Hello Everyone, I found this old exam, and I am not able to resolve it, Not sure if information is missing... anyway here's the text, maybe someone can help on how to proceed with such a problem:
"In a Petrochemical factory hydrocarbons for cracking are transported by pipes.The pressure and the temperature in the pipes are kept at 5atm and 56 C respectively.
Calculate the maximum quantity of pentane that can be added to an equimolar mixture of propane and n-butane without causing condensation".
Thanks folks
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Vapor Liquid Equilibrium
Started by Mariouma, Sep 27 2011 09:48 AM
2 replies to this topic
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#1
Posted 27 September 2011 - 09:48 AM
#2
Posted 27 September 2011 - 03:20 PM
Mariouma,
Since I have no idea what tools you have/had to solve this problem, I will provide a general guideline.
1. Assume an initial flow rate in the pipeline of propane and n-butane. Ex: 50 moles/hour of each, totalling an initial flow rate of 100 moles/hour. Find the dew point of this mixture.
2. Now assume you are adding pentane to this mixture. I would start with an initial guess of 20 moles/hour. Find the dew-point of the mixture at 5atm. If it is less than 56°C, the mixture is still a vapour, which means it can take more pentane. If the calculated dew-point is more than 56°C, it means the mixture is already condensing and there is too much pentane already in the pipeline.
3. Modify the initial pentane flow rate and repeat step 2 untill you have an answer of acceptable tolerance.
4. When you have the maximum additional pentane flow rate in moles/hour, you can have the answer in any format (ex: mole fractions)
Since I have no idea what tools you have/had to solve this problem, I will provide a general guideline.
1. Assume an initial flow rate in the pipeline of propane and n-butane. Ex: 50 moles/hour of each, totalling an initial flow rate of 100 moles/hour. Find the dew point of this mixture.
2. Now assume you are adding pentane to this mixture. I would start with an initial guess of 20 moles/hour. Find the dew-point of the mixture at 5atm. If it is less than 56°C, the mixture is still a vapour, which means it can take more pentane. If the calculated dew-point is more than 56°C, it means the mixture is already condensing and there is too much pentane already in the pipeline.
3. Modify the initial pentane flow rate and repeat step 2 untill you have an answer of acceptable tolerance.
4. When you have the maximum additional pentane flow rate in moles/hour, you can have the answer in any format (ex: mole fractions)
Edited by pavanayi, 27 September 2011 - 03:21 PM.
#3
Posted 28 September 2011 - 02:34 AM
Dear Mariouma
Pavanayi has explained the method. I have run PRO-II and I got folllowing answer:
We can add 6.8 kmol of pentane to every 100 kmol of the equi-molar mixture of propane and butane. This gives a molar composition of C3=C4=0.4682 and C5 = 0.0636
The 5 atm is absolute pressure. If the 5 tam is gauge pressure then the answer is that we can add 4.8 kmol of pentane to 100 kmol of the propane-butane equimolar mixture.
The answer may be different if you are using different method of VLE equation. I am using BWR EOS.
For approximate answer, you can use Dalton's law by taking vapor pressure of each component at 56 C.
Pavanayi has explained the method. I have run PRO-II and I got folllowing answer:
We can add 6.8 kmol of pentane to every 100 kmol of the equi-molar mixture of propane and butane. This gives a molar composition of C3=C4=0.4682 and C5 = 0.0636
The 5 atm is absolute pressure. If the 5 tam is gauge pressure then the answer is that we can add 4.8 kmol of pentane to 100 kmol of the propane-butane equimolar mixture.
The answer may be different if you are using different method of VLE equation. I am using BWR EOS.
For approximate answer, you can use Dalton's law by taking vapor pressure of each component at 56 C.
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