Transcript Diapositiva 1

Chapter 1
Dehumidification
Process
- Cooling Tower-
Objectives
• After studying this unit, the student should be
able to
•
Describe the function of the cooling tower
•
Identify the relationship between the wet-bulb temperature of the
ambient air and the temperature of the water leaving the tower
•
Describe three types of cooling towers
•
Describe various fan and drive types used on cooling towers
•
Describe the function of the fill in a cooling tower
•
Explain the purpose of makeup water and blowdown
Function of cooling tower
• Cooling tower is a heat rejection devices used to transfer
process waste heat to the atmosphere.
• Cooling towers are able to lower the water temperatures
more than devices that use only air to reject heat such
radiator, more cost effective and energy efficient.
Hot water in (95°F)
Fan
motor
Air in 95°F dry
bulb, 78°F wet
bulb
Air out
Cooled water out (85°F)
types of cooling tower
Natural draft
Cooling
tower
Forced draft
Induced draft
Natural draft CT
• atmospheric CT
• use natural forces (wind)
to move air through CT
• air flows in through the
sides, and out the top
• drift eliminators on the top
Forced draft CT
• Fans used to create a
draft
• Air forced in the bottom,
and flows out the top
• Typically solid sides
Induced draft CT
• Fans located at the top of
the CT
• Lifts air out of the CT,
preventing recirculation
• Probably the most
common type used in
chemical plants and
refineries
Induced draft CT
types of flow pattern
Counter flow
CT
Induced
draft
Cross flow CT
Warm water from
condenser
Spray nozzles
Prevailing winds
Float
Water to pump
Valve
Slats on all
four sides of
the tower
Make-up
water
Components of CT
Designed to slow the flow
of trickling water through
the tower
Fill in
Blowd
own
-replaced with fresh water
-designed to reduce the
amount of solid materials
in the water
components
Make
up
water
Tower
sump
Tower sump
•
•
•
•
•
Area where tower water collects
Sump water must not freeze
May be installed underground
Should be accessible for cleaning
Is usually equipped with a strainer to protect the pump
Make-up water
• Water continuously evaporates from the system
• Fresh water must be supplied to the system as needed
• Float valve
– As the water level drops, the valve will open and add supply
water
• Electrodes
– Used to sense the water level
Make-up water
Float ball
Water level
Make up
water
Float valve
Strainer
To pump
End of Chapter 1