New technologies are being developed to produce electricity cleaner and more efficient. Promising technologies among these are the solid oxide fuel cell and the supercritical carbon dioxide Brayton cycle. This study investigates the potential of integrating both technologies. The solid oxide fuel cell is known as a potentially clean and highly efficient technology to convert chemical energy to electricity. The high operating temperatures (600–1000 °C) allow the possibility of a bottoming cycle to utilize the high quality excess heat and also facilitate reforming processes, making it possible to use higher hydrocarbons as fuel. The supercritical carbon dioxide Brayton cycle has received attention as a promising power cycle. It has already been identified as a suitable cycle for relatively low temperature, compared to traditional gas turbines, heat sources for several reasons. Firstly because of the high efficiency, around 40%–45% for the common simple recuperative cycle. Secondly, because the turbine inlet temperature of a supercritical carbon dioxide is around 700 °C is low, compared to well over 1000 °C for a common air Brayton cycle. This is especially of interest because solid oxide fuel cell developers are targeting lower operating temperatures to avoid the use of exotic and expensive materials. And thirdly, the cycle can operate entirely above the critical point. Therefore the temperature increases gradually with the energy added to the cycle. This is more suitable for waste heat because the exergy loss decreases and more low temperature heat can be utilized compared to a steam Rankine cycle where most of the heat is added above the relatively high boiling point of pressurized water. A thermodynamic model of the solid oxide fuel cell- supercritical carbon dioxide Brayton cycle hybrid system is developed to explore and analyze different concepts of integration. Several conclusions are drawn. Firstly it is found that recirculating cathodic air increases the efficiency of the system and decreases the size of the heat exchangers. Secondly, applying a pinch point optimization decreases the size of the heat exchangers but increases the complexity of the system while the efficiency is not much affected. Thirdly, applying the recompression cycle in stead of a simple recuperative supercritical carbon dioxide cycle increases the efficiency of the system but not as significantly when operating the supercritical carbon dioxide as a stand-alone system while the complexity of the system increases even more. And finally, compared to a directly coupled solid oxide fuel cell-gas turbine system the solid oxide fuel cell- supercritical carbon dioxide Brayton cycle hybrid system is more efficient but significantly more complex. ... Read more

New technologies are being developed to produce electricity cleaner and more efficient. A promising technology among these is the solid oxide fuel cell (SOFC). It electrochemically converts chemical energy into electricity. This process is highly efficient and several types of fuel are suitable. Furthermore, the SOFC operates at a high temperature, thus producing high quality excess heat which can be converted into electricity in a thermodynamic power cycle to increase the efficiency. Commonly this is done by a directly coupled gas turbine (GT).
The supercritical carbon dioxide (sCO2) Brayton cycle has recently received attention for its potential as a next generation power cycle. It combines the advantages of the steam Rankine cycle and air Brayton cycle. So far, two heat sources are mainly considered for this cycle: Nuclear and concentrated solar power (CSP).

The aim of this study is to investigate the potential of integrating a SOFC with a sCOs Brayton cycle. A thermodynamic model of the SOFC- sCOኼ Brayton cycle hybrid system (SSHS) is developed to explore and analyze different concepts that effect the integration of both systems. Methane is converted to syngas in an indirect internal reforming (IIR) setup. The steam required for this process is either fed by a heat recovery steam generator (HRSG) or supplied by recirculating
anodic exhaust gas. Both options are considered. Recirculating the exhaust of the cathode is another options that is explored and analyzed. Two sCO2 cycle setups are analyzed in combination with the SOFC system: A simple recuperative
cycle and a recompression cycle.
Different setups of the SSHS are compared on efficiency, complexity of the system and size of the exchangers. For comparison, a directly coupled solid oxide fuel cell (SOFC)- GT hybrid system is considered as well.

It is found that the recompression cycle in combination with SOFC system is more efficient than the simple recuperative cycle but significantly increases the complexity of the heat exchanger network, recirculating cathodic air decreases the size of the heat exchangers and increases the efficiency and supplying steam through a HRSG decreases the efficiency. Compared to a directly coupled SOFC-GT system the SSHS is a significantly more complex system. However, it does not require a pressurized SOFC since the sCO2 Brayton cycle is indirectly coupled
to the SOFC. The most efficient setup of the SSHS, combining the recompression cycle with cathode recirculation, has a higher LHV efficiency than the directly coupled SOFC- GT hybrid system, 66.58% over 62.38%. This setup of the SSHS is rather complex though. Other setups of the SSHS show efficiencies similar to that of the directly coupled SOFC- GT hybrid system.
A promising result, but the practical feasibility of the SSHS is something that should be carefullyconsidered in future research and practice. ... Read more