POWER September 2014 - 46

WATER
in frac tanks located at the site prior to the
start of the cleaning (Figure 2). Before this
waste can be dealt with, it must be characterized
to determine if it is considered hazardous
or nonhazardous under the Resource
Conservation and Recovery Act (RCRA).
The strongly acidic cleaning wastes are
generally neutralized as they leave the boiler,
and then that waste is combined with neutralization
and passivation steps and rinses to
produce a combined waste that is not characteristically
hazardous for pH. The other chemical
cleaning solvents are not characteristically
hazardous by pH to begin with.
The other way that a BCCW can be classified
as a hazardous waste is if it contains
a concentration of one of the RCRA 8 toxic
metals. The primary metal that is of concern
is chromium. Chromium comes from stainless
steel feedwater heater and condenser
tubes. This accumulates in deposits in the
boiler. The regulation is specifically aimed
at hexavalent chromium. Normally, utilities
measure total chromium first, and only address
the hexavalent chromium issue if the
total chromium is greater than the RCRA
limit of 5 ppm.
EDTA solubilizes chromium in a reduced
trivalent chrome (Cr III) state, and it is not
sufficiently oxidized by oxygen in the passivation
stage of the cleaning to create a significant
amount of the hexavalent chromium.
Some utilities have gone to their state environmental
agencies with analytical data showing
that there is very little hexavalent chromium
in their BCCW, even if the total chrome is
greater than 5 ppm, and have sought and received
an exemption for this waste so that it
can be classified as nonhazardous.
For many years utilities have utilized an
exemption provided by the Bevill Amendment
and a subsequent letter from the Environmental
Protection Agency (EPA) to group
BCCW with other wastes that were uniquely
associated with coal-fired utilities (such as
fly ash and bottom ash) and treat them as exempt
from hazardous waste regulations. This
allowed the comingling of BCCW with fly
ash or bottom ash and disposal in the ash pile
without first having to determine if they were
characteristically hazardous.
In May 2000, the EPA made a regulatory
determination that moved BCCW from the
" uniquely associated " to a " not uniquely associated "
list, meaning that it would lose its Bevill
exemption. This determination was challenged
by user groups such as the Utility Solid Waste
Activities Group and Edison Electric Institute,
and comments were sent to the EPA. The EPA
has not responded to these comments in any
formal way. However, the agency's general
counsel has produced documents that clearly
assume that this change in the BCCW determination
has been implemented. This is still
an open issue, and utilities should be aware of
these regulations when blending BCCW with
a Bevill-exempted waste.
New regulations on coal combustion residuals
are in the offing and may affect the
way utilities manage fly and bottom ash
and how ash landfills are managed, and this
may change the discussion on comingling
BCCW with ash yet again. It is important to
note that a nonhazardous BCCW could still
be blended with ash, at least under current
regulations.
For many years, coal-fired utilities have
evaporated characteristically nonhazardous
BCCW (<5 ppm Cr) by spraying it directly
into the fireball of an operating coal-fired
boiler, typically at a rate of 30 to 50 gpm,
depending on the amount of coal going to
the boiler. This was the practice with EDTA
wastes in particular. The water is evaporated,
the organic EDTA is consumed in the fireball,
and metals are combined with the fly and bottom
ash leaving the boiler. The small rate at
which the BCCW was being added versus the
coal feed made no measurable differences to
any of the fly ash or bottom ash characteristics
or stack gases. Some even found a slight
benefit to NOx
emissions during the time the
BCCW was being evaporated. This practice
had been successfully used for many years by
coal-fired power plants.
However, changes to the definition of a
nonhazardous secondary material by the
EPA, together with changes to definitions of
what constitutes a commercial industrial solid
waste incinerator, essentially will prohibit
a conventional utility boiler from evaporating
BCCW in the future. These changes go
into effect at the latest in 2015, but they may
already be in place in some states.
If both evaporation and comingling with
fly ash go away, other options for properly
disposing of BCCW will need to be considered.
The amount of BCCW generated
with the combined solvent drains and rinses
can be very large, and off-site treatment or
disposal costs could double the cost of the
cleaning. On-site treatment, particularly of
EDTA wastes, can be time-consuming and
expensive. Other innovative recovery and
beneficial reuse of these wastes has been
considered in the past but never commercialized.
However, in the present regulatory
environment, these options may be in more
demand as utilities strive to get their boilers
clean while controlling costs and liability. ■
-David Daniels, is a POWER contributing
editor and senior principal scientist at
M&M Engineering Associates Inc.
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