Evaluation of dynamic responses of a BFB boiler furnace by means of CFD modelling

In the paper, a model for dynamic CFD simulation of BFB boiler furnaces is presented. A CFD model is used in the freeboard region while the bed region is modeled by means of a 0D model. The dynamic model is then applied on a 76 MW BFB boiler furnace to analyse response times to process changes. In the paper, a validation study was first carried out by simulating a known load change situation for which measured heat transfer and oxygen concentration data were available. The model proved to correctly predict the changes. With the validated model, effects of step changes in boiler load and fuel moisture content were then evaluated. According to the model, it takes roughly 30–40 min for the bed to settle to a new steady state. The gas properties after superheaters settle in only a couple of minutes. For the heat transfer to the water and steam side, response time scale is roughly 10 min. The study shows that the developed modeling tool is applicable to analysis of time delays and response times, which are otherwise difficult to analyse in real boilers during normal operation.