By Morné Engelbrecht
Managing Director and CEO, Carbon Energy Limited
After decades on the fringes of world energy production, advancements in underground coal gasification (UCG) are proving the process can deliver high-quality syngas on a commercial scale with limited impact on the surrounding environment, at a lower cost than current coal-to-gas production in Australia.
Carbon Energy Limited, based in Australia, has built on many years of work by that country’s leading research organization, the Commonwealth Scientific and Industrial Research Organisation (CSIRO), to further develop and demonstrate a UCG technology that has satisfied stringent technical and environmental assessments by a panel of government-appointed independent scientists. Decommissioning and rehabilitation processes have also been assessed by the state environmental protection authority.
Today UCG is poised to become a valuable option to help meet future domestic and global energy demand because it offers an environmentally responsible and economically attractive means of extracting energy from otherwise unmineable coal.
COMMERCIALIZATION OF UCG
One of the stumbling blocks that has held UCG back from becoming a fully commercial industry has been the inability to extract a consistent-quality syngas required for continuous feed into the selected downstream industrial process (whether for fuel or fertilizer production, electricity generation, or other uses that require syngas as a raw feedstock).
UCG requires ignition (heating of the underground coal seam to high temperatures between 1200 and 1600°C) to initiate the gasification process, and the subsequent injection of an oxidant (e.g., air or oxygen and steam) to maintain the syngas production. Traditional UCG approaches have employed a “batch process” using vertical wells and requiring manual intervention and reignition approximately every 30 days. This causes fluctuations in temperature and syngas quality.
Carbon Energy’s process, developed over more than 16 years of research and in-field trials, has been proven to address this issue by using a unique design that provides continuous automated gasification in a panel of coal to produce a high-quality syngas for up to 10 years (see Figure 1). This innovation, called the Controlled Retraction Injection Point (CRIP), was extremely important in achieving the consistently high-quality syngas that was produced continuously over many months during Carbon Energy’s demonstration at Bloodwood Creek in Queensland.
With horizontal in-seam injection and production wells, and an oxidant injection point that retracts as the coal face is gasified, the gasification process is maintained at a consistent temperature, which in turn produces consistent quality syngas. Moreover, a significant proportion of the potentially contaminating by-products produced with the syngas are destroyed in the path of the gasification face, contributing to the now-proven environmental credentials of the technology.
THE TIME FOR UCG IS NOW
Global primary energy demand is expected to rise 37% by 2040, according to the International Energy Agency’s “World Energy Outlook 2014”.1 With the world’s hunger for energy growing, unlocking new energy sources that are commercially sustainable and are amenable to carbon capture techniques is a priority. Coal is predicted to remain a significant source of energy for the world given its widespread availability and low cost. UCG is a technology that is able to maximize the energy extracted from coal, while ensuring a small environmental impact and footprint.
Carbon Energy’s technology has improved on previous UCG methods and been shown to extract 60 times more energy than coalbed methane extraction on the same area of coal. It is also able to produce syngas from coal seams previously considered too deep and uneconomical for traditional coal extraction technologies. Carbon Energy’s recently completed demonstration at Bloodwood Creek was operated at depths of more than 200 meters below the surface; however, operation at far greater depths is also possible and commercially viable.
Rigorous scientific assessments and independent review have shown that potential environmental issues around waste and impacts on groundwater have also been overcome. With site selection methodology developed by CSIRO, refined engineering design to geothermal standards, and demonstrated operating protocols, it has been demonstrated that environmental impacts are kept to a minimum. With the physical footprint of the UCG operations contained to 50 hectares of land while recovering a significant volume of energy, good relationships are maintained with landholders. Together with the proven environmental credentials, this should assist Carbon Energy to achieve a social license to operate its unique technology.
BLUE GUM GAS PROJECT
Carbon Energy’s proposed Blue Gum Gas Project neighbors the existing demonstration site in the Surat Basin at Bloodwood Creek, about 200 km west of Brisbane, Queensland, Australia. Once government approvals are received, Carbon Energy will build and operate a commercial-scale UCG plant that will produce syngas which will be processed above ground to deliver pipeline-quality synthetic natural gas (SNG). The plant will produce 25 PJ of natural gas per annum, which is approximately 0.687 billion Nm3/yr natural gas equivalent, suitable for use by existing connected homes and domestic industries. SNG production is expected to commence within three years of the start of construction.
Carbon Energy’s focus on developing SNG over power or ammonia production has been driven by commercial demand. The domestic natural gas market on the east coast of Australia will see a significant increase in natural gas prices as the export of coal seam gas commences. East coast manufacturers are eager to find a low-cost natural gas feedstock. The Blue Gum Gas Project will be located near existing infrastructure enabling ready transport of natural gas to customers.
Carbon Energy operated a demonstration (pilot) project at Bloodwood Creek in Queensland from 2008 to 2012 in order to fine-tune the application of their unique technology, and to collect necessary data to submit to the state government for approval to operate the technology in Queensland. Although most of the syngas over the demonstration period was flared, the syngas was used to power generators, with power used on site and also exported to the local electricity grid.
The pilot-scale demonstration project involved operating two underground gasifiers. The “panels” of coal where the gasifiers operated were constructed at a depth of about 200 meters, are 500 meters long, and 30 meters wide, with an average thickness of 8–9 meters. A panel of this size has sufficient coal to produce syngas continuously for five years. However, as proof of concept of the technology was achieved after almost two years of continuous production of high-quality syngas from the second gasifier, further expenditure on the pilot was unwarranted and the demonstration project was decommissioned.
The commercial-scale project will simply replicate the panel module at the scale required for the project. In the case of the proposed Blue Gum Gas Project, around 40 of these panels will be required to generate 25 PJ of syngas per annum.
An Independent Scientific Panel (ISP) was appointed by the Queensland government in 2009 to review and report on the pilot projects being conducted in the state at that time, focusing on the technical and environmental aspects of UCG technology. Technology developers were required to prepare a comprehensive report on their pilot projects and submit these reports to the ISP for review.
The final peer-reviewed ISP report on the pilot projects was released in July 2013. The government gave in-principle support to the ISP’s conclusions that the capability to commission and operate a UCG gasifier had been demonstrated, and that “the technology could, in principle, be operated in a manner that is socially acceptable and environmentally safe when compared to a wide range of other existing resource-using activities”. However, the government required that the technology developers demonstrate successful decommissioning prior to any approval being granted for a commercial-scale project.
Essentially, this meant that Carbon Energy needed to provide evidence that gasification had ceased at the pilot project site and that any of the relevant environmental values affected by the underground coal gasification process (excluding surface facilities and landform, which would be addressed under normal processes) could be restored to a condition agreed to with the Department of Environment and Heritage Protection (DEHP). There was a particular focus on groundwater quality, which could potentially be impacted adversely by UCG by-products.
To meet the government’s requirement, Carbon Energy prepared a comprehensive Decommissioning Report and Rehabilitation Plan and submitted these documents on 29 August 2014 and 1 October 2014, respectively. Preparation of these documents involved a full site investigation by an independent Suitably Qualified Person for contaminated land assessment (as authorized under the Environmental Protection Act 1994), which in turn involved a drilling program for collection and laboratory analysis of decommissioned gasifier cavity water and core samples, core samples from new near-cavity boreholes, and baseline core samples. Analysis of the data from these new wells was in addition to analysis of results from the ongoing monitoring of groundwater quality from 24 monitoring wells surrounding the gasifier cavity and located in the target coal seam and overlying and underlying rock formations.
The Queensland DEHP has advised Carbon Energy that its expert consultants have completed the review of Carbon Energy’s Decommissioning Report and Rehabilitation Plan. This review will be referred to the Department of Natural Resources and Mines (DNRM), which is the lead agency in the matter of UCG policy, for a government decision on commercialization of the technology in Queensland.
- The Decommissioning Plan was required to include:
- Evidence that gasification had ceased
- Quantification of any contaminant load
- Delineation of the zone of impact of any contamination
- Evidence that any contaminants were not increasing or moving outside of the lower-pressure zone maintained by Carbon Energy around the gasifier cavities.
The process data clearly showed that gasification stopped within 48 hours of initiating the shutdown procedure (see Figure 2). This was evidenced by changes in the composition of vented gas, which quickly returned to high percentages of natural methane gas with a sharp decline in the concentrations of hydrogen and carbon dioxide, and declining syngas flow rate and temperature.
Once gasification stops, it cannot start again naturally, due to the absence of oxygen 200 meters underground beneath a tightly sealed formation, with the UCG panel surrounded by groundwater.
The results of the groundwater quality investigation showed that:
- The majority of remaining UCG by-product was within the cavity.
- More than 90% of by-products were eliminated by steam venting during the shutdown procedure.
- Concentrations of remaining by-products are decreasing.
Both during operation and after decommissioning, pressure in the gasifier is maintained at a level below the regional groundwater pressure so that groundwater continuously flows toward and into the gasifier cavity. The pressure is controlled by Carbon Energy from the surface. This approach successfully contains UCG by-products within the small area of low pressure.
As previously indicated, the purpose of the Rehabilitation Plan was to demonstrate Carbon Energy’s ability to restore the relevant environmental values of the site, those essentially being groundwater quality. Given the baseline quality of the groundwater (which is not fit for human consumption), the applicable environmental values for the Bloodwood Creek site were identified as stock watering and human health.
Based on the results of the site investigation, a risk assessment and highly conservative fate and transport modeling based on the applicable environmental values, it was concluded that the current groundwater conditions within the cavity do not pose harm to human health or the environment.
The independent Suitably Qualified Person under the Environ-mental Protection Act 1994 signed off on the Rehabilitation Plan, which concluded that:
- The low levels of remaining by-products will rapidly and naturally reduce to baseline levels.
- No environmental receptors are likely to be impacted.
- No active remediation is required.
Parameters have been proposed for a range of chemicals against which groundwater analysis will be assessed on a regular basis and reported to the government. Monthly reporting of groundwater results from the groundwater monitoring network will also continue.
TAKING UCG TO THE NEXT STAGE
Carbon Energy has demonstrated its technology is a significant advance in UCG, in producing consistently high-quality syngas that can support commercially viable downstream use. More than 100 years since the first suggestion of gasifying coal underground, Carbon Energy’s approach is an attractive, environmentally responsible, and economically viable means of utilizing the energy potential of coal considered too deep for viable conventional mining.
- International Energy Agency. (2014, 12 November). World energy outlook 2014, press release, www.worldenergyoutlook.org/
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