Fundamental of ion exchange
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FUNDAMENTAL OF ION EXCHANGE. WATER SOFTENING. HARD WATER. Water containing calcium (Ca+2) and magnesium (Mg+2), the hardness minerals. HARDNESS can be: Calcium hardness Magnesium hardness Total hardness. MEASURMENT OF HARDNESS. Milligrams per liter (mg/L) Parts per million (ppm)

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FUNDAMENTAL OF ION EXCHANGE

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Fundamental of ion exchange

FUNDAMENTAL OF ION EXCHANGE

WATER SOFTENING


Hard water

HARD WATER

  • Water containing calcium (Ca+2) and magnesium (Mg+2), the hardness minerals.

    HARDNESS can be:

  • Calcium hardness

  • Magnesium hardness

  • Total hardness


Measurment of hardness

MEASURMENT OF HARDNESS

  • Milligrams per liter (mg/L)

  • Parts per million (ppm)

  • Grains per Gallon (gpg)

    1 mg/L = 1 ppm

    1 gpg = 17.1 ppm = 17.1 mg/L


Degree of hardness

DEGREE OF HARDNESS

Soft Less than 1.0 gpg

Slightly Hard 1.0 to 3.5 gpg

Moderately Hard 3.5 to 7.0 gpg

Hard 7.0 to 10.5 gpg

Very Hard 10.5 gpg and above


Problems caused by hard water

PROBLEMS CAUSED BY HARD WATER

  • Decreases the efficiency of the detergents.

  • Scaling of pipes, water heaters and boilers.


Benefits of using soft water

BENEFITS OF USING SOFT WATER

  • Soaps and detergents are used more efficiently.

  • Materials and surfaces are cleaned better.

  • Scales in boilers and water heaters are reduced.

  • Precipitates are eliminated from the canned food products.

  • Softened rinse water does not leave scale.

  • Fabric washed in soft water lasts longer.


Methods for hardness reduction

METHODS FOR HARDNESS REDUCTION

  • Deionization

  • Distillation

  • Reverse Osmosis

  • Cation Exchange


Cation and anion chart

CATION AND ANION CHART


Fundamental of ion exchange

RESIN

  • Plastic beads made of cross linked polystyrene with functional groups (sulphonates) that act as ion exchange sites.

  • The sulphonate group has a negative charge allowing it to attract and hold (exchange) positive ions or cations such as H+, Ca+2, Mg+2, Fe+2, Na+.


Resin

RESIN


Resin bead

RESIN BEAD

  • Cation resin bead attract and hold positively charged ions.

  • Those ions remain on the bead until the bead encounters other ions for which it has a greater affinity.


Fundamental of ion exchange

Resin bead releases Na+ and absorbs Ca+2 and Mg+2 ions for which it has a greater attraction.

Ions are not destroyed or changed chemically;

they are simply replaced on the resin bead.

This process is known as ion exchange.


Ion exchange

ION EXCHANGE

  • Resin beads attract Ca+2 and Mg +2 ions and

    release Na+

  • Water has been softened because the Ca+2 and Mg +2 concentrations, which cause water hardness have been reduced.


Fundamental of ion exchange

After a vast number of Ca+2 and Mg+2 ions have become attached to the resin beads, and most of the Na+ ions have been released, the resin can no longer soften the water.

If no new chemical reaction is set, the incoming Ca+2 and Mg+2 ions flow untouched through the unit because there is no room for them on the resin beads.


Fundamental of ion exchange

  • The reaction can be reversed by greatly increasing the concentration of sodium in the solution.

  • Reverse process drive the Ca+2 and Mg+2 ions off the resin beads and replace them with Na+ ions.

  • This process is called REGENERATION.


Regeneration

REGENERATION

  • At appropriate time, the resin beads are washed with a strong solution, also known as a BRINE SOLUTION.

  • Although the resin beads prefer Ca+2 and Mg+2 ions, the excessive concentration of Na+ ions overcomes this affinity.

  • The Ca+2 and Mg+2 are forced off of the resin beads and are discharged to waste.

  • The resin beads are ready to remove more Ca+2 and Mg+2 from the water.

  • The degree to which the resin is converted is dependent upon the concentration of sodium in the brine.


Fundamental of ion exchange

The softening reaction is given as:

2RNa+ + Ca+2 RCa+2 + 2Na+

2RNa+ + Mg+2 RMg+2 + 2Na+

The reverse reaction is give as:

2RNa+ + Ca+2 RCa+2 + 2Na+ High Sodium

Concentration

2RNa+ + Mg+2 RMg+2 + 2Na+ High Sodium

Concentration

NOTE: R represents the resin macro-molecule.


Operational modes

OPERATIONAL MODES

In practice softeners can be

  • In service

  • Exhausted and waiting for regeneration

  • In regeneration

  • In standby

  • Bypassed and out of service


Softening cycles

SOFTENING CYCLES

  • Service

  • Backwash

  • Brining

  • Slow Rinse

  • Fast Rinse


Service

SERVICE

During the service cycle, the raw water

  • enters the top of the tank

  • flows through the inlet flow distributors

  • Passes through the resin bed

  • Exits the tank through the gravel support bed and under drain system


Service1

SERVICE


Service2

SERVICE

  • A successful service cycle requires that all of the treated water be low in hardness

  • The resin capacity be fully utilized

  • You must avoid completely expending the bed, allowing the softener to pass hard water.


Service3

SERVICE

SERVICE FLOW RATE

  • Continuous Flow Rate: 1 to 5 gpm/ft3

  • Peak Flow Rate: 10 gpm/ft3

    PRESSURE DROP THROUGH THE VESSEL

  • 15 psi at Continuous Flow Rate

  • 25 psi at Peak Flow Rate


Backwash

BACKWASH

In Backwash, the raw water

  • enters the bottom of the bed through the underdrain system

  • exits through the top of the tank to waste


Backwash1

BACKWASH

  • Backwash is upflow and the resin bed is fluidized.

  • During backwash, the resin bed is expanded to remove solids trapped on the resin and to keep the bed from compacting.


Backwash2

BACKWASH


Backwash3

BACKWASH

  • The rate of flow must be controlled during the backwash to make certain the bed is expanded but not washing any of the resin out of the softener.


Backwash flow control

BACKWASH FLOW CONTROL

  • Flow controllers provide accurate backwash flow rates

  • These are installed in the waste line

  • Backwash flow controller is a plates with one or more orifices

  • The orifices are designed to give a constant flow rate over a broad range of pressure drop


Brining

BRINING

  • The resin limited exchange capacity must be restored periodically through process known as REGENERATION.

  • Regeneration can be controlled manually or automatically.

  • The frequency of regeneration depends on time (TIME REGENERATION) or quantity of produced water (DEMAND REGENERATION).


Brine making

BRINE MAKING

  • A brine tank is plastic or fiberglass tank with a perforated salt platform.

  • Granular salt is added to a brine tank.

  • A Brine valve keeps the tank filled with water to a preset level.

  • The solid salt is in contact with the water above the platform and thus dissolves in the water.

  • Saturated brine is 26% salt by weight.


Brine dilution

BRINE DILUTION

  • Experience has shown that using a 10% brine solution minimizes salt usage.

  • To create a 10% brine solution the brine is mixed with fresh water through an eductor.

  • The eductor must be matched to the softener size to create the right amount of diluted brine.


Brine application

BRINE APPLICATION

  • The regeneration reaction is much slower than normal softening.

  • Suggested flow rate for the brine is 0.25 to 0.9 gpm/ft3

  • It requires a significant contact time between the resin and the brine.

  • Suggested duration for the brining is 30 to 60 minutes applying 4 to 10 lb of salt per 1 ft3 resin.


Slow rinse

SLOW RINSE

  • To gradually push the brine out of the resin bed after regeneration.

    Recommended flow rate is 0.25 to 0.9 gpm/ft3.

  • Recommended duration is 30 minutes.


Slow rinse1

SLOW RINSE

Slow rinse is a continuation of the brine cycle after the the brine valve has closed, fresh water continues to flow through the eductor even though it is not allowed to draw brine.


Fast rinse

FAST RINSE

  • The purpose of the fast rinse is to completely rinse the brine from the softener so it can be returned back to service.

  • Recommended flow rate is 1.0 to 5.0 gpm/ft3.

  • Recommended duration is 10 minutes.


Fast rinse1

FAST RINSE

  • The fast rinse is a service to waste cycle.

  • The inlet water flows through the service piping and thru the bed.

  • The water exits the vessel through the drain or waste.


Types of water softeners

TYPES OF WATER SOFTENERS

  • Manual

  • Semi-Automatic

  • Fully Automatic

  • Demand Initiated Regeneration


Manual

MANUAL

  • The owner or the operator initiates some or all of the steps in the softener operation.


Semi automatic

SEMI - AUTOMATIC

  • The semi-automatic units require only the regeneration cycle to be initiated by the operator.

  • All necessary steps of regeneration and return to service are handled by the softener controls.


Fully automatic

FULLY AUTOMATIC

  • The fully automatic softener is usually equipped with a timer, which automatically initiates the regeneration cycle and every step in the regeneration process.

  • The regeneration is usually done during the periods of low water usage, such as hours between midnight and 4 a.m.


Demand initiated regeneration

DEMAND INITIATED REGENERATION

  • All operations are initiated or performed automatically in response to the demand for treated water.


Fundamental of ion exchange

  • Ion exchange water softening is an effective method for reduction of hardness and other ions in a water supply.

  • The cost is small in comparison to the benefits received.


Benefits

BENEFITS

Benefits of using water softener:

  • Extends the life of water-using appliances, water heaters and pipes.

  • Increases savings in detergents, soaps, shampoos, and other cleaning agents.

  • Lowers fuel cost. $$$


Fundamental of ion exchange

Considered as a luxury item by some, an ion exchange water softeners are recognized as a necessity by the millions who use them.


Water king inc

WATER KING, INC.

102 Charbonnet Road

Duson, LA 70529

Phone: (337) 988-2360

Fax: (337) 981-7922

E-mail: [email protected]

Web site: www.waterking.com


Fundamental of ion exchange

THE END


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