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hello friends,
In our Propane Deasphalting unit,we have a propane recovery system which recovers low pressure propane which comes along with the Deasphalted oil and with Asphalt.This is removed by flashing in columns at high temperature the overhead of which goes to condensors and then to propane bullet.From this bullet,it is pumped back to the high pressure circuit again from where it came as recycle.
Now the problem is ,the bullet was operating at 12-13 kg/cm2 gauge earlier(2 years back) now offlate the bullets pressure has raised to 18 kg/cm2.The condensor outlet temperature is 33-35deg celsius as usual(not changed).The propane in the bulet has 93 mole% propane rest some c4s ,c3s(other than propane) ,and some negligible c2. can any one suggest why this bullet pressure has raised though the condensor outlet temperature remained same and propane composition is reasonably the same?
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Propane Bullet Pressure
Started by Guest_vijay kumar_*, Oct 21 2004 12:33 PM
9 replies to this topic
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#2
Art Montemayor
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Posted 21 October 2004 - 09:44 PM
vijay:
If you can go to the following website:
http://webbook.nist....hemistry/fluid/
Select the Propane properties label from the drop-down menu and you can generate and follow the properties descriptions that I am going to cite. Note that at your hottest saturation temperature (35 oC) the corresponding vapor pressure of pure Propane is approximately 13.4 kg/cm2 gauge. This coincides and supports your original vapor pressure reading of 2 years ago. I realize that your stream is not pure Propane, but as you can see at 93% you are not far from the theoretical pure properties of Propane.
If your tank contents are truly still the same 93% as 2 years ago, then the corresponding temperature of the condensate from the propane condenser must have climbed to approximately 50 oC! But, as you state, the condensate temperature has remained at the same 33 – 35 oC as before. The only reason that the vapor pressure in the Propane tank has increased is due to a component(s) in the tank that has a vapor pressure higher than Propane. It isn’t the C4 components, so it must be the C2 fractions or some other lighter vapor – such as a non condensable like Nitrogen (I certainly hope it isn’t air!) that has crept into your closed cycle through some means or other.
Some gases like ethane or ethylene may dissolve in the liquid Propane and be trapped in the “dome” or vapor space of your liquid Propane tank. That is what I would surmise has happened. I don’t know how you take your composition analysis or samples, but I would certainly test the composition of the vapor space in the tank. This is what is causing your pressure to increase. This is to be expected in a closed, recycled process – ammonia and propane refrigeration cycles are analogous situations that also tend to accumulate “low boilers” or non-condensables that these tend to accumulate in the liquid tank unless you use a non-condensable purger or resort to manual purging.
I am almost willing to bet you a beer that that is what has happened.
Let us know if you find the cause of the vapor pressure increase.
Art Montemayor
Spring, TX
If you can go to the following website:
http://webbook.nist....hemistry/fluid/
Select the Propane properties label from the drop-down menu and you can generate and follow the properties descriptions that I am going to cite. Note that at your hottest saturation temperature (35 oC) the corresponding vapor pressure of pure Propane is approximately 13.4 kg/cm2 gauge. This coincides and supports your original vapor pressure reading of 2 years ago. I realize that your stream is not pure Propane, but as you can see at 93% you are not far from the theoretical pure properties of Propane.
If your tank contents are truly still the same 93% as 2 years ago, then the corresponding temperature of the condensate from the propane condenser must have climbed to approximately 50 oC! But, as you state, the condensate temperature has remained at the same 33 – 35 oC as before. The only reason that the vapor pressure in the Propane tank has increased is due to a component(s) in the tank that has a vapor pressure higher than Propane. It isn’t the C4 components, so it must be the C2 fractions or some other lighter vapor – such as a non condensable like Nitrogen (I certainly hope it isn’t air!) that has crept into your closed cycle through some means or other.
Some gases like ethane or ethylene may dissolve in the liquid Propane and be trapped in the “dome” or vapor space of your liquid Propane tank. That is what I would surmise has happened. I don’t know how you take your composition analysis or samples, but I would certainly test the composition of the vapor space in the tank. This is what is causing your pressure to increase. This is to be expected in a closed, recycled process – ammonia and propane refrigeration cycles are analogous situations that also tend to accumulate “low boilers” or non-condensables that these tend to accumulate in the liquid tank unless you use a non-condensable purger or resort to manual purging.
I am almost willing to bet you a beer that that is what has happened.
Let us know if you find the cause of the vapor pressure increase.
Art Montemayor
Spring, TX
#3
vijay kumar
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Posted 22 October 2004 - 01:38 AM
Hi Mr.Montemayor,
Let me first thank u for ur prompt reply and the effort u have taken to anlyse my problem.yeah thats right,we too suspected that the system has noncondensibles and hence we did a gc analysis in the gas taken from bullet vapor space.Also we bleed the vapor accumulated by our PSV bypass when the pressure goes up in the bullet over 19 kg/cm2.Any how i will have to again check with a GC analysis of the vapor from bullet vent and will come back to u.
also i will check with the link u have given!
thansk again
vijay
Let me first thank u for ur prompt reply and the effort u have taken to anlyse my problem.yeah thats right,we too suspected that the system has noncondensibles and hence we did a gc analysis in the gas taken from bullet vapor space.Also we bleed the vapor accumulated by our PSV bypass when the pressure goes up in the bullet over 19 kg/cm2.Any how i will have to again check with a GC analysis of the vapor from bullet vent and will come back to u.
also i will check with the link u have given!
thansk again
vijay
#4
gvdlans
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Posted 22 October 2004 - 03:28 AM
If you are sure about the composition and about the temperature, the only conclusion left is that your pressure reading is wrong...
Did you check that?
Did you check that?
#5
vijay kumar
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Posted 22 October 2004 - 07:45 AM
Hi,
Temperature and pressure datas were noted down after calibrating the instruments.(Also got the measurements crosschecked by local pressure and temperature gauges)
vijay
Temperature and pressure datas were noted down after calibrating the instruments.(Also got the measurements crosschecked by local pressure and temperature gauges)
vijay
#6
rxnarang
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Posted 24 October 2004 - 11:41 PM
My bet is on the composition. One beer for me too!
#7
vijay kumar
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Posted 25 October 2004 - 08:10 AM
HI NARANG,
I TOO DOUBT ON THE COMPOSITION.WE HAVE MADE A SAMPLE POINT IN THE VENT LINE OF THE BULLET.SAMPLE WILL BE SENT AND WE WILL COME TO KNOW THE RESULT IN THREE DAYS.
IF PROVED,THEN A BEER IS THERE FOR U TOO!
VIJAY
I TOO DOUBT ON THE COMPOSITION.WE HAVE MADE A SAMPLE POINT IN THE VENT LINE OF THE BULLET.SAMPLE WILL BE SENT AND WE WILL COME TO KNOW THE RESULT IN THREE DAYS.
IF PROVED,THEN A BEER IS THERE FOR U TOO!
VIJAY
#8
Guest_Guest_*
Guest_Guest_*
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Posted 01 November 2004 - 04:17 PM
Do you have any blanket gas system for maintaining a minimum pressure when the bullet is being unloaded?
Is it possible that there is a regulator on this system that has failed?
Is it possible that there is a regulator on this system that has failed?
#9
Guest_Ben Thayer_*
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Posted 12 November 2004 - 03:00 PM
I agree with Art (again!).
Slightly off topic but ammonia and propane (here in the US) are handled and delivered using some of the same railcars and tractor/trailers. propane usage is heavier in the winter for home heating and ammonia in the spring/summer for fertilizer. thus, the equipment is switching back and forth.
when i worked at an ammonia producer, a couple of times we had ammonia loaded on top of a propane heel in a trailer or the refinery next door had propane loaded on top of an ammonia heel or one night, a truck came in that had recovered a transfer from a bullet that had both ammonia and propane in it due to a driver error! we vented to our flare until the trailer was empty. this was the only safe thing to do.
because the ammonia and propane are not miscible, the vapor pressures are essentially additive and significant pressure can result.
moral of the story: the GC may need to look for something other than the usual players (nitrogen, C-2's etc.)
good luck and keep us informed
Slightly off topic but ammonia and propane (here in the US) are handled and delivered using some of the same railcars and tractor/trailers. propane usage is heavier in the winter for home heating and ammonia in the spring/summer for fertilizer. thus, the equipment is switching back and forth.
when i worked at an ammonia producer, a couple of times we had ammonia loaded on top of a propane heel in a trailer or the refinery next door had propane loaded on top of an ammonia heel or one night, a truck came in that had recovered a transfer from a bullet that had both ammonia and propane in it due to a driver error! we vented to our flare until the trailer was empty. this was the only safe thing to do.
because the ammonia and propane are not miscible, the vapor pressures are essentially additive and significant pressure can result.
moral of the story: the GC may need to look for something other than the usual players (nitrogen, C-2's etc.)
good luck and keep us informed
#10
Guest_KAT_*
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Posted 17 November 2004 - 08:10 AM
Hi Vijay,
I've read your enquiry thread and am interested in knowing the outcome of your investigation. Could you please post the results of your tests and what subsequently happened?
Cheers,
TK
I've read your enquiry thread and am interested in knowing the outcome of your investigation. Could you please post the results of your tests and what subsequently happened?
Cheers,
TK
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