Cork Institute of Technology

Bachelor of Science (Honours) in Process Plant Technology –Award

(EPPTN_8_Y4) (EPPTN_8_Y5) (EPPTE_8_Y4)

Summer 2008 Process Plant Design

(Time: 3 Hours) Instructions: Answer FIVE questions. Answer at least TWO questions from each section. All questions carry equal marks. Use separate answer books for each section.

Examiners: Dr. Francis Murphy Section A Mr. William Bateman Section B Mr. N. Kingston Mr. J. Phelan

Item Support Material Details Question Location

1. Steam Pipeline Sizing Chart – Pressure Drop Q5 (with paper)

2. Vapour Pressure V’s Water Temperature. Q7 (with paper)

3. CIBSE Table C4.36. -Velocity press loss factors. Q7, Q8 (with paper)

4. CIBSE Table C4.11, Page 4-16- “Water 75 C Medium Grade steel”. Q7 (with paper)

5. Lowara Pump HTF 32-125 Data Sheet 04195D Q7 (with paper)

6. CIBSE Table C4.16, Page 4-35- “Water 10 C Heavy Grade Steel”. Q8 (with paper)

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Section A: Process Plant Design

Q1. Determine the reinforcement requirements for a 300 mm diameter opening in a cylindrical

pressure vessel 1 m in diameter subjected to an internal pressure of 5 MPa. The shell and

nozzle allowable stress is 120 MPa. The shell and nozzle thickness are 25 mm and 32 mm,

respectively. The reinforcement scheme is shown in Figure (Question 1). (20 marks)

Figure (Question 1):

FORMULAE: (based on the ASME design philosophy)

The minimum required shell thickness is given by: trs =PRs

S− 0.6P

Reinforcement limit parallel to shell surface is the larger of ts+tn+0.5d or d.

Reinforcement limit normal to the shell surface is the smaller of 2.5ts or 2.5tn

SYMBOLS:

P = Design Pressure Rs = Shell Radius S = Allowable Stress d = opening diameter

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Q2. In the great Boston molasses flood, which took place during the year of 1919, a tank

failed by shear killing 21 and injuring more than 150 people. Seven steel sheets (joined to

make cylindrical tubes) were stacked to form the tank. Single riveted lap joints (single

shear) joined the horizontal seams between the tubes. Butt joints (double shear) and splice

plates joined the vertical seam of the bottom tube. For each tube above the first (bottom)

tube, six columns of lap joints fastened the steel sheet to form cylindrical tubes.

Keeping the basic facts and using the data given below, design a similar storage tank, 90

ft (27.4 m) diameter, 58 ft (17.7 m) tall, to hold 2.5 million gallons of molasses.

DATA:

1 US gallon = 3.8 x 10-3 m3;

Density of standard blackstrap molasses = 12 lb/gal (1432.48 kg/m3)

A36 structural steel yield stress = 36 ksi (248.3 MPa);

Recommended safety factor = 3;

Rivet strength: 25 mm diameter – 11.78 kips (52.42 kN) single shear;

Rivet strength: 35 mm diameter – 14.19 kips (63.14 kN) single shear.

FORMULAE:

Pressure = ρgh + atmospheric pressure.

Hoop stress, σH = pr/t Longitudinal stress, σL = pr/2t

Force per unit length (vertical seam) Fv = σHt

Force per unit length (horizontal seam) FH = σLt

SYMBOLS:

ρ = density , g = acceleration due to gravity, h = height,

p = pressure, t = thickness, r = radius,

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Determine:

(a) The height of molasses in the tank. (4 marks)

(b) The pressure at the bottom of the tank. (4 marks)

(c) The size and thickness of the seven steel sheets required. (4 marks)

(d) The hoop stress and longitudinal stress in the tank walls. (4 marks)

(e) The size/number of rivets required for both horizontal and vertical seams (4 marks)

Q3. (a) Determine the proper lengths of weld, L1 and L2, for the connection of a 76 x 51 x 11.1

mm steel angle to steel plate, as shown in Figure (Question 3). The connection is to

develop the full strength in the angle uniformly stressed to 140 MPa. Use 10 mm fillet

welds, whose strength per AWS specification is 1020 newtons per linear millimetre.

(15 marks)

Figure (Question 3)

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(b) Using Table (Question 3) and the same allowable stress, determine the lengths L1 and L2

for the connection of a 203 x 152 x 19 mm steel angle to steel plate. Use 12 mm fillet

welds, whose strength is 1224 newtons per mm. (5 marks)

Table (Question 3)

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Q4. It is required to store 50,000 m3 of natural gas, such that there will be a releasable volume

of this amount of gas from the storage system at peak periods. A number of vessels at a

storage pressure of 20 bar may be used.

(a) Giving reasons, select the type of vessel that you consider suitable. (3 marks)

(b) Select the number of vessels required again giving reasons. (3 marks)

(c) Calculate the overall dimensions of the vessels. (4 marks)

(d) Devise a management system that will ensure that the vessels are designed and

manufactured to an appropriate safe standard. (10 marks)

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Section B – Process Plant Services. Q5 a) Compare and contrast the construction and operating characteristics of a Fire Tube

Boiler with those of a Water Tube Boiler. [5 marks] b) Why is boiler feed water pre-treatment necessary. [5 marks] c) Why does TDS build up inside a steam boiler. What negative effects can high TDS have on boiler operation. How are TDS levels controlled within a steam boiler. [5 marks]

d) Steam is generated at 10 Bar g pressure inside the boiler house. A new process 65m from the boiler house required 5000 kg/h at a minimum supply pressure of 9.0 bar g. Using the steam pipe sizing chart provided suggest the most suitable pipe diameter and calculate the actual pressure available at the point of use. NB design for a maximum pressure drop of 0.1 Bar / 100m. [5 marks] Reference:-

Steam Pipeline Sizing Chart – Pressure Drop Q5 (with paper)

Q6 a) Describe with the aid of a neat sketch a typical refrigeration circuit. Label the four major components. Use arrows to indicate the direction of flow. Indicate relative pressures and liquid / gas phases after each of the four major components.

[5 marks] b) Cooling towers are often used in conjunction with large refrigeration systems. With the aid

of a neat sketch show a cross section through a cross draft cooling tower showing how the water flow and return can be connected to a refrigeration system with a water cooled condenser. Label all major components. [5 marks]

c) Problems can occur due to continuous recirculation with partial evaporation of water

inside a cooling tower. List two possible problems and describe the maintenance needed to prevent them. [5 marks]

d) Plate Heat Exchangers and Shell and Tube Heat Exchangers are commonly used for

heating and cooling of fluids. List five differences which might be considered when selecting either heat exchanger for a given application. [5 marks]

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Q7 a) The following diagram shows a reactor vessel working under vacuum. The pump is Model HTF4 32-125, manufactured by Lowara. Data sheet 04195D. Determine if the pump shown will cavitate under the operating conditions shown.

3 m

w/d = 1.0. For CIBSE Table C4.36.3 No. Air Operated Diaphram Valves

Reading 5000 Pa

N2 blanket

60 DegWater 3

m

1 m

PG

Pressure Gauge

welded mild steel elbowssteel pipe and

pump. No CIBSE chartsconnecting vessel toStainless Steel pipe

for stainless steel pipe.Use charts for mild

1 No. In-line strainerzeta = 3.0

Pump Details

Speed @2900 rpmQ=20 cubic m/h

Lowara HTF 32-125

b) The production personnel predict a situation where the water temperature in the tank

may increase to 85 Deg C on some occasions. Neglecting any change in flow velocity due to the higher water temperature, clarify if the change in vapour pressure alone would cause the pump cavitate. [5 marks]

Vapour Pressure V’s Water Temperature. Q7 (with paper)

CIBSE Table C4.36. -Velocity press loss factors. Q7 (with paper)

CIBSE Table C4.11, Page 4-16- “Water 75 C

Medium Grade Steel”.

Q7 (with paper)

Lowara Pump HTF 32-125 Data Sheet 04195D Q7 (with paper)

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Q8 (a) Pump and pipe work required to transfer 90 m3/h of effluent from a waste water storage tank to an effluent treatment tank. Cold water 10 Deg C. Effluent to be distributed in equal volumes to each of 6 injection points. All effluent injection points require a minimum of 10m residual head pressure to facilitate mixing once the effluent enters the treatment tank. Use heavy grade steel pipe and welded fittings. 24hrs/day, 7 days/wk operation. Use 1m/s flow velocity to minimise delta P. Estimate the pipe diameter for each section of pipe. [10 marks] Specify overall flow and pressure requirements for the pump. [10 marks]

References:-

CIBSE Table C4.36. -Velocity press loss factors for pipe work Q8 (with paper)

CIBSE Table C4.16, Page 4-35, “Water 10 C Heavy Grade Steel”. Q8 (with paper)

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