Process Equipment and Plant Design (Set 3) Flashcards
Concepts and heuristics necessary for design of equipment, processes, and process systems.
____ tower is the most suitable gas-liquid contacting device involving highly corrosive fluids.
Packed
At equal mass velocities, the values of film co-efficients for gases as compared to that for liquids are generally.
lower
The ratio of the largest load in a test to the original cross-sectional area of the test specimen is called the ____ stress.
ultimate
Baffle spacing is generally ____ the I.D. of the shell.
a. more than
b. not greater than
c. not less than one fifth of
d. both (b) and (c)
both (b) and (c)
The wall thickness of thin cylindrical shell with hemispherical ends is ____ that of the spherical ends.
more than
A ‘rupture disc’ is provided in chemical equipments as an accessory meant for
relieving excess pressure.
In a vertical short tube evaporator (Calendria type), the
a. tube dia of 2.5-7.5 cms, tube length of 75-200 cms and cylinderical drum dia of 1-6 metres are normally used.
b. area of central downtake is equal to 40 to 100% of total cross-sectional area of the surrounding tube.
c. liquor is inside the tube while the steam is outside the tube.
d. all (a), (b) & (c).
all (a), (b) & (c).
In a multipass shell and tube heat exchanger, the problem of differential expansion between the shell and tube passes is taken care of by using a
a. U-bend
b. floating head tube sheet
either (a) or (b)
In a shell and tube heat exchanger, the shortest centre to centre distance between the adjacent tubes is
called tube pitch.
Any shell opening greater than 5 cms for a storage tank must be reinforced for reason of
preventing the local overstressing of the shell around the opening.
Minimum tube pitch recommended for shell and tube heat exchangers is about ____ times the outside diameter of the tube.
1.25
Liquid redistribution should be done in a packed tower packed with raschig rings every 6 metres or ____ times the column diameter, whichever is lower.
2.5-3.0
Slope of countercurrent flow rotary drier is in the range of ____ meter/metre.
0 to 0.08
In case of saddle packing (e.g., berl and intralox saddles), the maximum size of the packing should not exceed ____ of the column diameter.
l/15th
Seamless pipe is made
a. from rolled strips formed into cylinders and seam-welded.
b. by extrusion & casting into static and centrifugal molds.
c. by forging a solid round, piercing it by simultaneously rotating & forcing it over a piercer point and further reducing it by rolling gas drawing.
both (b) and (c).
The thermal stress in a metallic bar does not depend upon the
cross-sectional area.
The minimum baffle height should be
twice the impeller diameter.
For turbulent flow (NRe > 2100) of low viscosity fluid (μ > 20cp) in steel pipes, the optimum inside pipe diameter is given by(where, Q = fluid flow rate, ft3/sec.ρ = fluid density, lb/ft3 μ = fluid viscosity, centipoise Di = optimum inside pipe diameter, inches)
Di, opt = 3.9 Q0.45 ρ0.13
To avoid the tearing off the plate of an edge, the margin (i.e., the minimum distance from the centre of the rivet hole to the nearest edge of the plate) should be equal to
1.5 d
The normal range of velocity of water in pipes is ____ m/sec.
1-2
Baffles are provided in a shell and tube heat exchanger to increase the turbulence and velocity of the shell side fluid. Which of the following shaped baffles does not fall in the category of transverse baffle?
Flat plate extending across the wall
A certain pressure vessel manufacturer avoids doing reinforcements calculations for openings by always providing a reinforcing pad extending upto double the diameter of the opening and of the same material and thickness as that of the shell wall. If area compensation is accepted as a code guideline, his approach leads to safe design
irrespective of the shape of the vessel.
In a ____ rivetted joint, the number of rivets decreases from the innermost row to the outermost row.
diamond
Large process vessels operating under extreme temperature and pressure conditions are normally clad/ lined with materials like stainless steel, aluminium, nickel & its alloys, copper & its alloys and titanium. The cladding thickness is generally about ____ percent of the total thickness.
10 to 20
Heat transfer co-efficient for a horizontal condenser as compared to a vertical condenser operating under similar conditions is
about 3 times
Pick out the wrong statement pertaining to the design of the distillation column.
a. Generally, a skirt clerance of 0.5” to 1.5’ is recommended to prevent plugging of the slots by residue build up.
b. The purpose of the slot is to disperse the gas into the liquid in the form of small bubbles.
c. If sufficient slot area is not provided, the gas may pass through the skirt clearance.
none of these.
The longitudinal stress induced in a thin walled cylinderical vessel under internal pressure is
pd/4t
In distillation columns, bubble caps are held in place over trays by
both (b) and (c)
“a hold down bar” and “bolts”
The buckling tendency of compression members is always in the direction of the
least radius of gyration.
In case of plain carbon steel, butt welded joints are used for shell plate thickness ≤ ____ cms.
3.8
The average velocity in the tubes of a 1-4 heat exchanger is ____ times that in 1-1 heat exchanger having the same size & number of tubes and operated at same liquid flow rate.
4
Hoop (circumferential) stress induced in a thin walled ‘Horton Sphere’ used for the storage of liquid ammonia under pressure is
pD/2t
When one of the fluids is highly corrosive and has fouling tendency, it should
preferably flow inside the tube for its easier internal cleaning.
The raio, propeller agitator dia/tank dia is normally taken as
0.15-030
A/an ____ is used for changing the direction of a pipeline.
elbow
Maximum plate efficiency is achieved in case of ____ flow.
cross
The LMTD correction factor (FT) is defined as the
ratio of true temperature difference to the LMTD.
The clearance between two tubes in a shell and tube heat exchanger is known as ‘ligament’, whose minimum value is ____ the outside diameter of the tube, but in no case it should be less than 4.5 mm.
one fourth
The ratio for the rate of washing to the final rate of filtration in a washing type of plate and frame filter is
0.25
Normally, the length to diameter ratio of rotary dryers varies form 4 to 10 and for its economic operation, the number of transfer units (NTU) for such dryers varies from
1.5-2.5
Value of Peclet number = 0, is the representative of
complete back mixing.
Poisson’s ratio of a material is the ratio of unit lateral strain to the unit axial elongation within its elastic limit. The value of Poisson’s ratio for structural and pressure vessel steel may be taken as
0.3
Removable connection of tubes to tube sheet is called
ferrule
Stress-strain diagram for low carbon steel/mild steel is shown below in the Fig.
https://www.indiabix.com/_files/images/chemical-engineering/process-equipment-and-plant-design/572-178-1.png The point ‘A’ on the Fig. represents the
elastic limit
Typical static submergence for bubble cap plate column operating at atmospheric pressure may be around
0.5”
In the allocated cap area, bubble caps are generally arranged on equilateral triangular pitch. Number of caps fixed on a plate is with a
a. clearance of 25-75 mm.
b. cap pitch of 1.3-2 times the cap diameter.
either ‘a’ or ‘b’.
The length of straight rectangular weir used on cross-flow trays is generally ____ the column diameter.
0.6-0.8 times
Le/D for couplings and unions would be
negligible
What is the slope of the operating line in the rectifying section of a distillation coloumn?
<1
Stage efficiency for packed tower varies with the
a. type & size of packing.
b. fluid rates and fluid properties.
c. operating pressure and column diameter.
all (a), (b) and (c).
The minimum plate spacing in most of the pertroleum refinery distillation columns (of dia > 3 ft) is normally ____ inches.
18
Joint efficiency (J) for a seamless pipe is
1
For a given design of bubble cap, the number of bubble caps to be used per tray is set by the
allowable gas velocity through the slots.
The shell side pressure drop in a shell and tube heat exchanger is maximum for ____ baffle.
orifice
The function of manholes provided in the shell of a distillation column is to
give access to the individual trays for cleaning, maintenance and installation.
Back-trapping in a distillation column results due to
excessive liquid gradient over the tray.
For a cylinderical vessel of moderate height, the weld joint efficiency for joints parallel to the cylinderical 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 cylinderical vessel, what value of weld joint efficiency should be used?
0.8
Diameter of bubble caps used in high pressure columns is ____ as compared to that used in identical vacuum columns.
more
The ideal size of round bubble caps to be used in industrial distillation column having a diameter of 3-6 metres is ____ cms.
15
Lap joints are preferred for plates having thickness ____ mm.
> 3
In a distillation column, minimum clearance to be maintained betweeen the overflow weir and the last row of the bubble caps is ____ cms.
7.5
Which of the following lengths of heat exchanger tubes are normally not used in practice ?
10 metres
A pipe is generally made of circular cross-section, because a circular cross-section has the
a. higher structural strength.
b. lowest surface area requirement for a given volume.
both (a) & (b).
In case of a shell and tube heat exchanger, the effect of L/D on inside film heat transfer co-efficient (hi) vanishes after a Reynold number of
10000
Equivalent diameter for heat transfer calculation for a duct of square cross-section having each side as ‘d’ will be
d
A cylindrical storage tank can have a self supported conical roof,
if its diameter is less than 15-20metres.
For high pressure process equipments/vessels, the connected nozzle should be
flanged
Smoker’s equation for the calculation of number of equilibrium stages in a continuous binary distillation column is used, when the
relative volatility is close to one (e.g., separation of close boiling isomers).
Column support for the roof of cylindrical storage tank must be provided for
large diameter tanks.
For a cylinderical internally pressurised vessel, which of the following closure types would withstand highest pressure, if each closure is of the same material and thickness?
ellipsoidal (2 : 1)
In inclined long tube vertical evaporators, the tubes are inclined at an angle of
45°
In a continuous distillation column, the optimum reflux ratio ranges from ____ times the minimum reflux ratio.
1.1 to 1.5
The wall thickness for a large high pressure pipeline is determined by the consideration of the
circumferential pipewall tension.
In the case of a shell and tube heat exchanger, the logarithmic mean temperature difference
is always less than arithmetic average value.
Skirt support is the most suitable for supporting ____ vessels.
tall vertical
Baffles may be eliminated for
high viscosity liquids (> 600 poise).
Generally, as the length of the liquid path on a tray is increased beyond 5 ft, the overall column efficiency
increases
In packed absorption tower, onset of flooding usually occurs at a pressure drop of about ____ mm of water column per metre height of packing.
50-75
For pipe flows, head is proportional to ____ at constant capacity (where D = pipe diameter).
1/D5
Friction factor for turbulent flow in a new pipe is given by
f = 0.04/(NRe)^0.16
The minimum tray spacing in distillation column of diameter less than 3 ft is normally ____ inches.
6
Oxygen carrying pipelines in chemical industries are coloured with ____ colour.
blue
Normally, the ratio of the total riser area to the tower cross sectional area (for bubble cap towers of diameter more than 3 ft) is around
0.1-0.2
Pick out the 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 plate column.
d. Weir height in case of a bubble cap plate ranges from 50 to 150 mm and is higher than the seive plate.
Weir height for a bubble cap plate column is the same as that for a seive plate column.
Maximum size of the raschig rings used in a packed tower is about ____ of the coloumn diameter.
1/30th
Longitundinal stress induced in a thin walled cylindrical storage vessel is
pD/4t
The type of stress developed in a metallic bar on subjecting it to a change in temperature without allowing it to be deformed is ____ stress.
thermal
The safe distance of habitation from a hazardous chemical plant (TLV of its product < 1000 ppm) should be about ____ kms.
25
Pick out the wrong statement pertaining to a shell and tube heat exchanger.
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.
both (b) & (c).
Maximum allowable vapour velocity in a bubble cap tower is determined by the
entrainment considerations.
Normally, the plate thickness of the bottoms and roofs of vertically cylindrical storage vessels as compared to that of the cylindrical shell is
less
The practical representative values of HETP for a number of commercial operations lies within a range of ____ metre.
0.4-0.9
Of the pressure vessels, with same thickness but different diameters, which one withstands higher pressure?
Smaller dia vessel.
Reflux ratio variation in a distillation column is between
minimum and infinity
Width and depth of grooves in the tube sheet holes normally are ____ inch respectively.
1/8 and 1/64
In condenser, the cooling water is passed in the tube side in a pass arrangement, because
it reduces heat transfer area.
In packed towers provided with pall rings liquid redistributors are positioned at heights of every 6 metres or 5-10 times the column diameter, whichever is less. Maximum size of the pall rings should not exceed ____ of the column diameter.
1/10-1/15th
Height of the flights in the rotary drier is in the range of
0.08 to 0.12 d
Vapor velocity in a distillation column for non-foaming mixture is in the range of ____ times the flooding velocity.
0.6 to 0.7
