Experimental And Theoretical Study On Semi-dry Flue Gas Desulfurization

Semi-dry flue gas desulfurization techniques are more and more widespread used because of its relatively simple constitution and lower capital and operating costs. Further more, the waste product is dry powder and easy to deal with. But the higher operating costs incurred due to poor sorbent utilization may make them uneconomical for application to medium or high-sulfur coal application. Some measures must be taken to solve this problem in order to decrease the operating costs and increase sorbent utilization and efficiency of SO2 removal. Some works have been done is presented in this paper.The effect of four hydration procedure parameters (initial temperature of hydrating-water, hydration time, water/solid ratio, and agitation rate) on desulfurizer's structural properties (particle surface area and particle porosity) was studied using orthogonal experimental method. The optimal value of the procedure parameters was obtained under the experimental conditions, which were 85 C for initial temperature of hydrating-water, 1 hour for hydration time, 4:1 for water/solid ratio, and 0.98m/s for agitation rate. A relatively optimal hydration condition was put forward.The porosity, specific surface area and desulfurization reactivity of hydrated lime prepared with different additives were tested. Certain amount of some additives increase the specific surface area and porosity of hydrated lime relative to those obtained without additives. In the desulfurization test, the sorbents prepared with those additives showed a greater increase in the desulfurization efficiency. This behavior is related to the change in structural characteristics. Effect of Compound additives that were made of two of those additives at different weight ratio on structural characteristics and desulfurization reactivity of sorbents was studied. Some compound additives that have greater desulfurization reactivity were obtained, and the relatively optimal weight ratio of constituent of these compound additives were put forward.An experimental study of semi-dry flue gas desulfurization(FGD) in a circulating fluidized bed has been performed. The influence of operation parameters, recycle of desulfurization ash, water spray humidification, stage slurry spraying and additions on SO2 removal has been investigated. The optimum operating parameters have been got. Results of experiment show that the approach to saturation temperature, Ca/S mole ratio and average diameter of slurry drops influence SO2 removal strongly. In consideration of the safety of F.F. and the operating cost, the optimum approach to saturation temperature is about 10C, theoptimum Ca/S ratio is 1.5, the optimum average diameter of slurry drops is about 75 m to 80 m . The efficiency of SO2 removal in absorption tower under the condition of approach tosaturation temperature 10C, Ca/S ratio1.5, average diameter of slurry drops 75 rn , inlet fluegas temperature 160C, velocity of flue gas in tower 3.2 + 0.lm/s and inlet concentration of SO2 800ppm is about 63%, and the total efficiency is about 87%. So the efficiency of F.F. is about 24%. Influence of other operation parameters on SO2 removal is not obvious.Water spray humidification can enhance the desulfurization performance of sorbents, andthe desulfurization efficiency of multistage water spray humidification is higher than single stage humidification when the amount of humidified water is large enough. The total desulfurization efficiency is higher than other mode of distribution when the humidified water decreasing geometrically in multistage water spray humidification. The optimum parameter values of humidified water are 30 percentage of total water evaporated, three stages spraying and geometrical decreasing mode of distribution. The efficiency of SO2 removal in absorption tower and in the whole system are 68% and 87% under above conditions.Recycle of desulfurization ash can also enhance the desulfurization performance of sorbents. The efficiency of SO2 removal in absorption tower and in the whole system are reached to 70.44% and 91.79% under...