Novel approach for the analysis of heat transfer in bagasse-fired furnaces

The heat exchange between the flame and the water walls and bundles of the combustion chamber is considered a complex case of heat transfer, as it takes place in parallel with the combustion process, which constitutes the internal heat source in the radiant medium. Soviet scientists developed the Normative Method for the calculation of total heat exchange in the furnace, based in both empirical and analytical results. This method describes successfully the main thermal indicators of the performance of the combustion chamber and their relationship with the constructive characteristics. However, the Normative Method was developed for coal-fired systems, and its application to biomass-fired (bagasse, in the present work) furnaces is not completely satisfactory. This paper describes the calculations of heat transfer in a combustion chamber, originally designed for combustion on dumper grate and retrofitted for the burning of bagasse in suspension. A new set of indices is proposed for the calculation of the thermal performance of boilers with combustion in suspension. Namely, the thermal-efficiency coefficient the fouling coefficient ({psi}{sub main}), the fouling coefficient ({xi}), the M parameter, the unequal temperature coefficient ({eta}), the adimensional gas temperature ({theta}), are shown to be relevant indices that can markedly improve the accuracy of the results produced by the Normative Method. For example, the error in furnace exit gas temperature has been as low as 0.35%. (author)