The Numerical Calculation And Optimization Of Char Particle Size In CFB Boiler

The high carbon content in fly ash of circulating fluidized bed boiler is oneof the main problem in the operation of thermal power generating units.According the analysis in theory, the char particles that unburned out in thefurnace and cannot be captured by the separator caused the carbon content in flyash.The numerical results give char particle size distribution along the height ofthe furnace during the coal combustion process, aim to regulate the coal particlesize distribution through adjusting furnace exit char particle size distribution.The mass proportion of char in the range of fly ash particles down to minimum,so as to reduce the carbon content in fly ash. In order to get char particle sizedistribution after the primary fragmentation, a series of experiments are carriedout on four typical kinds of coal included Inner Mongolia lignite coal, Pingshuomixed coal, Shuozhou lean coal and Zhengzhou bituminous coal. The influenceof coal components on the primary fragmentation, ash formation and burnoutcharacteristics are detailed analyzed, the correlations that can express therelationship between particle average size of char and the average size,temperature and characteristics of coal before primary fragmentation are established. The characteristic of coal are provided for the optimization of charparticle size distribution in the circulating fluidized bed boiler.The numerical calculation for1060t/h circulating fluidized Bed boiler studyon char particle size distribution along the height of furnace, this paperdevelop the optimization software of char particle size distribution in circulatingfluidized bed boiler and provide technical support for the boiler to reduce thecarbon content in fly ash. This software mainly includes grain-size distributionof the bed materials module, the distribution of the material density module,char combustion module and optimization module. This thesis studied theinfluence of different coal and coal particle size distribution on the carboncontent, flue gas oxygen content, temperature, combustion characteristics ofseparator, char particle size distribution and carbon content in fly ash. Theresults show that the more volatile content and the more fixed carbon content,the greater combustion rate is and the less carbon content in fly ash; The massproportion of char particle which is the main composition of fly ash and thecarbon content of fly ash decrease initially and increase afterwards as theincrease of mass proportion of fine char particle. When the carbon content in ashfly is the lowest, the coal particle size distribution is the optimization.