Fixed bed gasification is characterized by simplicity and reliability. At the same time, because the gasifying agent is in countercurrent contact with coal, the gasification process is relatively complete and the heat is reasonably utilized, so the thermal efficiency is high.
There are two kinds of fixed bed gasifiers: intermittent gasification (UGI) and continuous gasification (Lurgi). When the former is used to produce syngas, white coal (anthracite) or coke must be used as raw materials to reduce the CH4 content in syngas. There are thousands of such gasifiers in China, which have many disadvantages. The latter has more than 20 stoves in China, most of which are used to produce city gas; The preliminary gas purification system involved in this technology is extremely complicated and is not considered as the first choice technology.
(1), fixed bed batch gasifier (UGI)
Using lump anthracite or coke as raw material and air and water vapor as gasifying agent, synthetic feed gas or fuel gas is produced under normal pressure. This technology was successfully developed in 1930s, with less investment and simple operation. At present, it belongs to backward technology with low gasification rate, single raw material and high energy consumption. In the process of intermittent gas production, a large amount of blowing gas is discharged, and the blowing gas per ton of synthetic ammonia is 5 000 m3, which contains CO, CO2, H2, H2S, SO2, nitrogen oxides and fly ash. The sewage discharged from gas-cooled scrubber contains tar, phenols and cyanide, which causes environmental pollution. There are more than 900 small and medium-sized fertilizer plants in China, most of which are still using this technology to produce synthetic feed gas. With the development of energy policy and environment, it will be gradually replaced by new coal gasification technology in the near future.
(2) Lurgi gasifier
In 1930s, Lurgi Company of Germany successfully developed the fixed-bed continuous lump coal gasification technology, which was widely used at home and abroad because of its good raw material adaptability and large single-furnace production capacity. The gasifier pressure is (2.5 ~ 4.0) MPa, the gasification reaction temperature is (800 ~ 900)℃, the solid slag is discharged, and the gasifier has been shaped (MK ~ 1 ~ MK-5), in which the inner diameter of MK-5 furnace is 4.8m, the coal input is (75 ~ 84) tons/hour, and the pulverized coal output is achieved. Besides carbon monoxide and H2, coal gas also contains methane as high as 10% ~ 12%, which can be used as city gas, artificial natural gas and synthetic gas. The disadvantage is that the gasifier is complicated in structure, and there are rotating equipment such as coal separator and grate in the gasifier, so the manufacturing and maintenance costs are high; Coal into the furnace must be lump coal; Limited sources of raw materials; The discharged gas contains tar, phenol, etc. Sewage treatment and gas purification processes are complex, with long flow and many equipments, and the slag contains about 5% carbon. In order to solve the above problems, Lurgi Company and British Gas Company jointly developed the liquid slag gasifier (BGL) in 1984, which is characterized by high gasification temperature, discharge of molten ash, high carbon conversion rate, good synthetic gas quality, less wastewater generated by coal gasification, low treatment difficulty, and the production capacity of a single gasifier is 3-5 times higher than that of the same period last year. This is a promising gasifier. Fluidized bed gasification is also called boiling bed gasification. Small coal particles are used as gasification raw materials. Under the action of bottom-up gasifying agent, these fine particles keep continuous and disorderly boiling and suspension movement, and quickly mix and exchange heat, so that the temperature and composition of the whole bed are uniform. The main reason for the rapid development of fluidized bed gasification energy is that (1) production intensity is higher than that of fixed bed. (2) The small particles of broken coal are directly used as raw materials, which adapts to the development of coal mining technology and avoids the contradiction between supply and demand of lump coal. (3) It has strong adaptability to coal quality, and can use inferior coal with high ash such as lignite as raw material.
Fluidized bed gasifier usually includes Winkler, U-Gas, circulating fluidized bed (CFB) and pressurized fluidized bed (PFB is the gasification part of PFBC).
(1), CFB of circulating fluidized bed gasifier
The circulating fluidized bed gasifier (CFB) developed by Lurgi Company can gasify all kinds of coal, and can also use sawdust, bark and municipal combustible garbage as gasification raw materials, and steam and oxygen as gasification agents. The gasification intensity is twice that of moving bed, and the carbon conversion rate is high (97%). The ash discharged from the bottom of the furnace contains 2% ~ 3% carbon, and the circulating material returned to the gasifier during the circulation of gasification raw materials is 40% of the newly added raw materials. The gasification pressure is 0. 15MPa. The gasification temperature is controlled according to the raw materials. In general, the temperature of the circulating cyclone is controlled at (800 ~ 1050)℃. Lurgi's CFB gasification technology has been adopted by more than 60 factories around the world, and more than 30 factories are being designed and built, which is in a leading position in the world market.
CFB gasifier basically operates at normal pressure. If coal is used as raw material to produce synthesis gas, the gasification agent steam is 1.2kg, and the oxygen is 0.4kg per kilogram of coal, and gas (L.9 ~ 2.0) m3 can be produced. Gas composition co+H2 >; 75%, CH4 content is about 2.5%, CO2 content is 2 15%, which is lower than Texaco furnace gas and Lurgi MK furnace gas, which is beneficial to synthetic ammonia production.
(2) Ash-fused fluidized bed pulverized coal gasification technology
Ash fusion coal gasification technology takes dry pulverized coal with particle size less than 6mm as raw material and air or oxygen-rich water vapor as gasification agent. Pulverized coal and gasifying agent are continuously added from the bottom of the gasifier, and the residual carbon and the fly ash entrained in the crude gas that are not completely reacted at (1050 ~1100)℃ in the gasifier are recovered by a bipolar cyclone separator and then returned to the furnace. Crude gas contains almost no harmful substances such as tar and phenol, and is easy to purify. This advanced coal gasification technology has been successfully developed by China. This technology can be used to produce fuel gas, synthetic gas and combined cycle power generation, especially for small and medium-sized nitrogen fertilizer plants to replace intermittent fixed bed gasifier and bituminous coal to replace anthracite to produce synthetic ammonia feed gas, which can reduce the cost of synthetic ammonia 15% ~ 20% and has broad development prospects.
Shanghai Coking Plant (120 tons of coal/day)199410/month opened U gas, which was abnormal for a long time and stopped in early 2002. ICC Ash Melting Gasifier developed by Shanxi Institute of Coal Chemical Industry, Chinese Academy of Sciences, was tested on a 200 1 day synthetic gas industrial demonstration device of Shaanxi Chenghua Co., Ltd. 100 tons/day. CFB and PFB can produce fuel gas, but there is no precedent for producing synthetic gas in the world. Winkler has been used in synthesis gas production, but it has strict requirements on particle size and coal type, high methane content (0.7% ~ 2.5%) and low production intensity of equipment, which no longer represents the development direction. Entrained flow gasification is a kind of parallel flow gasification. There are two kinds of raw materials: coal water slurry and dry pulverized coal. In terms of patents, Texaco and Shell are the most representative. In the former, pulverized coal is first made into coal slurry and pumped into a gasifier at a gasification temperature of1350 ~1500℃; The latter is that the gasifying agent entrains pulverized coal into the gasifier and gasifies at the high temperature of 1500 ~ 1900℃, and the residue is discharged in the form of slag. In the gasifier, fine coal particles enter the reaction chamber through special nozzles, which will catch fire in an instant and directly produce flame reaction, and at the same time, they are in a state of insufficient oxidation conditions. Therefore, its pyrolysis, combustion and endothermic gasification reactions occur almost simultaneously. With the movement of gas flow, unreacted gasification agent, pyrolysis volatile matter and combustion products are wrapped by coal char particles and move at high speed, and the gasification reaction of coal char particles is carried out in motion. This movement state is equivalent to the "airflow transportation" of solid particles in the technical field of fluidization, which is customarily called entrained-flow gasification.
Entrained flow gasification has the following characteristics: (1) short residence time (generally1s); (2) High reaction temperature (usually1300-1500℃); (3) Small fuel particle size (solid and liquid, usually less than 0.1mm); ); (4) liquid slag discharge. In addition, entrained-flow gasification is usually operated under pressure (usually 20-50 bar) and pure oxygen.
Entrained bed gasification mainly has the following classification methods:
(1) can be divided into dry feeding and wet feeding according to the conveying performance of raw materials;
(2) According to the gasification pressure, it can be divided into atmospheric gasification and pressurized gasification;
(3) According to gasification agents, it can be divided into air gasification and oxygen gasification;
(4) According to the characteristics of slag, it can be divided into slag entrained flow bed and slag-free entrained flow bed.
In the slag entrained-flow gasifier, fuel ash is melted in the gasifier. The molten ash condenses on the relatively cold wall, eventually forming a protective layer, and then the liquid slag will flow out from the lower part of the gasifier along the protective layer. The amount of slag should ensure continuous slag flow. Generally, the mass flow of slag should be at least 6% of the total fuel flow. In order to form liquid slag with suitable viscosity at a given temperature, a substance called flux is usually added to the fuel. This flux is usually limestone and other calcium-rich substances. In the slagless entrained-flow gasifier, no slag is formed, which means that the fuel must contain a very small amount of minerals and ash, and the maximum ash content is usually 65438 0%. Due to the limitation of raw materials, slag-free entrained-flow gasifier is rarely used in industry.
Entrained bed has great compatibility with coal types (bituminous coal and lignite), particle size, sulfur content and ash. There are many single series, large capacity and pressure devices in operation in the world, and their cleanness and high efficiency represent the current technical development trend.
Dry powder is mainly supplied by K-T(Koppres-Totzek) furnace, Shell- Koppres furnace, Prenflo furnace, Shell furnace, GSP furnace and a b-CE furnace, while wet coal slurry is mainly supplied by Texaco gasifier and Destec furnace.
(1), Texaco gasifier
The coal-water slurry gasification process developed by Texaco Company (which became a part of Chevron Company in early 2002 and was acquired by GE Company in May 2004) is that coal is ground into coal-water slurry with a concentration of 60-65%, pure oxygen is used as gasification agent, and gasification reaction is carried out at high temperature and high pressure, the gasification pressure is 3.0-8.5 MPa, the gasification temperature is 1400℃, and liquid slag is discharged. The composition of coal gas is about 80% CO+H2, and it does not contain tar, phenol and other organic substances, so it has no pollution to the environment, with a carbon conversion rate of 96-99%, high gasification intensity, simple furnace structure, low energy consumption, high operation rate and wide application range of coal. At present, Texaco's largest commercial installation is Tampa Power Station, which belongs to DOE's CCT-3. It was established in 1989, put into operation in July, and 1996 was announced to enter verification operation in February. The device is a single furnace, with a daily processing capacity of 2000 ~ 2400 tons of coal, gasification pressure of 2.8MPa, oxygen purity of 95%, coal slurry concentration of 68%, cold gas efficiency of 76% and net power of 250MW.
Texaco gasifier consists of nozzle, gasification chamber and quenching chamber (or waste heat boiler). The nozzle has three channels, the process oxygen takes one or three channels, and the coal water slurry takes two channels, between the two oxygen jets. The nozzle of coal water slurry gasification often faces the problem of nozzle wear, which is mainly due to the erosion and corrosion of metal materials by coal water slurry at a high linear velocity (about 30m/s). Nozzle, gasifier and quench ring are the key technologies of Texaco coal water slurry gasification.
Since the end of 1980s, China * * * has introduced several Texaco coal-water slurry gasification units to produce syngas, and China has accumulated rich experience and knowledge in the design, installation, start-up and new technology research and development of coal-water slurry gasification.
Judging from the operation of the coal water slurry pressurized gasification device that has been put into operation, the main advantages are: the preparation, transportation and metering control of coal water slurry are simple, safe and reliable; The localization rate of equipment is high and the investment is low. Due to the imperfection of engineering design and operation experience, it has not reached the best state of long-term, high-load and stable operation, and there are still many problems. The main disadvantages are: the nozzle life is short, the quenching ring life is only one year, and the lignite pulping concentration is about 59% ~ 61%; The concentration of bituminous coal pulping is 65%; Because the water in gasified coal slurry consumes 8% coal, which is higher than the oxygen consumption of dry pulverized coal as raw material 12% ~ 20%, the efficiency is relatively low.
(2) Destec (global electronic gas) gasifier
Destek gasifier has built two sets of commercial devices, both in the United States: LGT 1 (gasifier capacity is 2,200 tons/day, 2.8MPa, 1987 put into operation) and Wabsh Rive (two furnaces, one for use and one for standby, single furnace capacity is 2,500 tons/day, 2.8MPa,1997 put into operation). It is divided into a first segment (horizontal segment) and a second segment (vertical segment). In the first stage, the two nozzles 180 degrees are opposite, and the impinging stream strengthens the mixing, which overcomes the defect that the Texaco furnace speed is bell-shaped (normal) distribution, and the highest reaction temperature is about 1400℃. In order to improve the cooling efficiency, in the second stage, 10% ~ 20% of the total coal slurry is used for cold quenching (different from Shell and Plumflo). The reaction temperature here is about 1040℃, and the outlet gas enters the fire tube boiler to recover heat. The molten slag flows down from the middle of the first section of the gasifier, and is solidified by water cooling to form slag slurry, which is discharged. The electric gas gasifier adopts a pressure spiral continuous slag discharge system.
The disadvantages of global E-Gas gasification technology are: short residence time of secondary coal water slurry and low carbon conversion rate; There is a huge separator to separate the ash in the primary gas from the ash and carbon residue in the secondary coal slurry. This furnace is suitable for producing fuel gas, but not synthetic gas.
(3) Shell gasifier
K-T gasifier is the earliest industrialized dry powder charging gasifier, and other gasifiers are developed on this basis. Shell successfully developed residue gasification in the early 1950s, and on this basis, it went through three stages: 1976, and tested more than 30 kinds of coal; 1978 cooperated with Krupp-Corpus (the predecessor of Krupp-Uhde) to build 150t coal plant in Harbin; After the two companies broke up, 1978, Luyuan, Houston, USA, processed 250t tons of high-sulfur bituminous coal or 400t tons of high-ash and high-moisture lignite every day. * * * It lasted 16 years, and from 1988, Shell coal technology was applied to the IGCC power station in Bougainvillea, the Netherlands. The design work of the device is 1.6 years, 1990, 10 month, 1993, 1994, 10 month, which has entered the three-year verification period and is now in the commercial operation stage. A stove can handle 2000 tons of coal a day.
The shell gasifier shell is about 4.5m in diameter, and the four nozzles are located on the same horizontal plane in the lower part of the furnace and evenly distributed along the circumference. With the help of impinging stream, the heat and mass transfer process is strengthened, and the gas velocity in the furnace section tends to be relatively uniform. The furnace lining is a water wall with a total weight of 500 tons. There is a gap of about 0.5m between the furnace shell and the water cooling pipe row, which is convenient for installation and maintenance.
The coal gas carries 20% ~ 30% of the total coal ash upward along the axis of the gasifier, and the circulating coal gas introduces quench near the top of the gasifier, and the quench gas accounts for about 60% ~ 70% of the generated coal gas. After cooling to 900℃, the slag solidifies, leaves the gasifier and enters the tubular waste heat boiler upward along the inclined pipeline. 70% ~ 80% of the total coal ash flows into the bottom of the gasifier in a molten state, freezes and solidifies, and is discharged from the bottom.
The pulverized coal is carried by N2 and delivered to the nozzle in the form of dense phase. Process oxygen (purity 95%) and steam also enter through the nozzle, and the pressure is 3.3 ~ 3.5 MPa. Gasification temperature 1500 ~ 1700℃, gasification pressure 3.0MPa, cold gas efficiency 79% ~ 81%; 13% of the calorific value of raw coal is converted into steam by a boiler; 6% sensible heat of gas from equipment and coolers is lost to atmosphere and cooling water.
Shell coal gasification technology has the following advantages: the oxygen consumption is lower than that of coal water slurry15%; The carbon conversion rate is high, reaching 99%, and the coal consumption is 8% lower than that of coal water slurry; It is convenient to adjust the load, and the load is reduced by 50% by closing a pair of nozzles; The furnace lining is a water wall, which is said to have a service life of 20 years and a nozzle life of 1 year. Main disadvantages: equipment investment is greater than coal water slurry gasification technology; The structure of gasifier and waste boiler is too complicated, which increases the processing difficulty.
Our company's direct liquefaction project uses this technology to produce hydrogen.
(4) GSP gasifier
GSP(GAS Schwarze Pumpe), known as "black water pump gasification technology", was successfully developed by the German Fuel Research Institute (DBI) in former East Germany on 1956. At present, this technology belongs to Future Energy GmbH (a subsidiary of Sustec Holding AG) established in 2002. GSP gasifier is a downward-jet pressurized entrained-flow liquid slag-discharging gasifier, and its coal feeding mode is similar to that of Shell, and its furnace structure is similar to that of Texaco gasifier. 1983 1983 the first set of industrial equipment was built by the black water pump joint venture, and the coal quantity of a single gasifier was 720 tons/day. 1985 was put into operation. At present, GSP gasifier is rarely used, only five plants have used it, and 1 has not been officially used in China. Ning Mei Group (controlled by our company) will introduce this technology into coal chemical projects.
In a word, entrained-flow coal gasification technology represents the development direction of gasification technology from the aspects of pressurization, large capacity and strong adaptability of coal types. The feeding state of coal water slurry and dry pulverized coal has its own advantages and disadvantages, and the boundary is not very clear. There are also different opinions in the domestic technical circles.