Evaporator Design for concentrating cane juice By G

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

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 ¡

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

Forced circulation Evaporator ¡ Applications: l l l ¡ Crystalline product Corrosive solutions Viscous solutions Frequent difficulties l l 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

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

Short tube vertical evaporators ¡ Applications: l l Clear liquids Crystalline product if propeller is used

Long tube evaporator ¡ Advantages: l l l 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)

Long tube evaporator ¡ Disadvantages: l l 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

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

Primary Design problems ¡ Heat Transfer ¡ Vapor Liquid separation ¡ Selection ¡ Product quality

Design ¡ Design parameters: l l l l 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

Rising Film Evaporator

Heat transfer Coefficients ¡ ¡ Shell side: we use Dittus – Boelter equation Tube side: we use Zukauskas correlation:

Arrangements ¡ Staggered arrangement: l l It allows maximum possible density of the tubes Maximum heat transfer

Final Calculations Final Design parameters: Tube: ID = 32 mm OD = 35 mm Height = 3. 5 m Shell side: OD = 1. 6 m Area = 1. 88 m 2 Down pour side : Diameter = 0. 4 m Evaporator: Area = 2. 01 m 2 Total height of the evaporator = 7 m Total no. of tubes in the evaporator = 1250