Research on molding-drying characteristics of heat fragmentation semi-coke of flame coal

Low-rank coal is prone to fragmentation and pulverization during pyrolysis,resulting in the formation of a large amount of pyrolysis semi-coke.Its short transport radius,easy formation of dust and self-ignition,and difficulty in utilization have become the bottleneck restriction the development of pyrolysis technology.The formation of heat fragmentation semi-coke can fully utilize the natural size distribution of semi-coke,which solves the problem of product transport.At the same time,as a clean coal product,it can be widely used as a substitute for bulk coal in the current rural area,which is an effective and economic solution.In this paper,the molding-drying characteristics of heat fragmentation semi-coke of long flame coal were quantitatively investigated.The water-soluble binder sodium humate and the inorganic binder bentonite with good thermal strength and stability were selected as composite binders.The cold compressive strength of the briquette under different binder formulations was tested by forming press.The optimum drying system was determined by blast drying method,and finally a 50 kg molding test was carried out.The experimental results show that the formation effect of composite binders of sodium humate and bentonite is better than that of single formulation,and the optimum molding conditions for flame coal are 6% sodium humate,5%bentonite,28% moisture content,20 MPa molding pressure and 65%( <1 mm) particle size ratio.The briquette is dried in three temperature ranges,avoiding the problems of large deformation rate,more cracks and lower mechanical strength of briquette caused by too fast jump of drying temperature.The optimal drying system for coal is 0.5 h at the initial temperature of 60 ℃,1 h at the transition temperature of 100℃,and 1.5 h at the final temperature of 130 ℃.The pilot test was carried out by the above-mentioned molding-drying method,and the results show that the volatilization of the heat fragmentation semi-coke coal is 10.55%( ≤12%) and a calorific value is 28.97 MJ/kg( ≥24 MJ/kg),the sulfur content is 0.33%( ≤0.5%),the cold compressive strength is 459 N( ≥400 N),the ash is 11.69%( ≤25%),which are superior to the national standards( GB 34170—2017) and Beijing local standard( DB 11/097—2014).The feasibility of the process is demonstrated.