Study On Particle Population Balance And Heat Balance In Large-Scale Circulating Fluidized Bed Boiler

For the past few years, circulating fluidized bed (CFB) combustion technology,which is unique in its combustion efficiency comparing with the pulverized-coal boiler,realization of direct desulphurization in combustion process, low emissions of nitrogenoxides and its wide fuel flexibility, has obtained a great achievement in its developmentwhich is moving in the direction of boilers with supercritical parameter as well. CFBtechnology with supercritical parameter can further increase the power generationefficiency of the existing CFB technology and combine low cost of pollution control incoal combustion with high power electricity generation, as well as promote theapplication of CFB in the power generation industry.Until now, there are not enough mature experiences of supercritical CFBtechnologies among the world, therefore the independent research and developmentbecomes an inevitable choice. As a result, it is necessary to study the key parameters indepth, such as the particle population balance and the heat balance of the existing largescale CFB boilers, so as to provide reference on boiler design or optimization operationfor supercritical CFB boilers.By sponsor of the Key Project in the National Science&Technology PillarProgram during the Eleventh Five-Year Plan Projects, in this paper, both laboratory andfield experimental study and numerical simulation research work about the particlepopulation balance and heat balance characteristics mainly on Baima’s300MW CFBboiler were carried out. The main research content and innovation points of this paperinclude:①Overall modeling of particle population balance on large-scale CFB boilerBased on previous studies and by adjusting several expressions according to thefield test results, an overall particle population balance model was reconstructed usingFORTRAN programming along with field test as verification. Combined with thecalculation results, analysis of the potential problems about material balancecharacteristics on both the existing large CFB boilers and supercritical CFB boilers aregiven attempts to provide some suggestions.②Cold tests on gas solid flow characteristics in two cyclone inlet ducts:The imported300MW CFB boiler applied a unique cyclone duct that made abreakthrough compared with the previous designs of its inlet duct of cyclone. The new design adopts a long inlet duct to help particles obtain enough high acceleration andpre-separation, which improves separation efficiency greatly and reduces carbon contentof fly ash in flue gas and therefore may influence the particle population balance. In thiscase cold test including the pressure drop and the acceleration performance of particlephases in the two inlet ducts were implemented.③Influence on primary and secondary air fan selection principle of particle populationbalance:Due to the huge amount of bed materials in the furnace, the residence of primaryand secondary air would be greatly different from those on a pulverized-coal boiler.The pipeline characteristics of both the primary and secondary air and the selectionprinciples of the primary and secondary air fans were studied for the first time in thelight of analyzing the particle population balance, together with several operating datafrom commercial CFB boilers.④Experimental study on heat balance of the imported300MW CFB boiler:According to DL/T964—2005test code, the performance of imported300MWCFB boiler was studied by VB programming. Experimental studies of dissipation heatloss were conducted on two types of300MW CFB boilers for the first time. In order toreduce the large amount of measurements, a simplified method with objective result wasintroduced and could be seen as the complement of the existing standards for similarboiler performance test calculation.⑤Combustion characteristics of the external circulation loop on Baima’s300MWcirculating fluidized bed boiler:Local measurements of gas concentrations and particles were sampled from theimported300MW CFB boiler’s external circulation loop using custom-made probes tostudy the combustion characteristics of hot cyclones and fluidized bed heat exchangersfor the first time. The experimental results may provide information for adjusting anddesigning the heat-surface arrangement and lay a foundation for modeling the flowstructure, combustion and heat transfer in similar large-scale CFB boilers.