Most industrial processes involve transfer of heat either from one
process stream to another process stream (interchanging) or from a utility stream to a
process stream. In the present energy crisis scenario all over the world, the target in
any industrial process design is to maximize the process-to-process heat recovery and to
minimize the utility (energy) requirements. To meet the goal of maximum energy recovery or
minimum energy requirement (MER) an appropriate heat exchanger network (HEN) is required.
The design of such a network is not an easy task considering the fact that most processes
involve a large number of process and utility streams. As explained in the previous
section, the traditional design approach has resulted in networks with high capital and
utility costs. With the advent of pinch analysis concepts, the network design has become
very systematic and methodical.
A summary of the key concepts, their significance, and the nomenclature
used in pinch analysis is given below:
Combined (Hot and Cold ) Composite Curves: Used to predict targets for
Minimum energy (both hot and cold utility) required,
Minimum network area required, and
Minimum number of exchanger units required.
DTmin and Pinch Point
: The DTmin value determines how closely the hot and cold
composite curves can be ‘pinched’ (or squeezed) without violating the Second Law
of Thermodynamics (none of the heat exchangers can have a temperature crossover).
Grand Composite Curve
: Used to select appropriate levels of utilities (maximize
cheaper utilities) to meet over all energy requirements.
Energy and Capital Cost Targeting
: Used to calculate total annual cost of utilities
and capital cost of heat exchanger network.
Total Cost Targeting:
Used to determine the optimum level of heat recovery or the
optimum DTmin value, by balancing energy and capital costs. Using this method, it is
possible to obtain an accurate estimate (within 10 - 15%) of overall heat recovery system
costs without having to design the system. The essence of the pinch approach is the speed
of economic evaluation.
Plus/Minus and Appropriate Placement Principles:
The "Plus/Minus"
Principle provides guidance regarding how a process can be modified in order to reduce
associated utility needs and costs. The Appropriate Placement Principles provide
insights for proper integration of key equipments like distillation columns, evaporators,
furnaces, heat engines, heat pumps, etc. in order to reduce the utility requirements of
the combined system.
Total Site Analysis
: This concept enables the analysis of the energy usage for an
entire plant site that consists of several processes served by a central utility system.
With further research, new topics like ‘Regional Energy
Analysis’, ‘Network Pinch’, ‘Top Level Analysis’,
‘Optimisation of Combined Heat & Power’, ‘Water Pinch’, and
‘Hydrogen Pinch’ are being developed. These basic terms and concepts have
become the foundation of what we now call Pinch Technology.
