MODELLING OF DYNAMICS OF COMBUSTION OF BIOMASS IN FLUIDIZED BEDS

Abstract

New process concepts in energy production and biofuels, which are much more reactive than coal, call for better controllability of the combustion in CFB boilers. Simplified analysis describing the dynamics of combustion in FB and CFB boilers is presented. Simple formulas for the estimation of the responses of the burning rate and fuel inventory to changes in fuel feeding are presented. Different changes in the fuel feed, such as an impulse, step change, linear increase and cyclic variation are considered. The dynamics of the burning with a change in the feed rate depends on the fuel reactivity and particle size. The response of a fuel mixture with a wide particle size distribution can be found by summing up the effect of different fuel components and size fractions. Methods to extract reaction parameters form dynamic tests in laboratory scale reactors are discussed. The residence time of fuel particles in the bed and the resulting char inventory in the bed decrease with increasing fuel reactivity and differences between coal and biomass is studied. The char inventory affects the stability of combustion. The effect of char inventory and oscillations in the fuel feed on the oscillation of the flue gas oxygen concentration is studied by model calculation A trend found by earlier measurements is explained by the model.

Keywords

Dates

  • Submission Date2004-03-06
  • Revision Date2004-05-10
  • Acceptance Date2004-05-27

References

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