Review
Johan Enslin
Abstract
Steam extraction from Rankine cycle turbines in order to heat the high pressure boiler water in a series of feed heaters, is common practice to increase the thermodynamic efficiency of cycles. Regenerative Cycles are so formed, which form the basis of most modern power generation rankine cycles used by electricity utilities globally. By utilizing Absorption Heat Transformer (AHT) principles, thermal powered hybrid heat pumps have been developed recently, making it possible to use these heat pumps for reclaiming rejected heat from rankine condensers for providing the required energy for feed water heating, allowing additional power to be generated from the (historically used) extract steam, without requiring more heat to be added in the boiler. Cycle efficiency is therefore increased. As the AHT-Hybrid heat transformer type heat pumps may generate higher temperatures than the boiler evaporation temperature in some lower temperature rankine cycles, the possibility exist that a much larger portion of the rejection heat in the condenser may be recovered and re-used regeneratively in the cycle. This enhanced regeneration gives rise to the extremely high thermodynamic efficiency achieved by the REHOS Power Cycle. These Heat Of Solution (HOS) heat transformers, can practically only be used within limited temperature ranges, depending on critical temperature and pressure parameters of the binary media mixtures used e.g. NH3 -in-Aqua may be practical only between -30°C and +140°C making it ideal for ORC systems used e.g. for geothermal power generation.