evaporator presentation
TRANSCRIPT
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Nestle Milkpak Ltd. SKP 2004
M.Arshad
Training onPowder Manufacturing
Evap & Egron Department
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Evaporator
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Introduction
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Contents:
Milk evaporation statistics
What is evaporation and why do it
Characteristics of evaporation Evaporator types
Falling film principle
Falling Film Evaporator elements
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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
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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%
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What is Evaporation?
Change from liquid phase to the vapour phase
For example,Boiling water
Heat
Water
Vapour
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What is Condensation
Change from vapour phase to the liquid phase
For example,
Condensing steam
Heat
Condensate
Vapour
?
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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)
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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
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Evaporation / ConcentrationMethods
Evaporator(indirect) - liquid in - liquid out
Spray Dryer(direct) - liquid in - solid out
Roller Dryer(indirect) - liquid in - solid out
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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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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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Falling Film Evaporator
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
Falling Film Evaporator
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Falling Film Evaporator
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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Falling Film Evaporator
Product IN
Going with the Product Flow...
Elements of a
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Falling Film Evaporator
Product IN
Pre-heater C,
PHC
Pre-heater 1,
PH1
Elements of a
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Falling Film Evaporator
Product IN
Pre-heater C
Pre-heater 1Pasteuriser
Steam
Condensate.
Elements of a
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Falling Film Evaporator
Product IN
Pre-heater C
Pre-heater 1Pasteuriser
Steam
Condensate
DSISteam.
Holding element
Elements of a
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Falling Film Evaporator
Product IN
Back Pressure Control
Distribution
CalandriaPre-heater C
Pre-heater 1Pasteuriser
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
Steam Back Pressure Control
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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Falling Film Evaporator
Product IN
Pre-heater C
Pre-heater 1Pasteuriser
Steam
Condensate
DSI
Steam Back Pressure Control
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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Falling Film Evaporator
Product IN
Pre-heater C
Pre-heater 1Pasteuriser
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