(60) 3. A carbon monoxide rich stream, comprised of 80. mol% CO, 14 mol% CO2, an
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(60) 3. A carbon monoxide rich stream, comprised of 80. mol% CO, 14 mol% CO2, and 6.0 mol% N2 is blended with 5% excess pure steam to form the fresh feed for a water-gas-shift reactor. In the reactor the following chemical reaction occurs: The diagram for the process is shown below. The single pass conversion of the reactor is 20% while the overall conversion of CO is 90%. The gas stream exiting the reactor enters a pressure swing absorber where all of the hydrogen is removed. The remaining gas stream is divided into a purge stream and a recycle stream. The recycle is added to the fresh feed There are 240. Ibmol/hr of CO fed into the process a) Determine the molar flow rate of the Fresh Feed stream b) Determine the molar flow rate of hydrogen exiting in the Product stream c) Determine the molar flow rate and composition (in mol%) of the Purge stream. d) What is the recycle ratio (Recycle/Fresh Feed)? Recycle Steam 100% H2O | Fresh Purge Pressure swing absorber Feed Water-gas- shift reactor 0.80 CO 0.14 CO2 0.06 N2 Product Pure H2Explanation / Answer
CO in fresh feed = 240 lbmol/hr
molar flowrate of carbon monoxide rich stream = 240 / 0.8 = 300 lbmol/hr
Theoretical requiremnet of steam = 240 lbmol/hr .............according to stoichiometry
steam actually supplied = 5% excess of theoretically required = 1.05 * 240 = 252 lbmol/hr
a) molar fowrate of fresh feed= 252 + 300 = 552 kbmol/hr
b) Overall conversion of CO = 90 %
H2 formed overall = CO reacted overall = 240 x 0.9 = 216 lbmol/hr
c) CO in purge = CO unreacted overall = 240 x (1-0.9) = 24 lbmol/hr
As per pass conversion is 20%
CO reacted to form 216 lbmol/hr of H2 = 216 lbmol/hr
CO fed to the reactor = 216 / 0.2 = 1080 lbmol/hr
CO unreacted = 1080 - 216 = 864 lbmol/hr
CO in recycle = 864 - CO in purge = 864 - 24 = 840 lbmol/hr
N2 in purge = N2 in feed = 0.06*flowrate of CO rich stream = 0.06*300 = 18 lbmol/hr
H2O reacted overall = CO reacted overall = 216 lbmol/hr
H2O unreacted overall = H2O in purge = H2O in feed - H2O reacted overall = 252 - 216 = 36 lbmol/hr
CO2 in purge = CO2 in feed + CO2 formed overall = 0.14*300 + 216 = 258 lbmol/hr
Total purge flowrate = 258 + 36 + 18 + 24 = 336 lbmol/hr
mole % CO2 = (258/336) x 100 = 76.7857
mole % CO = (24/336) x 100 = 7.14
mole % N2 = (18/336) x 100 = 5.357
mole % H2O = (36/336) x 100 = 10.714
d) Composition of recycle stream and purge stream is same.
CO in recycle = 840 lbmol/hr
mole % CO in recycle= 7.14
.: Molar flowrate of recycle = 840 / 0.0714 = 11764.7 lbmol/hr
R/F ratio = 11764.7 / 552 = 21.31
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