Indirect liquefaction (ICL) of coal liquefaction

The indirect liquefaction technology of coal is a process that all coal gasification is converted into synthesis gas, and then coal-based synthesis gas (carbon monoxide and hydrogen) is catalytically synthesized into hydrocarbon fuel oil and chemical raw materials and products at a certain temperature and pressure, including coal gasification to prepare synthesis gas, gas purification and exchange, catalytic synthesis of hydrocarbon products, product separation and recombination. 1923, German chemists first developed the indirect liquefaction technology of coal. In the early 1940s, in order to meet the needs of the war, Germany built nine indirect liquefaction plants. After World War II, due to the development of cheap oil and natural gas, these factories were closed and used for other purposes. After that, with the successful development of iron-based composite catalyst and the development and application of new reactors, the indirect coal liquefaction technology has been continuously improved. However, due to the complexity of indirect coal liquefaction process, large initial investment and high cost, compared with direct coal liquefaction, the interest of other countries except South Africa has gradually weakened.

There are three kinds of indirect coal liquefaction technologies, namely SASOFTO synthesis in South Africa, Mobil methanol to gasoline in the United States and direct synthesis under development. Indirect coal liquefaction technology has been commercialized abroad, and there are three commercial production plants in the world, namely Sasol Company in South Africa and indirect coal liquefaction plants in New Zealand and Malaysia. The indirect coal liquefaction plant in New Zealand adopts Mobil liquefaction process, but only carries out the first step of indirect liquefaction, that is, using natural gas or coal gasification synthesis gas to produce methanol, without further using methanol to produce fuel oil and other chemical products, with a production capacity of 6.5438+0.25 million barrels per day. The liquefaction process used in Malaysia's indirect coal liquefaction plant is similar to that of South Africa's Sasol Company, but the difference is that it uses natural gas as raw material to produce high-quality diesel and kerosene with a production capacity of 500,000 tons/year. Therefore, strictly speaking, South African Sasol Company is the only commercial producer of indirect coal liquefaction in the world.

South African Sasol Company was established in the early 1950s, and the first Sasol-1 plant for producing fuel oil from coal was built in 1955. After the oil crisis in the 1970s, Sasol No.2 Plant and Sasol No.3 Plant were successively built in 1980 and 1982. The three indirect coal liquefaction plants process about 46 million tons of raw coal every year, with a total product volume of 7.68 million tons. They mainly produce 1 13 products such as gasoline, diesel oil, wax, ammonia, ethylene, propylene, polymers, alcohols and aldehydes, among which oil products account for 60% and chemical products account for 40%. The gasoline and diesel produced by the company can meet the demand of 28% in South Africa, and its indirect coal liquefaction technology is in the leading position in the world.

In addition, SGI Company of the United States developed a new coal liquefaction technology, namely LFC (coal-to-oil) technology in the late 1980s. This technology is to extract solid high-quality clean coal and liquid fuel oil from non-coking coal such as sub-bituminous coal or lignite by using low-temperature dry distillation technology. SGI Company of the United States built a sub-bituminous coal commercial demonstration plant with a daily processing capacity of 1000t in 1992. Fischer-Tropsch synthesis refers to the heterogeneous hydrogenation of CO to hydrocarbons (C 1 ~ C25) and oxygenates with different chain lengths under the action of solid catalysts. This reaction was first discovered by F.Fischer and H.Tropsch in 1923, then perfected by Fischer and others, and industrialized in Ruhr Chemical Company in 1936, hence the name Fischer-Tropsch synthesis.

Due to different catalysts and different operating conditions, the stoichiometry of Fischer-Tropsch synthesis reaction will be very different, but it can be described by the following two basic reaction equations.

(1) hydrocarbon generation reaction

CO+2H2→(-CH2-)+H2O

(2) Water gas shift reaction

Carbon monoxide+H2O→H2+ carbon dioxide

The general formula of the synthesis reaction can be obtained from the above two formulas:

2CO+H2→(-CH2-)+ CO2

From the above two formulas, the general measurement formula of alkane and alkene formation can be deduced as follows:

(3) Alkane generation reaction

nCO+(2n+ 1)H2→CnH2n+2+nH2O

2nCO+(n+ 1)H2→CnH2n+2+NCO 2

3 NCO+(n+ 1)H2O→CnH2n+2+(2n+ 1)CO2

NCO 2+(3n+ 1)H2→CnH2n+2+2nH2O

(4) Olefin generation reaction

nCO+2nH2→CnH2n+nH2O

2nCO+nH2→CnH2n+nCO2

3nCO+nH2O→CnH2n+2nCO2

nCO2+3nH2→CnH2n+2nH2O

The main reaction of indirect liquefaction is the above reaction. Due to different reaction conditions, there are methane generation reaction, alcohol generation reaction (alcohol is needed to produce methanol), aldehyde generation reaction and so on. Indirect coal liquefaction can be divided into two processes: high temperature synthesis and low temperature synthesis. The main products synthesized at high temperature are naphtha, propylene, α-olefin and C 14 ~ C 18 alkanes. These products can be used as raw materials for the production of petrochemical substitutes, such as the production of ethylene from naphtha fractions and the production of advanced detergents from α -olefins It can also be processed into high-quality engine fuels such as gasoline and diesel. The main products of low temperature synthesis are diesel oil, aviation kerosene, wax and liquefied petroleum gas. The cetane number of diesel oil produced by indirect coal liquefaction can be as high as 70, which is a high-quality diesel blending product.

The indirect liquefaction technologies of coal-to-liquid mainly include sasol technology, SMDS technology of Shell, Syntroleum technology, AGC-2 1 technology of Exxon and Rentech technology. There are slurry bed, fluidized bed, fixed bed process and sand rope fixed bed process in South Africa. South Africa's international Sasol and Shell Malaysia synthetic oil plants have long-term operating experience.

Typical coal-based Fischer-Tropsch synthesis processes include: coal gasification and gas purification, shift and decarbonization; Fischer-Tropsch synthesis reaction; Oil processing and other three pure "series" steps. The crude gas produced by the gasification device is dedusted and cooled to obtain clean gas, and the qualified synthesis gas is obtained after CO wide temperature sulfur-tolerant shift and acid gas (including H2 and CO2) removal. The synthesis gas enters the synthesis reactor, and under certain temperature, pressure and catalyst, H2S and carbon monoxide are converted into straight-chain hydrocarbons, water and a small amount of oxygen-containing organic compounds. The product is separated by three phases, and chemicals such as alcohol, ketone and aldehyde are extracted by water phase. The oil phase adopts conventional petroleum refining methods (such as conventional and vacuum distillation), cuts product fractions as required, and obtains qualified oil products or intermediate products through further processing (such as hydrofining, hydrodewaxing, catalytic reforming, hydrocracking and other processes); Liquefied petroleum gas, polymer grade propylene, polymer grade ethylene and medium calorific value fuel gas are obtained by freezing separation and olefin conversion. The synthesis conditions of (1) are mild. In fixed bed, fluidized bed or slurry bed, the reaction temperature is lower than 350℃ and the reaction pressure is 2.0-3.0 MPa.

(2) High conversion rate. For example, if the hot metal catalyst is used in the SAS process of Sasol Company, the one-way conversion rate of syngas can reach more than 60%, and the total conversion rate can reach about 90% when the circulation ratio is 2.0. Shell's SMDS process uses cobalt-based catalyst, which has higher conversion rate;

(3) Limited by the chain growth and transformation mechanism in the synthesis process, the selectivity of the target product is low and there are many by-products. Normal chain hydrocarbons can range from C 1 to c100; ; With the decrease of synthesis temperature, the output of heavy hydrocarbons (such as wax oil) increases, while the output of light hydrocarbons (such as CH4, C2H4, C2H6, ...) decreases.

(4) The theoretical yield of effective product CH2-is low, only 43.75%, while the theoretical yield of process wastewater is as high as 56.25%;

(5) Coal consumption is high. Under normal circumstances, about 5 ~ 7t raw coal produces 1t refined oil.

(6) The reactants are all in gas phase, so the equipment is bulky and the investment and operation costs are high;

(7) Indirect coal-based liquefaction depends entirely on coal gasification. Without large-scale gasification, there would be no indirect coal-based liquefaction. China began to study the indirect coal liquefaction technology in the early 1950s. An indirect coal liquefaction test of 4500 tons/year was conducted in Jinzhou, but it was suspended due to the discovery of Daqing Oilfield. Due to the two oil crises in 1970s and a series of problems caused by the energy structure of "rich in coal but little in oil", China resumed the research on indirect liquefaction of coal to synthetic gasoline organized and implemented by Shanxi Institute of Coal Chemical Industry, Chinese Academy of Sciences in the early 1980s.

During the "Seventh Five-Year Plan" period, the coal-based synthetic gasoline technology developed by Shanxi Coal Chemical Institute was listed as a national key scientific and technological research project. 1989 completed the small test of Daixian Chemical Fertilizer Plant. During the Eighth Five-Year Plan period, the state and the Shanxi provincial government invested more than 20 million yuan to build an industrial experimental device with an annual output of 2,000 tons of gasoline in Jincheng Chemical Fertilizer Plant to produce 90 # gasoline. On this basis, the technical scheme of synthetic gasoline plant with an annual output of 654.38+10,000 tons is put forward. In 200 1 year, the National 863 Program and the Chinese Academy of Sciences jointly launched a major scientific and technological project of "changing coal into oil". Shanxi Institute of Coal Chemical Industry of China Academy of Sciences undertook the research of this project. The Ministry of Science and Technology invested 60 million yuan, the provincial government invested 10 million yuan and the support of local enterprises. After more than a year's research, the 1,000-ton slurry bed pilot platform was put into trial operation for the first time in September 2002, and the first batch of crude oil was synthesized. About 70% diesel oil with cetane number above 70 can be obtained from low-temperature slurry synthetic oil, and other products include liquefied petroleum gas. The core technologies of Fischer-Tropsch synthesis, such as catalyst, reactor and process engineering, have also made major breakthroughs.

The development and integration of process software for 10,000 tons of coal-based synthetic gasoline are under way, and the research on cobalt-based catalyst technology for diesel synthesis has been in the experimental stage since the early 1990s. After 20 years of research and development, China has the technical reserves to build a 10,000-ton production plant, and has independent intellectual property rights in key technologies and catalyst research and development. It can be said that China's own coal liquefaction technology has reached the advanced level in the world. Shanxi Institute of Coal Chemistry, Chinese Academy of Sciences and Lianshun Energy Co., Ltd. reached an agreement on establishing a synthetic oil laboratory. Lianshun Company invested/kloc-0.5 million yuan in the research and development of key technologies and related processes, and finally built an indirect liquefaction production plant with an annual output of/kloc-0.5 million tons of synthetic liquefied oil in Shuozhou, Shanxi in 3-5 years. China Academy of Sciences and Shanxi Provincial Government signed the Framework Agreement on Developing Shanxi Coal Indirect Liquefaction Synthetic Oil Industry. According to this agreement, in the next 5- 10 years, Shanxi Province will build a super-large enterprise group with millions of tons of coal-based synthetic oil as the core between Shuozhou and Datong through state investment and social financing.

At the same time of technology development, domestic coal enterprises have done a lot of work in introducing mature technologies and building indirect coal liquefaction devices. Pingdingshan Coal Industry Group, Ningxia Coal Industry Group and Shenhua Group carried out coal evaluation test and pre-feasibility study on the construction of indirect liquefaction commercial demonstration plant, and did a lot of preliminary work in technology introduction, investment and financing, project establishment and so on. The project is in the demonstration stage.