Rejets diphasiques accidentels et calcul d'évents pour la protection des installations dans l'industrie chimique

Accidental two-phase releases and vent-sizing for vessel protection in the chemical industry

Rhône-Poulenc Industrialisation

Abstract

The most severe accidents occurred in the chemical industry (Bhopal, Seveso, Griesheim) due to runaway reactions were not caused by the reactor explosion. A two-phase release of toxic material was sprayed over a densely populated area, through a vent system.

In the above three examples, the vents were not sized for the accident scenario.

The presence of large vents (pressure safety valves, rupture disks) to protect industrial equipments, is a source of potential two-phase release, should an accidental blow-down occur, if there is no catchment system. The occurrence of a two-phase release may be predicted using vapor/liquid disengagement correlations. When the DIERS methodology is applied for vent-sizing to protect vessels for the runaway reaction case, the occurrence of a two-phase release is considered. The two-phase release must be directed to a catchment system to avoid a pollution of the environment.

This paper gives an overview of the DIERS methodology applied to vent sizing for runaway reactions, with special attention to the areas/topics still discussed.

The influence of the cost and reliability of catchment/release treatment/disposal systems on process design and on protection using safety interlocks is discussed.