[ water treatment ] organics . In terms of conductivity , values below 0.1 μS / cm are frequently specified for some of the more stringent electrolysers . It should be noted , however , that due to the relatively low additional investment required to achieve conductivity below 0.1 µ S / cm , this is often preferred , as the water is rarely considered ‘ too pure ’ for the electrolyser .
How does EDI work
Most EDI stacks are manufactured based on the robust and proven plate-and-frame construction with alternating dilute ( product ) and concentrate ( reject ) cells that contain ion exchange resin . These cells are separated by alternating semipermeable anion and cation ion exchange membranes .
A number of these dilute and concentrate cells are grouped together to form an EDI stack in which the dilute and concentrate cells are hydraulically connected in parallel . Electrodes
are situated at the end of the EDI stack ( see Figure 1 ).
During operation , a transverse DC electrical field is applied to the electrodes . Ions entering the dilute cell in the feedwater stream , under the influence of this electric field , migrate from the dilute cell towards their respective electrode and become trapped in the concentrate cells ( see Figure 2 ).
As water moves through the dilute cell , it becomes free of ions , and under the influence of the electric field water electrolysis occurs , resulting in the ‘ splitting ’ of H 2
O into hydrogen ( H + ) and hydroxyl ( OH - ) ions , which serves two purposes : 1 . Facilitates the removal of weakly ionized compounds such as carbonic and silicic acids ;
2 . Electrochemically regenerates the ion exchange resin in the dilute cells
FEED TO |
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DILUTE CONCENTRATE |
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CATHODE COMPARTMENT
CATHODE
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DILUTING COMPARTMENT |
CONCENTRATING COMPARTMENT |
ANODE COMPARTMENT
ANODE
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REJECT PRODUCT |
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CATION MEMBRANE ANION MEMBRANE
Fig . 1 . Plate-and-frame EDI stack configuration
Hydrogen Tech World | Issue 12 | October 2023 31