MASS AND ENERGY BALANCE, ESPECIALLY WITH RESPECT TO THE TRANSPORT OF WASTE HEAT OUT OF THE SYSTEM, REPRESENT A CENTRAL QUESTION FOR THE DEVELOPMENT OF ADVANCED SOFC MODULE CONCEPTS. THE THEORETICAL-NUMERICAL TOOLS WHICH WILL BE DEVELOPED WITHIN THE PROJECT ALLOW THE ASSESSMENT OF THE FEASIBILITY OF DIFFERENT DESIGNS WITH RESPECT TO THESE PROBLEMS OF THERMAL CONTROLLABILITY AND OF EVENTUAL LIMITATIONS FOR SCALE-UP. ADDITIONALLY A BASIS FOR FURTHER MORE COMPLEX AND DETAILED INVESTIGATIONS OF COMPLETE SOFC PLANTS WILL BE ESTABLISHED.
Modelling was performed in the following stages:
the establishment of the analytical mass and energy balances for a local element in a solid oxide fuel cell (SOFC) (micromodel);
the enlargement and adaption of the balance equations (macromodel) according to the cell and module geometry under consideration (both crossflow monolithic design and tubular design);
the writing of a computer code and optimisation of the code with respect to convergence.
Calculations were carried out for the following cases:
crossflow monolithic design with hydrogen as a fuel;
crossflow monolithic design with internally reformed methane;
tubular design with hydrogen as a fuel.
The main conclusions which can be drawn from the results are:
the temperatures of the gases involved coincide to within a few degrees with the temperatures of the cell components;
reasonable fuel utilisations and efficiencies can be achieved with both designs;
in the tubular design investigated (Westinghouse type) there are inherently large temperature gradients;
temperature distributions of crossflow monolithic designs are significantly flatter than those of tubes;
the kinetics of the steam reforming reaction occurring in cell operation with internal reforming of methane (natural gas) strongly affects the temperature distribution within a module.
THE GENERATION OF ELECTRICAL ENERGY BY CERAMIC SOFC MODULES IS ACCOMPANIED BY THE PRODUCTION OF CONSIDERABLE AMOUNTS OF HEAT WHICH HAS TO BE TAKEN OUT OF THE MODULES (MAINLY BY THE AIR FLOW ACTING AS A COOLANT) IN ORDER TO PREVENT SUPERHEATING OF THE UNITS. THIS SEEMS TO BE OF GREAT IMPORTANCE, ESPECIALLY FOR HIGHLY INTEGRATED HIGH POWER CONCEPTS DISCUSSED MEANWHILE FOR SOFC APPLICATION. BY MEANS OF A THEORETICAL-NUMERICAL MODELLING THE MASS AND ENERGY BALANCE OF TYPICAL MODULE CONFIGURATIONS WILL BE DETERMINED. AS FAR AS POSSIBLE VALUES WHICH WERE ALREADY REALIZED IN THE LABORATORY, THEY WILL BE USED AS INPUT PARAMETERS (E G FOR ELECTRICAL CONDUCTIVITIES OR POLARIZATION PROPERTIES). SPECIAL EMPHASIS WILL BE LAID UPON THE INVESTIGATION OF THE MECHANISMS OF HEAT TRANSFER FROM THE MODULE CONSTITUENTS TO EACH OTHER AND TO THE GASES INVOLVED IN THE PROCESS BY CONDUCTION ABD ESPECIALLY RADIATION WHICH IS IMPORTANT DUE TO THE HIGH TEMPERATURE. PARAMETER VARIATIONS WILL YIELD INDICATIONS FOR PREFERABLE CONFIGURATIONS AND FOR ADEQUATE SOLUTIONS FOR THE COOLING OF THE SOFC-MODULES.