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Title:
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Combustion characteristics of low quality battle coals: mineral matter transformations
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Author(s):
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Published by:
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Publication date:
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ECN
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1999
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ECN report number:
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Document type:
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ECN-C--99-035
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ECN publication
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Number of pages:
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Full text:
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55
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Download PDF
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Abstract:
The results of an experimental study on the ash behaviour of selected lowquality battle coals for pf-fired boilers are presented. The study was run
parallel to a test program supported within the International Energy Agency
Coal Combustion Sciences Program annex 2 part 4 addressing the combustion
behaviour of these coals. A suite of coals and blends, varying in rank from
medium-volatile bituminous to subbituminous, was selected in consultation
with the Dutch electricity producers and extensively analysed, focusing on
ash composition. Relatively high levels of the elements Ca, Mg, Fe, Na and K
were found in these coals. The speciation of the inorganic constituents in
terms of mineral composition and size distribution was determined by means of
Computer Controlled Scanning Electron Microscopy (CCSEM). Single coals as
well as binary blends were fired in a 2.5 MWth boiler furnace simulator,
and ash and deposit samples were collected for off-line analysis and
evaluation. The results have been expressed and ranked in terms of slagging
and fouling propensity for each coal, and have been compared with the outcome
of a considerable number of commonly used predictive ash deposition indices.
Observations of significant slagging or fouling were in many cases related to
the presence of alkali and alkaline earth metals, which were often
ill-predicted due to the occurrence of mineral interactions. Selected tests
were performed in a laboratory-scale combustion simulator under well-defined
(low-NOx) conditions to elaborate further on the prevailing ash deposition
mechanisms. The observed mechanisms were generalised into three classes in
order to allow a certain extension of the conclusions towards new, similar
fuels. From these mechanisms guidelines were derived for coal blending aiming
to reduce ash deposition problems. The methodology of lab-scale fuel testing
to evaluate in advance their potential to induce or enhance typical
ash-related problems - here slagging and fouling - is currently being
extended to an integral assessment of ash behaviour and ash quality for
utilisation options. This report includes the initial development of a
procedure involving lab-scale fly ash production and miniaturised leaching
testing for advance evaluation of fly ash quality. 5 refs.
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