![]() ![]() For each enthalpy interval, we can predict the required area from the composite curves. The area calculated with this model is minimised when the heat transfer coefficients of all streams are equal. It is possible to predict the required surface area for the whole problem by using vertical enthalpy intervals. In contrast, for the cold utility, we should use the highest temperature and generate the lowest temperature. Thus, for the hot utility, we should use the lowest temperature and generate the highest temperature. In this method, our aim is to use the specified utility at an appropriate level. In pinch analysis, the grand composite curve (GCC) is an appropriate tool to show the interface between the process and the utility system (see Figure 6). In Figure 5, the trade-off between energy, capital cost and economic amount of energy recovery is illustrated thus, the trade-off can be carried out using energy and capital cost targets.Īfter recovering the heat using process-process heat exchangers, the remaining required heat for the plant should be obtained by the utility system. The correct setting of composite curves is defined by an economic trade-off between energy and capital cost. As a rule of thumb, rating with a DTmin less than 10☌ should be avoided. In Table 2, the minimum approach temperature for several industries is shown. To achieve the lowest DTmin, the type of heat exchanger and fluid regime are important. It can be concluded that DTmin determines the relative location of the hot and cold streams, so it is an important variable for setting the amount of heat recovery. This figure shows DTmin=10☌ for the proposed flow sheet therefore, the hot and cold utility recoveries are 960 and 120 units, respectively (see Figure 4). The scope for heat recovery can be determined by plotting all streams on a T-H diagram (see Figure 3). It is preferable to recover as much heat as possible between process streams. The supply and target temperature and enthalpy changes of four process streams are also given in Table 1.Ĭonsider steam at 200☌ and cooling water at 20° for heating and cooling utilities, respectively. For instance, the current typical flow sheet of a chemical process is shown in Figure 2. In particular, the article demonstrates how the technology’s design methodology can be used for improving the heat recovery networks of an olefin plant, as a case study.įor analysing a heat exchanger network, sources of hot and cold streams (source and sink) should be first identified using material and energy balances. In this article, the discussion covers the basic principles and capabilities of pinch technology, and how the technology can be utilised to determine scope for reducing energy consumption and costs. It is obvious that, without a screening approach, selection between many design options cannot be easily afforded in terms of the time and effort required. Consequently, targets can be set for the HEN to evaluate the performance of the process design, and it can enable both the energy and capital costs of the HEN to be assessed. Heating and cooling duties for the next layer of the onion are the heat recovery systems. The design philosophy starts at the heart of the onion model, the reactor, and moves out to the separation system (see Figure 1). Wherever heating and cooling of material streams take place, there is a potential opportunity to save energy. The term “pinch technology” was introduced by Bodo Linnhoff in 1991 to represent a thermodynamically based methodology that guarantees minimum energy levels in the design of heat exchanger networks (HEN) therefore, this approach has been used to save energy in processes and across complete sites. ![]() Most of the available methods for energy targeting, retrofitting and design of heat exchanger networks are based on the pinch method. Energy saving is one of the most important issues associated with cost, regulations and environmental performance in the petroleum and petrochemical industries. ![]()
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