Flame Inhibition by Potassium-Containing Compounds

A kinetic model of inhibition by the potassium-containing compound potassium bicarbonate is suggested. The model is based on the previous work concerning kinetic studies of suppression of secondary flashes, inhibition by alkali metals, and the emission of sulfates and chlorides during biomass combustion. The kinetic model includes reactions with the following gas-phase potassium-containing species: K, KO, KO2, KO3, KH, KOH, K2O, K2O2, (KOH)2, K2CO3, KHCO3, and KCO3. Flame equilibrium calculations demonstrate that the main potassium-containing species in the combustion products are K and KOH. The main inhibition reactions, which comprise the radical termination inhibition cycle are KOH + H=K + H2O and K + OH + M=KOH + M with the overall termination effect: H + OH=H2O. Numerically predicted burning velocities for stoichiometric methane/air flames with added KHCO3 demonstrate reasonable agreement with available experimental data. A strong saturation effect is observed for potassium compounds: approximately 0.1% volume fraction of KHCO3 is required to decrease burning velocity by a factor of 2; however, an additional 0.6% volume fraction is required to reach a burning velocity of 5 cm/s. Analysis of the calculation results indicates that addition of the potassium compound quickly reduces the radical super-equilibrium down to equilibrium levels, so that further addition of the potassium compound has little effect on the flame radicals.

本研究提出了一种针对含钾化合物碳酸氢钾（potassium bicarbonate）抑制作用的动力学模型。该模型的构建基于此前关于生物质燃烧过程中次生闪燃抑制、碱金属抑制效应以及硫酸盐与氯化物排放的动力学研究工作。该动力学模型涵盖以下气相含钾物种参与的反应：K、KO、KO₂、KO₃、KH、KOH、K₂O、K₂O₂、(KOH)₂、K₂CO₃、KHCO₃以及KCO₃。火焰平衡计算结果表明，燃烧产物中主要的含钾物种为K与KOH。构成自由基终止抑制循环的核心抑制反应为：KOH + H = K + H₂O 与 K + OH + M = KOH + M，其整体终止效应为：H + OH = H₂O。对添加了KHCO₃的化学计量比甲烷-空气火焰进行数值预测得到的燃烧速度，与现有实验数据吻合良好。含钾化合物表现出显著的饱和效应：仅需约0.1%体积分数的KHCO₃即可将燃烧速度降至原值的1/2；但若要将燃烧速度降至5 cm/s，则需额外添加0.6%体积分数的KHCO₃。对计算结果的分析表明，添加含钾化合物可快速将自由基超平衡态降至平衡态，因此后续添加该含钾化合物对火焰自由基的影响微乎其微。