'Dirty' coal can be tackled by these emerging power-plant technologies
Clean coal technology took on a major new importance in June when U.S. President Barack Obama ordered a 30-per-cent cut in carbon dioxide emissions from power plants by 2030. Now the race is on to develop technology that's effective, scalable and commercially viable.
It's a major issue: coal-fired power plants still produce 40 per cent of the world's energy, as well as more than 40 per cent per cent of the world's COemissions, and their use is going up in expanding economies like India and China. In 2013 alone China approved mining operations to extract 100 million tonnes of coal, six times more than the year before.
Many environmentalists' remain skeptical about clean coal technology, saying it's unproven, difficult to scale up and will perpetuate the world's use of coal. Others say it's a matter of being realistic and that clean coal needs to be part of the solution
Here's a snapshot of progress on four ways to clean up coal-based energy.
1. Carbon capture and storage (CCS)
This process gathers the carbon dioxide emitted from large sources such as power plants and deposits it in secure places where it can’t reach the atmosphere, such as underground geological formations.
In Saskatchewan, one energy company purchases carbon dioxide that otherwise would be emitted by a coal gasification plant in North Dakota, then ships it north via a 320-kilometre pipeline. The CO2 is injected into the ground, offsetting the greenhouse gas emissions from 510,000 vehicles.
SaskPower, owned by the provincial government, is planning to open a $1.35-billion CCS facility at a rebuilt coal-fired plant at its Boundary Dam facility in Estevan. The utility’s Boundary Dam Carbon Capture Project, backed by $240-million in federal funding, will be the world’s first post-combustion coal-fired CCS project when it opens, which is scheduled for this year.
By 2012, nearly 20 million tonnes of CO2 was stored by large-scale CCS projects around the world. About 3 million tonnes were stored in Saskatchewan, roughly 1 per cent of the world total.
CCS is a costly process, but the International Energy Agency (IEA) in Paris says that without this technology, it may cost 40 per cent more to take the carbon out of electricity production enough to meet international climate targets by 2050.
2. Flue-gas separation
Flue-gas separation deploys solvent and steam to remove the CO2 that would otherwise be released from a smokestack and then condenses the steam into a concentrate, producing CO2 that can be used commercially. It has been used by oil refineries to recover marketable CO2 and now the technology is being looked at for other facilities such as coal power plants, to protect the atmosphere from greenhouse gases.
There are different technologies for flue-gas separation. One, called oxy-fuel combustion, uses enriched or pure oxygen to burn fuel and create a flue gas composed primarily of CO2 and water, streamlining the separation process.
3. Pre-combustion capture
This technology removes the CO2 during the gasification process before it’s burned. The process converts fuel into a gaseous mixture of hydrogen and CO2. The CO2 can be compressed for transport, and then either sold or buried using carbon capture and storage. The separated hydrogen can be burned without producing any CO2.
Pre-combustion capture is already used in industry but still needs to be demonstrated in larger power-generation projects. The steps it takes for pre-combustion are more complicated than for post-combustion, although most of the building blocks are already in place in the industrial processes.
In addition to separating hydrogen from CO2, other post-combustion techniques include reacting fuel at high pressure with oxygen, air or steam (to produce hydrogen and carbon monoxide instead of CO2, which can also be captured). Carbon monoxide can be further reacted with steam in a catalytic reactor to produce more hydrogen for fuel and additional CO2 that can be transported for storage.
4. Gasification
Unlike some of the more experimental technologies that still need to be scaled up, gasification is proven and reliable. The concept – burning the gas that comes from coal – has actually been around since the 1780s; gasified coal was used throughout the 1800s to light city streets, before the electric light was invented. It’s increasingly important in countries that are expected to continue to rely on coal and have energy demand that’s expanding quickly because of growth. For example in 2012, GE entered into a joint venture in China with Shenhua Group to develop gasification technology.
The key is making gasification ever more efficient and sustainable. Specialized gas turbines are specially designed to capture and divert the CO2 early in the process and then to burn the fuel using a system that diffuses the flame so it burns more evenly than in earlier turbines. This type of diffuser (GE calls its system Multi Nozzle Quiet Combustor) can deliver anywhere from 70 to 880 megawatts of power, depending on the exact fuel, the details of the facility and the site.
Clean coal is far from the only solution to climate change, and there’s still a lot of work to be done to make it more effective. But its role is becoming more and more recognized. “I don’t see how we go forward without it,” says Steven Chu, President Obama’s former energy secretary and a Nobel Prize-winning physicist.
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