Compliance with air quality initiatives often involves the installation of a vapour collection system (VCS). The purpose of a VCS is to collect and direct vapours to a flare, incinerator or recovery unit. This practice creates a hazardous situation wherein an explosive vapour is tied into an ignition source.
This paper eramin.es nine factors in creating the most severe flame front possible in a practical full sized piping system. They are: gas types gas mixtures, pre-ignition pressure, temperature of the ignition energy temperature of the mixture, ignition location, pipe configuration, rotected side restrictions and endurance to stabilized flame. The paper also examines which of these factors are in the jurisdiction of the plant process and those factors for which proof of capability have been demonstrated by ommercially manufactured detonation flame arresters in actual tests.
Many certification standards define the acceptance testing of DFA's. They have been evolving and improving over the past two decades. A summary is made of which flame propagation parameters are addressed by various standards.
When reviewed in this context and applied to practical operating conditions, new levels of confidence and safety are created. The critical variables within the control of the industry are outlined. This information can be applied to reduce the current high frequency of vapour transportation explosions.
Interest in the nature of vapour line explosions in Alberta, Canada began in earnest in the 1960's When, for environmental reasons, operators of oil and sour gas wells were required to collect vapours and combust them through flare stacks. Although these actions protected the environment, they also subjected the operating personnel in the oil patch to the increased hazards from an explosion.
The first line of defence against flame propagation is a passive device called a "Flame Arrester" designed for end of line vent applications. Conventional end of line flame arresters when located in pipes have produced a dismal operation performance record. In Alberta oil fields, approximately 30 explosions per year occur with each costing approximately ﹩100,000 US or more.
Other publicized explosions which have occurred are the 1983 U.S. Green Lake barges, 1992 Malaysian tanker, 1991 Australian, Coode Island storage tanks, Houston Ship Channel explosions of a Flat Top Tanker in 1989 and a barge in February 1992.
Practical and theoretical knowledge of flame propagation in piping systems, along with the technology to arrest such a flame, has increased considerably in the last eight years. As a corporate citizen, Westech was pleased to contribute 2.8 million Canadian dollars towards the research for flame propagation technology and the development of a reliable Detonation Flame Arrester (DFA) device. The activities since 1985 included a global literature search, comprehensive explosion investigations (3), an analysis of ten field explosions (2), the assembly of flame arrester design parameters in accordance with the demands of industry and proof of capability facility. This facility consisted of a full sized DFA explosion test tube of 305 meters (1002 ft) in length and 457 mm (18") in diameter which appears to be the worlds largest and most highly instrumented.