Heat exchangers typical

Closed FW heaters are shell and tube heat exchangers typically designed to contain U-tube bundles expanded or welded into a single, stationary tube sheet (although some designs replace the tube sheet with inlet and outlet box headers). 

Fins are used to increase the effective surface area of heat-exchanger tubing. Many different types of fin have been developed, but the plain transverse fin shown in Figure 12.66 is the most commonly used type for process heat exchangers. Typical fin dimensions are pitch 2.0 to 4.0 mm, height 12 to 16 mm ratio of fin area to bare tube area 15 1 to 20 1. 

The cooled TR is frequently operated with a cooling jacket surrounding the reactor in a tube-and-shell configuration. This looks simply like a tube-in-sheU heat exchanger, typically with catalyst in the tube to catalyze the reaction. 

A heat exchanger typically involves two flowing fluids separated by a solid wall. Heat is first transferred from the hot fluid to ilie wall by convection. 

Effectiveness relations of the heat exchangers typically involve the dimensionless group UAje. TTiis quantity is called the number of transfer units NTU and is expressed as... 

In order to do preliminary estimating of sizes of shell-ind-tube heat exchangers, typical values of overall heat-transfer coefficients are given in Table 4.9-2. These values should be useful as a check on the results of the design methods described in this chapter. 

In addition to taking the heat away from the fuel cell stack, the cooling loop also cools down the reformate gas coming from the fuel processor and provides heat, if needed, in the air humidification process. Moreover, temperature control of the preferential oxidation process is needed (as shown in Figures 9-37 and 9-38). The heat is then rejected from the system to the environment by the heat exchanger, typically of a radiator type. Some heat may be rejected from the system in the condenser just before the exhaust gases leave the system. The condenser is needed to condense and save the water in the exhaust to maintain a neutral water balance in the system. 

A, 5A, and 13X zeoHtes are the predorninant adsorbents for CO2 removal by temperature-swing processes. The air fed to an air separation plant must be H2O- and C02-ftee to prevent fouling of heat exchangers at cryogenic temperatures 13X is typically used here. Another appHcation for 4A-type zeoHte is for CO2 removal from baseload and peak-shaving natural gas Hquefaction faciHties. 

Combinatorial. Combinatorial methods express the synthesis problem as a traditional optimization problem which can only be solved using powerful techniques that have been known for some time. These may use total network cost direcdy as an objective function but do not exploit the special characteristics of heat-exchange networks in obtaining a solution. Much of the early work in heat-exchange network synthesis was based on exhaustive search or combinatorial development of networks. This work has not proven useful because for only a typical ten-process-stream example problem the alternative sets of feasible matches are cal.55 x 10 without stream spHtting. 

Concentration of Rare Gas Crudes. The distillation of air is classically carried out in the double-column and auxihary equipment of Figure 5. Dry, C02-free air, chilled to partial liquefaction by heat exchange, is introduced into the lower nitrogen or high pressure column. This unit is typically... 

Reaction times can be as short as 10 minutes in a continuous flow reactor (1). In a typical batch cycle, the slurry is heated to the reaction temperature and held for up to 24 hours, although hold times can be less than an hour for many processes. After reaction is complete, the material is cooled, either by batch cooling or by pumping the product slurry through a double-pipe heat exchanger. Once the temperature is reduced below approximately 100°C, the slurry can be released through a pressure letdown system to ambient pressure. The product is then recovered by filtration (qv). A series of wash steps may be required to remove any salts that are formed as by-products. The clean filter cake is then dried in a tray or tunnel dryer or reslurried with water and spray dried. 

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%. 

Nickel—Copper. In the soHd state, nickel and copper form a continuous soHd solution. The nickel-rich, nickel—copper alloys are characterized by a good compromise of strength and ductihty and are resistant to corrosion and stress corrosion ia many environments, ia particular water and seawater, nonoxidizing acids, neutral and alkaline salts, and alkaUes. These alloys are weldable and are characterized by elevated and high temperature mechanical properties for certain appHcations. The copper content ia these alloys also easure improved thermal coaductivity for heat exchange. MONEL alloy 400 is a typical nickel-rich, nickel—copper alloy ia which the nickel content is ca 66 wt %. MONEL alloy K-500 is essentially alloy 400 with small additions of aluminum and titanium. Aging of alloy K-500 results in very fine y -precipitates and increased strength (see also Copper alloys). 

Typical apphcations for the nickel—copper alloys are in iadustrial plumbing and valves, marine equipment, petrochemical equipment, and feedwater heat exchangers (see Piping systems). The age-hardened alloys are used as pump shafts and impellers, valves, drill parts, and fasteners (see Pumps). 

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