基于能耗最优的管式降膜蒸发器液位控制方法

A Liquid Level Control Method Based on Optimal Energy Consumption for Tube Falling Film Evaporators

在氧化铝生产的蒸发过程中,液位作为一个重要状态指标影响着生产的安全性及蒸发效率。蒸发过程中的非线性因素和时滞因素增加了对液位控制的难度,传统的控制方法难以实现蒸发过程液位的精确调控,尤其是忽略了从能耗角度对液位实施控制。今对管式降膜蒸发器蒸发过程建立动态非线性时滞模型,提出了一种基于能耗最优的液位控制方法(LLCOEC),结合有效能以及汽水比对液位进行控制。将复杂的非线性时滞控制问题转化为一系列非线性规划问题,通过求解每一步长时间内出料流量的最优增量,从而确定整个调控时间内的控制量。通过仿真实验对比该方法与离散时间模型预测控制(DMPC),结果验证所提出的控制方法能更快速、准确地控制液位达到设定值,并同时提高蒸发过程中的有效能利用率、降低汽水比,为蒸发过程中的液位控制提供指导。

Liquid level is an important indicator that affects safety and evaporation efficiency during evaporation processes of alumina production. It is difficult to achieve precise control of liquid level using traditional controlling methods due to nonlinearity and time lag. Moreover, energy consumption is usually ignored in liquid level control. In this study, dynamic nonlinear modeling with time lag was established. A liquid level control method based on optimal energy consumption（LLCOEC） was proposed, which can control liquid level based on exergy and steam to water ratio. The nonlinear control problem with time lag was converted to a series of nonlinear programming problems. The control parameters were determined by solving the optimal flow increment in each step time. Simulation results show that the proposed control method has better performance than discrete-time linear model predictive control（DMPC）. Liquid level can more quickly and accurately reach optimal setting points. The effective energy utilization is improved and the steam to water ratio is reduced, which can help liquid level control in the evaporation process of alumina production.