优化前馈-反馈氨合成塔触媒温度控制

Optimization of Catalyst Temperature Feedforward-Feedback Control in Ammonia Synthesizer

以大型煤化工的关键设备氨合成塔的一段触媒温度控制为研究对象,针对氨合成塔滞后大的特性,在常规的前馈-反馈控制基础上,对前馈干扰引入时间可调整概念,目的是使得干扰项起作用的时刻同被控对象产生影响的时刻同步。同时采用史密斯预估控制方法原理,对氨合成塔的一段触媒温度控制过程中反向特性进行补偿。从而达到优化控制的目的。本文的控制策略分两部分,第一部分是将干扰项测量,将测得的干扰量作为前馈,在计算出前馈增益及方向后,保存在DCS控制系统中。再测试出干扰项对被控对象作用的滞后时间,待扰动发生时,再引入存储的前馈量,达到同步补偿目的。第二部分在反馈控制回路增加预估算法,先根据测量的干扰预先估算出反向特性补偿量,也存储在DCS控制系统中,待反向特性开始时,将估算出的补偿量,叠加填平到反向特性的凹部区。补偿后带反向特性控制回路变成常规滞后控制回路。这样前馈-反馈同时优化,大幅度改进氨合成塔一段触媒温度控制品质。为保证控制效果,方案中还采用了软测量和测点品质判断算法。

Taking the stage 1 of catalyst temperature control in ammonia synthesizer which is the key equipment in large scale coal chemical industry as the object of study, and according to the large lag of ammonia synthesizer, the concept of adjustable time for feedforward interference on the basis of conventional feedforward-fecdback control is proposed to synchronize the time when the synthesizer affects and the controlled object is affected. At the same time Smith predictive control method is adopted to compensate the reverse characteristic during the stage l of catalyst temperature control in ammonia synthesizer, and the purpose of optimization control is therefore achieved. In this paper, the control strategy is divided into two parts： First, take the measured value of the synthesizer variable as the feedforward and calculate the feedforward gain and direction, and then transfer them into DCS. The controlled object lag time generated by interference variable is then tested, and when interference happens the stored feedforward is invoked for the purpose of the synchronous compensation. Second, predictive algorithm is added in feedback circuit. According to the measured interference the reverse characteristic compensation is estimated in advance and then saved in DCS. When reverse characteristic starts, the estimated compensation is overlaid to the reverse characteristic and its concave can therefore be filled. The control circuit with reverse characteristic therefore turns out to be conventional lag control circuit. Through the feedforward-feedback synchronous optimization, the control quality of stage 1 of catalyst temperature in ammonia convener is improved greatly. To ensure the control effect, the algorithm to measure the quality of soft sensor and measuring points is adopted.