The main topic of the paper is the experimental investigation of a solid oxide fuel cell (SOFC) / micro gas turbine (MGT) hybrid power plant test rig. This comprises the proof of concept, the characterization of the operational range and the influence of the coupling on the MGT. The operational concept of the hybrid power plant is designed to reach a maximum flexibility in electrical power output. Therefore the power plant is operated at different MGT shaft speeds and electrical power outputs of the SOFC, thus leading to different SOFC temperatures.
Instead of a real fuel cell an emulator was developed and built to emulate the fluid dynamic and thermodynamic behavior of a real SOFC. The test rig is based on a Turbec T100PH micro gas turbine. A specially designed interface connects the facility to the tubing system and the SOFC emulator. For the present investigation the SOFC emulator has been equipped with a gas preheater. It emulates the varying heat output of the fuel cell. The gas preheater is composed of a natural gas combustor based on the FLOX® technology, with a swirl-stabilized pilot stage and allows a wide range of emulating different SOFC outlet temperatures. In addition installations have been integrated into a pressure vessel, representing the SOFC cathode volume, to analyze the increase in residence time and pressure loss.
Initially three different configurations of the test rig, no SOFC emulator – tube only, SOFC emulator with pressure vessels and fully equipped SOFC emulator (pressure vessels, installations and gas preheater) are compared regarding the influence of the different volumes, residence times and pressure losses. The operating range of the test rig equipped with gas preheater in cold (no fuel) as well as in hot conditions is investigated. As the velocity at the entrance of the gas turbine combustor increases with increased fuel cell outlet temperature the surge margin is strongly influenced. The operating range was determined for different shaft speeds and preheating (SOFC outlet) temperatures. Finally the transient behavior of the gas preheater and its impact on the MGT is analyzed. The results provide the required basis to implement a cyber physical system, in which the SOFC emulator is controlled by a SOFC model, as well as the basis for the real coupling of MGT and SOFC.
Analysis of the influence of heat transfer on the stationary operation and performance of a solid oxide fuel cell/gas turbine hybrid power plant