Computational Model for NO_x Reduction by Advanced Reburning

Abstract

Advanced reburning is a NO x reduction process wherein injection of a hydrocarbon fuel such as natural gas downstream of the combustion zone is followed by injection of a nitrogen-containing species such as ammonia. The authors recently reported a seven-step, 11-species reduced mechanism for NO reduction by advanced reburning processes. However, inclusion of even a seven-step reduced mechanism into a CFD code for turbulent combustion leads to substantial computational demands. In this work, the authors have further simplified the kinetic mechanism. A simpler four-step, eight-species reduced mechanism for NO reduction by advanced reburning has been developed from a 312-step, 50-species full mechanism through the use of a systematic reduction method. The four-step reduced mechanism is in good agreement with the full mechanism for most laminar flow cases. It also agrees qualitatively with three sets of experimental data, which show the influences of temperature, CO concentration, O2 concentration, and the ratio (NH3/NO)in. It can be applied for coal-, gas-, and oil-fired combustion. The four-step reaction sequence has been integrated into a comprehensive CFD combustion code for turbulent combustion, PCGC-3. The method of integration is described. Several computations are reported with the combined code to demonstrate the predictive behavior of the advanced reburning mechanism in turbulent, pulverized coal combustion. The model calculations show the effects of temperature and concentrations of CO, O2, and NH3 on NO reduction.

Systematic method of applying ANN for chemical kinetics reduction in turbulent premixed combustion modeling

“…For minor species, such as OH, H and CH 4 , errors are a little larger though profile agreements are still preserved. Predicted profiles of other involved species represent similar features even if not shown in figure. Comparatively scalar errors are a little larger in C 3 H 8 /air case than those in H 2 /air case due to inclusion of kinetics reduction process, but by referring to the errors resulting from traditional reduced mechanism [9,[28][29][30][31], the error magnitude is quite acceptable. Overall, the ANN-based method for chemical kinetics reduction can well replicate the flame dynamics in FVI at the influence of different vortex.…”

Reducing NOx Emissions Using Fuel Staging, Air Staging, and Selective Noncatalytic Reduction in Synergy

“…In current applications, the reburn fuel can be same as the primary fuel, and enlists natural gas, 28-32 pulverized coal, 31-34 micronized coal, 31 oil, 32 and gasified biomass. 18,35 Studies have been conducted to elucidate the effect of fuels on reburning.…”

“…Agents for the SNCR are ammonia (NH 3 ), hydrogen cyanide (HCN), urea ((NH 2 ) 2 CO), cyanuric acid (C 3 O 3 N 3 H 3 ), or ammonium sulfate ((NH 4 ) 2 SO 4 ). 32,38 Hybrid reburn has been tested in various configurations where the reducing agent is added (i) along with the reburn fuel, (ii) downstream of the reburn fuel injection, (iii) at the transition between reburn and burnout zones, and (iv) in the burnout zone. Configurations (i) and (ii) are the most used: the agent is thus introduced in a reducing zone where it decomposes to amino-radicals (NHi), which in turn reduce NO according to Reactions 4 and 5.…”

Detailed Modeling of NOx and SOx Formation in Co-combustion of Coal and Biomass with Reduced Kinetics

“…6,7,9−12 On the basis of the previous work, 6 Xu et al postulated a simpler 4 steps, 8 species reduced mechanism for the prediction of nitric oxide concentrations for advanced reburning, i.e., the hybrid reburning/selective noncatalytic reduction (SNCR). 7 A systematic reduction method 8 was used to derive the reduced mechanism, including the selection of the full mechanism, the development of the skeletal mechanism, and the selection of steady-state species. The reduced mechanism was derived from a 62 steps, 20 species skeletal mechanism, 6 which itself was based on a 312 steps, 50 species full mechanism.…”