[ water treatment ]
The differences stem from the recoveries that can be obtained in the initial pretreatment of each raw water source before it is polished to ultrapure quality . For groundwater , standard filtration can reach very high recovery values , > 98 %. Treated wastewater filtered with ultrafiltration will typically have a slightly lower recovery of 90 – 95 %. For seawater desalination , recovery is normally limited to 40 – 50 % due to increasing osmotic pressure . The treatment to ultrapure quality comes with its own recovery , typically 75 %.
With these rule-of-thumb numbers , it is possible to quickly estimate the water requirements for a given hydrogen project . The same electrolyser designed to produce 100,000 tons of hydrogen will require 900,000 m 3 of ultrapure water and will need to extract 1,200,000 m 3 of groundwater , 1,300,000 m 3 of treated wastewater or 3,000,000 m 3 of seawater .
Often , concern about the energy consumption of the water treatment process is brought up for discussion , especially when talking about seawater desalination . However , it is important to remember that while water treatment must overcome the attractive forces between water molecules and ions , electrolysis must overcome the strong covalent bonds between the atoms in the water molecules . As seen in Figure 4 , turning seawater into ultrapure water may require 3 – 4 times as much energy as using groundwater or treated wastewater , but it is still only around a thousandth of the energy required for electrolysis .
Production of ultrapure water
The process from raw water to ultrapure water can be divided into two basic steps : 1 . Pretreatment of raw water 2 . Polishing to ultrapure standard
The role of the pretreatment system is to make the raw water suitable as a feed source for the polishing system . This means bringing the water to a state where it resembles city
Fig . 3 . Raw water quantities required for production of ultrapure water for electrolysis
Hydrogen Tech World | Issue 6 | October 2022 25