Prediction of Nitric Oxide Destruction by Advanced Reburning

Abstract

Advanced reburning refers to a process wherein injection of a hydrocarbon fuel such as natural gas aft of the combustion zone is followed by injection of a nitrogen-containing species such as ammonia. In recent work, the authors used a systematic reduction method to develop a fourstep, eight-species reduced mechanism from a 312-step, 50-species full mechanism for advanced reburning processes. The four-step model has been integrated into a comprehensive computational fluid dynamics combustion code, PCGC-3. In this work, the integrated model for advanced reburning has been evaluated through comparisons with experimental data for species and temperature profiles as well as effluent NO concentrations. Comparisons are shown herein for a base case, with reburning only (natural gas addition) and with advanced natural gas reburning (natural gas addition followed by NH 3 addition). Profile comparisons show that the predicted flow-average axial NO concentration with advanced reburning followed the trends of experimental data, though the predicted initial NO level was lower than experimental data by 20-30%, partly due to both inaccurate prediction of flame structure and experimental error. Comparisons of effluent molar flux of NO with variation in swirl number, (NH 3 /NO) in and location of NH 3 injection show that predicted trends and magnitudes of change were consistent with measured trends, though the predicted NO reduction was typically much higher than measured. Measurements and predictions both showed that NO reduction increased with increasing swirl number, (NH 3 / NO) in and reburning zone residence time. Most of the NO reduction is caused by chemical reaction, and only a small part of the NO reduction is due to dilution. Study results provide directions for further research.

Numerical study on reduction of NOx and unburned carbon in micronized coal reburning

“…For the fuel NO modeling, the global models proposed by De Soete [12] and Xu [13] are considered as the fuel NO mechanism. It is assumed that the fuel-bound nitrogen of the coal is distributed between the volatiles and the char.…”

A Mechanistic Investigation of Nitrogen Evolution and Corrosion with Oxy-Combustion

“…Three gas-phase mechanisms were tested: SKG03 , GRI-Mech 3.0 (Smith et al, 2000), and GRI-Mech 3.0 + B96 which is the GRI-Mech 3.0 mechanism with advanced reburning reactions from Bowman (1997) added following a similar approach to Xu et al (2001).…”

“…• Natural gas was modeled as 100% CH 4 as done by Xu et al (2001). Approximate natural gas composition is given in Table 2 and is mostly methane.…”

“…Soot formation is also not described. Xu et al (2001) modeled advanced reburning with a reduced mechanism that was derived from the earlier GRI-Mech 2.11 mechanism with advanced reburning reactions from Bowman (1997) added. This advanced reburning model was used in the PCGC-3 CFD code.…”

A Comparison of Single Shot Diesel Spray Combustion Emissions With Trends Predicted by a Conceptual Model

“…However, NO can be destroyed in the presence of hydrocarbon fragments and this known pathway has been used to produce the NO-reburn process (Wendt et al, 1973;Smyth, 1996;Smoot et al, 1998;Han et al, 1999;Xu et al, 2001) which is used in industrial boilers to reduce nitric oxide emissions. In addition, NO destruction was predicted due to reactions in the fuel rich jet in model calculations of jet flames (Broadwell and Lutz, 1998).…”