PE 6

• Minimum plate spacing in most of the petroleum refinery distillation columns (of dia > 3 ft)

  18 inches
• Factors determining the number of bubble caps to be used per tray in a given design of bubble cap

  1. Allowable gas velocity through the slots

  2. Plate spacing

  3. Diameter of the column
• Shell side pressure drop in a shell and tube heat exchanger

  Maximum for Orifice baffle
• Functions of manholes provided in the shell of a distillation column

  1. Keep a check on the liquid gradient over the plate by direct visual observation

  2. Give access to the individual trays for cleaning, maintenance and installation

  3. Guard against foaming & entrainment by dumping antifoaming agent through it
• Cause of back-trapping in a distillation column

  Excessive liquid gradient over the tray
• Ideal size of round bubble caps to be used in industrial distillation column having a diameter of 3-6 metres

  15 cms
• Plate thickness for lap joints

  >3 mm
• Minimum clearance to be maintained between the overflow weir and the last row of the bubble caps in a distillation column

  7.5 cms
• Heat exchanger tube lengths normally not used in practice

  10 metres
• Equivalent diameter for heat transfer calculation for

  a duct of square cross-section having each side as

  'd' will be d
• Condition for a cylindrical storage tank to have a self supported conical roof

  If its diameter is less than 15-20 metres
• Conditions for using Smoker's equation for calculating the number of equilibrium stages in a continuous binary distillation column

  Relative volatility is close to one (e.g., separation of close boiling isomers)
• Requirement for column support for the roof of cylindrical storage tank

  Large diameter tanks
• Closure type that would withstand highest pressure for a cylindrical internally pressurised vessel

  Ellipsoidal (2 : 1)
• Optimum reflux ratio range in a continuous distillation column

  1.1 to 1.5 times the minimum reflux ratio
• Determining factor for wall thickness of a large high pressure pipeline

  Circumferential pipe wall tension
• Relationship between logarithmic mean temperature difference and arithmetic average value in a shell and tube heat exchanger

  Logarithmic mean temperature difference is always less than arithmetic average value
• Skirt support is the most suitable for supporting TALL VERTICAL vessels.
• Condition for eliminating baffles in a shell and tube heat exchanger

  High viscosity liquids (> 600 poise)
• Relationship between length of liquid path on a tray and overall column efficiency in a distillation column

  As the length is increased beyond 5 ft, the overall column efficiency increases
• Pressure drop at which onset of flooding usually occurs in a packed absorption tower

  50-70 mm of water column per metre height of packing
• Relationship between head and pipe diameter (D) for pipe flows at constant capacity

  Head is proportional to 1/D^5
• Minimum tray spacing in distillation column of diameter less than 3 ft

  6 inches
• Ratio of the total riser area to the tower cross sectional area for bubble cap towers of diameter more than 3 ft

  0.1 - 0.2
• wrong statement about the design of seive plate column and the bubble cap column.

  a. The downcomer design and the residence time in the downcomer is almost same for seive plate and bubble cap columns.

  b. Weir length for a bubble cap plate is the same as that for the seive plate.

  c. Weir height for a bubble cap plate column is the same as that for a seive sieveplate column.

  d. Weir height in case of a bubble cap plate ranges from 50 to 150 mm and is higher than the seive plate.
• Maximum size of the raschig rings used in a packed tower

  1/30th of the column diameter
• Type of stress developed in a metallic bar on subjecting it to a change in temperature without allowing it to be deformed

  Thermal stress
• Safe distance of habitation from a hazardous chemical plant (TLV of its product < 1000 ppm)

  25 kms
• wrong statement pertaining to a shell and tube heat exchanger.

  A. The minimum value of baffle spacing is 50 mm.

  B. The maximum value of baffle spacing is equal to the I.D. of the shell.

  C. The maximum unsupported tube span is generally about 75 times tube diameter, but is reduced to about 60 times for aluminium, copper & alloys of these.

  D. Disk and doughnut baffle is the most commonly used baffle.

  ANSWER: Disk and doughnut baffle is the most commonly used baffle.
• Corrosion allowance in the design of pressure vessel/chemical equipment is

  not necessary, if

  A. plain carbon steel and cast iron parts are used.

  B. wall thickness is > 30 mm.

  C. material of construction is high alloy steel.

  D. both(b) & (c).

  Both(b) & (c).
• Range of practical representative values of HETP for a number of commercial operations

  0.4-0.9 metre
• Of pressure vessels with same thickness but different diameters, the one that withstands higher pressure


  Smaller dia vessel
• Reflux ratio variation in a distillation column

  Minimum and infinity
• Width and depth of grooves in the tube sheet holes

  1/8 inch and 1/64 inch respectively
• Reason for passing cooling water in the tube side in a condenser

  It reduces heat transfer area
• Maximum size of the pall rings in packed towers with liquid redistributors

  1/10-1/15th of the column diameter
• Height of the flights in the rotary drier

  0.08 to 0.12 d (where d is the diameter)
• Vapor velocity in a distillation column for non-foaming mixture

  0.6 to 0.7 times the flooding velocity
• Joint efficiency (J) for a seamless pipe is 1
• For a cylindrical vessel of moderate height, the weld joint efficiency for joints parallel to the cylindrical axis is given as 1.0, while for joints along the girth (circumference) it is given as 0.8. In calculating the shell wall thickness using code formula for an internally pressurised cylindrical vessel, what value of weld joint efficiency should be used ? 0.8