Impact mechanisms of injection temperature and pressure on multi-field evolution and gas production characteristics in in-situ coal-to-hydrogen

Abstract

The quantitative regulation mechanisms of injection temperature and pressure on the spatiotemporal multi-field evolution in in-situ coal-to-hydrogen (ISCH) conversion remain poorly understood. We developed a coupled thermal–hydraulic-chemical (THC) model and performed full-factorial simulations to elucidate the competitive interactions between these parameters. Results demonstrate a distinct functional differentiation: injection pressure serves as the decisive lever for the spatial expansion rate, where increasing pressure from 8 MPa to 10 MPa surged the average expansion rate by 200.0%; conversely, injection temperature predominantly governs the induction period, with an increase from 673.15 K to 873.15 K reducing the initiation time by 59.2%. While the system exhibited convergence toward a quasi-steady configuration regardless of initial conditions, high-energy injection strategies effectively suppressed the localized accumulation of carbon byproducts by intensifying fluid transport. Crucially, this study identifies ‘‘heat–mass spatial decoupling”—characterized by the spatiotemporal mismatch between the high-temperature core and the reactant field—as the fundamental bottleneck restricting initial hydrogen production efficiency, rather than thermal energy depletion. Accordingly, this study suggests that enhancing spatiotemporal overlap through dynamic pressure modulation and gradient steam-to-oxygen regulation is essential for maximizing ISCH yield.

Keywords

In-situ coal-to-hydrogen / Coupled THC model / Injection parameters / Heat-mass decoupling / Dynamic evolution

References

[1] Zhao YS, Liang WG, Feng ZJ, Feng ZC, Yang D. Science, technology and engineering of in—situ modified mining by fluidization. J China Coal Soc 2021; 46(1):25-35. in Chinese.

[2] Zhao J, Wang L, Liu SM, Kang ZQ, Yang D, Zhao YS. Numerical simulation and thermo—hydro—mechanical coupling model of in situ mining of low—mature organic—rich shale by convection heating. Adv Geo—Energy Res 2022;6(6):502-14.

[3] Yang D, Zhao Y. Gas—liquid two—phase critical seepage law in single fracture and its random and compound mathematical model. Chin J Rock Mech Eng 2008:84-9.

[4] Xu WJ, Zhao YS. A numerical study on the multi—physics coupling mechanisms and spatiotemporal evolution of the in—situ coal—to—hydrogen process. J Clean Prod 2025; 534:147098.

[5] Su FQ, Yang JN, He XL, Dai MJ, Hamanaka A, Yu YH, et al. Influences of removable gas injection methods on the temperature field and gas composition of the underground coal gasification process. Fuel 2024; 363:130953.

[6] Khadse A, Qayyumi M, Mahajani S, Aghalayam P. Underground coal gasification: a new clean coal utilization technique for India. Energy 2007; 32(11):2061—71.

[7] Chen YP, Wang T, Zhang JH, Zhang MY, Xue JJ, Shi JT, et al. Simulation of water influx and gasified gas transport during underground coal gasification with controlled retracting injection point technology. Energies 2022; 15(11):3997.

[8] An N, Zagorščak R, Thomas HR. Transport of heat, moisture, and gaseous chemicals in hydro—mechanically altered strata surrounding the underground coal gasification reactor. Int J Coal Geol 2022; 249:103879.

[9] Kapusta K, Stańczyk K. Pollution of water during underground coal gasification of hard coal and lignite. Fuel 2011; 90(5):1927—34.

[10] Imran M, Kumar D, Kumar N, Qayyum A, Saeed A, Bhatti MS. Environmental concerns of underground coal gasification. Renew Sustain Energy Rev 2014; 31:600—10.

[11] Akbarzadeh Kasani H, Chalaturnyk RJ. Coupled reservoir and geomechanical simulation for a deep underground coal gasification project. J Nat Gas Sci Eng 2017; 37:487-501.

[12] Laouafa F, Farret R, Vidal—Gilbert S, Kazmierczak JB. Overview and modeling of mechanical and thermomechanical impact of underground coal gasification exploitation. Mitig Adapt Strateg Glob Change 2016; 21(4):547-76.

[13] Tian SY, Tian ZF, Xu CS, Jiang LL, Centofanti J. Impacts of geological and operational parameters on the performance of in—situ coal gasification using linked vertical wells. Fuel 2026; 406:136828.

[14] Yao XY, Li X, Wei B, Tian JJ, Yang SG, Ju YW. Numerical simulations of fracture propagation in overlying strata for deep underground coal gasification using controlled retraction injection point technology. Energy 2025; 317:134684.

[15] Guo W, Liu H, Zhu XD, Zhang YY, Liu SQ, Guo TT. Research on the expansion law of combustion cavity in deep coal seam underground gasification based on multi—physics field simulations and response surface method. Energy 2025; 326:136287.

[16] Cui CX, Liu YW, Chai XL, Tian L. Investigation on performance characteristics and thermal analysis of underground coal gasification in porous media based on non—steady flow. Fuel 2025; 389:134629.

[17] Wiatowski M, Kapusta K, Strugała—Wilczek A, Stańczyk K, Castro—Muñiz A, Suárez—García F, et al. Large—scale experimental simulations of in situ coal gasification in terms of process efficiency and physicochemical properties of process by—products. Energies 2023; 16(11):4455.

[18] Stańczyk K, Smoliński A, Kapusta K, Wiatowski M, Świądrowski J, Kotyrba A, et al. Dynamic experimental simulation of hydrogen oriented underground gasification of lignite. Fuel 2010; 89(11):3307—14.

[19] Ding JS, Wu CF, Gao B, Zhang SX, Zhang JB, Tan KY. Research on the underground gasification of lignite through an oxygen enrichment process: insights from experimental study and Aspen Plus process model. RSC Adv 2024; 14(49):36398-409.

[20] Yang LH, Zhang X, Zhu K. Hydrogen production in underground coal gasification (UCG). Energy Sources Part A Recovery Util Environ Eff 2016; 38(3):376-83.

[21] Wei ZX, Jiang LL, Hassanpouryouzband A, Chen SS, Chen YP, Ju YW, et al. Enabling large—scale enhanced hydrogen production in deep underground coal gasification in the context of a hydrogen economy. Energy Convers Manag 2025; 325:119449.

[22] Feng LL, Dong MF, Qin BT, Pang JB, Babaee S. H2 production enhancement in underground coal gasification with steam addition: effect of injection conditions. Energy 2024; 291:130379.

[23] Eftekhari AA, Wolf KH, Rogut J, Bruining H. Energy and exergy analysis of alternating injection of oxygen and steam in the low emission underground gasification of deep thin coal. Appl Energy 2017; 208(C):62-71.

[24] Perkins G, Vairakannu P. Considerations for oxidant and gasifying medium selection in underground coal gasification. Fuel Process Technol 2017; 165:145—54.

[25] Iriguchi R, Hamanaka A, Su FQ, Sasaoka T, Shimada H, Itakura KI, et al. Effects of water injection on reaction temperature and hydrogen production in horizontal co—axial underground coal gasification. Sci Rep 2024; 14:25551.

[26] Andrianopoulos E, Korre A, Durucan S. Chemical process modelling of underground coal gasification and evaluation of produced gas quality for end use. Energy Procedia 2015; 76:444-53.

[27] Zhang ZZ, Yang X, Shang XJ, Yang H. A thermal—hydrological—mechanical—chemical coupled mathematical model for underground coal gasification with random fractures. Mathematics 2022; 10(16):1-21.

[28] Gao W, Zagorščak R, Thomas HR. Numerical study of ground deformation during underground coal gasification through coupled flow—geomechanical modelling. Fuel 2022; 315:122833.

[29] Gür M, Canbaz ED. Analysis of syngas production and reaction zones in hydrogen oriented underground coal gasification. Fuel 2020; 269:117331.

[30] Wu FJ, Huang SY, Jiang Q, Jiang GC. Effects of pressure and heating rate on coal pyrolysis: a study in simulated underground coal gasification. J Anal Appl Pyrol 2023; 175:106179.

[31] Xie J, Xin L, Hu XM, Cheng WM, Liu WT, Wang ZG. Technical application of safety and cleaner production technology by underground coal gasification in China. J Clean Prod 2020; 250:119487.

[32] Zhang F, Chen WJ, Chen L, Wang SZ, Li YH, Yang JQ. Exergy analysis of underground coal gasification using supercritical water/carbon dioxide mixture as combined gasifying agent. Energy Convers Manag 2025; 336:119913.

[33] Gao W, Zagorščak R, Thomas HR. Insights into solid—gas conversion and cavity growth during Underground Coal Gasification (UCG) through Thermo—Hydraulic—Chemical (THC) modelling. Int J Coal Geol 2021; 237:103711.

[34] Kee RJ, Coltrin ME, Glarborg P. Chemically reacting flow. Hoboken, N.J: Wiley—Interscience; 2003.

[35] Nourozieh H, Kariznovi M, Chen ZX, Abedi J. Simulation study of underground coal gasification in Alberta Reservoirs: geological structure and process modeling. Energy Fuels 2010; 24(6):3540—50.

[36] Seifi M, Chen ZX, Abedi J. Numerical simulation of underground coal gasification using the CRIP method. Can J Chem Eng 2011; 89(6):1528—35.

[37] Arrhenius S. Über die Reaktionsgeschwindigkeit Bei der Inversion von Rohrzucker durch Säuren. Z Für Phys Chem 1889; 4U(1):226-48.

[38] Gao W, Zagorščak R, Thomas HR, An N. Simulation of underground coal gasification based on a coupled thermal—hydraulic—chemical model. Combust Theory Model 2022; 26(1):110-34.

[39] Seifi M, Abedi J, Chen ZX. Application of porous medium approach to simulate UCG process. Fuel 2014; 116:191-200.

[40] Zhao Y, Hu Y. Experimental study on effective stress behavior of coal under pore gas pressure. Chin J Geotech Eng 1995:26-31.

[41] Zhao YS, Qu F, Wan ZJ, Zhang Y, Liang WG, Meng QR. Experimental investigation on correlation between permeability variation and pore structure during coal pyrolysis. Transp Porous Medium 2010; 82(2):401—12.

[42] Zhang HQ, He YN, Tang CA, Ahmad B, Han LJ. Application of an improved flow—stress—damage model to the criticality assessment of water inrush in a mine: a case study. Rock Mech Rock Eng 2009; 42(6):911—30.

[43] Yang D, Zhao YS, Kang ZQ. Numerical simulation of in situ exploitation of oil shale by injecting high—temperature steam; pp. 483-500. Oil Shale 2019; 36(4):483-500.

[44] Kolditz O, Görke UJ, Shao H, Wang WQ. Thermo—Hydro—Mechanical—Chemical Processes in Porous Media: Benchmarks and examples. Berlin, Heidelberg: Springer; 2012.