TNRCC REGULATORY GUIDANCE

New Source Review
RG-138
November, 1995

SUBJECT:  Gasoline Terminal Loading Emissions 

Process Description 

During the loading of tank trucks at bulk gasoline storage
terminals, emissions occur which can be estimated utilizing the
methods outlined here.  Other gasoline terminal emission sources
such as fugitive (e.g., valve, flange, and pumps) and tank
emissions may be estimated utilizing factors readily available in
Petroleum Marketing Terminal Factors or from TNRCC approved
equivalent industrially derived sources and will not be discussed
here.  Gasoline "spills" or other upset emissions are also not
considered in this analysis.

Emissions 

Uncontrolled emissions are estimated utilizing the latest edition
of AP-42, Section 4.4.  Emissions are calculated using the
equation: 

          LL = (12.46)(SPM)/T

Where:
LL =  Loading loss, lb/thousand gallons of gasoline loaded
S  =  A saturation factor, see AP-42
P  =  True vapor pressure at maximum temperature of gasoline to be
loaded, psia.
M  =  Molecular weight of gasoline vapors, lb/lb-mole
T  =  Temperature of bulk gasoline loaded, degrees Rankine.

Hourly emissions are based on the highest emissions for any
60-minute period.  The permit, when issued, would thus restrict the
maximum gallons loaded in an hour to the basis of permit review for
the hourly period.  Similarly, the annual throughput in gallons
would be limited to the maximum throughput involved in the
representations for annual emissions.

Collection efficiencies (vapor collected to a BACT control device)
are as follows:

                                                         Collection
                                                         Efficiency
Unenhanced Loading                                              65%
Enhanced Loading (+3.0 to +5.0 inches
          water back pressure, blower, etc.)                    85%
Annual truck leak checking*                                     95%
Leak checks every six months*                                 97.5%
Vacuum loading                                                 100%

* Leak checking as required by NSPS Subpart XX



Air Pollution Controls

The BACT guideline for gasoline terminal loading emissions is
either a thermal oxidizer (99.9% VOC destruction efficiency),
carbon adsorption (0.04 - 0.09 lb gasoline per 1,000 gallons
loaded), or flaring (98.0% destruction efficiency).  These factors
are applied to the collected uncontrolled gasoline vapors.  

Chemicals which may be emitted from a gasoline terminal include
benzene, butane, methyl-tert-butyl ether, and tertiary butyl
alcohol.  Benzene emissions must be speciated so that an emission
rate, hourly and annually, is available. 

Sample calculation:

If uncontrolled gasoline emissions are 10 lb/hr and truck tanks are
leak-checked annually, uncollected emissions are:  

(1 - 0.95)(10) = (0.05)(10) = 0.5 lb/hr.

Utilizing a flare for the collected emissions, flare emissions
would be:

  (1 - 0.98)(10 - 0.5) = 0.02(9.5) = 0.19 lb/hr.

Total gasoline emissions are, therefore:

  0.5 + 0.19 = 0.69 lb/hr gasoline vapors.

If: 

Benzene is 0.68%(w) of the gasoline liquid, and
Mol. Wt. benzene = 78 lb/lb mole
Mol. Wt. gasoline (liquid) = 92.2 lb/lb mole 
Vapor Pressure of benzene @ 90øF = 2.6 psia.
Vapor Pressure of gasoline @ 90øF = 8.8 psia.
then:
Mole % benzene in liquid =  (0.68)(92.2)
                                (78)
                         = 0.804

Raoult's Law:

               Pb/Pbo = Xb

Where:
Pb = Partial pressure of benzene in the gasoline vapor
Pbo = Vapor pressure of pure benzene
Xb  = Mole fraction of benzene in the gasoline liquid
Then:

Pb  =(Pbo)(Xb) = (2.6 psia.)(0.00804) 
      = 0.0209 psia.


Dalton's Law:

               Pb/Pt  = Yb
              
Where:
Pt = Vapor pressure of the gasoline
Yb = Mole fraction of benzene in the gasoline liquid
Mol. Wt. gasoline (vapor) = 66 lb/lb mole

then:

Yb = 0.0209/8.8
   = 0.0024, and

the weight percent benzene in gasoline vapor becomes:

   =(100)(0.0024)(78)/66
   = 0.28 wt. %

Benzene emissions then are:

   (0.0028)(0.69) = 0.0019 lb/hr benzene

Permit Requirements 

After September 1, 1971, all new or modified sources of air
contaminants to include gasoline terminals must obtain a permit
from the TNRCC or meet the requirements of a TNRCC standard
exemption in effect at the time the source, i.e., terminals, is
constructed.  Should federal emission significance levels be
triggered, a federal PSD or nonattainment permit may also be
required.

An increase in throughput is considered a probable modification and
must be reviewed by the TNRCC New Source Review Program.

Federal Standards

New Source Performance Standards for Bulk Gasoline Terminals,
Subpart XX 

References
AP-42, Environmental Protection Agency, Compilation of Air
Pollutant Emission Factors, Volume I 
EPA Document, Bulk Gasoline Terminals- Background Information for
Proposed Standards, EPA-450/3-80-038a, December 1980.
-TNRCC Regulations V and VI
-TNRCC General Rules
-OAQPS TNN Electronic Bulletin Commission (AQPS   
TNN/CHIEF/AP42/Q&As/LEAKS-rd.txt)

TNRCC Contact
New Source Review Division, Core Section or Chemical Section