loading.txt

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Loading Operations
January 1995

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 loading operations:  

Accepted collection efficiencies (vapor collected to BACT control device) are as follows:

Unenhanced Loading                65%
Enhanced Loading                    85%
Annual Leak Checking*            95%
Semi-Annual Leak Checking     97.5%
Vacuum Loading                      100%

* Leak checking as required by New Source Performance Standards (NSPS) Subpart XX

Definitions

Unenhanced and enhanced loading are not BACT for compounds with vapor pressure greater
than 0.5 psia.  They are a way of decreasing loading losses if the off property impacts are too
high.

Unenhanced Loading- Loading loss emissions are sent to a control device, however, the trucks
are not leak checked.

Enhanced Loading- Loading loss emissions are sent to a control device, however, the trucks are
not leak checked.  A positive pressure of +3 to +5 inches of water is not exceeded in the truck
cavity.  This can be maintained by using a blower.

Vacuum Loading- Hard-piped loading maintaining a vacuum of less than -1.5 inches of water in
the truck cavity.  Each application containing vacuum loading will be looked at individually.  The
pressure in the truck must never become neutral or positive when vacuum loading.   

Loading fugitive emissions -  Uncollected loading emissions are called loading fugitives.  These
differ from process fugitives which are emissions that escape from valves, pumps, and any type of
connections in the piping. 

The control device may be a flare, an incinerator, a carbon adsorption system or a scrubber.  An
approved flare has 98 percent destruction efficiency.  An approved incinerator has 99.9 percent
destruction efficiency.  The recovery efficiency of a carbon adsorption system will be evaluated on
a case-by-case basis;  the Texas Natural Resource Conservation Commission (TNRCC) would
like to see <100 ppm organic escaping the bed.  Scrubber efficiency is estimated by the applicant. 
Scrubbers are usually used to control inorganics.  The applicant may refer to the standardization
packages for flares, absorber units, carbon absorption systems, and fugitive sources for methods
of calculating these emissions.

There are many emission sources to consider when loading chemicals.  Uncontrolled loading
fugitives, process fugitives from piping and components, tank emissions, and emissions from the
control device that is controlling the collected loading emissions must all be considered.  Process
fugitive emissions are emissions that result from leaking valves, pumps, flanges, and compressors. 
Fugitive emissions from equipment and piping that is associated with the loading procedure must
be accounted for in the project.  

Loading Operations

Tank truck loading operations can be subdivided into three general categories: atmospheric
trucks, pressure trucks used in atmospheric service, and pressure trucks.

A.   When loading compounds with a vapor pressure >0.5 psia, the collected emissions must
     be routed to a control device with a minimum of 98 percent destruction efficiency or 95
     percent removal efficiency.

     The BACT for atmospheric type tank trucks consists of annual leak checking according to
     NSPS Subpart XX standards (which provides for a 95 percent collection efficiency of
     loading emissions) for compounds with a vapor pressure greater than 0.5 psia.  Splash
     loading is not BACT.  Submerged or bottom loading is required.

     Even though trucks loading chemicals other than gasoline are not subject to the NSPS
     subpart, the leak testing requirements outlined in Subpart XX are used as a BACT leak-testing 
     benchmark for atmospheric trucks.  Trucks which contain compounds with vapor
     pressures less than 0.5 psia are not required to be controlled; however, impact review does
     still apply.  There may be cases where trucks handling material less than 0.5 psia may need
     to be controlled because of unacceptable off property impacts.  

     If off-property impacts are found to be unacceptable, the applicant may decide to either
     leak test two times per year (which would provide for a 97.5 percent collection efficiency)
     or proceed with a vacuum loading type system (100 percent collection).

B.   In some cases, applicants may use pressurized trucks in atmospheric type loading
     situations (for example, a pressure truck used to transport Jet A or gasoline).  It is
     possible for the applicant to obtain 100 percent collection efficiency in terms of estimating
     emissions if the following is applied:

1.   Pressure truck certification:  Is the pressure truck certified?  Most pressure trucks are
     required to undergo DOT testing in order to maintain their pressure rating.  If the truck is
     not pressure certified, a 100 percent collection efficiency should not be allowed (unless
     vacuum loading is being used).

2.   Are pressure rated connections being used?  A complete description of the loading and
     vapor recovery connections must be provided for a determination of collection efficiency. 
     Loading into a pressurized truck without using pressure-stressed type connections cannot
     be given 100 percent collection efficiency.  The efficiency will be determined on a case-by-case
     basis.

3.   A 100 percent collection efficiency can be given to those applicants that are loading a
     pressurized material into tank trucks designed to handle a pressure of 15 psig or greater. 
     Materials loaded into these types of tanks tend to be vapor at atmospheric temperature
     and pressure (the trucks are specifically designed for this type of service).  

     NOTE:  Recent permitting experience has indicated that not all pressure trucks are
     operated in a leak-free manner.  Some trucks are equipped with what is known as a spew
     gauge.  This is not considered to be BACT.  

     A spew gauge is a method of determining the liquid level inside a tank truck.  If a truck is
     equipped with a spew gauge, the vapor tightness of the tank truck is compromised during
     the loading operation.  Although the tank truck may be tested and pressure certified to
     operate at 15 psig or greater, the spew gauge will still allow emissions to the atmosphere. 
     The truck is no longer vapor tight, and the loading operation itself is no longer BACT.

     Depressurizations of trucks must be routed to a control device.  Hoses used during
     loading must be purged and are not allowed to drip liquid.  Spills must be properly
     attended to.