SOFTWARE DEVELOPMENT FOR MECHANICAL DESIGN OF SHELL AND TUBE HEAT EXCHANGER

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1 SOFTWARE DEVELOPMENT FOR MECHANICAL DESIGN OF SHELL AND TUBE HEAT EXCHANGER Dhaval. B. Upadhyay 1 1 Department of Mechanical Engineering,Sir Bhavshinhji Polytechnic institute Bhavnagar, Gujarat, Abstract Mechanical design of shell and tube heat exchanger for different size and requirement become very time consuming and complicated. In this paper an attempt is made to develop software for mechanical design of shell and tube heat exchanger so that Mechanical design becomes very fast and accurate. In the first part of this paper working and classification of shell and tube type heat exchanger is explain and in second part software architecture and flow chart is discussed. At the end of paper a case study is taken and using this software output produce is discussed. The design procedure given in TEMA and ASME section-viii, division-1 & 2 has been followed. Keywords shell and tube heat exchanger, software architecture, flow diagram, Mechanical design I. INTRODUCTION A heat exchanger is a device, which transfer internal thermal energy between two or more fluids at different temperature. Without this essential piece of equipment most industrial process would be impossible. There are various types of heat exchangers, each of which is designed to accommodate the requirements of the specific needs at hand. Shell and tube heat exchanger are by far the most common because of their relative simplicity and ability to handle the largest variety of fluids. They are also used in conventional energy production as condenser, feed water heaters, and steam generators for pressurized water reactor plants. They are proposed for many alternative energy applications including ocean thermal and geothermal. And they are used in some refrigeration and air conditioning services. Mechanical design of heat exchangers includes design of various pressure and non pressure parts. The structural rigidity and satisfactory service of heat exchangers depends on the appropriate mechanical design. Mechanical design is generally performed according to the design standardsand codes. Some mechanical design standards used in heat exchanger design are: TEMA (United States), IS: (India);BS: 3274 (United Kingdom) and BS: (United Kingdom). Most countries of the world follow the TEMA (Tubular Exchanger Manufacturers Association) standards for the mechanical design of unfired shell and tube heat exchangers. The TEMA standards are applicable for the maximum shell ID and wall thickness of 60 and 2 inch, a maximum design pressure of 3000 psi and a maximum nominal diameter (inch) design pressure (psi) of lb/in, respectively. Three basic classes of TEMA standards are: C, B and R. - The class C specifies the standards for general service exchangers. - The class B specifies the standards of heat exchangers for chemical services. - The class R specifies the standards of heat exchangers for more severe application in petroleum and related processes. II. WORKING OF SHELL AND TUBE HEAT EXCHANGER A shell and tube heat exchanger is a cylindrical vessel housing a set of tubes (called the tube bundle) containing a fluid at some temperature and immersed in another fluid at a different. The transfer of heat occurs between the fluid flowing over the tubes and the fluid flowing inside the tubes. The fluid flow inside the tube tubes is called tube side and fluid flow external to tube bundle is said to be shell side. The simplest type of shell and tube heat exchanger is shown in figure 1, where warm kerosene enters on the top shell side. The kerosene enters on the top shell side. The kerosene s flow path is guided between the tubes by baffle plates and exits at the bottom shell side nozzle cooled to DOI: /IJMTER OZZ9P 20

the desired temperature. The tube bundle is supported between two tubesheets with baffle plates spaced at intervals to support and brace the tubes.

2 the desired temperature. The tube bundle is supported between two tubesheets with baffle plates spaced at intervals to support and brace the tubes. In this figure the tube-side flow enters the tube bundle on the bottom left top left side with a horizontal baffle plate separating the two tube-side flows. Thistype of arrangement is called a 1-2 exchanger, one shell-side pass and two tube side passes. Figure 1. Shell and tube heat exchanger (fixed tubesheet type) All shell and tube heat exchanger are exposed to internal pressures, tube-side and shell-side. Thus in the United States the ASME section VIII Division I & 2 [12,13] Pressure Vessel Code governs the vessel design of such exchangers. The detailed design of shell and tube exchanger is govern by TEMA[3] (Tubular Exchanger Manufacturing Association); whose published standard classified exchanger by the severity of process requirements. III. CLASSIFICATION OF SHELL AND TUBE EXCHANGERS (1) Classification according service that shell and tube type heat exchanger provide in the process industries. [2] 1.Reboiler transfer heat to a liquid to produce a two phase, gas liquid mixture used in a distillation column. 2.Thermosiphon Reboiler provides natural circulation of the boiling fluids by a static liquid head. 3.Forced circulation Reboiler a Reboiler in which a pump is used to force the liquid through the heat exchanger (Reboiler) into the distillation column. 4.Condenser a heat exchanger to condensate vapors by removing heat from gas. 5.Partial condenser only partially condense a gas to provide heat to another medium to satisfy a process condition. The residual gas is recalculated through a heater and recycled. A common application is using excess steam to heat up a process fluid. A typical application of partial condenser on a distillation column is to condense only enough liquid for the reflux when the overhead product is vapor. 6.Final condenser- an exchanger where all the gas is condensed and all the heat is transferred to the medium. 7.Steam Generator a device that generates steam, such as a boiler, to provide energy for process requirements. The most classical example is the old steam locomotive. Which is a shell and tube exchanger mounted on wheels with the steam used to power the locomotion. (This unit is fired vessel and is not covered by ASME Section VIII division 1) 8.Vaporizer - an exchanger that fully or partially vaporized a All rights Reserved 21

3 9.Chiller an exchanger in which a process medium is cooled by evaporating a refrigerant, or by cooling and heating with little or no phase change. (2) General TEMA exchanger Classes R, C and B. [3] There are three basic categories of shell and tube heat exchanger in TEMA Class R, Class C, and Class B. the difference in class is the degree of severity of service the heat exchanger will encounter. Descriptions of the three classes are as follow. Class R - includes heat exchangers specified for the most sever service in the petrochemical processing industry. Safety and durability are required for exchangers designed for such rigorous conditions. Class C - includes heat exchangers designed for the generally moderate services and requirements. Economy and overall compactness are the two essential features of this class. Class B are exchangers specified for general process service. Maximum economy and optimum compactness are the main criteria of design. (3) The standard TEMA classification according to process requirement. [3] Process requirements dedicate the type of design to be used. Figure-2 shows some of the major types of constructions. The standard TEMA classification of exchanger is use the shell identification and number with the exchanger designation type. For example an BEM is an exchanger having an 18-in. shell with 150 tubes, a bonnet (integral) cover with a fixed tubesheet at one end (B), a fixed tubesheet and stationary head at the other end (M), and a one pass shell between both ends(e). (4) According to shell and tube heat exchanger construction style. [2] (1) Fixed tube sheet heat exchanger (Figure 1) In this design tube bundle attached to a tube sheet on each side of the tube bundle. The tubesheet are welded to the shell providing an absolute seal to prevent the shell side fluid from leakage. Often the tubesheets are extend beyond the shell diameter and have flange bolt holes that allow the tube heads to be bolted to the tubesheets. In fixed tube sheet, exchangers, tubes can fill the entire shell to achieve maximum heat exchange (of course this also increases shell side pressure drop) such that clearance between tubes are minimum. However this factor limits the shell side fluid to a relatively clean service, because the exterior of the closely packed tubes cannot be mechanically cleaned or inspected. Another limitation to the design is that there is no allowance for thermal growth of the tubes, except if an external expansion joint is used, which is quite common for this type of exchanger. Normally, single convoluted bellows are used since the maximum temperature difference is 200 F and cyclic loading is insignificant. Tube side headers, channel covers, and internals of tubes can be cleaned quit easily and the shell side can be cleaned only by circulating a cleaning fluid or backwashing. (2) U-tube shell and tube heat exchangers U-tube shell and tube hear exchangers consist of one tubesheet with tubes bent in a u-shape attached to the single tubesheet. This type of exchanger is used for large temperature differentials where there is a lot of tube growth. This type of design allows for easy access to the shell side of the tubes and removal of the tube bundle. The inside of tubes must be cleaned with special tools and then only when the bending radius is fairly large. This type of design is also very suitable for chemical cleaning. The maximum number of tubes per tubesheet is less than the fixed tubesheet design because of the minimum-bending radius required to form the U-shape. The U-tube design is also very applicable to high-pressure All rights Reserved 22

4 Figure 2 Different types of heat exchanger (Letter designations for different Types of heat exchangers) (iii) Floating Head shell and Tube heat exchangers This type of shell and tune heat exchanger has a floating head that is designed to accommodate thermal expansion of the tubes and to provide access to the tube-side and shell-side exchanger and its use should be considered against other possible designs. IV. SOFTWARE ARCHITECTURE AND FLOW CHART The program is based on the mechanical design of a fixed-tubesheet class R heat exchanger. The design procedure given in TEMA and ASME section-viii, division-1 & 2 have been followed. System of unit is also take care, as data available in TEMA and ASME section-viii, division-1 is in British unit, entry of such inputs are done in the same system of unit. following databases are used. 1. Bolting data 2. Dimensions of seamless and welded pipe as given in table for automatic election of All rights Reserved 23

5 3. Allowable stress value for shell, flanges, heads and tube sheets material. 4. Minimum design seating stress y, and gasket factor for asbestos composition. 5. Allowable stress value for Bolt material for shall and tube heat exchanger. 6. Allowable stress value for Nozzle material for shall and tube heat exchanger. 7. Mean coefficient of thermal expansion for Carbon steel and Low alloy steel. 8. Modulus of elasticity for Carbon steel and Low alloy steel. Figure 1. Software architecture for shell and tube heat exchanger Mechanical All rights Reserved 24

9 V. CASE STUDY DETAILS Water cooler is taken as a case study used in Indian oil corporation ltd. Detail design data is given below. Inlet temperature of shell side water = 5 C Inlet temperature of tube side water = 36 C Outlet temperature of shell side water = 10 C Outlet temperature of tube side water = 30 C Mass flow rate of tube side water = 3500 Kg/hour Tube length = 1 meter Design gauge pressure on shell side = 6.5 Kg/cm2 (0.637 N /mm2) Design gauge pressure on tube side = 7 Kg/cm2 (0.686 N /mm2) Shell side allowable pressure drop = 0.03 bar (3 x 10-3 N /mm2) Tube side allowable pressure drop = 0.02 bar (2 x 10-3 N /mm2) Corrosion allowance on shell and tube side = 1.5 mm Joint efficiency on shell and tube side = 0.9 Fouling factor for shell side stream = 3500 W/m2 C Fouling factor for tube side stream = 3000 W/m2 C Material property of different components at design temperature: Material property of shell and tube side stream at design temperature No. 1 Name of component Shell, Bonnet shell, Material used SA-53 product from pipe Maximum allowable stress at design pressure psi or shell and tube side Nozzle X 108 N / m2 (-28 C to 340 C) 2 Tubesheet, bonnet flange, bonnet head High alloy steel SA-240 Grade 304 N psi or X 108 N / m2 product from plate 3 Nut, Bolt High alloy steel SA-193 Grade B6 (410) (-28 C to 90 C) psi or 1.46 X 108 N / m2 (-28 C to 400 C) VI. OUTPUT OF MECHANICAL DESIGN SOFTWARE No. Mechanical design parameter By using software 1 Thickness of shell, mm 5 2 Thickness of Bonnet shell, mm 5 3 Outer diameter of gasket, mm Inside diameter of gasket, mm Gasket width, mm 23 6 Inner diameter of flange, mm Outer diameter of flange, mm Flange thickness 20 9 Bolt pitch circle diameter, mm Bolt diameter recommended, inches Number of bolts 8 12 Head thickness, mm 5 13 Tubesheet thickness, mm All rights Reserved 28

10 14 Shell inlet nozzle thickness 40 Sched. 15 Shell outlet nozzle thickness 40 Sched. 16 Tube inlet nozzle thickness 40 Sched. 17 Tube outlet nozzle thickness 40 ched. VII. CONCLUSION Mechanical design software gives fast, accurate and optimum results which is helpful in the design of shell and tube type heat exchanger in the industries. Various data required for the design of shell and tube type heat exchanger are included in the form of databases which make mechanical design very fast and user friendly. The limitation of this shoftware is that it is only useful to mechanical design of a fixed-tubesheet class R heat exchanger, however for other type of heat exchanger such type of software may be developed. REFERENCES [1] Arthur P. Fraaz, Heat exchanger Design, A wiley-interscience Publication, [2] A Keith Escoe, Mechanical Design of Process System Volume-2, Gulf Publication Company, [3] TEMA, Standards of Tubular Exchanger Manufacturers Association, [4] Stanley Yokell, A working guide to Shell and Tube Heat Exchangers, McGraw-Hill Publishing Company, [5] Su Thet Mon Than, Khin Aung Lin, Mi Sandar Mon, Heat Exchanger design", World Academy of Science, Engineering and Technology [6] Sepehr Sanaye, Hassan Hajabdollahi, Multi-objective optimization of shell and tube heat exchanger, Applied Thermal Engineering 30 (2010) [7] Kenneth J. Bell, Preliminary Design of Shell and Tube Heat Exchangers, in Heat Exchangers-Thermo hydraulic fundamental and Design, Edited by S. Kakak, A.E. Bergles, and F. Mayinger, Hemisphere Publishing Corp., New York, 1981, page no [8] Brownell, L.E. & Young, E.H., Process Equipment Design, Fourth Wiley Eastern Reprint, [9] R. K. Shah, Heat Exchanger Design Methodology An Overview, in Heat Exchangers Thermo hydraulic fundamental and Design, Edited by S. Kakak, A.E. Bergles, and F. Mayiner, Hemisphere Publishing Corp., New York, 1981, page no [10] G.T. Polley et al. rapid design algorithm for shell and tube and compact heat exchangers, trans I cheme, vol. 69, Part A, November 1991, page no [11] G. Walker, Industrial Heat Exchangers: A basic guide, second edition, Hemisphere Publishing Corp., [12] ASME, Boiler and pressure Code for unfired pressure vessels, Section VIII, Division 1, [13] ASME, Boiler and pressure Code for unfired pressure vessels, Section VIII, Division 2, [14] R.B. Puyear, Material selection criteria for shell and tube heat exchangers for use in the process industries, in Shell and Tube Heat Exchangers, Edited by William R. Apbllet, A Publication of American Society of Metals, 1982 [15] J.P.Gupta, Heat Exchanger and pressure Vessel Technology, Hemisphere Publishing Corp., 1986 [16] D.N. Paliwal et al. A program for the design of a heat exchanger as per TEMA standards, international journal of pressure vessels and piping, 1994, page no. All rights Reserved 29

S&T HEAT EXCHANGERS Part II: Main Parts, Conical Transitions, Shell & Heads, Nozzle Design.

S&T HEAT EXCHANGERS Part II: Main Parts, Conical Transitions, Shell & Heads, Nozzle Design. STUDY NOTES Instructor: Javier Tirenti training@arvengconsulting.com www.arvengconsulting.com Table of contents