SNCR in biomass combustion facilities: from theories to existing models

Abstract

With the significant use of biomass for energy purposes, as the only CO2-neutral carbon-based renewable energy source, besides several well-known advantages, certain disadvantages appear. One of them is the possible increased emission of nitrogen oxides, NOx, which is especially pronounced with the usage of agricultural biomass. Given the available resources of this biomass and increasingly stringent legal norms regarding NOx emissions, this problem needs special attention, which is the topic of this paper. The paper presents: mechanisms of NOx formation and conversion of nitrogen from fuel during combustion, a brief overview of available methods for denitrification, both conventional and newer ones that have not yet come to industrial-scale application. NOx emissions from biomass combustion are mainly caused by fuel-bound nitrogen, which is especially present in biomass with a high content of bound nitrogen such as agricultural biomass. Therefore, the focus is on selective non-catalytic reduction, SNCR, as a secondary measure of denitrification. Theoretical bases of SNCR, presentation of SNCR reagents, main pathways of chemical reduction reactions for different reagents, and reaction kinetics are given. Also, the general bases for setting numerical SNCR reduction models and reviewing existing ones, as well as experimental results from the available literature, are presented. Finally, examples of industrial applications of SNCR reactors and general recommendations for the application of this denitrification measure are introduced.