Calculations for Missing and Incomplete Data

Since most correlations for heat exchangers are empirically based, the heat transfer calculations for exchangers are only accurate to about 85-90% when all the necessary data are known. When some data have to be estimated, the accuracy gets worse. However, this accuracy is sufficient to teU if a heat exchanger is functioning as expected or not. 

In this problem, /i-xylene is to be recovered from a stream containing heavier aromatics. Neither product rate is measured, but feed rate and reflux rates and the /i-xylene content of the overhead are. No heat exchanger duties are measured. With some data from a readily available source, the energy use for the tower can 

FIGURE 13.2. Use of heat/mass balances to obtain missing data. 

Estimate /7-xylene product rate heat duty for the overhead condenser, bottom cooler, and reboiler. 

If the heat capacity data extrapolated are in error, the calculated duty would vary 0.1 Btu/(lb °F). This is within the precision of other data. 

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