By Andrew Nusca
Posting in Energy
British and Chinese researchers have developed a method of energy storage using liquid nitrogen to help handle brief demand spikes on the power grid.
A flat demand curve for electricity is the holy grail for a utility company, but real-world usage varies dramatically throughout the day.
But researchers at the University of Leeds and the Chinese Academy of Sciences have developed a cheaper, more environmentally-friendly alternative to the gas-fired generators used today to cope with additional demand.
The integrated "cryogen" system uses excess electricity to run a unit producing liquid nitrogen and oxygen.
Here's how it works: during peak demand, the system boils the nitrogen (to -196 degrees Celsius, or about -321 degrees Fahrenheit) using heat from the environment (that's about 15 or 20 degrees Celsius, or 59 to 68 degrees Fahrenheit) and waste heat (at 70 to 100 degrees Celsius, or 158 to 212 degrees Fahrenheit) from the power plant. The newly hot nitrogen gas drives a turbine or engine and generates electricity.
Meanwhile, the oxygen is fed to the combustor to mix with the natural gas before it is burned, creating an efficient combustion process that produces a concentrated stream of carbon dioxide, which can be removed in solid form as dry ice.
Researchers say that such a system could reduce the amount of fuel needed to cater for peak demand by as much as 50 percent. There is also fewer greenhouse gas emissions, thanks to the efficient combustion process (fewer nitrogen oxide emissions) and the capture of carbon dioxide in solid form.
Energy storage is important to utility companies because they must have enough power plants to handle not only "base" demand but also maximum peaks. That means that on any given day, utility companies have expensive, gas-fired power plants idling by, waiting for a big potential spike.
The researchers' system, like all energy storage solutions, allow the utility company to use its resources more of the time.
"This integrated system is truly novel," said Leeds professor and lead researchers Yulong Ding in a statement. "Because we are storing the excess energy for later, there is less need to ramp up the output of gas-fired plants whenever a peak in demand is expected, generating electricity that may simply not be used."
The researchers estimated that return on investment would come quickly thanks to the fuel saved, with additional benefit from what is effectively a carbon capture system, which will be required for all new fossil fuel power stations in the U.K.
The research team is currently applying for more government research funds and seeking industrial partners in the energy sector. They estimate that the technology is five to eight years from commercialization.
Full details of the project will be published in the International Journal of Energy Research.
Photo: Dry ice pellets. (Richard Wheeler/Wikipedia)
Aug 16, 2010
The article glosses over what's required to make dry ice. When you burn oxygen and methane, the CO2 produced will be in the form of hot CO2 gas. Making dry ice out of it will be no different than making dry ice out of the CO2 from a coal-fired plant. In other words, an enormous amount of energy. While with this process you happen to have refrigeration units handy, it's still an expensive process since you won't be getting the energy used to make the dry ice back (which you do with the liquid nitrogen and oxygen). In fact, what happens to the dry ice? It's convenient for collecting it and putting it somewhere, but where? At some point you have to let it sublimate, you're not going to keep it frozen forever.
Storing energy for future consumption & making use of waste heat are pretty exciting by themselves. Finding 2ndary uses for the liquid nitrogen & the LOX would be nice but not critical. I'd appreciate a link to a diagram that shows how the concept works in greater detail
Use of excess electrical generating capacity to produce a commodity that's more easily stored than electricity itself, or for that matter manifesting solar energy in the form of a commodity more easily stored than electricity, certainly is an option we should always consider. Now about using excess energy capacity (i.e. byproduct steam or heat) or excess electrical capacity at a given moment, to produce liquids air, oxygen and nitrogen: During hot parts of the year, you can use liquid nitrogen for air conditioning and refrigeration. Obviously we don't need to cool ourselves to liquid nitrogen temperature (-320 Fahrenheit), but there's no doubt that liquid nitrogen is a means of storing cold for later re-use - provided you can deal with the matter of boiloff. Liquid oxygen has uses, such as in steel mills or to provide concentrated oxygen for medical purposes.