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  Tutorial Part V  

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 | Pinch Analysis - The components of a study, end | 


  1. Utility selection and optimization

GCC.gif (15995 octets)Another masterpiece of Pinch Analysis is the residual heat curve also known as the Grand Composite Curve. This graph has 2 clearly distinct zones located above and below the Pinch point met where the abcissa has a zero value. It is a graphical representation of the net amount of heating (portion above the Pinch point) and cooling (below the Pinch) versus the temperature level. Since the Pinch point represents the temperature through which no heat transfer is allowed to minimize the utility requirements, it is consequently found where the residual heat available is zero. 

This tool is mostly used to optimize the utility level and load selection and to study the appropriate integration of heat pumps, cogen systems (CHP) or new unit operations like evaporators. For example, we can use it to maximize the use of low pressure steam and cooling water which are cheap utilities, and to maximize the production of low pressure steam by energy recovery below the Pinch as shown on the graph.


  1. Design and establishment of a strategic plan of action in energy efficiency

design.gif (10771 octets)Design rules are used to develop solutions that meet the prescribed targets. The design rules rest on the 3 basic Pinch principles:

No heat transfer across the Pinch

No heating utility below the Pinch

No cooling utility above the Pinch

This design phase ends with a final optimization and is followed by a budget cost estimation. Figure 7 shows the design grid representation used for this phase (not related to the hot water process example). The savings and the final profitability of each project is then calculated. The ultimate result is a set of integrated projects obtained for, typically, 2 recommended scenarios. As desired by the plant's management, each project can be implemented over the years.

The following table is a short example of results provided to the Client (TMP pulp mill). Often, 2 scenarios are presented, one for short payback projects (6-12 months), and a second one for 18 to 24 months payback period solutions for a much larger level of process integration and energy recovery.



About the conventional approach...

In the conventional approach to energy efficiency, the engineer will mostly refer to state-of-the-art knowledge for his process and proceed by inspection and intuition. Often, energy efficiency literature and reference books include extensive checklists of possibilities that can be many pages long (example), often giving very general ideas. Selecting and studying some of them can be a costly and time-consuming solution, and you never know what your targets are, if you have reached them, and if any better solution exists. In comparison, you can use Pinch Analysis to find and select your energy and capital cost targets ahead of design. The design rules will naturally and rapidly lead you towards the one out of 100 projects of the literature listings that is the most appropriate to your case.

Design for the hot water tank example

For the example presented here, the results of Step 1 through 7 gives the following design where the minimum steam consumption target is met.

design2.gif (15983 octets)


 | Case studies, publications and references | 

Many case studies have been presented in the past in the literature and in conferences. Pragmathic is also highly active in R&D activities to keep improving its expertise in this field. We have developped over the years very efficient and unique ways to get more precise targets for retrofit studies, and we use our own softwares for this purpose.

Please consult the Download section where we have many papers and congress presentations available for download. A textbook on Pinch Analysis is available here.

Here are some good papers to consult.

  1. "Step by step through the pinch", Smith, G., Patel, A., The Chemical Engineer, November 1987, p. 26.

  2. "Pinch Analysis - A state-of-the-art overview", Linnhoff, B., Trans IChemE, vol. 71, Part A, September 1993, p. 503.

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Updated Feb 19, 2014