Cooling Tower Roop

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Overview of CoolingTower

Prepared By:

Shubham katiyar

[email protected]


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LDPE

PRODUCT Low Density PolyEthylene

PRODUCT GRADE Indothene

PLANT TECHNOLOGY ATO FRANCE

PLANT CAPACITY 80,000 MTPA

(U-11 & U-12)

COMMISSIONING YEAR 1978

DETAIL ENGINEERING Technip and EIL

TYPE OF POLYMERISATION Free Radical Mechanism

NATURE OF REACTION Highly Exothermic (803 Kcal/Kg of

polymer)


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UNIQUE FEATURES OF LDPE

Tubular reactor

Operating pressure is very high (2000-2400 bars).

Operating Temp. is very high (300-310 0C).

Conversion is 20

23 %. High power consumption.

Reaction control needs skill .

Control room panel equipped with DCS. DM Water based cooling tower.


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PROCESS BLOCK DIAGRAM OF LDPE

PLANT

Hyper Comp.

Booster Comp.

LP

Separator

Extruder

Storage &

Bagging

MP

Separator

Hot

Water

Drum

Side injection

Oxygen

LPG/Propylene

OFF GAS

LPR

Cooler

MPR

Cooler

Primary comp.Fresh

ethylene

Top injection

Tubular reactorLP steam

Let down

valve


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Industries generate tremendous amount of

Heat

This Waste Heat is to be taken by cooling

water in various heat exchangers.

From cooling water the heat is dissipated into

the atmosphere and water is chemicallytreated and recirculated.


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There are two industrial method for disposing

heat.

Cooling of water on surface of a pond by

Spray ponds .

By a Cooling Tower.


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WHY COOLING TOWER ???

Rather than spray ponds , cooling tower has

more efficiency due to more exposure of

water surface and also occupies less area.


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COOLING TOWER THEORY

Each particle of water is assumed to be

surrounded by a film of air.

Difference in temperature of hot water

and cold air causes heat transfer and phase

change of water .


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PRINCIPLES

The heat transfer process involves

Latent Heat Transfer by vaporization of asmall portion of the water.

Sensible Heat Transfer by the difference in

temperature of water and air.About 80% of heat transfer is due to latent

heat and 20% to sensible heat.


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Cooling tower Theory

The Merkel Equation is

KaV/L = integral of (dT/h1-h2) under limits of T1and T2 which is entering and leaving watertemperature.

K=mass transfer constant

A = contact area

V = active cooling volume

L = water rate

T1 and T2 = entering and leaving water temperatures.h1 and h2 = entering and leaving water enthalpy.

The integral part of this equation is called as

L/G ratio which is said as

Tower characteristics .


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Cooling Tower heat balance


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L/G= h2-h1/T1-T2

Where

L/G =liquid to gas mass flow ratio

h2= enthalpy of air-vapor mixture at outlet wet bulb temperature

h1= enthalpy of air-vapor mixture at inlet wet bulb temperature

T1= hot water temperature

T2=cold water temperature


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Choosing a cooling tower


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TYPES OF COOLING TOWER

Natural Draft Cooling Tower

This type of cooling tower has a

unique design of converging diverging area

which causes air to flow naturally from

downwards to upwards

This type of tower is used for energy saving


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Mechanical draft cooling tower

This is of two type.

Forceddraft

This tower has a fan mounted at its base and

air is forced from bottom and discharge at

low velocity through top.

(* Fan is subjected to less corrosion but low

exit air velocity causes recirculation.*)


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Induced draft tower

This tower has a fan at top.

Classification based on relative direction of

water and air.

Counter flow arrangement.

water and air flows in opposite direction

obtaining max. heat transfer, water is

sprayed through nozzle.


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Cross flow Cooling tower

Water and air flows perpendicularly.Fill

material is at sides.

* Ultimately, the economic choice between

counter flow and cross flow is determined

by the effectiveness of fill,design conditionsand the cost of tower manufacture.


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Cross flow type cooling tower


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Counter v/s cross flow


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Cooling tower at LDPEMulti-Blade

1.Fan

Distribution AreaSplash

Bar GridAnd

Supports

Air FlowLouvers

Drift Eliminators LongitudinalPartition

Air Flow

End WallCasing

Air Flow


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Cooling tower at LDPE


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Fan blades


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Special rubber bush coupling


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Cooling Tower Operation Water make up (Wm) is sum of losses in cooling

tower. We = Evaporation loss

Wd = Drift loss

Wb = Blow down

Wm= We +Wd +Wb

We= 0.00085Wc(T1-T2)

Wc= Circulating water flowWd= 0.1% of Wc


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Cycles of Concentration

Blowdown is for discarding a portion ofconcentrated circulating water due to theevaporation process in order to lower the systemssolid concentration.

Cycles of concentration (COC) is the ratioof dissolved solids in recirculated water to

dissolved solids in make up water.

COC = (We+Wb)/Wb

So Wb= We/(COC-1)

Normally COC is in range of 5-7 cycles.


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Factors governing

Performance of cooling tower Time of contact between water and air.

Water concentration

Cooling Range Approach to wet bulb temperature.

Quantity of water to be cooled

Wet bulb temperature. Air velocity through the cell

Tower height


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At LDPE we have Induced Draft Cross Current flowtype cooling tower.

C t ti d t il


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Construction detailsMulti-Blade

1.FanDistribution AreaSplash

Bar GridAnd

Supports

Air FlowLouvers

Drift Eliminators LongitudinalPartition

Air Flow

End Wall

CasingAir Flow


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Water circulation


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LDPE Cooling Tower Details

Equipment No. 36-34-113

Capacity 4500 m3/hr

Heat load 56 X 10e6 Kcal/hr Hot water temp. design 46.5 deg. C

Cold water temp.design 33 deg. C

Design ambient wet bulb temp. 29 deg C

Approach 4 deg C

Make up water DM water


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Volume of cooling tower sump 780 m3 Volume of pump sump 355 m3

Volume of connecting channel 35 m3

Volume of distributed lines 500 m3

Total hold up 2000 m3

LDPEs water consumption is 2700 m3/hr


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Two pumps of 2285 m3/hr each

( GA 165/166/167) = 4570 m3/hr

One pump of 350 m3/hr

(GA 333/334) = 350 m3/hrTotal = 4920 m3/hr

assuming 80% pump efficiency

total discharge is 4000 m3/hr


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Water Treatment Water treatment is done by Chembond Drewtreat Ltd.

Chemicals added..

Orthophosphate For maintaining ph of water.

7.2-7.8 and corrosion inhibition

Biocide For microbiological control

Methyle Base Thiocynide.(MBT)

Quartarnary Amonium Compound

(* Temp. inside the cooling tower supports the bacteriawhich generates HNO3 and other acids.)


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A Dispersant is also added to not settledown the phosphate in sump or heatexchangers.

Candy Filter is used to remove turbidityfrom water. Its a column of sand

gravels,pebbles and water passes from it.

30% of total flow passes from it.


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Candy Filter


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Cooling tower inside cell


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Cooling Tower Roop