Selecting Cycle and Design Parameters of a Super Critical CO[sub.2] Cycle for a 180 kW Biogas Engine

The objective of this paper was to study the sCO[sub.2] cycle as a waste heat recovery system for a 180 kW biogas engine. The research methodology adopted was numerical simulations through two models built in different programs: Aspen HYSYS and GT Suite. The models were used to optimize the design and thermodynamic parameters of a CO[sub.2] cycle in terms of system power, system efficiency, expander, and compressor efficiency. Depending on the objective function, the sCO[sub.2] cycle could provide additional power ranging from 27.9 to 11.3 kW. Based on the calculation performed, “Recuperated cycle at maximum power” was selected for further investigation. The off-design analysis of the system revealed the optimum operating point. The authors designed the preliminary dimensions of the turbomachinery, i.e., the rotor dimension is 16 mm, which will rotate at 100,000 rpm.