POWER March 2012 - 30

PLANT DESIGN
Coping with Coal Dust
Plants can no longer sweep coal dust under the rug and ignore the health and safety
hazard it presents, because a single spark can cause a dust explosion that could put
a plant out of service, perhaps permanently. Managing dust in a power plant begins
with good housekeeping, followed by retrofits using properly designed equipment.
By Daniel Mahr, PE, Energy Associates, PC and Michael A. Schimmelpfennig, PE, Ameren Missouri
Courtesy: Chemical Safety Board
O
n February 7, 2008, at about 7:15 p.m.,
a series of huge explosions and fires
occurred at the Imperial Sugar refinery
northwest of Savannah, Georgia, causing
14 deaths and injuring 38 others, 14 seriously.
The facility, which converted raw cane sugar
into granulated sugar, had a material-handling
system that included the familiar railcar unloader,
belt conveyors, bucket elevators, and
silo storage. The explosions were fueled by
massive accumulations of combustible sugar
dust throughout the packaging building.
The initiating explosion occurred in the
enclosed belt conveyor below the silos.
That explosion lofted the dust accumulated
on floors and elevated surfaces throughout
the buildings. Secondary explosions and
fires heaved thick concrete floors and collapsed
brick walls, blocking stairwells and
exit routes. The destruction, as shown in the
photo above, was complete.
The U.S. Occupational Safety and
Health Administration (OSHA) reports
that between 1980 and 2008, 422 combustible
dust incidents were reported across
30
Five Requirements for a Dust Explosion
The dust explosion pentagon (Figure 1)
takes its first three elements from the familiar
" fire triangle " and adds two more.
If one of these five elements is missing,
an explosion cannot occur-but a fire
may still occur: combustible dust (fuel),
an ignition source (heat), oxygen in air
(oxidizer), dispersion of dust particles in
sufficient quantity and concentration, and
confinement of the dust cloud.
A flame need not be the ignition source.
Dry powders can build up static electricity
charges when subjected to the friction
of transfer, conveyor belt friction on pulleys
and idlers, and mixing operations.
Adequate precautions should be provided,
such as electrical grounding and bonding,
or inert atmospheres.
1. The coal dust explosion pentagon. Source: National Fire Protection Association
Ignition
Dispersion of dust particles
Confinement of dust cloud
Combustible dust
Oxygen in air
www.powermag.com
POWER | March 2012

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POWER March 2012

Table of Contents for the Digital Edition of POWER March 2012

Contents
POWER March 2012 - Cover1
POWER March 2012 - Cover2
POWER March 2012 - Contents
POWER March 2012 - 2
POWER March 2012 - 3
POWER March 2012 - 4
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