Evaporator Presentation

7/29/2019 Evaporator Presentation

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Nestle Milkpak Ltd. SKP 2004

M.Arshad

Training onPowder Manufacturing

Evap & Egron Department


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M.Arshad

Evaporator


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M.Arshad

Introduction


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M.Arshad

Contents:

Milk evaporation statistics

What is evaporation and why do it

Characteristics of evaporation Evaporator types

Falling film principle

Falling Film Evaporator elements


5/63Nestle Milkpak Ltd. SKP 2004 M.Arshad

Global Statistics on Milk (2004)

World fresh milk

production:

577 Mio Ton Nestle share:

12.1 Mio Ton

Nestle

2.1%

Others

97.9%

Nestle

Others



Statistics on Milk Processed withEvaporators (2004)

Fresh milk processed atNestl: 12.1 Mio Ton

Milk processed in

Evaporators: 8.0 Mio Ton

(66% of Nestl total milk)

SCM9%

Others

6%

UHT + steril

7%

Chocolate

7%

IceCream

5%Milk powders

50%

Evap

7%

White refr.

9%



What is Evaporation?

Change from liquid phase to the vapour phase

For example,Boiling water

Heat

Water

Vapour



What is Condensation

Change from vapour phase to the liquid phase

For example,

Condensing steam

Heat

Condensate

Vapour

?



Evaporation by means of steam

Heat transfer because of

temperature difference

Condensate

Steam

Milk

Vapour

Steam at

Higher temperature

Vapour at

Lower temperature

Surface to

exchange heat(indirect)



So during evaporation:

* Solids do not evaporate ,hence

* Concentration of solids in liquid phase increases

100 kg Milk, 12 % TS:

12 kg solids88 kg water Evaporator

76 kg vapour

24 kg Milk, 50 % TS:

12 kg solids12 kg water



Evaporation / ConcentrationMethods

Evaporator(indirect) - liquid in - liquid out

Spray Dryer(direct) - liquid in - solid out

Roller Dryer(indirect) - liquid in - solid out



Why Evaporate/concentrate

Volume ReductionFor example: to reduce transport volume of Milk from source to factory.

PreservationFor example: Milk Powder: suspended bacteriological activity due to lack of

water.

?

ConvenienceFor example: - Evaporated Milk.

- Instant Coffee/ Tea whitener


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Nestle Milkpak Ltd. SKP 2004 M.Arshad

Evaporator Types

The Old Vacuum Pan

Recirculation Evaporators

Climbing Film Evaporators

Falling Film evaporators

Plate Evaporators


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Energy Use =

1.25 KW/Kg H2O

Energy Use =

0.07 KW/Kg H2O

SPRAYDRYER

Fresh milk:

1000 kg

Energy Use

= 4.2 KW/Kg H2O

Energy Use

= 4.2 KW/Kg H2O

Evaporates

3.1 kg of water

Evaporates

121 kg of water

Evaporates

747 kg of water

Why are Evaporatorsthe preferredconcentration

equipment(example IMP)

time: 12-15 min Time: 1/4-1 min Time: 5-15 min

12.5% 97.3%95%49.5%Evaporator Spray dryer Afterdryer


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Evaporator Process ATSKP

Std silo

Condenser

Pre-heating

Thermo compressorPasteuriser

DSI

Back pressure

Evaporation in

1st Effect

2nd Effect

4

th

Effect-A&B3rd Effect-A&B

Ex-Evap

Homo tank

Buffer tank(if need)


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BRAN & LUEBBEMETERING SYSTEM

Flowsheet of SKP evap.


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Evaporator Process

Standardized Silo Plan

Batch card

Quality

MSA/DPSA


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Evaporator Process

CondenserSTD Milk Temp

Cooling tower

Preheating of milk

Vapour condensation


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Condenser

Vapoursarecondensedby

means of Cooling Water

This creates a SUCTION EFFECT

i.e. VACUUM

In

The BIG volume

0ccupied by the

VapoursIs suddenly

reduced to

To a very small

volume of liquid

Out


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Condensate

Condensate from Pasteurizer: -->Boiler House

Condensate from 1st effect: -

conductivity measurement, if OK

--> to Boiler House

Condensate from other effects andCondenser:

--> Other uses

Pure-Condensate

Condensate-

from Product

Vapour

Condenser

Pasteurizer

Condensate from Steam-recompressedvapours

Steam

Steam


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Pre-Heaters

Product IN

Pre-Heater C

Pre-Heater 1

Pre-heat Product to ~70 C

Thermal EconomyEnergy has already worked

upstream Gentle heating

Low T

Heating media (vapours) at the rightT readily available


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Evaporator Process

Balance TankBalance tank is a feeding source of Evaporator in

this we volume makeup

Buffer milk & wet rework

Th C


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Thermo-Compressor

Vapour Pump H P Driving Steam

recompresses and mixes

with the Sucked Vapour

Simple, no moving parts

Robust (not much to go wrong) Small Unit, for Large Volumes.

To Next Effect-or

To Condenser

Vapour, mixed

Compressed

with Steam

Driving Steam

Sucked Vapours

Heating Side

Fed to

of #1 Effect at

higher T


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Msteam

Psteam

Msuck

Mdisch

Psuck

Pdisch

1 2 3 4 5

1) Head

2) Steam Nozzle

3) Converging Section

4) Throat

5) Diverging Section

Thermocompressor Nozzle


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Pasteuriser

Pasteuriser

Heats Product, from ~70 C to ~ 85 C Heating time is Critical

long time = Coil

short time =PHE

= Straight Tube Running time > = 20h


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DSI


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DSIDirect Steam Injection

Short Time Heat Treatment

Heat Productfrom 85 C to say 108C

Followed by Holding Tube

-Holding time - 5 to 10 Sec

-Variable holding time as needed

-Watering effect ~ 4% for 20Ctemperature rise


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Why Back Pressure?

Product at high T >100 C

Uniform flow

To avoid boiling

Ensures:

Correct T is reached

Correct holding time Prevents:

Premature Flashing

Back Pressure


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Evaporator Process

Evaporation in1st Effect

Product Inlet Nozzle at ist effect


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Product Inlet Nozzle at ist effect

Flash-Vapour

Calandria Top Cover

Product Feed-Under Pressure

And Diverter

Flow through

S.S. Nozzle

d lThe Back pressure

will depend on "l"

and "d",

calculated for a

certain flowrate


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Evaporator Process

Evaporation in2nd Effect

E P


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Evaporator Process

Evaporation in

4th Effect-A&B

E t P


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Evaporator Process

Evaporation in3rd Effect-A&B

E t P


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Evaporator Process

Ex-EvapEx Evap is a point milk can divert in three direction

Balance tank for circulation

Buffer tank in case of problem on Egron

Homo tank for Egron feeding

E t P


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Evaporator ProcessHomo tank

Homo tank feeding source of EgronIts level always on minimum position 20 to 40 % forbetter quality

E t P


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Evaporator Process

Buffer tank

Capacity of Buffer Tank 3800 Lt

Milk taken in Buffer Tank when theproblem on Egron

If the dietetic product then milk transfer

in STD

If the nondietetic product then milk

reused in the balance tank

Temperature of milk should be 4 to 8

Falling Film Evaporator


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Is mainly a heat exchanger with vertical tubes.

The Product flows from top to bottom inside

the tubes --> FALLING

The Product is fed to form a thin FILM insidethe tube

FALLING FILM EVAPORATORcondensate

steam

Product In

Product Out

vapour

The film:


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Boiling Tube

Inside the Boiling Tube

- Thin Film of Product

- Evaporated Vapours

Outside the Boiling Tube

- Steam / Vapours

- Condensed Steam

VapoursSteam

Conde

nsate

Vapours

Prod

uct

The film:

Calandria Top

The film:


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Distribution Tray-

and

Calibrated orifices

Flooded

Tube-End-Plate

Product Strainer

Boiling Tube

Steam

outside

B. Tube

With Flash

Vapours

Vapour Tubes

with

With Product film

inside

Product from

back

pressure

device

The film:

Th fil


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Product

Boiling Tube

Boiling Tube

Center Line

Vapours help keeping

film against the tube

Product overflows into

tubes from all sides

Boiling Tube

End Plate of Tubes

The film:


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Boiling Tube

Vapours

Stea

m

Condensate

Vapour

s

Produ

ct

Critical

Liquid Product on all Heat Exchange Area Equal Distribution among tubes

Even Coverage on all inside of tube ==> Liquid Load.

Condensate

Vapours

Stea

m

Va

pours

Condensed

Water with

Increasing FILMthickness

Product FILM

ThicknessDecreasing as

Water evaporates

Liquid load


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n = number of boiling tubes d = diameter of boiling tube

in kg/(m.h)

In practice if < certain value:

Film unstable

Film may be torn off

Film will dry outFilm will burn

Fouling

Ultimately completely block tubes.

dnncecircumferepipeMeterflowmassProduct= Mproduct

Liquid load

How can we increase the Liquid Load?


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q

Vapours

4 T/h

Vapours

10 T/h Recirculation

6 T/h

Vapours

10 T/h

6 T/h 7.3 T/h

AB

6 T/h

over 40 tubes over 60 tubes

Mvap A

Mvap B

+

By Splitting the Effect

By Recirculation


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Falling film evaporator

Elements



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Cooling Water IN

Product IN

Pre-heater C

Pre-heater 1Pasteuriser

Steam

Condensate

DSI

Steam Back Pressure Control

Distribution

Calandria

Separator

Steam

Condensate

THC

Condenser

Cooling Water OUTProduct OUT

Elements of a


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Product IN

Going with the Product Flow...

Elements of a


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Product IN

Pre-heater C,

PHC

Pre-heater 1,

PH1

Elements of a


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Product IN

Pre-heater C


Steam

Condensate.

Elements of a


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Product IN

Pre-heater C


Steam

Condensate

DSISteam.

Holding element

Elements of a


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Product IN

Back Pressure Control

Distribution

CalandriaPre-heater C


Steam

Condensate

DSI

Steam

Separator

Product OUT

Holding element

Elements of a Falling Film Evaporator


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Steam

Product IN

Pre-heater C

Pre-heater 1

Steam

Condensate

DSI


Distribution

Calandria

Separator

Product OUT

Thermo-compressor

or THC

On the Vapour Side....

Sucked vapours

The Vapours are

recompressed by

the THC

Elements of aF lli Fil E t


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Product IN

Pre-heater C


Steam

Condensate

DSI


Distribution

Calandria

Separator

Steam

Condensate

THC

Condenser

Cooling Water IN

Condenses

Vapours

Cooling Water OUT

Elements of aF lli Fil E t


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Product IN

Pre-heater C


Steam

DSI

SteamBack Pressure Control

Distribution

Calandria

Separator

Product OUT

Steam

THC

Condenser

Cooling

Water

Water side ofCondenser can be

De-aerated

Other elements are De-

aerated by Diaphragms

Non-Condensables

are evacuated by

The Vacuum

System

When to Pasteurise ?


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Upstream of Evaporation

Pasteurisation prevents:Subsequent bacteriological Development

Pasteurisation provides:Heat stability to milk and thereby reduced

fouling in evaporator

P0 , T0


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say: 2 bar, 100C

Expansion Vessel at P1, T1

say :286 mbar, 68C

FLASH

When aliquid at higher P, T

it will evaporate some liquid to

cool it to the new mediums T.

the vapour so produced is called

Flash

Enters into a medium withlower P, T

Separator


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Droplets of liquid must be separated from theVapours:

Cyclone

Vapour Discharge at Top

Droplets, Liquid,

DownwardsCritical: Vapour Velocity

depends on:

-Mass flow

-Vapour Density.

Vapour Duct

Separator

Calandria

Vapour Discharge

Productto

Discharge Pump

De-Aeration


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System containsAir (gases) that

must be removed to have good

heat exchange

Air (gases) evacuated viaCalibrated diaphragms to:

- next Effect

- or to the Condenser.

SteamCondenser

Orifice

De-Aeration

Vacuum system


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Cooling

Water

Condenser

VACUUM is made by the

Condenser, but

VACUUM is MAINTAINED by

evacuating the non

condensablesby means of:

VACUUM SYSTEM

- Vacuum Pump

- Ejectors

Vapour Ducts


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Carry the vapours to the next

effect, to the Condenser or to THC

Critical:

Vapour velocity

Pressure Drop

How is an EvaporatorControlled ?


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Controlled ?

More Steam = More EvaporationProvided

Equipment operate within allowable:

Design thermal Load

THC operating range

Vapour velocities, calandria and separator

Liquid loads

Temperature profile

Control, Action & Reaction


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Steam Water

TS % C kg/h

Process

C

Productout

TS %kg/h kg/h

Product at Inlet

CONTROL ACTION REACTION

Advantages


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Small liquid content and high flow velocities: Short residence time, gentle evaporation

Small amount of cleaning agent needed

Good controllability and automation

High final concentrations possible Can operate at low delta T, since operation independent of thermal force

like in Circulation evaporators

Possible to use 15 m or longer tubes

Allows application of Falling Film principle for virtually allcapacities

Uniform thermal treatment of product


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Thank you

Evaporator Presentation

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