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January 2021

Simulation Changes the Climate Change Equation

By Ansys Advantage Staff

Climeworks-captured CO2 turned into stone with the Carbfix process. Carbfix developed a process that captures CO2 and other acid gases in water, then injects this water into the subsurface where the gases are stored as stable minerals. Credit Carbfix. Photo by Sandra O Snaebjornsdottir

Considering the enormous climate implications of CO2 emissions, it may be surprising to learn that the “high concentrations” of carbon dioxide we hear about aren’t high at all. CO2 molecules constitute only 0.04% of the Earth’s atmosphere. The problem is, that’s more heat-trapping CO2 than has ever been recorded — a manmade increase of 45% since the beginning of the Industrial Age, with one-quarter of that occurring just since 2000.

Even a small increase in CO2 contributes to the greenhouse effect, warming the planet, altering the Earth’s weather patterns and directly affecting life as we know it.

To meet Paris Agreement climate standards, the world has to do more than stomp the brakes and reduce or offset CO2 emissions. It has to reverse course by removing the emissions that are already in the atmosphere, and then either reusing or sequestering them, which means 0.04% is, indeed, a meaningful number in more ways than one.

Extracting CO2 from the atmosphere isn’t like squeezing water out of a wet sponge. At only 400 parts per million, CO2 is exceptionally diffuse, making capture tedious and tough — and until now, quite expensive.

Swiss company Climeworks is tackling those challenges with its carbon dioxide removal solution. The company has developed a commercially viable, filter-based direct air capture (DAC) technology. By removing carbon dioxide from the air, it hopes to inspire 1 billion people to take climate action. By accessing Ansys simulation software as a partner in the Ansys Startup Program, Climeworks increased the filter capability of its DAC plants, streamlined the facilities’ energy consumption, and reduced fatigue and failure risk under mechanical loading cycles.

Climeworks’ goals are to:

  • Reverse the effect of CO2 on climate change with direct air capture plants.
  • Develop efficient plants to decrease captured CO2 costs.
  • Reuse air-captured CO2 as a raw material for renewable fuels and materials.
  • Remove CO2 as a service.

Currently, there are 15 Climeworks DAC plants operating in Europe, some as commercial ventures, others for research. The flagship pilot plant in Switzerland can capture 900 tons of CO2 per year; a facility under construction in Iceland will have the capacity to capture four times that amount. 

Climeworks’ direct air capture technology combined with the storage process developed by the Icelandic company Carbfix removes carbon dioxide from the air and stores it permanently underground. Image copyright Climeworks.

Designing Small and Scalable, For Big Results

The concept of carbon capture and sequestration isn’t new. In fact, it dates to the 1970s. The technology behind some methods goes back even further, all the way to the 1920s, when natural gas companies began separating CO2 from their product streams. 

There are three traditional ways of capturing carbon: post-combustion, pre-combustion and oxy-fuel combustion, which is used in power plants to burn fuel with nearly pure oxygen instead of air. But each of these is typically tied to collecting the emissions from a large point source such as the flue of a power generation facility or manufacturing plant, which requires industrial-scale capture facilities to be economical. 

 By contrast, Climeworks’ DAC system is modular, consisting of multiple collectors that remove CO2 from the air rather than from point sources. And instead of capturing CO2 in a gas/ liquid laminar flow like other approaches, Climeworks incorporates adsorbent air contact filters that the CO2 sticks to. Climeworks also reduces or even eliminates the transportation costs associated with carbon capture: They can locate a DAC plant right on the storage site.

These innovations have reduced the size and price of Climeworks’ plants.

  Climeworks direct air capture plant Photo by Julia Dunlop

Analyzing 500 Variations

Climeworks’ CO2 collectors selectively capture carbon dioxide in a two-step process. First, air is drawn into the collector with a fan. CO2 is captured on the surface of a highly selective filter material that sits inside the collectors. Then, after the filter material is full of CO2, the collector is closed. Climeworks increases the temperature to between 80 C and 100 C (176 F to 212 F), which releases the CO2. Finally, the high-purity, high-concentration CO2 can be collected.

The gas is then either permanently and safely stored underground, where it can remain for millions of years, or repurposed in industrial applications. For example, the captured CO2 can be turned into carbon black (a component in electronics, printing and construction), used for carbonating beverages, or processed into synthetic, renewable fuels.

Because CO2 is so vast and dilute, capturing 1 ton requires moving 2,000 to 3,000 tons of air into small channels in the system. Climeworks engineers used Ansys Fluent to analyze airflow volume and speed, understand pressure loss and how it affects the system’s energy consumption, reduce pressure drop, and optimize sorbent volume, that is, how much CO2 will stick to the solid material air contractor filter.

Each plant works in batch mode, with the heating and cooling process beginning only after the filter is saturated. Because releasing the gas and regenerating the collector creates a vacuum in the collection chamber — and the cycle is repeated thousands of times — engineers used Ansys Mechanical to simulate structural stress and fatigue. 

Altogether, engineers modeled 500 geometry variations of the air collector while perfecting their design, and did it in far less time than it would have taken to test and build one physical prototype. In fact, engineers estimate that simulation was five to 10 times faster than physical testing would have been. And time savings is cost savings — for Climeworks, its customers and, ultimately, for a planet trying to avoid the high price of climate change.

Leading scientific studies indicate that by mid-century, 10 billion tons of carbon dioxide will need to be removed from the air every year. Using Ansys software, Climeworks has developed a direct air capture solution that can contribute to that lofty goal.

Climeworks founders Christoph Gebald (l) and Jan Wurzbacher in front of the Climeworks plant Copyright Climeworks. Photo by Julia Dunlop

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