This document discusses various types of industrial pollution and methods for treating polluted wastewater. It focuses on pollution from the chemical industry, which can be minimized by recovering undesired reaction products, excess raw materials, spent catalysts, and solvents before treating wastewater. Conventional wastewater treatment is only effective for water with low inorganic content, below 5000 ppm. For higher levels, reverse osmosis or evaporation using multiple effect evaporators is recommended. Multiple effect evaporators use less steam and power compared to single effect or batch evaporators.

1. On
MULTI EFFECT EVAPORATION
By
Rajendra prasad vellanki

2. Problem of Pollution
• Air Pollution
• Water Pollution
• Soil Pollution by waste solids
• Noise Pollution
We are considering only water and air
pollution

3. Water Pollution
Waste water is normally polluted with either organic
or inorganic substances
• Organic Substances – Biodegradable
• Inorganic Substances – Non-Biodegradable
(Not only they are non-biodegradable they affect
the process of biodegradation by microbes)

4. Air pollution
Pollution is caused by various activities like
vehicular traffic, industry, other human
activities.
We are considering industrial pollution &
pollution due to chemical industry in
particular.

5. Pollution is caused in chemical industry
because of following reasons.
i. Undesired products are formed in
chemical reactions.
ii. Cheaper Raw Materials used in excess
appear as pollutants.
iii. Solvents.
iv. Spent Catalyst.

6. • If Pollution is caused by these materials,
pollution will be minimised if these
materials are removed (or recovered?)
• We advise recovery of these materials
before sending waste water for
treatment.

7. i. Dilute Sulfuric Acid – can be
concentrated by evaporation.
ii. Reactants used in excess – recovered
by distillation or extraction
Raw Materials Used in Excess

8. Undesired Reaction Products → Can be
converted into biproducts.
E.g. Sodium Sulfate, Calcium Sulfate,
Calcium Chloride, Hydrochloric Acid
Sulfur Dioxide (Sod. Sulfite), H2S (Na2s &
NaHS), Potassium Bromide, Sodium
Bromide.

9. • Spent Catalysts
i. Aluminium Chloride –converted to PAC
& Sold.
ii. Nickel & Catalyst – Nickel is recovered.
iii. Palladium Or Carbon – Palladium is
recovered.

10. • Vent gases from Dryers, Centrifuges &
Vac Pumps
i. Normally Pollution is caused by solvent
vapours which are mixed with exhaust
air.
ii. Solvents can be recovered by scrubbing
or adsorption.

11. Conventional waste water
treatment
• Traditional method of effluent treatment
has been to collect all the waste water
& resort to Primary & Secondary
Treatment.

12. Primary Treatment
• Oil and grease separation
• Equalization
• Neutralization
• Clariflocculation
• Sludge drying beds

13. Secondary Treatment
• Aeration (Biological oxidation)
• Clarification
• Sludge drying beds
This works properly for waste water
containing not more than 5000 ppm of
inorganic and in some cases up to 10000 ppm
of inorganic solids.

14. • In practice in API industry it is found that the
TDS Levels in waste water are invariably >
20,000 PPM.

15. What if inorganic is more than
5000 ppm ?
• Reverse osmosis (RO)
• Evaporation
( Single, Double, Triple & Multiple Effect)

16. Reverse Osmosis
• Energy requirement is less compared to evaporation.
• Limitation is concentration of solids( as the solids
concentration goes on increasing the pressure required
goes on increasing and consequently power requirement
goes up.)
• Suitability of membrane should be evaluated carefully.
• Evaporation has to be resorted to as the ultimate means
for removal of solids.

17. Continuous Evaporation
• Single Effect Evaporator (with thermo
compressor)
• Double Effect Evaporator (with TC)
• Triple Effect Evaporator (with TC)
• Multiple effect evaporator (with TC)

18. Batch Evaporation
• Sensible heat can not be recovered
• Peak loads are high
• Very High Operating Cost
• Cooling requirements are high
• Very easy to operate

19. Why Multiple Effect Evaporators?
• Low steam consumption(0.33 Vs 1.2 in batch)
• Continuous operation enables recovery of
sensible heat almost completely
• Cooling water requirement is less
• Less manpower required

20. Apprehension
• Chocking of tubes
• Corrosion
• High Initial Cost
• High power requirement

21. Chocking Of Tubes
• In forced circulation evaporator the design does not
allow evaporation on tube surface (Evaporation is done
in flash chamber). Hence there is no possibility of solids
deposition on tube surface.
• Velocity of liquid in tubes is very high in FCE
• Vacuum operation makes it possible to operate at less
than 700
c(for single and double effect).SS316Lis suitable
for sodium chloride at this temp

22. High Power Consumption
• When there is no possibility of solid
deposition ( e.g. dilute stream) RFE/FFE is
used which consumes less power.
• Selection of the pumps is done to minimize
power (e.g. axial flow pumps)

23. COST COMPARISION OF EVAPORAOTRS
Comparison Of Cost (for coal fired boiler)
Evaporator
Steam Cost per 1000
Kg
Power Cost per 1000
Kg
Types of water Evaporation of water Evaporation
Conventional
evaporator
Rs.720 Rs.54
in reactor
Single Effect
RS.360with TC RS.90
Double Effect
with TC RS.270 RS.100
Triple Effect
with TC RS.180 RS.120