Evaporation is a key process used to concentrate solutions by removing solvents, primarily in food processing, pharmaceuticals, and chemical manufacturing. Single effect evaporators discharge vapours without reusing their energy, while multiple effect evaporators enhance efficiency by reusing vapours for heating across multiple stages. Both systems have specific advantages and disadvantages, impacting their suitability for various applications.

1. EVAPORATION

2. INTRODUCTION
◦ The purpose of evaporation is to vaporise the solvent in order to
enrich the solute in the solution. At the end of the operation
substance recovered is known as the Concentrate. As the solution
boils in turn releases vapour which may :
◦ Either be condensed in a condenser, in which case the process is
known as SINGLE EFFECT EVAPORATOR
◦ Or be used to heat another evaporator, in which case it is known as
MULTIPLE EFFECT EVAPORATOR

3. EVAPORATION
◦ Evaporation is an important unit operation commonly employed to
remove water from dilute liquid foods to obtain concentrated liquid
products. Removal of water from foods provides microbiological
stability and assists in reducing transportation and storage costs.
Evaporation differs from dehydration, since the final product
remains in liquid state.

4. SINGLE EFFECT EVAPORATOR
◦ Single effect evaporator is a device used to concentrate solutions,
typically by removing solvents (such as water) through evaporation.
This system is commonly used in industries like food processing,
pharmaceuticals and chemical manufacturing.
◦ In single effect evaporator the vapours produced are discarded
without further utilising their inherent heat.

5. WORKING PRINCIPLE
A conventional evaporator is heated by steam which
condenses and transmits heat energy to the solution to
be evaporated.
Heat supply: Steam is used as a heating medium.
Steam passes through a heat exchanger, typically
jacketed or tubular heat source.
Evaporation: The solution to be concentrated is
introduced into the evaporator. As the heat is applied,
the solvent evaporates leaving the solute behind and
increasing the concentration of the solution.
Condensation: The vaporised solvent is collected,
condensed back into liquid form and removed from
the system.

6. ◦ A typical evaporator consists of 3 components:
◦ Heat exchanger
◦ Evaporating system
◦ Separator
A heat exchanger, where the liquid undergoes boiling and evaporation and
separator that facilitates the separation of vapour from the liquid directing it to
the condenser or other equipment.
KEY COMPONENTS

7. ADVANTAGES
◦ Simple design and easy to operate.
◦ Low initial cost.
◦ Suitable for small-scale operations.
◦ Easy to clean and maintain.
DISADVANTAGES
◦ Low energy efficiency, high steam consumption.
◦ Higher operating costs.
◦ Limited capacity for large-scale use.
◦ Unsuitable for heat-sensitive materials.

8. APPLICATIONS
◦ Food Industry: Concentration of juices, syrups, and dairy products.
◦ Pharmaceuticals: Preparation of herbal extracts and syrups.
◦ Chemicals: Solvent recovery and waste reduction.

9. MULTIPLE EFFECT EVAPORATOR
◦ A multiple-effect evaporator (MEE) is a system used to improve the energy
efficiency of evaporation processes by utilizing steam multiple times across
several stages (effects).
◦ Commonly used in industries like sugar refining, pharmaceuticals, chemical
processing.
◦ By utilising the vapour generated in one evaporator to heat the next, it reduces
over all steam consumption, making it more efficient than single effect
evaporators i.e; if the vapours are reused as the heating medium in another
evaporator chamber then the evaporator system is called MEE.

10. WORKING
◦ An evaporator with 3 effects (3 stages) is a tube type forced
circulation evaporator in which strong steam is used for first effect
to evaporate solvent from the feed.
◦ In the second effect, the vaporised solvent is used to evaporate the
feed at atmospheric pressure.
◦ In the third effect, vapour from the second effect is used as
the heat source. The lower pressure allows evaporation at
a reduced temperature, further concentrating the solution
while reusing energy efficiently.
◦ In the final effect, the solution reaches its
maximum concentration. Vapour produced here is
either condensed or used elsewhere, and the
remaining concentrated product is collected.

11. PRINCIPLE
◦ The principle of a Multiple Effect Evaporator is based on:
◦ Reusing Vapour Heat: Vapour generated in one effect serves as the
heat source for the next effect.
◦ Pressure Gradient: Each effect operates at a progressively lower
pressure, reducing boiling points and enabling efficient
evaporation.
◦ This maximises energy utilisation and minimises steam
consumption.

12. Types of Feed Arrangement
◦ It's divided in to Four category on the basis of feed direction:-
1. Forward Feed Arrangement
Both feed and steam introduced in the first effect.

13. 2. Backward feed Arrangement
◦ Feed is introduced in last effect and steam is introduces in first effect.

14. 3. Mixed Feed Arrangement
◦ Feed is introduced in intermediate effect move forward and then backward to
effect 1 and steam introduced in first effect

15. 4. Parallel Feed Arrangement
◦ Feed is introduced directly in all three evaporators without transferring it
from one to the another

16. APPLICATIONS
◦ Food Industry: Large-scale production of condensed milk, tomato paste, and
sugar.
◦ Pharmaceuticals: Solvent evaporation in drug manufacturing.
◦ Chemicals: Concentrating solutions in large-scale processes.
◦ Pulp and Paper: Recovery of black liquor.

17. ADVANTAGES
◦ Advanced System,
◦ Easy Operation And Maintenance, ,
◦ It is continuous operation
◦ Cost Effective Operations.
◦ Solvent recovery is possible.

18. DISADVANTAGES
◦ High Initial Cost: Complex design increases capital investment.
◦ Complex Operation: Requires skilled operation and maintenance.
◦ Larger Space Requirement: Multiple stages need more installation area.