Infrastructure Challenges in Carbon Capture, Utilization and Storage (CCUS)
Carbon Capture, Utilization and Storage (CCUS) will be a critical component of achieving Net Zero emissions targets set by industry and governments.
The infrastructure required to transport captured CO2 from the source to the disposal or use site is a challenge that is not often considered.
This includes natural gas pipelines and storage wells that might be repurposed for CO2 or new pipelines and wells that are designed specifically for CO2 service.
Don’t We Already Have CO2 Pipelines?
True, there are CO2 pipelines that have been in operation for many years but the length of these lines and the number of years in service pales in comparison to the industry experience with pipelines carrying natural gas and liquid hydrocarbons. This limited experience with CO2 pipelines makes it difficult to evaluate the risks that would be associated with new CO2 pipelines based on experience alone.
In addition, most of the CO2 sources for the current CO2 pipelines are naturally occurring in wells, which are relatively pure compared to CO2 that is captured from industrial processes. Captured CO2 can contain a variety of contaminants such as sulfur and nitrogen oxides (SOx and NOx), hydrogen, carbon monoxide and methane.
These contaminants can alter the flow characteristics of the CO2 and cause corrosion in the pipeline. The presence of these contaminants might require specialized pipeline design and qualification testing to ensure that the selected pipeline materials are compatible with the CO2 source. This could become especially complex to manage for pipelines that receive CO2 from multiple industrial sources, where the types and concentrations of contaminants might vary.
C-FER Yourself
The Alberta Carbon Trunk Line is a CO2 pipeline carrying 1.6 million tonnes/year from industrial sources to an enhanced oil recovery operation in Alberta.
For more information visit Wolf Midstream’s website.
Doesn’t CO2 behave a lot like natural gas in a pipeline?
CO2 is generally transported at higher pressure than natural gas so that the CO2 is so compressed that it acts like a liquid, even though it is still a gas (this is referred to as the “dense-phase” condition). This high pressure allows CO2 to be transported efficiently through the pipeline.
Unfortunately, most natural gas pipelines were not designed to operate at the pressure required to achieve the efficient dense-phase of CO2. CO2 could still be transported in these pipelines at a lower pressure, but this can significantly increase the cost of transporting CO2.
Dense-phase CO2 also behaves differently from natural gas if a hole or through wall crack occurs in a pipeline. Even as the CO2 escapes from the pipeline, the dense-phase state of the gas can maintain the pressure in the pipeline and cause the crack to grow if the steel property called fracture toughness is not sufficient to stop the crack growth.
Because CO2 behaves in this way and natural gas does not, CO2 pipelines require material with higher fracture toughness than what is generally used to construct natural gas lines. Therefore, it may not be feasible to convert existing natural gas pipelines to hydrogen service because of the fracture toughness material requirement.
CO2 also behaves differently once it has escaped from a pipeline. The release can form a cloud that is heavier than air which tends to stay at ground level and flow into low lying areas. Large releases can cause accumulations of CO2 that displace the air, creating an unbreathable atmosphere that poses a hazard to people and animals.
Therefore, models that assess pipeline risk must consider this hazard to ensure that the pipeline is safe, in the event of a release.
C-FER Yourself
Shell Quest is a Carbon Capture and Storage (CCS) operation that captures and storges 1.2 million tonnes of CO2 per year in Alberta.
Where is the CO2 going to go?
One of the key components of CCUS is storing CO2 permanently underground in porous formations such as saline aquifers or depleted hydrocarbon reservoirs. One of the most promising large-scale uses of CO2 is in enhanced oil recovery where CO2 is injected into mature oil reservoirs to displace the oil and improve overall oil recovery while leaving a large portion of the CO2 in the reservoir permanently. Some companies are also investigating how to incorporate CO2 into products such as concrete to make it stronger. This can have the dual benefit of removing CO2 from the atmosphere and improving the product.
As more CO2 capture and storage operations come online, a network of CO2 pipelines will be required to move CO2 from capture sites to storage or use sites. It is expected that underground CO2 storage will also be added to these pipeline networks to manage fluctuations and interruptions in CO2 production and injection.
This will ensure uninterrupted operations and the unplanned release of CO2. This is the same way that underground storage facilities are key components of current natural gas and liquid hydrocarbon pipeline networks. These temporary underground storage facilities could include salt caverns where geological conditions allow the creation of caverns.
Like legacy pipelines, the compatibility of legacy underground storage wells and reservoirs with CO2 will have to be evaluated to determine if existing infrastructure can be used for the new storage facilities.
For storage in reservoirs and saline aquifers, water in the storage formation will mix with the CO2 to form acidic fluids that could corrode well casing and damage the well cement. This could lead to loss of CO2 to other underground formations or potentially back into the atmosphere.
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