Analysis Of The Ash Characteristic During Co-Firing Of Biomass And Coal

Co-firing of biomass and coal is one of the effective ways to use biomass as a renewable resource. The research of co-firing of biomass and coal is mainly on characteristics of pyrolysis, combustion and pollutant emissions but rarely on the ash characteristics. The analysis of ash characteristics during co-firing of biomass and coal means a lot for the prevention of slagging and corrosion of heating surface. The ash characteristics during co-firing of biomass were comprehensively expounded based on confirming the appropriate ashing time and temperatures, and the analysis of the ash oxide composition and mineral phase.First of all, the appropriate ashing time and temperatures of co-firing of biomass and bitumite were determined by muffle furnace and scanning electron microscope. It was found that the appropriate ashing time was 2h. The ashing temperature of co-firing of platanewood and bitumite should be adopted at 650,700 and 800℃, and the ashing temperatures of co-firing of wheat straw and bitumite should be adopted at 600,650,750 and 800℃.Secondly, the ash oxide composition and mineral phase of co-firing of biomass and coal was studied by EDS and XRD, and the ash melting temperatures of co-firing of biomass and coal were measured by ash fusion temperature pyrometer. With the increasing of platanewood proportion, the SiO2 and Al2O3 contents decreased, but the contents of K2O, CaO and MgO were the reverse. The Na2O and Fe2O3 contents were at a low level which had no obvious change. With the increasing of wheat straw proportion, the Al2O3 contents decreased, but the contents of K2O and SiO2 were the reverse, while the Na2O, CaO and Fe2O3 contents had no obvious change.Anorthite appeared in the ash at the 30% mixture radio of platanewood. The albite appeared and the mullite disappeared at 50% mixture radio of platanewood. The crystalline phase intensity reduced with the increasing of ashing temperature. Albite and hematite appeared at the 30% mixture radio of wheat straw, the mullite disappeared at 50% mixture of wheat straw radio due to the reducing of Al2O3 content. Diopsidc and leucite appeared at 70% mixture of wheat straw due to the increasing of CaO and K2O content, meanwhile, the hematite disappeared. The intensity of platanewood ash and wheat straw ash was quite low, which indicates that the ashing temperature of 1000℃would cause a low crystallinity.The ash melting temperature decreased with the increasing of mixture ratio of platanewood and wheat straw. The aluminosilicates with low melting points were the immediate cause of a low ash fusion point, and they were formed by alkali oxides with high content in the biomass ash and silicon, aluminum oxide.Finally, support vector machine (SVM) was employed to model the ash fusion characteristics during co-firing of biomass and coal. The slagging tendency and ash fusion temperatures during co-firing of biomass and coal were predicted by the optimized SVM. It was found that the SVC model could achieve an excellent accuracy and it could substitute the coal slagging index to identify the slagging tendency of co-firing of biomass and coal. The SVR model gained a better predicting performance on ash melting temperatures using limited training samples compared to RBFNN and GRNN, and it could guide the mixture of biomass and coal in boiler.