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What is a Cooling Tower Water Treatment?2020-09-21T23:08:50-07:00

If you use a cooling tower within your industrial facility, you will likely need to pair it with a water treatment system, of which there are many different types. The presence of a water treatment system allows for more efficient processes in the cooling tower as well as a longer lifespan for equipment. The problems of untreated water are many and can include the development of corrosion, scaling, organic growth, and fouling.

A standard water treatment system for cooling towers is a combination of technologies that works to get rid of impurities within the blowdown, circulation water, and feed water.

The exact configuration of your water treatment system depends on numerous factors, which include the type of cooling tower within your facility, regulatory requirements pertaining to discharge, the quality of feed water, the exact chemistry of the circulatory water, and the kind of heat exchanger that’s situated in the cooling tower. If you’re currently looking at different water treatment systems for cooling towers, this guide should assist you in making the right decision.


Key Takeaways:

  • Cooling tower’s are essential for your water treatment system within your industrial facilities.
  • We discuss how the cooling tower’s work and how to know if you need one for your type of facility.
  • Understanding the process of a cooling tower will help you understand the water treatment system as well.

How Does a Cooling Tower Water Treatment System Work?

There are many different types of water treatment systems that you can pair with your cooling tower. The processes of these treatment systems can vary depending on the cooling tower requirements as well as the quality of the circulation water and feed water. While these processes can vary, there are some basic steps that are included with most water treatment systems.

Makeup Water Intake

Makeup water is a kind of water that replaces leaked and evaporated water from a cooling tower. This process begins by drawing the water directly from a specific source, which could be well water, city-treated effluent, city water, raw water, and other kinds of surface water. In some situations, the quality of the water may be high enough for you to forego the water treatment process.

In the event that a water treatment system is necessary, the system will be used to remove silica and hardness. It can also be used for the stabilization of the pH levels in the water. You can test the pH levels of water with a pH sensor. When this phase of the water treatment process occurs, the cooling tower evaporation cycles will be stabilized. The bleed rate of the water will also be minimized.

Filtration and Ultrafiltration

The next and arguably most important step of the the process is to filter the water through filtration or ultrafiltration, both of which help to remove suspended particles within the water. These particles can include turbidity, sediment, and other kinds of organic matter. This step of the water treatment process should occur in the early stages to protect the resins and membranes in the system from fouling later on. If you opt for ultrafiltration, it’s possible to remove enough suspended particles to reach less than a single micron of particles.

Water Softening/Ion Exchange

If you find that your makeup water or source water has a high amount of hardness in it, you may need to use ion exchange or water softening processes to get rid of this hardness. This system works by using a softening resin, which will be charged directly by a sodium ion. When the hardness passes through the resin, the iron, calcium, or magnesium molecule will be grabbed by the resin before the sodium molecule is released into the water.

If these contaminants remain in the water, rust and scale deposits will develop, which only serves to reduce the efficiency of the cooling tower. When you want to measure the hardness of the water in your cooling tower, you can do so by identifying the conductivity of the water. These measurements can be taken with a standard conductivity sensor.

Added Chemicals

It’s at this phase of the process that chemicals are typically added to the water. These chemicals can include:

  • Scale inhibitors – Inhibitors like phosphoric acid can prevent the formation of scale deposits
  • Corrosion inhibitors – Inhibitors like bicarbonates are able to neutralize acidity within the water, which helps to protect any metal components
  • Algaecides and biocide – Chemicals like bromine can lessen the growth of biofilms and microbes

If you perform extensive water treatment before reaching this phase of the water treatment process, it’s likely that you won’t need to use as many chemicals, which can save you a significant sum of money.

Side-Stream Filtration

If the water in your cooling tower will be recirculated throughout the system, the use of a side-stream filtration system can help to remove any contaminants that have entered the water via a leak or drift contamination. Around 10 percent of the water that circulates in your cooling tower will filter through this system.

Blowdown Treatment

The final phase of the water treatment process is centered around treating the bleed or blowdown that’s taken from the tower. Although the exact amount depends on how much water is needed for circulation in the cooling plant, some of the water will be recycled and recovered through ion exchange or reverse osmosis. When treating this water, you can remove any solid waste and other contaminants from the water, which allows the treated water to be sent back to the cooling tower and reused.

There are times, however, when the water from the blowdown must be discharged. This discharge must meet regulatory requirements. If water is scarce in your surrounding area, sewer connection fees could be very high. It’s possible to reduce these costs by using demineralization systems. If the effluent is being sent to the environment, the discharge from the cooling tower bleed will need to meet separate municipal discharge regulations.

How to Know If You Need a Cooling Tower Water Treatment for Your Plant

If you want to be certain that your cooling tower operates efficiently and that the system won’t be damaged, it’s highly recommended that you use a water treatment system in your cooling tower. When the water in a cooling tower isn’t treated, the problems that can result include corrosion and the development of scaling. Over time, the buildup of these issues can lead to lessened productivity, more downtime for the plant, and high replacement costs for damaged equipment, all of which you would do best to avoid.

By treating your cooling tower water and removing any contaminants within, you should be able to boost the efficiency and overall success of your cooling tower. There are numerous reasons why you should consider obtaining a water treatment system for your cooling water. For instance, it’s possible that the pH levels or alkalinity levels in the water are too high or too low. Regulating the pH and alkalinity levels is important to maintain the correct balance and chemistry of the water. Lower pH levels should lessen the possibility of scale development. The pH levels in your water should be monitored constantly to keep equipment corrosion and scale formation at bay.

You might also need a water treatment system because of a high amount of total dissolved solids or hardness in the water. The presence of high amounts of calcium bicarbonate and other solids can create substantial scaling in the cooling tower. If these contaminants aren’t removed or prevented altogether, the solids will spread to heat transfers and other piping throughout the tower, which can cause system failure or downtime. Water should be treated regularly to avoid scale formations. When scale develops, it’s very difficult and costly to remove.

You might want to select a water treatment system if there are microorganisms within the cooling tower water. Microbial growth is particularly common in open-recirculating cooling towers. Eventually, bacteria, algae, and fungi can develop if water is left untreated. It’s also possible that legionella will grow, which can cause people to get sick or even die. To maintain water quality, the growth of any harmful bacteria should be taken care of immediately through water treatment.

Water treatment systems may also be necessary in the event that your cooling tower has an insufficient water supply. If water in your area is scarce, local regulations may prevent you from taking too much water or sending too much water back to the environment. As touched upon previously, connecting sewer and water lines can be very costly, which is why you might want to opt for using demineralization systems to reduce some of these costs.

The costs associated with water treatment systems for cooling towers depend on what kind of water is being treated. The equipment needed for treating feed water can cost you around $50,000-$100,000. These costs can increase to as much as $250,000 in the event that a softener is needed. The treatment of circulation water with a side-stream filtration unit can cost around $100,000-$300,000.

When you want to treat tower blowdown, you can expect the costs for a recovery system to be upwards of $300,000. In the event that regulatory requirements dictate zero liquid discharge, the equipment that you need could cost you anywhere from $3-$5 million. If you’re unsure about which treatments are right for your cooling tower, you may want to consult with a water treatment specialist. Water treatment specialists typically work for public utility companies and municipalities, which is where you can find one to assist you.

The use of a water treatment system is practically essential if you want your cooling tower to run efficiently and for the equipment within to remain undamaged. While there are numerous systems that you can use to treat cooling tower water, understanding the treatment process gives you everything you need to know in order to begin the water treatment process.

Cooling Tower Water Treatment2020-01-27T14:44:51-08:00

Cooling Tower Water Treatment

WHAT IS A COOLING TOWER?

Cooling is the process of thermal energy transfer via thermal radiation, heat conduction or convection. In industrial processes, cooling is achieved through various mechanisms requiring different equipment. The most commonly accepted industrial cooling mechanism is the use of a cooling tower.

Cooling Water

Water is used as the heat transfer medium in cooling towers. Water has several key properties that make it a good choice as a heat transfer medium:

  • High specific heat
  • High heat of vaporization
  • High boiling point
  • Low cost

TYPES OF COOLING TOWER:

While design and operational differences may make it difficult to generalize, there are three basic types of cooling towers:

  • Once-through cooling system
  • Dry Cooling Tower (Closed recirculating system)
  • Wet Cooling Tower (Open recirculating system)

Typically located near a plentiful body of water, once through cooling systems continuously draw water from the source and discharge it after it has passed through the heat exchanger. By contrast, dry cooling towers and wet cooling towers recycle water continuously. Wet cooling towers, or open recirculating systems, differ from dry cooling towers in that the cooling water in a wet cooling tower is exposed to the atmosphere. This allows steam to evaporate each time the cooling water is recirculated.

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Risks of Open Recirculating Cooling

An open recirculating cooling tower design is preferred for promoting large decreases in coolant temperature and where feed water is an expensive resource. One drawback to wet cooling towers is that repetitive evaporation concentrates dissolved and suspended solids. These solids eventually reach a saturation point and begin to precipitate and deposit, leading to scaling or corrosion.

COOLING TOWER SCALING AND CORROSION

Scaling

When insoluble materials, like calcium carbonate, calcium phosphate, magnesium salts and silica, precipitate out of cooling water, they form solid deposits called scale. A layer of scale as thin as 1/64 inch can reduce heat exchanger efficiency by 15%. Reduction in heat exchanger efficiency leads to wasted energy and increased operating costs. Scaling may be promoted by variations in pH, temperature, alkalinity, and concentration of scale-forming constituents in water.

Corrosion

Most metals used in cooling tower systems are very susceptible to corrosion. Surfaces must be kept clean to prevent under-deposit corrosion, which can lead to system failures. Corrosion can be uniformly distributed throughout the system, or it can be localized.

COOLING TOWER WATER TREATMENT

Water may be treated with chemical inhibitors to extend the saturation point of insoluble materials and prevent scaling and corrosion. Water treatment with cooling tower chemicals is preferred to supplying fresh water due to environmental and cost concerns.

Cooling Tower Blowdown

Cooling tower chemicals can increase the saturation point in cooling water. However, there is a limit to the solids concentration or cycle of concentration that can managed by a chemical inhibitor.  For this reason, dissolved solids in cooling water are reduced by removing or “blowing down” a percentage of water from the system and replacing it with fresh water.

Cooling Tower Blowdown Control

Measuring and controlling conductivity allows accurate calculation of blowdown quantities and timing. Measuring and maintaining conductivity is critical, because poor blowdown control may lead to:

  • Scaling and corrosion (when conductivity is too high) or
  • Wasted resources, including water and cooling tower chemicals (when the system could tolerate higher conductivity feed water)

Cooling tower blowdown treatment is managed by using conductivity sensors to monitor cooling tower makeup water. Based on the reading from the sensors, a conductivity controller can open or close valves, allowing automatic cooling tower bleed off or side stream filtration. Cooling tower bleed off is when cooling water with high conductivity levels is discharged from the system. Replacing cooling tower bleed off with fresh source water lowers the conductivity of cooling water.

Side stream filtration is another way of lowering cooling water conductivity, wherein a portion of cooling water is passed through a sand filter, removing some of the solids. Side stream filtration is typically monitored using total suspended solids (TSS) sensors.

The best conductivity sensors for cooling tower water monitoring are typically robust, online sensors with a cell constant of 1.0.

Cooling Tower Water Treatment Sensors and Controllers

ADDITIONAL CONSIDERATIONS

Risks of Closed Recirculation Cooling

Unlike wet cooling towers, dry cooling towers have a relatively low temperature profile and do not rely on evaporation. This reduces the risk of scaling in these systems. However, the risk of corrosion is still significant in dry cooling towers, due to the high solubility of dissolved oxygen at low temperatures. Additionally, low temperatures may promote microbial fouling due to the ability of bacterial populations to survive in the cooling tower environment.

Microbiological Deposits

Makeup water and wind can carry microorganisms into a cooling water system. Under certain conditions, microbial communities multiply in the system, causing problems. Microbiological stress can affect any component in a cooling system. In fact, microbiological stress is often the most significant stress on cooling systems, as it can promote other types of stresses. For example:

  • Corrosion occurs under the bacterial slime layer
  • Inorganic molecules become trapped in the slime layer, leading to scaling

Preventing Microbiological Deposits in Cooling Towers

An effective microbial control program focuses on the specific microbial communities damaging a cooling system. Appropriate biocides may be selected, perhaps in conjunction with dispersants to penetrate and remove deposits. Chlorine oxidizing biocide is commonly used in biocontrol along with some non-oxidizing biocides. In heavy stress systems, bromine or chlorine dioxide serve as more powerful oxidizing disinfectants.

Cooling tower water treatment for microbial control can be monitored one of two ways:

ORP sensors can be used as part of a cost effective treatment control system. However, it is important to note that ORP is not a direct concentration measurement. When treating cooling water with multiple oxidizing biocides, all of the oxidizing species will impact the ORP reading.

Microbiological treatments may require control of pH and other water quality parameters to ensure maximum effectiveness. For example, chlorine oxidizing biocide is most effective between pH 6.5 and 7.5. Cooling tower water treatment systems often include pH sensors and pH controllers to monitor the pH of makeup water.

cooling tower water treatment video

SENSORS & INSTRUMENTATION FOR COOLING TOWER WATER TREATMENT:

The most important instrumentation control parameters in cooling tower water treatment are Conductivity and pH. Additional water quality parameters that should be measured online or sampled frequently include turbidity, total suspended solids (TSS), free chlorine, and oxidation reduction potential (ORP).

Sensorex Cooling Tower Water Treatment Sensor & Control Packages

ParameterImportant for preventingProduct typePart numberDescriptionHow to order
pHMicrobiological fouling, corrosionSensorS272CDTCOnline process pH probe with automatic temperature compensation
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pHMicrobiological fouling, corrosionControllerTX3000pH/mV transmitter and controller
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ORPMicrobiological foulingSensorS272CDTC-ORPOnline process ORP probe with automatic temperature compensation
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ORPMicrobiological foulingControllerTX3000pH/mV transmitter and controller
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Free ChlorineMicrobiological foulingSensorFCL502Amperometric free chlorine sensor with direct 4-20mA output (recommended range = 0-2ppm)
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Free ChlorineMicrobiological foulingLocal DisplayLPM100Local display for sensors with direct 4-20mA output
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ConductivityScaling, foulingSensorCS8300TCOnline contacting conductivity sensor with detachable cable assembly (cell constant k = 1.0)
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ConductivityScaling, foulingControllerCX2000User friendly conductivity transmitter/controller (compatible with CS8300TC)
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