Reactivity and kinetics of biomass pyrolysis products for in-situ reduction of NOx in a bubbling fluidized bed

Utilizing the strong reducing properties of biomass pyrolysis products to control NOx emissions is emerging as a cost-effective and simplified method for retrofitting substandard industrial boilers. Clarifying the reactivity and kinetics of NOx reduction can effectively guide and remove NOx. However, the NOx reduction kinetics study deviated from industrial applications due to diffusion, heat and mass transfer limitations by using thermogravimetric and fixed beds. Therefore, a bubbling fluidized bed with an online monitoring system was designed and constructed to maximize the NOx reduction efficiency of biomass pyrolysis products for NOx in-situ reduction kinetics studies. The maximum NOx reduction efficiency of pyrolysis products of unit mass biomass was gained as a function of biomass supply and pyrolysis temperature. The reduction efficiency by the complete pyrolysis of unit mass biomass was optimized at 600 degrees C and 20 mg of biomass supply. However, when the temperature increased to 700 degrees C and above, the reduction efficiency of pyrolysis products of unit mass biomass was linearly related to the supply, reaching a maximum at biomass supply of unit mass biomass less than 10 mg. At 867 degrees C pyrolysis temperature, the maximum reduction efficiency of 95 % was achieved by fitting with a Gaussian model. The reaction order of NOx with pyrolysis products was close to 1, and the apparent activation energy for the NOx reduction by biomass volatiles was about 49 kJ/mol, while that by pyrolysis char was around 70 kJ/mol. This work provides theoretical and kinetic guidance for the scale-up and industrial application of controlling NOx emissions from biomass boilers using pyrolysis products.