POWER March 2014 - 50

THE FUTURE OF COAL-FIRED GENERATION
Table 1. Comparison of Subtitle C vs. Subtitle D. Source: EPA
Subtitle C
Effective date
Timing will vary from state to state,
as each state must adopt the rule
individually, which can take one to
two years or more.
Enforcement
Corrective action
Financial assurance
Permit issuance
Requirements for storage, including
containers, tanks, and
containment buildings
Surface impoundments built
before rule is finalized
State and federal enforcement
Monitored by authorized states
and EPA.
Yes.
Federal requirement for permit
issuance by states.
Yes.
Remove solids and meet land
disposal restrictions; retrofit with a
liner within five years of effective
date. Would effectively phase out
use of existing surface impoundments.
Surface
impoundments built
after rule is finalized
Landfills built before rule is
finalized
Landfills built after rule is
finalized
Requirements for closure and
post-closure care
Must meet land disposal restrictions
and liner requirements. Would
effectively phase out use of new
surface impoundments.
No liner requirements, but groundwater
monitoring required.
Liner requirements and groundwater
monitoring.
Subtitle D
Six months after final rule is
promulgated for most provisions;
certain provisions have a longer
effective date.
Enforcement through citizen suits;
states can act as citizens.
Self-implementing.
Considering subsequent rule using
CERCLA 108 (b) authority.
No.
No.
Must remove solids and retrofit
with a composite liner or cease
receiving CCRs within five years of
effective date and close the unit.
Must install composite liners. No
land disposal restrictions.
No liner requirements, but groundwater
monitoring required.
Liner requirements and groundwater
monitoring.
Yes; monitored by states and EPA. Yes; self-implementing.
to be retrofitted with a composite liner to
prevent ash contaminants from leaching into
the groundwater. Although the addition of a
composite liner to an ash pond may appear
to be a simple remedy, the EPA is anticipating
the cost of this path will create a strong
incentive to decommission these ponds and
transition to a landfill operation.
Compliance Strategies
Without a clear understanding of which path
the EPA intends to take for regulating CCRs,
it is difficult to home in on a single technology,
wet or dry, to meet forthcoming regulations.
What is clear is that the EPA is intent
on shuttering coal ash pond operations, and
the February spill at Duke Energy's Dan
River Steam Station's ash pond is likely to
reinforce that position.
Several options exist to divert existing ash
slurry systems away from ash ponds. Utilities
may have the option of keeping an existing
ash slurry system and installing new ash-drying
equipment, or they can convert their ash
slurry handling systems to a totally dry system.
Both options have their pros and cons
48
but are viable solutions to meet expected
CCR regulations.
Ash Slurry Options. The first option to
maintain an ash slurry system is to implement
dewatering bins in lieu of an ash pond
(see " Reducing Bottom Ash Dewatering
System Maintenance " in the November 2013
issue at powermag.com). With this option,
dewatering bins are used both as a receiver
and separator for the ash slurry mixture.
Typically, a pair of dewatering bins is employed
to maintain uninterrupted boiler operations.
The first bin will continue to receive
ash slurry until the collected solids (bottom
ash) have reached a predetermined capacity.
At that point, ash slurry flow is directed to
the second bin. With the second bin serving
as the active receiver for the ash slurry, the
first bin can begin to " dewater " its content
of bottom ash. Overflow and drainage water
from the bins are further processed (typically,
with settling and surge tanks) for reuse in
closed-loop slurry systems. Trucks are then
used to remove the damp ash from the dewatering
bins for off-site disposal.
Dewatering bin technology is a very mawww.powermag.com
ture
option, with several manufacturers offering
equipment packages.
The primary advantages to this system are
the reuse of the existing slurry system, short
outage time, and the maturity of the dewatering
bin system. This type of system can be
erected independent of power plant operations
and (because existing ash slurry systems
are used) the only interfaces are with
existing slurry piping and recirculated water.
There are some disadvantages with dewatering
bins. These systems are not dry, and in
order to dewater the ash slurry, a significant
amount of auxiliary power is required. As is
typical with many wet systems, the dewatering
bins are prone to leaks, and screens used
for dewatering are subject to plugging. Because
of the water quality used in this system,
excessive fouling and plugging of piping and
equipment is common. In some cases, plant
operations have required shutdowns due to
excessive buildup of contaminants in the system.
Boiler efficiency is unaffected, as the
original ash hoppers are retained.
A second ash slurry option diverts the slurry
from the ash pond to a remote submerged
scraper conveyor system. Clyde Bergemann
Power Group offers this ash slurry packaged
system known as ASHCON. In this system,
large overflow troughs are used in a similar
manner to dewatering bins, and a submerged
scraper continuously withdraws ash from the
water and conveys it to an ash pile for secondary
use or landfilling.
Advantages of the ASHCON system are
similar to those of dewatering bins, but there
are some key benefits. The primary differentiator
between the ASHCON system and dewatering
bin option is the elevation at which
the technology operates.
Because the ASHCON system is much
lower to the ground, the existing water supply
pumps and jet pumps under the boiler
should not need to be modified. Dewatering
bins operate at a much higher elevation, thus
requiring additional lift in the form of higher-horsepower
pumps. As noted, dewatering
bins operate in a batch process (usually with
redundant bins), whereas the ASHCON system
is a continuous process that eliminates
the maintenance and operator involvement
associated with batch processing.
Little to no outage is required, as the
system can be erected without interrupting
power plant operations. The system reuses
existing ash hoppers and has a small footprint
relative to an ash pond.
For facilities that operate multiple boilers,
a single ASHCON system can be designed to
handle the flow from each slurry system, thus
reducing the need for redundant systems.
One disadvantage with this system is that
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