1. Evaporator Design for concentrating cane juice
By,
G Bharani
Harsh Gautam
M Jeevan
M N Karthik

2. Evaporator types and applications
Heating medium separated from evaporating liquid by tubular heating surface.
Confined by coils, jackets, double walls flat plates
Brought into direct contact with evaporating liquid
Heating by solar radiation
1)Highest heat transfer coefficients are obtained in forced ciculation evaporators when the liquid is allowed to boil in the tubes ( most used in indus)

3. Forced circulation Evaporator
Advantages:
High heat transfer coefficients
Positive circulation
Relative freedom from salting scaling and fouling
Disadvantages
High cost
Power for circulating pump
Relatively high holdup or residence time

4. Forced circulation Evaporator
Applications:
Crystalline product
Corrosive solutions
Viscous solutions
Frequent difficulties
Plugging of tube inlets by salt deposits
Poor circulation due to higher than expected head losses
Salting due to boiling in tubes
Corrosion and erosion
Circulation is maintained regardless of the evaporation rate so this type of evaporator is well suited to crystallizing operation

5. Short tube vertical evaporators
Advantages:
High heat transfer coefficients at high temperature differences
Low headroom
Easy mechanical de-scaling
Relatively inexpensive
Disadvantages:
Poor heat transfer at low temperature difference
Relatively high hold up

6. Short tube vertical evaporators
Applications:
Clear liquids
Crystalline product if propeller is used

7. Long tube evaporator Advantages: Low cost
Large heating surface in one body
Low holdup
Small floor surface
Good heat transfer coefficients at reasonable temperature differences (Rising film)
Good heat transfer coefficients at all temperature differences (Falling film)

8. Long tube evaporator Disadvantages: High head room
Generally unsuitable for salting and severely scaling liquids
Poor heat transfer coefficients of rising film version at low temperature differences
Circulation usually required for falling film

9. Long tube evaporator Applications: Frequent difficulties:
Clear liquids
Foaming liquids
Corrosive solutions
Large evaporation loads
Low temperature operation- falling film
Frequent difficulties:
Poor feed distribution in falling film

10. Primary Design problems
Heat Transfer
Vapor Liquid separation
Selection
Product quality
Heat surface represents largest part of evaporator cost. Selection based on highest heat transfer coeficeint Btu/hr/deg
Usually to prevent entrainment, Fouling or corrosion on the surfaces where vapor is condensed
evaporator performance is rated on the basis of steam economy (Kg of solvent evap/Kg of steam), The vapor produced can be reused to preheat the next evaporator, To inc efficiency add thermo compression evap.
Crystalisation(The conc shd not reach beyond 78 Brix), salting( it’s a growth on walls which results in inc in solubility with inc in temp) , scaling ( growth on the heating surfaces) , product quality corrosion and foaming.
Low hold up time, low temp operation to avoid thermal degradation dictates materials of construction to avoid metallic contamination or catalytic effect

11. Design Design parameters: Cross sectional area of tube
Length of each tube
Pitch in the tube bundles
Total area of the vessel
Height of head space
Cross sectional area of down pour
No. of tubes

12. Rising Film Evaporator

13. Heat transfer Coefficients
Shell side:
we use Dittus – Boelter equation
Tube side:
we use Zukauskas correlation:
We take

14. Arrangements Staggered arrangement:
It allows maximum possible density of the tubes
Maximum heat transfer

15. Final Calculations Final Design parameters: Tube: ID = 32mm OD = 35mm
Height = 3.5m
Shell side:
OD = 1.6m
Area = 1.88m2
Down pour side :
Diameter = 0.4m
Evaporator:
Area = 2.01m2
Total height of the evaporator = 7m
Total no. of tubes in the evaporator = 1250