1. Not All Juices are Created Equal!Not All Juices are Created Equal!
• 100% Pure or 100% Juice
Guarantees 100% pure fruit juice
• “Cocktail”, “Punch”, “Drink”, “Beverage”
Terms which indicate diluted juice containing less than
100% juice, often with added sweeteners
• “From Concentrate”
Water is removed from whole juice to make concentrate;
water is then added back to reconstitute juice
• Fresh Frozen
Freshly squeezed, packaged and frozen without
pasteurization
2.
3. Main FunctionsMain Functions
Focus
• Pre-concentrate foods prior to drying, freezing or
sterilization: fruit juices, milk, coffee
• Preservation by reducing water activity: molasses,
condensed milk, evaporated milk
• Convenient food for consumers or manufacturers:
soups, pastes, fruit concentrates
• Reduce transportation and storage cost
Other Uses
• Reboilers at bottom of distillation column
4. Elements of EvaporatorsElements of Evaporators
Essentially evaporators consist of:
• A heat exchanger (calandria): to transfer heat from
low-pressure steam to the product under vacuum
• A means of separating the vapours produced
• Mechanical or steam ejector vacuum pump
5. Purpose of Vacuuming thePurpose of Vacuuming the
Product SideProduct Side
• Decreases boiling point of the liquid, thereby, the
product boils relatively at low temperatures, thus
minimising the heat damage
6. Types of evaporatorsTypes of evaporators
for food processing include:for food processing include:
Most Common
• Natural Circulation
• Rising Film
• Falling Film
• Forced Circulation
Special Purpose
• Batch pan
• Wiped film
• Plate tubular
• Rising/Falling Film
7. Natural CirculationNatural Circulation
Advantages:
• Low capital and
maintenance cost
Disadvantages:
• Unsuited for high
viscosity products
100% LiquidPartial
Vapour
http://www.apv.com/Technologies/Downloads/Evaporator_HB.pdf
8. Rising FilmRising Film
Advantages:
• Good for highly viscous
products
Disadvantages:
• Low heat transfer
coefficient due to slow film
development
• Requires T difference
greater than 25°F
• Long residence times
Vapour/
Liquid
Separator
Preheater
http://www.apv.com/Technologies/Downloads/Evaporator_HB.pdf
9. Falling FilmFalling Film
Advantages:
• Operates with low T
difference
• Very short residence
times
Disadvantages:
• Not suitable for highly
fouling products
http://www.apv.com/Technologies/Downloads/Evaporator_HB.pdf
10. Forced CirculationForced Circulation
Advantages:
• Suitable for products
susceptible to scaling
or crystallization
Disadvantages:
• High costs due to
pump and piping
requirements
http://www.apv.com/Technologies/Downloads/Evaporator_HB.pdf
11. Which is right for you?Which is right for you?
Two Major Criteria:
•Is this equipment best suited for the duty?
•Is the equipment arranged for the most
efficient and economic use?
14. Advantages of Falling Film EvaporatorsAdvantages of Falling Film Evaporators
for Orange Juice Concentrationfor Orange Juice Concentration
• Juice is fed from the top over the heating surface
in a thin film, and falls with gravity, so low energy
costs
• Very small retention time, avoiding sugar loss
• No stagnation of juice over the tube surfaces and
minimized scaling
• High evaporation rates
18. Falling Film EvaporatorFalling Film Evaporator
Production Rate?
1,890,000 liters per day
500,000 gallons per day
Typical Size?
Typical Cost?
19. Falling Film Evaporator
Production Rate?
1,890,000 liters per day
500,000 gallons per day
Typical Size?
23 m high X 3 m wide or
75 ft high X 10 ft wide
Typical Cost?
20. Falling Film Evaporator
Production Rate?
1,890,000 liters per day
500,000 gallons per day
Typical Size?
23 m high X 3 m wide or
75 ft high X 10 ft wide
Typical Cost?
$2,000,000
21. Juice contains 12% soluble solids. You want to obtain a concentrate of 65%
soluble solids. How much water has to be removed?
Q1 =100 kg/h
X2 = 65%
Q3 = ?
Q2= ?
X1 = 12%
Assume 1 hr
0.12(100kg/hr) = 12 kg soluble solid 0.65Q2 = 12kg Q2 = 18.46
kg/hr
Q = Q + Q Q = 81.54 kg/hr
Mass BalanceMass Balance
23. The heat transfer coefficient of the orange juice
( ) ( ) ( )
+=
L
V
V
L
VLLbD
k
hL
µ
µ
ρ
ρ
25.0
34.09.09.0
ReRe(Pr)3.1
b = 128 (for SI units)
k
Cp µ
=Pr
Korange
= 0.148 + 0.00493W
D = Tube diameter
µ
ρDV
=Re
V = Velocity
W is % water content
Cporange
= 3851J/kg K
ρorange
= 1.03g/l
µorange
(70°F) = 89x - 2040
Governing EquationsGoverning Equations
Where x = ° Brix
24. Operability IssuesOperability Issues
• Operating window
• Maintain plant operation during failures
• Safe operation
• Prevent damage to equipment
• Startup and shutdown
• Flexibility
• Resiliency to disturbances
• Monitor process and diagnose problems
26. Affecting UAffecting U
• Decrease velocity of feed (Increases U)
– Increases residence time
– Feed pipe sizing
– Tube length
****Must be done during Design
Stage****
27. Affecting AAffecting A
• Use larger (smaller) tubes
– Permitting more (less) H.T.
• Nozzle
– At top of evaporator
– Can spread liquid out more
– Caution: we must maintain even wetting
****Must be done during Design
Stage****
28. AffectingAffecting ∆∆TT
• Temperature Sensitivity
– Juice spoiling temperature
– Tsteam has a maximum
• Preheating
– Bring fresh juice closer to boiling point
∴decreasing ∆T
• Increase Steam Pressure
