A comparative thermodynamic analysis of two tri-generation systems utilizing low-grade geothermal energy

A comparative thermodynamic analysis and optimization is presented for two different designs of geothermal energy-based tri-generation systems. The two considered systems are distinguished by their power generation units, as organic Rankine cycle is employed in one system while Kalina cycle is used in the other system. To provide cooling and heating loads, a LiBr/water absorption chiller and a water heater are coupled to the Organic Rankine and Kalina cycles. To assess the systems' performances, thermodynamic models are developed and a parametric study is carried out prior to the optimization with respect to the second law efficiency, as the objective function. Also, an exergy destruction modeling is conducted to identify the major sources of irreversibilities within the components of the considered systems. The Kalina cycle-based system is found to be more efficient as its maximum second law efficiency is 50.36% while the organic Rankine cycle-based system has a maximum second law efficiency of 46.51%. The results also indicate that, for a heat source temperature of 120 °C, the Kalina cycle-based system can produce more power than the other system by around 12.2%, under the optimized conditions.