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.