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Technical Interview Questions 1 | Chemical Plant


This blog contains interview Questions

Question 1: Define chemical engineering 
Question 2: What is molecular sieve? 
Question 3: What are the various graphical methods for the calculation of number of plates in distillation column? 
Question 4: What is normal tray spacing (Distance between two plates) in distillation column? 
Question 5: What are the different types of tray efficiencies? 
Question 6: What is relative volatility of fluids? How it impact distillation? 
Question 7: Distinguish between liquid-liquid extraction and leaching? 
Question 8: State operational problems in distillation column 
Question 8.1: What is flooding? 
Question 8.2: What is weeping in distillation column? 
Question 8.3: What is Entrainment in distillation column? 
Question 8.4: What is Foaming in distillation column? 
Question 8.5: What is loading in distillation column? 
Question 9: What is pervaporation? 
Question 10: What is reverse osmosis?

Question 1: Define chemical engineering

Answer: The constitution of India defines chemical engineering as “The branch of engineering which deals with applications of principles of the physical science together with the principle of economics and human relations to fields that pertain directly to process and process equipment in which matter is treated to change in state, energy content and composition”

Question 2: What is molecular sieve?

Answer: Molecular sieve means a solid micro porous alumina silicate with uniform pore geometry it is called as zeolite
Molecular sieve - Technical interview Questions


Question 3: What are the various graphical methods for the calculation of number of plates in distillation column?

Answer: There are three methods

  • Mccabe thiele method
  • Ponchon sevrit method
  •  Lewis sorel method

Question 4: What is normal tray spacing (Distance between two plates) in distillation column?

Answer: As per thumb rule. Normal tray spacing is 2 ft. or 0.6m. Height should not exceed 30m. Hence maximum numbers of try is about 50 trays due to fabrication limit diameter of column should be less than 7m and height less than 35meter.

 tray spacing (Distance between two plates)


Question 5: What are the different types of tray efficiencies?

Answer:

There are three types of tray efficiencies

  •  Local or point efficiencies
  •   Murphee plate efficiencies
  •   Overall efficiency
In most of cases overall plate efficiencies is used which is founded by

Overall plate efficiency = No of ideal trays required / No of actual trays required


Question 6: What is relative volatility of fluids? How it impact distillation?

Answer: The relative volatility is the ratio of the K values for two components. It is denoted by ‘α’
               
                                α = k1 /k2

In distillation if relative volatility is high then it is easy to separate fluid mixture and few numbers of trays required but if relative volatility is near 1 then it’s difficult to distillate fluid mixture.

Relative volatility is reduced if column pressure is increased.

Question 7: Distinguish between liquid-liquid extraction and leaching?

Answer: In liquid-liquid extraction solvent is used as solvent to separate liquids and in leaching (also known as solid-liquid extraction) solute is using to separate like separate oil from oil cake using hexane.

Question 8: State operational problems in distillation column

Answer: Mainly there are four problems occurring


  •   Flooding
  •  Weeping/Dumping
  •  Entrainment
  •  Foaming

In Packed bed column there are main three problems

  •  Channeling
  •  Loading
  •  Flooding



Question 8.1: What is flooding?

Answer:

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.

Question 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.

Question 8.3: What is Entrainment in distillation column?

Answer: 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.

Question 8.4: What is Foaming in distillation column?

Answer: 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.

Question 8.4: What is channeling in distillation column?

Answer:  

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.

Question 8.5: What is loading in distillation column?

Answer:

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.


Question 9: What is pervaporation?

Answer: 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


Question 10: What is reverse osmosis?

Answer: 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

Thanks for reading -
Naitik Patel
Industrial Guide

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