Selective Removal. Reliable Water Quality. Proven Technology.

Ion exchange is one of the most established and versatile technologies used in industrial water treatment.

It can be used to remove hardness, reduce alkalinity, remove specific contaminants, completely demineralise water or polish already treated water to extremely low conductivity.

At Hydra-Clear, we design, manufacture and maintain ion exchange systems for industrial, pharmaceutical, food and beverage, power generation and high-purity water applications.

The principle is simple.

The engineering behind applying it correctly is not.

How Ion Exchange Works

Ion exchange uses small polymer resin beads containing chemically active functional groups.

As water passes through the resin bed, selected dissolved ions in the water are exchanged for ions held on the resin.

Which ions are removed depends on the resin chemistry.

For example, a conventional sodium-cycle water softener exchanges hardness ions such as calcium and magnesium for sodium.

A demineralisation system uses different resin types to remove both positively and negatively charged ions from the water.

Once the resin has exhausted its exchange capacity, it is regenerated using the appropriate chemical solution so that it can be returned to service.

Cation and Anion Exchange

Dissolved salts in water separate into positively and negatively charged ions.

These are known as cations and anions.

Typical cations include:

• Calcium
• Magnesium
• Sodium
• Potassium
• Iron
• Manganese

Typical anions include:

• Chloride
• Sulphate
• Nitrate
• Bicarbonate
• Silica species

Ion exchange resins are selected according to which of these ions need to be removed.

Water Softening

Water softening is one of the most common applications of ion exchange.

A sodium-cycle softener removes hardness-forming calcium and magnesium from the water and replaces them with sodium.

The total dissolved solids are not substantially reduced.

The hardness has simply been exchanged.

Softening is commonly used for:

• Boiler feedwater
• Reverse osmosis pretreatment
• Cooling systems
• Process water
• Food and beverage production
• Laundry and washing applications
• General industrial utilities

Once the resin becomes exhausted, it is regenerated using sodium chloride brine.

Correct softener design considers much more than vessel diameter.

We calculate resin volume and regeneration frequency from factors including:

• Incoming hardness
• Required flow
• Daily water consumption
• Resin operating capacity
• Regeneration level
• Peak demand
• Service velocity
• Pressure drop
• Required redundancy

A softener should be sized around both flow rate and ionic load.

Duplex and Triplex Softening

Where a continuous supply of softened water is required, multiple vessels can be used.

Typical arrangements include:

Duplex Duty/Standby

One vessel supplies softened water while the second is available during regeneration or as standby capacity.

Duplex Duty/Duty

Both vessels can operate together where higher flow is required, with the control system managing regeneration according to demand.

Triplex Systems

Three vessels can provide duty/duty/standby, duty/duty/duty or other operating philosophies depending on the required flow and redundancy.

Hydra-Clear designs the sequencing and controls around the actual site requirement rather than applying the same configuration to every application.

Dealkalisation

Dealkalisation is used where reducing alkalinity is more important than removing all dissolved salts.

This can be particularly useful in boiler applications.

Depending on the process selected, dealkalisation can reduce bicarbonate alkalinity and therefore help reduce carbon dioxide generation within the steam system.

Potential benefits can include:

• Reduced boiler chemical demand
• Lower condensate corrosion risk
• Reduced carbon dioxide loading
• Improved boiler-water control

The most appropriate process depends on the incoming water chemistry and boiler operating conditions.

Demineralisation

Where substantially lower conductivity is required, cation and anion exchange can be combined to remove dissolved mineral salts from the water.

A conventional demineralisation system normally contains separate cation and anion resin stages.

Cation Stage

The cation exchanger operates in the hydrogen form.

Positively charged ions such as calcium, magnesium and sodium are exchanged for hydrogen ions.

The salts present in the feedwater are therefore converted into their corresponding acids.

Anion Stage

The water then passes through an anion exchanger.

Negatively charged ions such as chloride, sulphate and bicarbonate are removed and exchanged for hydroxide ions.

Hydrogen and hydroxide then combine to form water.

The result is water containing dramatically lower concentrations of dissolved ionic material.

Twin-Bed Demineralisation

A twin-bed demineralisation system uses separate cation and anion vessels.

This arrangement can provide very low conductivity water while allowing each resin type to be regenerated independently.

Depending on the required performance, systems may include:

• Strong acid cation resin
• Weak acid cation resin
• Strong base anion resin
• Weak base anion resin
• Degassing
• Multiple ion exchange stages
• Final polishing

The exact arrangement is determined by the feedwater chemistry and required product-water quality.

Mixed-Bed Polishing

Mixed-bed ion exchange combines cation and anion resin within the same vessel.

Because the two resin types are intimately mixed, the water effectively passes through a very large number of alternating cation and anion exchange stages.

This allows extremely low concentrations of ionic contamination to be achieved.

Mixed beds are commonly used as a final polishing stage downstream of:

• Reverse osmosis
• Conventional demineralisation
• High-purity water systems

Applications include:

• Pharmaceutical manufacturing
• Electronics
• Laboratory water
• Power generation
• High-pressure boiler systems
• High-purity process water

Ultrapure Water

At 25°C, theoretically pure water has a resistivity of approximately:

18.2 MΩ·cm

which corresponds to a conductivity of approximately:

0.055 µS/cm

These values are at the extreme end of high-purity water production.

Achieving and maintaining water at this level requires considerably more than simply installing an ion exchange vessel.

Water temperature, dissolved carbon dioxide, organic contamination, microbiological control, storage, pipework materials, instrumentation and the distribution system can all influence the measured water quality.

For genuinely high-purity applications, ion exchange is therefore normally engineered as part of a complete water treatment and distribution system.

Reverse Osmosis + Ion Exchange

Ion exchange and reverse osmosis are not competing technologies.

They are often at their most effective when used together.

Reverse osmosis can remove the majority of the dissolved ionic load before the water reaches the ion exchange stage.

This dramatically reduces the load placed on the polishing resin.

A treatment train might therefore use:

Pretreatment → Reverse Osmosis → Mixed Bed Polishing

or:

Pretreatment → Reverse Osmosis → EDI → Final Polishing

depending on the required water quality.

Using RO upstream can significantly extend resin run lengths and reduce the quantity of regeneration chemicals required compared with treating the full raw-water ionic load using ion exchange alone.

Counter-Current Regeneration

The method used to regenerate an ion exchange vessel can have a significant influence on chemical efficiency and treated-water quality.

In conventional co-current regeneration, regenerant flows through the resin in the same direction as the service flow.

In counter-current systems, the regenerant travels in the opposite direction.

Correctly designed counter-current regeneration can provide:

• Improved regeneration efficiency
• Reduced chemical consumption
• Lower ionic leakage
• Improved product-water quality

The appropriate regeneration philosophy depends on the resin, vessel configuration and required performance.

Organic Scavengers

Ion exchange-type resins can also be used to remove naturally occurring organic material from water.

Organic scavenger systems are particularly useful where colour, tannins or other dissolved organic compounds create problems for downstream treatment.

Applications can include protection of:

• Reverse osmosis membranes
• Anion exchange resin
• High-purity water systems
• Industrial process equipment

Resin selection is based on the type and concentration of organic contamination present.

Selective Ion Exchange

Not every application requires complete demineralisation.

Specialist resins can be selected to preferentially remove particular contaminants.

Depending on the application, selective ion exchange can be used for removal or reduction of substances such as:

• Nitrate
• Heavy metals
• Ammonium
• Boron
• Selected dissolved metals
• Specific process contaminants

The effectiveness of selective ion exchange depends heavily on competing ions within the water.

For that reason, resin selection should always be based on a representative water analysis.

Regeneration Is Part of the Process Design

Ion exchange plants operate in cycles.

A properly engineered system therefore needs to consider what happens during regeneration as carefully as what happens during normal service.

Depending on the resin and application, regeneration may involve:

• Sodium chloride
• Hydrochloric acid
• Sulphuric acid
• Sodium hydroxide

The system design must consider:

• Regenerant concentration
• Chemical volume
• Flow rate
• Contact time
• Slow rinse
• Fast rinse
• Waste neutralisation
• Drain capacity
• Chemical storage
• Safety
• Automation
• Vessel availability during regeneration

Poor regeneration control wastes chemical and reduces resin performance.

Resin Capacity and Run Length

An ion exchange vessel does not have an unlimited treatment capacity.

The amount of water that can be treated between regenerations depends on the ionic load applied to the resin.

Hydra-Clear can calculate predicted run length from:

• Water analysis
• Flow rate
• Daily consumption
• Resin type
• Resin volume
• Operating capacity
• Regeneration level

This allows the system to be designed around the required operating cycle rather than simply specifying a nominal vessel size.

Designing for Low Operating Cost

Ion exchange can be extremely effective, but poor system design can result in unnecessary consumption of:

• Salt
• Acid
• Caustic
• Water
• Energy
• Resin

We therefore assess the relationship between capital cost and long-term operating cost.

For example, increasing resin volume may increase the initial equipment cost but reduce regeneration frequency.

Counter-current regeneration may reduce chemical demand.

RO pretreatment may dramatically extend mixed-bed resin life.

The correct solution depends on the complete operating economics.

Ion Exchange System Control

Modern ion exchange systems can be fully automated.

Hydra-Clear systems can incorporate Siemens PLC and HMI control for monitoring and sequencing functions including:

• Service operation
• Vessel changeover
• Regeneration initiation
• Backwash
• Chemical draw
• Slow rinse
• Fast rinse
• Conductivity
• Flow
• Pressure
• Tank level
• Regenerant level
• Alarm management

Regeneration can be initiated by:

• Treated-water volume
• Time
• Conductivity
• Calculated capacity
• Operator command

For critical systems, automatic duty/standby sequencing can maintain treated-water production while one vessel regenerates.

Resin Replacement & Servicing

Ion exchange resin has a long service life when operated correctly, but it does not last indefinitely.

Resin performance can deteriorate because of:

• Organic fouling
• Iron contamination
• Oxidation
• Osmotic or mechanical damage
• Chemical attack
• Resin loss
• Poor regeneration
• Long-term degradation

Hydra-Clear provides resin inspection, replacement and recommissioning for both our own systems and third-party water treatment equipment.

Our engineers can undertake:

• Resin removal
• Vessel inspection
• Internal distribution inspection
• New resin installation
• Resin classification and selection
• Regeneration
• Rinsing
• Performance testing
• Recommissioning

We can also investigate poor-performing ion exchange systems before automatically recommending resin replacement.

Sometimes the resin isn't the problem.

Ion Exchange Resin Supply

Hydra-Clear can supply a wide range of ion exchange media including:

• Strong acid cation resin
• Weak acid cation resin
• Strong base anion resin
• Weak base anion resin
• Softening resin
• Mixed-bed resin
• Organic scavenger resin
• Selective ion exchange resins

We also maintain stocks of commonly used cation and anion resins for service and replacement requirements.

Ion Exchange or Reverse Osmosis?

The correct technology depends on the water and the required product quality.

Ion exchange can provide advantages including:

• Very low final conductivity
• Selective ion removal
• High-quality polishing
• Effective hardness removal
• Low electrical energy requirement

Reverse osmosis can provide advantages including:

• Removal of a broad range of dissolved contaminants
• Reduced chemical regeneration
• Continuous separation
• Significant reduction of ionic loading before polishing

In many applications, the best solution uses both technologies.

We design the treatment train around the requirement rather than trying to make one technology solve every problem.

Talk to a Water Treatment Engineer

If you are considering water softening, demineralisation, mixed-bed polishing or another ion exchange process, send Hydra-Clear your incoming water analysis, required treated-water quality and flow requirements.

We can calculate the ionic load, determine the appropriate resin process and design the treatment system around the actual application.

The vessel holds the resin. The engineering determines how well it works.

Call 0800 999 6770 or contact Hydra-Clear to discuss your ion exchange application.