Shell details, heat exchanger

Increasing the chosen value of process energy consumption also increases all temperature differences available for heat recovery and hence decreases the necessary heat exchanger surface area (see Fig. 6.6). The network area can be distributed over the targeted number of units or shells to obtain a capital cost using Eq. (7.21). This capital cost can be annualized as detailed in App. A. The annualized capital cost can be traded off against the annual utility cost as shown in Fig. 6.6. The total cost shows a minimum at the optimal energy consumption. 

Figure 11-36 shows details of the construction of the TEMA types of shell-and-tube heat exchangers. These and other types are discussed in the following paragraphs. 

Figure 1.7 Simple detail of shell-and-tube heat exchanger. The water box may be designed for as many as eight passes, and a variety of configurations of shell-side baffles may be used to improve heat transfer, (a) Several water box arrangements for tube-side cooling, (b) Assembly of simple two-pass exchanger with U-tubes. [Fig. 38.2, The Nalco Water Handbook, 1st ed. (1979), reprinted with permission from McGraw-Hill, Inc.)...

Typical film coefficients can be used to build rough overall heat transfer coefficients. This should suffice in most cases to establish that the design is within ballpark accuracy. Later, for final design, certain critical services will be checked in detail. Typical film resistances for shell and tube heat exchangers and overall heat transfer coefficients for air cooled heat exchangers are shown in Chapter 2, Heat Exchangers. 

Heat exchangers used in gas production facilities are shell-and-tube, double-pipe, plate-and-frame, bath-type, forced-air, or direct-fired. In this chapter we will discuss the basic concepts for sizing and selecting heat exchangers. This is just a brief overview of this complex subject and is meant to provide the reader with a basis upon which to discuss specific sizing and selection details with heat exchange experts in engineering companies and with vendors. 

The various components which make up a shell and tube heat exchanger are shown in Figures 9.63 and 9.64 and these are now considered. Many different mechanical arrangements are used and it is convenient to use a basis tor classification. The standard published by the Tubular Exchanger Manufacturer s Association (TEMA 97 ) is outlined here. It should be added that noting that Saunders 98 has presented a detailed discussion of design codes and problems in fabrication. 

Pikulik and Diaz (1977) give a method of costing major equipment items from cost data on the basic components shells, heads, nozzles, and internal fittings. Purohit (1983) gives a detailed procedure for estimating the cost of heat exchangers. 

The principal types of shell and tube exchanger are shown in Figures 12.3 to 12.8. Diagrams of other types and full details of their construction can be found in the heat-exchanger standards (see Section 12.5.1.). The standard nomenclature used for shell and tube exchangers is given below the numbers refer to the features shown in Figures 12.3 to 12.8. 

The complex flow pattern on the shell-side, and the great number of variables involved, make it difficult to predict the shell-side coefficient and pressure drop with complete assurance. In methods used for the design of exchangers prior to about 1960 no attempt was made to account for the leakage and bypass streams. Correlations were based on the total stream flow, and empirical methods were used to account for the performance of real exchangers compared with that for cross flow over ideal tube banks. Typical of these bulk-flow methods are those of Kern (1950) and Donohue (1955). Reliable predictions can only be achieved by comprehensive analysis of the contribution to heat transfer and pressure drop made by the individual streams shown in Figure 12.26. Tinker (1951, 1958) published the first detailed stream-analysis method for predicting shell-side heat-transfer coefficients and pressure drop, and the methods subsequently developed... 

The detailed allocation of fluids to tube-side or shell-side can only be made later in the heat exchanger network design. Also, the area targeting formula does not recognize fluids to be allocated to the tube-side or shell-side. Area targeting only recognizes the individual film heat transfer coefficients. All that can be done in network area targeting... 

Figure 7.1-6. Construction details of a high-pressure heat exchanger. Left The connection between shell and the covered plate is not testable right The corrected well testable arrangement [15],...

Two-pass shell-and-tube heat exchanger showing construction details. (Ross Heat Ixdtattgrr Division of American-Standard.)... 

A chart to estimate the costs of ejectors for thermocompression has been developed.Approximate costs of compressors for mechanical vapor recompression also can be found. In addition, these publications contain details of cost estimation for heat exchangers. For more detailed estimation of cost of shell-and-tube exchangers, see Purohit. " Plate-and-frame and spiral-plate heat exchanger costs can be estimated using Kumana. " ... 

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