SOFC-based micro-CHP system as an example of efficient power generation unit
Microscale combined heat and power (CHP) unit based on solid oxide fuel cells (SOFC) for distributed generation was analyzed. Operation principle is provided, and the technology development in recent years is briefly discussed. System baseline for numerical analysis under steady-state operation is given. Grid-connected unit, fuelled by biogas corresponds to potential market demand in Europe, therefore has been selected for analysis. Fuel processing method for particular application is described. Results of modeling performed in ASPEN Plus engineering software with certain assumptions are presented and discussed. Due to high system electrical efficiency exceeding 40%, and overall efficiency over 80%, technology is an example of highly competitive and sustainable energy generation unit.
The paper presents key assumptions of the mathematical model which describes heat and mass transfer phenomena in a solar sewage drying process, as well as techniques used for solving this model with the Fluent computational fluid dynamics (CFD) software. Special attention was paid to implementation of boundary conditions on the sludge surface, which is a physical boundary between the gaseous phase -air, and solid phasedried matter. Those conditions allow to model heat and mass transfer between the media during first and second drying stages. Selection of the computational geometry is also discussed -it is a fragment of the entire drying facility. Selected modelling results are presented in the final part of the paper.
Heat exchangers of different types find application in power systems based on solid oxide fuel cells (SOFC). Compact plate fin heat exchangers are typically found to perfectly fit systems with power output under 5 kW el . Micro-combined heat and power (micro-CHP) units with solid oxide fuel cells can exhibit high electrical and overall efficiencies, exceeding 85%, respectively. These values can be achieved only when high thermal integration of a system is assured. Selection and sizing of heat exchangers play a crucial role and should be done with caution. Moreover, performance of heat exchangers under variable operating conditions can strongly influence efficiency of the complete system. For that reason, it becomes important to develop high fidelity mathematical models allowing evaluation of heat exchangers under modified operating conditions, in high temperature regimes. Prediction of pressure and temperatures drops at the exit of cold and hot sides are important for system-level studies. Paper presents dedicated mathematical model used for evaluation of a plate fin heat exchanger, operating as a part of micro-CHP unit with solid oxide fuel cells.
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