Control Structure and Tuning Method Design for suppressing Disturbances in a multi-phase Separator

Abstract

In this project report the control structure for a three phase separator for a oil production unit is examined. The purpose is to analyse the control structure, and make the suggestion for how a control structure based on single loop control, can be designed to reject large disturbance occurring in the system. The second goal is to make a tuning method based on the plant properties to prevent process shutdown, that keeps the process running smooth. The assignment text states that the following tools can be used to develop the control structure: feed forward control, gain scheduling, first and second order filters, PI- and PID-controllers. A process model containing all process variables is derived in the report. For verification purposes and development of control structure and tuning, the model is implemented in MATLAB and Simulink where simulations are done. The model is normalised such that the control structure is tested for the general case. Plant verification model is based on dimensions from a real plant, but process parameters are changed for comparing with other plants. Tools like gain scheduler, anti-windup, derivative filter and low pass filter are derived and designed for the purpose.The report shows which parameters that limit the process performance and which techniques that should be used to reduce their impact to the system. There is also made analysis for how control loops and the controller can regard the limitations. An important part of this is the development of a signal filter to reduce measurement noise in the system.As a basis for controller tuning SIMC is used. The system is analysed to find a method adapted for separator tuning. The customised method is tested for different plants and compared to SIMC to verify the abilities to control the plant. Analyses of the system, is done for a linear system, even though the system is nonlinear. To be able to use linear system techniques, analysis is done for the system linearised around setpoint and chosen points within the working area.The result of the report, is a suggestion for how single loop control structure, and tuning can be performed for a separator based on the plant properties.