Need for Cooling Water Treatment
When assessing the cost effectiveness of a facility’s water treatment program for open-loop cooling and closed-loop
cooling and heating systems, facility executives should consider the program’s effectiveness more than the cost. In an
age of tight budgets and a slow economy, there may be pressure to trim water treatment costs by reducing or eliminating
one or several applications or procedures, while attending to only the most obvious problems. This can compromising
water chemistry and lead to higher costs.
A preventive approach that is tailored for each facility may cost more initially, but it pays back in system efficiency and
reduced maintenance and repair costs.
Water is an excellent fluid for closed-loop and open-loop cooling and heating systems because it is so efficient at
conducting and transferring heat. It’s also often laden with minerals, organisms and particulates that reduce system
effectiveness and diminish the life of a system’s pipes and tubing. There are three major problems in these water
systems: microbiological growth, corrosion and deposition or scale. All can be controlled by carefully balancing the
chemistry of the water.
Microbiological problems, such as bacterial and algal growth, are primarily a problem in open-loop systems using cooling
towers. Some experts contend that the control of these biological factors is paramount to any effective water treatment
program. The chief biological pests are bacteria and algae, but fungi may be present as well. Control of these is possible
with the use of biocides.
There are two classes of biocides: oxidizing and non oxidizing.
The common oxidizing biocides are chlorine or hypochlorite, ozone and bromine. All provide a broad base of control, but
their effectiveness depends on the water’s pH, a measure of acidity or alkalinity. Chlorine should be used up to a water
pH of 8, above that, chlorine’s effectiveness dramatically decreases. Ozone is not significantly affected by pH.
There are also non oxidizing biocides that are used in closed systems. These chemicals starve, suffocate or eliminate
bacteria’s ability to reproduce. This class of chemicals has a very short half-life at the pH at which most closed systems
operate, making it important to monitor them closely.
Bacteria levels should be tested weekly using simple dip slides and a comparison chart.
Microbiological growth is among a larger class of potential problems called foulants, which includes particulate matter
scrubbed from the air by the cooling tower or minerals in suspension inside closed systems. Some of these materials can
be removed by filtration or by using dispersants, which allow for the materials to coagulate and be trapped by the filters
or removed during blow downs.
The other major categories of problems are scale and corrosion. Corrosion can be a bigger problem in closed systems
while scale is a bigger problem in open systems. Corrosion is more likely to occur in water with a pH rating below 8.5, and
scale is more likely for levels higher than 8.5. But neither scale nor corrosion is exclusive to any one cooling or heating
system, and both must be treated in tandem because one can help fuel the growth of the other.
Scale is caused by precipitation of minerals in the water onto the surface of metal components. The likelihood of a
buildup of scale is determined by the hardness of water, which is based on its composition of minerals, such as calcium
and magnesium. These minerals can be become particularly troublesome in the recirculated water of an open-loop
system as pure water evaporates, leaving behind the minerals.
Scale can be controlled chemically using substances such as polyphosphates, phosphonates and various polymers.
Makeup water also is necessary to replace water lost in the cooling tower. This can dilute concentrations of minerals.
Minerals are also purged during blow downs. The blow down operation itself is critical, and even automatic systems can
fail. Regular inspection and testing are important to prevent blow down failure.
Scale is treated in a couple of ways. Commonly, water softeners are used to pretreat the feed water to remove the
minerals that cause scale. Deionizers may also be used. The system water can also be treated with dealkalinizing
chemicals that lower the pH and change the chemistry of the minerals to lessen their ability to form scale. Then, Halley
says, to avoid corrosion problems, which can occur at a lower pH, the water pH is raised again using other chemicals.
For closed cooling systems, corrosion may be the most damaging water treatment problem to deal with. By pitting metal
surfaces, it provides a habitat for scale and bacteria to form. Although it also takes longer to develop than scale,
corrosion is impossible to fix without replacing parts or equipment, so prevention is key. Corrosion is controlled using a
number of different chemicals, depending on the type of system, discharge regulations and desired pH. The most
common chemical treatment for systems with steel pipes is sodium nitrite. It works by helping to create an iron oxide film
on metal surfaces to protect them, Selby says. The danger in using it, however, is that some bacteria live off of the nitrite.
Where this may be the case, sodium molybdate is used. For less durable copper tubes in a closed system, a class of
chemicals called azoles is used. Zinc can be used to enhance the effect of some of these filming agents, but its use is
sometimes limited by discharge regulations that don’t allow the zinc to be discharged into the wastewater.
Monitoring for corrosion is very important to prevent problems, and not particularly difficult. Closed systems need to be
adjusted less often than open systems, which are subject to more frequent chemical applications because of blow downs.
However, corrosion tests should still be conducted weekly. The equipment to do the tests and the tests themselves are
very inexpensive given the alternative of having to replace tubes or heat exchangers, he says.
While much of water treatment seems like a course in chemistry, other options may help minimize the use of chemicals.
One uses ozone and the other copper and silver as biocides for cooling tower applications. Ozone generators use
ambient air and ionizes it to produce ozone. With copper and silver ion technology, once the proper amounts are set,
there are no other chemicals to add. Copper is effective against algae and silver against bacteria.
Both technologies can eliminate slime build up, which may help reduce one of the conditions for scaling, but neither
ozone nor copper and silver are particularly effective against scale or corrosion build up. Copper also may cross a
narrow threshold of safety and cause galvanic reactions with steel, causing pitting. Plus, there are restrictions on how
copper can be discharged.
Finding the right balance of water treatment options is critical to a safe and effective strategy, and efforts to cut costs
may be an expensive mistake. There’s always pressure to control costs. The problem comes when cost is the emphasis
and effectiveness is not.
When assessing the cost effectiveness of a facility’s water treatment program for open-loop cooling and closed-loop
cooling and heating systems, facility executives should consider the program’s effectiveness more than the cost. In an
age of tight budgets and a slow economy, there may be pressure to trim water treatment costs by reducing or eliminating
one or several applications or procedures, while attending to only the most obvious problems. This can compromising
water chemistry and lead to higher costs.
A preventive approach that is tailored for each facility may cost more initially, but it pays back in system efficiency and
reduced maintenance and repair costs.
Water is an excellent fluid for closed-loop and open-loop cooling and heating systems because it is so efficient at
conducting and transferring heat. It’s also often laden with minerals, organisms and particulates that reduce system
effectiveness and diminish the life of a system’s pipes and tubing. There are three major problems in these water
systems: microbiological growth, corrosion and deposition or scale. All can be controlled by carefully balancing the
chemistry of the water.
Microbiological problems, such as bacterial and algal growth, are primarily a problem in open-loop systems using cooling
towers. Some experts contend that the control of these biological factors is paramount to any effective water treatment
program. The chief biological pests are bacteria and algae, but fungi may be present as well. Control of these is possible
with the use of biocides.
There are two classes of biocides: oxidizing and non oxidizing.
The common oxidizing biocides are chlorine or hypochlorite, ozone and bromine. All provide a broad base of control, but
their effectiveness depends on the water’s pH, a measure of acidity or alkalinity. Chlorine should be used up to a water
pH of 8, above that, chlorine’s effectiveness dramatically decreases. Ozone is not significantly affected by pH.
There are also non oxidizing biocides that are used in closed systems. These chemicals starve, suffocate or eliminate
bacteria’s ability to reproduce. This class of chemicals has a very short half-life at the pH at which most closed systems
operate, making it important to monitor them closely.
Bacteria levels should be tested weekly using simple dip slides and a comparison chart.
Microbiological growth is among a larger class of potential problems called foulants, which includes particulate matter
scrubbed from the air by the cooling tower or minerals in suspension inside closed systems. Some of these materials can
be removed by filtration or by using dispersants, which allow for the materials to coagulate and be trapped by the filters
or removed during blow downs.
The other major categories of problems are scale and corrosion. Corrosion can be a bigger problem in closed systems
while scale is a bigger problem in open systems. Corrosion is more likely to occur in water with a pH rating below 8.5, and
scale is more likely for levels higher than 8.5. But neither scale nor corrosion is exclusive to any one cooling or heating
system, and both must be treated in tandem because one can help fuel the growth of the other.
Scale is caused by precipitation of minerals in the water onto the surface of metal components. The likelihood of a
buildup of scale is determined by the hardness of water, which is based on its composition of minerals, such as calcium
and magnesium. These minerals can be become particularly troublesome in the recirculated water of an open-loop
system as pure water evaporates, leaving behind the minerals.
Scale can be controlled chemically using substances such as polyphosphates, phosphonates and various polymers.
Makeup water also is necessary to replace water lost in the cooling tower. This can dilute concentrations of minerals.
Minerals are also purged during blow downs. The blow down operation itself is critical, and even automatic systems can
fail. Regular inspection and testing are important to prevent blow down failure.
Scale is treated in a couple of ways. Commonly, water softeners are used to pretreat the feed water to remove the
minerals that cause scale. Deionizers may also be used. The system water can also be treated with dealkalinizing
chemicals that lower the pH and change the chemistry of the minerals to lessen their ability to form scale. Then, Halley
says, to avoid corrosion problems, which can occur at a lower pH, the water pH is raised again using other chemicals.
For closed cooling systems, corrosion may be the most damaging water treatment problem to deal with. By pitting metal
surfaces, it provides a habitat for scale and bacteria to form. Although it also takes longer to develop than scale,
corrosion is impossible to fix without replacing parts or equipment, so prevention is key. Corrosion is controlled using a
number of different chemicals, depending on the type of system, discharge regulations and desired pH. The most
common chemical treatment for systems with steel pipes is sodium nitrite. It works by helping to create an iron oxide film
on metal surfaces to protect them, Selby says. The danger in using it, however, is that some bacteria live off of the nitrite.
Where this may be the case, sodium molybdate is used. For less durable copper tubes in a closed system, a class of
chemicals called azoles is used. Zinc can be used to enhance the effect of some of these filming agents, but its use is
sometimes limited by discharge regulations that don’t allow the zinc to be discharged into the wastewater.
Monitoring for corrosion is very important to prevent problems, and not particularly difficult. Closed systems need to be
adjusted less often than open systems, which are subject to more frequent chemical applications because of blow downs.
However, corrosion tests should still be conducted weekly. The equipment to do the tests and the tests themselves are
very inexpensive given the alternative of having to replace tubes or heat exchangers, he says.
While much of water treatment seems like a course in chemistry, other options may help minimize the use of chemicals.
One uses ozone and the other copper and silver as biocides for cooling tower applications. Ozone generators use
ambient air and ionizes it to produce ozone. With copper and silver ion technology, once the proper amounts are set,
there are no other chemicals to add. Copper is effective against algae and silver against bacteria.
Both technologies can eliminate slime build up, which may help reduce one of the conditions for scaling, but neither
ozone nor copper and silver are particularly effective against scale or corrosion build up. Copper also may cross a
narrow threshold of safety and cause galvanic reactions with steel, causing pitting. Plus, there are restrictions on how
copper can be discharged.
Finding the right balance of water treatment options is critical to a safe and effective strategy, and efforts to cut costs
may be an expensive mistake. There’s always pressure to control costs. The problem comes when cost is the emphasis
and effectiveness is not.
Spartan Environmental Technologies
Air and Water Treatment
Air and Water Treatment
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Spartan Environmental
Technologies, L.L.C.
7383 Lauren J Dr
Mentor, OH 44060
USA
Phone: 800-492-1252
Fax: 440-368-3569
E-mail: info@
spartanwatertreatment.com
Technologies, L.L.C.
7383 Lauren J Dr
Mentor, OH 44060
USA
Phone: 800-492-1252
Fax: 440-368-3569
E-mail: info@
spartanwatertreatment.com