Experimental study on pore structure and mechanical dehydration of coal gasification fine slag

Coal gasification fine slag is a kind of solid waste with high carbon content produced in the process of coal gasification. There is an urgent need to analyze the various pore sizes and their characteristics, and then design a proper method for dewatering gasification fine slag. In this study the low-temperature adsorption analysis, high-pressure injection analysis (mercury porosimetry) as well as the two types of filter press are used to first analyze the gasification slag pore characteristics and then dewatering efficiency, respectively. Results show that the full pore size combined analysis method portray that the pore size increases rapidly between 100 ~ 2000 nm, which is significantly different and larger than the pore size at low-temperature nitrogen adsorption analysis (4.37 nm). As a result, the combined pore size method of high-pressure mercury injection and low-temperature nitrogen adsorption predicts more precise results. Micropores, transition pores, mesopores, and macropores account for 6.62%, 7.84%, 18.46%, and 67.08% of the total. A filter press with a diaphragm plate and frame is an efficient dewatering device for fine coal gasification slag. The final filter cake moisture is 50.87%, which is significantly lower than the vacuum belt filter with 69.22%. A new option for coal gasification fine slag dewatering equipment is the ultra high-pressure filter press; the moisture content of filter cake obtained is 44.70%, and the dewatering effect is outstanding. This study will help to better design the dehydration methods of the wet slags. Ultimately, it will help recycling the water, reducing the ash quantity as well as the cost of the ash landfill.