POWER March 2014 - 51

THE FUTURE OF COAL-FIRED GENERATION
2. DRYCON cooling conveyor installation in Florida. Courtesy: Clyde Bergemann
Power Group
the ash is dewatered as it is slowly dragged up
an incline. Ash is then fed to removable containers
or a transfer conveyor for storage.
The submerged scraper system has advantages
similar to those of the remote submerged
scraper system. In addition to these advantages,
a submerged scraper system eliminates the
need for clinker grinders, hopper jets and slurry
pumps, and hopper gatehouse assemblies.
Auxiliary power is reduced, as the power
needed to drive high-, medium-, and low-pressure
pumps associated with slurry systems is
more than that required by the new conveyor
system. This technology is also mature, as the
first submerged scraper systems were installed
nearly 100 years ago.
For plants without extra real estate to implement
a remote submerged scraper system,
this system has an even smaller footprint.
Submerged scraper conveyor systems have
also been designed to combine economizer
ash and pyrite removal into the same system,
thus reducing overall maintenance costs.
The submerged scraper conveyor option also
minimizes water usage and is less complex
than dewatering bins.
Unfortunately, because of the significant
3. DRYCON cooling and transfer conveyor to ash storage. Courtesy: Clyde
Bergemann Power Group
modifications needed to the ash hopper, a
major outage is required for installation. The
system is still not a dry system and requires
wastewater treatment for any water that
overflows the trough. The same combustion
characteristics exist, thus no change in boiler
efficiency will be observed.
Dry Conversions. The newest technology
for replacing an ash slurry system is a
complete dry ash conversion. An example of
a dry system designed to replace ash slurry
systems is Clyde Bergemann Power Group's
DRYCON (Figure 2).
The DRYCON system replaces the existing
ash slurry system with a dry conveyor
system at the bottom of the boiler. This poses
challenges, as the removal of a water-quenching
system requires a new method to cool hot
ash. To combat this cooling problem, these
systems introduce cool ambient air across the
conveyor system and into the furnace. This
air cools the conveyor components while
burning the remaining carbon in the ash. The
cooling air increases in temperature before
entering the boiler through the throat.
The addition of warmed ambient air for
it still operates as a wet system; overflow water
from the troughs must be treated as process
wastewater. High power consumption
and no change in boiler efficiency are other
disadvantages.
Submerged Scraper Conveyor Option.
March 2014 | POWER
Similar to the remote submerged scraper conveyor
system, the submerged scraper system
can be directly integrated into the ash hopper.
The existing ash slurry system is removed and a
water trough with a chain conveyor is installed
in its place. The water quenches the hot ash, and
www.powermag.com
cooling ash may appear to be problematic,
as this air volume could affect the combustion
characteristics of the boiler. In order
to ensure that no adverse effects on boiler
combustion occur, the amount of ambient air
used for ash cooling is limited to 0.75% of
the combustion air. This method of cooling is
quite effective, as it has been shown to reduce
the ash temperature from 750F at the outlet
49
http://www.powermag.com
POWER March 2014

Table of Contents for the Digital Edition of POWER March 2014
