Hydrogen Rich Natural Gas as a Fuel for SOFC Systems

Abstract

With the increase in installed renewable power in Europe and especially in Germany, the need for energy storage becomes urgent. One interesting option due to its high energy density is the generation of hydrogen from renewable electricity using electrolysis. Produced hydrogen can either be sold as fuel for mobile applications or it can be stored in existing infrastructure. One major storage capability is the natural gas pipeline network in which a huge amount of energy can be stored and distributed based on already available infrastructure. Stored hydrogen could be converted into electricity on demand. Low temperature fuel cells are ideally suited for operation with pure hydrogen but not suited for hydrogen/natural gas mixtures. In these conditions high temperature SOFC with high efficiency and fuel tolerance are the much better choice. DLR has been investigating fuel cells and fuel cell systems for many years - ranging from small portable devices to large aircraft onboard power supply systems in the 30 kW range. In stationary fuel cell systems hybrid power plants combining fuel cells and gas turbines are one major interest of the institute. This publication focuses on the effect of hydrogen rich natural gas mixtures on pressurized SOFC systems. Rising hydrogen contents reduce system efficiency for several reasons. E.g. internal reforming acts as a heat sink, with less natural gas to reform, the cells have to be cooled in another way. This leads to higher parasitic losses due to higher air supply. Traditional system control requires information on the heating value of the fuel gas, which is set manually. With changing hydrogen content in the fuel, online information for fuel flow control becomes important. In this context we will discuss several control possibilities from a system perspective. All results presented are based on simulation results for a 100 kW class pressurized SOFC system published earlier [1], which was developed for the hybrid power plant project at DLR.