POWER July 2011 - 56

ASH MANAGEMENT
The Better Environmental Option:
Dry Ash Conversion Technology
After the 2008 incident involving the failure of a large surface impoundment containing
wet coal ash, the EPA began investigating all coal-fired power plants
employing this wet coal ash management method. Now a new dry ash management
technology offers coal-fired power plants an environmentally suitable
alternative for handling coal ash that also increases energy efficiency.
By Angela Neville, JD
E
xisting coal ash management regulations
are undergoing close scrutiny by the U.S.
Environmental Protection Agency (EPA).
This action was initiated in the wake of the 2008
incident in which a containment dike at a Tennessee
Valley Authority coal ash disposal pond
failed, spilling approximately a billion gallons
of wet coal ash over about 300 acres and into
a nearby river. Consequently, many coal-fired
electric power producers are now investigating
alternative methods of handling coal ash that do
not require using water.
Bottom ash is agglomerated ash particles
formed in pulverized coal furnaces that are
too large to be carried in the flue gases and
that impinge on the furnace walls or fall
through open grates to an ash hopper at the
bottom of the furnace. Physically, bottom ash
is typically grey to black in color, is quite angular,
and has a porous surface structure.
Typically, bottom ash as a byproduct at
coal-fired power plants is conveyed in a hydraulic
system in which the ash is entrained
in a high-flow, circulating water system and
delivered to either an ash pond or dewatering
storage bins. In the alternative, bottom
ash can be conveyed by a mechanical drag
system to dewatering storage bins.
Now a new bottom ash management technology
has been developed that does not require
the use of water and thereby avoids the
creation of wet ash that has to be stored in
surface impoundments or dewatering storage
bins. DRYCON is a mechanical conveying
system that handles hot bottom ash being discharged
directly below the boiler throat. Ron
Grabowski, vice president of sales at Clyde
Bergemann Delta Ducon, discussed the technology
with POWER in May.
How the Dry Ash Conversion
Technology Works
Hot bottom ash falls onto the DRYCON conveyor,
where it is simultaneously conveyed
and cooled, Grabowski explained. The DRYCON
technology uses the negative draft of a
56
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POWER | July 2011
pulverized coal-fired boiler to draw ambient
air through the conveyor. This airflow cools the
hot ash while supplying about 1% of the combustion
air into the boiler. The dry bottom ash
can then be stored in a silo and off-loaded into
trucks for disposal or resale (Figure 1).
" DRYCON is the next generation of dry
bottom ash systems, " he said. " One of the
unique design features of DRYCON is that
it does not use belt technology; rather, it
conveys the bottom ash via a series of hightemperature
alloy pans. "
With the new system, ash is conveyed on
top of the pans as they move gently via externally
mounted rollers. This design allows
the new system's conveyor to incline at a
40-degree angle from grade. This feature can
reduce the footprint of the conveyor and provide
additional flexibility not found in other
conveyors, according to Grabowski.
1. High and dry. The new dry bottom ash-
handling system promotes higher efficiency
by returning heat energy to the boiler. In addition,
with this new system in place, plants can
also avoid using large amounts of water for
ash cooling and conveying. Courtesy: Clyde
Bergemann Delta Ducon
2. Breaking up is easy to do. " Jaw crushers " are shown above the inlet of the DRYCON
conveyor. This equipment breaks up and crushes large clinkers before they enter the new
system's conveyor. Courtesy: Clyde Bergemann Delta Ducon
http://www.powermag.com
POWER July 2011

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