Water Quality Management | Berg Chilling Systems - Part 2

Benefit from Improved
Water Quality Management
Part II

Medium Hardness Water
Great Lakes/St. Lawrence River Water
Moderately Hard, 120-140 ppm, pH of 7.6-7.8

Corrosion inhibitors are required for
iron and copper, and scale inhibitors
are necessary when used in cooling
tower water systems.

Treated water from these
sources is ideal for closed water
systems (chilled water) mold
cooling applications and can be
heated in extruder barrels or
temperature control units
without forming scale deposits.

The water provides a very
economical makeup water for
cooling tower systems. When
properly treated cycles of
concentrations can run up to 3-4.

However at 3-4 cycles of
concentrations scaling will occur
when in contact with hot heat
transfer systems.

Low Hardness Water
Interior Lakes/ Runoff Water
Hardness levels vary from 30 to 80 ppm, pH levels of 7.2to 7.6 are common

Low hardness water is also
ideal for closed water systems when
treated with corrosion inhibitors, and scale
formation will not occur when heated.

In tower water systems low
hardness makeup water
allows for up to six cycles
of concentration making for
reduced chemical costs than
medium hardness waters.

Low hardness tower water is
less susceptible to scale
formation when heated than
medium hardness water

High Hardness Water
Well Water
Well water is used when low or medium hardness water in unavailable. The high hardness
makes well water only appropriate for closed water applications.

Some well waters may also
contain corrosive contaminants
such as high levels of chlorides
and sulphates, both of which can
make chemical treatment difficult.

Well water can be used as
tower water make-up but
only with an aggressive
chemical or
chemical/softening
programmes.

Any well water application
requires regular, daily testing and
monitoring of equipment and
chemical levels. Equipment
breakdown or chemical program
upset will cause rapid scaling in
all heat transfer equipment.

Glycol Systems
Glycol is commonly used with water in chillers to provide freeze protection. The percentage of glycol
depends on the coldest temperature that the glycol reaches during operation.

In a chiller this temperature is
normally the saturated suction
temperature in the evaporator,
and normally this temperature is
10°F below the chiller set point
temperature.

With this fact in mind, since
water freezes at 32°F we only
use glycol when the chiller set
point is below 42°F, or if we are
cooling a coil that is exposed
to winter outside air.

Some glycol products
contain a corrosion inhibitor
however glycol should not
be used only for this
purpose.

Its presence also adds
viscosity to the cooling fluid
requiring higher hp pumps
and higher flow rates to do
the same as a pure water
system. It is only to be used
for freeze protection.

There are generally two glycols that
are used – propylene glycol, a
food-grade and non-toxic glycol and
ethylene glycol which although is
toxic to humans and requires special
handling and spill containment
practices.

Glycol at concentrations above
1-2% is toxic to bacteria. At low
concentrations (0.1-1%) glycol is
a nutrient for bacteria, and the
by-product of the bacterial
process is very acidic.

Anytime you drain a glycol
system you must do a thorough
system flushing and immediately
treat with a corrosion inhibitor.

Water Quality and System Design:

For most types of plastics the molds require
cool water temperatures to minimize part
cycle times and maximize productivity.
Water Quality and System Design:

Since the required temperatures for these molds cannot be reliably
maintained with cooling towers during warm weather, and since the mold
passages are small and easily fouled most plastic plants dedicate a chiller to
the molds and plastic processing sections of extruders and use tower water
for the shell and tube heat exchangers for hydraulic cooling, chiller
condensers, air compressors, extruder feed throats and gear boxes. The
exchangers in this equipment are usually shell and tube that are easily acid
washed if cleaning is necessary.

Smart plant water system design uses chiller cooling only as needed, and
maximizes energy savings by using water cooled equipment whenever
possible. Tower water (ambient) cooling costs a fraction of the operating
expense of a chiller. Many plants select water-cooled chillers, air compressors
and air dryers to put onto a cooling tower and dedicate a chiller for only cool
water applications.

Temperature set points for these may
be between 140 - 180°F.
The high concentration of calcium in
the tower water will cause scale
formation where tower water directly
contacts the heaters and hot heat
exchange surfaces.
Precipitated scale will also migrate
downstream to foul molds and other
process equipment.

If your plant has medium hard
make-up plant water, or if only
very clean water can be
tolerated in your molds and
processing equipment, and
your exchangers can be
adequately cooled with tower
water there are solutions
available if you do not have a
spare chiller available.

Softening
Softening uses a sodium zeolite resin that can be regenerated by brine to remove all
calcium hardness from the make-up water.

This will eliminate any hardness
scale formation when the tower
water contacts hot heat transfer
surfaces, however the softened
water changes its balance from
being scaling water to corrosive
water.

The solution is to install a small valved by-pass around the
softener and maintain just enough hardness in the water to
remove the corrosiveness and low enough in concentration
to not precipitate when heated. This is a relatively low cost
solution however be cautioned that thorough monitoring by
the plant on a daily basis must be performed.

Clean Water Tower Systems
Safe, reliable and worry-free plant operation can be assured by converting your tower
system to a Clean Water Tower System.

An efficient plate and frame
exchanger is installed in the
tower system with standard 85°
F/95°F water providing the
cooling on one side of the
exchanger and a closed loop
process water system operates
on the other side.

The process equipment sees a
minor increase in temperature
and the cooling water system
becomes a standard closed loop
system that can tolerate high
hardness without scaling.

The difference between this water and tower water from the
same source is that there will be no make-up to replenish the
scaling process, the hardness level is a fraction of the tower
water hardness, there is no contact with the air so there is
none of the particulate present to cause fouling or deposition,
and the water treatment is a simple, add as required process
assuming that the system stays tight.

Other Solutions:
Reverse osmosis, deionized water processes and
other forms of water conditioning can remove
hardness and other unwanted contaminants.
There is usually a high cost to buy, install, and
operate this equipment.

You may also encounter the non-chemical devices
that claim to eliminate all chemical treatment,
remove existing scale, and run without the need to
do daily plant tests.

Many come with testimonials and references that
are hard to trace, and may sound very convincing.
Caution and consultation before you decide to try is
imperative.

Berg Chilling Systems can assist you in achieving
your goal of maximum productivity, long
equipment life and efficient plant equipment
operating expense.

For more information on
BERG Chilling Systems INC.
please visit:
www.berg-group.com

Water Quality Management | Berg Chilling Systems - Part 2

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