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Dear All,
It is a little bit time I am not on-line, but now I need help to make a calculation.
Someone ask me to provide a calculation report for anti-detonation dimensioning of a blowdown line. This line is part of a natural gas compression plant and is on compressor discharge side. It is first time I deal with this problem.
Can someone suggest me how this calculation could be made or where I can find something related?
Thanks in advance
Tommy
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Anti-detonation Dimensioning
Started by Tommy, Mar 07 2005 08:12 AM
4 replies to this topic
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#2
gvdlans
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Posted 08 March 2005 - 06:23 AM
Tommy,
Please explain your problem in a little bit more detail. I simply don't understand what you mean. Normally you prevent explosions (deflagrations or detonations) by making sure there is no flammable gas mixture (no oxygen present), not by dimensioning a pipe...
I assume your blowdown line is connected to a flare header and the flare header has a continuous purge to prevent air ingress. Please confirm.
Please explain your problem in a little bit more detail. I simply don't understand what you mean. Normally you prevent explosions (deflagrations or detonations) by making sure there is no flammable gas mixture (no oxygen present), not by dimensioning a pipe...
I assume your blowdown line is connected to a flare header and the flare header has a continuous purge to prevent air ingress. Please confirm.
#3
Tommy
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Junior Member
Posted 09 March 2005 - 06:31 AM
gvdlans,
I had more details about this calculation. I have to perform a calculation considering fire case in the flare header and its propagation to blowdown line, verifying pipe resistance to detonation.
Is there any standard that can help me in this problem?
Thanks
Tommy
I had more details about this calculation. I have to perform a calculation considering fire case in the flare header and its propagation to blowdown line, verifying pipe resistance to detonation.
Is there any standard that can help me in this problem?
Thanks
Tommy
#4
Guest_Guest_ShaunHill_*
Guest_Guest_ShaunHill_*
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- guestGuests
Posted 09 March 2005 - 06:13 PM
Tommy,
This is a very unusual approach to this problem. I have designed many gas compressor stations and this is the first time I have heard of someone approaching the problem of fire in the flare system this way.
Gernerally speaking, fires and explosions occur in flare headers because of air ingress into the flare system. We normally prevent this from occuring by putting a purge gas on the flare system to keep air out (I normally use natural gas, but I have heard of people using nitrogen or steam). If your flare stack is fairly large, you can use a velocity arrestor (NOT a flame arrestor or detonation arrestor) to reduce the purge requirements. There are some vendors that can provide information on this, I usually deal with Tornado.
The other time that explosions often occur in flare systems is right after a shutdown. If the flare is ignited before being fully and properly purged there may still be sufficient oxygen in the line to support a combustable atmosphere.
I don't believe that you should be worried about propogation back to your blowdown line. While I haven't personally been around when this has happened, I have heard accounts of flare explosions, and I understand that normally the failure occurs at the flare knock-out drum. I believe that this is because it has the largest surface area compared to the material thickness making the knock-out drum the weak link. I have actually heard of buried knock-out drums being blown out of the ground.
What sort of gas are you compressing? Is it extremely sensitive to combustion or reaction in some way that makes it difficult to prevent explosion using these means? I am normally dealing with natural gas so maybe you have a different situation.
This is a very unusual approach to this problem. I have designed many gas compressor stations and this is the first time I have heard of someone approaching the problem of fire in the flare system this way.
Gernerally speaking, fires and explosions occur in flare headers because of air ingress into the flare system. We normally prevent this from occuring by putting a purge gas on the flare system to keep air out (I normally use natural gas, but I have heard of people using nitrogen or steam). If your flare stack is fairly large, you can use a velocity arrestor (NOT a flame arrestor or detonation arrestor) to reduce the purge requirements. There are some vendors that can provide information on this, I usually deal with Tornado.
The other time that explosions often occur in flare systems is right after a shutdown. If the flare is ignited before being fully and properly purged there may still be sufficient oxygen in the line to support a combustable atmosphere.
I don't believe that you should be worried about propogation back to your blowdown line. While I haven't personally been around when this has happened, I have heard accounts of flare explosions, and I understand that normally the failure occurs at the flare knock-out drum. I believe that this is because it has the largest surface area compared to the material thickness making the knock-out drum the weak link. I have actually heard of buried knock-out drums being blown out of the ground.
What sort of gas are you compressing? Is it extremely sensitive to combustion or reaction in some way that makes it difficult to prevent explosion using these means? I am normally dealing with natural gas so maybe you have a different situation.
#5
processji
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Posted 09 November 2006 - 06:36 AM
I am currently working on modification to a Process oil and gas platform.We are adding launchers and receivers. Main drive behind this project is to stop flaring and divert gas to onshore. Currently the gas is flared.The gas is 80 mol% methane 8% ethane and 5% propane.We have a We have a 24" flare header to the scrubber.A 20" line from scrubber to sub sea flare.Gas flow rate is 72 mmscfd.
Once flaring is stopped we need to provide a purge.
I am looking for a way to estimate purge rate with the 80% methane stream.Purge gas is at 65 psia and 94 Deg F.I read in API-521 that there is a article by H W Husa HOW TO COMPUTE SAFE PURGE RATES published in hydrocarbon processing and petroleum refiner 1964.
Any inputs regarding this will be useful.
i can be reached at goldsuresh@hotmail.com
regards
K Suresh
Once flaring is stopped we need to provide a purge.
I am looking for a way to estimate purge rate with the 80% methane stream.Purge gas is at 65 psia and 94 Deg F.I read in API-521 that there is a article by H W Husa HOW TO COMPUTE SAFE PURGE RATES published in hydrocarbon processing and petroleum refiner 1964.
Any inputs regarding this will be useful.
i can be reached at goldsuresh@hotmail.com
regards
K Suresh
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