Waste heat recovery in asphalt mixing plant
AssigneeThe McCarter Corporation
InventorRoger A. Powell
Life of this patent
Estimating the term…
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.
Claims23
In an asphalt mixing plant comprising:
- feed bin means for receiving solid material from the group consisting of virgin aggregate and used asphalt-aggregate compositions at substantially ambient temperatures and for temporarily containing said material prior to delivery to a drying device;
- drying means for temporarily containing aggregate including means for showering the aggregate through a moving air stream;
- burner means for directly supplying heat to the aggregate and the moving air stream in the drying means;
- and
- means for effecting a flow of exhaust gas out of the drying means to carry away moisture from the drying means;
- wherein the improvement comprises duct means for conducting at least part of the exhaust gas from the drying means to said feed bin means, at least part of the wall of said duct means serving to conduct heat from said exhaust gas to the solid material in said feed bin means while isolating said exhaust gas from said material to prevent moisture from said exhaust gas from condensing on said material, and means for initiating condensation of moisture from said exhaust gas substantially adjacent to but upstream of the location where the exhaust gas within the duct means first reaches the location at which said part of the wall of said duct means conducts heat from said exhaust gas to said solid material.
A method for preparing asphaltic concrete comprising the steps of supplying heat to a quantity of aggregate, effecting a flow of exhaust gas to carry moisture away from said aggregate through a duct, and conducting heat from said exhaust gas to a solid ingredient of asphaltic concrete, while said ingredient is physically separated from said aggregate, through a solid, heat-conductive, wall of said duct in contact with said ingredient, while condensing moisture within said duct, and isolating said condensed moisture from said solid ingredient, said method including the step of initiating condensation of the water vapor in said exhaust gas in said duct at a location substantially adjacent to but upstream of the location at which the exhaust gas within said duct first comes into close proximity to said solid ingredient.
A method for preparing asphaltic concrete comprising the steps of supplying heat to a quantity of aggregate, effecting a flow of exhaust gas to carry moisture away from said aggregate through a duct, and conducting heat from said exhaust gas to a solid ingredient of asphaltic concrete, while said ingredient is physically separated from said aggregate, through a solid, heat-conductive, wall of said duct in contact with said ingredient, while condensing moisture within said duct, and isolating said condensed moisture from said solid ingredient, said method including the step of spraying water into the interior of said duct at a location adjacent the location at which the exhaust gas within said duct first comes into close proximity to said solid ingredient, thereby initiating condensation of the water vapor in said exhaust gas.
Dependencies are inferred from the claim text.