Control of Volatile Organic Compounds Emissions from Manufacturing

in addition to C3 and process diluent. The stream is continuous and
exists in most of the existing polypropylene plants. The process using
a high-yield catalyst does not require these vents, and the reduction in
total emi ssi on factor is significant.
4. Stream E: Slurry Vacuum Filter System Vents - This stream is
from the system which separates the atactic and isotactic polymer. It
is one of the largest VOC emission streams venting process diluent and
alcohol remaining in the polymer. It is a continuous stream at atmospheric
pressure and exists in both the conventional and high-yield slurry
process pl ants .
5. Stream F: - This stream originates
from the by-product and diluent recovery section and can be the second
largest VOC emission stream in the entire process. The diluent recovery
section which consists of an evaporator, an extractor and distillation
units is part of all processes and emits process diluents and alcohol
vapors.
6. Stream G: Dryer Vents - This vent emits hydrocarbons diluted
in air or nitrogen at a relatively high temperature (104OC) and atmospheric
pressure. The emissions consists of vapor of hexane, methanol, and
propane.
7. Stream H: Extrusion/Pelletizing Vent - This vent can continuously
emit significant quantities of hydrocarbon that may remain in the polypropylene
powder as it exits the dryer and enters the extruder feed chute. At
this point, the powder is in equilibrium with a vapor that can contain
up to 25 percent hydrocarbon by weight. As a result of heating and
compression in the extruder, there is some VOC loss through the extruder/
pel 1 eti zi ng section and futher 1 osses from the powder/pel let transfer
system downstream from the product dryer since the transfer medium acts
as a stripping gas.
The stream properties and VOC concentrations of Streams A to H can
vary depending on process conditions. The variation generally depends
on the product grade or type being manufactured and other variables such
as temperature, pressure, catalyst concentration or activity, and the
amount of hydrogen used for molecular weight control. The concentration
and the magnitude of each stream is, of course, hightest under start-up
or shutdown conditions because of process conditions away from equil ibrium.