If you have a boiler as part of your process system, you need to consider your water treatment options for the boiler feed water. In this post, we will explain the advantages and disadvantages of the various water treatment options.

Water Softener

A water softener uses zeolite resin to treat hard water. The zeolite needs to be regenerated for reuse.

Disadvantages:

• No reduction in total suspended dissolved solids or in levels of silica and anions such as chloride or alkalinity, resulting in relatively poor water quality vs. other technologies
• Inefficient regeneration process leads to high salt usage and a negative environmental impact from high salt discharge

Advantages:

• Inexpensive
• Simple
• Durable
• Safe (at least for people, if not for the environment)

Two-Stage or Mixed Bed Deionization (DI or MBDI)

This is an ion exchange method of treating water with cation and anion resins, either by vessels arranged in series or (in the case of mixed bed) with a single vessel containing both resins. These resins must be regenerated as the cations and anions (respectively) are consumed.
 
Disadvantages:

• Hazardous chemicals required for regeneration of the resins
• High and variable chemical costs
• Manpower intensive
• High total dissolved solids

Advantages:

• Excellent reduction of all dissolved solids
• Good for high pressure applications
• Can achieve high purity

Portable Exchange DI Tanks

These systems treat water with a bed of cation and anion resins. Usually a two-tank system, the tanks are sent off-site for treatment.
 
Disadvantages:

• High and variable costs
• Limited service centers for tank treatment
• High TDS means high operating costs

Advantages:

• Same as a Mixed Bed DI
• No chemicals required on-site

Reverse Osmosis

This purification process involves pressure-driven semi-permeable membranes to separate ions and particulates from a water stream. The process is driven by pressure over and above osmotic pressure of the feed solution. An anti-scalant, coupled with high membrane crossflow velocities, is needed to prevent fouling and enable long runs between cleanings. RO generates a purified permeate stream (filtrate) and a concentrate stream (reject).
 
Disadvantages:

• Not adequate (as a stand-alone) for high-pressure boilers
• High electrical costs
• Significant reject steam volume
• Doesn’t reject dissolved gas (such as CO2)
• Susceptible to bio-fouling
• Requires pre-treated water (no chlorine and low levels of suspended solids)

Advantages:

• All solids are rejected
• Long periods between cleaning
• Operating costs not affected by TDS
• Enables high cycle boiler operation
• Doesn’t require strong acids or bases
• Not labor intensive
• Can be used ahead of MBDI or Portable Exchange DI systems, significantly reducing solids loading and thus operating costs

Caloris is a provider of RO membrane filtration systems. The main equipment involved with such a system usually involves pre-treatment pumps for chemicals, a pre-filter, feed pump and the RO unit itself.
 
Here are a few examples of how to incorporate an RO system into your boiler feed water process:

• RO prior to an existing water softener — this reduces total dissolved solids and reduces the need for regeneration drastically
• RO replacement of water softener
• Double-pass RO prior to existing mixed bed DI — this reduces operating costs by reducing the need for regeneration
• Double-pass RO and electrodeionization (EDI) — this replaces a resin-based system
• RO to replace an abandoned blowdown heat recovery system — the RO is much more economical than the heat recovery system

Which Water Treatment System is Right for You?

For help with determining which water treatment system will work best in your treatment process, contact Caloris today by calling 410-822-6900 or send email to problem.solved@caloris.com.