December 04, 2008

Pinch Technology: Some Basics


Most Industrial processes involve heat transfer from one process stream to another process stream (interchanging) or from a utility stream to a process stream. In the present energy crisis scenario, target in any industrial process is MER – Maximum Energy Recovery or Minimum Energy Requirements.



In the early days of pinch technology, the main emphasis was on heat exchanger network (HEN) design. Today pinch technology stretches far wider in the fields of overall process improvement and utility system design

Pinch Technology analyses process utilities (particularly energy and water) to find optimum way to use them, resulting in financial savings. It does this by making an inventory of all producers and consumers of these utilities and then systematically designing an optimal scheme of utility exchange between them. Energy and water re-use are at the heart of pinch technology.

With the application of pinch technology, both capital investment and operating cost can be reduced. Emissions can be minimized and throughput maximized.

What is Pinch Technology?
The term “Pinch Technology” was introduced by Linhoff and Vredeveld to represent a new set of thermodynamically based methods that guarantee minimum energy levels in design of heat exchanger networks. It also ensures minimizing the capital costs and fewer emissions.

Basis of Pinch Analysis

Pinch Technology represents a simple methodology for systematically analyzing chemical processes and the surrounding utility systems with the help of the First and the Second Law of Thermodynamics.

1st Law of Thermodynamics: Provides the energy equation for calculating the enthalpy changes (ΔH) in the streams passing through a heat exchanger.

2nd Law of Thermodynamics: Determines the direction of heat flow. That is, the heat energy may only flow in the direction of hot to cold. This prohibits ‘temperature crossovers’ of the hot and cold stream profiles through the exchanger unit.

In practice the hot stream can only be cooled to a temperature defined by the ‘temperature approach’ of the heat exchanger. The temperature approach is the minimum allowable temperature difference (ΔTmin) in the stream temperature profiles, for the heat exchanger unit. The temperature level at which ΔTmin is observed in the process is referred to as the “pinch point” or “pinch condition”. The pinch defines the minimum driving force allowed in the exchanger unit. Thus, the prime objective of pinch analysis is to achieve financial savings by better process heat integration (maximizing process-to-process heat recovery and reducing the external utility loads).



Pinch principle

The point where ΔTmin occurs is known as the “Pinch”. Once the pinch has been identified, it is possible to consider the process as two separate systems: one above and one below the pinch as shown in the figure.
The system above the pinch requires a heat input and is therefore a net heat sink. Below the pinch, the system rejects heat and so is a net heat source



To summarize, the understanding of the pinch gives three rules that must be obeyed in order to achieve the minimum energy targets for a process:

  • Heat must not be transferred across the pinch, i.e., no temperature crossovers.
  • There must be no external cooling above the pinch.
  • There must be no external heating below the pinch.


JUST FOR FUN & General Knowledge
After so much of pinch technology I would like to mention a few more pinches here :)
Ever heard about Network Pinch, Hydrogen Pinch, Water Pinch or Z Pinch?

NETWORK PINCH:When optimizing energy consumption in an existing industrial process, a number of practical constraints must be recognized. Traditional Pinch Technology focuses on new network designs. Network Pinch addresses the additional constraints in problems associated with existing facilities.

HYDROGEN PINCH:The Pinch Technology approach applied to Hydrogen management is called Hydrogen Pinch. Hydrogen pinch enables a designer to set target for the minimum hydrogen plant production and/or imports without the need for any process design.

WATER PINCH:This is a systematic technique for analyzing water networks and reducing water costs for processes. It uses advanced algorithms to identify and optimize the best water reuse, regeneration, and effluent treatment opportunities. It has also helped to reduce losses of both feedstock and valuable products in effluent streams.

Z PINCH:In fusion power research, the Z-pinch, or zeta pinch is a type of plasma confinement system that uses an electric current in the plasma to generate a magnetic field that compresses it (Pinch). The name refers to the direction of the earliest experimental devices in England, where the current flowed down a vertical quartz tube, the Z-axis on a normal mathematical diagram.

By Associate Writer - Nidhi Garg

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3 comments:

DINP said...

Where can I get more information about pinch technology?

pinch technology said...

Good summary. I'm not sure that Z-Pinch is really part of the same "pinch technology" family as the rest though.

Energy, water and hydrogen pinch are all variations on a theme: plotting resource quality vs quantity in the form of composite curves.

A recent development is the use of pinch to manage time as a resource. This was recently published in Chemical Engineering magazine. Link to article here:
http://accessintelligence.imirus.com/Mpowered/book/vche1/i5/p70

profmaster said...

Thanks Dear for a very good Info on use of Pinch in the non technical fields also.

It opens up further usage of pinch in many more areas.

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