Design and optimisation of European supply chains for carbon capture, transport, and sequestration

The global anthropogenic emissions of greenhouse gasses experienced an exponential increase compared to pre-industrial levels and, among these, CO2 is the most abundant, with an overall emission that rose globally from 2 Gt/year in 1850 to over 35 Gt/year in 2010. Carbon capture and storage has been highlighted among the most promising options to decarbonise the energy sector, especially considering the European context which heavily relies on fossil fuel-fed facilities. When dealing with the strategic design and planning of a European carbon capture and storage infrastructure, the necessity of employing quantitative mathematical tools to treat the combinatorial complexity of such large-scale and multi-echelon networks clearly emerges. In this work, mixed integer linear programming models were utilised for carbon capture and storage supply chain optimisation at European scale. The modelling framework has been developed according to a mixed integer linear programming model representing Europe in terms of emissions from large-stationary sources (i.e., coal and gas power plants). Regarding the capture facilities, post-combustion, pre-combustion and oxy-fuel combustion have been included as possible options, whereas both pipelines and ships have been described in techno-economic terms as potential transport means. The European geological storage potential has been retrieved from the EU GeoCapacity Project. Uncertainty in geological storage capacities has emerged among the major challenges for fostering an effective implementation of such complex systems. Accordingly, a tailored mathematical technique has been employed to tackle such risks and obtain optimal network configurations in terms of resiliency of the transport infrastructure. Then, a risk assessment has been incorporated within the modelling framework. This evaluation accounted for the societal risk generated by a potential leakage in the transport system (quantified according to the seriousness of the hazard) and was coupled with the choice of installing risk mitigation options (e.g., concrete slabs, deep burying, marker tape, surveillance). The societal response to carbon capture and storage has been further analysed through the concept of social acceptance, described through the amount of risk perceived by a given population inhabiting the region where an infrastructure is planned. The social response has been modelled as proportional to the project size, to the amount of population and to the differential behaviour of the European countries. Besides, a set of constraints has been employed to balance the spread of installation and operation costs among countries, with the aim of enhancing economic costs share and cooperation policies between the different players. Finally, a preliminary analysis has been assessed on possible utilisation pathways for carbon conversion and utilisation into products. The carbon capture and storage models were optimised using the GAMS software through the CPLEX solver. Results from the deterministic framework demonstrated the good European potential for carbon sequestration and gave some indications on the total cost for CO2 capture, transport and sequestration. Capture costs were found to be the major contribution to total cost, while transport and sequestration costs were never higher than 10% of the investment required to set in motion and operate the whole network. The overall costs for a European carbon capture and storage SC were estimated in the range of 27-38 €/t of CO2. The risk generated by uncertainty in geological storage capacities was found negligible with respect to the overall cost of the network, but slightly higher investments for transport and sequestration were needed to improve the resiliency of the system. The societal risk-constrained optimisation demonstrated the possibility to design a safe transport infrastructure with minor additional costs. In fact, mitigation actions never represented more than 11% of cost for installing and operating the transport network. However, no feasible solution could be found for a carbon reduction target higher than 50%, because of the unacceptable level of societal risk. When maximising social acceptance from the public (through minimising risk perception), results led to a massive exploitation of offshore sequestration solutions with a (possibly unacceptable) total costs of about 50.88 €/t of sequestered CO2, i.e. +34% with respect to the economic optimum, due to a more complex network configuration characterised by high transport (+434%) and sequestration (+853%) costs. A multi-objective optimisation analysis, however, allowed identifying a possible intermediate solution between the two conflicting objectives (i.e., economics against acceptance), capable of limiting risk perception without excessively compromising the economic performance of the network. Regarding the model including costs share mechanisms among European countries, results showed that the additional European investment for cooperation (max. +2.6% with respect to a non-cooperative network) might not constitute a barrier towards the installation and operation of such more effective network designs. Finally, a preliminary model investigated the production of chemicals from CO2 (specifically, polyether carbonate polyols and methanol) as an alternative to geological sequestration. The results showed that CO2 conversion and utilisation mainly affects the total cost of the supply chain, which could be reduced with respect to a mere carbon capture and storage network. On the other hand, the contribution of CO2 utilisation over capture in terms of environmental benefits was shown to be almost negligible.