Effect of temperature and reaction atmosphere on nitric oxide emission during a char grate‐fired process in local flue gas recirculation

Abstract

AbstractLocal flue gas recirculation (LFGR) is an effective technology for reducing nitrogen oxide (NOx) emissions from coal‐fired industrial boilers. The temperature and reaction atmosphere changes when flue gas is recycled, thereby affecting both the grate‐fired process and NOx emission. In this paper, the boundary of LFGR was simulated by changing the experimental parameters. On a small‐scale one‐dimensional fixed‐bed system, the effects of temperature, O2 flux, and CO, CO2, and recycled NO concentrations on oxidation‐reduction layering and char nitrogen conversion during the char grate‐fired process were studied. The effect of temperature and recycled flue gas components on nitric oxide (NO) emissions during the char grate‐fired process was then analyzed based on the mass proportion of oxygen‐absent and oxygen‐present parts. The results show that, with the introduction of recycled flue gas, increasing the temperature will also increase the reduction layer mass and proportion, and, subsequently, inhibit NO emissions; increasing the O2 flux will reduce the reduction layer proportion and subsequently promote NO emissions; increasing the CO and CO2 concentrations will reduce the NO emitted from the oxidation layer, yet has limited effects on the entire char bed; and recycled NO will significantly reduce the NO emissions. The effect of LFGR‐induced changes in temperature and reaction atmosphere on NO emissions can be ascribed to the negative effect of the increase in O2 flux and the positive effect of the increase in temperature and CO, CO2, and recycled NO concentrations.