Environmental Engineering Reference
In-Depth Information
Feed
Feed
Product
Product
H
H
C
C
PROCESS
PROCESS
T
T
HOT UTI LI TY
HOT UTI LI TY
120
120
100
100
HEAT
RECOVERY
HEAT
RECOVERY
80
80
Pinch
(MAT)
Pinch
(MAT)
60
60
40
40
20
20
60 H
60 H
COLD UTILITY
COLD UTILITY
30
30
Figure 2. Heat Integration between Hot and Cold
Moving the cold stream to the left on the enthalpy axis without changing its supply and
target temperatures until we have a desired small vertical distance between the hot stream and
the cold stream we obtain some overlap between the two streams that result in heat
integration between the hot and the cold and less hot and cold utilities. As seen depicted in the
graph below with shrinkage in the red and blue lines span.
Now we want to represent all the hot streams in the process by one long hot stream and
we will call this line the hot composite curve. We will also do the same thing with all the cold
streams in the process.
The next step will be drawing the two composite curves/lines on the same page in a
Temperature (T)-Enthalpy diagram with two conditions:
1. The cold composite curve should be completely below the hot composite curve, and
2. The vertical distance between the two lines/curves in terms of temperature should be
greater than or equal to a selected minimum approach temperature called global ∆Tmin
The resulting graph is depicted below and known as thermal pinch diagram.
Net Heat Sink
Above the Pinch
Net Heat Sink
Above the Pinch
Opportunity for
heat recovery
Opportunity for
heat recovery
Net Heat Source
Below the Pinch
Net Heat Source
Below the Pinch
Figure 3. Composite Curves
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