Technological challenges facing the current carbon market

Carbon capture technology could significantly reduce emissions. But what issues need to be addressed before these processes can be utilised?.

Charles L Kimtantas and Joe Selby
Bechtel Energy Technologies and Solutions

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Article Summary

As the world continues to grapple with the impacts of climate change, the need for innovative solutions to reduce carbon emissions has become increasingly pressing. One such solution that has gained significant attention in recent years is carbon capture technology, which holds the potential to significantly reduce emissions from industrial processes and power generation.

However, with new technologies and the application to new or different sources of carbon dioxide (CO₂) come questions about their readiness and feasibility. This article explores the current state of technology readiness for carbon capture and what challenges must still be addressed before widespread adoption can occur.

CO2 and other greenhouse gases (GHG) accumulate in the atmosphere and act like a greenhouse to trap the sun’s heat. Excessive GHG are causing the atmosphere to trap more heat (see Figure 1), and this can cause:     
• The atmospheric temperature to increase, deserts to form, and natural ice sources to melt, thereby leading to increasing ocean levels and flooding of low-lying coastal areas of the world.
• An intensification of weather events such as hurricanes, tornadoes, thunderstorms, and rainstorms, and the resulting increase in risk to life and damage to property.
CO₂ emission reduction targets
Scientists from around the world have determined target requirements to reduce the impact of CO₂ on the environment of the world, as listed below:
• “To keep global warming to no more than 1.5°C – as called for in the Paris Agreement – emissions need to be reduced by 45% by 2030 and reach net zero by 2050.” (UN, 2022)
• “The United States has set a goal to reach 100% carbon pollution-free electricity by 2035, which can be achieved through multiple cost-effective pathways, each resulting in meaningful emissions reductions in this decade.” (The White House, 2021)
• “The NDC (Nationally Determined Contribution) sets an economy-wide target for the US to reduce its net greenhouse gas (GHG) emissions by 50-52% below 2005 levels in 2030.” (SDG Knowledge Hub, 2021)

Understanding carbon capture technology
Carbon capture is the removal of CO₂ from a stream, usually a vapour stream, by various technologies with the potential to recover the CO₂ in a usable form or to sequester the CO₂ for long-term storage. The primary CO2 capture systems are categorised as:
• Solvent based
• Chemical reaction: amine, ammonia, sodium hydroxide (NaOH) or potassium hydroxide (KOH)
• Physical adsorption
• Solid adsorption
• Membrane
• Distillation – cryogenic or high pressure
• Solid generation – refinery coker

Solvent-based carbon capture
Solvent-based carbon capture technologies are divided into chemical reaction and physical solvent systems. Chemical reaction-based systems employ a chemical to react with the CO₂. The reacted solvent is then regenerated, the CO₂ is released, and the regenerated solvent is reused.

Physical solvent-based systems use a solvent that can physically adsorb the CO₂. The rich solvent is then regenerated, typically with pressure reduction and heat, to release the CO₂, and the regenerated solvent is reused. A simplified flow diagram of the two systems and a list of the typically used solvents are presented in Figure 2.

Solid adsorption-based carbon capture
Solid adsorption carbon capture systems use a solid adsorbent to capture the CO₂ within the solid adsorbent. The solid adsorbent contains many small pores that allow the CO₂ to accumulate in the adsorbent. Most solid adsorbent systems use multiple adsorbent beds that can be switched from adsorbing the CO₂ to regenerating the CO₂ out of the adsorbent. This regeneration can be done using a temperature or pressure change, depending on the type of adsorbent being used (see Figure 3).

Membrane-based carbon capture
Membrane-based carbon capture uses semi-permeable membranes to selectively separate the CO₂ from the other gases that are present. Depending on what the other gases are, the CO₂ may pass through the membrane, or the other gases might pass through the membrane, leaving the CO₂ behind. A wide variety of membranes are available, and a few of these are listed in Figure 4, along with some typical membrane configurations used to maximise the CO₂ recovery and purity.

Distillation – cryogenic or high-pressure-based carbon capture
Distillation of CO2 from various streams, such as flue gas from combustion power plants, process heaters, and combustion generator turbines, is accomplished using a combination of compression to medium to high pressures (500-3,000 psig) and cooling of the fluid to very low temperatures, possibly even to cryogenic temperatures near -50ºF. A simplified block diagram of a system is presented in Figure 5.

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