RETRACTED: Techno-Economic Comparison of Onshore and Offshore Underground Coal Gasification End-Product Competitiveness

Nakaten, Natalie; Kempka, Thomas

doi:10.3390/en10101643

Cited by 12 publications

(5 citation statements)

References 29 publications

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“…Also, in situ coal conversion generates signifi- cantly smaller volumes of waste products (e.g., fly ashes) as well as pollutants, and moreover induces lower dust pollution, water consumption and methane emissions into the atmosphere. Coupled with existing technologies for carbon dioxide capture and storage (CCS) or even CO 2 utilisation to produce chemical feedstock such as methanol, in situ coal conversion has the potential to recover energy from coal with a low CO 2 footprint (Roddy and Younger, 2010;Sarhosis et al, 2013;Nakaten and Kempka, 2019).…”

Section: Formation Of By-products During In Situ Coal Conversionmentioning

confidence: 99%

Numerical Analysis of Potential Contaminant Migration from Abandoned In Situ Coal Conversion Reactors

et al. 2022

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Abstract. In the context of a potential utilisation of coal resources located in the Mecsek mountain area in Southern Hungary, an assessment of groundwater pollution resulting from a potential water-borne contaminant pool remaining in in situ coal conversion reactors after site abandonment has been undertaken in the scope of the present study. The respective contaminants may be of organic and inorganic nature. A sensitivity analysis was carried out by means of numerical simulations of fluid flow as well as contaminant and heat transport including retardation to assess spatial contaminant migration. Hereby, the main uncertainties, e.g., changes in hydraulic gradient and hydraulic contributions of the complex regional and local fault systems in the study area, were assessed in a deterministic way to identify the relevant parameters. Overall 512 simulations of potential groundwater contamination scenarios within a time horizon exceeding the local post-operational monitoring period were performed, based on maximum contaminant concentrations, cumulative mass balances as well as migration distances of the contaminant plume. The simulation results show that regional faults represent the main contaminant migration pathway, and that contamination is unlikely assuming the given reference model parametrisation. However, contamination within a simulation time of 50 years is possible for specific geological conditions, e.g., if the hydraulic conductivity of the regional faults exceeds a maximum value of 1 × 10−5 m s−1. Further, the parameter data analysis shows that freshwater aquifer contamination is highly non-linear and has a bimodal distribution. The bivariate correlation coefficient heatmap shows slightly positive correlations for the pressure difference, the fault permeability and the simulation time, as well as a negative correlation for the retardation coefficient. The results of this sensitivity analysis have been integrated into a specific toolkit for risk assessment for that purpose.

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Section: Formation Of By-products During In Situ Coal Conversionmentioning

confidence: 99%

Numerical Analysis of Potential Contaminant Migration from Abandoned In Situ Coal Conversion Reactors

et al. 2022

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“…During the process of gasification, the gasification area is gradually enlarged along the linking hole. The product gases can be obtained, as they are useful in the creation of many products, such as chemical feed stocks, liquid fuels, hydrogen, synthetic gas, and the generation of electric power [17][18][19][20][21][22]. Recently, UCG technology has attracted greater attention as an alternative to conventional mining methods, especially when exploiting coal resources located deep underground or exploiting low quality coal resources with high ash and high sulfur.…”

Section: Introductionmentioning

confidence: 99%

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

Hamanaka

Itakura

et al. 2018

Energies

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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.

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“…ERWs are commonly drilled in offshore projects where large oil and gas reservoirs areas are drained from one or more platforms. This can minimize environmental impacts and field-development costs by reducing drilling sites or offshore platforms [8][9][10]. ERWs can be drilled from one platform to reach reservoirs at a great distance.…”

Section: Introductionmentioning

confidence: 99%

The Maximum-Allowable Well Depth While Drilling of Extended-Reach Wells Targeting to Offshore Depleted Reservoirs

et al. 2018

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In depleted offshore reservoirs, pore pressure declines and consequently horizontal in-situ stresses decrease as well. This causes a very limited well depth for extended-reach drilling targeting to offshore depleted reservoirs. In this paper, based on analyzing the safe mud weight window of the depleted offshore reservoirs, a model of predicting the Maximum Allowable Measured Depth (MAMD) for extended-reach drilling targeting to offshore depleted reservoirs is developed. Meanwhile, the numerical method of the model is proposed, and the key affecting factors of the MAMD are also investigated. The results show the pore pressure depletion has obvious effects on the MAMD. With the depletion of pore pressure, the safe mud weight window appears narrower and even disappears, consequently the predicted MAMD becomes shorter. For a normal regime depositional environment in the depleted reservoirs, it may be impossible to drill with conventional drilling method in the nearby directions of the maximum horizontal in-situ stress, while it may be much safer and attain a long MAMD when drilling in the directions near the minimum horizontal in-situ stress. Moreover, the MAMD will decrease with the increase of Poisson's ratio and Biot's parameter, and its response to Poisson's ratio is more obvious. For a specific target depleted reservoir, the extended-reach drilling with a high borehole inclination may have a longer MAMD than that with a low borehole inclination. This paper presents a method for promoting the design of extended-reach drilling targeting to offshore depleted reservoirs.

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RETRACTED: Techno-Economic Comparison of Onshore and Offshore Underground Coal Gasification End-Product Competitiveness

Cited by 12 publications

References 29 publications

Numerical Analysis of Potential Contaminant Migration from Abandoned In Situ Coal Conversion Reactors

Numerical Analysis of Potential Contaminant Migration from Abandoned In Situ Coal Conversion Reactors

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

The Maximum-Allowable Well Depth While Drilling of Extended-Reach Wells Targeting to Offshore Depleted Reservoirs

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