【摘要】：隨著我國(guó)經(jīng)濟(jì)的快速增長(zhǎng),火電廠排放的氮氧化物(NO_x)也逐年增多,對(duì)人類健康和自然環(huán)境造成一定威脅。近年來(lái),國(guó)家對(duì)燃煤電廠NO_x排放做出更嚴(yán)格的規(guī)定,因此,研究安全、環(huán)保、經(jīng)濟(jì)的氮氧化物脫除技術(shù)非常重要。選擇性催化還原(Selective Catalytic Reduction,SCR)技術(shù)具有設(shè)計(jì)簡(jiǎn)單、控制方便、脫硝效率高等優(yōu)點(diǎn),廣泛應(yīng)用在燃煤電廠中。長(zhǎng)期以來(lái),對(duì)SCR脫硝系統(tǒng)的研究主要關(guān)注脫硝原理、催化劑、反應(yīng)器流場(chǎng)等方面,SCR系統(tǒng)控制方法的研究沒(méi)有得到重視。但脫硝系統(tǒng)控制精度不僅決定煙氣排放是否達(dá)標(biāo),也影響著電廠運(yùn)行成本。本文分析研究了SCR脫硝系統(tǒng)的動(dòng)力學(xué)過(guò)程,基于吸附脫附及化學(xué)反應(yīng),構(gòu)建脫硝系統(tǒng)機(jī)理模型,同時(shí)將前饋控制與動(dòng)態(tài)矩陣控制方法相結(jié)合,設(shè)計(jì)出基于智能前饋的SCR系統(tǒng)噴氨量預(yù)測(cè)控制方法,提高噴氨量的控制精度。論文從以下三個(gè)部分進(jìn)行研究:闡述了動(dòng)態(tài)矩陣控制算法(Dynamic Matrix Control,DMC),同時(shí)考慮到SCR脫硝系統(tǒng)實(shí)際運(yùn)行時(shí)存在的約束條件,設(shè)計(jì)了DMC串級(jí)控制回路,并通過(guò)仿真分析了動(dòng)態(tài)矩陣控制參數(shù)對(duì)控制效果的影響。其次介紹了最小二乘支持向量機(jī)(Least Squares Support Vector Machine,LS-SVM)的基本原理及特點(diǎn)。介紹了SCR系統(tǒng)布置、工藝流程和反應(yīng)原理兩種噴氨量控制方式:固定摩爾比控制方式和脫硝反應(yīng)器出口NO_x定值控制方式。設(shè)計(jì)了基于出口NO_x定值控制方式的PID控制方案,并進(jìn)行仿真,根據(jù)電廠實(shí)際運(yùn)行特點(diǎn),分析總結(jié)了SCR脫硝系統(tǒng)特點(diǎn)及現(xiàn)有控制方案存在的不足。分析SCR反應(yīng)過(guò)程的動(dòng)力學(xué)原理,建立SCR系統(tǒng)機(jī)理模型,作為被控對(duì)象。脫硝系統(tǒng)的輸入?yún)?shù)受鍋爐燃燒狀態(tài)影響很大,而且,SCR反應(yīng)器中的化學(xué)反應(yīng)、出口NO_x檢測(cè)以及噴氨閥門的調(diào)整都存在慣性和遲延,在工況變化時(shí)僅依靠反饋控制難以實(shí)現(xiàn)出口NO_x濃度的準(zhǔn)確快速控制。因此,本文依據(jù)電廠歷史數(shù)據(jù),采用鍋爐側(cè)可調(diào)參數(shù)作為輸入,以鍋爐出口NO_x濃度作為輸出,利用最小二乘支持向量機(jī)算法構(gòu)建鍋爐出口NO_x濃度模型,該模型作為智能前饋控制器,將出口NO_x濃度轉(zhuǎn)變成閥門開(kāi)度信號(hào),根據(jù)鍋爐側(cè)參數(shù)變化實(shí)時(shí)輸出前饋控制信號(hào),來(lái)快速響應(yīng)鍋爐側(cè)工況的變化,將前饋控制與動(dòng)態(tài)矩陣控制方法相結(jié)合,設(shè)計(jì)出基于機(jī)理模型的噴氨量最優(yōu)控制系統(tǒng)。仿真結(jié)果表明,本模型實(shí)現(xiàn)NO_x濃度的全工況快速準(zhǔn)確控制,減小了氨逃逸。
[Abstract]:With the rapid economic growth in China, the emission of nitrogen oxides (NO_x) from thermal power plants is increasing year by year, which poses a certain threat to human health and natural environment. In recent years, the state has made more stringent regulations on NO_x emissions from coal-fired power plants, so it is very important to study the safe, environmentally friendly and economical nitrogen oxides removal technology. Selective catalytic reduction (Selective Catalytic Reduction,SCR) technology is widely used in coal-fired power plants because of its simple design, convenient control and high denitrification efficiency. For a long time, the research of SCR denitrification system has been paid little attention to, such as the principle of denitrification, catalyst, reactor flow field and so on. But the control precision of denitrification system not only determines whether the flue gas emission is up to standard, but also affects the operation cost of power plant. In this paper, the kinetic process of SCR denitrification system is analyzed and studied. Based on adsorption desorption and chemical reaction, the mechanism model of denitrification system is constructed, and the feedforward control is combined with the dynamic matrix control method. A predictive control method for ammonia injection in SCR system based on intelligent feedforward is designed to improve the precision of ammonia injection. In this paper, the following three parts are studied: the dynamic matrix control algorithm (Dynamic Matrix Control,DMC) is introduced, and the DMC cascade control loop is designed considering the constraints of SCR denitrification system. The effect of dynamic matrix control parameters on the control effect is analyzed by simulation. Secondly, the basic principle and characteristics of least squares support vector machine (Least Squares Support Vector Machine,LS-SVM) are introduced. The SCR system layout, process flow and reaction principle are introduced in this paper. Two kinds of ammonia injection control methods, namely, fixed molar ratio control and NO_x fixed value control at the outlet of denitrification reactor, are introduced. The PID control scheme based on export NO_x fixed value control is designed and simulated. According to the actual operation characteristics of power plant, the characteristics of SCR denitrification system and the shortcomings of existing control schemes are analyzed and summarized. The kinetic principle of SCR reaction process is analyzed and the mechanism model of SCR system is established as the controlled object. The input parameters of the denitrification system are greatly affected by the combustion state of the boiler, and there are inertia and delay in the chemical reaction in the SCR reactor, the detection of the outlet NO_x and the adjustment of the ammonia injection valve. It is difficult to realize the accurate and fast control of NO_x concentration at outlet only by feedback control when the working condition changes. Therefore, according to the historical data of the power plant, the boiler side adjustable parameters are used as input, the boiler outlet NO_x concentration is taken as the output, and the NO_x concentration model of boiler outlet is constructed by using the least square support vector machine algorithm. As an intelligent feedforward controller, the model converts the outlet NO_x concentration into the valve opening signal, and outputs the feedforward control signal according to the boiler side parameter change in real time to quickly respond to the boiler side working condition change. Combining feedforward control with dynamic matrix control, an optimal control system for ammonia injection is designed based on mechanism model. The simulation results show that the model can quickly and accurately control the concentration of NO_x and reduce the ammonia escape.
【學(xué)位授予單位】：華北電力大學(xué)(北京)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TM621.8;TP273

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本文編號(hào)：2236993