Effects of air distribution on furnace temperature and CO/NO/N2O/SO2 emissions in a lab‐scale CFB furnace cofiring both biomass/coal and petroleum coke/coal

Abstract

AbstractThe effects of air distribution (excess ratio of primary air, ERPA; excess ratio of secondary air, ERSA; and excess ratio of total air, ERTA) on furnace temperature and CO/NO/N2O/SO2 emissions were systematically studied in a 0.2 MW lab‐scale circulating fluidized bed (CFB) furnace cofiring both biomass/coal and petroleum coke/coal. Unlike the ERSA, the high ERPA proved to be conducive to an even temperature distribution along the height of the furnace. As a result of the interaction of the heat release of combustion and endothermic air, a high ERPA equated to a low temperature in the dense phase zone while a low ERSA equated to a high temperature in the dilute phase zone. The generation and transformation of NO/N2O/SO2 depended greatly not only on the N and S contents of the fuel but also on the temperature and ERPA or the oxygen injected into the dense phase zone; the effect of ERSA was minimal. Meanwhile, the concentration of CO was mainly affected by the ERTA. Along with increased ERPA, the concentration of CO decreased, the concentrations of NO and N2O increased, and the SO2 content increased and then decreased. The high petroleum coke cofiring ratio caused high furnace temperature in the dense phase zone and low furnace temperature in the dilute phase zone. In addition, increasing petroleum cofiring ratio resulted in high NO and SO2 emissions because of the high N and S contents of the fuel. The results provide guidance for both biomass/coal and petroleum coke/coal cofiring in CFB furnace. © 2016 Curtin University of Technology and John Wiley & Sons, Ltd.