[ water treatment ]
Fig . 2 . Rule of thumb for consumption of ultrapure water per MW of electrolyser capacity
For projects where a water-based cooling system is chosen , the specific design of the cooling solution will determine the water usage . For an evaporative cooling tower , relevant parameters include the starting water quality , the ratio between conductive and evaporative cooling , drift ratio , and concentration factor . All these factors make it complicated to come up with an accurate number , but to get a first estimate , a good rule of thumb is that 400 L / h of cooling water is needed per MW of electrolyser capacity , or roughly twice the amount required for electrolysis .
It is important to keep in mind that cooling water and water for electrolysis will have very different quality requirements .
Consumption of raw water
To determine the impact of a green hydrogen system on the local water systems , it is necessary to focus not only on the consumption of ultrapure water , but also on how much water must be taken from the raw water source to produce the ultrapure water .
Water can come from many sources . For most of the smaller projects seen today , water from the drinking water network is used . However , as hydrogen plants increase in size , this approach becomes unsustainable , and water must be sourced from elsewhere .
The three most common raw water sources for large-scale hydrogen projects are : groundwater , treated wastewater , and seawater . From the perspective of a water treatment system , surface water from rivers and lakes will in many ways be similar to treated wastewater , so these can be considered one .
Each type of raw water will require different water treatment systems , and this affects how much raw water must be extracted . Of these , you need to extract the least raw water when using groundwater and the most when using seawater ( Figure 3 ). Extraction of treated wastewater will be similar to that of groundwater .
24 Hydrogen Tech World | Issue 6 | October 2022