Process Equipment and Plant Design Flashcards by Kynille Denisse Zerna

Fresh water carrying pipelines in chemical industries are coloured with __________ color.

sea green

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Which of the following material is seldom used for pressure vessel construction?

Rimmed still

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The ratio of shear stress to shear strain is called

shear modulus

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25 percent cut segmental baffle means that the baffle

height is 75% of the I.D. of the shell.

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Liquid/petroleum fuel storage tanks are built underground (as in the case of petrol pumps) when the storage capacity is less than __________ kilolitres.

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Le/D for fully open globe value may be around

300

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Lug support is
A. the most suitable for thick vertical vessels.
B. same as bracket support.
C. usually provided for vessels of much smaller height than skirt-supported vessels.
D. all (a), (b), and (c).

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Pick out the WRONG statement pertaining to the use of valve tray, sieve tray, and bubble cap trays in a continuous distillation column.
A. Bubble cap trays though the most expensive are the best in situations, where low vapor rates is to be handled and a positive liquid seal is essential at all flow rates.
B. Murphree efficiency of all three trays are nearly equal, however, the peak efficiency is generally higher for sieve and valve trays than the bubble cap.
C. Maintenance costs for valve and sieve trays are comparatively more than bubble cap trays due to their relatively complicated construction features.
D. Valve trays have the highest turndown ratio (i.e. the ratio of the highest to the lowest vapor flow rates) and thus provide the maximum flexible operating range.

C. Maintenance costs for valve and sieve trays are comparatively more than bubble cap trays due to their relatively complicated construction features.

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With the increase in the number of shell passes, the value of F_T

increases

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Holes of a sieve tray are arranged in a triangular pitch of __________ times the hole diameter.

2.5 to 5

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In the 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

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The stress developed in a material without any permanent set is called the

elastic limit

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In a shell and tube heat exchanger, the ‘tube pitch’ is defined as the

shortest centre to centre distance between adjacent tubes.

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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?
A. Sensible heat changes for vapor & liquid are negligibly small.
B. Reflux is not a saturated liquid.
C. Molar latent heat of the two components is equal.
D. Heat of mixing of normal liquid is assumed to be zero.

B. Reflux is not a saturated liquid.

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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

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The value of the fouling factor depends upon the
A. characteristic of the process fluid.
B. velocity of process fluid containing suspended solids.
C. suspended solids in the fluid.
D. all (a), (b) and (c).

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In the case of a bubble cap distillation column of diameter greater than 1.2 metres, the cap diameter is roughly about __________ cms.

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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.

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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)

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In a heat exchanger, shell side fluid velocity can be changed by changing the tube

layout and pitch

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Where does the maximum tensile strength occur in a thick cylindrical vessel subjected to internal pressure?

At the inner surface.

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It is not desirable to design a heat exchanger for LMTD correction factor, FT, of less than

0.80

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A rivetted joint does not fail by __________ of rivets.

A. tearing
B. shearing
C. tearing of the plate across a row
D. none of these

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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.

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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 A. baffle spacing B. clearance C. pitch D. 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 conditions can be assumed to be about __________ kcal/hr.m2.°C.

7500

Pick out the WRONG statement A. For all the cylindrical process vessels operating above atmospheric pressure, formed heads are used for closing the vessel. B. Fouling factor of river water is less than that of seawater. C. Risers provided in bubble cap trays in the distillation column facilitate the flow of both liquid and vapor. D. both (b) and (c).

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.

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.

Shell side heat transfer co-efficient in the case of a square pitch as compared to the triangular pitch under similar conditions 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 a diameter of upto 4 ft.

Cross flow

What is the value of 'q' for saturated liquid feed to a distillation column?

In perforated plate towers, the 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. D. all (a), (b) and (c).

The main purpose of providing stepping on the trays is to

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 Q^0.36 ρ^0.18

Pick out the correct statement. A. When highly corrosive fluids are to be handled, the plate towers prove to be cheaper and easier to construct than packed tower. B. Packed towers are generally preferred over plate towers, if the liquids have a foaming tendency. C. The pressure drop through the packed towers is generally more than the pressure drop through plate towers designed for same duty. D. none of these.

B. 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. A. It is used for high viscosity liquor having large rate of scaling. B. The tube bundle is suspended on bracket. C. There is no central downtake. D. Downtake is formed by the annular space between the bundle and the shell.

A. 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. A. The pressure drop due to the caps & slots and the static submergence should be as high as practicable for reasonable operation. B. Tendency towards stable operation is increased by increasing the skirt clearance of the caps, lowering the rate of liquid flow per unit plate width or increasing the spacing between the caps. C. The dimensionless ratio of liquid gradient to pressure drop head caused by the bubble cap assembly should be less than 0.4. D. 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 A. absorbing the contraction/expansion of pipeline due to temperature changes. B. prevention of fluid leakage around moving parts. C. facilitating smooth opening and closing of a valve. D. reducing the resistance of fluid flow.

B. prevention of fluid leakage around moving parts.

Pressure drop (Δp) and the superficial gas mass velocity (G) in the case of a 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 A. ratio of liquid depth to tank diameter (i.e. the filling ratio) recommended for most purposes is 1. B. filling ratio for dispersing gas in a liquid is 2 for sufficiently long contact period. C. flat bottom and conical bottom vessels have low agitation efficiency for agitation of heavy solids in liquids. D. dished bottom vessel has very high power consumption.

D. 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

D. all a, b, c. flow rates of each fluid. type and size of packing. concentration of each fluid.

Pick out the wrong statement. A. Safety valves are provided in heat exchangers for removal of non-condensables. 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.

A. Safety valves are provided in heat exchangers for removal of non-condensables.

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 A. practical limit reached, due to low heat transfer rate because of inadequate temperature difference. B. economic limit reached, when the plant cost exceeds the saving of steam. C. both a & b D. neither a nor 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 A. is more accurate in finding the number of equilibrium stages. B. accounts for the enthalpy changes in the process. C. facilitates direct calculation of heat load on reboiler & condenser from, the diagram used in this method. D. 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. heat transfer co-efficient is proportional to 0.8th power B. pressure drop is proportional to the square C. both 'a' & 'b' D. neither 'a' nor '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 operation 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 the increase in the reflux ratio for a fixed production from a continuous binary distillation column, the __________ decreases.

fixed charges initially

The slope of the 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 the 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. A. 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. B. 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. C. 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. D. 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.

D. 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

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: A. The tensile strength of a brittle material is less than its compressive strength. B. The compressive strength of a ductile materia] is less than its tensile strength. C. In a thick cylindrical shell, the hoop stress is maximum at the inner radius. D. The value of crushing load is more than that of buckling load for long colmns.

D. The value of crushing load is more than that of buckling load for long colmns.

Generally, elliptical dished heads

D. all of a, b, and c

Pick out the wrong statement pertaining to the comparative evaluation of performance of the packed tower and the plate tower.

C. 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 A. much more than that for fully open globe valves. B. much less (say 2% than that for fully open globe valves). C. around 7. D. both (b) and (c).

D. 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 A. lower fixed charges for the column. B. greater cost for the reboiler heat supply. C. greater cost for the condenser coolant. D. all (a), (b) and (c).

D. all a, b, and c

In a distillation column, the minimum residence time for liquid in the downspout is about __________ seconds

Thickness of the frame of a plate and frame filter as compared to that of plates is

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. D. 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.

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 viscosity above __________ poise.

600

Ratio of tube length to shell diameter for a shell and tube heat exchanger is

D. both b and c 4 : 1 to 8 : 1 for liquid-liquid exchanger. < 4 : 1 for gas-gas exchangers.

The dust collection efficiency of a cyclone separator A. decreases with increase in gas flow rate. B. is inversely proportional to the mass of the dust particle. C. is directly proportional to the radius of the dust particle path. D. none of these.

D. 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

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

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