The amount of CO2 in the atmosphere increases year after year which contributes to the rise of global surface temperatures. Direct air capture (DAC) and sequestration is one method to reduce the amount of CO2 in the atmosphere thereby reducing global warming. The importance of DAC can be seen from the Intergovernmental Panel on Climate Change’s “Special Report on Global Warming of 1.5°C” which requires carbon negative technologies such as DAC in order to meet international climate goals 1. This has spurred many companies’ pursuit of DAC technologies such as Carbon Engineering (which utilizes a KOH absorption unit 2), Climeworks (which utilizes amines that are impregnated onto fiber supports 3), and Global Thermostat (which uses amines that are impregnated onto ceramic supports 4). All three of these processes utilize absorbents which chemisorb the CO2 from the air. There are other technologies for DAC such as moisture swing sorbents 5, and metal organic frameworks (MOFs) which are potential future materials for DAC 6.
Problem with DAC currently
The problem with current DAC technologies is that they are too expensive, with costs surpassing the current U.S. DOE goal of 27-39 $/tonCO2 7. Carbon Engineering and APS which utilize K+ and Na+ hydroxide absorption estimate their costs at $94-232/tonCO2 2 and $610-780/tonCO2 8, respectively. Climeworks and Global Thermostat, which utilize amines impregnated on fiber and ceramic supports, estimate their costs at $100-600/tonCO2 9 and $88-163/tonCO2 10,11, respectively. Therefore, significant advances are still required before DAC can become an economically viable method for reducing the amount of atmospheric CO2 for the purpose of greenhouse gas reduction. One reason the cost of these processes are so expensive is the cost to operate the process. These processes are energy intensive, requiring 1.8 MWh/tonCO2, 2.7 MWh/tonCO2, 2.7 MWh/tonCO2, and 1.9 MWh/tonCO2 for Carbon Engineering 2, APS 8, Climeworks 3, and Global Thermostat 10,11, respectively. A DAC technology with significantly less operating energy would make the technology more economically viable. To better understand how these cost estimates were calculated, please refer to the APS Report “Direct Air Capture of CO2 with Chemicals” 8.
Capital costs of constructing and implementing a DAC technology is also important for its economic viability. Since DAC technologies are still in their infancy, numbers for this are hard to come by but some key parameters can be used as a guide. The more complex a process, the use of never before used over industrially proven materials, volumetrically inefficient sorbent materials, and extremity conditions of the process are some parameters that increase the final capital cost. For example, Carbon Engineering process is complex and intensive which will require increased capital costs. Carbon Engineering however uses an industrially proven material which require less capital cost in comparison 2. Climeworks and Global Thermostat on the other hand are using never before used materials which require increased capital costs, but with a less complex and intensive process. An ideal DAC process uses a simple process with industrially proven materials efficiently at moderate temperature and pressures to keep capital costs low.
Location Location Location
Did you know that CO2 produced in one area of the planet quickly dissipates evenly over the whole planet? This means that CO2 can be captured from the air anywhere on the planet to reduce the overall CO2 emissions 12. However, from a technological standpoint, the location of the DAC plant is very important for the economic viability of the technology. This is due to the dilute nature of CO2 in air. In air, 420 ppm of CO2 occupies only 0.76 g/m3 (at 25 °C and 1 atm) and therefore a substantial amount of air would be required to capture 1 ton of CO2(1'300'000 m3/tonCO2). This dilute nature makes it uneconomical to significantly condition the air (that is, change its temperature, humidity, or pressure) when trying to capture the CO2 and therefore, the CO2 must be captured from the air at its ambient conditions. For example, changing the pressure by compressing the air into the process would cost $22 per kPa increase per ton of CO2 captured (assuming an energy cost of $0.06 kW/h) 13. Therefore, the DAC process must capture the CO2 at ambient air conditions, which vary around the planet. This is illustrated in the two maps below with the mean annual temperature varying from 35°C to -41°C and the mean annual absolute humidity varying from 0.12 g of H2O/kg of air to 22 g/kg.
There is an optimal location on Earth for each type of DAC technology during the capture step. This optimal location will have favorable atmospheric conditions of temperature, humidity, and pressure which will reduce the overall cost per ton of CO2 sequestered in the process. This idea has been alluded to in prior art. Keith et al. (2010) noted that the local atmospheric conditions such as humidity, pressure, and freezing temperatures all influence the hydroxide absorption units 14. This was further substantiated for the effect of humidity on the water consumption of the KOH process from experimental results from Carbon Engineering’s pilot plant 2.
Prior Art US 2008/0289495 A1
However, prior art has yet to mention the cumulative effect of these atmospheric parameters on process economics let alone the optimal atmospheric conditions on Earth for a particular DAC technology process. For example, US. Pat. No. 2008/0289495 A1 Global Thermostats technology located in one of the wettest regions on Earth, the Amazon Rainforest, as well as in one of the most arid regions on Earth, the Namib Desert 15. Moisture content level differences of this magnitude would undoubtedly have an effect on the process which makes the selection of the plant location of primordial importance to its viability.
Some technologies have severe limitations that prevent them from working in particular geographical locations due to their ambient atmospheric conditions. For absorption technologies such as hydroxide solutions or amines on solid supports, this is the temperature which the absorbent freezes. This was noted by Keith et al. (2010) that freezing temperatures would cripple water based KOH DAC systems 14. DAC technologies utilizing absorption would also suffer from significantly slower uptake rates of CO2 during the capture step at colder temperatures. This is an important consideration because the uptake rate in absorption based technologies at 25°C are 2 orders of magnitude lower than adsorption based technologies, which is illustrated in work by Stuckert and Yang (2011) 13. Significantly slower uptake rates imply that more air would be required to capture the same amount of CO2, which would increase operating costs, rendering the technology impractical. This limits the application of current absorption-based DAC technologies to warmer climates.
Finding the Ideal Location
Cold dry climates include Canada, Norway, Alaska, Russia, Finland, Greenland, Tibetan plateau, Atacama Desert, and Antarctica have optimum conditions for our process. If we pair them up with potential clean cheap abundant energy source include wind power, hydroelectricity, small modular nuclear reactors, solar, or geothermal, we will be able to capture CO2 for the lowest $/tonCO2. After capturing the CO2, we will be sequestrating the CO2 into the earth in one of the many potential sequestration sites that scatter our globe. To learn and understand ideal locations more, explore the maps of our world...
Our Direct Air Capture (DAC) Technology
We at TerraFixing have the goal of capturing and sequestering CO2 at the lowest $/tonCO2 to fiscally allow DAC to be a solution to global warming. We designed our process by incorporating the location of the process in the equation, with the aim of reducing the operating and capital costs into a simple scalable solution. The result, our DAC technology is geared for cold dry climates with operating energies as low as 1 MWh/tonCO2 utilizing a simple process with 5 unit operations using industrially proven materials efficiently at moderate temperatures and pressures to keep capital costs low. Our technology is also fundamentally different from many other DAC companies which are based on absorption. Our technology is based on using adsorption, allowing use in cold climates such as Canada, Norway, Alaska, Russia, Finland, Greenland, Tibetan plateau, and Antarctica.
Operating our process at low temperatures is beneficial because low temperatures intrinsically favors separation processes. This is because the minimum amount of work to separate and concentrate CO2 is a function of the temperature at which the separation occurs. This can be seen in the graph showing the minimum work required to separate all of the CO2 at a particular feed concentration and concentrate it up to 100% for temperatures of -50°C, -25°C, 0°C, 25°C, and 50°C. This phenomena, which is governed by the second law of thermodynamics, is illustrated in the graph in which energy requirements are 45% greater at 50°C than at -50°C. Specifically, for the DAC of CO2 at 400 ppm, a separation process occurring at 50°C theoretically has a minimum energy of separation of 538 MJ/tonCO2 whereas an operating temperature of -50°C would lower this value to 371 MJ/tonCO2. Thus, it is favorable to perform DAC separations at low temperatures in climates such as Canada, Norway, Alaska, Russia, Finland, Greenland, Tibetan plateau, and Antarctica.
Our Competitive Edge
DAC as an industry is currently in its infancy and not all solutions that target DAC are the same. Our technology differs from others with the ability to:
Have DAC plants in the cold climates of Canada, Norway, Alaska, Russia, Finland, Greenland, Tibetan plateau, and Antarctica. Other DAC companies with their absorption based processes would not be able to operate in freezing conditions. (The blue regions in the interactive web plot indicate real time satellite temperatures below zero)
Operate with the lowest $/tonCO2 in the DAC industry. This is due to the lowest MWh/tonCO2 as well as utilizing a simple process with 5 unit operations using industrially proven materials efficiently at moderate temperatures and pressures to keep capital costs low.
Requires only one input in the process, electrical energy. This is in opposition to Climeworks, Global Thermostat, and Carbon Engineering, which advertise 3 inputs, water, heat, and electricity.
No utilizing fossil fuels for heating in the process which Global Thermostat and Carbon Engineering incorporate.
A scalable solution to global warming with our DAC unit is designed to fit into a shipping container and utilize scales of economy.
Our DAC plant can be located in areas that would be undesirable for farming, away from population centers, without the need to cut down forests such as polar deserts, which would allow for mass DAC to bring our atmospheres CO2 concentration back to pre industrialization levels.