People sometimes worry about UCG and the possibility of uncontrolled fires taking place in the ground below. Coal can only burn in the presence of air, and underground fires in coal mines are the result of an uncontrolled air supply reaching the exposed coal face.
UCG takes place in undisturbed coal seams, connected to the surface by small boreholes for the injection and removal of gasification products. The process is completely sealed from the surface by the geological strata above and interruption of the air/oxygen supply will stop the process completely. In short, there is no possibility, that uncontrolled fire could arise with modern UCG technology.
* How will the local population benefit from UCG?
Energy extraction from coal, oil or gas reservoirs bring employment and wealth to the local population and a UCG production station in the area would do the same. Industry is attracted by the availability of lower cost energy, which in turn brings expertise, training and opportunity. Furthermore, as UCG is a high technology business, it also brings and requires, engineering and management skills. Back to top
* What can be done if things go wrong?
There are strict regulations to ensure that the underground dispersal and above ground emissions to the atmosphere are maintained within prescribed levels in a safe and non-polluting condition at all times. The regulations for industrial, plant, large scale power plant, groundwater contamination and health and safety are extremely vigorous in all developed countries, and emerging nations following closely. Plant malfunctions of a safety or environmental nature are anticipated and fully addressed in the design of a UCG plant.
* What is the impact of UCG on ground water?
Strict controls are imposed on the by-products of combustion produced underground, and the operating design ensures that leakage to the surrounding strata cannot take place. Modern UCG operates in a negative pressure with respect to the adjacent strata so that outward flow from the cavity is prevented at all times.
Regulations require that the groundwater surrounding the process is declared permanently unsuitable for other purposes like irrigation or animal consumption, and that the hydrogeology surrounding the process is monitored and modelled.
* How clean is UCG as an energy technology?
UCG is a gasification technology that meets the high environmental emission standards required of modern energy production. The energy chain for UCG has major environmental advantages, because energy for transportation is negligible and there are virtually no leaks of methane and other gases to atmosphere.
* Is the gas produced dangerous?
The production syngas contains methane (natural gas) carbon monoxide, and hydrogen which are sent in underground pipes under pressure to the power station or chemical works where it will be used. The gases are hazardous (like natural gas) but pipeline construction for high pressure gases is well developed technology designed to eliminate gas escapes and provide a high level of protection to life and property. The pipelines are similar to the national gas grid, which are recognized as one of the safest forms for moving energy over long distances.
* What are the environmental risks?
The environmental impacts of a UCG process are visual, acoustic, and include air emissions and groundwater effects. Like any geological extraction process, the geological and hydrogeological risks of UCG have to be carefully managed.
Control has advanced considerably since the early UCG trials and all UCG processes now have active control of the operational conditions in the cavity to ensure an inward flow of groundwater and to prevent gas seepage. The contaminant risk and product gas quality from potential UCG sites is fully assessed in advance and would be monitored during and after operations.
A wide range of risk management techniques and management tools from around the world are available for regulatory purposes.
* What happens above ground?
The inherent environmental benefits of UCG are the simplicity of surface plant, the absence of coal storage and transportation, and the easy removal of minor polluting constituents from the production syngas. The coal seam is accessed by drilling small boreholes from surface, which supply the oxygen and allow the gasification products to reach the surface. the surface installation above the coal seam consists of some temporary water and gas storage equipment and the drilling rigs themselves, all of which are removed when the coal seam below is exhausted. The typical life of a UCG production station might be 5 years.
The production wellheads are connected by pipeline for onward transmission to the power station or other point of use, which might be up to 100km from the UCG production station.
* How important is indigenous coal?
A good question, particularly for Europe is whether indigenous coal, in spite of the still vast resources that exist in the Member State Countries, should ever be extracted again in large quantities, because of the perceived environmental disadvantages of coal and coal mining. The development of clean coal technology over the past decade has largely dispersed the polluting image of coal, and coal can now be combusted cleanly using the right techniques.
The benefits of UCG as a clean coal technology are particularly important, because no coal or ash handling is required at surface and the network of UCG process wells are temporary and much less conspicuous than a colliery. UCG also avoids completely the safety issues and associated equipment of men underground.
* What are the Security of Supply issues for coal?
The first is the recognition that in spite of renewables and nuclear options and the presence of still large supplies of natural gas around the world, coal will remain a supplier of large scale energy to the world's economies, until the 2050's and beyond. This is new thinking for countries like the UK, where until recently a mixture of "wind-plus-gas"1, was going to meet its energy requirements for the foreseeable future. Coal is in plentiful supply; the European reserve alone is 130BT and the US equivalent, which is the largest in the world, is 246BT. The US is committed to exploiting coal as a security alternative to Middle East oil. Even Europe, alarmed at its growing dependence on Russian oil and gas, is prepared to look at alternatives like coal and nuclear in its energy and research policies.
The security-of-supply advantages of coal are generally accepted, but differences remain about the conversion route for power generation. Both supercritical thermal plant and IGCC coal plant are being installed in similar numbers, and both are capable of similar plant efficiencies, but gasification appears to be edging in the lead when CO2 CCS or so-called capture ready plant is also being planned. The advantages of pre-combustion capture from gasification apply equally well to UCG; in fact, the high concentration of the CO2 in UCG product gas makes separation more favourable.
What happens if UCG is discounted as a national option?
Countries with large coal resources like the United States, India, China, Australia and yes the UK, have large indigenous sources of energy in the ground below which are available for exploitation. Mining is the conventional method of extraction for easily mined coal but estimates suggest this represents only15-20% of the total coal resource. UCG offers the strong probability of converting the inaccessible coal resource into national coal reserves. Furthermore, the coal is a national resource and freely available to the country of origin. The UCG option offers improved security of supply, potential major reduction in the cost of energy imports, and self reliance in the event of world energy disruptions.
* Why should national politicians support UCG project?
UCG is a method of extracting and exploiting energy from indigenous coal resources and coals, which would otherwise be uneconomic for conventional mining.
UCG provides a country with a source of energy which is independent of the supply disruptions of imported energy and the option adds significantly to a nation's security of supply. Coal is in plentiful supply: the European reserve alone is 130 billion tonnes, while that of the US is the largest in the world at 246 billion tonnes. The world reserve figure is 900 billion tonnes
The cost of electricity production is lower than with natural gas and the increasing cost of importing gas and coal from overseas are reduced. The rapid disappearance of cheap natural gas is also putting UCG in a prime position as an exploitation and conversion technology, taking advantage of recent advances in drilling, completion and exploration technology.
Finally, UCG offers improved safety for the extraction industry.
* What are the right sites for UCG?
Site selection is very important.To achieve the necessary separation from ground water pathways and the isolation of the cavity by means of naturally occurring, impermeable geological strata. However, such criteria is in no way limiting as UCG can be used, on-shore, off shore and in many locations that convential mining would prohibit. Back to top
* What is the commercial history of UCG?
UCG first reached commercial stage in the Former Soviet Union, which still has large UCG operations supplying gas to power stations. Europe and Australia revived interest with UCG trials in Northern Spain and Queensland and in the UK the DTI undertook a series of supporting feasibility studies. India and China and more recently South Africa also recognise the potential of UCG as a national energy option, with feasibility studies underway in the Gujurat Region of India, the Firth of Forth in Scotland, the Majuba Coal field in South Africa and the Surat Basin in Queensland, Australia. Another significant development is the stock exchange offering of A$22M by Linc Energy in 2006 to extend the development of its UCG to utilisation opportunities in gas turbines and GTL plant.
Can UCG be combined with CO2 Capture and Storage?
In a carbon constrained world, UCG must demonstrate that carbon in the fuel can be prevented from entering the atmosphere as CO2. Most UCG processes are oxy-fuelled, which means only CO2 and water are produced after gasification, thereby making CO2 separation simpler and cheaper than other processes.
In addition, the production gases are also open to pre-combustion capture, and can benefit from the high concentration and pressure of the CO2 in the product gas. UCG is unique as a gasification process in producing CO2 and methane as well as the carbon monoxide and hydrogen found in surface gasification. This is because lower temperatures and higher temperatures in parts of the UCG cavity favour the formation of methane. Much of the CO2 from UCG can be captured more cheaply than in other applications, and UCG has the option of supplying either pure hydrogen or methane/hydrogen mixtures. The latter have favourable burning properties in turbines and the costs of transmission are lower than for hydrogen alone. Back to top
* What is the state of UCG Technology?
Underground coal gasification works by constructing vertical wells into a coal seam to supply the injection gases O2 and H2O, and to discharge a mixture of production gases, CO, H2, CH4 and CO2 to surface. While the principle is deceptively simple, control of the gasification process has been at the heart of UCG development over many years.
Most coals can be gasified in-situ but opening up the coal seam between the two vertical boreholes is necessary, and techniques such as fraccing, reversed combustion and electrical discharge have all been employed. The method, adopted in the FSU and used subsequently in the recent Australian UCG trial, rely on closely spaced vertical wells to move the combustion front through the coal field.
The alternative is directional drilling, which allows wells to be constructed at a precise horizon in coal seams and links these accurately to other wells which connect to surface. Bottom hole drilling assemblies have sensors to detect seam boundaries and even look ahead of the drilling bit to identify, in advance, faults and areas of unacceptable structure. Directional drilling and moveable injection was first used in the final US trials (late 1980's) and taken to greater coal-seam depth in the European trials (1988-1998). These latter trials have also shown that moving the injection point within the channel, figure 2, gives greater control of the process and leads to a wider gas cavity and more efficient process overall. It appears that the latest tests of the FSU method, namely the flaring test in the Majuba coal field (2007), are using some form of directional drilling to improve access to the coal field.
The latest technology of UCG, whether it uses vertical wells only, directional drilling or moveable injection are now well proven at the pilot scale (4-25MW thermal output). It was clear from the UCG conference in London that a number of entrepreneurial and established organisations are making feasibility studies of commercial schemes, seeking suitable sites, and defining development programmes.
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