The Seren Project
Underground Coal Gasification
This project aims to provide the technological base that will enable Wales to create a new industry in UCG, which will make a significant contribution to Wales’ quest to become self sufficient in energy
What is Underground Coal Gasification?
Underground Coal Gasification (UCG) is the process by which coal is converted in-situ into a gas product that can be combusted for power generation or used as a chemical feedstock. UCG exploits coal resources that are either uneconomical to mine with conventional mining methods or are inaccessible due to depth, geology or other mining and safety considerations.
How does Underground Coal Gasification work?
Coal seams are accessed from the surface via boreholes. An injection borehole introduces oxygen or air to the coal seam in order to combust a proportion of the coal in-situ. In addition, water is added to the system and drives the gasification of the remaining coal, producing a versatile synthetic gas product (known as ‘syngas’) that is extracted via a second borehole. This syngas can be combusted directly for energy generation and can also be converted into a variety of high-value products, such as transport fuels, fertilisers for food production, plastics, methanol, waxes and detergents.
By developing the knowledge and know-how, not only will Wales reap the short term benefits of secure energy supplies and job creation, but Wales will also position itself at the forefront of this emerging worldwide technology. The ability to export Welsh knowledge and technology will be an associated aim of the project. The specific project aims are to:
- help develop a UCG programme in Wales;
- support a demonstration project in UCG which could ultimately lead to its commercialisation in Wales;
- create a ‘centre of expertise’; and
- stimulate investment in UCG by addressing concerns and uncertanities.
Every UCG project is planned for an end user, which is usually a power plant. The size of the power plant depends on the amount of electricity required per day (MWh/day) in that area for a period of time (normally over a number of years). The Seren project has developed a tool to assess the resource required to meet this demand. This tool is known as a Coal Assessment Tool.
What activities are we engaged in?
The project has two main research theme areas.These are the scientific / technical research area; and the environmental research area.
Seren’s work in the scientific / technical research area investigates the optimisation of the UCG process by understanding the impact of its operation parameters. The UCG process is not well understood, with widespread scientific and technical gaps. Further work is required to access the practicality and commercial viability of the UCG process by achieving stable gasification conditions.
The environmental research area is concerned with groundwater and surface water contamination, subsurface and surface disturbance (subsidence) and the air pollution impact of UCG.
In order for the project to achieve its aims, Seren is addressing the following main issues:
- Testing via a high pressure high temperature rig
- Develop a UCG model
- Energy model (yield calculator) This calculates the maximum energy (MJ/Kg of coal) of the syngas that can be generated from a UCG process. The thermodynamics of the process and the chemical reactions that take place are taken into consideration. It is important to know this ultimate yield because it determines the potential for UCG. The energy model calculates the total gasified char; the total affected coal; the total water needed for the gasification; the energy left in the cavity and how this energy may be used; and the gasification efficiency of the UCG process.
- Coal resources assessment tool This calculates the coal resources that are required for a specific power plant at a specific site. It also calculates the tons of coal that need to be gasified per day in order to provide the power plant with the energy it needs every day (tons/module day), the energy that is produced from every ton of gasified coal ( MWh / ton of coal), and the size of the UCG model.
- Chemical model This determines the composition of the syngas, its heating value (MJ) and its flowrate (MJ/m3) under specific gasification conditions. When 1kg of coal is gasified under specific process parameters (pressure, temperature, oxidants, etc), it is important to know the flowrate of the syngas produced as this will provide the information needed to optimize the UCG process. The main input variables are the chemical equations of the UCG process and the mass and energy balances of the chemical compounds, pressures, the adiabatic flame temperature (calculated), equilibrium constants of the chemical reactions and the type of coal.
- Provide a generic groundwater risk assessment framework and environmental impact assessment A methodology for environmental impact assessment will be developed. This will be recognised by the agencies associated with licensing UCG applications.
Seren has developed a bespoke high pressure high temperature rig. The rig can be used to test different coal in order to determine how it will react with various gases at pressures of up to 50 bar and temperatures of up to 900°C. The rig can be run in two different ways and provide gasification data or environmental data which will help the commercial assessment of coals throughout Wales.
The gasification of coal chars with a combination of oxidants at different pressures and temperatures will determine the effect of several operation variables, namely temperature, pressure and gasifying agent composition. Additionally, information on other process parameters, such as gas yield, carbon conversion, cold gas efficiency, heating value of the gas, pressure and temperature operation limits, together with the re-activities of the coal, can be provided.
The environmental data is produced by the devolatilisation of coal at different pressures and temperatures in order to quantify and analyse the resulting contaminants.
Research and experimental work is currently being carried out on different types of Welsh coal.
The UCG model that is being developed will provide all the initial information required by investors who are deciding whether or not to proceed with a UCG project at a specific site. This model can provide information for desk top studies and pre-feasibility or feasibility studies for a UCG project at a specific site, including economic evaluation. It will establish a knowledge base for the assessment of the entire UCG process.
The model will provide guidelines on assessment for UCG, including three different software tools. These are an energy model, a coal resource assessment tool and a chemical model.
The main input variables are the type of coal and its proximate analysis, the adiabatic flame temperature in the cavity plus experimental data.
The main input variables are the size of the power plant; the operating time period of the plant (in years); the type and richness of the coal; and the gasification efficiency of the coal (calculated from the energy model). Information about the available coal resources in the area and the width of the coal seam can be obtained from existing maps (provided by BGS) or from drilling.
This work will involve the identification of the contaminants resulting from laboratory experiments testing coals of various rank under varying gasification and pyrolysis conditions, thereby determining the controls on the solubility and mobility of the potential contaminants in groundwater. Finally, this data will be combined with hydro-geochemical and geotechnical models to feed into the existing Environmental Risk Assessment Framework. This will enable the implementation of a UCG commercial operation in Wales that complies with current legislation.