Normal and steady bed temperature provides a basis for the stabilization and safe operation of the circulating fluidized bed boiler (CFBB) unit. Because the bed temperature is affected by many operating factors, it often fluctuates unexpectedly. The bed temperature auto-control system seldom could be put into service during the operation of large capacity CFBB unit. On the basis of operation data of a commercial 450t/h CFBB, which is the first biggest CFBB made in China, the authors systematically analyze the main factors which influence the changes of bed temperature, such as fuel supply rate, air supply rate, oxygen concentration, dense zone height and the unit load et al. The record of the operation data show that the lag of the bed temperature is common phenomenon while fuel supply is changed, and the lag time varies with the fuel supply time, fuel supply operating mode and fuel supply rate; Coal quality and its grain diameter spectrum also have notable influence on bed temperature; Primary air rate has different influences on bed temperature at different operating conditions, and its adjustment range on bed temperature is limited while it is used to bed temperature control; The change of oxygen concentration can reflect combustion conditions in the furnace; The change of dense zone height will result in the change of bed temperature, so the adjustment of fluidization air rate is necessary; Bed temperature is one of the main factors which lead to the change of boiler load. At last, regulating rules on bed temperature control are analyzed and summarized. The conclusions can provide references for the design of control system and safe operation of CFBB unit.
Study on the coordinated control of the bed temperature and the main steam pressure in the circulating fluidized bed boiler
