Green Industrial Hydrogen via Reversible High-Temperature Electrolysis
Authors: Schwarze Konstantin , Posdziech Oliver , Kroop Simon , Lapeña-Rey Nieves , Mermelstein Joshua 
Published: February 2020

With its roadmap for moving to a competitive low-carbon economy in 2050, the European Commission sets greenhouse gas emissions targets for different economic sectors. A main challenge will be the integration of renewable energy sources into industrial processes to reduce carbon dioxide emissions.
The vision of the GrInHy project is to provide ‘green’ hydrogen via electrolysis using renewable electricity and to provide grid management services as reversible generator in the iron and steel works of Salzgitter Flachstahl GmbH (Germany). Because a significant share of the energy input can be provided in the form of waste heat, high-temperature electrolysis is able to achieve highest electrical system efficiencies and, therefore, is one of the most promising technologies to fulfill this vision.
The GrInHy project targets the industrial integration and validation of a high temperature electrolysis with a nominal electrolyser power of 150 kWAC in one scalable module. Based on steam, the project aims at an overall electrical efficiency of more than 80 %LHV. Other objectives are to proof a system lifetime over 7,000 hours and stack lifetimes over 10,000 hours with a degradation lower than 1 %/1000 hours.
The prototype is designed as reversible generator (RSOC). In the Solid Oxide Electrolyser Cell (SOEC) mode hydrogen can be produced, whereas the Solid Oxide Fuel Cell (SOFC) mode is able to generate electricity from hydrogen or natural gas. The system consists of the RSOC Unit delivered by Sunfire and the Hydrogen Processing Unit (HPU) delivered by Boeing Research and Technology Europe (Figure 1). Both are integrated in 2 separate 20’ containers including all auxiliary systems. The RSOC shall utilize steam and electricity from the onsite power plant to generate hydrogen. Hydrogen is fed to the HPU which compresses the hydrogen to minimal 8 bar(g) and removes the remaining steam by pressure swing absorption to fulfil the quality criteria “5.0”. Afterwards dry hydrogen is injected an existing ring pipeline that supplies a variety of processes at the steel work.
The RSOC prototype is based on a stack unit comprising 1440 3YSZ-ESC-cells. Those cells are set up in 6 Interchangable Modules (ICM) each containing 240 cells. The system is supplied with cold feed gases and/or steam from a so called Coldbox that realizes the fluid controls. The feed gases are further processed and preheated to operating temperature in two separate highly integrated Hotboxes. Each Hotbox supplies 3 of the 6 ICMs with educt gases and recuperates heat from the product gases. For operation in SOFC mode with natural gas, a steam reformer is integrated which uses gas electrode off-gas for humidification. In this mode, the system reaches a power output of 25 kWAC in completely automated operation. At full load the efficiency is > 50 % based on the lower heating value.
Details from the system operation in natural gas fuel cell mode (NG-FC), in hydrogen fuel cell (H2-FC) mode and in electrolyser mode (EL) will be presented. In hydrogen fuel cell mode the nominal power is 30 kWAC at an efficiency of more than 45 %LHV. In electrolyser mode the system consumes approx. 50 kg/h steam and 150 kWAC electrical power to produce 40 Nm³/h hydrogen with an overall efficiency of more than 80 %LHV. The RSOC is also able to operate in overload and is therefore able to reach up to 50 Nm³/h hydrogen output at an AC power input of approximately 200 kWAC. This is currently the largest high temperature electrolyser module worldwide.

Figure 1