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This section contains information on TEMA nomenclature, selecting the most economic exchanger configuration for a defined service, allocating the streams to shell or tube side, specifying appropriate mechanical components, defining baffle layout, deciding if a small predesigned exchanger is appropriate, and estimating the size and cost of shell and tube exchangers.
400 Shell and Tube Exchanger Design and Selection Abstract This section contains information on TEMA nomenclature, selecting the most economic exchanger configuration for a defined service, allocating the streams to shell or tube side, specifying appropriate mechanical components, defining baffle layout, deciding if a small predesigned exchanger is appropriate, and estimating the size and cost of shell and tube exchangers Contents Chevron Corporation Page 410 TEMA (Tubular Exchanger Manufacturers Assoc.) Nomenclature 400-2 420 General Design Considerations 430 Stream Placement 400-11 440 Pass Arrangements and Multiple Shells 400-12 450 Bundle and Tubesheet Arrangements 400-13 451 Front Head Design 452 Fixed Tubesheets 453 U-tubes Versus Floating Rear Heads 454 TEMA F Shell 460 Shell Side Baffle and End Spaces 400-14 470 Small Exchangers 400-15 480 Estimating Methods 400-16 481 Step by Step Procedure 482 Surface Area Calculations 483 Tube Count and Number of Tube Passes 484 Shell Diameter 485 Exchanger Investment Cost 400-1 400-2 December 1989 400 Shell and Tube Exchanger Design and Selection Heat Exchanger and Cooling Tower Manual 410 TEMA (Tubular Exchanger Manufacturers Assoc.) Nomenclature The Tubular Exchanger Manufacturers Association (TEMA) has developed nomenclature for describing shell and tube heat exchangers It includes a simple code for designating the size and type of the exchanger In addition, standard terminology has been set up to specify typical parts and connections TEMA size is the shell inside diameter in inches rounded to the nearest integer, followed by the straight length of the tubes in inches rounded to the nearest integer The two dimensions are separated by a hyphen (-) For kettle reboilers, the port diameter in inches precedes the shell inside diameter The two dimensions are separated by a slash (/) Port diameter is the size of the opening the bundle slides through TEMA type consists of three letters describing the stationary or front end head, shell, and rear head, in that order The letter designations are shown on Figure 400-1 For example, a 20-foot straight length U-tube bundle, 3-foot shell diameter, with a single shell pass and removable shell cover would be a TEMA SIZE 36-240 TYPE AEU The same bundle installed in a 5-foot diameter kettle reboiler would be a TEMA SIZE 36/60-240 TYPE AKU Standard terminology to describe components and connections of shell and tube exchangers is provided in Figure 400-2 TEMA sets mechanical standards for three classes of exchangers reflecting the severity of the service For most refinery services, the most restrictive class is used—TEMA Class R For other services (chemical plants for example), TEMA Class C or B exchangers are used In general, Class R exchangers have thicker shells, larger and thicker heads, thicker tubes, and larger miscellaneous parts TEMA requirements are noted where appropriate throughout this manual 420 General Design Considerations Single- and two-phase exchangers and most condensers have very similar configurations The typical layout is summarized in the following list and shown in Figures 400-3 and 400-4 (Steam generators (2 types), reboilers, and condensers are described in Sections 340, 350, 360 and 370.) The typical shell and tube exchanger geometry includes the following items: December 1989 • TEMA E shell style • U-tubes for rear head type with full support plate at tangent • TEMA A-type front head • Single segmental baffles with cut of 18 to 25% of shell I.D and with cut oriented vertically • Baffle spacing of 20 to 100% of shell I.D 400-2 Chevron Corporation Heat Exchanger and Cooling Tower Manual Fig 400-1 400 Shell and Tube Exchanger Design and Selection Heat Exchanger Nomenclature (TEMA, Figure N-1.2) (Courtesy of TEMA) Chevron Corporation 400-3 December 1989 400 Shell and Tube Exchanger Design and Selection Fig 400-2 Heat Exchanger and Cooling Tower Manual Heat Exchanger Components (1 of 3) (TEMA, Table N-2 and Figure N-2) (Courtesy of TEMA) Stationary Head—Channel 21 Floating Head Cover—External Stationary Head—Bonnet 22 Floating Tubesheet Skirt Stationary Head Flange—Channel or Bonnet 23 Packing Box Channel Cover 24 Packing Stationary Head Nozzle 25 Packing Gland Stationary Tubesheet 26 Lantern Ring Tubes 27 Tierods and Spacers Shell 28 Transverse Baffles or Support Plates Shell Cover 29 Impingement Plate 10 Shell Flange—Stationary Head End 30 Longitudinal Baffle 11 Shell Flange—Read Head End 31 Pass Partition 12 Shell Nozzle 32 Vent Connection 13 Shell Cover Flange 33 Drain Connection 14 Expansion Joint 34 Instrument Connection 15 Floating Tubesheet 35 Support Saddle 16 Floating Head Cover 36 Lifting Lug 17 Floating Head Flange 37 Support Bracket 18 Floating Head Backing Device 38 Weir 19 Split Shear Ring 39 Liquid Level Connection 20 Slip-on Backing Flange December 1989 400-4 Chevron Corporation Heat Exchanger and Cooling Tower Manual Fig 400-2 400 Shell and Tube Exchanger Design and Selection Heat Exchanger Components (2 of 3) (TEMA, Table N-2 and Figure N-2) (Courtesy of TEMA) Chevron Corporation 400-5 December 1989 400 Shell and Tube Exchanger Design and Selection Fig 400-2 Heat Exchanger and Cooling Tower Manual Heat Exchanger Components (3 of 3) (TEMA, Table N-2 and Figure N-2) (Courtesy of TEMA) December 1989 400-6 Chevron Corporation Heat Exchanger and Cooling Tower Manual Typical Longitudinal Section Shell and Tube Exchanger Chevron Corporation Fig 400-3 400-7 400 Shell and Tube Exchanger Design and Selection December 1989 400 Shell and Tube Exchanger Design and Selection Fig 400-4 Heat Exchanger and Cooling Tower Manual Typical Cross Section, Shell and Tube Exchanger December 1989 400-8 Chevron Corporation Heat Exchanger and Cooling Tower Manual 400 Shell and Tube Exchanger Design and Selection • 3/4-inch O.D., 14 BWG (average) thickness (0.584 inch I.D.) carbon steel tubes • Tube length variable with one or two tube passes depending on service • 45 degree rotated square layout with tube pitch = 1.25 × tube O.D for liquid and two-phase hydroprocessing shell side service • 90 degree square layout with tube pitch = 1.25 × tube O.D for boiling, condensing, and single-phase gas shell side service • Two or more pairs of sealing strips (bars) • Dummy tubes in pass partition lane when two tube passes • Two rows of impingement rods at inlet nozzle when warranted Overall Exchanger Configuration The Company preference is a TEMA AEU exchanger for most services U-tubes are the cheapest rear head type that allows for thermal expansion of the tubes The TEMA A type front head has a removable channel cover This allows for inspection and cleaning of the tube side without pulling spool pieces in the piping Shell Side Nozzle Placement Single inlet and outlet shell side nozzles are normally located at opposite ends of the exchanger with one on the top and one on the bottom of the shell This arrangement allows vents and drains to be located in piping Route two-phase flow based on the following rule: “Heat up and cool down.” This means hot fluid being condensed should enter on the top and exit on the bottom of the exchanger Likewise, cold fluid being boiled should enter on the bottom and exit on the top The “Heat up and cool down” rule does not apply to single-phase flow Transverse and Support Baffles The normal configuration for the tube side consists of U-tubes with a full support plate at the tangent This is shown in Figure 400-3 The plate blocks flow over the U-bends Otherwise, the bends must be supported to protect against vibration For baffles, use single segmental baffles with a cut of around 18 to 25% of the shell I.D for most efficient conversion of pressure drop to heat transfer The baffle cut should be vertical for best drainage of the shell side at shutdown Baffle thickness is set by TEMA Baffle spacing should be 20 to 50% of the shell I.D It is usually set to maintain good heat transfer (economic pressure gradient or shear controlled flow regime) Guidelines for economic exchanger velocity and pressure drop are provided in Section 220 of this manual In some cases (particularly for gas and two-phase flow shell side), additional supports may be required to prevent vibration See Section 260 of this manual for more information Chevron Corporation 400-9 December 1989 400 Shell and Tube Exchanger Design and Selection Heat Exchanger and Cooling Tower Manual Tube Selection Tubes are normally 3/4-inch outside diameter, 14 BWG (minimum) thickness (0.56inch inside diameter), and made of carbon steel Length is limited by the plot space for pulling the bundle and standard bundle pulling equipment TEMA has named 8, 10, 12, 16 and 20 feet as standard tube lengths Other lengths are possible Alloy tubes are appropriate for some services The cost of upgrading to alloy tubes should always be weighed against possible process adjustments to permit carbon steel construction Section 800 of this manual discusses materials selection for different services Tubepass Layout Most exchangers should be limited to one or two tube passes Using U-tubes with two passes is best and cheapest, however some services dictate pass with a more expensive rear head (vertical thermosiphon reboilers or crude/overhead condensers, for example) Tube Pitch For liquid and two-phase services, use 1-inch, 45 degree rotated square pitch This promotes mixing Use 1-inch, 90 degree square pitch for boiling, condensing, and single-phase gas on the shell side For boiling, the vertically oriented lanes promote circulation For condensing and single-phase gas, in-line tubes minimize pressure drop without sacrificing heat transfer Both 45 and 90 degree pitch provide 0.25inch inspection and cleaning lanes through the bundle Preventing Shell Side Flow Bypassing Single- and two-phase exchangers with impingement protection typically include two pairs of sealing strips (bars) The bars block the leakage stream flowing around the baffles between the bundle and shell (“C” stream shown in Figure 200-3 in Section 213) For vertical cut baffles, the bars straddle the nozzles (located at the top and bottom of the bundle) Note that the bars on the bottom act as skid bars for bundle removal For an exchanger with two tube passes, the single pass partition lane runs perpendicular to the baffle cuts Dummy tubes are positioned in the pass partition lane to block flow bypassing (“F” stream shown in Figure 200-3 in Section 213) Dummy tubes are spaced four to six tube rows apart between baffle cuts and are the same diameter as the tubes Impingement Protection When impingement protection is warranted, the preferred method is to install two rows of rods (typically tubes over solid rods) adjacent to the inlet nozzle Section 524 contains design details and applications of impingement rods along with descriptions of other types of impingement protection Tolerances and Clearances All tolerances and clearances are TEMA December 1989 400-10 Chevron Corporation Heat Exchanger and Cooling Tower Manual 400 Shell and Tube Exchanger Design and Selection 430 Stream Placement Allocating the streams to the shell or tube side is determined by weighing factors which sometimes conflict These factors include stream temperature, pressure, relative flowrate, viscosity, corrosiveness, relative heat transfer film coefficient, and pressure drop limitations Guidelines for allocating the streams to the shell or tube side are given in Figure 400-5 Fig 400-5 Allocating the Streams for Shell and Tube Heat Exchangers In Order of Decreasing Priority: Stream Property Compared to Other Stream Preferred Side Shell Tube Match Coefficients and Pumping Power — — Lower Film Coefficient Expected (hshell / htube