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Monday, March 23, 2009

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Earlier post "Quick Estimate Flare Tip Pressure Drop" haspresented some clues in obtaining flare tip pressure drop for sonicand subsonic tip. Particularly for subsonic flare tip, a simple pressuredrop versus flow curve was presented. This graph may be used forquick estimation during conceptual stage so that it minimizeunnecessary time lost. However, the graph has limited to 0.5 - 40kPa with correspondent minimum and maximum flow. Someconceptual studies may have flaring capacity resultant pressure dropmore than 40 kPa, the graph may not be useful. In this post, a simpleformula will be presented in order to estimate pressure drop for anyflow rate for dedicated flare tip.

dP = 10 ^ (a x Log Q + b)

wheredP = tip pressure drop, kPaQ = Flow at standard condition, dm3/s (note 1)a & b = coefficient correspondent to tip size as list in following table

Tip Nom. Dia. (mm) a b

250 1.772663 -5.287376

400 1.92372 -6.671917

450 1.948852 -7.034009

500 1.945342 -7.329128

600 1.954552 -7.791866

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1 of 3 27/04/2011 13:39

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750 1.968898 -8.24243

900 1.89152 -8.14936

1050 1.722666 -7.781574

1200 1.532001 -7.181798

Note 1 : The standard condition may be different from project to project (read more in"Avoid Confusion In "Standard" Flow Definition". Present standard definition is at101.325 kPa abs and 15 degC.

ExampleEstimate pressure drop of a subsonic flare tip with flow of 30,000 Sm3/h.

Q = 30,000 x 1000 / 3600 =8333.3 dm3/s @ Std

(i) A DN250 tip,dP = 10 ̂( 1.772663 x Log Q - 5.287376)dP = 10 ̂( 1.772663 x Log 8333.3 - 5.287376)dP = 46 kPa (outside curve)

(ii) A DN400 tip,dP = 10 ̂( 1.92372 x Log Q - 6.671917)dP = 10 ̂( 1.92372 x Log 8333.3 - 6.671917)dP = 7.4 kPa

(iii) A DN450 tip,dP = 10 ̂( 1.948852 x Log Q - 7.034009)dP = 10 ̂( 1.948852 x Log 8333.3 - 7.034009)dP = 4.0 kPa

(iv) A DN500 tip,dP = 10 ̂( 1.945342 x Log Q - 7.329128)dP = 10 ̂( 1.945342 x Log 8333.3 - 7.329128)dP = 2.0 kPa

You may compare results with chart in "Quick Estimate Flare Tip Pressure Drop".

Quick Estimate Flare Tip Pressure DropSeveral Criteria and Constraints for Flare Network - ProcessSeveral Criteria and Constraints for Flare Network - PipingProvide More than One Flare KOD in SERIESFlare Tip Quick Selection ChartFlare Smokeless Ringlemann Chart

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