Oxygen Consumption and Heat-Release Characteristics of Low-Temperature Coal Oxidation Considering a Minimum Oxygen-Concentration Threshold

Conventional standard oxygen-consumption-rate models can retain an apparent dependence on reactor height and gas flow rate when outlet oxygen concentrations become low. To examine this issue, programmed-temperature oxidation experiments were conducted using gas-fat coal from the Zhuxianzhuang Coal Mine. Two packed coal-bed configurations were used: a full bed (coal-bed height, 20 cm; packed-coal volume, 250 cm3) and a half bed (coal-bed height, 10 cm; packed-coal volume, 125 cm3); both were operated at inlet flow rates of 80, 100, and 120 mL min−1. Outlet O2, CO, and CO2 samples were collected near the end of each isothermal hold and analysed by gas chromatography. An empirical effective oxygen-concentration correction parameter was introduced to revise the conventional standard oxygen-consumption-rate model, and corresponding standard CO and CO2 generation-rate and calculated heat-release-intensity models were derived. The outlet oxygen concentration exhibited four apparent stages with increasing temperature: slow decrease, rapid decrease, renewed slow decrease, and stabilization. Above approximately 195 °C, the outlet oxygen concentration approached a nonzero plateau. On the basis of this plateau and the consistency of results obtained under the tested conditions, a value of 1.21 vol.% was selected as an empirical correction parameter for the present system. The conventional model produced increasingly separated oxygen-consumption-rate curves at high temperatures and yielded R2 = 0.930. After introducing the correction parameter, the curves obtained under the tested conditions showed improved convergence and R2 increased to 0.993. The revised standard CO and CO2 generation rates and calculated heat-release intensities likewise showed reduced dependence on reactor height and flow rate within the present dataset and increased exponentially with temperature. These empirical correlations describe the tested coal under the specified reactor and heating conditions. Independent validation is required before extending them to other coals or operating conditions.