Energy companies in the US, backed by research grants from their government, have been developing fracking (hydraulic fracturing) as a means of releasing gas and oil from shale rock for around 20 years.
Over that time, they’ve perfected the technology required to turn a drill bit sideways to bore along the shale seam and experimented with different mixtures of sand and water and various chemicals to create the most productive set of cracks in the rock, and keep them open once the pressure is removed, so the fuel continues to flow.
The reason we’re seeing so much about fracking now is price. Conventional gas and oil has become expensive and the UK is having to import both in increasing quantities. As the price rises, expensive new technologies start to make commercial sense. Now the UK government is encouraging energy company Cuadrilla to drill exploratory wells here, and hopes that commercial production will follow.
Most of the fuel released by fracking in the US is gas, with a little bit of crude oil produced almost as a by-product. The likelihood is that will also be the case here. Gas is a valuable fuel for domestic and industrial use and is widely used in power generation too, and in the US, falling gas prices have been welcomed by industry and households, but diesel cars run on diesel oil so why are we interested?
Many service stations now have LPG (Liquefied Petroleum Gas) pumps on the forecourt. LPG is a mixture of gasses – primarily propane and butane – that can be liquefied by pressurising them at normal temperatures. LPG cars (and vans and trucks) just need a strong pressure vessel to store the fuel and an engine conversion, but the starting point is a petrol engine with spark ignition, not a diesel. Similar conversions are available to run ‘petrol’ engines on natural gas.
Natural gas is mostly methane, even lower in carbon and therefore cleaner burning than LPG, but it only liquefies at very low temperatures or enormous pressures, which is impractical in cars. The alternative is to compress it and store it still as CNG, Compressed Natural Gas. As fracking has reduced the price of gas in the US, the trucking industry in particular has become interested in converting diesel engines to run on CNG. There are two ways of doing this:
- A complete conversion to CNG involves reducing the compression ratio, adding a gas mixing system to the air intake, removing the diesel injectors and replacing them with spark plugs, so it’s no longer a diesel engine! The problem is that the auto-ignition temperature of natural gas is hundreds of degrees higher than that of diesel fuel (about 600 degrees Celsius), so it won’t ignite by compression alone in an engine. Dual fuelling avoids this issue.
- In a CNG/diesel setup, diesel oil is used to start the engine, then when the throttle is opened, CNG is admitted into the manifold along with the air. A special engine management system is needed to control the proportions of air/diesel/CNG. These engines can run on very small amounts of diesel, all that’s needed is a tiny ‘spark’ to start the gas/air mixture burning. However it can revert instantly to normal diesel only operation if CNG isn’t available.
CNG/Diesel engines are more efficient than petrol/CNG, and can be even more efficient than diesel alone. Because there is relatively little carbon in CNG, sooty particulate emissions are low, and gas is virtually free of sulphur too.
Unfortunately neither conversion is cheap, and while they are undoubtedly practical for trucks that last ten years or more, payback time on a car conversion is longer than most private motorists, or fleets, will keep the car. UK specialists AAG Ltd (www.cngvehicles.co.uk) reckon a typical car averaging 40mpg will pay for its conversion after 60,000 miles. In the US, CNG specialists Guidetti CNG (www.guidetticng.com) market a system suitable for vans and pick-ups – with a minimum engine size of 6.0-litres! Conversion is neat and tidy, but some space has to be sacrificed to accommodate the CNG tank.
If fracking does result in substantially cheaper gas compared to oil prices, then CNG conversions might make economic sense. CNG refuelling points that connect to a domestic gas supply are already available, and could become common.
Or Fuel Conversion?
If converting each individual vehicle is too expensive, how about converting the fuel? It’s not a new idea, the Fischer-Tropsch (F-T) process was developed in Germany in 1925 to produce fuel oil from gasified coal. Since then, the process has been adapted to use different feedstocks. Until recently, it was not widely used because oil has been cheap compared to other fuels, and it was generally confined to times and places where oil supply was restricted, notably Germany during World War II and South Africa during the apartheid regime.
The F-T process consists of multiple steps, each adapted depending on the feedstock and the desired outcome, but essentially it takes Carbon in the form of carbon monoxide and Hydrogen and builds Hydrocarbon molecules. The oxygen from the carbon monoxide is combined with some of the hydrogen to produce H2O (water). When adapted to work with natural gas, it is generally referred to as a Gas to Liquid (GTL) process.
Oil companies already use GTL whenever their oil wells also produce gas in remote locations where there is little demand for it as a domestic fuel. Rather than flare off the gas, they convert it to oil and add it to the crude in their pipeline. Qatar, in the Persian Gulf, is an extreme case, it has vast gas reserves and a small population, so unsurprisingly it has the world’s biggest GTL plant, Shell’s Pearl GTL.
Will it happen?
Not soon, that’s for sure. In April last year, Cuadrilla’s CEO Francis Egan was predicting gas production in three years, and in January this year, the company’s new chairman, Lord Browne of Madingley, was saying it will take five years and the drilling and fracking of 20 to 40 wells to judge whether the UK has a viable shale gas industry. With tighter environmental regulation, gas production here is never going to be as cheap as in the US. In September last year, Ed Davey, the energy secretary, said that fracking for shale gas in the UK will not have “any effect” on gas prices. And unless there is a surplus of cheap gas, there is no chance of any of it being made into cheap transport fuel.