MDI Emissions Reporting Guidelines for the ... - Polyurethanes

MDI Emissions Reporting Guidelines for the Polyurethanes Industry
liquid and the temperature of the vapor space may be different from the
ambient temperature. Empirical formulas are provided to determine the
required temperatures if the ambient temperature and the daily range are
given.
Determination of the breathing losses through the new EPA method is quite
tedious. A software program to evaluate storage tank losses (working losses
and breathing losses) was developed by the EPA. The software (TANKS) is
available for downloading from the EPA at
http://www.epa.gov/ttnchie1/software/tanks/.
3. Comparison of results
The simplified method used for the MDI Emissions Estimator is an adaptation
of the new EPA method. In developing the simplified method, the following
assumptions are made:
The pressure term in the vapor space expansion factor is ignored. It
can be shown that for liquids having a low vapor pressure the pressure
term is negligible relative to the temperature term and can thus be
ignored.
The vented vapor saturation factor is 1.0. It can be shown that for
liquids having a low vapor pressure the vented vapor saturation factor
approaches 1.0.
The average liquid surface temperature and the vapor temperature
are the same as the ambient temperature.
Under these circumstances, the simplified method will yield identical results
to the new EPA method.
Table C-1 provides a side-by-side comparison of the working losses and
breathing losses for the three methods discussed above.
COMPARATIVE EXAMPLE
The following illustrative example demonstrates the equivalency between the
simplified method and the new EPA method when simplifying assumptions are
made:
A fixed roof vertical tank contains MDI. The tank has a volume of 11,750
gallons (10’ D x 20” H) and is half full. The tank is located in New York. From
meteorological data, the daily average ambient temperature is 54.55 o
F
C-4