摘要:
燃煤耦合零碳的生物质是现阶段燃煤过程中减少CO2排放成本最低和技术最成熟的技术。根据我国生物质资源分布国情,受生物质资源收集成本限制,在现有燃煤火电机组上只能进行低比例的耦合掺烧,但分布式供能燃煤工业锅炉具备进行大比例耦合甚至全部改烧生物质燃料的条件。目前链条炉和流化床锅炉掺烧和全烧生物质在国内已得到较为广泛的应用,然而相对更高效和自动化程度更高的煤粉工业锅炉大比例耦合生物质的研究和工业应用案例较少。针对近年来国内新发展的低NOx预热解式煤粉工业锅炉大比例直燃耦合生物质甚至全烧生物质的可行性,通过CFD数值模拟进行初步探索,重点对大比例耦合生物质对预热解式煤粉工业锅炉温度场、壁面热流密度、气氛场和NOx排放的影响进行评估。数值计算结果表明:预热解式煤粉工业锅炉大比例耦合生物质后,炉内的温度场、壁面热流密度和气氛场总体分布趋势与纯煤粉燃烧相似;随着生物质耦合比例的增加,主燃区燃烧过程得到强化,但由于生物质含水量较高,火焰总体存在着火延迟现象,主燃区消耗氧气的速率有所降低,挥发分与CO摩尔分数明显升高。受生物质燃料中含氮量高和火焰推迟的双重影响,随着生物质耦合比例的增加,NOx排放先增加后减少。研究结果表明预热解式煤粉燃烧技术可实现煤粉工业锅炉大比例耦合生物质甚至全部改烧生物质,在适当控制生物质燃料收到基氮含量的条件下,大比例耦合生物质可显著降低锅炉NOx排放。
Abstract:
Co-firing of carbon-neutral biomass with coal is the most economic and promising technology to reduce CO2 emission from coal combustion currently. Limited by the biomass distribution feature and collection cost in China, the biomass co-firing in large-scale coal power plants can only be at a small ratio of biomass. However, for the industrial boilers used for distributing energy system, it is able to co-fire biomass at a high ratio and even purely burn biomass. Biomass combustion in the grate furnace and circulated fluidized bed has been widely adopted, in contrast, the study and application of biomass co-firing in the pulverized coal industrial boilers of higher efficiency and automation degree at a high-ratio is rare. In this paper, the biomass high-ratio co-firing in a new developed pre-pyrolysis pulverized coal industrial boiler is studied. The effects of biomass co-firing ratio on temperature distribution, wall heat flux, specie distribution and NOx emission are discussed. The CFD modeling results show that biomass co-firing or even pure combustion follows the similar temperature and specie distribution of pure coal combustion. With the increase of biomass co-firing ratio, the combustion in the primary zone is strengthened, however, due to the higher moisture content in biomass, the flame is overall delayed, the oxygen consumption rate decreases, and the volatile and CO concentrations increases in the primary combustion zone. Because of the dual effects from flame delay and higher nitrogen content in biomass, with the increase of biomass co-firing ratio, the NOx emission increases first and then decreases. This study indicates that the pre-pyrolysis pulverized coal combustion technology is feasible to co-fire biomass at a high ratio and even hundred percent. When the nitrogen content of biomass is controlled, the NOx emission can be significantly reduced by biomass co-firing.
百度学术
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