Heat exchanger networks exchangers

Of course, some processes do not require a reactor, e.g., some oil refinery processes. Here, the design starts with the sepauration system and moves outward to the heat exchanger network and utilities. However, the basic hierarchy prevails. 

Having found the best nonintegrated sequence, most designers would then heat integrate. In other words, the total problem is not solved simultaneously but in two steps. Moving outward from the center of the onion (see Fig. 1.6), the separation layer is addressed first, followed by the heat exchanger network layer. 

Heat Exchanger Network and Utilities Energy Targets... 

The analysis of the heat exchanger network first identifies sources of heat (termed hot streams) and sinks (termed cold streams) from the material and energy balance. Consider first a very simple problem with just one hot stream (heat source) and one cold stream (heat sink). The initial temperature (termed supply temperature), final temperature (termed target temperature), and enthalpy change of both streams are given in Table 6.1. 

After maximizing heat recovery in the heat exchanger network, those heating duties and cooling duties not serviced by heat recovery must be provided by external utilities. The outer-most layer of the onion model is now being addressed, but still dealing with targets. 

The energy cost of the process can be set without having to design the heat exchanger network and utility system. These energy targets cam be calculated directly from the material and energy balance. Thus... 

Cerda, J., Westerberg, A. W., Mason, D., and Linnhoff, B., Minimum Utility Usage in Heat Exchanger Network Synthesis—A Transportation Problem, Chem. Eng. ScL, 38 373 1983. 

In addition to being able to predict the energy costs of the heat exchanger network and utilities directly from the material and energy balance, it would be useful to be able to calculate the capital cost, if this is possible. The principal components that contribute to the capital cost of the heat exchanger network are... 

Let us take each of these components in turn and explore whether they can be accounted for from the material and energy balance without having to perform heat exchanger network design. 

To understand the minimum number of matches or units in a heat exchanger network, some basic results oigraph theory can be used. A graph is any collection of points in which some pairs of points are... 

FIgur 7.4 If film transfer coefficients difier significantly, then nonvertical h t transfer is necessary to achieve the minimum area. (Reprinted from Linnhoff and Ahmad, Cost Optimum Heat Exchanger Networks I. Minimum Energy and Capital Using Simple Models for Capital Cost," Computers Chem. Engg., 7 729, 1990 with permission from Elsevier Science, Ltd.)... 

Calculate the capital cost target for the mixed specification heat exchanger network from Eq. (7.21) using the cost law coefficients for the reference specification. 

Different utility options such as furnaces, gas turbines, and different steam levels can be assessed more easily and with greater confidence knowing the capital cost implications for the heat exchanger network. 

The design of the heat exchanger network is greatly simplified if the design is initialized with an optimized value for... 

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