Production of syngas from steam gasification of three different ranks of coals and related reaction kinetics

The steam gasification properties of three different ranks of coals, Shengli lignite (SL), Shenhua subbituminous coal (SH), and Tavan Tolgoi anthracite (TT), were investigated using a lab-scale fixed-bed reactor, and the thermodynamic equilibrium constant and kinetics of the reaction were analyzed. The results showed that the aromaticity and condensation of aromatic structures in SL, SH, and TT became higher, and the maturity of organic substance became lower. The steam gasification reaction showed that the syngas from low-rank SL had a high H₂/CO molar ratio, while the syngas from high-rank TT had relatively high CO content. The direct carbon gasification reactions for these three different ranks of coals were far from in equilibrium; the water gas shift reaction of SL was near equilibrium, and the degree of reaction for SL was higher than that of SH and TT. We studied a random pore model (RPM), shrinking core model (SCM), and hybrid model (HM), and the hybrid model was found to be the most suitable model of the three for fitting the steam gasification reactions of the three types of coal. It had high fitting correlation coefficient R² values (ranging from 0.9939 to 0.9990) and small average error θ values (ranging from 0.009 to 0.016). The apparent activation energy E values of SL, SH, and TT fitted by HM were 179.10, 48.14, and 63.06 kJ/mol, respectively, and the corresponding pre-exponential factor k₀ values were 3.14 × 10⁷, 1.01, and 1.22 min⁻¹, respectively. This study finds that the steam gasification of SL, SH, and TT coal samples consists of homogeneous phase reaction and shrinking core reaction.