DM Plant working

Raw water is passed through a MacroFilter for the reduction of excess turbidity, suspended solids bad colour, odour, residual chlorine and volatile organic compounds. 

This water is subsequently sent into a two bed DM plant.

The process of demineralization in which the ions present in water are removed is accomplished in stages, deploying ion-exchange resins. 

Twin-Bed Demineralizers are used to remove ionized impurities from the water. 

Deionization or demineralization is the process of removing up to 95% of the dissolved mineral salts from the raw water by way of ion exchange technology. 

A DM plant comprises of two separate vessels internally connected in series. The first vessel is filled with strongly acidic cation (SAC) exchange resins and the second one is filled with strongly basic anion (SBA) exchange resins

Two distinctly different types of resins are utilized for this process.

When water containing cations (positively charged ions such as sodium(Na+), calcium(Ca2+), magnesium (Mg2+), potassium(K+) etc.) passes through the cation resin bed, the cation resin exchanges the positive ions for hydrogen ions (H+). 

To keep the water electrically balanced, for every monovalent cation (e.g. Na+), one hydrogen ion is exchanged and for every divalent cation (eg., Ca2+ or Mg2+), two hydrogen ions are exchanged.

Chemical reactions (cation exchange)

RH2 + Ca(HCO3)2 -----> R Ca + 2H2CO3

RH2 + MgSO4 -----> R Mg + H2SO4

RH + NaCl -----> R Na + HCl

RH + KNO3 -----> RK + HNO3.

Similarly, when the cation-free water flows through the anion resin bed, the anion resin exchanges the negative ions (chlorides(Cl-), sulphates(SO42-), carbonates(CO32-), Bicarbonates(HCO3-), Nitrate(NO3-)) for hydroxide ions (OH-).

Chemical reactions (anion exchange).

R(OH)2 + H2CO3 -----> RCO3 + 2 H2O

R(OH)2 + H2SO4 -----> RSO4 + 2 H2O

ROH + HCl -----> RCl + H2O

ROH + HNO3 -----> RNO3 + H2O

The hydrogen ions from the cation bed combine with the hydroxyl ions from the anion bed to form high purity water.

Weak Acid Cation and Weak Base Anion are also used in DM plants to handle water containing high amounts of alkalinity, chlorides and sulphates.

Mixed Bed Demineralizer (MBD) plants

MBD plant intimately combines strongly acidic cation and strongly basic anion resins within a single pressure vessel. 

Mixed bed demineralizer plants are also called as polishing units and are used for applications that require a higher level of water quality.

Thorough mixture of cation and anion exchangers in a single column makes an MB plant very effective as post-treatment to either a twin-bed DM plant or Reverse Osmosis Plant.

 These units are used downstream of the DM unit to achieve very high purity levels in the treated water. 

Standard units are mounted on self-supporting, fully assembled skids with necessary piping / valves and include the necessary chemical regeneration systems, piping and valves.

Mixed bed resins are regenerated with acid and alkali but the resins must be separated before this can be done. 

Bed separation is done by backwashing. The backwashing carries the lighter anion resin to top and the cation resin sinks to bottom.

Where ultra pure water is required two mixed beds are provided. The first mixed bed is known as primary mixed bed and the second as secondary mixed bed.

All DM plants are available in Manual, Semi-Automatic and Fully-Automatic versions. Fully automatic units also include Programmable Logic Controllers (PLC) based control systems. These systems can be further upgraded for a direct link to DCS.

Plants are designed based on the ion exchange technique of counter current regeneration. 

The units consist of two corrosion free pressure vessels which are internally connected in series.

 The first vessel contains a Cation absorbing exchanger and second vessel an anion absorbing exchanger. 

The water flow passes through the bed of the Cation exchanger and subsequently through the bed of an anion exchanger. 

Through this process, the systems remove dissolved salts from water to a specified degree. 

The regeneration is required after using up the total exchange capacity. 

The Cation Resin is regenerated with an acid and anion resin is regenerated with alkali solution.

 The system consists of acid/alkali proof pressure vessel with internal fittings and initial charge of Cation and Anion exchanger, set of regeneration equipment, hydraulic ejectors, acid and alkali tanks and conductivity meter to monitor treated water quality. 

These DM Plants offer a practical range of capacities and flow rates necessary to serve wide variety of applications.

We also have both and Fully automatic DM plants in our product range. 

Water Softeners are also widely used in the intuitional and residential sector to prevent scaling in tiles , fittings and pipelines. 

Models are sized on requirement and water characteristics. Manual, semi-automatic and fully automatic versions of the softeners are available.

Thanks for reading - DM Plant working
Naitik Patel
Industrial Guide

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