Sour power

A waste by-product of crude oil processing could become a valuable fuel in its own right, if tests being carried out by US researchers are successful.

The team, from the University of North Dakota’s Energy and Environmental research centre (EERC), is looking into the feasibility of generating electricity using a turbine fuelled by impure (sour) natural gas.

Sour gas is usually viewed as an unsuitable fuel as it contains impurities including hydrogen sulphide, which are highly corrosive to mechanical components such as pumps, compressors, and piston engines. It is usually simply burnt off, adding to pollution problems, and wasting a potential energy source.

Project manager Darren Schmidt explained that at the test site, an oil field in Newburg, North Dakota, the sour gas is pumped into a seven-mile long pipeline with flares at each end. ‘There’s enough gas exiting these flares that if we turned it all into power we could produce about 300kW’ he said.

The team believes it has found a way around this waste by using a special turbine generator developed by industry expert Capstone. Known as the microturbine, the generator is thought to be ideal for the application thanks to its use of air bearings which, unlike traditional mechanical bearings, are unaffected by the corrosive properties of the sour gas.

Like a jet engine, the Capstone MicroTurbine mixes fuel with air to create combustion. This combustion turns a magnet generator, compressor and turbine wheels on a single-shaft air bearing at high speed, with no need for additional lubricants, oils or coolants.

The turbine is being used to generate power for pumps used in the oil recovery process. Schmidt said that while the turbine currently has 30kW of power capacity, it has the potential to produce 300kW from a sour gas pipeline. While the energy generated is at present being used to offset pumping costs at the Newburg oil-field, Schmidt does not rule out the possibility of the approach one day contributing towards the national grid.

‘A lot of the oil fields are located in areas where you have an investor-owned electric co-op, he said. ‘The electric co-op wants to see anything that’s good for other businesses in the area – and the oilfields are a big economic contributor. I can see a situation where they would be interested in taking electricity back across the line from the oil field.’ he said.

The turbine has now been operating for around two and a half weeks and will be monitored over the next year. But results are already highly promising, said Schmidt. ‘For this tiny project we have a two to three-year return on investment, and have dropped emissions by about 75 per cent.’ The project is being jointly sponsored by the US Department of Energy, the North Dakota Department of Commerce, and oil company Amerada Hess.

Note: US researchers are working on a glucose fuel cell that could be plugged into a soldier’s arm to power his radio. The researchers at Sandia National Laboratories are investigating glucose as a power source for fuel cells, rather than hydrogen. One planned fuel cell device consists of an array of tiny glass needles on a patch, which could be plugged into a glucose energy source such as a human arm. The device could also siphon excess glucose out of the blood for diabetics, the researchers claim. Other glucose fuel cell potential applications include security system movement sensors that could be plugged into trees, removing the glucose from tree sap. However, as yet the researchers have only produced enough electricity to power an LED.