POWER October 2015 - 29

FUGITIVES CAPTURED AT
BIG STONE STATION RCD BUILDING
CASE STUDY:
At Ottertail Power (OTP-BSP), the rotary car
dumper (RCD) is the heart of Big Stone Station's
600 megawatt lignite and PRB fuel delivery system,
receiving 2-3 trains/week. The dumper pit also
receives push-in by a front-end loader from an
outdoor stockpile. The act of dumping and pushing
coal produced clouds of dust fugitives evading
capture by the existing collection system hoods and
lead to excessive dust layers settling in the conveyor
pit areas and substantial accumulation specifically
at the vibratory feeders, conveyor #1 and the tail
end of conveyor #2. OTP-BSP required a system
capable of reducing/eliminating dust from escaping
collection, reducing housekeeping costs, complying
with current NFPA codes, lowering outlet emissions,
while maintaining operator visibility from the control
room and availability during cold weather operation
(-40°F to 120°F). Additionally, the project required
an accelerated schedule to coincide with an outage
for boiler environmental upgrades (32 weeks ARO
to operational).
SOLUTION:
Air-Cure evaluated several approaches, incorporating
its patented RCD technology, to address the barrel,
dumper pit, and coal push-in ramp for reclaiming.
A new Air-Cure system was installed providing
150,000 ACFM of collection volume on the dumper
pit, feeders, and transfer points along with ventilation
of the basement conveyor belts. The new 984RF
baghouse utilizes a low pressure / high volume
(LPHV) pulse for filter bag rejuvenation, cyclonic
pre-separation and low can velocity to minimize the
dust load to the filter media resulting in low PM2.5.
The design incorporated:
1. Front side hoods on a bridge spanning the pushin
ramp for suspending the dust capture hoods
over the pit to reduce/eliminate dust escapees on
the dump-side. The bridge also aligns the capture
hoods over the push-in ramp during coal reclaim.
2. A shroud between the bridge and the coal pushin
entrance creating a stilling chamber during
RCD operation and an enclosed discharge during
coal reclaim. The stilling chamber enhances the
confinement of fugitive dust by increasing the
retention time for capture by the collection system.
3. Baffles on the barrel which make contact with the
back-side hoods.
4. Dust disposal utilizing a dilute phase pneumatic
dust conveying system to a cyclone receiver,
designed to transport 15 to 20 yd3/train of coal
dust and reintroduce the dust into the coal stream.
The integrated system achieves 99% capture
efficiency within the RCD building and zero opacity
at the entrances. The ambient air within the dumper
enclosure and the basement belt conveyor area is
CIRCLE 16 ON READER SERVICE CARD
8501 Evergreen Blvd
Minneapolis, MN 55433
Tel: 763-717-0707
Fax: 763-717-0394
www.aircure.com
maintained well below OSHA requirements. Total stack emissions
are below 0.005 grains/dscf, meeting their air quality permit and the
system is operational 24/7 in the South Dakota climate. OTP-BSP's new
housekeeping schedule plans for cleaning once per month; however,
this system was commissioned in July and these photos were taken in
September and the building had not required housekeeping yet.
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http://www.aircure.com
POWER October 2015

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