desulphurization process for CFB

desulphurization process

MxG---B Drier desulphurization Process Description

CFB desulphurization process is made up of absorbent preparation system, absorption tower, re-circulatory system, dust catcher, gas system, sprinkler system, ash handling system, electrical systems and control system and so on.

The flue gas comes out from the preheater will be introduced into the Venturi device in the bottom of the absorption tower through the dust catcher and at the same time the flue gas will be accelerated when it is walking.

Absorbent through one set of spraying device inject into the lower part of the tower and set up a sprinkler equipment at the entrance of Venturi, and the atomized water which is injected make the temperature of the  flue gas down into about 70-90 and the high-speed flue gas continue to mist the flue gas. The humidifier flue gas combine with the absorbent and the absorbent react with the S02 in the flue gas to produce into calcium sulfite, calcium sulphate and so on. The flue gas with a large of particles discharge from the upper of the absorbing tower and then into the second dust catcher (Bag dust catcher or electricity dust catcher). Most of the solid particles through the re-cycle system under the dust catcher return to the absorption tower so that could continue to make reaction, and like this circulation come to 100-250 times. After through the ash residue handling system, a small number of desulphurization residue into residue house.  

After purification, the flue gas through the suction fan into the chimney. As the flue gas temperature above the dew point temperature of 15-20 and so no need reheating for flue gas.

CFB chemical principle is Ca (OH) 2 powder, S02 in the smoke and air and almost all S03, HCl, HF and so on under the condition of moisture, will react on the surface of Ca (OH) 2 particle for liquid-phase. Within the circumfluence flue gas circulating fluidized bed, Ca(OH)2  powder, gas and injected water under the fluid state will be mixed completely and through several recycled  for Ca(OH)2 in order to achieve desulphurization efficiently.

The following reaction describes the reaction in the RCFB absorption tower during the temperature of 70 ~ 90 .

S02 was the absorbed by droplets: S02 + H20-+ H2S03
S02 which have been absorbed at react with the absorbent to introduce into the calcium sulfite: Ca(OH)2+H2S03---'CaS03+2H20
S02 directly react with the absorbent to into the calcium sulfite: S02 + Ca (OH) 2 - CaS03
Some CaS03 contact with  the excess oxygen in flue gas, oxidation into calcium sulfate: CaS03 +1 / 202 → CaS04

  In the absorption tower, the average speed for the flue gas will be controlled within the 45ms, and the speed is relatively low, the flue gas residence time in the tower is more than four seconds making more than 95% desulphurization carried out in the tower; At the entrance of the absorption tower will be equipped, and about 30% of the absorbent cycles to further enhance the collision between the absorbent and constantly exposed the new the new surface of the absorbent particles and again react with S02 to increase the  using rate for absorbent.

After the desulphurization, the flue gas with a large number of solid particles discharge from the top of the tower and into the second dust catcher to deal with. Some particles separated from the Elec-dust catcher using air flume with measurement device return to the gas absorption tower, and as the high absorbent circulation rate, the absorbent staying time up to 20 to 60 minutes that can greatly improve the utilization of absorbent. Through the cycle, the vapor could mix completely and assure the moisture content is  less than 1 in the desulphurization residue. This process not only prevents the ash felt, corrosion, but also be favorable to the ash delivery. The small particles that discharge outside the electro-precipitator can be directly taken through the positive pressure pneumatic conveying system to the residue storehouse, SINOTRANS using. Having been desulphurization for boiler flue gas, dust catcher remove dust could reach the national emission standards and by induced draft fan emission the flue gas to chimney