9 replies to this topic

[sacarove]

Dear all,

I am using an adjust to change the splitter ratio so that I can match the downstream temperature. I noticed that the splitter is greater than one on one stream and negative on the other.

How can I fix it to a maximum of 1?

 

Thanks

Sacarove 

Attached Files

•  Splitter.JPG   43.96KB   18 downloads
•  SPLITTER.zip   59.71KB   55 downloads

Edited by sacarove, 02 October 2013 - 06:30 AM.

[thorium90]

Perhaps you could zip n upload the file, would clarify things abit.

[sacarove]

Dear all,

I am using an adjust to change the splitter ratio so that I can match the downstream temperature. I noticed that the splitter is greater than one on one stream and negative on the other.

How can I fix it to a maximum of 1?

 

Thanks

Sacarove 

 

Hi I have uploaded the file.

I am using v8

[thorium90]

Stream "mixture" has a temperature of 59.85C and 3937kPa. Stream "out" you have set as 1042kPa. One side of your process has a valve that expands and therefore cools down the fluid to a lower temperature. The other side of your process has an expander unit that also expands and therefore cools down the fluid to a lower temperature. So how can you put a unit op to adjust the split ratio between the two streams so that you get back the same 59.85C when both sides will get cooled down below 59.85C and will never be able to achieve it? Your simple process makes no meaning, perhaps you can explain what is it you are trying to model?

Attached Files

•  mixture.png   93.93KB   7 downloads

Edited by thorium90, 02 October 2013 - 09:48 AM.

[sacarove]

Hi Thorium,

yes it is a bit strange, but theses are the measured data(From DNV report) on chokes.

 I am trying to predict the downstream temperature by changing the split factor between the valve and the expander.

it can be a bit difficult to explain all the details to you now. But I want to fix the split ratio so that is does not exceed 1.

 

Thanks

Sacarove

[thorium90]

There is no fix since what you have modelled is not thermodynamically possible and hysys is already telling you that by giving you an impossible split. Is it possible you have misunderstood how the process works?

[amiprocess]

I agree with "thorium90"

 

Sacarove:

you are trying to make same temperature as inlet. But you are reducing pressure. After pressure reduction without any heat source it is not possible to keep the outlet temperature same as inlet.

 

But you can adjust the spliting ratio to get a certain temperature(design selection) in expander outlet by fixing a desired temperature in final outlet. Then you can get the required heat flow to achieve the desired outlet temperature in expander module heat stream. 

 

Thank you.

[curious_cat]

Stream "mixture" has a temperature of 59.85C and 3937kPa. Stream "out" you have set as 1042kPa. One side of your process has a valve that expands and therefore cools down the fluid to a lower temperature. The other side of your process has an expander unit that also expands and therefore cools down the fluid to a lower temperature. So how can you put a unit op to adjust the split ratio between the two streams so that you get back the same 59.85C when both sides will get cooled down below 59.85C and will never be able to achieve it? Your simple process makes no meaning, perhaps you can explain what is it you are trying to model?

 

 

@thorium:

 

You are probably right and there's a blunder. 

 

But I just wanted to get your opinion on an alternative scenario I was thinking. Tell me if it is wrong or possible. 

 

Say @sacarove's fluid has a lot of H2 in it (I'm not sure, what is the composition?). H2 will still cool on pressure reduction through an isentropic expander (t), but since H2 has an inversion temp. of ~ -70 C it would heat up when throttled through a valve (v) at his Temperature of ~50 C,  right?  

 

In which case, there ought to be a certain split that may indeed be possible that would drop pressures without a net cooling? The strategy seems in theory not impossible?

 

Thoughts?

 

PS. I just noticed that his first sketch shows H2O + Oil + Gas so my assumption of a H2 rich stream seems bad. Which makes the rest of my argument academic. Can't think of any other reasonable gas combinations that have an inversion temperature below ambient. 

 

@sacrove: 

 

Might you be overconstraining the problem? Perhaps you'll have to let the downstream pressure also float if the downstream T = upstream T is your hard constraint? Just a thought. 

Edited by curious_cat, 07 October 2013 - 06:14 AM.

[thorium90]

In that case, there could be a possibility. Using the OP's original file and changing the component to pure H2 and the temperature to 50C I've attached the following picture of the process you have described.

Attached Files

•  Pure H2.jpg   91.22KB   4 downloads

[curious_cat]

In that case, there could be a possibility. Using the OP's original file and changing the component to pure H2 and the temperature to 50C I've attached the following picture of the process you have described.

 

Exactly what I had in mind thanks! 

 

Interesting how weak the JT heating effect is. I hadn't intuitively expected that.

Edited by curious_cat, 07 October 2013 - 10:55 AM.