The Otway Project in Victoria has demonstrated CO2 can be stored safely underground in Australia The Callide Oxyfuel Project in Queensland is the largest demonstration of oxyfuel technology in the world to date The IEA says CCS is a critical component in the portfolio of low-carbon technologies combating climate change The IEA expects CCS to contribute 14% of global emissions reduction by 2050 The Intergovernmental Panel on Climate Change says without CCS, the cost of reducing emissions to 2100 increases 138% Canada’s Boundary Dam – the first large scale CCS project in the power sector – began operation in October 2014 Since 1986, the Sleipner Project has been storing a million tonnes of CO2 per year in the North Sea

Carbon capture and storage


What is CCS?
What is carbon capture?
Transport of CO2
Storage and monitoring of CO2

What is CCS?

When fossil fuels such as coal, oil and natural gas are combusted they emit carbon dioxide (CO2).

To prevent this CO2 from entering the atmosphere and contributing to climate change, the CO2 can be captured at the power station or at the steel, LNG, cement or other industrial facility. The captured CO2 can then be stored safely and permanently in deep underground geological structures, or by other physical, chemical or biological means.  While all users of fossil fuels emit CO2, it is not presently feasible to capture CO2 from mobile sources such as cars, trucks and aeroplanes, and therefore it is expected that large stationary sources of CO2 emissions will be the focus for carbon capture.

Carbon capture and storage (CCS) is not a new technology. It is a proven suite of technologies. The process can be broken down into three separate parts:

  • First, capture: CO2 emissions are separated (‘captured’) from the stream of gases released from the combustion of fossil fuels.
  • Second, transport: the separated CO2 is compressed to a liquid-like state so that it can be transported, via pipeline, rail, ship or truck, to a suitable underground geological structure.
  • Third, storage: the compressed CO2 is injected deep underground where it will remain, safely, permanently, and well-monitored, in a process known as geosequestration.

CCS is already a reality in many parts of the world.  CO2 capture technologies are commercially available; there is a lot of experience to draw on concerning transporting CO2; and geological storage of CO2 is also well-established.  For example, oil and gas sector projects such as Sleipner (Norway) and Weyburn-Midale (Canada) have been injecting into depleted oil and gas wells since 1996 and 2000 respectively.


Image courtesy of the Cooperative Research Centre for Greenhouse Gas Technologies, http://www.co2crc.com.au
 

The three individual parts have been demonstrated by the oil and gas industry for decades. The challenge is combining these three parts to form a ‘fully integrated’ system that can be applied on a commercial scale to emission sources like the thousands of fossil-fuel power plants around the world. Built into new power stations or bolted on to existing ones, the potential for reducing greenhouse gas emissions is significant.

There is no single technology available today that will enable global greenhouse gas emissions from energy production to be stabilised and reduced. A portfolio of technologies will be required and CCS will make up a vital component of this portfolio.

As the International Energy Agency points out:

Given the past and current trends in fossil fuel use and the related CO2 emissions, the urgency of CCS deployment is only increasing. This decade is critical for moving CCS through and beyond the demonstration phase. This means that urgent action is required, beginning now, from industry and governments to develop technology and the required business models, and to implement incentive frameworks that can help drive CCS deployment in the power sector and industrial applications. (IEA Insights Series, CCS 2014: what lies in store for CCS? page 5)

What is carbon capture?

When coal, oil and natural gas are burned, they emit carbon dioxide (CO2). To stop this CO2 from entering the atmosphere and contributing to climate change, the CO2 can be captured at a power station or at a steel, LNG, cement or other industrial facility. The captured CO2 can then be stored safely and permanently in deep underground geological structures, or by other physical, chemical or biological means.

Carbon capture and storage is not a new technology and has been widely used across the world as a means of capturing and storing CO2. As a proven technology it has a wide application of use.

How it works:

  • CO2 emissions are separated from the stream of gases released from the combustion of fossil fuels.
  • The separated CO2 is compressed to a liquid-like state so that it can be transported, via pipeline or truck, to a suitable underground geological structure.
  • The compressed CO2 is injected deep underground where it will remain, safely, permanently, and well-monitored, in a process known as geosequestration.

These steps have been successfully demonstrated by the oil and gas industry for decades. The challenge is to apply these three steps to create a fully integrated system that can be applied to coal-fired power stations across Australia and the world. By including carbon capture in the construction of new coal-fired power stations or attaching it to existing power stations there is potential for significant reduction in greenhouse gas emissions.

Along with developments in renewable and sustainable energy technologies, the inclusion of CCS in the energy mix gives the greatest opportunity to reduce greenhouse gas emissions and reduce the consequences of climate change.

The International Energy Agency (IEA) estimates that CCS could account for almost 20% of emission reductions needed by 2050 to stabilise atmospheric CO2 at 450 ppm (parts per million). Reaching this goal will require significant commitment – financially, politically and physically – if this goal is to be realised.

The three major methods of capturing CO2 produced through the burning of fossil fuels for electricity generation are:

  • Pre-combustion - the fuel is first processed in a way that allows CO2 to be removed prior to combustion, leaving a combustible gas that is predominantly hydrogen, which is then burnt to create electricity.
  • Post-combustion - the fuel is burnt in the normal way but with a process added to remove CO2 from the flue gases leaving the combustion process.
  • Oxyfuel combustion capture - the fuel is burnt in a mixture of pure oxygen and recycled flue gas rather than air, resulting in flue gases that are predominantly CO2 which can be captured for geological storage with very little additional processing.

All three of these methods are at similar levels of technical development for application to coal fired power stations, although post and pre combustion are used in other industry sectors.

Development of the three processes is ongoing as they provide different opportunities for reducing greenhouse gas emissions from power generation.

Pre-combustion capture

In a conventional coal-fired power plant, coal is burnt directly to provide the energy for electricity generation and CO2 is released as a by-product. Some CCS technologies aim to capture this CO2 after the fuel is combusted. Pre-combustion capture differs because it removes CO2 before combustion.

Coal is made up primarily of carbon and hydrogen. Using a process called Integrated Gasification Combined Cycle (IGCC) technology, the carbon can be removed. This is accomplished not by burning, but by reacting the coal with air or oxygen to produce a synthetic gas that consists of hydrogen, CO2 and carbon monoxide. The hydrogen gas is then separated. Combusting hydrogen produces only water vapour as a by-product. The carbon monoxide is further reacted to form more CO2 and hydrogen. The CO2 is removed (captured) and is ready for transport and geological storage. The technology is capable of removing 90% of the CO2 emissions generated from coal.


Image courtesy of the Cooperative Research Centre for Greenhouse Gas Technologies, http://www.co2crc.com.au

Post-combustion capture

Provided by Global CCS Institute

Post-combustion CO2 capture involves separating CO2 from the gas stream produced after coal or other fossil fuels are burnt (combusted) for electricity. With many examples of the technology already in use, it’s the most developed capture process, capable of removing up to 90% of emitted CO2.

The most commonly used process for post-combustion CO2 capture is made possible by liquid chemicals called amines. A CO2-rich gas stream, such as a power plant’s flue gas, is bubbled through an amine solution. The amines bind to the CO2 as it passes through the solution but allow the other gases to pass through unimpeded.

The CO2-saturated amine solution is then removed and heated to release the captured CO2, which is then ready for transport and carbon storage. The amines themselves can be recycled and re-used.


Image courtesy of the Cooperative Research Centre for Greenhouse Gas Technologies, http://www.co2crc.com.au

The main challenge facing post-combustion technology development is improving its cost and efficiency.

One of its key advantages is that it is well suited to retrofitting (“bolted on”) to existing plants and so is a suitable technology to apply to the thousands of coal-fired power plants across the world, as well as other industrial sources.

The capture of CO2 by this method is being applied or explored for different processes, including:

  • Absorption (chemical/physical solvent scrubbing)
  • Monoethanolamines (MEA)
  • Advanced amines, including KS® solvents or Fluor Econamine Plus
  • Chilled ammonia
  • Aqueous ammonia adsorption; cryogenic separation; and gas separation membranes.

For PCC, solvent scrubbing is currently regarded as the state-of-the-art process, while solid adsorbents and membrane-based processes are regarded as second or even third generation technologies. That being said, there is still extensive effort being applied to improving the solvent scrubbing process, to improve its CO2 capture performance and drive down costs.

Post-combustion capture can be attractive to existing power generating and industrial facilities as it can be retrofitted to the existing operation easily relative to the other CO2 capture technologies. Post-combustion capture can technically be applied to a range of facilities, including:

  • Natural gas processing
  • Chemical and fertiliser production
  • Coal and gas-fired power plants
  • Cement kilns and
  • Iron and steel production.

Oxyfuel combustion

Provided by Global CCS Institute

With oxyfuel combustion fossil fuels are burnt in pure oxygen instead of normal air. Virtually all the gas that’s emitted is composed of CO2 and water vapour. The vapour is condensed out and the CO2 is then captured.

Conventional boilers combust coal in air, which consists of 78% nitrogen, 21% oxygen, and trace gases including CO2. This results in a flue gas stream that’s rich in nitrogen and dilute in CO2, (around 12 - 15%) making CO2 capture more challenging. By removing the nitrogen first and combusting the coal in nearly pure oxygen, it produces a much more concentrated stream of CO2 (around 90%), which allows for much easier CO2 capture.

Oxyfuel combustion with CO2 storage is currently in demonstration phase.

In 2008, the world’s first pilot project to demonstrate oxyfuel technology at a coal-fired power plant commenced. The Schwarze Pumpe project in western Germany is owned by the European energy company, Vattenfall, and it successfully demonstrated the capture of CO2 emissions with a purity of over 99%.

In Biloela, Queensland, a low-emissions oxyfuel demonstration project has been established at the Callide Power Station and has been operating for two years. Oxyfuel combustion capture applies a new technology to conventional power plant boilers to capture CO2 emissions. This has the advantage in that it can be retrofitted to the thousands of power plants already in operation around the world, as well as being applied to new power plants. It has the potential to be one of the most cost-effective methods of capturing CO2 emissions from coal-fired power plants. Research is being carried out to reduce costs and improve efficiency.

Transport of CO2

Once carbon has been captured there are four methods of transporting the CO2 to storage locations: pipelines, rail, ship and truck. Depending on where the CO2 has been captured and its intended storage location, a mix of some or all of the transportation methods could be used.

Pipelines

The oldest CO2 pipeline is the 16 inch Canyon Reef Carriers (CRC) CO2 pipeline in West Texas, which has been in operation since 1972. The pipeline is owned by Kinder Morgan and transports CO2 approximately 225 kilometres from gas processing facilities to Kinder Morgan’s Scurry Area Canyon Reef Operators (SACROC) oilfield.

In the United States of America more than 6,000 kilometres of pipeline have been laid specifically to transport CO2.

The first offshore CO2 pipeline built was in Snøhvit, a natural gas field, which transports 0.7 Mtpa CO2 a distance of 160 km to the Barents Sea, off Norway. It has been in operation since late 2007.

In Victoria, the CO2CRC Otway project (the world’s largest research and geosequestration demonstration project) 2.25 kilometres of pipeline have been installed between December 2007 and January 2008, to carry captured CO2 to a depleted gas reservoir. More than 65,000 tonnes of CO2 has been stored.

Like pipelines that carry natural gas, important considerations must be taken into account including access and right of way, community involvement and funding for infrastructure. Image: Pipeline testing at Otway. Courtesy of CO2CRC

Trucks

The transportation of gases such as oxygen, nitrogen and CO2 by truck is already a very common practice around the world. The liquid CO2 is kept at minus 30°C and is very stable. CO2 is non-toxic and is not a regulated waste. As CO2 is used in beer, soft drinks and in many food products, it is already transported regularly across Australia.

Liquefied CO2 can be carried in tanks on trucks which have been specially adapted to transport CO2 through the use of cryogenic vessels.

Ships

The transportation of CO2 by ship is already a common practice in Europe with four pressurised CO2 carriers transporting CO2 for use in food products. Depending on the final destination of the CO2, transport of CO2 by ship provides flexibility in changing capture sites, transport routes and storage sites.

Rail

Railroad transport of CO2 is a viable option if the existing infrastructure links the capture plant with the storage destination. It becomes economically viable if there are large amounts of CO2 being transported.

Storage and monitoring of CO2

Storage

Provided by Global CCS Institute

Geological storage or geosequestration is a key technology in CCS and offers the greatest potential for the permanent removal of CO2. It involves safely storing captured, liquefied, and transported CO2 deep underground.

Geological storage of CO2 requires certain characteristics of the rocks. The rocks need to have both sufficient porosity and permeability. The porosity determines the total CO2 that could be stored in the rocks while the permeability is a measure of how well the pores within these rocks are connected allowing the CO2 to flow through the rock. This rock formation needs to be overlain with a reservoir seal, which is basically a rock with very low permeability so that CO2 will not flow through it.

A common misconception is that these storage sites are like vast caves or caverns underground. In fact, they consist of tiny pores within the rock, which act like a sponge to house the liquefied CO2. These tiny pores add up to a huge volume, with the capacity to store millions of tonnes of CO2. They are overlain by a non-porous ‘cap’ rock that prevents the CO2 from escaping.

There are a number of geological storage options for CO2 including saline water saturate rocks and depleted oil and gas fields.

Saline water saturated rocks

These are underground formations of deep porous sedimentary rock, such as sandstone, that are saturated with salty water which is unfit for human consumption or agricultural use, and covered by a layer of impermeable cap rock (such as shale or clay), which acts as a seal. Once injected into the formation, the CO2 dissolves into the saline water in the reservoir rock.

CO2 storage in deep saline formations usually takes place at depths below 800m. At this depth, the CO2 will be at high enough pressures to remain in a liquid-like state.

Saline formations have the largest storage potential globally and a number of CO2 storage demonstration projects are proving their effectiveness to maximise storage capacity and containment.

In many ways, the saline formations are similar to oil and gas reservoirs except that they contain saline water instead of hydrocarbons.  Nature has captured and contained oil and gas in rock formations for centuries and scientists are learning from nature to do the same with CO2.

Saline aquifers have been demonstrated as a storage option in the Sleipner, In-Salah and Snøhvit projects that each store approximately 1 Mtpa CO2. The Cooperative Research Centre for Greenhouse Gas Technologies (CO2CRC) is testing injection in a saline formation in Victoria and testing the associated monitoring technologies.

Oil and gas systems

The second main type of geological storage is depleted oil and gas fields. These have a proven ability to store hydrocarbons over millions of years, demonstrating very good reservoir characteristics. CO2 injection is already widely used in the oil industry for Enhanced Oil Recovery (EOR) from mature oilfields. The CO2 makes the oil easier to produce and is used in tertiary oil recovery for heavier oils. CO2 is used in EOR projects in North America, for example the Weyburn project in Canada and the Salt Creek project in Wyoming.

The CO2CRC Otway project has injected and stored more than 65,000 tonnes of CO2 in a depleted gas reservoir deep underground and further injections into different formations are being planned. This makes it the world’s largest research and geosequestration demonstration project. Otway includes a comprehensive monitoring program.

Other storage projects

In Australia, numerous studies have been completed to identify potential geological storage sites. These have been high level based on existing data. Atlases for geological storage have been produced for Queensland, New South Wales and Victoria. However, much more detailed data is required to understand the geological storage potential and opportunities in Australia.

The COAL21 fund is supporting a number of projects that aim to provide a better understanding of the geological potential.

Monitoring

The geosequestration process does not end when the CO2 is successfully stored underground. Sites are carefully monitored, both during and long after the CO2 is injected underground. Technologies and protocols for monitoring and verification that were originally developed by the oil, gas and waste storage industries are being used to track the CO2 migration within porous rock formations and ensure that the injected CO2 remains trapped in their reservoirs.

Current CO2 storage projects such as the CO2CRC Otway project in Australia are developing and demonstrating sophisticated monitoring and verification techniques to confirm the safety and effectiveness of CO2 storage, and understand how the CO2 behaves in the storage site.

In an article in the Proceedings of the National Academy of Sciences in the United States of America, a study of the monitoring procedures for the sequestration of CO2 at the Otway site in Victoria concluded that “Quantitative verification of long-term storage has been demonstrated. A direct measurement of storage efficiency has been made, confirming that CO2 storage in depleted gas fields can be safe and effective, and that these structures could store globally significant amounts of CO2.”

To read a full copy of the report click here.