Presented byMd.Mainuddin Hasan2646-Mech-2007

Syed mohammad khalil2570-Mech-2007

Asif ayaz2587-Mech-2007

Contents

Introduction to circulating system and cooling towerClassifications

The circulating water systemSupplies cooling water to the turbine condenserActs as heat rejecting source from system to surroundingVital for performance of powerplant

Once-through systems

Closed loop system

Combination system

System classification

Once-through systems Water from natural resorvoir is usedThe pumped water is circulated and discharged backHeat is exchanged form hot water to cold water

Discharge methodsSurface Discharge: Water is released in thin layer on surface.Submerged Discharge: Water is released buoyant jet below the surface of a body.Diffuser Discharge: Water is through number of nozzles from a submerged long pipe.Heat rejection is accomplished by evaporation in all methods

Closedloop system

Water is taken from the condenser pass through a cooling device and return it to the condenser.Cooling devices Cooing towerSpray pondsSpray canals

Combination systemOnce through system is combined with cooling deviceCooling device cools the water returning to resorvoir

Parts of circulating systemIntake structure

Circulating water pumps

Circulating water condutes

Vacuum breaking system

Cooling TowersA cooling tower is a heat rejection unit.

Rejects heat though the cooling of a water stream

Supplies cooling water to turbine condensor,

Major ComponentsCooling Tower (Supply) Basin Water is supplied from the discharge of the Circulating Water System to a Distribution Basin, from which the Cooling Tower Pumps take a suction.

Cooling Tower Pumps These large pumps supply water to the Cooling Towers.

Classification of cooling towerBy Air flow generation methodsBy air-to-water flowBy use in fieldBy Heat transfer methods

Air flow generation methodsThere are three methods of air generationNatural draftMechanical draft (a)induced draft (b)forced draftFan assisted natural draft

Air flow generation methodsNatural draftHot air moves through towerFresh cool air is drawn into the tower from bottomNo fan requiredConcrete tower

Natural draft cooling tower

Mechanical draft Induced draft

A mechanical draft tower with a fan at the discharge which pulls air through tower.

The fan induces hot moist air out the discharge

This produces low entering and high exiting air velocities

Induced draft

Series of induced draft cooling tower

Air flow generation methodsForced draftA mechanical draft tower with a blower type fan at the intakeThe fan forces air into the tower, creating high entering and low exiting air velocities.

Forced draftForced draftA mechanical draft tower with a blower type fan at the intakeThe fan forces air into the tower, creating high entering and low exiting air velocities.

Forced draft

Forced draft cooling tower

By air flow generation methodFan assisted natural draft. A hybrid type that appears like a natural draft though airflow is assisted by a fan

Fan assisted cooling tower

By air to water to water flowCrossflow is a design in which the air flow is directed perpendicular to the water flowAir flow enters one or more vertical faces of the cooling tower to meet the fill materialWater flows (perpendicular to the air) through the fill by gravity

By air to water to water flow

by air-to-water flowCounterflowIn a counterflow design the air flow is directly opposite to the water flowAir flow first enters an open area beneath the fill media and is then drawn up verticallyThe water is sprayed through pressurized nozzles and flows downward through the fill, opposite to the air flow

CounterflowIn a counterflow design the air flow is directly opposite to the water flowAir flow first enters an open area beneath the fill media and is then drawn up verticallyThe water is sprayed through pressurized nozzles and flows downward through the fill.

ADVANTAGESADVANTAGES OF COUNTER FLOW cooling towers due to their pressurized spray water distribution system: More efficient use of air due to finer droplet size from pressure sprays.ADVANTAGES OF COUNTER FLOW cooling towers due to their vertical air distribution system: The vertical air movement across the fill allows the coldest water to be in contact with the driest air maximizing tower performance.

DISADVANTAGESDISADVANTAGES OF COUNTER FLOW cooling towers due to their pressurized spray water distribution system: Increased system pumping head requirements. Increased energy consumption and operating costs. Distribution nozzles difficult to inspect and clean. Requires individual risers for each cell, increasing external piping costs.

Classification of cooling tower by use in fieldcanbe classified by use into either HVAC (air-conditioning) or industrial duty (a) Industrial cooling towers (b)HVAC

Classification by use in fieldHVAC:

An HVAC cooling tower is a subcategory rejecting heat from a chiller

Chiller removes heat from a liquid via a vapor-compression. This liquid is circulated through a heat exchanger to cool air or equipment as required.Air cooled chillers are also available

Schematic of chiller

Industrial cooling towersIndustrial cooling towers can be used to remove heat from various sources in industriesThe primary use of large, industrial cooling towers is to remove the heat absorbed in the circulating cooling water systems

Real life image

By heat transfer methodWet cooling towers or simply cooling towers operate on the principle of evaporation. The working fluid and the evaporated fluid (usually H2O) are one and the same.

By heat transfer methodDry coolers operate by heat transfer through a surface that separates the working fluid from ambient air, such as in a heat exchanger, utilizing convective heat transfer. They do not use evaporation