To establish an advanced control system for a multi solid circulating fluidized bed boiler (MSFB), a simplified dynamic model of the 70 t/h MSFB unit was developed. Equations of material balance and enthalpy balance were obtained for six regions in the unit : dense bed zone, reducing zone and oxidizing zone in the combustor, cyclone, hot solid reservoir and external heat exchanger. The solid circulating rate inside the combustor was determined to predict the observed temperature profile in the combustor of the 70 t/h unit. It was shown that calculated results of gas components, char conversion and temperature profile were able to describe steady-state operation data considerably well. The solid circulating rate strongly affected the temperature profile in the combustor. It was also found from calculated results for unsteady-state operations that slower responses followed after the sharp responses accompanied with load change and that the char reactivity and the external solid circulating rate affected the peak temperature and the settling time of the responses.
