Experimental And Theoretical Study On Circulating And Suspension Semi-dry Flue Gas Desulfurization

Compared with wet lime/limestone flue gas desulphurization technology (WFGD), semi-dry flue gas desulphurization technique(SDFGD) has many advantages, such as lower investment, dry production,etc. But the low utilization ratio of absorbent is fatal factor which limits the widely application of SDFGD. With these factors in mind, current technologies of semi-dry flue gas desulfurization are reviewed while focus on the removal efficiency and utilization of calcium-based sorbents.On the bases of great number of international and national references, one novel semi-dry flue gas desulfurization-Circulating and Suspension SDFGD Technology, which is new in China and suitable for the current situation in China, is presented in this paper. A bench scale test facility was designed and built. The process features simple design, operational reliability, low maintenance costs and removal of heavy metal.An experimental study has been performed on the semi-dry FGD. The influence of operation parameters on SC>2 removal has been investigated. The approach to saturation temperature and Ca/S mole ratio influence SOa removal strongly. The optimum operating parameters have been got. The optimum approach to saturation temperature is about 10癈, the optimum CA/S ratio 1.5, the optimum recycle ratio 5, and the optimum humidified water is about 30 percent of total water evaporated.The effects of additives were studied directly in the semi-dry FGD process. Hygroscopic additives had significant effects on improving lime utilization and SC>2 removal; Buffer additives had little or no effect. The mechanisms responsible for improvements in performance with the use of additives were investigated and discussed. Experiments showed that over 90% removal of SC? could be achieved in this semi-dry FGD process with the appropriate use of additives and operating conditions.An mathematical model in constant rate desiccation stage of SDFGD was built in this paper. The model of FGD tower was based on film theory and treated the atomized slurry droplet as a sphere with the fluid phase uniformly distributed around the discrete individual sorbent particle. Both the gas phase mass transfer and liquid phase mass transfer coefficients were included in the tower model along with a relationship to predict the resistance to lime dissolution. This approach was said to allow predictions of the mass transfer coefficients and to model the enhancement due to increasing solid concentration as evaporation proceeds. It can be seen that the calculated results from the model agreed well with the experimental results.