生物质气化气层流 MILD 燃烧火焰特性及排放研究

Flame Characteristics and Pollutant Emissions During the Laminar MILD Combustion of Biomass Gasified Gas

摘要

生物质气化气(BGG)因其来源广泛、可再生及全生命周期碳中性等特性，被认为是天然气的重要潜在替代能源．本文以生物质水蒸气气化燃气(BGG-S)为研究对象，构建了热同流引导的层流 MILD 燃烧实验系统，调节热同流的氧气浓度和温度，结合 OH-PLIF(平面激光诱导荧光)技术，研究火焰形态、温度分布、自由基浓度以及污染物生成特性，以解决 BGG-S 复杂组分导致的点火困难、燃烧不稳定、NO_x和CO排放控制难等问题．结果表明，在层流MILD燃烧条件下，热同流能够显著提高BGG-S的燃烧稳定性和燃烧效率，通过预热和稀释作用优化燃烧条件，使火焰结构更加均匀，火焰长度与宽度均显著增加，出现“无焰燃烧”现象，达到理想化 MILD 燃烧状态．热同流O₂体积分数为2%～8%的层流 MILD 燃烧条件下，NO_x排放为83.0×10^-6～115.3×10^-6，减排率为66.7%～78.7%；CO排放低于100×10^-6，减排率为79.3%～85.7%．热同流通过降低局部峰值温度及增强燃料的还原作用，显著抑制了NO_x生成．此外，火焰推举与OH自由基分布验证了局部自点火的存在，局部自点火现象使火焰不再局限于火焰锋面，而是扩展至更大范围，呈现分布式燃烧状态，反应区宽度的增加和停留时间的延长进一步降低了 CO 排放．研究表明，热同流条件下的 BGG-S 层流 MILD 燃烧具有良好的稳定性和超低污染排放特性，为清洁燃烧技术的发展提供了参考．

Abstract

Biomass gasified gas (BGG) is considered an important potential alternative to natural gas because of its wide availability，renewability，and carbon neutrality throughout its lifecycle. This study focused on BGG steam (BGG-S) as the research subject and constructed an experimental system for laminar moderate or intense low-oxygen dilution (MILD) combustion involving a hot coflow. By adjusting the oxygen concentration and temperature of the hot coflow and utilizing the OH planar laser-induced fluorescence(OH-PLIF) technology，this study investigated the flame morphology，temperature distribution，radical concentrations，and pollutant formation characteristics. The aim was to address issues such as ignition difficulty，combustion instability，and those encountered in controlling NO_x and CO emissions caused by the complex composition of BGG-S. The results showed that under the laminar MILD combustion conditions，the hot coflow significantly enhanced the combustion stability and efficiency of BGG-S. The optimization of the combustion conditions through preheating and dilution led to a more uniform flame structure，a notable increase in flame length and width，and the occurrence of a “flameless combustion” phenomenon，achieving an ideal MILD combustion state. Under the laminar MILD combustion conditions with hot coflow O₂ volume fractions of 2%—8%，NO_x emissions ranged from 83.0×10^-6 to 115.3×10^-6，showing reductions of 66.7%—78.7%，and CO emissions were lower than 100×10^-6，showing reductions of 79.3%—85.7%. The hot coflow effectively suppressed NO_x formation by lowering local peak temperatures and enhancing the reducing effect of the fuel. In addition，flame liftoff and the OH-radical distribution confirmed the occurrence of localized auto-ignition，which extended the reaction zone beyond the conventional flame front，promoting the state with distributed combustion. The broader reaction zone and prolonged residence time further reduced CO emissions. This study demonstrates that the laminar MILD combustion of BGG-S under hot coflow conditions offers excellent stability and ultralow pollutant emissions，providing insights into the advancement of clean combustion technologies.

关键词

MILD 燃烧 / 生物质气化气 / 火焰特性 / 污染物排放 / OH-PLIF

Key words

MILD combustion / biomass gasified gas / flame characteristics / pollutant emission / OH-PLIF

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基金资助

国家自然科学基金资助项目(52122609)

西藏自治区重点研发项目(XZ202401ZY0063)