Page 182 - Chemical engineering design

FLOW-SHEETING
31.4 kmol
From cooler-condenser HNO 3 D
2349.0 kg
H 2 O D 130.5 kmol D 1978.2 kg 159
D
From absorber HNO 3 D 62.9 kmol D 3962.7 kg
H 2 O D 146.8 kmol D 2641.8 kg
Totals HNO 3 D 1978.2 C 3962.7 D 5940.9 kg
H 2 O D 2349.0 C 2641.8 D 4990.8 kg
10,931.7 kg
5940.9
So, concentration of mixed acids D ð 100 D 54 per cent.
10,931.7
Summary, stream composition:

Acid product (13)

Stream kmol kg
HNO 3 94.3 5940.3
H 2 O 277.3 4990.8

10,931.7

Overall plant yield

The overall yield can be calculated by making a balance on the combined nitrogen:
mols N 2 in HNO 3 produced 94.3/2
Yield D D D 94.3 per cent
mols N 2 in NH 3 feed 100/2
Note: the acid from the cooler-condenser could be added to the acid flow in the absorber,
on the appropriate tray, to produce a more concentrated final acid. The secondary air flow
is often passed through the acid mixer to strip out dissolved NO.

Scale-up to the required production rate
Production rate, 20,000 t/y HNO 3 (as 100 per cent acid).
With 8000 operating hours per year

20,000 ð 10 3
kg/h D D 2500 kg/h
8000
From calculations on previous basis:
100 kmol NH 3 produces 5940.9 kg HNO 3 .
2500
So, scale-up factor D D 0.4208
5940.9
To allow for unaccounted physical yield losses, round off to 0.43