Assessment Of Switchability And Optimization For Load Change Processes

In the process industry, it is common for plants to produce more than one type of product, hence load change operation occurs frequently. Load change can be referred to as a dynamic transition process, which moves the system from its current operating point to another. Also load change operation will lead to fluctuations in key variables, such as temperature, pressure, flow and so on. So load change should, for economic reasons, be accomplished in the shortest time. Moreover it is well-known that the industry process exhibits inherent severe nonlinearity behaviors during load change process. Generally, a two-layer control system is used to the load change process. It consists of two layers:optimization layer and control layer. The design of dynamic control layer and economic optimization layer should be integrated, unfortunately in the lack of effective analytical tools they are carried out independently. In this paper, based on the dynamic characters of load change and the two-layer control system, a transition trajectory optimization algorithm is designed integrating the economics and dynamic switchability for load change process.The main work and contributions of the thesis are listed as follows:Based on the dynamic transition feature of load change process, a method to assess the switchability for load change operation is defined. Considering the excellent characteristics of Gap metric theory in nonlinear measurement, we calculates nonlinear degree of load change transition trajectory to quantify the switchability for load change operation. This method can be not only used to analyze the switchability for load change operation in the SISO systems, but also in the MIMO systems. This method provides a more reasonable and effective tool of the dynamic trajectory optimization for integrating the economics and switchability.Aiming at the demand in load change process, in order to integrating the economics and switchability in the optimization layer of load change process, a two-objective trajectory optimization algorithm is proposed. This method conbines the assessment of switchability with the traditional economic optimization, provides a more reasonable and effective load transfer trajectory for load change operation. It can be used to solve the severe control problem caused by the mismatch between optimization layer and control layer. The model of continuous stirred tank reactor is simulated to verify the advantages of this method.