Abstract: In an asphalt mixing plant, a portion of the heat used to vaporize water in the process of drying aggregate is recovered by conducting dryer exhaust gases through parallel ducts which extend serially through the aggregate cold feed bins. These parallel ducts are vertically elongated for optimum heat transfer and to avoid impeding aggregated flow. The ducts have vertically extending external fins for greater contact with the aggregate in the bins. They also have horizontally extending internal fins for improved heat transfer between the exhaust gases and the ducts. The ducts are peaked, and conforming protective caps are provided to prevent damage to the ducts during loading of the bins. Water injection is used to initiate condensation of water vapor in the exhaust gases.

Abstract: In a continuous drum mix asphalt plant, dust is exhausted from an intermediate zone of the drum mixer between its drying and mixing zones. The dust is exhausted radially through openings into a collection housing, which communicates with a dust collector and exhaust blower. An end housing at the discharge end of the drum communicates with the same dust collector and blower. Dampers are provided to control the relative proportion of air exhausted from the drum through the respective housings. Aggregate deflectors on the interior wall of the drum at the intermediate zone allow air and dust to flow while inhibiting the flow of aggregate. The collection housing surrounding the intermediate zone is of a size such as to produce a reduction in the velocity of the air as it passes out of the drum. Consequently, it serves as a knock-out box for the collection of larger particles which are carried out of the drum, but which settle out of the air stream as a result of the velocity decrease.