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

Abstract

Local flue gas recirculation (LFGR) is an effective technology for reducing nitrogen oxide (NO x ) 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 NO x 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, O 2 flux, and CO, CO 2 , 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 O 2 flux will reduce the reduction layer proportion and subsequently promote NO emissions; increasing the CO and CO 2 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 O 2 flux and the positive effect of the increase in temperature and CO, CO 2 , and recycled NO concentrations.