Cycling Up Water in a Recirculating Cooling Tower System

The FUNCTION of a cooling tower is to reduce the temperature of an open recirculating cooling water stream so that the water can be reused. The main PURPOSE of a cooling tower is to conserve water.

You will get efficient and thoughtful service from AOSUA.

A cooling tower is a heat rejection device that cools the water by evaporation. This is accomplished by recirculating water and passing ambient air through it. Heat energy is removed through this evaporation process, thus dropping the temperature of the remaining recirculating water. Approximately 970 BTU's are removed from the recirculating water for every pound of water that is evaporated. As the water evaporates in a cooling tower system, it leaves behind all of the dissolved solids that were present in the fresh makeup water used to replenish system losses (due to evaporation and system bleed).  Remember that only water evaporates - any dissolved solids or suspended solids that remain behind in the water become more concentrated as additional water is evaporated. As the concentration of dissolved solids builds up in the recirculating water, it is said to be "cycling up". Here is an example: Our makeup water has a dissolved solids concentration of 500 ppm.  If we allow the dissolved solids in this water to concentrate up in an open recirculating water loop to ppm, we would be running at 3 cycles of concentration.

What happens when some of the minerals that make up the dissolved solids reach their saturation point? We will investigate that situation in our blog next week.

Every closed loop cooling system needs a modest amount of chemical treatment. Most are used once and then checked on yearly. We recommend a sodium nitrite-based inhibitor with biocide to prevent biological contamination. This treatment is usually done at a 1% concentration so not much is needed. These inhibitors will protect both the ferrous and non-ferrous materials in your piping system. Many treatment chemicals come with a colorant which allows the treatment to be visually monitored.

Contact Dry Coolers for a specific suggestion, quantity and pricing.

A properly designed system will have ports at the high points for venting air. While the system is running, vent the high points in the process discharge piping to remove air from the pipe. Most problems with the initial start-up are associated with filling the system and releasing air out of the process piping. Blocked air can resist or prevent proper water flow. We do NOT recommend automatic air release valves. They are too prone to leaks.

If it sounds like there are marbles in your pump, it is more likely caused by cavitation. Cavitation is caused by a rapid change in water pressure that leads to the formation of vapor-filled cavities. These pockets can and will ruin your pump impeller and should be corrected immediately. Poor suction conditions are the most common cause.

Consult Dry Coolers for advice.

Typically, the piping should be sized large enough so that frictional pressure drops within the piping system make up less than 10% of the operating pressure of the system. For example, a system operating at 100 psi should have less than 10 psi of frictional pressure losses in the piping system. Pressure losses in a piping system can be readily determined using the &#;equivalent length&#; method that is found in most piping handbooks. Since most piping systems are not complex, we have developed over the years a simple rule of thumb for sizing the piping. We generally recommend 5-10 feet per second in supply pipe and 3-5 FPS in return pipe.

Don&#;t want to do the math? Consult Dry Coolers for help.

It is often necessary to determine the volume of water held in a cooling system so that appropriate concentrations of corrosion inhibitor and/or glycol can be added. The volume of water in your system is determined by adding the volume of water in your pipes, tanks, cooling equipment, and your process equipment. At your request, Dry Coolers can provide the cooling equipment volumes.

The following table may be used as a guide for determining the volume within pipes.



SYSTEM VOLUME CALCULATIONS:
Volume in Piping
Volume in Tanks
Volume in Equipment
TOTAL VOLUME (GAL)

Are you interested in learning more about cooling tower open loop? Contact us today to secure an expert consultation!

Dow Chemical, 800-447-
Propylene Glycol: DowFrost | Ethylene Glycol: Dowtherm SR-1

Houghton Chemical Co, 617-254-
Propylene Glycol: Safe-T-Therm | Ethylene Glycol: Wintrex

Interstate Chemical Co, 800-422-
Propylene Glycol: Intercool NFP | Ethylene Glycol: Intercool NFE

Huntsman Petrochemical, 713-235-
Propylene Glycol: Jeffcool P155 | Ethylene Glycol: Jeffcool E105

Noble Company, 800-678-
Propylene Glycol: NoBurst-100

DOW/Union Carbide, 800-331-
Propylene Glycol: Ucar Protherm Norkool | Ethylene Glycol: UcarTherm TriTherm

KostUSA, 800-661-
Propylene Glycol: KostChill PG | Ethylene Glycol: KostChill EG

ETHYLENE GLYCOL (EG)
Is the green liquid we used to have in our car radiators.  It&#;s the least expensive, hurts heat transfer the least, and hurts pump performance the least.  It is toxic so its falling out of general usage. It is very corrosive so a suitable inhibitor package must be used to protect your piping and equipment.  Never use ethylene glycol for corrosion protection!  Its only use is to prevent slushing and freezing of your coolant.

PROPYLENE GLYCOL (PG)
It&#;s the pink liquid we currently have in our car radiators.  It&#;s about 20% higher in cost than EG, hurts heat transfer due to its high viscosity, hurts pump performance due to its high viscosity, and is needed in slightly higher concentrations than EG for equal freezing protection.  Its winning appeal is its low toxicity. It is corrosive so a suitable inhibitor package must be used to protect your piping and equipment.  Never use propylene glycol for corrosion protection!  Its only use is to prevent slushing and freezing of your coolant. 

DO NOT USE AUTOMOTIVE ANTI-FREEZE. Coolants for automobiles have inhibitors based on aluminum. Their inhibitor package is wrong for our industrial cooling systems.

Freeze Protection requires a glycol concentration level sufficient to prevent the formation of ice crystals at the lowest temperature experienced by the fluid. Freeze protection is imperative when the system requires pumping.  Slush is formed when you get colder than its freeze protection rating.

Burst Protection only requires a glycol concentration high enough (generally 30% by volume or more) to prevent bursting and other mechanical damage from freezing, but not necessarily high enough to keep the fluid pumpable. Burst protection requires less glycol than freeze protection and is suitable for chilled water systems that are dormant in the winter. As the temperature drops below the freezing point of the fluid in a system with burst protection, ice crystals begin to form, and the solution becomes a slush. The fluid expands as ice is formed. This mixture may or may not be pumpable, but it is fluid enough so that the excess volume flows into an expansion tank without damage to the system. As the temperature drops further and all the water freezes, the glycol will begin to freeze and contract.

For freeze protection, the required concentration of inhibited glycol fluid in a system depends on the operating conditions of the system and the lowest expected ambient temperature. Dry Coolers has ability to look up the winter extreme low condition for your geographic location. Contact us to help you determine the cold temperature design point. For corrosion protection, it&#;s also important to consider the materials of construction, the age of the system and other variables. Your local glycol supplier representative can help you analyze the specific requirements for your system.

We strongly recommend you purchase the glycol pre-mixed and avoid the chance of adding improper diluted glycol solution to your system. 

DO NOT USE AUTOMOTIVE ANTI-FREEZE. Coolants for automobiles have inhibitors based on aluminum. Their inhibitor package is wrong for our industrial cooling systems.

The table below shows the protection from freeze damage provided by various concentrations of DOWFROST propylene glycol inhibited fluids. To determine the concentration required, select the lowest expected ambient temperature and decide whether the cooling system requires freeze protection to keep it pumpable, or burst protection to simply prevent damage from fluid expansion.

As a further measure of protection against dilution error, or unexpected cold temperatures, select a temperature that is at least 5°F colder than the lowest expected ambient temperature. If, for example, the lowest expected temperature is -15°F, select the line in the table below for -20°F. The table shows that at this temperature, a solution of 45% DOWFROST is required for freeze protection. A concentration of 30% is needed to provide burst protection at this temperature.

PERCENT VOLUME GLYCOL CONCENTRATION REQUIRED 

We recommend the use of a full stream CyClean centrifugal separator to filter 100% of the cooling tower water flow.

The fan on a cooling tower draws in thousands of cubic feet per minute of outside air that contains sand, dust, insects, and fibers from vegetation. These airborne contaminants mix with the process cooling water and eventually these suspended particles find their way into heat transfer surfaces. After a period of time these surfaces become fouled and insulated causing equipment to run hotter and replacement or repair is necessary.

By removing 98% of these suspended solids mechanically, fouling is greatly reduced and chemical water treatment and bleed from the system can be reduced significantly.

Full stream filtration protects the system from dirt deposits such as winds blowing over newly plowed fields, chunks of scale eroding from steel pipe or foreign deposits encountered by adding new piping to an existing system.

By utilizing a purge receptacle, expensive treated process water is not wasted in the purge cycle. A small continuous flow of dirt laden process water removed by the separator is filtered and contained in the receptacle while the clean water is returned to the cooling system. The receptacle can then be isolated for easy contaminant removal without interrupting the process water flow and zero discharge to the sewer.

The key to good filtration is to provide a system where the dirt laden water can enter the suction of the pump that discharges into the CyClean separator for maximum filtration of the system. If the solids can be kept in suspension, they will eventually enter the suction of the pump and then be filtered by the separator before they foul your equipment.

Because evaporative towers scrub the air that passes through them, they are prone to collecting debris from the air. This debris can accumulate and cause flow restrictions as well as aggravate corrosion. After the water evaporates, dissolved minerals are left behind and accumulate rapidly until the mineral come out of solution (known as scale). 

For these reasons, a properly engineered and administered water treatment program must be employed continuously with the cooling tower. In an open tower cooling system, the water quality must be regularly monitored and treated to control the following conditions:

&#; Lime scale and other water mineral deposits
&#; Corrosion of all types
&#; Micro-biological growth, such as algae, bacteria, fungus and molds
&#; Suspended solids accumulations, such as airborne dirt and debris that is washed into the cooling tower water

Dry Coolers recommends consulting a local water treatment supplier (Calgon, Nalco, Culligan, etc.) that is familiar with your local water quality to monitor your treatment program.

Dry Coolers can provide the chemical pumping equipment to inject proper chemicals into your cooling tower water, but a local professional knowledgeable with your local water issues is best. Here are a few we&#;ve worked with before:

ChemTreat
ChemAqua
Nalco
Suez

Consult with the above supplier relative to your specific needs.

For more closed loop cooling towerinformation, please contact us. We will provide professional answers.