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[SodiumNa]

Ok I'm not asking you to answer it for me, I just dont know which stream to pick as a starter.

I am mixing feed with a recycle stream and then it goes into a reactor then condenser. Some propane and all water is removed and then some is purged ... and the rest recycled.

I am given the overall conversion rate for hydrogen (taking into account the purge stream) is = 0.9 which I know = h consumed / h put in

When it says consumed, do I need to take into account the h consumed during the reaction and the purge? Or just the reaction (meaning when it says taking into account, has it removed that from the equation for me)

The other thing given is the recycle ration = 0.5 = flow rate of recycled / flow rate of feed.

finally the composition of the recycle stream is

27% co2
64% h2
5%inert
4% propane

and the feed contains hydrogen , co2 and inerts but no composition is given.

I picked the basis to be 100 kmol of feed .. from this i worked out the recycle flow rate to be 60 kmol and worked out compositions (i used the recycle ratio to get the flow rate) ... however my problem is i dont know the composition of the feed so i just used x mol of h2 ... y mol of co2 and z mol of inert ... and so all the way through my cycle i have lots of unknowns ... is there a better way ... thank you!

[kkala]

"I am mixing feed with a recycle stream and then it goes into a reactor then condenser. Some propane and all water is removed and then some is purged ... and the rest recycled.
I am given the overall conversion rate for hydrogen (taking into account the purge stream) is = 0.9 which I know = h consumed / h put in
When it says consumed, do I need to take into account the h consumed during the reaction and the purge? Or just the reaction (meaning when it says taking into account, has it removed that from the equation for me)
The other thing given is the recycle ratio = 0.5 = flow rate of recycled / flow rate of feed.
finally the composition of the recycle stream is
27% co2 64% h2 5%inert 4% propane
and the feed contains hydrogen , co2 and inerts but no composition is given.
I picked the basis to be 100 kmol of feed .. from this i worked out the recycle flow rate to be 60 kmol and worked out compositions (i used the recycle ratio to get the flow rate) ... however my problem is i dont know the composition of the feed so i just used x mol of h2 ... y mol of co2 and z mol of inert ... and so all the way through my cycle i have lots of unknowns ... is there a better way ... thank you!"

In my opinion given data is not adequate to define quantities. More info on the reaction is at least needed. Assuming your basis of 100 kmol/h of feed, flows in kmol/h, and the given data, a try for clarification follows:
1. Assume feed (F) composition (kmol/h): H2=x, CO2=y, inerts=z (as you did). Then x+y+z=100.
2. recycle R to feed F ratio is 0.5 (check it, is it F/R instead?), so R=0.5*100=50. (Molar)% composition of R is known, so recycle is composed of H2=32, CO2=13.5, inert=2.5, C3H8=2.
3. Upstream reactor: H2=x+32, CO2=y+13.5, inert=z+2.5, C3H8=2 (adding the two streams).
4. My understanding: overall H2 consumed = H2 put in = x (??).
Interpretation1 of "overall conversion rate" of H2 is that 0.9*x is converted in the reactor, then H2 removal downstream condenser=x-0.9x=0.1*x (including purge). H2 removal results from overall H2 balance in the system (in-converted=out).
Interpretation2 is that 0.9*(x+32)of H2 is converted, then H2 removal =x-0.9*(x+32)=0.1*x-28.8 (including purge). Since 0.1*x-28.8 cannot be negative, x should be at least 288, which is impossible (x<100).
Consequently we proceed with interpretation1.
5. Downstream reactor: H2=x+32-0.9*x=0.1*x+32, CO2=??, inert=z+2.5, C3H8=??, H2O=??, other HC=??
(3CO2+10H2---C3H8+6H2O is a strange reaction, unheard of. Stoichiometry from reaction is needed to proceed. Probably some data is missing?)
6. That is why additional data seems necessary, as well as clarifications on given data. Algebraic equations may not be possible to avoid.

Edited by kkala, 25 December 2009 - 08:20 AM.