Numerical Investigation On DeNOx With SNCR In A Grate-Firing Furnace

Based on comparison and analysis of the existing DeNOx technologies and characteristics of the combustion process of small and medium-sized boilers, simulation study of the combustion process and SNCR for grate-firing furnace was carried out, and the feasibility of promoting SNCR with methane additive was analyzed to solve issues of narrow temperature window and short residence time of SNCR, and to accout for difference in combustion mode, structure and scale of the grate-firing furnace from pulverized coal fired furnace.A mathematical model for combustion process on the grate for a grate-firing furnace of 35t/h steam production was developed by using micro-element method, and the computational simulation for coal combustion process was conducted. Results of coal combustion process on the grate was used as the boundary conditions for the simulation of the furnace, and temperature and velocity distribution in the furnace was simulated by using a computational fluid dynamics (CFD) software, FLUENT. SNCR process of the grate-firing furnace was designed preliminarily and simulated. The process of promoting SNCR with methane additive for the furnace was investigated by integrating simplified reaction dynamics and CFD aiming at providing reference and theoretical foundation for actual application.Based on comparison of the simulated results with the experimental data, the coal combustion process on the grate can be predicted by the combustion model developed, and the modeling results can provide reference to the optimization and design for the grate-firing furnace. The simulated results for the furnace indicate that zone suit for SNCR is a narrow region of furnace central part which is above the front arch and rear arch. Five rectangular nozzles can be arranged uniformly in the front and the back wall of the furnace for SNCR of the grate-firing furnace. Based on preliminary studies, promoting SNCR process with methane additive in the grate-firing furnace was simulated by integrating CFD and simplified reaction dynamics, and the simulated results indicate that NOx removal efficiency is increased by 9% approximately and ammonia slip is lowered to 50ppm approximately with methane additive.