Engineering challenges of ocean liming

• The addition of calcium oxide powder to the ocean could be used to sequester atmospheric CO2.
• For every tonne of CO2 sequestered, between 1.4 and 1.7 tonnes of limestone would have to be processed.
• The thermal and electrical requirements could be up to 5.6 and 1.2 GJ tCO2−1 respectively.
• OL could cost approximately US$72–159 t−1 of CO2.

The relationship between the level of atmospheric CO2 (carbon dioxide) and the impacts of climate change is uncertain, but a safe concentration may be surpassed this century. Therefore, it is necessary to develop technologies that can accelerate CO2 removal from the atmosphere. This paper explores the engineering challenges of a technology that manipulates the carbonate system in seawater by the addition of calcium oxide powder (CaO; lime), resulting in a net sequestration of atmospheric CO2 into the ocean (ocean liming; OL). Every tonne of CO2 sequestered requires between 1.4 and 1.7 t of limestone to be crushed, calcined, and distributed. Approximately 1 t of CO2 would be created from this activity, of which >80% is a high purity gas (pCO2 > 98%) amenable to geological storage. It is estimated that the thermal and electrical energy requirements for OL would be 0.6–5.6 and 0.1–1.2 GJ tCO2−1 captured respectively. A preliminary economic assessment suggests that OL could cost approximately US$72–159 t−1 of CO2. The additional CO2 burden of OL makes it a poor alternative to point source mitigation. However, it may provide a means to mitigate some diffuse emissions and reduce atmospheric concentrations.