In today’s industrial landscape, effective heat management is essential for optimizing processes and ensuring operational efficiency. Cooling towers and ponds serve as vital components in this endeavor, acting as heat rejecting devices that help maintain optimal temperatures in various applications, from power plants to food processing facilities. With a range of designs available each with unique characteristics and benefits understanding the types of cooling solutions and their specific advantages is crucial for industries aiming to enhance performance while minimizing costs and environmental impact. This overview will explore the different types of cooling towers and ponds, their respective advantages and disadvantages, and their applications across various sectors, providing a comprehensive understanding of how these systems contribute to efficient industrial operations.

Exploring Evaporative Coolers: A High Level Overview

They are generally called ‘evaporative coolers,’ and below, A high-level description of the following:

Ponds

Crossflow

Counter flow

Induced Draft

Forced Drat

Natural Draft

Hyperbolic

Types of Ponds

Ponds are generally covered by the simple lake type ‘cooling pond’ or a ‘spray’ type pond.

What are Cooling Ponds?

Cooling ponds are usually big bodies of water that would appear more like a lake or large pond. They traditionally are used to process and cool the warm water created by an industrial process such as:

Power plant operations [nuclear plants, coal-fired plant]

Refineries

Mills [paper, steel etc]

Chemical plants

Food processing plants

The cooling process is achieved via warm/hot water from the process being pumped into the pond, which then will be allowed to flow naturally to allow cooling via radiation, evaporation, and conduction before being recirculated back into the cooling system via the system pumps.

Due to the heat transfer inefficiencies by using this method, a large water surface is required.

Advantages of Cooling Ponds

Oleson and Boyle note the following advantages:

Construction costs are quite low, where land and soil conditions allow

They can serve as a settling pond for any suspended solids produced by the water being cooled

Limited cooling water make-up required, can be replenished by rain

Disadvantages of Cooling Ponds

They also note the following disadvantages:

Large area of land needed

Low soil permeability

Issues if there is ice

Can cause fog

How do Spray Ponds Work?

Using no mechanical fans, spray ponds are an alternative design that utilizes nozzles mounted a few feet [1.5m to 2.0m] from the water surface of the pond/basin that atomizes the warm water received from a process to increase its surface area and contact time with the surrounding air.

This boosts the efficiency and available cooling performance of the equipment.

The warm water enters via the nozzles and is recirculated back to the system by pipework connected at a low level to the pond basin.

Like with the cooling pond, they are commonly used to process and cool the warm water created by an industrial process such as:

Power plant operations [nuclear plants, coal-fired plant]

Refineries

Mills (paper, steel etc)

Chemical plant

Advantage

a) Pumping cost is low

b) Head required is less

c) Lesser wastage of water

d) Low drift losses

e) Least choking

f) Easy to maintain

g) High Durability and long life

Disadvantages

a) Large area is required. Approximately 25-50 times the area of cooling tower

b) Spray losses due to evaporation and windage losses

c) There is no control over the temperature of cooled water.

e) Cooling efficiency is low.

f) Cooling effect reduces with reduced wind velocity.

g) When load on the plant increases it does not respond to change.

Types of Cooling Towers

Cooling towers can be broken down into 2 main types of designs and 2 sub designs:

Mechanical Draft Tower	Fans used	Induced Draft	Counter Flow	Cross Flow
Fans Used	Forced Flow	Counter Flow
Natural Draft Tower	No fans used	Natural Draft	Counter Flow	Cross Flow

Mechanical Draught Towers:

Mechanical draft towers will incorporate a mechanical fan to create the airflow needed to ensure evaporative cooling takes place, removing the unwanted heat, in turn, lowering the temperature of the water before being pumped back into the system.

Designers of building services systems will generally use 1 of 3 types within their designs:

Cross flow: Induced draft

Counter flow: Induced draft

Counter flow: Forced draft

Counter flow vs Cross flow Cooling Towers

The differences are straightforward between cross flow and counter flow cooling towers and can be as follows:

Cross flow

The cooling tower fill pack is installed vertically at a slight angle near the outside walls, allowing the airflow to travel horizontally through it, whilst the water, to be cooled, drops downwards [cross flow].

Counter flow

The cooling tower fill pack is installed horizontally half way up the tower, allowing the airflow to travel vertically through it whilst the water, to be cooled, drops downwards [counter flow].

What are the advantages of a Cross flow cooling tower vs Counter flow?

A Counter flow tower, up to about 3.5MW requires less footprint than a similar Crossflow type.

Crossflow has better access for maintenance that the Counter flow

Cross flow is easier to maintain than Counter flow

In a Crossflow tower, due to using a hot water basin at the top of the tower to feed the warm water into the ‘fill’, the pressure requirements are usually less than for a similar installation using a cross flow tower that has pressurized nozzles.

Crossflow tower has better efficiency and control of cooling at lower loads.

What is an Induced Draft Cooling Tower?

An induced draft tower is constructed with a tall stainless steel casing [square or round], with axial fans located at the top, pulling air into the tower that enters via the side.

The external casing of the tower, where the entering air is drawn through, will be packed with a material [wood slats or plastic], usually referred to as ‘Fill,’ specifically designed to allow the warm water to flow down and the air through. This is referred to as ‘Cross Flow.’

The reason for the material is to increase the ‘wetted’ area of the tower allowing for more evaporative cooling to occur.

The fill can also be installed horizontally, providing a ‘Counter Flow’ type design as described above.

Once the air has passed through the material, the warmer air will then be pulled up through the fan, mounted at the top, and released into the atmosphere, with the rejected air being warmer and more humid, which is what can be seen as a ‘plume’ sometimes during cooler months from the top of the tower.

The water will be introduced at the top of the tower via pipework from the condenser system and allowed to flow freely through the fill material under gravity, allowing an even water distribution.

There will be a catchment basin at the bottom of the tower to collect the water, ready for pumping back into the condenser system.

Advantages

a) Less floor space area required

b) Induced draft design with fan motor

c) More efficient compared to spray ponds.

Disadvantages

a) The carry over losses which are 0.2-0.6 % of water flow, cause corrosion of blades forms the fog around the tower with the increase in carry-over losses makeup water required is also increased.

b) The drift droplets have the same chemical impurities as the circulating water and the deposition of these chemicals on object causes potential environmental concern.

c) Cooling tower where sewage effluent is used for making up is high conductivity for the growth of algae.

d) More maintenance.

What is an Forced Draft Cooling Tower?

A forced draft cooling tower operates using centrifugal fans to push ‘force’ ambient air through the tower at a low level, helping to remove the heat generated within a production/system process.

The warm air then flows up through the tower, picking up heat from the water flowing in the opposite direction through the ‘fill’ before being ejected through the top of the tower.

What is the advantage of forced draft cooling tower?

Easy to replace and swap like for like

Able to overcome static pressure on ducting if used to route the rejected heat from the tower

Moving parts are not within the hot humid air stream, helping prolong the life of the equipment

Maintenance of the fans are generally easier for removing as are installed at low level within the tower.

What are the disadvantages of a forced draft cooling tower?

A forced draft cooling tower consumes more power/energy than an Induced type tower.

Can cause issues with recirculation of hot air back into the tower as the expelled air ‘drifts’ away and not pushed, like with an induced tower.

Only can have counter flow meaning maintenance of the internal parts of the tower is more restricted.

Natural Draft Cooling Towers

These cover anything that does not incorporate a mechanical fan to create the airflow needed to ensure evaporative cooling takes place and removes the unwanted heat from the water.

A great example of a natural draft cooling tower is the Hyperbolic type.

Hyperbolic (Hyperboloid) Cooling Towers

After the shape Hyperboloid, a hyperbolic cooling tower is probably the most recognizable shape and type of tower that near power stations, but are also used in similar industries to the cooling ponds/spray pond type cooling systems above.

Why is a Cooling Tower Hyperbolic?

The cooling tower is designed and constructed as a hyperboloid shape for a few reasons:

Ease of design / construction due to limited types of materials used

To manage costs with a ‘lighter design’ – less materials

To aid the convection of air and the cooling as it travels up through the tower

Low maintenance and operational costs

Resist weathering and winds ensuring a long life cycle

Large cooling capacity

Minimal fogging

Definition of Hyperboloid

According to Merriam Webster, a Hyperboloid shape is defined as:

a quadric surface whose sections by planes parallel to one coordinate plane are ellipses while those sections by planes parallel to the other two are hyperbolas if proper orientation of the axes.

How does a Hyperbolic Natural Draft Cooling Tower work?

Natural draft towers operate with no mechanical fans; much like the spray pond above, it uses spray nozzles within the tower that introduce the warm water that is to be cooled at a set height to the surrounding air.

After the water has been atomized, creating tiny water droplets will interact with the air transferring its heat via evaporation.

The air will increase moisture and temperature, become less dense, and rise through the tower

As the air rises, it will draw in cooler air through holes/vents constructed into the bottom of the tower. The cooler air will maintain the process of warming up as it comes into contact with the water, transferring heat, and flowing up through the tower.

The cycle is continuous, as long as there is load and water flow.

Once the hot air has reached the top of the structure, it will move into the natural atmosphere.

The water, once cooled, will drop to the base of the cooling tower, where it will be collected in a basin and pumped back into the cooling system to be recycled.

Operational benefits of the Natural Draft Cooling Tower

Minimal electrical power required as no mechanical fans

Low maintenance as limited no moving parts, maybe some blockages at the nozzles

Low corrosion due to the use of materials such as stainless steel and concreate/cement

Reduced requirement of space to construct compared to ponds

Industrial Applications

Floating spray coolers and surface aerators can be used in pulp & paper mills, power plants, steel mills, food processing plants and other industrial applications to meet cooling requirements.

especially during peak loadings. The spray cooler concept employs a multiple nozzle assembly supported on a floating platform. A pump-manifold-nozzle design produces effective heat transfer while the floating platform offers quick, flexible installation. Heated water is sprayed many times into the air to achieve the desired heat dissipation, cooling the water to within about 9-10°F (-13 to -12°C) of the actual wet bulb temperature with continuous influent flow to the cooling pond.

Spray coolers provide the optimal design for peak heat transfer efficiently, with low power consumption (individual units can be cycled on/off to save energy) and less drift loss than with wet cooling towers.

Compared to cooling towers, capital costs for spray coolers are lower with existing ponds and operating costs are lower as chemical treatment is not needed to prevent bacteria growth. Spray cooler technology also does not provide an environment conducive to Legionella bacteria growth, which has been discovered inside cooling towers and released via the cooling tower mist. While spray coolers do require more land than wet cooling towers, their footprint is less than 5% of what cooling ponds consume.

Conclusion

Cooling towers and ponds play a crucial role in industrial processes by effectively managing heat dissipation. Each type, whether it’s mechanical draft towers, natural draft towers, or cooling ponds, has its unique advantages and disadvantages that cater to specific operational needs. While cooling ponds offer low construction costs and serve multiple purposes, they require significant land and may face environmental challenges. On the other hand, cooling towers, particularly induced and forced draft varieties, provide efficient cooling in a compact design but may involve higher maintenance and operational costs.

Ultimately, the choice between these systems depends on factors such as available space, budget, and specific cooling requirements. Understanding the nuances of each type helps industries optimize their cooling solutions, ensuring efficient operation while minimizing environmental impact.

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Reference

1.Water Cooling System | Difference Between Cooling Tower and Spray Pond

https://www.sugarprocesstech.com/cooling-system/

2.COOLING TOWER | Types of Towers and Ponds

https://constructandcommission.com/types-of-cooling-towers-and-ponds/