Vapor maximum explosion pressure

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. 

This is valid for the same degree of gas mixture turbulence and the same ignition source and is illustrated in Figure 7-58. Influence of the vessel shape is shown in Figure 7-56. The behavior of propane is considered representative of most flammable vapors including many solvents [54]. The maximum explosion pressure does not follow the cubic law and is almost independent of the volume of a vessel greater than 1 liter. For propane, town gas, and hydrogen, the volume relationship can be expressed ... 

When systems involving solvent vapor are considered, use the nomogram for propane/air mixtures because most comvian solvent vapors have maximum explosion pressures of 7.1 to 7.6 bar, and the Kg falls between 40 and 75 bar meter/sec (see Ref. [54]). 

FPN No. 2) The explosion characteristics of air mixtures of gases or vapors vary with the specific material involved. For Class I locations. Groups A, B, C, and D, the classification involves determinations of maximum explosion pressure and maximum safe clearance between parts of a clamped joint in an enclosure. It is necessary, therefore, that equipment be approved not only for class but also for the specific group of the gas or vapor that will be present. 

Flammability limits for vapors are determined experimentally in a specially designed closed vessel apparatus (see Figure 6-14 on page 255). Vapor-air mixtures of known concentration are added and then ignited. The maximum explosion pressure is measured. This test is repeated with different concentrations to establish the range of flammability for the specific gas. Figure 6-5 shows the results for methane. 

Figure 6-16 Pressure rate and maximum explosion pressure as a function of vapor concentra-...

A small quantity of liquid ethanol is placed in an explosion bomb together with twice the theoretical amount of oxygen at 25 C and 1 atm. pressure. Taking the heat of vaporization of the alcohol as 9.5 kcal. mole at 25 C, calculate the maximum explosion temperature and the maximum explosion pressure, assuming... 

The maximum explosion pressure of most gases and vapors in a mixture with air is within the range 7.5-10 bar at atmospheric pressure. It increases proportionally with the starting pressure. This means that if there is an increase in the starting pressure from one to 10 bar, the maximum explosion pressure will reach... 

The maximum explosion pressure, denoted and expressed in Pa is the peak value of the time-dependent pressure measured in a closed container upon deflagration of an explosive mixture of defined composition. The maximum explosion pressure is the maximum value of the explosion pressure determined by varying the composition of the mixture. The explosion pressure of gases and vapors is determined in resting mixtures according EN13673-1. 

The size of the vapor cloud formed by the jet increases with mass flow rate at the orifice and hence with orifice size. As a result the size of the central region of the e2q)losion ("explosion center") where the maximum explosion pressure occurs increases also. This size is the relevant parameter for the energy scaling of overpressure decay with distance outside the vapor cloud. 

Vapor cloud explosions in partially confined areas with obstacles exhibit a further increase of the maximum explosion pressure compared to unconfined explosions due to additional turbulent flame acceleration at obstacles. In experiments we found an increase up to a factor of four and a scaling behavior similar to that of the unconfined case. 

The maximum explosion pressure derived from the p-x-diagram increases with orifice diameter. This is shown in Fig. 6, line a). Line a) exhibits an almost linear relationship between maximum explosion pressure in the vapor cloud and orifice diameter for the unconfined explosion after supercritical jet release of propane. Line b) in Fig. 

Chapter I, Vapor Cloud Explosions, presents recent research on the safety hazards and explosion damage potential associated with the accidental release of combustible vapor clouds. Stock et al. report on experiments with explosive clouds formed by turbulent jets of propane, natural gas, or hydrogen released through various-sized orifices. They found significant scale effects, e.g., the maximum explosion pressure increased with the size of the vapor cloud and with the turbulence level in the jet. Desrosiet and coworkers have experimented with asymmetric explosions of vapoi clouds. They present results on how the ignition asymmetry of a hemi-... 

Toluene is a notoriously poor electrical conductor even in grounded equipment it has caused several fires and explosions from static electricity. Near normal room temperature it has a concentration that is one of the easiest to ignite and, as previously discussed, that generates maximum explosion effects when ignited (Bodurtha, 1980, p. 39). Methyl alcohol has similar characteristics, but it is less prone to ignition by static electricity because it is a good conductor. Acetone is also a good conductor, but it has an equihbrium vapor pressure near normal room temperature, well above UFL. Thus, acetone is not flammable in these circumstances. 

A confined explosion occurs in a confined space, such as a vessel or a building. The two most common confined explosion scenarios involve explosive vapors and explosive dusts. Empirical studies have shown that the nature of the explosion is a function of several experimentally determined characteristics. These characteristics depend on the explosive material used and include flammability or explosive limits, the rate of pressure rise after the flammable mixture is ignited, and the maximum pressure after ignition. These characteristics are determined using two similar laboratory devices, shown in Figures 6-14 and 6-17. 

Problem A mixture of hydrogen gas and the theoretical amount of air, at 25 C and a total pressure of 1 atm., is exploded in a closed vessel. Estimate the maximum explosion temperature and pressure, assuming adiabatic conditions. In order to simplify the calculation, the mean heat capacities of nitrogen (8.3 cal. deg. " mole " ) and of water vapor (11.3 cal. deg. " mole" ), for the temperature range from 25 to 3000 C, may be used they may be regarded as independent of the (moderate) pressure. 

The hazard potential of a vapor cloud esqjlosion after turbulent jet release depends on maximum esqjlosion pressure Pmax inside the cloud and on the cloud size. For unconfined vapor cloud explosions the pressure wave measured at a distance r outside the cloud decays inversely proportional to r. The peak overpressure is proportional to the energy-scaled radius... 

Assume a continuous release of pressurized, hquefied cyclohexane with a vapor emission rate of 130 g moLs, 3.18 mVs at 25°C (86,644 Ib/h). (See Discharge Rates from Punctured Lines and Vessels in this sec tion for release rates of vapor.) The LFL of cyclohexane is 1.3 percent by vol., and so the maximum distance to the LFL for a wind speed of 1 iti/s (2.2 mi/h) is 260 m (853 ft), from Fig. 26-31. Thus, from Eq. (26-48), Vj 529 m 1817 kg. The volume of fuel from the LFL up to 100 percent at the moment of ignition for a continuous emission is not equal to the total quantity of vapor released that Vr volume stays the same even if the emission lasts for an extended period with the same values of meteorological variables, e.g., wind speed. For instance, in this case 9825 kg (21,661 lb) will havebeen emitted during a 15-min period, which is considerablv more than the 1817 kg (4005 lb) of cyclohexane in the vapor cloud above LFL. (A different approach is required for an instantaneous release, i.e., when a vapor cloud is explosively dispersed.) The equivalent weight of TNT may be estimated by... 

The data are collected and analyzed in the same fashion as for the vapor explosion apparatus. The maximum pressure and the maximum rate of pressure increase are determined, as well as the flammability limits. 

FIG. 26-9 Maximum pressure as a function of volume percent concentration for methane in air in a 20-L test sphere. The initial temperature and pressure are 25°C and 1 atm. The stoichiometric concentration is 9.51% methane. [C. V. Mashuga and D. A. Crowl, Application of the Flammability Diagram for Evaluation of Fire and Explosion Hazards of Flammable Vapors," Process Safety Progress, vol. 17, no. 3 copyright 1998 American Institute of Chemical Engineers (AlChE) and reproduced with permission.]... 

A critical safety issue of using diesel-ethanol blends relates to flashpoint and flammability. E-diesel blends containing 10-15% ethanol have the vapor pressure and flammability limits of ethanol. This means that ethanol concentrations in enclosed spaces such as fuel storage and vehicle fuel tanks are flammable over the temperature range 13-42 °C. Thus, there are higher risks of fire and explosion than with diesel fuel, or even gasoline. Other vehicle performance-related concerns are (a) a decreased maximum power (b) an increased incidence of fuel pump vapor lock and (c) a reduced fuel pump and fuel injector life due to the decreased lubricity of ethanol. 

Finally, it has often been stated that the maximum pressure which could exist at the source of a superheat explosion is that equivalent to the vapor pressure of the cold liquid at its superheat-limit temperature. For most organic liquids this value would be 30 bar. For pure water, it rises to 90 bar. For concentrated salt solutions, much higher values are possible. 

K, there is a significant increase in pressure and values of 30 bar (or higher) were recorded. Assuming that the water-R-22 interface temperature had to attain the superheat-limit value before an explosion occurred, these data are in remarkable agreement with in Table XVI. Also shown in Fig. 11 is the vapor pressure of R-22 calculated for the interface temperature between the water and the saturated R-22 (232 K). Essentially all measured pressures fall below this curve, and this suggests that the maximum pressure transient corresponds to the vapor pressure determined in this manner. (Another limit could be chosen as the critical pressure of R-22, 50 bars, but this value significantly exceeds any measured pressure.)... 

At the top of the compression stroke in one of the cylinders of an automobile engine (that is, at the minimum gas volume), the volume of the gas-air mixture is 150 mL, the temperature is 600 K, and the pressure is 12.0 atm. The ratio of the number of moles of octane vapor to the number of moles of air in the combustion mixture is 1.00 80.0. What is the maximum temperature attained in the gas if octane burns explosively before the power stroke of the piston (gas expansion) begins The gases may be considered to be ideal, and their heat capacities at constant pressure (assumed to be temperature-independent) are... 

---