Power-to-Gas through High Temperature Electrolysis and Carbon Dioxide Methanation: Reactor Design and Process Modeling

Abstract

This work deals with the coupling between high temperature steam electrolysis using solid oxide cells (SOEC) and carbon dioxide methanation to produce a synthetic natural gas (SNG) directly injectable in the natural gas distribution grid via a power-to-gas (P2G) pathway. An intrinsic kinetics obtained from the open literature has been used as the basis for a plug flow reactor model applied to a series of cooled multitube fixed bed reactors for methane synthesis. Evaporating water has been considered as coolant, ensuring a high heat transfer coefficient within the shell side of the reactor. A methanation section has been designed and optimized in order to moderate the maximum temperature within the catalytic bed and to minimize the catalyst load. Then, process modeling of a plant coupling high temperature electrolysis and methanation is presented: the main goal of this analysis is the calculation of overall plant efficiency (in terms of electricity-to-SNG chemical energy). Plant size has been set considering a 10 MW el SOEC-based electrolysis unit; heat produced from the exothermal methanation is entirely used for water evaporation before the steam electrolysis. A heat exchanger network (HEN) has been designed in order to reduce the number of components, resulting in an external heat requirement equal to 185 kW (≈1.9% of the electrolysis power). The SOEC-based power-to-gas system presented a higher heating value based efficiency equal to ≈86% (≈77% if evaluated on lower heating value basis).

CNG und LNG aus biogenen Reststoffen – ein Konzept zur ressourcenschonenden Kraftstoffproduktion

“…Vor der Methanisierung muss dem Synthesegas zusätzlich Wasserstoff beigemischt werden, um CO und CO 2 zu methanisieren und die Anforderungen zur Gasnetzeinspeisung zu erfüllen. Um diesen möglichst effizient bereitzustellen, ist die Einbindung einer Hochtemperatur‐Elektrolyse (SOEC) in den Gesamtprozess vorteilhaft , . Wird bei konventionellen Niedertemperaturverfahren wie der alkalischen oder der PEM‐Elektrolyse flüssiges Wasser nach Gl.…”

“…Steht jedoch genügend Wind‐ oder Solarenergie zur Erzeugung von Wasserstoff zur Verfügung, kann theoretisch der gesamte Kohlenstoff als Kraftstoff nutzbar gemacht werden. Die innovative Kopplung von Hochtemperaturelektrolyse und thermochemischer Vergasung ermöglicht durch stoffliche und thermische Integration die optimale Nutzung bestehender Synergien . Erfüllt das produzierte Gas die geltenden Anforderungen, kann es ins Erdgasnetz eingespeist werden und ist als vollwertiges Substitut für fossiles Erdgas zu betrachten.…”

“…Zukünftig sollte ein noch breiteres Spektrum an biogenen Substraten zur Gaserzeugung genutzt werden. So [3][4][5]. Erfüllt das produzierte Gas die geltenden Anforderungen, kann es ins Erdgasnetz eingespeist werden und ist als vollwertiges Substitut für fossiles Erdgas zu betrachten.…”

Electricity Arbitration and Sector Coupling with an Experimentally Validated Reversible Solid Oxide Cell Reactor System Connected to the Natural Gas Grid

“…Moreover, methane can be fed directly to the existing natural gas grid and is therefore easily transportable . Standalone power to methane systems using SOC reactors have been proposed by researchers . Similarly, standalone SOFC systems running on methane/natural gas have been extensively studied and demonstrated .…”

The thermodynamics and reactor optimization of CO2 methanation

“…It was found that the electrical efficiency of power to methane ranges from 71.64% to 81.08%, varies with thermal management strategies [185]. The efficiency of SOEC-based, hightemperature methanation process integrated with effective thermal reuse system can reach to 86% [186]. On the other hand, rather than water electrolysis to generate pure hydrogen, the direct coelectrolysis of water and CO2 to produce syngas (mainly CO+H2) were investigated as CO2 mitigation solution [187,188].…”