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Technology Options for Coupled Underground Coal Gasification and CO2 Capture and Storage

Final Report Summary - TOPS (Technology Options for Coupled Underground Coal Gasification and CO2 Capture and Storage)

Executive Summary:
The TOPS project took a radical and holistic approach to coupled UCG-CCS, and thus the site selection criteria for the coupled process, considering different end-uses of the produced synthetic gas, covering other options beyond power generation, and evaluated novel approaches to UCG reagent use in order to optimise the whole process. This approach aimed at minimising the need for on-site CO2 storage capacity as well as maximising the economic yield of UCG through value added end products, as well as power generation, depending on the local conditions.
The main objective of the TOPS project, therefore, was to develop a generic, technology based UCG-CCS site characterisation workflow, and the accompanying technologies, which would address the dilemma faced by the proponents of reactor zone carbon storage, and offer technological solutions to source sink mismatch issues that are likely to be faced in many coalfields. Another objective was to investigate different end use alternatives for the UCG product gases, and their potential to reduce the requirement for CO2 geological storage.
These objectives were achieved through integrated research into the field based technology knowledge gaps, such as cavity progression and geomechanics, potential groundwater contamination and subsidence impacts, together with research into process engineering solutions in order to assess the role/impact of site specific factors (coal type, depth/pressure, thickness, roof and floor rock strata, hydrogeology) and selected reagents on the operability of a given CO2 emission mitigation option in a coalfield:
- A large high pressure UCG reactor was used to carry out laboratory gasification experiments on lignite and bituminous coals with O2/CO2 and H2 as the reagent to evaluate the quality of product gasses produced and the process efficiency towards coupled UCG-CCS.
- The existing conventional UCG site selection criteria were reviewed and new, TOPS project proposed site selection criteria, which included techno-economic and life cycle environmental considerations, were developed.
- European and international UCG resources and CO2 storage sites were assessed for coupled UCG-CCS, a database was built and GIS maps provided.
- A coupled thermo-mechanical-chemical model was developed and applied to assess UCG cavity progression and coal type, thickness, depth and reagent dependent behaviour in the subsurface.
- Industrial scale field UCG models were developed using real data and representative geologies to evaluate overburden behaviour, surface subsidence and hydrological impacts of UCG.
- A generic UCG-CCS site evaluation workflow, that is aligned with EU regulations and the EU storage directive, was developed.
- A robust technoeconomic analysis method for the evaluation of different UCG-CCS and syngas utilisation options was developed and applied to onshore/offshore UCG-CCS scenarios for power generation, SNG and Urea production.
- Life Cycle Impact Assessment and Life Cycle Cost models for UCG-CCS were developed and the global environmental impacts and costs of UCG-CCGT power generation and CO2 capture; UCG-Methanol and associated power generation and CO2 capture; and UCG-Ammonia and associated power generation and CO2 capture were evaluated.
The project was carried out as an international research collaboration funded by the European Union’s Seventh Framework Programme. It benefited from a newly constructed, unique and large scale high pressure gasification reactor which enabled a comprehensive experimental programme to characterise the gasification process for different coal ranks, reagent use and pressure conditions.
The research consortium included a multi-disciplinary team of experts in coalfield geology, reservoir and mining engineering geomechanics, hydrogeology, process engineering with many years of experience in international UCG and CCS applications. Furthermore, the project teamed up with internationally recognised experts from Australia, South Africa, US and China to provide international perspective and expert input to the project outcomes.

Project Context and Objectives:
Over the past half century, coal gasification has been proven as a feasible process for utilising coal, with above ground gasification providing a precise process with the ability to control nearly every variable. In contrast, underground coal gasification (UCG) relinquishes a significant degree of control for the ability to utilise coal without mining, while precision in this case comes from careful site selection and process monitoring/control aiming to ensure the quality and quantity of produced gas during the life of a project.
In recent years, a number of researchers, who considered combining underground coal gasification with CO2 capture and storage (CCS) as a potential option to mitigate against the climate change impacts of CO2 emissions (Blinderman and Friedmann, 2006; Burton et al., 2006; Kempka et al., 2009; Roddy and Younger, 2010; Kempka et al., 2011a), have suggested that UCG creates unique opportunities for CO2 storage in the post-gasification structures, coined as reactor zone carbon storage (RZCS).
Reactor zone carbon storage may have some advantages as identified by these previous researchers, such as: substantial apparent capacity (1,700- 4,500 tonnes CO2 could be stored in the cavity of a single burn at 1,000 m depth and for a conventional geothermal gradient (30ºC/km), if 50% of that cavity were available); high permeability and injectivity; the potential for secondary coal adsorption storage, autoclosure through swelling of the coal; existing well set that could significantly reduce storage costs by 40-60%; potential for engineering control; potential to site within highly secure settings (coals beneath shales; seams at supercritical TP conditions).
However, the same authors recognised that potential problems with cavity storage may outweigh its potential benefits, noting that the cavity itself is likely to be disturbed and may be difficult to characterise before CO2 storage commences; that CO2 is likely to interact with other coal gasification products complicating potential environmental impacts and that the inherent uncertainty in subsurface operations, could substantially complicate CO2 storage efforts. Most importantly, this storage potential, even if it were available, could be orders of magnitude smaller than the capacity required to store the CO2 produced during the UCG process. Additionally, the potential CO2 storage capacity would only be available after the end of the gasification operation, (i.e. the timeline of CO2 production and storage capacity availability would not match), rendering on site coupled UCG-CCS rather difficult in many geological settings.
Kempka et al. (2011b) and Nakaten et al. (2011) pointed out that using CO2 in subsequent processes may increase the CO2 mitigation potential compared to applying geological CO2 storage only. For instance, a feasibility study for UCG-CCS with coupled urea (fertiliser) production in the Jamalganji coal deposit located in Bangladesh demonstrates the potential re-use of 14.6 - 18.6 % of the total CO2 produced in the coupled process compared to that geologically stored in UCG voids (11.6 -16.3 %) at site-specific conditions. Supporting this argument, the Bulgarian UCG-CCS feasibility study (EU-RFCS project UCG&CO2STORAGE) indicated that only about 20.5 % of the CO2 produced may be stored in the voids subsequent to a prospective UCG operation in the on-shore Dobroudzha coal deposit (Bulgaria) resulting from relatively low local geothermal gradients while using a conservative calculation approach.
Therefore, the TOPS project took a radical and holistic approach to coupled UCG-CCS, and thus the site selection criteria for the coupled process, considering different end-uses of the produced synthetic gas, covering other options beyond power generation, and evaluated novel approaches to UCG reagent use in order to optimise the whole process. This approach aimed at minimising the need for on-site CO2 storage capacity as well as maximising the economic yield of UCG through value added end products, as well as power generation, depending on the local conditions.
The main objective of the TOPS project, therefore, was to develop a generic, technology based UCG-CCS site characterisation workflow, and the accompanying technologies, which would address the dilemma faced by the proponents of reactor zone carbon storage, and offer technological solutions to source sink mismatch issues that are likely to be faced in many coalfields. Another objective was to investigate different end use alternatives for the UCG product gases, and their potential to reduce the requirement for CO2 geological storage.
These objectives were achieved through integrated research into the field based technology knowledge gaps, such as cavity progression and geomechanics, potential groundwater contamination and subsidence impacts, together with research into process engineering solutions in order to assess the role/impact of site specific factors (coal type, depth/pressure, thickness, roof and floor rock strata, hydrogeology) and selected reagents on the operability of a given CO2 emission mitigation option in a coalfield:
- A large high pressure UCG reactor was used to carry out laboratory gasification experiments on lignite and bituminous coals with O2/CO2 and H2 as the reagent to evaluate the quality of product gasses produced and the process efficiency towards coupled UCG-CCS.
- The existing conventional UCG site selection criteria were reviewed and new, TOPS project proposed site selection criteria, which included techno-economic and life cycle environmental considerations, were developed.
- European and international UCG resources and CO2 storage sites were assessed for coupled UCG-CCS, a database built and GIS maps provided.
- A coupled thermo-mechanical-chemical model was developed and applied to assess UCG cavity progression and coal type, thickness, depth and reagent dependent behaviour in the subsurface.
- Industrial scale field UCG models were developed using real data and representative geologies to evaluate overburden behaviour, surface subsidence and hydrological impacts of UCG.
- A generic UCG-CCS site evaluation workflow that is aligned with EU regulations and the EU storage directive was developed.
- A robust technoeconomic analysis method for the evaluation of different UCG-CCS and syngas utilisation options was developed and applied to onshore/offshore UCG-CCS scenarios for power generation, SNG and Urea production.
- Life Cycle Impact Assessment and Life Cycle Cost models for UCG-CCS were developed and the global environmental impacts and costs of UCG-CCGT power generation and CO2 capture; UCG-Methanol and association power generation and CO2 capture; and UCG-Ammonia and association power generation and CO2 capture were evaluated.
The project was carried out as an international research collaboration funded by the European Union’s Seventh Framework Programme. It benefited from a newly constructed, unique and large scale high pressure gasification reactor which enabled a comprehensive experimental programme to characterise the gasification process for different coal ranks, reagent use and pressure conditions.
The research consortium included a multi-disciplinary team of experts in coalfield geology, reservoir and mining engineering geomechanics, hydrogeology, process engineering with many years of experience in international UCG and CCS applications. Furthermore, the project teamed up with internationally recognised experts from Australia, South Africa, US and China to provide international perspective and expert input to the project outcomes.

Project Results:
please find attached full report
Potential Impact:
The consortium members both at institutional level as well as individuals have recognised that of impact of the TOPS project has been substantial both in academic terms but also in terms of economic and societal contribution.

Academic impact
This is evidenced by the numerous publications that have been produced during the duration of the project, authored by teams across the academic research and industry partners and covering the full spectrum of activities:
- Experimental gasification studies
- Thermo-mechanical-chemical modelling studies
- Field scale modelling results
- Techno-economic analysis
- Life cycle environmental and cost modelling
It is also expected that many more publications will follow in the period following the project completion a the more mature and integrated analysis has been conducted during the later period of the project and the formal reporting to the EU has been the first opportunity where all project results have been compiled together. The end of the formal project period is also the time when the doctoral researchers are completing their research work, which coincides with the most productive stage in terms of generating impact from their academic research.

There have been key learnings in the TOPS project that have shifted our understanding of underground gasification processes. Through the experimental work conducted it was shown that the gas of the highest quality is obtained in the oxygen blown stages when O2/CO2 reagent is used, independent of the coal type used for the tests. It was also shown that introduction of CO2 to the leads to significant deterioration of gas quality, mainly due to increase in content of unreacted CO2 that ends up in the produced gas. It was also shown that UCG using recirculation of CO2 may not be feasible in locations where the elevated gasification pressure is necessary due to operational and environmental onstraints.

The project also advanced significantly the scientific method in the field of underground coal gasification, having developed two new models that can be used by practitioners and industry to design and evaluate the UCG potential of specific coal resources: a Thermo-Mechanical-Chemical UCG Model developed by Imperial College and a Thermo-Mechanical UCG Model developed by GFZ.

Finally the detailed analysis, experimentally for a full suit of properties that are essential in UCG resource evaluation and through the use of the developed modelling tools for three project specific and characteristic coal types at deferent depths and with different gasifier layouts, this project has created a blue-print for UCG resource evaluation considering geological, engineering, environmental and cost considerations all culminating in the development of a UCG – CCS workflow that can be used in Site Selection, Characterisation and the development of site development plan, economic analysis and monitoring/remediation plans.

Economic and societal impacts
Besides academic impact, the TOPS project has had a demonstrable contribution of its excellent research to society and the economy. In this sense the project contributions have been rich and diverse and are also expected to increase following the completion of the project.

At individual level, the TOPS project has given individuals the opportunity to develop new skills. PhD students, researchers, academics, industry employees have had the chance to expand their horizons into different disciplines moving from narrow science / engineering domains to integrated geoscience, chemical engineering, geomechanical and flow subsurface engineering, environmental engineering and economics. In this process the organisations currently employ them have been enriched and new opportunities for the people and the companies they will be working for in the future are arising.

The website that was designed for the project has provided the means for engagement with the wider public, undergraduate and masters students at university, as well as policy/decision makers across the participating countries within Europe and internationally.

It is also recognised that interaction with stakeholders at the TOPS workshops organised by the consortium has improve the quality of the research carried out and its impact, raises the profile of individuals and the organisations involved in the project, and provided the opportunity to develop the science/engineering teams’ communication skills. It also enables members of the public to act as informed citizens and can inspire the next generation of researchers and professionals.

Through this project it has been possible to interact across continents, across European countries, across institutions in industry, academia and research. Besides the cross-fertilisation of ideas and the better understanding of the context of UCG – CCS implementation and priorities in different geographic regions, it has been an opportunity for the TOPS project members to learn how their detailed work fits in the big picture, which is how to make a coal prospect in a given geographic region, an industrial scale UCG – CCS project and a financial success. The building blocks are there and have been tested, the project team is skilled and as soon as the opportunity arises they can engage with relevant end users.

The following pages outline in a tabulated was the impact of the TOPS project in academic, economic and social terms, summarised here as:
- Capacity building: through technical and personal skill development for the individuals / authors of the TOPS project deliverable reports and project publications listed.
- Conceptual: contributing to knowledge exchange and the understanding of scientific/technical issues, advancing the state-of-the art in the scientific/engineering disciplines studied throughout the project.
- Instrumental: influencing the development of policy, practice or service provision, shaping legislation, altering behaviour through the TOPS work flow development.

List of Websites:
https://www.tops-ucg.ic.ac.uk/