Environmental Engineering Reference
In-Depth Information
Understanding and Applying the Grand Composite Curve
The graph below shows that utility pinches are formed according to the number of
utilities used. Each time a utility is used a “utility pinch” is created. It also shows that the
GCC right noses, sometimes known as “pockets”, are areas of heat integration/energy
recovery and hence does not need any external utilities. These right noses/pockets represent
another possibility of heat integration among hot and cold process streams at a minimum
approach temperature
∆
T higher than that of the
∆
Tmin. In such cases an ooprtunity for lost
work recovery can exist on the expense of process to process heat integration.
The GCC curve can be used by engineers to select the best match between the utility
profile and process combined heat and power requirements profile. For instance, the steam
system shown below in figure 19 needs to be integrated with the process demands to
minimize low pressure steam flaring and high or medium pressures steam let downs.
In addition, GCC can also helps in selecting steam header pressure levels and loads.
Figure 18. Understanding the Grand Composite Curve
Before closing this part of GCC and its use in selecting process requirements of utilities
mix, I need to mention one important fact here about a rule in pinch technology that is
generally accepted by many people in the industrial community.
This rule says that: “do not use cold utility above the pinch” to avoid buying extra heating
and cooling utiltities. This rule is absolutely true when we talk only about cost of heating
