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On the basis of measurements on the fluidized bed heat exchanger (FBHE) in a 600MW supercritical CFB boiler fueled by lean coal under different boiler load, the actual operation characteristics of the FBHEs, such as post-combustion characteristics and heat absorption shares in the FBHE were obtained in this paper, as well as ash flow rate through the FBHE. The measured and calculated results indicate that the post-combustion phenomenon exists in the FBHEs of the boiler fueled by lean coal. As steam parameter raises from subcritical to supercritical parameter, heat absorption share of heating surface in the FBHEs are quite different from each other regardless of boiler load. Moreover, as the boiler load decreases, ash flow rate through FBHE arranging reheater is almost the same, while ash flow rate through FBHE arranging superheater changes significantly. These results can provide referential materials for the optimized design and operation of the FBHE in large-scale CFB boilers.

The construction of large scale CFB units with high steam parameters is the best way to make large-scale clean use of low calorific value coal such as slime and gangue. The ash and slag heat loss of CFB units burning low calorific value coal is large. Roller slag coolers widely used in in-service CFB units have a low efficiency in terms of heat recovery and utilization of ash and slag for CFB boiler, while air-water combined slag cooler can effectively recover heat from ash and slag. By analyzing and studying the influence of air-water combined slag cooler and roller slag cooler on boiler efficiency and power consumption, the coal consumption of ultra-supercritical CFB units with different slag coolers was calculated, and the technical economy of different types of slag coolers was also compared. The results indicate that the air-water combined slag cooler should be selected for the CFB unit with high price of standard coal and large amount of bottom slag, and better economy of the unit could be obtained. In order to take into account the economy and operational reliability of slag cooler system, the scheme of mixing air-water slag cooler with roller slag cooler can be adopted to optimize the selection of slag cooler system for a ultra-supercritical CFB unit. These results can provide referential materials for the selection and optimization of slag cooler system of large-scale CFB boiler.