chrome.txt

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Chromium Plating Facilities
April 1995

                     Technical Disclaimer

References to abatement equipment technologies are not
intended to represent minimum or maximum levels of Best
Available Control Technology (BACT).  Determinations of BACT
are made on a case-by-case basis as part of the
New Source Review (NSR) of permit applications.  BACT
determinations are always subject to adjustment in
consideration of specific process requirements and recent
developments in abatement technology.  Additionally, specific
health effects concerns may indicate stricter abatement than
required by the BACT determination.

The represented calculation methods are intended as an aid in
the completion of acceptable submittals; alternate calculation
methods may be equally acceptable if they are based on, and
adequately demonstrate, sound engineering assumptions or data. 
It is the responsibility of applicants to remain abreast of
regulation developments which may affect their industries.

TNRCC Rule 116.111(3) in Regulation VI requires that BACT be
applied to all facilities that must obtain a permit.  BACT is
defined as any control method which is technically feasible
and economically reasonable.  BACT determinations are made on
a case-by-case basis.  The applicant is encouraged to talk
with a TNRCC NSR Permit Engineer to determine the BACT for the
facility.  Current BACT practices are:  

1.  Use of well designed capture hoods over chromium plating
    and acid pickle tanks.
2.  Chromium emissions exhausted to an appropriate abatement
    device or system like scrubbers, mist eliminators, etc.
3.  Use of a fume/foam suppressant in chromium plating and
    acid pickle tanks.  

Chromium Emission Reduction Techniques

1.  The principal techniques used to control emissions for
chromic acid mist from decorative and hard chromium plating
and chromic acid anodizing operations include add-on control
devices and chemical fume suppressants.  

2.  Since electroplating and anodizing operations are normally
conducted in open-top tanks, a system of slot hoods or canopy
hoods are usually constructed to capture the chromic acid
mist.  The slot hoods are the more prevalent.  The ventilation
rates in cubic feet per minute for either type of design
must be adequate to ensure the capture efficiency. 
Technically acceptable hoods should be designed and built in
accordance with the (Industrial Ventilation) handbook or an
equivalent configuration that is acceptable to the permit
engineer.  Hoods designed in the above manner can be assumed
to have a ninety-eight percent capture efficiency of the
chromic acid mist being entrained from the gassing at the
surface of the tank(s).  The correct design of the hood system
and air flow rate (velocity across the surface) are as
necessary as the correct abatement device.  

3.  The hood(s) must ventilate to an acceptable abatement
device(s).  The control devices most frequently used are mist
eliminators and wet scrubbers that are operated at relatively
low pressure drops.  If the device requires periodic was down
with fresh water (no caustic) and the water returned as makeup
water (returns lost chromic acid to plating bath), then the
manufacturer's literature, test data and details on the
washdown cycle should be clear.  Once-through water or
recirculated water is used as the scrubbing liquid because
chromic acid is highly soluble in water.  Typically, the wet
scrubbers used in chrome plating operations are single and
double packed-bed scrubbers and less frequently fan-separator
packed-bed and centrifugal-flow scrubbers.  Scrubbers remove
chromic acid droplets from the gas stream by humidifying the
gas stream to increase the mass of the droplet particles,
which are then removed by impingement on a packed bed.  

4.  Chevron-bladed and mesh-pad mist eliminators are the types
of mist eliminators most frequently used to control chromic
acid mist.  The mechanism by which mist eliminators remove
chromic acid droplets from gas streams is the inertial
impaction of droplets onto a stationary set of blades or a
mesh pad.  Mist eliminators are usually operated as dry units
that are periodically washed down with water to clean the
impaction media.  

5.  Chemical or mechanical fume suppressants can be added to
decorative or hard chromium plating tanks and chromic
anodizing baths.  The manufacturer's claim as to reduced
emissions should be supported by test data and a warranty. 
Manufacturer's emission reduction claims of ninety-nine
percent are common.  For some hard chromium applications, some
fume or foam suppressants cause pitting in the plating and
consequently require a mechanical approach for a suppressant. 
A common mechanical suppressant is to float polypropylene
balls (ping pong balls) on the surface of the tank, usually in
two layers.  Polypropylene balls are generally used on hard
chromium plating baths to reduce evaporation of plating
solution and inhibit misting.  They are generally not used in
automated plating or anodizing operations because plating
racks drag the balls out of the baths.  The balls tend to be
pushed away from the anodes and cathodes where the surface of
the bath is agitated by gassing, thus reducing their
effectiveness for inhibiting misting.  

These levels are guidelines to help the applicant get an idea
of what the TNRCC is currently considering as BACT; however
these control levels are subject to change.   Part D of
section VI of the PI-1 form requires the applicant to submit
a BACT analysis.  Any BACT proposal that is different from the
requirements stated above needs to be explained in detail. 
Any control system alternative evaluated should be well
designed and engineered for its application.