Page 183 - Chemical engineering design

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CHEMICAL ENGINEERING
All the stream flows, tabulated, were multiplied by this factor and are shown on the
flowsheet, Figure 4.2. A sample calculation is given below:
Stream (6) gas from condenser
Mass 100 kmol NH 3 basis Mass flow for 20,000 t/y
(kg) (kg/h)
NO 471   202.5
 
 
NO 2   967.2

2249.4
640.0 ð0.43 D 275.2
O 2
 
N 2 20,160.0  8668.0


 
H 2 O 68.4 29.4
Total 23,588.8 10,143.1
Energy balance
Basis 1 hour.
Compressor
Calculation of the compressor power and energy requirements (see Chapter 3).
13,027.7
Inlet flow rate, from flow sheet D D 0.125 kmol/s
29 ð 3600
Volumetric flow rate
288 3
Ž
at inlet conditions, 15 C, 1bar D 0.125 ð 22.4 ð D 2.95 m /s
273
From Figure 3.6, for this flow rate a centrifugal compressor would be used, E p D 74 per
cent.

n 1 /n
n P 2
Work (per kmol) D Z 1 T 1 R 1 (3.31)
n 1 P 1
m
P 2
Outlet temperature,T 2 D T 1 (3.35)
P 1
As the conditions are well away from the critical conditions for air, equations (3.36a) and
(3.38a) can be used
1
m D 3.36a
E p
1
n D 3.38a
1 m
for air can be taken as 1.4
1.4 1
m D D 0.39
1.4 ð 0.74
1
n D D 1.64
1 0.39