Measurement of Submicron Ash Emissions and Associated Trace Elements From A Pilot-Scale Boiler Simulation Furnace

Concerns about the health effects of solid particulate emissions from coal fired power plants have recently focussed on the fine or sub-micron particles.   The potential health effects of these particles when inhaled are exacerbated by the presence of toxic trace elements, many of which are concentrated in the fine ash.

At present there is very little real data on the emission of fine ash and associated trace elements.  More data would provide emission factors for environmental assessments and better define the design requirements for dust collectors such as electrostatic precipitators (ESP) or fabric collectors.

The objective of this project was to provide this data for one or two coals and, in doing so, demonstrate that pilot-scale combustion plant would be effective for producing this data for a wide range of coals and for a range of combustion conditions.

The only known method of sampling ash into its size fractions for weighing and trace element analysis is the use of a Cascade Impactor (CI).  This project included familiarisation with the use of a CI before doing the actual measurements.

Sampling at the inlet and outlet of the ESP fitted to the pilot scale Boiler Simulation Furnace produced results that were not completely satisfactory.  The reported total mass of ash collected was questionable and many of the trace element concentrations were below detection limits.  An inherent problem with the use of a CI is that it is not always feasible to collect enough ash of each size fraction to give adequate sensitivity.

The planned testing of a second coal was abandoned because the necessary sampling time would have been prohibitively long.  This is likely to be the case for most coals.

The trace element data that came from this project has limited value because the sensitivity of measurement was limited; many of the results were near or below detection limits.

The project achieved the objective of establishing whether pilot scale combustion testing is a viable means of acquiring data on fine ash and trace element emissions: as it stands, the methodology and the sampling apparatus have been shown to be unsuitable for semi-routine production of accurate data.