Abstract
Emission characteristics of heat recirculating porous burners with high temperature heat extraction are studied numerically. Two types of burners are considered: counterflow porous burner (CFB) and reciprocal counterflow porous burner (RCFB). The combustion of methane-air mixtures flowing through the porous media is modeled by solving steady state governing equations to obtain the flame temperature and species profiles. Formation of CO, NO, NO2, and NOx is studied in CFB and RCFB in a range of equivalence ratios from 0.3 to 1.0 and heat extraction temperatures from 300 to 1,300 K. The contribution of various NO formation mechanisms is comparatively analyzed and related to the NO generation predicted by a detailed chemistry mechanism. The effect of high temperature heat extraction on the formation of CO and NOx is analyzed. Numerical predictions indicate a constant monotonic decrease of NOx concentration with increasing temperature of energy extraction. The formation of CO is observed to follow the similar trend. For heat extraction at 1,300 K, simulations predicted 3.6 ppm of NOx and 3.9 ppm of CO for CFB and 4.1 ppm of NOx and 3.5 ppm of CO for RCFB when these burners are operated at an equivalence ratio of 0.7.
Highlights
Oxides of nitrogen (NO and NO2), termed as NOx, are well-known to be detrimental to the environment
This article presents the results from numerical investigation of the emission characteristics of counterflow porous burner (CFB) and reciprocal counterflow porous burner (RCFB) when energy is extracted from these burners at high temperature
The simulation results for the CFB and RCFB show that the NOx generated by RCFB is more than that of CFB by approximately 1 ppm in all the cases studied here
Summary
Oxides of nitrogen (NO and NO2), termed as NOx, are well-known to be detrimental to the environment. Starting from ozone-depletion, photochemical smog to acid rain, these chemical compounds are responsible for many adversities to the environment and human life. NOx are generated from automobiles and industries involving thermal power generation and boilers. Nitrogen as a main air component is inevitably present in all the combustion systems. This makes combustion process a major contributor to the total concentration of atmospheric NOx. In last few decades, many researchers have been working to study the mechanism of NOx generation in flames (Marteney, 1970; Iverach et al, 1973; Bowman, 1975; Miller and Bowman, 1989)
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