Study on Ash Fusion Behaviors and Physico-Chemical Characteristics of Semi-coke and its Blended Fuel with Coal

摘要

With the rapid development of coal chemical industry in China, a large number of low-volatile carbon-based fuels such as semi-coke are in urgent need of combustion and utilization, and the co-combustion with high-volatile coal shows the potential to realize the large-scale utilization of semi-coke in coal-fired power plant. Because the blending coal can hardly match the design coal, it is easy to aggravate the degree of deposition and slagging on the heating surface and affect the operation of the boiler. However, the melting behavior of ash produced by blended coal with semi-coke combustion needs further study. In this paper, the ash melting behavior and physico-chemical characteristics of semi-coke and its blended fuel with coal were experimentally studied. Firstly, the relation of ash composition and ash melting behavior was observed by comparing the ash composition and ash fusion point of semi-coke and raw coal. Secondly, the influence of blending ratio and blending mode on the ash melting behavior of semi-coke blended fuel was studied by micro-computer ash melting point meter. Finally, the microstructure and physico-chemical properties of the melted ash at the softening temperature were evaluated by scanning electron microscope (SEM) technique with X-ray spectrometer (EDS) and X-ray diffractometer (XRD) technique. The experimental results showed that the mineral composition and oxide content in the semi-coke were different from the raw coal, which led to the change of coal ash fusibility. Meanwhile, the ash fusion point of semi-coke blended fuel could not be expressed linearly by the ash fusion point of its raw coal, and the influence of blending mode including in-furnace blending and out-furnace blending on the ash fusion point could be neglected. While the microstructure and physico-chemical properties were affected by the blending mode. Compared to the in-furnace blending, the carbon content was lower in out-furnace blending. Furthermore, the blending mode had a significant influence to the mineral composition.