A research team at the Massachusetts Institute of Technology (MIT) has devised a procedure for halving the carbon output of energy generated from coal. If it proves economical in the real world, it may have wide implications for many countries’ energy policies.
In a paper appearing in the Journal of Power Sources doctoral student Katherine Ong and Professor Ahmed Ghoniem outline an unconventional hybrid cycle that doesn’t involve burning the coal.
This system requires no new technologies that need more time to develop. It’s just a matter of coupling these existing technologies together well– Katherine Ong, MIT doctoral student
Instead, the process pulverises the coal into dust and passes steam through it. This releases hydrogen and carbon monoxide, which enter a solid oxide fuel cell where the gases react with natural oxygen to produce electricity.
The decrease in carbon comes from extracting gas from the coal rather than burning it, which copies a technique widely used in industrial chemistry to produce hydrogen gas.
By not burning the coal, the technique avoids the spewing of ash and other airborne particulate.
Ong told MIT News that another advantage of this cycle is that both of its elements, the gasification and the fuel cell operation, take place at a temperature of about 800°C. This means that energy is not lost in changing temperature between processes, and that the process can work at an efficiency of up to 60%.
A state-of-the-art ultra-supercritical coal station that relies on a more conventional fuel cycle achieves a lower performance. For example, the Maitree Super Thermal plant proposed for Bangladesh, which will use the latest conventional technology, is expected to run at around 600°C, and to reach an energy efficiency of about 45%. A standard coal plant runs at about 30%.
Ong added that the technologies involved in the process were already familiar, and that an operational prototype could be produced "within a few years". "This system requires no new technologies that need more time to develop. It’s just a matter of coupling these existing technologies together well."
David Tucker, a research scientist at the US Department of Energy’s National Energy Technology Laboratory in West Virginia, told MIT News: "The exploration of unconventional hybrid cycles represents the future of clean energy production in this country."
At present, about 40% of the world’s electricity is generated by coal, and many countries that are building up their electricity systems have no little choice but to use coal-fired plants.
As well as Bangladesh, countries in sub-Saharan Africa such as South Africa, Tanzania, and Zimbabwe have tied their national economies to large coal station projects, and it has been calculated that 200 MW of new coal-burning capacity came online every day between 2010 and 2014.
In the diagram above, steam (represented by purple arrows) is forced through pulverised coal, which causes hydrogen and carbon monoxide (the red arrows) to rise to the fuel cell where it reacts with oxygen (blue arrows) to produce power.