Abstract
Primarily released by the conversion of primary fossil energy sources, anthropogenic greenhouse gas emissions influence global warming fundamentally. Since they enable increasing the share of sustainable energy sources in the energy supply and reducing greenhouse gas emissions through targeted integration, power-to-X technologies promise to be an important element of compliance with impending regulations and laws. VDI 4663 guideline for strategically optimizing (technical) processes applies the physical optimum, a promising performance indicator for a unified, time-independent, and structured evaluation of power-to-X technologies that defines an operation under physically optimal conditions as a limit value. This study applies VDI 4663 to a power-to-X system and evaluates different components. It specifically examines current power-to-gas applications, the physical optimum as a limit-oriented indicator and its application to complex processes, the physically optimal operation of electrolysis and methanation, heat transfer as a critical component of methanation, the evaluation of a heat exchanger based on the physical optimum, and targeted process optimization based on VDI 4663. The outcome is an energy index for the evaluation of a heat exchanger, factoring in its structural design. The physical optimum of electrolysis and methanation developed here can also be employed as the basis for targeted optimization. This study serves as a basis for the evaluation of other power-to-X systems and introduces the application of VDI 4663. Additionally, the applicability of the physical optimum to chemistry-based processes is validated.
Highlights
A fundamental change in the supply of energy is observable worldwide, as demonstrated by the following examples
The power-to-methane process evaluated by Viktor, Schabbach, Link, and Fischer (2017), for instance, has an overall efficiency of 56%, while other sources cite overall efficiencies of 46 to 68% for the same process (Viktor, Schabbach, Link Fischer 2017; MüllerSyring 2011; Zukunft ERDGAS GmbH 2017)
For instance, require electricity to produce a pressure difference in a fluid flow, they are evaluated from the demand perspective, which is defined by the energy required by the process in real terms and the energy required under physically optimal conditions (PhO output) (Keichel 2017)
Summary
A fundamental change in the supply of energy is observable worldwide, as demonstrated by the following examples. The United Nations Framework Convention on Climate Change (UN-FCCC) calls for an 80–95% reduction of greenhouse gases over 1990 across all sectors by 2050 (United Nations Framework Convention in Climate Change 2017). In keeping with the New Zealand Energy Strategy 2011–2–21, New Zealand has set itself the goal of providing 90% of its electricity from sustainable energy sources by 2025 (Ministry of Economic Development New Zealand 2011).
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