Design of an H2-O2 fired Solid Oxide Fuel Cell-Gas Turbine Test Set Up

Abstract

The issue of climate change has fostered the innovation of new technology in an attempt to curb the rising emissions, with the energy sector being one of the biggest contributors of carbon emissions. Renewable Energy has shown promise in reducing the emissions by up to 32 %. However the problem of intermittency of
renewable energy sources is still a big reason why they aren’t more mainstream. Therefore, hydrogen has been seen as an energy carrier to provide integration amongst the various sectors of energy generation, transportation, household heating and industrial use. The use of hydrogen as a fuel for re-electrification and power production can be done via IC engines, gas turbines and fuel cells.
This thesis is interested in the possible applications of re-electrification of hydrogen using a system consisting of an SOFC and a gas turbine. It aims to design a small lab scale, test-setup of such a power cycle. The setup
would consist of a small gas turbine and a solid oxide fuel cell.
To that end, this thesis introduces the importance of hydrogen as an energy storage medium followed by the advantages of the SOFC-GT systems in providing higher thermal efficiencies. This is followed by the introduction of the H2-O2 power cycles, namely the Graz and the Toshiba cycles. From previous research done at TU Delft, a basic schematic of the system has been shown, consisting of an SOFC, a combustor, and gas turbine, heat exchangers and an ejector for re-circulative cooling of the SOFC. This is the setup that has to be
designed and so the theory behind the components is presented.
Firstly, the theory behind solid oxide fuel cells, and their modelling is presented. The cooling of the SOFC has been looked into in greater detail. This is followed by the theory of combustion and turbulence modelling.
Two combustor types, a swirl based and a micromix have been considered. Out of these the micromix has been chosen because of its superior mixing capabilities. Finally, the theory behind ejectors, heat exchangers and
sizing of turbomachinery is presented. This concludes the theoretical background of the study. A 0-D model of the SOFC is made based on the Sunfire/Staxera Mk-200 ISM with the 3YSZ KeraCell 11 by Kerafol. This model is then used as a basis of design for the entire thermodynamic H2-O2 cycle. The designed thermodynamic cycle has an overall efficiency of 67.28 %. LHV of hydrogen.
The micromix combustor design is introduced next. A conceptual micromix geometry is presented following which, 2 different configurations are scaled and designed using the theory of jets in cross flow. The two configurations are compared after performing a CFD analysis using the k−ε model with equilibrium chemistry for combustion. The comparison is based on mixing performance, pressure drop and temperature contours. Following the design of the combustor, the supplementary components such as the heat exchangers and the
ejector are designed. The turbine is selected as a small radial turbocharger with a pressure ratio of 8 and is sized using the Balje diagrams. material recommendations are given for the combustor and high- temperature
heat exchangers. The final H2-O2 thermodynamic cycle is presented with the updated component designs. The final thermal efficiency is found to be 64.09 % LHV.
Finally, a basic control scheme is developed for the system and the start-up procedure is briefly discussed.