PEM-Elektrolyse-Systeme zur Anwendung in Power-to-Gas Anlagen
Jülich / Forschungszentrum Jülich GmbH, Zentralbibliothek (2017) [Book, Dissertation / PhD Thesis]
Page(s): IV, 135 Seiten : Illustrationen, Diagramme
Hydrogen can be produced emission free from electric energy by the technology of water electrolysis. In addition to alkaline electrolysis also polymer-electrolyte-membrane (PEM) electrolysis is used for hydrogen production in power-to-gas applications for several years. For an economical use of the technology high efficiencies of the electrolyser and thecomplete plant are required. Subject of this work is an energetic investigation of PEM-electrolysers for the integration in power-to-gas applications. Therefore, a model of the complete plant is described, which can be initialized by single cell measurements. With the provided model correlations between operating parameters and specific losses of the electrolyser are identified. It can be shown that the operating parameters have a significant influence on the thermal management of the stack. Thus, for operating at atmospheric pressure and temperature of 80° C over 50 percent of the system losses are required for heating energy. These heating losses result from high content of water vapor in the product gases. With these results an optimized operating strategy for the electrolyser is derived. In addition to the parameters of temperature and pressure, the thickness of the membrane is investigated. To reduce the heating losses at current densities lower 1 A cm-2 the pressure of the product gases can be increased by just a few bar. For low stack losses, the temperature should be maintained at 80° C. The optimal thickness of the membrane depends on the permeation losses and the ohmic losses of ion conduction. For current densities over 1.5 A cm-2 and pressures up to 50 bar membranes with a thickness smaller 100 μm should be used. For an operating range under 1.5 A cm-2 and pressures up to 50 bar optimal membranes should have a thickness up to 300 μm. By the definition of an optimal operating strategy for the electrolyser an energetic consideration of the complete plant can be made. Particularly, the optimal operating pressure of the electrolyser under consideration of the gas compression and the gas drying is determined. To evaluate the optimization, the results are compared with two reference processes of current state of the art electrolysers. In dependence on the operation mode, optimal pressure levels between 2 and 10 bar results. In the power-to-gas plant, the electrolyser has the highest energy consumption with a percentage of up to 94 percent. For the gas compression a percentage of up to 5 percent is required. The gas drying with a percentage of under 1 percent has a very low impact on the total efficiency of the plant. With the obtained results, the potential of power-to-gas applications for a future production of hydrogen is estimated. By developments on the cell area, future power-to-gas plants can achieve efficiencies between 68 and 72 percent in relation the lower heating value. This includes the losses for power conditioning, hydrogen production, gas drying and gas compression.
Tjarks, Geert Hauke