Page 252 - Chemical Process Equipment - Selection and Design
P. 252

222  HEAT TRANSFER  AND  HEAT  EXCHANGERS
                            TABLE 8.19. Thermal Conductivities of Insulating Materials for Low Temperatures
                                      [k Btu/(hr)(sqft)("F/ft)l
                                               Bulk/                                Bulk
                                              Density,   Temp                      Density,   Temp
                                 Material     (Ib/cuft)   ("F)   h      Material   (Ib/cuft)   ("F)   h
                            Corkboard           6.9     100   0.022   Rubber board,
                                                       -100   0.018   expanded,
                                                       -300   0.010   "Ru batex"     4.9     100   0.018
                            Fibreglas with                                                  -100   0.015
                             asphalt coating                                                -300   0.004
                             (board)            11.0    100   0.023   Silica aerogel,
                                                       -100   0.014   powder         5.3     100   0.013
                                                       -300   0.007   "Santocel"              0    0.01 2
                            Glass blocks,                                                   -100   0.010
                             expanded,
                             "Foamglas"         10.6    100   0.036   Vegetable fiber-
                                                       -100   0.033   board, asphalt   14.4   100   0.028
                                                       -300   0.018   coating               -100   0.021
                            Mineral wool                                                    -300   0.013
                             board,
                             "Rockcork"         14.3    100   0.024   Foams:         2.9    -100   0.01 5
                                                       -100   0.017   Polystyrenea   5.0    -100   0.019
                                                       -300   0.008   Polyurethaneb
                               'Test  space pressure,  1.0 atm;  k= 0.0047  at   mm Hg.
                               bTest space pressure,  1.0 atm;  k= 0.007 at   mm Hg.
                               (Marks Mechanical Engineers Handbook,  1978,  p. 4.64).


                 When the pressure is moderate and no condensation is likely, brick   lining.  For  instance,  a  catalytic  reformer  4ft  OD  designed  for
                 construction is  satisfactory. Some  of  the  materials  suited  to  this   65Opsig and 1100°F has a shell 1.5 in. thick, a light weight castable
                 purpose are listed in Table 8.21. Bricks are available to withstand   lining 4-5/8in.  thick  and  an  inner  shell of  metal  1/8in. thick.  A
                 3000°F. Composites of insulating brick next to the wall and stronger   catalytic cracker 10 ft dia designed for 75 psig and 1100°F has a 3 in.
                 brick inside are practical. Continuous coats of  insulants are formed   monolithic concrete  liner  and  3in.  of  blanket  insulation on  the
                 by plastering the walls with a several inch thickness of  concretes of   outside.  Ammonia synthesis reactors  that  operate  at 250atm  and
                 various compositions. "Gunite"  for instance is a mixture of  1 part   1000°F are  insulated  on  the  inside to  keep  the  wall  below  about
                 cement  and  3  parts  sand  that  is  sprayed  onto  walls  and  even   700"F, the temperature at which steels begin to decline in strength,
                 irregular surfaces. Castable refractories of lower density and greater   and also to prevent access of  hydrogen to the shell since that causes
                 insulating  powers  also  are  common.  With  both  brickwork  and   embrittlement. An air gap of  about 0.75 in. between the outer shell
                 castables, an  inner  shell of  thin  metal  may  be  provided  to  guard   and  the  insulating liner  contributes  significantly to the  overall in-
                 against leakage through  cracks that  can develop in the  refractory   sulating quality.





                      TABLE 8.20.  Thermal Conductivities of Insulating Materials for High Temperatures [k Btu/(hr)(sqft)oF/ft)]
                                                       Bulk     Max
                                                      Density,   Temp
                                  Material             Ib/cuft   ("F)   100°F   300°F   500°F   1000°F   1500°F   2000'F
                      Asbestos paper, laminated         22       400   0.038   0.042
                      Asbestos paper, corrugated        16       300   0.031   0.042
                       Diatomaceous earth, silica, powder   18.7   1500   0.037   0.045   0.053   0.074
                       Diatomaceous earth, asbestos and bonding   18   1600   0.045   0.049   0.053   0.065
                        material
                       Fiberglas block, PF612            2.5     500   0.023   0.039
                       Fiberglas block, PF614           4.25     500   0.021   0.033
                       Fiberglas block, PF617           9        500   0.020   0.033
                       Fiberglas, metal mesh blanket, #900   -   1000   0.020   0.030   0.040
                       Glass blocks, average values    14-24    1600    -     0.046   0.053   0.074
                       Hydrous calcium silicate, "Kaylo"   11   1200   0.032   0.038   0.045
                       85% magnesia                     12       600   0.029   0.035
                       Micro-quartz fiber, blanket      3       3000   0.021   0.028   0.042   0.075   0.108   0.142
                       Potassium titanate, fibers       71.5     -      -     0.022   0.024   0.030
                       Rock wool, loose                 8-12     -     0.027   0.038   0.049   0.078
                       Zirconia grain                  113      3000    -      -     0.108   0.129   0.163   0.217
                         (Marks, Mechanical Engineers Handbook, 1978, p. 4.65).
   247   248   249   250   251   252   253   254   255   256   257