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Pinch technology guarantees minimal heat exchanger energy consumption

Oct. 18, 2004
Pinch technology doesn't refer to the finer points of thievery. Instead, it represents a set of thermodynamically based methods that guarantees a heat exchanger network consumes the least amount of energy.

They don’t need to be forced or cajoled to do it. Every plant professional with anything on the ball already has an interest in cutting monthly utility bills. Their mantra is reminiscent of a limbo dance: How low can you go? This month, we’re going to find out the answer to that question.

It’s obvious that a plant can’t operate with zero energy, but the task of locating and excising the ever-present fat can’t be done in a dictatorial or arbitrary manner. Mother Nature won’t let you get away with it.

Linnhoff and Vredeveld introduced the term "pinch technology" to represent a set of thermodynamically based methods that guarantees a heat exchanger network will consume the minimum amount of energy. The technique may be math-intensive, with its enthalpy balances and mass balances, but it also can be used to optimize the consumption of other utilities, cooling water being a prime example.

This is a tool worthy of your consideration. That’s why I ask you to join me for another dive into the morass we call the Web in search of practical, zero-cost, non-commercial, registration-free resources about pinch technology. Remember, we search the Web so you don't have to.

Find the minimum

“Pinch Technology: Basics for Beginners“ by Mukesh Sahdev, Indian Oil Corp. Ltd., defines pinch technology, gives its basic concepts, reveals the steps in the analysis, highlights its benefits and applications, opines about its future outlook, and offers references and other links. This is a multi-part article that explains, among other things, how to construct the curves you’ll need for a graphical solution to your pinch problem. Sahdev uses a few simple heat exchanger networks to explain the methodology and to illustrate the calculations. Aim your mouse here to see what’s needed for achieving a final, practical answer to the question of what constitutes minimum energy consumption for your process.

“What is Pinch Technology?” is a bilingual collection of articles taken from the class notes of Professor Fidel A. Mato at the Department of Chemical Engineering of the University of Valladolid, Spain. The text and example he uses assume a reactor and the heat exchanger network that supports it, the object being to minimize the energy needed to make everything function. This series of articles can make for a daunting read. It only hints at the intensity of effort and calculations needed to use pinch technology to analyze a system containing interdependent variables.

Warning: Don’t bother trying to download the free pinch technology software the site mentions. The URL to which it’s supposed to link doesn’t exist. I was unable to locate it during several hours of searching other sites, despite the number of references to it that various search engines provided. An e-mail inquiry about its current location went unanswered.

Process integration in all its manifestations offers a methodology for optimizing an entire plant, not just a single piece of process equipment. Confine the discussion to optimizing energy efficiency and you’ll find that pinch technology is the predominant form of process integration, a fact that makes the two terms nearly synonymous. Regardless of which term you use, it’s not a project to be undertaken lightly. “Succeed at Process Integration,” an article by Alan P. Rossiter, a private consultant from Bellaire, Texas, describes the steps in a pinch project and offers seven measures you can take to help make your process integration effort a success. Squeeze your way to the five-page PDF for Rossiter’s take on the issue.

Take on the big picture

It’s one thing to capture economic benefits by applying pinch analysis to a single process unit, but it’s quite another to go for the gold and capture the benefits of a plant-wide analysis. “Strategic energy assessment using pinch analysis,” by Bruce L. Pretty and Michael A. Rutkowski at Veritech, Inc., Sterling, Va., discusses using pinch technology for long-range planning and describes an approach for achieving such a plan. Although the article focuses on refinery operations, it could be applied to any plant that needs to move heat hither and yon. The details are warmed up and ready for your mouse at Veritech-energy.com. By the way, the article points out that the most successful pinch projects occur when there’s no attempt made to prejudge the results.

A rarity

Those of you with some facility on an Excel spreadsheet might find “Spreadsheet Modeling of Heat Exchanger Networks Using the Effectiveness: NTU Method” by Pretty, Brancaccio and Polley to be worthwhile. The PDF document lists the relevant equations and correlations. Unfortunately, the site doesn’t provide the completed XLS document as a download for your convenience. You’re going to need to slog through that construction process yourself following the guidelines provided. Anyway, click here and demonstrate your digital and calculational prowess.

Hitting paydirt

The research for this column uncovered a relatively long Web resource authored by Linnhoff March, a consultancy and software vendor based in Northwich, Cheshire, England. This opus magnus, “Introduction to Pinch Technology,” offers guidelines for extracting the relevant pinch data from your process flowsheet, setting energy targets for multiple utilities, dealing with trade-offs between capital expense and energy savings, making process modifications, integrating heat engines and heat pumps into the heat exchanger network design, data extraction principles and total site improvement. Kick off your shoes, sit back and dial in Environmentalexpert.com to access this 63-page white paper.

Pinching water

Unless you’re making soft drinks, the more water you bring into the plant, the greater the probability that you’ll need to deal with a wastewater stream somewhere along the line. And it’s doubtful that wastewater has anything to do with your plant’s core competencies. You can dry things out a bit by reading “Water Minimisation by Pinch Technology –- Water Cascade Table for Minimum Water and Wastewater Targeting” by Yin Ling Tan, Abdul Manan Zainuddin and Chwan Yee Foo from the Chemical Engineering Department at the Universiti Teknologi Malaysia in Johor, Malaysia. The three developed a concept they call “Water Cascade Table,” the purpose of which is to simplify the analysis of the plant’s water network. This 16-page PDF explains the computations needed for a continuous process and then segues into dealing with a batch process. On your next lunch break, float your mouse over to Cape.canterbury.ac.nz and break out the old calculator for an hour of intellectual fun and games.

The technology also can be applied to your plant’s water consumption. Again, the goal is to minimize the amount of water flowing through a process. This is particularly important if you’re paying good money for chemicals to treat the water to tame one or more of its nasty habits. Instead of working from a thermal gradient though, a water-based pinch analysis uses a concentration gradient as the driving force. The basic approach is outlined in “Practical techniques and methods to develop an efficient water management strategy.”

The caveats

If you’re going to investigate the concept, I think you’ll find an article titled “Pinch technology without tears,” by G.T. Polley from Pinchtechnology.com, to be a must-read. The article notes that pinching for energy conservation was hailed as the next big thing in the mid-1980s, but has yet to become the major tool of those working with energy-intensive operations. The paper goes on to offer some reasons why this might be the case, including a few apparent shortfalls in the method itself that arise when the technology is used blindly, unsupported by a liberal application of sound engineering judgment, a commodity with which, I am sure, everyone reading this is well endowed. But I digress. The Polley article goes on to recommend ways to overcome the difficulties it identifies. Dispatch ol’ mousie here to bring back these pearls of wisdom.

Russ Kratowicz is executive editor for Plant Services
magazine. E-mail him at
[email protected].