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.

建议构建一种包含碳酸氢钾抑制作用的动力学模型。该模型建立在先前关于二次闪光抑制动力学研究、碱金属抑制及生物质燃烧过程中硫酸盐和氯化物排放的研究基础之上。动力学模型涵盖了以下气相含钾物种的反应：K、KO、KO2、KO3、KH、KOH、K2O、K2O2、(KOH)2、K2CO3、KHCO3和KCO3。火焰平衡计算表明，燃烧产物中主要的含钾物种为K和KOH。主要的抑制反应，即自由基终止抑制循环，包括KOH + H=K + H2O和K + OH + M=KOH + M，其总体终止效应为H + OH=H2O。对添加KHCO3的化学计量甲烷/空气火焰的数值预测燃烧速度与现有实验数据表现出合理的一致性。观察到钾化合物具有显著的饱和效应：大约需要0.1%的体积分数的KHCO3来使燃烧速度降低至一半；然而，为了达到5 cm/s的燃烧速度，则需要额外的0.6%体积分数。计算结果的分析表明，钾化合物的添加能够迅速降低自由基的超平衡状态至平衡水平，因此进一步添加钾化合物对火焰自由基的影响微乎其微。