Numerical optimization of the influence of multiple deep air-staged combustion on the NOx emission in an opposed firing utility boiler using lean coal

• Published in: Fuel (Guildford) Vol. 269; p. 116996
• Main Authors: Wang, Yongqiang, Zhou, Yuegui
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.06.2020; Elsevier BV
• Subjects: Atmospheric models; Boilers; Burnout; Carbon monoxide; Chemical reduction; Coal; Coal combustion; Combustion; Computer simulation; Design optimization; Emission standards; Emissions control; Field tests; Firing (igniting); Flue gas; Gas temperature; Mathematical analysis; Multiphase flow; Multiple deep air-staged combustion; Nitrogen oxides; NOx formation and destruction model; Numerical optimization; Opposed firing boiler; Pulverized coal; Temperature distribution; Two phase flow; Coal combustion; NOx formation and destruction model; Numerical optimization; Opposed firing boiler; Multiple deep air-staged combustion
• ISSN: 0016-2361; 1873-7153
• DOI: 10.1016/j.fuel.2019.116996

•The validated NOx formation models reasonably predict the lean coal NOx emission.•The NOx emissions are significantly reduced under deep air-staged combustion.•Less varied NOx profile of different air distributions under deep air-staged combustion.•Significant NOx reduction in burnout zone under double air-staged combustion. Multiple deep air-staged combustion is a promising technology to significantly reduce NOx emission in the opposed firing utility boilers using low-volatile coal. The gas-solid two-phase flow, pulverized coal combustion and NOx emission characteristics of an existing 600 MW coal-fired boiler were numerically simulated to evaluate the influence of excess air coefficient in primary combustion zone (αM), variational air distribution modes and multiple deep air-staged combustion on the NOx formation and destruction process in the furnace. The detailed NOx formation and reduction models were proposed to consider the reduction reaction between hydrocarbon and NO under fuel rich conditions and well validated by the experimental results in the laboratory and field tests. The results show that the αM has an important influence on flue gas temperature distribution and forms a reducing atmosphere in the primary combustion zone to significantly reduce NOx concentration. The NOx concentration at the furnace outlet is greatly decreased when the deep air-staged combustion is adopted with αM of 0.75, and the CO concentration maintains within a lower level. Compared with the balanced air distribution, the pagoda and inverse pagoda air distributions are found to be ineffective to enhance NOx reduction performance under deep air-staged combustion. However, the pagoda air distribution effectively reduces NOx emission under middle air-staged combustion condition. The NOx emission is further reduced by adopting the multiple air-staged combustion due to the higher CO concentration formed in the burnout zone. The results are helpful to the design and operation optimization of the opposed firing utility boilers using lean coal.