预干燥对神华褐煤富氧燃烧特性的影响机理的研究

The technology of oxy-fuel combustion of lignite integrated with lignite pre-drying system is an attractive means to reduce the carbon emissions from lignite-fired power plants. Pre-drying integrated with oxy-coal combustion is also an important part of the development of advanced clean coal technologies worldwide. However, research on oxy-fuel combustion of pre-dried lignite for power generation in China is rather weak, which greatly restricts the level of efficient and clean utilization of lignite resources in China. Therefore, study on the effects of pre-drying on the oxy-fuel combustion characteristics of lignite and pollutants formation behavior in domestic lignite-fired power plants is important and much needed. In this proposal, the following aspects of pre-drying of lignite will be investigated, including the comparison of pre-drying characteristics of Shenhua lignite using simulated recirculated flue gas, study of the effects of pre-drying on the oxy-fuel combustion behavior of Shenhua lignite, study of effects of pre-drying using recirculated flue gas on the physical and chemical structure of lignite, study of interaction of carbon dioxide and the surface chemical structure of lignite during pre-drying, comparative study of the combustion characteristics of pre-dried Shenhua lignite with other coals, study of the devolatilization characteristics of pre-dried Shenhua lignite including the sulfur- and nitrogen-containing impurities in char and volatile matter, study of the oxy-fuel combustion characteristics of char from pre-dried lignite pyrolysis, study of the feasibility of the use of recirculated flue gas from oxy-fuel combustion units to pre-dried Shenhua lignite. The project findings will improve scientific knowledge of lignite, assist to improve the efficiency of lignite-fired power plants, and allow clean utilization of Shenhua lignite resources.

集成预干燥系统的褐煤富氧燃烧技术是降低燃用褐煤电厂碳排放的有效措施，也是目前国内外洁净煤技术发展的重要前沿技术。因此，研究燃煤电厂的褐煤预干燥对国产褐煤富氧燃烧特性及污染物排放的影响具有重要意义。本申请利用褐煤富氧燃烧再循环烟气（主要组分是CO2）对神华褐煤进行预干燥处理，研究预干燥对褐煤富氧燃烧特性的影响规律和机理；研究预干燥对褐煤物理结构和表面化学结构的影响规律和机理；研究预干燥过程中CO2与褐煤表面化学结构的交互作用；对比研究预干燥后神华褐煤的富氧燃烧特性与其他褐煤的区别；研究预干燥后褐煤的脱挥发分特性，包括脱挥发分过程中杂质元素硫和氮在挥发分及半焦中的分配；研究预干燥后褐煤半焦的富氧燃烧特性，并研究褐煤富氧燃烧过程及污染物生成的规律。本项目研究的成果将为燃用神华褐煤的电厂进行富氧燃烧技术改造、降低燃煤电厂碳排放提供科学依据。

本项目研究褐煤的预干燥工艺对褐煤富氧燃烧特性的影响。.对比分析了空气、过热蒸汽、富氧烟气预干燥对褐煤化学结构和反应活性的影响，研究了在干燥过程中褐煤孔隙水的迁移规律及褐煤孔结构和比表面积的变化规律及其影响因素。利用Aspen Plus软件对富氧燃煤电厂褐煤的干燥过程进行了模拟分析，研究了干燥介质、烟气温度、流量、烟气中CO2浓度和H2O含量对褐煤干燥特性的影响，对电厂的煤耗成本及电厂经济性的合理化进行了评估。.研究了不同干燥条件对褐煤在固定床中热解的反应特性。结果表明干燥气氛对褐煤在氮气气氛下进行热解气体的产率组成有影响，H2的含量在富氧烟气气氛预干燥下的产率高于空气烟气气氛下的产率；CO和CH4的含量在富氧烟气气氛下的产率低于空气烟气气氛下的产率。不同干燥载气的褐煤在N2气氛下热解焦油组分的分析中，富氧烟气气氛干燥的醇醛酮酸酯类物质的含量大于空气气氛。.研究了不同的干燥条件对褐煤和半焦的富氧燃烧反应特性的影响。结果表明：干燥后的褐煤与原煤相比，其可燃性指数、燃尽指数和燃烧综合指数均高于原煤。可燃性指数在富氧条件下有所升高，而燃尽指数和燃烧综合指数有所降低。在富氧条件下，氧气浓度的升高使可燃性指数、燃尽指数和燃烧综合指数均提高。.研究了水分对褐煤燃烧和着火特性的影响。结果表明水分含量对褐煤着火现象有显著的影响。一方面水分会导致煤颗粒明显的着火延迟，水分含量高、颗粒大，则着火时间延长；另一方面高水分会导致煤颗粒在着火和燃烧过程中产生破碎现象，从而使煤颗粒整体燃烧时间大大缩短。.研究了神华褐煤燃烧的动力学特性，发现褐煤的脱挥发分及半焦燃烧过程符合一级化学反应模型。CFD模拟结果表明富氧燃烧能提高燃料利用率，减少烟气的热损失，减少鼓风机消耗电能，符合节能环保的要求和发展方向。.本项目的相关研究成果对褐煤在电厂富氧燃烧工艺和富氧燃烧系统的设计提供十分有意义的理论依据。