Optimal Operation of a Waste Incineration Plant

A case study of a waste incineration plant operating close to optimality by using simple feed-back control schemes is presented. Using off-line optimization the structure of the optimization problem is exploited and a set of variables is found, such that if the process is controlled with those variables are at their setpoints, operation is near-optimal. The procedure applied to the waste incineration plant is first to obtain a steady state plant model, which is optimized on grid points in the operating region in order to determine the set of active constraints and the optimally unconstrained variables and their optimal values. The variables assuming a constant optimal value are candidates for self-optimizing variables. This yields four operational regions, each with a set of corresponding self-optimizing variables. For each region a simple control structure is defined to 1) satisfy constraints and 2) to control the self-optimizing variables to their optimal setpoints. To be able to change between different regions, a switching table is set up. Using these switching rules, the plant can be controlled close to optimality within the different regions and when a disturbance causes the system to change from one region to another. Finally some dynamic simulation results are presented to show the control performance within the regions and across region boundaries.