Ideal Locations

In order to make direct air capture a solution to global warming, ideal locations must be selected. These ideal locations are places with:

  1. Optimal conditions during the capture step for a particular direct air capture technology,

  2. Utilizing clean cheap abundant energy sources,

  3. Near a sequestration site.

By locating our direct air capture solution in these ideal locations, we can achieve $/tonCO2 that can allow humanity to effectively curb global warming.

Optimum Conditions

Figure 1 - Mean annual temperature in Celsius between 2000-2010.

The conditions of temperature and humidity vary drastically with regard to location. A simplistic way to observe this is by plotting the mean annual averages on a map. This can be seen in Figure 1 showing the mean annual temperature and Figure 2 showing the mean annual absolute humidity. Temperatures on our planet can range from 54°C to -89°C with mean annual temperatures ranging from 35°C near the equator to -41°C closer to the poles. With warmer air being able to hold onto more humidity than colder air, this trend is similar for humidity on the planet with the mean annual absolute humidity ranging from 0.12 gH2O/kgAir in Antarctica to 22 gH2O/kgAir in the Amazon rain forest. So, with there being such a wide variation in temperature and humidity, how does temperature and humidity impact direct air capture?

Temperature and humidity effect the direct air capture process mainly during the capture step. During the capture step, the air is put into contact with the sorbent, transferring the CO2 from the air to the sorbent. With CO2 being so diffuse in the air, it is uneconomical to significantly change the temperature or humidity of the incoming air.

Each direct air capture technology has ideal locations in terms of temperature and humidity on the planet. For companies like Carbon Engineering, Global Thermostat, and Climeworks which employ absorption based technologies, these are locations that are humid as well as warm. Humid, such that water loss as well as damage to amines are prevented; and warm, such that uptake rates between the absorbent and the air are fast.

For our adsorption technology at TerraFixing its colder and drier climates. Cold temperatures benefit all separation as well as increase adsorption capacities, which reduce sensible heat losses in the process and capital cost for the process. Dry climates allows water to be removed from the separation equation, allowing increased performance for adsorbents. These cold dry climates include Canada, Norway, Alaska, Russia, Finland, Greenland, Tibetan plateau, Atacama Desert, and Antarctica have optimum conditions for our process.


Figure 2 - Mean annual absolute humidity kg in gH2O/kgAir between 2000-2010.

Sequestration Sites

After capturing and concentrating CO2 in cold dry climates, CO2 needs to be resequestered into Earth's crust in order to reverse global warming. To do this, CO2 is first pressurized and pumped into the ground to a depth greater than 800 m where CO2 stays as a supercritical fluid, taking up minimal amount of space. There are two depths of interest:

  • Between depths of 800 m and 3000 m, CO2 can be stored in capped rock geographic formations 1. These formations can hold CO2 preventing it from rising and being re-emitted back to the surface.

  • At depths greater than 3000 m, CO2 is denser than water, and CO2 can be stored in porous water filled formations. Sequestering CO2 into these formations have minimal risk of CO2 leaking out over long periods of time because CO2 will continuously sink within the formation.

In order to ensure that CO2 stays sequestered once it is placed into the ground, care should be taken to avoid sequestering CO2 in seismically active regions as well as near fault lines which are depicted in Figure 3. Avoiding these red and yellow regions reduces the risk that CO2 placed within the Earth is unintentionally re-released to the atmosphere.

To reduce costs to make direct air capture feasible, the direct air capture plant should be located near the sequestration site. By locating the process near the sequestration site, an expensive CO2 pipeline is not required to transport the CO2 from the capture location, to the sequestration site.

There are many prospective places to sequester CO2 on the planet. This can be seen in Figure 4 with a large portion of Earth's surface being potentially suitable for CO2 sequestration. This map is based on work from the USGS World Petroleum Assessment which equivalates potential hydrocarbon reserves in sedimentary basins, which are already storing carbon, with locations to sequester CO2. Carrying over data from highly prospective CO2 sequestration sites in Figure 4, Figure 5 shows other potential geological formations for sequestration including, basalt and ultramafic formations. These sites are less common but allow CO2 to readily react with the rock formation. This was observed in the Carbfix Project in Iceland where CO2 was mineralized within a year of injection 2. Another prospective sequestration site is saline formations. Saline formations are layers of sedimentary porous rocks filled with salty water. These formations are fairly widespread and exist in large portion of sedimentary basins across the world and represents an enormous potential for CO2 sequestration. These sedimentary basins are depicted in Figure 6 which all are potential CO2 sequestration sites.

With Earth having many potential sequestration sites, direct air capture projects can be located near sequestration site regardless of desired climate. For our technology, the desired cold dry climates of Canada, Norway, Alaska, Russia, Finland, Greenland, Tibetan plateau, Atacama Desert, and Antarctica all have many prospective locations to sequester CO2.

Figure 3 -The GEM Global Seismic Hazard Map depicts the geographic distribution of the Peak Ground Acceleration with a 10% probability of being exceeded in 50 years, computed for reference rock conditions. (Pagani et al., 2018) Red indicates high Seismic hazard activity with the lowest risk being white.

Figure 4 - High level estimate of the prospectively of geological storage of CO2 for sedimentary basins of the world. (Bradshaw and Dance, 2005). This is based on the USGS World Petroleum Assessment which equivalates potential hydrocarbon reserves in sedimentary basins with locations to sequester CO2.

Figure 5 - Map of CO2 sequestration facilities, pilot projects, and long-term storage potential in geologic formations. (Keleman et al., 2019). This takes the high prospective CO2 storage locations from Bradshaw and Dance, 2005, and combines it with potential basalt formations and ultramatic formations.

Figure 6 - Map depicting major sedimentary basins of the world. (Rosenbauer and Thomas, 2010)

Clean Cheap Abundant Energy

Energy is required to run the fans, compressors, heaters, and vacuum pumps of a direct air capture process. This energy can be provided multiple ways using electricity, waste heat, or combustion. For example, Carbon Engineering and Global Thermostat use electricity to power fans, pumps, etc. but also have incorporated the use of fossil fuels as a cheap source of heat. This use of fossil fuels raises fundamental questions about how green their process is. We at TerraFixing believe that a key element of an energy source is that it must be clean. Clean energy is important because we want to have a net carbon negative impact on the environment. To reverse global warming. Different energy sources that align with this agenda are wind power, hydroelectricity, solar power, geothermal power, and small modular nuclear reactors just to name a few.

One key element that dictates the viability of a direct air capture process is the cost of the energy. For instance, our process requires 1 MWh/tonCO2 in the most favorable climates, if electricity costs $100/MWh, our processes operating cost would be $100/tonCO2. Thankfully, $100/MWh is a very expensive cost for electricity, with electricity costs varying based on the type of energy, and its location. For instance, wind energy in 2018 in the Interior of the United States levelized purchase power agreement cost was on average $12/MWh ranging between $6/MWh and $25/MWh 3. Therefore, building the our direct air capture plant near the cheaper $6/MWh source would provide cheap energy reducing our operating costs.

In order to solve global warming, CO2 emissions from today need to be captured, as well as emissions from the past, and the numbers are massive. In 2018, 33.1 gigatons of CO2 was released into the atmosphere. And if we want to bring CO2 levels in the atmosphere back down to pre-industrialization levels, 1580 gigatons of CO2 is needs to be captured and sequestered into the ground. This requires a substantial amount of energy to do, requiring an abundant energy source. To put the numbers in perspective, at an energy cost of 1 MWh/tonCO2, to capture todays emissions requires 33100 TWh of electricity, which is more than all of the electricity produced in 2020. Therefore, to make a dent in todays CO2 emissions and those of our ancestors, a plentiful abundant energy source that is not yet utilized is required.

Wind Power

Much of the Earths highest wind power density energy resources has yet to be developed. This is because the location where the strongest winds blow are far away from population centers. These strongest winds are commonly found closer to the poles with colder winds being denser as well as faster, and therefore carry more kinetic energy. With winds having higher kinetic energy, wind energy can be captured more efficiently, leading to lower $/MWh. The wind power density across the planet can be seen in Figure 7 which shows the wind power density being highest in locations like Canada, Greenland, Norway, and Alaska with Antarctica being the windiest place on the planet. Utilizing these clean abundant wind energy sources would be able to power our technology to capture, concentrate, and sequester CO2 emissions back into the Earth. Another benefit of wind energy is that it is scalable in these colder regions. Direct air capture plants can be designed per wind turbine, and exponentially grow as scales of economy improve. With land in these cold climates being plentiful with little use, wind turbines and our DAC plant can be scaled to the largest sizes to meet our goal of reversing global warming.

Figure 7 - The wind resource map provides an estimate of mean wind power density at 100m above surface level. Power density indicates wind power potential part of which can be extracted by wind turbines. Higher wind power densities are correlated with lower $/MWh. (World Bank and the Technical University of Denmark)

Figure 8 - Potential hydroelectricity dams with design capacity larger than 1000 MW overlaid on the map of gross hydropower potential. (Zhou et al., 2015)

Undeveloped Hydroelectricity

Another clean energy source that can power our direct air capture process is hydroelectricity. This source of electricity is relatively low cost, with current hydroelectric dams already serving populated centers. One unique opportunity for our direct air capture technology is to partner our plant with a potential hydroelectricity sources. Currently, there are many locations in Canada, Alaska, Russia, and the Tibetan Plateau that have yet to be developed due to lack of demand. With a long term commitment from us to reverse global warming, these energy sources can power our technology, sequestering significant quantities of CO2.

Solar Power

Both the Atacama Desert & Tibetan Plateau have very dry climates that are moderately cold which is beneficial to our process. Each of these regions also have very high solar power densities that can be exploited, leading to lower $/MWh. With clean solar power also being a scalable solution, and there being abundant amounts of solar energy that hit these regions, this increases the feasibility that solar energy can be used to run our process.

Small Modular Nuclear Reactors

With the promise of future small modular nuclear reactors being portable and safe while providing cheap fission energy anywhere, our process can be located in the most ideal locations of optimal conditions next to a sequestration site.

Geothermal

Current geothermal energy makes up a small fraction of the worldwide electricity production, but geothermal offers a cheap clean heat and electricity source. Our direct air capture process could potentially be powered in Iceland, Norway, Alaska, and Russia that have potential geothermal electricity.