(2aa) Optimization-Based Assessment Framework for Identification of the Optimal CO2 Utilization Strategy to Energy Products

This paper presents a novel optimization-based assessment framework for identification of the optimal carbon capture and utilization for energy products (CCU4E) strategy. To achieve this goal, we first generated a superstructure involving a series of technologies (e.g., catalytic conversion, thermochemical energizing, biological fixation) to produce value-added energy products (e.g., methanol, dimethyl ether, ethanol, formic acid, gasoline) from captured CO₂ as a feedstock. This study then developed an optimization model for strategic planning of CCU4E and for assessing the technical, economic and environmental performances. With the proposed model, we investigate how the optimal systems is sensitive to practical constraints, such as the availability of CO₂, the market size of energy products and what benefits are expected. As a result, we can identify the optimal CCU4E strategy over various technological pathways to produce different targeted energy products, which makes CO₂-based energy products economically and environmentally viable.

Global emissions of CO₂ from fossil fuels have been increasing by 2.7% annually over the past decade and are now 60% above 1990 levels, the reference year for the Kyoto Protocol [1]. Carbon capture and utilization for energy products (CCU4E) is one of the attractive solutions addressing global warming and energy security [2]. CCU4E supports reducing CO₂ emission by capturing and improving domestic energy security by utilizing CO₂ as a raw material for energy products. The goal of this study is to propose an optimization model for planning the CO₂ utilization to energy products, which supports identifying the optimal CO₂ utilization strategies. To achieve this goal, we developed the superstructure of CCU4E by selecting captured CO₂ as a main feedstock and possible final products as well as required technologies, and generating the superstructure by integrated technologies to convert CO₂ forward to final products as shown in Figure 1. The technologies include reaction and conversion technologies (e.g., direct CO₂ hydrogenation, reverse water-gas shift, methanol-to-gasoline, methanol dehydration) component separation (e.g., amine-based CO₂ absorption, CO PSA), and product purification (i.e., flash drum, distillation column).

In this study the utilization of CO₂ includes not only CCU4E, and CO₂ capture but utilization for non-energy (CCU4NE). To ensure precise information of a real industries, we first estimated the CO₂ potentials for CCU4E by multiplying the amount of CO₂ captured from CO₂ capture facility and the ratio between CCU4E and CCU4NE [3,4]. For technical and economic information of the involved technologies, unit processes in the CCU4E framework were simulated using Aspen Plus V.10 [5]. More detailed process simulation and modeling could be found in the literature [4]. The mass flow, energy flow, sizing and costing data were then obtained as parameters of the optimization model. To identify the optimal CO₂ utilization strategies, we develop an optimization model using a mixed integer linear programming (MILP) technique based on the information available on the technologies. The optimization model includes the objective function, maximizing profit which is subject to various constraints such as technology capacity, feed availability, market size of energy products, and mass flows. With the proposed models, we can identify the optimal strategy to utilize CO₂ to different energy products objecting to maximize profit. Finally, we applied the optimization model along with the obtained parameter to a real energy sector, including global and local energy markets. By considering various scenarios that reflect regional characteristic of different countries (e.g., hydrogen prices, final product market sizes, CO₂ potentials, and governmental policy for mitigating CO₂ emission), we identified practical CCU4E strategies for each country.

In this study, we proposed and developed an optimization-based assessment framework for CCUE strategies. The framework can contribute to the establishment of the best CO₂ utilization strategy over various technological pathways to produce different targeted energy products, which makes CO₂-based energy products economically and/or environmentally viable. It can also support a policymaker or stakeholder to identify a suite of strategic solutions to utilize captured CO₂ for energy products.

References

[1] Global Carbon Atlas, Fossil Fuel Emission, http://www.glo balcarbonatlas.org/en/CO2-emissions, (accessed 16 July 2020).

[2] A. Al-Mamoori, A. Krishnamurthy, A. Rownaghi , F. Rezaei, 2017, CarbonCaptureand UtilizationUpdate. Energy Techonol, 5, 834–849.

[3] IEA (2020), World Energy Model, Paris https://www.iea.org/ reports/world-energy-model

[4] TN. Do, C. You, J. Kim, 2022, A CO2 utilization framework for liquid fuels and chemical production: techno-economic and environmental analysis. Energy Environ Sci., 15, 169–184

[5] Aspen Plus. Version 10.0, Aspen Technology Inc, 2019, http:// www.aspentech.com.