Convion, Espoo, Finland, reports that it has successfully begun testing of a new 50-kW biogas fuel cell system, prior to delivery and installation at a wastewater treatment plant in Turin, Italy. The company’s C50 biogas system uses a Solid Oxide Fuel Cell (SOFC) incorporating MK351 stacks from Plansee and Fraunhofer IKTS that have been produced using Powder Metallurgy interconnects. In initial trials, the system reportedly achieved a net AC efficiency in excess of 55%, and when fitted with an exhaust gas recovery unit the C50 is able to achieve an overall efficiency of more than 82%.
Convion first developed its cogeneration plant in 2015 and, with a capacity of 20 kW, this system exceeded expectations. The company has now successfully upgraded the unit to its full nominal power output of 58 kW, resulting in the C50 SOFC power plant. As part of the European project DEMOSOFC, it is shortly due to be installed in a wastewater treatment plant operated by SMAT in Collegno, Turin.
Upon commissioning in Italy later in the spring, the biogas fuel cell system will start generating power for the plant’s own use. An installation consisting of Convion C50 products will power the wastewater treatment process and provide a secured supply of electricity and heat for the plant. With the available biogas production, fuel cells will produce approximately 30% of the Collegno plant’s own electricity need and all of the thermal energy needs by efficiently utilising biogas produced in an anaerobic digestion process of waste water sludge.
The Collegno plant is representative of an important segment of small to medium sized wastewater treatment facilities where energy recovery has often not been feasible by conventional generator types. SOFC technology with unparalleled efficiency and long maintenance intervals opens up new opportunities, particularly in these smaller facilities. Alone in Europe, there are thousands of wastewater treatment plants in the sub-megawatt power scale where energy embedded in sewage waste water currently goes unutilised, stated Convion.
MK35x stack design from Fraunhofer IKTS and Plansee
Plansee and Fraunhofer IKTS have been working together for several years and say that they are constantly developing the design of the MK35x stack. The production of interconnects used in the MK35x stack demands a detailed and wide-ranging knowledge of various material alloys and specialist expertise throughout the entire manufacturing chain. Plansee manufactures the interconnects for this using a Powder Metallurgy processes. Using this production method, it is possible, for example, to create different structures on the top and bottom side independently on the same interconnect.
Systems such as Convion’s C50 provide valuable operating data that help both the system developer and component producers to constantly improve the technology. In order to maximise the knowledge gained from the test data, Convion, Fraunhofer IKTS and Plansee have been in close contact ever since it was decided to deploy MK351 stacks.
The MK351 stack has been endurance-tested for 20,000 hours in a realistic system environment. Over the test period, performance degradation was reportedly very low at 0.7% / 1,000 h. But improvement activities still continue. Small modifications to the interconnect allowed pressure loss on the air flux side to be reduced from 16.7 mbar to 6.7 mbar at 4 sl/min in the optimised MK352 stack design, an improvement which is particularly welcomed by the system manufacturers. It reduces the power consumption of the air feed, which in turn increases the electrical efficiency of the system.
The new MK352 stack design is also being endurance-tested. Currently, it has more than 11,000 operating hours on the clock. Performance degradation is again reported to be at a very low level of 0.7% / 1,000 h, while cycle stability was improved from 0.8% to 0.5% per 10 cycles, as was demonstrated in a test over 120 combined RedOx and start/stop cycles.