FGD demonstration project

The wet limestone/Lime-Gypsum FGD technology is the most popular technology in the world, which removes sulfur dioxide (SO2) from the flue gas by the absorbent (limestone slurry) process in the absorber. The production of the reaction calcium sulfite (CaSO3) is changed into gypsum (CaSO4·2H2O) by forced oxidation process. In the WLST process, the flue gas enters into the absorber through the inlet duct located in the middle of the absorber and contacts with limestone slurry in countercurrent. SO2 is absorbed by limestone slurry. After the mist eliminator clean gas flows upwards to the duct, and then is discharged into the atmosphere through stack. The limestone slurry absorbed SO2 reacts with oxygen at the bottom of the absorber to produce gypsum. The limestone slurry used in the FGD system is firstly produced by wet mill system, and then sent to absorber by pumps. The gypsum slurry in the absorber is discharged into gypsum hydrocyclone of dewatering system by bleed pumps. Then the underflow of hydrocyclone with 50% solid content goes into vacuum belt filter to produce gypsum solid containing free water less than 10%. The whole FGD process consists of seven main subsystems, including gas system, absorber system, absorbent preparation system, process water system, gypsum dewatering system, discharging & recycling system and compressed air system. The main WLST process type adopted by Fujian Longking are: cylindrical empty spraying absorber, countercurrent flow between absorbent and flue gas, absorption and oxidation taking place in the same tank, absorber equipped with spraying zone and forced oxidation. Compared with other desulphurization process, the characters of the WLST are as follows: Process Characters 1) Higher removal efficiency reaching over 95%. 2) Lower absorbent stoichiometric ratio, about 1.03. 3) Lower ratio of liquid to gas (L/G), which can reduce energy consumption of FGD system. 4) Higher purity byproduct gypsum, which can be reused comprehensively. 5) Using empty absorber not only cut down the radius of absorber to a great extent, but also reduces the inner components and the possibility of fouling. 6) Using cheap limestone as absorbent can effectively control the operation cost. 7) The system has a higher reliability with the availability over 98%. 8) The system is flexible to the change of the coal quality. While increasing the sulfur content, it remains higher removal efficiency. 9) The system is also flexible to the change of the boiler load and SO2 content. The FGD retains reliable with higher removal efficiency.