Günther Zwahlen

Bio: Günther Zwahlen is an academic researcher. The author has contributed to research in topics: Minimum ignition energy & Ignition system. The author has an hindex of 1, co-authored 1 publications receiving 134 citations.

Dust Explosions: Course, Prevention, Protection

Abstract: 1 Introduction.- 2 Historical Review.- 2.1 Occurrence of Dust Explosions.- 2.2 The Nature of Dust Explosions.- 2.3 Apparatus for the Testing of Airborne Dusts.- 3 Dust as a Dispersed Substance.- 4 Material Safety Specifications.- 4.1 Preliminary Remarks.- 4.2 Material Safety Specifications of Dust Layers (G. Zwahlen).- 4.2.1 Flammability.- 4.2.2 Burning Behavior.- 4.2.2.1 Combustibility Test at Room Temperature.- 4.2.2.2 Combustibility Test at Elevated Temperature.- 4.2.2.3 Burning Rate Test.- 4.2.3 Deflagration.- 4.2.3.1 Screening Test for Deflagration.- 4.2.3.2 Laboratory Test for Deflagration.- 4.2.4 Smolder Temperature.- 4.2.4.1 Determination of the Smolder Temperature.- 4.2.5 Autoignition.- 4.2.5.1 Determination of the Relative Autoignition Temperature, as per Grewer.- 4.2.5.2 Hot Storage Test in the Wire Mesh Basket.- 4.2.6 Exothermic Decomposition.- 4.2.6.1 Determination of the Exothermic Decomposition Temperature in an Open Vessel, as per Lutolf.- 4.2.6.2 Determination of an Exothermic Decomposition in an Oven Purged with Nitrogen, as per Grewer.- 4.2.6.3 Differential Thermal Analysis.- 4.2.6.4 Determination of an Exothermic Decomposition Under Choked Heat Flow.- 4.2.7 Explosibility.- 4.2.7.1 Impact Sensitivity.- 4.2.7.2 Friction Sensitivity.- 4.2.7.3 Thermal Sensitivity.- 4.3 Material Safety Specifications for Dust Clouds Describing the Explosion Behavior.- 4.3.1 Combustible Dusts.- 4.3.1.1 Preliminary Remarks.- 4.3.1.2 Particle Size Distribution.- 4.3.1.3 Explosibility.- 4.3.1.4 Explosible Limits.- 4.3.1.5 Explosion Pressure Versus Explosion Violence.- 4.3.2 Flock.- 4.3.2.1 Preliminary Remarks.- 4.3.2.2 Explosible Limits.- 4.3.2.3 Explosion Pressure/Violence of Explosion.- 4.3.3 Hybrid Mixtures.- 4.3.3.1 Preliminary Remarks.- 4.3.3.2 Explosible Limits.- 4.3.3.3 Explosion Pressure /Violence of Explosion.- 4.3.4 Conclusions.- 4.4 Safety Characteristics of Airborne Dust Describing the Ignition Behavior.- 4.4.1 Minimum Ignition Energy.- 4.4.1.1 Preliminary Remarks.- 4.4.1.2 Apparatus for the Determination of the Minimum Ignition Energy.- 4.4.1.3 Ignition Behavior of Combustible Dusts.- 4.4.1.4 Ignition Behavior of Flock.- 4.4.1.5 Ignition Behavior of Hybrid Mixtures.- 4.4.1.6 Conclusions.- 4.4.2 Ignition Temperature.- 4.4.2.1 Preliminary Remarks.- 4.4.2.2 Apparatus for Temperature Determination.- 4.4.2.3 Ignition Effectiveness of a Glowing Coil.- 4.4.2.4 Conclusions.- 4.5 Safety Characteristics of Airborne Dusts Describing the Course of an Explosion in Pipelines.- 5 Protective Measures Against the Occurrence and Effects of Dust Explosions.- 5.1 Preliminary Remarks.- 5.2. Preventive Explosion Protection.- 5.2.1 Preliminary Remarks.- 5.2.2 Prevention of Explosible Dust/Air Mixtures.- 5.2.3 Prevention of Dust Explosions by Using Inert Matter.- 5.2.3.1 Admixture of Nitrogen.- 5.2.3.1.1 Preliminary Remarks.- 5.2.3.1.2 Combustible Dusts.- 5.2.3.1.3 Hybrid Mixtures.- 5.2.3.1.4 UseofVacuum.- 5.2.3.1.5 Admixture of Solids.- 5.2.4 Prevention of Effective Ignition Sources.- 5.2.4.1 Preliminary Remarks.- 5.2.4.2 Mechanically Generated Sparks.- 5.2.5 Hot Surfaces/Autoignition.- 5.2.6 Static Electricity.- 5.2.7 Conclusions.- 5.3 Explosion Protectio'n Through Design Measures.- 5.3.1 Preliminary Remarks.- 5.3.2 Explosion Pressure-resistant Design for the Maximum Explosion Pressure.- 5.3.2.1 Explosion Pressure-resistant Design.- 5.3.2.2 Explosion Pressure Shock-resistant Design.- 5.3.3 Explosion Pressure-resistant Design for a Reduced Maximum Explosion Pressure in Conjunction with Explosion Pressure Venting.- 5.3.3.1 Preliminary Remarks.- 5.3.3.2 Explosion Pressure Venting of Vessels.- 5.3.3.3 Explosion Pressure Venting of Elongated Vessels (Silos).- 5.3.3.4 Explosion Pressure Venting of Pipelines.- 5.3.4 Explosion-resistant Construction for Reduced Maximum Explosion Pressure in Conjunction with Explosion Suppression.- 5.3.5 Technical Diversion or Arresting of Explosions.- 5.3.5.1 Preliminary Remarks.- 5.3.5.2 Extinguishing Barrier.- 5.3.5.3 RotaryAir Locks (Rotary Valves).- 5.3.5.4 Rapid-Action Valves: Gate or Butterfly Type.- 5.3.5.5 Rapid-Action Valve: Float Type.- 5.3.5.6 Explosion Diverter.- 5.3.6 Conclusions.- 6 Concluding Remarks.- 7 Acknowledgements.- 8 Appendix.- 8.1 Explosion Pressure Venting.- 8.1.1 Vessel: Area Determination by Calculation or Nomogram.- 8.1.2 Elongated Vessels (Silos).- 9 References.- 10 Symbols and Abbreviations.- 11 Conversion Factors.- 12 Subject Index.

Overview of dust explosibility characteristics

Abstract: This paper is an overview of and introduction to the subject of dust explosions. The purpose is to provide information on the explosibility and ignitability properties of dust clouds that can be used to improve safety in industries that generate, process, use, or transport combustible dusts. The requirements for a dust explosion are: a combustible dust, dispersed in air, a concentration above the flammable limit, the presence of a sufficiently energetic ignition source, and some confinement. An explosion of a fuel in air involves the rapid oxidation of combustible material, leading to a rapid increase in temperature and pressure. The violence of an explosion is related to the rate of energy release due to chemical reactions relative to the degree of confinement and heat losses. The combustion properties of a dust depend on its chemical and physical characteristics, especially its particle size distribution. In this paper, the explosion characteristics of combustible dusts will be compared and contrasted with those of flammable gases, using methane as an example. These characteristics include minimum explosible concentration, maximum explosion pressure, maximum rate of pressure rise, limiting oxygen concentration, ignition temperature, and amount of inert dust necessary to prevent flame propagation. The parameters considered include the effects of dust volatility, dust particle size, turbulence, initial pressure, initial temperature, and oxygen concentration. Both carbonaceous and metal dusts will be used as examples. The goal of this research is to better understand the fundamental aspects of dust explosions.

Coal dust explosibility

Abstract: This paper reports US Bureau of Mines (USBM) research on the explosibility of coal dusts. The purpose of this work is to improve safety in mining and other industries that process or use coal. Most of the tests were conducted in the USBM 20 litre laboratory explosibility chamber. The laboratory data show relatively good agreement with those from full-scale experimental mine tests. The parameters measured included minimum explosible concentrations, maximum explosion pressures, maximum rates of pressure rise, minimum oxygen concentrations, and amounts of limestone rock dust required to inert the coals. The effects of coal volatility and particle size were evaluated, and particle size was determined to be at least as important as volatility in determining the explosion hazard. For all coals tested, the finest sizes were the most hazardous. The coal dust explosibility data are compared to those of other hydrocarbons, such as polyethylene dust and methane gas, in an attempt to understand better the basics of coal combustion.

Dust explosions in spherical vessels: The role of flame thickness in the validity of the ‘cube-root law’

Abstract: A well known limitation of the ‘cube-root law’ is that it becomes invalid when the flame thickness is significant with respect to the vessel radius. In the literature, flame thicknesses in dust-air mixtures ranging from 15 to 80 cm have been reported, which exceed the radii of the 20 litre sphere and the 1 m3 vessel. Therefore, we have developed a model (the three-zone model) for the pressure evolution of confined dust explosions in spherical vessels which takes the flame thickness into account. The pressure-time curves that are generated with this model show a good resemblance with those measured in practice. It is shown by numerical simulations that the maximum rate of pressure rise can be normalized with respect to the vessel volume as well as to the flame thickness and that the ‘cube-root law’ becomes inaccurate for relative flame thicknesses exceeding 1%. Furthermore, the actual burning velocity and the flame thickness during real dust explosions can be obtained by fitting the model to the experimental pressure-time curve.