How they work

• Intake

Raw water is drawn into a plant through gravity and/or pumps and is usually passed through a metal grate or mesh screen to prevent large objects from entering the system.

• Clarification

The water then continues for clarification, which is the step used to remove suspended solids from a solution.

• Disinfection

If biological contamination and/or water potability is a concern, the water may then be disinfected to remove any pathogens.

• Lime softening

In some cases, a lime softening step may be added to reduce hardness in streams with high mineral content.

• Ion exchange (IX)

In some cases, the raw water treatment system may include an IX unit for hardness removal, or other specialized treatment needs.

• Distribution

Following treatment, the water is pumped or otherwise routed for use elsewhere in the facility.

How they work

An effective boiler feed water treatment system works by both removing harmful impurities prior to entering the boiler as well as controlling the acidity and conductivity of the water. While treatment trains vary, a typical system will consist of primary treatment and possibly polishing depending on the boiler pressure, steam use, and chemistry of the boiler feed and makeup water.

• Makeup water intake

As boilers are used, they lose water to steam consumption, loss of condensate return, and leaks. This water must be replaced with what is known as makeup water. Makeup water may be drawn from a treated city supply or a raw water treatment system.

• Filtration

The stream is typically filtered through one or more filtration units for removal of sediment, turbidity, and organic material.

• Softening

IX is often used for removing hardness from boiler feed water, including bicarbonates, sulfates, chlorides, and nitrates.

• Dealkalization

Alkalinity can cause foaming and carryover in boilers, as well as corrosion in piping. Therefore, boiler feed streams are often treated with strong anion IX, or weak acid IX followed by degasification, which serve to remove bicarbonate, sulfate, and nitrate ions, reducing pH.

• Reverse osmosis (RO) and nanofiltration (NF)

RO and NF are not always used for boiler feed water treatment, however, they can be useful for removal of bacteria, salts, organics, silica and hardness. RO and NF are both types of membrane filtration, meaning that they employ a semi-permeable membrane to capture any contaminants too large to fit through their pores, while allowing water molecules to flow through.

• Primary ion exchange (IX)

For large volumes of water or high pressure boilers, deionizers may be used instead of membrane filtration.

• Deaeration or degasification

Deaeration/degasification is the removal of dissolved oxygen and carbon dioxide from the liquid stream, which is important for preventing corrosion.

• Polishing

Depending on the boiler requirements, polishing technologies may be required. This step can follow RO or primary IX. Typical polishing technologies include mixed bed deionization (DI), electrodeionization (EDI), or offsite regenerable DI.

• Distribution

Following all treatment steps, the boiler feed water is piped to the boiler, where it is heated to form steam. The condensate can then be combined with treated makeup water, and the cycle begins again.

Although these steps represent common boiler feed water system trains, it is important to understand that an individual boiler’s unique makeup/chemistry is an extremely complex calculation that will dictate the technologies needed.

How they work

An effective cooling tower water treatment system works by removing harmful impurities in line with the manufacturer recommendations for water quality requirements for the type of cooling tower used

• Makeup water intake

As water circulates through a cooling tower system, a portion is lost to evaporation, bleed to drain, and leaks. This water must be replaced with what is known as makeup water. Like boiler makeup water, cooling tower makeup water may be drawn from a variety of sources, whether raw water, municipal water supplies, wells, or recycled plant wastewater. In some cases, source water must also be treated for hardness or silica removal and/or pH adjustment.

• Filtration

Upon intake, the stream is typically filtered through one or more filtration units for removal of sediment, turbidity, and organic material.

• Softening

If there’s high hardness in the source/makeup water, a softening resin or membrane softener can be used. These contaminants, if present, will otherwise cause scale deposits and rust.

• Chemical addition

Next, the stream will usually undergo some form of chemical treatment, which can include the application of corrosion inhibitors to neutralize acidity; algaecides or biocides to reduce growth of biological contaminants; and/or scale inhibitors to prevent contaminants from forming scale on pipes and other components.

• Side-stream filtration

Many cooling towers are designed to recirculate water following use. If this is the case, a side-stream filtration unit will be helpful in removing any problematic contaminants that have entered through drift contamination, leaks, etc

• Post-treatment

There are various types of post-treatment options that may be used depending upon plant conditions. If large quantities of water are required for cooling, or if water is scarce at the facility’s location, plants may opt to treat the blowdown water with RO or IX and reuse it.