Modeling of a Methane Fuelled Direct Carbon Fuel Cell System

Direct Carbon Fuel Cells (DCFCs) have great thermodynamic advantages over other high temperature fuel cells such as MCFC and SOFC. They can have 100% fuel utilization, no Nernst loss (at the anode) and the CO₂ produced at the anode is not mixed with other gases and is ready for reuse or sequestration. So far only studies have been reported on cell development. In this paper we study in particular the integration of the production of clean and reactive carbon particles from methane as a fuel for the direct carbon fuel cell. In the thermal decomposition process heat is upgraded to chemical energy in the carbon and hydrogen produced. The hydrogen is seen as a product as well as the power and heat. Under the assumptions given the net system electric efficiency is 22.9 % (based on methane LHV) and 20.7 % (HHV). The hydrogen production efficiency is 65.5 % (based on methane LHV) and 59.1 % (HHV), which leads to a total system efficiency of 88.4 % (LHV) and 79.8 % (HHV). Although a pure CO₂ stream is produced at the anode outlet, which is seen as a large advantage of DCFC systems, this advantage is unfortunately reduced due to the need for CO₂ in the cathode air stream. Due to the applied assumed constraint that the cathode outlet stream should at least contain 4% CO₂ for a proper functioning of the cathode, similar to MCFC cathodes a major part of the pure CO₂ has to be mixed with incoming air. Further optimization of the DCFC and the system is needed to obtain a larger fraction of the output streams as pure CO₂ for sequestration or reuse.