Page 188 - Applied Process Design For Chemical And Petrochemical Plants Volume III
P. 188

66131_Ludwig_CH10E  5/30/2001 4:33 PM  Page 151










                                                                    Heat Transfer                                          151

                         b. Cooler-condenser zone, diffusivity:            t g   135°F
                                     3>2               1>2                 p v   2.537 psia at 135°F
                                    T k        1    1
                      k d   0.0166           a        b                    p g   32.5   2.537   29.96
                                         1>3 2
                                    1>3
                               p¿t1V A   V b 2  M A  M B
                     V A for water vapor   14.8                                        938,700
                                                                            t w   96.7            93.6°F
                     V B for hydrocarbon mixture:                                     1299,0002112
                                    Mol Fraction
                              V A                 Weighted V B                 Note that this assumes that water is warmed from the
                                                                               gas cooling before it enters this section. This is not
                             37        0.148         05.45
                     C 2 H 2
                                                                               rigorously correct.
                             14.3      0.531          7.6
                     H 2
                             29.6      0.098          2.9
                     CH 4
                     CO      22.2      0.223         04.95                  t   135   93.6   41.4°F
                                                                           Latent heat at 135°F   1,017.0 Btu/lb
                                                   20.90   V B
                                                                           Assume temperature of condensate, t c   100°F
                     Use average temperature of (135   104)/2 for k d   322°K
                                                                           then: p c   0.949 psia (steam tables)
                                                                           p g     32.5 0.949   31.55 psia
                                       13222  3>2      1    1  1>2
                      k d   0.0116                    a      b
                                32.5                   18  14                     p g '   p g  31.55   29.96
                                                   4
                                    3114.82  1>3    120.92 1>3 2            p gf '                       31.7 psia
                                14.7                                                   p g '      31.55
                                 2
                      k d      0.572 ft >hr                                      2.3 log    2.3 log  29.96
                                                                                       p g
                         Average mol weight of mixture:                    h o (t g   t c )   K G M v   (p v   p c )
                                                                             h io   (t c   t w  )  70.81135   1002
                          114219702   1,420
                      M                    14.33 lb>mol
                             970   78.8
                                                                                 5.41             2.537   0.949
                                                                                       118211,017.02a         b
                                    3
                         Average lb/ft of mixture in cooler-condenser zone:   £  a  31.7 §            14.7
                                                                                    b
                                                                                 14.7
                         14.33  460   32  32.5
                              a         ba    b   0.0766 lb>ft 3                         1,1401100.0   93.62
                          359  460   120  14.7
                                                                           2,480   4,960   7,300
                           2>3      0.0397    2>3
                      a   b    a             b    0.936                           7,440   7,300
                                 10.0766210.5722
                        k d
                       c p    2>3  10.554210.03972  2>3                        (See the preceding note regarding h io  ).
                      a   b    a             b    0.569
                        k           0.0513                                     Close enough check.
                                                                                  7,440   7,300
                         c. Relation between diffusion and heat transfer:   U t                7,370
                                                                                       2
                                   2>3
                            h o 1c >k2
                      K G                                        (10-102)        U t      73.70
                                                                                                              2
                                     2>3                                    U                      177 Btu>hr 1ft 21°F2
                          cp gf M m a  b                                        t g   t w  135   93.6
                                  k d
                      h o      same as in gas cooling zone     70.8        Interval 130°F—125°F
                                                                           t g   130°F
                                170.8210.5692
                       K G                                                 p v   2.223
                           10.55421p gf 2114.33210.9362
                                                                           p g   32.5   2.223   30.277 psia
                           5.41
                                       2
                               mol>hr 1ft 21atm2
                           p gf                                                        179,640
                                                                            t w   93.6            93.0°F
                                                                                      1299,0002112
                      10. Cooler-condenser interval: 135°F—130°F.
                         *Note: The value of h io is not correct for the condens-  Flow gas-vapor rate   (970)(14)   (61.8)(18)   14,713
                         ing coefficient as described in step 6 of this outline. In
                         this case, the error is small, but that is not necessarily  W  14,713
                                                                                                        2
                                                                            G s             23,600 lb>hr 1ft 2
                         true for other situations.                             a s  0.624
   183   184   185   186   187   188   189   190   191   192   193