Ion exchange resin | Essential knowledge of DM Plant

Hello Readers

In this blog we will cover following topics

1. Introduction
2. Selectivity of Resin
3. Types of Resins
4. Ion exchange terms
5. Resin problems and troubleshoot
6. Impact of various Chemicals

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1. Introduction of Ion exchange resins

Water containing dissolved salts ( Electrolyte, ions) of Na+, Ca⁺², Mg⁺² SO₄^-2Cl^-Silica etc. This impurities makes problems in heating or cooling system of Scaling , chocking etc.

Ion exchange resins made to remove this impurities. It is available for household use to Industrial uses.

2. Selectivity of Resin

Selectivity of resin is depending upon ions present in solution being replaced. Ex: Ca⁺², Mg⁺² are replaced by Cation resins, SO₄^-2OH- , Cl- ions are removed by Anion resins. Rest of the ions are replaced by Mixed bed resins contains both Cation and Anion specialty grade.

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3. Types of Resins

A. Strong acid cation resins B. Weak acid cation resins

C. Strong base anion resins D. Weak base Anion resin

A. Strong acid cation resins

Strong acid cation contains SO₃H⁺group.
These resins working on entire pH scale.
It can be use in all softening applications even in two bed DM plants.
Made from Styrene & Divinayl benzene

B. Weak acid cation resins

Weak acid cation resins containing -COOH group as exchange site.
It regenerate perfectly as theoretically acid requirement but Strong acid cation resin requires 200 - 300% acid.
It is made from methacrylic acid
It gives best efficiency at 1. Low flow rates 2. Low temperature

C. Strong base anion resins

This resins derive their function group from Ammonium exchanging sites with two extensions.
Type 1 has methyl groups, Type 2 has ethanol replaces one of the methyl groups.
Type 1 resin are used for total anion removal on all waters.
Type 2 resin are used on high temperature, High alkinity and high silica. It is less effective than type one for all anion removal.

D. Weak base anion resins

Resin containing Polyamine functional group which adsorbing free mineral acidity
This resin regenerated with calculated Caustic NaOH amount
Usable in high amount of chloride and sulphate in raw water this resin is not much affect on Si & Alkinity.

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4. Ion exchange terms

TEC - Total Exchange Capacity.

This term is refer the portion of TEC of resin volume

Colorthrow - After some time passing resin changing its color due to its structure broken by oxidants. It indicates service life of an resin.

Fines - When resin manufactured it also produce smaller particles. When it is high in resin it not pass liquid flow. It also increase Pressure drop across Ion exchange column.

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5. Resin problems and troubleshoot

Raw water supply -
Raw water supply parameters must maintain for long resin active life

Maximum temperature allowable limit -

Cation resin - 120°C Anion strong base - 48°C

Anion Weak base - 38°C
Free Chlorine 0.5 ppm
Turbidity - 5 ppm
Iron - dissolved form
Manganese - Dissolved form
Hydrogen sulfide - 0.5 ppm
Oil - Nil

Resin is a chemical structure which exchange from water with active exchange sites. If contaminated water is used resin may be harm with permanent ions. this contamination makes ion exchange resin non regenerative.

Colloidal matter coats surface of ion exchange resin particles. There are some pre treatments available which installed to run DM Plant longer time.

Floculation / Coagulation system
Clarifying system
Sand Filters
MGF [ mix grade filters]
ACF [ Activated carbon filters ]
Bag filters
Candle filters
RO [ Reverse osmosis membrane ]

There is a specialty resins for each type of contamination and filtration purpose. More than 70 types of resins are available for various ion exchange treatments.

High raw water flow -

Raw water flow must be fixed as per resin quantity. If higher flow rates are there is possibility of early exhaust of resin. Exhausted resin required regeneration. Regeneration process is regular basic process.

Idle time -

When DM plant is not in use for 7 days or more Resins must be in wet condition with brine. Dry condition for resin is dangerous. If shutdown is lesser than 7 days resin must be wet with water.

When plant startup going on Brine or Water must be washed with fresh pure water.

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