In-Situ, Real Time Gas Composition Measurements for SOFC’s using Laser Spectroscopy

The use of standard gas composition measurement techniques, such as gas chromatography, in large scale solid oxide fuel cells (SOFC’s) operating at high temperatures can be both complex and time consuming. One of the main constraints is the necessity to condense out the water vapour present in the gas streams prior to measurement in the Gas Chromatograph (GC). True gas compositions can only be extracted through back-calculation, with each measurement taking in the order of minutes, and a number of measurement points needed to make the final measurement. For system status monitoring such a time delay between condition changes and measurement is a serious disadvantage. One of the main concerns for systems running on natural gas is the risk of methane slippage through the internal reformer, which increases the risk of carbon formation on the SOFC anode, invariably leading to irreversible loss of performance. It is therefore highly advantageous to measure gas stream compositions within the SOFC system in real time, enabling a rapid response to composition deviation outside of acceptable limits. Gas chromatography can never be made to work as a real-time system status monitoring product solution. A suitable, in-situ, solution for measurement is tuneable diode laser spectroscopy, TDLS. Using this technique it is possible to measure both the gas concentration and system pressure simultaneously for a number of different species, without condensing out the water vapour: reducing analysis time considerably and reducing errors associated with back calculation. In this paper, data taken on an operational fuel cell system is presented for methane, and a comparison with results obtained using a GC is made.