Pinch analysis

Pinch analysis is a methodology for minimising energy consumption of chemical processes by calculating thermodynamically feasible "energy targets" (or minimum energy consumption) and achieving them by optimising heat recovery systems, energy supply methods and process operating conditions. It is also known as "process integration", "heat integration", "energy integration" or "pinch technology".

The process data is represented as a set of energy flows, or streams, as a function of heat load (kW) against temperature (deg C). This data is combined for all the streams in the plant to give "composite curves", one for all ‘hot streams’ (releasing heat) and one for all ‘cold streams’ (requiring heat). The point of closest approach between the hot and cold composite curves is the "pinch temperature" ("pinch point" or just "pinch"), and is where design is most constrained. Hence, by finding this point and starting design there, the energy targets can be achieved using heat exchangers to recover heat between hot and cold streams. In practice, during the pinch analysis, often cross-pinch exchanges of heat are found between a stream with its temperature above the pinch and one below the pinch. Removal of those exchanges by alternative matching make the process reach its "energy target".

The techniques were first developed in the late 1970’s by teams led by Bodo Linnhoff at ICI and UMIST (now Manchester University). Many refinements have been developed since and used in a wide range of industries, including non-process situations. Both detailed and simplified (spreadsheet) programs are now available to calculate the energy targets. A commonly used, free Pinch analysis program is PinchLeni.

In recent years, Pinch Analysis has been extended beyond energy applications. It now includes:

Mass Exchange Networks (El-Halwagi and Manousiouthakis, 1989)

Water Pinch (Wang and Smith, 1994; Hallale, 2002)

Hydrogen Pinch (Hallale et al., 2003)

References

*El-Halwagi, M. M. and V. Manousiouthakis, 1989, "Synthesis of Mass Exchange Networks", AIChE J., 35(8), 1233-1244
*Kemp, I.C. (2006). "Pinch Analysis and Process Integration: A User Guide on Process Integration for the Efficient Use of Energy, 2nd edition". Includes spreadsheet software. Butterworth-Heinemann. ISBN 0750682604. (1st edition: Linnhoff et al, 1982).
*Hallale, N. (2002). A New Graphical Targeting Method for Water Minimisation. Advances in Environmental Research. 6(3): 377-390
*N.Hallale, I.Moore, D. Vauk, "Hydrogen optimization at minimal investment", Petroleum Technology Quarterly (PTQ), Spring (2003)
*Wang, Y. P. and Smith, R. (1994). Wastewater Minimisation. Chemical Engineering Science. 49: 981-1006