Plotting both composite curves on a temperature-enthalpy plot reveals a pinch at the point where the cold and hot curves are closest in temperature. The same is then done with the cold streams. First one combines all hot streams into single composite curve on a temperature-enthalpy graph. This method uses a graphical approach and makes obvious the presence and location of the pinch in the system. Because of this, there have been devised multiple approaches with which to solve a pinch system.Įxample of composite curve method taken from Sieder et al. Pinch technology is a highly used and advanced technology throughout industry. Typical choices for minimum approach temperatures are between 5 ☌ and 30 ☌ (Towler and Sinnott 2013). The trade-off between operating costs and capital costs should be used to choose the minimum approach temperature for the network. Low temperature differences decrease the need for additional utilities, but require increasingly large heat transfer areas, meaning larger heat exchangers. While technically any value greater than zero can allow for heat transfer, very small values are not often feasible. The minimum approach temperature represents the smallest gap in temperature across which heat transfer will occur in the system. For more information see the trade-off section of the Sensitivity analysis and design optimization page. In some cases transfer across the pinch is necessary to produce the optimal network.
There is a trade-off between operational and capital costs. Minimizing the size and quantity of heat exchangers plays a large role in decreasing capital costs. Minimum utility requirement is not necessarily the optimum solution, however, the solution with the lowest overall cost is. This yields the minimum utility requirement solution to the heat exchanger network. In the hot region, streams are matched so that heat is transferred from the coolest possible source. The network is separated into hot and cold regions, above and below the pinch respectively. This page focuses on pinch analysis in the context of heat exchanger networks (HENs), however similar methods can be used in the design of mass exchanger networks (MENs).įor maximum energy recovery (MER), energy should not be transferred across the pinch. By designing around this point energy from utilities can be minimized. A pinch occurs at the closest point of approach between hot and cold streams in the network. Pinch analysis is a methodology used to minimize energy consumption of chemical processes by optimizing energy recovery methods.
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