A new method of electricity generation combines the advantages of large-scale nuclear power generation with modern combined cycle gas turbine-based power technology (CCGT).
The innovation, developed and patented at international consultant services company, PB Power has been designed to create a hybrid system, for either retrofitting to existing nuclear stations or newbuild installations.
The process, known as NuGas, links the steam cycles of two power plants — one nuclear, the other gas turbine in combined cycle — to provide improved efficiency and greater flexibility. The system combines the advantages of both nuclear and gas power generation, which will create a reliable, efficient hybrid system, according to one of the engineers behind the design, Paul Willson, a PB project director.
Willson said that gas turbines used in today’s CCGT power stations are the result of billions of pounds of research funding. ‘Manufacturers are finding that even the smallest incremental improvements needed to achieve a combined cycle efficiency of 60 per cent have become prohibitively expensive and complex to achieve without sacrificing reliability,’ he said.
Willson said he and another PB engineer thought one way to improve the efficiency and reliability of CCGT would be to combine it with nuclear power — which has been a proven reliable and carbonfree source of energy. ‘NuGas is very elegant and simple,’ he said. ‘Some say it’s almost obvious.’
Linking the steam systems of the two plants reduces the losses inherent in power generation. This increases the combined generated output and delivers an a level of efficiency of more than 63 per cent compared with 57 per cent for power generation in a comparable conventional CCGT plant.
Willson said he achieved these efficiency figures through sophisticated computer-generated models of nuclear and gas turbine plants.
As an example, he said, the thermal efficiency gains achieved by integrating a 1,200MWe nuclear plant with a conventional 400MW
CCGT block would provide an additional 42MW of power without burning any more gas. The combined plant is a lower risk option for plant upgrading, as it uses existing technology operating under conventional conditions.
Operating at a higher efficiency means that less carbon dioxide is emitted for each unit of electricity generated — a key driver for power utilities around the world. With careful consideration of the plant layout and connections between the two plants the overall safety of the nuclear plant would be affected.
‘The nuclear cycle is an absolute standard Pressurised Water Reactor (PWR) cycle,’ said Willson. ‘We don’t change anything. You can dismantle the gas turbine and take it away and the nuclear power station would remain the same.’
‘The only thing that is missing that would make the heat recovery and the steam generator standard in the CCGT is a steam drum and an evaporator section in that boiler,’ he added.
That doesn’t mean the CCGT could not function if the nuclear part of the plant shut down. ‘When the nuclear plant shuts down, and the gas turbine remains in service what happens is you revert to a steam raising boiler,’ he said.
‘The super heater is able to keep the steam temperatures under control and the remaining heat that isn’t picked up in the super heater goes to evaporating steam and the plant reverts in a perfectly civilised way into behaving just like a combined cycle plant.’
NuGas can be applied to newbuild nuclear plants or retrofitted to existing plants. While the new-build design would allow for maximum optimisation, the retrofit option will give exceptional returns on investment with minimal impact on the normal day-to-day operation of the nuclear plant while the CCGT unit is being constructed.
Willson said space is the key issue when deciding whether a NuGas system can be fitted on to a nuclear plant. He added that between 30 and 40 existing nuclear power plants around the world are thought to be suited to retrofitting with a NuGas system.