Modelling and Control of the Secondary Combustion Chamber in an Energy from Waste Plant

Abstract

Thermal conversion of municipal and industrial waste is an environmentally friendly way to recover energy from waste. There are many governmental requirements regarding air emissions from such processes. A tight control is required for the operation of the combustion chamber as there are many unknown disturbances, the biggest being the composition of the waste. Classic PID controllers will only just provide the required control, hence model predictive control, MPC, was proposed to optimise the control. This thesis covers the preparatory work for the implementation of MPC.

This report describes how a transient model of the secondary combustion chamber was derived. The model consists of material and energy balances for six control volumes with a simplified approach the combustion reaction. The report also gives a short description of the entire process in a typical Energos energy from waste plant and some basics on MPC and Kalman filtering.

Model simulations were performed in Cybernetica's software ModelFit. Operational data from an Energos plant was used as input to the model and measured outputs were compared to predicted outputs. Parameter estimation was also performed using the process data. The implementation of model predictive control for this system was considered.

A first order divided difference Kalman filter was implemented in ModelFit for model updating that improved the accuracy of the predictions. This is an important step on the way towards MPC.