Not All Juices are Created Equal!

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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

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EVAPORATORS
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Main 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

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Elements 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

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Purpose of Vacuuming the Product Side

• Decreases boiling point of the liquid, thereby,
  the product boils relatively at low temperatures,
  thus minimising the heat damage

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Types of evaporators 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

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Natural Circulation

• Advantages
• Low capital and maintenance cost
• Disadvantages
• Unsuited for high viscosity products

Partial Vapour
100 Liquid
http//www.apv.com/Technologies/Downloads/Evaporat
or_HB.pdf
8
Rising Film

• Advantages
• Good for highly viscous products
• Disadvantages
• Low heat transfer coefficient due to slow film
  development
• Requires T difference greater than 25F
• Long residence times

Vapour/Liquid Separator
Preheater
http//www.apv.com/Technologies/Downloads/Evaporat
or_HB.pdf
9
Falling Film

• Advantages
• Operates with low T difference
• Very short residence times
• Disadvantages
• Not suitable for highly fouling products

http//www.apv.com/Technologies/Downloads/Evaporat
or_HB.pdf
10
Forced 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/Evaporat
or_HB.pdf
11
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?

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Concentrated Orange Juice Plant
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CLASS EXCERISE!!!

• Which evaporator is right for making concentrated
  OJ?

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Advantages of Falling Film Evaporators for
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

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Falling Film Evaporators used in the making of
Concentrated Orange Juice
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Falling Film Evaporator
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Falling Film Evaporator

• Production Rate?
• Typical Size?
• Typical Cost?

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Falling Film Evaporator

• Production Rate?
• 1,890,000 liters per day
• 500,000 gallons per day
• Typical Size?
• Typical Cost?

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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?

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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

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Mass Balance
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
Q2 ?
X2 65
X1 12
Q3 ?
Assume 1 hr 0.12(100kg/hr) 12 kg soluble
solid 0.65Q2 12kg Q2 18.46
kg/hr Q1 Q2 Q3 Q2 81.54 kg/hr
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Governing Equations
 
Q
The heat transfer coefficient of the steam
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Governing Equations
The heat transfer coefficient of the orange juice
b 128 (for SI units)
Korange 0.148 0.00493W
W is water content
D Tube diameter
Cporange 3851J/kg K
?orange 1.03g/l
?orange(70F) 89x - 2040
V Velocity
Where x Brix
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Operability 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

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Operability-Flexibility

• QUADT
• Change Q by
• Affecting U
• Affecting A
• Affecting DT
• (DT Tsteam Tproduct)

http//www.cheresources.com
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Affecting U

• Decrease velocity of feed (Increases U)
• Increases residence time
• Feed pipe sizing
• Tube length
• Must be done during Design Stage

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Affecting 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

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Affecting DT

• Temperature Sensitivity
• Juice spoiling temperature
• Tsteam has a maximum
• Preheating
• Bring fresh juice closer to boiling point
  \decreasing DT
• Increase Steam Pressure

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CLASS EXCERISE!!!

• What special hygienic considerations must be
  taken into account when working with food
  products?

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Hygiene Considerations

• Cleaning of equipment daily
• Stainless Steel Construction
• Ensure sanitary plant and working conditions
• Food grade lubricants
• Food grade storage containers/utensils

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Troubleshooting

• Falling Film - Orange Juice
• Steam Hammer
• Metal Erosion
• Fouling Solids Content

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References

• http//www.niroinc.com/evaporator/esys.html
• http//www.cheresources.com/evapzz.shtml
• Geankoplis, Christie J., Transport Processes and
  Unit Operations, 3rd Ed., Prentice Hall, 1993, p.
  263-267
• http//www.apv.com/Technologies/Downloads/Evaporat
  or_HB.pdf