BLEVE Boiling Liquid Expanding Vapour Explosion

Transcription

1 BLEVE Boiling Liquid Expanding Vapour Explosion Michael Plagge Physics Department Compact Muon Solenoid Experiment European Organization for Nuclear Research (CERN) Institute of Process Equipment and Environmental Engineering Department of Process Design and Safety Otto-von-Guericke-University Magdeburg October 21, 2011

2 Definition [1] A boiling liquid expanding vapour explosion, called BLEVE, is caused by a failure of a pressure vessel containing a flammable pressurized liquid due to exposure to fire or any kind of external heating. Example: Tank with liquid propane Pressure is suddenly released due to a valve failure or leak caused by aged material etc. Fraction of the propane will vaporize immediately Vapourization process is fed by the heat of the liquid cooling of the liquid to atmosphere boiling point Ignition of the vapour, gas and liquid leads to a fireball [1] Drysdale, D., An Introduction to Fire Dynamics, 3rd Ed., John Wiley & Sons, / 11

3 Example - Mexico City 1984 [2] About 5.35 a.m on the morning of 19 November 1984 a major fire and a series of explosions occured at the PEMEX LPG terminal at San Juan Ixhuatepec (San Juanico), Mexico City. Some 500 hundred people were killed and the terminal was destroyed. Sequence of events: Rupture of an eight inch pressure pipeline Safety systems failed, LPG release continued Accumulation of a LPG vapour cloud, area about 200x150 m, 2 m height Ignition of the vapour resulting in two main and a lot of minor BLEVEs, explosions and detonations as well as several severe fires Two major BLEVEs were registered with a value of over five on the Richter scale for earth quakes. Fragments and parts traveled up to 1200 m [2] Lees, F. P., Loss Prevention in the Process Industries, Volume 3, 2nd Ed., Butterworth-Heinemann, / 11

4 Example - Mexico City 1984 [2] Before the incident [2] Lees, F. P., Loss Prevention in the Process Industries, Volume 3, 2nd Ed., Butterworth-Heinemann, / 11

5 Example - Mexico City 1984 [2] After the incident [2] Lees, F. P., Loss Prevention in the Process Industries, Volume 3, 2nd Ed., Butterworth-Heinemann, / 11

6 Example - Mexico City 1984 [2] Schematic view of damage and accelerated fragments or missiles [2] Lees, F. P., Loss Prevention in the Process Industries, Volume 3, 2nd Ed., Butterworth-Heinemann, / 11

7 Fireball - Caculation example [3,4] Traffic accident caused BLEVE by a fuelling vehicle A truck filled with about 20 m 3 of liquid propane has an accident and undergoes external heating due to a fire. The full amount of propane shall be consumed in an occuring BLEVE. x in m q in kw/m 2 Effects [5] rd degree burns, 50% lethality nd degree burns some pain below pain threshold x = ground distance, q = heat intensity See References and MS Excel file for equations and assumptions. [3] Lees, F. P., Loss Prevention in the Process Industries, Volume 2, 2nd Ed., pp. 16/182, Butterworth-Heinemann, [4] Marx, M., Advanced explosion protection, Lecture, Otto-von-Guericke-University Magdeburg, [5] Hyms, I., The effects on people and structures of explosion, blast, thermal radiation and toxicity, In Pitts, J.I. 1984, op. cit., see [1]. 7 / 11

8 Flash evapouration / Flashing A flash vapourization due to a damage or rupture of a vessel could be assumed as a point source. The concentration C in distance r and time t after flashing can be calculated by [6]: a 3 r C(r, t) = 6(kt) 1.5 π 0.5 e C 0 - initial concentration after flashing k - turbulent exchange coefficient a - diameter of the vapour cloud 2 4kt C 0 Example: Rupture of a spherical vessel containing liquid propane (about 523 m 3 ) would create a vapour cloud with a radius of 53 m. The concentration in 100 m from the vessel after 60 s will be around mg/m 3 (equal to 0.18 ppm). Values are corrected [7]. [6] Hauptmanns, U., Technical Risks II: Incident effects, Lecture, Otto-von-Guericke-University Magdeburg, [7] en/p/ xml?f=templates&fn=default.htm 8 / 11

9 Flash evapouration / Flashing CERN CMS Nitrogen vessel at point 5 Concentra)on (10 m, t) Concentra)on in kg/m3 1,60 1,40 1,20 1,00 0,80 0,60 0,40 0,20 0, Time t in s Calculation of a dense gas with the point source model briefly described above. Do not use this for real applications, see Lees, F. P., Loss Prevention in the Process Industries, Volume 1, 2nd Ed., pp. 15/162, Butterworth-Heinemann, 1996, for dense gas modeling. 9 / 11

10 Flash evapouration / Flashing CERN CMS Nitrogen vessel at point 5 Concentra)on in kg/m3 0,18 0,16 0,14 0,12 0,10 0,08 0,06 0,04 0,02 0,00 Concentra)on (20 m, t) Time t in s Calculation of a dense gas with the point source model briefly described above. Do not use this for real applications, see Lees, F. P., Loss Prevention in the Process Industries, Volume 1, 2nd Ed., pp. 15/162, Butterworth-Heinemann, 1996, for dense gas modeling. 10 / 11

11 Flash evapouration / Flashing CERN CMS Nitrogen vessel at point 5 0,06 Concentra)on (30 m, t) Concentra)on in kg/m3 0,05 0,04 0,03 0,02 0,01 0, Time t in s Calculation of a dense gas with the point source model briefly described above. Do not use this for real applications, see Lees, F. P., Loss Prevention in the Process Industries, Volume 1, 2nd Ed., pp. 15/162, Butterworth-Heinemann, 1996, for dense gas modeling. 11 / 11