Under pressure: the company putting turbines in gas pipes

Andrew Purvis talks to Andrew Mercer of 2OC

"There's enough pressure in the world's gas pipelines to make every nuclear power station redundant."

That’s the bold claim of Andrew Mercer, setting out the rationale behind his Bath-based renewables company, 2OC. Founded in 2005, it aims to harvest clean electricity and heat from the waste energy produced by gas pressure reduction stations (PRSs), of which there are 12,500 in Britain. 

“I can recognise them in a heartbeat,” Mercer says, describing them as “pipes, shaped like an L on its back, going into a big lump of metal – typically next to a gasometer”.

Not the most technically precise description, perhaps – and Mercer acknowledges as much with a laugh: “I’m an accountant by training,” he apologises.

With a capacity for lateral thinking to match his head for figures, Mercer’s first success was in software development. His company, One Meaning, which created what was to become Microsoft’s Universal Modelling Language (UML), was sold to Oracle in 1999. Next he set up the mentoring organisation Footdown, and at one of its forums met Michael Edge, who made his money building and selling Chase de Vere, the financial services company, and is now chairman of 2OC.

They soon discovered that they shared a passion for environmental solutions, and so started casting around for a suitable company in which to invest. It wasn’t long before they heard about a project in Switzerland that was generating electricity using a turbo-expander. “That’s the piece that goes in the pipe, which bypasses the pressure reduction station,” Mercer explains.

At which point a little further explanation is probably called for. When gas emerges from the ground, it does so at high pressure – and this has to be reduced before the gas can be used safely in homes and by industry. “It passes from a small pipe to a larger one,” says Mercer, “through [something called] a Joule-Thomson valve.” The reduction in pressure is accompanied by cooling to as low as -40˚C, creating a permafrost in the valve, pipes and subsoil. “It’s like holding your finger over an aerosol nozzle,” Mercer says. “It gets very cold.”

On the positive side, high pressure gas can be used to drive a turbine in the pipe, generating electricity – the turbo-expander used in the Swiss project. On the negative side, super-cooled gas has to be preheated using gas boilers – a perverse waste of energy. “We know how much pressure is in the system,” Mercer says, “so we can work out how much energy is being put through the valves” – hence his statement about closing down nuclear power stations.

On the back of this resource, called geo-pressure, 2OC was formed. “The name was chosen because it’s CO2 reversed,” says Mercer, “indicating that we were part of the solution that would reverse the effects of fossil fuel generation. Two degrees centigrade was also the temperature change beyond which warming of the planet was believed to be unstoppable.”

At that time, geo-pressure was a hotly debated subject and the technology was at first excluded from the Government’s Renewables Obligation (RO). This is the scheme by which electricity generators have to buy a minimum proportion of their power from renewable energy sources. So if geo-pressure were recognised as ‘renewable’, then anyone generating power from it would have a clear market advantage.

The debate hinged on how much of it was natural, and how much was due to compression – the man-made pressure used to push gas around the network, especially at peak times. “We spent a lot of time with the National Grid, working it out,” says Mercer, “and even with compression at its maximum, [the man-made element] accounts for only 12-14%.”

“But is geo-pressure renewable? The debate was long and littered with U-turns”

Then there was the question as to how a technology could be renewable if it depended on natural gas – a finite resource. The debate was long and littered with U-turns, but finally, in January 2008, the Government concluded that “geo-pressure is renewable and can be carried by a variety of fluids that will in time replace the natural gas in these reservoirs.”

With neither the time nor the temperament to wait for government approval, Mercer had by then developed the technology several stages further. Known as CHiP (Combined Heat and intelligent Power), this uses the world’s most efficient combustion engine to generate 14MW of electricity. “The energy we are using now is exactly the same,” he says, “and we are still bypassing the valve with the turbine. All we have done is choose a different part of the Renewables Obligation to generate the electricity. It’s a different technique.”

Fuelled by vegetable oil (from rapeseed grown by local farmers as part of their normal food crop rotation) but also able to run on biogas, the engine is sited next to a pressure reduction station. Heat from the engine is used to warm the super-cooled gas in the PRS, allowing the gas boilers to be switched off – with huge savings in energy and emissions. At the same time, turbines inside the pipeline generate 3.5MW of electricity, and surplus heat is captured and converted into a further 1MW.

“The higher the pressure of gas in the system, the greater the electrical efficiency”

The combined output is nearly 20MW – enough to power 50,000 homes – plus 5MW of heat to warm the gas supply. “At peak times, when the little turbo expander is working its heart out, we can get it up to 80% electrical efficiency,” says Mercer. Use any spare heat in a district heating system, and CHiP can achieve an overall efficiency of 95% or more. The intelligent part is that peak electrical output exactly matches peak demand for gas in the winter; the higher the pressure of gas in the system, the greater the efficiency.

In a joint venture with the National Grid, called Blue-NG, Mercer and his team are now building the first CHiP energy centre in Beckton, east London. Planning permission has also been granted for a second plant in Ealing, in the west of the capital, and both should be supplying local homes and industry by late 2011.

Now Mercer is applying the technology to CSP (concentrated solar power – see 'Can the Sahara light up Europe?'), which uses mirrors to focus the sun’s energy on water, converting it to steam to drive turbines. The mirrors have to be cooled with fans, river water or seawater, all of which have environmental drawbacks. “Imagine putting a CSP plant by a pressure reduction station,” Mercer says. “You take the cold from the gas to cool it and at the same time generate more electricity. You can double the output and halve the cost.” His company owns the intellectual property rights to that idea, and a project will begin shortly.

Next on Mercer’s radar are computer data centres. These too need to be kept cool – a process which uses vast amounts of energy: so much so that computers may soon overtake aviation as a source of CO2. “There is more heat per square inch coming off a processor than off a nuclear power station,” says Mercer, “and every MW generated requires a MW to cool it.” And 2OC's solution to this? To develop the iQuadgen, a super-efficient power generation and cooling plant, to be located close to data centres. The iQuadgen integrates high performance technologies, like the turbo expanders and fuel cells, with renewable energies, such as solar and geothermal.

Though he sounds like a man who scours the modern world for areas of energy wastage, Mercer’s passion is “localising and autonomy” rather than climate change. “In the next few years,” he says, “we are going to have power blackouts, we are going to have water problems. I think it would be quite sensible to be self-sufficient.” With this in mind, he is building a zero carbon house in Bath, built into a hillside for insulation. “It will be off grid, off water, off sewage,” he says – and he has signed an agreement with the council, allowing them to demolish the house if it ever connects to the mains.

“Energy, whether we like it or not, is the primary platform through which we change our society,” Mercer reckons, “and we are running out of resources.” This, he hopes, will force people “to think more sustainably and make the transition to a different way of living.” With its heritage orchard, beehives and 30 acres in which to grow food, his eco-estate is an example of that. “The vision behind it,” he says, “is to exert a lighter pressure on the earth.” All the while harnessing, he might have added, the pressure surging through the gas pipes beneath it…

Andrew Purvis is a regular contributor to the Observer and the Daily Telegraph.

17 June 2010

Andrew Purvis