Cooling Towers - a laymans view

Cooling Towers - a laymans view

Introduction

This is not a technical paper so before you read on please understand that this blog is a laymans viewpoint and has been assisted by information provided by two of RABScreen's customers.

DHD Cooling who work in partnership with both RABScreen and Galebreaker to provide the CAS or continuous attachment system. As specialists in the cooling tower market they are well placed to offer both advice and guidance on the full range of cooling or heat exchanger applications.

Tower Systems, a valuable customer, and supplier of all things cooling tower related. Specialist installers and maintainers they have a wealth of expertise and knowledge of different manufacturers and their systems.

Background

Most of us are familiar with the concept of cooling towers which are commonly seen at power plants as large concrete monoliths with steam or hot air rising from the top. The history of these cooling towers dates back to the beginning of the 20th century, when two Dutch engineers were the first to build a tower using a ‘hyperboloid’ shape. Very wide on the bottom, curved in the centre and flared at the top, the structure meant fewer materials were required to construct each tower, it was naturally more robust, and it helped draw in air and aid its flow upwards. It quickly became the de facto design for towers across the world.

What are cooling towers used for?

Cooling towers are primarily used for heating, ventilation, and air conditioning (HVAC) and industrial purposes. Cooling towers provide a cost-effective and energy efficient operation of systems in need of cooling. A large number of industrial facilities use large quantities of water to cool their plants.

HVAC systems are used typically in large office buildings, schools, and hospitals.

Industrial cooling towers are larger than HVAC systems and are used to remove heat absorbed in the circulating cooling water systems used in power plants and other industrial facilities.

Understanding The Different Types Of Cooling Towers

Date: September 26, 2016

courtesy of https://www.amarillogearservice.com/

Cooling towers were essentially created to eliminate excess warmth from water used in industrial operations and send it out into the surrounding biosphere. Surprisingly, there are many different techniques for achieving this process. Since there is a high degree of variation between how these devices operate, they are classified within a number of distinct groups.

There are three main types of cooling towers that are defined by how water or air pass through them. These types include crossflow, counterflow, and hyperbolic. There are also two varieties classified solely on airflow, known as induced draft and passive draft cooling towers.

Cross flow cooling towers

Crossflow cooling towers use a splash fill that allows in-flowing to air move in a horizontal path over the stream of water from the upper reservoirs. Crossflow systems are some of the more expensive equipment types, but they are also some of the easiest to maintain. However, these cross flow cooling towers are more vulnerable to frost than others.

Counterflow cooling towers

In a counterflow system, the in-flowing air flow generation travels in a vertical path over the splash fill as the water streams down from the reservoir above. Counterflow systems are usually smaller than their crossflow counterparts. These cooling towers are more expensive due to the fact that more energy is needed to push the air upward against the down-flowing water.

Hyperbolic cooling towers

Hyperbolic systems are well-built and require a minimal amount of resources. Though they require few resources, these large cooling towers are able to efficiently manage large-scale tasks within big chemical or power plants.

Hyperbolic systems use a chimney stacking technique that allows the cooler, outside air to push the damp, warmer air inside the tower. Splash fill is placed around the bottom of the tower and the water that sprays over it is cooled by the passage of upward-flowing air.

Induced draft cooling towers

Induced draft or mechanical draft cooling towers use some type of mechanical pressure, like a fan system, to push air upward inside the tower. Induced draft systems can also force air into the tower with a blow-through or pull it out through a draw-through.

Passive draft cooling towers

Passive or natural draft towers combine the upward motion of warmed air with a steep chimney architecture to organically pull air throughout the tower. Although passive draft systems may have either a counter or crossflow transport design, hyperbolic towers are always passive draft.

Natural draft cooling towers

Natural draft cooling towers - mostly used in power stations, but is also found in energy-intensive facilities like oil refineries, petrochemical plants and natural gas plants. They are installed to remove heat from the circulating water system. For air intake protection and filtration see https://www.rabscreen.com/High_Performance_Cooling_Tower_Filters

Forced draft cooling towers

Forced draft cooling towers - remove low-potential heat generated in the production process. They use atmospheric cooling with wet technology and forced draft. A counterflow of air and hot water in the cooling fill results in a heat transfer. For air intake protection and filtration see https://www.rabscreen.com/High_Performance_Cooling_Tower_Filters

Mechanical draft cooling towers

Mechanical draft cooling towers - the most widely used in buildings and rely on power-driven fans to draw or force the air through the tower. They are normally located outside the building. The two most common types of mechanical draft towers to the HVAC industry are induced draft and forced draft. For air intake protection and filtration see https://www.rabscreen.com/High_Performance_Cooling_Tower_Filters

Closed circuit cooling towers

Closed circuit cooling towers - involves no contact between the air and the fluid being cooled. This tower has two separate fluid circuits, one in which the fluid is recirculated on the outside of the second circuit, which is a bundle of tubes through which the hot water is flowing. The air drawn through this cascading water provides evaporative cooling similar to an open cooling tower, except that the cooled water never makes direct contact with the air. Closed-circuit cooling towers require much more energy to achieve the same cooling as an open circuit cooling tower. For air intake protection and filtration see https://www.rabscreen.com/High_Performance_Cooling_Tower_Filters

Open circuit cooling towers

Open circuit cooling towers - a direct, open-circuit cooling tower is an enclosed structure that distributes warm water over a labyrinth-like packing, or fill, which provides an expanded air-water interface for heating of the air and evaporation to take place. The water is cooled as it falls through the fill and is then collected in a cold water basin below. The heated moisture-laden air leaving the fill is discharged into the atmosphere. For air intake protection and filtration see https://www.rabscreen.com/High_Performance_Cooling_Tower_Filters

Wet cooling towers

Wet cooling towers - use water to cool machinery that heats up (hence the "wet" part of the name) and these towers use the natural process of evaporation to cool machinery. These towers rely on an exchange of heat between the machinery, the water in the tower, and the air passing through the tower. For air intake protection and filtration see https://www.rabscreen.com/High_Performance_Cooling_Tower_Filters

Evaporative cooling towers

Evaporative cooling towers - are essentially large boxes designed to maximize evaporation of water. To do this, they contain material, typically PVC plastic sheets, that create large surface areas for water evaporation to occur. This material is what fills the inside of the cooling tower and is called "Cooling Tower Fill". Evaporative cooling is the process in which the evaporation of water removes heat from a system. For air intake protection and filtration see https://www.rabscreen.com/High_Performance_Cooling_Tower_Filters

Crossflow cooling tower systems

Crossflow cooling tower systems - in crossflow systems, the air is drawn perpendicularly across falling water. In this system, no pressurized nozzles are necessary to facilitate the falling water, instead passing through a distribution basin. For air intake protection and filtration see https://www.rabscreen.com/High_Performance_Cooling_Tower_Filters

Factory assembled cooling towers

Factory assembled cooling towers - Factory assembled cooling towers with atmospheric cooling are used for industrial and HVAC applications in cases where no high cooling efficiency is required and no large area is available.?The exchange of cooling air is provided by a fan unit driven by an electric motor. The compact cooling tower is designed as a standalone unit which can be placed almost anywhere. In order to increase the total cooling efficiency, another cooling tower cell can be added. For air intake protection and filtration see https://www.rabscreen.com/High_Performance_Cooling_Tower_Filters

Field erected cooling towers

Field Erected Cooling Towers are custom designed for individual site and thermal requirements and built from pultruded composite materials designed specifically for Cooling Tower Applications. Constructed from steel frames, GRP casing and the highest quality components, these cooling towers are durable and superbly adapted for use in harsh industrial environments. For air intake protection and filtration see https://www.rabscreen.com/High_Performance_Cooling_Tower_Filters

Air cooled condensers

An air cooled condenser (ACC) is a direct dry cooling system where steam is condensed inside air-cooled finned tubes. The cool ambient air flow outside the finned tubes is what removes heat and defines the functionality of an ACC. For air intake protection and filtration see https://www.rabscreen.com/High_Performance_Cooling_Tower_Filters

Adiabatic Coolers

Adiabatic coolers are a modern alternative to traditional cooling towers, involving significantly lower maintenance and OPEX. For air intake protection and filtration see https://www.rabscreen.com/High_Performance_Cooling_Tower_Filters

Adiabatic and Hybrid Coolers

In the middle ground between wet and dry cooling solutions there are adiabatic and hybrid cooling units. These systems use water to lower the effective cooling temperature of the air during warm periods to improve performance. There are various types of system available but the best performing of these are the wetted pad systems and the full deluge hybrid solutions.For air intake protection and filtration see https://www.rabscreen.com/High_Performance_Cooling_Tower_Filters

Dry Air Coolers

Dry air coolers provide cooling for many applications, especially where water is scarce or costly and for higher temperature systems. They are available in horizontal, vertical, V type and W type configurations and use air flow generation methods at ambient air temperature to remove latent heat. For air intake protection and filtration see https://www.rabscreen.com/High_Performance_Cooling_Tower_Filters

Summary

No matter which cooling tower design you select to be your heat exchanger the basic heat transfer methods are the same. Calculate the heat load and take advice from your cooling tower system providers to improve energy efficiency, reduce water treatment chemicals and maintain your cooling and air conditioning process. For further techical advice please contact:

RABScreen - https://www.rabscreen.com/

Tower Systems Limited - https://www.towersystems.co.uk/

DHD Cooling Limited - https://dhdcooling.co.uk/