Heat exchanger fixed tube

Condenser shell and tube heat exchanger, fixed tube sheets, heat transfer area 25 m2, design pressure 2 bar, materials stainless steel. 

Fixed-Tube-Sheet Heat Exchangers Fixed-tube-sheet exchangers (Fig. ll-36fo) are used more often than any other type, and the frequency of use has been increasing in recent years. The tube sheets are welded to the shell. Usually these extend beyond the shell and serve as flanges to which the tube-side headers are bolted. This construction requires that the shell and tube-sheet materials be weldable to each other. 

FIGURE 3 Sectional view of a typical fixed tubesheet shell-and-tube heat exchanger (A) tubes (B) tubesheets (C) shell (D) tube-side channel and nozzles (E) channel cover (F) pass divider plate (G) stationary rear head (bonnet type) (H) tube support plates (or baffles). 

From Figures 5.22 and 5.23, it is seen that there is room to accommodate the thermal expansion of the tubes. In the case of the finned heat exchanger, the tubes can expand in an expandable shell, whereas in the case of the U-tube heat exchanger, expansion room is provided because of the existence of free fixed tubes in a firm shell. 

Intermediate heat exchangers. Horizontal tube-and-shell IHXs with three modules connected in series, made of U-shaped tubes are used in the BN-350. The IHX of each loop consists of two sections connected in parallel both for primary and secondary coolant flows. The IHX is located in a suction loop upstream of the primary coolant pump, while in the secondary circuit it is in a pressure loop downstream of the circulating pump. The IHX tube bundles can be removed if necessary and replaced with new ones. The most stressed units in the IHX are the fixing joints for the tube module covers and for the fi-ame which stiffens the flat walls of the IHX body. Measurements of temperatures and stresses in various items of the IHX were carried out during reactor plant operation. On this basis requirements were formulated to limit the rate of the IHX heating-up in steps of 10% specified power with delays of 5-10 h in each step. By 1995 the IHXs have operated more than 160000 h at various power levels without any disturbances and failures. 

In petrochemical plants, fans are most commonly used ia air-cooled heat exchangers that can be described as overgrown automobile radiators (see HeaT-EXCHANGEtechnology). Process fluid ia the finned tubes is cooled usually by two fans, either forced draft (fans below the bundle) or iaduced draft (fans above the bundles). Normally, one fan is a fixed pitch and one is variable pitch to control the process outlet temperature within a closely controlled set poiat. A temperature iadicating controller (TIC) measures the outlet fluid temperature and controls the variable pitch fan to maintain the set poiat temperature to within a few degrees. 

Catalytic methanation processes include (/) fixed or fluidized catalyst-bed reactors where temperature rise is controlled by heat exchange or by direct cooling using product gas recycle (2) through wall-cooled reactor where temperature is controlled by heat removal through the walls of catalyst-filled tubes (J) tube-wall reactors where a nickel—aluminum alloy is flame-sprayed and treated to form a Raney-nickel catalyst bonded to the reactor tube heat-exchange surface and (4) slurry or Hquid-phase (oil) methanation. 

Construction Codes Rules for Construction of Pressure Vessels, Division 1, which is part of Section T11 of the ASME Boiler and Pressure Vessel Code (American Society of Mechanical Engineers), sei ves as a construction code by providing minimum standards. New editions of the code are usually issued every 3 years. Interim revisions are made semiannually in the form of addenda. Compliance with ASME Code requirements is mandatoiy in much of the United States and Canada. Originally these rules were not prepared for heat exchangers. However, the welded joint between tube sheet and shell of the fixed-tube-sheet heat exchanger is now included. A nonmandatoi y... 

The U-tube bundle has the advantage of providing minimum clearance between the outer tube hmit and the inside of the shell for any of the removable-tube-bundle constructions. Clearances are of the same magnitude as for fixed-tube-sheet heat exchangers. 

For fixed tubesheet design of shell and tube heat exchangers don t allow too high a temperature difference between tubeside and shellside without providing a shellside expansion joint. The author has seen 70 F (one company) and 100°F (another company) used as this limit. An easy way to calculate the maximum stress is as follows ... 

To determine the outside heat transfer area of a heat exchanger bundle consisting of 100 tubes, in. O.D. tubing, 18 BWG (gauge thickness) X 16 ft long. For fixed tubesheets (2), thickness is 1.0 in. each. 

A useful application is for tank and vessel heating, with the heater protruding into the vessel. Bayonet heat exchangers are used in place of reactor jackets when the vessel is large and the heat transfer of a large mass of fluid through the wall would be difficult or slow, because the bayonet can have considerably more surface area than the vessel wall for transfer. Table 10-43 compares bayonet, U-tube, and fixed-tubesheet exchangers. ... 

Comparison of Bayonet, U-Tube, and Fixed Tubesheet Heat Exchangers... 

Figure 9.62. Heat exchanger with fixed tube plates (four tube, one shell-pass)...

The tube-plates (tube-sheets) in shell and tube heat exchangers support the tubes, and separate the shell and tube side fluids (see Chapter 12). One side is subject to the shell-side pressure and the other the tube-side pressure. The plates must be designed to support the maximum differential pressure that is likely to occur. Radial and tangential bending stresses will be induced in the plate by the pressure load and, for fixed-head exchangers, by the load due to the differential expansion of the shell and tubes. 

Fixed tube heat exchangers are usually less than 50,000 ft2 (4,650 m2). 

In the case where a rapid removal or addition of heat is needed, it may not be possible to use a single fixed bed or large diameter. In this case, the reactor can be built up of a number of tubes, containing the catalyst particles and encased in a single body (Smith, 1981). Then, the heat exchange can be easily done by circulating a fluid in the space between the tubes. 

Figure 8.4. Example of tubular heat exchangers (see also Fig. 8.14). (a) Double-pipe exchanger, (b) Scraped inner surface of a double-pipe exchanger, (c) Shell-and-tube exchanger with fixed tube sheets, (d) Kettle-type reboiler, (e) Horizontal shell side thermosiphon reboiler, (f) Vertical tube side thermosiphon reboiler, (g) Internal reboiler in a tower, (h) Air cooler with induced draft fan above the tube bank, (i) Air cooler with forced draft fan below the tube bank.

Figure 17.13. Multibed catalytic reactors (a) adiabatic (b) interbed coldshot injection (c) shell and tube (d) built-in interbed heat exchanger (e) external interbed exchanger (f) autothermal shell, outside influent-effluent heat exchanger (g) multishell adiabatic reactor with interstage fired heaters (h) platinum-catalyst, fixed bed reformer for 5000 bpsd charge rate reactors 1 and 2 are 5.5 ft dia by 9.5 ft high and reactor 3 is 6.5 x 12.0 ft.

Figure 17.18. Heat transfer in fixed-bed reactors (a) adequate preheat (b) internal heat exchanger (c) annular cooling spaces (d) packed tubes (e) packed shell (f) tube and thimble (g) external heat exchanger (h) multiple shell, with external heat transfer (Walas, 1959).

Figure 17.24. Types of reactors for synthetic fuels [Meyers (Ed.), Handbook of Synfuels Technology, McGraw-Hill, New York, 1984], (a) ICI methanol reactor, showing internal distributors. C, D and E are cold shot nozzles, F = catalyst dropout, L = thermocouple, and O = catalyst input, (b) ICI methanol reactor with internal heat exchange and cold shots, (c) Fixed bed reactor for gasoline from coal synthesis gas dimensions 10 x 42 ft, 2000 2-in. dia tubes packed with promoted iron catalyst, production rate 5 tons/day per reactor, (d) Synthol fluidized bed continuous reactor system for gasoline from coal synthesis gas.

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