Patent Application
20060246391
1. Field of the Invention
The invention relates generally to an apparatus and method for heating transported materials and in particular to an apparatus and method for continuous heating of carbonaceous materials above the ignition temperature of the carbonaceous materials, such as tunnel kilns, conveyor ovens, or other continuous heating ovens.
2. Background Art
Prior devices for continuous heating or heating of moving materials to high temperatures above normal food cooking temperatures, such as tunnel kilns and conveyor ovens have been used primarily for non carbonaceous materials such as brake linings, tiles, and ceramics. Food cooking ovens typically avoid temperatures above the combustion flash point of any carbonaceous material in the foods to be heated. The use of high temperature tunnel kilns for heating carbonaceous materials has been generally limited to placing the target material in an enclosed casing or muffler that is moved through the oven with the carbonaceous material therein, so that the carbon materials were shielded from direct atmospheric convection heating of the oven. Such prior ovens therefore relied upon conductive heating through the layers of the muffler enclosure. Typically such muffler enclosure devices included a layer of another carbonaceous material such as coke breeze to protect the surface of the carbonaceous materials from oxidation. The entire muffler, coke breeze coating, and the carbonaceous material contained therein all moved together through the oven.
A tunnel oven for heating transported carbonaceous materials includes an enclosure having a passage and a transport device for moving solid carbonaceous materials through and along a length of the passage. A direct convection heater is operably connected to the enclosure to heat the solid carbonaceous material as the material is moved along the length of the passage. A temperature controller is operably coupled to the heater to provide one or more selected temperatures along the length of the passage. An atmosphere controller controls the heating atmosphere along the length of the passage so that the surface of the solid carbonaceous material is protected against oxidation.
Other aspects and advantages of the invention will be apparent from the following description and the appended claims.
Those skilled in the art will understand from this disclosure that one example of separating devices 23 and 25 are known as vestibules. Vestibules are basically a chamber that has a front door and a back door. The back door is positioned adjacent to the tunnel oven entry end 22 and is effectively sealed to the oven. In operation the back door is closed, and the front door is opened to receive the carbonaceous materials while the back door remains closed. When the carbonaceous materials are within the vestibule, the front door is also close and then the backdoor is opened to allow the carbonaceous materials to move through the back door and then into entrance end 22 and the tunnel oven passage 26. The reverse procedure is employed to let the carbonaceous materials exit the end 24 of the tunnel oven passage 26. A first door to the vestibule adjacent the oven is opened while the second door is closed. When the carbonaceous materials are within the vestibule, the first door is closed and the second door is opened to let the carbonaceous materials exit without loosing the atmosphere maintained in the tunnel oven.
Those skilled in the art will also understand from this disclosure that an alternative example the separating devices 23 and 25 might be a moving air curtains. Moving air curtains provide a plurality of aligned high velocity air jets that move air past the entrance end 22 and also past the exit end 24. The solid carbonaceous materials can pass through the air curtain; however the rapidly moving air creates a boundary layer barrier to the transfer of gaseous atmosphere. When the carbonaceous materials are in the tunnel oven the air curtain acts to separate the exterior atmosphere from the interior atmosphere in the tunnel oven.
A transport device 40 may be used to carry and transport the carbonaceous materials through the tunnel oven according to one embodiment of the invention. One example of a transport device includes a plurality of materials carrying carts 42a-d having temperature resistant metal wheels 44 guided along temperature resistant tracks 46. It will be understood that the number of carts 42 may be any number consistent with the size of the carts and of the tunnel oven such that the letter designations a-d are representative and are not intended to limit the number. The carts 42a-d may each movably support one of a plurality of container 48a-d for carrying carbonaceous materials 50. The containers 48a-d may be made of a high temperature resistant and relatively inert material such as refractory material so that the containers 48a-d do not oxidize or otherwise chemically react or interfere with the combustion of the fuel gasses and the heating of the carbonaceous materials 50. It will be understood by those skilled in the art based upon this disclosure that other high temperature transport devices might be constructed for transporting carbonaceous materials along the length 28 of the passage 26 through the enclosure tunnel oven 10. For example, and without limitation, a conveyor belt system with the requisite thermal and chemical resistance or a plurality of temperature resistant and chemically inert rollers might be used without departing form certain aspects of the invention.
In the embodiment depicted in
In one embodiment of the invention a positive pressure P1 is provided within the passage 26 and adjacent to the entrance end 22. The pressure P1 is adjusted using the pressure and volume of methane gas, adjusted at regulators 61 and 62, and the volume of air (the source of oxygen, O2), and adjusted at regulators 63 and 64. The oxygen sensors 57 are used to monitor the oxygen level within the tunnel oven and to increase the oxygen proportionately to the methane gas when additional methane gas fuel is added to raise the temperature, or to reduce the oxygen when the methane gas fuel is reduced to lower the temperature. The proper pressure and mixture is controlled so that the positive pressure is maintained. A gradient of pressure is desirably provided along the length of the passage 26 with higher pressure P1 at the entrance end 22 and lower pressure P2 at the exit end 24, such that both P1 and P2 are higher that the external atmospheric pressure. For example, the individual burners may each have separate regulators 61, 62, 63, and 64 corresponding to each burner 32a-j and 34a-j, respectively. Each burner 32a-e and 34a-e may be adjusted to progressively decrease from the entrance burners 32a and 34a to burners 32j and 34j adjacent the exit end 24. Alternatively several regulators may control separate zone comprised of several burners. Thus, for example the burners 32a and 32b may be adjusted at one pressure an volume setting to obtain the desired heating rate and the desired pressure P1 and a lower pressure volume of methane gas and air injected in a zone with the burners 32i and 32j so that a pressure P2 is obtained that is greater than the atmospheric pressure and slightly lower than the positive entrance pressure P1.
The temperature is controlled also by the amount of heat provided by combustion of the fuel with the O2 in the air. To avoid the carbonaceous material oxidizing in the air an excess amount of methane fuel is provided. Thus, direct convection heating of the carbonaceous material 50 to temperatures above the combustion temperature of the carbonaceous material can be accomplished without oxidizing the surface of the carbonaceous material 50. The heat generated is therefore controlled by regulating the amount of air (O2) injected into the burners. The oxygen sensors are used to monitor the atmosphere quality so that the oxygen level is lean and an excess amount of fuel or combustible hydrocarbon evolved from the heated carbonaceous materials is present for combustion. Thus, the temperature and atmosphere are controlled according to the temperature sensed at sensors 56 and the oxygen sensed by oxygen sensors 57 along the inside of the tunnel oven adjacent to the burners or in the zone or area surrounding the burner that is thus adjusted.
With reference to
In the event the volatiles or portions of the volatiles released from the carbonaceous materials are long chain hydrocarbons prior to heating they may be expected to break down into lighter shorter chain hydrocarbons at a sufficiently high temperature above the ignition temperature of other portions of the carbonaceous materials. The long chain volatiles might not ignite while in the tunnel oven passage. Such chains may be further cracked in a cracking zone 74 positioned along the conveyance tubes 72 so that the hydrocarbons can be efficiently burned in the roof combustion chamber 36. The heat generated in the roof is conveyed to the tunnel oven passage and to the materials transported by conduction through the ceiling 68 and by radiant energy heat transfer from the ceiling 68 into the passage 26 and directly to the carbonaceous material 50. Thus, the mixture of air to fuel in the roof combustion chamber 36 can be adjusted to be stochiometricly balanced or to provide an excess proportion of oxygen without the O2 combining with the carbonaceous materials 50 transported through the oven 10.
The temperature can be further controlled by a cooler mechanism 80 that may comprise a water spray nozzle 82 adjustably supplied with water through a valve 84 in fluid communication with a water supply 86. It will be understood that the number an placement or positioning of the cooler mechanism 80 is not intended to be limited by one water cooler mechanism 80 and spray nozzle 82 depicted as a schematic example in
In one embodiment the atmosphere is further controlled to avoid oxidation of the solid carbonaceous material 50 by injecting carbon dusts 92. A carbon dust injection mechanism 90 may be used that includes a carbon dust source 84. The dust injecting mechanism is usefully designed to introduce the carbon dust without introducing significant additional air and without allowing too much of the internal atmosphere to escape from the tunnel oven. In one embodiment a dust injector 90 may include a distributor roller 94 having a plurality of troughs 96 cut into the surface. The roller is rotated in a seal 98 such that carbon dust 92 contained in a hopper 100 is distributed from the hopper into the tunnel oven 10 as the distributor roller 94 is rotated. Thus even when a1 of the excess hydrocarbon fuel is depleted by combustion in the passage and/or in the combustion chamber 70, the dust particles have a significantly larger percentage of surface area and form the preferred oxidation sites for any remaining oxygen. The solid carbonaceous material 50 is therefore relatively protected against oxidation reaction in the area or zone where the carbon dust is injected. The carbon dust is the same material as the carbonaceous material 50 so that its presence does not adversely affect the heating processes occurring in the material 50. It will be understood that the number an placement or positioning of the carbon dust injection mechanism 90 is not intended to be limited by one carbon dust injection mechanism 92 depicted as a schematic example in
In another embodiment of the invention the atmosphere may be controlled to provide preferred reaction with injected hydrocarbon gas 104 or vaporized hydrocarbon oil 106 as for example through an injector 108. As with the carbon dusts 92, The combustion components in the hydrocarbon gas 106 or vaporized oil 106 will be more readily combusted than the solid carbonaceous material 50 so that the carbonaceous material 50 will be protected against oxidation.
While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.
