US government boffins say they – or perhaps their rivals – will soon roll out a new and much more efficient type of turbine generator which is expected to be a boon to so-called "thermal" powerplant technologies such as coal, gas, oil and nuclear.
Most kinds of renewable generation – wind, tidal, hydro, solar-photovoltaic etc – would not benefit, but a couple of less widely-known ones would: namely solar-thermal and geothermal.
“This machine is basically a jet engine running on a hot liquid,” says top boffin Steve Wright of Sandia National Lab in new Mexico. “There is a tremendous amount of industrial and scientific interest in supercritical CO2 systems for power generation using all potential heat sources.”
People are interested in used supercritical CO2 generators because they use the heat supplied much more efficiently than the legacy kit now in use – for instance the basic steam turbines used to take the heat from a nuclear reactor and turn it into grid electricity. If an existing nuclear powerplant were fitted with supercritical-CO2 kit it would produce half again as much power as it did before.
The new generators work by using the heat from a thermal source – primary reactor coolant, burning fossil fuels, focused sunlight – and using it to heat up "supercritical" carbon dioxide, which is just at the point between being a gas and being a liquid. When confined under conditions of terrific heat and pressure, CO2 becomes a highly efficient means of using that heat to drive a turbine and so power an electrical generator. The fluid operates on a Brayton cycle, moving round and around a "loop" to be used repeatedly – much like the water/steam in a Rankine-cycle steam turbine installation.
The Sandia lab has two trial supercritical-CO2 installations running, and according to Wright and his colleagues the results from them indicate that this is definitely going to be the way of the future.
“Sandia is not alone in this field, but we are in the lead,” Wright said in a statement issued on Friday. "We're past the point of wondering if these power systems are going to be developed; the question remains of who will be first to market. Sandia and [the US Department of Energy] have a wonderful opportunity in the commercialization effort."
Apart from use in power plants, it would seem possible that the new tech will find a use in heavy transportation systems such as ships or perhaps railways. Wright and his colleagues report that:
The combination of low temperatures, high efficiency and high power density allows for the development of very compact, transportable systems that are more affordable because only standard engineering materials (stainless steel) are required, less material is needed, and the small size allows for advanced-modular manufacturing processes.
Reportedly a Brayton-cycle device could produce 20 megawatts of electricity from hardware taking up no more than four cubic metres of volume. With the latest warships and commercial vessels increasingly making use of electrical transmissions, this could prove highly attractive to designers.
On the powerplant front, supercritical-CO2 would appear likely to strengthen the economic case for those energy sources which can make use of it, further leaving behind those which cannot. In the UK it would be likely to ease the path of new nuclear construction (and perennial modern British favourite gas, of course). Meanwhile still heavier hidden electricity taxes and accompanying government inducements might be required if planned levels of wind power are to appear. ®
