Underground Coal Gasification (UCG) is a mining-gasification process that produces synthesis gas from in situ coal by injecting air (or oxygen and steam) and extracting the produced gas via boreholes. The resulting synthesis gas (‘syngas’) produced by UCG can be used directly as a fuel-gas or deep-cleaned to produce many other products like chemicals, liquid fuels, hydrogen and synthetic natural gas. UCG has significant environmental, safety and practical advantages over conventional coal mining and utilization, foremost being cost and emissions reductions. In South Africa, facilities of an industrial-scale Fischer–Tropsch (FT) have been operating for decades on coal-to-liquid and gas-to-liquid conversion. Oxygen-blown UCG produces syngas, which contains a mixture of carbon monoxide (CO) and hydrogen, and these molecules can be conditioned to serve as feed for synthetic-crude-oil (‘syncrude’) conversion technologies based on the FT process. African Carbon Energy (Pty) Ltd. (Africary) completed a study integrating its UCG technology with mini gas-to-liquids plant. Syngas from Africary’s Theunissen Underground Coal Gasification (TUCG) project will be used for power production and synthesis of liquid fuels in a unique poly-generation configuration. The TUCG process will consist of two parallel gasifiers, operated on different agents, making the component parts of UCG and coal-to-(any product) (CtX) tightly linked and interdependent, but reducing both cost and emissions. UCG-CtX offers a lower capital investment to conventional underground mining and surface gasification due to the removal of the surface gasifier and coal-mine operations. The gas clean-up systems will remove undesirable components from each gasifier and blend the cleaned syngas for H2:CO ratio control and provide implementation of carbon capture and sequestration. This study has minimized the complexity and optimized the process flow to provide own-use electricity and about 4000 barrels/day equivalent fuels at a capital cost estimate (2017) of about US$ 350 million and operating cost of around 28 US$/barrel.
Syngas from Africary's Theunissen underground coal gasification (UCG) project will be used for power production and synthesis of liquid fuels and commodity chemicals. However, some of the coal components, especially condensable water, oils, tars, inorganic trace elements, and a small fraction of fly ash and particulate matter, make their way to the surface via the production well and can cause adverse impacts on downstream processes. Africary's standard design incorporates a cold gas clean-up system that relies on relatively mature techniques based on highly effective wet scrubbers and acid gas removal (AGR) systems such as Rectisol ® , but with the downside of low energy efficiency and waste water generation. In this paper, novel technologies for removing contaminants and species separation from the hot (T > 300°C) raw syngas are compared. Comparisons are made between supersonic gas separation (SGS), Ranque-Hilsch vortex tube (RHVT), vortex gradient separation (VGS), and inertia vacuum filtering (IVF), and a vortex-based gas separation concept is proposed for UCG applications.underground coal gasification, gas cleaning, supersonic gas separation, Ranque-Hilsch vortex tube, vortex gradient separation, inertia vacuum filter.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.