Effects of alkali and alkaline-earth metals and retention time on the generation of tar during coal pyrolysis in a horizontal fixed-bed reactor

The effects of alkali and alkaline earth metals and the retention time of tar precursors during the diffusion processes on the yield and composition of tar are discussed. The removal of these metals increased the tar yield of coal. Increase in the absorbance of tar was attributed to the increase in aromatic ring systems. Ion-exchangeable Na plays a dominant role in the retention of tar precursors, mainly polycondensed aromatic rings, by connecting them with the char matrix. Increasing the retention time in interparticle diffusion decreased the tar yield, especially for polycondensed aromatic rings. Increasing the retention time in inner-furnace diffusion slightly decreased the tar yield.261