【作者】 杨静；

【导师】 马双忱；

【作者基本信息】 华北电力大学 ， 工程硕士（专业学位）， 2017， 硕士

【摘要】 作为在火电企业广泛应用的主流脱硫技术,湿式石灰石—石膏法烟气脱硫(Wet FGD)工艺有两项关键技术指标:脱硫率和亚硫酸钙氧化率。经过多年的研究和工业应用,该技术脱硫率能满足污染物排放标准,并能达到超净排放的严苛要求,但亚硫酸钙的氧化控制仍存在亚硫酸盐超标、系统结垢、石膏品质差等一系列问题。因此,如何科学有效地对脱硫系统的强制氧化环节进行控制,保证较高的亚硫酸钙氧化率,从而防止系统结垢,同时降低脱硫系统能耗,生产高品质石膏,是当前电厂脱硫系统有待解决的热点问题。脱硫系统既包含SO2气体的吸收,又包括亚硫酸盐的后续氧化,是一个连续复杂的过程。而目前,脱硫系统只是简单地pH调节,也即酸碱控制,国内还没有意识到要对烟气脱硫浆液氧化程度进行合理控制,即实现氧化还原反应控制,对脱硫过程而言,偏颇于一种控制是不够的,需要两种控制的协同。本课题通过实验探究亚硫酸钙氧化过程中pH与ORP的变化规律,从影响脱硫系统氧化反应的基本原理作为出发点,提出pH与ORP双控制策略,即以pH、ORP作为浆液氧化控制参数,依托实时监测的pH、ORP动态变化确定脱硫浆液的氧化状态,并及时对氧化风量做出相应调整。为验证双控制理论在湿法脱硫浆液氧化控制中的可行性,实验研究了不同底物浓度下氧化率曲线变化特征;pH、ORP随时间的变化特征;氧化过程的pH、ORP响应等,得到了理想的实验结果。考虑了亚硫酸钙氧化过程中ORP变化的多种影响因素,如反应温度、浆液pH、DO、[HSO3-]/[SO42-]等,设计L16(45)的正交试验,重点研究脱硫浆液氧化过程不同阶段ORP影响因子对脱硫浆液体系ORP的贡献程度,得到影响ORP变化因子的主次顺序,并分析了各因子变化对ORP的影响趋势。阐明了浆液氧化过程中的反应机理,得到不同氧化阶段ORP变化的“主效因子”,对电厂脱硫浆液氧化系统分阶段精确控制氧化提供理论指导。在西南某电厂开展现场试验,利用先进的ORP测量手段,探明脱硫浆液氧化的最佳ORP控制范围,结合实时在线离子监测参数数据,验证ORP指示浆液氧化状态的实际可行性,并得到以ORP指示浆液氧化状态为基础的氧化风机开启台数的经验数值,同时实现脱硫系统氧化风机运行的最优化。本论文率先引入脱硫浆液pH、ORP双控制理念,不仅可以精确控制浆液的氧化状况,避免氧化风机开度的盲目增大,实现节能降耗,同时实时控制又克服了传统氧化控制的滞后性,保证了脱硫系统的稳定高效运行,生成的商品级石膏也可为燃煤电厂带来一定的经济效益。论文工作为该技术的发展和应用奠定了基础。更多还原

【Abstract】 As the main desulfurization technology widely used in thermal power plants,wet limestone-gypsum flue gas desulfurization(Wet FGD)process has two key technical indicators: desulfurization rate and calcium sulfite oxidation rate.After years of research and industrial applications,desulfurization rate of the technology can meet the standards of pollutant emissions,and achieve the stringent requirements of ultra clean emissions.But there exists a series problems in the control of oxidation in Wet FGD slurry oxidation system,such as deposition and slagging in WFGD system、inadequate oxidation and per-oxidation.Therefore,how to control the process of forced oxidation desulfurization system scientifically and effectively,to make sure the high rate of calcium sulfite oxidation,thereby preventing scaling,while reducing the energy consumption of FGD system,is the hot issues for desulfurization system of power plant to solve in the current.The desulfurization system which includes the absorption of SO2 and the oxidation of sulfite is a complex process.At present,the desulfurization system has simple p H control.China is not aware of the meaning of oxidation control to the flue gas desulfurization slurry.In terms of desulfurization process,it is not enough to rely on a control method,which requires the coordination of the two control methods.The change of p H and ORP in the process of calcium sulfite oxidation was inquired by experiment.Based on the nature of the oxidation reaction of the desulfurization system as a starting point,the p H and ORP dual control strategy is proposed,that is to put p H and ORP as control parameters of slurry oxidation,relying on real-time monitoring the changes of p H and ORP to determine the oxidation state of desulfurization slurry,and in time to make the appropriate adjustments to oxidation air flow.In order to verify the feasibility of the double control theory in the oxidation control of desulfurization slurry,the change characteristics of oxidation rate curve under different substrate concentration were studied in the experiment.The response of p H and ORP to oxidation process were also obtained.The ideal experimental results were obtained.ORP is a function of many factors in the process of the oxidation of Ca SO3: the reaction temperature,the slurry p H、DO(Dissolved Oxygen)、[HSO3-]/[SO42-] and so on.A L16(45)orthogonal experiment was designed to research the factors of ORP changing in desulfurization slurry oxidation in the different period.The order of the contribution of each factor to ORP in desulfurization slurry according to the influences of different factors on ORP was obtained.And the impact trend of the various factors to the ORP changing was analyzed later.In this paper,the reaction mechanism of slurry oxidation was clarified,and the "major factor" of ORP changing in different oxidation stage was obtained,which provided a theoretical guide for precise control of oxidation in FGD slurry oxidation system.The field test was carried out in a power plant in the southwest of China,usingadvanced ORP measurement means to find the best ORP control range of desulfurization slurry oxidation.Combined with real time online ion monitoring parameter data,the field test verified the practical feasibility of ORP to indicate the oxidation state of slurry.And we got the opening experience of the number of oxidation fan based on ORP,at the same time,achieved the optimization of the oxidation fan operation in FGD system.This paper first introduced the concept of p H and ORP dual control into the desulfurization slurry.It can not only control the oxidation state of slurry accurately,but also avoid the blind control of oxidation fans to save energy.Real time control overcome the hysteresis of traditional oxidation control and ensure the desulfurization system operate stably and efficiently.The product gypsum can also bring some economic benefits to coal-fired power plant.The work laid the foundation for the development and application of the technology.更多还原