单塔双循环烟气脱硫系统结晶过程的模拟研究
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摘要
单塔双循环湿法烟气脱硫系统中,二水硫酸钙结晶是影响该工艺运行的关键技术之一。在单因素条件下分别研究晶种浓度、晶种粒径、相对过饱和度(RS)和p H值对硫酸钙结晶速率、晶体粒径、形貌以及结垢特性的影响。结果表明:晶种浓度和粒径对二水硫酸钙结晶影响显著,当晶种过100目筛,适当增加晶种浓度(C≤2 g/L),有利于晶体快速生长,且晶体生长得更为粗壮和均匀,结垢量也不断减少;相对过饱和度增大会大大提高结晶速率,但适中的相对过饱和度(RS=6)更利于形成以片状和棒状为主且粒径分布均匀的晶体,结垢量相对较少;反应溶液p H在5~6之间时,结垢量少,对晶体形貌有利且与脱硫塔中实际酸碱度相符。以上结论对单塔双循环脱硫工艺具有一定的参考价值。
Crystallization of calcium sulphate dihydrate is one of the key technologies that affect the operation of the process in single-tower and double-cycle wet flue gas desulfurization system. In a bench scale experiment the effects of parameters such as seed concentration, seed size, relative super-saturation(RS) and p H value on the crystallization rate, crystal size and morphology as well as scale formation were studied. The experimental study suggested that seed crystal concentration and grain size greatly affected the crystallization of calcium sulphate dehydrate, and when seed crystal exceeded 100 mesh, properly increasing seed concentration(C≤2 g/L) was conducive to rapid crystal growth, which led to the advantages: crystal growth was more uniform and the amount of scale reduced; with the increases of relative supers-saturation, the crystallization rate was greatly improved, but the moderate super-saturation condition(RS=4) would be more favorable to formation of lamellar and rod-like crystals with uniform particle size distribution, amount of scale is relatively small; when p H value of the reaction solution ranged between 5 and 6, conforming to the actual p H value in the desulfurization tower, the amount of scale declined and crystalline grain became bigger with the ideal morphology.
Crystallization of calcium sulphate dihydrate is one of the key technologies that affect the operation of the process in single-tower and double-cycle wet flue gas desulfurization system. In a bench scale experiment the effects of parameters such as seed concentration, seed size, relative super-saturation(RS) and p H value on the crystallization rate, crystal size and morphology as well as scale formation were studied. The experimental study suggested that seed crystal concentration and grain size greatly affected the crystallization of calcium sulphate dehydrate, and when seed crystal exceeded 100 mesh, properly increasing seed concentration(C≤2 g/L) was conducive to rapid crystal growth, which led to the advantages: crystal growth was more uniform and the amount of scale reduced; with the increases of relative supers-saturation, the crystallization rate was greatly improved, but the moderate super-saturation condition(RS=4) would be more favorable to formation of lamellar and rod-like crystals with uniform particle size distribution, amount of scale is relatively small; when p H value of the reaction solution ranged between 5 and 6, conforming to the actual p H value in the desulfurization tower, the amount of scale declined and crystalline grain became bigger with the ideal morphology.
引文
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[2]燕中凯,刘媛,岳涛,等.我国烟气脱硫工艺选择及技术发展展望[J].环境工程,2013,31(6):58-61,66.Yan Zhongkai,Liu Yuan,Yue Tao,et al.Selection of flue gas desulfurization process and prospects of desulfurization technology development[J].Environmental Engineering,2013,31(6):58-61,66.
[3]GB 13223-2011,火电厂大气污染物排放标准[S].GB 13223-2011,Emission Standard of Air Pollutants for Thermal Power plants[S].
[4]Johnosn D W,Murphy D W,Myers R B.Collection Scoop for Flue Gas Desulfurization System with Bleed Streams or EX SITU Forced Oxidation:United States Patent;US007294322B2[P].2007-11-13.
[5]唐小健.双循环单塔脱硫系统及工艺:中国专利,CN102764583A[P].
[6]李元,杨志忠.湿法烟气脱硫关键影响因素及新型单塔双循环技术[J].环境工程,2016,34(1):69-73.Li Yuan,Yang Zhizhong.Influence of key factors on limegypsum wet flue gas desulfurization and two circulations per tower technology[J].Environmental Engineering,2016,34(1):69-73.
[7]蒋惠梦,余苏玲,肖述明,等.湿法烟气脱硫喷淋塔的持液特性[J].环境工程学报,2017,11(3):1746-1754.Jiang Huimeng,Yu Suling,Xiao Shuming,et al.Liquid holdup characteristic of wet flue gas desulfurization spraying scrubber[J].Chinese Journal of Environmental Engineering,2017,11(3):1746-1754.
[8]Miao M,Xin F,Wen S,et al.Direct transformation of FGD gypsum to calcium sulfate hemihydrate whiskers:preparation,simulations,and process analysis[J].Particuology,2015(19):53-59.
[9]闫维明.湿法脱硫中吸收塔浆液固体成分与石膏脱水的关系探讨[J].热力发电,2009,38(1):99-100.Yan Weiming.An approach to the relationship between solid components in slurry of absorbtive tower and dehydration of gypsum in the desulphurization system[J].Thermal Power Generation,2009,38(1):99-100.
[10]Annalize K,Walter W F,Zola K,et al.Effect of ionic impurities on the crystallization of gypsum in wet-process phosphoric acid[J].Industrial&Engineering Chemistry Research,2001,40(5):1364-1369.
[11]徐海,郦和生,王岽.硫酸钙结晶过程及其影响因素研究[J].工业水处理,2011,31(5):67-69.Xu Hai,Li Hesheng,Wang Dong.Study on Ca SO4crystallization process and its influential factors[J].Industrial Water Treatment,2011,31(5):67-69.
[12]徐宏建,潘卫国,郭瑞堂,等.二水硫酸钙结晶特性的影响研究[J].热力发电,2010,39(11):45-48.Xu Hongjian,Pan Weiguo,Guo Ruitang,et al.Study on affecting factors upon behavior of Ca SO4·2H2O crystallization[J].Thermal Power Generation,2010,39(11):45-48.
[13]刘同海.湿法磷酸体系中二水硫酸钙结晶过程的研究[D].合肥:合肥工业大学,2016.Liu Tonghai.Study on the Crystallization Process of Calcium Sulfate Dihydrate in the Wet Process Phosphoric Acid System[D].Hefei:Hefei University of Technology,2016.
[14]陈曲仙,杨柳春,陈敏,等.二水硫酸钙结晶的影响因素研究[J].湘潭大学:自然科学学报,2014,36(3):60-66.Chen Quxian,Yang Liuchun,Chen Min,et al.Study on the influence factors of calcium sulfate dihydrate crystallization[J].Journal of Xiangtan University:Natural Science,2014,36(3):60-66.
[15]Rashad M M,Mahmoud M,Ibrahim I A,et al.Crystallization of calcium sulfate dihydrate under simulated conditions of phosphoric acid production in the presence of aluminum and magnesium ions[J].Journal of Crystal Growth,2004,267(1/2):372-379.
[16]Abdel-Aal E A,Rashad M M,El-Shall H.Crystallization of calcium sulfate dihydrate at different supersaturation ratios and different free sulfate concentrations[J].Crystal Research and Technology,2004,39(4):313-321.
[17]Sandhya S,Sureshbabu S,Varma H K,et al.Nucleation kinetics of the formation of low dimensional calcium sulfate dihydrate crystals in isopropyl alcohol medium[J].Crystal Research and Technology,2012,47(7):780-792.
[18]许小云,刘瑾,樊建明.二水硫酸钙结晶过程研究进展[J].应用化工,2005,34(6):325-327.Xu Xiaoyun,Liu Jin,Fan Jianming.Research progress on the crystallization course of dihydrate calcium sulphate[J].Applied Chemical Industry,2005,34(6):325-327.
[19]刘家祺.分离过程与技术[M].天津:天津大学出版社,2001.Liu Jiaqi.Separation Processes and Technologies[M].Tianjin:Tianjin University Press,2001.