【作者】 胥波；

【导师】 蔡宁生；

【作者基本信息】 清华大学 ， 动力工程及工程热物理， 2008， 硕士

【摘要】 通过对已有氮氧化物(NOx)脱除技术和中小锅炉燃烧过程特点的比较分析,针对在链条炉内利用选择性非催化还原(SNCR)脱除NOx过程中存在的反应温度窗口狭窄和停留时间较短,以及因链条炉燃烧方式和炉膛结构尺寸与煤粉炉不同而难以参考煤粉炉上SNCR过程的问题,本文开展了链条炉炉内燃烧过程和SNCR脱除NOx过程的模拟研究,并对加入甲烷促进其反应过程的可行性进行了初步的模拟分析。本文利用单元体方法对一台35t/h链条炉炉排上方煤层燃烧过程建立了数学模型,对炉排上煤的燃烧过程进行了数值模拟;利用炉排燃烧过程模拟结果作为炉膛空间模拟的边界条件,采用计算流体力学(CFD)软件FLUENT对链条炉内的温度和流场分布进行了模拟,以此为基础对此锅炉上的SNCR过程进行了初步设计,进而对SNCR过程进行了模拟,并采用简化反应动力学模型和CFD结合的方法对加入CH4促进SNCR脱除NOx的过程进行了模拟,以期为实际应用提供参考和理论基础。模拟结果与实测数据的对比表明,本文建立的煤燃烧模型可较准确地模拟和预测典型链条炉排的燃烧过程,进而为研究层燃炉排的燃烧过程和炉排优化设计提供参考。炉内工况模拟结果表明链条炉适合SNCR反应的位置处于炉拱上部的炉膛中部狭窄区域。在此基础上在前墙和后墙各平均布置了5个矩形喷嘴对SNCR系统进行了初步的设计。在前期研究的基础上,采用CFD结合简化反应模型的方法对加入适量的甲烷促进脱除NOx过程进行了初步模拟分析,结果表明,加入适量甲烷可使常规SNCR的NOx脱除效率提高9%左右,氨泄漏降低至50ppm,可为实际应用提供指导。更多还原

【Abstract】 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.更多还原