Thermodynamic analysis of hybrid cycles based on a regenerative steam Rankine cycle for cogeneration and trigeneration

Abstract

In this study, different feasible integrated configurations were proposed and thermodynamically evaluated for cogeneration of power and fresh water/cooling, and trigeneration of power, cooling and fresh water. A steam regenerative Rankine cycle with condensation and steam extractions, driven by a concentrated solar tower, was designed to supply the thermal heat requirements of absorption cooling and multi effect distillation, or thermal vapor compression-multi effect distillation. The results showed the configurations that utilize steam extraction with a lower temperature and pressure were more efficient. For power and fresh water cogeneration, utilizing the condensation steam to integrate multi effect distillation with a power cycle was thermodynamically more efficient than the integration of thermal vapor compression-multi effect distillation using extraction steams. Integrated Rankine cycle-multi effect distillation configuration was found to be very competitive with the direct supply of electricity to reverse osmosis systems, particularly at higher fresh water productions. However, further examinations are required considering geographical, environmental and economic factors. For power and cooling cogeneration, all proposed absorption cooling configurations were more efficient than supplying electricity directly to vapor compression cooling. Moreover, despite significantly lower steam requirements of double and triple effects absorption cooling, integration of a single effect absorption cooling to the power cycle was more efficient. The most efficient trigeneration configuration was identified when multi effect distillation and single effect absorption cooling were integrated to a Rankine cycle. The results and conclusions of this study can be generalized to other coal and natural gas power plants that employ similar Rankine cycle configurations.