12 replies to this topic

[zebmech]

Dear members,

I need your help in calculation of efficeincy of a two phase seperator which is installed in the Urea production section of our plant. The only available data I have with me is as attached. The stream contains CO2 vapours which requires separation of water vapours from CO2 gas.

I need to find out what is the efficeincy of the vapour liquid separator at which it is working. The only problem I am facing is that the our DCS dont display any flow data nor their are any flow instruments installed in the field in this area. I have been asked to find out the separator efficiency making use of temperature and pressure data that is available on the DCS. Please suggest me the approch I may use to calculate its efficiency.

Regards,

zebmech
 

Attached Files

•  E-25.xls   19KB   117 downloads
•  Separator MV-16.pdf   13KB   114 downloads

Edited by zebmech, 22 May 2013 - 05:39 AM.

[Bobby Strain]

You cannot determine efficiency unless you can measure the liquid entrained with the gas on the outlet stream. You might get some indication of moisture present by analyzing the second stage compressor performance. But you won't likely be able to tell unless there is lots of entrainment. Your best option is to check the design parameters for the separator. You can design one with your process data at my website, and compare with your size. You can find the site by Googling my name.

 

Bobby Strain

[ankur2061]

zebmech,

 

Bobby is absolutely right in saying that unless you can find out the entrained water in the vapor stream from your separator you cannot measure the efficiency. Efficiency for 2-phase gas-liquid separator can be denoted by the following formula:

 

E =100*(F - C) / F

 

where:

 

E = separation efficiency, %

F = total liquid feed rate to the separator (in your case the water feed), kg/h (lb/h)

C = Liquid carryover in the separator vapor stream (in your case water in the overhead vapor), kg/h (lb/h)

 

By the way the amount of water dropping out from your separator MV-16 (550 liters/h) is unusually high. Is your compressor designed to handle so much wet CO2 gas? Is the metallurgy of your compressor system compatible to handle acid corrosion due to carbonyl acid formation?

 

Regards,

Ankur.

[zebmech]

You cannot determine efficiency unless you can measure the liquid entrained with the gas on the outlet stream. You might get some indication of moisture present by analyzing the second stage compressor performance. But you won't likely be able to tell unless there is lots of entrainment. Your best option is to check the design parameters for the separator. You can design one with your process data at my website, and compare with your size. You can find the site by Googling my name.

 

Bobby Strain

Thanks Bobby! I will re-check the design parameters. Also, kindly provide me the address of your website.

 

Regards,

zebmech

[zebmech]

zebmech,

 

Bobby is absolutely right in saying that unless you can find out the entrained water in the vapor stream from your separator you cannot measure the efficiency. Efficiency for 2-phase gas-liquid separator can be denoted by the following formula:

 

E =100*(F - C) / F

 

where:

 

E = separation efficiency, %

F = total liquid feed rate to the separator (in your case the water feed), kg/h (lb/h)

C = Liquid carryover in the separator vapor stream (in your case water in the overhead vapor), kg/h (lb/h)

 

By the way the amount of water dropping out from your separator MV-16 (550 liters/h) is unusually high. Is your compressor designed to handle so much wet CO2 gas? Is the metallurgy of your compressor system compatible to handle acid corrosion due to carbonyl acid formation?

 

Regards,

Ankur.

Dear Mr. Srivastava,

 

I thank you for this valuable information.

 

The CO2 compressor we have at our plant is a 4 stage compressor with 3 interstage seperators installed between them. The 1st one is MV-16, then MV-17 and then MV-18. But as per our observation, it seems that MV-16 is separating less water from CO2 stream than it should. Hence, its efficeincy needs to be calculated.

 

Regards,

zebmech

[Bobby Strain]

Do you have access to a process simulator like HYSYS?

 

Bobby

[PaoloPemi]

as said by Ankur and Bobby, without reliable data (i.e. inline measurements) you can't evaluate the real working condition for that separator,

there are some alternatives,

for example you can simulate a VLE equilibria at measured (calculated) t,p and estimate the liquid phase amount (and flow), however this approach relies entirely on the accuracy of thermodynamic model which may be not accurate with water (i.e. you could calculate a liquid amunt  very different from real condition),

another way to test a separator is to measure the amount of condensate at two different inlet flows (starting from a very low flow), for a separator working with good efficiency this should be a near linear function,  generally the efficiency reduces when the flow increases being the maximum with minimum flow (best separation),  if there are problems for this separator you should detect an abnormal variation when flow increases, however I do not know if this procedure is applicable in your case (it would require to bypass the separator).

Edited by PaoloPemi, 24 May 2013 - 03:15 AM.

[zebmech]

Do you have access to a process simulator like HYSYS?

 

Bobby

No, We don't have access to HYSYS but we do have HTRI Xchanger Suite 6.0. Will it be of any help?

 

Regards,

zebmech

[staffel]

HTRI Xchanger should include VMGThermo but as said by others I doubt that a simulation can return a reliable value for that efficieny 

[Bobby Strain]

I don't know what is in the exchanger package, but the flash calculations probably require additional modules. Your best bet is to go to the Ariel website and download their compressor program. It has VLE calculation capabilities. And, it's free.

 

Bobby

[zebmech]

I don't know what is in the exchanger package, but the flash calculations probably require additional modules. Your best bet is to go to the Ariel website and download their compressor program. It has VLE calculation capabilities. And, it's free.

 

Bobby

Dear Booby,

 

You have been a great source of help to me. Kindly suugest the ariel website link to download the suugested compressor program as I couldn't find any.

 

Regards,

zebmech

[breizh]

Zebmech.

 

http://www.arielcorp...ce_program.aspx

 

Google : Ariel software 

 

Breizh

[zebmech]

Zebmech.

 

http://www.arielcorp...ce_program.aspx

 

Google : Ariel software 

 

Breizh

Thanks Breizh!

 

Regards,

zebmech