Dust venting nomographs

Dust venting nomographs, 514-520 Calculations, 513-517 Dust, mist calculations, 226-236 Brownian movement, 226. 236 Drag coefficients, chart, 235 Intermediate law, 226 Newton s law, 226, 228... 

Figure 7-65A. Venting nomograph for dusts, Pg,at = 0-1 bar ga. Reprinted with permission, NFPA 68-1988, Deflagration Venting, (1988) National Fire Protection Association, Quincy, MA 02269. See note Figure 7-63A.

Venting, dusts, (deflagration), nomograph, API, 514-520 Relief valves, 400 Code requirements, 415, 420 Installation, 422, 429-434 Safety-relief, 400 Relieving pressure, 411-417 Resistance coefficient, K, (flow), 71, 72 Flow coefficient, Q, 81, 83 Pipe sizing, 83, 84, 86 Sudden contraction, 80 Sudden enlargement, 80 Tables/charts, 73-76, 77, 78-80 Valves, 81... 

The dust hazard class, Rst, vessel volume and strength, and the relieving pressure of the vent closure are the key components of the relief determination using the nomographs [27]. Although stated by Ref. [27] to be non-exact... 

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. 

The experimental approach is to produce nomographs and equations for calculating vent area to relieve a given overpressure. The NFPA 68 guide (NFPA, 1994) also lists tables of experimental data for gases, liquids, and dusts that show P and dP/dt. The experimental data used must be representative of the specific material and process conditions, whenever possible. 

Dust Explosions. Bartknecht (1989), Lees (1986), and NFPA 68 (1994) contain a considerable amount of dust explosion test data. The nomographs in NFPA 68 can be used to estimate the pressure within a vessel, provided the related functions of vent size, class of dust (St-1,2, or 3), otK, vessel size, and vent release pressure are known. 

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