Underground Coal Gasification Reactor Research Articles

Assessment of Combustion Cavern Geometry in Underground Coal Gasification Process with the Use of Borehole Ground-Penetrating Radar

In this study, the shape and size of a combustion cavity with a fracture zone in the gasified coal seam was determined with the use of control boreholes and a ground-penetrating radar (BGPR) test. The underground coal gasification (UCG) field-scale experiment was performed in Carboniferous strata in coal seam 501 at a depth of approx. 460 m in the Wieczorek hard coal mine in the Upper Silesian Coal Basin, Poland. After the termination of the UCG reactor, five coring boreholes were drilled to identify the geometry of the resulting combustion cavity and the impact of the UCG process on the surrounding rock mass. Borehole ground-penetrating radar measurements were performed using a 100 MHz antenna in three boreholes with a length of about 40–50 m. This enabled the identification of the boundaries of the combustion cavity and the fracture zone in the coal seam. The fracture zones of rock layers and lithological borders near the control borehole were also depicted. As a result, the cavity was estimated to have a length of around 32 m, a width of around 7 m and a height of around 5 m. The analyses performed with the control boreholes and the BGPR provided sufficient information to determine the geometry of the combustion cavity and the fracture zone.

Pollutants release from the residues remaining after underground gasification (UCG) of ortho- and meta-lignites

One of the most significant environmental risks related to underground coal gasification (UCG) is groundwater contamination, which could potentially occur after process shutdown. This work comprises the results of laboratory tests on characteristics of UCG solid residues which were produced in the ex situ underground gasification of ortho- and meta-lignites and which may be a potential source of pollutants release to the surrounding area. Two multi-day trials were carried out in a large scale UCG ex situ reactors. The gasification tests were conducted in an artificial coal seam in the atmospheric pressure system. Two different types of lignite were gasified, i.e. meta-lignite from Velenje Coal Mine (Slovenia) and ortho-lignite from Oltenia Coal Mine (Romania). The aim of this study was to examine whether the type of lignite has an influence on the composition of the post-gasification residues, including contaminants that can be leached to the surrounding aquatic environment from the cavity formed as a results of UCG. The solid post-process residue samples obtained from different sections of the reactor were characterized and the leaching behaviour of some organic and inorganic parameters present in post-process residue was investigated. Additionally, the partitioning of metals and metalloids during underground gasification of two types of lignites (ortho- and meta-lignite) was discussed. The effect on lignite properties on the behaviour of metals and metalloids in the process of gasification and leaching to the water phase was also confirmed in the study. Leaching tests have been performed in terms of evaluation the capability for inorganic and general organic compounds elution from post-process residues after UCG of lignites. The study shows that samples originating from various parts of the UCG reactor differ strongly and may release contaminants to the vicinity of the georeactor. However, no dangerous trace elements such as Cr, Cd, Hg and Pb occurred in the aqueous extracts, which may indicate that in the post-operational phase, the UCG of lignite is a process safe for the aquatic environment.

Numerical study of ground deformation during underground coal gasification through coupled flow-geomechanical modelling

This paper presents a coupled flow-geomechanical model to study the ground deformation due to geoenergy applications involving complex thermo-hydraulic-chemical–mechanical coupled processes, such as underground coal gasification (UCG). The model is developed by coupling two sub-models, that is, the chemical reactions associated flow model that can predict temperature development and cavity growth and the geomechanical model that considers the temperature-dependent thermo-mechanical properties of geologic materials and the conversion of coal to the cavity. Numerical simulations of a field-scale UCG project with the linked vertical wells (LVW) were conducted through coupled flow-geomechanical modelling. The effects of the thermo-mechanical properties of the strata adjacent to the coal seam and the UCG operational conditions on the temperature distribution, cavity formation, and ground deformation in the operating stage of UCG were studied. Simulated results showed that temperature of over 1200 K would be obtained between the injection well and the production well in the coal seam while the 400 K isotherm only moved less than 2 m vertically in the strata near the UCG reactor. Cavity with long forward length and short backward length was formed between the injection well and the production well. Ground deformation during UCG was caused due to the combined effects of temperature and cavity evolution. The parametric sensitivity study showed that when the initial elastic modulus of the surrounding strata decreased from 4 GPa to 1 GPa, its effect on the ground deformation beyond the right side of the production well was not of significance. The ground deformation was not sensitive when the initial thermal expansion coefficient of the surrounding strata was reduced to the order of magnitude of 1.0-6 (K−1). In addition, adjusting the supply rate of O2 and modifying the location of the horizontal gasification channel can control the ground deformation during UCG. The coupled flow-geomechanical model presented in this paper can be helpful in the safety control of UCG.

Transport of heat, moisture, and gaseous chemicals in hydro-mechanically altered strata surrounding the underground coal gasification reactor

Underground coal gasification (UCG) has a great potential to be accompanied by the technology of (enhanced) coal bed methane ((E)CBM) and carbon capture and storage (CCS), enhancing coal energy efficiency and mitigating climate change. This study aims to assess the environmental impact of three field-scale UCG hypothetical sites targeting deep-buried seams during the UCG operational stage in the combined CBM-UCG application. For this purpose, a risk assessment methodology is developed with consideration of the geomechanical and hydrogeological impact of UCG operations on the overlying strata by analogy to longwall mining operations. A series of numerical simulations are conducted to investigate the effect of variations in the saturation conditions around the UCG reactor, the change of rock permeability, and the UCG reactor operation duration on the propagation of heat, moisture and gaseous chemicals. The results demonstrate that CBM-UCG activities in the three sites are not likely to cause negative impacts on the environment during the UCG process when the behaviour of the reactor and the change of the surrounding strata are in control as expected. This work can provide insights in terms of environmental decision making, regulation and management to prevent reduction in gasification efficiency, to conduct the post-UCG (E)CBM process and to mitigate the UCG gas leakage and contamination of surrounding aquifers, highlighting where additional information is required in CBM-UCG activities.

The effect of rock permeability value on groundwater influx in underground coal gasification reactor

Rock permeability value is one of the most significant rock’s physical properties that affect groundwater influx processes in underground coal gasification (UCG). This value of rock permeability (K), namely the vertical permeability of flanking rocks (Kv) and horizontal permeability of coal (Kh). The purpose of this study was to determine the extent of the influence of the value of rock permeability on the potential of groundwater influx. The effect of rock permeability on groundwater influx into the UCG gasification reactor cavity in the presence of thermal loads and mineral composition content is large and significant to consider. Based on the resistance to heat loads, the type of sandstone lithology is relatively more resistant compared to siltstone and claystone lithology.

Preliminary modeling for module estimation on the underground coal gasification project

Designing the module is one of the initial works of the underground coal gasification (UCG) feasibility study, consisting of the coal area to be gasified as panels and the coal to be left as pillars. Three models have been designed with each panel dimension 380 m in length, 150 m in width and 18 m thick. The finite element method is used in the study and the 2D and 3D geotechnical simulations have been carried out with variations of the pillars. As a result of 2D modeling, the critical strength reduction factor (SRF) is 0.25 with the highest deformation on the surface is 0.04 m (SMA-C) and 0.03 (SM-D) if the pillar is 50 m width. If SRF is increased to 0.37, the deformation on the surface is 0.36 (SMA-C) and is 13.5 (SM-D), respectively. From the 3D modeling results, if it is assumed that the velocity of the UCG reactor hole rate is 0.24 m/day until it reaches the final target length of the reactor hole 380 m, the maximum deformation of the soil surface at the SMA-C and SM-D locations is 0.074 m and 0.096 m, respectively. Determination of the module is important in the feasibility study and evaluation of the UCG site.

Thermo-fluid–mechanical numerical simulations of surface subsidence at the site of underground coal gasification

This work deals with modelling surface subsidence that aims to help industrialize underground coal gasification (UCG). UCG is a long-known, but poorly industrialized, method of energy extraction from coal. Risks of surface subsidence and groundwater pollution are two main hurdles that are affecting the potential industrialization of UCG. The particular challenge is the existence of groundwater because of implications to both its pollution and its influence on surface subsidence. Additionally, the coal combustion and the complex geometry of the UCG reactors impacts surface subsidence. To meet these challenges, the thermal and fluid analyses should be included in the model, and surface subsidence should be modelled in three dimensions to capture the collapsed shape of the UCG reactor. Based on the nature of these challenges and an earlier successful implementation, Itasca's commercial FLAC3D software with intrinsic thermal and fluid models was chosen to model surface subsidence. This study determines that the inclusion of fluid analysis improves the predictions of surface subsidence when compared with measurements at the highly watered Shatsk UCG site. In turn, thermal analysis mildly influences the modelled surface subsidence. The fluid analysis shows that the flow in the upper aquifer influences surface subsidence to a greater extent than the flow in the lower aquifers. High temperatures cause an upward flow in the lower aquifer located above the UCG reactor but does not change the flow pattern in the upper aquifer. The fluid analysis also reveals that if the UCG reactor is filled with water, surface subsidence does not occur.

Insights into solid-gas conversion and cavity growth during Underground Coal Gasification (UCG) through Thermo-Hydraulic-Chemical (THC) modelling

This paper presents the application of a thermal-hydraulic-chemical model to simulate (1) a laboratory small-scale borehole combustion experiment using high-ash-content coal and (2) an ex-situ large-scale UCG experiment using low-moisture-content hard coal. The focus was to study temperature development, syngas composition, pore structure alteration of coal, and cavity growth pertinent to the UCG process. Both numerical simulations reproduced the temperature development trends along the gasification channel. Compared with the measured cavity with a horizontal length of 15 cm and a maximum vertical extension of 5.4 cm that was created in the 10-h-long borehole combustion experiment, a similar simulated cavity was formed in the first simulation, which had a horizontal length of 10 cm and a maximum vertical extension of 5.1–5.7 cm. This simulation indicated that the proposed model can be used to estimate the cavity growth with the process of UCG due to solid-gas conversion. In the second simulation, the simulated composition of syngas showed good agreement with the experimental results. It also revealed that fierce gasification and combustion mainly occurred close to the inlet, and thus created an L-shaped cavity in the 20-h-long UCG process. Moreover, the UCG process was distinctly divided into three stages from the perspective of solid loss and pore structure alteration at a representative node owing to thermal expansion, compressional shrinkage, pyrolysis, and gasification and combustion. The second stage of 3–11 h was the main period for combustion and gasification of the UCG process, namely, 70% of the solid mass was converted into syngas at temperatures above 1320 K, and the porosity increased linearly with time and the permeability showed exponential growth. Furthermore, a parametric sensitivity study based on the second simulation indicated that the simulated cavity growth of UCG was sensitive to the kinetics of char combustion, while the assumed pyrolyzed production ratios in the model were not of significance to the cavity growth during UCG. It is claimed that the coupled thermo-hydraulic-chemical model adopted in this paper provides novel insights into the UCG reactor's dynamic behavior, including solid-gas conversion and cavity growth.

In situ sorption phenomena can mitigate potential negative environmental effects of underground coal gasification (UCG) - an experimental study of phenol removal on UCG-derived residues in the aspect of contaminant retardation

The aim of the study was to investigate the sorption interactions between phenol and materials obtained from four different underground coal gasification (UCG) ex-situ simulations. These interactions are significant in terms of the impact of the UCG on the groundwater environment. Sorption parameters were determined for two sample types: raw coal mined from the coal-bed and then subjected to the gasification process; and char residue acquired from the cavity formed as a result of the UCG processes. Laboratory-scale tests were carried out using deionized water and aqueous solutions with increasing concentrations of phenol (from 50 mg/dm3 to 2000 mg/dm3) at 298 K. On the assumption of physical interactions (non-specific physisorption) and due to a nonlinear mass distribution of adsorbed substances as a function of equilibrium concentration, the Freundlich isotherm model was applied to describe adsorption phenomena. The isotherms have good fitting (R2 from 0.5716 to 0.9811). Relatively high percentage phenol removal efficiency was observed for all tested chars (from 17.0% to 99.8% for the 1.0–2.5 mm fraction and from 6.9% to 99.6% for the 10.0–12.5 mm fraction). Additionally, the sorption characteristics was used to evaluate the retardation coefficients. The largest delay in the organic pollutant migration in the environment around a UCG reactor occurs for phenol transport in the layer of the post-process char from ‘Wesoła’ after 40 bar pressure experiment.

A numerical investigation into the environmental impact of underground coal gasification technology based on a coupled thermal-hydro-chemical model

This study aims to improve the understanding of the potential environmental impact of the underground coal gasification (UCG) process based on a numerical investigation of the gaseous and dissolved chemicals’ transport in the strata surrounding the UCG reactor. A coupled thermal-hydro-chemical (THC) model in the framework of COMPASS code is employed and further developed for this purpose. The model is compared against analytical solutions in the verification process and applied against a former UCG trial (Hoe Creek UCG programme) for validation purpose. The numerical model is then applied to investigate the potential environmental impact of UCG in three different geological materials (sandstone, coal, and shale) in two steps: the potential gas propagation during UCG process and the solute transport in UCG decommissioning stage. The results indicate that the gas propagation is limited to a near-cavity area in geological strata with low permeability and high air entry value such as shale, which is mainly attributed to the dry zone generated by the high temperature, while a larger gas plume is observed for materials with poor water retention characteristics, such as coal and sandstone. Besides, the gas propagation is retarded to some extent due to the reducing effect of high pressure on gas diffusion. The propagation of dissolved chemicals via diffusion is limited to near-cavity areas, i.e. 2 m, in three studied materials after 10 years. Based on the improved understanding of the various chemicals’ migration in different materials, by selecting the target coal seam surrounded by strata layers with high air entry value and low permeability, the gas losses from the reactor during the UCG reactor operation stage can be minimized and the potential negative environmental impact of ash leaching and solute propagation in UCG decommissioning stage can be avoided. This work also provides further insight and suggestions into the importance of investigating the adsorption capacities of different geological media to evaluate their performance as a natural cleaning system.

Subsidence and heat propagation modeling on the underground coal gasification (Case study at Muara Enim Formation, South Sumatera)

One of the important issues to study underground coal gasification (UCG) is the prediction of surface subsidence. Several parameters that influence these conditions are the thickness of cap rock, the physical and mechanical characteristics, the structure condition, the minerals composition of the rock, and external conditions. This study had been carried out simulation and modeling to determine the level of surface subsidence risk and the effect of high temperatures due to the activities. The modeling results show that the thickness of the rock above the UCG coal seam greatly affects the surface subsidence. The depth is more than 200 m and found that the SF value is 1.59 which indicates UCG reactor depth of ≥ 200 m is safe from the risk of subsidence. From the characteristic aspect of the cap rock, the claystone types which not contain kaolinite minerals are more prone to collapse than those of contain kaolinite minerals. From this models, the gasifier at 150 m depth was estimated that there will be a decline of -7.23 m, and the minimum subsidence is at 275 m about 0.1 m. The heat propagation modeling results show that at 50 m the temperature is estimated to be 213- 289°C, but if the thickness of the cap rock is > 200 m depth, the temperature is around 29-28°C.

Experimental study of underground coal gasification (UCG) of a high-rank coal using atmospheric and high-pressure conditions in an ex-situ reactor

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 h, 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/Nm3) in comparison to syngas produced at atmospheric pressure conditions (6.92 MJ/Nm3). 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.

Underground coal gasification – A numerical approach to study the formation of syngas and its reactive transport in the surrounding strata

In this work, a method to study the formation of syngas during the underground coal gasification (UCG) process and its reactive transport in the surrounding strata is proposed. It combines a thermodynamic equilibrium stoichiometric model of the cavity reactions with a coupled thermo-hydraulic-chemical–mechanical (THCM) framework of COMPASS code for the transport of UCG products away from the cavity. With the input information of coal properties obtained from the South Wales coalfield, gasification reagents (air and steam) and thermodynamic conditions (initial temperature and pressure), the thermodynamic equilibrium model developed provides the maximum yield of gasification products and temperature from a UCG system. Gasification results giving the syngas composition with the highest percentage of methane and carbon dioxide, are then used as the chemical (gas) and thermal boundary conditions for the coupled thermo-chemical model of the THCM framework to analyse the variations of temperature and gas concentrations, in strata surrounding the UCG reactor. For that purpose, a set of numerical simulations considering three porous media (coal, shale and sandstone) with different physico-chemical properties is conducted. The gasification results demonstrate that increasing the amount of steam injected in the UCG reactor decreases the temperature of the system as well as the concentration of carbon monoxide and nitrogen, while benefiting the production of hydrogen, methane and carbon dioxide. The numerical simulations performed using the THCM model indicate that multicomponent gas diffusion and advection are competing transport mechanisms in porous media with intrinsic permeability higher than 1 mD (sandstone), while the gas diffusion becomes a dominant transport process in porous media with an intrinsic permeability lower than 1 mD (coal and shale). Moreover, the simulation results of reactive transport of methane and carbon dioxide in different porous media demonstrate the significance of considering the adsorption effect in the gas transport in the overall UCG process. In particular, the retardation of the gas front due to gas sorption is the most pronounced in coal, followed by shale and then sandstone. In conclusion, the model presented in this study demonstrates its potential application in managing the environmental practices, reducing pollution risk and securing greater public and regulatory support for UCG technology.

Optimization of synthesis gas heating values and tar by-product yield in underground coal gasification

Increasing global energy demand is a central challenge of the 21st century. Apart from renewable energy concepts, sustainable bridging and buffering technologies are needed which simultaneously offer long-term energy supply guarantees. Underground coal gasification (UCG) shows a promising potential to meet these requirements of future energy markets by in situ conversion of coal to a valuable synthesis gas that can be used in various industrial applications. Currently conducted in more than 14 countries worldwide, a main focus of international UCG efforts lies in improved technical control to reach the desired high gas qualities and simultaneously reduce the tar by-product yield as a potential source of groundwater contamination. Referring to an innovative thermodynamic UCG model parameterized with exemplary base-case data from the UCG field trials Hanna-I, Centralia-Partial Seam CRIP (PSC) and Pricetown, we investigated pyrolysis temperature, operating pressure, water influx and gasification agent injection, optimizing synthesis gas heating values and reduced tar production. General best-fit scenarios were performed assuming an idealized UCG reactor. Besides these best-fit simulations, selected worst-case scenarios considering gas losses were tested. Overall, the model results indicate that operational process improvement potentials vary over wide ranges in the order of few percent to more than 50% compared to the examined base cases. In view of selected available literature data, near-zero tar production rates and simultaneous Lower Heating Value (LHV) improvements in the range of ∼2–40% are feasible.

Evaluation of a Compact Coaxial Underground Coal Gasification System Inside an Artificial Coal Seam

The Underground Coal Gasification (UCG) system is a clean technology for obtaining energy from coal. The coaxial UCG system is supposed to be compact and flexible in order to adapt to complicated geological conditions caused by the existence of faults and folds in the ground. In this study, the application of a coaxial UCG system with a horizontal well is discussed, by means of an ex situ model UCG experiment in a large-scale simulated coal seam with dimensions of 550 × 600 × 2740 mm. A horizontal well with a 45-mm diameter and a 2600-mm length was used as an injection/production well. During the experiment, changes in temperature field and product gas compositions were observed when changing the outlet position of the injection pipe. It was found that the UCG reactor is unstable and expands continuously due to fracturing activity caused by coal crack initiation and extension under the influence of thermal stress. Therefore, acoustic emission (AE) is considered an effective tool to monitor fracturing activities and visualize the gasification zone of coal. The results gathered from monitoring of AEs agree with the measured data of temperatures; the source location of AE was detected around the region where temperature increased. The average calorific value of the produced gas was 6.85 MJ/Nm3, and the gasification efficiency, defined as the conversion efficiency of the gasified coal to syngas, was 65.43%, in the whole experimental process. The study results suggest that the recovered coal energy from a coaxial UCG system is comparable to that of a conventional UCG system. Therefore, a coaxial UCG system may be a feasible option to utilize abandoned underground coal resources without mining.

Prediction of Steam Jacket Dynamics and Water Balances in Underground Coal Gasification

Underground coal gasification (UCG) converts coal to a high-calorific synthesis gas for the production of fuels or chemical feedstock. UCG reactors are generally operated below hydrostatic pressure to avoid leakage of UCG fluids into overburden aquifers. Additionally, fluid flow out of and into the reactor is also determined by the presence of the steam jacket, emerging in close reactor vicinity due to the high temperatures generated in UCG operation. Aiming at improving the understanding of the substantial role of the steam jacket in UCG operations, we employ numerical non-isothermal multiphase flow simulations to assess the occurring multiphase fluid flow processes. For that purpose, we first validate our modeling approach against published data on the U.S. UCG field trials at Hanna and Hoe Creek, achieving a very good agreement between our simulation and the observed water balances. Then, we discuss the effect of coal seam permeability and UCG reactor pressure on the dynamic multiphase flow processes in the reactor’s vicinity. The presented modeling approach allows for the quantification and prediction of time-dependent temperature and pressure distributions in the reactor vicinity, and thus steam jacket dynamics as well as reactor water in- and outflows.

Evaluation of Coal Combustion Zone and Gas Energy Recovery for Underground Coal Gasification (UCG) Process

During underground coal gasification (UCG) operations, evaluation of coal gasification cavity evolution and precise control of the underground reactor are important for efficient gasification. It is also essential to estimate the energy recovery of a UCG system and the whole gasification process to ensure an effective combustion and gasification rate. An experimental simulation of UCG using an artificial coal seam comprising a compacted broken coal block was conducted using ex situ UCG models. The main goal of the experiments was the establishment of evaluation methods for the gasification zone and energy recovery during UCG. To investigate the distribution and extent of fracture activity, and to evaluate the propagation of the combustion area in the UCG reactor, we used acoustic emissions (AE) monitoring. This was combined with traditional measurements of temperature variation and product gas content. This paper presents the results of AE analysis of the fracturing activities and damage mechanisms of the...

Thermo-Mechanical Simulations of Rock Behavior in Underground Coal Gasification Show Negligible Impact of Temperature-Dependent Parameters on Permeability Changes

A coupled thermo-mechanical model has been developed to assess permeability changes in the vicinity of an underground coal gasification (UCG) reactor resulting from excavation and thermo-mechanical effects. Thereto, we consider a stepwise UCG reactor excavation based on a pre-defined coal consumption rate and dynamic thermal boundary conditions. Simulation results demonstrate that thermo-mechanical rock behavior is mainly driven by the thermal expansion coefficient, thermal conductivity, tensile strength and elastic modulus of the surrounding rock. A comparison between temperature-dependent and temperature-independent parameters applied in the simulations indicates notable variations in the distribution of total displacements in the UCG reactor vicinity related to thermal stress, but only negligible differences in permeability changes. Hence, temperature-dependent thermo-mechanical parameters have to be considered in the assessment of near-field UCG impacts only, while far-field models can achieve a higher computational efficiency by using temperature-independent thermo-mechanical parameters. Considering the findings of the present study in the large-scale assessment of potential environmental impacts of underground coal gasification, representative coupled simulations based on complex 3D large-scale models become computationally feasible.

Control oriented modeling and optimization of one dimensional packed bed model of underground coal gasification

To account for nonlinear nature and huge model uncertainties of underground coal gasification (UCG) process, a robust model based control strategy is to be employed. The available models in the literature do not lend themselves to control applications easily. In this work a control oriented one dimensional (1-D) packed bed model of UCG is developed, which can be used in a closed loop configuration with a robust controller to maintain a desired heating value of the exit gas mixture by manipulating the flow rate of injected gases. The model is also capable of predicting time and space profiles of some important parameters, which include solid temperature, composition of exit gas mixture, rates of different chemical reactions and expected life of the UCG reactor in response to different operating conditions and coal properties. Most of these parameters are either impossible or very expensive to measure. There is uncertainty in some coal properties which is addressed by optimizing few input parameters using sequential quadratic programming (SQP) algorithm, a nonlinear optimization technique. The model results are compared with actual field trials which show a good agreement for the calorific value of exit gas.

Coupled Hydro-thermal Analysis of Underground Coal Gasification Reactor Cool Down for Subsequent CO2 Storage

The present study investigates the time dependency of a UCG (Underground Coal Gasification) reactor cool down process by comparing natural cool down with forced cooling driven by water flushing. The convective heat transport out of the UCG reactor was calculated using an analytical approach coupled to a numerical heat flow model of the geology surrounding the UCG reactor. Our results show that forced cooling by water flushing at flow velocities of 1 m/s can decrease the required time to retain initial in-situ temperature conditions by a factor of more than 300.