Experimental Study On Agglomeration Of Fluidized Bed With Biomass Combustion

With the decreasing of fossil fuel resources and the emission limitation of greenhouse gases, bioenergy becomes one of the most important regenerative energies. Compared with other technologies, power generation through combustion process is simple, economical and feasible. However, the high content of alkali metals in biomass causes many problems, such as agglomeration of the bed materials, deposit and erosion of heat transfer surfaces.The agglomeration characteristics in biomass combustion process in a fluidized bed combustion reactor of bench scale were mainly researched in this thesis. Experiments on biomass-coal blends combustion and pyrolysis in thermal gravimetric analyzer were made, the controlling of agglomeration was also investigated. Analysis methods, such as Scanning electron microscopy, energy-dispersive X-ray (SEM/EDX), X-ray fluorescence (XRF) and X-ray diffraction (XRD) were used. The research contents are as follows:1. Combustion and pyrolysis characteristics of biomass (corn stalk and fruit tress) and biomass-stone coal blends were investigated by thermal gravimetric analysis. The results show that the ignition temperature and burn-out time of the biomass-coal blends decreases with the increase of ratio of biomass to stone coal in the blends. Chemical reaction parameters of stone coal, biomass and biomass-stone coal blends were achieved by the analysis of TG/DTG curves.2. The influence of combustion temperature and alkali metals in biomass (corn stalk, fruit tress and corn core) is investigated experimentally in a fluidized bed combustion reactor of bench scale. The results indicate that the defluidization time decreases and the agglomeration problem becomes more severe as the bed temperature increases. The analysis shows that the occurrence mode of alkali metals is the main reason for agglomeration rather than ash proportion in bed material. The adhesive, which adhere to different bed material particles and form the agglomerates, has high concentration of Si, K, Ca, Mg and so on.3. A series of experiments were made in the same fluidized bed combustion reactor of bench scale at 900℃, contradistinctively. River sands, dolomite, clay and stone coal ash were used as bed materials separately. The results show that the four kinds of bed materials have pronounced effects on controlling of agglomeration. The particle size analysis of bed material after experiment shows that clay has the most pronounced effect on controlling of agglomeration, then the stone coal ash, the third one is dolomite, the last one river sands. The SEM/EDX analysis of the agglomerates indicates the surfaces of agglomerates are covered by flocculent materials, which could prevent the agglomerates from augmenting and accumulating. Compared with other bed materials, the stone coal ash is economical.