Direction of cost-effective carbon capture and storage technologies

A. Al-Qahtani, A. AL-SANAD and V. MULGUNDMATH, Saudi Aramco, Dhahran, Saudi Arabia

Around the world, many nations and companies are transitioning toward the decarbonization of energy. Aramco has taken a pivotal role by earmarking strategic initiatives, including its Corporate Decarbonization Initiative to ensure a sustainable future. This initiative aims to reduce the amount of carbon emissions that must be captured to reach a carbon balance or net-zero emissions strategy. One of the key pathways to reduce carbon emissions is to capture and store (sequester) carbon. To reach a net-zero carbon balance or net-zero emissions, the inherent carbon from hydrocarbons that would otherwise be released into the atmosphere as fugitive carbon must be captured and removed or reused.

Carbon capture and storage (CCS) technologies capture carbon dioxide (CO₂) emissions at the source or directly from the air. CO₂ emissions are then transported away and stored deep underground or turned into useful products. Capturing carbon has been practiced for decades to help improve the quality of fossil fuels like coal and natural gas; however, pioneering next-generation technologies means that CO₂ can be removed and sequestered indefinitely. Research is continuing to explore new ways to add value to waste CO₂ by turning this waste gas into marketable, low-carbon industrial and commercial products.

Carbon capture technologies can be categorized as the following: pre‐combustion, oxy‐combustion and post‐combustion (FIG. 1). The following are definitions of each of these categories:

1. Pre‐combustion: Pre‐combustion carbon capture involves the removal of CO₂ from fossil fuels before combustion is completed. Examples include coal gasification and steam methane reforming (SMR), where the feedstock is partially oxidized to form syngas, followed by the water‐gas shift (WGS) to produce a pure CO₂ and hydrogen (H₂) stream from which CO₂ can be separated.
2. Oxy‐combustion: This type of carbon capture, or oxyfuel combustion, refers to combustion with pure oxygen. In this process, fossil fuel is burned in oxygen, instead of air, to ensure controlled and complete combustion. The resulting flue gas consists of mainly CO₂ and water vapor. The water is condensed through cooling, and the result is an almost pure CO₂ stream that can be transported and stored.
3. Post‐combustion: Post‐combustion capture involves the removal of CO₂ from flue gas after the fossil fuel has been burned. Post‐combustion methods are end‐of‐pipe solutions for most existing industrial combustion processes. Flue gases for post‐combustion capture generally have anywhere from 5% CO₂–15% CO₂ concentration and are at near atmospheric pressure.

CCS technologies can be grouped under three phases in case of deployment: commercially ready technologies, emerging technologies and concept technologies.

1. Commercially ready technologies [technology readiness level (TRL) 8–9]: These include technologies that can be categorized as commercially available or near‐commercially ready. These technologies have been tested or operated as a demonstration or widely deployed in various commercial applications. In the near or medium term, it is expected that these technologies would likely involve further development to achieve incremental improvement and economies of scale to reduce system costs.
2. Emerging technologies (TRL 4–6): These are emerging CO₂ capture technologies that have been validated at pilot scale, that are in line to be demonstrated at pre‐commercial scale and that may become commercially available in the coming years.
3. Concept technologies (TRL 1–3): These are emerging technologies that are at a low level of maturity and that have a long lead time to get to the market.

Most of the ready-deployed technologies are based on post‐combustion CO₂ capture and are deployed as part of large‐scale CCS projects at existing power-generation plants. The deployment of CO₂ capture technology has mainly been focused on low‐cost process emissions-based opportunities, including at power-generation plants and for industrial applications such as natural gas processing, cement, iron and steel, and chemicals. Carbon capture processes can be classified according to their gas separation/capturing principles—namely, chemical absorption, physical absorption, adsorption, calcium and reversible chemical loops, membranes, and cryogenic separation.

CO₂ capture activities have mostly focused on power-generation plants (primarily coal‐fired power plants and gas‐fired power plants), as these make up the largest stationary source of CO₂ emissions. More recently, industrial applications of CO₂ capture have begun to gather momentum, mainly in the steel and cement industries, and, to a lesser extent, in the oil refining and chemicals industries.

CO₂ storage involves the production and recovery of CO₂ from industrial processes, and is typically followed by drying and compression. The captured CO₂ can be injected into depleted oil and natural gas fields for enhanced oil recovery or sequestered in deep geological formations such as saline aquifers. Alternatively, CO₂ can be used as a chemical feedstock (e.g., for eFuels), curing in the cement process and algal biofuels production, and chemicals, among other various ranges of CO₂ utilization options.

It is worth mentioning that carbon capture from gas streams is not new. CO₂ capture technologies based on chemical solvents (amines) were first commercially deployed in the 1930s to separate CO₂ and other acid gases from methane in natural gas production. Prior to 1972, all CO₂ captured was vented to atmosphere, except for a small proportion used or sold for other purposes, such as urea production or beverage carbonation.

The main driver of carbon capture is the capture cost or the capture abatement in $/MMt of CO₂. The cost of CO₂ capture from low-concentration sources, such as coal-fired power generation, has reduced by approximately 30%–50% over the past decade due to research and development (R&D) and economies of scale, and it is decreasing for other applications, as well. The cost of CO₂ capture can vary greatly by point source and by capture technology. Fuel transformation applications that produce a concentrated CO₂ stream and/or that require CO₂ to be separated as an inherent part of the process (such as in natural gas processing) have low CO₂ capture costs and have been favored for deployment.

One of the main factors in carbon capture, utilization and storage (CCUS) projects is to realize a positive net present value (NPV) and to find cost-effective ways to design, operate and maintain the CCUS project. Due to the low commercial utilization of CO₂, most CO₂ projects would depend on permanent sequestration.

To make the CCS business attractive, several cost-effective approaches should be considered. The following are some considerations to help the economics of the business.

The location of the sequestration sink. One of the key requirements to optimize the cost of any CCS project is to allocate the nearest, best-fit candidate sink to reduce the required pipelines, distance and compression requirements. The overall costs will be reduced further if pressure requirements for transporting CO₂ are reduced, and if higher-capacity pipes and the nearest sinks from the emitters’ sources can be identified. Mostly, such privileges with ideal sinks are unavailable, but the best-fit candidate would have ideal conditions to design and safely operate the CCS process with the optimum cost during the lifetime of the project.

Although the most popular sink for 100% permanent CO₂ sequestration is a saline aquifer, other types of sequestration are also assessed and used around the world. A detailed assessment of the subsurface and its associated risks could optimize the cost at the full value chain. For example, any potential of lowering pressure in the candidate sink would affect the cost of the capture and transportation, and possibly optimize power requirements.

Existing infrastructure. One of the design philosophies to reduce the capital expenditure (CAPEX) of a CCS project is to capitalize on the existing infrastructure of the facilities, (rotating and stationary equipment, pipelines, etc.). This can be achieved by reusing existing infrastructure safely for CO₂ transport and storage.

If capitalizing on the existing infrastructure provides good outcomes to optimize CAPEX, several considerations should be accounted for before any repurposing of existing infrastructure for CO₂ transport and sequestration. Some of these considerations could include installing new equipment or monitoring systems, which would add additional costs.

Several physical, chemical and process engineering aspects should be assessed to ensure the compatibility of the materials and equipment to adopt the modified process safely and economically. The integration of the infrastructure at existing facilities with the CCS value chain (or segment) could help to reduce CAPEX. For example, facilities with a huge inventory, and with tank farms associated with triethylene glycol (TEG) systems, could be an opportunity to favor TEG dehydration in the capture part. That would also reduce the need for new chemical tanks and could optimize the cost of dehydration units, leading to a reduction of the overall facility’s footprint.

Sharing concept. To reduce the cost of CCS, sharing the infrastructure concept among several emitters could provide the most cost-effective approach. Infrastructure sharing of stationary and rotating equipment would provide a significant cost reduction. One tactic is sharing pipelines and final compression (pumping) of the captured CO₂ through dedicated hubs. In doing so, there is a huge potential of reducing the overall CAPEX and operating expenditure (OPEX) for the emitters.

The sharing concept is not limited to pipelines and equipment—it could also be extended to several applications, such as cooling water, relief systems, utilities, store houses, maintenance yards and others. In addition, the concept of remote operation and centralized maintenance would help to enhance OPEX. Another benefit of sharing the main infrastructure is the ability to modularize and standardize equipment and pipelines. Care should be taken that each emitter does not breach the CO₂ specifications ahead of transporting or pumping it to the subsurface.

In all, the sharing concept would help reduce the overall cost of the project in both CAPEX and OPEX.

Investing to develop new technologies. One of the long-term solutions to optimize CCS project cost is leveraging the investment of innovation and deploying new cost-effective technologies. A breakthrough in any segment of the value chain would impact the total cost of the project. For example, employing special coatings, alloy materials or cost-effective materials in pipelines could optimize several segments and units of the value chain, such as eliminating or reducing maintenance on dehydration units.

Another aspect that makes the CCS business attractive is the development of new applications for CO₂ utilization. Finding a market for CO₂ utilization would positively impact the economics of the CCS project. For such cases, the business could profit by increasing the value and purity of CO₂ through increasing the demand on CO₂ supply.

Enabler mechanisms. As the market for CO₂ is limited and utilization is minimal, the only way to get CCS projects deployed is through incentive mechanisms and stringent policy regulations for mitigating CO₂ emissions. In all the existing projects and operating facilities, policies are essential for running a CCS business. Regulations, carbon emitting taxes and other means of incentives should be considered for current projects. Utilizing carbon credits and carbon trading and unlocking a blue ammonia business could comprise supporting mechanisms for the CCS business, as well.

Takeaway. The authors believe that CCS has the potential to significantly reduce global emissions. It is a central element to support the decarbonization of oil and gas business and operations. It is also an essential element of an integrated ammonia and H₂ production program. In addition, CCS has the potential to contribute to the Saudi Green Initiative’s goals of reducing greenhouse gas emissions, and to support the economic diversification and sustainable development of the country’s economy. HP

AYIDH AL-QAHTANI is a Process Engineer at Saudi Aramco’s Energy Transition Engineering Department within the Hydrogen Systems Engineering Division in Dhahran, Saudi Arabia. He is a chemical engineer with 6 yr of experience in engineering services and technical support, and has worked in gas plant facilities, including acid gas removal, dehydration and sulfur recovery. Al-Qahtani has been involved in operations, process and technical support, and has led gas plant startups from pre-commissioning to gas production. Al-Qahtani has also earned a Fundamental Engineering certificate.

ABDULLMAJEED AL-SANAD is a Process Engineer at Saudi Aramco. He works with the Process and Control Systems Department within the Flare and Relief Systems Group. He has 8 yr of experience. Al-Sanad has been involved in major tasks at the company, such as NGL recovery plant commissioning and Saudi Aramco’s decarbonization strategy development. He has also led several milestones in the company’s flaring minimization programs. He earned a BS degree in chemical engineering from King Fahd University of Petroleum and Minerals (KFUPM).

VINAY MULGUNDMATH is an Engineering Specialist within Saudi Aramco’s Energy Transition Engineering Department’s Hydrogen Systems Engineering Division. Prior to joining Aramco, he held the role of Chief Technologist at the Net Zero Technology Centre in Scotland. He has also been a board member of the Scottish Environment Protection Agency (SEPA) and the Scottish Energy Advisory Board. Dr. Mulgundmath is a non-executive advisor to the Scottish Carbon Capture & Storage research group, and to Scotland’s Hydrogen Accelerator at the University of St. Andrews. He is also an honorary administrator at the University of Aberdeen’s Directorate of Research & Innovation. He earned an MS degree in process engineering, and a PhD degree in chemical engineering with a specialization in post-combustion carbon capture technologies.