Experimental study of deep and flexible load adjustment on pulverized coal combustion preheated by a circulating fluidized bed

Peak shaving of coal-fired power plants is a key to promoting renewable energy generation in a grid system. In this study, the deep and flexible load regulation characteristics of pulverized coal preheating combustion are explored. The determination criteria of the variable load related to the preheating temperature, preheated coal gas, combustion temperature and main flue gas (NO, N2O, CO and O2) emission concentrations are established, and the temperature hysteresis coefficient is introduced to characterize the hysteresis of the combustion process. The results show that this system has a deep load regulation capability and can operate stably over a wide load range from 25% to 113%. The chemical reactivity of the pulverized coal is enhanced with thermal modification, which ensures stable combustion in the combustion chamber at ultralow loads. Moreover, the optimal rate of variable load is achieved when the load step is 25%, and the maximum rates of variable load for the preheating process and combustion process are 4.17%/min and 3.13%/min, respectively. Furthermore, an excessively high load step will trigger a large amount of combustion hysteresis, which negatively affects the variable load process.