超临界机组燃料—汽压系统建模与控制策略研究

发布时间：2018-08-22 14:34

【摘要】：当今社会能源与环境问题日益突出,超临界机组由于具有效率高、能耗低等特点,日益成为火电厂装机的趋势。超临界机组的燃烧控制系统是整个控制系统的重要组成部分,目前大多数火电厂燃煤来源广、热值偏差大,严重影响了燃烧系统的控制,其控制水平又进一步影响到整个机组控制的安全性与经济性。因此,在燃煤煤种多变的情况下,研究一种适用于超临界机组的煤质自适应控制策略,提高机组运行的安全性与经济性,优化超临界机组的控制系统,成为亟待解决的问题。设计了自适应煤质前馈校正,以功煤系数为出发点,借助组合预测模型的思想建立一个对入炉煤量的预测模型,采用方差倒数法求取前1小时功煤系数对当前时刻功煤系数的最优权重,实现对入炉煤功煤系数以及入炉煤煤量的预测。用入炉煤量的预测模型对某660MW机组#4锅炉入炉煤量进行预测,结果表明,用实时入炉煤量的预测值作为实际给煤量,其准确度能达到97.0%左右,提高了入炉煤量的准确性。主蒸汽压力是表征超临界机组机炉能量供求关系的重要参数,其主要影响因素为燃料量。目前大部分火电厂燃料煤种杂、热值波动大,造成主蒸汽压力波动频繁,严重影响机组的安全运行。在燃料量的前馈控制系统的基础上,设计了二阶自抗扰控制器,在燃料量的反馈控制系统中用自抗扰控制代替传统的PID进行闭环反馈控制,主要是借助扩张状态观测器估计出燃煤热值自发扰动,并在动态过程中将其实时补偿,进一步提高入炉煤量的准确性,防止因燃煤热值波动造成主蒸汽压力的频繁波动。采用压力节点的方法将超临界直流锅炉动态数学模型分为3个压力节点,对每个压力节点列出质量守恒与能量守恒方程,然后对方程进行化简、无量纲化,最后将3个压力节点串联即可得到超临界机组燃料汽压系统模型。利用某660MW超临界机组设计数据进行建模、计算,得出超临界机组燃料汽压系统在100%THA、75%THA、50%THA工况下的模型计算参数。在三种工况下,对求得的模型分别进行传统的PID控制与自抗扰控制仿真,结果表明:与传统PID控制相比,自抗扰控制的抗干扰能力更强,具有更好的鲁棒性,对主蒸汽压力有更好的控制品质。通过比较传统PID控制器和自抗扰控制器控制效果可知,具有消除扰动效果的自抗扰控制方案是具有前景的控制方案。
[Abstract]:Nowadays, the problems of energy and environment are becoming more and more serious. Because of its high efficiency and low energy consumption, supercritical units are becoming the trend of power plant installation. The combustion control system of supercritical unit is an important part of the whole control system. At present, most thermal power plants have wide sources of coal combustion and large deviation of calorific value, which seriously affects the control of combustion system. Its control level further affects the safety and economy of the whole unit control. Therefore, it is an urgent problem to study a kind of coal quality adaptive control strategy for supercritical units, to improve the safety and economy of operation, and to optimize the control system of supercritical units. The adaptive feedforward correction of coal quality is designed. Based on the work coal coefficient and the idea of combined prediction model, a prediction model of coal quantity into the furnace is established. The optimum weight of the work coal coefficient of the first hour to the current time is obtained by using the reciprocal method of variance, and the prediction of the work coal coefficient and the coal quantity into the furnace is realized. The coal quantity of #4 boiler of a 660MW unit is predicted by using the prediction model of coal quantity into the furnace. The results show that the accuracy of using the prediction value of the input coal quantity in real time as the actual coal quantity can reach about 97.0%, which improves the accuracy of the coal quantity into the boiler. The main steam pressure is an important parameter to characterize the energy supply and demand of supercritical units, and the main influencing factor is the fuel quantity. At present, most thermal power plants have mixed fuel and coal, and their calorific value fluctuates greatly, which results in frequent fluctuation of main steam pressure, which seriously affects the safe operation of units. Based on the feedforward control system of fuel quantity, a second-order ADRC is designed. In the feed-back control system of fuel quantity, the closed-loop feedback control is carried out by using ADRC instead of traditional PID. The main purpose of this paper is to estimate the spontaneous disturbance of coal-fired calorific value by means of the expanded state observer and compensate it in real time in the dynamic process to further improve the accuracy of coal intake and prevent the frequent fluctuation of main steam pressure caused by the fluctuation of coal-fired calorific value. The dynamic mathematical model of supercritical once-through boiler is divided into three pressure nodes by the method of pressure node. The conservation equations of mass and energy are listed for each pressure node, and then the equations are simplified and dimensionless. Finally, three pressure nodes are connected in series to obtain the model of supercritical unit fuel steam pressure system. Using the design data of a 660MW supercritical unit to model and calculate, the model calculation parameters of the fuel steam pressure system of the supercritical unit under the condition of 100th THA75THA50THA are obtained. Under three conditions, the model is simulated by traditional PID control and auto disturbance rejection control respectively. The results show that compared with the traditional PID control, the ADRC has stronger anti-interference ability and better robustness. The main steam pressure has better control quality. By comparing the control effect of the traditional PID controller and the active disturbance rejection controller, it can be seen that the active disturbance rejection control scheme with the effect of eliminating disturbance is a promising control scheme.
【学位授予单位】：华北电力大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM621

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