Utilizing the Waste Heat of SOFC by Newly Developed Cogeneration System

Abstract

It is known that generated by solid oxide fuel cell (SOFC) high temperature exhaust gas streams leaving the stack has a temperature around 700°C. Starting from this idea, the high temperature gas streams can be used in various applications but in our design it can be used for as an extra power generation in addition to SOFC system. Because of thermoelectric (TE) modules offer many advantages over other technologies, it is selected for power generation in our design. A TE module can be used for heat recovery as well as converting the heat to electricity directly by principle of Seebeck effect. They can be used to generate additional power with the SOFC exhaust gas. In this study, SOFC-TE modules cogeneration system designed by us, can produce electricity benefiting from the waste heat of SOFC. In our SOFC design, the exhaust heat is recovered in a heat exchanger to preheat the fuel and air entering to the stack. Other amount of the exhaust heat is utilized in heat recovery unit for recovering the waste heat from there with using TE modules as a heat recovery unit. To cool surface of TE modules, water is chosen as a circulation fluid which comes from water tank. When a temperature differential is established between the hot and cold ends of TE modules, a voltage is generated. Produced electricity can be used in various applications such as electronic controlling system of SOFC system and operating electrolysers for H2 and O2 production. H2 produced from the electrolyser is sent to the reformer mixing here with H2 produced from the reformer then are given to SOFC. O2 produced from the electrolyser is given to the air pump, as a result air is being oxygen-rich air, and then is sent to SOFC. So, it is clearly seen that, O2 enriched air will provide more efficient operation to SOFC and other aspect is; H2 and O2 produced by utilizing the waste heat generated from SOFC, shows the economic relevance of SOFC.