Latest research about preventing boilovers
Volume 24 Number3
Editor's Note: In March, a contingent from authorities and companies working together to provide fire protection for the Port of Rotterdam in The Netherlands attended the annual Industrial Fire World Emergency Responder Conference and Exposition. In Rotterdam, all authorities and companies work together. This has resulted in the establishment of the Rotterdam Rijnmond Industrial Fire Response Unit. The organization has a steering committee, workgroup and work teams. They also have equipment which is suitable to extinguish full surface tank fires of storage tanks up to 90 meters (295 feet) in diameter. At present, research is being carried out for the Industrial Fire Response Unit by Inburex Consulting, an independent international company providing services in many fields of industrial and process safety. This includes, explosion prevention and protection, fire safety, process safety, transport and storage Safety as well as safety management and various work in its own testing laboratory. In earlier research activities into the formation mechanisms of boilovers carried out by Dr. H.-G. Schecker and Dr. Broeckmann, whose PhD was in the field of heat transfer mechanisms and boilover in burning oil-water systems. There is a wide range of knowledge and experience in this field. Dr. Broeckmann and his co-workers are currently carrying out the research on the applicability of the new approach which is described in this article.
In the chemical and petrochemical industries bulk quantities of flammable liquids, mostly raw and auxiliary materials, are stored. Fuels like oil or gasoline pose a specific threat due to their storage in large storage tanks. Fires at such storage tanks are uncommon but can happen and can cause extensive damage and considerable losses. So they represent a risk which should not be underestimated.
The worst case scenario of a full surface storage tank fire occurs when burning material is violently ejected from the tank due to the vaporization of a second phase liquid. Usually this second phase has a lower boiling point and a higher density than the bulk of the liquid stored in this tank. In general this second phase is a water layer at the bottom of the tank, which was either present during drilling or introduced during transport or the result of condensation. This effect is better known as boilover.
There are various studies and theories concerning the mechanisms causing this hazard. In general this effect could be summarized in this statement:
During the fire heat accumulates in the oil and induces various processes, among other things, destabilization of the naturally occurring composition (W/O-emulsions, hydrocarbon fractions with a wide boiling range and hetero-azeotropic boiling points). Due to this effect the original composition of the crude oil is changed by the way that the light ends are vaporized and burned at the surface during the fire. The loss of low boiling point components changes the composition of the fuel within the surface layer. The remaining fuel will not vaporize because of its high boiling points resulting in an increase temperature of the top surface layer. Heat convection causes an increase in temperature of the fuel layer below the top layer.
The result is a hot heavy oil fraction moving downwards to form a hot-zone. When this hot-zone reaches the accumulated water at the bottom of the tank, the water gets superheated and rapidly vaporizes. Due to this expansion of volume at the bottom of the tank the steam ejects from the tank over a wide distance, dragging burning liquids along in its path.
The objective of this research was to establish the best practices in the control and mitigation of boilovers from crude oil by means of stabilizing the composition of the crude oil during the fire by using additives.
Based upon a literature study potential options to control or mitigate the effects of a boilover using additives are presented.
The basic principle of this research is to investigate which mix of additives is suitable to create a thermically stable liquid with a high flashpoint in the crude oil of the storage tank on fire (thus prevention of the hot-zone formation).
The additives must be able to keep the original properties of the liquid in the storage tank under the rigid conditions throughout the full surface tank fire. These requirements are the key issues for selecting the appropriate additives. There are several parameters which influence the stabilization process.
The use of additives in crude oil to improve the flow behavior of the crude oil for its transport through pipelines, may also influence the properties of the additives. The effect the products used to influence the flow behavior have on the additives is still unknown.
The focus in this research is on the use of additives to control or prevent boilovers. Additives may sufficiently stabilize the thermically unstable contents of the storage tank with crude by forming a thermically stable liquid with a higher boiling point than the fractions had before the additives were present.
Contributing to this research are Jeanne van Buren, Industrial Fire Response Unit, Rotterdam-Rijnmond, The Netherlands; Ab de Moor, Chairman, Workgroup, Industrial Fire Response Unit, Rotterdam, The Netherlands; Martin Gosewinkel, Inburex Consulting GmbH, Hamm/ Westf., Germany; Rene Dworschak, Inburex Consulting GmbH, Hamm/ Westf., Germany; Jens H?tger, Inburex Consulting GmbH, Hamm/ Westf., Germany and Dr. Bernd Broeckmann, Inburex Consulting GmbH, Hamm/ Westf., Germany.