Dynamic modelling of a CFB boiler including the solids, gas and water-steam systems

Due to the widespread deployment of non-flexible renewable energy sources, an increasing trend is to use coal-fired boilers as support to the base energy production. High flexibility is usually required, and consequently, it is fundamental to be able to accurately predict and study dynamic behavior of the boilers. This point is particularly crucial for Circulating Fluidized Bed (CFB) technology. Indeed, while bringing excellent fuel flexibility and emission control, different case specific boiler configurations and arrangements induce significant variations in the dynamic behavior. This calls for a computational tool capable for accurate and specific dynamic studies of the entire system. One-dimensional process modelling and dynamic simulation, including the relevant automation functionalities, offers the best solution. Modelling and simulation of CFB boiler plants includes, however, many challenges, including modelling of combined volumes of gas and solid particles, complex fluidization phenomenon inside the furnace and in the circulating loop(s), strong coupling with the heat transfer to cooling systems, and the reactions for the combustion and sulfur capture. In addition, the model build-up phase and calculation speed shall not become limiting factors for applicability in engineering projects. This paper presents the latest enhancements in the Apros simulation environment, including improved managing of the furnace solid balance, heat exchange calculation from the circulating solids, and integration of dynamic behavior of the solid material looping. These developments were evaluated in a modelling study for a 750 MWth bituminous coal-fired CFB boiler. The modelling methodology is presented and the boiler model capability is demonstrated with simulation results.