Biomass fuels play an important role in the field of fluidized bed combustion, but due to the diversity and uncertainty of fuels, there are usually some problems of high CO emission that cannot be directly solved by combustion adjustment. In this paper, a 75 t/h biomass fluidized bed was taken as the research object. It was observed from the field test that the gas incomplete combustion loss reached 12.13% when mono-combustion of wheat straw was conducted, and the CO concentration in the exhaust gas exceeded 30k ppm. Combined with the CPFD numerical simulation, the combustion characteristics and influence of secondary air layout on CO reduction performance were discussed in detail. The results revealed that the gas temperature gradually increased along furnace height under the initial condition, and the maximum temperature was more than 1000 °C at furnace outlet. The air curtain of the secondary air jets was insufficient, and the wheat straw rose rapidly as it entered into the furnace. By arranging adjacent secondary air ports above each fuel-feeding inlet, the residence time of particles in the furnace could be significantly increased, thus, the furnace temperature distribution was more reasonable and the CO emission was reduced by 58.6%.
As an industrial solid waste, the discharge of a large amount of red mud (RM) causes serious environmental problems; thus, a large proportion of RM co-combustion has been proposed to solve the consumption problem. In this paper, an experiment with various proportions of RM co-combustion was conducted on a 0.2 t/h circulating fluidized bed (CFB) boiler. Desulfurization performance, combustion characteristics, and ash deposition characteristics were analyzed, especially under the large proportional co-combustion conditions. As the study results showed, the desulfurization efficiency was positively correlated with the RM co-combustion proportion. When the RM co-combustion proportion reached 50%, the desulfurization efficiency was over 94%. After a period of cyclic combustion, the highest desulfurization efficiency exceeded 99.5%. The smaller size of RM was beneficial to improve the combustion efficiency and the combustion stability. However, a large area of sintering formed on the top of the heating surface in the furnace, which was lighter than the sintering of high alkali fuels such as Zhundong coal. Meanwhile, the content of sulfates, such as Na2SO4 and CaSO4, in the ash increased, which clearly proves that RM has the desulfurization effect. Therefore, a large proportion of co-combustion could meet the requirements of in-situ desulfurization and realize the resource utilization of RM.
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