Prevention of Grain Elevator and Mill Explosions (1982) / Chapter Skim
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Appendix B: Dust Explosions
Appendix B: Dust Explosions
Pages 115-122
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From page 115... ...
A sample of dust in a dust holder is blown downward through a vertical furnace of specified dimensions and construction that has been heated to she initial temperature. If a sheet of flame appears at the exit of the furnace, the furnace temperature is said to be above the auto-ignition temperature of the dust l 115
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From page 116... ...
Bartknecht points out that f or vessel volumes less than approximately 20 1 iter, kSt ceases to be a constant and becomes smaller as the vessel size decreases. Thus, the rate of pressure rise observed in small vessels is less than the potential rate of pressure rise that one would observe in a large vessel (it is probable that radiative losses to the wall considerably lower the combustion rate in the smaller vessel)
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From page 117... ...
a/s ~ ~ °C) ~ ° ~ ~ J ~ (g/m3 Alfalfa meal 455 7.6 460 200 0.32 100 Cereal grass 360 3.5 550 220 0.80 200 Corn 655 41 400 250 0.04 5S Corncob grit 760 21 450 240 0.045 45 Corn dextrin pure 725 48 400 370 0.04 40 Cor ns ta r ch cause rc ia l product 745 48 380 330 0.04 45 Corns tarch through 325 mesh 790 62 390 350 0.03 40 Flax strive 560 5.5 430 230 0.08 80 Grain dust, winter wheat, corn, oats 790 38 430 230 0.03 55 Grass seed, blue 165 1.4 490 180 0.26 290 Rice 640 18 440 220 0.05 SO Rice bran 4 20 9 .0 4 90 -- - 0 .08 4 5 Safflower meal 580 20 460 210 0.025 55 Soy flour 540 5.5 540 190 0.10 60 Soy protein 660 65 520 260 0.05 35 Wheat, untreated 710 25 500 220 0.06 65 Wheat flour 655 26 380 360 0.05 50 Wheat starch, edible 690 45 420 0 .025- 45 Wheat straw 680 41 470 220 0.050 55 SOURCE: U.S.
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From page 118... ...
His approach, which is based only on the rate of pressure rise in a spherical vessel, can be'used to determine proper vent areas-for dust explosions (National Fire Protection Association 19787. EXPLOSION DYNAMICS Combustion explosions of the type that occur in grain elevators take place because a combustible mixture of grain dust (fuel)
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From page 119... ...
119 TABLE B-2 Probable Ignition Sources source No. of Facilities USD a Un known Welding E1 ectrical failure Tramp metal Fire other than welding Other foreign objects Friction, choked leg Overheated bearings identi f fed ape rk Friction sparks Li ghtning Extension cords in legs Faulty motors Static electricity Fire from slipping leg belt Elaounable vapor Smoldering grain Smoking material Fi re cracker Voltatile chemical from soybean processing External cob pile fire Heating system Gas in bin ignited Extinguishing fire Leak in gas pipe ignited Electrical control panel explosion S1 ipping conveyor belt EMRI T Datab Un known Welding Fr i ction i n e levator 1 eg Fire other than welding E1 ectri Cal Lightning M\ otors Spontaneous combustion Other fore ign objects Static electricity NOTE: Data probably are not mutually exclusive.
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From page 120... ...
The explosion produces ' a reasonably large fireball of Burning dust near the piece of process equipment and, because of vibration and.air motion ahead of the burning region, stirs up dust that was layered in the personnel area and the entire atmosphere of the area becomes combustible. This leads to a major secondary explosion in the facility.
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From page 121... ...
. National Materials Advisory Board, Classification of Dusts Relative to Electrical Equipment in Class II Hazardous Locations, Report NMAB 353-4, National Academy Press, Washington, D.C., 1982.
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