Carbon sequestration is gaining ground as a way to reduce greenhouse gases on a large scale.
Photo: ©istockphoto.com/Dominik Dabrowski

It is widely accepted that increasing amounts of greenhouse gases emitted into the atmosphere are trapping the sun’s heat and that human activity is responsible for the phenomenon. But what if the solution lies underground? That is the idea behind carbon capture and storage (CCS) — capturing carbon dioxide (CO₂) produced by large emissions sources such as power plants and other industries and storing it underground before it is emitted into the atmosphere. The concept is gaining ground in Canada and has become the leading way to mitigate greenhouse gases from fossil fuel industries.

The main culprit is CO₂, the largest human-induced contributor of greenhouse gases, according to a 2005 report by the Intergovernmental Panel on Climate Change (IPCC) entitled Carbon Dioxide Capture and Storage. According to the exhaustive document, CCS could help reduce the cost of mitigating climate change when implemented as part of a variety of energy options. 

For years, Natural Resources Canada’s CanmetENERGY has been partnering with industry and academia to develop CCS technologies. Researchers at CanmetENERGY are at the forefront of CCS development and they have been working on a number of pilot projects with domestic and international partners.

Natural Resources Canada’s CanmetENERGY has been at the forefront of CCS research and development, and has been working on a number of pilot projects with domestic and international partners.

CCS involves a suite of technologies, from capturing the CO₂ and transporting it, to injecting it deep underground. It is not just a concept; CCS is actually happening in Canada. The oil fields near Weyburn and Midale, Saskatchewan, for example, are the site of the largest CO₂ storage operations in the world. In this project, CO₂ is captured from a coal-based (synfuels) plant in Beulah, North Dakota, then compressed and carried through more than 300 kilometres of pipeline to the oil fields at Weyburn-Midale. The energy companies that operate these oil fields, Cenovus and Apache Canada, are extending the productive life of their depleting oil reservoirs by injecting CO₂ to boost production. Nearly three million tonnes of CO₂ are injected and stored annually as part of these operations; since 2000, some 17 million tonnes have been safely stored.

In addition to being a successful commercial operation, Weyburn-Midale is also the site of the world’s first CO₂ measuring, monitoring and verification project – the International Energy Agency’s Weyburn-Midale CO₂ Monitoring and Storage Project. This ambitious project is undertaken by a partnership of domestic and global players in CCS from academia, industry and government (including Natural Resources Canada, Alberta and Saskatchewan). It provides an unparalleled learning opportunity to track the behaviour of the injected CO₂ over time, determine its fate, and assess the security of storing CO₂.

The IEA considers Weyburn-Midale crucial to the advancement of CCS because of the ongoing monitoring and comprehensive scientific analysis of the behaviour of CO₂ stored in geological formations. A best practices manual will be developed for carbon injection and storage as part of the final phase of the research.

Acid gas injection, employed since the 1980s, is another example of CCS in action. The technology involves putting acid gas — a waste stream of CO₂ and hydrogen sulphide produced by natural gas processing plants — back into geological formations. Acid gas injection is in operation in Alberta and British Columbia, storing up to one million tonnes of CO₂ annually. It could be a useful source for furthering CCS knowledge as it is used commercially and comes with a built-in regulation model as a result of its use by the natural gas industry.

Capture is the most complicated and costly piece of the puzzle. A CanmetENERGY publication, Canada’s CO₂ Capture and Storage Technology Roadmap, identifies capture as the most expensive of the CCS components, but one that “also has the greatest potential for future cost reductions, which may range from 25 to 30 percent by 2025.

For CCS to be effective and attainable, CO₂ capture needs to be demonstrated on a large scale. That means the prime candidates for capturing CO₂ are large emitters such as power plants, refineries and the cement and petrochemical industries. There are currently three main methods of capture, and the technology behind these processes has been tested to varying degrees.

Pre-combustion, as the name implies, takes place before the burning of fossil fuels. It is a technique by which coal or other hydrocarbons are gasified (instead of combusted) to produce a synthetic gas made up of hydrogen and carbon monoxide. This gas mixture is then treated in a shift converter that converts the carbon monoxide to CO₂, and a physical solvent is used to separate the CO₂ so it can be stored. The technology behind pre-combustion is already being used in fertiliser manufacturing and as part of the hydrogen production process.

Pre-combustion, as the name implies, takes place before the burning of fossil fuels. It is a technique by which coal is gasified (instead of combusted) to produce a synthetic gas made up of hydrogen and carbon monoxide. This gas mixture is then treated in a shift converter that converts the carbon monoxide to CO₂, and a physical solvent is used to separate the CO₂ so it can be stored. The technology behind pre-combustion is already being used in fertilizer manufacturing and as part of the hydrogen production process.

Post-combustion involves separating CO₂ from the gas produced after the burning of fossil fuels or biomass. A similar technology has been employed by the natural gas industry for some time to remove CO₂ from natural gas. According to the IEA, post-combustion “is a commercially available, mature technology used at hundreds of locations around the world.” In this approach, the most widely used of the capture technologies, chemical solvents are used to remove the CO₂ from the gas stream. They are then heated to release the CO₂ as a pure product that can be stored in geological formations without further treatment/processing.

Oxyfuel carbon capture is an alternative and more complex method that involves the combustion of coal in an oxygen-enriched environment, resulting in a highly concentrated stream of CO₂. The advantages are twofold: the high concentration of CO₂ can be more easily captured and stored, and no nitrous oxide is produced because of the pure oxygen environment.