First published in Cleantech magazine, May 2009. Copyright Cleantech Investor 2009

by Simon Bennett

Carbon Capture and Storage (CCS), we are told, could be demonstrated today, and could be rolled out on a massive scale tomorrow, saving millions of tonnes of carbon dioxide at each facility. However, the risks for investors will remain high unless a few dramatic technology improvements surface soon. We assess aspects of CCS which are likely to prove interesting to investors and identify five sources of potentially disruptive innovations.

We all know the story by now: climate change is a global problem on an unprecedented scale. The big picture tells us that fossil fuel use continues to grow worldwide, notably in China. Even in Europe, the efforts to decarbonise electricity production are looking rather marginal compared to the size of the challenge. Carbon capture and storage technologies appear to cut to the heart of these issues. By capturing and sequestering the carbon dioxide (CO₂) in the flue gases of existing and new power stations, emerging economies can continue to nourish themselves on the coal and gas that fattened the Western world. Plus, by retrofitting the technology to existing European facilities, emissions cuts can be achieved much more rapidly than by relying on new renewables or the enigmatic goal of energy efficiency.

This story is compelling and many leading climate scientists have become convinced that ambitious emissions targets cannot be met without some deployment of CCS. A major reason is the unrelenting growth of coal use in Asia, which threatens to dwarf carbon reduction feats elsewhere if left unchecked. However, no site has yet integrated electricity production with carbon capture and storage.

The inescapable truth is that, in contrast to renewable energy technologies such as photovoltaics, it will never be cheaper to use fossil fuels with CCS than to use fossil fuels without CCS, regardless of the price of coal or oil. As a result, CCS will always be dependent on there being a cost to emitting greenhouse gases, the so-called ‘carbon price’ that is provided to a limited extent by the EU emissions trading scheme or the Norwegian carbon tax. If CO₂ were to be treated more like a priced commodity than a waste product, then the rationale for the big polluters to build a new industry around it becomes starkly apparent.

At a recent conference on CCS, Lord Oxburgh, Chair of the Carbon Capture and Storage Association, pointed out that if you add up all the CO₂ that could be captured in future it amounts to a trillion dollar global business. This places it alongside the current oil industry in scale. Therefore, those who succeed in developing effective technologies along this value chain stand to gain quite considerable prizes when the ‘winning’ technologies become adopted by some of the world’s biggest companies.

UK MEP Chris Davies is another who is convinced by the ‘painful necessity’ of CCS. He brokered a deal at the European Parliament that followed last year’s CCS Directive, and agreed a multi-billion Euro funding scheme for CCS demonstration in Europe. Since then, a further €1.05 billion has surfaced in the EU economic stimulus package and it is expected that the few pilot plants today will be translated into a small fleet of demonstrations in the next five to ten years.

The UK Chancellor, Alistair Darling, committed in the April Budget to a new funding mechanism to finance “at least two, and up to four, carbon capture and storage demonstration projects”. Other governments are also swinging behind CCS. Initiatives include the new Australian-led Global CCS institute, the 21 countries in the Carbon Sequestration Leadership Forum and America’s financial commitment in President Obama’s recovery plan.

What will all this money be spent on? And is it likely to achieve the substantial cost reductions that are considered necessary in the absence of a sudden surge in the carbon price?

CCS Fundamentals

CCS is really a collection of technologies rather than a single procedure. At each stage of the process there are several technical options, such as the choice of separating the CO₂ either before or after combustion of the fuel. Perfecting post-combustion capture would make it possible to retrofit existing power stations, whereas pre-combustion capture could increase the efficiency of the overall process. Similarly, the captured CO₂ could be stored on land near the combustion site if a suitable aquifer is nearby, or it could be piped to an offshore platform for injection into a disused oil or gas field. Capture could even be improved by using a high oxygen oxyfuel combustion method that reduces the challenges of separation - or the CO2 could be transported by ship rather than pipe.

In reality, each of these stages is challenging and is receiving research and industrial attention. If Europe’s CCS demonstration network is able to achieve the targeted twelve projects, then hopefully a range of technical permutations will be tested. This is great, but a review of the projects being promoted by the big oil companies, utilities and engineering firms engenders a nagging feeling that the current pace of progress is not going to deliver the long-term goals.

Challenges

Since the process of capturing CO₂ is energy intensive and is likely to reduce the efficiency of electricity generation by at least 10%, then an accompanying efficiency enhancement for post-combustion plants ought to be a priority. But the best coal combustion efficiencies are hovering around 47%, whilst eternal promises of breaking the 50% barrier share space alongside nuclear fusion on the far horizon.

Separating CO₂ from flue gases is another lingering problem for post-combustion approaches. Some assessments place the cost of capture at €25-30/tonne from a total CCS cost of €35-50/tonne. Three capture methods are presently known: membranes, compression, and amine scrubbing. Membranes suffer from clogging by impurities and poor temperature tolerance. Cryogenic compression involves liquefaction of gases and is consequently very energy intensive. Amine scrubbing is therefore being pursued by all the major projects. However, there is little global experience in this field, and amine scrubbing has a pollution problem of its own related to the losses of volatile solvents.

The final step in the CCS value chain is the monitoring of storage sites to ensure that the CO₂ is not escaping. The best way to perform long-term monitoring has not yet been resolved, but one of the few known methods involves seismic surveys. The cost of a seismic survey, however, is currently so expensive that each site may only be able to afford it every few years. With the level of acceptable public risk looming as a major unknown quantity, reliable and economical monitoring could affect the ultimate success of CCS.

These uncertainties do not indicate that CCS could not be demonstrated now. There is much evidence that EU-funded demonstrations can build on the knowledge already accumulated by StatoilHydro, BP, Vattenfall and others who are operating combustion, storage and CO₂ transport facilities. Rather, the concern is that, once these CCS permutations have been demonstrated at scale, they should be ready for deployment, yet investments currently rely on improving known technologies that might inherently limit the achievement of vital cost reductions.

The scale of the market, the amount of government support and the constraints in critical parts of the value chain suggest that breakthrough technologies in CCS could be very fertile spaces for cleantech investment. The dominance of utilities and oil majors has so far left little room for start-ups, but the scramble for demonstration project funding could change this picture. Early developments may be in favour of post-combustion capture, which is a more mature technology area with more familiar risks. This implies that the areas of efficiency gains and CO₂ capture could be potentially both interesting and rewarding for challengers to break into. We review five emerging technologies in these areas – and in the monitoring area – in the following section.

Better Coal Combustion

1. Coal Direct Chemical Looping
New ‘super alloys’ are being tested to endure temperatures of 700°C. E.ON hopes to begin construction of the world’s first >50% efficiency coal power station next year, but the cost could run to €2,000 per kW. Post-combustion capture of 90% of the CO₂ could reduce this efficiency to as low as 40%, or even less. An alternative is chemical looping combustion (CLC), which uses a metal oxide during the combustion process to deliver a gas stream that is just water and CO₂. To remove the CO₂, all that is required is condensation of the water. Developed in the 1950s to obtain carbon dioxide for soft drinks, when this process is applied to coal conversion a high temperature gasification step is generally required, similar to that which makes pre-combustion capture costly.

Coal direct chemical looping (CDCL) has been developed at the Ohio State University and patents are currently pending. It avoids the initial gasification step by using iron oxide (a recyclable oxidising agent) to reform pulverised coal into two gaseous streams. One stream is relatively pure hydrogen, which provides a fuel for electricity generation, and the other is a mixture of CO₂ and water vapour:  the separated CO₂ can be compressed for storage following recovery of the water.

Prof. L.-S. Fan believes that efficiencies of greater than 50% are possible in combination with the existing turbine system. “Achieving such a high efficiency will require a demonstration plant greater than 5MW, but we think such a demonstration plant can be constructed within five years provided that the ongoing work at 25kW proves successful,” he says. “Since at least 97% of the CO₂ in coal is captured in the fuel reactor at low cost, we see CDCL as one of the most promising coal conversion technologies for CCS.”

CO₂ Capture

2. Enzymes for Capture
Denmark-based biotech firm Novozymes has recently released some findings on a new direction for post-combustion capture that could overcome some of the problems associated with amine scrubbing. The Novozymes team knew that carbonic anhydrase enzymes are used in nature to absorb and desorb carbon dioxide and they recognised the potential to apply this to carbon capture. Their experiments indicate that by using the enzyme to selectively convert CO₂ to soluble bicarbonate, thus extracting it from the flue gases, the efficiency of amine scrubbing could be significantly increased.

“We are always looking at ways to use biotechnology to improve environmental performance,” says Per Falholt, Executive Vice President for R&D. “There is increasing pressure to use carbon sustainably and we had an idea about what kinds of enzymes to look at.” He is quick to stress that the work is running at only a very small scale in the lab so far, but the initial results are promising. Enzymes appear to enhance the effectiveness of systems with, or without, amine-based absorbers, reaching efficiencies of over 90%.

“We don’t have proof of concept yet, but we are starting to find out if it makes sense to scale up to pilot-scale,” explains Mr Falholt. From experience he is aware that the cost of enzymes can be a limiting factor in the early stages of demonstration; it can take a couple of years to get the enzymes right, and Novozymes has begun working with other companies and universities on these challenges. However, Mr Falholt is optimistic that this represents an exciting and unforeseen development for capture technologies, and that the use of amines could be avoided in the future. “We don’t know if it is possible, but we have found that the more you base yourself on pure enzyme systems the better it is, environmentally and economically,” he says.

3. Physical Separation
Another development seemingly under the radar of the major players is the separation of CO₂ using physical rather than chemical or biological methods. Based on work for the removal of CO₂ from contaminated gas reserves, it has emerged that centrifugal separation and condensation of gases could be applied to carbon capture. Technically, the process involves cooling gases by expansion so that CO₂ condenses to micron-sized droplets that can be removed by using a ‘rotating particle separator’.

Although researchers at Eindhoven University have mainly worked in collaboration with Shell on methane purification, application to flue gas purification has also been considered. “It’s very exciting,” Prof. Brouwers says. “We are now preparing scale-up in the area of contaminated gas, but shortly after we will develop it for clean coal.” Because the particle separator can be easily scaled and is efficient for different types of separation, it could be used for pre-combustion (removal of CO₂ from H₂ fuel) or post-combustion capture (extraction of CO₂ from flue gases).

As Prof. Brouwers explains, “the big advantage is the ability to play with the concentration of CO₂ in the exhaust. We need it to be high enough to form droplets, but not as high as the 100% demanded by oxyfuel plants; this means we could even use the same method to separate oxygen from air and thus enhance the combustion step. We are experimenting and think it could be a very cheap method of separating carbon dioxide.”

4. Ionic Liquids
University of Colorado researchers have taken a different approach. Spun-off from the Department of Chemical and Biological Engineering in 2008, ION Engineering is the first company established to develop ionic liquids for CO₂ capture. The ability of tailored ionic liquids (ILs), or ‘molten salts’, to selectively absorb gases has been known for over ten years, but effective salvation of CO₂ with pure ILs has proved elusive. Now, with the acceptance that volatile by-products present a persistent hazard to the use of water-based amine solvents, the fact that ILs do not evaporate has made their use in combination with amines an interesting commercial prospect.

“Without water you could obviate the need for stainless steel and you are not losing latent heat, as well as avoiding volatile emissions,” says ION Engineering CEO Alfred ‘Buz’ Brown. “It’s very encouraging and the results suggest that a capture cost of €15-19/tonne is where we’re going to be.” Although ILs can be expensive to produce, ION’s tests show benefits from higher loading rates, lower circulation rates and the ability to recycle the solvent. Like Eindhoven’s work on physical separation, ION is looking at both contaminate gas clean-up and CCS. “On the power plant side we’ve got discussions with utilities that may be willing to fund the four to six pilots we’re aiming for in the coming year,” says Dr Brown.

Although amine scrubbers continue to be used as the standard against which new ideas are optimised, larger-scale testing of these exciting new capture technologies means that this may not be the case for much longer.

Monitoring

5. Satellite Imaging
For four years BP has been assessing monitoring techniques in the Algerian Desert. At its In Salah Gas development the CO₂ associated with the gas is being re-injected back underground and some valuable studies of onshore carbon storage are being undertaken. At the beginning of the project BP identified 20 possible techniques for monitoring the behaviour of sequestered CO₂. A method that has surpassed its expectations is satellite imaging, or more specifically, Interferometric Synthetic Aperture Radar (InSAR).

Using passing satellites to emit and receive reflected electromagnetic radiation, ground movements can be surveyed to an accuracy of 2mm. This means that movements in the surface caused by changes in pressure due to CO₂ leakage could potentially be picked up by regular surveys at a frequency that would be extremely expensive using 3D seismic technology. Improvements are still required; for instance, to understand the causal links between carbon storage and land subsidence. However, as InSAR is a rapidly growing area of academic work on topics such as groundwater monitoring, there may be opportunities for entrepreneurial researchers and start-ups to seize some of the value in the unavoidable long-term monitoring of storage sites.

Simon Bennett is a researcher in the Centre for Energy Policy and Technology (ICEPT) at Imperial College London.