Page 368 - Applied Process Design For Chemical And Petrochemical Plants Volume II
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Packed Towers                                           357






































                                                                                             Figure 9-76.  Partial pressure
                                                                                             of  ammonia  over  aqueous
                                                                                             solutions of ammonia.  Used
                                                                                             by  permission  of  Leva,  M.,
                                                                                             Tower  Packings and  Packed
                                                                                             Tower  Design,  2nd  Ed.,  U.S.
                                                                                             Stoneware  Co.  (now,  Norton
                                                                                             Chemical  Process  Products
                                                                                             Corp.) (1953).






           Detemzine Number of Transjk Units, N                    This problem steps off six full transfer units and approx-
                                                                 imately % of the seventh. Report as 6.33 units.
             The number of transfer units is determined graphical-
           ly by:                                                Performance Interpretation

             1. Bisecting the vertical distance (line C) of Figure 9-7’7   The  point  X1  represents 0.092  mol  NHs/mol  H20,
               between the 8% aqua operating line and the equilib-   which is equivalent to 8 \vt%  ammonia solution. If a weak-
               rium curve B.                                     er product  were  desired  fewer  transfer  units would be
             2. Starting at Y2, draw horizontal line to line C. Extend   required.
               this horizontal to right of C far enough to make “r,   Point  (e) is the intersection of  the equilibrium curve
               to line C” equal to “line C to end,” then step vertical-   and  the  operating line  and represents the  equilibrium
               ly to operating line, D. Move horizontally to line C, so   condition  for  tower  outlet  liquor,  and  the  maximum
               that (a) (b) = (b) (c). Continue moving up the tower   liquor concentration.
               in this stepwise fashion.                           Note that the 10% (wt)  aqua product operating line is
             3. At end, XlY,,  if steps do not end at exact point, esti-   shown on the diagram, but such a concentration cannot
               mate fraction of vertical step required and report as   be reached when operating at 150 psig. A greater pressure
               fractional transfer unit.                         is required in order to lower the equilibrium curve.
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