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.