Industrialisation of underground coal gasification in South Africa and the commercial optimisation of the Theunissen UCG project

Abstract

South Africa faces long-term energy challenges, such as energy access and affordability; diminishing reserves of coal; environmental concerns; balancing the electricity grid whilst incorporating an increasing proportion of variable renewable energy sources; mounting environmental liabilities caused by defunct mining operations, and fluctuating exchange rates and their influence on energy commodity prices. Underground coal gasification (UCG) is an advanced clean coal technology that offers a breakthrough solution to the country's energy challenges as UCG has the capacity to cost-effectively liberate vast domestic coal resources that currently cannot be economically exploited using traditional mining technologies. The technology offers flexibility in terms of coal types and load size, making it the ideal renewable energy compliment. By managing the gasification agent and operational conditions, it is possible to achieve a wide range of desired compositions and control the quantity of gas produced. Johan Brand and his late partner teamed up as African Carbon Energy (Pty) Ltd ('Africary') to initiate UCG-based electricity production by aligning it with the government's request for independent power producers and coal-to-liquids. Africary promotes the implementation of UCG with several UCG projects immediately ready and awaiting financial close. All Africary projects utilise commercially available gas clean-up and chemical process systems, including the processing of by-products for marketable commodities, thereby preventing environmental pollution. A concept study for integrating UCG with a mini-GTL system in a unique poly-generation configuration was presented. The process consists of two parallel gasifiers, operated on different agents, making the UCG, coal to liquids (CTL) and power generation tightly linked and interdependent, but reducing both cost and emissions. In addition, UCG offers a lower capital investment compared 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 H?:CO ratio control and provide the implementation of carbon capture and sequestration. The latest study provide optimised process flow and reduces complexity to provide own use electricity and about 2 000 barrels of oil per day (bbl/day) diesel and 200 ton/day liquefied natural gas (LNG) at a capital cost estimate of about $ 350 million and operating cost of around 28 $/bbl (in 2017 $ terms).