Abstract: The boiler combustion technology of circulating fluidized bed( CFB) is a kind of clean coal combustion technology,and its flexibility to cope with load change will attract more attention in the future.Recent studies about load change are focused on the optimization of peak shaving,which lack the research of influence factors on CFB boiler itself.The circulation rate will change and reach a new equilibrium state as load of CFB boiler changes.The structure of loop seal is an important factor on the circulation state.Therefore,in order to investigate the influence factors on CFB boiler response rate to load change,the flow behavior of a 75 t/h in standpipe and loop seal of a CFB boiler with circulating rate change was simulated based on CPFD method.The dynamic response rate to circulating flow rate change under different loop seal structure was studied.The results indicate that there are some"flow-dead zone"on the away-recycle-valve side of the standpipe and the bottom of the loop seal.The gas-solid flow in that zones have relatively high moving velocity only in restricted areas,so the moving area of small particle limits the time to reach a higher flux equilibrium state when the circulation rate increases.The flow-dead zone decreases the response rate to the load change.When the loosening air and fluidizing air are 0.14,0.3 m/s respectively and the circulating flow rate increases from 50 kg/( m~2·s) to 60 kg/( m~2·s),the system response time decreases sharply first and then increases moderately with the increase of horizontal section length.The shortest response time is 67 s,when the ratio of loop seal horizontal section length to the standpipe diameter is 3.5.Keeping the fluidizing air and adjusting the loosening air,the system response time decreases with the increase of loosening air while the relation between system response time and the loop seal structure keeps similar.The response rate of loop seal to circulating flow rate change is closely related to the size of flow-dead zone in the loop seal.