Shell-side

and DiPrima, R.C., Elementary Differential Equations and Boundary Value Problems, 8th ed., John Wiley Sons, New York, 2005, chap. 1. Geankopolis, C.J., Transport Processes and Unit Operations, 3rd ed., Prentice-Hall, Englewood Cliffs, NJ, 1978. 

Bennett, C.O. and Myers, J.E., Momentum, Heat, and Mass Transfer, McGraw-Hill, New York, 1962. 

Stewart, W.E., and Lightfoot, E.N., Transport Phenomena, John Wiley, New York, 2002. 

Ordinary Differential Equations, Dover, New York, 1956. 

and Loney, N.W., Molecular diffusion in the laminar sub-layer during turbulent flow in a smooth tube, Chem. Eng. Sci., 59, 1191 (2004). 

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Oxidation Step. A review of mechanistic studies of partial oxidation of propylene has appeared (58). The oxidation process flow sheet (Fig. 2) shows equipment and typical operating conditions. The reactors are of the fixed-bed shell-and-tube type (about 3—5 mlong and 2.5 cm in diameter) with a molten salt coolant on the shell side. The tubes are packed with catalyst, a small amount of inert material at the top serving as a preheater section for the feed gases. Vaporized propylene is mixed with steam and ak and fed to the first-stage reactor. The feed composition is typically 5—7% propylene, 10—30%... 

The dehydrogenation of 2-butanol is conducted in a multitube vapor-phase reactor over a zinc oxide (20—23), copper (24—27), or brass (28) catalyst, at temperatures of 250—400°C, and pressures slightly above atmospheric. The reaction is endothermic and heat is suppHed from a heat-transfer fluid on the shell side of the reactor. A typical process flow sheet is shown in Figure 1 (29). Catalyst life is three to five years operating in three to six month cycles between oxidative reactivations (30). Catalyst life is impaired by exposure to water, butene oligomers, and di-j -butyl ether (27). 

The highly exothermic nature of the butane-to-maleic anhydride reaction and the principal by-product reactions require substantial heat removal from the reactor. Thus the reaction is carried out in what is effectively a large multitubular heat exchanger which circulates a mixture of 53% potassium nitrate [7757-79-1/, KNO 40% sodium nitrite [7632-00-0], NaN02 and 7% sodium nitrate [7631-99-4], NaNO. Reaction tube diameters are kept at a minimum 25—30 mm in outside diameter to faciUtate heat removal. Reactor tube lengths are between 3 and 6 meters. The exothermic heat of reaction is removed from the salt mixture by the production of steam in an external salt cooler. Reactor temperatures are in the range of 390 to 430°C. Despite the rapid circulation of salt on the shell side of the reactor, catalyst temperatures can be 40 to 60°C higher than the salt temperature. The butane to maleic anhydride reaction typically reaches its maximum efficiency (maximum yield) at about 85% butane conversion. Reported molar yields are typically 50 to 60%. 

Fig. 23. Two types of hollow-fiber modules used for gas separation, reverse osmosis, and ultrafiltration applications, (a) Shell-side feed modules are generally used for high pressure appHcations up to - 7 MPa (1000 psig). Fouling on the feed side of the membrane can be a problem with this design, and pretreatment of the feed stream to remove particulates is required, (b) Bore-side feed modules are generally used for medium pressure feed streams up to - 1 MPa (150 psig), where good flow control to minimise fouling and concentration polarization on the feed side of the membrane is desired.

The second type of hoUow-fiber module is the bore-side feed type illustrated in Figure 23b. The fibers in this type of unit are open at both ends, and the feed fluid is usually circulated through the bore of the fibers. To minimize pressure drops inside the fibers, the fibers often have larger diameters than the very fine fibers used in the shell-side feed system and are generally made by solution spinning. These so-called capillary fibers are used in ultrafiltration, pervaporation, and in some low to medium pressure gas appHcations. Feed pressures are usually limited to less than 1 MPa (150 psig) in this type of module. 

Tube-Cooled Converter. The tube-cooled converter functions as an interchanger, consisting of a tube-filled vessel with catalyst on the shell side (Fig. 7c). The combined synthesis and recycle gas enters the bottom of the reactor tubes, where it is heated by the reaction taking place in the surrounding catalyst bed. The gas turns at the top of the tubes and passes down through the catalyst bed. The principal advantage of this converter is in... 

The most likely places for SCC to be initiated are crevices or areas where the flow of water is restricted. This is due to the buildup of corrodent concentrations in these areas. For example, chloride can concentrate from 100 ppm in the bulk water to as high as 10,000 ppm (1%) in a crevice. Deposits are initiating sites because of crevices formed beneath them. The low water velocities in shell-side cooling are also detrimental. 

The Snamprogetti process utilizes a tubular isothermal reactor (tubes filled with catalyst) for the first reactor with cooling water on the shell side to control temperature. The Huls process uses either an adiabatic or isothermal reactor for the first reactor. 

Both Mitsubishi and Mitsui TLEs differ drastically from other designs. Mitsubishi offers a TLE with an integral steam dmm and cyclone for vapor—hquid separation. The pyrolysis gas flows in the shell side, and is claimed to accomplish the decoking of the furnace and the transferline exchanger in one operation. The Mitsui quench cooler uses three concentric tubes as the tube element, and requires steam—air decoking to clean the TLE (58,59). 

APm.AP,., Pressure drop for ideal-tube-bank cross-flow and ideal window respectively AP for shell side of baffled exchanger kPa Itf ft ... 

Th,Tl High and low temperature respectively on shell side of a heat exchanger K OF... 

VVi, VK Total mass rate of flow on tube side and shell side respectively of a heat exchanger kg/s IVh... 

N. Shell side of microporous hollow fiber module for solvent extraction... 

Based on area of contact accorcing to inside or outside (iameter of tubes depencing on location of interface between aqueous and organic phases. Can also be applied to gas-liquid systems with liquid on shell side. 

Shell-Side Heat-Transfer Coefficient Calculation... 

Calculate the shell-side heat-tran.sfer coefficient for an ideal tube bank hi. 

Calculate the pre.s.sure drop acro.ss the. shell side (excluding nozzles). Units for pressure drop are Ibf/ft. ... 

For subcooling, a liquid inventory may be maintained in the bottom end of the shell by means of a weir or a hquid-level-controUer. The subcoohng heat-transfer coefficient is given by the correlations for natural convection on a vertical surface [Eqs. (5-33 ), (5-33Z )], with the pool assumed to be well mixed (isothermal) at the subcooled condensate exit temperature. Pressure drop may be estimated by the shell-side procedure. 

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