Page 339 - Applied Process Design For Chemical And Petrochemical Plants Volume II
P. 339

328                       Applied Process Design for Chemical and Petrochemical Plants

             From Figure 9-51 the pressure drop is 0.38 mm Hg/ft or   The Flexipac@ structural packing have better efficiency
           0.85 mm Hg total.                                     than available random packing, particularly at low liquid
                                                                 rates, per Reference 101.
           Top Section
                                                                 Intalox High Perfmmance Metal Structured Packing [I 0.21
             The top vapor load at an L/D  of 0.8 is 8,620 lb/hr. The
           total pressure drop for 7  theoretical trays is slightly less   According to the manufacturer’s literature  [ 1021, this
           than 2 mm Hg and pv is 0.002 lb/ft3 at 8 mm Hg top pres-   packing surpasses the best of other sheet-metal structured
           sure. Duplicating the  calculations made for  the bottom   packings in terms of  efficiency and capacity. See Figure
           section results in                                    9-611.  The unique  surface-texturing feature provides for
                                                                 greater use  of  the packing surkce to achieve enhanced
           D = 5 ft 9 in.                                        levels of  mass  transfer,  and  the  overall geometry allows
           Packing height = 2.8 ft                               greater capacities and efficiencies to be  obtained. Tests
           Pressure drop = 1.06 mm Hg                            have been conducted on this and other packings at the
           Therefore, use column diameter  = 6 ft 9 in.
                                                                 University of Texas at Austin’s “Separation Research Pro-
                                                                 gram, Center for Energy Studies” for distillation capacity
                              Nomenclature
                                                                 and efficiency, and published in Reference 103.
                                                                   For good and uniform performance of  any structured
              A = cross-sectional area, ft2
             D = diameter, ft                                    packing it is  essential to have uniform, consistent vapor
             F,  = V,  (&) ‘I2                                   and  liquid  distribution; therefore,  much  care  must  be
              G = vapor rate, lb/sec-ftZ                         given to the design details. See earlier discussion in this
             g,  = 32.2 (Ib mass) (ft)/(lb force) (sec)2         chapter.
              L = liquid rate, lb/sec-ftZ                          For specific final performance sizing of a distillation col-
           L/D  = reflux ratio                                   umn  using  Norton’s  Intalox@ structured  packing  the
             Pf = packing factor                                 designer is referred to the manufacturer’s technical rep-
             Qc  = condenser duty, Btu/hr                        resentatives,  and  should  not  assume  the  preliminary
             Q = reboiler duty, Btu/hr                           results obtained from any manufacturer’s bulletin includ-
             V,  = reboiler vapor rate, lb/hr                     ed here will  necessarily serve as a final design. As  a pre-
             V,  = superficial vapor velocity, ft/sec             liminary examination of  a design problem  (used by  per-
              p1 = liquid density, lb/ft3                         mission of Norton Chemical Process Products)  :
             pv = vapor density, lb/ft3
              1\, = latent heat of vaporization, Btu/lb
                                                                    1. Calculate flow parameter, X
           Koch l%xipac@ Structured Packing

             This type comes in four sizes, Types 1 through 4, and is
                                                                      L = liquid mass rate, lb/sec
           constructed of  corrugated  metal  sheets  (See Figure  9-   G = vapor or gas mass rate, lb/sec
           6GG). The types vary by  corrugation size; the larger the   pg = gas density, Ib/ft?  at conditions
           type number, the greater is the depth of corrugation. The   p~ = liquid density, lb/ft3 at conditions
           deeper corrugations give higher capacity and lower pres-   A = area, ft2 tower cross-section area
           sure drop. According to Koch reference [ 1011, at the same
           efficiency,  in  countercurrent  gas-liquid  operation,  this   2. Read  chart, Figure  9-55, and  obtain  C,,  ft/sec,  at
           packing has a higher  capacity and  lower pressure drop    packing type shown.
           than any available dumped or structured packing. The ter-   3. Calculate efficient capacity, CSC:
           minology for Figure 9-54 is:

            F,  = V&   = [G/3,600  @,  1 (A)](&),   Wsec   (9  - 67)   (5 = surface tension, dynes/cm
                                                                      p = liquid viscosity, cp
           where  G = vapor rate, lb/hr                             4. Calculate:
                  V = vapor rate, ft/sec
                  pv = vapor density, lb/ft3
                  A = cross-sectional area, ft2
                 AP  = pressure drop, in. water/ft  height            V = superficial gas velocity, ft/sec, or m/sec  depending on
                                                                         the units used
             Chart parameter lines are gpm/ft* cross-section.         V = G/ (pd), ft/sec
   334   335   336   337   338   339   340   341   342   343   344