NO x control through reburning using biomass in a laboratory furnace: Effect of particle size

Abstract

This article describes an experimental study to evaluate the effect of the particle size distribution of the reburn fuel on the effectiveness of the reburning process to reduce NO x emissions in a large-scale laboratory furnace. Rice husk, with three distinct particle size distributions, was used as reburn fuel. Initially, flue-gas data (gaseous pollutants and particle burnout) was obtained for a wide range of experimental conditions with the “three” rice husks. Subsequently, in order to improve the understanding of the relationship between reburning effectiveness and reburn fuel particle size, detailed measurements of local mean O 2, CO, CO 2, HC and NO x concentrations, and gas temperatures have been gathered from the reburn zone for three furnace operating conditions that used the “three” rice husks. The results suggest that, for the present combustor and operating conditions, there is an optimum particle size range for enhanced NO x reduction through reburning. Below or above the optimum particle size range of the rice husk the reburn mechanism is less effective probably because the biomass devolatilization process either finishes before or extends well beyond the end of the reburn zone, respectively, impeding the exposure of NO to CH i and HCCO and facilitating the CH i and HCCO interaction with oxygen. In addition, the results show that the particle burnout decreases slightly as the NO x reduction increases, regardless of the rice husk particle size range. Given that the present combustor has only the roof section and the upper four segments lined with a layer of refractory, it can be anticipated that reburning using rice husk as reburn fuel in full-scale equipment would have even a lower impact in particle burnout than that observed in this study.