Economy of multiple effect evaporator MCQs With Answer

Economy of multiple effect evaporator MCQs With Answer

Understanding the economy of multiple effect evaporators is essential for B.Pharm students involved in pharmaceutical concentration and solvent recovery. This introduction covers steam economy, heat transfer, gained output ratio (GOR), and factors affecting evaporation efficiency in multi-effect systems used for syrups, extracts, and active pharmaceutical ingredient (API) concentrates. Topics include calculation of economy (kg water evaporated per kg steam), impact of number of effects, temperature drops, non-condensable gases, fouling, and mechanical vapor recompression (MVR). Clear grasp of these concepts helps optimize energy use and product quality in pharmaceutical manufacturing. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What does “economy” of a multiple effect evaporator typically refer to?

• Ratio of heat lost to heat supplied
• kg of water evaporated per kg of steam used
• Number of effects multiplied by steam pressure
• Volume of feed processed per hour

Correct Answer: kg of water evaporated per kg of steam used

Q2. The theoretical maximum economy of an ideal n-effect evaporator (ignoring losses) is:

• n/2
• n
• 2n
• sqrt(n)

Correct Answer: n

Q3. In practice, the actual economy of a multiple effect evaporator is usually:

• Equal to the number of effects
• Greater than the number of effects
• Less than the number of effects due to heat losses and temperature differences
• Independent of heat losses

Correct Answer: Less than the number of effects due to heat losses and temperature differences

Q4. What is the main advantage of increasing the number of effects in an evaporator?

• Decrease in required feed flow rate
• Increase in steam economy (more evaporation per unit steam)
• Increase in product contamination risk
• Higher condenser duty

Correct Answer: Increase in steam economy (more evaporation per unit steam)

Q5. Which factor reduces the economy of an evaporator?

• Smaller temperature differences between effects
• Improved insulation
• Heat losses and non-condensable gases
• Proper vacuum operation

Correct Answer: Heat losses and non-condensable gases

Q6. Gained Output Ratio (GOR) is another term for:

• Heat transfer coefficient
• Economy or kg water evaporated per kg steam
• Boiling point elevation
• Steam pressure in the first effect

Correct Answer: Economy or kg water evaporated per kg steam

Q7. If a 3-effect evaporator produces 300 kg of water using 100 kg of steam, the economy is:

• 0.33 kg/kg
• 1 kg/kg
• 3 kg/kg
• 300 kg/kg

Correct Answer: 3 kg/kg

Q8. What is the effect of increasing boiling point elevation (BPE) of the solution on evaporator performance?

• Increases theoretical economy
• Reduces heat transfer driving force and lowers capacity
• Makes no difference to performance
• Eliminates need for vacuum

Correct Answer: Reduces heat transfer driving force and lowers capacity

Q9. Mechanical Vapor Recompression (MVR) is used to:

• Reduce fouling on heat surfaces
• Compress and reuse vapor to improve economy
• Increase the number of effects automatically
• Lower feed concentration

Correct Answer: Compress and reuse vapor to improve economy

Q10. In a forward-feed multiple-effect evaporator, feed enters:

• The coldest effect first and progresses to the hottest
• All effects simultaneously
• The hottest effect first and progresses to the coldest
• The middle effect first

Correct Answer: The hottest effect first and progresses to the coldest

Q11. Which configuration gives higher thermal efficiency: forward-feed, backward-feed, or mixed-feed?

• Forward-feed generally offers better economy for heat recovery
• Backward-feed always offers the best economy
• Mixed-feed is always optimal
• All configurations have identical economy

Correct Answer: Forward-feed generally offers better economy for heat recovery

Q12. What is entrainment in evaporators?

• Condensation of vapor in the condenser
• Carryover of liquid droplets with vapor leaving the effect
• Formation of scale on heating surfaces
• Increase in feed temperature

Correct Answer: Carryover of liquid droplets with vapor leaving the effect

Q13. How does fouling/scaling on heat transfer surfaces affect evaporator economy?

• Increases heat transfer and improves economy
• Reduces available heat transfer area, lowering capacity and economy
• Has no measurable effect
• Only affects product color

Correct Answer: Reduces available heat transfer area, lowering capacity and economy

Q14. Which of the following is a common method to reduce non-condensable gases in an evaporator?

• Increase steam pressure drastically
• Use vacuum deaeration or venting from effects
• Add anti-foaming agent only
• Decrease number of effects

Correct Answer: Use vacuum deaeration or venting from effects

Q15. The primary driving force for heat transfer in an evaporator is:

• Mass flow rate of feed
• Temperature difference between heating steam and effect juice
• Pump power
• Concentration of solute

Correct Answer: Temperature difference between heating steam and effect juice

Q16. Boiling point rise (BPR) in concentrated pharmaceutical solutions typically:

• Decreases with concentration
• Is independent of solute type
• Increases with solute concentration and reduces effective driving force
• Is irrelevant in evaporator design

Correct Answer: Increases with solute concentration and reduces effective driving force

Q17. Specific steam consumption refers to:

• kg of steam required per kg of water evaporated
• Total steam flow per hour
• Heat loss per square meter
• Number of effects per unit volume

Correct Answer: kg of steam required per kg of water evaporated

Q18. If an evaporator has economy of 4 kg/kg, what is the specific steam consumption?

• 4 kg steam per kg water evaporated
• 0.25 kg steam per kg water evaporated
• 1 kg steam per kg water evaporated
• Cannot be determined

Correct Answer: 0.25 kg steam per kg water evaporated

Q19. Which heat exchanger type is commonly used as heating surface in evaporators?

• Shell and tube
• Plate heat exchanger only
• Air-cooled condenser
• Direct fired furnace

Correct Answer: Shell and tube

Q20. In pharmaceutical evaporation, why is gentle handling (low residence time, low shear) important?

• Prevents microbial contamination
• Prevents degradation of heat-sensitive APIs and preserves product quality
• Allows higher steam pressures
• Reduces the need for cleaning

Correct Answer: Prevents degradation of heat-sensitive APIs and preserves product quality

Q21. What happens to economy if the overall heat transfer coefficient decreases due to fouling?

• Economy increases
• Economy remains unchanged
• Capacity drops; more steam may be required, reducing practical economy
• Number of effects increases automatically

Correct Answer: Capacity drops; more steam may be required, reducing practical economy

Q22. Why is vacuum used in some evaporator effects for pharmaceutical concentrates?

• To decrease boiling point and protect heat-sensitive materials
• To increase boiling point
• To increase viscosity of product
• To sterilize the product

Correct Answer: To decrease boiling point and protect heat-sensitive materials

Q23. What is the common consequence of severe entrainment in an evaporator?

• Reduced evaporation rate only
• Product contamination in downstream effects and condensers
• No effect on product quality
• Lowering of feed concentration

Correct Answer: Product contamination in downstream effects and condensers

Q24. Which control strategy helps maintain economy during variable feed conditions?

• Fixed steam rate regardless of feed
• Automated steam flow and feed control to maintain temperature and capacity
• Manual adjustment only
• Shutting down effects randomly

Correct Answer: Automated steam flow and feed control to maintain temperature and capacity

Q25. How does vapor recompression affect evaporator economy compared to adding more effects?

• MVR can significantly improve economy without adding effects, often more compact
• MVR always reduces economy
• Adding effects is always cheaper than MVR
• MVR increases steam consumption

Correct Answer: MVR can significantly improve economy without adding effects, often more compact

Q26. Which is a direct indicator of good evaporator energy efficiency?

• High steam pressure only
• High economy (kg water evaporated per kg steam)
• Low feed temperature
• High number of pumps

Correct Answer: High economy (kg water evaporated per kg steam)

Q27. In multi-effect evaporators, the temperature difference per effect typically:

• Equals the steam latent heat
• Is shared among effects; smaller per effect as number increases
• Is independent of number of effects
• Must be zero

Correct Answer: Is shared among effects; smaller per effect as number increases

Q28. For pharmaceutical syrup concentration, what is a key design consideration besides economy?

• Color of the evaporator paint
• Product stability, residence time, and avoidance of degradation
• Number of valves only
• Use of seawater as coolant

Correct Answer: Product stability, residence time, and avoidance of degradation

Q29. Which statement about temperature driving force and effect count is true?

• More effects always increase the temperature driving force per effect
• More effects decrease the temperature drop available per effect, potentially needing larger heat transfer area
• Effect count does not influence heat transfer area requirements
• Fewer effects increase fouling

Correct Answer: More effects decrease the temperature drop available per effect, potentially needing larger heat transfer area

Q30. What role does a condenser play in a multiple effect evaporator system?

• It supplies steam to the first effect
• Condenses final vapor and removes latent heat, enabling vacuum or reflux
• It heats the feed directly
• It increases the boiling point of the solution

Correct Answer: Condenses final vapor and removes latent heat, enabling vacuum or reflux

Q31. How is economy affected if the condensate from the final effect is returned to the boiler without energy recovery?

• Economy improves automatically
• Energy recovery is reduced and overall plant efficiency decreases
• No impact on economy
• Feed concentration doubles

Correct Answer: Energy recovery is reduced and overall plant efficiency decreases

Q32. Which of these reduces scale formation in evaporators?

• Allowing solution to overheat
• Using anti-scaling chemicals and controlled supersaturation
• Increasing residence time unnecessarily
• Raising steam pressure to maximum

Correct Answer: Using anti-scaling chemicals and controlled supersaturation

Q33. In a pharmaceutical plant, why might a single-effect evaporator still be chosen despite lower economy?

• Because single-effect always uses less floor space
• For simplicity, lower capital cost, and when product is heat-sensitive but small scale
• It provides the highest economy possible
• It eliminates need for condensers

Correct Answer: For simplicity, lower capital cost, and when product is heat-sensitive but small scale

Q34. Which is an acceptable method to measure evaporator economy on-line?

• Measuring steam flow and mass of distillate to compute kg/kg
• Measuring only feed temperature
• Counting number of effects
• Visual inspection of vapor

Correct Answer: Measuring steam flow and mass of distillate to compute kg/kg

Q35. For pharmaceutical solutions with high viscosity, which evaporator type is preferred?

• Falling film evaporator due to gentle handling
• Rising film evaporator for high-viscosity feeds
• Forced circulation or wiped film evaporator to handle high viscosity
• Air drier instead of evaporator

Correct Answer: Forced circulation or wiped film evaporator to handle high viscosity

Q36. What is the primary reason for using multiple effects instead of a single large effect?

• To complicate plant operation
• To improve energy utilization by reusing vapor heat in successive effects
• To increase steam consumption
• To decrease product quality

Correct Answer: To improve energy utilization by reusing vapor heat in successive effects

Q37. How does non-condensable gas accumulation affect evaporator heat transfer?

• Enhances condensation and heat transfer
• Creates resistance to heat transfer and reduces effective condensation
• Has no effect if steam pressure is high
• Only affects product color

Correct Answer: Creates resistance to heat transfer and reduces effective condensation

Q38. If an evaporator shows sudden drop in economy, likely causes include:

• Reduced feed solids only
• Scale buildup, increased non-condensables, or steam leakage
• Improved insulation
• Lower condenser temperature always

Correct Answer: Scale buildup, increased non-condensables, or steam leakage

Q39. In designing number of effects, which is a key economic trade-off?

• Between capital cost (more effects cost more) and reduced operating steam cost (higher economy)
• Between color and taste only
• More effects always cost less capital
• No trade-off exists

Correct Answer: Between capital cost (more effects cost more) and reduced operating steam cost (higher economy)

Q40. Which parameter is most directly improved by good insulation of evaporator bodies and steam lines?

• Feed viscosity
• Reduction of heat losses, improving practical economy
• Number of effects
• Boiling point elevation

Correct Answer: Reduction of heat losses, improving practical economy

Q41. When operating a triple-effect evaporator, the vapors from the first effect are typically used to:

• Heat the third effect
• Generate steam for the boiler
• Heat the second effect
• Condense directly to waste

Correct Answer: Heat the second effect

Q42. Which operational change can temporarily raise evaporator economy but might harm product quality?

• Lowering steam temperature gradually
• Increasing steam pressure and temperature to force faster evaporation
• Improving heat transfer coefficient
• Reducing feed solids concentration

Correct Answer: Increasing steam pressure and temperature to force faster evaporation

Q43. For solutions that foam readily, what is a recommended practice in evaporators?

• Ignore foam and operate at higher temperature
• Add appropriate antifoam agents and use demisters/foam breakers
• Increase the number of effects randomly
• Replace steam with hot air

Correct Answer: Add appropriate antifoam agents and use demisters/foam breakers

Q44. Which measurement is most useful to monitor for early detection of scaling?

• Change in color of condensate
• Increase in required steam per unit distillate or drop in heat transfer coefficient
• Decrease in feed tank level only
• Fluctuation in laboratory humidity

Correct Answer: Increase in required steam per unit distillate or drop in heat transfer coefficient

Q45. What is the effect of increasing feed temperature into the first effect?

• Decreases evaporator capacity always
• Reduces sensible heating required and can improve economy slightly
• Has no impact on energy usage
• Increases boiling point rise

Correct Answer: Reduces sensible heating required and can improve economy slightly

Q46. In pharmaceutical evaporation, why is steam quality important?

• Poor steam quality can introduce impurities and reduce heat transfer efficiency
• Steam quality only affects color
• Quality of steam does not matter as long as pressure is high
• Low-quality steam reduces feed viscosity

Correct Answer: Poor steam quality can introduce impurities and reduce heat transfer efficiency

Q47. A multi-effect evaporator’s overall thermal economy can be expressed as:

• Mass of steam per mass of feed
• kg water evaporated per kg steam supplied to the plant
• Concentration ratio times steam flow
• Sum of temperatures of all effects

Correct Answer: kg water evaporated per kg steam supplied to the plant

Q48. What is a common pharmaceutical application of multiple effect evaporators?

• Drying of tablets directly
• Concentration of herbal extracts and sugar syrups
• Sterilization of surgical instruments
• Coating of capsules

Correct Answer: Concentration of herbal extracts and sugar syrups

Q49. If the first effect operates at 120°C and the final effect at 60°C in a 3-effect system, the total temperature drop is 60°C. The average temperature drop per effect approximately is:

• 20°C per effect
• 60°C per effect
• 180°C per effect
• 10°C per effect

Correct Answer: 20°C per effect

Q50. Which maintenance practice most improves long-term economy of evaporators?

• Regular cleaning of heat transfer surfaces and condensers to prevent fouling
• Never inspecting the evaporator
• Increasing feed solids abruptly
• Running at maximum steam always

Correct Answer: Regular cleaning of heat transfer surfaces and condensers to prevent fouling

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

Mail- Sachin@pharmacyfreak.com