Comparison of Deflagration to Detonation Transition (DDT) Criteria with Test Data From Unconfined Ethylene-Air Vapor Cloud Explosion | AIChE

Comparison of Deflagration to Detonation Transition (DDT) Criteria with Test Data From Unconfined Ethylene-Air Vapor Cloud Explosion

Type

Conference Presentation

Conference Type

AIChE Spring Meeting and Global Congress on Process Safety

Presentation Date

March 13, 2011

Duration

30 minutes

Skill Level

Intermediate

PDHs

0.50


Deflagration to detonation transitions (DDT) were previously observed in a set of large-scale unconfined vapor cloud explosion (VCE) tests involving ethylene-air mixtures in a moderately congested environment. The test rig congested region was 48 feet long by 12 wide by 6 feet high, with a regular array of vertical circular tubes providing the congestion (pitch-to-diameter ratio of 4.5, area and volume blockage ratios of 22% and 4.1%, respectively). The test rig was configured without any confinement (i.e., no wall or roof sections). The fuel-air mixture completely filled the congested region in these tests, but did not extend beyond it. DDTs were observed at ethylene concentrations ranging from 5.9% (lean) to 9.3% (rich). A comparison has now been made between a DDT criterion established for the FLACS code and this test data. The FLACS DDT criterion utilizes the maximum dimensionless pressure gradient and was established by benchmarking primarily against hydrogen-air tests in confined geometries (i.e., pipes and channels). The comparison with the existing ethylene-air VCE DDT data indicates a different critical value for the maximum dimensionless pressure gradient than that developed based on the confined hydrogen-air tests. Alternative DDT criteria were also explored as part of this work.


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