Page 418 - Chemical process engineering design and economics

398 Chapter 7

Next, calculate the cross-sectional area of the bed by first calculating the mo-
lar gas density. Although the temperature, pressure, and molar flow rate will vary
through the reactor, use the reactor inlet conditions to calculate the molar density.

27.92 1
3
3
— ——— = 0.6365 kgmol/m (0.0397 lb/ft )
0.08314 527.6
The volumetric flow rate in the bed,

9230
5 3
y v = ——— = 14,500 nrVh (5.12xl0 ft /h)
0.6365

From Equation 7.11.3 and using the superficial velocity of 1.0 fVs (0.3048
m/s) given by Fulton and Fair [27], the cross sectional area of the bed,

14500m 3 1 h I s
2
2
A B = ————— ——— —————=13.21 m (142 ft )
1 h 3600s 0.3048m
Next, calculate the bed diameter to determine if it exceeds the shipping
limit of 13.5ft (4.11 m) specified in Equation 7.11.4.

1/2
D = [(4 / 3.142) (13.21)] = 4.101 m (13.5 ft)
When adding the vessel-wall thickness the reactor diameter will be greater. At a
design pressure of 500 psig (34.5 barg), Fulton and Fair [27] calculate a wall
thickness of 4 in (10.2 cm). To keep below the snipping diameter of 13.5 ft (4.11
m), use an inside diameter of diameter of 12.5 ft (3.81 m).

The actual bed cross-sectional area is

3.142 (3.810) 2
2
2
A B = ——— ———— = 11.40 m (37.4 ft )
4 1
From Equation 7.11.6, the bed length,

73.20
L B = ———— = 6.421 m (21.1 ft)
11.40

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