Analysis and validation of a simplified model of a wet flue gas cleaning system

Combustion of waste produces large variations in flue gas composition. These variations lead to dynamic effects in the emission control system. Variations in scrubber liquid pH is a typical effect, influencing the absorption of pollutants. A dynamic model for a wet system for SO2 removal was built using an existing plant in Hobro, Denmark as a model system. An experimental validation showed that the model has a good agreement with operating data. There was one important limitation to model performance. The absorption of HCI were not modelled and the experiments proved this to be an important process characteristic. A linear analysis of the model showed that the process is approximately a first order system. The process gain is however changing with changing chemical composition of the scrubber liquid, which makes a robust controller design hard to achieve. Some concluding remarks are made on plant and control system design.