DM Plant, Softener and Condensate Polishing

Ion-exchange resins that remove hardness or every dissolved salt — for boilers, power and process.

What ion exchange does

Ion-exchange resins swap unwanted ions in water for harmless ones and are then regenerated with chemicals. A softener swaps calcium and magnesium (hardness) for sodium using brine. A demineralisation (DM) plant removes essentially all dissolved salts: a cation unit exchanges metal ions for hydrogen, a degasser vents carbon dioxide, an anion unit exchanges the remaining anions for hydroxide, and a mixed bed polishes to below 0.1 µS/cm conductivity. Condensate polishing units (CPU) do the same for returned steam condensate in high-pressure boilers.

Stages and units

Process flow — typical sequence

PretreatmentFiltration and, where needed, RO ahead of DM to cut regeneration chemical use.
Softener (SAC in sodium form)Removes hardness; regenerated with sodium chloride brine.
Strong acid cation (SAC) unitExchanges Ca, Mg, Na for H⁺; regenerated with hydrochloric acid.
DegasserBlower-aerated tower strips dissolved CO₂, reducing anion load.
Strong base anion (SBA) unitExchanges chloride, sulphate, silica, bicarbonate for OH⁻; regenerated with caustic soda.
Mixed bed (MB)Intimately mixed cation and anion resin for final polishing to ultrapure quality.
Regeneration systemAcid and alkali dosing, measuring tanks, neutralisation pit for spent regenerant.
Condensate polishingFilters and mixed beds handle returned condensate with iron and trace contaminants.

Plant types

Softener

Single or twin for continuous supply; boilers, cooling towers, process.

Two-bed DM

SAC + degasser + SBA — general process and low/medium-pressure boilers.

Two-bed + mixed bed

High-pressure boilers, power, electronics.

RO + mixed bed / EDI

Modern low-chemical route to ultrapure water.

CPU

Condensate polishing for utility and captive power boilers.

Resin replacement and revamps

Assessment, resin selection and regeneration optimisation of existing plants.

Applications

Boiler feed and power plants: Scale-free tubes, lower blowdown, protected turbines.
Pharmaceutical purified water: Mixed bed or EDI after RO under a validated system.
Electroplating, electronics, laboratories: Rinse and process water at defined conductivity.
Textile, chemical, food processing: Softened process water for dyeing, reactions and CIP.

How we deliver a DM or softener plant

Feed analysis and outlet specification → resin volume, run length and regeneration design → vessel, internals and piping design → supply, erection, commissioning → regeneration optimisation and resin health monitoring under O&M.

Frequently asked questions

What is the difference between a softener and a DM plant?

A softener exchanges calcium and magnesium for sodium — hardness is removed but TDS stays. A DM (demineralisation) plant removes all cations and anions with cation and anion resin beds, giving low-conductivity water for boilers and process.

DM plant or RO+EDI — which should I choose?

For low-TDS feed and moderate flow, a two-bed or mixed-bed DM plant is simple and cheap. For high-TDS feed or where regeneration chemicals are a problem, RO followed by EDI or mixed bed uses far fewer chemicals. We compare both on life-cycle cost.

What outlet quality does a mixed bed give?

Typically below 0.1 µS/cm conductivity and silica below 20 ppb — suitable for high-pressure boilers, turbines and electronics.

What is condensate polishing?

Treatment of returned steam condensate to remove iron, corrosion products and trace salts before it goes back to the boiler — protects high-pressure boilers and turbines.