Process Equipment and Plant Design Flashcards
Fresh water carrying pipelines in chemical industries are coloured with __________ color.
sea green
Which of the following material is seldom used for pressure vessel construction ?
Rimmed still
The ratio of shear stress to shear strain is called
shear modulus
25 per cent cut segmental baffle means that the baffle
height is 75% of the I.D. of the shell.
Liquid/petroleum fuel storage tanks are built underground (as in case of petrol pumps), when the storage capacity is less than __________ kilolitres.
45
Le/D for fully open globe value may be around
300
Lug support is
all (a), (b) and (c).
Pick out the wrong statement pertaining to the use of valve tray, seive tray and bubble cap trays in continuous distillation column.
Maintenance cost for valve and seive trays are comparatively more than bubble cap tray due to their relatively complicated construction features.
With increase in the number of shell passes, the value of FT
increases
Holes of a sieve tray are arranged in triangular pitch of __________ times the hole diameter.
2.5 to 5
In case of a shell and tube heat exchanger, the minimum shell thickness for carbon steel (inclusive of corrosion allowance) depends on shell diameter and is in the range of __________ mm.
5-11
The stress developed in a material without any permanent set is called the
elastic limit
In a shell and tube heat exchanger, the ‘tube pitch’ is defined as the
shortest centre to centre distance between adjacent tubes.
Which of the following is not a valid assumption in continuous binary distillation for calculating the number of equilibrium stages by Mc-Cabe-Thiele’s method ?
Reflux is not a saturated liquid.
Overall distillation column efficiency for most of the refinery columns can be given by (for μ = 0.07 - 1.4 cp and relative volatility < 4) (where η = overall column efficiency, % μ = molal average viscosity of feed at average column temperature and pressure, cp Δp = pressure drop per tray, psi)
η = 17 - 61.1 log μ
The value of fouling factor depends upon the
all (a), (b) and (c).
In case of bubble cap distillation column of diameter greater than 1.2 metres, the cap diameter is roughly about __________ cms.
10
Tube side pressure drop in a 1-2 heat exchanger (for turbulent flow of fluids through the tubes) is about __________ times, that in a 1-1 heat exchanger having the same size & number of tubes and operated at the same liquid flow rate.
8
To keep the power input constant for a stirred vessel operating under fully developed turbulent flow conditions (constant power number), if the impeller diameter is increased by 20%, the impeller speed should be decreased by a factor of
(1.2)^5/3
In a heat exchanger, shell side fluid velocity can be changed by changing the tube
both (a) & (b) (layout & pitch)
Where does the maximum tensile strength occur in a thick cylindrical vessel subjected to internal pressure ?
At the inner surface.
It is not desirable to design a heat exchanger for LMTD correction factor, FT, of less than
0.80
A rivetted joint does not fail by __________ of rivets.
none of these
Triangular pitch tube layout as compared to square pitch in a shell and tube heat exchanger
permits the use of more tubes in a given shell diameter.
Bracket supports are the most suitable for supporting __________ vessels.
thick walled vertical
In a multipass shell and tube heat exchanger, the shell side cross flow area does not depend upon
none of these
Two iron pipes of the same nominal diameter but different schedule numbers will have the same
inside diameter
Steam side heat transfer co-efficient for design consideration under ordinary condition can be assumed to be about __________ kcal/hr.m2.°C.
7500
Pick out the wrong statement
both (b) and (c).
b. Fouling factor of river water is less than that of sea water.
c. Risers provided in bubble cap trays in the distillation column facilitate the flow of both liquid and vapor.
Lessing ring is formed by the addition of a partition across the centre of a raschig ring, which results in an area increase of about __________ percent.
20
In chemical process equipments, the conical bottom heads used, usually has an apex angle of
60°
Smaller sized packings are generally dumped to the packed columns, and the large ones of size greater than __________ mm are stacked individually, which provides better control over bed porosity and offers lower gas pressure drop.
75
Shell side heat transfer co-efficient in case of square pitch as compared to the triangular pitch under similar condition of fluid flow and tube size is
less
Correct use of ‘factor of safety’ is very important in equipment design. It is defined as the ratio of the
ultimate stress to working stress.
The operating velocity in the absorption tower is usually 40-50% of the flooding velocity. Packed absorption towers are normally designed for a pressure drop of about __________ mm of water column per metre height of packing.
20-40
__________ tray arrangement is recommended for distillation column having diameter up to 4 ft.
Cross flow
What is the value of ‘q’ for saturated liquid feed to a distillation column ?
1
In perforated plate towers, the
all (a), (b) and (c).
a. hole sizes may be around 1/8” or 3/16”.
b. total hole area may be around 6 to 15% of tower cross-sectional area.
c. pressure drop is less compared is similar bubble cap towers.
The main purpose of providing stepping on the trays is to
facilitate handling of large flow rate of liquid.
The operating pressure drop range in a bag filter is about __________ mm water gauge.
50-150
The ends of a cylinderical vessel can be closed by a head, which can be one of the four shapes. For the same thickness, choose the one which can withstand the highest pressure.
Ellipsoidal
For laminar flow (NRe < 2100) in steel pipe, the optimum inside pipe diameter is given by
Di, opt = 3 Q0.36 ρ0.18
Pick out the correct statement.
Packed towers are generally preferred over plate towers, if the liquids have a foaming tendency.
Wall thickness of schedule 40 pipe as compared to that of schedule 80 pipe is
less
Pick out the wrong statement pertaining to the design of a basket type evaporator.
It is used for high viscosity liquor having large rate of scaling.
Pick out the wrong statement pertaining to the design of the bubble cap tray of a distillation column to give stable operation and even vapour distribution.
none of these.
Speed of the drum of the rotary vacuum filter normally ranges from __________ rpm.
0.1 to 2
A stuffing box is used for
prevention of fluid leakage around moving parts.
Pressure drop (Δp) and the superficial gas mass velocity (G) in case of packed absorption tower operating in the preloading range are related as
Δp = G^2
Pick out the wrong statement.
In an agitated vertical cylinderical reaction vessel, the
dished bottom vessel has very high power consumption.
Needle valves are generally not used for
very large diameter pipes.
Height equivalent to a theoretical plate (HETP) is the height of packing that will give the same separation as one theoretical plate in gas-liquid mass transfer operations like distillation, absorption/stripping and humidification/dehumidification. HETP which is experimentally determined, depends upon the
a. flow rates of each fluid.
b. type and size of packing.
c. concentration of each fluid.
all a, b & c.
Pick out the wrong statement.
a. Safety valves are provided in heat exchangers for removal of non-conden-sables.
b. Liquid metals and dowtherm are used for very high temperature heating.
c. In a shell and tube heat exchanger, high pressure fluid is generally routed through the tube.
d. A loop seal or U-seal is provided in a vertical condenser sub-cooler to prevent quick draining of the condensate.
Safety valves are provided in heat exchangers for removal of non-conden-sables.
With increase in gas flow rate to fabric surface area ratio (Nm3/hr/m2 fabric surface area), the size & the cost of a bag filter
decreases
A head comprises of straight flange section, corner torus, section and central dished section. Crown radius and knuckle radius in a head is related respectively to the
central dished section and corner torus section.
Number of evaporators which can be used in service in a multiple effect evaporation system is limited by the
both (a) & (b).
Which of the following is used to set the diameter of the distillation column ?
Allowable vapour velocity.
Ponchon Savarit method is based on the use of enthalpy concentration diagram, which contains the bubble point curve (saturated liquid curve), dew point curve (saturated vapour curve) and equilibrium tie lines. As compared to McCabe-Thiele’s method, this method
all ‘a’, ‘b’ & ‘c’.
The optimum size ratio for two mixed reactors in series depends on the kinetics of the reaction and the conversion level. For reaction orders more than one, the
smaller reactor should come first.
In a shell and tube heat exchanger, tube side __________ of the mass velocity.
a.b heat transfer co-efficient is proportional to 0.8th power
c. pressure drop is proportional to the square
both ‘a’ & ‘b’
Which of the following is not a graphical method (but is an analytical method) for the calculation of theoretical number of stages in case of continuous binary distillation?
Sorel-Lewis method.
Saddle supports are used for supporting __________ vessels.
horizontal cylinderical
The diameter of a propeller agitator used in agitation tank ranges from __________ percent of the tank diameter and its peripherial speed is normally 300 to 500 metres/minute.
15 to 30
In packed towers provided with saddle packing, liquid redistributors are positioned at every __________ times column diameter or 6 metres whichever is less.
5-8
Optimum reflux ratio in a continuous distillation column is determined by the
total cost consideration (fixed cost of the column plus the cooling water & steam cost).
Cooling water fouling factors vary in the range of 0.001 to 0.003
(BTU/hr.ft2 . °F)-1
Minimum recommended baffle spacing in a shell and tube heat exchanger is about (where, D = shell diameter )
0.2 D
The maximum liquid gradient over a tray must not exceed
0.5” -1.25”.
An underdesigned steam trap will
back up condensate and cause water hammer in steam line.
The slope of the feed line in distillation opeartion is given by (where, q = fraction of the feed stream that is liquid.)
-q/(1-q)
Speed of industrial paddle agitator ranges from __________ rpm.
20 to 100
__________ strain is measured using a ‘strain rosetter’.
Linear
Thin spherical shells subjected to internal pressure, develop __________ stresses.
radial
With increase in the reflux ratio for a fixed production from a continuous binary distillation column, the __________ decreases.
fixed charges initially
The slope of operating line in the rectifying section of a distillation column is unity, if the reflux ratio is
∞
Vertical vessels are not supported by
saddles
With increase in pressure drop (for a given particle size), the dust collection efficiency of a cyclone separator will
increase
Spherical shaped pressure vessel is considered to be the most ideal, because it can
withstand higher pressure for a given metallic shell thickness.
An adequate clearance between the tray and the shell wall of a distillation column is provided to
allow for thermal expansion and facilitate installation.
Overall tray efficiency of a distillation column is the ratio of the number of
ideal trays required to the number of real trays required.
Pick out the wrong statement about the design of a sieve plate column.
An increased weir height improves the tray efficiency at the cost of high plate pressure drop; optimum wear height being 40-90 mm for column pressure above atmospheric and 6-12 mm for vacuum columns.
For segmental downcomers, the chord length is 60-80% of the column diameter. An initial value of downcomer area of 12% is taken in the design.
Width of the calming section provided at the inlet and outlet sides of the plate is 75 mm for column diameter below 1.5 metres and 100 mm for larger diameter columns.
Minimum recommended downcomer residence time for the disengagement of entrained vapour is the same for both foaming and non-foaming liquids, which is about 20 seconds.
Minimum recommended downcomer residence time for the disengagement of entrained vapour is the same for both foaming and non-foaming liquids, which is about 20 seconds.
Generally, no corrosion allowance in wall thickness of a part is required, if the thickness is more than __________ mm.
30
Multiple blade paddle agitator is used for mixing high viscosity liquids/paste in which the paddle diameter is commonly 0.8 times the tank diameter. However, the width of the blade is in the range of __________ times the paddle diameter.
0.1 to 0.25
In a __________ rivetted joint, the rivets in the various rows are opposite to each other.
chain
Pick out the wrong statement:
The tensile strength of a brittle material is less than its compressive strength.
The compressive strength of a ductile material is less than its tensile strength.
In a thick cylindrical shell, the hoop stress is maximum at the inner radius.
The value of crushing load is more than that of buckling load for long colmns.
The value of crushing load is more than that of buckling load for long colmns.
Generally, elliptical dished heads
all (a), (b) and (c)
Pick out the wrong statement pertaining to the comparative evaluation of performance of the packed tower and the plate tower.
The total weight of a dry plate tower is usually much more than that of a dry packed tower designed for the same duty.
The circumferential (hoop) stress in a thin walled cylinderical vessel under internal pressure is
pd/2t
Le/D for fully open gate valves would be
b. much less (say 2% than that for fully open globe valves).
c. around 7.
both (b) and (c).
LMTD correction factor is used in heat exchanger design for
multipass shell and tube heat exchanger.
Floating head heat exchangers are used for the
cases where temperature difference between the shell and the tubes is more (>50°C).
The most common standard size of bubble caps used in industrial operation is
6” dia cap with 4” dia riser.
Compensation against openings in process vessels for giving inlet and outlet connections, for providing sight glasses and manholes etc. is provided for strength and rigidity. The most efficient type of compensation is of __________ type.
nozzle or rim
In case of a continuous distillation column, increase in reflux ratio may result in the
all (a), (b) and (c).
In a distillation column, the minimum residence time for liquid in the downspout is about __________ seconds.
8
Thickness of the frame of a plate and frame filter as compared to that of plates is
more
Which of the following factors affect the pressure drop in a co-current gas-liquid absorption packed tower ?
a. Size, shape, orientation and surface of the packing particles.
b. Density and viscosity of fluids.
c. Fluid flow rates.
All (a), (b) and (c).
The thickness of heat transfer plates used in the plate type heat exchanger ranges from __________ mm, pressed in a single piece provided with grooves & corrugations.
1.25 to 3.125
Rivets are generally specified by the
shank diameter
Length to diameter ratio of most rotary driers is in the range of
4 to 10
Tube wall thickness depends on the cor-rosiveness of the fluids and their operating pressure & temperature and is specified by Birmingham wire gauge (B.W.G)-a number which varies from 8 to 18 with the numbers 14 and 16 being more commonly used. Outside diameter of tubes varies from about 15 to 50 mm; however a tube of less than __________ mm outside diameter is generally not recommended for fouling fluids.
19
Angled baffles are preferred in the agitation tank to control the swirling action; if the viscosity of the liquid to be mixed is about 200 poise. However, the baffle may be completely eliminated for mixing liquids having viscoisty above __________ poise.
600
Ratio of tube length to shell diameter for a shell and tube heat exchanger is
b. 4 : 1 to 8 : 1 for liquid-liquid exchanger.
c. < 4 : 1 for gas-gas exchangers.
both(b) & (c).
The dust collection efficiency of a cyclone separator
none of these.
In a shell and tube heat exchanger, the overall heat transfer co-efficient is proportional to the tube side (volumetric flow rate)0.8. This is valid, only when the ratio of the tube side film resistance to the total resistance is almost equal to
1
Which of the following types of reactors is the safest from operation point of view ?
A vapor phase reactor.
In a bag filter, the pressure drop increases directly as the
density of the gas and inversely as viscosity of the gas.
The LMTD correction factor (FT) is applied in __________ heat exchangers.
all multipass
Movement of pipeline caused by thermal expansion is taken care by providing
expansion joint.
changes in its direction.
change in the shape of pipeline.
all (a), (b) and (c).
For a cylindrical shell, (subject to the thickness of uppermost course being more than the minimum for diaofthe tank in question), the thickness of the courses of shell
decreases upwards.
In the design of a paddle agitator, the ratio paddle dia/tank dia is normally taken as
0.1
0.8
The design stress, which is more than the damaging stress, is the least unit stress that will render a member unfit for service before the end of its normal life. The design stress factor or factor of safety indicates the margin between design stress and the __________ stress.
damaging
Hole diameter of the seive trays in the distillation column ranges from __________ mm.
3 to 12.5
Factor of safety (i.e., overdesign factor) in heat transfer equipments is about __________ percent more than the actual/theoretical design factor.
15-20
For annular flow of a fluid, the ratio of the equivalent diameter for pressure drop calculation to the equivalent diameter for heat transfer calculation is
d1/(d1+d2)
In actual operation of distillation column, the vapour is not distributed uniformly among the bubble caps, primarily because of the
liquid gradient on the tray.
The minimum shell thickness for tank ≤ 15 metres diameter is limited to __________ mm, for reasons of elastic stability.
5
If ‘D’ is the inside diameter of the shell of a shell and tube heat exchanger, then the baffle spacing is usually in the range of
D/5 or minimum 2” to 5D.
Brass valves are usually made for pipe sizes __________ inches.
≤2
At the following point for a given packing and set of fluids, the pressure drop per metre of packed height, with variation in fluid rates and operating pressure
remains same
In a shell and tube heat exchanger, triangular pitch arrangement as compared to square pitch arrangement
results in higher shell side pressure drop.
Pick out the wrong statement about routing of fluids in a shell and tube heat exchanger.
Higher pressure fluid stream should be routed through the shell side.
The necessary wall thickness for a metallic storage vessel is a function of the
a. ultimate tensile strength (or yield point) of the material and operating temperature.
b. operating pressure and welding/joint efficiency.
c. diameter of the vessel.
all (a); (b) and (c).
In a multiple effect evaporator system having ‘n’ effects, the amount of water evaporated per unit surface area in approximately equal to __________ times that in a single effect.
(1/n)th
Pick out the wrong statement
In a flanged and standard dished head, the crown radius is ≤ shell outside diameter.
In a flanged and shallow dished head, the crown radius is > shell outside diameter.
Flat head covers are most suitable for larger vessels operating at very high pressure.
Flanged only head is a type of flat head in which gradual change in the shape at the centre results in reduced local stresses.
Flat head covers are most suitable for larger vessels operating at very high pressure.
Pick out the wrong statement pertaining to the design of a horizontal tube evaporator.
It is unsuitable for concentrating those liquids, which form a scale or deposit salt.
It is suitable for process, in which the final product is a liquor instead of solid.
Its usual dimensions are: tube dia = 2-3 cms; evaporator body dia = 1-4 metres and evaporator height = 2.5-4 metres.
Liquor flows inside the tube, while the steam is outside submerging the tube.
Liquor flows inside the tube, while the steam is outside submerging the tube.
Weep holes provided in the plates of a distillation column
facilitate draining out liquid from a tray when the unit is not in operation.
are normally located near the overflow weir so that any delivery of liquid during operation follows approximately the same path as the overflow fluid.
must be large enough (usually 1/4” to 5/8” dia) to prevent plugging but should not deliver excessive amount of fluid during operation.
all (a), (b) and (c).
Steam is preferred to be used as a heating medium in heat exchangers, because of its
high latent heat.
__________ shapedroof is the most commonly used roof for cylinderical storage tanks.
Conical
Pick out the wrong statement pertaining to ‘Horton sphere’ used for the storage of liquid ammonia.
Diameter of Horton sphere is normally 6 to 25 metres and it is supported by 6 to 12 nos. tubular or rolled section column.
Thickness of spherical shell is half that of the cylinderical vessel under same operating pressure condition. Besides, the ratio of surface area to volume is less for sphere than any other shape ; hence insulation required is less.
Horton sphere is used for the storage of gases and volatile liquid at a moderate pressure of 1 to 10 kg/cm2 .
Horton sphere is used for the storage of liquid at sub-zero temperature at very high pressure upto 200 kg/cm2 .
Horton sphere is used for the storage of liquid at sub-zero temperature at very high pressure upto 200 kg/cm2 .
Value of Peclet number = ∞, is the representative of
plug flow.
Le/D for a Tee (used as elbow, entering branch) would be
both (b) and (c). (b.more than that for Tee (used as elbow, entering run). c. around 90.)
In most of the shell and tube heat exchangers, the tube pitch is generally __________ the tube diameter.
1.25-1.50 times
In a distillation column, bubble caps are located on trays with a pitch of __________ times the outside diameter of the caps.
1.3 to 2
1.2 to 3.8 cms is the value of the
a. downcomer liquid seal in case of a balanced tray design.
b. static submergence in case of a bubble cap tray for column operating under pressure (≥ 1 atm.).
c.skirt clearance for bubble caps.
all (a), (b) and (c).
Accidents in chemical plants are mostly due to
faulty operating procedures.
For identical operating conditions, the pressure drop over __________ tray is the highest out of the following.
bubble cap
A perforated plate has holes of diameter dn arranged in a pitch ph. Each hole has a tube of I.D. dt passing through it. The ligament efficiency is given by
(ph - dt)/ph
__________ is the determining factor for the number of bubble caps to be used per tray.
Permissible slot velocity
Pick out the wrong statement about distillation operation
Distillation under vacuum is a substitute for steam distillation.
In differential (simple) distillation, the vapour is removed as soon as it is formed without appreciable condensation.
In flash (equilibrium) distillation, a definite fraction of liquid is vaporised in such a way that the evolved vapour & residual liquids are in equilibrium with each other.
Flash distillation, differential distillation & steam distillation are all continuous distillation processes.
Flash distillation, differential distillation & steam distillation are all continuous distillation processes.
Low pressure steam (with saturation temperature between 105 to 120°C) is usually used in the vacuum evaporators, which normally employ a vacuum of about __________ mm Hg (referred to a 760 mm mercury barometer).
650
Which of the following is the best tube material from thermal conductivity point of view alone?
Copper
Normal screwed fittings are used for pipes upto a diameter of __________ inches.
3
In a shell and tube heat exchanger, the clearance of the tube is generally
not less than one-fourth of the tube diameter or 3/16”.
Diameter of the seive tray column is determined by the
upper limit of the vapour velocity.
For a given fluid, as the pipe diameter increases, the pumping cost
decreases
Maximum acceptable total liquid gradient over a tray is about __________ mm.
12.5
In case of a ‘thin’ pressure vessel, the ratio of its diameter to wall thickness is
> 10
High pressure fluid in a shell and tube heat exchanger should preferably be routed through the
tubes to avoid the expansion of high pressure shell construction.
Bubble cap tray is the most commonly used tray in large distillation column, because
of its flexibility and nearly constant efficiency under varying conditions of operation.
In common bubble cap distillation column design practice, riser area is approximately equal to (where, Aa = Annular passage area, and Sa = Slot area)
Aa = Sa
Heat transfer co-efficient, hG(Kcal/hr.m2 .°C) and mass velocity of air, G (kg/hr.m2 ) for air flow parallel to the surface in case of constant drying rate in batch drying is related as hG = 0.0176G0.8. But when the flow of air perpendicular to the surface is encountered, this equation changes to
hG = 1.004G0.37
In the agitators, the power required will be changed with the increase of diameter of agitator (D) as
D5
Apex angle of conical heads used in the bottom heads of chemical process equipments is usually
60°
Pressure drop due to pipe fittings can be estimated by the equation,
, where, Le = equivalent length of straight pipeline which will incur the same frictional loss as the fitting and D = diameter of the fitting. The value of (dimensionless) for 45° elbow and 180° close return bends would be respectively around
45 and 75
A pressure vessel is said to be made of ‘thick’ shell, if the ratio of its diameter to wall thickness is
10
