Study On Improving The Removal Of Fine Particles And SO₃ Acid Mist In Coal-fired Flue Gas By Heterogeneous Condensation

The emissions of fine particles and SO₃ acid mist in coal-fired power plants are still difficult to be effectively controlled and large amount of them discharge into the atmosphere,leading adverse impacts to human health and environment.Heterogeneous vapor condensation is one of the most promising preconditioning techniques for improving the removal of fine particles and SO₃ acid mist.Fine particles and SO₃ acid mist are activated and enlarged by heterogeneous vapor condensation,and then the grown ones can be removed by the traditional pollution control equipment.According to the features of traditional pollution control equipments in coal-fired power plants,it is of great significance to improve the removal efficiency of traditional pollution control equipment for fine particles and SO₃ acid mist by heterogeneous vapor condensation.To investigate the removal of coal-fired fine particles and the formation of generated fine particles during the desulfurization process by heterogeneous vapor condensation,the experiments were carried out in a self-design wet flue gas desulfurization（WFGD）system.The results indicate that the supersaturation atmosphere can be established by increasing the humidity and reducing the temperature of the flue gas before WFGD system.In desulfurization process,the application of the heterogeneous vapor condensation not only leads to an improvement of coal-fired fine particle removal（especially for the fine particles with the size in the range of 0.1-1μm）,but also causes an inhibition of generated fine particle formation（especially for the fine particles with the size in the range of 1-10 μm）.For the high-humidity flue gas,which is generated by burning lignite,water-coal-slurry,biomass et al,a novel process was proposed to improve the removal of fine particles and S03 acid mist by heterogeneous condensation during WFGD processes.The results indicate that the removal efficiency of fine particles and SO₃ acid mist can be improved by the increase of the inlet flue gas moisture and liquid-to-gas ratio.However,higher temperatures of inlet flue gas and desulfurization slurry are adverse to the improvement of removal efficiency.With the application of this method,the number removal efficiency of fine particles can be improved from 5-10%to 35-45%,and the mass removal efficiency of SO₃ acid mist can be improved from 35-40%to 55-65%.Furthermore,for the high-humidity flue gas with high-temperature and high-sulfur（SO₃）,the other novel process,which is based on the condensation of SO₃ and water vapor,was further proposed to abate the emission of fine particles and SO₃ acid mist.In this process,the removal efficiencies of electric precipitator（ESP）and WFGD system for fine particles and SO₃ acid mist are improved simultaneously.The results indicate that the higher SO₃ concentration in flue gas and the larger temperature reduction before ESP are beneficial for the improvement of the removal of fine particles and SO₃ acid mist,while the higher flue gas temperature is unfavourable.With the application of this method,the fine particle emissions in the final exhausted flue gas can be reduced by 35-45%,and the SO₃ acid mist emissions can be reduced by 65-75%.For the high-humidity flue gas,which is generated by burning anthracite,bitumite,et al,a novel process based on heterogeneous vapor condensation in desulfurized flue gas was proposed to reduce the emission of fine particles and SO₃ acid mist in final exhausted flue gas.First,the supersaturation atmosphere is established by adding humid air into desulfurized flue gas.The results indicate that with the increasing of mixing ratio and desulfrized flue gas humiture,the emission of fine particles and SO₃ acid mist decrease.With the increase of humid air temperature,the emission of fine particles and SO₃ acid mist increase.Moreover,the humidity of humid air only has a little influence.With the application of this method,the fine particle emissions in the final exhausted flue gas can be reduced by 25-45%,and the SO₃ acid mist emissions can be reduced by 15-35%.Since the supersaturation atmosphere established in the desulfurized flue gas by adding humid air is not uniform,the other novel process,which combined of heterogeneous vapor condensation and two impinging streams（TIS）,was further proposed to reduce the emissions of fine particles and SO₃ acid mist.In this process,fine particles and SO₃ acid mist can not only be enlarged by heterogenous vapor condensation in supersaturation atmosphere,but also can be enlarged by collision-coalescence in impinging region.With the application of this method,the fine particle emissions in the final exhausted flue gas can be reduced by 40-50%,and the SO₃ acid mist emissions can be reduced by 30-40%.Furthermore,the process for establishment of supersaturation atmosphere by decreasing desulfurized flue gas temperature via heat exchanger was proposed.The results indicate that the influence of original desulfurized flue gas temperature is not obvious,thus the applicability of this process is better.With the application of this method,the fine particle emissions in the final exhausted flue gas can be reduced by 35-40%,and the SO₃ acid mist emissions can be reduced by 35-45%.For the single-scrubber with dual circuit（SSDC）desulfurization process and double-scrubber with dual circuit（DSDC）desulfurization process,the novel processes were proposed to establish the supersaturation atmosphere in absorption region of SSDC and second scrubber of DSDC via the application of a heat exchanger.The results indicate that for the single-scrubber with dual circuit,the removal of fine particles and SO₃ acid mist can be improved by decreasing the temperature of slurry in absorption region and increasing the liquid-to-gas ratio in absorption region.With the application of this method,the number removal efficiency of fine particles can be improved from 20-25%to 40-50%,and the mass removal efficiency of SO₃ acid mist can be improved from 35-40%to 50-60%.For the double-scrubber with dual circuit,the higher temperature drop in heat exchanger and the higher liquid-to-gas ratio in second scrubber are benefical for the removal of fine particles and SO₃ acid mist.With the application of this method,the number removal efficiency of fine particles can be improved from 40-45%to 55-65%,and the mass removal efficiency of SO₃ acid mist can be improved from 60-65%to 70-80%.