Chemical Process Equipment Design

7/30/2019 Chemical Process Equipment Design

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Code No: 07A70803 R07 Set No. 2

IV B.Tech I Semester Examinations,May/June 2012CHEMICAL PROCESS EQUIPMENT DESIGN

Chemical EngineeringTime: 3 hours Max Marks: 80

Answer any FIVE QuestionsAll Questions carry equal marks

1. Discuss the construction and functioning of falling film evaporators with a neatdiagram. [16]

2. (a) A double pipe heat exchanger is used to heat 1000 kg/h of oil from 30 0C to40 0C using hot water at 90 0Cin counter current flow. The hot water flows ata velocity of 2500 m/h through the annulus of the heat exchanger. The outerdiameter of the inner pipe is 2.5cm and the inside diameter of outer pipe in4.0 cm. The wall thickness of the inner pipe is 2mm. Neglect wall and scaleresistances. Calculate the length of the heat exchanger.DATA:

Properties Water OilCp (kJ/kgK) 4.2 1.9K (W/mK) 0.7 0.14 (kg/m3) 1000 850

(m2

/s) 0.4 10- 6

0.7 10- 5

Heat Transfer coefficients may be calculated using the equation appropriately.Nu = 0.023(NRe)

0.8 (Npr)1/3

(b) Explain the salient features of the following heat exchangers with respect totheir construction and limitations.

i. Double pipe heat exchangers

ii. 1-1 Pass shell and tube heat exchanger. [10+6]

3. (a) What are the various types of stainless steel used as materials of construction?State their properties and applications as materials of construction.

(b) State the purposes of lining chemical process equipment. Discuss the applica-tion of at least three types of lining used for process equipment. [8+8]

4. (a) What do you understand wind girders? Explain their use in large storagetanks.

(b) Explain the meaning of ovalization of storage tank.

(c) How does it occur? Write the salient features of a self - supported conicaltank. [64]

5. A mixture of benzene and toluene containing 40 percent benzene and 60 percenttoluene is to be separated in fractionating column to give product (distillate) con-taining 96 percent benzene and a bottom product containing 95 percent toluene.Feed is a mixture of two third vapor and one third liquid. Find out the number of

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(a) Discuss the features of the storage vessels for the following

(i) Storage of non-volatile liquids

(ii) Storage of gases

(iii) Storage of volatile liquids

(b) Explain the design procedure for a horizontal storage tank with saddle supports.

[6+10]

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theoretical stages required if reflux ratio of 1.5 times the minimum is used and ifrelative volatility is 2.5. [16]

6. The aqueous reaction A+B products with known kinetics -rA= (500lit/mol.min)CACB is to take place in an experimental tubular reactor.Under the following conditions:Conversion desired =0.9, Volumetric flow rate V=0.05lit/min, concentration ofreactants in feed, CA=CB=0.01mol/lit.Estimate the volume of the reactor Required. [16]

7. A constant pressure filtration test gave data that can fit an expression, dt/dV =9.3V + 8.5; (t in seconds, V in liters). If the resistance of the filter medium isassumed unaffected with pressure drop and the compressibility coefficient of thefilter cake is 0.3, what will be the time taken for the collection of 3.5 liters offiltrate at a filtration pressure twice that used in the test? [16]

8. Explain the design procedure with required equations step wise to find the size ofthe gasket and the number and size of the bolts for a non- standard flange joint.

[16]

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1. Derive the performance equation for Recycle reactors. In turn, give the equationsfor the extremes of negligible and infinite recycle and name the flow types? [16]

2. Explain the following in the design of a sieves plate column.

(a) Coning

(b) Dumping

(c) Weeping

(d) Flooding. [16]

3. (a) Draw a neat diagram of a 1 -1 shell and tube heat exchanger. Show all theparts including baffles, tie rods, tube sheets and spacer tubes.

(b) A heat exchanger has to cool 50,000 kg/h of alcohol from 65 0C to 40 0C.

using 35,000 kg/h of water entering at 300

C,calculate the surface area of theexchanger for:

i. Parallel flow and

ii. Counter flow of the fluids. Explain why the surface required is less forcounter current flow.DATAOverall heat transfer coefficient based on outer tube =550 W/m KSpecific heat alcohol = 3.76 kJ/kg KSpecific heat of water = 4.2 kJ/kg K. [8+8]

4. Derive an expression for calculating rate of heat transfer in single effect evaporator.[16]

5. A sludge forming a uniform non-compressible cake is filtered through a filter pressout of which one frame is kept under study. At a constant pressure difference of2.8 kg/cm2, a 10 cm cake is formed in one hour with a filtrate volume of 6000liters. Three minutes are needed to drain liquor from filter. Two minutes areneeded to fill the filter with water. Washing proceeds exactly as filtration using1200 liters. Opening, dumping and closing take 6 minutes. Assume the filtrate hassame properties of wash water and neglect the resistance offered by cloth and flowlines. How many liters of filtrate are produced in 24 hours on the average? [16]

6. (a) Explain, what do you understand by class 1, class 2 and class 3 types ofPressure Vessels.

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(b) A pressure vessel is required to store a liquid at 18 kg/cm 2. The cylindricalshell of the vessel is closed at both ends by a 2:1 elliptical heads with 5 cmstraightflange. The maximum ratio of liquid height to vessel diameter is 2.The permissible stress of material of fabrication is 1150kg/cm2. Welded join-tefficiency is 85%. Maximum diameter of the vessel could be 2.5m. CalculateThe height of the vessel. [4+12]

7. (a) A high pressure vessel is to be designed to with stand a pressure of 150MN/m2.The material of fabrication has a yield stress of 500 MN/m2. Find the wallthickness required by maximum shear stress theory. The factor of safety is1.8.

(b) A thick cylindrical shell having an inside diameter of 3m is subjected to an

internal pressure of 6 kg/cm2. The permissible stress of the material is 1100kg/cm2. Calculate:

i. The required thickness and

ii. The corresponding deflection. [8+8]

8. (a) Discuss the important characteristics to be considered for selecting a materialof construction.

(b) i. It is desired to select a suitable material of construction to transport thefollowing materials in a pipe at a pressure of 2 atmospheres. Suggestsuitable material of construction for each of the following cases.

A. 98 percent w/w sulfuric acid at 750 c

B. 30 percent w/w hydrochloric acid at 600 c

C. Concentrated aqueous sodium hydroxide solution at 500 c

D. Boiling concentrated nitric acid

E. 10 percent w/w hydrofluoric acid.

ii. Suggest suitable materials of construction for storing each of the followingchemicals

A. A 100m3 storage tank for storing nitric acid

B. A 2m diameter, 20m high distillation column for distilling acryloni-trile.

C. A tank for storing 30 percent w/w aqueous solution of sodium chloride

D. A storage tank for toluene

E. A packed absorption column for absorbing hydrochloric acid into wa-ter. [6+5+5]

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(a) What are the various types of stainless steel used as materials of construction? State

their properties and applications as materials of construction.

(b) State the purpose of lining chemical process equipment. Discuss the application of

atleast three types of lining used for process equipment. [8+8]

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1. Explain with neat diagram the methods of feeding in multiple effect evaporators.[16]

2. An oil is to be stored in a horizontal circular tank fabricated from mild steel. The

capacity of the tank is to be 25m3. The tank covers with flat plates. Calculate themaximum tensile bending stress and direct shear stress from the following data.

[16]DATA:

Density of oil = 920 kg/m3

Plate thickness = 8mmDensity of steel = 800 kg/m3

Inside Diameter of tank = 3mLength of the tank = 5m

3. (a) Explain the merits and demerits of a fixed tube sheet, U-tube and floatingshell and tube heat exchangers. Draw their schematic diagrams also.

(b) Explain the function and classification of baffles in a heat exchanger alongwith the figures of the various baffles. [8+8]

4. A distillation column is to be designed to separate A and B continuously. Thefeed is 35 % of A and 65% B at its dew point. The distillate and the residuecompositions are 0.95 and 0.025 respectively.

(a) Find the quantities of distillate and bottoms per hour.

(b) Find the number of equilibrium stages required in the column if the refluxratio is 2.5Assume the relative volatility as 2.5. [16]

5. Under appropriate conditions acetaldehyde vapor reacts to give methane and car-bon monoxide by the reaction,CH3CHO CH3 + CO0.1kg / sec of acetaldehyde vapor is to be decomposed at 520 0C and 1 atm, ina tubular reactor. The reaction is irreversible and second order with respect toacetaldehyde. Value of rate constant, K= 0.43m3/kg mole sec. What will be the

volume of the reactor for 35% and 90% decomposition of acetaldehyde? [16]

6. The output from a crystallizer is a 10% by volume slurry of crystals which have adensity of 2.2 g/cm3. The acceptable crystal loss from the centrifuge is such that

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it is necessary to retain a crystal size of 40. Obtain an estimate of the cost of themost suitable type of centrifuge. The efficiency of centrifuge is 60%. [16]

7. A vessel is made of stainless steel and the shell thickness is 6mm. The shell andtop head are connected by a flanged joint. The flange of 1400nm diameter is usedfor which the design thickness of the shell is found to be 8mm. Design gasket size,bolt size and number of bolts from the following data:Specification of gasket:Gasket material : AsbestosInternal diameter of gasket = 1400mmExternal diameter =1460 mmThickness = 3mm

Gasket factor = 2Design pressure = 0.4N/mm2

Permissible tensile stress in bolts = 60 N/mm2. [16]

8. A distillation column is used to separate mixture of water and acetone. The feedconsisting of 85 percent of water and 15 percent acetone enters the distillation col-umn at the rate of 1200 kg/h. The feed temperature is 300 C. The top productcontains 98 percent acetone and its temperature is 570 C. The bottom productcontains 0.5 percent acetone and its temperature is 1000 C. The reflux ratio is 10.

Estimate the steam and cooling water required for the distillation. Dry saturatedSteam is supplied at 25 psig, The rise in temperature of cooling water is limited to250 C.DATA:Specific heat of acetone = 2.2kJ/kgKSpecific heat of water = 4.2 kJ/kgKBoiling point of 98 percent = 570 CLatent heat of acetone at 570 c=320kJ/kgLatent heat of water at 570 c = 2500kJ/kgLatent heat of steam = 2174 kJ/kg. [16]

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1. A continuous fractionating column is to be designed for separating 10,000 kg perhour of a liquid mixture containing 40 mole percent methanol and 60 mole percentwater into an overhead product containing 97 mole percent methanol and a bottom

product having 98 mole percent water. A mole reflux ratio of 3 is used. Calculate:(a) Moles of overhead product obtained per hour and

(b) Number of ideal plates and location of the feed plate if the feed is at its bubblepoint.

Equilibrium data:

X 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9Y 0.417 0.579 0.669 0.729 0.78 0.825 0.871 0.915 0.959

Where, x= mole fraction of methanol in liquid

Y= mole fraction of methanol in vapor. [16]

2. (a) What are formed heads? Discuss the factors for their selection for a pressurevessel.

(b) A vertical cylindrical vessel with hemispherical head is to be installed. Thediameter and thickness of the vessel are 200mm and 12mm respectively. Thetangent to tangent length is12m. The vessel contains oil of specific gravity of900 kg/m3. The vessel is filled to its 80 percent capacity. Determine the totallongitudinal stress. [6+10]

3. A PFR is to be used for carrying out a gas phase reaction. A 4R. The reactor

operates at 2000c and 4 atm. pressure. The conversion desired is 75%. Feed rateto the reactor is 2.6kmol/hr.Rateconstant is 0.05. min - 1. Estimate the volume ofPFR. [16]

4. (a) Acetone is synthesized by catalytic hydrogenation of isopropyl vapor in a reac-tor at 4000 C and 40 psig pressure. For this purpose, liquid isopropyl alcoholis vaporized, heated and fed to a reactor. The reactor exit gases includingwater, unconverted isopropyl alcohol and the products of the reaction are fedto a condenser in which most of the acetone, water and alcohol are condensed.The remaining traces of acetone and alcohol are removed in a water scrubber.

The effluent from the scrubber is combined with the condensate and sent to adistillation column to obtain pure acetone. The bottom product consisting ofwater and alcohol is sent to another distillation column. The top product is anazeotrope from the second distillation column and is recycled to the reactor.

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The convertion of alcohol per pass through the reactor is 85 percent. Draw apreliminary flow sheet of the process.

(b) Write short notes on the following:

i. Time basis for flow sheet preparation

ii. Scaling factor for flow sheet calculations. [10+6]

5. (a) What are the types of condensers that are used in evaporator installations?

(b) 3.78 kg/sec steam at 13.5 KN/m2 is to be condensed in a jet condenser usingcooling water at 2880k. If the cooling water exit temperature is 3160K andthe steam is not super heated, what is the cooling water requirement? At 13.5KN/m2,steam temperature =3250K and latent heat = 2379 KJ/kg. [16]

6. Write the principle of operation of fixed bed and moving bed centrifugal filters andbriefly the explain construction of any one type with neat diagrams. [16]

7. (a) A reaction mixture contained in a vessel is to be heated from 250 C to 900 Cby steam flowing through the coils having an area of 6m2. Calculate the timerequired for heating the contents from the following data.DATAWeight of the mixture =200kgCp of reaction mixture (kJ/kgk) =3.7Overall heat transfer coefficient (W/m2 0K) = 650

Steam temperature = 1200

c(b) Ethylene glycol flowing at the rate of 2000kg/h is to be cooled from 1000 C

to 500 C in a concentric tubular heat exchanger using water available at 250

c and the exit temperature of water is to be limited to 400 C. Water flowsthrough the annulus of the exchanger in counter current flow. Calculate thelength of the exchanger from the following data.DATA:Inside diameter of outer pipe = 2.2 cmOut side dia of inner pipe = 1.2 cmWall thickness of inner pipe = 1.5 mm

Properties Ethylene Water (kg/m3) 1100 1000 (mNs/m2) 3.2 0.85Cp (J/kgK) 2600 4200K(W/mK) 0.26 0.61

Use the following in appropriate form for calculation of heat transfer coeffi-cients

hdk

= 0.023 (Re)0.8 (Pr)0.33. [6+10]

8. (a) A cylindrical vessel of diameter 50cm is subjected to an internal pressure of800 kg/cm2. Allowable tensile stress of the material is 1500 kg/cm2. Assumingthat the vessel is a thick walled cylinder find:

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i. The minimum thickness of the vessel and

ii. Maximum radial deflection that occurs at the inner surface andiii. The percentage increase in thickness if the equation for a thin cylinder isused for calculation of thickness.

(b) Discuss the fabrication of a high pressure vessel by ribbon winding. [12+4]

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Chemical Process Equipment Design