Soot formation during coal pyrolysis

Coal pyrolysis experiments were performed in the post-flame region of a CH{dollar}rmsb4/Hsb2{dollar}/air flat flame burner running in fuel-rich conditions, where the temperature and gas compositions were similar to those in the near burner region of a large-scale coal-fired furnace. Volatiles released from the coal particles formed a cloud of soot particles at high temperatures in the absence of oxygen. The soot particles in the cloud were extracted using a thermophoretic sampling technique and were also collected using a water-cooled, nitrogen-quenched suction probe. Test variables included residence time, reaction temperature and coal type.; Based on the thermophoretic sampling experiments, primary coal-derived soot particle diameter ranged from 40 to 80 nm. Soot agglomerates as large as 30 {dollar}mu{dollar}m were also observed in the samples obstained from the bulk collection experiments.; Soot yields in terms of weight percentage of dry ash-free coal were measured in the bulk soot collection experiments. The measured soot yields were related to residence time, reaction temperature and coal rank. Soot agglomeration was indicated by the increase of the mass fraction of large soot particles ({dollar}>{dollar}5 {dollar}mu{dollar}m) with residence time. A simplified model was developed to describe the soot formation and agglomeration processes. The data obtained regarding coal-derived soot are useful in predictions of radiative heat transfer and pollutant formation in the near-burner region of pulverized coal-fired furnaces.