【摘要】：隨著我國經(jīng)濟的快速增長,火電廠排放的氮氧化物(NO_x)也逐年增多,對人類健康和自然環(huán)境造成一定威脅。近年來,國家對燃煤電廠NO_x排放做出更嚴格的規(guī)定,因此,研究安全、環(huán)保、經(jīng)濟的氮氧化物脫除技術非常重要。選擇性催化還原(Selective Catalytic Reduction,SCR)技術具有設計簡單、控制方便、脫硝效率高等優(yōu)點,廣泛應用在燃煤電廠中。長期以來,對SCR脫硝系統(tǒng)的研究主要關注脫硝原理、催化劑、反應器流場等方面,SCR系統(tǒng)控制方法的研究沒有得到重視。但脫硝系統(tǒng)控制精度不僅決定煙氣排放是否達標,也影響著電廠運行成本。本文分析研究了SCR脫硝系統(tǒng)的動力學過程,基于吸附脫附及化學反應,構建脫硝系統(tǒng)機理模型,同時將前饋控制與動態(tài)矩陣控制方法相結合,設計出基于智能前饋的SCR系統(tǒng)噴氨量預測控制方法,提高噴氨量的控制精度。論文從以下三個部分進行研究:闡述了動態(tài)矩陣控制算法(Dynamic Matrix Control,DMC),同時考慮到SCR脫硝系統(tǒng)實際運行時存在的約束條件,設計了DMC串級控制回路,并通過仿真分析了動態(tài)矩陣控制參數(shù)對控制效果的影響。其次介紹了最小二乘支持向量機(Least Squares Support Vector Machine,LS-SVM)的基本原理及特點。介紹了SCR系統(tǒng)布置、工藝流程和反應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器出口NO_x定值控制方式。設計了基于出口NO_x定值控制方式的PID控制方案,并進行仿真,根據(jù)電廠實際運行特點,分析總結了SCR脫硝系統(tǒng)特點及現(xiàn)有控制方案存在的不足。分析SCR反應過程的動力學原理,建立SCR系統(tǒng)機理模型,作為被控對象。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反應器中的化學反應、出口NO_x檢測以及噴氨閥門的調(diào)整都存在慣性和遲延,在工況變化時僅依靠反饋控制難以實現(xiàn)出口NO_x濃度的準確快速控制。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算法構建鍋爐出口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)變成閥門開度信號,根據(jù)鍋爐側參數(shù)變化實時輸出前饋控制信號,來快速響應鍋爐側工況的變化,將前饋控制與動態(tài)矩陣控制方法相結合,設計出基于機理模型的噴氨量最優(yōu)控制系統(tǒng)。仿真結果表明,本模型實現(xiàn)NO_x濃度的全工況快速準確控制,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.
【學位授予單位】：華北電力大學(北京)
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TM621.8;TP273

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本文編號：2236993