Solar pyrolysis of low-rank coal: The effect of heat flux density and particle size

Solar pyrolysis of low-rank coal (LRC) meets the high-quality utilization of LRC and stores intermittent solar energy. The high heating rate and unilateral heating characteristic of concentrated solar energy result in particle size effects on LRC pyrolysis that differ from those observed with conventional heating methods. This work researched the solar pyrolysis characteristics of LRC for the different heat flux densities (0.56, 0.65, 0.74 MW/ m2) and particle sizes (100-1000 mu m). As the heat flux density increases, the coke and tar yields decrease simultaneously, promoting the occurrence of extra-particulate secondary reactions. With the increasing particle sizes, the coke and tar yield increased, primary reactions predominantly occur. Compared to the reactivity of 300-1000 mu m, there is strong diffusion resistance at the large particle size, reducing the gasification rate. For 100-300 mu m, the gasification rate is the lowest and the graphitization is the highest according to structural characterization. The influence of the heat transfer exceeds the diffusion resistance. This study reveals the effect of the heat flux density and particle sizes in the solar pyrolysis of LRC product evolution. The results show that LRC is suitable for solar pyrolysis and gasification to produce chemicals and other fuels.