Cooling towers are widely used by many industries to deal with excess heat that is produced by manufacturing processes and other industrial activities. Put simply, a cooling tower is a device that works to lower the temperature of a water stream. This is done so that the hot water in circulation is cooled enough to be used again in the boiler. Most cooling towers rely on using evaporation to lower the temperature of the circulating water.
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Since , Marley Flow Control has been a proud industry leader in cooling tower manufacturing. An Australian-owned and operated brand, we offer a high level of expertise and an extensive range of ready to order products. Our wealth of knowledge has allowed us to work with some of the country’s largest businesses that we are pleased to call our clients.
As industry leaders, we have a high level of expertise and can provide a wide range of cooling tower services. If you need help with your cooling tower, contact our highly experienced team to discuss your options today.
Cooling towers can differ significantly based on size, build, materials used and mechanisms of operation. Understanding the differences between various cooling tower types is essential for choosing the right one for your needs.
Below we answer some important questions you might wish to ask before deciding which cooling tower would be best for you.
How is airflow generated in cooling towers?
Cooling towers operate by using constant and reliable airflow which can be produced and maintained in a variety of ways.
A cooling tower can operate using:
- Natural draft. Such cooling towers are constructed in ways that utilise the design of the tower to move the air up by using fans.
- Mechanical draft. These rely on a centrifugal fan or propeller pulling the air from the bottom. The fan is usually placed at the top of the tower and blows warm air out of the tower while also sucking in the cool and dry outside air.
Natural draft cooling towers – best uses
Cooling towers that use natural airflow are usually located outside, which allows them to release warm air directly into the environment. This is why these are normally used in industrial settings – such as power plants located near the load centres and away from the fuel source point. In such cases, using a natural draft cooling tower allows saving on the costs of power that would otherwise be needed to operate cooling fans.
Mechanical draft cooling towers – best uses
These cooling towers tend to be significantly smaller than natural draft towers, which makes them suitable for use inside the plants and other facilities. As you are also able to monitor and control the speed of the cooling fans, mechanical draft towers are preferred where capability control is important.
Also, as these towers use power to operate the cooling fans, they are widely used where cheaper power is accessible – for example, at power plants located close to the fuel source.
Climate conditions also need to be taken into consideration, as natural draft towers are not well suited for areas with long, hot, dry summers. In such cases, the air density difference that is needed for an efficient operation of natural draft towers is hard to achieve, so mechanical draft towers are preferred.
How is heat transferred in cooling towers?
Cooling towers can use dry heat or wet heat transfer methods.
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Dry cooling towers – best uses
A dry cooling tower simply transfers heat through a surface separating hot water from the air. As no water evaporation occurs, no additional water is needed. Hot water from the condenser just keeps circulating through the tubes exposed to ambient air that absorbs its heat, cooling it down. Sometimes, fans are installed to improve the airflow.
As this type of heat transfer is quite inefficient and involves high energy usage, it is reserved for situations where water supply is limited – or where regulations specifically disallow any plume.
Wet cooling towers – best uses
Also known as open circuit cooling towers, these towers use the natural process of water evaporation as a cooling method. What is emitted as a result is just heated water droplets that cause no harm to the environment.
Wet cooling towers are very popular because of their cost-efficiency and use of renewable resources (water). They are most likely to be your first choice if you have access to an adequate water supply.
How are cooling towers constructed?
Depending on your needs, you can have your cooling tower field erected – or you may decide to go for a package type tower.
Field erected cooling towers – best uses
These are large non-transportable towers that weigh over 1,500 tonnes per cell and have a significant cooling capacity. Because of their size, they need to be assembled on site. These towers are also often built to custom specifications.
Power plants, oil refineries, petroleum sites and steel processing plants often use field erected cooling towers.
Package type cooling towers – best uses
These towers are smaller in size than field erected towers – so they are assembled at a factory and then can be easily transported to the usage site.
Facilities with comparatively low heat rejection requirements – such as office buildings, hospitals and shopping centres – normally use cooling towers of this type.
We can design, build, inspect and repair your cooling tower
Marley Flow Control offers a comprehensive range of cooling tower design, installation, inspection and repair services. We can repair both the fill and mechanical components of a cooling tower and offer an ongoing full functional annual assessment of your tower. We also provide comparisons between a comprehensive refurbishment or a new cooling tower.
Our team of highly experienced technicians has the skills and equipment to fit new motors, driveshafts, gearboxes and fans in the field, including long laser alignments of up to four metres.
For more crossflow vs counterflow cooling towersinformation, please contact us. We will provide professional answers.
MortenA
Chemical
- Aug 20,
- 2,998
You could ask some of the vendors to send you their input sheet. They may have that for your inspiration.
Best regards
Morten
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davefitz
Mechanical
- Jan 27,
- 2,927
I think that the CTI cooling tower institute has a standard specification sheet that you could fill out.
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SNORGY
Mechanical
- Sep 14,
- 2,510
Nivrah,
By "cycles of operation", I assume you meant to say "cycles of concentration".
There are a number of things you need to specify in addition to the above. In no particular order:
* maximum and minimum wet and dry bulb temperatures
* seismic zone and wind loading
* induced draft - single crossflow / double crossflow
* type of fill (film versus splash versus wood versus PVC)
* how many cells (as it relates to turndown / redundancy / etc.)
* limitations on blowdown (and whether it is continuous or intermittent)
* limitations on evaporation and drift
* flow balancing and distribution across the top of the tower
* provisions (if required) for degassing the return water
* provisions for winterization (if applicable) - usually by fan control
* any requirements for plume abatement
Marley / SPX would be a good resource.
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davefitz
Mechanical
- Jan 27,
- 2,927
other items may be :
noise levels at ( 30 meters)
heat duty ( MWth on design day)
heat duty during steam turbine bypass operation
fan motor details ( max permitted motor size, etc)
The sizing is almost wholly dependent on the hottest design day; the unit is oversized for all other days. So the client must be careful of the details specified for such an occurrence.
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Nivrah
Mechanical
- Feb 15,
- 43
Snorgy,
Sorry for the typo..i meant cycles of concentration. .
the cold water would be used for cooling our turbines and compressors. curently, they use untreated water at 15 degrees C.
Our mill uses a conservative wet bulb temp of 24 deg C for new cooling tower selections. this is for the absolute hottest day annually. it would also mean that on very hot days, the water out will be around 25's Deg C or higher. i wonder if the turbines and compressors can handle that!
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rmw
Mechanical
- Feb 6,
- 5,724
You will have to find out from your turbine supplier what their back pressure limit is and then find out from yur condenser supplier what the HEI predicted performance will be at that inlet water temperture. When you can answer those two questions, you will have the answer to what you asked.
rmw
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SNORGY
Mechanical
- Sep 14,
- 2,510
I am not a turbine specialist, but I would initially suspect that for a turbine, even at 25 C water, you probably have enough approach temperature that cooling shouldn't be an issue. A good question for the turbine supplier. Is it just the surface condenser that is the issue?
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rmw
Mechanical
- Feb 6,
- 5,724
No, it is a combination of the two. For one thing, the turbine will have some discreet back pressure limit regardless of what kind of condenser it has under it, good bad or very bad. A major turbine manufacturer that I am very familiar with has a 5.5 in Hg back pressure limit. That is set by a lot of factors way too deep to go into here.
So a condenser designed to produce a back pressure much lower than 5.5" Hg, say 2.5" Hg with 25C water probably wouldn't have a problem. On the other hand, same turbine with a condenser designed to have 2.5" Hg with 15C water (thinking of a real case) is approaching getting in serious trouble with 25C water and probably at 5.5" Hg at 29C water.
rmw
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Nivrah
Mechanical
- Feb 15,
- 43
rmw and snorgy,
he turbine spec sheet says that the max inlet temperature in the generator and oil coolers are 25 Deg c . The leak off condenser can take a maximum of 27 deg C. So I guess, the condenser back pressure limit has been set up in such a way that it works fine as long as the inlet water is less or equal to 27 deg C.
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stgrme
Mechanical
- Oct 5,
- 135
Generally, the generator and oil coolers are supplied with cooling water from a closed cooling water system, which will have a higher temperature than the circulating water supplied to the condenser. The leak-off (gland steam) condenser is usually located in the condensate (feedwater) system downstream of the condensate pumps. Neither one of these systems set the limits for the backpressure on the turbine. Look further in the turbine spec sheets or ask the turbine manufacturer for the limits on backpressure.
Best of luck!
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SNORGY
Mechanical
- Sep 14,
- 2,510
Nivrah, rmw,
When it was stated:
"the cold water would be used for cooling our turbines and compressors. curently, they use untreated water at 15 degrees C."
I had at first glance thought that this was a simple cooling issue, rather than a surface condenser issue.
rmw's observations re: surface condenser vs turbine cack pressure are correct.
Nobody needs the potential for anything other than completely dry steam in contact with turbine blades.
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rmw
Mechanical
- Feb 6,
- 5,724
Turbines have low pressure limits too.
Actually the lower a condenser back pressure gets, the wetter the last stages of the turbine get and the further up the steam path the wet zone travels. Several of the last rows are "armoured" so to speak with wear shields to handle the moisture. The rows further up the steam path aren't.
In non-reheat turbines and in Nuclear turbines, the entire LP section can be in the moisture zone.
rmw
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Nivrah
Mechanical
- Feb 15,
- 43
gents,
the objective here is to maintaing cooling water at lower than 25 deg C.There are alarm limits in the turbine controls in that inlet cooling water > 25 deg C will send operators in panic mode. So, it is a simple cooling issue as SNORGY pointed out.
Here in Australia, summer days can be very hot. So since the alarm limits have already been set up at 25 Deg C max, i will have to stick to providing cooling water equal to or less than 25 Deg C.
My superiors have agreed on the issues of hot days in given our geographic location and we have decided to use a S/T heat exchanger rather than a cooling tower. Two reasons follow: A S/T HX will have 20 deg C max cold inlet water on hot summer days --> easy to keep oulet water to less than 25 deg C.
Secondly, had we use a cooling tower, we would have run into corrosion issues. this is because our mill uses high dosages of Sodium hypo for water treatment in CT.this promotes a corrosion intensive environment.
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