1 Options available
It was originally hoped that pinch analysis techniques would allow energy targets to be found using only a pocket calculator. Sadly, this is not true except for the very simplest plants. Hand calculation is tedious and there is a high risk of mistakes.
Computer software is therefore almost essential to perform a pinch analysis. Three broad types exist; dedicated high-level programs, general process simulators, and simplified targeting software. Early examples such as TARGET (written at UMIST) and PROTAB (developed by ICI) were developed relatively quickly into highly sophisticated programs such as Supertarget (Linnhoff March) and Advent/Aspen Pinch (Aspen Tech). Later Hyprotech developed HX-NET® and this became the main Aspen specialized pinch software. These programs use complex targeting procedures and can perform auto-mated network design (with a manual option to allow the user to design his own
network). As a result, they are relatively costly to purchase or license. An alternative is to use software only for the essential calculations of energy and cost targets and to generate the composite and GCC, without including network
design. One program to take this approach was HERO (Chepro Ltd). Because of the limited functions of such programs, they are very much cheaper than full net-work design software. The spreadsheet supplied free with this book is of this type; its specification is given in Section 8.6.2. Finally, a number of process simulators incorporate a pinch analysis section, early examples being HYSIM® and HEXTRAN®, and more recently Aspen Plus® and Hysys®.
Simulators include a basic UA-type model of heat exchangers, and can be therefore used to perform network design if targets have been calculated by a spreadsheet (or if one does not wish to use pinch techniques at all). They are particularly useful for manually retrofitting existing networks.
2 Spreadsheet accompanying this book
To allow users to perform pinch analysis on their own plants as easily as possible, a free spreadsheet is supplied with this book. This performs the key targeting cal-culations and plots, as follows:
- Input of stream data (either as CP or heat load).
- Calculation of composite curve data, Problem Table, energy targets and pinch temperature.
- Plotting of composite curves and GCC.
- Plotting stream population over temperature range and basic grid diagram.
- Tables and graphical plots of variation of energy and pinch temperature over a range of Tmin
Area and cost targeting is not performed because of the considerable extra com-plexity, the frequent lack of suitable data on heat exchanger coefficients, and the flat nature of most cost-Tmin plots. Topology traps can still be identified from the graphs of utility use and pinch temperature against Tmin. Most of the composite and GCC in this book have been generated using the spreadsheet. It was written for Microsoft Excel® but should run in similar compatible spreadsheets; however, fully correct operation cannot be guaranteed. A brief user guide is given in the Appendix. The spreadsheet was the winning entry in a competition run by the Institution of Chemical Engineers for young process engineers, and was written by Gabriel Norwood.