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Firelock Valves Dust Explosion

  1. Rotary valve passive isolation engineering calculations report (detailed)
  2. Baum Pneumatics rotary valve firelock engineering design Report
  3. Feeder chute dust explosion calculation results

feeder-chute-spec-temp

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feeder-chute-dust-explosion.gif

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passive isolation calculations for firelock feeders

Below is a short summary of BAUM PNEUMATICS research into the maximum safe clearance in firelock feeders as per NFPA69.

These calculations are based on mathematical model of a dust cloud explosion with chemistry, heat transfer, particle interaction and fluid flow implemented into a Computational Fluid dynamics (CFD) solver and is verified against real world test results on a 20L Siwek apparatus for explosion testing (ASTM E1226 − 12a), we used the verified model on 3D feeder assembly to assess flame quenching distances based on vane thickness, clearance. etc. and to calculate max pressure and dp/dt exerted during explosion. Stress analysis of the housing structure is performed separately based on recommended Pred (the parameter that governs venting area calculations), we use the explosion model to simulate how far we can safely go on clearances, and still decouple a flame (0.012″ maximum, per side). the model can also be used to assess effectiveness of vent area calculation for different hazard scenarios.

  • Dried all fine SPF wood dust with Kst of 202.3 was used in calculations
  • Wood dust size, explosion characteristics, and heat transfer was considered in the calculations
  • Particle motion and Fluid-Particle interactions were calculated to account for redistribution of charge due to explosion

The results showed that the trade-off between clearance and blade thickness can be used to maintain firelock behavior of the feeders.

The maximum safe clearance of 0.012 (in) was calculated above which the clearance is unlikely to stop the flame from propagating.

NFPA Recommended Clearance of 0.0079 (in) or 0.2 (mm)

Flame does not propagate through Blade/ Body clearance! Blade thickness is 0.25 (in).

Calculated Maximum Allowed Clearance of 0.012 (in) or 0.3 (mm)

Blades can successfully stop flame propagation through the 0.012 (in) clearance! Blade thickness is 0.5 (in).

Failed Calculated Clearance of 0.014 (in) or 0.35 (mm)

Second explosion occurs at right hand side. Clearance of 0.014 (in) fails to stop flame propagation. Blade thickness is 0.5 (in).

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Simple methods of dust management

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