EFFECTS OF BIOMASS ON DYNAMICS OF COMBUSTION IN CFB

Abstract

Fludized bed technology is very suitable for the combustion of biomass. Nevertheless substitution of coal with biomass affects boiler operation and especially dynamics and controllability. Non-homogeneity of biomass and fuel feeding disturbances cause process unstability, such as variations in temperatures and pressures, which reduce lifetime of equipment and structures. Because of process unstability higher air coefficient must be used in order to avoid CO emissions, which is not economical. Combustion profiles for coal, wood and peat, measured at the VTT Processes Pilot circulating fluidized bed (CFB) reactor, have been compared. Process stability and char inventories have been studied by the measurements and the model. Biofuels are usually very reactive and their combustion profiles are quite different compared to coals. Because of high reactivity and low char content combustion process with biofuels is very sensitive for fuel feeding. Also low char inventory effect on load changes combined with combustion profile that differs from coals. Because of different combustion profile heat transfer can be a limiting factor in load changes despite the high reactivity and fast oxygen response.

Keywords

Dates

  • Submission Date2004-03-06
  • Revision Date2004-04-20
  • Acceptance Date2004-08-27

References

  1. [1] Kn?big, T. Werther, J., ŭand, L.-E. and Leckner, B. Comparison of large- and small-scale circulating fluidized bed combustors with respect to pollutant formation and reduction for different fuels. Fuel, 1998. Vol. 77, No. 14, pp. 1635-1642.
  3. [2] Tourunen, A.S, Saastamoinen, J.J., H䭤l䩮en, J.P., Paakkinen, K.M., Hypp䮥n, T.E., Kettunen, A.M., Study of Operation of a Pilot CFB-reactor in dynamic conditions, Submitted to 17th FBC: 17th International Conference on Fluidized Bed Combustion 8-21.5.2003, ASME, Jacksonville, Florida.
  5. [3] Stephanopoulos, G., Chemical Process Control: An Introduction to Theory and Practice, Prentice/Hall International, Inc., New Jersey, 1984
  7. [4] Mikkonen, H., Lepp䫯ski, K. & Mononen, J. 1999. Implementation of the Combustion Power Control in a 23,4 MW Bubbling Fluidised Bed Boiler. University of Oulu, Department of Process Engineering, Systems Engineering Laboratory. Publications, series A, Oulu.
  9. [5] Lehtom䫩, K. Wahlstr?m, F., Kortela, U. & Luukkanen, J. 1983. New Combustion Control Methods in Powerplants Burning Inhomogenous Fuels. The Fifth Power Plant Dynamics, Control and Testing Symposium in Knoxville Tennessee, USA. Knoxville, The University of Tennessee.
  11. [6] Tourunen, A., Saastamoinen, J., H䭤l䩮en, J., Paakkinen, K., Kettunen, A., and Hypp䮥n, T., Dynamic measurements in a laboratory scale circulating fluidized bed combustor. Circulating Fluidized Bed Technology VII, pp. 669-676, John R. Grace, Jesse (J.-X.) Zhu, and Hugo de Lasa, (Eds.), Ottawa 2002 (Proceedings of the 7th International Conference on Circulating Fluidized Beds, Niagara Falls, Ontario, Canada, May 5-8, 2002).
  13. [7] Saastamoinen, J., Modelling of Dynamics of Combustion of Biomass in Fluidized Beds. In this Journal issue.
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