Heat Transfer Behaviour of Australian Coals

The aim of this project was to study the leachability of environmentally sensitive trace elements from stockpiles of Australian thermal coals and to address the concerns that have been expressed by some overseas purchasers (in particular Japanese power stations). Although there is no evidence to suggest that trace elements are leached in significant concentrations from the exported Australian coals, it was thought prudent to obtain data on the leachate water present at the bases of coal stockpiles and from sedimentation pits at coal loaders and power stations. ACARP have been advised of reports of certain Australian coals and in particular Hunter Valley coals causing heat transfer problems in coal fired power station, both in Australia and overseas. The problems are reported to be evidenced by elevated gas temperatures at furnace exit resulting from reduced furnace absorption. This results in difficulties in controlling superheater and reheater steam and metal temperature, the heavy use of furnace sootblowers with subsequent risk of furnace wall tube erosion and high gas temperatures at exit to the boiler with consequent increases in boiler efficiency losses and operating problems with gas cleanup equipment.

There is a suspicion that there is a general association between high SiO2 and Al2O3 levels in ash and the severity of the problem.

As a consequence ACARP requested this technical review of the impacts of the ash quality of Hunter Valley coals on utility performance focussing on the issues of furnace heat transfer and the consequences of reductions in furnace heat transfer.

The present review is intended to be sufficiently comprehensive to ensure that major issues are identified and discussed. It is not intended that this be comprehensive due to the targeted nature of the study.