Four thematic issues were decided to have the major impact on the decision-making:
- Fuel characteristics and presumed performance
- Bed material characteristics and performances.
- Design aspects of gasifier and auxiliary equipment.
- Operational aspects.
The guidelines that summarise the project outcome are not exhaustive but concentrate on operational matters, i.e. avoiding difficulties connected with the alkali contents in the fuel and bed material. Agricultural (fuel production and preparation) aspects are covered to a lesser extent. Likewise, ash utilisation and other post-process topics are not taken into account. The agglomeration tendency depends on different mechanisms combined to a complex picture and it is difficult to point at one single explanation for the obtained results. But if alkali/chlorine is present in relatively high amounts, in combination with poor fluidised bed performance, operational problems are evident. It may be wise to acknowledge that both fuel specific and technology specific reasons contribute to the sintering tendencies. Since the system tends to be both sensitive and complex chemically, technical aspects such as reactor design/geometry, fuel/gas distribution and flow rates all contribute to the encountered difficulties with high alkali bio fuels. These guidelines might cast some light on the problematic but the challenge remains, however, to determine which one of the fuel specific/technology specific reasons is dominating at certain conditions.