DAC and Location

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. 

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 a 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 into 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. 

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 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.