IGCC integrated coal gasification combined cycle power generation system is an advanced power generation system that combines coal gasification technology with high efficiency combined cycle. It consists of two parts, namely, coal gasification purification part and gas-steam combined cycle power generation part. The first part mainly includes gasifier, air separation unit and gas purification unit (including sulfur recovery unit), and the second part mainly includes gas turbine power generation system, waste heat boiler and steam turbine power generation system. The process flow of IGCC is: gasifying coal into gas with medium and low calorific value, removing pollutants such as sulfide, nitride and dust from the gas after purification to become clean gas fuel, and then sending it to the combustion chamber of the gas turbine for combustion, heating the gas working medium to drive the gas turbine to do work, and the exhaust gas of the gas turbine enters the waste heat boiler to heat water, generating superheated steam to drive the steam turbine to do work. The schematic diagram is shown below.
IGCC technology combines efficient gas-steam combined cycle power generation system with clean coal gasification technology, which has high power generation efficiency and excellent environmental protection performance, and is a promising clean coal power generation technology. Under the current technical level, the net efficiency of IGCC power generation can reach 43% ~ 45%, and it is expected to reach higher in the future. However, the pollutant emission is only110 of the conventional coal-fired power station, the desulfurization efficiency can reach 99%, and the sulfur dioxide emission is about 25 mg/nm3. (At present, the national sulfur dioxide is 1200mg/nm3), the emission of nitrogen oxides is only 15%-20% of that of conventional power plants, and the water consumption is only1/2-13 of that of conventional power plants, which is beneficial to environmental protection.
Classification and function of integrated coal gasification combined cycle power generation
As can be seen from the figure, the whole IGCC system can be roughly divided into several parts: coal preparation, coal gasification, heat recovery, gas purification and gas turbine and steam turbine power generation. There are three possible schemes for coal gasifier: spouted bed, fixed bed and fluidized bed. In the whole IGCC equipment and system, gas turbine, steam turbine and waste heat boiler are very mature products that have been commercialized for many years, so the key to the final commercialization of IGCC power generation system is coal gasifier and gas purification system. Specifically, the requirements for IGCC gasifier and gas purification system are:
A) The gas production rate, calorific value, pressure and temperature of the gasifier meet the design requirements.
B) Gasifier has good load regulation performance, which can meet the requirements of power plant for load regulation.
C) The composition and purification degree of gas shall meet the requirements of gas turbine for load regulation.
D) It has good adaptability of coal.
E) The system is simple, the equipment is reliable, the operation is simple, the maintenance is convenient, and it has the availability required for the long-term safe and reliable operation of the power plant.
F) Low investment and operation cost of equipment and systems.
1) spouted bed gasifier
Spouted bed is the most widely used gasifier in IGCC demonstration project at present. It is a high temperature and high pressure pulverized coal gasifier. The pressure of the gasifier is 20-60bar, and more than 90% of pulverized coal particles are required to be less than100 μ m. Oxygen, oxygen-enriched air or steam are used as gasifying agents. When oxygen is used as gasifying agent, the flame temperature in the center of gasifier can reach 2000℃. Due to high temperature gasification, it is impossible to contain many hydrocarbons, coal tar and phenols in the produced crude gas. The main components of gas are carbon monoxide, H2, carbon dioxide and steam. The temperature of hot gas leaving the gasifier is 1200- 1400℃, which is usually higher than the softening temperature of ash. In order to prevent the sticky fly ash softened in the hot gas from sticking in the downstream equipment (waste heat boiler) of the gasifier, the dedusted cold gas is pressurized and sent back to the outlet of the gasifier to be mixed with the hot gas, and the temperature of the hot gas is reduced to 50℃ below the softening temperature of the fly ash. Then the hot gas passes through the waste heat boiler of the gasifier (radiation and convection steam occur smoothly) to generate saturated steam, and the temperature of the hot gas is reduced to about 200℃, which is about 50% of that of coal.
Fly ash is heated together with gas in the form of fly ash, and the auxiliary gas must be dedusted, washed and desulfurized to become clean gas, and then sent to the combustion chamber.
Because the spouted bed gasifier gasifies pulverized coal at high temperature and high pressure, the adaptability of coal species is wide and the carbon conversion rate is high, which can reach more than 99%.
At present, the spouted bed gasifiers used in IGCC demonstration plants in Europe and America include Texaco and CE furnaces in the United States, Shell furnaces in the Netherlands and Prenflo furnaces in Germany. Coal feeding methods include wet coal-water slurry feeding (such as Texaco furnace) and dry coal feeding (such as Shell and Plumflo furnace).
Because of its large capacity, high efficiency and wide fuel adaptability, spouted bed gasifier has strong competitiveness in developing IGCC power plants with large capacity and high efficiency in the future.
2) Fluidized bed gasifier
Fluidized bed gasifier can make full use of the high-intensity heat and mass transfer between gas and solid in the bed, so that the temperature distribution in the whole bed is uniform and the mixing conditions are good, which is beneficial to gasification reaction. At the same time, low-temperature fluidized bed combustion can be used, and desulfurizer (limestone or dolomite) can be added during combustion and gasification to remove most SO2 and H2S. Because the reaction temperature in the fluidized bed gasifier is generally COntrolled at 850- 1000℃, macromolecular organic substances such as tar, hydrocarbons, phenol, benzene and naphthalene can be basically decomposed into simple diatomic or triatomic gases, the main costs of which are co and H2, and the content of CH4 is generally less than 2%.
At present, the fluidized bed gasifier used in IGCC system includes KRW furnace, U-shaped gas furnace and Winkler furnace.
3) Fixed bed gasifier
Fixed-bed gasifier is the earliest developed gasifier, similar to coal-fired gasifier. The lower part of the furnace is a grate supporting the upper coal seam. Usually, coal is added from the top of the gasifier, and the gasifying agent (oxygen or air and steam) is supplied from the lower part of the gasifier, so the gas-solid flow is reversed. This kind of gasifier, like the coal-fired layer furnace, has certain requirements for coal particle size.
There are two kinds of outlet group designs for fixed bed gasifier. The only outlet of raw gas is designed at the top of the coal seam above the drying area, which is called a single-stage gasifier. At this time, the temperature of the gas at the outlet is 370-590℃. At this gas temperature, gas oil and coal tar will undergo cracking and polymerization reactions, thus generating different tar and asphalt. At the same time, when the high temperature gas passes through the coal seam, the coal will burst, producing a lot of coal dust, which will be taken out of the gasifier with the raw gas. Therefore, the crude gas quality of this single-stage gasifier is relatively poor. Another design is that there are two gas outlets, except the outlet at the upper part of the drying zone, and the other is at the top of the gasification zone, and half of the gas output leaves the gasification zone. Because the amount of gas flowing through the volatile analysis area and the drying area is only the amount of single-stage furnace, it is beneficial to prevent coal explosion from producing a large amount of coal dust and will not produce temporary tar and asphalt. Therefore, the quality of crude gas produced by two-stage furnace is relatively good.
The fixed-bed gasifier used in IGCC system is mainly Lurgi gasifier, and the first IGCC demonstration plant in Germany in the world adopts Lurgi fixed-bed segmented solid slag removal gasifier. The biggest disadvantage of this gasifier is that when coking coal is used, it is easy to block the bed, resulting in poor airflow and unstable gas quality. In addition, since it takes 0.5- 1 hour for coal to slowly move down into ash in the gasifier, the gasification capacity of a single gasifier cannot be designed to be very large. Moreover, the discharged gas also contains a lot of asphalt, coal tar and phenol, which makes the gas purification process very complicated. In order to improve the above problems and strengthen the gasification process of coal, British Gas Company developed it into a liquid slag Lurgi furnace on the basis of solid slag Lurgi furnace. Because of the high temperature in the combustion zone, the liquid slag gasifier is beneficial to improve the oxidation rate of coal and the conversion rate of carbon, and shorten the residence time of coal in the furnace. The diameter of coal particles is wider than that of solid slag gasifier. But the particle size less than 6mm should be limited to 10%. The liquid slagging gasifier has the following characteristics: 1) The carbon conversion rate is the highest among the three gasifiers, and the physical heat loss of slagging is large. 2) relatively safe and reliable; 3) The gas production capacity is limited, which is the lowest among the three furnace types.
Related information:
The world's largest IGCC power station has passed the feasibility study review.
Minutes of the Review Meeting of Feasibility Study Report of CLP Langfang IGCC Thermal Power Plant Project
The review meeting of feasibility study report of Datang Shenzhen IGCC project was held in Shenzhen
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