Mechanical equilibrium operation integrated modelling of hybrid SOFC - GT systems: Design analyses and off-design optimization

摘要

A novel model has been built in this research integrating mechanical equilibrium operation, electrochemical reactions and other thermodynamic processes to gain insights into SOFC - CT hybrid systems in both energetic and operational aspects. To deliver the recommended SOFC pressure of 4-7 bar, a centrifugal compressor of high compression ratio is employed, and the matching issues of turboma-chinery are newly analyzed to account for the disruption of SOFCs to the operation of single-shaft gas turbines. The number of independent parameters decreases in hybrid system modelling when speed and flow compatibilities are contained to ensure turbomachinery running stably without acceleration or deceleration. Compared to conventional gas turbines, however, the coupling of SOFCs substantively introduces at least two independent variables to the flow compatibility equation, in which two of the unknown terms are essentially assigned by different air and fuel utilization. When the turbine is appropriately designed with pressure loss considerations, an electric efficiency of 48.0％ can be achieved by the simple system without surge risk of the compressor. Results also highlight the improvement effects of the coupling technology under off-design conditions. In ideal case, an electric efficiency of 44.4％ can still be achieved at 46％ designed power output.