Combustion characteristics of coals using a drop-tube furnace

Fourteen coals were selected for char refiring tests using a drop-tube furnace (DTF) in order to compare with previous tests on a 1 MW combustion facility. Each coal was sieved into two size fractions (53-75 and 106-125 mum) and characterised using proximate analysis and conventional petrographic tests as well as a test for % unreactives using image-analysis. The coal fractions were then pyrolysed at 1300 degreesC for 200 ms in 1 vol% oxygen in nitrogen. The reactivity, morphology and surface area of the chars were evaluated using thermal, optical and adsorption techniques, Each char fraction was then passed through the DTF at 1300 degreesC using a residence time of 600 ms and a furnace atmosphere of 5 vol% oxygen in nitrogen to evaluate burnout propensity, The characteristics of the coals, the chars and the residues after refiring were compared to determine whether any links exist between burnout, intermediate char products and coal composition. The link between % unreactives and burnout was confirmed for high volatile bituminous coals. Results obtained from two low volatile coals confirmed that their burnout was better than predicted from their properties. For the S. American (Guasare) coal poorer than expected burnout was obtained, as in previous work, but only for the larger size fraction. (C) 2001 Elsevier Science Ltd. All rights reserved.