It is similar to the Rankine cycle using water as the motive fluid but with the novelty of introducing salts and their hygroscopic properties for the condensation.
Boiler blowdown with the concentrated hygroscopic compounds is used thermally to pre-heat the steam turbine condensate, and as reflux in the steam-absorber.
Here the outlet steam is absorbed by cooled hygroscopic compounds using the same principles as in absorption refrigerators.
Because of the thermal recovery of the boiler blowdown, the hygroscopic reaction in the steam condenser, and the use of an air-cooler to dissipate the heat of condensation, the efficiency of the cycle is higher, with a higher electrical output, reduces or eliminates the need for cooling water,[1] reduces the operating costs,[2] and the capital cost of the utility power plant.
The air-cooler used in the hygroscopic cycle cools a liquid flow with concentrated hygroscopic compound, with an overall volumetric heat capacity much higher than the steam traditionally condensed in the air cooled condenser mentioned earlier, thus reducing the power needed for ventilation,[8] and needing less surface area for heat exchange and obtaining a lower overall cost of the plant.
Depending on the salts chosen, in particular those with a high dilution capacity (i.e. LiBr), saturation temperature of the hygroscopic fluid can be up to 40 °C higher than the steam leaving the turbine.
[11] Hygroscopic compounds are all those substances that attract water in vapour or liquid from their environment, thus their use as desiccant.
A hygroscopic cycle demonstration plant has been built, demonstrating the concepts of the cycle, which includes the absorption of vapour in an absorber where hygroscopic compounds are recirculated, obtaining condensations with temperatures higher than the saturation temperature.
Recent developments have been the Kalina cycle,[17] but with the actual configuration, it is expected to have an impact in locations with poor access to water, and a good integration with combined cycle plants, and any thermoelectric plants (CSP, biomass, coal).
The current state of development is being led by Francisco Javier Rubio Serrano, where his research team and company, IMASA INGENIERÍA Y PROYECTOS, S.A. are developing other configurations, and researching hygroscopic fluids for each particular application together with their most suitable construction materials.