General Electric (GE) Global Research has announced that it’s developing a prototype turbine that could fit onto a desk. Using “supercritical carbon dioxide,” just one of these devices could power a small town of 10,000 homes.
“The world is seeking cleaner and more efficient ways to generate power,” Doug Hofer, a steam turbine specialist at GE, said in a statement. “The concepts we are exploring with this machine are helping us address both.”
A supercritical fluid is any substance at such high temperatures and/or pressures that the boundaries between what is liquid and what is gaseous vanish. They can move through solids like gases, but they can also dissolve materials as if they were still in liquid form. In addition, small alterations to the pressure or temperature can produce dramatic density changes.
All in all, supercritical fluids have some fairly bizarre properties, and supercritical carbon dioxide is no exception to this. GE claim that by harnessing these physical curiosities, they’ll be able to power turbines with it in order to generate power more efficiently than just using steam.
Steam turbines, which are normally 10 times bigger than this prototype, convert around 45 percent of their heat into electrical energy; GE believe their new, far smaller turbine would be around 50 percent efficient.
Any substance is capable of absorbing, storing and releasing heat, and some are more efficient at doing this than others. Water, for example, takes a considerably long time to heat up, just as it does to emit this heat and cool back down again. Carbon dioxide, on the other hand, can be heated up far quicker and cooled down far quicker.
Theoretically, using carbon dioxide to store heat instead of water would make powering turbines more energy efficient. Fortunately, concentrated solar power (CSP) plants may be able to help out here.
A concentrated solar power plant focusing tower, which stores excess heat within molten sand. GE
One of the primary problems with solar power is that it isn’t available at night, and engineers have come up with some rather ingenious ways to store any extra solar power within chemical “batteries” so that it can be dispensed after sundown. Morocco is building one of these CSP plants right now – in this case, molten sand is used to store this excess solar power as thermal energy for up to three hours.
GE are proposing to use carbon dioxide to store the heat instead. After using molten salts to initially store the incoming radiation as heat, it is then transferred to blocks of solid carbon dioxide, also known as dry ice.
When heated, the dry ice suddenly expands, and beyond a certain temperature it becomes supercritical. This will allow it to dramatically flow into the nearby prototype turbine at speeds far greater than steam ever could.
All in all, this system is far more efficient at storing and transferring heat than pre-existing water-based turbine systems. If this prototype is deployed in a CSP plant, it could transfer up to 68 percent of the stored energy back to the grid – more efficient than any gas-fired power plant. In addition, compared to normal turbines that can take up to 30 minutes to fully spin up, a supercritical carbon dioxide turbine would take just a minute.
Although you probably won't have one of these on your desk any time soon, it's a pretty neat idea.