耦合换热效应时低温预热天然气MILD燃烧行为及分区重构

Nitrogen oxides (NOx) is the major contaminants in the implementation of natural gas substitution to optimize the energy structure and improve the ecological environment. At present, MILD (Moderate & Intensive Low Oxygen Dilution) combustion technology received wide attention due to its inherent ultra-low NOx emission. However, in large-scale furnace, the detailed MILD combustion and heat transfer behaviors, especially the effects of heat exchange on the combustion stability, did not receive enough attention. In this project, MILD combustion characteristics of natural gas using low preheating temperature air will be comprehensively carried out on a 1MW test platform, and the refined macroscopic parameters can be measured during the tests. Simultaneously, the numerical simulation of microscopic field distribution and detailed kinetic calculation are performed to obtain detailed and accurate fundamental data of the natural gas MILD combustion in large-scale furnace. Accordingly, three-dimensional combustion regime coupled with heat transfer will be proposed, and the dominant heat transfer mechanism in different area of the furnace can be figured out, then the “dual effects” of furnace-wall heat exchange on the MILD combustion are expected to be uncovered. Moreover, the impacts of import parameters and boundary conditions over the stability of MILD combustion will be explored under enhanced furnace-wall heat transfer conditions, and then the combustion characteristics and heat transfer behaviors between MILD combustion and conventional combustion in different furnace area can be comprehensively compared. The results from above-mentioned work can provide important scientific evidence to further promote the application of MILD combustion technology in the industrial boiler (kiln) furnace.

氮氧化物是我国实施天然气替代以优化能源结构和改善生态环境过程中需要重视的关键污染物，MILD燃烧技术因其固有的超低氮排放优势倍受青睐，然而有关低温预热条件下大型炉膛空间内MILD燃烧与传热行为尤其是换热对燃烧的影响尚未受到广泛关注。本项目基于1MW试验平台开展低温预热天然气MILD燃烧综合特性研究，结合精细化宏观特性参数的测定、详细化动力学与微观量场分布信息的模拟计算，获得详实准确大型炉膛内MILD燃烧系列基础数据，构建耦合换热的三维燃烧模式分区，弄清低温预热MILD燃烧方式下炉内不同区域的传热主导机制，揭示该方式下壁面换热对MILD燃烧的“双重影响”规律，同时探索强换热条件下改变进口参数与边界条件对MILD燃烧的稳定能力，进而发现低温预热MILD燃烧方式下炉内不同区域的燃烧、传热行为与常规燃烧方式的异同，为进一步推动MILD燃烧在工业锅（窑）炉上的广泛应用提供重要的科学依据。

天然气在我国能源低碳化进程中扮演日益重要的角色。积极发展新的变革性天然气低氮燃烧技术，通过主动燃烧控制从源头实现氮氧化物的减排对我国生态环境协调发展具有重要意义。本项目围绕具有先天低氮排放优势的MILD燃烧过程中尚未被广泛关注的传热-燃烧相互作用机制开展试验和模拟研究，基于初始条件构建了考虑散热效应的三维燃烧模式分区图，确定了无焰燃烧所处边界条件区域（温度/氧浓度/换热量）；分析了当量比和不同稀释剂对燃烧分区的影响规律，发现CO2最利于无焰燃烧的实现(CO2>H2O>N2)，揭示了 CO2和H2O的化学效应作用机制（主导着火延迟、抑制火焰温度、改变中间产物CH2O形成）；探索了非绝热条件下MILD燃烧的建立与转变过程，获得了换热量大小改变燃烧模式的影响规律（HTC-UMC-USC），揭示了非预热MILD燃烧方式下换热对无焰燃烧的双重作用机制；开展了低温预热天然气MILD燃烧综合特性试验及数值模拟，分析了炉壁温度对常规与MILD燃烧切换稳定性的影响，发现低温预热时无焰燃烧存在关键壁温，否则燃烧失稳；发展了碳氢燃料燃烧过程中氮氧化物（NOx）生成与还原路径贡献率的定量计算新方法，建立了常规燃烧和MILD燃烧方式下NO排放与特征温度之间的关联性，明晰了甲烷及其宽比掺氢MILD燃烧方式下NOx的转化路径，基于上述研究提出了耦合分级燃烧实现了MILD燃烧方式下NOx的深度减排方法。本项目研究结果为给定条件下无焰燃烧的判定与实现提供了理论依据，为强换热条件下炉内实现无焰燃烧提供理论指导和方向；有利于促进MILD燃烧技术与工业锅（窑）炉设备工况条件、热工制度的有机结合，拓宽MILD燃烧技术在钢铁、陶瓷、采暖、建材等多种领域的应用并有效的实现低氮排放。