Effects of flue gas recirculation on nitrogen oxide formation in 1000 MW S-CO2 coal-fired boiler with partial expansion furnace

Abstract

Abstract Since the heat transfer coefficient of supercritical carbon dioxide (S-CO2) is approximately 1/2–2/3 of traditional steam boiler, the S-CO2 boiler structure, cooling wall arrangement and combustion system is different from traditional boiler configuration. This paper takes a 1000 MW S-CO2 coal-fired boiler with partial expansion furnace and partial flow strategy arrangement for cooling wall as research object, the coal combustion and NOx generation characteristics in the furnace were numerically examined with the flue gas recirculation rate of 0–35%. The calculation results show that under staged combustion, the flue gas recirculation increases the ignition temperature of the pulverized coal and reduces the combustion temperature. And the expansion of the upper furnace further reduces gas temperature. Besides, as the flue gas recirculation rate increases, the gas temperature decreases. The flue gas recirculation may lower the production of NOx in the main combustion zone, and reduce the production of NOx further in the expansion zone. The average NOx concentration at the outlet decreases from 439 to 365 ppm when the flue gas recirculation rate increases from 0 to 27%. While the flue gas recirculation rate increases from 27% to 35%, the average NOx concentration is not changed obviously.