Energy and exergy assessments of a novel trigeneration system based on a solid oxide fuel cell

Abstract

Energy and exergy assessments are reported of a novel trigeneration system based on a solid oxide fuel cell (SOFC), for steady-state operation and using a zero-dimensional approach. The trigeneration system also includes a generator-absorber heat exchanger for cooling and a heat exchanger for the heating process. The influences of two significant SOFC parameters (current density and inlet flow temperature) on several variables are investigated. The results show that the energy efficiency is a minimum of 33% higher when using the trigeneration system compared with the SOFC power cycle. In addition, the maximum energy efficiencies are found to be 79% for the trigeneration system, 69% for the heating cogeneration, 58% for cooling cogeneration and 46% for electricity production. Moreover, the highest trigeneration exergy efficiency is almost 47% under the given conditions. It is also shown that, as SOFC current density increases, the exergy efficiencies decrease for the power cycle, cooling cogeneration, heating cogeneration and trigeneration. As current density increases, the trigeneration energy and exergy efficiencies decrease, and an optimal current density is observed to exist at which the net electrical power is a maximum. As SOFC inlet flow temperature increases, the trigeneration energy and exergy efficiencies and net electrical power increase to a peak and then decrease. The main exergy destructions occur in the air heat exchanger, the SOFC and the afterburner.