Experimental study on the influence of electrical conductivity of hygroscopic compounds on the performance of a hygroscopic cycle

Dry climate conditions and the risk of desertification have increased significantly due to the effects of climate change. This fact, combined with the growing energy demand, leads to the need of research focused on improving the performance and efficiency of power plants. In the Hygroscopic Cycle Technology, recently implemented at industrial scale, steam condensation is performed in an absorber using solutions of hygroscopic compounds in water. Hygroscopic effects increase the condensing temperature for a given pressure, allowing the implementation of dry coolers at high ambient temperatures and eliminating cooling water consumption. In this work, due to their relevance in the cycle performance and control, the influence of the concentration of hygroscopic salts in the cycle has been studied, providing insight into proper operational ranges and key parameters. An experimental study of the influence of make-up water quality, with the concentration of impurities measured by water electrical conductivity and cycle mass flow ratio values has been performed in a pilot plant. The results, used to validate a mass and species conservation model, have allowed to obtain operational charts of the cycle and may help to reduce the amount of instrumentation required for cycle control. It was found that the decrease in electrical conductivities with boiler blowdowns in the cycle stabilized at a boiler blowdown ratio of 5%. Blowdown ratios above 10% did not result in substantially lower boiler Cycles Of Concentration in comparison with the increase of thermal energy losses and pumping power (0.42 kJ/kg for each additional 1% of blowdown). It was also found that the ratio between the cooling reflux and turbine steam conductivity had to be higher than 1.1 for condensation by absorption to occur, and that a minimum blowdown ratio of 0.04% was required to avoid using a droplet separator to control live steam quality. Hence, a compromise in the boiler blowdown ratio must be found for each particular application. Finally, hygroscopic effects in condensing pressure and temperature have been experimentally verified at pilot plant scale, leading to potentially higher cycle power output values and higher temperatures in the cooling stream of industrial power cycles, which may make it easier to reject heat from the cycle.