Pinch analysis

In 1971, Ed Hohmann stated in his PhD that 'one can compute the least amount of hot and cold utilities required for a process without knowing the heat exchanger network that could accomplish it.

In late 1977, Ph.D. student Bodo Linnhoff under the supervision of Dr John Flower at the University of Leeds[1] showed the existence in many processes of a heat integration bottleneck, ‘the pinch’, which laid the basis for the technique, known today as pinch-analysis.

At that time he had joined Imperial Chemical Industries (ICI) where he led practical applications and further method development.

Many refinements have been developed since and used in a wide range of industries, including extension to heat and power systems and non-process situations.

In order to reduce capital cost, in practice a minimum temperature difference (Δ T) at the pinch point is demanded, e.g., 10 °F.

The problem of integrating heat between hot and cold streams, and finding the optimal network, in particular in terms of costs, may today be solved with numerical algorithms.

The network can be formulated as a so-called mixed integer non-linear programming (MINLP) problem and solved with an appropriate numerical solver.

Temperature vs. heat load diagram of hot stream (H 2 O entering at 20 bar, 473.15 K, and 4 kg/s) and cold stream (R-11 entering at 18 bar, 303.15 K, and 5 kg/s) in a counter-flow heat exchanger. "Pinch" is the point of closest approach between the hot and cold streams in the T vs. H diagram. Note: this diagram is incorrect; the hot stream should lie above and to the left of the cold stream.
Temperature profiles (temperature vs. distance diagram) of hot stream (flowing from left to right) and cold stream (flowing from right to left) in counter-flow heat exchanger of above case.