CO2 submarine storage in glass containers: life cycle assessment and cost analysis of four case studies in the cement sector

Since carbonation of cement materials over their life cycle represents a large and growing net sink of CO2 (Xi et al., 2016), the capture and storage of CO2 emissions during the production of cement leads to negative emissions. This paper describes the application of a new patented technology for the storage of CO2 in glass containers into the deep seabed (Submarine Carbon Storage, SCS), to cement plants located in four different locations in the world (Italy, Spain, Bulgaria, and Morocco; cases A, B, C, and D respectively). This technology is based on the bottling of liquid CO2 at high pressure in capsules made of glass that are sent to the bottom of the ocean by a proper pipeline. A Life Cycle Assessment that considers all the stages of the process and twelve impact categories, with a focus on the climate change category, showed an average impact of 0.11 tCO2eq per ton of CO2 stored for Case A, 0.084 for B, 0.086 for C and 0.132 for D. The part of the process with the highest GHG impact is the capsule production, due to the consumption of natural gas and electricity and to the calcination taking place during the production of glass. The cost analysis has included the capital costs (glass furnace, machinery, infrastructures, engineering, procurement & construction) and the operational costs (energy consumption, labor costs, materials, long-term monitoring), considering also the funding structure through financing and equity. The costs of the four case studies, 29 $/tCO2 stored for Case A, 19 $/tCO2 for case B, 16 $/tCO2 for Case C and 21 $/tCO2 for case D, are in the range identified in Caserini et al. (2017). The CAPEX is quite similar between the four cases, whereas the OPEX cost variation is larger; the parameters that most affected the cost were the electricity price, the natural gas price and the amount of CO2 stored (tied to the size of the cement plant). Although further work is needed to assess in detail some critical aspects of the design, the result of this stage of the research allows concluding that the application of the SCS in cement plants could represent an interesting option for negative emissions, but the contribution of cement-based products as a negative emissions source is limited due the slowness of CO2 uptake during the lifetime of cement materials.