A carbon monoxide rich stream (stream A) is comprised of 90. mol% CO, 9.0 mol% C

Question

A carbon monoxide rich stream (stream A) is comprised of 90. mol% CO, 9.0 mol% CO2, and 1.0 mol% N2. The gas stream is blended with pure steam (stream S) in a stoichiometric ratio of water to CO and fed into the water-gas-shift reactor. In the reactor the following chemical reaction occurs:

H2O + CO <----> CO2 + H2

The diagram for the process is shown below. The single pass conversion of the reactor is 10.% 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. There are 500. lb-mol/hr of CO fed into the process.

Determine the flow rate of hydrogen (in lb/hr) exiting in the product stream (Prod).

Determine the flow rate (in lb-mol/hr) and composition (in mol%) of the purge stream (P).

What is the recycle ratio (R/F)?

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Hi,

I ave been working on the problem above but i am lost on certain parts. When it says stream sis stochiometric CO to Water, that is based on the original equation? Is the final output based on the total final conversion or the single pass out of the reactor? Is the hydrogen output calculated based on the 500 CO pumped in?

Thanks for the help

Explanation / Answer

Feed contains : 500 lb moles/hr of CO. This corresponds to 90% of feed. Hence Feed entering the system= 500/0.9= 556 lb moles/hr. This also contains 9% CO2 and 1% N2. N2 in the feed= 556*1/100= 5.6 lb moles/hr.   Steam entering the process= 500 lb moles/hr. Moles of CO2= 556-500-5.6= 50.4 lb moles/hr

Under steady state conditions, 1 mole of steam entering the process gives 1 mole of H2 and some of it is lost in the inerts.

All the nitrogen gets accumulated in the inerts. Hence moles of Nitrogen in the inerts = 5.6 lb moles/hr

Overall conversion of CO is 90%. Moles of CO converted = 500*0.9= 450 moles/hr. Moles of steam used= 450 lb moles/hr. Moles of hydrogen formed= 450 lb moles/hr, moles of steam unreacted=500-450= 50 lb moles/hr =moles of CO unreacted. Moles of CO2 at the exit of reactor = 450+50.4 = 500.4 m

The gas after Pressure swing adsorption contains Nitrogen, unreacted CO, CO2 and H2O.

Under steady state conditions, 50 lb moles/hr of steam has to leave through purge. ( since entering =500 lb moles/hr and Hydrogen formed = 450 lb moles/hr)

So Purge contains Steam : 50 lbmoles/hr of steam= moles of CO , CO2= 50.4 lb moles/hr and N2= 5.6 lbmoles/hr

Composition of purge ( also composition of recycle)

CO= 50/(50+50.4+5.6+50)= 0.32

Let R = Recycle, writing CO balance across the reactor

(R*0.32+500 )*0.1= 450

R*0.32= 4500-500 = 4000, R= 4000/0.32= 12500 lb moles/hr

R/F = 12500/(556+500)= 11.83

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