What is EDI?
The EDI process produces industrial process water of very high purity, using less than 95% of the chemical products used in the conventional ion exchange processes. With EDI system membranes and electricity replace the million gallons of acid and caustic chemicals that the old processes required daily.
How does it work?
An EDI stack has the basic structure of a deionization chamber. The chamber contains a ion exchange resin, packed between a cationic exchange membrane and a anionic exchange membrane. Only the ions can pass through the membrane, the water is blocked.
EDI is useful for any application that requires constant and economic removal of water impurities without using dangerous chemical. Some examples are:
- Reuse of residual water in food and beverages industry
- Chemical production
- Pharmaceutical industry
- Boiler Feed Water
- Reduction of ionizable SiO2 and TOC (total organic carbon)
Since installation EDI units perform quite reliably, providing the customers with high purity production water for either power plant boiler feed or microchip rinse water. The water produced has met or exceeded customer high-purity water specifications. In addition, when a diluite stream cleaning was required as result of fouling, product quality was completely recovered.
As a substitute for the more traditional ion-exchange process, EDI brings advances in both energy and operating expenses to the high purity water treatment train. By eliminating the periodic regeneration requirement of ion exchange resin, environmental benefits are also realized by avoiding the handling and processing of acid and caustic chemicals brought to the site.
Some of the advantages of the EDI as opposed to the conventional systems of ionic interchange are:
- Simple and continuous operation
- Chemicals for regeneration completely eliminated
- Cost effective operation and maintenance
- Low power consumption
- Non pollution, safety and reliablility
- It requires very few automatic valves or complex control sequences that need supervision by an operator
- It requires little space
- It produces high pure water in a constant flow
- It provides complete removal of dissolved inorganic particles
- In combination with reverse osmosis pre-treatment, it removes more than 99.9% of ions from the water
- EDI cannot be used for water having hardness higher than 1, since the calcium carbonate would create a scab in the camera of the concentrated one, limiting the operation
- It requires purification pretreatment
- Carbon Dioxide will freely pass through an RO membrane, dissociating and raising the conductivity of water. Any ionic species formed from the carbon dioxide gas will lower the outlet resistivity of the water produced by EDI. The management of CO2 in water is typically handled in one or two ways: the pH of the water can be adjusted to allow the RO membrane to rejuect the ionic species or the carbon dioxied can be removed from the water using a strip gas.
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