Environmental Engineering Reference
utilities. However, in some situation we can have a trade off between heating utilities cost and
benefits obtained from reducing power import or exporting power to the grid.
With the aid of GCC we might find situations in which it is better from work generation
point of view to use cold water above the pinch to produce steam and generate electricity,
then using steam turbines exhaust for process heating than literally doing process to process
integration using minimum approach temperature ∆ T among hot and cold process streams
much higher than the originally selected minimum approach temperature ∆ T_min.
Figure 19. Combined Heat and Power System Example
In summary, the Grand Composite Curve can be utilized to help optimize combined heat and
power systems (CHP) shown in figure 19, select the load and return temperature of hot oil
circuits, best integration between process and furnaces exhaust and process refrigeration
levels as well as the synthesis of the multiple-cycle refrigeration systems [1,3].
H EAT E XCHANGERS N ETWORK (HEN) S YNTHESIS
Upon deciding on process reaction-separation system design, the optimization of major
design variables such as reactor conversion, selectivity, recycle inert concentration, etc.,
minimization of process waste, minimization of utility waste via heat integration, process
modifications for the sake of more heat integration has been explored and the plant utility
system is configured, the material and energy balance can now be more or less fixed and
hence the hot and cold streams which contribute to the heat exchanger network can be