5364182 Counter-flow asphalt plant with multi-stage combustion zone overlapping the mixing zone

Abstract

A drum mixer is provided with a rotatable cylinder in which aggregates, reclaimed asphalt pavement and liquid asphalt are mixed to produce an asphaltic composition. The drum cylinder includes a first region, in which virgin aggregate is heated and dried by heat radiation and the stream of hot gases produced by a burner flame flowing in countercurrent flow to the aggregate itself to establish a highly beneficial heat transfer relationship. A second region doubles as combustion and mixing zones. In the mixing zone the reclaimed asphalt pavement and liquid asphalt is added and mixed with the aggregates. The combustion zone is formed along the center of the mixing zone by an elongated combustion assembly disposed along the central axis thereof. The combustion assembly and chamber extend from the discharge end of the drum through the mixing zone to the heating and drying zone to segregate the hot gases from the asphalt, thereby preventing degradation of the final product. The hot gas stream is withdrawn from the drum cylinder at the upstream or inlet end thereof and delivered by ductwork to air pollution control equipment. Accordingly, while the liquid asphalt, recycle material and virgin aggregate are mixed in the mixing zone in an annular region between the drum cylinder and the combustion assembly, contact with the burner flame or with the hot gas stream is eliminated.