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The Mechanism of Demineralization Water Plant

In Industrial water treatment, demineralization refers to removing dissolved solids from feed water and process streams.

Demineralization is a type of water purification, which refers to any treatment process that removes minerals from water. The term demineralization is for ion exchange processes used for the total removal of ionic mineral contaminants.

Often, the terms demineralization and deionization are used interchangeably. It utilizes both anion and cation resins

Following demineralization, the treated water will be of a high purity level comparable to distilled water but typically at a much lower cost.

A demineralization system's specific design and components can vary from one application to the next based on process conditions and the composition of the stream to be treated.

Still, most demineralization systems will include the following components:

One or more columns, Regenerate dosing system, Chemical feed storage tanks, PLC, control valves, and piping, Resin

When the well’s dry, we know the worth of water. Benjamin Franklin

There is some flexibility in the configuration of a demineralization system to meet various process conditions and purity goals optimally.

In designing a demineralization system, consideration should be given to variability of the feed water, level of purity needed, system footprint, tolerance for ion leakage (in particular sodium and silica), and chemical feed requirements.

Workings of DM Plant

In the presence of water, minerals and salts dissociate into their constituent ions. These dissolved solids consist of negatively-charged ions known as anions and positively-charged ions known as cations.

Present within a resin that consists of plastic beads to which an anionic functional group has been bound. These functional groups loosely hold ions of a negative charge through mutual electrostatic attraction.

During an active cycle, water with dissolved ions is introduced to the resin. The ions in the solution will exchange places with the ions on the resin beads, clinging to the resin's functional groups even as the resulting solution is drained away.

When one ion has a greater affinity for the functional group than the already present ion, the specific ionic contaminants present will dictate whether both types are needed.

In a reaction, the exchange of ions replaces contaminant ions with other, less objectionable ions. For example, in a sodium softening system, the objective is to remove hardness ions from the solution by replacing them with sodium ions.

As a result, the treated solution will have little to no hardness, containing a greater concentration of sodium ions.

In demineralization, cations in the feed water are exchanged for hydrogen ions, and cations are exchanged for hydroxyl ions.

Demineralization systems are available in two-bed or mixed-bed configurations.

Two-bed IX

Two bed or dual bed exchangers use two or more resin beds to treat a stream, each containing a specific type of resin. In two-bed demineralization, a stream is first treated with a strong acid cation resin that captures the dissolved cations and releases hydrogen ions in exchange.

Mixed-bed IX

Mixed-bed exchangers offer a higher water quality compared to twin-bed systems. While mixed-bed exchangers produce higher quality water, they also require a more involved resin regeneration process.

Additionally, mixed-bed units are more susceptible to resin fouling and inferior system function due to fluctuations in stream contents and are typically used downstream of other treatment measures.

For freshwater applications, demineralization can be an excellent alternative to distillation, as it can produce water similar in quality to distilled water but through a more cost-effective ion exchange process.