January 2022

Carbon Capture/CO2 Mitigation

Tips to avoid pitfalls in CO2 capture projects

In recent years, growing concern about increasing atmospheric carbon dioxide (CO2) levels has put mounting pressure on governments and on processing industries to curb carbon emissions.

Shah, G. C., Consultant

In recent years, growing concern about increasing atmospheric carbon dioxide (CO2) levels has put mounting pressure on governments and on processing industries to curb carbon emissions. Consequently, this has accelerated CO2 capture projects. However, an array of challenges that could, if not addressed adequately, hamper these otherwise well-intentioned projects. This article examines the pitfalls that a risk manager should consider to eliminate or minimize risks to ensure safety, environmental sustainability and economic success.

CO2 mitigation/elimination technologies adoption

Many companies/organizations in the global hydrocarbon processing industry are investing in new technologies and processes to mitigate or eliminate CO2 emissions. However, differences among science communities and industry exist in how quickly this transition should take place. Atmospheric experts stress the need for rapid transition, while industry professionals urge a calibrated and gradual approach. On a national level, a rapid transition to less-familiar technologies or nascent low-carbon or zero-carbon technologies could cause massive economic and societal disruptions. Some experts maintain that lofty phrases such as “carbon capture,” “zero-carbon economy” and “carbon-free world” tend to fuel hype while presenting a consequent lack of adequate thought to the risks associated with these relatively less-familiar technologies. However, astute risk managers recognize the need to do both: making quick transitions coupled with pragmatic risk minimization.

The scope of curtailing and/or managing atmospheric CO2 levels is vast and includes the direct capture of CO2 from atmosphere, along with planting trees, shifting to non-fossil fuel technologies, and capturing CO2 from flue gas, among others. Flue gas CO2 emissions are a significant portion of emissions. This article focuses on the processes and projects to capture CO2 from flue gases.

Post-combustion CO2 management involves the removal of CO2 from flue gas, compression, liquefaction, storage and reuse, where practicable. Several approaches exist for removing/concentrating CO2 from flue gas (e.g., absorption, adsorption, permeable membranes and cryogenic separation). As shown in FIGS. 1 and 2, absorption and adsorption technologies have gained wide industrial acceptance.

FIG. 1. Amine-based CO2 absorption process schematic.
FIG. 2. Adsorption-based CO2 recovery from flue gas.

Absorption technologies use organic amines such as monoethanolamine (MEA) and its blends. Starting from MEA absorption, technologies have improved to minimize several weaknesses of the MEA process, including oxidation of the solvent, corrosivity and intense energy requirements. In recent years, technologies have focused on adsorption-based routes, where CO2 from flue gases are adsorbed on solid sorbents (e.g., activated carbon, zeolites and others). These processes include fixed beds with solid sorbents, which undergo adsorption followed by thermal desorption. Although the adsorption-based technologies avoid the disposal challenges of liquid solvents, they still must contend with the eventual disposal of solid sorbents. A fluid-bed catalyst process is also being offered by a technology licensor, promising lower capital and operating costs. Unsurprisingly, each process has its benefits and risks. In addition to the risks of the carbon capture process from flue gases, transporting CO2 and storage risks merit careful consideration, as well.

PITFALLS TO AVOID

The following are six pitfalls to avoid when developing CO2 capture projects.

Considering CO2 capture in isolation

Hastily formulated CO2 capture projects could result in missing other strategically important segments, including CO2 transport, long-term storage and the potential reuse/recycle of CO2. Depending on a plant’s location, infrastructure to transport CO2 to storage caverns could involve a significant investment, along with financial and environmental risks. In the long term, massive investments are needed in pipeline and storage infrastructure. Tank and rail transport—though a viable option for relatively small quantities—quickly become uneconomical for large-scale transports. Each mode of transportation also has potential risks. Several major issues to consider include:

  • Permitting and right-of-way considerations: Permitting for CO2 pipelines involves detailed application preparation, design reviews, emergency response plans and public reviews. Establishing good public rapport will help expedite the permit approval process. Transporting CO2 by ship and/or subsea pipelines must comply with several international codes and regulations and would require environmental risk assessment—akin to those performed for National Environmental Policy Act (NEPA) projects. Unsurprisingly, this is a very rigorous and time-consuming process. For inland pipelines, determining a suitable route requires geo-tech work, including soil conditions, topography, climate variations and areas with heavy population density, among others.
  • Corrosion: Although liquefied CO2 does not present a flammability hazard and dry CO2 does not present a corrosion hazard for ordinary carbon steel, prudent pipeline designs should include monitoring and safeguards against impurities such as sulfur, mercaptans or hydrogen sulfide (H2S), water and others, depending on the stack gas composition. One key safeguard may include upgrading to austenitic 316 stainless steel, as low-alloy carbon steel corrosion could be a problem.
  • Monitoring and specification requirements: In addition to monitoring for corrosion, online instrument/control systems should be provided to ensure that product specifications adhere to parameters set for storage in caverns. For example, instrumentation could include online analyzers for water, sulfur and impurities, hydrocarbons and oxygen—and flowmeters/meter provers and interlocks can help halt flows to storage caverns in the event of off-spec CO2.
  • Tank car and truck/marine transport: These types of transportation entail significant handling risks of asphyxiation and thermal shock. Tank cars or truck transports tend to involve considerable handling risk. Loading/unloading racks should include automatic programmable logic controller (PLC) sequenced operations or some other means to minimize human interaction. In addition, loading/unloading stations should have ample ventilation to minimize the asphyxiation hazard.
  • Transport disruptions: Risk analyses must consider potential disruptions and safety mishaps (e.g., ship collision and/or fire, truck/train accidents) and should provide adequate warning systems and safeguards to minimize mishaps. The potential of asphyxiation for workers in ships also merits consideration. In the event of a subsea pipeline rupture, cryogenic CO2 will be released and could affect (carbonic acid and the resulting low pH) marine life. However, unlike hydrocarbon spills, CO2 will escape. Depending on the magnitude of the leak, the CO2 vapor cloud could pose an asphyxiation hazard for ships/vessels in the vicinity.
  • Reuse and recycle: Reuse and recycling are key pillars of a sustainable/circular economy. The reuse of CO2 for enhanced oil recovery (EOR) or in the cement industry can help improve project economics. However, in the long term, EOR might be impacted by stricter government regulations. Fortunately, considerable work is in progress to develop new avenues for the reuse and recycling of CO2.

Technology selection

Obviously, a technology that does not meet safety, productivity and environmental goals would ruin an investment, as well as tarnish a company’s public image. Companies must take a systems approach in selecting technology that matches the organization’s existing process. The following are several pitfalls to consider:

  • Equipment sizes for the CO2 absorption technology: Liquid solvent-based technologies could entail large equipment and solvent flowrates—hence, larger real estate. A congested layout would make it difficult to accommodate new equipment additions and structural foundation requirements. In addition, utility requirements (e.g., steam consumption, power requirements, nitrogen and instrument air) must be accounted for. CO2 capture processes tend to be steep in capital and operational expenses.
  • Maturity and reliability of the technology: Nascent technologies lack long-term reliability data. Conversely, technology that is “too mature” could face obsolescence problems. For example, amine-solvent-based processes are relatively mature in comparison with recent membrane processes, which have less environmental impact but lack operational history. It is a delicate balancing act between reliability and obsolescence.
  • Liquid solvent or solid adsorbent disposal issues: Even in disposal, one must consider the potential adverse environmental effects resulting from the disposal process. Numerous approaches are available for amine disposal, including physical (membrane), chemical or biological treatments. Each of these processes have benefits and challenges. Regardless, the goal is to minimize the overall environmental impact.
  • Liquid or solid sorbent sensitivity to chemical species in the flue gas, such as oxygen, nitrogen oxides (NOx) and sulfur compounds: For example, some sorbents may be too sensitive to sulfur or sulfur derivatives and may require sulfur removal in the flow conditioning step (FIGS. 1 and 2). This will add to the project’s cost. In addition, particulates from flue gas could cause plugging problems, operational challenges and low productivity.
  • Amine emissions could pose multi-phase environmental issues: Amine emissions can affect air quality and cause water pollution (as rainwater will dissolve amines), which can lead to soil contamination problems. Similarly, environmental systems must be robust enough to handle amine and byproduct spills.
  • Acceptance from communities: Despite well-intended efforts to improve the environment, CO2 capture projects can receive a tepid response or even fierce resistance and/or legal challenges from nearby communities if their concerns are not addressed adequately (such as regarding noise levels and traffic during construction, long-term noise levels, amine emissions, odor concerns and other issues). Resultant litigation and delays could render the project unsustainable and could generate—in the short term—public concern or distrust about a company’s environmental stewardship.
  • Operational upsets: In the event of an operational upset that results in unburnt hydrocarbons in flue gas, the CO2 capture plant could spread a flammability hazard over a wide area. Control philosophies should address this hazard, along with similar plant upset issues.
  • Flue gas CO2 concentrations and effective absorption: Depending on the source, CO2 concentrations in flue gas vary. For example, gas turbine flue gases typically contain 3 vol%–4 vol% CO2. Flue gas in gas-fired heaters or boilers has CO2 levels of 8 vol%–10 vol%, and fuel-oil-fired boilers have even higher CO2 levels. Low concentrations of CO2 mean a lower driving force for absorption and may require higher concentrations of amine. Plants must establish an operating window for CO2 concentrations.
  • System integration: Although instrument and control system vendors have made significant efforts to interoperability, at the plant level, personnel must spend a considerable amount of time and resources to ensure smooth operations. For example, if the distributed control system (DCS) is provided by X and the CO2 capture vendor has its system based on DCS Y, then data protocols must be addressed carefully. Inadequate consideration of DCS alignment will cause recurring data-management issues, along with operational and safety problems.

Improving operations to minimize CO2 formation

Furnace or boiler operations at high levels of excess air will increase flows through the CO2 capture process and lead to suboptimal operations, while scant excess air could cause unsafe conditions. Optimizing the operation of upstream equipment will improve CO2 capture and enhance overall productivity. In addition, switching to fuels that generate lower amounts of CO2/Btu (the amount of CO2 produced per Btu of heat release) will help lower the size of the CO2 capture equipment. For example, the amount of CO2 released per MMBtu of heat output for natural gas is approximately 40%–50% lower than that generated by fuel oils, such as diesel. However, this option may not be viable for brownfield projects.

Long-term considerations

The CO2 capture plant/project lifespan may be 25 yr–30 yr; therefore, it requires some thought on several broad issues. Some of the issues may not be easily manageable or even amenable to quantitative analysis; nonetheless, decisions must be made in the face of volatile information. Several of these issues include:

  • Supply chain robustness and CO2 markets: As with any project or plant operations, supply chain reliability is crucial. Similarly, demand for CO2 will impact operating rates and emissions.
  • Stability of disposal contractors: Implicit requirements of solid waste disposal and Resource Conservation and Recovery Act (RCRA) regulations include an assessment of a waste disposal contractor’s financial stability; the same will apply for waste disposal from CO2 capture projects.
  • Environmentally advanced technology suppliers: The move toward environmentally responsible processes and technologies will continue. In selecting any technology, one should identify segments that are problematic from an environmental sustainability view, such as high solvent or adsorbent consumption that requires proper disposal. Other aspects to consider are high energy requirements and systems with lower reliability. After these problematic systems are identified, a strategy should be put into place to gradually move away from these systems. History shows that technologies with large environmental footprints tend to become extinct and get replaced with environmentally savvy technologies. CO2 technologies should be able to facilitate environmental upgrades without a massive infusion of investment.

Infrastructure

In the context of this article, infrastructure means systems. This includes equipment and operational databases and information networks. Many safety and environmental regulations (e.g., process safety management, risk management plans and hazard communications) have implicit data requirements, such as emissions inventory, operating rates, safety data sheets and equipment data. With the addition of CO2 capture projects, the need for infrastructure will become more acute. To maintain optimal operations, relevant and reliable information should be quickly accessible. A corollary to this requirement is that database systems and information technology (IT) infrastructure should be user friendly. Inefficiencies and inadequacies of these systems impact productivity and could also impair safety.

Geopolitical considerations

Although geopolitical stability may be hard to quantify and is typically not part of a safety/environmental professional’s involvement, large-scale CO2 capture projects in locations that could be impacted by geopolitics should be carefully reviewed.

Takeaway

Company executives and safety/risk managers recognize that climate change issues and policies could become mired in intense debates, false narratives, regulatory bureaucracy, socioeconomic disruptions and business uncertainty. However, they also see the need for a rapid but risk-managed transition to low-carbon or zero-carbon technologies. The need for such a transition merits careful consideration. This type of rapid transition could be enabled by a strong infrastructure for project management, data analytics, risk minimization, digitization and a trained and cohesive workforce. Organizations should consider multiple risk assessments at various stages of the project or important milestones. As the project progresses, risk assessments (e.g., hazard and operability analysis, layer of protection analysis and safety integrated level assessment) will address tactical safety, environmental and operational issues. Therefore, the long-term success of CO2 capture projects requires focused attention on strategic and tactical issues. HP

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