System Considerations on On-Board Methanol Steam Reforming as Hydrogen Supply for High Temperature PEM Fuel Cells.

Due to their high tolerance to fuel contaminants, High Temperature PEM fuel cells offer a suitable technology for the operation on reformate-gas. Methanol steam reforming enables compact system designs because of its low reaction enthalpy. On-board water storage for steam reforming lowers the energy density of the fuel, making it questionable for mobile applications. Technological options and operation strategies for water recycling in mobile applications are presented based on experimental data and system modeling using the simulation tool AspenPlus®

High Temperature Polymer Electrolyte Fuel Cell Systems for Aircraft Applications

Auslegung eines Hochtemperatur Polymer Electrolyt Brennstoffzellensystems unter Berücksichtigung luftfahrtrelevanter Parameter. Von der Auswahl geeigneter Brennstoffe bis zur Auslegung eines mit Methanol Dampfreformierung gekoppelten Systems

Techno-economic Study of an Electrolysis-Based Green Ammonia Production Plant

This paper presents an investigation of a storage option of green hydrogen (H2) in the form of ammonia (NH3) based on system simulations considering detailed technical properties. Experimental data from a 1 MW PEM electrolyzer is used to develop an electrolyzer model and downstream a kinetic reactor for NH3 synthesis. Exemplarily, the electricity is supposed to be supplied by a hydropower plant in Norway. An economical evaluation of the plant is performed for optimized process parameters. The costs of H2 and NH3 are calculated based on electrolyzer investment costs published for deployment between 2020 and 2030 and several electricity cost scenarios. From the results, a broad economic optimum of the operating range of the electrolyzer in the entire plant is obtained. This work provides a basis for the future evaluation of complex plants with electrolyzers for the production of green ammonia as well as strategies for the reduction of costs of green NH3 in the future

Evaluation of a 3 kWel Reformer-operated High Temperature PEM System – Experiment and Simulation

High temperature polymer electrolyte membrane fuel cells (HT-PEMFC) can be operated with reformate containing carbon monoxide levels up to several vol.-%. This enables the design of a coupled reformer fuel cell system with reduced complexity and enhanced robustness. An experimental study and an Aspen Plus system model is presented. The experimental results were obtained with a methane reforming unit (WS Reformer) and a fuel cell module with three stacks and 76 cells each (SerEnergy). The characterization of the components was focused on the effect of different process parameters on system behaviour and total system efficiency. Mainly the variation of CO concentration, operation temperature, load and water content of the anode feed gas were investigated. Both subsystems were modelled using Aspen Plus flowsheeting software. The reforming and the water gas shift reactors were realized by a Gibbs reactor model. Kinetic limitations have been taken into consideration by applying a temperature approach in Aspen Plus, which allows for non-equilibrium conditions in the product gas. The reformate gas composition from the model shows good agreement with the experimental results. The hydrogen conversion efficiency reaches 72 to 75 %. Based on the experimental results the fuel cell module was modelled taking into account the dependence of performance on the operation parameters of the module. This was realized by the implementation of a performance map. The Aspen model of the coupled process including hydrogen generation and fuel cell system was then used for process optimization. Thermal integration was realized by applying the Pinch Method. As a result, an optimized system configuration could be identified. For the coupled reformer-HTPEM-system an overall electric efficiency of 30 - 40 % can be achieved

Heat and fuel coupled operation of a high temperature polymer electrolyte fuel cell with a heat exchanger methanol steam reformer

In this work a methanol steam reforming (MSR) reactor has been operated thermally coupled to a high temperature polymer electrolyte fuel cell stack (HT-PEMFC) utilizing its waste heat. The operating temperature of the coupled system was 180 C which is significantly lower than the conventional operating temperature of the MSR process which is around 250 C. A newly designed heat exchanger reformer has been developed by VTT (Technical Research Center of Finland LTD) and was equipped with commercially available CuO/ZnO/Al2O3 (BASF RP-60) catalyst. The liquid cooled, 165 cm2, 12-cell stack used for the measurements was supplied by Serenergy A/S. The off-heat from the electrochemical fuel cell reaction was transferred to the reforming reactor using triethylene glycol (TEG) as heat transfer fluid. The system was operated up to 0.4 A cm2 generating an electrical power output of 427Wel. A total stack waste heat utilization of 86.4% was achieved. It has been shown that it is possible to transfer sufficient heat from the fuel cell stack to the liquid circuit in order to provide the needed amount for vaporizing and reforming of the methanol-water-mixture. Furthermore a set of recommendations is given for future system design considerations

PEM fuel cells direct hybrid system in aviation

The Institute for Engineering Thermodynamics has been working on battery and fuel cell direct hybrids for aircraft. This type of hybrid is more restricted in terms of load distribution in comparison to one using DC/DC converters. However it is more efficient, has fewer components and is therefore more cost effective. Due to the limited capabilities of load distribution the design process is more complex. All the components have to be carefully matched to each other. During this process many aspects related to the conditions under which the hybrid energy storage system has to operate have to be considered. Partial system failures, temperature changes, humidity changes etc. must be handled as they cannot be compensated for by simply adjusting the boost factor of a converter. Also recharging of the battery is quite difficult as several limitations have to be taken into account and the possibilities of adjusting the current into the battery are very limited. The only means to controlling charge current into the battery is by operating the fuel cells less efficiently. Furthermore the coulomb-efficiency of a battery causes a quite severe difference in the energy supplied to charge the battery from the fuel cell and that returned when discharging it. So the main question is how much battery recharging is required for safe operation of the airplane for example if the pilot has to touch-and-go or in case of failure of the fuel cell system. In some cases it may even be better to only use the battery for take-off and climb at the beginning of a flight. The fuel cell system consists of several stacks that can be run entirely independent from one another. The system therefore has quite some redundancy built in. However as this system is coupled with the battery system most of the load, in case of single unit failure, is shifted to the battery system which then quickly discharges. Depending on the characteristics of the ACinverter this could result in strong declination of the aircrafts range as well as strongly reduced maximum power. However there are possibilities to overcome this problem

Antares DLR-H2 – Flying Test Bed for Development of Aircraft Fuel Cell Systems

Fuel cell systems provide a zero-emission and low noise solution for on-board power generation in aircraft. To assure safe and reliable fuel cell operation in aircraft, system testing has to be conducted under realistic operating conditions. On the one hand these conditions can hardly be simulated in laboratory; on the other hand evaluation of the systems with a wide-body aircraft like an Airbus A320 is inflexible, time and cost consuming. Therefore the aerodyne Antares DLR-H2 has been developed as a flying test bed to provide a system carrier for time and cost effective airborne fuel cell system testing. In this presentation the test platform Antares DLR-H2 will be described with the new fuel cell system generation and latest results, comprising laboratory measurements (fuel consumption, power output) and insights on the system design, especially focusing on the concept of direct hybridization, allowing a simple and therefore reliable possibility of coupling fuel cells and batteries

Low-Temperature NOx Reduction by H2 in Diesel Engine Exhaust

For the NOx removal from diesel exhaust, the selective catalytic reduction (SCR) and lean NOx traps are established technologies. However, these procedures lack efficiency below 200 °C, which is of importance for city driving and cold start phases. Thus, the present paper deals with the development of a novel low-temperature deNOx strategy implying the catalytic NOx reduction by hydrogen. For the investigations, a highly active H2-deNOx catalyst, originally engineered for lean H2 combustion engines, was employed. This Pt-based catalyst reached peak NOx conversion of 95 % in synthetic diesel exhaust with N2 selectivities up to 80 %. Additionally, driving cycle tests on a diesel engine test bench were also performed to evaluate the H2-deNOx performance under practical conditions. For this purpose, a diesel oxidation catalyst, a diesel particulate filter and a H2 injection nozzle with mixing unit were placed upstream to the full size H2-deNOx catalyst. As a result, the Worldwide harmonized Light vehicles Test Cycle (WLTC), urban cycle segment of the Common Artemis Driving Cycle (CADC UC) and Transport for London Urban Inter Peak (TfL UIP) driving cycle revealed NOx conversions up to 90 % at temperatures as low as 80 °C. However, outside the low-temperature region, H2-deNOx activity dropped significantly evidencing the need for an additional underfloor SCR system. Moreover, slight N2O formation was observed in the engine tests making further catalyst development necessary, since N2O is considered a critical component due to its global warming potential. Additionally, the H2 demand for low-temperature deNOx in diesel passenger cars was estimated and a novel on-board H2 production strategy based on DEF electrolysis was developed. This method provided both H2 as well as gaseous NH3. Subsequent simulations of H2 production demonstrate small size factors (≤ 525 cm3) and rather low energy consumption of the H2 supply unit, e.g. 0.25 kWh for the TfL UIP driving cycle

Porous Transport Layers for Proton Exchange Membrane Electrolysis under Extreme Conditions of Current Density, Temperature and Pressure

Hydrogen produced via water electrolysis powered by renewable electricity or green H2 offers new decarbonization pathways. Proton exchange membrane water electrolysis (PEMWE) is a promising technology although current density, temperature and H2 pressure of the PEMWE will have to be increased substantially to curtail the cost of green H2. Here, we report a porous transport layer for PEMWE that enables operation up to 6 A cm 2, 90 °C and 90 bar H2 output pressure. It consists of a Ti porous sintered layer on a low-cost Ti mesh (PSL/mesh-PTL) by diffusion bonding. This novel approach does not require a flow field in the bipolar plate. When using the mesh-PTL without PSL, the cell potential increases significantly due to mass transport losses reaching ca 2.5 V at 2 A cm-2 and 90 ºC. On the other hand, the PEMWE with the PSL/mesh-PTL has same cell potential but at 6 A cm-2, thus increasing substantially the operation range of the electrolyzer. Extensive physical characterization and pore network simulation demonstrate that the PSL/mesh-PTL leads to efficient gas/water management in the PEMWE. Lastly, the PSL/mesh-PTL was validated in an industrial size PEMWE in container operating at 90 bar H2 output pressure