Abstract
Oxy-combustion with high flame temperature, low heat loss, high combustion efficiency, and low NOx emissions is being extensively studied. The thermal radiation from soot particles and gases in oxy-combustion accounts for the vast majority of the total heat transfer. Based on a detailed chemical reaction mechanism coupled with the soot particle dynamics model and optically thin radiation model, the influence of the flame structure and temperature distribution on the thermal radiation in oxygen-enriched counterflow diffusion flames was studied in this paper. The results revealed that reasonable assignment of total recycled flue gas and the degree of dilution of fuel and oxidant were critical, which can be used to adjust the overall radiation situation of the flame. At the same adiabatic flame temperature, as the fuel concentration decreased and the oxidant concentration increased (the stoichiometric mixture ratio is from 0.3 to 0.6), the soot formation decreased, which led to the particle radiation disappearing while the main radiation zone of gases moved 0.04 cm toward the fuel side. At the same stoichiometric mixture fraction (0.4), the radiation area was broadened and the radiation of soot particles was gradually enhanced with the adiabatic flame increasing from 2300 K to 2700 K.
Highlights
Traditional coal-fired boilers use air for combustion, in which N2 in the air dilutes CO2 in the flue gas
Oxy-combustion technology can be used to obtain a high concentration of CO2 in the products of the combustion system, which is beneficial to the storage and utilization of CO2
Changing the structure of the flame can significantly change the soot formation and oxidant characteristics of the flame, and the bright yellow flame, which is full of soot particles, can be changed to a blue flame with radical chemiluminescence, even in the case of adiabatic flame temperature (Tad ) constant
Summary
Traditional coal-fired boilers use air for combustion, in which N2 in the air (approximately 79% by volume) dilutes CO2 in the flue gas. Changing the structure of the flame (changing the concentration of the inert gas in the oxidant and fuel) can significantly change the soot formation and oxidant characteristics of the flame, and the bright yellow flame, which is full of soot particles, can be changed to a blue flame with radical chemiluminescence, even in the case of adiabatic flame temperature (Tad ) constant This phenomenon has been observed in many types of non-premixed flames, such as counterflow flames [13,14,15] and laminar coflow diffusion flames [16,17]. The spatial distribution of radiation medium, including gases and soot particles, and the overall radiation of the flame in oxygen-enriched counterflow diffusion flame is studied by numerical calculations coupled with a detailed chemical reaction mechanism, soot particle dynamics model, and radiation model These fundamental oxycombustion studies shed light on how best to utilize RFG to control the flame temperature, SVF, and heat flux, to achieve savings in fuel and oxygen resources and obtain the best working conditions
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