LAUSR

The alkali content in the ash is commonly thought to be the “bad actor” in determining coal ash deposition rates on boiler heat transfer surfaces. This paper reports results of 16 tests in which ash aerosol deposition rates were measured for three coals, burned under air- and oxy-fired combustion conditions. A 100 kW down-fired laboratory combustor coupled with a specially designed deposition probe was employed. Ash aerosol particle size distributions and size-segregated compositions were measured using electric-mobility, light-scattering, and low-pressure impactor techniques. Net sodium vaporization (assumed to be the fraction of sodium collected as a <0.6 μm fume) was compared to literature data. For ash deposition rates, emphasis was on the tightly bonded “inside” deposits rather than the loosely bound “outside” deposits, which could not be collected or weighed precisely. Over a limited range of these tests, where PM1 was indeed greatly enriched in sodium, deposition rates did correlate with the sodium...