Heat exchanger network multiple

A typical chemical plant flowsheet has a mixture of multiple units connected both in series and in parallel. As noted in the previous chapter, the common topology consists of reaction sections and separation sections. Streams of fresh reactants enter the plant by being fed into the reaction section (or sometimes into the separation section) through a heat exchanger network. Here the chemical transformations occur to produce the desired species in one or more of a potentially wide array of reactor types continuous stirred tank, tubular, packed bed, fluidized bed, sparged, slurry, trickle bed, etc. 

The pinch decomposition is very useful in heat exchanger network design, as it decomposes the problem into two smaller problems. It also indicates the region where heat transfer matches are most constrained, at or near the pinch. When multiple hot or cold utilities are used, there may be other pinches, termed utility pinches, that cause further problem decomposition. Problem decomposition can be exploited in algorithms for automatic heat exchanger network synthesis. 

Linnhoff March Ltd.), and UniSim ExchangerNet (Honeywell Inc.) allow the design engineer to plot composite curves, optimize AT in, set targets for multiple utilities, and design the heat exchanger network. 

To this point, it has been assumed that the log-mean tenperature correction factor, F, for all exchangers is the same and equal to 0.8. The reason that F is not assumed to be equal to unity is that, for heat exchangers in most practical applications, the flows of the hot and cold streams are never purely countercurrent. The most common type of heat exchanger in use in the chemical process industries is the shell-and-tube (S T) type. These units are typically made as multiples of the basic 1-shell pass, 2-tube pass (1-2) design. When estimating the fixed capital investment associated with the purchase and installation of the heat-exchanger network, the number of 1-2 S T exchangers is needed in addition to the total surface area of the network. 

AIChE (American Institute of Chemical Engineers) Chemical Professional s Code of Conduct, 831. 832-833 Coffey stills, 92 Colburn equation, 636-639 Cold utilities, HENs (heat-exchanger networks) minimizing, 529-530 minimum approach temperature, 526 multiple utilities, 558 pinch points, 529-530 Cold zones, 712. 714... 

A low temperature of approach for the network reduces utihties but raises heat-transfer area requirements. Research has shown that for most of the pubhshed problems, utility costs are normally more important than annualized capital costs. For this reason, AI is chosen eady in the network design as part of the first tier of the solution. The temperature of approach, AI, for the network is not necessarily the same as the minimum temperature of approach, AT that should be used for individual exchangers. This difference is significant for industrial problems in which multiple shells may be necessary to exchange the heat requited for a given match (5). The economic choice for AT depends on whether the process environment is heater- or refrigeration-dependent and on the shape of the composite curves, ie, whether approximately parallel or severely pinched. In cmde-oil units, the range of AI is usually 10—20°C. By definition, AT A AT. The best relative value of these temperature differences depends on the particular problem under study. 

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