Cryogenic removal of carbon dioxide from the atmosphere

A method for removal of atmospheric carbon dioxide (CO2) comprising:

• moving air at atmospheric pressure with a fan into a recuperative heat exchanger;
• cooling the air in the recuperative heat exchanger to a first temperature that is above a deposition point of atmospheric CO2;
• determining a temperature of cooled air leaving the recuperative heat exchanger and adjusting a rate of airflow of the air into the recuperative heat exchanger to maintain the temperature of the cooled air at the first temperature by determining at a first time that the temperature of the cooled air leaving the recuperative heat exchanger is above a first threshold temperature and in response decreasing the rate of airflow into the recuperative heat exchanger and by determining at a second time that the temperature of the cooled air leaving the recuperative heat exchanger is below a second threshold temperature and in response increasing the rate of airflow into the recuperative heat exchanger;
• passing the cooled air over a deposition surface chilled to a to a second temperature below the deposition point of atmospheric CO2 to cause formation of solid CO2 and removal of CO2 from the air, the deposition surface within a deposition chamber;
• determining a temperature of air after passage over the deposition surface and adjusting a temperature of the deposition surface to maintain the temperature of air after passage over the deposition surface below the deposition point of atmospheric CO2;
• determining that the temperature of air after passage over the deposition surface is above a first threshold temperature and in response decreasing the temperature of the deposition surface;
• determining that the temperature of air after passage over the deposition surface is below a second threshold temperature and in response increasing the temperature of the deposition surface;
• removing the solid CO2 from the deposition surface with a scraper;
• moving, with the scraper, the solid CO2 as a solid out of the deposition chamber;
• returning the cooled air after removal of the solid CO2 to the recuperative heat exchanger to cool incoming air;
• and
• returning air from the recuperative heat exchanger to the atmosphere with at least some of the CO2 removed.

A system for removal of atmospheric carbon dioxide (CO2) comprising:

• a cryogenic refrigerator comprising a compressor, a heat exchanger, a gas coolant loop, and a liquid coolant loop, wherein a temperature of the liquid coolant loop is controlled by an amount of compression provided by the compressor to gas within the gas coolant loop;
• a fan configured to inject air from the atmosphere into the system at atmospheric pressure, wherein the air has a concentration of CO2 below about 500 ppm;
• a dehumidifier configured to receive the air from the fan and remove water vapor from the air;
• a recuperative heat exchanger configured to receive the air from the dehumidifier and cool the air to a first temperature about 5° C. to 1° C. above a deposition point of atmospheric CO2, wherein the recuperative heat exchanger is a shell and tube countercurrent flow heat exchanger that includes fins on the inside of tubes in the recuperative heat exchanger configured to increase the surface area contacted by the air as it passes through the recuperative heat exchanger;
• a first temperature sensor configured to detect a temperature of cooled air leaving the recuperative heat exchanger and first control circuitry configured to adjust a speed of the fan to decrease a rate of airflow into the recuperative heat exchanger responsive to determining that the temperature of the cooled air leaving the recuperative heat exchanger is above a first threshold temperature and configured to adjust a speed of the fan to increase the rate of airflow into the recuperative heat exchanger responsive to determining that the temperature of the cooled air leaving the recuperative heat exchanger is below a second threshold temperature;
• a deposition chamber configured to receive the cooled air from the recuperative heat exchanger and contact the cooled air with a deposition surface chilled, by the liquid coolant loop of the cryogenic refrigerator, to a second temperature below the deposition point of atmospheric CO2 to cause formation of solid CO2 and removal of CO2 from the air;
• a second temperature sensor configured to detect a temperature of the air leaving the deposition chamber and second control circuitry configured to decrease the temperature of the deposition surface responsive to determining that the temperature of the air leaving the deposition chamber is above the deposition point of atmospheric CO2 and configured to increase the temperature of the deposition surface responsive to determining that the temperature of the air leaving the deposition chamber is below a threshold temperature, wherein the second control circuitry is configured to adjust the temperature of the deposition surface by changing the amount of pressure provided by the compressor in the cryogenic refrigerator;
• a scraper configured to remove solid CO2 from deposition surface and move the solid CO2 as a solid out of the deposition chamber;
• and
• a return pathway from the deposition chamber that passes through the recuperative heat exchanger where the cooled air cools the air injected from the atmosphere and returns the cooled air to the atmosphere with at least some of the CO2 removed.