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New life for coal-fired power
Pilot plant marks world first for carbon dioxide and sulphur dioxide capture.
A key step in emissions control for coal-fired power generation is being taken at Aberthaw power station, UK.
The operator, RWE Generation SE, has partnered with Shell Cansolv to develop a 3-MW pilot plant for carbon dioxide (CO2) and sulphur dioxide (SO2) capture at the power station.
The pilot plant, which started operation in January 2013, is the world’s first integrated CO2/SO2 capture facility.
Coal is the world’s cheapest and most abundant fossil fuel, but burning it releases CO2 and SO2 into the atmosphere.
This has prompted calls for a radical reduction or even the abandonment of coal for applications such as power generation.
However, the power-generation industry can now apply effective capture techniques to cut emission levels substantially at coal-fired power plants.
One solution is downstream scrubbing of flue gases to capture CO2. This process, referred to as post-combustion capture, removes the CO2 before the flue gases reach the atmosphere through the power station‘s stacks.
According to climate scientists, this approach could play a significant role in helping to reduce the effects of climate change.
Estimates suggest that capturing CO2 at emission points and storing it underground could deliver about 20% of the reductions that the Intergovernmental Panel on Climate Change has recommended to avert the worst effects of climate change.
RWE Generation SE and Shell Cansolv are using the combined plant at Aberthaw to test technology for treating flue gases.
This work is a vital part of the research programmes on carbon capture. Devin Shaw, Global Sales Manager, Shell Cansolv, says, “The post-combustion plant at Aberthaw captures 50 tonnes of CO2 a day.
By using CANSOLV™ scrubbing technologies, this ground-breaking regenerable system can capture 90% of the flue gas CO2 and essentially all of the SO2.”
According to Shaw, there are other benefits to consider when using the regenerable system.
“This technology means that the plant avoids the landfill disposal issues associated with conventional, non-regenerable scrubbing systems,” he says.
“Reusing the absorbent by recycling cuts waste and reduces costs by minimising the need to restock.
We believe that this makes CANSOLV technology applicable for a broad range of industrial applications.”
CO2 and SO2 scrubbing systems are proven technologies that have been used to clean gases in the oil industry for more than 80 years, but this is the world’s first application of an integrated CO2–SO2 capture system at a power-generation facility.
Applying CO2 capture to the flue gases of a coal-fired power plant is new and the scrubbing technique must be adapted to meet power plant conditions.
For example, the flue gas streams of a coalbased power station contain 3–5% oxygen, whereas most of the gas streams dealt with in the chemical industry contain no oxygen, as they are pre-combustion streams.
The Aberthaw project is a useful opportunity to test a new generation of CO2 solvents and SO2 solvent enhancements.
The power-generation industry can now apply effective capture techniques to cut emission levels substantially at coal-fired power plants.
Aberthaw marks a significant point in the commercial application of combined CO2 and SO2 capture techniques.
According to Mattias Hartung, Chief Operating Officer at RWE Generation SE: “This pilot plant at our Aberthaw power station is another step on the road to giving us the choice of technologies we need to create a modern, efficient and diverse energy portfolio that is capable of guaranteeing continuity of supply while reducing costs and CO2 emissions.”
Shell Cansolv has developed a miniplant to demonstrate the concept, but this system, which fits on the back of a truck, is too small to give realistic performance figures.
The Shell Cansolv and RWE Generation SE pilot plant is large enough to fit into a commercial process environment and will deliver invaluable information on applying the process at a commercial scale.
The Aberthaw unit is designed to be modular and transportable on skids.
Shell Cansolv had the unit designed in Canada and sourced all the necessary materials in North America and Europe before sending them to China for construction of the plant.
Shell Cansolv employees went to China to supervise the construction and to ensure that the unit met the standards RWE Generation SE had defined.
Once fabrication was complete, the system was sent to the UK for erection.
There were some technical and logistical challenges to be overcome.
“One of the key issues was getting the two units, which operate in series, to work together as intended,” Shaw explains.
This is obviously a crucial aspect of the work that we are doing at Aberthaw, and we are delighted to have achieved an effective solution.
There were also some challenges in securing a licence to operate the system in the UK.
This reflected the facts that the proposed system was the first of its kind, which required a complete examination of the technology by the regulatory authorities, and that it had been developed through a multinational design and fabrication process, which complicated the statutory process of checking component quality and standards.”
The initial feedback on the performance of the combined capture system at Aberthaw has been good. The units are performing as expected and a CO2 removal rate of 90% has been achieved, along with well over 99% removal of SO2.
The pilot plant will also be run at various levels of CO2 capture to help optimise the combined capture process with a view to applying it in larger units.
Shaw is looking forward to applying the combined capture process at full size in a commercial plant.
“Using our system to manage all the flue gas emissions at a 150-MW plant will pose significant challenges in chemistry, engineering and operations.
In terms of chemistry, the main challenge will be scaling up the capacity for CO2 capture.
The engineering and operational challenges will focus on minimising the energy use of the capture units.
CO2 scrubbing currently has higher energy requirements than we would like for deployment in power stations.
The experience we gain in the Aberthaw pilot project will help us deliver improved scrubbing solutions that require less energy for CO2 capture,” he concludes.
CANSOLV is a Cansolv Technologies Inc. trademark.