【作者】 高阳；

【导师】 杨婷婷；

【作者基本信息】 华北电力大学(北京) ， 检测技术与自动化装置， 2017， 硕士

【摘要】 随着我国经济的快速增长,火电厂排放的氮氧化物(NO_x)也逐年增多,对人类健康和自然环境造成一定威胁。近年来,国家对燃煤电厂NO_x排放做出更严格的规定,因此,研究安全、环保、经济的氮氧化物脱除技术非常重要。选择性催化还原(Selective Catalytic Reduction,SCR)技术具有设计简单、控制方便、脱硝效率高等优点,广泛应用在燃煤电厂中。长期以来,对SCR脱硝系统的研究主要关注脱硝原理、催化剂、反应器流场等方面,SCR系统控制方法的研究没有得到重视。但脱硝系统控制精度不仅决定烟气排放是否达标,也影响着电厂运行成本。本文分析研究了SCR脱硝系统的动力学过程,基于吸附脱附及化学反应,构建脱硝系统机理模型,同时将前馈控制与动态矩阵控制方法相结合,设计出基于智能前馈的SCR系统喷氨量预测控制方法,提高喷氨量的控制精度。论文从以下三个部分进行研究:阐述了动态矩阵控制算法(Dynamic Matrix Control,DMC),同时考虑到SCR脱硝系统实际运行时存在的约束条件,设计了DMC串级控制回路,并通过仿真分析了动态矩阵控制参数对控制效果的影响。其次介绍了最小二乘支持向量机(Least Squares Support Vector Machine,LS-SVM)的基本原理及特点。介绍了SCR系统布置、工艺流程和反应原理两种喷氨量控制方式:固定摩尔比控制方式和脱硝反应器出口NO_x定值控制方式。设计了基于出口NO_x定值控制方式的PID控制方案,并进行仿真,根据电厂实际运行特点,分析总结了SCR脱硝系统特点及现有控制方案存在的不足。分析SCR反应过程的动力学原理,建立SCR系统机理模型,作为被控对象。脱硝系统的输入参数受锅炉燃烧状态影响很大,而且,SCR反应器中的化学反应、出口NO_x检测以及喷氨阀门的调整都存在惯性和迟延,在工况变化时仅依靠反馈控制难以实现出口NO_x浓度的准确快速控制。因此,本文依据电厂历史数据,采用锅炉侧可调参数作为输入,以锅炉出口NO_x浓度作为输出,利用最小二乘支持向量机算法构建锅炉出口NO_x浓度模型,该模型作为智能前馈控制器,将出口NO_x浓度转变成阀门开度信号,根据锅炉侧参数变化实时输出前馈控制信号,来快速响应锅炉侧工况的变化,将前馈控制与动态矩阵控制方法相结合,设计出基于机理模型的喷氨量最优控制系统。仿真结果表明,本模型实现NO_x浓度的全工况快速准确控制,减小了氨逃逸。更多还原

【Abstract】 -With the rapid growth of economy,Emissions of nitrogen oxides(NO_x)in thermal power plants are also increasing year by year,which bring some threat to the human health and the natural environment.In recent years,the state has made more stringent requirements on NO_x emissions to coal-fired power plants.Therefore,it is very important to study the safety,environmental protection and economic nitrogen oxides removal technology.Selective catalytic reduction technology has the advantages of simple design,convenient control and high efficiency of denitrification,which is widely used in coal-fired power plant.For a long time,the research of SCR denitrification system mainly focuses on the research of the principle of denitrification,the catalyst,the flow field of the reactor and so on.The research on the control method of SCR system has not been paid enough attention to.But the control precision of the system is not only to determine whether the flue gas emission is satisfied to the standard,but also affects the operation cost of the power plant.This paper studies the dynamic process of SCR denitrification system.Based on adsorption desorption and chemical reaction,my paper constructed the denitration system mechanism model.At the same time,I connect the feed-forward control and Dynamic matrix control method.And the input and output constraints are added to design the optimal control system of the ammonia injection quantity based on the mechanism model to improve the control precision of the ammonia injection quantity.The thesis is carried out from the following three parts:This paper expounds the dynamic matrix control algorithm,considering the constraint conditions for the existence of SCR denitration system in actual operation,the design of DMC cascade control loop are analyzed by simulation of dynamic matrix control parameters on the control effect.Secondly,this paper introduces the basic principle and characteristics of the least square support vector machine.Introduce the SCR system layout,process flow and reaction principle and introduce two kinds of ammonia injection quantity control method: Fixed molar ratio control mode and Control mode of NO_x fixed value for the outlet of the denitrification reactor.A conventional PID control scheme is completed based on the design of the control mode of the export NO_x fixed value.And through simulation,combined with the simulation curve and the actual operating characteristics of the power plant,the characteristics of SCR denitrification system and the shortcomings of the existing control schemes are analyzed and summarized.The dynamic principle of SCR reaction process is analyzed,and the mechanism model of SCR system is established.The input parameters of denitration system is influenced by boiler combustion state seriously,and chemical reaction in SCR r eactor,outlet NO_x detection as well as the adjustment of the injection valve exist inertia and delay,which only feedback control is difficult to achieve accurate and fast adjustment of the export concentration of NO_x on the change of the condition.Therefore,based on the historical data of the power plant,the boiler side can be used as the input,and the output of the ammonia is used as the output,and the NO_x concentration model of boiler outlet is constructed by using the least square support vector machine algorithm.The model is used as an intelligent feed-forward controller and convert outlet NO_x concentration into valve opening signal.According to the parameter variation of boiler side,the model output the real time feed-signal in response to the change of the side condition of the boiler.Combining feed-forward control with dynamic matrix control,I design the optimal control system of ammonia injection quantity based on the mechanism model.The simulation results show that this model can control the whole working condition of NO_x concentration,and reduce the ammonia escape.更多还原