Fragmentation of small coal particles under fluidized-bed combustor conditions

Abstract

Particles of four coals sereened to mean diameters (do) of 1.5 and 2.5 mm were subjected to rapid radiant heating under nitrogen and/or 5% oxygen, and the product particles were collected after some seconds. The number distributions of size for the products were compared to the original distributions. The 1.5-mm particles suffered limited breakage with some dust and a small amount of do/2 fragments produced. The amount of breakage was independent of volatile matter content, but greater with higher vitrinite materials. The behavior was consistent with the predictions of a model based on thermally induced stress. The manner of breakage of 2.5-mm particles of a very high VM coal and an anthracite were contradictory, with only some particles of the former breaking, but most of the latter. Increasing the pressure to 1.0 MPa led to less breakage with the high VM coal, suggesting that pressure from the volatiles is contributing to breakage. The degree of fragmentation under 1.0 MPa increased for the anthracite, which is consistent with the operation of the thermal stress model. The influence of oxygen on breakage in this case is determined by the volatile matter content.