ECN publication
Alkali distribution for low temperature gasification
Published by: Publication date:
ECN Biomass, Coal and Environmental Research 5-1-2011
ECN report number: Document type:
ECN-E--10-103 ECN publication
Number of pages: Full text:
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During the 2006-2009 EOS-LT programme on biomass co-firing it became clear that there is potential for biomass to add to the targets set in the Long-Term Energy Research Strategy (EOS-LT) of the Dutch Ministry of Economic Affairs. The strength of indirect co-firing is that it is an efficient technology to produce a combustible gas and it allows for capture of undesired ash components from the gas phase. However, it also became apparent that additional measurements were needed to determine to what extent this is true. In the 25 kWth lab scale MILENA gasifier different fuels were tested to obtain data on the alkali distribution regarding the gas phase and solid phase. Low temperature gasification is a method to prevent alkalis (ash components) to evaporate, as to keep them in the solid phase. The research done during the 2010 EOS-LT period showed that for straw pellets about 10-20 wt.% of the ash related components (potassium, sodium etc.) end up in the gas phase (most of which is fine dust) and will be sent to the boiler. For chlorine the percentage sent to the boiler is about 13%. In case of RDF the amount of biomass ash related components ending up in the gas phase is less. This does not hold for chlorine however. The amount ending up in the gas phase is 18% and is based on a blend of RDF and beech wood. When switching to 100% RDF the total amount that will end up in the boiler can become quite substantial. Indirect co-firing of difficult fuels shows good potential regarding the effect of capturing alkalis in the solid phase. In case of RDF the amount of chlorine ending up in the boiler will be larger than for straw pellets, but the amount of available potassium is lower. KCl related corrosion issues might therefore be less when RDF is gasified. Agglomeration was not observed during these tests, but the balance of the gasifier shows an increase of agglomeration related components in the bed material. Eventually these can cause agglomeration, but refreshing of the bed material is a simple measure to prevent this.

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