Power plant desulfurization
Guide: As China's environmental protection pressures increase year by year, national emission requirements are further tightened, and power plant flue gas desulfurization technology has also developed rapidly. At present, there are dozens of types of flue gas desulfurization technology. According to whether the desulfurization process adds water and the dry and wet form of desulfurization products, flue gas desulfurization is divided into three major types of desulfurization processes: wet, semi-dry and dry. The first two phases of power plant desulfurization technology have introduced the main wet desulfurization process and dry desulfurization process, and analyzed the advantages and limitations of various desulfurization processes. This paper introduces the advantages of combining dry and wet desulfurization processes. Semi-dry desulfurization process.
Through the introduction, everyone should have a basic understanding of the dry and wet desulfurization process. The main advantages of the wet desulfurization process are fast reaction rate and high desulfurization rate. The shortcomings will produce a large amount of waste water and easy to cause secondary pollution. The main advantage of the dry desulfurization process is that the by-product is solid, which is beneficial for comprehensive application, but the reaction rate is slow and the disadvantage of lower desulfurization rate is obvious. The semi-dry method is to use different state reactions for the desulfurization process and the desulfurization product treatment, especially the semi-dry method for desulfurization in the wet state and the desulfurization product in the dry state, and the wet desulfurization process has the fast reaction speed and the desulfurization efficiency. The high advantage has the advantage of the dry desulfurization process without the discharge of waste water and the treatment of desulfurization products in the dry state, which is an important development direction of the sulfur removal process.
Spray semi-dry method
Process introduction
Process introduction
The spray semi-dry method uses a spray drying principle to atomize an absorbent slurry into an absorption tower. In the absorption tower, the absorbent chemically reacts with the sulfur dioxide in the flue gas, absorbs the heat in the flue gas to evaporate and dry the water in the absorbent, and the waste residue after the desulfurization reaction is discharged in a dry state.
Advantages and disadvantages
The process is simpler than the limestone-gypsum method and the investment is small. The disadvantage is that the desulfurization rate is low, generally 70-80%, the operation flexibility is small, the calcium-sulfur ratio is high, the operation cost is high, and by-products cannot be utilized. The domestic use is less, and the Qingdao Huangdao Power Plant uses this process, and there are problems such as the accumulation of ash on the tower wall and the serious wear and tear of the atomizer.
Calcium spray tail humidification activation method
Process introduction
Process introduction
The ground limestone powder is sprayed by airflow to a region where the upper portion of the furnace is at a temperature of 900 to 1250 ° C, and CaCO 3 is immediately decomposed and reacted with SO 2 in the flue gas and a small amount of SO 3 to form CaSO 4 . The unreacted CaO in the furnace in the activator reacts with the injected water to form Ca(OH)2, which reacts rapidly with Ca(OH)2 to form CaSO3, which is partially oxidized to CaSO4.
Advantages and disadvantages
The advantage is that the equipment investment is small, but under the condition of calcium injection in the furnace, CaCO3 pyrolysis produces high activity CaO. Although it is difficult to obtain a high desulfurization rate directly in the furnace, the CaO which is not reacted with SO2 in the furnace is behind the boiler. The water spray humidification and hydration are Ca(OH)2, which can react with SO2 again at low temperature, which can significantly improve the system desulfurization rate and the utilization rate of calcium-based sorbent, but the desulfurization rate is generally 60%-70%. In general, the desulfurization rate in the furnace and the utilization rate of the calcium-based sorbent are not high enough, and the competitiveness of the technical and economic performance is not strong enough.
Flue gas circulating fluidized bed method
Process introduction
Flue gas circulating fluidized bed method
The flue gas containing dust and SO2 from the boiler rises from the bottom of the desulfurization tower through the venturi and enters the tower. The quicklime is digested with water in the digester and stored in the slaked lime silo. A certain amount of slaked lime powder and water are added to the upper end of the venturi throat, mixed with the flue gas in the desulfurization tower, and reacted with SO2 in the flue gas to form calcium sulfite and calcium sulfate. The flue gas carrying the reaction product and coal ash is cooled to a temperature slightly above the dew point and enters the back bag filter. After the reaction product and the coal ash are treated by the dust remover, they are returned to the tower through the air chute, and are again circulated to participate in the desulfurization reaction. In the flue gas purification of waste incinerator, the end of activated carbon is added before the precipitator, and the cycle is repeated to achieve the effect of removing heavy metals and dioxins. The desulfurized ash is discharged into the ash silo through the silo pump. Since the slaked lime, coal ash and reaction products are circulated repeatedly between the desulfurization tower and the precipitator, the reaction time is increased, the effect of the slaked lime is fully exerted, the amount is reduced, and the desulfurization efficiency is improved.
Advantages and disadvantages
Flue gas circulating fluidized bed method has high desulfurization efficiency, and can achieve more than 90% desulfurization efficiency for high sulfur coal (containing more than 3% sulfur). It is the largest single tower treatment capacity in dry and semi-dry desulfurization technologies. And one of the most advantageous methods for comprehensive desulfurization benefits ;)
Due to the recycling of the bed material, the utilization rate of the absorbent is improved; under the same desulfurization efficiency, the absorbent can be saved by 30% compared with the conventional semi-dry method; the desulfurization product is solid ash discharged in the solid state; . The main disadvantage is the poor adaptability to boiler load changes; desulfurization and dust removal affect each other, and dedusting equipment must be added with dust removal equipment, and the operation control requirements are high.
Suggest
Comprehensive comparison of various desulfurization processes, the current design requirements of desulfurization equipment are high-capacity units or designed coal type sulfur containing more than 2% of the preferred wet process, desulfurization efficiency requirements of more than 90%. For older units with a capacity of less than 200 MW or a remaining life of less than 10 years, and units with a sulphur content of less than 2% for the design of coal, it is recommended to use dry, semi-dry or other relatively economical desulfurization technology. The desulfurization efficiency requirement is only 75. %. The specific selection method selects the best economic benefit process according to factors such as absorbent, water, by-product market and specific requirements.
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