Page 121 - Separation process engineering

Goal Seek was used to find the value of V/F that makes cell B25 equal to 0.0 by changing the value in B9.
Cell B25 multiplies cell B24 by 1000 to make the result obtained from Goal Seek more accurate. Goal
Seek converged for any guess of V/F from 0 to 1.0. The results are given in Figure 2-B4 for the conditions
given in Problem 2.D16: T = 10°C and p = 250 kPa. Since the constants in Eq. (2-3) are for temperature
units in °R and pressure units of psia, the temperature is input in °R (cell B7) and pressure is input in psia
(cell D7).

Figure 2-B4. Spreadsheet for Multicomponent Flash for Problem 2.D16 with Values in Each Cell.

We could also try not writing the Rachford-Rice terms and use Goal Seek to set the sum of x in cell B19
i
= 1.0. In this problem, Goal Seek works for Σx = 1.0 with V/F guess > ~.5 but does not work for low
i
values of V/F guess (See Problem 2.H2.). This difficulty reinforces the need to check results from any

software package, even one as common and robust as a spreadsheet (Shacham et al., 2008).
Note that there are many other possible approaches to solve this problem with a spreadsheet, and other
software tools such as MATLAB or Mathematica could be used (Binous, 2008)