(4hp) Modeling, Simulation and Optimization of Direct and Indirect Mineralization Strategies for CO2 Capture

Carbon neutrality is a major and necessary goal to cope with the Paris agreement, trying to reduce the
impact of anthropogenic activities in the environment. The advent of ambitious plans to decarbonize
the future energy system (such as the European Green deal or the Swiss energy strategy) encompass
important modifications in the way we supply energy but also how to deal with unavoidable emissions.
Sectors such as waste management, will need to capture CO2 coming from incineration plants,
generating ‘negative’ CO2 emissions and compensating for sectors in which carbon capture is complex
or unfeasible. Among these technologies, generally labeled carbon capture usage and storage (CCUS),
mineralization is a promising one. Mineral silicates naturally present in some rocks but also in industrial
waste (incineration bottom ash, steel slag, etc.) are able to, upon activation, capture CO2 by forming
carbonates (mainly CaCO3 and MgCO3) which are extremely stable. Although mineralization is not a
new technique for CCUS, the products it yields are gaining market value, coupled with an increasingly
stringent CO2 emission policy and taxation system.

In this work we built a framework for simulation and optimization of mineralization techniques,
accounting for costs and environmental impacts and coupled with heat integration features. The
simulation was developed using the commercial software Aspen Plus (Aspen Technology Inc.). Models
for CO2 capture using monoethanolamines (MEA) were coupled with direct (Huijgen et al., 2006;
Gerdemann et al., 2007) and indirect (Criado et al., 2014; Fagerlund et al., 2012) carbonation strategies.
The optimization problem follows a mixed-integer linear programming formulation and is able to
design the most profitable (or more environmentally-friendly) system under the current market
assumptions, highlighting the synergies brought by heat integration. A municipal solid waste (MSW)
incinerator is used to showcase the application of the technology, coupling a flue gas with adequate
CO2 composition for MEA application (between 10 and 15 % V/V) and bottom ash rich in silicates.
According to industrial data, 1 ton of incinerated MSW generates 0.19 ton of bottom ash and up to 1.6
ton of CO2. The amount of bottom ash is, nevertheless, insufficient to guarantee the full carbon capture
(it accounts up to 5% of the required material) and therefore external mineral sources are used.

Preliminary results point for a profitable system; direct carbonation can provide an extra revenue
between 200 and 3,000 $/ton of stored CO2 and indirect between 150 and 2800 $/ton of stored CO2,
depending on economic incentives (such as a CO2 tax), the cost to buy extra minerals (with or without
transport) and the market value considered for value-added products. Similarly the environmental
impact can achieve reductions up to 4 ton of CO2-eq per ton of CO2 stored, which is in line with results
previously reported (Ostovari et al., 2020). Direct carbonation seems to perform better economically
but also environmentally compared to the indirect pathway, by using water rather than chemical
additives and having a more straightforward and easier to implement process. This work aims to
contribute to the on-going discussion on the collective strategy for curbing emissions.

References

1. Aspen Technology Inc.: www.aspentech.com.
2. Criado, Y. A., Alonso, M., and Abanades, J. C.: Kinetics of the CaO/Ca(OH)2
Hydration/Dehydration Reaction for Thermochemical Energy Storage Applications, Ind. Eng.
Chem. Res., 53, 12594–12601, 2014.
3. Fagerlund, J., Nduagu, E., Romão, I., and Zevenhoven, R.: CO2 fixation using magnesium silicate
minerals part 1: Process description and performance, Energy, 41, 184–191, 2012.
4. Gerdemann, S. J., O’Connor, W. K., Dahlin, D. C., Penner, L. R., and Rush, H.: Ex Situ Aqueous
Mineral Carbonation, Environ. Sci. Technol., 41, 2587–2593, 2007.
5. Huijgen, W. J. J., Ruijg, G. J., Comans, R. N. J., and Witkamp, G.-J.: Energy Consumption and Net
CO2 Sequestration of Aqueous Mineral Carbonation, Ind. Eng. Chem. Res., 45, 9184–9194, 2006.
6. Ostovari, H., Sternberg, A., and Bardow, A.: Rock ‘n’ use of CO2: carbon footprint of carbon
capture and utilization by mineralization, Sustain. Energy Fuels, 4, 4482–4496, 2020.