[ heat transfer ]
The freshwater generation systems HyDuo MEP ( left ) and HyDuo AQUA ( right ) simultaneously cool the electrolyzer and generate highquality water . Image © Alfa Laval
With Alfa Laval HyDuo , two processes can be done at the same time : electrolyzer cooling , ensuring the right temperature of the hydrogen production process , and water purification , producing the right water quality for electrolysis . Utilizing waste heat as an energy source in the water purification process comes with many advantages , including lower dosage of chemicals , smaller footprint , greater reliability , and lower electricity consumption . Moreover , it improves process efficiency by up to 27 %.
Using excess heat to produce pure water
First , feed water enters the evaporation section of the plate pack , where the plates are warmed by the hot water that comes from the electrolyzer . This causes the water to evaporate at around 30 – 65 ° C in a vacuum of 75 – 99 %, which is maintained by the brine / air ejector . ( The exact temperature and vacuum ranges depend on the model of the freshwater generator and the temperature of the electrolyzer ’ s hot water ). This means that only clean freshwater vapor reaches the condenser section of the plate pack , which is cooled by a flow of seawater . Here the vapor is condensed into fresh water , which is pumped out of the freshwater generator . The vapor produced during the evaporation stage
rises into the separator section , where any droplets of entrained seawater are removed . Gravity causes these droplets to fall back into the brine sump at the bottom of the freshwater generator .
Thermal desalination processes have long been used on offshore oil and gas platforms to produce fresh water from seawater . This method can therefore be directly applied to hydrogen production and is particularly advantageous offshore and in areas where fresh water is scarce . With this technology , the required water quality can be achieved in most cases without additional post-treatment .
In contrast , traditional desalination systems typically rely on membrane-based solutions where various chemicals are essential for ensuring smooth operation ( e . g ., biocides , activated carbon , anti-scaling ). This is due to the sensitivity of membranes to variations in water impurities . However , when using a thermal solution , the need for chemicals is dramatically reduced , with their use limited to anti-scaling purposes . In some cases , the anti-scaling chemicals can even be avoided if operations run using lower hot-water temperature .
16 Hydrogen Tech World | Issue 11 | August 2023