Title:
Detailed Chemical Kinetics Modelling of NOx Reduction in Combined Staged Fuel and Staged Air Combustion of Biomass
Author(s):
Houshfar, E., Løvås, T., Skreiberg, Ø.
Document(s):
Paper
Abstract:
Fuel and air staging are used to study the potential for reduction of NOx emissions from biomass fuelled reactors. The two well-known methods to reduce NOx emissions in a combustion process by primary measures are air-and fuel staging. Air staged reactors use primary air injection in the fuel bed, and a secondary air injection in the combustion chamber. A rich combustion in the first stage (close to stoichiometric condition) gives the maximum conversion of fuel-N to N2 (minimum NOx emissions after complete combustion). Fuel staging has been introduced as an alternative emission reduction technique due to the practical demands of air staging (high combustion temperature in the primary zone). Fuel-staging is a method of fuel reburning. The present study shows the effect of different variables on NOx reduction capability. Reactor models consisting of sequences of ideal reactors are employed in combination with a recently available detailed chemical kinetics mechanism, especially suitable for biomass combustion. Nitrogen in the fuel is known to be the largest contributor to NOx emissions; hence the nitrogen content of the fuel is found to be an important parameter in the reduction of nitrogenous emissions. Furthermore, the potential for NOx reduction is found to be highly affected by the amount of excess air in the primary zone, in advance of the secondary air inlet, with a clear optimal reduction close to a primary air excess ratio of 1. Increasing reactor temperature however has an inverse effect on the reduction potential due to the onset of thermal NOx production. Fuel staging is found to have a higher potential for reduction in the majority of the investigated range of primary excess air ratios. Only in the region close to stoichiometric conditions in the primary zone is a higher NOx reduction observed for air staging. The achieved NOx reduction under the optimum conditions was up to 76 percent.
Keywords:
modelling, NOx emission, reduction, biomass combustion, modeling
Topic:
Thermochemical conversion - Combustion and co-combustion
Subtopic:
Combustion and co-combustion for large utility and industrial scale applications
Event:
18th European Biomass Conference and Exhibition
Session:
VP2.4.4
Pages:
1128 - 1132
ISBN-13:
978-88-89407-56-1
ISBN-10:
88-89407-56-5
Paper DOI:
10.5071/18thEUBCE2010-VP2.4.4
Price:
FREE
