Influence of Co-Combustion on the Quality of Coal Fly Ash

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Title: Influence of Co-Combustion on the Quality of Coal Fly Ash

Author(s): A. J. Saraber and J. W. van den Berg

Publication: Special Publication

Volume: 221

Issue:

Appears on pages(s): 735-750

Keywords: chicken manure; coal fly ash; co-combustion; refuse derived fuel; wood

Date: 5/1/2004

Abstract:
In most Dutch power stations secondary fuels are co-combusted. It is important that the quality of the generated fly ash does not degrade because of co-combustion, as this will hinder utilization. Therefore, a project was started to assess the consequences of co-combustion of selected fuels (demolition wood, chicken manure and refuse de-rived fuel) on the properties of the fly ashes. The co-combustion experiments were carried out in the KEMA Test boiler (pilot-scale, 1 MW1h). The properties of the generated fly ashes were analyzed and the behavior of the fly ashes when applied as pozzolanic filler was assessed. It was concluded that the cystalline components as identified by X-ray diffraction are the same as normally found in Dutch fly ashes (ASTM class F), with exception of fly ash from chicken manure. The glass content is reduced by co-combustion depending on the co-fired fuel. If chicken manure is co-combusted, the chemical composition changes due to the increase of Ca, P, K and S. Co-combustion of demolition wood and refuse derived fuel (RDF) causes an increase of Ca, Na and K. The pozzolanic behavior of fly ash appears not to be influenced by co-combustion of demolition wood. However, co-combustion of RDF causes a decrease in pozzolanic behavior, but relatively high percentages are possible up to the point where it no longer meets the limits. Co-combustion of chicken manure appears to have a positive influence, but this is related to other reaction mechanisms than pozzolanity. It can be stated that fly ashes from high percentages of co-combustion are able to meet the basic requirements of the European standard (EN 450). It all depends on the nature of the co-fired fuel and especially on its inorganic matter and ash content.