Could SCR catalyst technology adoption be a roadmap for power plants seeking economical and efficient CO2 point-source solutions?

As the quest to develop a net-zero carbon emissions electricity grid marches on, global entities like the International Energy Agency (IEA) increasingly point to a big role for carbon capture, utilization, and storage (CCUS). The IEA goes so far as to say reaching net-zero will be nearly impossible without CCUS.

Proposed governmental greenhouse gas emissions standards, intense scrutiny of carbon footprints, and a flood of public- and private-sector investment have fueled an explosion of interest in CCUS technology and solutions. Still, widespread point-source CO2 capture on the industrial level is in the early stages.

Nowhere is this more apparent than in the natural gas–fired power plant environment. Successfully mitigating CO2 emissions at their source during electricity production would tip the balance toward natural gas power being embraced as a plentiful and reliable source of clean power in the net-zero era.

While CCUS technology long has existed—particularly as the foundation of enhanced oil recovery—a major hurdle to widespread adoption has been the high cost and inefficiency associated with conventional liquid amine–based CO2 capture methods. Traditional carbon capture technologies often require substantial energy input, resulting in reduced plant efficiency and increased operational costs. The capital required for implementing large-scale CO2 capture facilities has also been significant, deterring power plant operators from pursuing these solutions. Moreover, the footprint required for these systems often makes it impractical to retrofit existing facilities.

As we grapple with the complexities of implementing point-source carbon capture in the power plant sector, the triumphs of selective catalytic reduction (SCR) system adoption may offer valuable lessons. Since the early 1990s, SCR catalysts have been widely employed to reduce nitrogen oxide (NOx) emissions from fossil fuel combustion, leading to cleaner, smog-free air.

The journey to economical and space-efficient SCR systems offers more than a case study, though. Some emerging point-source capture (PSC) technologies (Figure 1) are currently being engineered to work in concert with and as an extension of existing SCR systems, offering the potent punch of combined NOx and CO2 reduction.

1. The CORMETECH PSC concept for natural gas–fired power plants combines SCR and carbon capture to address both NOx and CO2. Courtesy: CORMATECH

Back to the Future: The SCR Innovation Curve

SCR systems were first patented in the U.S. in 1959. Early applications to reduce NOx were installed on natural gas combined cycle (NGCC) plants, followed closely by installations on coal-fired power plants in the early 1990s.

By 2006, 100 GW of SCR-equipped coal-fired capacity was operational. More than 300 coal-fired plants have received SCR technology in the U.S. alone, principally retrofits on existing steam generators, with many more installations internationally. Many of those installations, which continue to operate successfully today, have SCR catalysts manufactured by CORMETECH.

Significant operating experience and technological advances have made SCR a safe, reliable, and economical approach to NOx reduction. Modern SCR systems can reduce NOx emissions from coal-fired and combined cycle plants by more than 90%, and gas-fired applications typically achieve greater than 95% NOx reduction. The systems’ modular design affords seamless retrofit into existing plants and straightforward integration into new builds.

Moving to Net-Zero Carbon Emissions

The world is rapidly progressing toward a net-zero carbon emissions electricity grid, with developed nations leading the way. The IEA has presented the “essential conditions” for the global energy sector to reach net-zero carbon emissions by 2050 to limit global warming.

While urgency existed to reduce toxic smog causing NOx emissions, CO2 emissions pose an existential crisis to people and the planet. The path to net-zero is multi-faceted and nuanced, where SCR reduction was targeted to a particular industry and technology. However, CCUS is receiving an increasing share of industry and government investment because the potential to capture CO2 at the emission source is a proven and straightforward strategy that the SCR analog shows has worked before.

Recognizing the adjacency between environmental catalyst technology and CO2 monolith adsorber development, the U.S. Department of Energy has awarded CORMETECH pilot funding to advance direct air capture (DAC) and PSC technologies. For PSC, CORMETECH—with support from power industry partners including Southern Company and Middle River Power—will deploy in early 2024 at the U.S. National Carbon Capture Center a fully integrated process model intended to achieve at least a 20% cost reduction versus established liquid amine system technology.

The CORMETECH approach begins with a patent-pending sorbent-infused honeycomb-structure monolith adsorber module. This breakthrough technology employs a fully functional wall for increased CO2 capture versus a monolith surface coated with sorbent. This design approach eliminates solvent regeneration and much of the capital costs for pumps, heat exchangers, piping, and controls.

The modular system housing the infused monoliths employs a temperature-swing adsorption/desorption process to separate CO2 from flue gas. Direct steam injection facilitates desorption, and once condensed, readies the CO2 for transport and utilization or sequestration. Borrowing from CORMETECH’s expertise in catalyst geometry, modular design, regeneration, and recycling, this emerging PSC concept promises a significantly smaller and more integrated emissions control footprint than existing liquid amine systems with significantly lower costs.

Central to the cost-reduction is a patented circular-sustainability platform that already lengthens CORMETECH catalyst product life through regeneration of deactivated catalysts and then extends to recycling end-of-life catalysts to produce raw material for the manufacture of new catalysts. Applying this same model to CO2 adsorbers opens the door to the PSC system’s adsorbers being regenerated (versus fully replaced) with next-generation sorbents that would make them even more effective and powerful CO2 capture engines. Other major advantages of this approach are that virtually no landfill waste is generated and the carbon footprint is greatly reduced.

The Advantage of Adsorbent-Based CO2 Capture in NGCC Plants

  • Simple, efficient, highly scalable design with low capital cost.
  • Much smaller footprint than liquid amine systems
  • Adsorbers operate at low pressure drop, allowing the use of low-cost fans.
  • High efficiency due to increased contact area between flue gases and the adsorber.
  • Adsorbent PEI (polyethyleneimine) is contained (in a fixed position) within the monolith’s internal pore structure eliminating direct contact of the bulk flue gas with the adsorbent.
  • No movement of the adsorbent produces negligible stack emissions and no operation loss of the adsorbent.
  • No equipment corrosion concerns as the adsorbent is contained and not recirculated.
  • High efficiency as the adsorber only requires low-quality steam available from the heat recovery steam generator to regenerate.

Manageable lifecycle costs as demonstrated through CORMETECH expertise and capabilities for monolith regeneration.

CORMETECH’s new design approach is elegant in its simplicity, yet features strong integration with existing power plant systems. This process occurs in a multi-bed cyclic process unit but without the need for a vacuum, which enhances scalability to large NGCC plants. The process uses familiar components (such as SCR modules), there are no liquid amine solutions used in the process, pressure drop on the gas side is kept low to minimize the impact on plant efficiency, and the thermal swing in operation is low so thermal energy requirements are minimized. Like an SCR system, CORMETECH’s modular deployment is scalable for specific applications.

Even with the passage of the U.S. Clean Air Act Amendments of 1990, no one could have imagined that a few decades later power plant generated NOx emissions would be 87% lower, even as fossil fuel–powered plants continue to be the backbone of the U.S. electricity grid. SCR catalysts enabled cleaner power generation across coal, natural gas, and newer hydrogen-oriented facilities.

Could the potential answer to CO2 abatement that doesn’t compromise affordable and reliable electricity generation emerge from the SCR adoption roadmap? Don’t bet against it.