Cathode Recirculation Research Articles

Development of a Dynamic Cathode Ejector Model for Solid Oxide Fuel Cell-Gas Turbine Hybrid Systems

Solid oxide fuel cell-gas turbine (SOFC-GT) hybrid systems are attractive for future power generation with ultra-low criteria pollutant and greenhouse gas emissions. One of the challenges for SOFC-GT systems is to sufficiently pre-heat incoming air before it enters the fuel cell cathode. An ejector for cathode exhaust recirculation has the benefits of reliability, low maintenance, and cost compared to either recuperators or cathode recirculation blowers, which may be also be used for air pre-heating. In this study, a dynamic Simulink model of an ejector for cathode exhaust recirculation to pre-heat incoming fuel cell air has been developed. The ejector is to be utilized within a 100 MW SOFC-GT dynamic model operating on coal syngas. A thorough theoretical development is presented. Results for the ejector were found to be in good agreement with those reported in literature.

Cathodic Recirculation System Using a Dual-ejector to Improve Oxygen Utilization of a Submarine Fuel Cell

In terms of the system efficiency, it is very useful to apply the ejector into the fuel recirculation system of a fuel cell system since the ejector needs no parasitic power to operate. Since the conventional automotive fuel cell use hydrogen and air as their fuel, the only hydrogen is needed to be recirculated for the better fuel efficiency. On the other hand, the submarine fuel cell needs both hydrogen and oxygen recirculation systems because the submarine drives under the sea. In particular, the cathodic recirculation has to meet the tougher target since the oxygen based pressurized stack generally used in the submarine applications generates the significant amount of the water in the stack during the operation. Namely, the oxygen utilization has designed less than 50% in the whole operating range for the better exhausting of the generated waters. And thereby in terms of the oxygen utilization, the entrainment ratio of the ejector should be more than 1 within the whole operating range. However, the conventional ejector using a constant nozzle can not afford to satisfy the mentioned critical requirement. To overcome the problem, the dual-ejector and its control strategy are designed. The performance of the proposed dual-ejector is verified by the experiments based on the real operating conditions of the target submarine system. Furthermore, the proposed design method can be used for the other fuel recirculation system of a large-scale fuel cell system with the critical requirement of the fuel utilization.

Cathodic Recirculation System Using a Dual-ejector to Improve Oxygen Utilization of a Submarine Fuel Cell

Cathodic Recirculation System Using a Dual-ejector to Improve Oxygen Utilization of a Submarine Fuel Cell

Design of a thermally integrated bioethanol-fueled solid oxide fuel cell system integrated with a distillation column

Solid oxide fuel cell systems integrated with a distillation column (SOFC-DIS) have been investigated in this study. The MER (maximum energy recovery) network for SOFC-DIS system under the base conditions ( C EtOH = 25%, EtOH recovery = 80%, V = 0.7 V, fuel utilization = 80%, T SOFC = 1200 K) yields Q Cmin = 73.4 and Q Hmin = 0 kW. To enhance the performance of SOFC-DIS, utilization of internal useful heat sources from within the system (e.g. condenser duty and hot water from the bottom of the distillation column) and a cathode recirculation have been considered in this study. The utilization of condenser duty for preheating the incoming bioethanol and cathode recirculation for SOFC-DIS system were chosen and implemented to the SOFC-DIS (CondBio-CathRec). Different MER designs were investigated. The obtained MER network of CondBio-CathRec configuration shows the lower minimum cold utility ( Q Cmin ) of 55.9 kW and total cost index than that of the base case. A heat exchanger loop and utility path were also investigated. It was found that eliminate the high temperature distillate heat exchanger can lower the total cost index. The recommended network is that the hot effluent gas is heat exchanged with the anode heat exchanger, the external reformer, the air heat exchanger, the distillate heat exchanger and the reboiler, respectively. The corresponding performances of this design are 40.8%, 54.3%, 0.221 W cm −2 for overall electrical efficiency, Combine Heat and Power (CHP) efficiency and power density, respectively. The effect of operating conditions on composite curves on the design of heat exchanger network was investigated. The obtained composite curves can be divided into two groups: the threshold case and the pinch case. It was found that the pinch case which T SOFC = 1173 K yields higher total cost index than the CondBio-CathRec at the base conditions. It was also found that the pinch case can become a threshold case by adjusting split fraction or operating at lower fuel utilization. The total cost index of the threshold cases is lower than that of the pinch case. Moreover, it was found that some conditions can give lower total cost index than that of the CondBio-CathRec at the base conditions.

Model and Simulation of a SOFC CHP Plant Fuelled with Hydrogen

In this paper the characteristics and problems of a SOFC CHP system is investigated in the hypothesis of hydrogen feeding. The possibility of SOFC systems fed by hydrogen is not deeply investigated: the main advantage of SOFC is the possibility to be fed by different fuels, while hydrogen has to be produced. Nevertheless, in case of a context with possibility of producing hydrogen at low cost by means of renewable sources (e.g. hydroelectricity), it could be of interest to investigate a SOFC system fed with hydrogen fuel due to a better system performance and environmental benefits. A model is proposed describing the operation of an air-cooled SOFC system: results are discussed pointing out the thermal management and its effect on the electrical performance of system. It is shown that the design of a high temperature cathode recirculation system allows one to overcome the thermal management while obtaining higher electrical performances.

Early start-up of solid oxide fuel cell hybrid systems with ejector cathodic recirculation: Experimental results and model verification

A new test rig, founded in part by Rolls-Royce Fuel Cell Systems Limited, by the EU integrated project ‘FELICITAS’, and by the national project PRIN-2005, has been designed and built at the University of Genova to study different early start-up layouts and strategies for solid oxide fuel cell (SOFC) hybrid systems, using ejector-based cathodic recirculation. The test rig, which is flexible enough to analyse different emulated turbomachine layout (single shaft, two shafts, regenerated cycles or not, and so forth), different ejector configurations, and different stack arrangements, is unique. It also allows the early start-up performance to be fully investigated with particular attention to the analysis of the hybrid system fluid dynamic behaviour when the stack is off and the control system operates at critical conditions. The experiments have been carried out using a patented start-up combustor emulator (outlet temperature higher than 950°C), and monitoring the pressure and temperature quick rise to prevent mechanical and thermal stress to the fuel cell stack and to maintain turbomachine stability. The experimental results have also been used to verify the time-dependent hybrid system models based on TPG-TRANSEO tool. The results show good agreement with experimental data. This is essential to increase confidence with predictive time-dependent simulation tools during the start-up phase, where experimental data are hardly available and fuel cell materials may operate under risky conditions.