Stack Outlet Research Articles

Multiscale multiphysics modeling of ammonia-fueled solid oxide fuel cell: Effects of temperature and pre-cracking on reliability and performance of stack and system

Ammonia is a promising carbon-free fuel for solid oxide fuel cells (SOFCs). However, direct feeding of ammonia into the SOFC may lead to serious degradation due to the nitriding. Conversely, the pre-cracking of ammonia introduces complexity to the system design and causes increased power losses in the system. Therefore, it is crucial to explore all these aspects simultaneously. In this context, this study introduces a novel multiscale modeling approach by integrating a 3D multiphysics simulation of the ammonia-fueled SOFC stack with system-level modeling to investigate the reliability and performance of the stack and system. Two different cell technologies developed for low temperature (LT) and high temperature (HT) operation are investigated at LT (600 – 700°C) and HT (700 – 800°C) ranges. The results indicate that fuel inlet temperature should be 55°C and 18°C higher than the minimum temperature in 0% pre-cracking case for HT and LT cases, respectively. The increase in the required air flow rate for cooling in the 100% pre-cracking case compared to the 0% pre-cracking case is around 100% and 216% for the HT and LT cases, respectively. However, stack power production and power losses in the system components are comparable for LT and HT cases which leads to similar system performance. A larger share of the active area is affected by nitriding in LT cases than HT ones. However, a smaller cracking ratio at LT (∼ 82%) compared to HT conditions (∼ 92%) is needed for elimination of nitriding. While the LT and HT cases are comparable in terms of system power production, the lower stack outlet temperatures in LT cases require novel and more expensive catalysts for ammonia pre-cracking and HT cases need more expensive steels.

Performance and Durability of Next Generation Automotive Membrane Electrode Assemblies in Automotive Short Stacks

The space for polymer electrolyte membrane fuel cell (PEMFC) systems for the application especially in small cars is a limiting factor. Hence, high power density at high current density is required to fulfill the power demand and space requirements of a fuel cell system when installed into a car. Additionally, the fuel cell operation at elevated temperature supports this requirement facilitating smaller cooling systems. Hence, within the EU funded project GAIA (next Generation AutomotIve membrane electrode Assemblies), a consortium of leading OEMs, industrial partners and academic/research partners/organizations/institutions aimed to develop well beyond state of the art membrane electrode assemblies (MEAs) for high power application at elevated operating temperature.Therefore, electrocatalysts, membranes, ionomers, gas diffusion and microporous layers were developed with respect to minimizing the resistances by improving their interfaces. The potential of the developed next generation MEAs was determined using automotive short stacks aiming a beginning of life power density of 1.8 W/cm2 at 0.6 V. The durability target was defined with less than 10 % voltage loss of the beginning of life performance after 6000 operating hours (extrapolated from a testing time of 1000 h). For verification of the durability, an automotive drive cycle was adapted from real life driving data and applied for durability determination. This drive cycle contained very challenging operating conditions such as e.g., an applied current density up to 3 A/cm2 and an increased operating temperature of 105 °C at the stack outlet.In this study, the project achievements in performance and durability at high power and high temperature operation of the developed next generation automotive MEAs were demonstrated within automotive short stacks. During the projects progression, the application of a newly developed gas diffusion layer with increased degree of graphitization and a microporous layer with large pore structure significantly increased the performance at high current density. The stability of the catalyst coated membrane (CCM) was drastically increased by a membrane with a PBI-X reinforcement developed within the project, which replaced a standard PTFE reinforcement. Additionally, a new ionomer with increased high temperature stability was implemented that inhibited ionomer migration at high temperatures. The addition of a radical scavenger to the catalyst layer inhibited the destruction of the CCM by radicals as observed at high temperature operation with the state-of-the-art material. Finally, besides the improvement of the MEA material properties, the fuel cell operating parameters were optimized in-situ using an automated optimization algorithm to find the optimum operation parameters for the newly designed MEA. This optimization demonstrated a significant contribution to the achievement of the performance and durability target as it allowed the operation of the developed MEA at its “sweet spot”.

Flameback identification and air intrusion prevention in small flow hydrogen flare stack emissions

In some hydrogen production, storage and applications, the flare stack is used as an indispensable protection system for the emission and ignition of surplus hydrogen. However, there is a risk of flameback when emissions at small flow rate. Thus, a series of studies were carried out to explore the flameback identification and air intrusion prevention in small flow emissions. In this study, a flare stack with a molecular sealing, which was 12 m in height and 100 mm in diameter, was selected as the physical object. And a 3D numerical model was established. (1) The small flow hydrogen flare stack emissions were performed when the nitrogen purge was completed, and in this study the purge was finished in 80 s (2) The flameback case of the numerical model in this paper was used along with the US Bureau of Mines experimental to verify the accuracy of the flameback limit flow theoretical model. Furthermore, the lower limit of the theoretical curve was extended from 100 mm to 1 mm by theoretical calculation. (3) In order to comprehensively consider the combined influence of turbulence and buoyancy at the flare stack outlet, we proposed a new dimensionless parameter Fd to represent the flow state by the Reynolds and Richardson numbers. Based on this, a general flameback identification criterion was proposed. (4) When the nitrogen/hydrogen ratio was within the range of 40–56 vol%, nitrogen auxiliary pressurization effectively inhibited air intrusion and the expansion of the flammable range.

Assessment of SO2 Emissions from Cement Industries Utilizing Limestone with High Pyritic Sulfur Content: Case Study of Cement Plants in the Jaintia Hills District, Meghalaya, India

In properly operated Cement Plants, SO2 emissions are mostly caused by pyritic sulfur (sulfides) in the used limestones, accounting for approximately 85% of the raw mill in the plant. However, the pyritic sulfur content in limestones of the Jaintia Hills district of Meghalaya and their influence on the SO2 Emission from cement industries of Meghalaya have not been studied so far. The current study is conducted to perform an in-depth investigation of pyritic sulfur content in limestone reserves used by Meghalaya Cement Industries to assess the SO2 emission in the cement industries using high pyritic sulfur limestones and review the existing technology for the recommendation of the most suitable technology to minimize the SO2 Emissions. Random testing of collected limestone samples from various locations of Captive Mining sites in Cement Industries is performed to assess average pyritic sulfur concentration along different mining benches. Pyritic Sulfur Content (wt.%) in collected limestones varies from 0.15% to 3.5%. Polynomial Regression Analysis shows that Avg.SO2 Emission(Y) from Klin Stack can be represented as a function of pyritic sulfur content (X) (wt.%) of used limestones in the process: Y = 273.7X2 + 21.46X + 422.76. Based on the pyritic sulfur content in limestones, it is observed that “the more the Pyritic Sulfur content is, Darker the Limestone Samples are.” Hence, A Colour Scale has been prepared to visualize higher pyritic sulfur content in limestones. For longer-term sustainability, installing a Flue-Gas Desulfurization (FGD) unit at the kiln stack outlet may be included in the manufacturing process of cement plants to reduce the SO2 Emissions from Stack.

When less is more: Reducing environmental noise from open cycle gas turbines with acoustically transparent stacks

Sound radiation from large open cycle gas turbine power stations is strongly refracted by high temperature and velocity gradients in the near field of the exhaust stack outlet. Recent research by the authors has shown that in the presence of a cross-flow, the exhaust plume bends downwind and in doing so leads to significant increases in far-field sound pressure levels of up to 10dB compared to levels predicted from spherical spreading. This paper is the second in a series that explores a unique “acoustically transparent silencer,” which limits sound refraction consequently reducing downwind SPLs by separating the sound from the bulk exhaust flow. The efficacy of the approach is demonstrated two ways; initial characterization studies conducted in the reverberation chambers at the newly renovated Acoustic and Vibration Laboratory, University of Adelaide, and subsequent trials undertaken on a laboratory scale of 250 kW gas turbine in the field. Numerous designs are explored to quantify the effective insertion loss, where it will be shown as the transmission loss of the stack walls is reduced, the effective insertion loss increases, thus demonstrating that less is more. Reductions in ground-plane SPLs of up to 10 dB are achieved with less material and weight compared to traditional hard-walled stacks.

System level performance analysis and parameter optimization of hydrogen production based on solid oxide electrolytic cell

The high-temperature solid oxide electrolytic cell (SOEC) is expected to be widely used in large-scale energy storage, the chemical industry, distributed energy, and other fields due to its high efficiency and cleanliness. Moreover, selecting the operation point of the SOEC system with variable load under high-temperature conditions and striking a balance between safety and efficiency are difficult. Therefore, a 3 kW SOEC system model is built following the electrochemical reaction principle and the considered system layout. Based on this, the influence of operating parameters on stack voltage and power, stack outlet temperature, system H2 production, specific energy consumption, system efficiency, and the power consumption distribution of auxiliary equipment are analyzed. Finally, the operating current, temperature, air flow, and H2O utilization rate were taken as optimization variables, and the safe range of operating parameters was taken as the constraint condition to optimize system efficiency. The results show that under the given operating conditions and assumptions, the energy efficiency of the SOEC system can be adjusted from 60 % to 100 %, and the temperature difference can be controlled within 100 ℃. The durability of the system is improved by maximally reducing the temperature difference while ensuring the high efficiency of reactor operation.

Variation in the formation characteristics of PBDD/F, brominated PAH, and PBDE congeners along the secondary copper smelting processes

Simultaneous determination of 58 congeners of polybrominated dibenzo-p-dioxins and dibenzofurans (PBDD/Fs), brominated polycyclic aromatic hydrocarbons (Br-PAHs), and polybrominated diphenyl ethers (PBDEs) from multiple stages of industrial-scale secondary copper smelting plants was conducted with the aim of understanding their variations and control. In addition to the historical manufacture of PBDEs as brominated flame retardants, this study confirmed that PBDEs can be unintentionally produced and released from the secondary copper industry. The average mass emission factors of PBDD/Fs, PBDEs, and Br-PAHs from different sources were 10.0, 5.21 × 103, and 7.24 × 103 μg t−1, respectively. Therefore, the emission of brominated persistent organic pollutants (POPs) in the secondary copper industry should be of concern. The concentration of brominated POPs increased from the gas cooling stage to stack outlet due to the possible “memory effect” and the regenerated POPs were mainly low-brominated homologs. A comparison of brominated POPs with corresponding chlorinated analogs in the same process indicated that the formation pathway of Br-PAHs was consistent with that of chlorinated PAHs. However, unlike chlorinated dioxins and furans, PBDD/Fs can also be formed from PBDEs as precursors, leading to obvious increases in highly brominated furans. Therefore, inhibiting the unintentional formation of PBDEs is important for controlling brominated POPs emissions.

Computational modeling of woodstove pollutants in dilution tunnels

ABSTRACT The computational modeling of the dilution tunnels used for experimental measurement of the woodstove pollution was presented. Two EPA-approved test labs for residential wood heat appliances, referred to as Lab-1 and Lab-2 dilution tunnels were simulated. The Ansys-Fluent software was enhanced with the addition of user-defined functions (UDF) and was used to simulate the airflow velocity, temperature, and particle concentration in the dilution tunnels. Particular attention was given to the variation of concentration profile at the test section and its uniformity. The simulation results suggested that roughly uniform or somewhat non-uniform particle concentrations entering from the woodstove stack into the dilution tunnel led to the uniform concentration at the outlet of the tunnel. This is particularly the case for the Lab-1 dilution tunnel. However, for the Lab-2 dilution tunnel, a highly non-uniform concentration at the woodstove stack outlet flowing at a high velocity into the dilution tunnel led to a non-uniform profile for the particle concentration at the test section. For this case, replacing the second elbow that is downstream from the mixing section with a tee reduced the nonuniformity of the concentration profile at the tunnel outlet. Implications: This study numerically investigated two dilution tunnels used in EPA-approved test labs. The dilution tunnel is used to dilute and cool the exhaust flow of the woodstove’s stack. A properly working dilution tunnel provides a uniform concentration at the test section. Under different conditions, particulate matter (PM) laden turbulent flows in the tunnels are simulated to assess the dilution tunnel’s performance. The goal is to understand the conditions that the dilution tunnels provide uniform concentration at their test section. The presented results suggest that using a tee instead of an elbow would enhance mixing and the chance for generating uniform concentration at the test section.

Performance improvement of proton exchange membrane fuel cell stack by dual-path hydrogen supply

Proton exchange fuel cell stack typically operates in dead-ended anode mode to achieve high fuel utilization, but this can cause issues such as flooding and fuel starvation. To mitigate these problems, this study proposes a dual-path hydrogen supply strategy with simultaneous isostatic hydrogen supply from the stack inlet and outlet. When applied in a water-cooled stack containing 20 single cells, the split ratio of the two branches is maintained at about 1.0, which means that hydrogen supplied from the two paths is equal. Both dead-ended anode mode and dual-path hydrogen supply mode are tested under two different cathode back-pressure conditions to verify the effectiveness of the proposed strategy, and parameters such as pressure drop, voltage change, and fuel utilization are discussed in detail. Results show that the proposed strategy provides more hydrogen downstream of anode flow channels and promotes water redistribution, thus effectively improving the stack performance. Compared with dead-ended anode mode, dual-path hydrogen supply mode increases the stack voltage by 4.28% at 0.9 A/cm2. Furthermore, the effect of different purge periods is also probed on the proposed strategy.

Optimal design of thermostat for proton exchange membrane fuel cell cooling system

The temperature conversion and control of hydrothermal system is crucial for the performance and durability of fuel cell engines. We firstly built the simulation and experiment platform for the cooling system, include confluence mode and split mode for the thermostat. Through the model calculation, in the split mode, the error of the stack outlet is about 0.8%, and the temperature shock time error is about 5%, the maximum temperature error when switching between large and small cycles is about 0.7%, and the temperature fluctuation is small in the confluence mode. The calculated results are in good agreement with the experimental results, which proved the rationality of the model. Secondly, the influence of the temperature fluctuation caused by the cycle switching of the system size on the catalyst activity and the electrochemical reaction rate is researched, by studying the different position settings of the thermostat in the system. It is found that the thermostat confluence mode increases the response speed and a wider temperature control area. Finally, based on the hysteresis characteristics of the temperature melting of the paraffin-type thermostat, the system uses an electronic thermostat to replace the thermostat. Through the optimized control strategy, temperature fluctuations are basically eliminated, and the temperature management of the cooling system is optimized.

Features selection and substitution in PEM fuel cell water management failures diagnosis

AbstractA data‐driven strategy considering sensor reliability and cost is presented for polymer electrolyte membrane fuel cell (PEMFC) fault diagnosis. An increase of pressure drop in the flow field is a reliable indicator of PEMFC flooding fault. Still, it highly depends on the pressure measurement accuracy of the stack inlet and outlet. The abnormal sensor will mislead the diagnosis results, and an extra pressure sensor in the outlet means higher system cost. Thus, the related behavior is investigated. The throttle opening set, one of the control signals, is chosen to replace the cathode pressure drop. The throttle opening set, the stack voltage, and cell voltage monitoring (CVM) standard deviation are employed as diagnostic features, and the support vector machine (SVM) is used as the classifier. Compared to the approach using single‐cell voltages, the strategy mentioned above minimizes extra sensors and avoids the computation load of dimensionality reduction. High accuracy in diagnosing flooding and dehydration via identifying experimental data of different fault severity verifies the effectiveness of the presented strategy.

An optimal coordinated proton exchange membrane fuel cell heat management method based on large-scale multi-agent deep reinforcement learning

To improve the operating efficiency of proton exchange membrane fuel cells (PEMFCs), an optimal coordinated control strategy for addressing the poor coordination problem between the water pump and radiator in a PEMFC stack heat management system is proposed in this paper. To this end, a cooperative exploration strategy large-scale multiagent twin-delay deep policy gradient (CESL-MATD3) algorithm has been developed for this control strategy. In this algorithm, both the water pump and radiator are treated as individual agents, and the strategies of centralized training and decentralized execution are applied; thus, coordinated control over the two agents is realized. Moreover, the concepts of curriculum learning, imitation learning, and various novel parallel computing techniques are incorporated into the design of this algorithm, resulting in enhanced training efficiency; thus, a coordinated control strategy with better robustness is obtained. According to the experimental results, compared with other advanced control algorithms, this coordinated control strategy-based algorithm achieves better performance and robustness for PEMFC stack temperature management. The proposed method can effectively improve the response speed of the controllers, reduce the fluctuation and oscillation of the stack temperature and the temperature difference between the stack outlet and inlet (stack temperature difference) during heat management, and reduce the maximum overshoot of the stack temperature by 99.12% and of the stack temperature difference by 97.97%.

Congener profiles and process distributions of polychlorinated biphenyls, polychlorinated naphthalenes and chlorinated polycyclic aromatic hydrocarbons from secondary copper smelting

Secondary copper smelting is an important industrial source of unintentionally produced persistent organic pollutants (UPOPs) emissions. Herein, field study on industrial-scale plants was conducted to clarify the levels and profiles of polychlorinated biphenyls (PCBs), polychlorinated naphthalenes (PCNs) and chlorinated polycyclic aromatic hydrocarbons (> 3 rings, Cl-PAHs) from secondary copper smelting plants. The three UPOPs emission levels from the oxygen-enriched smelting furnace were higher than that from the anode furnace, which was attributed to the low-grade raw materials used. The toxic equivalent quantity concentrations of Cl-PAHs were 1.3–4.4 and 4.6–18.9 times higher than that of PCBs and PCNs, respectively. Thus, the emission control of Cl-PAHs in the secondary copper industry should be of concern. The chlorination degree of PCBs and PCNs was ~4 after the gas-cooling stage but was reduced to 1–2 in the stack outlet. This result indicated that the PCBs and PCNs congeners that were generated during the cooling stage were mainly higher-chlorinated. After purification by air pollution control devices (APCDs), the high-chlorinated congeners were removed simultaneously with the fly ash, whereas the low-chlorinated congeners may be regenerated and transferred into the stack gas due to possible memory effect within the APCDs.

Thermal analysis and management of proton exchange membrane fuel cell stacks for automotive vehicle

The thermal management of a proton exchange membrane fuel cell (PEMFC) is crucial for fuel cell vehicles. This paper presents a new simulation model for the water-cooled PEMFC stacks for automotive vehicles and cooling systems. The cooling system model considers both the cooling of the stack and cooling of the compressed air through the intercooler. Theoretical analysis was carried out to calculate the heat dissipation requirements for the cooling system. The case study results show that more than 99.0% of heat dissipation requirement is for thermal management of the PEMFC stack; more than 98.5% of cooling water will be distributed to the stack cooling loop. It is also demonstrated that controlling cooling water flow rate and stack inlet cooling water temperature could effectively satisfy thermal management constraints. These thermal management constraints are differences in stack inlet and outlet cooling water temperature, stack temperature, fan power consumption, and pump power consumption.

Sound propagation through elevated, heated jets in cooler cross-flow: An experimental study.

Sound propagation through hot exhaust plumes with cooler cross-winds is present in many real world systems. One particular example is the sound propagation from exhaust stacks attached to open cycle gas turbine power stations. The research presented in this paper investigates the sound propagation from a reduced-scale exhaust stack, with a cross-flow from experiments conducted in a wind tunnel. Experimental measurements of the flow and temperature fields provide insight into the complex sound radiation characteristics. Results from the acoustic measurements show the change in the sound directivity arising from the inclusion of the hot exhaust plume, leading to non-axisymmetric sound directivity and a concentration of sound downwind of the exhaust stack outlet. In certain cross-flow conditions, the hot exhaust plume can increase the sound observed downwind by up to 11 dB when compared to the scenario of sound propagation from an exhaust stack in the absence of a heated jet or cross-flow. This paper describes the acoustic directivity at various radial distances from the exhaust stack, acoustic frequencies, jet temperatures, and cross-flow free-stream velocity. The results from this paper emphasise the importance of taking into consideration the hot exhaust plume with cooler cross-flow when estimating sound levels downwind of the stack.

Design and Computational Fluid Dynamics Modeling for a Municipal Solid Waste Incineration Process

Municipal Solid Waste (MSW) incineration is among the important opportunities to control the pollutions caused by improper dumping and flue gas emissions so as to meet the environmental guidelines. The objective of this study was to design and develop a model for the MSW incineration process. The paper explains the design and development of MSW incinerator involving details of the Computational Fluid Dynamics (CFD) procedures through model design to the post process. CFD model was developed to reveal these features of the incineration process in the MSW incinerator. The model predicts the temperature in combustion chambers as well as at stack outlet of the incinerator. The solid waste characterization was done, and the laboratory analysis shows that, the Higher Heating Value (HHV) of the MSW is 11.65 MJ/kg on dry basis. The elemental composition MSW consists of 54.8%, 5.27%, 34.61%, 2.37% and 0.3% for Carbon, Hydrogen, Oxygen, Nitrogen and Sulphur respectively which are the input parameters for the CFD. The model simulation was positively achieved during combustion process and temperature in combustion chambers ranged between 930 K and 1700 K.

Size and exergy assessment of solid oxide fuel cell-based H2-fed power generation system with alternative electrolytes: A comparative study

This work aims to analyse and compare the thermodynamic performance and size of two types of solid oxide fuel cell (SOFC)-based plants. The former is the conventional H2-fed plant based on SOFC with an oxygen-ion conducting electrolyte (SOFC-O), and the latter is based on SOFC using a proton-conducting electrolyte (SOFC-H). Thermodynamic analysis reveals that in the SOFC-H system, due to H2O formation at the cathode side, not only the anode concentration losses decreases, but also the partial pressure difference between H2 and H2O increases which leads to an increase in Nernst voltage compared to the SOFC-O system. Due to this, SOFC-H and SOFC-O based plants exhibit different performance in terms of the cell voltage, power, efficiency, stack outlet temperature and size of heat exchangers used for preheating the fuel and air. The results indicate, for current densities less than around 3,000 A/m2, the energy and exergy efficiencies of SOFC-H-based system are more than those of the SOFC-O-based plant. This results in reduced area of heat exchangers per unit power used in the SOFC-H-based plant as compared with the SOFC-O-based plant. In addition, the sensitivity analysis demonstrates that using thin cells in the SOFC stack is favourable for the SOFC-H-based plant.

(Invited) A New Method for Combining P2X and Electricity-Balancing Using SOECs

Solid Oxide Electrolysis Cells (SOEC) can be used for efficient power-to-X (P2X) conversion. Here X symbolizes the myriad of end products that can be made using green power, H2O and CO2. The SOEC converts H2O and CO2 into gas (most often H2 and/or CO) which can be catalyzed into a broad range of fine- and speciality-chemicals, as well as bulk transportation fuels.Dynamic operation of the SOECs can help balance the electricity consumption with the electricity production from intermittent energy sources, such as wind and solar. P2X can therefore assist the on-going transition to a non-fossil energy infrastructure by substituting fossil-based chemicals and fuels with sustainable alternatives, while simultaneously providing energy balancing services.It is important to realize that the requirement for electricity balancing ranges in time from milliseconds to months. Batteries offer quick response times and are increasingly being used to provide fast ancillary services to the electrical grid. Unfortunately battery-based electricity storage costs hundreds of $ per kWh of capacity, which renders them impractical for large-scale storage exceeding time-scales of about one hour. This is where dynamic electrolysis operation with part load enters the scene.During operation of SOECs at part load, i.e. below the thermo-neutral point of operation, the endothermic reaction heat will dominate the internal heat balance and generate thermal gradients in the SOEC stack. The gas exiting the stack will therefore be colder than the gas entering the stack, such that an external (electric) heater is required to pre-heat the gas before the gas can enter the stack. The thermal gradients cause temperature variations inside the stack that increases with increasing stack size. It is an advantage to avoid thermal gradients, as these cause thermo-mechanical stresses and variations in the cells’ resistance across the stack. Thermo-mechanical stresses may lead to cracks in the brittle ceramic cells and delamination at interfaces. Varying cell resistance causes variations in current density and electrode overpotential across the stack, which increases the risk of accelerated degradation. Thus, thermal gradients hinder an increase of the footprint (i.e. the size) of SOEC stacks. Consequently, upscaling to MW-systems faces considerable complexity related to wiring, piping and heat management of hundreds of smaller kW-sized stacks. This limits cost reductions related to economy-of-scale, in particular if the SOEC MW-systems are to be used for dynamic operation and electricity balancing.In this work, we demonstrate theoretically and experimentally how pseudo thermo-neutral operation can be achieved at part load. The uniform temperature profile is established by overlaying the DC voltage in electrolysis mode with a rapid alternating voltage, such that the Joule heat balances the endothermic reaction heat. The alternating voltage causes the stack to be operated a few milliseconds in SOFC (or SOEC) mode before it returns to SOEC (or SOFC) mode. The frequency of the alternating voltage is around 20 – 100 Hz. This means the stack temperature and outlet gas composition is not affected by the alternating voltage. During SOFC mode, excessive heat is generated to balance the endothermic SOEC operation. As the SOFC operation produces more heat than the SOEC operation consumes per time interval, a net-production of fuel is realized.By controlling the time and cell voltage in respectively SOEC and SOFC mode the overall load can be continuously changed from 0% (corresponding to OCV) to 100% (corresponding to DC operation at thermo-neutral voltage) while keeping the gas outlet temperature equal to the gas inlet temperature.The operation method therefore enables very fast load variations without having to change the stack temperature or gas compositions. This enables dynamic operation of MW SOEC stacks to enter the market for fast electricity balancing, where batteries are currently applied.Importantly, the operation method seems to decrease the stack degradation rate, which we speculate is caused by desorption of impurities that otherwise adsorb on the surface of the electrodes.The potential for the novel operation method to combine chemicals and fuel production with electricity balancing at time scales spanning from milliseconds to months, can hopefully help commercialize and upscale the SOEC technology towards MW-systems.

Effects of Working Fluids on the Performance of a Roots Pump for Hydrogen Recirculation in a PEM Fuel Cell System

In this paper, the performance of a Roots pump for hydrogen recirculation in proton exchange membrane (PEM) fuel cell system is simulated based on CFD modeling. The Roots pump is in a three-lobe configuration with helical rotors, and it is developed specifically for fuel cell systems between 60 to 110 kW. A three-dimensional model of the Roots pump is established to predict the pump performance, including the flow rate and power consumption under various operating conditions. Extensive simulations were conducted and then verified experimentally by operating with working fluids of air and helium. Based on the validated CFD model, the contents of water vapor and nitrogen in the hydrogen recirculated are taken into account to evaluate the Roots pump performance numerically according to the actual conditions of the recirculating hydrogen at the stack outlet. It is shown that the volumetric efficiency and isentropic efficiency are improved with the increase fraction of water vapor and nitrogen. It is found that the performance of the Roots pump integrated in the PEM fuel cell system is between the performance of the pump working with air and helium. Finally, correlations of volumetric efficiency and isentropic efficiency are given based on the CFD results to show the general pattern of this kind of hydrogen pump. It is believed that these equations are very helpful to the design and operation control of the PEM fuel cell system.

Robust polymer electrolyte membrane fuel cell temperature tracking control based on cascade internal model control

To optimize fuel cell system efficiency, compared with the regulation control of temperature, the latest engineering practice is more inclined to perform tracking control. The fuel cell temperature subsystem has the characteristics of slow response and strong nonlinearity, which poses challenges to tracking control. This paper proposes a cascade internal model control (CIMC) to make the stack outlet temperature track the target value when fuel cell load currents changes. Both simulation and experiment show that the control method has good rapidity, accuracy and robustness. The Simulation results based on AMESIM® shows that the step response static errors of static points test and step signal test are all 0 °C. The response time of step signal test is around 47s. Both of the step response and dynamic response the overshooting are 0 °C without divergence. The experiment results on a real 120 kW commercial fuel cell system test bench are similar with the simulation results with 0 °C static error at different working conditions, 44s response time for step response and overshooting around 1 °C at the dynamic working condition, which is acceptable for the tested PEMFC stack.