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Flexibilisation and integration of solid oxide electrolysis units in power to synthetic natural gas plants

Anghilante, Régis. Flexibilisation and integration of solid oxide electrolysis units in power to synthetic natural gas plants. PhD, Génie des Procédés et de l'Environnement, Institut National Polytechnique de Toulouse, 2020

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Abstract

The solid oxide electrolysis technology (SOE) could improve the conversion efficiency of power-tosynthetic natural gas (SNG) plants and reduce their costs, provided that i) a performant thermal integration is implemented ii) the technology is implemented at industrial scale, and iii) plants can absorb the intermittency of renewable power sources. First, the energy analysis of three innovative power-to-SNG plant concepts is implemented. For each concept, a full explicit thermal integration is proposed. Plants with integrated SOE units show efficiencies higher than 78.5% (based on the HHV of the SNG) for the production of CNG and LNG, significantly higher than plants with PEM units with a 64.4% efficiency for CNG production. Second, the thermal response of SOE units to electrical power loads is investigated with a 1D dynamic model at the cell level (SOEC). Electrolyte support cells present a higher thermal stability than electrode support cells and should be preferred for fluctuating power applications. The model was then extended to a full H2 production and storage unit and coupled with different electrical power profiles. The units shows an energy consumption of 3.4-3.8 kWh·Nm-3 H2 and a high power-to-H2 conversion efficiency (93-103%) because of the steam recovery from the methanation unit. A first dimensioning of the H2 storage tank and the methanation unit is proposed, assuming a windmill power profile. Fluctuating power profiles reduce the efficiency of power-to-SNG plants, increase their costs and complexify their operation. Multifuel plants seem to be the most promising option to tackle the issue of intermittent power production. Extending the operation range of SOECs to exothermic and endothermic modes would improve power-to-H2 conversion efficiencies compared to on/off operation. In case of constant power load though, SOECs should preferably be operated at the thermoneutral point or in exothermic mode. Third, SNG production costs corresponding to the aforementioned plant concepts are evaluated, starting with a bottom-up cost evaluation of SOE units. The SNG production costs are in the range of 82-89 €·MWh-1 CH4 (HHV) with SOE units, which is lower than with PEM units, but remains two times higher than the average price of conventional natural gas for all sectors in France

Item Type:PhD Thesis
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Institution:Université de Toulouse > Institut National Polytechnique de Toulouse - Toulouse INP (FRANCE)
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Research Director:
Floquet, Pascal and Brisse, Annabelle
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Deposited On:01 Jun 2021 07:27

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