Direct fired axial flow co-current heating system for hot-in-place asphalt recycling

Abstract

A direct fired, axial flow, co-current primary heater for use in a hot in place asphalt recycling system includes internally substoichiometric inspiriting burners operating at slightly greater than the stoichiometric amount by tertiary air flow controlled by a variable speed induced draft fan. A cool down box at the end of the burner box reduces emissions exiting at the back of the system. The sides of the burner box may pivot outwardly to increase the width of coverage.

1 . A direct fired, axial flow, co-current primary heater for a hot in place asphalt recycling system, the heater comprising:
 (a) a heater container having front, rear, left, right and top sides for positioning over an asphalt road surface for travel over the asphalt in a first direction of travel, such that the bottom edges of the sides is positioned adjacent the asphalt to substantially prevent escape of gases from the interior of the container;   (b) a burner positioned at the front of the container for heating the gas in the container, the burner comprising:
 (i) a combustion chamber; 
 (ii) a fuel injector for injecting fuel into the combustion chamber in a direction opposite to the first direction; 
 (iii) a first combustion gas inlet for inputting a first supply of combustion gas into the first chamber to mix with the fuel, configured to restrict the amount of gas input into the combustion chamber less than the stoichiometric amount required for complete combustion of the fuel; 
 (iv) a combustor for igniting the mixture of fuel and gas; and 
 (v) a second combustion gas inlet for inputting a second supply of combustion gas into mixture downstream of the combustor; 
   (c) a variable speed induced draft fan for drawing the flow of second combustion gas from the second combustion gas inlet; and   (d) a fan controller for controlling speed of the fan responsive to the amount of oxygen in the gas stream exiting the burner to maintain the oxygen above the stoiciometric amount to fully combust the fuel.   
     
     
         2 . The primary heater of  claim 1  wherein the second combustion gas inlet comprises an adjustable inlet for controlling the amount of second supply of combustion gas into the combustion chamber. 
     
     
         3 . The primary heater of  claim 2  further comprising a controller responsive to the pressure in the heater container to control the adjustable inlet to maintain the pressure in the heater container at a level less than the pressure outside the heater container. 
     
     
         4 . The primary heater of  claim 1  wherein the second combustion gas inlet inputs the second supply of combustion gas into the heater container. 
     
     
         5 . The primary heater of  claim 1  wherein the flow resistance of the first combustion gas inlet is greater than the flow resistance of the second combustion gas inlet. 
     
     
         6 . The primary heater of  claim 5  wherein the fan controller controls the speed of the fan to maintain the amount of excess gas leaving the second combustion gas inlet at below about 15% above the stoichiometric amount. 
     
     
         7 . The primary heater of  claim 6  wherein the second combustion gas inlet comprises an adjustable inlet for controlling the amount of second supply of combustion gas into the combustion chamber and further comprising a controller responsive to the pressure in the heater container to control the adjustable inlet to maintain the pressure in the heater container at a level less than the pressure outside the heater container. 
     
     
         8 . The primary heater of  claim 1  wherein the fuel injector is configured to inject a high momentum flow of fuel into the combustion chamber in the direction opposite to the first direction. 
     
     
         9 . The primary heater of  claim 1  wherein the burner comprises a plurality of burners extending along the front side of the container in axial alignment perpendicular to the first direction. 
     
     
         10 . The primary heater of  claim 1  wherein the combustion gas is air. 
     
     
         11 . The primary heater of  claim 7  wherein the adjustable inlet comprises an annular channel and opening about the periphery of a circular cross-section combustion chamber and wherein a slideable annular collar block is moved in a axial direction to open and close the adjustable inlet. 
     
     
         12 . The primary heater of  claim 1  wherein the first combustion gas inlet is configured with respect to the fuel injector to provide about 75% of the stoichiometric gas requirements for combustion of the fuel. 
     
     
         13 . The primary heater of  claim 1  wherein the left and right sides are extendable outwardly to increase the width of the heater container. 
     
     
         14 . The primary heater of  claim 13  wherein the left and right sides are pivotable about an axis adjacent their top to permit the bottom of the sides to extend outwardly. 
     
     
         15 . The primary heater of  claim 1  further comprising a cooling container adjacent the rear side for collecting and cooling emissions from the road surface following the passage of the heater container over the road surface. 
     
     
         16 . The primary heater of  claim 15  wherein the emissions from the cooling container are directed to mix with the emissions in the heater container. 
     
     
         17 . The primary heater of  claim 16  further comprising an incinerator communicating with the heater container for receiving and combusting the emissions received from the heater container and cooling container to combust the emissions before returning residual gases to the environment. 
     
     
         18 . The primary heater of  claim 17  wherein the fan is positioned to draw the emissions from the heater container and cooling container and direct them to the incinerator. 
     
     
         19 . The primary heater of  claim 15  wherein the cooling container comprises a first outlet from the interior of the cooling container to the heater container, a second outlet from the interior of the cooling container to the fan, and a controller for controlling the amount of emissions from the road surface travelling through one or both of the outlets to control the temperatures of the emissions entering the incinerator. 
     
     
         20 . The primary heater of  claim 19  further comprising an inlet to permit cooler outside gases to enter the cooling container. 
     
     
         21 . The primary heater of  claim 19  further comprising a sensor for sensing the amount of gaseous emissions from the asphalt surface behind the cooling container. 
     
     
         22 . The primary heater of  claim 21  further comprising a controller responsive to the sensor for controlling the amount of gases exiting the cooling container through the second outlet. 
     
     
         23 . A burner for a primary heater of a hot in place asphalt recycling system positioned at the front of the container for directing heat axially co-current with the direction of travel of the asphalt recycling system, the burner comprising:
 (a) a combustion chamber;   (b) a fuel injector for injecting fuel into the combustion chamber in the co-current direction;   (c) a first combustion gas inlet for inputting a first supply of combustion gas into the first chamber to mix with the fuel, configured to restrict the amount of gas input into the combustion chamber less than the stoichiometric amount required for complete combustion of the fuel;   (d) a combustor for igniting the mixture of fuel and gas; and   (e) a second combustion gas inlet having a flow resistance less than that of the first combustion gas for inputting a second supply of combustion gas into mixture downstream of the combustor;   (f) a fan for controlling the amount of combustion gas exiting the second combustion gas inlet; and   (g) a controller, responsive to the amount of oxygen in the mixture downstream of the second combustion gas inlet, controlling the fan to maintain the amount of excess gas leaving the adjustable inlet at below about 15% above the stoichiometric amount.   
     
     
         24 . The primary heater of  claim 1  wherein the primary heater is a part of a train of heaters in axial alignment for travel in the first direction and wherein the primary heater provides at least 75% of the total heat applied to the asphalt surface by the train. 
     
     
         25 . The primary heater of  claim 24  wherein the primary heater is the first heater of the train. 
     
     
         26 . The primary heater of  claim 24  wherein the train comprises four primary heaters, further comprising a pair of scarifiers for milling the asphalt from the surface, the first scarifier positioned behind the second primary heater in the train and the second scarifier positioned behind the fourth primary heater of the train. 
     
     
         27 . A process of hot in place asphalt recycling of an asphalt surface using a primary heater in a heater box, comprising the steps of:
 (a) by combustion of a fuel air mixture by a burner, creating heat and directing the heat in the heater box in an axial direction, in direction from the front to the rear of the box, co-current with the direction of movement over the asphalt, combustion by the burner comprising the steps of:
 (i) directing stream of fuel at high momentum in the axial co-current direction; 
 (ii) directing a first stream of air into the stream of fuel so that first stream is entrained with the fuel, the amount of air in the first stream being insufficient to cause complete combustion of the fuel; 
 (iii) partially combusting the fuel in the mixture of fuel and first stream of air; 
 (iv) directing a second stream of air into the mixture, the amount of air in the second stream being sufficient, when combined with the amount of air in the first stream of air, to exceed the amount required for complete combustion of the fuel; and 
 (v) combusting the remaining uncombusted fuel in the stream; 
   (b) applying negative pressure in the axial co-current direction on the combustion gases and on the second stream of air; and   (c) controlling the amount of excess air leaving the burner to an amount less than about 15% above the amount required for complete combustion of the fuel by controlling the amount of negative pressure applied on the second stream of air.   
     
     
         28 . The process described in  claim 27 , wherein at step (a)(iv), controlling the amount of second stream of air entering the mixture by increasing or decreasing the area through which the second stream of air travels to enter the mixture. 
     
     
         29 . The process as described in  claim 28 , wherein the amount of second stream of air is controlled to maintain the pressure in the heater box less than the pressure outside of the heater box.