Abstract:
A method and apparatus for thermally killing weeds and other unwanted vegetation from areas where their presence is undesirable. The method and apparatus are especially useful for killing weeds located adjacent auto or rail roadways or airport runways. The method of killing weeds involves first spraying the weeds with an amount of water sufficient to cover a substantial portion of the exposed outer parts of the weeds, and then subjecting the water covered weeds to an elevated temperature sufficient for the time of exposure to kill them. The apparatus for thermally killing weeds by this method includes a water sprayer unit and a heater enclosure or box, the water sprayer unit being located in front of the heater box. The heater box has burners located at the forward end thereof that impact a heatable element capable of generating infra-red radiation. A porous apron extends between the bottom of the heater box and the ground to allow exhausting of combustion products and water vapor.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a continuation-in-part of application Ser. No. 09/247,207 filed Feb. 9, 1999 Now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to a method and an apparatus for thermally killing weeds. 
     The use of chemical herbicides to kill weeds has come under increasing attack as being environmentally unfriendly. 
     A number of alternative ways of killing weeds have been suggested. 
     Thermal killing of weeds has achieved some measure of success as an alternative to the use of herbicides. Some such devices burn propane or other gaseous or liquid hydrocarbons to produce flames or hot air aimed directly at the weeds. See, for example, the devices described in U.S. Pat. No. 5,020,510 and 5,189,832. One of the problems associated with this approach is setting fire to the weeds, which generates air pollution and, possibly, wild fires. 
     It has also been suggested to use hot foams to kill weeds. See, for example, U.S. Pat. No. 5,575,111. 
     It has been further suggested to spray hot water on weeds followed by compressing the sprayed weeds or applying a foam blanket to the sprayed weeds, the purpose of both approaches being to hold the hot water against the plants for an extended period of time. See, for example, U.S. Pat. Nos. 5,430,970 and 5,433,758. 
     It is an object of this invention to provide a method and apparatus for thermally killing weeds that is effective, economical, and minimizes the potential for inadvertently causing fires. 
     SUMMARY OF THE INVENTION 
     The invention is a method and apparatus for thermally killing weeds, grasses, or other unwanted vegetation adjacent auto or rail roadways, airport runways, or any area where it is desired to remove such unwanted vegetation. 
     The method of this invention for thermally killing weeds involves first applying water at ambient temperature onto the weeds targeted to be eliminated and subsequently heating the water and the weeds to a temperature sufficient to cause bursting of cell walls and denaturing of plant proteins which results in the death of the exposed tops of the weeds. 
     The apparatus for thermally killing weeds comprises a water spray unit and an associated heater enclosure or box located in trailing relationship to the heater. The heater box has a top or roof, side walls, and end walls. The bottom of the heater box is open to the atmosphere. The heater box has an infrared heat generating element located on the underside of the roof. The infrared heat generating element may be corrugated or otherwise shaped to provide maximum exposure of the weeds to infrared heating. The open bottom of the heater box is, in operation, located close to ground level, and has a porous apron extending from the bottom of the heater box into contact with the ground. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of a first embodiment of the apparatus of the present invention; 
     FIG. 2 is a partial side view, in section, of the heater box of the first embodiment of the apparatus of the present invention; 
     FIG. 3 is a bottom view of the first embodiment of the apparatus of the present invention; 
     FIG. 4 is a bottom view of the second embodiment of the apparatus of the present invention; 
     FIG. 5 is a lateral cross-sectional view taken along line  5 — 5  of FIG. 4 of the heater box of the second embodiment of the apparatus of the present invention; and 
     FIG. 6 is a longitudinal cross-sectional view of the heater box of the second embodiment of the apparatus of the present invention. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     The thermal weed killer apparatus  10  of the invention is mobile and can be moved over the ground in an area where it is desired to kill unwanted vegetation. Such movement can be effected in a number of ways. A preferred way is to pivotally attach apparatus  10  to one end of a boom  12 , the other end of boom  12  being connected to a motorized vehicle (not shown). Other means of attachment to a motorized vehicle can be used. Also, apparatus  10  could be configured for either manual or self-contained motorized movement, or towing behind a motorized vehicle. 
     A metal heater enclosure or box  20  has an open bottom  22  which, in operation, is located closely adjacent the ground, as seen in FIG. 1. A plurality of chains  23  extend between the bottom  22  of heater box  20  and the ground to provide a porous apron. Other flexible means providing such a porous apron may be used instead of chains. 
     Heater box  20  is comprised of a metal top  24 , a pair of parallel metal side walls  26  and a pair of parallel metal end walls  28 . A layer of insulation  30  is located between top  24  and infrared element  32  located below and parallel to top  24 . 
     Infrared element  32  is made of metal or other heat absorbing material capable of generating infrared radiation when heated, and is preferably corrugated with a plurality of ridges  34  extending downwardly and parallel to end walls  28 , as shown. 
     A heater manifold enclosure  40  extends between side walls  26  closely adjacent the front end wall  28 . Located inside manifold enclosure  40  is a U-shaped manifold pipe  42  communicating with a plurality of burners  44  extending outwardly from manifold pipe  42  and manifold enclosure  40  toward rear end wall  28 . Manifold pipe  42  communicates with a flexible or rigid conduit  46  via union  47 , and conduit  46  communicates manifold pipe  42  with a supply tank of flammable fuel (not shown), such as propane. Such a propane tank may be mounted on the heater box  20  of apparatus  10 , but it can be carried by the motorized vehicle to which apparatus  10  is attached or in a separate trailer. 
     In order to accomplish efficient combustion, it is important that the liquid fuel be preheated sufficiently to vaporize it prior to combustion. Such preheating can be accomplished in a number of ways. One way is to configure manifold pipe  42  in a U-shape, as illustrated. Such a U-shape configuration heats up the liquid fuel entering manifold pipe  42  by having the initial leg thereof being in close proximity to the final leg thereof, the final leg being heated by burners  44 . 
     Although manifold pipe  42  is illustrated as being U-shaped to effect preheating of the liquid fuel, manifold pipe  42  may be straight or have other shapes with preheating being accomplished in other ways, such as by passing conduit  46  through the space between infrared element  32  and the top  24  of heater box  20 , or having a separate heater for preheating the liquid fuel. 
     An air blower  48  supplies air via rigid or flexible conduit  49  to the fuel entering manifold pipe  42  at an appropriate location, such as at union  47 . 
     A water sprayer unit  50  is attached to the front end wall  28  of heater box  20  by a plurality of support arms  52 . Sprayer unit  50  has a plurality of holes and/or nozzles  54  located thereon. A flexible or rigid conduit  56  communicates sprayer unit  50  with a tank of water (not shown), which can be mounted on the heater box  20  of apparatus  10 , but it can also be carried by the motorized vehicle to which apparatus  10  is attached. 
     The water supplied to sprayer  50  is preferably maintained at ambient temperature to reduce costs and the complexity of the thermal weed killer apparatus, but the water may be preheated to facilitate operation of apparatus  10  at a higher rate of speed by thereby requiring less residence time of heater box  20  over the wetted weeds. 
     Although the water sprayer unit  50  is preferably attached to heater box  20  of apparatus  10 , it could be mounted on the vehicle to which apparatus  10  is attached or could be attached to a separate vehicle. 
     It is desirable to locate a secondary spray system on the apparatus to allow any weed fires that might be started to be extinguished. To this end, secondary water spray unit  60  may be attached to heater box  20  by means of a plurality of support arms  62 . A rigid or flexible water supply conduit  64  communicates with the water supply tank of apparatus  10 . 
     In operation, apparatus  10  is moved, via boom arm  12  mounted on a motorized vehicle, over a highway shoulder, railroad ballast area, or other area where it is desired to kill weeds. Apparatus  10  is moved in the direction indicated by the arrows in FIGS. 1-3. 
     Water is fed to sprayer  50  and exits holes/nozzles  54  to douse weeds passing beneath sprayer  50 . 
     Propane or other flammable fuel is fed from a supply tank to manifold pipe  42  via conduit  46 . Air is supplied from blower  48  via conduit  49 . The fuel and air mixture is lit as it exits burners  44 . The heat generated by burners  44  heats infrared element  32  to produce infra-red radiation within heater box  20 , which is directed downwardly through open bottom  22  and onto the moisturized weeds passing beneath heater box  20 . The water on the weeds enhances conduction of heat to the plant&#39;s exposed surfaces and helps retain heat to thereby lengthen the time of exposure of the weeds to elevated temperatures. The temperature generated by heater  20  is sufficient to vaporize at least some of the sprayed-on water from the weeds. The sprayed-on water significantly assists in subjecting the weeds to a killing temperature. 
     Although infrared radiation generated by infrared heating element  32  is the primary source of heat applied to the target weeds, there is some direct contact of taller weeds with the flames issuing from burners  44 . In addition, some turbulent hot air is generated by the burners  44  which can also contact target weeds and assist in vaporizing water from the leaf surfaces of these previously sprayed weeds. 
     Apparatus  10  is moved over the weeds at a speed to vaporize all or substantially all of the thin film of water coating the weeds but not to such conditions as would cause the weeds to combust. However, if the apparatus is being operated in weather or other conditions where it is difficult to prevent the weeds from catching on fire, secondary sprayer unit  60  may be operated to prevent such fires. 
     The porous apron formed by chains  23  or other porous curtain material allows water vapor and combustion products to escape to the atmosphere. The mechanical action of the porous apron also helps extinguish any flames should they occur. 
     A second embodiment of the heater enclosure or box is shown in FIGS. 4-6. Parts common to the weed killer apparatus  10  of the invention described above relative to the first embodiment have the same reference number. Parts of the second embodiment that are similar in function to those parts of the first embodiment have the same reference number but increased by  100 . 
     Heater enclosure or box  120  is open at the bottom and includes a sloping metal top  124 , a pair of parallel metal side walls  126 , a front metal end wall  128  and a parallel rear metal end wall  128 ′. The metal top  124  of heater box  120  slopes downwardly from adjacent the front (leading) end wall  128  to the rear (trailing) end wall  128 ′ thereof. The slope of metal top  124  relative to the ground may vary from one degree to about 45 degrees. 
     A layer of insulation  130  is located between top  124  and infrared element  132  located therebelow. The major plane of infrared heating element  132  is substantially parallel to the major plane of metal top  124 . Infrared heating element  132  is made of metal or other heat absorbing material capable of generating infrared radiation when heated, and is preferably corrugated with a plurality of ridges  134  extending downwardly, and parallel to the longitudinal side walls  126 , as shown. 
     The upper surface of infrared heating element  132  is in contact with the lower surface of insulation layer  130 . The lower surface of infrared heating element  132  faces toward the open bottom of heater box  120 . 
     A heater manifold enclosure  140  extends between side walls  126  adjacent the front end wall  128 . Located inside manifold enclosure  40  is a U-shaped manifold pipe  42  communicating with a plurality of burners  44  extending outwardly from manifold pipe  42  and manifold enclosure  140  toward rear end wall  128 ′, burners  44  being located between and beneath the ridges  134  of infrared element  132 , as shown. Manifold pipe  42  communicates with a flexible or rigid conduit  46  via union  47 , and conduit  46  communicates manifold pipe  42  with a supply tank of flammable fuel (not shown), such as propane. Such a propane tank may be mounted on the heater box  120  of apparatus  110 , but it can be carried by the motorized vehicle to which apparatus  110  is attached or in a separate trailer. 
     In operation of the second embodiment just discussed, thermal weed killer  110  is mounted for movement across the ground in the same manner as for apparatus  10 , as illustrated in FIG.  1 . Flames from the outlets of propane burners  44  move across the underside of the angled infrared heating element  132  toward the ground located adjacent the bottom of rear end wall  128 ′. Such flames contact and impact the target weeds located adjacent rear end wall  128 ′ with direct flames, thus increasing the treatment effects of the thermal weed killer  10 . In addition, the velocity of air supplied from blower  48  can be adjusted to create turbulent hot air under the angled infrared heating element  132  which moves downwardly across the angled underside of heating element  132  toward the ground located adjacent the bottom of rear end wall  128 ′ where it contacts target weeds, moving them about. This movement helps maximize contact between the target weeds and the hot air, the infrared energy from heating element  132 , and the direct flames from the burners  44 . Together, the impact of these three thermal factors enhances the vaporization of water from the leaf surfaces of the previously sprayed weeds thereby maximizing the thermal weed killing effect. 
     It will be obvious to those having skill in the art that many changes may be made to the details of the above-described embodiments of this invention without departing from the underlying principles thereof. The scope of the present invention should, therefore, be determined only by the following claims.