EXPLOSIONS NEAR THE SURFACE OF ORGANIC LIQUIDS J. DENGEL 1 , R. WENDLER 1 , W. DENZER 1 , J. BUCHHOLZ 1 , M. BECKMANN-KLUGE 1 , J. STEINBACH 2 , B. PLEWINSKY 1 and H. HIERONYMUS 1à 1 Federal Institute for Materials Research and Testing (BAM), Berlin, Germany 2 Technische Universita ¨t Berlin, Berlin, Germany T his work presents experimental investigations of the explosion behaviour of diethylketone and methanol with pure oxygen and oxygen/nitrogen mixtures. The experimental setup consists of a tube with a length of 2000 mm, an inner diameter of 50 mm and an observation unit. Besides pressure recordings, characteristics for hetero- geneous detonations and deflagrations were observed by high-speed photography. Different regimes of the explosion behaviour were determined as a function of the initial pressure and of the content of oxygen in the gas phase. Furthermore, the experiments showed that the formation of droplets is a necessary condition for the formation of detonations near the surface of organic liquids. Keywords: heterogeneous explosions; detonation; deflagration; explosion ranges. INTRODUCTION Oxidation reactions involving liquid solvents and gaseous oxidisers are common practical processes in the chemical process industries. To improve the efficiency of such pro- cesses different options exist. On the one hand the substi- tution of air by pure oxygen or oxygen inert gas mixtures or higher process pressures constitute useful methods for this purpose. On the other hand the explosion hazards increase thereby and additional assessments of process safety are necessary. Whereas a high level of knowledge exists for explosions in gas systems, the explosions in heterogeneous systems are not extensively investigated up to now. This paper presents the experimental results of the inves- tigations of explosions in two phase systems consisting of diethylketone or methanol with a smooth surface and the gaseous oxidiseroxygen or oxygen – nitrogen mixtures. Explosions in such systems are called surface explosions. According to the nomenclature of explosions in gases two types of explosions are defined. These are deflagrations and detonations. In analogy to gas systems we define surface deflagrations and surface detonations in the heterogeneous systems under investigation. The surface detonations under investigation are related to the film detonation reported in the literature (e.g., Pinaev and Subbotin, 1982; Lyamin and Pinaev, 1984; Frolov et al., 1985). Usually film detonations have been reported where the films of fuel covered the wall of a tube. In con- trast to our systems, the thickness of the films usually was essentially below 1 mm. The reported film detonations were initiated by shock waves whereas our systems are ignited by a weak ignition source, i.e., an exploding wire. It is also possible to ignite our systems by an even weaker ignition source like a glowing wire. Film deto- nations were observed in tubes only. Surface detonations were observed also above a circular surface in an autoclave (Hieronymus et al., 2001b). Previous investigations showed that in a system consist- ing of an organic liquid with a smooth surface and pure oxygen under high pressure deflagrations and detonations are possible even if the fuel concentration in the gaseous phase is below the lower detonation limit and even below the lower explosion limit (Hieronymus et al., 2001a, b). For example, the detonation limit of a gaseous cyclohexane – oxygen mixture with a vapour content corre- sponding to the saturated vapour pressure of cylohexane at 293 K was experimentally found to be about 3 bar in a tube with an inner diameter of 50 mm. For higher pressures of the system detonations are impossible since the amount of cyclohexane in the gas phase is too low. However, in the presence of liquid cyclohexane, detonations were observed in the same tube up to system pressures above 20 bar (Hieronymus et al., 2001a). Another example is described for a heterogeneous toluene – oxygen mixture in an autoclave. The liquid toluene was in a circular layer of 3 mm and 4.5 mm in height and 400 mm in diameter. At 293 K and at pressures above 3 bar, the gas phase composed of the vapour of toluene and oxygen is below the lower explosion limit (Hieronymus et al., 2001b). Nevertheless, detonations have been observed in such à Correspondence to: Dr H. Hieronymus, Federal Institute for Materials Research and Testing (BAM), Unter den Eichen 87, 12205 Berlin, Germany. E-mail: hartmut.hieronymus@bam.de 452 0957–5820/05/$30.00+0.00 # 2005 Institution of Chemical Engineers www.icheme.org/journals Trans IChemE, Part B, September 2005 doi: 10.1205/psep.04199 Process Safety and Environmental Protection, 83(B5): 452–458