Kinetic characteristics of pulverized coal combustion in the two-phase flow

• Two-phase flow combustion of pulverized coal was simulated in micro fluidized bed.
• The evolution of CO and CO2 were examined during two-phase flow combustion.
• The numerical relations of rate constant with each factor were established.
• Kinetic parameters of coal combustion from micro fluidized bed are lower.

The kinetic characteristics of pulverized coal combustion in the two-phase flow were studied using the micro fluidized bed kinetic analyzer (MFBKA) so as to get closer to the actual working condition. On the basis of the performance of CO and CO2 emissions, the effect of various operating parameters, such as reaction temperature, superficial gas velocity, coal particle size, oxygen concentration and coal properties, on the combustion rate was investigated. The yield ratio of CO to CO2 remained 1:1 until the reaction temperature exceeding 850 °C and then decreased gradually, indicating that the combustion mechanism changed at such temperature. The increase of superficial gas velocity and oxygen concentration and the reduction of coal particle size had positive effects on promoting the combustion process, but their contributions became feeble as the superficial gas velocity and the oxygen concentration were respectively greater than 0.10 m/s and 50vol%, and the coal particle size was smaller than 74 μm. The relations of reaction rate constant with various operating parameters were established. The kinetic parameters of pulverized coal combustion determined by MFBKA presented the same changing tendency as the results of thermogravimetric analysis (TGA), but the former apparent activation energy is relatively lower because of its optimized kinetic conditions.