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Flare Gas Flow Estimation


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#1 Arsal

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Posted 25 November 2015 - 09:20 AM

Ultrasonic flow meter is used to measure the flow meter of flare header due to high accuracy and good  turn down ratio.the basic data is mandatory to purchase which is required by vendor but we could not understand how to find these data,as required data is mandatory which are following.

 

Flow @ Max,min,operating ,

Temp @ Max,min,operating ,

Pressure @ Max,min,operating

 

So i am estimating the operating flow in a flare header by 0.3% of crude feed from CDU and similarly take 0.2-0.3 %  of feed from other downstream unit which involve specially reciprocating compressor due to slight leakage from their stuffing boxes.

 

How i will find Max,min,operating flow,temp and pressure of flare header ? 

we only have the flare relief load,max design temperature and pressure data available.

 

If any body have a idea how to estimate these data for procurement of accurate flow meter please give your technical comments?


Edited by rao arsalan, 25 November 2015 - 09:43 AM.


#2 shan

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Posted 25 November 2015 - 10:55 AM

Flare gas measurement is for the normal release scenarios not for the emergency cases.  If you have no other data available to determine the ultrasonic flow meter range, you may use the possible largest PSV normal release as the max and purge gas as the min.



#3 Arsal

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Posted 26 November 2015 - 03:31 AM

Thankyou Shan.

 

what about operating flow.and consider similar for Temperature and pressure as well? if u please more elaborate this concern.



#4 Arsal

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Posted 26 November 2015 - 04:44 AM

Furthermore,what is suitable location of ultrasonic flow meter,either After KOD or before KOD?



#5 fallah

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Posted 26 November 2015 - 12:52 PM

Furthermore,what is suitable location of ultrasonic flow meter,either After KOD or before KOD?

 

rao arsalan,

 

It's hughly recommended the ultrasonic flow meter to be installed downstream of flare KOD due to probability of having two phase flow at upstream of KOD and subsequent error in measurement...
 



#6 Arsal

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Posted 26 November 2015 - 10:58 PM

Fallah,

Thankyou,

 

Location of Ultrasonic flow meter is very clear now.but still not clear about the following to set a flow meter range.

 

Flow @ Max,min,operating ,???

Temp @ Max,min,operating ,???

Pressure @ Max,min,operating???



#7 fallah

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Posted 28 November 2015 - 02:27 AM   Best Answer

 

Flow @ Max,min,operating ,???

Temp @ Max,min,operating ,???

Pressure @ Max,min,operating???

 

rao arsalan,

 

In general:

 

Flow: Maximum, highest load in flare load summary. Minimum, purge gas flow rate. No operating flow rate can be specified.

 

Temperature: Maximum, highest relieving temperature. Operating, ambient temperature. Minimum, lowest relieving temperature

 

Pressure: Maximum, allowable back pressure. Minimum, purge gas pressure.  No operating pressure can be specified.
 



#8 Arsal

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Posted 28 November 2015 - 12:13 PM

I am very satisfied with your answer...but again one issue that we dont have purge gas flow rate specified in the data...and normally few flare gasses always in the header so we are not concerned with the purge gas ...can u please elobrate how estimate with out purge gas data????.....
Is any direct calculations to find out purge gas requirement?

Edited by rao arsalan, 28 November 2015 - 12:24 PM.


#9 fallah

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Posted 28 November 2015 - 12:24 PM

I am very satisfied with your answer...but again one issue that we dont have purge gas flow rate specified in the data...and normally few flare gasses always in the header so we are not concerned with the purge gas ...can u please elobrate how estimate with out purge gas data????.....
Is any direct calculations to find out purge gas requirement?

 

rao arsalan,

 

You can use API guidelines for purge gas flow estimation; as the purge gas flow rate needs to have a velocity of 0.3 m/s...
 



#10 Arsal

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Posted 28 November 2015 - 12:29 PM

Thankyou Fallah for your such useful technical comments.

#11 Mahdi1980

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Posted 01 December 2015 - 12:23 AM

rao arsalan

 

For normal operating flow you can estimate it based on the overall efficiency of your plant in worse case.

For instance, if your raw material is 1000 kg/h and the overall yield of reaction (considering recovery of un-reacted materials ) is 98% it means that 20 kg normally goes to flare and multiplying by 1.25~1.5 safety factor( based on your condition) the normal flow rate will be achieved. For this example it could be  25~30 kg/h. 

I hope it helps you.



#12 Mahdi1980

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Posted 01 December 2015 - 03:24 AM

rao arsalan

 

For maximum operation flow, if one flare is just used, you should consider the capacity of all PSVs at total shut down of the plant and put it as maximum flow for Ultrasonic flow meter.

Sometimes, it is 20~50 times higher than the normal flow.






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