Pressure explosion

The pressure developed by decomposition of acetylene in a closed container depends not only on the initial pressure (or more precisely, density), but also on whether the flame propagates as a deflagration or a detonation, and on the length of the container. For acetylene at room temperature and pressure, the calculated explosion pressure ratio, / initial > deflagration and ca 20 for detonation (at the Chapman-Jouguet plane). At 800 kPa (7.93... 

The measured explosion pressure ratio for deflagration in a container only a few diameters in length approaches the theoretical value often it is about 10. However, in a pipe hundreds or thousands of diameters in length, deflagration may cause very tittle pressure rise because only a small fraction of the contents is hot at any time. 

The energy required to initiate an explosion and the maximum explosive pressure developed by a number of polyester—epoxy powder coatings has been studied in some detail (89). The variables studied included composition, level and type of pigmentation, particle size, and concentration in air. The lowest MEG for unfilled and unpigmented powders was 33—35 g/m. ... 

FIG. 26-30 Siipp ression of explosions, Pressures in an ethylene explosion and a sodium bicarbonate suppressed ethylene explosion, Tests conducted by Fike Corp, in a 1-m vessel. Ethylene concentration = 1,2 times stoichiometric concentration for combustion, (dp/dt)e = 169 bar/s (2451 psi/s), = reduced explosion pressure = 0,4 bar gauge (5,8 psig), (F/om Chatrathi, Explosion Testing, Safety and Technology News, vol. 3, issue 1, Pike Cotp., 1.98.9, hy permission. )... 

Pied = maximiim explosion pressure during venting, bar g Pstat = vent closure release pressure, bar g V = vessel volume,... 

For apphcation of Eq. (26-48), x should not exceed 300 m (984 ft). The reason for selec ting 100 percent, instead of the upper flammable limit (UFL), in the equation for Vj is that in an incipient explosion vapor above the UFL may be mixed with additional air and, thereby, contribute to explosion pressure. 

The strength of the protected vessels or apparatus may be either explosion pressure resistant or explosion pressure shock resistant. 

Despite the use of explosion-pressure-resistant equipment for the full explosion pressure or other design measures outlined later, everything possible must be done to prevent effective ignition sources, because loss of product and interruption of production are equally undesirable. 

Containment (Explosion-Pressure-Resistant Design for Maximum Explosion Overpressure) An explosion-resistant construction is understood to mean the possibihty of designing vessels and equipment for the full maximum explosion ove (pressure, which is generally of the order P = 9 bar. The explosion-resistant vessel can then be designed as explosion pressure resistant or explosion pressure shock resistant. This protective measure is generally employed when small vessel volumes need to be protected, such as small filter units, fluidized-bed dryers, cyclones, rotaiy valves, or mill housings. 

Explosion-Pressure-Resistant Design for Reduced Maximum Explosion Overpressure with Explosion Suppression Explosion suppression systems provide one means to prevent the buildup of an inadmissibly high pressure, which is the consequence of explosions of combustible material in vessels. They operate by effectively extinguishing explosion flames in the initial stage of the explosion. An explosion of combustible material can generally be regarded as successfully suppressed when the maximum explosion overpressure can be lowered to a reduced explosion overpressure of not more than 1 bar (see Fig. 26-40). 

Minimum ignition energy (mj) Maximum explosion pressure (psi) " Maximum rate of pressure rise. (psi/s) Maximum oxygen concentration to preyent ignition (% by volume)... 

It is more likely than a PR valve to be effective in relieving an explosion pressure. 

These devices are tested only for internal explosions and not for external explosions pressurizing the devices from the outside. As an example, a factory-sealed push-button start/stop station connected to an explosion-proof motor starter cannot suffice as a seal for the motor starter conduit entry. A separate seal must be installed at the point of conduit entry. 

An explosion pressure, is tlie pressure in excess of the initial pressure at wliich the explosii e mixture is ignited. The rate of pressure rise is represented by dP/dt, a pressure cliange witli respect to time. Tliis is a measure of tlie speed of... 

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. 

Failure followed by inunediate combustion Runaw ay chemical reaction before failure Runaway nuclear reaction before failure BLEVEs (boiling liquidexpanding vapor explosion pressure vessel containing a flash-evaporating liquid) External Heating Immediate combustion after release No combustion after release... 

The maximum explosion pressure is a function of and is directly proportioiuil to die initial pressure. Blast waves are pressure waves of finite amplitude tliat are generated in air by a rapid release in energy and an instantaneous rise in pressure. The most conunon plant explosion types eiicomitered in iiidustiy are chemical, nuclear, expanding vapors, and pressurized gas. 

Rupture disks may be used to satisfy the requirements of the code for conditions such as corrosion and polymer formations, which might make the safety/relief valve inoperative, or where small leakage by a safety valve cannot be tolerated. They are particularly helpful for internal explosion pressure release. 

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