Natural gas is available in vast amounts, and a
British company has pioneered an efficient way to convert it to
electricity and heat in a way that does away with power stations
and lines. Tom Shelley reports
The fossil fuel of the future has to be the vast reserves of natural gas that exist as solid methane hydrates on and in the beds of the world's oceans, amounting to more than double the combined total of all conventional coal, oil and gas reserves, perhaps more.
Now that natural gas production has peaked, especially in the North Sea, engineers and researchers are beginning to look seriously at the technical challenges of recovering methane from hydrates without further wrecking the world climate, hopefully reducing carbon dioxide emissions rather than increasing them.
It is thus timely that a British team has succeeded in developing a small scale combined heat and power gas fired generating system, with an 80% overall efficiency, and has now installed the first commercial units.
Bowman Power, based in Southampton, has developed a family of micro gas turbine generators producing 80 kW of electrical energy and around 150kW of heat. Founder and CEO Tony Davies told Eureka that the shaft is directly coupled to the generator, which rotates at 70,000 to 90,000 rpm, and produces alternating current at 2 to 3kHz and 500V. The output is rectified to DC and re-inverted to produce a normal three phase 50Hz supply. Efficiency of the turbine generator on its own is only about 16%, but use of a recuperator raises this to 30%. Use of the otherwise waste heat to produce hot water or power an absorption chiller raises the overall efficiency figure to around 80%.
The secret of its success lies in its very sophisticated control system, with a central control board plus local control boards connected by CANbus. The local boards include an engine controller, system health monitoring board, a gas safety system board to monitor gas leakage and ensure purging on start up, and a power manager board controlling the interface to the grid. A digital signal processor samples and controls output power wave form quality 8,000 times per second.
Works cost is around £50,000 per unit and installed price around £70,000. Customers with working systems include the Enfield Town Leisure Centre, the Chewton Glen Hotel near Christchurch which uses a system to power and heat its orangery, and Hexham Hospital which has two. The company is currently seeking business development finance through Oxfordshire Investment Opportunity Network, a business angel network, and was encountered presenting at Venturefest, an annual event that aims to link innovative entrepreneurs with investors.
Natural gas has four hydrogen atoms for each carbon atom, unlike oil which has two, or coal which has almost none, so it has much less global warming potential when burned.
Dr Sharaf El Din, of Alexandria University in Egypt, speaking at a conference in London, estimated that methane hydrates on deep water continental ocean shelves contain some 400 million trillion cubic feet, (11 million trillion cubic metres) as opposed to 5,000 trillion cubic feet on shore. The methane molecules are held within a cage of water molecules. They are stable at depths of more than 300 to 500m, depending on ocean temperature, and may form up to 40% of sediment layers which may be as much as 1,000m thick. 1 volume unit of methane hydrate yields up to 189 volume units of gas.
Locations are well known because oil companies carefully avoid methane hydrate deposits when drilling. Failure to do so can lead to hot fluids coming up drill pipes decomposing the hydrates in the sediments so the pipes are no longer properly supported.
Deposits are found throughout the world, including areas off the coasts of Scotland and Ireland.
Schemes for recovering the methane have, until now usually involved injecting steam or some other hot fluid so as to make the hydrate decompose, releasing the gas. The big worry with this approach is that methane has 21 times the global warming effectiveness of carbon dioxide, molecule for molecule, so leakage from operations on a major scale could be disastrous.
A possible way out of the problem, may however, have been shown by a European Union project, which involves recovering drilled cores of hydrate bearing material and keeping them under pressure during the retrieval and subsequent examination in a laboratory in order to study them. The project is called HYACINTH, standing for deployment of HYACE tools in New Tests on Hydrates, and is co-ordinated by Dr Tim Francis of the UK based company, Geotek.
Since methane hydrate has mechanical properties similar to those of water ice, the engineering problems are far from trivial. Handling and cutting up solid core samples includes the use of ball valves, strong enough to survive being used to cut through solid material. The rotary corer was developed by the Technical University of Berlin and the Technical University of Clausthal. It includes a downhole mud motor. A dry auger bit extending beyond the reach of the circulating sea water is used to cut the core, providing as contamination a free core as possible. Other participants in the program include the University of Bristol, the British Geological Survey and Fugro Engineers in The Netherlands.
Asked after the meeting what he thought the next step should be, Captain David Schubert, Commanding Officer of the Naval Research Laboratory in Washington, DC was heard to exclaim, "I don't want to meet any more know where to find em experts, I want a get em up expert!" Asked how he thought this might best be achieved, he responded that he had in mind something like HYACINTH, but on a much bigger scale, digging up hydrates on the sea floor, placing them in a pressurised container and bringing it to the surface.
Naval submarines tend not to go much below 300m, but ROVs, remotely operated vehicles, can be made to happily work at any depth. We asked a semi retired naval architect if it was feasible to build a large ROV capable of mining methane hydrates, and keeping them under pressure until brought to the surface. He was somewhat cautious in his answer but immediately asked if he could have Captain Schubert's email address so we feel we can safely deduce that it is. The only government to own up to having a serious programme aimed at recovering continental shelf methane hydrates is Japan. Others we have asked have declined to answer.
http://www.bowmanpower.com Bowman Power
http://www.oion.co.uk Oxfordshire Investment Opportunity Network
Eureka says: The energy crisis could be solved without recourse to having to deal with unstable Middle Eastern countries or take further risks using nuclear energy. Since methane contains four hydrogen atoms for each carbon atom, switching to methane as a fuel could reduce the risk of global warming without having to reduce energy usage.
* Methane in the form of methane hydrates on the bed of continental shelf oceans floors is a fossil resource which should last well beyond the lifetimes of our readers
* Using it to fuel micro turbine combined cycle generator-heat sources avoids all the costs of centralised power generation and distribution
For more technical developments see www.eurekamagazine.co.uk
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