Carbon Capture and Storage at the Oil Sands

Q: From where is the CO2 extracted? How?

A: The source of CO2 is from our Scotford Upgrader which receives bitumen from the Athabasca Oil Sands Project mining operation and adds hydrogen to the bitumen, breaking up the large hydrocarbon molecules - this process is called hydrogen-addition or hydrogen-conversion. The hydrogen used for this process is made at the Upgrader using three hydrogen manufacturing units that employ a steam methane reforming technology. A major by-product of this process is concentrated CO2 which is the feedstock for the Quest CCS capture unit. Within the capture unit, an absorber vessel will use an amine solvent to capture the CO2 from the process stream. The CO2 will then be released from the amine by heating. CO2 will be compressed and dehydrated into a dense fluid for pipeline transport to the underground storage site.

Q: How is the CO2 compressed? Would valves be used in this process and how? What kind?

A: The Quest CO2 is compressed using an eight stage integrally geared centrifugal compressor with interstage coolers and a knock-out drum installed to cool the process stream and remove water. After the 6th stage of compression the CO2 is routed through a triethylene glycol (TEG) drying unit to reduce the water content to meet pipeline quality requirements. Maximum discharge pressure is roughly 140 bar, although the pipeline will likely operate at a lower pressure.

The compressor antisurge valve is used to let down pressure from the 8th stage to the inlet when the compressor is in a recycle mode of operation. High reliability and precision is needed in this application.

As well, letdown valves are installed on the first, sixth and eighth stages to safely release pressure to a dedicated CO2 vent system. To prevent backflow from the pipeline to the compression facility there are also two non slam check valves installed.

Q: What are the challenges of getting the CO2 to the storage site?

A: Quest will transport the CO2 to the storage site by an underground CO2 pipeline. Although the pipeline will not be carrying hydrocarbons, it will be built and operated to meet or exceed high vapor-pressure pipeline standards. Some examples of measures taken to maximize pipeline safety during design and construction include:

• selecting materials for the pipeline based on their suitability for CO2 transport – for example, the pipeline will be made from low-temperature carbon steel material with specific toughness requirements
• employing the latest CSA-Z662 Pipeline Standards for CO2 Pipelines that were issued in 2011
• protecting the pipeline from external corrosion by using three layers of fusion bonded epoxy coating and cathodic protection; and,
• burying the pipeline at a minimum depth to the top of pipe of 1.5 metres versus the regulated depth of 0.9 metres.

A: Within the Capture unit where the CO2 contains varying amounts of water, a large amount of 304 and 316 stainless steel is used. Using stainless steel addresses the risk of corrosion from wet CO2 and stainless steel can easily handle the lower temperatures which can occur when dropping CO2 from a high pressure to a low pressure due to the Joule Thompson effect.

By extensively drying the CO2 using the TEG process, risk of pipeline corrosion is reduced. This allows pipeline and injection facilities to be constructed from carbon steel. Pipeline valves are constructed from low temperature carbon steel except for a few situations using stainless steel valves.

An area of focus when selecting materials for CO2 service is the choice of elastomers for valve sealing, gaskets o-rings etc. When an elastomer is in supercritical CO2 service, the CO2 can diffuse into the material and when the pressure is reduced the elastomer can blister, swell or even rupture. For these reason Quest has avoided specifying elastomer seals and instead are using metal seated valves wherever possible. If elastomers are unavoidable in a situation such as a pilot relief valve, we have selected elastomers with a history of successful service and are also performing laboratory testing to confirm they are suitable for our service.

Q: What kinds of controls are to be utilized?

A: The pipeline and wells will be operated and monitored continuously from the control room at the Scotford site. Shell will also employ a comprehensive monitoring program to confirm the pipeline is operating safely.

Q: How about actuation - pneumatic, electric, or manual?

A: Quest utilizes pneumatic actuators for the bulk of the Capture unit actuated valves due to ready availability of compressed air from existing Scotford Upgrader utilities. We will use hydraulic actuated valves for pipeline line block valves and the compressor discharge block valve. For actuated valves on the pipeline, hydraulic actuators are used since the remote locations do not readily available power or compressed air.

Q: Is heat an issue? Corrosive factors?

A: Heat is not an issue, and flow modeling was done to ensure that temperature changes associated with the CO2 flow through the pipeline will not interfere with the ability to maintain it in dense phase which ensures that no corrosion occurs.

We will be taking a number of measures to maximize the safety of the pipeline. For example at the capture site we will be dehydrating the CO2 before it is injected. Removing the water and transporting “dry” CO2 essentially eliminates the risk of internal corrosion. Systems and processes will also be in place to continuously monitor the CO2 in the pipeline from the site. We will be protecting the pipeline from external corrosion by using three layers of fusion bonded epoxy coating and cathodic protection.

Q: Is there anything valve, actuator or control manufacturers could do to help make this project better or more efficient?

A: Valves and actuation requirements for the CO2 pipeline must meet the following:

1. High toughness materials with resistance to low temperature excursion encountered during CO2 venting (temperatures can reach -70degC)
2. Ability to seal, both internally (seat) as well as externally ( packer) at low temperatures
3. Limit or eliminate the use of elastomers in seats by using metal to metal sealing
4. High wear resistant seats to ensure that galling does not affect the sealability

There are several key valve suppliers with this capability and operating history which is very valuable to the project.

Knowledge gained will prepare the ground for CO2 capture initiatives to help combat climate change. TCM is a joint venture between the Norwegian state, Statoil, Shell and Sasol.

Len Heckel brings 30 years of experience in oil and gas business, engineering and plant operations, including 10 years at the Scotford complex. For the past 15 years he has been involved in developing and evaluating business opportunities in Shell’s refining and upgrading activities. He has spent the last 3 years as the business and commercial manager for the Quest CCS project prior to taking on the Business Opportunity Manager role in 2012.

Kate Kunkel is Senior Editor of Valve Magazine. Reach her at kkunkel@vma.org