group b sdl presentation

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

Main FunctionsMain FunctionsFocus• 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

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

Purpose of Vacuuming the Purpose 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

Types of evaporators Types 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

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

Rising FilmRising Film Advantages:• Good for highly viscous

productsDisadvantages:• 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

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

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

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?

Concentrated Orange Juice PlantConcentrated Orange Juice Plant

CLASS EXCERISE!!!

Which evaporator is right for making concentrated OJ?

Advantages of Falling Film Evaporators Advantages 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

Falling Film EvaporatorsFalling Film Evaporators used in the making of

Concentrated Orange JuiceConcentrated Orange Juice

Falling Film EvaporatorFalling Film Evaporator

Falling Film EvaporatorFalling Film Evaporator

Production Rate?

Typical Size?

Typical Cost?

Falling Film EvaporatorFalling Film Evaporator

Production Rate?

1,890,000 liters per day

500,000 gallons per day

Typical Size?

Typical Cost?

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?

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

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

Q1 = Q2 + Q3 Q2 = 81.54 kg/hr

Mass BalanceMass Balance

iio

oo hf

r

r

k

rf

hU

1ln

11

2

12  

Tk

Lg

k

hl

L

VLL

3

13.1

TUAQ

The heat transfer coefficient of the steam

Governing EquationsGoverning Equations

Q Q

The heat transfer coefficient of the orange juice

L

V

V

LVLLbD

k

hL

25.0

34.09.09.0 ReRe(Pr)3.1

b = 128 (for SI units)

k

C pPrKorange= 0.148 + 0.00493W

D = Tube diameter

DV

Re

V = Velocity

W is % water content

Cporange= 3851J/kg K

orange = 1.03g/l

orange(70°F) = 89x - 2040

Governing EquationsGoverning Equations

Where x = ° Brix

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

Operability-FlexibilityOperability-Flexibility

• Q=UAT

Change Q by:• Affecting U• Affecting A• Affecting T T = Tsteam – Tproduct)

http://www.cheresources.com

Affecting UAffecting U

• Decrease velocity of feed (Increases U)– Increases residence time – Feed pipe sizing– Tube length

****Must be done during Design Stage****

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****

Affecting Affecting TT

• Temperature Sensitivity– Juice spoiling temperature

– Tsteam has a maximum

• Preheating– Bring fresh juice closer to boiling point

decreasing T

• Increase Steam Pressure

CLASS EXCERISE!!!

What special hygienic considerations must be taken into account when

working with food products?

Hygiene ConsiderationsHygiene Considerations

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

TroubleshootingTroubleshooting

Falling Film - Orange Juice

• Steam Hammer

• Metal Erosion

• Fouling & Solids Content

ReferencesReferences

• 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/Evaporator_HB.pdf