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By Janice McMahon

Carbon sequestration and related projects have become “hot button” topics in Board rooms around the world as corporations large and small grapple with the potential positive and negative impacts of emission reductions. Before any decisions can be made about if, how, or why your company should endeavor to improve its carbon footprint, enter the carbon market, or undertake carbon sequestration projects, it is important to understand the very basics of carbon sequestration.

Sequestration means removal or separation; banishment or exile. Many researchers consider Carbon Dioxide (CO2) to be a greenhouse gas that contributes to global warming. While there is much debate over this issue and the science surrounding it, popular opinion supports the theory that capturing human-produced CO2 emissions is a step towards reducing the effects of global warming. Carbon Sequestration then is the process (natural or artificial) of converting CO2 to a storable form of carbon (C). That’s a pretty straightforward definition, but the processes by which carbon is captured and stored are just a little bit more complicated though easily understandable in theory.

Let’s start with the two primary ways that carbon is captured; indirect and direct.

Indirect Carbon Sequestration

Indirect carbon sequestration (terrestrial sequestration) is part of the natural carbon cycle where plants “breathe” in carbon dioxide (CO2) from the air. CO2 is the gaseous form of carbon bound with two oxygen atoms. The plants convert the CO2 to Carbon (C) which they need to grow and “exhale” oxygen. In this process some of the Carbon is stored in the plant itself and some is passed into the surrounding soils through the root system and via the decay of plant material.

Examples of indirect sequestration activities include:

Afforestation Projects

Soil carbon accumulation is generally thought to best occur on afforestation sites that have been planted with trees after 10 or more years of non-forest usage. Evidence suggests that most soil carbon accumulation occurs in the upper 12 inches of the soil profile and occurs at varying rates depending on soil type and plant species. Take for example the comparison of a southern Oak-Hickory forest to a Northeastern Maple-Beech-Birch forest.ESI Carbon

The amount of carbon sequestered in both the plant matter and the soil is significantly different in these examples due to the soils, the trees, and the growing seasons. However, in both cases additionality is created through the planting of new forests and long-term agreements to manage the forests sustainably.

Sustainably Managed Forest Projects

Sustainably managed forest projects seek to increase the efficiency of timber production, site reclamation, and carbon sequestration. By specifically choosing the species of trees planted based on the soil profile and actively managing the growth and harvesting of timber, optimal growth rates and subsequently optimal carbon sequestration and timber harvest are achieved. One acre of sustainably managed southern pine forest has the potential to sequester one to four tons of carbon per year. This equates to approximately three to fourteen tons of CO2 depending on site specific variables and management activities.

Direct Sequestration

Direct carbon sequestration is the process of directly capturing CO2 from the source of emission such as a coal fired power plant, separating the CO2 from other emissions, and compressing the carbon dioxide for long-term storage in carbon sinks. These carbon sinks are typically geological formations such as unminable coal seams, caverns, saline deposits, and oil fields which lends the term geological sequestration to this process. In some cases, oceanographic storage is used where captured CO2 is pumped to the bottom of the ocean.

A good example of direct sequestration can be found near Weyburn, Saskatchewan, Canada where more than 8,000 metric tonnes of 96% pure CO2 is sequestered each day in an enhanced oil recovery operation. The CO2 is captured at the Dakota Gasification Company in Beulah, North Dakota through a process of gasifying coal using oxygen and steam. This increases efficiency of the combustion for power generation, reduces other byproducts (gases), and concentrates the CO2 making it easier to capture. The CO2 is captured from the gas stream and piped to a compression unit where it is compressed to 2700 PSI.

Once captured and compressed, the CO2 is transmitted 205 miles through pipelines at very high pressure to the Weyburn oil field where the CO2 is pumped into 100 injection wells that support 300 producing wells. When CO2 is pumped at high pressure into the injection wells, it mixes with the oil causing it to swell, become less viscous, and move out of the pores in the rocks.

Without the CO2 injection production would be 10,000 barrels per day. With the injection it is nearly 30,000 BPD.

Throughout the entire process 70% of the carbon dioxide captured is actually sequestered 1,400 feet below ground where it dissolves in oil and water or mineralizes.

In either type of sequestration the primary goal is the same – to reduce the amount of carbon dioxide that is released into the atmosphere. And, while the specifics of each project will be very different, the basic theory of carbon sequestration is relatively straightforward.

  • Capture the Carbon Dioxide (directly or indirectly)
  • Trap the captured carbon in soils, plants, geological formations, underwater, or in other sinks.
  • Ensure a sufficient duration of sequestration

 

About the author:
Janice McMahon is the Forest Management/Sustainable Services Division Director for Environmental Services, Inc where she specializes in natural resource management projects including carbon sequestration projects, development/implementation of management plans for enhancement of carbon stocks, development of carbon and environmental asset tracking programs, and prescribed fire management plans for use in restoring ecosystems. She is responsible for managing carbon development projects under multiple protocols, exchanges, and registries and is currently working on projects in the United States, Central America, South America, Southeast Asia, and Africa. Ms. McMahon routinely leads lectures and seminars throughout the United States and internationally regarding the carbon markets and associated opportunities. Ms. McMahon has a B.S. degree in Wildlife Ecology & Conservation from the University of Florida and a M.S. in Forestry and Wildlife Science from Auburn University.