Low emission energy efficient 100 percent RAP capable asphalt plant
View Patent ↗An HMA plant which uses combination direct exhaust heated and indirectly steam heated pre-heating drum in combination with a sealed indirect hot oil heated rotary shaft mixer, where the steam given off from the heated HMA is maintained, separated from the sulfur containing exhaust of a hot oil heater, so as to minimize the production of acid in liquid form.
1. A method of mixing HMA comprising the steps of:
providing a pre-heater configured to move RAP in a first direction and to preheat said RAP to a temperature approaching, but not more than the boiling point of water inside of said pre-heater;
directing such pre-heated RAP to a mixer;
using said mixer for providing direct heating of said pre-heated RAP to a temperature above the boiling point of water;
providing an oil heater to heat oil and to provide the heated oil to movable portions of said mixer, so as to heat such movable portions and thereby indirectly heat HMA disposed within mixer;
providing exhaust from an oil heater to an open central counter-flow heated gas passage within the pre-heater;
providing steam from the mixer to a steam void in the pre-heater;
maintaining separation of the steam and the exhaust of the oil heater until such time as the water vapor has condensed from the steam to a liquid state; and
regulating the temperature and the amount of exhaust and steam provided to the pre-heater, so that the steam in the steam void does cool sufficiently to condense to a liquid before being exhausted separate from the air exiting the pre-heater.
2. The method of claim 1 wherein said pre-heater is a counter flow pre-heater where hot gases flow in a second direction over said RAP as it moves through said pre-heater in said first direction; and
wherein said first direction is substantially opposite said second direction and wherein said temperature above the boiling point of water is approximately 600 degrees F.
3. The method of claim 2 wherein said pre-heater has a material input end and a material output end; and receives said steam from said mixer and said exhaust from oil heater both at said material output end.
4. The method of claim 3 wherein said pre-heater is inclined upward from said material output end to said material input end.
5. The method of claim 1 further comprising a weighing cold feed conveyor and wherein said oil heater heats said oil to an oil temperature above the boiling point of water.
6. The method of claim 1 wherein said pre-heater is constructed with a material and exhaust gas zone through which said RAP and said exhaust move in substantially opposite directions and a separate steam zone which receives said steam and allows said steam to indirectly pre-heat said RAP flowing from said material input end to said material output end and thereby allow for pre-heating of said RAP without introducing moisture therein from said steam; a wherein said oil heater heats said oil to an oil temperature above the boiling point of water.
7. The method of claim 6 wherein said pre-heater is regulated with a weighing cold feed conveyor providing information for regulation which relates to the weight of the RAP and the rate of RAP entering said pre-heater and wherein said oil temperature is approximately 750 degrees F.
8. The method of claim 7 wherein said pre-heater is coupled to a cyclone separator.
9. The method of claim 8 wherein said pre-heater is coupled to a filter house.
10. The method of claim 9 wherein said pre-heater is insulated exterior of an outside wall of said steam zone.
11. A method of mixing HMA comprising the steps of:
providing a pre-heater configured to move RAP in a first direction and to preheat said RAP to a temperature approaching, but not more than the boiling point of water inside of said pre-heater;
directing such pre-heated RAP to a mixer;
using said mixer for providing direct heating of said pre-heated RAP to a temperature above the boiling point of water;
providing an oil heater to heat oil and to provide the heated oil to movable portions of said mixer, so as to heat such movable portions and thereby indirectly heat HMA disposed within mixer;
providing exhaust from an oil heater to an open central counter-flow heated gas passage within the pre-heater;
providing steam from the mixer to a steam void in the pre-heater;
maintaining separation of the steam and the exhaust of the oil heater until such time as the water vapor has condensed from the steam to a liquid state;
regulating the temperature and the amount of exhaust and steam provided to the pre-heater, so that the steam in the steam void does cool sufficiently to condense to a liquid before being exhausted separate from the air exiting the pre-heater;
wherein said pre-heater is a counter-flow pre-heater where hot gases flow in a second direction over said RAP as it moves through said pre-heater in said first direction;
wherein said first direction is substantially opposite said second direction and wherein said temperature above the boiling point of water is approximately 600 degrees F.;
wherein said pre-heater has a material input end and a material output end; and
receives said steam from said mixer and said exhaust from oil heater both at said material output end;
wherein said pre-heater is inclined upward from said material output end to said material input end; and
further comprising a weighing cold feed conveyor.