Study on non-isothermal kinetics and the influence of calcium oxide on hydrogen production during bituminous coal pyrolysis

The non-isothermal characteristics and pyrolysis kinetics of bituminous coal at different heating rates of 10, 20, and 30 ℃/min were studied by coupling TG-MS/DSC techniques. A fixed-bed reactor was used to investigate the coal-CaO-H₂O reactions to understand hydrogen production and the effects of CaO under different water feeding rates. The pyrolysis phase, the maximum mass loss rate, the characteristic peak temperature, and the release of the main volatile gases were studied. Based on the improved Coats-Redfern method by introducing the function of Q (E/RT), the activation energies and pre-exponential factors of non-isothermal pyrolysis of bituminous coal were estimated iteratively by regression to enhance their accuracy. The values of E were calculated as 22, 22, 19 kJ/mol in the first stage, 67, 75, 78 kJ/mol in the second stage, 114, 96, 133 kJ/mol in the third stage at the heating rates of 10, 20, and 30 ℃/min. Finally, the concentration and selectivity of gaseous products from the pyrolysis of bituminous coal were studied. The concentrations of H₂, CO, and CO₂ in the gas products increased with the addition of CaO and the increase of water feeding rate. Besides, the concentration of CH₄ increases with the increase of water feeding rate but decreases significantly with the addition of CaO. It is also worth noting that the pyrolysis process was enhanced by CaO addition to in-situ CO₂ captured and catalytic cracking reactions at the initial stage of the pyrolysis process.