Abstract
Ash resistivity is an important factor in the collection efficiency of electrostatic precipitators (ESPs). There is good experience in the industry regarding resistivity of coal fly ash and well-established models for its prediction based on coal ash composition. The same is not true for biomass ash and this paper reports much-needed data for three different biomass types. Coal pulverised fuel ash (PFA), can be used as an aluminosilicate additive to mitigate biomass ash deposition issues. The effects of PFA additive on the resistivity of biomass ashes is also reported here. Biomass ash resistivity is an order of magnitude lower than that of typical coal ashes, and thus re-entrainment of particles in ESPs may become an operational issue, exacerbated by the presence of moisture and sulphur. PFA additive can increase the resistivity, but also leads to higher ash loading. Regression analysis indicates that potassium in biomass ash impacts significantly upon resistivity, contrary to previous studies. Various existing resistivity models were tested for predicting biomass ash resistivity; they produced significant overestimates when compared to experimental results due to omission of potassium as a component of the ash. Modifications to existing models or new models are required to predict resistivity of biomass ashes, and the data reported here will be important for developing such a model.
Highlights
As a result of increased scientific understanding of the effects of atmospheric pollution, most industrialised nations have enforced legislation to limit emissions of fly ash particulates; legislation that will become more stringent as time passes
The purpose of this study is to examine the changes in biomass ash resistivity resulting from the use of a potential aluminium-silicate based additive for deposition control, coal pulverised fuel ash (PFA), along with analysis of the important ash constituents affecting the ash
Of the samples within this study, the coal PFA and white wood ash (WWA) samples contain the highest concentration of submicron particles at 1.5%, while olive cake ash (OCA) contained the least at 0.6%
Summary
As a result of increased scientific understanding of the effects of atmospheric pollution, most industrialised nations have enforced legislation to limit emissions of fly ash particulates; legislation that will become more stringent as time passes. Low-NOx burners have been increasingly used to reduce emissions from pulverised fuel (P.F.) boilers and this has significant implications for ESP performance Their use has been found to increase residual carbon content within fly ash to above 5% [9], a result of the lower oxygen stoichiometry in an attempt to reduce thermal NOx production. For conductive materials such as unburnt carbon or metallic particles, with resistivities below 106 Ωm, particles can leave the plant without being captured [1]. The purpose of this study is to examine the changes in biomass ash resistivity resulting from the use of a potential aluminium-silicate based additive for deposition control, coal pulverised fuel ash (PFA), along with analysis of the important ash constituents affecting the ash. While the current work is not focused on this aspect, emissions and elemental partitioning of trace metals during biomass co-firing (which will result in similar fly ash concentrations) have been studied previously [24,25,26,27]
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