Page 466 - Dust Explosions in the Process Industries

Sizing of Dust Explosion Vents 433

data from the investigation by Brown and Hanson (1933). It is felt that the experiments
of Brown and Hanson were considerably closer to the reality most often encountered in
industry than those on which the nomograph method was based. This exemplifies that
much excellent experimental work that was performed in the past an various aspects of
the dust explosion problem often seems to be overlooked by some more recent investi-
gators. The paper by Brown and Hanson indeed deserves to be read carefully even today.
The dusts used by Brown and Hanson were dried to less than 8% moisture, and it seems
reasonable to assume that their Ks, values would not have been lower than the values 75
and 100 bar ds used for comparison with the Lunn predictions. If the starch was from
corn, a Ks, of 100 bar m/s is a low estimate.
Coniparisons between “nomograph”-method predictions and data from more recent
realistic experiments are given in Section 6.2.

6.1.3
THE SWEDISH METHOD

In this method, issued by Danielson (198l), the explosion violence classification of the
dust is by (dP/dt),, from standard 1.2 liter Hartmann bomb tests (see Chapter 71, as in
the vent ratio method. Dusts are classified in three groups:
Group 1: (dPIdt),, I300 bar/s.
Group 2: 300 barIs < (dP/dt),, < 600 bar/s.
Group 3: (dPIdt),, 2 600 bark
The required vent area per unit enclosure volume is specified for each of the three
groups, but the value decreases with increasing enclosure volume. For Group 1
dusts and hinged vent panels of maximum mass 20 kg/m2, the tabular relationship
between vent area A (m2),volume V (m3>,and Pred(bar(g)) can be approximated by the
equation

For Group 2 dusts and using hinged vent covers of maximum mass 12kg/m2,the Swedish
method corresponds approximately to the equation

For enclosures of LID > 3, the Swedish method requires that the enclosure be divided into
the minimum number of fictitious subvolumes needed for all of these to have LID I3.
The required vent area for the actual enclosure is then the sum of the areas calculated for
all the fictitious subvolumes.
After the enforcement of the European Union “Atex 1OOa” Directive (see Chapter 8)
in 2003, continued use of the traditional Swedish venting guidelines will be harmonized
with common European requirements.