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Integrated High-Temperature Electrolysis and Methanation for Effective Power to Gas Conversion

Final Report Summary - HELMETH (Integrated High-Temperature Electrolysis and Methanation for Effective Power to Gas Conversion)

Executive Summary:
A highly efficient Power-to-Gas process has been realized by the European research project HELMETH. It has the potential to be the most efficient storage solution for renewable energy utilizing the existing natural gas grid without capacity limitations and to be a source for “green” Substitute Natural Gas (SNG) to avoid fossil carbon dioxide emissions. The objective of the HELMETH project is the proof of concept of a highly efficient Power-to-Gas process by realizing the first prototype that combines a pressurized high temperature steam electrolysis with a CO2-methanation module. The efficiency is significantly increased by using the heat of reaction from the exothermic methanation reaction to produce steam for the high temperature electrolysis. Since the produced SNG is fully compatible with the existing natural gas grid and storage infrastructure, practically no capacity limitations apply to store energy from fluctuating renewable energy sources. A significant advantage of the HELMETH PtG technology in contrast to PtG plants with low temperature electrolysis modules is its higher efficiency resulting to considerably lower electricity demand per SNG output. The HELMETH consortium consists of the partners Karlsruhe Institute of Technology (coordinator), Politecnico di Torino, Sunfire GmbH, European Research Institute of Catalysis A.I.S.B.L. Ethos Energy Italy, National Technical University of Athens and DVGW-German Technical and Scientific Association for Gas and Water. The research project with a duration of nearly 4 years had a total budget of approximately 4 million euro and was co-financed by the European Union's Seventh Framework Programme for the Fuel Cells and Hydrogen Joint Technology Initiative under the Grant agreement no. 621210.

Figure 1: Schematic HELMETH PtG process, which enables an efficient conversion and storage of energy from fluctuating renewable sources


-WP1Conceptional Design and Simulation
At first the European natural gas grid regulations were evaluated in order to specify the overall system requirements and especially the targeted SNG quality criteria. This process was essential for the development of the methanation module, which has to produce SNG that is fully compatible with the existing natural gas infrastructure. Based on the development of the overall system specifications, several PtG integration schemes with different methanation reactor concepts were investigated by detailed process simulation. The consortium chose a multi-step methanation module with a boiling water cooling that is producing saturated steam for the electrolysis module.

-WP2 SOEC based Electrolyser Module Development
Short stack tests of the high temperature steam electrolysis module showed degradation rates below the set target of 0.5 % / 1000 h. The development of high corrosion and high temperature resistant direct laser metal sintered heat exchangers resulted in several prototypes that were evaluated. Further electrolysis stack tests were conducted in co-electrolysis (simultaneous feed of CO2 and Steam) mode and provide a good basis for assessing the potential to produce a synthesis gas for the methanation process. This offers the chance to further increase the overall PtG efficiency.

-WP3 Methanation Module Development
In order to reach high methane yields in the methanation module, different Nickel and Ruthenium catalysts were tested and optimised. A catalyst with lower Ni concentration and indication of better long term stability was developed. Extensive tests in stand-alone mode were performed with the methanation module in order to characterize its performance. The gas pressure was varied from 10 to 30 bar and a load modulation from 20 to 100 % (60 kW equivalent SNG production at 30 bar and 100 % load). Hereby the boiling water cooling showed an extremely stable and effective heat removal capability, while being able to control the steam temperature accurately. Start-up time of the methanation reactor from hot-standby was in the range of minutes; however it could be significantly reduced in fully automated plants. At the end of the test campaigns the methanation module produced SNG excelling the quality targets by far. For stand-by operation a hot stand-by at the optimum boiling water temperature of 250 °C proved to be most effective.

-WP4 System Integration and Testing
Finally, both modules were coupled and commissioned at the Sunfire premises. The thermal integration of both units was performed by a steam line from the methanation module to the steam inlet of the electrolyser module and by connecting the hydrogen outlet of the electrolyser to the methanation. The demonstration plant was operated semi-automated in part load. Although the coupling wasn’t completely successful, an efficiency of the integrated system of about 76 %HHV could be achieved. A technical obstacle identified within the HELMETH project, is the need for new technical solutions for accurate steam mass flow control at extremely low volume flow rates at the electrolyser inlet. Since the electrolyser modules operates at pressures in the range of 15 bar, while the differential pressure between the not communicating anode and cathode side should remain well below 100 mbar to avoid stack damage, even small fluctuations in the steam volume flow rate are critical. A further technical challenge is the development of high temperature thermal insulation materials, which maintain their insulation properties at high pressures. Approx. 2.5 % of loss in the overall efficiency was identified to be caused by this reason. By scaling up the HELMETH concept, parasitic losses could be reduced, resulting in an overall PtG efficiency over 80 %. In addition, a scale up techno-economic study was performed for different renewable energy supply profiles identifying optimum plant sizes and operation strategies.

Figure 2: Final HELMETH prototype, consisting of the methanation module (left container) coupled to electrolyser module (right container)

-WP5 LCA, Market and Socioeconomic Studies
A full-scale Life Cycle Assessment of the overall process against benchmark scenarios was completed, alongside with the evaluation of the impact of CO2 sources on the system CO2-footprint. Business cases for various operation scenarios of the Power-to-Gas units were elaborated and evaluated, while a complete exploitation road map was developed.

Project Context and Objectives:
WP1 Conceptional Design and Simulation
The HELMETH project is the first PtG operation thermally combining high temperature steam electrolysis and CO2-methanation. Basic objectives for that undertaking were the fixing of battery limits and an assessment of the particular module size. Process inputs and outlet specification had to be evaluated with special interest in the European gas grid regulations. For the methanation process different reactor types and concepts required to be investigated in order to ensure SNG quality, steam production, load modulation/flexibility and other key aspects. Concerning the SOEC module, feasibility of Co-electrolysis (simultaneous feed of CO2 and steam) and effects on the overall PtG efficiency had to be evaluated. With the tools of process modelling the thermal coupling of the individual modules needed to be examined in order to choose the best way of integration. With fixed boundary conditions and set module configurations resp. sizes, process modelling was required to determine the overall PtG efficiency based on realistic assumptions. From that point on Process Flow Diagram (PFD) and Piping and Instrumentation Diagram (P&ID) had to be set up. Based on the individual P&IDs preliminary safety analysis were required to ensure the feasibility of the overall HELMETH PtG configuration.

WP2 SOEC based Electrolyser Module Development
The main objective of the HELMETH project was the demonstration of the technical feasibility to achieve a conversion efficiency of > 85 % from renewable electricity to methane. In order to achieve this target, a pressurized high-temperature electrolyser system with an operating pressure in the range of 10-30 bar and an power input of 10-15 kW had to be developed for the thermal integration with an CO2 methanation step, where the exothermic synthesis is used to provide steam for the HTE process.
The pressurized system had to be optimized in terms of balancing the trans-membrane pressure and the overall system pressure as well as the optimization of steam conversion rates and to achieve a working range of 20...100 % load to compensate fluctuations of renewable electricity sources.
Furthermore, the co-electrolysis capability of the SOEC stack was investigated experimentally. With it, the efficiency of the PtG process can be further increased and other applications like Power-to-Liquid processes can be explored.
A pressure vessel was used to integrate all hot BoP components in order to separate pressure and temperature from each other. Pressurization of the unit required the optimization of all hot parts like heat exchangers, electrical heaters and the stack unit. Therefore, the hot BoP components and the enclosure of the SOEC stacks have been redesigned for an optimisation of flow velocities and heat transfer inside the heat exchangers at elevated pressures. The ability for part load operation was included in the development.
Material research regarding the hot BoP components was conducted by an intensive literature study and appropriate experiments with the most promising materials. Target was the optimization of material choice in terms of long-term stability, high-corrosion resistance and low chromium evaporation rates to minimize potential stack contaminants.
A new heat exchanger design and manufacturing route using additive manufacturing by Direct Metal Laser Sintering (DMLS) was investigated, where the availability of powders for the selected materials was taken as first step. In a second step, heat exchanger prototypes were manufactured and experimentally investigated, before integrating them into the SOEC hotbox. The target was to investigate the potentials of 3D printing processes to manufacture complex structures that improve heat transfer and reduce pressure drops.
As a final step the stand-alone operation of the pressurized HTE for more than 200 hours was targeted to prove the feasibility of operation under controlled conditions.

WP3 Methanation Module Development
The main objective of WP3 was the realization and testing of the HELMETH CO2-methanation module, including all groundwork in terms of catalyst development/testing/selection, lab tests of reactor concepts, selection of proper reactor material and numerical investigation of heat- and mass-transfer. For selecting the most suitable catalyst, optimization in terms of cost-effectiveness, high methane selectivity and extended temperature stability was required. Activity test in small scale had to proof the performance of the different catalysts. With proper candidate materials lab scale reactor concept tests had to be done in order to show the methanation module configuration feasibility and to determine the reaction kinetics under real operating conditions of interest. For the final CO2-methanation module a cost- and performance optimized multistep design that produces a methane gas quality corresponding to the natural gas standards in a 30-60 kW range was targeted. A material selection for reactor manufacturing that can withstand the oxidizing/reducing environment, carburizing conditions and show mechanical strength for pressure vessels while being easy weldable and available was mandatory. For stand-by operation solutions had to be evaluated and for regular operation a load modulation from 20 – 100 % was necessary. During operation the cooling system needed to generate a stable and pressurized steam supply as feed for the SOEC module.

WP4 System Integration and Testing
The objective of the HELMETH project was the proof of concept of a highly efficient Power-to-Gas (PtG) technology with methane as a chemical storage and by thermally integrating high temperature electrolysis (SOEC technology) with methanation in order to achieve conversion efficiency of up to 85 %.
For the operation of the PtG plant, a control and safety system has been designed. The safety of the plant was approved by a notified body. For the operability of the demonstration plant, the focus of the control system was reliability before automation. Here, the main objective was the development of reliable operation procedures for the coupled unit.
The interactions of methanation unit and electrolyser unit were studied. Specific attention had to be paid to part load capability, stand-by options and the reaction to pressure and flow fluctuations.
Furthermore, studies for scale-up of the PtG plant and optimal system integration had to be performed, considering electricity imbalances on a short-term and seasonable scale.

WP5 LCA, Market and Socioeconomic Studies
The general objective of WP5 was to assess the environmental impacts, the financial viability and the exploitation potential of the HELMETH concept system.
Regarding the environmental aspect, the main target was to evaluate and quantify the combined influence of the most critical parameters: (a) the type of electricity source for the electrolysis stage (level of carbon load of relevant input); (b) the Power-to-Gas (PtG) efficiency (HELMETH High Temperature (HT) vs conventional Low Temperature (LT) electrolysers) and (c) the type of CO2 source for the methanation stage. An additional objective was to identify the limits of “carbon-negative” and “better-than-Natural Gas (NG)” of producing Substitute Natural Gas (SNG) in terms of Global Warming Potential (GWP).
As concerns the economic related targets, the corresponding activities aimed to analyse the economic feasibility of the PtG plant by quantifying the capital and operational expenditure, as well as to analyse the potential competition and to benchmark the price of SNG against alternatives. Furthermore, appropriate pricing strategies were expected to be suggested, based on present and future scenarios.
Finally, the exploitation activities aimed to develop a short- and mid-term roadmap of corresponding actions, while the HELMETH technology implementation plan was expected to be proposed

Project Results:
WP1 Conceptional Design and Simulation
In order to evaluate the battery limits of the individual modules and the combined HELMETH PtG unit, several specifications were set up. Based on a detailed evaluation of the European gas grid regulations, the required SNG quality criteria were fixed as the following allowable gas concentrations (CH4 ≥ 92.5 vol.-%, CO2 ≤ 2.5 vol.-%, H2 ≤ 5 vol.-%) The maximum of 5 vol.-% hydrogen is estimated to be acceptable in the European in future (midterm), whereas a limit of 2 vol.-% is realistic for the current practice. In order to reach that SNG quality, the operating pressure range of the multistep methanation module was set from 10 to 30 bar, with clear benefits at 30 bar. For the reactor concept of the methanation module different configurations and reactor types were investigated. Concepts included adiabatic and cooled reactors, product gas recycle and water condensation stages between reactors. Detailed process modelling of the different routes let to a design with boiling water cooled reactors as shown in the following.

Figure 3: Schematic HELMETH CO2-methanation process (simplified)

The SOEC operating temperature was set to 750 – 870 °C at about 14 bar with a targeted steam conversion of 80 % and an electrical power demand of approx. 15 kW. Due to the early development stage of the high pressure SOEC, a thermal one-way integration was specified. Meaning that hot steam is feed from the methanation to SOEC, but in contrast only cold and dry hydrogen is exchanged.
For the future this thermal one-way integration leaves options in terms of overall efficiency increase, as the SOEC product gases are still hot after heat recuperation.
On Stack level SOEC Co-electrolysis was numerically and experimentally (see WP2) investigated. By simultaneous feeding steam and CO2 into the electrolyser, a synthesis gas is produced, containing mainly hydrogen and carbon monoxide. This can offer the benefit of a reduced steam demand of the SOEC. (The Co-electrolysis mode was not used in the final modules).
For a calculation of the overall PtG system, several assumptions in terms SOEC steam conversion, heat exchanger performance and heat losses of the modules had to be made. Starting from simple energy balances towards more mature models including the thermal integration, steam pressure reduction at the methanation unit, heat exchanger performance and heat exchanger network as well as heat losses, a realistic PtG efficiency in industrial scale of 85.1 % was calculated. This efficiency is defined as the higher heating value of the produced methane per electricity demand.
Based on these promising results, PFD and P&ID for the individual modules were set up and a following safety analysis of the individual modules showed the feasibility of the complete concept. The two major hazards from pressure vessels and explosive atmospheres/ combustible gases required the set-up of proper countermeasures. Anyway, before operating the particular modules an inspection by a technical authority was required by law and successfully done.

WP2 SOEC based Electrolyser Module Development
Module design and pressure vessel:
In a first step, the SOEC module was designed and constructed. The design of the Integrated stack Module – ISM (SOEC stack with thermal insulation and sensors) and the hotbox (heat exchangers, electrical gas heaters, electrical evaporator; all with thermal insulation) was done by sunfire based on experiences under ambient conditions. On each electrode side, an electrical gas heater is integrated in between the heat exchanger and the ISM so that the gas inlet temperatures can be tuned as required. An electrical evaporator (in front of the HEX at H2 side) is used for the steam supply in case the electrolyser is working as stand-alone system without coupling to the methanation module. After the initial operation of the system, a redesign of the hotbox components was performed to optimize the components layout for the low flow velocities and increased heat loss rates with pressure. Based on the hotbox design, the pressure vessel was specified. The pressure vessel itself was manufactured by a specialised manufacturer and according to the Pressure Equipment Directive and delivered with a CE mark.
For the calculation of the maximum wall temperature, the heat transfer from the surface of the hotbox and ISM (both thermally insulated; containing the components at working temperatures up to 850°C) to the inner shell surface of the pressure vessel was estimated by heat radiation coupling. Additionally, the cooling effect by heat transfer through the pressure vessel shell and convective cooling of the outer surface was considered. As a result, a maximum wall temperature of the pressure vessel of 150°C was calculated.
Taken into account that the unit has to be installed in a container, a horizontal layout of the pressure vessel was chosen. The lid was mounted on wheels and so it can be opened without any additional technical equipment.

Figure 4: 3D model of the hotbox (left) and pressure vessel as installed in the container (right)

Material selection and evaluation/testing:
Different metallic powders have been considered as basic material for the Direct Metal Laser Sintering (DMLS) fabrication process of optimized 3D printed heat exchangers. The considered materials were from the groups of alumina or chromia forming ferritic and austenitic stainless steels and nickel alloys. Finally, Inconel 718 (2.4668) was chosen as the best option for long term oxidation resistance and creep strength. A standard characterization protocol was conducted for the assessment of powder properties and of the sintered samples. Sinterability of the powder was studied as a function of the process parameters.
The next step was to fabricate small samples simulating final HEX structures, to assess their integrity and to apply the heat treatment recipe defined on flat samples to such structures. The samples geometry was defined considering both the potential heat exchange achieved by such structures and the processability of the structure by additive manufacturing. A minimum thickness of 1 mm of the additive manufacturing walls to be used for the building of the heat exchanger was chosen.
Counter-flow heat exchangers with two different geometries were studied by numerical simulation and experimental validation, by looking to the H/L ratio, the HxL parameter and the possibility to generate compact HEX. As a consequence of these results the final design of HEX was performed by minimizing the channel height and width, thus guaranteeing both heat exchange and fluid velocity. A triangular section of the channels was selected for the proposed design.
Once the heat exchanger design was defined it had to be transferred to DMLS design considering the actual processability of the conceived structures. To this purpose several iterations were performed in terms of DMLS design and of experimental DMLS trials to obtain the final structure. Based on the developed small DMLS samples their material integrity was assessed as well as the accuracy of the manufacturing route. The DMLS structures exhibited a very limited internal porosity, absence of through-passing porosity (which would provide leakages or fluid contamination) and a good reproducibility of geometrical features.
The resistance to oxidation and the chromium release rate from the DMLS Inconel 718 was tested in view of the final application of the HEX within the whole HELMETH system. Due to the possibility of chromium poisoning of the SOEC, it was decided to verify a further protection of the DMLS Inconel 718 via a coating deposition. This was performed on the simplified samples resembling the internal structures of the HEX. As a feasibility study for this purpose, different deposition techniques and coating materials were studied.
Originally thermal spray coating like HVOF was considered to apply as protective layer, however this technique isn’t applicable for complex internal structures of a HEX. Thus, the research was focused on a diffusion process like pack or even better gas aluminizing. This process is currently applied for turbine blades protection, thus being highly compatible with superalloys. Different aluminizing parameters were applied and the resulting morphologies of surface modified layers were inspected as well as their respective oxidation resistance performances. The oxidation performances were improved with respect to the basic material, however some spalling phenomena were recorded at certain locations of the samples.

Heat exchanger design, manufacturing and characterization:
After the validation of the numerical HEX modelling tool, it was used to design the two final DMLS HEX prototypes. In the second HEX a simplification of the internal channels configuration was applied to facilitate the removal of not sintered powder. Additionally, special attention was paid to the manifold design and to the connecting regions between core part and manifolds.

Figure 5: Final HELMETH HEX prototype made by DMLS

It was decided to use the DMLS HEX only at the oxygen side of the electrolyser. The very high oxidation resistance demonstrated by the DMLS Inconel 718 made the Consortium confident that the application of a further protective coating was not necessary for the HELMETH demonstration. Thus, the HEX was delivered without any coating. The final prototype was at first tested for leakages and then sent to another consortium partner for numerical and experimental performance testing.
The tests have been conducted at atmospheric pressure following the theory of similarity for the heat transfer in triangle ducts at laminar flow. An already generated CFD model was adjusted to the design and used to predict HEX performance before testing and to calculate the performance at elevated pressure with the obtained atmospheric measurement results. Very satisfying results with stable linear trends in temperatures at different loads were detected. However, a stable heat loss of approx. 19 % from the hot stream enthalpy release was identified and considered.

Short stack tests:
Several short stack tests (10-cells) were performed. The two goals of the tests were the co-electrolysis feasibility of the stack and the verification of long-term stability in steam electrolysis mode. For these tests, besides steam also CO2 was added in the feed gas flow for the SOEC short stack. Ideally, CO2 should behave similar to H2O at the cell from the electrochemical point of view, which means the overall conversion of the feed gas flow could simply be calculated by the flow rates and the electrical current used for electrolysis. Experimental results show that the CO2 to steam ratio fed into the stack can be adjusted to a produced syngas composition that is suitable for direct methanation

For a high efficiency of the system, high gas conversion ratios are required. Therefore, a test was performed with a co-electrolysis gas composition and a stepwise increase in gas conversion form 50 % to 90 % and corresponding voltage increases. The increase met the expectations and demonstrated that high gas conversion ratios for co-electrolysis are possible with the actual sunfire stack technology.

Long-term degradation in steam electrolysis mode was investigated in a next step. Again, the test was performed with a 10-cell stack in a furnace environment. A stable operation point (j = -500 mA/cm²; steam conversion = 80 %; T = 850 °C) was set and the development of the voltage was observed. Extrapolating from about 320 h of steady operation point, showed that the degradation rate was 0.47 % / 1.000 h which is below the target value of the project (0.5 % / 1.000 h) as required.

SOEC stack integration and characterization:
It was decided to use the standard electrolyte material 3YSZ instead of the better performing 5YbSZ (with the later material current densities of 1 A/cm² were achieved with cell tests and 0.8 A/cm² with cell tests within HELMETH).The reason is that the higher conductivity in the ceramic electrolyte material is related to a lower mechanical strength. The hydrogen electrode was a Ni-GDC compound and the oxygen electrode was LSCF. With this electrolyte material, the targeted current density of 1 A/cm² cannot be achieved. A realistic value is 0.5-0.65 A/cm². In total three stacks (30 cells each) were integrated in one so called ISM (Integrated Stack Module; containing the stacks, thermocouples, current rods, voltage probes and thermal insulation), resulting in an electrolysis DC power input of about 8 kW. The stacks had passed the standard quality tests at sunfire. Electrochemical performance indication (OCV and low current test during stack joining) and mechanical leakage test were within the sunfire specification for all used stacks.
Due to design adaption of the ISM to pressurized operation, a test of the ISM at atmospheric conditions is not possible. For the evaluation of suitable electrode materials, several 30-cell stack tests at atmospheric conditions had been conducted and are continued by sunfire.
In addition, it was recognized that the available testing equipment for SOEC stacks at sunfire is not sufficient and it was improved. The existing test equipment was upgraded in terms of reliability and for larger stack sizes, e.g. ISM.

Module integration and testing:
For the stand-alone operation, an ISM with three stacks (90 cells in total) was used. The additive manufactured HEX was integrated into the Hotbox for the final combined operation.
Different tests were carried out. To evaluate the influence of total pressure on the voltage (and thus the electrical efficiency) the pressure level was increased at fixed current density and flow rates. As an outcome, the voltage is independent of the pressure level (Figure 6) which is a favourable result. On the other hand, the temperature is slightly increased likely due to enhanced thermal losses with increasing pressure.

Figure 6: Increase of pressure at constant current and flow rates

Finally, the efficiency of the stand-alone operation has been assessed. While the electrical efficiency of the stack only depends on the voltage, the efficiencies of the complete systems (hotbox, without auxiliaries) need to include the power of the electrical gas heaters (for compensation of thermal losses and incomplete heat recuperation) and electrical evaporator (as for the stand-alone operation no steam source is available). The results show that the electrical efficiency of the stack is in the range of 110 %HHV. Taken the heat loss compensation into account, still above 100 % electrical efficiency was obtained. The reason for electrical efficiencies above 100% is that the required energy for the electrolysis is partly coming from the thermal energy of the steam. The electrical evaporation in the stand-alone mode reduces the value by roughly 20 %, which fits to the expectations.

Altogether the stand-alone tests were conducted for several 100 hours. Unfortunately, several ISMs were destroyed since the pressure control turned out to be challenging at transient conditions and if disturbances occurred, damaging cells resp. sealing materials.

WP3 Methanation Module Development:
Besides the SOEC, the CO2-methantion module was the second key module of the HELMETH PtG unit. At first an optimized catalyst had to be developed in terms of cost effectivity, activity and selectivity. For that reason several Nickel-based catalysts supported on metal oxides and hydrotalcite were developed. The role of the support and a dopting with other elements showed a key role in activity and stability performance. Ruthenium-based catalysts were ruled out at an early project state due to cost reasons. The most suitable catalysts were used within lab scale reactor tests that evaluated the catalyst performance and the complete methanation reactor concept.
Tests of the complete methanation module configuration proved its feasibility. From the reactor lab tests a LHHW (Langmuir-Hinshelwood Hougen-Watson) type reaction rate was determine for the real operating conditions of interest. This rate equation is very different from literature sources, as it extends especially the pressure range validity to about 30 bar.
In order to build the final methanation module, a selection of constitutive materials was performed. Main criteria for selecting a proper material are the resistance against oxidizing/reducing environment and carburizing conditions, resistance to plasticization at chosen conditions and a satisfactory mechanical strength. Due to reasons of weldability, costs and commercial availability, Nickel-superalloys were not investigated and austenitic stainless steels proved as most suitable solution. From these finally 316Ti (1.4571) was chosen.
Based on the results from WP1, a multistep methanation module with an integrated boiling water cooling was selected. It offers excellent SNG quality and a sufficient steam production.
Tests of the methanation module were performed at different pressures ranging from 10 to 30 bar, load modulations from 20 to 100 % and different cooling medium temperatures. For stand-by operation a hot stand-by at 250 °C proved to be most feasible. The mentioned boiling water temperature of 250 °C was ideal in terms effective heat removal, SNG quality, steam pressure reduction and vessel thickness (for future plants). In general a lower boiling water temperature (and corresponding steam pressure) is favourable, while high temperatures are only useful at low reactant concentrations.
Surprisingly the chemical reaction is even at temperatures as low as 220 °C “igniting” with the chosen reactor configuration and catalyst but showing not the required reactant conversions. Temperatures above 250 °C resulted in high conversions but hat some drawbacks in terms of heat of reaction removal capability and steam pressure reduction. Extensive parameter studies at different reactant gas flows and pressures revealed that the performance of the catalytic bed is controlled by the catalyst (reaction rate) including transport phenomena and not by heat transfer, which shows a minor role.
In terms of SNG output quality the module proved to exceed the required HELMETH quality criteria by far with a final optimized fixed bed configuration.
At every operating point the measured hydrogen concentration is below the maximum allowable 5 %.
Overall the methanation proved to be very effective. Actual results and objectives are compared in Figure 7. The “+” is hereby indicating that the maximum capability of the module was not reached, but limited by the installed BoP component size.
With the gathered LHHW rate equation and putting additional numerical effort in the effect of mass transport limitations with industrial scale catalyst particles as applied in the final module, the numerical work was able to successfully reproduce the experimental results.

Figure 7: Comparison of methanation module objectives vs. results

WP4 System Integration and Testing:
For the final demonstration operation, the DMLS manufactured heat exchanger from WP2 was integrated successfully into the electrolyser hot BoP part, replacing the conventional heat exchanger on the oxygen side. Also, a new stack module was installed.
It was decided to equip the methanation unit and the high-temperature electrolyser with independent and separate control and safety systems. Both units have been approved separately by a notified body due to Pressure Vessel Directive. So, they are intrinsically safe. A safety analysis of the interfaces showed no additional threats and thus no further action was required. Due to the complexity of possible mutual interactions and the intended permanent supervision of the methanation module, no superior control system was implemented.

For the system design and the coupling of both sub units, the approach was to reduce the number of connection pipes and necessary information exchanges to a minimum. Therefore, only the steam pipe from the methanation unit and the hydrogen line in the opposed direction have been installed. No signal exchange is required, as both units are able to operate on their own based on the varying inlet parameters.

The demonstration plant was assembled at the sunfire facility in Dresden. Therefore the CO2 methanation unit, developed and built in Karlsruhe, was set up inside a container and after the extensive stand-alone testing transported to sunfire in order to perform the coupling and combined operational tests. The methanation container was installed as close as possible to the electrolyser container.

Figure 8: Coupled PtG plant (left container: methanation; right container: electrolyser)

For the combined operational tests, the methanation module was operated at a stable operating point with a gas feed-in pressure of 10 bar. The required hydrogen was drawn from a line that included the SOEC outlet and bottled hydrogen. From a methanation point of view the main focus was on a stable steam supply for the electrolysis. Steam from the methanation module cooling system was generated at 250 °C (40 bar) and then reduced in pressure down to 12.7 bar. When the inlet control valve of the electrolyser unit was opened, the steam flew from the methanation to feed the electrolyser and was converted to hydrogen as methanation feed.

Although the inlet pressure of the steam from the methanation unit was very stable, the HTE system showed fast pressure fluctuations that are expressed in cell voltage fluctuations. With a safety function, the current was adjusted to maintain the average cell voltage at a level below 1.8 V to prevent overheating due to excessive exothermal behaviour. An instable mass flow control prevented an extended testing of the PtG plant and therefore the coupling wasn’t completely successful. The HELMETH project has shown that the pressurized operation requires more R&D to achieve a higher Technology Readiness Level.

The overall efficiency of the pilot plant calculated with the measured values of the stand-alone operations is in the range of 76 % based on the HHV of methane. This is obviously lower as the simulations indicated in WP1 (85 % possible efficiency). The difference was analysed and the biggest shares could be identified. The results of the methanation unit indicate that the realised unit performed close to the calculated values from the process simulations, while most of energy losses took place within the electrolyser module. There were two major reasons identified: the steam utilisation and the thermal insulation of the electrolyser pressure vessel. An increase of the steam conversion rate from 0.7 to 0.9 would increase the efficiency by 4 %. Improvement of the thermal insulation, resulting in lower heat losses, can lead to an improvement of efficiency by 2.5 %.

So, the potential of the PtG process using high temperature electrolysis coupled to an advanced methanation system in industrial scale will lead to overall efficiencies of > 80 %, based on real measured values of the small-scale prototype and sensitivity analysis of the losses therein. This value is by far the highest efficiency for a real built PtG plant, and considerably higher than any other technology known and published so far.

Part of WP4 was the investigation of an optimal system integration and scale-up of the system. The main part of this work consisted in simulations of the Power-to-Gas plant in different future energy scenarios, where the electric grid is powered by renewable energy sources, whose electric output is volatile and varies periodically throughout the year as weather conditions change. Three different scenarios are considered: the first provides a national analysis of Germany in the year 2050, the second scenario is about the coupling of a photovoltaic plant with the methanation plant; at the third scenario the coupling of a wind farm with the Power-to-Gas plant is considered. For each scenario the specific SNG productivity and optimal size of PtG plant was determined, considering the presence of additional short term storages (e.g. hydro or batteries), which may impact the load profile in future with increasing short term storage capability. The big advantage of HELMETH concept is that long term storage (weeks, months) can be realized without practical storage capacity limits by utilizing the existing natural gas infrastructure.

WP5 LCA, Market and Socioeconomic Studies
Towards providing a general overview of the GWP (Global Warming Potential) behaviour of the HELMETH concept system operation, all individual results were interpolated into one single contour diagram, covering a wide range of possible electric and CO2 feeds. Figure 9 can be characterized as the “Carbon map” of the HELMETH concept system operation (assuming 85 % HHV PtG efficiency). The vertical Y-axis contains the GWP of the electricity feed for all relevant consumptions (CO2 separation/compression, electrolysis/BoP of PtG, O2 conventional production and treatment of water input), ranging from the top value of the German grid in 2020 (567 g CO2-eq/kWh), down to the minimum GWP of Wind power generation (14 g CO2-eq/kWh). All possible carbon loads of the electric feed for PtG are therefore represented. On the horizontal axis is the range of carbon load for supplying 1 kg of CO2 for methanation. The reference process for SNG production is the extraction/transportation to Germany of fossil natural gas. According to the Ecoinvent LCA database, the NG grid of Germany contains imports from Russia (36%), Norway (27%) and Holland (19%), plus a national production of 18%. The calculation of the GWP for the reference case results in 12 g CO2-eq/MJ of NG, with the Russian imports contributing almost 70% of this value (contribution of 8.34 g CO2-eq/MJ), due to increased extraction losses and long pipeline distances. If only the Russian imports were considered, the reference GWP would be raised in the level of 20 g CO2-eq/MJ of NG, instead of 12.

Figure 9: “Carbon map” of the HELMETH concept system operation.

Three regions are identified within the contour graph:
• “Worse than NG”: GWP of producing 1 MJ of SNG > 12 g CO2-eq.
All the grey sections represent the cases where the GWP of SNG is higher than the corresponding potential of the reference case. Light grey stands for cases which are close to the reference GWP (12 g CO2 eq/MJ) and dark grey for higher GWP of SNG (see legend with colour palette values to the right).
• “Better than NG – Positive impact”: GWP of producing 1 MJ of SNG between 0 and 12 g CO2-eq.
The white strip represents lower GWP than the reference case, however positive.
• “Carbon negative”: GWP of producing 1 MJ of SNG is below zero.
The green regions represent the cases where the avoided GWP during Direct Air Capture or biomass growth is higher than the corresponding impact of power input generation and CO2 treatment.
The three hatched areas (green, light grey and dark grey from left to right) represent (a) the non-fossil CO2 sources, (b) fossil sources only with CO2 compression impact and (c) fossil sources with separation and compression impact.
It is shown that carbon negative operation is achieved only by non-fossil CO2 sources (as expected) and an electric side GWP of around 140-150 g CO2-eq/kWh. The projections for the German grid for 2050 range between 72 and 190 g CO2-eq/kWh, while the electric carbon load of other European countries (France, Switzerland, Norway) falls below 70 CO2-eq/kWh, even in current terms. Therefore, carbon negative operation is feasible, even without a full renewable electric input.
Lower GWP than extracting and transporting NG is achieved by biogenic/atmospheric sources and electric carbon load of around 180-190 g CO2-eq/kWh and also by a fossil CO2 source (carrying only the corresponding compression impact) and a near fully renewable electric input (below 40 g CO2-eq/kWh). The latter can represent the case of a fossil power plant or an industrial source already capturing CO2 emissions.
Corresponding results and findings have been produced for all benchmark cases considered: NG and Bio-CH4 injection to grid, heat production form NG, mobility from CNG. It has also been shown that the HELMETH concept can achieve a “Carbon negative” and “Better than NG” operation with “less clean” (higher carbon load) electric feed when compared to standard LT-electrolysers.

The high temperature electrolysis components like electrolysis units and H2 handling systems are estimated to become less expensive and the projected yearly costs are expected to decrease significantly in the near to medium term future. This combined with higher plant capacities would be the ideal background for a power to gas system to be more business relevant.
The highest share in operational expenditure is the electricity costs. For the OPEX calculations, three reference plant capacities of 5, 20 and 100 MW were chosen. Two separate pricing models were analysed:
a) Fixed input electricity cost model: Here the input electricity costs remain constant and is not sensitive to the availability of surplus energy. However, constant price model does not incorporate the advantages of lower electricity prices during surplus hours and it would be difficult to negotiate a price between the electricity operators and the SNG plant operators as the fixed price required for SNG operators to remain profitable and competitive would be too low for the renewable electricity producers to remain profitable.
b) Variable cost model: Here, the input electricity costs are sensitive to the availability of surplus energy and is designed to change accordingly. A potential variable pricing model should be designed in such a way that an increase in surplus results in a decrease in the actual amount liable to be paid.

The variation in total SNG costs with respect to a corresponding variation in plant efficiency was analysed. As expected, a comparison of the total costs shows that high temperature electrolysis and methanation is approximately 31.25% cheaper as opposed to low temperature electrolysis combined with methanation.

The key to PtG success will be to find attractive early markets and the right upscaling models for the different technologies (SOEC, methanation) that take into account viable business models. Further exploitable products were identified: hydrogen generation for industrial applications or refineries at small and medium scale and production of syngas from renewable electricity, steam and CO2. It was shown, that industrial hydrogen from HTE will be competitive provided that: 1) The lifetime of the electrolysers increases from about 10,000 h to at least 50,000 h; and 2) the costs are reduced by a factor of four. Both targets seem to be achievable within the defined exploitation plan. Syngas production is on the other hand still in the phase of technical feasibility studies, albeit the market potential is high.
A detailed investigation of market potentials and business cases was performed. Results show an encouraging business outlook for the commercial application of HTE technology in the field of industrial hydrogen supply. Results show the gaps in terms of product costs and lifetime together with legal constrains as main challenges for a viable business.
Figure 10 shows the next development steps for sunfire’s pressurized HTE technology starting from TRL 4. Currently, a 10 kW proof-of-concept system has been build. The roadmap of exploitation activities during project life and beyond will be developed to identify measures to achieve a commercial stage (TRL 9). More details on the exploitation plans are given in the next chapter.

Figure 10: Development Steps for HT electrolysis on its way to a marketable product
Potential Impact:

The key objective of the HELMETH project was an optimized methanation process in combination with SUNFIRE’s high-temperature electrolysis (HTE) for the storage of fluctuating renewable electricity. HTE allows superior efficiencies compared to low-temperature variants (alkaline / PEM based electrolysers). It is the key element of SUNFIRE’s business plan due to its synergies to the SOFC technology.

HTE allows superior efficiencies of more than 90 %LHV if steam is provided from external sources or if waste heat can be used from external processes. Within the HELMETH project, coupling of HTE with exothermal methanation for the production of synthetic natural gas (SNG) has been investigated. This has the potential of reaching conversion efficiencies in the range of 85 %HHV. Taking into account the current maturity levels of the technologies within HELMETH as well as realistic parasitic losses, efficiencies of 80 % for a large scale SNG plant are realistic. These high conversion efficiencies allow an economic storage of volatile renewable electricity. Storage of SNG is preferred compared to pure hydrogen: Due to its specific density, an existing infrastructure, and regulatory requirements; the Power to Gas method might be a technically and economic feasible way for load balancing without government subsidy.

In order to achieve a viable business case, new business models need to be elaborated that take into account the interests of different players in the electricity field like wind park operators and owners of thermal power stations. It is evident, that PtG won’t be economical in small power classes, but at power levels > 5 MW due to specific cost of the processing plants. Several steps of upscaling will be necessary to reach this target. The highest cost saving potential lies in the HTE itself. Here, viable business cases need to be addressed at smaller scale in order to increase the production volume and with it decrease the production costs. Therefore, further products have been defined in the fields of hydrogen and syngas production:

1. High-temperature electrolyzes – Hydrogen supply to:
• Industrial H2 users (iron & steel, glass, semiconductor)
• Refineries
2. Compact pressurized electrolyzers with integrated methanation: PtG process
3. Syngas generation by co-electrolysis of steam and carbon dioxide for: PtG / PtL / PtX (X means any hydrocarbon) processes

The usage of renewable electricity for hydrogen generation allows a considerable reduction of global CO2 emissions within industry and power generation. Coupling different sectors like heat, hydrogen, fuel and electricity generation (e.g. via a reversible SOC system) allows a high flexibility in terms of an economic integration volatile renewable electricity.

Exploitation of results

High-temperature electrolyzers
Sunfire has a high interest of commercializing the HTE for industrial applications, due to cost- competitiveness at small and medium scale (H2 production 50 ... 400 Nm³/h). This is paving the way for future MW-scale applications in refineries, SNG (power-to-gas) or power-to-liquids.
Sunfire’s exploitation plan is based on increasing the Technology Readiness Levels (TRL) from the current status of TRL 4 to 5 up to a market entry which can be started with TRL 8.

SOEC operation at ambient pressure has reached TRL 5 with the successful RSOC system operation in cooperation with Boeing. The next development steps are already work-in-progress in order to get TRL 6 and 7 by 2018. A market entry with early products is planned for 2019/20. This development activities are outside the HELMETH scope.
Pressurized SOEC is in a lab-test status. A first prototype has been operated within HELMETH. At the end of the project a TRL of 4 was obtained in 2017, having seen the technology validated in a controlled environment. The main bottlenecks of the technology have been identified: The pressured operation requires a (costly) pressure vessel and a sophisticated pressure control system. Also, the steam mass flow control is critical resulting in higher pressure fluctuations at small flow changes. Therefore, Sunfire is currently prioritizing the upscaling and market readiness of its ambient pressure technology, since a faster market entry can be reached by ambient SOEC due to less operational risks and less costs.
The pressurized operation has the advantage of up to 4...8%-points higher efficiencies, resulting in savings in the electrical energy input. In order to reach higher technology readiness levels for a pressurized SOEC and the coupling with a methanation module, further research related to the technical bottlenecks, identified within HELMETH, is needed.

SNG applications
The exploitation plan for the developed PtG technology will be elaborated after the finalization of the business modelling. SNG applications require system sizes of at least 5 MW to become competitive. It is therefore expected, that a further upscaling step will be required.
A potential market entry of SNG applications won’t be before 2021/22.

Syngas generation
Syngas generation by co-electrolysis of steam and carbon dioxide is currently at TRL 2. First stack tests show the technical feasibility of the concept. However, long-term operation hasn’t been tested yet. It has been revealed that recuperative cooling of synthesis gas, which is required for high system efficiencies, bear the risk of carbon formation. Carbon formation limits and prevention strategies have been investigated by sunfire and KIT. The next step will be the testing of a small-scale (10 kW) prototype system. In parallel, Sunfire performs a detailed techno-economic analysis in a partnership with Nordic Blue Crude.

Dissemination activities
Sunfire’s dissemination activities in terms of high-temperature electrolysers are widespread and oriented on different target groups. As a summary, the following activities are addressed:
• Fairs (Hannover Fair, Fuel Cell Expo): Sunfire is presenting its results against the industry, scientific community and policy makers.
• Membership in the FCH-JU Board: Effecting the board decisions in terms of electrolysis, participation in political decision processes like RED-2.
• Scientific conferences: Sunfire is regularly presenting its results in the world-wide leading conferences on SOC and hydrogen technologies.
• Workshops: The state-of-the-art for the SOC and PtX technologies is presented for PhD students and newbies from industrial companies.
• Individual designation of industry: Sunfire is in close contact with end-customers from refineries or the iron and steel industry and with potential system integrators resp. leading companies in the field of technical gases.

KIT-Karlsruhe Institute of Technology
While SUNFIRE GmbH as the key commercial partner was mainly responsible for the exploitation of the project results, KIT was the lead partner for the coordination of dissemination activities including the set-up of the public webpage ( The website supplies relevant information for potential users of technologies developed by HELMETH as well as to the broad public. It was continuously updated during the project with new developments and public available deliverables/posters/papers. The public webpage of HELMETH had around 27.000 visitors within the last project year, exceeding the set target of 5000 visitors per year by far. Activities for raising awareness like press releases, wikipedia entries and distribution of leaflets at relevant events were performed.

The actual achievements of the HELMETH project were presented at several conferences / events and several scientific publications were published in cooperation with the project partners (detailed list of all dissemination activities and scientific publications is attached to this report). More detailed information is provided in the public deliverable on the dissemination activities.

The main technical task within the project for KIT was the design, construction and characterization of the methanation module. The possibilities to apply patents for several features, related to the research for the methanation module, are currently under evaluation.

The generated knowledge within HELMETH is also an important input to other ongoing European research projects related to PtG (e.g. Store&Go) and further projects in research and development of PtX applications are expected. The project and its results are also incorporated in the scientific education at KIT. Roughly 15 students were working within the projects frame and preparing 9 student theses directly linked to HELMETH plus several in related topics. The results of research work performed by KIT will be the core of one doctoral thesis.

POLITO -Politecnico di Torino
Dissemination activity has been essentially carried out via poster and oral presentations at international conferences. During these events, knowledge sharing with people from scientific and industrial communities was carried out. The main scientific sectors related to the dissemination activity are applied catalysis, industrial chemistry and chemical reaction engineering. Moreover, three articles were published on international scientific journals: they mainly focused on catalysts preparation/characterization, activity/stability tests and process modelling of power-to-gas systems based on high-temperature electrolysis. Investigation on methanation catalysts improved the knowledge about experimental condition and laboratory set-up to carry out kinetic modelling of CO2 methanation according to scientific standards. A well-established methodology could be used during the analysis of other catalytic processes (especially if focused on synthetic fuels production). Among the project activities, the test bench design enabled the analysis and the evaluation of advantages and drawbacks concerning experimental investigation on pressurized carbon dioxide methanation, improving the experience about a proper set-up of lab-scale test units. Process modelling activity enabled the possibility to investigate integration and operation of a power-to-gas system, even during intermittent functioning (strictly related to fluctuating electricity input). The overall activity during the project produced a general advancement of knowledge about methanation at multi-scale level (catalyst, reactor and system scale), exploitable for academic education and research activity.

EEI- Ethos Energy Italy SPA
The gained knowledge on the applicability of coatings should be further developed to find a suitable application in fuel cell market. The further development includes testing of coating on fuel cell stack plate and not only on the heat exchangers. At the same time commercial partners interested in testing and in qualification of new suppliers should be found. At the moment, a big effort should be spent to get in the market of fuel cells.

ERIC- European Research Institute of Catalysis A.I.S.B.L.
The potential impact of the activities made by ERIC is related to the development of proprietary preparation of improved catalysts for CO2 methanation, which have been tested under environmental relevant reaction conditions with respect to reference commercial catalysts. This catalyst allows to improve the reactor economics and meet the necessary quality of SNG. In addition, it is possible to commercialize a complete apparatus, without depending on external catalyst producers which may pose restrictions on catalyst use.
An intense dissemination activity at both relevant international conferences and main international journals, in large part in cooperation with other project partners, has been made by ERIC. The list of these activities is given in the following chapter.

NTUA- National Technical University of Athens
In terms of the social/environmental impact of HELMETH, the requirements of carbon negative operation and the potential reduction of GWP have been calculated. Carbon negative operation is achieved by non-fossil CO2 sources and an electric feed GWP of below 140-150 g CO2-eq/kWh. Therefore, carbon negative operation is feasible, even with current or near future grid power input. In other words, a full renewable input is not a necessity. Furthermore, lower GWP than extracting and transporting fossil NG is achieved by biogenic/atmospheric sources and electric carbon load of below 180-190 gr CO2-eq/kWh and fossil CO2 source (however carrying only the corresponding compression impact) and a near fully renewable electric input (below 40 gr CO2-eq/kWh). Existing PtG concepts powered by LT-electrolyzers feature higher requirements in terms of «clean» electric feed in order to achieve «Carbon negative» or «Better-than-NG» environmental performance. Relevant calculations show a requirement of 30% lower GWP of the electric feed, in order to reach the GWP values of PtG operation with HT-electrolysers.
In the best case examined (input from biogenic/atmospheric CO2 source and renewable generation), a carbon sink effect of -40 gr CO2-eq/MJSNG has been calculated, leading to more than 9 kt of CO2 captured in SNG during the lifetime operation (80,000 h) of an upscaled (1 MW) HELMETH concept system. If considering a potential heat application of the produced SNG, the relevant GWP impact is reduced by 75% (reduction of over 60 g CO2-eq/MJheat) compared to conventional Natural Gas combustion. In mobility applications, the GWP impact is reduced by 80% (reduction of over 90 g CO2-eq/km), when compared to the total emissions of a medium CNG car (113 g CO2-eq/km – driving emissions of 92 g CO2-eq/km), consuming 3.5 kgCNG/km.
Regarding the dissemination activities, NTUA organised a training seminar on May 2016 (“Energy Storage Technologies: Focus on Power-to-Gas Technology”), attracting an audience of 30 people (students, researchers, professors, plus 5 professional engineers from the Natural Gas Supplying Company of Attica (EPA) and the Public Power Corporation (PPC)). NTUA also participated with poster presentations in various conferences and dissemination events.
The HELMETH scientific results can be utilized as knowledge having a potential for providing a service for academic target groups. NTUA aims to include the HELMETH results and P2G concept in graduate (core course of 8th semester of NTUA Mechanical Engineering studies: “Combustion Theory and Systems”) and post-graduate lectures for engineering students at NTUA. An audience of 50 graduate and 30 post-graduate students would be expected per academic year. Additionally, one relevant dissertation per academic year.

DVGW- Deutscher Verein des Gas- und Wasserfaches
The scientific results of the HELMETH project, especially from the LCA and socioeconomic studies will be included in the workshops of DVGW (Gaskurs, Workshop Biogas). The training programme has a strong professional value that will generate new professionals with specialized knowledge.

List of Websites:
Public website:

Contact Coordination: Dr. Dimosthenis TRIMIS (E-mail:
Contact Communication: Dr. Stefan HARTH (E-mail: Mr. Manuel GRUBER (E-mail:

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