Process Control and Coordinating Optimisation for the Multi- Feed Demethaniser in Ethylene Complex

Abstract

In the chemical process, it is essential to control the product quality and optimal utilisation in limited energy. To achieve the goal of energy savings during the process control, three kinds of process control and coordinating optimisation strategies are proposed and compared in a two-input-two-output system. The first strategy contains both setting value control of inputs and optimisation of two set points to acquire the control of the objective output. The second strategy is realised by cascade control of the expected objective output and coordinating optimisation of the energy to acquire optimal set point of the setting value control of the other input. For the third one, the objective output and the other output are both controlled by cascade control, and the set point of the other output is optimised to achieve energy-saving goal. A case study on the multi-feed demethaniser in ethylene complex is employed to identify the efficiency of the process control and coordinating optimisation strategy. It turns out that the combination of the process control of the overhead composition and coordinating optimisation of reboil flow rate control is the most efficient on energy savings in proposed strategies during the improvement of the product quality.