Page 430 - Chemical process engineering design and economics

410 Chapter?

v s = 4.195 / 3.577 = 1.173 m/s (3.85 ft/s)

The actual pressure drop from Equation 7.14.5, when D = 7.0 ft, is (Ap) =
B
3018 Pa/m (0.133 psi/ft).
From Equation 7.14.9, the bed volume,
3
V B= 4164 71300 = 3.203m 3 (113.1ft )

and from Equation 7.14.10 the bed length,

L B = V B / A B = 113.1 / 38.59 = 2.931 ft (0.893 m)
which, according to Equation 7.14.10, is below the recommended-minimum bed
1
height of A (7.0) = 3.5 ft (1.07 m). Increase L B to 3.5 ft (1.07 m), which will
allow for a safety factor. The packed volume of a commercial styrene reactor,
reported by Scheel and Crowe [29], has a bed height of 5.28 ft (1.61 m) and a
3
diameter of 6.40 ft (1.95 m). The packed volume for the reactor is 168.9 ft (4.78
3
3
3
m ), whereas the calculated reaction volume is 113.1 ft (3.20 m ). The differ-
3
3
ence is 55.8 ft (1.58 m ), which is not completely unreasonable, considering the
assumptions that were made. Also, it is not known if the height of the bed for
the commercial reactor includes ceramic balls for promoting uniform flow dis-
tribution. If it does, then the height of the catalyst bed will be less, bringing the
calculated height in closer agreement with the commercial reactor. The present
calculation puts us into the right ballpark, and the final decision on the reactor
dimensions will be based on pilot-scale tests.
Allowing space for internals, the reactor length,
L R = L B + L, = 3.5 + 3.0 = 6.5 ft (1.98m)

According to Step 13 in Table 7.15, L R requires no rounding.
The total pressure drop across the reactor is calculated from Equation
7.14.6 is

Ap = (0.133) (3.5 + 3) = 0.8645 psi (0.0596 bar)
The actual bed volume,

3
3
V B = L B A B = 1.07 (3.577) = 3.827 m (135 ft )
From Equation 7.14.9 the catalyst mass,

4
W B = 1300 (3.827) = 4975 kg (LlOxlO Ib)

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