Cork Institute of Technology. Summer 2008 Process Plant Design (Time: 3 Hours)

Transcription

1 Cork Institute of Technology Bachelor of Science (Honours) in Process Plant Technology Award (EPPTN_8_Y4) (EPPTN_8_Y5) (EPPTE_8_Y4) Instructions: Answer FIVE questions. Answer at least TWO questions from each section. All questions carry equal marks. Use separate answer books for each section. Summer 2008 Process Plant Design (Time: 3 Hours) 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 C Velocity press loss factors. Q7, Q8 (with paper) 4. CIBSE Table C4.11, Page Water 75 C Medium Grade steel. Q7 (with paper) 5. Lowara Pump HTF Data Sheet 04195D Q7 (with paper) 6. CIBSE Table C4.16, Page Water 10 C Heavy Grade Steel. Q8 (with paper) 7. n/a

2 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) PR The minimum required shell thickness is given by: t rs = s S 0.6P Reinforcement limit parallel to shell surface is the larger of t s +t n +0.5d or d. Reinforcement limit normal to the shell surface is the smaller of 2.5t s or 2.5t n SYMBOLS: P = Design Pressure R s = Shell Radius S = Allowable Stress d = opening diameter 2

3 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 m 3 ; Density of standard blackstrap molasses = 12 lb/gal ( kg/m 3 ) A36 structural steel yield stress = 36 ksi (248.3 MPa); Recommended safety factor = 3; Rivet strength: 25 mm diameter kips (52.42 kn) single shear; Rivet strength: 35 mm diameter kips (63.14 kn) single shear. FORMULAE: Pressure = ρgh + atmospheric pressure. Hoop stress, σ H = pr/t Longitudinal stress, σ L = pr/2t Force per unit length (vertical seam) F v = σ H t Force per unit length (horizontal seam) F H = σ L t SYMBOLS: ρ = density, g = acceleration due to gravity, h = height, p = pressure, t = thickness, r = radius, 3

4 Determine: (a) The height of molasses in the tank. (b) The pressure at the bottom of the tank. (c) The size and thickness of the seven steel sheets required. (d) The hoop stress and longitudinal stress in the tank walls. (e) The size/number of rivets required for both horizontal and vertical seams (4 marks) (4 marks) (4 marks) (4 marks) (4 marks) Q3. (a) Determine the proper lengths of weld, L 1 and L 2, 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. Figure (Question 3) (15 marks) 4

5 (b) Using Table (Question 3) and the same allowable stress, determine the lengths L 1 and L 2 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) 5

6 Q4. It is required to store 50,000 m 3 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. (b) Select the number of vessels required again giving reasons. (c) Calculate the overall dimensions of the vessels. (d) Devise a management system that will ensure that the vessels are designed and manufactured to an appropriate safe standard. (3 marks) (3 marks) (4 marks) (10 marks) 6

7 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] 7

8 Q7 a) The following diagram shows a reactor vessel working under vacuum. The pump is Model HTF , manufactured by Lowara. Data sheet 04195D. Determine if the pump shown will cavitate under the operating conditions shown. Stainless Steel pipe connecting vessel to pump. No CIBSE charts for stainless steel pipe. Use charts for mild steel pipe and welded mild steel elbows Pressure Gauge Reading 5000 Pa 3 No. Air Operated Diaphram Valves w/d = 1.0. For CIBSE Table C No. In-line strainer zeta = 3.0 Pump Details Lowara HTF rpm Q=20 cubic m/h PG N2 blanket 3 m Water 60 Deg 3 m 1 m 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 C Velocity press loss factors. Q7 (with paper) CIBSE Table C4.11, Page Water 75 C Q7 (with paper) Medium Grade Steel. Lowara Pump HTF Data Sheet 04195D Q7 (with paper) 8

9 Q8 (a) Pump and pipe work required to transfer 90 m 3 /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 C 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) 9

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