contact and consequent reduction in blowing times (U.S. EPA, 1980). Also, asphalt losses from
vertical stills are reported to be less than those from horizontal stills. All recent blowing still
installations have been of the vertical type (U.S. EPA, 1995).
Asphalt blowing can be either a batch process or a continuous operation; however,
the majority of facilities use a batch process. Asphalt flux is sometimes blown by the oil refiner
or asphalt processor to meet the roofing manufacturer’s specifications. Many roofing
manufacturers, however, purchase the flux and carry out their own blowing.
Asphalt Saturation--After asphalt has been blown into saturant or coating asphalt, it is used to
produce asphalt felt and coated asphalt roofing and siding products in the processes depicted in
Figures 4.6.1-4 and 4.6.1-5. The processes are identical to the point at which the material is to be
coated. A roll of felt is installed on the felt reel and unwound onto a dry floating looper. The dry
floating looper provides a reservoir of felt material to match the intermittent operation of the felt
roller to the continuous operation of the line. Felt is unwound from the roll at a faster rate than is
required by the line, with the excess being stored in the dry looper. The flow of felt to the line
and the tension on the material are kept constant by raising the top set of rollers and increasing
looper capacity. The opposite action occurs when a new roll is being put on the felt reel and
spliced in, and the felt supply ceases temporarily.
Following the dry looper, the felt enters the saturator, another point of POM
emissions within the asphalt roofing process. Moisture is driven out of the felt in the saturator
and the felt fibers and intervening spaces are filled with saturant asphalt. If a fiberglass mat web
is used instead of felt, the saturation step and the subsequent drying-in process are bypassed. The
saturator also contains a looper arrangement, which is almost totally submerged in a tank of
asphalt maintained at a temperature of 450 to 500(F (232 to 260(C). The absorbed asphalt
increases the sheet or web weight by about 150 percent. At some plants, the felt is sprayed on
one side with asphalt to drive out the moisture prior to dipping. This approach reportedly results
in higher POM emissions than does use of the dip process alone (U.S. EPA, 1980).