Potential and assessment of urea-based SNCR in a small-scale multi-fuel biomass furnace

• Combined experiments/kinetic simulation performed with urea-based SNCR in a biomass furnace. • Parameter study conducted of urea amount (NSR), temperature and residence time. • Over 90 % NO x reduction achieved at the optimum temperature of 950 °C. • 70% NO x reduction reached in steady state when complying with NH 3 legal limits. • Different NH 3 :HNCO ratios analysed for the urea decomposition. The aim of this work was to assess the potential NO x reduction achieved with urea-based SNCR in a small-scale biomass grate furnace operated with miscanthus pellets and forest biomass residues. Therefore, experiments were performed to test the main parameters of SNCR efficiency, namely the urea amount (normalised stoichiometric ratio), temperature and residence time, and the results were compared with those of a kinetic simulation applying ideal reactors in conjunction with a detailed nitrogen chemistry mechanism. The urea decomposition was estimated using different NH 3 :HNCO ratios, which were compared in the course of this work. The experimental and simulation results confirm an optimum temperature of around 950 °C, enabling a NO x reduction of over 90 % for both investigated fuels in this biomass furnace. However, at steady state, the NO x reduction was limited to 60–70 % due to the legal limits for NH 3 . At lower temperatures or residence times, a significant increase in NH 3 emissions was observed. Due to the use of urea in this SNCR system, an increase in N 2 O emissions was detected, and the simulations also predicted non-negligible HNCO emissions. For a simulation of these two species, a suitable NH 3 :HNCO ratio for urea decomposition is needed. Finally, the optimum operating point for achieving 60–70 % NO x reduction and for complying with the NH 3 legal limits shows that a great potential for using SNCR exists in small-scale biomass furnaces, if the required temperature and residence time can be provided.