POWER November 2015 - 46

SAFETY
Minimizing Coal Dust Combustion
Hazards: Lessons from Laramie
River Station
Coal dust combustion events injured employees and damaged equipment at
Laramie River Station in May 2013. Any dust-filled facility could consider
implementing some of the plant's corrective actions to reduce the risk of
experiencing a similar incident.
Basin Electric Power Cooperative
W
hen Laramie River Station (LRS),
near Wheatland, Wyo., was built
nearly 35 years ago, it was stateof-the-art.
Constructed by the Missouri Basin
Power Project (MBPP), the plant has three
570-MW coal-based units: Unit 1 began operating
in 1980, Unit 2 in 1981, and Unit 3
in 1982.
The MBPP is made up of six organizations:
Basin Electric Power Cooperative
(BEPC), Tri-State Generation and Transmission
Association, Western Minnesota Municipal
Power Agency, Lincoln Electric System,
Heartland Consumers Power District, and
Wyoming Municipal Power Agency. BEPC
is the plant's operator.
LRS includes a coal system consisting
of 23 conveyors with nearly 25,000 feet of
conveyor belt, 16 dust collectors, 25 feeders,
21 main plant silos and pulverizers,
three coal yard silos, and a rotary dumper.
The entire coal supply system extends more
than one mile.
It's a massive system and one that has
had consistent and constructive maintenance
throughout its history. However, events at LRS
in the spring of 2013 caused BEPC to evaluate
and make changes to how the coal system was
inspected and operated thereafter.
Developing a Team
On two separate occasions in May 2013, coal
dust combusted within the system, resulting
in injuries to three employees and forcing repairs
to Units 1 and 2. BEPC employees and
plant management reacted quickly to ensure
similar incidents would never occur again.
That summer, representatives from the Operations,
Maintenance, Planning, and Safety
and Engineering departments met to form the
LRS Coal System Focus Team.
" These team representatives were people
from throughout the employee ranks with the
46
ability to effect real, positive change, " said
Brian Larson, LRS plant manager.
During its first meeting, the focus team
declared that its mission was to improve coal
system safety and reliability using a combination
of technology and cleaning to meet
respirable dust level requirements prescribed
by the Combustible Dust National Emphasis
Program (NEP).
" The team realized it would take a combination
of major capital projects, maintenance
technique refinements, and operation procedure
adjustments, " Larson said. " There was
no 'silver bullet.' "
During the second meeting, the team split
up the coal system into eight areas and conducted
a criticality analysis using 11 different
criteria, including generation impact, risk
exposure, dusting (Figure 1), and reliability.
The plant's cascades/main plant silos area
became the team's primary focus.
Through the first eight months, the focus
team worked to gain the knowledge needed
to make an impact on the LRS coal system.
To support the focus team's work and share
knowledge, BEPC formed the " Co-op Wide
Dust Team. " This team consisted of personnel
from all of BEPC's coal-based facilities-
LRS, Dry Fork Station, Antelope Valley
Station, Leland Olds Station, and subsidiary
Dakota Gasification Co.'s Great Plains Synfuels
Plant. The team met quarterly, rotating
between the different facilities to study and
learn the different coal systems, share knowledge,
and cultivate ideas.
In February 2014, BEPC contracted
CoalTech Consultants Inc. to conduct an assessment
of the LRS coal system. The focus
team also joined the Powder River Basin
Coal Users' Group (PRBCUG) and sent a
few members to the PRBCUG annual meeting
in 2014 to collect more information.
With the initial analysis complete and the
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POWER | November 2015
broad knowledge gained by studying coal
systems used throughout the BEPC fleet and
elsewhere, the time had come to implement
some changes.
Upgrading Main Plant Cascades
and Silos
To prevent coal dust combustion within a
bunker, the coal system focus team determined
that the plant would benefit by adding
the following:
■ An internal bunker carbon monoxide (CO)
monitoring system to identify undesired
combustion in its early stages.
■ A fixed internal fire suppression system
to suppress undesired combustion with no
risk exposure.
■ A fixed internal wash-down system to
prevent offline combustion events in an
empty bunker.
BEPC engineers tackled the CO monitoring
project by investigating an air-sampling
1. Gauging dust levels. A surface film
thickness gauge is used to measure coal dust
accumulation and ensure that levels meet
National Environmental Policy Act standards.
Courtesy: Basin Electric Power Cooperative
http://www.powermag.com
POWER November 2015

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