Development and validation of a dynamic flowsheet model for a 350 MWe supercritical circulating fluidized bed boiler

Abstract

The circulating fluidized bed (CFB) boiler is highly recommended in peak shaving for its wide load regulating range compared with the pulverized coal (PC) boiler. However, the research on dynamic flowsheet model of the CFB boiler is quite limited due to its complex flow regime. In this paper, both steady state and dynamic flowsheet model of a supercritical 350 MWe CFB boiler was developed based on Aspen Plus and Aspen Dynamics software coupled with comprehensively user defined combustion kinetics and heat transfer coefficient with FORTRAN subroutines. This model was then validated by the operating data of the 350 MWe supercritical CFB boiler. Based on this model, the dynamic characteristics of three typical step signal disturbances, coal flow rate, primary flow rate and secondary air flow rate, were further analyzed to provide theoretical references to dynamic operation. Also, the quantitative relation between the stabilization time and step signal amplitude was calculated. The calculated dynamic characteristics demonstrates that the heat distribution does not vary much after adding step signal disturbances of coal flow rate, primary air flow rate and secondary air flow rate. The step signal disturbance of secondary air flow rate has less influence to the CFB boiler system compared with that of primary air flow rate. The superheated steam temperature is more sensitive to step signal disturbances compared with reheated steam temperature. The higher step signal amplitude results in longer stabilization time. Above all, this dynamic flowsheet model can not only be used to conduct dynamic behavior prediction and analysis but also provide transfer functions to the further development of CFB automatic control system.