Environmental Engineering Reference
In-Depth Information
The Grid Diagram for the Step -By-Step HEN Design
Pinch
CP
(kW/ ºC)
310 ºC
QH_min = 2870 kW
Q= 1900 kW
520 ºC
330 ºC
H1=10
Q= 350 kW
380 ºC
300 ºC
H2=5
Q= 2750 kW
550 ºC
300 ºC
412.5 ºC
317.5 ºC
C1=20
Q= 120 kW
380 ºC
320 ºC
C2=2
QC_min = 50 kW
300 ºC
Figure 25. Grid Diagram for C2 matching with hot utility away from the pinch
The Grid Diagram for the Step -By-Step HEN Design
Pinch
CP
(kW/ ºC)
310 ºC
QH_min = 2870 kW
Q= 1900 kW
520 ºC
330 ºC
H1=10
Q= 50 kW
Q= 350 kW
380 ºC
300 º C
H2=5
Q= 2750 kW
550 ºC
412.5 ºC
317.5 ºC
300 ºC
C1=20
Q= 120 kW
380 ºC
320 ºC
C2=2
QC_min = 50 kW
300 ºC
Figure 26. Grid Diagram for H2 matching with cold utility below the pinch
Now after we completed the network above the pinch we go below the pinch. In this
simple example we have only one hot steam H2 below the pinch. The hot stream H2 needs to
be cooled down from 310 ºC to 300 ºC. The amount of load needed to be removed from this
stream is equal to 50 kW. Therfore the amount of cooling utility required using cooler will be
50 kW, which is exactly the cooling utility target obtained earlier during the utilities targeting
step. Combining the design above the pinch and below the pinch gives us the complete design
of the heat exchanger network that satisfy our two objectives of minmum number of units and
minimum utitilties consumption at T_min equal to 10 ºC.
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