Carbon warriors

As weapons are crafted in anticipation for a battle between carbon capture technologies, PEi investigates which products will survive to reap the undoubted rewards when commercialization hits.

Robin Rowshangohar, Assistant Editor

History is filled with stories of great captures carried out for the good of a cause. From key battles in major wars to composers who find a tune that becomes a timeless hum across the globe. Some of the heroics may have been heavily structured and perfectly executed, others more abstract and freewheeling, but all of them are great if only for a display of vision and commitment to seize what is desired. Many companies, both international and domestic, far reaching and specialized, are in pursuit of something of great desire today. Carbon dioxide. The quest to capture this greenhouse gas has accelerated, forcing those behind the eclectic mix of potential solutions to step up the pace of development.

Coal plays a huge part in the global generation mix and is likely to do so for many years as the volatility surrounding oil and natural gas supply approaches boiling point and renewables continue their steady subsidized stroll into the world of power generation. Despite the challenge posed by extracting carbon from heavier fuels such as coal, the rewards on offer have meant that much of the research and development in carbon capture has focussed on coal fired power plants.

The two most favoured techniques in development at the moment are oxygen firing and post combustion capture. Within these two there are a number of individual methods being trialled with the ultimate intention of operating on a large enough scale at a cheap enough price to benefit when the market is ready to adopt them.

As Alstom’s vice president, technology, Charles Soothill says: “When CO2 really bites in ten years’ time, we need to have solutions that can address the issue from existing plants.” So, if the market is expected to be ready for solutions in ten years’ time, will the products currently only in the demonstration phase, be ready to capture carbon on a commercial scale and at an affordable price?

Oxyfuel firing

One of the companies most active in developing an oxygen combustion carbon capture method is Alstom with its Oxyfuel technology. Oxyfuel replaces the air in the combustion chamber with high levels of oxygen to produce a flue gas of concentrated CO2, which can then be captured. This technique could provide many benefits; not least through cheaper plant costs thanks to a boiler size compacted by around 20 per cent.

Over the last couple of years the company has carried out three trial campaigns on its technology and has successfully demonstrated it on a pilot scale. It is now looking to move onto the next stage of development. Pilot tests were carried out with a range of coals and oxygen levels in the fluid, ranging from 21 to 70 per cent. The results are clear to Alstom, which has concluded that it has demonstrated partial capture of CO2 and feels it has the potential to get close to 100 per cent as development progresses.

Tanks of oxygen and carbon dioxide used in successful Alstom tests of CFB-based carbon capture technology
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The real significant step of the Alstom tests is that they have successfully, for 300 hours, proved that you can burn coal in a circulating fluidized bed boiler with high concentrations of oxygen. The testing process has also provided valuable heat transfer data in terms of coefficients and the combustion efficiency. Emissions of pollutants and other trace elements have also been measured with no cause for alarm, an important factor when trying to capture carbon from coal.

Soothill believes the trials so far have left Alstom in a secure position to progress: “This gives us the basis, the design tools, to scale up to the next size demonstration plant.”

Being developed in partnership with the US Department of Energy (DOE), the next test phase is likely to be carried out in North America, although Soothill stresses that the company is looking at potential demonstration sites across the world. Wherever it is, the next phase will be interesting as the technology still has many aspects that need more investigation such has controlling the bed temperature and the erosion rates of the boiler in the high oxygen environment.

Given that all research goes smoothly, when could oxyfuel firing carbon capture become a commercial product? “If a demonstrator can produce a programme over the next three of four years then at that point you might be at a point to launch a commercial programme,” says Soothill. “We are talking 2011-2015.”

Post combustion

Alstom is also exploring post-combustion scrubbing and anti-sublimation technologies. The commercialization of its oxyfuel firing in ten years’ time would tie in with Soothill’s prediction of when the market will be ready to adopt the measures. So how does this compare with the back box method Powerspan has been developing?

According to the company’s CEO, Frank Alix, Powerspan’s technology could be ready in five years: “We are about to move into pilot phase testing and we would expect that to last for about two years. Then we would move into commercial scale testing and that generally is another two to three year programme.”

The US based clean energy technology company has recently announced an agreement with FirstEnergy to test its carbon removal technique at the R.E Burger power station in Ohio. The Powerspan capture process uses an ammonia-based solution to capture CO2 in flue gas and prepare it for sequestration. Initial laboratory tests under conditions comparable to a commercial scale boiler have demonstrated that the technology should be capable of 90 per cent removal. With testing scheduled to begin in 2006 the project could be finished a year later and from there, if all tests are successful, onto the next stage.

Concept for CO2 scrubbing in Powerspan’s ECO process
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But again, this is reliant on the company learning how to overcome challenges such as ammonia vapour loss, which Alix is very much aware of: “We need to capture it [the vapour] and not lose it out of the stack. We think we know how to do that, but we need to demonstrate that on a very large scale.” While this is not a potentially fatal flaw, it underlines the type and scale of engineering and technical challenges that are currently standing in the way, and as the scale of demonstration grows, who knows what new obstacles may be found?

What is clear is that there will be several outside factors influencing when a carbon capture technology becomes commercial. Greater air separation systems will have to be developed for oxyfuel firing as many of those currently available are still in the early stage of development. Also, methods will have to be trialled and developed to reduce the cost and ease of compressing the captured CO2, a factor that will affect its desirability and value as a product. All of these and more will affect the final cost, the ultimate deciding factor when choosing an option.

Cost estimates

Present estimates from the DOE peg the technologies at around the same level in terms of the effect they will have on the price of electricity once installed and these have fallen significantly in just the last few years. The goal for the DOE is to achieve no more than a 20 per cent rise, which it has predicted Powerspan’s process to meet. Original estimates predicted that oxyfuel technologies would increase the price of electricity by over 50 per cent, whereas recent estimates suggest around 25 per cent.

As Alix says: “You couldn’t make the case that any of these are commercially ready. You can only make the case that they all show tremendous promise in reducing the costs as they are understood today.”

At present all of the competing technologies are fairly balanced so the next few years of development could prove crucial. What is clear is that carbon captors will need the cooperation and development of other areas, which it will rely on for growth and support in a battle to emerge as the preferred option.

Ancient Greek mythology gave us the legend of Jason and the Argonaughts and how they captured the Golden Fleece. It is a story of how a young man achieved his rightful place on the throne by capturing a sacred ram’s fleece. He achieved this through cooperation, applying methods and techniques he had learnt on his journey and perhaps above all, by never letting adversity quell his ambition. As developers of carbon capture technologies are learning today, the same characteristics will be needed if they are to claim not only a throne for themselves, but perhaps even a place in mythology.

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