Abstract:
The present invention discloses a regenerative particle/vapor separator to thermally convert various liquids used to treat stored agricultural products into vapor by: 1) Entraining the liquid in a turbulent mist and then effectuating a change of the liquid into a vapor intermixed with the mist; and, 2) Separating the vapor out of the mist while retaining the remaining mist for subsequent conversion to vapor. Some liquids used to treat stored agricultural products undergo the further step of thermally decomposing into beneficial gaseous byproducts which are also separated out of the mist. The vapor and/or gaseous byproducts are then applied to a stored mass of agricultural products to variously sanitize, clean, and chemically and biologically alter them.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    Not Applicable. 
       FIELD OF THE INVENTION 
       [0002]    The present invention deals generally with a device for thermally converting various liquids used to treat stored agricultural products into vapor by: 1) Entraining the liquid in a turbulent mist and then effectuating a change of the liquid into a vapor intermixed with the mist; and, 2) Separating the vapor out of the mist while retaining the remaining mist for subsequent conversion to vapor. Some substances used to treat stored agricultural products undergo the further step of thermally decomposing into beneficial gaseous byproducts which are also separated out of the mist. The vapor and/or gaseous byproducts are then applied to a stored mass of agricultural products to variously sanitize, clean, and chemically and biologically alter them. 
       BACKGROUND OF THE INVENTION 
       [0003]    The ability to store harvested agricultural products for extended periods of time is an important element in ensuring an adequate food supply because cyclical growing seasons are asynchronous with the steady demand for staple foodstuffs. Globally, conventional and cold storage techniques are well known techniques for the long term storage of pome fruit, onions, potatoes, and the like even in relatively poorly developed nations. See e.g. K. Moazzem &amp; K. Fujita,  The Potato Marketing System and Its Changes in Bangladesh: From the Perspective of a Village Study in the Comilla District,  42 The Developing Econ. 63-94 (March 2004). Wherever such agricultural products are stored, the process of treating these agricultural products to sanitize, clean, and chemically and biologically alter the exterior surfaces of the product is a common process. 
         [0004]    Traditionally such treatments were made by dipping, drenching or spraying the agricultural product with the desired chemicals. This is wasteful and inefficient and has the further disadvantage of creating a significant amount of contaminated post-treatment effluent that must be disposed of safely. Further, such methods require that the agricultural product must be physically transported into, and out of, a treatment device “assembly line” style. To address these limitations, more efficient and cost-effective methods of treating agricultural products directly in situ in the storage facility have been developed. These rely on devices that generate a mist containing the chemical to be deposited on the agricultural product and then allowing or causing the mist to permeate the stored mass of product. Mists, however, suffer from the disadvantage of insufficiently penetrating the deeper layers of piled agricultural product to which they are applied. As a result, some devices have been created that use heat to vaporize at least some of the chemical. These devices all share the same shortcoming: they are incapable of completely ensuring that only vapor is generated. As a result, larger non-vaporous particles remain intermixed with vapor particles and thus distribution throughout a pile of stored agricultural product, while improved, is still uneven. It is thus a first goal of the present invention to provide a device that ensures the complete vaporization of chemicals subjected to it without the creation residual droplets and mist in the delivered hot gaseous stream. 
         [0005]    Furthermore, in the case of peroxyacetic acid (PAA), a commonly used post-harvest sanitizing agent, a mere physical change from liquid to vapor is not all that occurs. As it is heated, PAA thermally decomposes into a number of intermediate byproducts, a significant fraction of which are hydroxyl radicals and elemental oxygen. These substances are powerful oxidizers and are known to eliminate a number of common surface pathogens from various surfaces. Unfortunately, vaporous PAA works best when applied at higher temperatures because the antimicrobial components created when PAA thermally decomposes (hydroxyl ions and elemental oxygen) are highly reactive with other substances in the environment and as such the vapor must be relatively hot so that free hydroxyl ions and elemental oxygen are formed directly on, or very close to, the surface to be sanitized. While it is possible to create such a vapor and apply it at relatively low temperatures, the resulting concentration of antimicrobial hydroxyl ions and elemental oxygen is comparatively low on, or near, the surface to be sanitized thus necessitating a longer application time. However, by selectively increasing the concentration of hydroxyl ions and elemental oxygen relative to other substances in the generated vapor, higher concentrations of both substances remain when applied. By this means PAA vapor may be applied to agricultural products that otherwise would be damaged by the higher vapor temperatures called for when using other methods extant in the prior art. Co- pending U.S. Provisional App. 61/619894 describes such a process. U.S. Pat. NO. 6,596,231 describes a related process used to sterilize PET bottles. However, this invention comprehends a lengthy tubular heating chamber in which the PAA is transported linearly down the heating chamber where it is terminally injected into passing PET bottles. Because of its size and mode of use, such a device is not portable and is thus unusable in conventional agricultural applications where treatments must occur where agricultural products are temporarily stored. It is thus a second goal of the present invention to provide a highly compact, portable device that may be transported to various agricultural storage facilities, wherein the device creates a PAA vapor that contains a relatively high concentration of hydroxyl ions and elemental oxygen for application on a stored mass of agricultural product at relatively low temperatures. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention is comprised of: 1) A metal heating vessel; 2) A vapor collector; 3) A heating assembly; 4) An air blower; and, 5) A pump for delivering liquid to the heating vessel for vaporization/dissociation. 
         [0007]    The metal heating vessel is in the general form of a hollow double-walled cylinder with a closed top and bottom. Formed in the closed top are one or more first circular openings and through each of these first circular openings a metal vaporizing unit is installed. Each vaporizing unit is in the form of an open top cylinder and is installed in the closed top such that the edges forming the open top of the vaporizing unit are both: 1) Flush with the first circular opening; and, 2) Lie in the plane of the closed top. By this means the cylindrical body of each vaporizing unit extends into the interior of the heating vessel. Each vaporizing unit is in turn perforated around its circumferential periphery by a series of heating slits each of which is formed at a level about 1 cm from the bottom of the vaporizing unit. Each of these heating slits is oriented so that forced air entering from the bottom of the vaporizing unit is directed radially along the lower portion of the curved outer wall of the vaporizing unit to form a whirling vortex inside the vaporizing unit. 
         [0008]    Into the open top of each vaporizing unit a metal vapor separator is installed. Each vapor separator is the general form of a funnel or truncated cone and is installed in its associated vaporizing unit such that the edges forming the wider, open top of the vapor separator are both: 1) Flush with the open top of the vaporizing unit; and, 2) Lie in the plane of the closed top of the heating vessel. Each vapor separator thus seals the interior of its associated vaporizing unit such that the only exit path for particles generated in the vaporizing unit is through the smaller, open bottom of the vapor separator and thence out of its larger, open top. 
         [0009]    Surmounting the closed top of the heating vessel is an inverted conical vapor collector. Affixed to the smaller opening of this conical vapor collector is a vapor distribution duct. This vapor distribution duct is used to transport generated vapors to a remote, stored mass of agricultural product. It will be readily apparent that the conical vapor collector and vapor distribution duct may be omitted and the closed top of the heating vessel may be exposed directly to the interior aspect of the storage facility. 
         [0010]    Extending into the bottom part of the heating vessel and proceeding up and to the closed top are one or more chemical supply lines: one for each vaporizing unit. Each chemical supply line proceeds into each vaporizing unit such that chemical provided through the chemical supply line rests on the bottom of the vaporizing unit. The amount of chemical pumped through each chemical supply line is controlled to ensure that the amount of chemical in each vaporizing unit never rises to the level of the circumferential row of heating slits in the lower portion of each vaporizing unit. 
         [0011]    One or more apertures allowing heated air from one or more heating assemblies perforate the wall of the heating vessel near its closed bottom. The heating assemblies are attached to the heating vessel and the air blower is in turn attached to the heating assemblies such that output air from the air blower passes through the heating assemblies entering the heating vessel. 
         [0012]    The invention is used to apply peroxyacetic acid (PAA) in the following manner: First, the heating unit and the blower are activated and together they provide heated air to the interior of the heating vessel. The heated air circulates inside the heating vessel, and begins to warm the vaporizing units. The heated air accelerates through the circumferentially disposed heating slits in the bottom of each vaporizing unit, forms a vortex inside the vaporizing unit, and exits from the vaporizing unit and heating vessel through the smaller, open bottom of the vapor separator. Second, a supply of PAA to be applied to a stored mass of agricultural product is pumped through the chemical supply lines and comes to rest in the bottom of each vaporizing unit. Here, the PAA becomes entrained as droplets and mist in the swirling vortex of hot air. Third, as the temperature in the bottom of the vaporizing unit rises, the PAA mist in the vaporizing unit undergoes a state change from liquid mist to gas. As the gas heats further, the PAA begins to thermally decompose into a number of intermediate byproducts, a significant fraction of which are relatively light hydroxyl radicals and elemental oxygen. Being relatively less massive than most of the other byproducts, these substances remain closer to the central axis of the rotating air vortex in the vaporizing unit and preferentially exit through the smaller, open bottom of the vapor separator while heavier, more massive particles remain inside the vaporizing unit repeatedly reforming and dissociating into a new population of transitory byproducts. This process continues ensuring a relatively steady output of a stream of vapor containing a high concentration of hydroxyl radicals and elemental oxygen. Fourth, the vapor that exits each heating vessel is collected by the aforementioned inverted conical vapor collector and routed by means of the aforementioned vapor distribution duct to the stored mass of agricultural product. Finally, as the PAA is consumed in the vaporizing unit, additional PAA is supplied to the vaporizing unit and the cycle continues. 
         [0013]    The invention is used to apply 1,4-dimethylnaphthalene (1,4-DMN) in the following manner: First, the heating unit and the blower are activated and together they provide heated air to the interior of the heating vessel. The heated air circulates inside the heating vessel, and begins to warm the vaporizing units. The heated air accelerates through the circumferentially disposed heating slits in the bottom of each vaporizing unit, forms a vortex inside the vaporizing unit, and exits from the vaporizing unit and heating vessel through the smaller, open bottom of the vapor separator. Second, a supply of 1,4-DMN to be applied to a stored mass of agricultural product is pumped through the chemical supply lines and comes to rest in the bottom of each vaporizing unit. Here, the 1,4-DMN becomes entrained as droplets and mist particles in the swirling vortex of hot air. Third, as the temperature in the bottom of the vaporizing unit rises, the 1,4-DMN mist in the vaporizing unit undergoes a state change from liquid mist to gas. Being relatively less massive, the gaseous vapor remains closer to the central axis of the rotating air vortex in the vaporizing unit and preferentially exits through the smaller, open bottom of the vapor separator while heavier, more massive liquid mist particles remain inside the vaporizing unit until they too change state and are discharged from the vaporizing unit. This process continues ensuring a relatively steady output of a nearly pure stream of 1,4-DMN vapor. Fourth, the vapor that exits each heating vessel is collected by the aforementioned inverted conical vapor collector and routed by means of the aforementioned vapor distribution duct to the stored mass of agricultural product. Finally, as the 1,4-DMN is consumed in the vaporizing unit, additional 1,4-DMN is supplied to the vaporizing unit and the cycle continues. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a partial cut-away view of the interior of the heating vessel and conical vapor collector showing internal details. 
           [0015]      FIG. 2  is a detail view of a cross section of the interior of the heating vessel showing a vaporizing unit, its air entry ports and slits, and its associated vapor separator. 
           [0016]      FIG. 3  is a partial elevation view of a cross section of the heating vessel showing internal details. 
           [0017]      FIG. 4  is a partial schematic view of the present invention. 
           [0018]      FIG. 5   a  is an elevation view of the interior of one vaporizing unit with associated vapor separator showing how air enters a vaporizing unit. 
           [0019]      FIG. 5   b  is an elevation view of the interior of one vaporizing unit with associated vapor separator showing the circulating vortex in a vaporizing unit. 
           [0020]      FIG. 6   a  is an elevation view of the interior of one vaporizing unit with associated vapor separator showing path less massive particles describe as they circulate in, and ultimately escape from, a vaporizing unit. 
           [0021]      FIG. 6   b  is an elevation view of the interior of one vaporizing unit with associated vapor separator showing path more massive particles describe as they circulate in, and largely remain confined within, a vaporizing unit. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    Referring now to  FIGS. 1 ,  2 , and  3 , heating vessel  100  is in the general form of a hollow cylinder having a closed top  101  and closed bottom. Except for closed top  101 , heating vessel  100  is double walled; the resulting space between the inner and outer walls being filled with high-temperature insulating material  102  such as fiberglass cloth, vermiculite fiberglass cloth, refractory silica fabric, or the like. At least the inner walls of heating vessel  100  and closed top  101  are formed of steel or aluminum or some other suitable metallic material capable of withstanding heat in excess of about 600° C. Apertures  103  are formed through the inner and outer walls of heating vessel  100  and any interposed insulating material  102  allowing for the introduction of forced hot air into the enclosed space inside heating vessel  100 . Surmounting heating vessel  100  and enclosing it, is removable conical vapor collector  200 . Affixed to the smaller open top of conical vapor collector  200  is vapor collection duct  201 . Vapor collection duct  201  is used to adapt conical vapor collector  200  to distribution ductwork  202  used to distribute vaporized/dissociated particles for deposition on a mass of stored agricultural product. 
         [0023]    Formed in closed top  101  are first circular openings  104  and through each first circular opening  104  a vaporizing unit  105  is installed. Each vaporizing unit  105  is in the form of an open top cylinder and is installed in closed top  101  such that the circumferential edges forming the open top of vaporizing unit  105 : 1) Are flush with first circular opening  104 ; 2) Lie in the plane of closed top  101 ; and, 3) Circumferentially seal closed top  102  and vaporizing unit  105  together along first circular opening  104 . By this means the cylindrical body of each vaporizing unit  105  extends into the closed lower part of heating vessel  100 . Each vaporizing unit  105  is also formed of steel or aluminum or any other suitable metallic, ceramic, or vitreous material capable of withstanding heat in excess of about 600° C. Each vaporizing unit  105  is perforated around its circumferential periphery by a series of air entry ports  106  each of which is formed at a level about 1 cm from the bottom of vaporizing unit  105 . Air entry ports  106  may be created in many forms—punched louvers and “cheese grater” beveled slits being two—but in this exemplary embodiment of the present invention air entry ports  106  are formed using a punch such that when viewed from the outside of vaporizing unit  105 , each air entry port  106  is an inward-dimpled, semi-circular depression wherein the air entry slit  107  is formed along the depressed linear edge of the semi-circular depression. Each air entry port  106  is further oriented such that the linear edge of the aforementioned semi-circle depression and its associated air entry slit  107  forms an angle ranging between about 0° and about 135° with respect to the plane of closed top  101  preferably in the range of about 60° to about 90°. In this exemplary embodiment of the present invention, this angle is about 75° and as such forced air admitted into vaporizing unit  105  proceeds radially along the curved inner surface of vaporizing unit  105  forming a rotating vortex of air inside vaporizing unit  105  such that the greatest turbulence and highest pressure is generally localized in the lower part of vaporizing unit  105 . This turbulence initiates the vaporization process by first causing a physical conversion of the liquid into a more easily vaporized liquid mist. 
         [0024]    Into the open top of each vaporizing unit  105  a metal vapor separator  108  is installed. Each vapor separator  108  is the general form of a truncated funnel and is installed in its associated vaporizing unit  105  such that the edges forming the wider, open top  110  of vapor separator  108 : 1) Are flush with the open top of vaporizing unit  105 ; 2) Lie in the plane of closed top  101 ; and, 3) Circumferentially seal vaporizing unit  105  and vapor separator  108  together. Each vapor separator  108  thus seals the interior of its associated vaporizing unit  105  such that the only exit path for particles generated in the vaporizing unit  105  is through the smaller, open bottom  111  of vapor separator  108  and thence out of its larger, open top  110 . Each vapor separator  108  is also formed of steel or aluminum or any other suitable metallic, ceramic, or vitreous material capable of withstanding heat in excess of about 600° C. 
         [0025]    The static and dynamic pressure head encountered when air is forced into a particular vaporizing unit  105  is controlled by the ratio of the area of the smaller, open bottom  111  of vapor separator  108  and the sum of the open areas of the multiplicity of air entry slits  107  in the vaporizing unit  105  and friction loss. This ratio varies between about 0.50 and about 2.00, preferably in the range of about 0.80 and about 1.25. In this exemplary embodiment of the present invention this ratio is about 1.00. 
         [0026]    Extending into the closed bottom part of heating vessel  100  and proceeding up toward the bottom (inside surface) of closed top  101  are one or more chemical supply lines  109 —one for each vaporizing unit  105 . By routing chemical supply lines  109  through the open interior of heating vessel  100 , transported chemicals are preheated before being deposited in vaporizing unit  105 . Each chemical supply line  109  is preferably routed through the bottom of each vaporizing unit  105  and extends up slightly to provide a shallow pool of chemical in each vaporizing unit  105 . Alternative arrangements in which each chemical supply line  109  penetrates through the side, and proceeds immediately down to the bottom of, each vaporizing unit  105  are equally effective. Chemical supply lines  109  are preferably formed of steel or aluminum or any other suitable metallic material capable of withstanding heat in excess of about 600° C. The amount of chemical supplied through each chemical supply line  109  is adjustable to ensure that the amount of chemical in each vaporizing unit  105  never rises to the level of the circumferential row of air entry ports  106  in the lower portion of each vaporizing unit  105 . 
         [0027]    Turning now to  FIG. 4 , heating units  300  are preferably linear flow, electrically powered hot air generators like the Forsthoff Type 7500. Such units are adjustable and capable of heating forced air to temperatures as high as about 700° C. Those having skill in the art will recognize that equivalent heating units are readily available from other manufacturers. Similarly, equivalent units are available using other sources of energy, including but not limited to various hydrocarbon fuels such as propane, natural gas, kerosene, and other organic gases and liquids. In this exemplary embodiment, the output ports of heating units  300  are physically insinuated trough apertures  103  in the double wall of heating vessel  100  such that air forced through heating units  300  is injected into heating vessel  100 . 
         [0028]    Air blower  400  is preferably a regenerative, side channel radial blower like the Rietschle- Thomas HB-229. Such units are capable of supplying about 100 m 3 /h of ambient air at 0 mbar pressure differential when supplied with 240 VAC at 60 Hz and about 84 m 3 /h of ambient at 0 mbar pressure differential when supplied with 240 VAC at 50 Hz. Those having skill in the art will recognize that equivalent air blowers or compressors are readily available from other manufacturers. Similarly, equivalent units are constructed using a variety of technologies, including, but not limited to, axial flow, rotary screw, and rotary vane. In this exemplary embodiment, the output port of air blower  400  is bifurcated and supplies half of its output air to each of heating units  300 . Air blower  400  is preferably connected to mains power by means of variable frequency drive  401 . By this means, the operator can vary the frequency of the AC voltage supplied to air blower  400  and thus its speed and output. 
         [0029]    Chemical pump  500  is preferably a peristaltic metering pump like the Heidolph Pumpdrive  510   x  with a multichannel head capable of independently supplying chemical to each chemical supply line  109 . Those having skill in the art will recognize that equivalent chemical pumps are readily available from other manufacturers. Similarly, equivalent units are constructed using a variety of technologies, including but not limited to diaphragm, gear, and piston pumps. In this exemplary embodiment, each chemical supply line is placed in a single reservoir  501  containing one liquid, but it will be readily apparent that each of chemical lines  109  may be placed in a different reservoir containing a different liquid. Also, it will be readily apparent that chemical supply lines  109  may be connected and fed by the same single channel pump. Similarly, separate single or multi-channel chemical pumps  500  may be used to supply different liquids to different chemical supply lines  109  at different rates. By this means a multiplicity of chemicals may be simultaneously vaporized and/or dissociated and applied to a mass of stored agricultural product. 
         [0030]    Referring now to  FIGS. 1 ,  2 ,  3 , and  4 , a first exemplary embodiment of the present invention is configured with: 1) A heating vessel  100  having an inner shell approximately 34 cm deep and 34 cm in diameter (approximately 10,000 cc); 2) Six vaporizing units  105  measuring approximately 8 cm deep and 7 cm in diameter (approximately 300 cc) with approximately 20 air entry ports  106  and associated air entry slits  107 ; and, 3) Six concentrically mounted conical vapor separators  108  measuring approximately: a) 7 cm in diameter at the larger, open top  110 ; b) 2 cm in diameter at the smaller, open bottom  111 ; and, c) 4 cm deep. 
         [0031]    This first exemplary embodiment of the present invention is used to apply peroxyacetic acid (PAA) to stored potatoes in the following manner:
   1) A commercially available preparation of 4 liters of 5% PAA is diluted with water in a ratio of 1:4 to form 20 liters of 1% aqueous PAA solution;   2) Heating units  300  are activated and set to generate heated air at a temperature of about 280° C.;   3) Air blower  400  is activated and its associated variable frequency drive  401  is set to deliver 240 VAC line voltage at 50 Hz. Since the ratio of the sum of the open areas of the six smaller, open bottoms  111  of the six vapor separators  108  and the sum of the open areas of the  120  air entry slits  107  circumferentially disposed around the periphery of all six vaporizing units  105  approximates unity, heating vessel  100  presents a combined static and dynamic pressure head of less than about 10 mbar under normal operating conditions. Since the system is preferably mounted on a cart or other conveyance such that when used it may be placed in close proximity to the stored mass of agricultural product to be treated, distribution ductwork  202  can be kept short enough that the combined static and dynamic pressure head presented to air blower  400  by heating vessel  100 , vapor collection duct  201 , and distribution ductwork  202  is no greater than about 20 mbar. As such, air blower  400  is capable of delivering about 75 m 3 /h of superheated air into the center cavity of heating vessel  100 . When operated this way, the temperature of the air in heating vessel  101  fluctuates in a range between about 245° C. and about 300° C., preferably about 275° C. Similarly, the air inside the vaporizing units  105  fluctuates in a range between about 260° C. and about 280° C., preferably about 270° C.   4) Referring now to  FIGS. 4 ,  5   a ,  5   b ,  6   a , and  6   b , the superheated air provided by heating units  300  and air blower  400  finds its way into vaporizing units  105  by means of air entry ports  106  each with an associated air entry slit  107 . In this exemplary implementation of the present invention, air entry ports  106  and their associated air entry slits  107  are oriented such that as the hot air in heating vessel  100  enters each vaporizing unit  105  it is directed into the bottom of vaporizing unit  105  and along its curved inner wall as shown by arrow  120 . By this means, a constant rotating vortex of hot air  122  circulates in each vaporizing unit  105 .   5) When the air inside vaporizing units  105  has stabilized at the proscribed temperature, chemical pump  500  begins to deliver about 0.26 ml of 1% aqueous solution of PAA to each vaporizing unit  105  per second of operation. This amount represents the observed maximum steady state consumption of 1% aqueous PAA using vaporizing units  105  of the size described above and with the invention operating at the temperature and air flow rates described above. The operator must ensure that the pool of 1% aqueous PAA solution  121  in each vaporizing unit  105  does not rise to the level of the open areas of air entry slits  107  circumferentially disposed around the periphery of vaporizing units  105 . The top layer of the pool of 1% aqueous PAA solution becomes entrained as droplets and mist particles in the vortex of hot air circulating in the vaporizing unit. These droplets and mist particles quickly change state to a true vapor containing gaseous PAA and superheated steam. The PAA then dissociates via two main reactions:   
 
         [0000]      CH 3 CO 2 —OH→CH 3 CO 2   − +OH − →CH 3 +CO 2 +OH −   (i)
 
         [0000]      CH 3 CO 2 —OH→CH 3 COOH+O   (ii)
 
         [0000]    The intermediate acetic acid decomposes via a third independent reaction: 
         [0000]      CH 3 COOH→(CH 3 CO) 2 O+C 2 H 2 O+H 2 O   (iii)
 
         [0000]    The heavier components in this gaseous mixture, specifically the remaining droplets and mist particles of 1% aqueous PAA solution, the acetic anhydride (CH 3 CO) 2 O, acetic acid CH 3 COOH, acetate anions CH 3 CO 2   − , ethenone C 2 H 2 O, and CO 2  tend to segregate towards the outer aspect of the vortex near the curved wall of vaporizing unit  105  as shown by arrow  124  while the lighter CH 3  molecules, oxygen atoms, OH −  ions, and H 2 O molecules tend to remain closer to the spinning core of the vortex as shown by arrow  123 . As a result, these lighter components selectively pass up and out through the lower, open area  111  of vapor separator  108  while the heavier components tend to remain behind.
   6) The vapor generated by all six vaporizing units  105  is collected by means of vapor collector  200  and vapor collection duct  201  and sent via associated distribution ductwork  202  to a storage facility for a period of 3.5 hours. This process consumes all 20 liters of diluted 1% aqueous solution of PAA.   
 
         [0038]    Referring again to  FIGS. 1 ,  2 ,  3 , and  4 , this first exemplary embodiment of the present invention is used to apply the sprout inhibitor 1,4-dimethylnaphthalene (1,4-DMN) to stored potatoes in the following manner:
   1) In the United States, 1,4-DMN is usually applied to stored potatoes to achieve a concentration in the potato ranging from about 5.0 ppm to 10.0 ppm. Generally, 3.79 liters (one U.S. gallon) of 1,4-DMN if properly vaporized will treat the following potato weights achieving the associated concentration of 1,4-DMN in the potatoes:   
 
         [0000]                                                          Potato Weight (cwt)   1,4-DMN Air Concentration (ppm)                                        17,000   5.0           11,250   7.5           8,500   10.0                        
Assuming a storage facility with 100,000 cwt of potatoes is to be treated to achieve a 1,4-DMN concentration of 5.0 ppm in the potatoes, approximately 22.3 liters (5.9 U.S. gallons) of commercially available 1-4-DMN solution containing approximately 97% 1,4-DMN must be vaporized and introduced into the storage facility.
   2) Heating units  300  are activated and set to generate heated air at a temperature of about 280° C.;   3) Air blower  400  is activated and its associated variable frequency drive  401  is set to deliver 240 VAC line voltage at 50 Hz. Since the ratio of the sum of the open areas of the six smaller, open bottoms  111  of the six vapor separators  108  and the sum of the open areas of the  120  air entry slits  107  circumferentially disposed around the periphery of all six vaporizing units  105  approximates unity, heating vessel  100  presents a combined static and dynamic pressure head of less than about 10 mbar under normal operating conditions. Since the system is preferably mounted on a cart or other conveyance such that when used it may be placed in close proximity to the stored mass of agricultural product to be treated, distribution ductwork  202  can be kept short enough that the combined static and dynamic pressure head presented to air blower  400  by heating vessel  100 , vapor collection duct  201 , and distribution ductwork  202  is no greater than about 20 mbar. As such, air blower  400  is capable of delivering about 75 m 3 /h of superheated air into the center cavity of heating vessel  100 . When operated this way, the temperature of the air in heating vessel  101  fluctuates in a range between about 245° C. and about 300° C., preferably about 275° C. Similarly, the air inside the vaporizing units  105  fluctuates in a range between about 260° C. and about 280° C., preferably about 270° C.   4) Referring again to  FIGS. 4 ,  5   a ,  5   b ,  6   a , and  6   b , the superheated air provided by heating units  300  and air blower  400  finds its way into vaporizing units  105  by means of air entry ports  106  each with an associated air entry slit  107 . In this exemplary implementation of the present invention, air entry ports  106  and their associated air entry slits  107  are oriented such that as the hot air in heating vessel  100  enters each vaporizing unit  105  it is directed into the bottom of vaporizing unit  105  and along its curved inner wall as shown by arrow  120 . By this means, a constant rotating vortex of hot air  122  circulates in each vaporizing unit  105 .   5) When the air inside vaporizing units  105  has stabilized at the proscribed temperature, chemical pump  500  begins to deliver about 0.35 ml of 1,4-DMN to each vaporizing unit  105  per second of operation. This amount represents the observed maximum steady state consumption of 1,4 DMN using vaporizing units  105  of the size described above and with the invention operating at the temperature and air flow rates described above. As before, the operator must ensure that the pool of 1,4-DMN  121  in each vaporizing unit  105  does not rise to the level of the open areas of air entry slits  107  circumferentially disposed around the periphery of vaporizing units  105 . The top layer of the pool of 1,4-DMN becomes entrained as droplets and mist in the vortex of hot air circulating in the vaporizing unit. These 1,4-DMN droplets and mist particles quickly change state to a true vapor containing gaseous 1,4-DMN. The heavier droplets and mist particles tend to segregate towards the outer aspect of the vortex near the curved wall of vaporizing unit  105  as shown by arrow  124  while the lighter 1,4-DMN molecules tend to remain closer to the spinning core of the vortex as shown by arrow  123 . As a result, the essentially pure 1,4-DMN vapor selectively passes up and out through the lower, open area  111  of vapor separator  108  while the heavier droplets and mist particles tend to remain behind where they too are subsequently converted to molecules of 1,4-DMN.   6) The vapor generated by all six vaporizing units  105  is collected by means of vapor collector  200  and vapor collection duct  201  and sent via associated distribution ductwork  202  to a storage facility for a period of about 3.0 hours. This process consumes all 5.9 liters of 1,4-DMN.   
 
         [0045]    It will be readily apparent to the those skilled in the art that the above disclosed exemplary embodiment of the present invention can be altered in numerous obvious ways, /including for example, merely scaling the size of the unit up or down to incorporate a lesser or greater number of vaporizing units  105 , associated vapor separators  108 , heating units  300 , and air blowers  400 . 
         [0046]    Similarly, increasing or decreasing the volume of each vaporizing unit  105  and associated vapor separator  108  while simultaneously increasing or decreasing the air flow through heating vessel  100  and adjusting the output of heating units  300  to maintain the temperature of the air inside vaporizing units  105  within a proscribed range to vary the maximum output of the device is also within the spirit and scope of the present invention. 
         [0047]    Similarly, increasing or decreasing the volume of hot air pumped through heating vessel  100  while maintaining the volume of each vaporizing unit  105  and associated vapor separator  108  while increasing the flow rate of liquid to be vaporized by each vaporizing unit  105  to increase or decrease the output derived from each vaporizing unit  105  is also within the spirit and scope of the present invention. 
         [0048]    Similarly, supplying more than one chemical to different vaporizing units  105  and supplying different chemicals to different vaporizing units is also within the spirit and scope of the present invention. 
         [0049]    Similarly, while the preferred embodiment of the present invention has been described in connection with application of various chemicals to a stored mass of agricultural product, it will be readily apparent that the device may be used to apply one or more chemical vapors to other surfaces and products. 
         [0050]    Moreover, although only a few exemplary embodiments of the present invention have been described in detail, those skilled in the art will readily appreciate that numerous minor modifications and rearrangements of the exemplary embodiments are readily conceivable. Accordingly, all such modifications and rearrangements are intended to be included within the scope of this invention as defined in the following claims.