Technical Interview Questions 1 | Chemical Plant

1. What is Definition of Distillation?

Distillation is a procedure in which vaporization is followed by condensation to separate out components of fluid mixture with help of thermal energy.

2. What is Unit operation & Unit process?

Unit Operation - 

Unit Operation is defined as operation in which mass & concentration of  component is changed from inlet to outlet with external sources

Example - Distillation Drying, Evaporation, Drying, Mixing, Crystallization, Leaching, in all this mass and concentration of components are changed but no change in  chemical

Unit Process - 

Unit Process is defined as when two chemicals proceed and formed another chemical product.

Example - Nitration, Halogenation, Hydrogenation, Amination, Sulphonation, Chlorination in which products are chemically changed

3. What are types of valves?

1. Globe valve

2. Gate valve

3. Ball valve

4. Butterfly valve

5. Diaphragm valve

6. Plug valve

7. Needle valve

8. Angle valve

9. Pinch valve

10. Slide valve

11. Flush bottom valve

12. Solenoid valve

13. Control Valve

14. Flow regulating valve

15. Back pressure regulating valve

16. Y-type valve

17. Piston valve

18. Pressure regulating valve

19. Check valve

Read in details

    4. What are types of Pumps?

    Classification of Pumps

    Pumps are Classified in 2 categories
    • Centrifugal Pump
    • Positive Displacement Pump
    Positive displacement pumps are further sub divided in 2 categories
    • Rotary Pumps
    • Reciprocating pump
    Rotary pumps are further classified in following 3 categories
    • Screw pump
    • Gear pump
    • Mono pump
    Reciprocating pump is further classified in 2 categories

    • Piston Pump
    • Plunger pump
    Piston pumps are Simplex Piston pumps & Duplex Piston Pump
    Plunger Pumps are metering pump & Diaphragm pump 

    Classification of Pumps

    5. Types of Distillation

    • Flash Distillation
    • Batch Distillation
    • Continuous Distillation 
    • Steam Distillation
    • Extractive Distillation
    • Azeotropic Distillation

    6. What is LMTD ? Why we use LMTD to calculate overall heat transfer co efficient in shell & tube heat exchanger than arithmatic average?

    As we seen heat transfer co efficient 
    U = Qt / ( At* LMTD )
    In heat exchanger hot fluid is losing heat and cold fluid is receiving heat this is not linear.
    This is the reason why LMTD is used rather than Trial and error method. 

    7. Which factors affecting heat transfer between fluids?

    A. Types of fluid
    Gas can transfer more heat comparison to liquid, and liquids can transfer more heat comparison to solid.

    B. Types of material
    Conductive material can easily transfer heat in comparison of resistivity material & Non metals.

    C. Thickness of material
    Equipment's with less thickness can easily transfer against higher thickness material.

    D. Surface area
    Heat transfer rate is directly proportional to surface material.
    More active surface area more heat transfer.
    Fourier's law
    Q = - k A dt/dx

    E. Liquid pressure

    Liquids with high pressure can transfer more heat.
    In high pressure molecules of fluid is more closer so vibration of heat can easily transfer atom to atom.

    F. Turbulence of fluid
    Fluid turbulence is directly proportional to turbulence of fluid.
    Turbulence flow has high tendency of transfer heat than laminar flow.
    This is the reason baffles are provided in heat exchanger.

    G. Temperature difference between fluids.
    High Temperature difference between two fluid can transfer more heat.

    H. Thermal conductivity of equipment material of construction [MOC]
    Each metal has unique conductivity to transfer heat. Copper has high thermal conductivity then Iron So, Copper can easily heat respect to Iron.

    I. Velocity of fluids in heat exchanger
    High velocity fluids prevent scaling and chocking in heat transfer equipments so more heat transfer takes place in high velocity fluids.

    J. Direction of Flow of fluids in exchange.
    There are three flow patterns
    Co current flow - Both fluids flowing in parallel stream
    Split flow - Both fluids flow in right angle
    Counter current flow - Both fluids are flowing in opposite direction

    Heat transfer rate in fluids patterns
    Co current flow < Split flow < Counter current flow

    K. Amount of liquids

    Heat exchanger gives more output when more amount of flow given.

    Heat exchangers

    7. What is Head & Pressure in Centrifugal pump? How to convert pressure to head?

    8 State operational problems in distillation column

    Mainly there are four problems occurring
    •   Flooding
    •  Weeping/Dumping
    •  Entrainment
    •  Foaming
    In Packed bed column there are main three problems

    •  Channeling
    •  Loading
    •  Flooding

    8.1: What is flooding?

    Flooding is brought about by excessive vapour flow, causing liquid to be entrained in the vapour up the column. 

    The increased pressure from excessive vapour also backs up the liquid in the down comer, causing an increase in liquid holdup on the plate above.

    Depending on the degree of flooding, the maximum capacity of the column may be severely reduced. 

    Flooding is detected by sharp increases in column differential pressure and significant decrease in separation efficiency.

    8.2: What is weeping in distillation column?

    Answer: This phenomenon is caused by low vapour flow. 

    The pressure exerted by the vapour is insufficient to hold up the liquid on the tray. Therefore, liquid starts to leak through perforations. 

    Excessive weeping will lead to dumping. That is the liquid on all trays will crash (dump) through to the base of the column (via a domino effect) and the column will have to be re-started. 

    Weeping is indicated by a sharp pressure drop in the column and reduced separation efficiency.

    8.3: What is Entrainment in distillation column?

    Entrainment refers to the liquid carried by vapour up to the tray above and is again caused by high vapour flow rates. 

    It is detrimental because tray efficiency is reduced: lower volatile material is carried to a plate holding liquid of higher volatility. 

    It could also contaminate high purity distillate. Excessive entrainment can lead to flooding.

    8.4: What is Foaming in distillation column?

    Foaming refers to the expansion of liquid due to passage of vapour or gas.

    Although it provides high interfacial liquid-vapour contact, excessive foaming often leads to liquid buildup on trays. 

    In some cases, foaming may be so bad that the foam mixes with liquid on the tray above.

    Whether foaming will occur depends primarily on physical properties of the liquid mixtures, but is sometimes due to tray designs and condition. Whatever the cause, separation efficiency is always reduced.

    8.4: What is channeling in distillation column?

    In packed column, misdistribution is detrimental to packing efficiency and turndown. 

    Misdistribution occurs at low liquid and /or vapour flow, or if the liquid feed is not distributed evenly over the packing Misdistribution delivers less liquid to some area than to others, resulting in reduced mass transfer. 

    For example, the column wall directly under the distributor is poorly irrigated.

    Down in the bed, the liquid tends to flow toward the wall. 

    This condition is also known as channeling. At very low flow rates, there may be insufficient liquid to wet the surface of the packing.

    8.5: What is loading in distillation column?

    It means the actual flow quantities up and down through the equipment. 

    The "loadings" are then compared with the maximum allowable quantities as determined by the physical size of the equipment as well as the operating P and T and properties of the flowing fluids.

     For example, through a section of fractionating trays, that comparison would be expressed as "percent of flood". Typical design is 80 to 85 percent of flood for a fractionator.

    9: 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 Vacuum

    10: 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.

    Thanks for reading -
    Naitik Patel
    Industrial Guide

    Share this blog with your friends from here 👇

    Previous Post Next Post