Converging for Neat Operation

Under these conditions, the resulting reboiler heat input in the low-pressure column Cl is 17.91 MW. The resulting condenser heat removal in the high-pressure colmnn C2 is 18.62MW. These are very close, but if the system is to be operated neat (no auxiliary reboUers or condensers), these heat duties must match exactly. 

One way to do this is to manually adjust the feed split in Tl until (2ri is equal to Qc -This can be automated by going to Flow Sheeting Options on the Data Browser window and selecting Design Spec. This is similar to the Design SpecA ary in the column blocks, 

On the page tab (Fig. 5.34c) aparameter DELTAQ is specihed with the desired value 

Total capital investment is also reduced. This is somewhat counterintuitive because one column with two heat exchangers would be expected to be less expensive than two columns with three exchangers. However, the colmnn diameters and the heat-exchanger areas are smaller in the heat-integrated design. 

An additional aspect of this heat-integration simulation is the calculation of the heat-transfer rate in the condenser/reboiler heat exchanger. In this steady-state simulation, we 

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