Study on the composition and structure characteristics and dry decarbonization separation of coal water slurry gasification fine slag

Efficient separation and high-valued utilization of coal gasification ash or slag limit the clean and green development of coal chemical industry. In this paper, a coal-water slurry gasification fine slag (CWSFS) was studied by wet screening and classification. The relationship between the particle composition with different sizes and the structural characteristics was investigated by means of proximate analysis, XRF, XRD, BET and SEM. A classification method of CWSFS was proposed to guide the high-valued utilization of coal gasification slag. Then, dry separation of a coal-water slurry gasification fine slag was carried out using a combined treatment method of crushing and dissociation and airflow classification. The results show that the CWSFS particles of different sizes have obvious differences in fixed carbon content, ash composition and mineral types. For the CWSFS with the particle size above 74 μm, the fixed carbon content is more than 60%, the calorific value is more than 20 MJ/kg, the specific surface area is relatively high and the main component is the residual carbon that contains magnetite and brookite. For the CWSFS with particle sizes between 13–74 μm, the fixed carbon content is between 20%–60%, the calorific value is between 11–19 MJ/kg, the specific surface area is small and the main mineral types are pyroxene, marcasite and hematite, etc. For the CWSFS with a particle size between 0–13 μm, the fixed carbon content is less than 20% and the calorific value is less than 10 MJ/kg, which mainly includes the amorphous glass phase that was rich in aluminum, iron and calcium, quartz and a small amount of fayalite, muscovite and other minerals. According to the fixed carbon content of CWSFS with different particle sizes, the above three components with varying particle size ranges are defined as high-carbon component, medium-carbon component and low-carbon component, respectively. The dry separation test shows that the air flow crushing and classification process can achieve a higher product yield of 29.60% and a high ignition loss of 93.76%, compared to the traditional disc crushing-classification process. Airflow crushing was proved to be able to effectively increase the dissociation degree of residual carbon and greatly improve the separation and enrichment rate of residual carbon.