Ammonia Synthesis from Nitrogen and Hydrogen in Chemical Engineering Contents

Problem Solution
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Chemical Engineering

Problem Solution
Contents
Solution 1.........................................................................................................................................3
Solution 2.........................................................................................................................................3
Solution 3.........................................................................................................................................5
Solution 4.........................................................................................................................................7
Solution 4a)..................................................................................................................................7
Solution 4b).................................................................................................................................7
Solution 4c)..................................................................................................................................8
Solution 4d).................................................................................................................................9
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Problem Solution
Solution 1
In the synthesis of ammonia from nitrogen and hydrogen, the product gas leaving the ammonia
synthesis is fed to a condenser where essentially pure ammonia is condensed to liquid
Vapour Condenser liquid pure NH3
Based on the feed composition given on the flow diagram, answer the following questions
a) If condenser operates at 1 atm. Pressure (absolute) at what temperature the condenser
must be operated to recover 90% of the ammonia in feed as liquid?
b) If condenser operates at -60o C what would be the pressure to recover 90% of the
ammonia in feed as liquid?
c) If the feed stream is at 1 atm. Pressure what is the dew point temperature of the feed
stream?
Solution 1
As given in question
NH3 = 20 mole%, N2 = 18 mole%, H2 = 54 mole%, Inert = 8 mole%
Solution 1a)
The given Pressure P = 1 ATM, recovery of ammonia = 0.9 =
We know that,
PNH3 = yNH3P = 0.2 x 1 = 0.2 atm
Since, PNH3 = yNH3P = 0.2 x 1 = 0.2 atm
Since partial pressure for ammonia is given = 0.2 atm,
Given for 90% recovery = 0.2*0.9 = 0.18 atm
Now I must use
Antoine equation is derived as log10
p sat
= A− B
T +C
From table of Antoine equation constant
A = 7.55466, B = 1002.711, C = 247.885
Putting this value in above equation
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Problem Solution
log 0 .18=7.55466− 1002.711
T +247.885
−.74473=7.55466− 1002.711
T +247.885
1002.711
T +247.885 =7.55466+.74473
1002.711
8.299 =T +247.88 5
T =−127o K
Ans
Solution 1b)
T = -60 oC + 273 = 213 oK
From table of Antoine equation constant
A = 7.55466, B = 1002.711, C = 247.885 T = 213 K
log p=7.55466− 1002.711
213+247.885
logp=5. 379 or p = 105.379 x 0.9 = 215398/760 = 283 atm.
Solution 1c)
As given in question ZH = 0.54, ZN = 0.18, ZNH3 = 0.2,
For 90% nitrogen = p = 0.2*0.9 = 0.18 atm
Antoine equation is derived as log10
p sat
= A− B
T +C
From table of Antoine equation constant
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