(654c) Towards Prediction of Ash Deposition Rates from Combustion of a Wide Variety of Fossil and Biomass Solid Fuels.

This paper focuses on prediction of ash deposition rates from the combustion of solid fuels. To this end we present results from multiple coals, petroleum coke, rice husks, torrefied wood and mixtures of these, burned under oxy-fired and air-fired conditions, with and without additives. Rates of ash deposition were measured on a specially designed deposition probe inserted for various time intervals at a flue gas temperature of approximately ~1200K, which is typical of fouling conditions in the super-heater region of a boiler. Deposits were divided into inside deposits that were difficult to remove and outside deposits that could be removed by shaking. In the absence of chlorine, the rate of deposition of these inner deposits was independent of the composition of the submicron particle glue, and could be predicted by correlations involving only PM₁ concentration in the flue gas, and not its composition. The outer, more loosely bound deposits appeared to correlate with the particulate alkali content in the flue gas. The additive tests involving added chlorine did not fit the simple correlations for all the other 38 tests. More sophisticated correlating methods are currently being used to determine how to predict all the deposition rate data (obtained from the 100kW rig) from flue gas and fuel compositions alone. These must ultimately be combined with aerodynamic models to allow extrapolation to full scale turbulent flows. The hope is that on-line ash aerosol particle size measurements, together with knowledge of fuel compositions, will allow real time measurement and, possibly control, of deposition rates on heat transfer surfaces in full scale systems.