16 August 2010 – Researchers at the UK’s Leeds University and the Chinese Academy of Sciences have found a way to manage short-lived draws on the electricity grid with half the fuel usually needed.
According to The Engineer, the concept would heat super-chilled liquid nitrogen to its boiling point and use the hot gas to drive turbines that will generate electricity when energy demand is at its peak.
Studies show electricity drawn from the national grid varies at different times of day – peaking in the early evening for a couple of hours after school and working hours. There are also the notorious short-lived spikes such as the moment when millions put the kettle on during a peak-time television commerical break.
But matching the highs and lows in demand with a steady supply is a major challenge. Energy companies typically top up a ‘base’ supply of energy with electricity from power plants that are just switched on to cope with the peaks. However, the gas fired generators often used to feed these peaks are notoriously inefficient and expensive to run and sit idle for long periods of time.
Yulong Ding, a professor of engineering at Leeds University, and his fellow researchers believe their concept is more environmentally friendly and less expensive to run.
Their idea would require using excess energy from a plant to run a unit producing liquid nitrogen and oxygen – or ‘cryogen’. At times of peak demand, the super-cool liquid nitrogen would be heated to its boiling point around -196 ºC.
Ding said that this would be accomplished by using environmental heat in the range of 15 ºC to 20 ºC and waste heat from the power plant. “The waste heat has a temperature of anything ranging from 70 ºC to 100 ºC,” he told The Engineer. ‘The waste heat can be used to super-heat the nitrogen.’
This will give the hot nitrogen gas more power as it drives a turbine or an engine, generating ‘top-up’ electricity. Ding said that this could cut the amount of fuel needed to cater for peak demand by as much as 50 per cent.
Meanwhile, the oxygen would be fed to the combustor to mix with the natural gas before it is burned. This makes the combustion process more efficient and produces less nitrogen oxide.
The method, known as ‘oxy-fuel’, is also used as a form of carbon capture because it produces a concentrated stream of CO2 that can be removed easily in solid form as dry ice and stored elsewhere.
Ding estimated that power generators would quickly see payback from installing such units in their plants because of the fuel saved. He added that there is also the bonus of the built-in carbon capture system – which will eventually become mandatory on all new fossil fuel power stations in the UK.
The Leeds University team is currently applying for more government research funds and searching for industrial partners in the power generation or utility sector. Ding does not believe the technology is too far away from commercialization.
‘The components for the system are already mature technologies so we can have them and I think the key is integrating,’ he said. “So if there are power companies interested in going forward, it could be a five- to eight-year time scheme.”
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