Reduction of fine particulate matter by blending lignite with semi-char in a down-fired pulverized coal combustor

With the increasing use of low-rank coal, the upgraded semi-char produced through low-temperature pyrolysis of lignite is one of promising alternatives towards the clean and high efficient utilization. The co-firing of these pyrolytic semi-chars with parent coals has received more attention. In this paper, a kind of semi-char, produced from Hulunbuir (HB) lignite under a pyrolysis temperature of 504 degrees C, was burned in a 25 kW self-sustained pulverized coal combustor. Different mass blending ratios of semi-char (0%, 40%, 60% and 100%) were used. The results indicate that the PM0.1 yield from pure combustion of HB lignite is 1.6 times of that from semi-char. The PM0.1 yields of the coal/char blends are much less than the linear summation of yields of two blending fuels without considering their interactions. As for coarser PM mode, the reductions still exist for both PM0.1-1 and PM1-10 particles. The different PM yields of pure combustion cases are attributed to less volatile mineral species and also less fragmentation degree of semi chars during combustion. A mechanism is postulated for PM reduction during the combustion of coal blends. PM0.1 amounts are decreased since the volatilized mineral species is considerably scavenged by the previously formed semi-char surfaces, as partly evidenced from a time scale analysis. The scavenged compounds then serve as "glue" to convert ash particles to larger agglomerates, which may result in the reduction of PM0.1-10 yields. (C) 2016 Elsevier Ltd. All rights reserved.