Final Report Summary - CATION (Cathode Subsystem Development and Optimisation)
Executive Summary:
1. Executive summary
Fuel cells and hydrogen have a potential for reducing emissions of greenhouse gases and air pollutants, facilitating the increased use of renewable energy sources, raising overall efficiencies of conversion. In addition the high temperature fuel cell technology SOFC has the potential for high electrical efficiency, 55-60%, and total efficiency up to 90% for CHP units combined with low emissions. However, the cost and lifetime of SOFC systems is a problem that must be solved before breakthrough on the commercial markets can happen.
In large SOFC systems the air subsystem is the largest source of parasitic losses and major factor in decreasing the electrical efficiency of the system. Almost all components are based on existing products developed for some other purposes and are not optimized for SOFC systems. By making the air side components for the SOFC systems, big improvements in terms of costs, reliability, performance and lifetime will be achieved. The CATION project has focused on the development of SOFC system’s air side fluid and thermal management and mechanical solutions, and the individual components included. A parallel optimization of the anode subsystem has been carried out in the EU funded project ASSENT.
The main objective of the CATION has been to find optimal process and mechanical solutions for the cathode and stacks subsystems with the aim of having commercially feasible and technologically optimised subsystem solutions ready for future ~ 250 kWe atmospheric SOFC systems. The aspects taken into account in the development have been mainly electrical efficiency, controllability, reliability, mass production and cost effectiveness of developed subsystems and the individual components.
After the exit of Wärtsilä from the CATION project, AVL took over the cathode sub-system validation task. The cathode sub-system was designed and tested based on the existing AVL SOFC CHP platform. This required an adaption of the platform towards the process requirements considering the operation of the TOFC stack module consisting of two TOFC DG modules with each 6 kWe rated power. However, the cathode sub-system required the integration of the cathode recirculation which is carried out with a specifically designed ejector system. After building the SOFC platform and integrating the TOFC stack module a sub-system validation test was performed. During the project developed air sub-system concept including all necessary components were successfully validated.
Based on the design to cost (DtC) analyses carried out in the projects, a good understanding on the economies of scale was achieved. It can be concluded that with additional stack related development steps a commercially feasible system having an investment cost (excl. stacks) of less than 2000 €/kW can be achieved. SOFC systems present a lower total lifecycle cost than microturbines both for industrial and household applications, thus guaranteeing both environmental and economic sustainability of the SOFC technology.
The ultimate objective to have 250 kWe atmospheric SOFC system in future will be reached within the time because Convion Oy (former Wärtsilä) will be launched 50 kWe 2014 and their product portfolio contains systems up to 300 kWe. The knowledge and results obtained from the CATION project have been extensively utilized in the development of Convion’s systems, providing among others improved cost, performance and technical maturity of the system. Also all deliverables were delivered and all milestones and objectives were reached during the project. Conclusion is that CATION project was finalised successfully.
Project Context and Objectives:
2. Project content and main objectives
The main objective of the CATION has been to find optimal process and mechanical solutions for the cathode and stacks subsystems with the aim of having commercially feasible and technologically optimised subsystem solutions ready for future ~ 250 kWe atmospheric SOFC systems. The aspects taken into account in the development have been mainly electrical efficiency, controllability, reliability, mass production and cost effectiveness of developed subsystems and the individual components. However, Wärtsilä terminated its fuel cell activities and partnership in the project after mid-term review (M18). The remaining work was divided between VTT, TOFC and AVL, AVL taking considerably more responsibility than in the original plans. This change added project time for half a year in order for AVL to successfully implement all components to fit their system.
In order to reach the main objectives, some sub-objectives were set and reached:
• To provide modelling input for optimal cathode subsystem layout and choosing the best ones for further analysis including sensitivity and reliability analysis for the most promising subsystem
• To develop components which are optimal for the cathode subsystem and to evaluate their feasibility and manufacturing technologies
• To develop a compact and cost-effective stack module where the stack/system interface and related solutions are optimized
• To validate overall cathode subsystem solution in real fuel cell system
The actual work of the CATION focuses on evaluating different process alternatives and optimal process and mechanical solutions for the cathode-side subsystem and the stack/system interface. The evaluated alternatives include among others traditional parallel single-pass air feed to the stacks, air-in-series connection of the stacks and air recirculation. Possibilities of combining different functions into single components, such as integrated heat exchanger-afterburner, are also taken into account. Relevant process options were first evaluated by conceptual system simulation, and these results were used as a basis for detailed feasibility evaluation. The other part of the work was to develop an optimized stack-system interface. The current stack technology is more or less optimized to be a well-performing single-stack system.
Based on the obtained results, the most suitable concept was selected for prototyping and validation. This part includes component/subsystem prototype manufacturing and testing of the chosen solution. For large systems, full-scale test benches were impractical to accomplish without building a full system. Therefore, the prototype manufacturing and testing is being done with downscaled components.
The main part of the CATION experiments and simulations focus on (1) novel designs and optimization of non-stack components, (2) the manufacturing process and control techniques for mature components, (3) component durability/robustness in the application environment, (4) costs assessment vs. target costs, (5) demonstration of End of Life specifications, (6) concept for recycling and disposal of systems, including the associated costs and (7) Life Cycle Analysis (LCA) according to developed guidelines.
Design to cost analysis (DtC) has been conducted within both projects to support the understanding of overall commercial feasibility of different process approaches. The conducted analyses had two different aims: to understand the economies of scale when increasing the power output of the system, and to pin-point the relative importance of the anode side subsystem for the overall system cost. The DtC analysis was started with evaluating the detailed system costs based on known BoP component and solution cost behaviors as a function of scale, and the development conducted for anode side components during ASSENT was taken into account.
After the exit of Wärtsilä from the CATION project, AVL took over the cathode sub-system validation task. The cathode sub-system was designed and tested based on the existing 10 kWel AVL SOFC CHP platform which was developed in recent projects. This required an adaption of the platform towards the process requirements considering the operation of the TOFC stack module consisting of two TOFC DG modules with each 6 kWel rated power. The anode sub-system could be kept similar to the existing design. However, the cathode sub-system required the integration of the cathode recirculation which is carried out with a specifically designed ejector system. The ejector was designed first by preliminary simulations based on the process parameters of the cathode sub-system. From this simulation results the main geometry of the ejector was determined. Furthermore, a polynomial function of the ejector performance was derived to be used in the process simulation in order to consider the ejector behaviour for process variation simulations. After freezing the process parameters the ejector performance was validated by CFD simulations compared with the preliminary simulations. Based on the cathode recirculation concept the packaging of the platform was adapted to integrate the ejector. Also the interface between the BoP and the TOFC stack module had to be adapted. After building the SOFC platform and integrating the TOFC stack module a sub-system validation test was performed and compared with the original process simulation.
Environmental performance (LCA) comparison was built between a SOFC system with ejector-based cathode recirculation and a gas microturbine. It was demonstrated that the studied SOFC system is able to yield environmental benefits on the environmental load from a life cycle point of view for all the impact categories considered with respect to the conventional technology. This finding from the environmental point-of-view was confirmed in terms of economic performance by the Life Cycle Cost comparison. At commercial level, it can be concluded that SOFC systems present a lower total LCC with respect to microturbines both for industrial and household applications, thus guaranteeing both environmental and economic sustainability.
Based on the design to cost (DtC) analyses carried out in the projects, a good understanding on the economies of scale was achieved, and also a cost split between different (sub)functions in an SOFC system was generated. As a result, it can be concluded that with certain additional stack related development steps a commercially feasible system having an investment cost (excl. stacks) of less than 2000 €/kW can be achieved. At commercial level, it can be also concluded that SOFC systems present a lower total lifecycle cost than microturbines both for industrial and household applications, thus guaranteeing both environmental and economic sustainability of the SOFC technology.
Project Results:
3. S&T results/foreground
3.1 System layout design
In Conceptual Evaluation of Subsystems Alternatives reported the results of modelling seven different conceptual layouts and also resulted in reaching Milestone 1. Modelling work was done on both system and component level and computational fluid dynamic (CFD) modelling of the ejector was done to support the systems modelling. The results show that using a modular stacks instead of a single stack or utilizing and ejector and air recirculation can both improve system performance. Three burner positions were simulated and the optimal one for current stacks determined. The characteristic advantages and disadvantages of each layout concept were studied to determine how to proceed and a rudimentary sensitivity analysis was done to all layouts. As a result, modular stack case and the ejector cases were seen as the best ones and chosen for further studies.
Sensitivity and Reliability Analysis focused on sensitivity analysis of the ejector cases and reliability analysis of all layouts. The simulation results gained with a more accurate ejector model show that even though the ejector is quite sensitive to changes to many key parameters, it is possible to design it appropriately so that the end result of using an ejector is beneficial. Thus the ejector seems like a promising concept for further development. In the reliability analysis, all of the different layout concepts of were compared to each other by listing and ranking different risks according to their severity, safety risks being ranked highest. The results show that using the ejector involves some additional risks compared to the base case but on the balance the layout concept seems viable. The air in series –stack layout involves greatly increased risks that could be alleviated with careful system design. The results showed that modular stack case had higher risks involved than any of the other cases, yet using careful system design it could well be viable. The ejector cases performed well in both the risk analysis and the more accurate system simulations. As such, the results of the conceptual study of the layout alternatives – were that both the modular stack case as well as the ejector air recirculation seemed viable.
Summary: System layout design work has been completed according to Annex1 requirements in an excellent manner during first period. Communication between partners and work packages worked well and the results were used directly in other development works. All in all, this work can be considered a success and valuable information for the other development was gained.
3.2 Component testing and cost analysis
Design and Testing of ejector for AVL SOFC CHP system: The ejector was designed based on the input parameters used as boundary conditions derived from the process simulation in subsystem validation part of the work. The design was optimized to keep the pressure drop between force inlet and discharge outlet at a minimum since this pressure drop needs to be compensated by additional blower power compared to a system without cathode recirculation. Furthermore, it had to be checked that the required blower pressure is within the limits of the blower specifications. In a parameter study the optimal ejector geometry and dimensions have been investigated.
In a second step the design was further validated by CFD simulations in AVL FIRE (AVL CFD software product). Both results are very close to each other which demonstrate that the preliminary simulation is a good tool to find a proper design of the ejector.
Since the position of the ejector nozzle was already identified to have a significant impact on the ejector performance the horizontal position of the nozzle was investigated. It was estimated that the nozzle position could be shifted due to manufacturing tolerances and thermal expansion during operation by +/- 1mm compared to the base design. Therefore, two more CFD calculations were performed for following configurations:
• nozzle position shifted 1mm to the left (“plus”) compared to the base configuration
• nozzle position shifted 1mm to the right (“minus”) compared to the base configuration
While the overall pressure drop between force inlet and discharge outlet stays almost similar for the “minus” configuration it reduces by 1 mbar for the “plus” configuration. However, the entrainment ratios decrease down from 97 % (base configuration) to 94 % (“minus” configuration) and 93 % (“plus” configuration) respectively. This impact is seen to be acceptable since it is within the measuring tolerance of the pressure drop during operation.
Eventually, the ejector was tested first in the system under hot conditions without the stack module. Instead of the stack module short cut tubes were used to bridge the cathode and anode inlets and outlets on the BoP side. The anode short cut tubes were insulated to minimize heat losses. The cathode short cut tubes were cooled to enable ejector testing. Since no gas flow meter can be installed between ejector discharge outlet and suction inlet to measure the recirculation ratio it was decided to indirectly measure the ratio by a thermal heat balance over the ejector. Therefore, the temperatures at all three ports were measured. Together with the force inlet mass flow an energy and mass flow balance can be established which allows calculating the suction and discharge mass flows.
Based on these results it was decided to proceed with the whole sub-system validation testing with the suggested ejector design.
Testing of Bosal prototype air heat exchanger: During the design phase of the SOFC CHP platform for this project, it was investigated whether the existing heat exchangers should be replaced by a heat exchanger from the project partner Bosal. Based on the requirements in terms of the thermal performance derived from the process simulation Bosal made a preliminary design study for the heat. The main dimensions exceeded the dimensions of the existing heat exchanger which would have made a fast integration within the project timeframe into the existing AVL SOFC CHP platform without major effort to redesign the packaging very difficult. Therefore, it was decided to stay with the existing heat exchanger supplier.
However, it was decided that AVL tests a prototype heat exchanger from Bosal in order to validate the performance. The prototype heat exchanger is smaller in size compared to what would have been required for the 12 kWe SOFC CHP platform. Or in other words, the pressure drops are high for the required amount of heat to be transferred. Nevertheless, this enabled a useful assessment of the performance for integration activities in future design generations. The heat exchanger came already fully insulated. The insulation is attached inside the outer metal cover.
The prototype heat exchanger was tested on an AVL component test rig. The hot and cold gas flow was simulated close to real operating conditions. At the cold side air was used as in the real system. To simulate the real exhaust gas on the hot side a mixture of air (91.9 vol.%) and steam (8.1 vol.%) was used. The real exhaust gas would also contain CO2 which was not available for this test. However, the specific heat of the simulated mixture (=1.17 kJ/kg*K at 500 °C) is roughly the same as in the real system (1.21 kJ/kg*K at 500 °C). The ratio between the cold and the hot gas flow was kept constant at 0.992 as in the real system for the whole experiment. Since the heat exchanger is smaller in size the mass flows were varied in range of reasonable pressure drops.
The results of the test are very promising. It is expected that the temperature for the cold gas outlet will meet the system requirements (> 700 °C) especially for higher hot gas inlet temperatures (850 – 900 °C). Regarding the pressure drops the test has shown that the heat exchanger has to be bigger for the real system to meet the target of a total pressure drop (cold + hot side) of about 20 mbar.
Integrated mixer: The integrated mixer offers considerable cost and volume benefits: It is assembled on one of Bosal’s plate HEX assembly lines. The injection holes are drilled in the HEX plates by the laser that welds the HEX core. The catalytic coating is also an existing feature, and requires no additional development or tooling. The partly integrated cases required an additional manufacturing line: in case a, the design uses 7 different materials, including 4 ceramics: a ceramic monolith, a mounting mat to fix the monolith, and a ceramic tube, limiting the thermal expansion of part of the connection channel. Case b is more compact, but susceptible to uncontrolled partly oxidation. Its CO emissions increase over time, reflecting poisoning or ageing of the catalytic coating.
Cost analysis for whole system: The conducted analyses have had three different aims: to understand the economies of scale when increasing the power output of the system, to evaluate the relative differences between different cathode subsystem approaches, and to pin point the effects of different stack parameters for the final system cost. Additionally, a natural goal was to get an understanding whether a competitive final system cost is possible to be reached with the analysed solutions or not.
The Design to Cost (DtC) analysis was started with evaluating the detailed system costs based on known BoP component and solution cost behaviours, and was done iteratively with conceptual IPM design for different power ranges. By this was a good understanding on the economies of scale was achieved, and also a cost split between different (sub)functions in an SOFC system was generated. As a result, it can be concluded that a pre-commercial cost level (~4300 €/kW excluding stacks) can be achieved with a 16 stack frame system (~115 kW), with the stack consisting of 100 cell each. The commercial cost level (~2000 €/kW excluding the stacks) is almost achievable with 32 stack frame system (~230 kW), but further development is still needed. The main emphasis on the further development needs to be on stack parameters, as the main cost driver from system point of view is the balance of stack system.
Also some more radical changes were analysed, namely the removal of external compression system. By having an internal compression of the stacks/stack frames, the IPM layout design can be made significantly more compact and the direct and indirect cost effects of the compression elements and corresponding feed-through can be eliminated. Based on conceptual design and DtC analysis, a 48 stack frame IPM can be made in a mechanically feasible manner, leading into a further cost reduction of approx. 150 €/kW. Based on the above results, it can be stated that with the stack and cathode subsystem solutions developed within the CATION project and some further stack development, a commercial SOFC system is certainly achievable.
Summary: Component testing and costs analysis work was completed successfully, to say the least. An ejector prototype for highly efficient recirculation of the cathode air in a solid oxide fuel cell system was designed, modelled, built, tested and found suitable for use in a real environment. Furthermore, an air side heat exchanger, designed particularly for SOFC systems with air recirculation was built and tested. With small modifications, the heat exchanger concept was found suitable for its purpose. Together these results are directly applicable to SOFC system development. Furthermore, the gathered test data and the modelling information provide important and highly useful input to the design of SOFC systems and further development of system components.
3.3 Balance of stack development
Stack module: Five full size OAM stack modules were tested to verify if they were feasible within the CATION project. The test included fuel utilization, air utilization, and load variations as well as load and thermal cycles. Both modules passed the test and it was decided to continue with the present stack design. Additionally one of the modules was tested for more than 1100 h, including more than 400 hours at nominal operation, 6 thermal cycles, 5 load cycles (25-0 A on with NG as fuel and unchanged flows), three rounds of fuel (up to 65%) and air (18-24%) utilization variations, and operation at 32.5 A. At nominal operation the BoL (Beginning of Life) power is 6 kW for one OAM stack module.
It was decided that the design of the OAM stack module was to be used for further work in the CATION project. This decision was based on the OAM stack modules passing a D1 test, as described below. Passing this test required that the non-stack parts of the modules did not show any weaknesses during the tests and that they caused no damage to the stacks. The latter was shown by that the stacks showed no weaknesses that they would not have shown during the same test sequence performed in standard stack test equipment. Long term performance was not included in the decision criteria.
The D1 test included:
• Nominal operation (Pre-reformed NG as fuel, 60% fuel utilization, 21% air utilization, 25 A current, 6 kW power, all temperatures was 650-750 oC).
• Instant load cycles (only load varied).
• Thermal cycles (to room temperature and back to operation).
• Fuel utilization increase (65%).
• Air utilization variations (18%, 21%, and 24%).
• 32.5 A load point at otherwise nominal operation.
Component test: Tests have been carried out to verify the performance of the module components. The accuracy and sustainability has been verified for the compression system. The feed through module was proven to be leak tight both before and after module test. The bypass leakage was measured to be below 1% of the air supply on all tested modules; the external leakage was in all cases below 0.1% and did not increase from before to after fuel cell operation tests. Development and testing of the stacks was carried out in another TOFC project.
One problem which at the beginning of the CATION project was very crucial to find a better solution for was the electrical insulation between the stacks and the fuel manifold. The previously used gasket was only resistive enough for having two stacks electrically in series. A sub-project identified several possible options and tested their electrical resistance both instantaneously and over time. The result was that a suitable material was identified as such allows for the four stacks in one module to be operated in a serial configuration. This is of importance for the system cost, as it decreases the required number of load supplies and a higher output voltage is possible to obtain.
Hotbox: Main result of this work was the design and manufacturing/modification of existing IPM to be able to accommodate 4 OAM stack frames and to use this test set up to hot box validation tests. The hotbox validation test was successfully performed using the hotbox design created in the CATION –project. Successful operation of the system for 2000+ hours validates the hotbox design as viable in a SOFC system environment.
Other achievements: AVL have in collaboration with Wärtsilä and TOFC completed risk analysis, DFMEA, on the stack modules, on which they also performed damage modelling. Additionally AVL prepared their 10 kW test station for a degradation test of one stack module. FEM analysis has been applied to the stack module design and materials to ensure that no unwanted deformations occur and CFD analysis has been applied to both the cathode and anode flow to ensure proper flow distribution
Summary: All work in stack of balance work has been finalised very successfully and a 6kW SOFC module has been developed. Design is ready for pre commercial market and seemed so good that TOFC is taking it to production. It has been tested in a “real” system for more than 2000h and more than 20 modules are tested in test stations making it a solid result.
3.4 Subsystem validation
Subsystem validation: The design study has shown that the required size of the ejector allows for reasonable integration into the system. Furthermore, the required pressure at the ejector inlet can be provided by the existing blowers of the system and does not require a re-sourcing. Furthermore, the integration of the new TOFC stack module could be achieved with little modifications. These facts widen the flexibility of AVLs SOFC CHP platform significantly and can be seen as a major output of this project.
The system was operated at 6 – 8 kWel for a significant amount of time. The cathode recirculation was indirectly measured by two different methods. Both methods suggest a recirculation rate of about 40 %. The results of the project allowed for the following insights:
• Static ejector is suitable for cathode recirculation in terms of performance and the possibility to integrate it in a reasonable way into a very compact system packaging
• Pressure drop of the stack cathode side influences the recirculation rate significantly. Pressure drop of TOFC stack module is small enough to enable a high recirculation rate
• Cathode recirculation generates less harsh temperature gradients at the cathode inlet which was shown by very moderate temperature differences between cathode inlet and the stack itself
• Cathode recirculation rate varies only slightly in a wide operating range and therefore allows a good characteristic for system operation
• Pressure level needed for the ejector can be handled by the blowers of the AVL SOFC CHP platform which enables an easy adaption of the BoP in case of cathode recirculation
• Air heat exchanger can be built ~30 % smaller compared to a system without cathode recirculation
• Cathode recirculation allows for high electrical DC efficiencies up to 66 %.
Within this project AVL could significantly push the system development further towards a commercial system technology. AVL has already developed successfully a stationary SOFC CHP platform in the 10 kWel range based on natural gas steam reforming and anode gas recirculation. In this project the next step by improving the cathode path enabled an important knowledge gain on a theoretical and practical level. The ejector concept is seen to play a significant role when it comes to substantial cost reduction. For AVL as an engineering consultant this knowledge gain is of major importance and widens the technology portfolio of AVL’s stationary SOFC CHP platform. In this way future customers can be attracted and served much better. The hardware demonstration of the system is an important tool to convince industrial customers when it comes to a series product development stage.
Life Cycle Analysis: A comparative Life Cycle Assessment (LCA) and Life Cycle Cost analysis (LCC) have been performed to evaluate the environmental and economic performance of a Solid Oxide Fuel Cells designed with cathode sub-systems developed in the project. An environmental performance comparison was built between a SOFC system with ejector-based cathode recirculation and a gas microturbine. It was demonstrated that the studied SOFC system is able to yield environmental benefits on the environmental load from a life cycle point of view for all the impact categories considered with respect to the conventional technology. At commercial level, it can be concluded that SOFC systems present a lower total LCC with respect to microturbines both for industrial and household applications, thus guaranteeing both environmental and economic sustainability.
Summary: Experimental system validation subsystem in real SOFC system was done successfully to prove that air sub-system concept including all necessary components were developed during the CATION project and could be implemented into future large-scale commercial SOFC power plant.
3.5 Foreground
After the exit of Wärtsilä from the CATION project, AVL took over the cathode sub-system validation task. The cathode sub-system was designed and tested based on the existing AVL SOFC CHP platform. This required an adaption of the platform towards the process requirements considering the operation of the TOFC stack module consisting of two TOFC DG modules with each 6 kWe rated power. However, the cathode sub-system required the integration of the cathode recirculation which is carried out with a specifically designed ejector system. After building the SOFC platform and integrating the TOFC stack module a sub-system validation test was performed. During the project developed air sub-system concept including all necessary components were successfully validated.
Based on the design to cost (DtC) analyses carried out in the projects, a good understanding on the economies of scale was achieved. It can be concluded that with additional stack related development steps a commercially feasible system having an investment cost (excl. stacks) of less than 2000 €/kW can be achieved. SOFC systems present a lower total lifecycle cost than microturbines both for industrial and household applications, thus guaranteeing both environmental and economic sustainability of the SOFC technology.
The ultimate objective to have 250 kWe atmospheric SOFC system in future will be reached within the time because Convion Oy (former Wärtsilä) will be launched 50 kWe 2014 and their product portfolio contains systems up to 300 kWe. The knowledge and results obtained from the CATION project have been extensively utilized in the development of Convion’s systems, providing among others improved cost, performance and technical maturity of the system. Also all deliverables was delivered and all milestones and objectives were reached during the project. Conclusion is that CATION project was finalised successfully.
Potential Impact:
4. Potential impacts
4.1. General impacts
The CATION project directly contributed to the overall objectives of Call FCH-JU-2009-1,
Area SP1-JTI-FCH.3: Stationary Power generation & CHP, Topic SP1-JTIFCH. 2009.3.4: Component improvement for stationary power applications by addressing the following fuel cell functions and the corresponding components in particular:
• Power generation unit (integrated stack/BoP)
• Heat exchangers/Thermal management
• Air and fluid flow equipment including subcomponents
• Fluid supply and management including pumps, valves and flow meters
The outcome of the project is as planned benefiting all of the project participants, and also the fuel cell community in general. While CATION project was a particularly fruitful effort in technological development, further development will be essential for SOFC technology in reaching commercial competitiveness and maturity. Successful publicly funded demonstrations will play an important role in bridging “a valley of death” of commercializing large fuel cell systems due to inherently higher single unit costs and associated financial risks compared to small systems, making steps to series manufacturing and reaching volume advantages.
4.2. The exploitation of results
4.2.1. TOFC
During the CATION project TOFC has developed a module with 4 open air manifold stacks. The cathode flow to the stacks is simplified as one big square channel with all the stacks placed directly in the air stream. This allows very easy and cheap cathode integration by a simple combined flange. Result is possibility of cheaper systems with less and simpler cathode piping and allows the modules to be operated in series (with need of air ejection). The product has been brought to a pre commercial as first version state where pilot production is possible and reliable in small volumes but still need verification testing and design & optimization for cost, assembly, production, integration etc. TOFC is take this product to pre commercial sale and will transfer it to pilot production. Depending on yield and marked demand TOFC will produce at maximum two modules per week for pre commercial sale and testing in-house and at integration partners. This pilot production itself and the produced product and testing of this will be part a new development program and give valuable input on the complete added value chain. Having a small scale production is deemed necessary to ever foresee and overcome the challenges from design and concept input over sub suppliers handling, in house production, end of line testing, system design and installation, operation and end of life handling, just to mention a few. TOFC intends to start a development program that will take the current pre-commercial distributed generation module to a product that can handle a commercial marked. This product should have the potential to be a major player in the marked. Even thou many challenges is already known and to some extend solution ideas are ready this will be a traveling in to the void and impossible to predict, but TOFC estimates that it will take 5 years before the product is ready. During this period there will properly be possibilities of upgrading the current module. The project is planned as a four stage project as follow:
• Concept generation: Based on experience from current product and production new concepts are generated to ensure a wide solution space for the later selection.
• Concept selection: Evaluation of the above mentioned concepts. Among this is the current concept but the comparison evaluation will be stronger than 2just2 updating the current
• Product development: The selected concept is taking to working prototype level and thoroughly tested
• Product implementation: The prototype is taken to production. Experience tells that this is not an easy task
The development in the CATION project has been closely aligned with the interest of TOFC and it has certainly made a difference.
4.2.2. Bosal
Bosal has drafted a business plan for all heat exchangers for industrial applications, of which SOFC plate heat exchangers are part of. A business unit (Bosal ECI) has been carved out of the R&D department of Bosal’s Lummen (Belgium) plant. This business unit is based in Vianen, The Netherlands, where a Bosal automotive supply plant is now being transformed to a heat echanger plant. All hardware procured for tooling and production line will be installed in this plant. SOFC heat exchangers developed during the CATION project are expected to take up 40% of the order volume for this plant by the end of 2015. These products are aimed for the European market for heating appliances, as mCHP systems enter this market. East Asia and the US are mainly targeted for SOFC power plants, in the 25 – 1000 kWe power range. Commercial production for field testing has started in 2014. The ramp up to serial production is projected in 2016, while 2015 already sees a substantial increase in projected sales.
4.2.3. Convion (former Wärtsilä)
Within the project a number of conceptual mechanical layouts including SOFC stacks, feed piping and key components were developed for the various flow configurations. Convion has developed a stack module assembly based on TOFC stacks having improved power density and lower manufacturing costs compared to earlier designs. This stack module can be utilized in Convion’s stack-flexible SOFC system. Convion has designed commercial SOFC systems in the power class of 50-300kW since its founding in late 2012, inheriting the IPR and key personnel from the Wärtsilä fuel cell development unit. Convion has completed the design of its first 50kW product in spring 2014 and has recently started the manufacturing of a pilot system to be commissioned in 2015. Commercialization and ramp-up of production as well as introduction of a higher power range is foreseen for 2016-2018. The knowledge and results obtained from the CATION project have been extensively utilized in the development of Convion’s systems, providing among others improved cost, performance and technical maturity of the system.
4.2.4. AVL
The primary goal of AVL as an engineering consultant company is to license the technology to industrial customers who manufacture and sell SOFC CHP products. System demonstration during CATION project with TOFC stack module and cathode recirculation extends AVLs SOFC CHP technology portfolio for following developments of new commercial products
4.2.5. UNIGE
During CATION project UNIGE research team had the opportunity of sharpening the application of the Life Cycle Assessment methodology to Solid Oxide Fuel Cell systems. This field of application has been object of several projects in the last years within the department but CATION project was the first where the dynamics of sub-systems were studied in such deep detail. Besides, UNIGE research team had the chance to test the specific methodological choices - refining ISO 14040 general rules for fuel cell systems – derived from a specific guidance issued within FCH JU initiatives. The assessment studies conducted within CATION project can be in fact considered as a validation test of the methodological guidance for performing LCA on fuel cells. Moreover, UNIGE research team developed a specific toolbox for integration of a cost indicator associated to the assessment of the environmental load of a fuel cell system along its life cycle. A specific toolbox has been developed by UNIGE for integrating LCA and LCC findings. It cannot be considered as a commercial product, but it can be considered as a research tool that can be from now used by the research team in its future analysis.
4.2.6. VTT
VTT Technical Research Centre of Finland as a research institute will utilise increased expertise and knowhow in the area of SOFC system development for contract research with European enterprises and getting more FCH JU join project with European partners.
4.3. Dissemination activities
Even if the project was very much industrial oriented there were quite a lot scientific activities including two scientific papers, one master thesis, eight oral presentations in international conferences, one commercial flyer and two exhibitions in Hannover messe.
List of Websites:
Public website address: http://cation.vtt.fi/
Contact information:
Dr. Jari Kiviaho
Coordinator
VTT Technical Research Centre of Finland
jari.kiviaho@vtt.fi
+358 50 5116778
1. Executive summary
Fuel cells and hydrogen have a potential for reducing emissions of greenhouse gases and air pollutants, facilitating the increased use of renewable energy sources, raising overall efficiencies of conversion. In addition the high temperature fuel cell technology SOFC has the potential for high electrical efficiency, 55-60%, and total efficiency up to 90% for CHP units combined with low emissions. However, the cost and lifetime of SOFC systems is a problem that must be solved before breakthrough on the commercial markets can happen.
In large SOFC systems the air subsystem is the largest source of parasitic losses and major factor in decreasing the electrical efficiency of the system. Almost all components are based on existing products developed for some other purposes and are not optimized for SOFC systems. By making the air side components for the SOFC systems, big improvements in terms of costs, reliability, performance and lifetime will be achieved. The CATION project has focused on the development of SOFC system’s air side fluid and thermal management and mechanical solutions, and the individual components included. A parallel optimization of the anode subsystem has been carried out in the EU funded project ASSENT.
The main objective of the CATION has been to find optimal process and mechanical solutions for the cathode and stacks subsystems with the aim of having commercially feasible and technologically optimised subsystem solutions ready for future ~ 250 kWe atmospheric SOFC systems. The aspects taken into account in the development have been mainly electrical efficiency, controllability, reliability, mass production and cost effectiveness of developed subsystems and the individual components.
After the exit of Wärtsilä from the CATION project, AVL took over the cathode sub-system validation task. The cathode sub-system was designed and tested based on the existing AVL SOFC CHP platform. This required an adaption of the platform towards the process requirements considering the operation of the TOFC stack module consisting of two TOFC DG modules with each 6 kWe rated power. However, the cathode sub-system required the integration of the cathode recirculation which is carried out with a specifically designed ejector system. After building the SOFC platform and integrating the TOFC stack module a sub-system validation test was performed. During the project developed air sub-system concept including all necessary components were successfully validated.
Based on the design to cost (DtC) analyses carried out in the projects, a good understanding on the economies of scale was achieved. It can be concluded that with additional stack related development steps a commercially feasible system having an investment cost (excl. stacks) of less than 2000 €/kW can be achieved. SOFC systems present a lower total lifecycle cost than microturbines both for industrial and household applications, thus guaranteeing both environmental and economic sustainability of the SOFC technology.
The ultimate objective to have 250 kWe atmospheric SOFC system in future will be reached within the time because Convion Oy (former Wärtsilä) will be launched 50 kWe 2014 and their product portfolio contains systems up to 300 kWe. The knowledge and results obtained from the CATION project have been extensively utilized in the development of Convion’s systems, providing among others improved cost, performance and technical maturity of the system. Also all deliverables were delivered and all milestones and objectives were reached during the project. Conclusion is that CATION project was finalised successfully.
Project Context and Objectives:
2. Project content and main objectives
The main objective of the CATION has been to find optimal process and mechanical solutions for the cathode and stacks subsystems with the aim of having commercially feasible and technologically optimised subsystem solutions ready for future ~ 250 kWe atmospheric SOFC systems. The aspects taken into account in the development have been mainly electrical efficiency, controllability, reliability, mass production and cost effectiveness of developed subsystems and the individual components. However, Wärtsilä terminated its fuel cell activities and partnership in the project after mid-term review (M18). The remaining work was divided between VTT, TOFC and AVL, AVL taking considerably more responsibility than in the original plans. This change added project time for half a year in order for AVL to successfully implement all components to fit their system.
In order to reach the main objectives, some sub-objectives were set and reached:
• To provide modelling input for optimal cathode subsystem layout and choosing the best ones for further analysis including sensitivity and reliability analysis for the most promising subsystem
• To develop components which are optimal for the cathode subsystem and to evaluate their feasibility and manufacturing technologies
• To develop a compact and cost-effective stack module where the stack/system interface and related solutions are optimized
• To validate overall cathode subsystem solution in real fuel cell system
The actual work of the CATION focuses on evaluating different process alternatives and optimal process and mechanical solutions for the cathode-side subsystem and the stack/system interface. The evaluated alternatives include among others traditional parallel single-pass air feed to the stacks, air-in-series connection of the stacks and air recirculation. Possibilities of combining different functions into single components, such as integrated heat exchanger-afterburner, are also taken into account. Relevant process options were first evaluated by conceptual system simulation, and these results were used as a basis for detailed feasibility evaluation. The other part of the work was to develop an optimized stack-system interface. The current stack technology is more or less optimized to be a well-performing single-stack system.
Based on the obtained results, the most suitable concept was selected for prototyping and validation. This part includes component/subsystem prototype manufacturing and testing of the chosen solution. For large systems, full-scale test benches were impractical to accomplish without building a full system. Therefore, the prototype manufacturing and testing is being done with downscaled components.
The main part of the CATION experiments and simulations focus on (1) novel designs and optimization of non-stack components, (2) the manufacturing process and control techniques for mature components, (3) component durability/robustness in the application environment, (4) costs assessment vs. target costs, (5) demonstration of End of Life specifications, (6) concept for recycling and disposal of systems, including the associated costs and (7) Life Cycle Analysis (LCA) according to developed guidelines.
Design to cost analysis (DtC) has been conducted within both projects to support the understanding of overall commercial feasibility of different process approaches. The conducted analyses had two different aims: to understand the economies of scale when increasing the power output of the system, and to pin-point the relative importance of the anode side subsystem for the overall system cost. The DtC analysis was started with evaluating the detailed system costs based on known BoP component and solution cost behaviors as a function of scale, and the development conducted for anode side components during ASSENT was taken into account.
After the exit of Wärtsilä from the CATION project, AVL took over the cathode sub-system validation task. The cathode sub-system was designed and tested based on the existing 10 kWel AVL SOFC CHP platform which was developed in recent projects. This required an adaption of the platform towards the process requirements considering the operation of the TOFC stack module consisting of two TOFC DG modules with each 6 kWel rated power. The anode sub-system could be kept similar to the existing design. However, the cathode sub-system required the integration of the cathode recirculation which is carried out with a specifically designed ejector system. The ejector was designed first by preliminary simulations based on the process parameters of the cathode sub-system. From this simulation results the main geometry of the ejector was determined. Furthermore, a polynomial function of the ejector performance was derived to be used in the process simulation in order to consider the ejector behaviour for process variation simulations. After freezing the process parameters the ejector performance was validated by CFD simulations compared with the preliminary simulations. Based on the cathode recirculation concept the packaging of the platform was adapted to integrate the ejector. Also the interface between the BoP and the TOFC stack module had to be adapted. After building the SOFC platform and integrating the TOFC stack module a sub-system validation test was performed and compared with the original process simulation.
Environmental performance (LCA) comparison was built between a SOFC system with ejector-based cathode recirculation and a gas microturbine. It was demonstrated that the studied SOFC system is able to yield environmental benefits on the environmental load from a life cycle point of view for all the impact categories considered with respect to the conventional technology. This finding from the environmental point-of-view was confirmed in terms of economic performance by the Life Cycle Cost comparison. At commercial level, it can be concluded that SOFC systems present a lower total LCC with respect to microturbines both for industrial and household applications, thus guaranteeing both environmental and economic sustainability.
Based on the design to cost (DtC) analyses carried out in the projects, a good understanding on the economies of scale was achieved, and also a cost split between different (sub)functions in an SOFC system was generated. As a result, it can be concluded that with certain additional stack related development steps a commercially feasible system having an investment cost (excl. stacks) of less than 2000 €/kW can be achieved. At commercial level, it can be also concluded that SOFC systems present a lower total lifecycle cost than microturbines both for industrial and household applications, thus guaranteeing both environmental and economic sustainability of the SOFC technology.
Project Results:
3. S&T results/foreground
3.1 System layout design
In Conceptual Evaluation of Subsystems Alternatives reported the results of modelling seven different conceptual layouts and also resulted in reaching Milestone 1. Modelling work was done on both system and component level and computational fluid dynamic (CFD) modelling of the ejector was done to support the systems modelling. The results show that using a modular stacks instead of a single stack or utilizing and ejector and air recirculation can both improve system performance. Three burner positions were simulated and the optimal one for current stacks determined. The characteristic advantages and disadvantages of each layout concept were studied to determine how to proceed and a rudimentary sensitivity analysis was done to all layouts. As a result, modular stack case and the ejector cases were seen as the best ones and chosen for further studies.
Sensitivity and Reliability Analysis focused on sensitivity analysis of the ejector cases and reliability analysis of all layouts. The simulation results gained with a more accurate ejector model show that even though the ejector is quite sensitive to changes to many key parameters, it is possible to design it appropriately so that the end result of using an ejector is beneficial. Thus the ejector seems like a promising concept for further development. In the reliability analysis, all of the different layout concepts of were compared to each other by listing and ranking different risks according to their severity, safety risks being ranked highest. The results show that using the ejector involves some additional risks compared to the base case but on the balance the layout concept seems viable. The air in series –stack layout involves greatly increased risks that could be alleviated with careful system design. The results showed that modular stack case had higher risks involved than any of the other cases, yet using careful system design it could well be viable. The ejector cases performed well in both the risk analysis and the more accurate system simulations. As such, the results of the conceptual study of the layout alternatives – were that both the modular stack case as well as the ejector air recirculation seemed viable.
Summary: System layout design work has been completed according to Annex1 requirements in an excellent manner during first period. Communication between partners and work packages worked well and the results were used directly in other development works. All in all, this work can be considered a success and valuable information for the other development was gained.
3.2 Component testing and cost analysis
Design and Testing of ejector for AVL SOFC CHP system: The ejector was designed based on the input parameters used as boundary conditions derived from the process simulation in subsystem validation part of the work. The design was optimized to keep the pressure drop between force inlet and discharge outlet at a minimum since this pressure drop needs to be compensated by additional blower power compared to a system without cathode recirculation. Furthermore, it had to be checked that the required blower pressure is within the limits of the blower specifications. In a parameter study the optimal ejector geometry and dimensions have been investigated.
In a second step the design was further validated by CFD simulations in AVL FIRE (AVL CFD software product). Both results are very close to each other which demonstrate that the preliminary simulation is a good tool to find a proper design of the ejector.
Since the position of the ejector nozzle was already identified to have a significant impact on the ejector performance the horizontal position of the nozzle was investigated. It was estimated that the nozzle position could be shifted due to manufacturing tolerances and thermal expansion during operation by +/- 1mm compared to the base design. Therefore, two more CFD calculations were performed for following configurations:
• nozzle position shifted 1mm to the left (“plus”) compared to the base configuration
• nozzle position shifted 1mm to the right (“minus”) compared to the base configuration
While the overall pressure drop between force inlet and discharge outlet stays almost similar for the “minus” configuration it reduces by 1 mbar for the “plus” configuration. However, the entrainment ratios decrease down from 97 % (base configuration) to 94 % (“minus” configuration) and 93 % (“plus” configuration) respectively. This impact is seen to be acceptable since it is within the measuring tolerance of the pressure drop during operation.
Eventually, the ejector was tested first in the system under hot conditions without the stack module. Instead of the stack module short cut tubes were used to bridge the cathode and anode inlets and outlets on the BoP side. The anode short cut tubes were insulated to minimize heat losses. The cathode short cut tubes were cooled to enable ejector testing. Since no gas flow meter can be installed between ejector discharge outlet and suction inlet to measure the recirculation ratio it was decided to indirectly measure the ratio by a thermal heat balance over the ejector. Therefore, the temperatures at all three ports were measured. Together with the force inlet mass flow an energy and mass flow balance can be established which allows calculating the suction and discharge mass flows.
Based on these results it was decided to proceed with the whole sub-system validation testing with the suggested ejector design.
Testing of Bosal prototype air heat exchanger: During the design phase of the SOFC CHP platform for this project, it was investigated whether the existing heat exchangers should be replaced by a heat exchanger from the project partner Bosal. Based on the requirements in terms of the thermal performance derived from the process simulation Bosal made a preliminary design study for the heat. The main dimensions exceeded the dimensions of the existing heat exchanger which would have made a fast integration within the project timeframe into the existing AVL SOFC CHP platform without major effort to redesign the packaging very difficult. Therefore, it was decided to stay with the existing heat exchanger supplier.
However, it was decided that AVL tests a prototype heat exchanger from Bosal in order to validate the performance. The prototype heat exchanger is smaller in size compared to what would have been required for the 12 kWe SOFC CHP platform. Or in other words, the pressure drops are high for the required amount of heat to be transferred. Nevertheless, this enabled a useful assessment of the performance for integration activities in future design generations. The heat exchanger came already fully insulated. The insulation is attached inside the outer metal cover.
The prototype heat exchanger was tested on an AVL component test rig. The hot and cold gas flow was simulated close to real operating conditions. At the cold side air was used as in the real system. To simulate the real exhaust gas on the hot side a mixture of air (91.9 vol.%) and steam (8.1 vol.%) was used. The real exhaust gas would also contain CO2 which was not available for this test. However, the specific heat of the simulated mixture (=1.17 kJ/kg*K at 500 °C) is roughly the same as in the real system (1.21 kJ/kg*K at 500 °C). The ratio between the cold and the hot gas flow was kept constant at 0.992 as in the real system for the whole experiment. Since the heat exchanger is smaller in size the mass flows were varied in range of reasonable pressure drops.
The results of the test are very promising. It is expected that the temperature for the cold gas outlet will meet the system requirements (> 700 °C) especially for higher hot gas inlet temperatures (850 – 900 °C). Regarding the pressure drops the test has shown that the heat exchanger has to be bigger for the real system to meet the target of a total pressure drop (cold + hot side) of about 20 mbar.
Integrated mixer: The integrated mixer offers considerable cost and volume benefits: It is assembled on one of Bosal’s plate HEX assembly lines. The injection holes are drilled in the HEX plates by the laser that welds the HEX core. The catalytic coating is also an existing feature, and requires no additional development or tooling. The partly integrated cases required an additional manufacturing line: in case a, the design uses 7 different materials, including 4 ceramics: a ceramic monolith, a mounting mat to fix the monolith, and a ceramic tube, limiting the thermal expansion of part of the connection channel. Case b is more compact, but susceptible to uncontrolled partly oxidation. Its CO emissions increase over time, reflecting poisoning or ageing of the catalytic coating.
Cost analysis for whole system: The conducted analyses have had three different aims: to understand the economies of scale when increasing the power output of the system, to evaluate the relative differences between different cathode subsystem approaches, and to pin point the effects of different stack parameters for the final system cost. Additionally, a natural goal was to get an understanding whether a competitive final system cost is possible to be reached with the analysed solutions or not.
The Design to Cost (DtC) analysis was started with evaluating the detailed system costs based on known BoP component and solution cost behaviours, and was done iteratively with conceptual IPM design for different power ranges. By this was a good understanding on the economies of scale was achieved, and also a cost split between different (sub)functions in an SOFC system was generated. As a result, it can be concluded that a pre-commercial cost level (~4300 €/kW excluding stacks) can be achieved with a 16 stack frame system (~115 kW), with the stack consisting of 100 cell each. The commercial cost level (~2000 €/kW excluding the stacks) is almost achievable with 32 stack frame system (~230 kW), but further development is still needed. The main emphasis on the further development needs to be on stack parameters, as the main cost driver from system point of view is the balance of stack system.
Also some more radical changes were analysed, namely the removal of external compression system. By having an internal compression of the stacks/stack frames, the IPM layout design can be made significantly more compact and the direct and indirect cost effects of the compression elements and corresponding feed-through can be eliminated. Based on conceptual design and DtC analysis, a 48 stack frame IPM can be made in a mechanically feasible manner, leading into a further cost reduction of approx. 150 €/kW. Based on the above results, it can be stated that with the stack and cathode subsystem solutions developed within the CATION project and some further stack development, a commercial SOFC system is certainly achievable.
Summary: Component testing and costs analysis work was completed successfully, to say the least. An ejector prototype for highly efficient recirculation of the cathode air in a solid oxide fuel cell system was designed, modelled, built, tested and found suitable for use in a real environment. Furthermore, an air side heat exchanger, designed particularly for SOFC systems with air recirculation was built and tested. With small modifications, the heat exchanger concept was found suitable for its purpose. Together these results are directly applicable to SOFC system development. Furthermore, the gathered test data and the modelling information provide important and highly useful input to the design of SOFC systems and further development of system components.
3.3 Balance of stack development
Stack module: Five full size OAM stack modules were tested to verify if they were feasible within the CATION project. The test included fuel utilization, air utilization, and load variations as well as load and thermal cycles. Both modules passed the test and it was decided to continue with the present stack design. Additionally one of the modules was tested for more than 1100 h, including more than 400 hours at nominal operation, 6 thermal cycles, 5 load cycles (25-0 A on with NG as fuel and unchanged flows), three rounds of fuel (up to 65%) and air (18-24%) utilization variations, and operation at 32.5 A. At nominal operation the BoL (Beginning of Life) power is 6 kW for one OAM stack module.
It was decided that the design of the OAM stack module was to be used for further work in the CATION project. This decision was based on the OAM stack modules passing a D1 test, as described below. Passing this test required that the non-stack parts of the modules did not show any weaknesses during the tests and that they caused no damage to the stacks. The latter was shown by that the stacks showed no weaknesses that they would not have shown during the same test sequence performed in standard stack test equipment. Long term performance was not included in the decision criteria.
The D1 test included:
• Nominal operation (Pre-reformed NG as fuel, 60% fuel utilization, 21% air utilization, 25 A current, 6 kW power, all temperatures was 650-750 oC).
• Instant load cycles (only load varied).
• Thermal cycles (to room temperature and back to operation).
• Fuel utilization increase (65%).
• Air utilization variations (18%, 21%, and 24%).
• 32.5 A load point at otherwise nominal operation.
Component test: Tests have been carried out to verify the performance of the module components. The accuracy and sustainability has been verified for the compression system. The feed through module was proven to be leak tight both before and after module test. The bypass leakage was measured to be below 1% of the air supply on all tested modules; the external leakage was in all cases below 0.1% and did not increase from before to after fuel cell operation tests. Development and testing of the stacks was carried out in another TOFC project.
One problem which at the beginning of the CATION project was very crucial to find a better solution for was the electrical insulation between the stacks and the fuel manifold. The previously used gasket was only resistive enough for having two stacks electrically in series. A sub-project identified several possible options and tested their electrical resistance both instantaneously and over time. The result was that a suitable material was identified as such allows for the four stacks in one module to be operated in a serial configuration. This is of importance for the system cost, as it decreases the required number of load supplies and a higher output voltage is possible to obtain.
Hotbox: Main result of this work was the design and manufacturing/modification of existing IPM to be able to accommodate 4 OAM stack frames and to use this test set up to hot box validation tests. The hotbox validation test was successfully performed using the hotbox design created in the CATION –project. Successful operation of the system for 2000+ hours validates the hotbox design as viable in a SOFC system environment.
Other achievements: AVL have in collaboration with Wärtsilä and TOFC completed risk analysis, DFMEA, on the stack modules, on which they also performed damage modelling. Additionally AVL prepared their 10 kW test station for a degradation test of one stack module. FEM analysis has been applied to the stack module design and materials to ensure that no unwanted deformations occur and CFD analysis has been applied to both the cathode and anode flow to ensure proper flow distribution
Summary: All work in stack of balance work has been finalised very successfully and a 6kW SOFC module has been developed. Design is ready for pre commercial market and seemed so good that TOFC is taking it to production. It has been tested in a “real” system for more than 2000h and more than 20 modules are tested in test stations making it a solid result.
3.4 Subsystem validation
Subsystem validation: The design study has shown that the required size of the ejector allows for reasonable integration into the system. Furthermore, the required pressure at the ejector inlet can be provided by the existing blowers of the system and does not require a re-sourcing. Furthermore, the integration of the new TOFC stack module could be achieved with little modifications. These facts widen the flexibility of AVLs SOFC CHP platform significantly and can be seen as a major output of this project.
The system was operated at 6 – 8 kWel for a significant amount of time. The cathode recirculation was indirectly measured by two different methods. Both methods suggest a recirculation rate of about 40 %. The results of the project allowed for the following insights:
• Static ejector is suitable for cathode recirculation in terms of performance and the possibility to integrate it in a reasonable way into a very compact system packaging
• Pressure drop of the stack cathode side influences the recirculation rate significantly. Pressure drop of TOFC stack module is small enough to enable a high recirculation rate
• Cathode recirculation generates less harsh temperature gradients at the cathode inlet which was shown by very moderate temperature differences between cathode inlet and the stack itself
• Cathode recirculation rate varies only slightly in a wide operating range and therefore allows a good characteristic for system operation
• Pressure level needed for the ejector can be handled by the blowers of the AVL SOFC CHP platform which enables an easy adaption of the BoP in case of cathode recirculation
• Air heat exchanger can be built ~30 % smaller compared to a system without cathode recirculation
• Cathode recirculation allows for high electrical DC efficiencies up to 66 %.
Within this project AVL could significantly push the system development further towards a commercial system technology. AVL has already developed successfully a stationary SOFC CHP platform in the 10 kWel range based on natural gas steam reforming and anode gas recirculation. In this project the next step by improving the cathode path enabled an important knowledge gain on a theoretical and practical level. The ejector concept is seen to play a significant role when it comes to substantial cost reduction. For AVL as an engineering consultant this knowledge gain is of major importance and widens the technology portfolio of AVL’s stationary SOFC CHP platform. In this way future customers can be attracted and served much better. The hardware demonstration of the system is an important tool to convince industrial customers when it comes to a series product development stage.
Life Cycle Analysis: A comparative Life Cycle Assessment (LCA) and Life Cycle Cost analysis (LCC) have been performed to evaluate the environmental and economic performance of a Solid Oxide Fuel Cells designed with cathode sub-systems developed in the project. An environmental performance comparison was built between a SOFC system with ejector-based cathode recirculation and a gas microturbine. It was demonstrated that the studied SOFC system is able to yield environmental benefits on the environmental load from a life cycle point of view for all the impact categories considered with respect to the conventional technology. At commercial level, it can be concluded that SOFC systems present a lower total LCC with respect to microturbines both for industrial and household applications, thus guaranteeing both environmental and economic sustainability.
Summary: Experimental system validation subsystem in real SOFC system was done successfully to prove that air sub-system concept including all necessary components were developed during the CATION project and could be implemented into future large-scale commercial SOFC power plant.
3.5 Foreground
After the exit of Wärtsilä from the CATION project, AVL took over the cathode sub-system validation task. The cathode sub-system was designed and tested based on the existing AVL SOFC CHP platform. This required an adaption of the platform towards the process requirements considering the operation of the TOFC stack module consisting of two TOFC DG modules with each 6 kWe rated power. However, the cathode sub-system required the integration of the cathode recirculation which is carried out with a specifically designed ejector system. After building the SOFC platform and integrating the TOFC stack module a sub-system validation test was performed. During the project developed air sub-system concept including all necessary components were successfully validated.
Based on the design to cost (DtC) analyses carried out in the projects, a good understanding on the economies of scale was achieved. It can be concluded that with additional stack related development steps a commercially feasible system having an investment cost (excl. stacks) of less than 2000 €/kW can be achieved. SOFC systems present a lower total lifecycle cost than microturbines both for industrial and household applications, thus guaranteeing both environmental and economic sustainability of the SOFC technology.
The ultimate objective to have 250 kWe atmospheric SOFC system in future will be reached within the time because Convion Oy (former Wärtsilä) will be launched 50 kWe 2014 and their product portfolio contains systems up to 300 kWe. The knowledge and results obtained from the CATION project have been extensively utilized in the development of Convion’s systems, providing among others improved cost, performance and technical maturity of the system. Also all deliverables was delivered and all milestones and objectives were reached during the project. Conclusion is that CATION project was finalised successfully.
Potential Impact:
4. Potential impacts
4.1. General impacts
The CATION project directly contributed to the overall objectives of Call FCH-JU-2009-1,
Area SP1-JTI-FCH.3: Stationary Power generation & CHP, Topic SP1-JTIFCH. 2009.3.4: Component improvement for stationary power applications by addressing the following fuel cell functions and the corresponding components in particular:
• Power generation unit (integrated stack/BoP)
• Heat exchangers/Thermal management
• Air and fluid flow equipment including subcomponents
• Fluid supply and management including pumps, valves and flow meters
The outcome of the project is as planned benefiting all of the project participants, and also the fuel cell community in general. While CATION project was a particularly fruitful effort in technological development, further development will be essential for SOFC technology in reaching commercial competitiveness and maturity. Successful publicly funded demonstrations will play an important role in bridging “a valley of death” of commercializing large fuel cell systems due to inherently higher single unit costs and associated financial risks compared to small systems, making steps to series manufacturing and reaching volume advantages.
4.2. The exploitation of results
4.2.1. TOFC
During the CATION project TOFC has developed a module with 4 open air manifold stacks. The cathode flow to the stacks is simplified as one big square channel with all the stacks placed directly in the air stream. This allows very easy and cheap cathode integration by a simple combined flange. Result is possibility of cheaper systems with less and simpler cathode piping and allows the modules to be operated in series (with need of air ejection). The product has been brought to a pre commercial as first version state where pilot production is possible and reliable in small volumes but still need verification testing and design & optimization for cost, assembly, production, integration etc. TOFC is take this product to pre commercial sale and will transfer it to pilot production. Depending on yield and marked demand TOFC will produce at maximum two modules per week for pre commercial sale and testing in-house and at integration partners. This pilot production itself and the produced product and testing of this will be part a new development program and give valuable input on the complete added value chain. Having a small scale production is deemed necessary to ever foresee and overcome the challenges from design and concept input over sub suppliers handling, in house production, end of line testing, system design and installation, operation and end of life handling, just to mention a few. TOFC intends to start a development program that will take the current pre-commercial distributed generation module to a product that can handle a commercial marked. This product should have the potential to be a major player in the marked. Even thou many challenges is already known and to some extend solution ideas are ready this will be a traveling in to the void and impossible to predict, but TOFC estimates that it will take 5 years before the product is ready. During this period there will properly be possibilities of upgrading the current module. The project is planned as a four stage project as follow:
• Concept generation: Based on experience from current product and production new concepts are generated to ensure a wide solution space for the later selection.
• Concept selection: Evaluation of the above mentioned concepts. Among this is the current concept but the comparison evaluation will be stronger than 2just2 updating the current
• Product development: The selected concept is taking to working prototype level and thoroughly tested
• Product implementation: The prototype is taken to production. Experience tells that this is not an easy task
The development in the CATION project has been closely aligned with the interest of TOFC and it has certainly made a difference.
4.2.2. Bosal
Bosal has drafted a business plan for all heat exchangers for industrial applications, of which SOFC plate heat exchangers are part of. A business unit (Bosal ECI) has been carved out of the R&D department of Bosal’s Lummen (Belgium) plant. This business unit is based in Vianen, The Netherlands, where a Bosal automotive supply plant is now being transformed to a heat echanger plant. All hardware procured for tooling and production line will be installed in this plant. SOFC heat exchangers developed during the CATION project are expected to take up 40% of the order volume for this plant by the end of 2015. These products are aimed for the European market for heating appliances, as mCHP systems enter this market. East Asia and the US are mainly targeted for SOFC power plants, in the 25 – 1000 kWe power range. Commercial production for field testing has started in 2014. The ramp up to serial production is projected in 2016, while 2015 already sees a substantial increase in projected sales.
4.2.3. Convion (former Wärtsilä)
Within the project a number of conceptual mechanical layouts including SOFC stacks, feed piping and key components were developed for the various flow configurations. Convion has developed a stack module assembly based on TOFC stacks having improved power density and lower manufacturing costs compared to earlier designs. This stack module can be utilized in Convion’s stack-flexible SOFC system. Convion has designed commercial SOFC systems in the power class of 50-300kW since its founding in late 2012, inheriting the IPR and key personnel from the Wärtsilä fuel cell development unit. Convion has completed the design of its first 50kW product in spring 2014 and has recently started the manufacturing of a pilot system to be commissioned in 2015. Commercialization and ramp-up of production as well as introduction of a higher power range is foreseen for 2016-2018. The knowledge and results obtained from the CATION project have been extensively utilized in the development of Convion’s systems, providing among others improved cost, performance and technical maturity of the system.
4.2.4. AVL
The primary goal of AVL as an engineering consultant company is to license the technology to industrial customers who manufacture and sell SOFC CHP products. System demonstration during CATION project with TOFC stack module and cathode recirculation extends AVLs SOFC CHP technology portfolio for following developments of new commercial products
4.2.5. UNIGE
During CATION project UNIGE research team had the opportunity of sharpening the application of the Life Cycle Assessment methodology to Solid Oxide Fuel Cell systems. This field of application has been object of several projects in the last years within the department but CATION project was the first where the dynamics of sub-systems were studied in such deep detail. Besides, UNIGE research team had the chance to test the specific methodological choices - refining ISO 14040 general rules for fuel cell systems – derived from a specific guidance issued within FCH JU initiatives. The assessment studies conducted within CATION project can be in fact considered as a validation test of the methodological guidance for performing LCA on fuel cells. Moreover, UNIGE research team developed a specific toolbox for integration of a cost indicator associated to the assessment of the environmental load of a fuel cell system along its life cycle. A specific toolbox has been developed by UNIGE for integrating LCA and LCC findings. It cannot be considered as a commercial product, but it can be considered as a research tool that can be from now used by the research team in its future analysis.
4.2.6. VTT
VTT Technical Research Centre of Finland as a research institute will utilise increased expertise and knowhow in the area of SOFC system development for contract research with European enterprises and getting more FCH JU join project with European partners.
4.3. Dissemination activities
Even if the project was very much industrial oriented there were quite a lot scientific activities including two scientific papers, one master thesis, eight oral presentations in international conferences, one commercial flyer and two exhibitions in Hannover messe.
List of Websites:
Public website address: http://cation.vtt.fi/
Contact information:
Dr. Jari Kiviaho
Coordinator
VTT Technical Research Centre of Finland
jari.kiviaho@vtt.fi
+358 50 5116778
