Underground coal gasification (UCG) can convert coal resources to high-calorific value syngas, which is important for the exploration of resources and the application of clean coal technology. This study investigated the gasification process of lignite in Heilongjiang Province through an oxygen enrichment approach and examined the impact of the oxygen concentration on the gasification efficiency. Furthermore, a high-fidelity Aspen Plus process model was designed to predict the gasification products of lignite. These findings indicate that the abrupt increase in the gasification temperature and pressure is governed by the concentration of oxygen in the gasification agent. An increased concentration of oxygen results in a higher gasification temperature, thereby influencing the thermodynamic reaction processes within the gasifier. The combustion reaction of lignite transitions into a coke reaction when the oxygen concentration is elevated to 90%. At this time, the relative concentration of CO₂ generated from lignite combustion progressively diminished from 78.33%, while the relative concentrations of H₂ and CO produced through coke reactions gradually increased from 3% and 2.07%, respectively. When the oxygen concentration reaches 100%, the relative contents of H₂ and CO generated through gasification reach their respective maxima, measuring 18.90% and 23.91%. The calorific value attained a peak of 6.65 MJ N⁻¹ m⁻³ simultaneously. Furthermore, the ash yield of lignite may be a critical factor influencing the process of underground coal gasification. The gasification efficiency of lignite near T₆ is suboptimal when the oxygen concentration falls below 100%, potentially attributable to the influence of ash. In summary, lignite in Heilongjiang Province can be effectively developed through underground gasification technology via an oxygen enrichment process. Furthermore, the Aspen Plus model we developed can effectively assist in predicting the products of lignite gasification in Heilongjiang Province.

The first coalification jump (FCJ) has a significant effect on changes in the microstructural properties of coal and plays a crucial role in understanding the efficient utilization of low-rank coal. One lignite (QSY-2), two subbituminous (MHJ-10 and YCW-2), and three high-volatile A-grade bituminous coals (YX-12, JF-18, and HY-5) from the Ningdong coalfield were selected for research, avoiding the influence of regional geology. The evolution characteristics of the microstructures before and after the FCJ were investigated via spectroscopic experiments. The complex and unstable molecular structure of low-rank coal gradually decomposes and polymerizes at 350 °C. The aliphatic structure shows a V-shaped change trend as metamorphism increases. The inflection point is around an R_o of 0.6%. Demethylation and polymerization occur simultaneously during the FCJ. The reconnection of benzene substances with the aromatic ring increases the density of aromatic rings in the YCW-2 sample, significantly enhancing its aromaticity. The removal of oxygen-containing functional groups, especially methoxy and carbonyl groups, provides the possibility for the formation of CH₄ and CO₂ during the metamorphosis of lignite to subbituminous coal. Furthermore, high temperatures result in a loss of moisture content during the FCJ, which is the primary factor leading to a reduction in the hydroxyl content in coal. The selected samples are primarily composed of organic matter, with low levels of heteroatoms in the coal. It is preliminarily determined that coalification is not significantly affected. This study provides a theoretical foundation for investigating the molecular structure evolution of low-rank coal during the FCJ.