Chemical Engineering Interview Questions and Answers
Question - 11 : - What Are Some Common Problems Associated With Dense Phase Pneumatic Conveying?
Answer - 11 : - Dense phase pneumatic conveying, typically experiences one common problem from system to system: plugging in the line due to a malfunctioning booster valve. Dense phase systems require these booster systems to introduce new, pressurized air. These boosters are nearly always accompanied by a check valve. If the check valve becomes stuck, the product is allowed to plug the line.
Question - 12 : - What Are Some Common Problems Associated With Dilute Phase Pneumatic Conveying?
Answer - 12 : -
Probably the most common problem encountered in dilute phase pneumatic conveying is the wearing of the rotary valve that serves as an air lock where the product is introduced into the system. If excess air is allowed to pass by the rotary valve, this can cause bridging of the material the flow can be slowed or stopped.
Question - 13 : - What Is Some Common Piping Materials Used To Transport Slurries?
Answer - 13 : -
When selecting a piping material to transport slurries, corrosion and erosion considerations must be accounted for.
Some of the most popular piping materials include:
- Carbon Steel
- Stainless Steel
- High Density Polyethylene (HDPE)
- Acrylonitrile butadiene stryene (ABS)
- Unplasticized polyvinyl chloride (uPVC)
- Fiberglass reinforced plastic (FRP)
- Elastomer-lined carbon steel
Answer - 14 : -
Manufacturers of these systems recommend bin agitation or blowing air into the top of the feeding bin. These methods can prevent fine particle from bridging near the rotators valve. Two types of particles that are especially prone to bridging include titanium dioxide and calcined- kaolin clay.
Question - 15 : - What Is The Best Way To Handle Bend Or Turns In Slurry Piping Systems?
Answer - 15 : -
Even long radius elbows should be avoided in slurry pipes and lines. They are often the site of severe erosion or solid/liquid separation. Only gentle pipe bends or sweeps should be used to turn a slurry line. Industrial experience has shown that a bend-radius-to-pipe-diameter ratio of 3-5 is recommended.
Question - 16 : - How Can You Determine The Proper Pipe Thickness For A Slurry Line?
Answer - 16 : -
Design of slurry piping systems should follow ANSI/ASME B31.1 and B31.11 Codes. A simple equation for this calculation is as follows: t = (PD) / (2S) + C where: t = pipe wall thickness, in. P = maximum design pressure of the pipe, psig S = maximum allowable design stress, psig C = corrosion or erosion allowance, in.
Question - 17 : - What Is The Practical Particle Size Limit For Pneumatic Conveying?
Answer - 17 : -
As a rule, pneumatic conveying will work for particles up to 2 inches in diameter with a typical density. By "typical density”, we mean that a 2 inch particle of a polymer resin can be moved via pneumatic conveying, but a 2 inch lead ball would not.
Question - 18 : - What Can Cause Bulk Solids To Stop Flowing From A Bin?
Answer - 18 : -
Causes of such problems can fall into one of two categories: Material strength or Bin Geometry: Factors that can affect material strength include. Moisture is especially with particles, which fuse together with moisture.
Question - 19 : - What Is The Most Common Cause Of Solid Size Segregation In Bulk Solid Systems?
Answer - 19 : -
Many engineers usually point directly to the pneumatic conveying system as a source of such a problem. The truth is that in most cases, segregation occurs because of the differences in sizes of the articles. As a rule-of-thumb, if the size ratio extends outside of around 1:1.3, then there will most likely be segregation. This being said, one should inspect the equipment responsible for determining the particle size rather than the pneumatic conveying system if this problem is occurring. Reference: Richard Farnish, the Wolfson Centre for Bulk Solids Handling Technology
Question - 20 : - How Can One Determine The Particle Size Distribution For A Given Bulk Solid?
Answer - 20 : -
While there are high-tech methods of performing such an analysis (laser-diffraction and video imaging system are available), the simplest way is to use a sieve stack. For example, to analyze a particular solid, one would stack several different mesh sizes into a cylinder with the largest mesh opening on the top and progress down through the cylinder to finer mesh. The cylinder would contain a pan on the bottom. Before beginning, weight the test sample, each piece of mesh, and the pan. Then, the sample is loaded into the top of the test cylinder and the cylinder is exposed to a combination of movements (shaken) to allow the solids to pass through the appropriate mesh sizes.