Page 95 - Sustainability in the Process Industry Integration and Optimization

72 Cha p te r F o u r

A + W
T* T* A
A–(Q–W) Q
100% conversion
Heat→Work
PINCH
Q–W HE W Q
PINCH HE W
100% conversion Q–W
B Heat→Work B–Q

Integration above the pinch Integration below the pinch
(a) (b)

FIGURE 4.29 Appropriate placement of heat engines.

HP Steam
T* T* Q HP
Q FUEL
Q HP W
Q LP
Q LP LP Steam Boiler
Condensate

PINCH

CW

Q C,min ΔH
FIGURE 4.30 Integrating a steam turbine above the Pinch.

extra power. In contrast, gas turbines—which use fuel as input—are
typically used only as a utility heat source for the processes and can
be placed only above the Pinch.
Heat Pumps
Heat pumps present another opportunity for improving the energy
performance of an industrial process. Their operation is the reverse
of heat engines. That is, heat pumps take heat from a lower-
temperature source, upgrade it by applying mechanical power, and
then deliver the combined flow to a higher-temperature heat sink
(Figure 4.31).
An important characteristic of heat pumps is their coefficient of
performance (COP). This metric for device efficiency is defined as the