(459d) Industrial Decarbonization Via the Optimal Integration and Design of an HT-PEM Cogeneration Energy System

Achieving the international climate goals as defined by the Paris Climate Agreement, the COP 12, and other climate agreements, depends on adapting existing technologies or creating new ones to operate on new energy sources, to become more efficient, and to emit less carbon dioxide. In the field of industrial decarbonization, the key question facing modern engineers is how can industry decrease or eliminate carbon emissions from industrial electrical and thermal energy production.

To accomplish this, decarbonized and renewable energy producing technologies such as heat pumps, biomass gasification units, resistive heaters are being researched and developed to replace modern fossil fuel-based technologies. However, beyond investigating the performance curves and environmental impact of the technologies independently or on a case-by-case basis, research is needed on how such technologies can be optimally designed and integrated to fulfill the energy requirements of any industrial process. To this end, very limited research on the optimization-based design and integration of decarbonized thermal and electrical energy producers for industrial processes has been completed. Some notable works in this field include the work of Wallerand et int. Marechal [1] and Wissocq et int. Le Bourdiec [2] for creating optimization tools to design and integrate heat pumps and other thermodynamic systems into industrial processes.

To contribute towards optimization-based design and integration of decarbonized energy systems and to a gap in decarbonized energy production in the range of 100-200 C [3], this paper presents a tool for the optimal design and process integration of a high temperature proton exchange membrane (HT-PEM) fuel cell cogeneration system. Via electrochemical reactions and cell inefficiencies, the HT-PEM fuel cell utilizes green hydrogen to produce decarbonized electricity and heat for any industrial process with heating requirements of up to 200 C [4].

For this purpose, a mechanistic 1D flux-based model of an HT-PEM fuel cell system modeled after the BASF Celtec membrane HT-PEM system is developed to be embedded in an MINLP cogeneration optimization problem. The model is validated against experimental polarization data from BASF, returning a low root mean squared error of 0.08735 and a good qualitative match over the whole operating range, as shown in figure 1. The validated model is integrated into an adapted heat exchanger network to create the cogeneration optimization problem. The cogeneration optimization problem develops a heat exchanger network to satisfy the heating requirements of the industrial process via pinch analysis. The thermal energy is provided by the thermal output of the HT-PEM cells which have been designed by the solver to operate at an optimal temperature and provide enough thermal energy to the heat exchanger network. Simultaneously, the HT-PEMs are designed to be able to generate enough electricity to fulfill the processes electrical power requirements. The HT-PEM cogeneration optimization problem is solved by the Lindo MINLP solver using an ethylene separation process as a case study [5].

Solving the optimization problem returns an optimized heat exchanger network map, a heat exchanger network composite curve (c.f. figure 2) , the selected design variables for the fuel cell stacks (c.f. figure 3), and general performance general performance metrics of the fuel cell. For the ethylene separation process case study, the HT-PEM fuel cells were designed to produce 578.6 MWh of thermal and 368.7 MWh of electrical power per year at an annualized cost of $508,189 per year. To compare the viability of the HT-PEM cogeneration against other energy producing technologies, a high level sensitivity analysis is completed which evaluates the economic performance of the HT-PEM system against the performance of a heat pump, resistive heater, and natural gas boiler. Three key economic parameters: the electricity price, hydrogen price, and HT-PEM capital costs are varied. Although the alternative technologies are more financially viable given the current electricity price, hydrogen prices and capital costs, the HT-PEM system exhibits a strong sensitivity to electricity and hydrogen prices. With small variations of the electricity and hydrogen prices, the HT-PEM rapidly becomes the most economically viable solution for heat and electricity production among the considered technology options.

Citations
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[1] A. S. Wallerand, M. Kermani, I. Kantor, and F. Maréchal. “Optimal heat pump integration in industrial processes”. In: Applied Energy 219 (2018), pages 68–92.

[2] T. Wissocq, S. Ghazouani, and S. Le Bourdiec. “A methodology for designing thermodynamic energy conversion systems in industrial mass/heat integration problems based on MILP models”. In: Energy 185 (2019), pages 121–135.

[3] C. Lauterbach, B. Schmitt, U. Jordan, and K. Vajen. “The potential of solar heat for industrial processes in Germany”. In: Renewable and Sustainable Energy Reviews 16.7 (2012), pages 5121–5130.

[4] S. V. M. Guaitolini, I. Yahyaoui, J. F. Fardin, L. F. Encarnacao, and F. Tadeo. “A review of fuel cell and energy cogeneration technologies”. In: IREC (2018), pages 1–6.

[5] A. Lincoff, I. Grossmann, and G. Blau. “Separation system for recovery of ethylene and light products from naphtha-pyrolysis gas stream”. In: Process Design Case Study (1983).

[6] D. Jakobs “Optimization of a high temperature proton exchange membrane for industrial cogneration”. Unpublished masters thesis (2023). RWTH Aachen