Heat Integration and Heat Recovery

Heat recovery is described in detail in Chapter 6 of this book. Of course standard methods such as pinch point analysis (see for instance [4]) are part of an energy study. Input data for a pinch point analysis are the heat streams in a plant and their temperature levels. There are some rules deduced from the pinch point theory. The consultant will evaluate if the actual heat exchanger network in the plant fulfills these rules. Then pinch point analysis or use of a software tool that applies the analysis, for example: Aspen Energy Analyzer, formerly Aspen HX-Net (http://www.aspentech.com/products/aspen-hx-net.cfm) or KBC Supertarget (http://www.kbcenergyservices.com/default.energy.asp?id=134) gives proposals for new heat integration measures, that means the exchange of heat between sources and sinks. Normally these measures need additional investments in equipment, piping and instrumentation, therefore their profitability has to be evaluated (see Section 4.5.3). Additionally an experienced energy consultant is able to detect other opportunities for heat integration by analyzing the P&ID diagrams.

There are several examples where measures that are relatively easy to implement have a significant potential:

• The use of bottom product of a column for preheating the feed stream is a classical example. A simple liquid-liquid heat exchanger can save a lot of energy.

• It is worth evaluating the reuse of warm water. Instead of losing the energy the customer can invest in an absorption heat pump and use the energy for the generation of chilled water. The consultant will calculate the profitability of this measure. If the heat streams are smaller, then warm water reuse for building heating sometimes is a solution.

• If steam is generated in the plant, then we try to redesign the process in a way that the steam pressure is high enough to feed the steam into the steam net. If the temperature (that means the pressure) is too low, then the steam might be used for trace heating.

• In pharmaceutical plants a high fraction of the energy consumption is often used for ventilation. Here we check if a heat exchanger, which heats the fresh air with the outlet stream, is profitable.

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