Flame Inhibition by Potassium-Containing Compounds.

Area of Science:

• * Combustion Science
• * Chemical Kinetics

Background:

• * Previous studies on secondary flash suppression, alkali metal inhibition, and sulfate/chloride emission during biomass combustion.
• * Identification of key gas-phase potassium-containing species (K, KO, KO2, KO3, KH, KOH, K2O, K2O2, (KOH)2, K2CO3, KHCO3, KCO3).

Purpose of the Study:

• * To propose a kinetic model for potassium bicarbonate inhibition in flames.
• * To investigate the primary inhibition reactions and their radical termination cycle.
• * To analyze the effect of potassium compounds on radical super-equilibrium and flame behavior.

Main Methods:

• * Development of a kinetic model incorporating gas-phase potassium species.
• * Flame equilibrium calculations to identify dominant potassium-containing species.
• * Numerical prediction of burning velocities for methane/air flames with added potassium bicarbonate.
• * Analysis of radical super-equilibrium and saturation effects.

Main Results:

• * Flame equilibrium calculations show K and KOH as the main potassium species.
• * Key inhibition reactions identified: KOH+H=K+H2O and K+OH+M=KOH+M, leading to H+OH=H2O.
• * Predicted burning velocities show good agreement with experimental data.
• * A strong saturation effect was observed; significant KHCO3 addition is needed for substantial burning velocity reduction.

Conclusions:

• * The kinetic model successfully explains potassium bicarbonate's flame inhibition.
• * Potassium compounds effectively reduce radical super-equilibrium to equilibrium levels.
• * Further addition of potassium compounds has diminishing effects on flame radicals due to saturation.