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Technical Interview Questions -3 contains questions asked in Chemical Pharma Petrochemical technical interview


31. What is surging in compressors and how it can be prevented?
32. Distinguish between latent heat & sensible heat.
33. What is crystallization? Give Name of crystallizers.
34. Why Earthing is provided in Solvent line?
35. What is ISO & kaizen?
36. Write the name of strong acid and strong, Give examples of weak acid and weak base.
37. Give Boiling Point of ….
38. Define Write the name of one equipment use for measuring humidity.
39. Differentiate compressors, fans and blowers?
40. What is dew point and why it is important in instrument air?
41.  What is pervaporation?
42.  What is reverse osmosis?

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31. What is surging in compressors and how it can be prevented?

In centrifugal and axial compressors when the suction volume falls below a certain limit i.e. when the compressor is not getting enough volume of gas to compress, the gas from discharge side will flow back to the compressor( which would reduce the speed of compressor )and join together with the suction side to increase the volume input.

Thereafter the speed of compressor picks and it come to normal operation. But meanwhile such revere in flow will cross huge pressure gradient across the compressor and vibration thus may damage the impeller. This momentary reverse flow lapses for very short time

To prevent surging we need to install an anti-surging system. The anti-surging system shall have a mechanism to measure the suction flow and discharge flow time to time along with a control valve. When the suction volume falls below a certain set value a part of discharge gas will be directed towards the suction to maintain the minimum suction volume.

As normally compression leads to increase in temperature the gas recycle sis taken after the “after cooler” to ensure the discharge temperature is within control.

32. Distinguish between latent heat & sensible heat.

Latent heat

Latent heat is the enthalpy change associated with temperature change of a body along with phase change.

Sensible heat 

The enthalpy change associated with temperature change of a body in the same phase.

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33. What is crystallization? Give Name of crystallizers.

Crystallization

It is the unit operation in which purification and producing  the  crystal from liquid mixture.

Name of crystallizers

  • Vacuum crystallizer
  • Agitated tank crystallizer
  • Swenson-walker crystallizer
  • Draft tube crystallizer

34. Why Earthing is provided in Solvent line?


When fluid flows, the static charge will produce. It is enough to ignite solvent.  So there is chance of explosion. To avoid this, earthing is provided in solvent line.

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35. What is ISO & kaizen?

ISO

ISO (International Organization for standardization) is an international standards- setting body composed of representatives from various national standards organizations.

Kaizen

It is Japanese word that refers to activities that continuously improve all functions & involve all employees from the CEO to the assembly line workers.

36. Write the name of strong acid and strong, Give examples of weak acid and weak base.

Strong Acid

HClO4 - Perchloric Acid
HCl - Hydrochloric Acid
H2SO4- Sulfuric Acid
HNO3 - Nitric Acid

Strong Base

NaOH - Sodium Hydroxide
KOH – Potassium Hydroxide
Ca(OH)2 - Calcium Hydroxide
Ba(OH)2 – Barium Hydroxide

Weak acid

HCOOH        (formic acid)
CH3COOH (acetic acid)
HF(hydrogen fluoride)
H2S (hydrogen sulfide)

Weak Base

NH3 (ammonia)
C5H5N (pyridine)
NH4OH (ammonium hydroxide)
N(CH3)3 (Trimethyl ammonia)

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37. Give Boiling Point of ….


Methanol
64.7° C

Ethanol
78.3° C

Benzene
80.1° C

Toluene
110.6° C

Isopropyl alcohol
82.6 °C

Ethyl acetate
77.1° C

38. Define Write the name of one equipment use for measuring humidity.

Humidity is the amount of water vapour in the

Relative Humidity

It’s the ratio of the amount of moisture in the air to the maximum amount of moisture that could exist in the air at a specific temperature.

Specific Humidity

It’s the  ratio  of the mass of moisture  in  the mixture  to mass  of moisture in air.

Measuring equipment

Hygrometer

Hydrometer

A hydrometer is an instrument that measure the specific gravity (relative density) of liquid.

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39. Differentiate compressors, fans and blowers?


  • Fans, blowers and compressors are differentiated based on the method used to move the air and specific ratio (specific ratio= discharge pressure/suction pressure). 
  • As per the American Society of Mechanical Engineers (ASME) the compression ratio for fans is up to 1.11, blowers‑ 1.11 to 1.2 and for compressors above 1.2

40. What is dew point and why it is important in instrument air?

 The Dew Point is the temperature at which water vapor starts to condense out of the air (the temperature at which air becomes completely saturated). Above this temperature the moisture will stay in the air.

Electronic instruments uses instrument air received from instrument compressors must be free of any moisture. Small amount of moisture may condensate & it may harmful to instruments So the instrument air should be free of moisture. This is ensured by keeping the dew point below ‑400 C or below.

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41.  What is pervaporation?

Pervaporation is one of the membrane separation processes which are now days for the liquid-liquid separation. In this process, liquid mixture is directly brought into contact with a membrane and the permeate is removed as vapour by applying Vaccum

What is definition of Pervaporation?

It is membrane separation technique for liquid-liquid separation

42.  What is reverse osmosis?

Reverse osmosis is a filtration process typically used for water.

It works by using pressure to force a solution through a membrane retaining the solute on one side and allowing the pure solvent to pass to the other side.

This is the reverse process of normal operation

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Thanks for reading - Technical Interview Questions -3
Naitik Patel
Industrial Guide

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