Explosion pressure, dust explosions

Explosions in the petrochemical industry can be classified into four basic types Vapor Cloud Explosions, Pressure Vessel Explosions, Condensed Phase Explosions, and Dust Explosions. Baker 1983 and CCPS Explosion Guidelines also provide information for characterizing some of these types of explosions. 

Hartmann and associates (24G-28G) have conducted a great deal of experimental work on the combustion of dust dispersions. Explosions can be caused by particles as large as 700 microns. Many different dusts, including rosins, metal powders, and coal, have been investigated. Zirconium powder is the most explosive. Coal dust explosibility is closely associated with its volatile combustible content. Representative pressure rises as high as 75 pounds per square inch in an enclosed volume are reported. In all cases this maximum pressure is attained at mixture strengths well beyond stoichiometric. 

Definition of Dnst Explosion A dust explosion is the rapid combustion of a dust cloud. In a confined or nearly confined space, the explosion is characterized by relatively rapid development of pressure with a flame propagation and the evolution of large quantities of heat and reaction products. The required oxygen for this combustion is mostly supplied by the combustion air. The condition necessary for a dust explosion is a simultaneous presence of a dust cloud of proper concentration in air that will support combustion and a suitable ignition source. 

The equipment in which the dust is handled or stored should be designed to contain the pressure resulting from an internal explosion. Most dusts show maximum pressures of ca 345—700 kPa (50—100 psi) however, the rate of pressure rise changes from ca 700 to 70,000 kPa/s (100—10,000 psi/s). Equipment-containment design can be coupled with explosive-venting design for the equipment and the building. 

For example, in rotary vacuum dryers it is possible to prevent the formation of explosible dust-air mixtures by setting and monitoring a certain partial vacuum (negative pressure). This pressure value must be determined by experiment for each type of dust. With pressures of less than O.I bar, in general, hazardous effects of dust explosions need not be anticipated. If the vacuum system malfunctions, the partial vacuum must be released by inert gas and the instaUation shut down. 

Tlie maximum explosion pressure is a function of the initial pressure, P. If tlie initial pressure is increased by a factor of 2, tlie maximum explosion pressure and the maximum pressure rise will also increase by a factor of about 2 for both naminable gas and dust mixtures. Wlien tlie initial pressure is less tlian 10 mbar, il is usually no longer possible to Iwve an explosion. 

Compressed air lines are very susceptible to a combustion gciienition e.xplosion, fueled by oil or cliar on tlie pipe walls. E.xplosions in pipelines c ui cause considerable damage. Pipelines witliin wliich gas, vapor, or dust explosions can occur must be designed to have sufficient mechanical streiigtli to withstand pressure or stress beyond tliat required by the application. 

There are several sources of potential danger in catalytic hydrogenations these are failure of equipment because of excessive pressures, solvent fires, explosions and fires from mixtures of hydrogen in air, and, with finely divided carbon supports, dust explosions. None of these should cause concern, for all may be avoided easily. 

Using a nomograph requires only the vessel volume in meters, selecting the dust class. St-1, St-2 or St-3 from Table 7-28. Using Tables 7-29 or 7-30 select the Kst value determined experimentally. The reduced pressure, Pfed. (maximum pressure actually developed during a vented deflagration, termed reduced explosion pressure) must not exceed strength of vessel (see earlier discussion) and the Psut, i.e., the vent device release pressure. Note that the static activation pressure, Pjj, must be determined from experimental tests of the manufacture of relief panels such as rupture disks. 

Unfortunately, rate of pressure rise and maximum explosion pressure listed in Table 7-31 are subject to uniqueness of the test conditions and are the function of particle size, dust concentration and uniformity, available... 

Donat, C., Selecting and Dimensioning of Pressure Relief Devices for Dust Explosions, Staub-Reinhaltung der Luft, 31, No. 4, 1971, pp. 17-25. 

Dowtherm(R) pressure drop, charts, 94,113 Draft tubes, mixing, 309, 313 Dust clouds, 517 Dust explosions, 513 Calculations, 513 Dust separator, applications, 278 Characteristics, 234 Table, 232... 

Explosion calculations, 499-504 Estimating destruction, 501 Overpressure, 502 Pressure piling, 501, 504 Relief sizing, 505 Scaled distance, 502, 503 Schock from velocity, 503 TNT equivalent, 499-504 Explosion characteristics of dusts, 515 Explosion suppression, 518 Explosion venting, gases/vapors, 504 Bleves, 504 Explosions, 482 Blast pressure. 496 Combustion, 482 Confined, 482 Damage, 498-501 Deflagration, 482 Detonation, 483... 

Jacobson, A.R. Cooper J. Nagy, Exploability of Metal Powders , BuMines Rept 6516 (1964) 3) J. Nagy, A.R. Cooper J.M. Stuper. Pressure Develdpment in Laboratory Dust Explosions , BuMines Rept 6561 (1964). 4) J. Nagy, H.G. 

A confined explosion occurs when there is a rapid combustion of a fuel and an oxidizer inside an enclosure (e.g., building, vessel, or duct), developing sufficient pressure to cause the enclosure to rupture. Examples of confined explosions include gas or dust explosions inside buildings, storage tanks, or process equipment. 

Other references include CCPS Guidelines for Engineering Design for Process Safety (Ref. 78) NFPA 68 Venting of Deflagrations (Ref. 79) NFPA 69 Explosion Prevention Systems (Ref. 80) NFPA 654 Prevention of Fire and Dust Explosions in the Chemical Dye, Pharmaceutical, and Plastics Industries (Ref. 81) and VDI 3673 Pressure Release of Dust Explosions (Ref. 82). 

VDI3673. Pressure Release of Dust Explosions Verein Deutscher Ingenieure. Kommission Reinhaltung der Luft, Dusseldorf VDI Verlad GmbH, Dussel-dorf. 

It decomposes explosively at the m.p., 98°C [1], and shows a high rate of pressure increase on exothermic decomposition [2], The heat of decomposition was determined as 1.34 kJ/g by DSC, and Taii24 was determined as 88°C by adiabatic Dewar tests, with an apparent energy of activation of 223 kJ/mol [3], When finely divided, it also shows significant dust explosion hazards, with a maximum explosion pressure of 7.75 bar, and a maximum rate of pressure rise above 680 bar/s [4], Further work on homogeneous decomposition under confinement has been reported [5],... 

Dust explosions and spontaneous ignition hazards for calcium stearate and related plastics additives are detailed and discussed [1], A maximum pressure increase of 6.6 bar and a maximum rate of rise above 680 bar/s have been recorded [2],... 

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