■Two techniques :
Circulating semi-dry method; lime / limestone-gypsum wet FGD technique.
■ Basic Principles:
Circulating semi-dry method or NID Technique: Use lime (CaO) or Ca (OH) 2 dry powder as desulfurizer which to be neutralized with SO2 in flue gas after assimilation. The final products in dry power state to be collected by ESP or Fabric Filter.
Lime/limestone–Gypsum Wet FGD Technique:Dust-removed flue gas uses lime or limestone milk as desulfurizer to absorb SO2, and the ultimate product is gypsum.
■ Performance Parameters:
Circulating Semi-dry Method: Desulfurizing rate can reach more than 90% when calcium-sulfur ratio to be 1.2~1.3.
Wet-Method Technique: Desulfurizing rate can reach more t han 95% when calcium-sulfur ratio to be ≤1.05.
For flue gas desulphurization applied for coal-fired power plants and industrial furnaces and kilns,normally circulating semi-dry method is suitable for units less than 300MW, while Lime/Limestone-Gypsum wet method is adaptable for large-scale units.
Circulating Semi-dry Method: Compact structure, simple process, small area occupancy, low investment, low operation cost, no generation of effluent, and high cost-performance ratio.
Lime / Limestone-Gypsum Wet Method of FGD Technique: High desulfurizing rate, low calcium – sulfur ratio, reliable operation, and high operation cost.
Dozens of products have been put into operation, of which circulating semi-dry method has the greatest performance among similar techniques in China.