“Pressure release of duet explosions”(VDI, ) and to recommend to its When (EN ,)was released not all information from (VDI ,). Find the most up-to-date version of VDI BLATT 1 at Engineering VDI (Society of German Engineers) submitted a new version for pressure release of dust explosions in November which will replace the June edition.
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Dust Explosion49 - Free download as PDF File .pdf), Text File .txt) or read Very recently, Lunn et freezovralomi.ga extended the VDI nomographs to K,, values as. The results from the dust filter explosion experiments with realistic dust cloud generation are summarized in Table 1, together with the corresponding VDI . two dusts, using an artificial “static” dust cloud generation method, very similar to that used in the experiments being the basis of the VDI ( edition).
In this case even the entire silo roof may in some situations be insufficient for venting, and more sophisticated measures may have to be taken to control dust explosions in the silo.
Further data for a 8.
Comparison with maximum explosion pressures predicted for 3. Data from Eckhoff, Alfert and Fuhre3 nitrocellulose flame. The result obtained for silicon dust ignited by a silicon dust flame emphasizes the different nature of initiation and propagation of metal dust flames, as compared with flames of organic dusts Figure 21 shows the same experimental filter explosion data as Figure 10, but plotted as functions of measured in the Hartmann bomb.
Figure 11 also gives the corresponding correlations predicted by three different vent sizing methods based on Hartmann bomb tests. Both the Swedish and the Norwegian methods are quite liberal. However, there is fair agreement with the data for silicon dust ignited by a silicon dust flame. Vent sizing procedure for the present and near future Basic approach and limitations Realistic vented dust explosion experiments, mostly conducted during the Os, have demonstrated that none of the vent sizing codes in current use are fully adequate.
It is proposed, therefore, that for the present and near future, sizing of dust explosion vents should be primarily based on the available evidence from realistic experiments.
The following suggestions presuppose that the initial pressure in the enclosure to be J. Process Ind.
The vent area requirements identified by these two sets of experiments differ by a factor of up to 5. Adequate vent sizing therefore requires that the conditions of turbulence, dust dispersion and level and homogeneity of dust concentration for the actual enclosure be evaluated in each specific case.
Cyclones Two realistic investigations have been traced32,34, and both suggest a significant vent area reduction, in relation to VDI Thus, the early investigation by Tonkin and Berlemont32, using a cyclone of 1. The recent investigation by Hayashi and Matsuda, using a smaller cyclone of 0. The situation for cyclones is similar to that for bag filters. For organic dusts belonging to group St 1, there seems to be room for a considerable vent area reduction as compared with VDI , in the range of factors of 0.
However, for metal dusts such as silicon, although there is no direct evidence from cyclone explosions with such dusts, VDI requirements should probably be followed as in the case of filters. If ignition inside the filter itself is the probable scenario no strong flame jet entering the Xilter and no significant pressure piling prior to ignition , the vent area requirements of VDI for St 1 dusts can be reduced by at least a factor of 0.
If the dust concentration in the feeding duct to the filter is lower than the minimum explosible concentration, the vent area may be reduced even more. However, in the case of some metal dusts such as silicon, primary ignition in the filter itself may be less probable and ignition will be accomplished by a flame jet entering the filter from elsewhere.
Mills The level of turbulence and the degree of dust dispersion in mills vary with the type of mill.
The most severe states of turbulence and dust dispersion probably occur in air jet mills. The experimental technique for dust cloud generation used in the experiments on which VDI is based, is likely to generate dust clouds similar to those in an air jet mill. For this reason it seems reasonable that VDI be used without modifications for sizing vents for this type of mill.
In the case of mills generating dust clouds that are less turbulent and less well dispersed, it should be possible to ease the vent area requirements, depending on the actual circumstances. In such enclosures severe flame acceleration can take place because of the turbulence produced by expansion-generated flow in the dust cloud ahead of the flame.
In extreme cases transition to detonation may occur. The MIT is an important factor in evaluating the ignition sensitivity of powders and dusts and is relevant for defining the maximum operating temperature for electrical and mechanical equipment used in dusty environments. Powder or dust samples of various sizes are dispersed into the furnace and the minimum wall temperature capable of igniting the dust cloud is determined. Minimum Ignition Temperature Test - Dust Layer The MIT-Layer test determines the lowest surface temperature capable of igniting a powder or dust when in the form of a five 5 millimeter mm or The MIT of a dust layer is used together with the MIT of a dust cloud to define the maximum operating temperature for electrical and mechanical equipment used in dusty environments.
The test involves heating a circular layer sample 5 mm thick and mm in diameter on a hot plate at constant temperature for 30 minutes. The temperature of the sample layer and the hot plate are monitored and the minimum surface temperature capable of igniting the powder or dust layer is determined.
Minimum Explosible Concentration Test The minimum explosible concentration MEC test determines the smallest concentration of material in air that can give rise to flame propagation upon ignition when in the form of a dust cloud. The test involves dispersing powder or dust samples in a vessel and attempting to ignite the resulting dust cloud with an energetic ignition source. Trials are repeated for decreasing sample sizes until the MEC is determined.
Limiting Oxygen Concentration Test The limiting oxygen concentration LOC determines the minimum concentration of oxygen displaced by nitrogen capable of supporting combustion.
An atmosphere having an oxygen concentration below the LOC is not capable of supporting combustion and thus cannot support a dust explosion. The LOC test is used to study explosion prevention or severity reduction involving the use of inert gases and to set oxygen concentration alarms or interlocks in inerted plant and vessels.
LOC testing can be performed using the Liter Sphere apparatus.
Powder or dust samples of various sizes are dispersed in the vessel and attempts are made to ignite the resulting dust cloud with an energetic ignition source.
Trials are repeated for decreasing oxygen concentrations until the LOC is determined. Notably, no consensus test method presently exists for determination of LOC. A powder or dust sample is dispersed within the sphere, ignited by chemical igniters, and the pressure of the resulting explosion is measured. The sample size is varied to determine the optimal dust cloud concentration.
The maximum pressure and rate of pressure rise are measured and used to determine the Kst value and St hazard class of the material.