Presentation

This session is the first part of an introductory course on heat integration or pinch method.

It presents the basic concepts of heat integration (pinch, composites, algorithm for minimizing the pinch).

Session IT2En presents in details a practical example of this method, with the design of the heat exchanger network.

Heat integration

• Method for determining the best exchanger and utility network in an energy facility or process factory
• Based on thermodynamic laws and the study of heat exchange between the fluids to be cooled (availabilities) and heated (needs)
• Fundamental concept: the pinch

Heat integration

• main value:
• visual and graphical method that allows the engineer to keep a physical approach of the phenomena
• energy optimization is performed without any a priori assumption on the network configuration of heat exchangers, which is defined only in a second time
• helps reduce both capital costs and operating expenses, while generally they vary in opposite directions

Enthalpy-temperature diagram

• Pinch P

Composite curves

• basic principle: to sort all the heat needs depending on T levels, to match the best hot and cold fluids
• sum of enthalpies of cold and hot streams, in each interval
• pinch: minimum distance between these curves

Composite curves

• lower zone: excess heat, cold target
• upper zone: heat sink, hot target
• if the pinch value is zero, minimum heat input Qh_min and discharge Qc_min

Composite curves

• if pinch increased (α), heat absorbed at high temperature (β), or released at low temperature (γ)
• cross-pinch heat transfer
• heat exchanger oversizing and additional utilities

Three rules

• Do not choose too high a value of the minimum pinch
• Do not heat a cold fluid with a hot utility
• Do not cool a hot fluid with a cold utility

Pinch minimization

• graphical method:
• by dragging the cold composite horizontally, its distance from the hot composite (the pinch) varies, as well as thermal irreversibilities

Pinch minimization

• algorithmic method (Problem Table Algorithm PTA):
• shift minimal and maximal temperatures by ΔTmin/2
• decrease for hot streams
• increase for cold streams
• thus, heat exchange is possible between hot and cold streams of same shifted temperature

Pinch minimization

• algorithmic method:
• determine the temperature intervals of the problem by sorting the bounds of the upper and lower temperatures of each stream
• build the enthalpy balances of each temperature interval which determines the hot and cold composites
• sum up the enthalpy deficits
• bring as hot utility the equivalent value of the maximum enthalpy deficit
• See: Gourlia case study (session IT2En)

Introduction to the pinch method

This session allowed us to present the basic concepts of heat integration.

The design of a heat exchanger network will be presented in session IT2En.