The flue gas circulating fluidized bed desulfurization process consists of absorbent preparation, absorption tower, desulfurization ash recycling, dust collector and control system. In this process, dry hydrated lime powder is generally used as absorbent, and other dry powder or slurry with absorption and reaction ability to sulfur dioxide can also be used as absorbent.
The untreated flue gas discharged from the boiler enters from the bottom of the absorption tower (i.e. fluidized bed). There is a venturi device at the bottom of the absorber. The flue gas accelerates after flowing through the venturi tube, and is mixed with very fine absorbent powder here. There is fierce friction between particles and between gas and particles to form a fluidized bed. Under the condition of spraying uniform water mist to reduce the flue gas temperature, the absorbent reacts with sulfur dioxide in the flue gas to form CaSO3 and CaSO4. After desulfurization, the flue gas carrying a large amount of solid particles is discharged from the top of the absorption tower and enters the recycling dust collector. The separated particles return to the absorption tower through the middle ash bin. Because the solid particles are recycled for hundreds of times, the utilization rate of absorbent is high.
The by-product produced by this process is in the form of dry powder. Its chemical composition is similar to that of the spray drying desulfurization process. It is mainly composed of fly ash, CaSO3, CaSO4 and unreacted absorbent Ca (OH) 2. It is suitable for waste mine backfilling, road foundation, etc.
For typical flue gas circulating fluidized bed desulfurization process, when the sulfur content of coal is about 2% and the calcium sulfur ratio is not greater than 1.3, the desulfurization rate can reach more than 90% and the flue gas temperature is about 70 ℃. This process is currently used in 100000 ~ 200000 kW units abroad. Because of its small floor area and low investment, it is especially suitable for flue gas desulfurization of old units.
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