17Despite a body of research carried out on thermally coupled processes in soils, understanding 18 of thermo-osmosis phenomena in clays and its effects on hydro-mechanical behaviour is 19 incomplete. This paper presents an investigation on the effects of thermo-osmosis on 20 hydraulic behaviour of saturated clays. A theoretical formulation for hydraulic behaviour is 21 developed incorporating an explicit description of thermo-osmosis effects on coupled hydro-22 mechanical behaviour. The extended formulation is implemented within a coupled numerical 23 model for thermal, hydraulic, chemical and mechanical behaviour of soils. The model is 24 tested and applied to simulate a soil heating experiment. It is shown that the inclusion of 25 thermo-osmosis in the coupled thermo-hydraulic simulation of the case study provides a 26 2 better agreement with the experimental data compared with the case where only thermal 27 expansion of the soil constituents was considered. A series of numerical simulations are also 28 presented studying the pore water pressure development in saturated clay induced by a 29 heating source. It is shown that pore water pressure evolution can be considerably affected by 30 thermo-osmosis. Under the conditions of the problem considered, it was found that thermo-31 osmosis changed the pore water pressure regime in the vicinity of the heater in the case where 32 value of thermo-osmotic conductivity was larger than 10 -12 m 2 .K -1 .s -1 . New insights into the 33 hydraulic response of the ground and the pore pressure evolution due to thermo-osmosis are 34 provided in this paper.

No abstract

This paper presents the results of an extensive experimental analysis of underground coal gasification (UCG) using large bulk samples in an ex-situ reactor under atmospheric and high-pressure (30 bar) conditions. The high-rank coal obtained from the South Wales (UK) coalfield is employed for that purpose. The aim of this investigation is to define the gas production rates, gas composition, gas calorific value, process energy efficiency and temperature changes within the UCG reactor during the gasification process based on the pre-defined reactants and flow rates. Two UCG trials, each lasting 105 hours, consisted of six stages where the influences of oxygen, water, air and oxygen enriched air (OEA) under different flow conditions on the gasification process were investigated. Based on the results of two multi-day experiments, it is demonstrated that the gasification under high pressure conditions produces syngas with higher average calorific value (8.49 MJ/Nm 3 ) in comparison to syngas produced at atmospheric pressure conditions (6.92 MJ/Nm 3 ). Hence, the overall energy efficiency of the high-pressure experiment is higher compared to the atmospheric pressure test, i.e. 57.67% compared to 51.72%. This is related to the fact that the high-pressure gasification produces more methane (11.97 vol.%) than the atmospheric pressure gasification (2.30 vol.%). Under elevated pressure, the temperatures recorded in the roof strata are about 100°C higher compared to the UCG process under atmospheric pressure conditions. This work provides new insights into the gasification of carbon-rich coals subject to different gasification regimes and pressures.

An experimental campaign on the methane-oriented underground coal gasification (UCG) process was carried out in a large-scale laboratory installation. Two different types of coal were used for the oxygen/steam blown experiments, i.e., “Six Feet” semi-anthracite (Wales) and “Wesoła” hard coal (Poland). Four multi-day gasification tests (96 h continuous processes) were conducted in artificially created coal seams under two distinct pressure regimes-20 and 40 bar. The experiments demonstrated that the methane yields are significantly dependent on both the properties of coal (coal rank) and the pressure regime. The average CH4 concentration for “Six Feet” semi-anthracite was 15.8%vol. at 20 bar and 19.1%vol. at 40 bar. During the gasification of “Wesoła” coal, the methane concentrations were 10.9%vol. and 14.8%vol. at 20 and 40 bar, respectively. The “Six Feet” coal gasification was characterized by much higher energy efficiency than gasification of the “Wesoła” coal and for both tested coals, the efficiency increased with gasification pressure. The maximum energy efficiency of 71.6% was obtained for “Six Feet” coal at 40 bar. A positive effect of the increase in gasification pressure on the stabilization of the quantitative parameters of UCG gas was demonstrated.

The results of ex-situ small-scale laboratory tests performed in a bespoke batch reactor simulating coal gasification to find the most optimal experimental conditions for producing methane-rich syngas in the context of UCG are presented in this paper. The influence of gaseous reactants (oxygen and steam), their supply rates and thermodynamic conditions (temperatures of 650°C, 750°C, 850°C and pressures of 20 bar and 36 bar) on the gasification of semi-anthracite (South Wales coalfield) and bituminous (Silesian basin) coals is investigated. Increasing the gasification pressure from 20 bar to 36 bar and doubling the amount of steam with respect to oxygen benefit the methane generation. Although temperature increase from 650°C to 850°C also benefits methane generation, gasification at 750°C provides the most optimal conditions for methane-rich syngas production. Overall, the highest methane generation occurs at 750°C, 36 bar and H2O:O2=2:1 yielding peak methane concentrations of 44.00 vol.% and 35.55 vol.%, and average methane concentrations of 15.34 vol.% and 14.64 vol.% for the semi-anthracite and bituminous coals, respectively. These findings demonstrate that an increase in coal rank favours the methane generation. Owing to high methane content, the syngas produced at such conditions contains the highest calorific value, although the generation of hydrogen and carbon monoxide is reduced in comparison to the experiments conducted at 850°C. This study shows that gasification of bituminous and semi-anthracitic coals at elevated pressures can provide stable generation of methane-rich syngas whose quality can be controlled by the gasification temperature through the dynamics of steam and O2 supply rates.