG as standby gas source for peak shaving
As the peak shaving gas source of pipeline natural gas, it can carry out peak shaving on the civil fuel system to ensure the safe and stable gas supply of the city. In the United States, Britain, Germany, the Netherlands, France and other countries, LNG peak shaving devices are widely used in natural gas transmission and distribution systems, which plays a role in peak shaving for the fluctuation of domestic and industrial gas, especially for the sharp increase of gas consumption in winter. It has been built and put into use in Shanghai ｡
LNG fuel for (IV) vehicles
As a clean energy for sustainable development, LNG has obvious environmental and social benefits. After replacing fuel with LNG, it can reduce 90% of sulfur dioxide emissions and 80% of nitrogen oxide emissions. The environmental benefits are very obvious. It is a high-quality alternative fuel for automobiles. It can be predicted that cities will gradually replace fuel with LNG or natural gas in terms of automobile fuel. In recent years, it has been valued and promoted by many countries in the world. Russia has accumulated a lot of experience in using LNG for automobile transportation, railway transportation, water transportation and air transportation. Most transportation companies in the UK use LNG as vehicle fuel ｡
According to the different storage methods of natural gas, natural gas vehicles are roughly divided into CNGV (compressed natural gas vehicles),LNGV (liquefied natural gas vehicles), and ANGV (adsorbed natural gas vehicles). Currently, CNG vehicles are widely used in China, and LNGV vehicles are being promoted. ANGV vehicles are in the development stage. With the popularization of LNG, LNGV vehicles will gradually develop into heavy vehicles, it will also partially replace small CNG cars and buses. Currently, LNG bus demonstration stations built in China include Urumqi, Beijing and Changsha in Xinjiang, and Beihai and Zhanjiang cities are under preparation for construction. Currently, tens of thousands of CNG cars have been modified nationwide. However, LNG as vehicle fuel is especially worth promoting. CNG (compressed natural gas) filling stations should be taken into account while LNG filling stations are being built, it can meet the current and future requirements ｡