Carbon capture and storage technologies: Where do we stand?

by Nils A. Roekke and Ola Maurstad

30-03-06

In a Norwegian context, gas-fired power plants with carbon capture and storage can help reduce our greenhouse gas emissions, improve the energy balance, and potentially supply environmentally friendly electricity to Europe and electrify the continental shelf. Internationally, the same technology has a great potential application in coal-fired power plants.
How far have we come today when it comes to capturing and storing CO2?

Perhaps nowhere else in the world does carbon capture and storage (CCS) rank higher on the political agenda than in Norway. Modern gas-fired power plants that emit CO2 are referred to in Norway as old-fashioned technology, even though they represent the cutting edge in high technology. Although such power plants will help reduce emissions in many countries, Norway uses mostly hydropower, so gas-fired power will actually increase greenhouse gas emissions.
 

The government’s Soria Moria Declaration appears to resolve the gas-power debate by declaring the government’s intent to support gas-fired power that uses CCS technology. For the research community that the Gas Technology Centre at NTNU-SINTEF represents, it is exciting to study technology that can help Norway meet its Kyoto targets through action -- and not just through emissions trading. In the shorter term, the capture of CO2 can be used in enhanced oil recovery (EOR) and improve profitability. In the longer term, we envision a storage solution in geological structures under the seabed.

The growth in global energy consumption has mainly been met through increased consumption of fossil fuels, such as coal, oil, and natural gas. Burning fossil fuels causes the carbon in the fuel to react with oxygen from the air, creating CO2 and releasing heat that can be used as energy.
Technologies for CO2 capture and storage are a fascinating solution because they allow the continued use of fossil energy, but with highly reduced emissions. Typically, 80-90 % of the CO2 can be captured in this way. This technology can play a key role on the road to more sustainable energy systems and should be seen in connection with reducing energy demand, increasing energy efficiency, and increasing production of renewable energy.

Areas of application
It is easiest to use the technology on major point sources of emissions from combustion of coal, oil, and natural gas, as well as biomass. As a point of interest, it is worth mentioning that biomass is “CO2 neutral” if its removal is compensated by new growth. Applying CCS technology in addition will then actually result in a net removal of CO2 from the atmosphere (negative emissions).
Internationally, however, research is focused mainly on coal-fired power plants, while in Norway it is focused on gas-fired power plants -- which can probably be explained by looking at the resources in the different countries. Although energy production represents a greater potential for emissions reductions, emissions from various industrial processes such as cement production represent “low-hanging fruit” (low costs) for CCS. Here, process flows with high concentrations of CO2 often represent opportunities for relatively simple and inexpensive CO2 capture.

Why hasn’t the technology been realized?
Despite considerable attention and the introduction of many new technological solutions, no power plants with CCS of any reasonable size have been realized so far. This is true for both gas-fired power plants and coal-fired power plants, both in Norway and throughout the rest of the world.
If technological solutions based on commercially available components are available, why aren’t the power plants being constructed? The main reason is the cost and the associated financial risk. Capturing CO2 requires significant investment. For a gas-fired power plant that produces 400 MW of electricity, a carbon capture system for waste gas would double the investment costs. Moreover, capture and compression of CO2 for transport requires an increased use of natural gas, thus increasing the fuel costs per produced kWh el (kilowatt hour of electricity).

Transporting CO2 from the power plant to a storage area or EOR application requires an infrastructure, such as pipelines. Several numbers have been tossed around among various actors with respect to the costs of CCS.
As we do not yet have experience from a realized large-scale facility, all of these are associated with uncertainty. This is illustrated in the recent report “Carbon dioxide capture and storage,” where the IPCC estimates a cost in the area of $ 20-70 per ton CO2 emissions that are prevented.

Where does the technology stand today?
CCS technology for gas-fired and coal-fired power plants is divided into three main categories: a) post-combustion, b) pre-combustion, and c) oxy-fuel.
Post-combustion means that CO2 is captured in an exhaust-scrubbing system after combustion (end-of-pipe solution). This technology is the most technologically mature, and can in principle be attached toa power plant without being tightly integrated into the power plant.
Pre-combustion technology converts natural gas or coal to a hydrogen-rich gas while capturing CO2 at the same time. This hydrogen-rich gas is used afterwards as a fuel in a gas-fired power plant so that the exhaust contains very little CO2. This technology is considered somewhat more complex but also mature, with commercially available components.

Internationally, there is a lot of focus on integrated gasification combined cycle (IGCC) as an environmentally friendly way to exploit coal, and there are several pilot facilities. Here, coal is gassified to a hydrogen-rich mixture that is burned in a gas-fired power plant where CO2 can potentially be removed from the fuel flow so that the exhaust contains very little CO2.
With the technology oxy-fuel, the combustion takes place with pure oxygen instead of air (which mixes in large amounts of nitrogen and complicates the capture of CO2 from the waste gas) so that the exhaust contains only water vapour and CO2, which is both inexpensive and can easily be separated by cooling. However, oxygen production demands an expensive and energy-intensive air-separation facility.

The oxy-fuel technology is more mature for coal than for natural gas. This is because combustion of coal can take place in a boiler, while the necessary modifications that have to be made in today’s gas turbines to accept the new fuel mix will result in unacceptably poor performance.
Because it is an expensive process that can take a number of years, gas turbine producers must be convinced that a considerable market exists before they invest. A number of other power plant concepts with CCS that do no fit squarely into these three categories are also being worked on. Many of these new concepts include membranes and fuel cells, which will require a break-through in material technology.

In the United States, CO2 from natural sources is being re-injected into the ground for EOR on a commercial basis. They also have experience with transporting CO2 in pipelines. Shipping of liquid CO2 is also possible.
When it comes to storage, the Norwegian Sleipner project is the world’s first and largest. Here, CO2 is separated from a well flow with natural gas (because buyers in Europe do not want too much CO2 in the natural gas they purchase) and is injected into the saline aquifers under the ocean floor.

Importance of efficiency
The efficiency of a gas-fired power plant is a measurement of how effectively the energy in the natural gas is utilized. It is defined as produced electric power delivered to the grid divided by the natural gas’s lower calorific value (a measure of the chemical energy in natural gas).
The efficiency determines the consumption of natural gas and how much CO2 is formed per kWh electricity produced. Increased efficiency means lower consumption of natural gas, less formation of CO2 (less must be captured), and usually also lower emissions of NOx and other polluting gases. As a rule, increased investment should result in greater efficiency; however, energy producers do not wish to maximize efficiency, but rather to minimize production costs of electricity. High gas prices and increased quota process for CO2 are, however, factors that will give added incentive for greater efficiency.

Further research does not restrict action
As already mentioned, additional investment is required to implement CCS. An additional feature of today’s technology is a reduction in the efficiency (of about 10 percentage points). This corresponds to an increased fuel consumption of over 20 %. There is thus good reason to seek improvements for the sake of both costs and resources.
Further investment in research should nevertheless not hinder the possibilities we see already with the use of current technology. On the plus side, it is possible for Norway to re-inject the CO2 for EOR in the North Sea. This can generate considerable value. Likewise, for every ton of CO2 we remove, we save about EUR 20-25 in quota costs.

In total, CCS can turn out to be a good and future-oriented solution that can be profitable for Norway. It is more future-oriented of us to implement the entire CO2 chain in Norway than to buy quotas. This implies increased Norwegian value added because we ourselves further refine our natural gas into environmentally friendly energy that can be sold abroad.
It is unlikely Norway would profit from selling lumber as much as it would by turning that same lumber into paper? The same applies to natural gas. However, we will emphasize that some strategic steps must be taken to realize CCS. Someone has to take the risk in the value chain and start up, and the only natural actor that can do this in a market-oriented economy is the state.

Source: Cicero Senter for Klimaforskning