A common saying in the water treatment industry is that cooling tower manufacturers do not know (or care) about water treatment. Likewise, the cooling tower manufacturer says he knows how to cool water and does not address water treatment.
"Should filters be used on cooling water systems?" is a question I am
often asked. So what do I say? Well, it depends on a number of
considerations, but my first response is absolutely an unqualified
"Yes." Filters are a cost-effective investment. Filters remove
suspended solids from the cooling water and thus reduce many problems.
So, what are these considerations?
"Do all closed chilled water systems need water treatment?" is a
question I have been asked numerous times. Why is it asked? Well, I
know of persons who have been in charge of closed chilled water systems
that do not use any water treatment chemicals whatsoever -- and operate
trouble-free.
An oxidizing microbiocide is as any chemical that is an oxidizing
agent. They are chemicals that kill and destroy not only the
microorganism but also the nutrients found in cooling water. Their
action is essentially "wet oxidation" or "burning" under water. No
microbiological organism is immune to this action -- provided that the
oxidizing biocide can reach the microorganisms.
Cooling water microbiological control is important all year long -- and
even more important during the warm days of summer. This is not only
due to warmer water temperatures but also due to more nutrients and
microbiological organisms entering the cooling tower system from the
air.
In addition to deposit-forming microorganisms and iron-depositing,
sulfate-reducing and nitrifying bacteria, there are two other
mechanisms that cause MIC: denitrifying bacteria and acid producers.
What is MIC? It stands for microbiologically influenced corrosion --
yes, corrosion in water systems due to microbiological organisms. These
microbes do not "eat" metals such as mild steel, stainless steel,
copper alloys or galvanized steels. Rather, they produce byproducts
that are corrosive to these metals.
Cooling tower water systems are composed of three major sections:
cooling tower, chiller or heat exchangers, and piping. Each section
must be considered when designing a cooling tower water system. Often,
initial capital cost of equipment is a strong driving force. Little, if
any, water treatment costs are incorporated in the design and equipment
purchase decision.
Part 1 identified the steps in setting up a
corrosion monitoring program, including the use of corrosion coupons. Two additional corrosion-monitoring techniques are available: electric
resistance (ER) and linear polarization resistance (LPR). In Part 2, I'll look at these methods in detail.
These are some of the common questions end users and owners often ask.
However, often they are asked after equipment replacement has occurred
or about to be due to corrosion. Here, I hope to
provide you some guidelines and helpful advice for corrosion testing of
the components in your cooling water system so that they will last
longer.
Water conservation may be achieved by simply increasing the cycles of
concentration. This has been made possible by the development of
outstanding deposit control inhibitors -- those known as crystal
modifiers. Another method currently gaining popularity for water
conservation is the use of "used" waters in place of fresh, often
potable, waters. Used waters are any water that has been already used
for other means and often is discharged.
How do you select the cooling water treatment program to best protect
your cooling tower water system? Is it the water quality? The entire
system metallurgy? The operating characteristics (i.e., maximum water
temperature, minimum water flows, and/or periodic shutdown operation)?
Or, is it simply to select the “multicomponent” chemical blend that
works for “all” conditions -- one that sounds like the best?
vaporative cooling water systems offer this opportunity in two ways:
first, by reducing fresh water requirements by using less water and
second, by utilizing "used" waters in place of fresh waters. In this
column, I will write about conserving fresh water.
Detailed information is needed on all cooling-water-contacted equipment
prior to ever considering water quality or water treatments. The design,
materials of construction and operating conditions are critical factors
that will greatly influence the selection of acceptable water treatment
chemicals.
Paul Puckorius continues his series on cooling water treatment vs. cooling systems with a look at the heat transfer equipment in a process cooling system.
Selecting and implementing a water treatment program does not initially
require knowledge of the water quality. Yet this is often what is done.
Instead, the first step is to identify the various components that the
cooling water will contact that require protection from deposits and
deterioration.
Once-through cooling water systems are similar to drinking water systems: The water comes in, is
used and discharged. Once-through cooling water systems generally
utilize river, lake or ocean water where plentiful supplies are
available.
The objective of all cooling
water treatment is not to treat the cooling water -- it's to protect
the equipment. Paul Puckorius begins a series on proper water treatment.
Condenser tube metallurgy requires better water treatment. Often, carbon steel tubes are selected due to costs. If this is done,
the condenser's water treatment requirements are considerably different
than with copper tubes. It requires special startup and routine water
treatment chemicals and procedures. If not implemented, severe
corrosion and early carbon steel tube failure likely will occur.
Water treatment specialist and columnist Paul Puckorius explains that how you treat your cooling tower depends on its materials of construction as well as its components.
Water conservation via water reuse has environmental and economical benefits. The key to successful water reuse is to identify the quality and quantity of used water and their impact on the process that will use it.
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