tank-car.txt

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Tank Truck and Rail Car Cleaning
December 1994

TNRCC Rule 116.111(3) in Regulation VI requires that Best Available Control Technology
(BACT) be applied to all facilities that must obtain a permit.  BACT determinations are made on a
case-by-case basis.  Current BACT guidelines for tank truck and rail car cleaning are:  

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 (flare, thermal oxidizer, scrubber, carbon, etc.), emissions from uncontrolled
truck/rail car cleaning, heel tanks, waste water treatment system, fugitives (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 Best Available Control Technology (BACT)
review.  The following paragraphs will discuss some of the BACT criteria for tank truck/rail
car cleaning facilities.

     BACT Guidelines 

     Tank trucks/rail cars (vessels) handling material with a vapor pressure of 0.5 psia or
     greater (at a temperature of 100 F) should be degassed to a control device prior to
     opening.  After the degassing operations are complete, the vessel needs to be checked
     for the presence of residual product (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 material with a maximum vapor pressure of 0.5 psia or greater (at a
     temperature of 100 F) shall be connected to a vapor recovery system (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 100 F), 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 VOC destruction efficiency of 98.0 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 99 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 (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 TNRCC Regulation II, Section 112.3.

     If a carbon adsorber is being used to control emissions from the cleaning operation, the
     emissions should 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 (waste water) is typically removed from the bottom of the
     cleaned vessel.  The waste water may either be loaded into another tank truck for
     removal off site,  routed to a waste water storage tank prior to tank truck load out and
     removal off site, or routed to a waste water treatment system.  

     The primary settling tank of the waste water treatment system (if applicable) should be
     an enclosed vessel.  

     If emissions from the wastewater system exceed 5 tons/year, the applicant will need to
     investigate possible ways of controlling the wastewater emissions (for example,
     stripping or covering the rest of the treating system).  The applicant may also be
     requested to control wastewater emissions with emission rates of less than 5 tons/year if
     impact problems are indicated by the modeling exercise.

     Storage tanks (heel tanks and waste water 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 waste water (if applicable) from
     the cleaning facility will be subject to BACT.  Possible control of heel tank truck
     loading may be required for material with a vapor pressure of 0.5 psia or greater (at
     maximum temperature), depending on the amount of material handled.

     (NOTE:  There may be TNRCC standardization packages specifically addressing 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 (see below), 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.