Cavity Models for Underground Coal Gasification
01 Jan 2018-pp 207-221
TL;DR: In this paper, the authors discuss various experiments and models of underground coal gasification cavities, with a focus on the effects of reaction chemistry and thermomechanical spalling on cavity evolution.
Abstract: Underground coal gasification is an in situ coal utilization technique that has immense potential as a future clean coal technology. UCG possesses a number of advantages including the ability to use deep and unmineable coals. The most important component of UCG is the underground “cavity”—which serves as a chemical reactor with rich interplay of kinetics and transport. Field and laboratory-scale experiments have revealed several interesting features of the UCG cavity. Modeling studies on the UCG cavity involve fundamental models and CFD simulations. In this chapter, we will discuss various experiments and models of UCG cavities, with a focus on the effects of reaction chemistry and thermomechanical spalling on cavity evolution.
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TL;DR: In this article, the intrinsic reaction rates of two Australian coal chars (made under laboratory conditions) with O2, CO2, and H2O at increased pressures (up to 30 atm) have been made using a pressurized thermogravimetric analyzer.
Abstract: Measurements of the intrinsic reaction rates of two Australian coal chars (made under laboratory conditions) with O2, CO2, and H2O at increased pressures (up to 30 atm) have been made using a pressurized thermogravimetric analyzer (TGA). It was found that the reaction order in CO2 and H2O was not constant over the pressure range investigatedvarying from 0.5 to 0.8 at atmospheric pressure and decreasing at pressures above approximately 10 atm. The apparent reaction order in oxygen was less affected by pressure over the range 1 to 16 atm. Char surface area after reaction at higher pressures was generally greater than that after reaction at lower pressures. This resulted in a reduced effect of pressure on the intrinsic rates at 10% conversion. Activation energies for all three reactions were not significantly affected by an increase in reaction pressure. The intrinsic rate data obtained in this work were used to estimate the high-temperature reactivity of the chars using a basic knowledge of the pore structu...
219 citations
25 Aug 1978
TL;DR: In this article, the authors present a calculational model that describes certain aspects of the in situ gasification process and predict and correlate reaction and thermal front propagation rates and product-gas composition as a function of coal bed properties and process operating conditions.
Abstract: This report presents a calculational model that describes certain aspects of the in situ gasification process The primary aim of this preliminary work was to predict and correlate reaction and thermal-front propagation rates and product-gas composition as a function of coal bed properties and process operating conditions We restricted initial efforts to a one-dimensional transient Darcy flow in a permeable packed bed The numerical calculations include a detailed description of the reacting systemchemistry (13 species), with appropriate reaction rates and overall heat and mass transport in the system A comparison of calculated results with experimental data from a packed-bed combustion tube showed good agreement for reaction-zone propagation rates and produced-gas compositions However, we believe the sensitivity of the calculations to other reaction-rate and transport-coefficient models needs to be investigated
122 citations
28 Aug 1981
TL;DR: In this paper, a 1 cm borehole is drilled through a block of coal which is cut to fit in a 55 gallon oil drum, and blocks are burned for a period of several hours at a prescribed flow schedule, with appropriate instrumentation.
Abstract: LLNL has been conducting laboratory-scale experiments simulating underground coal gasification in order to better understand the physical and chemical phenomena governing the process. A 1 cm borehole is drilled through a block of coal which is cut to fit in a 55 gallon oil drum. Inlet gas may be air or oxygen/steam mixture at various ratios. The blocks are burned for a period of several hours at a prescribed flow schedule, with appropriate instrumentation. Gas quality is found to be relatively independent of coal type for the range of sub-bituminous coals tested. After the burn the blocks of coal are cut open to examine the cavity. A mathematical modeling effort supports these experiments. So far the models have been restricted to pure carbon, to simplify the chemistry in the model. No steam/char reaction is modeled. Only the carbon/oxygen surface reaction is allowed, hence the growth of the cavity wall is limited by the rate of transport of oxygen to the wall. When plug flow is assumed in the cavity the model predicts reasonable cavity shape downstream, but an incorrect shape upstream. When aerodynamic flow, including viscosity and vortex formation, is calculated in the cavity reasonable cavity shapes are obtained.
100 citations
TL;DR: Underground coal gasification (UCG) has re-emerged as an energy technology for coal conversion and utilization given its attractive economics, ability to access inaccessible coals, and versatility of use as mentioned in this paper.
97 citations
TL;DR: In this paper, the authors examined the feasibility of hydrogen production from underground coal gasification (UCG) in Western Canada, for the servicing of the oil sands bitumen upgrading industry.
95 citations