oa South African Journal of Chemical Engineering - CFBC fuel flexibility : added value of advanced process optimization

Volume 19, Issue 3
  • ISSN : 1026-9185



A major advantage of circulating fluidized bed combustors (CFBC) is the high flexibility according to fuel type, composition and specific properties like particle size, moisture and morphology. On the other hand, flow and transport characteristics of large scale fluidized beds are far from ideal mixing conditions. Hence, fuel flexibility design for new or existing plants is a multi-parameter optimization problem with numerous aspects from storage and feeding equipment over optimum feeding location to the effect on fuel burn-out, emissions and wear. The combination of plant audits, specific measurements (e.g. primary air nozzle pressure drop as a measure for flow distribution and bed flow pattern) and the application of advanced computational fluid dynamics are presented in this contribution. Specific fuel flexibility challenges and solutions considering

  • air staging,
  • wear reduction and
  • limestone injection for direct desulphurization
are shown for 3 selected German and Polish CFB plants (150-490 MW) and fuel compositions varying between
  • coal/RDF mixture,
  • up to 40% substitution of coal with wood pellets and/or wood chips and
  • 100% biomass with different fuel specifications.
The examples demonstrate the added value of a joint process optimization approach for an efficient analysis of the complex coupling flow and transport mechanisms in CFBs. The increased insight and understanding is a major support for finding proper design and operation conditions for the application of flexible fuel compositions.

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