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I wish to remove water and nitrogen from my reactor effluent in order to decrease downstream equipment sizes and subsequently capital costs.

Stream composition:

${H_2S}$.................5.6%

${SO_2}$.................3.3%

${S_2}$.................9.2%

${COS}$.................0.9%

${CS_2}$.................0.1%

${CO_2}$.................1.3

${H_2}$.................1.4%

${H_2O}$.................34.5%

${N_2}$.................43.7%

Removing these components would result in a approximately 90% less flow rate.

Restrictions:

  • The sulphur MUST stay above melting point, $\pm$130 $^\circ$C at 1 atm.
  • ZERO sulphur compounds must leave the water or nitrogen streams. (meaning that if these compounds are in the water or nitrogen streams, they have to be removed at a later stage as well.)

What I have done thus far:

I used the Clausius-Clapeyron equation to solve for a pressure where the dew point of water is higher than the melting point of sulphur. I found that at 3.5 atm of pressure and approximately 130 $^\circ$C, liquid water forms but sulphur stays liquid, and density separation can be performed with the added bonus that sulphur is insoluble in water. However, I cannot think of way to remove the nitrogen or a cheaper,more efficient way to remove the water.

Chris Mueller
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22134484
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1 Answers1

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Due to my lack of reputation I can only answer instead of commenting which I would have prefered. Thus my explanation will rather cover some basic ideas and suggestions rather than an elaborate separation process. Also you should not I have not graduated yet and I'm eager to learn myself. So instead of downvoting I would like to receive constructive comments on what I got wrong or what I could improve. Mainly my point is to get a discussion started and see if we could use some ideas to help you.

What do we start with?

From what I see you already have a two phase system.

Vapor Phase

  • $H_2S$
  • $SO_2$
  • $COS$
  • $CS_2$
  • $H_2$
  • $N_2$

Liquid Phase

  • $S_2$
  • $H_2O$

At your given Temperature and Pressure. Please note that I did not have access to all VLE data of all your components, you will have to check that for varying pressures.

1st Separation Step

I would start with separating those two phases.

2nd Separation Step

$N_2$ has the lowest boiling point of all components in your vapor phase. Except for $H_2$. You could lower the temperature to -60,2 °C and then $H_2$ and $N_2$ would stay in vapor state, all other components would be liquified. This would allow for an easy phase separation. Sidenote: I'm no chemist however $H_2$ and $N_2$ react to ammonium, which has a higher boiling point. However you did not consider reactions of the components before so I just assume this might not be a problem.

3rd Separation Step

As you pointed out $S_2$ and $H_2O$ have a significant difference in density. So you could use a mixer/settler setup e.g. to separate them. You would then have to combine the $S_2$ stream with your other $N_2$ free stream.

What I don't really see yet, is how you get your initial reactor effluent. From what I know there is no way $S_2$ would be in gasous state unless you operate under very high temperaturs or under a vacuum. In both cases that would have been a crucial information here to begin with.

I hope this answer helps you a little bit.

idkfa
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  • The effluent comes from a thermal furnace of a sulphur recovery plant. It operates at about 1500C. It is then cooled by a waste heat boiler to about 650C before going into a few catalytic reactors to reduce the SO2 and H2S to S2 and H2O. After each catalytic reactor the stream is cooled to allow the sulphur to be extracted. I want to remove the water and nitrogen before they enter the catalytic reactors to decrease the size. – 22134484 Jun 13 '15 at 11:35
  • In "1st seperation" step that you proposed, water is still a gas, that is why I thought about pressurising the system to make sure only those two components form liquid. They can be simultaniously removed from the effluent and separated in a single "step". – 22134484 Jun 13 '15 at 12:01
  • I was referring to " I found that at 3.5 atm of pressure and approximately 130 ∘C, liquid water forms" at this point. – idkfa Jun 13 '15 at 12:02
  • I will look into your 2nd step, I thought about that myself, but the energy required to cool something from 130 to -60 is quite alot. But it is the most used method if you are working with high flow rates. – 22134484 Jun 13 '15 at 12:04
  • Obviously, my bad. Also, H2 and N2 wont react at such low temperatures. The main reason for the furnace being 1500C is to thermally disassociate the NH3. The reverse reaction doesnt/barely takes place. I have not run this in my simulation program yet to verify this claim, but literature suggests that it doesnt. – 22134484 Jun 13 '15 at 12:08
  • As for the costs of cooling, this is something you will have to evaluate. You should always have the complete process in mind during design phase. Compare the cooling costs with the benefits of lower flow rates. – idkfa Jun 15 '15 at 10:00