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