rcttc.txt

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Tank Truck and Rail Car Cleaning
November 1994

                    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 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 effect 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 permit submittals; alternative
calculation methods may be equally acceptable if they are
based on, and adequately demonstrate, sound engineering
assumptions or data.

These guidelines are applicable as of the date of this
document, but are subject to revision during the permit
application preparation and review period.  It is the
responsibility of the applicants to remain abreast of any
guideline or regulation developments which may affect their
industries.

BACT Discussion

There are several sources of emissions associated with a tank
truck/rail car cleaning operation.  These sources can include
the control device handling the emissions captured by the
vapor recovery system like a flare, thermal oxidizer,
scrubber, carbon beds, etc., and emissions from uncontrolled
tank truck/rail car cleaning, heel tanks, wastewater treatment
system, fugitives from pipes, valves, flanges and boiler
emissions.  Some facilities use natural gas fired boilers for
steam and/or hot water cleaning.  For new construction permits
and permit amendments, each of the above emission sources will
be required to go through a BACT review.  The following
paragraphs will discuss some of the BACT criteria for tank
truck/rail car cleaning facilities.  

BACT Guidelines

Tank truck/rail car vessels handling material with a vapor
pressure of 0.5 psia or greater at a temperature of 100F
should be degassed to a control device prior to opening. 
After the degassing operations are complete, the vessel needs
to be checked for presence of residual product or heel.  All
vessels handling and/or containing liquid material shall be
deheeled prior to cleaning.  There shall be no standing liquid
inside the vessel when cleaning operations commence.  

Vessels handling materials with a maximum vapor pressure of
0.5 psia or greater at a temperature of 100F shall be
connected to a vapor recovery system like a vacuum system
which will maintain a negative pressure inside the vessel
during the entire cleaning process.  The discharge of the
vacuum system shall be routed to a control device. 
Maintaining a vacuum on the vessel during the cleaning process
will ensure that 100 percent of the emissions generated by the
cleaning operation itself are collected and controlled.  For
vessels handling material with a maximum vapor pressure of
less than 0.5 psia at a temperature of 100F, the emissions
resulting from the cleaning operation can be vented to the
atmosphere provided that the off-property impacts are
acceptable.  

The destruction or removal efficiency of the control device
used to control emissions from the cleaning operation itself
depends upon the system being used.  A flare should obtain a
volatile organic compound destruction efficiency of
ninety-eight percent.  If the material is routed to a thermal
oxidizer, the destruction efficiency should be 99.9 percent. 
If the oxidizer is followed by a scrubber for handling the
by-products of halogenated combustion or if the scrubber is
controlling emissions from inorganic acid tank trucks and/or
rail cars, the scrubber should obtain a minimum removal
efficiency of ninety-nine percent.  It is very possible that
some of the material handled by tank truck and/or rail car
cleaning facilities will fall in the halogenated category.  If
this is the case, please be aware that by-products of
combustion like hydrogen chloride, hydrogen bromide, hydrogen
fluoride need to be estimated and possibly controlled. 
By-products of combustion for compounds containing sulfur
(sulfur dioxide (SO2) emissions) and nitrogen (nitrogen oxide
emissions) will also need to be estimated.  If sulfur
containing compounds are being combusted, the resulting SO2
emissions must meet the off-property impact concentrations as
described in TRNCC Regulation II, Section 112.3.  

If a carbon adsorber is being used to control emissions from
the cleaning operation, the emissions should be estimated on
a case-by-case basis.  BACT is three canisters in series with
a continuous hydrocarbon analyzer located between the second
and third canister to monitor for breakthrough.  The
breakthrough concentration will be determined on a
case-by-case basis and will typically be less than 100 ppmv. 
The carbon adsorption system is typically considered an option
for control of compounds not suitable for combustion.  

The used cleaning solution or wastewater is typically removed
from the bottom of the cleaned vessel.  The wastewater may
either be loaded into another tank truck for removal off-site,
routed to a wastewater storage tank prior to tank truck load
out and removal off-site or routed to a wastewater treatment
system.  The primary settling tank of the wastewater treatment
system, if applicable, should be an enclosed vessel.  

If emissions from the wastewater system exceed five tons per
year (TPY), the applicant will need to investigate possible
ways of controlling the wastewater emissions.  For example,
stripping or covering the rest of the treating system is one
example of emissions control.  The applicant may also be
requested to control wastewater emissions with emission rates
of less than five TPY if impact problems are indicated by the
modeling exercise.  

Storage tanks, heel tanks and wastewater tanks should follow
current BACT guidelines.  A floating roof or vapor control
system will be required if the vapor pressure of the material
stored is 0.5 psia or greater at maximum temperature and the
tank is larger than 25,000 gallons in capacity.  

Loading operations related to the removal of heel and
wastewater, if applicable, from the cleaning facility will be
subject to BACT.  Possible control of heel tank truck loading
may be required for a material with a vapor pressure of 0.5
psia or greater at maximum temperature, depending on the
amount of material handled.  

Some TNRCC standardization packages specifically address some
of the above mentioned control devices or operations.  

After the engineer reviewing the application has determined
that BACT is applied and that the emissions are calculated
correctly, dispersion modeling may be required to verify that
the expected emission rates from the cleaning facility will
not cause or contribute to an unacceptable odor or impact
situation off-site.