Abstract:
An apparatus and method designed to introduce jets of air or other fluids at some velocity into a chamber designed to dry, combust, heat or cool solid materials and gases, such as solid fuels, biosolids, biofuels or other solid materials and their off-gases. The apparatus may be designed to introduce these jets in a particularly beneficial arrangement with some velocity and often with a vertical component (usually downward) to produce large and small scale recirculation regions combined with impingement of the jet stream onto the lower surface of a chamber, thereby greatly increasing the rates of heat and mass transfer between the fluid and the solids near the bottom (as well as other parts) of the chamber, and mixing of the gases and fluids in the chamber. The present invention may be particularly useful to enhance drying of high moisture content solids, heating or cooling materials, and to enhance combustion of solid fuels and other materials inside chambers designed for this purpose, and may result in improved exhaust emissions.

Description:
RELATED APPLICATIONS  
       [0001]     This application claims the benefit of United States Provisional Application Ser. No. 60/708,324, filed on Aug. 16, 2005. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates generally to the field for drying and combusting, or incinerating, solid fuels and materials, such as biomass and biosolids, as well as gases in a combustion chamber where the solid fuels are primarily located at the bottom of the chamber, such as those in a multiple hearth furnace or other machines with similar chambers or arrangement of materials, and more particularly to the creation of a flow field with impingement and recirculation regions to enhance the heat and mass transfer, and hence, the cooling, drying, heating and mixing of gases, vapors, liquids, and solids in a machine or furnace designed to dry, heat, cool, and/or combust solid fuels and materials.  
         [0004]     2. Description of the Related Art  
         [0005]     Multiple hearth furnaces and other similar machines for drying and burning solid fuels and materials as well as the off-gases from these fuels and materials are known. Examples of these types of furnaces and machines can be found in patents such as U.S. Pat. No. 2,108,997 (Schilling), U.S. Pat. No. 3,958,920 (Anderson), U.S. Pat. No. 4,013,023 (Lombana et al.), U.S. Pat. No. 5,080,025 (Nell et al.), U.S. Pat. No. 5,094,177 (Lado), U.S. Pat. No. 5,752,452 (Leger), U.S. Pat. No. 5,957,064 (Barry et al.) and U.S. Pat. No. 6,948,436 (Mooney et al.). But the furnaces and systems disclosed in these patents suffer from a variety of problems, such as poor drying, poor cooling, poor heating, poor combustion, poor air-fuel mixing and/or poor heat and mass transfer performance.  
         [0006]     As such, as will become apparent from the following description and discussion, the present invention has been conceived and developed to provide an improved apparatus and method for enhancing heat and mass transfer. As will be discussed more fully hereinbelow, the present invention exhibits a variety of advantages and objectives, one or more of which may be applicable depending on various circumstances.  
         [0007]     For example, one object of the present invention may be to provide an apparatus that will overcome the deficiencies of the prior art. Another object of the present invention may be to provide an apparatus and method that improves the effectiveness of the drying process for high moisture content solid fuels or other materials. Another object of the present invention may be to provide an apparatus and method that improves the combustion process by enhancing the mixing of the air and fuel by creating an impingement and recirculating flow field to repeatedly force the air inside the chamber to come into contact with the solid fuel or other material on or near the floor of the chamber. Another object of the present invention may be to provide an apparatus and method to improve the emissions performance of a furnace by reducing CO and NOx emissions. Another object of the present invention may be to provide an apparatus and method to enhance the cooling of hot materials, such as those inside a chamber with the solid material on the floor of the chamber. Another object of the present invention may be to provide an apparatus and method for heating of cooler materials, such as those inside a chamber with the solid material on the floor of the chamber. Another object of the present invention may be to provide an apparatus and method for heating or cooling of any material with a solid surface, regardless of whether the material is inside or outside a chamber, and regardless of whether the surface of the solid material is horizontal, vertical, inverted, or any angle in between. Another object of the present invention may be to provide an apparatus and method to be used to take advantage of the inherent impingement and recirculation flow field, such as applying coatings (such as paint, epoxies, etc.), air or gas mixing, air or gas and particulate mixing, liquid applications, liquid mixing applications, propulsion and propulsion control systems, and other combustion applications. Another object of the present invention may be to provide an apparatus and method for a new furnace, drying apparatus or machine, or cooling or heating apparatus which is designed to take advantage of the present invention.  
         [0008]     It is intended that any other advantages and objects of the present invention that become apparent or obvious from the detailed description or illustrations contained herein are within the scope of the present invention.  
       SUMMARY OF THE INVENTION  
       [0009]     In a broad aspect, one purpose of the present invention is to provide a heat and mass transfer enhancement apparatus and related methods, not offered by the prior art and that result in a much improved machine for drying, heating, cooling, and burning solid materials which is not apparent, obvious, or suggested, either directly or indirectly by any of the prior art.  
         [0010]     The apparatus of the present invention can take on many variations in order to produce the intended flow field and fluid motion, with some of these variations depending on the shape of the device into which it is installed. In one form commonly envisioned, it may be installed into a circular chamber which has both a relatively flat, horizontal floor and ceiling. In this configuration, the apparatus could be a pipe curved around to form a circle in the horizontal plane and located between the hearth floor and ceiling. The size of the circle is preferably roughly half the diameter of the outside of the chamber. Holes or slots may be drilled or cut into the pipe to allow air, or another working fluid, to escape in a generally downward direction, preferably with some velocity, such as in the form of a jet. The configuration and placement of the jets in a circular fashion naturally creates a pattern of two opposite rotating recirculation flows in the horizontal plane following the circular arrangement of the jets (called “dual donut vortices” or “double ring vortex”) which greatly promotes drying and combustion of the solid fuels and materials. The pressurized air or other fluid is fed into the pipe through a connection, such as a pipe or tube, from the outside of the chamber. The working fluid is provided to the device at an elevated pressure from an external source, such as a fan, compressor, blower, or other pressurized source. The flow is controlled with usual means of flow control, such as a valve, a pressure controller, and/or a variable speed on the blower or fan.  
         [0011]     An alternate form of the jet arrangements may be to have multiple circular pipes in the same plane concentric with the furnace. One alternate mounting of the air or fluid jets can be at the end of multiple straight sections of pipe, entering radially through the outside wall of the furnace and terminating in a circle of the same radius as the circular pipe, with holes or slots for jets near the end of the pipe, or along the pipe in various configurations. This arrangement facilitates ease of removal for maintenance or replacement without interrupting furnace operation. Other arrangements of the jets in multiple circles, or in a linear fashion will also provide large and small-scale dual vortices that will similarly enhance the local heat and mass transfer.  
         [0012]     In one aspect, the invention may be an apparatus comprising: a surface upon which a material may be disposed; and at least one conduit spaced apart from the surface and having at least one passageway through which a jet may be directed into contact with the material. Another feature of this aspect of the invention may be that at least one conduit is circular. Another feature of this aspect of the invention may be that at least one conduit is straight. Another feature of this aspect of the invention may be that the apparatus is a furnace. Another feature of this aspect of the invention may be that the furnace is a multiple hearth furnace. Another feature of this aspect of the invention may be that the furnace is a traveling grate furnace. Another feature of this aspect of the invention may be that the jet is a stream of air. Another feature of this aspect of the invention may be that the jet is a stream of fluid. Another feature of this aspect of the invention may be that the surface is a hearth or stationary floor. Another feature of this aspect of the invention may be that the surface is a conveyor belt, traveling grate, or other moving floor. Another feature of this aspect of the invention may be that the at least one conduit is above the surface and the jet may be downwardly directed into contact with the material.  
         [0013]     In another aspect, the present invention may be a furnace comprising: at least one hearth; a supply conduit; and at least one conduit in fluid communication with the supply conduit, spaced apart from the hearth and having at least one passageway through which a jet may be directed into contact with material on the hearth. Another feature of this aspect of the invention may be that the supply conduit is attached to an exterior surface of a furnace wall, and at least one conduit is a generally straight section of conduit and disposed through the furnace wall. Another feature of this aspect of the invention may be that at least one passageway is disposed near an inner end of the straight section of conduit, the inner end terminating within the furnace. Another feature of this aspect of the invention may be that the straight section of conduit is disposed through the furnace wall in two places. Another feature of this aspect of the invention may be that the supply conduit is attached to an exterior surface of a furnace wall, and the at least one conduit is a generally circular section of conduit disposed within the furnace. Another feature of this aspect of the invention may be that the at least one conduit is above the hearth and the jet may be downwardly directed into contact with the material.  
         [0014]     In yet another aspect, the present invention may be a method of enhancing heat and mass transfer comprising: supplying a fluid into a conduit; allowing the fluid to flow though a passageway in the conduit to create a jet; and directing the jet into contact with a material. Another feature of this aspect of the invention may be that the fluid is air. Another feature of this aspect of the invention may be that the jet is directed into contact with a material in a chamber. Another feature of this aspect of the invention may be that the chamber is in a furnace. Another feature of this aspect of the invention may be that the furnace is a multiple hearth furnace. Another feature of this aspect of the invention may be that the furnace is a traveling grate furnace.  
         [0015]     The foregoing has outlined, in general, certain physical aspects of the invention and is to serve as an aid to better understanding the more complete detailed description which is to follow. In reference to such, there is to be a clear understanding that the present invention is not limited to the method or detail of construction, fabrication, material, or application of use described and illustrated herein. Any other variation of fabrication, use, or application should be considered apparent as an alternative embodiment of the present invention.  
         [0016]     Other features, aspects and advantages of the present invention will become apparent from the following discussion and detailed description. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     The following drawings further describe by illustration the advantages and objects of the present invention. Each drawing is referenced by corresponding figure reference characters within the “DETAILED DESCRIPTION OF THE INVENTION” section to follow.  
         [0018]      FIG. 1  is a cross sectional view of an example of a multiple hearth furnace, without the present invention, from a previous patent showing the path of air and solids through the machine.  
         [0019]      FIG. 2  is another cross sectional view of the prior art without the present invention from a previous patent showing the multiple chambers with their opposing “in hearth” and “out hearth” flow pattern. This more recent embodiment also shows what is known as Flue Gas Recirculation (FGR) and identifies the afterburner, drying, combustion, and cooling sections of a multiple hearth furnace.  
         [0020]      FIG. 3  is a cross-sectional view of a multiple hearth furnace, without the present invention, showing the general air and exhaust gas flow pattern inside the prior art multiple hearth furnace.  
         [0021]      FIG. 4  is a perspective view of a specific embodiment of the present invention installed within a multiple hearth furnace.  
         [0022]      FIG. 5  is a bottom view of a specific embodiment of the present invention installed within a multiple hearth furnace.  
         [0023]      FIG. 5A  is a magnified diagram of a part of the present invention designated at  5 A in  FIG. 5 .  
         [0024]      FIG. 6  is a side, cross-sectional view of a multiple hearth furnace with the present invention installed and operating and showing the general flow field of the multiple hearth furnace while the invention is operating.  
         [0025]      FIG. 7  is a bottom view of a possible alternative configuration of the present invention installed within a multiple hearth furnace, and shows the device with radially-in supply pipes and jets instead of the circular supply pipe, which may facilitate easy installation and withdrawal without interrupting furnace operations.  
         [0026]      FIG. 7A  is a magnified diagram of a part of the present invention designated at  7 A in  FIG. 7 .  
         [0027]      FIG. 8  is a bottom view of another possible alternative configuration of the present invention installed within a multiple hearth furnace, and shows a linear arrangement of supply pipes and jets.  
         [0028]      FIG. 8A  is a magnified diagram of a part of the present invention designated at  8 A in  FIG. 8 .  
         [0029]      FIG. 9  is a side view of traveling grate furnace having a specific embodiment of the present invention installed therein. 
     
    
       [0030]     While the invention will be described in connection with the preferred embodiments, it will be understood that it is not intended to limit the invention to those embodiments. On the contrary, it is intended to cover all alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0031]     In view of the poor drying, cooling, heating, poor air-fuel mixing, poor exhaust emissions and other limitations now present in the prior art, one aspect of the present invention is to provide a new and useful method and device for heat and mass transfer enhancement for drying and burning of solid fuels and materials as well as the off-gases from these fuels and materials inside a chamber, such as those in a multiple hearth furnace, stationary or traveling (moving or vibrating) grate furnaces, fluid bed furnaces, and other similar machines. New and more efficient furnaces could be designed around this apparatus in order to utilize and exploit this unique method and apparatus for achieving superior drying, heating, cooling, combustion, emissions or other improved heat and mass transfer performance. This apparatus is simple in construction, universally usable for new as well as existing facilities, and greatly enhances the performance in operation of the machine in comparison to existing machines without this apparatus.  
         [0032]     Examples of the prior art machines without the present invention are shown in  FIGS. 1 and 2 , which are diagrams from previous patents related to the performance of multiple hearth furnaces. For example,  FIG. 1  corresponds to FIG. 1 from U.S. Pat. No. 5,752,452 (Leger), and  FIG. 2  corresponds to FIG. 3 from U.S. Pat. No. 5,957,064 (Barry et al.). Referring to the drawings in detail, wherein like numerals denote identical elements throughout the several views, there is shown in  FIG. 3 a  cross-section of a multiple hearth furnace  400  without the present invention, which illustrates the general flow field (per lines and arrows) inside a furnace without the present invention. The multiple hearth furnace  400  may include an outer wall  412  and a plurality of hearths ( 406 - 409 ), one upon another, with alternating in, and then out, hearths. Each hearth  406 - 409  may include a floor  406   a - 409   a  and a ceiling  406   b - 409   b . The furnace  400  further includes a center shaft  417  to which are connected a plurality (typically two or four) rabble arms  418  which extend outwardly from the shaft  417  into the spaces or chambers between the hearths  406 - 409 , and include angled plow blades or “teeth”  419 , the purpose of which will be explained below. The alternating arrangement of the “in” hearths  406 / 408  and “out” hearths  407 / 409  have corresponding outer drop holes  450  and inner drop holes  451  that alternate between inside, near the center shaft  417 , and outside, near the outer wall  412  of the furnace, as further illustrated in  FIG. 5  discussed below. The solid fuels or material, such as biosolids, are pushed, plowed, or “rabbled” through each hearth by means of the rotating center shaft  417  and the rabble arms  418  and angled plow blades or “teeth”  419  that rabble the material along the floors  406   a - 409   a  of the hearths  406 - 409  in a spiral pattern either from the outside toward the center (in hearth) or from the center toward the outside (out hearth). As the solid material fuel, such as biosolids, move downward through the furnace drop holes  450 / 451 , the combustion air supply and exhaust gases move upward through the furnace (as indicated by lines and arrows), through the same drop holes, but in the opposite direction. The air, exhaust gases, and other airborne materials (dust, ash, VOCs released from the heating of the solids, etc.) travel through the path of least resistance, as shown in  FIG. 3 . There is very little mixing of the air and gases passing mostly through the center of the hearth chamber with the solids located on the floors of the hearth chambers.  
         [0033]     Referring now to  FIGS. 4 and 5 , a specific embodiment of the present invention is illustrated in a circular pipe configuration  100  as installed in a multiple hearth furnace  400  that, for the purpose of scale, may be about 15 feet in diameter for this example. The circular pipe  100  may be attached to or hung from the hearth ceiling in any conventional manner. In this specific embodiment, the circular pipe  100  is fed with a working fluid through a pipe or conduit  102  from the outside of the furnace  400 . This pipe or conduit is supplied with air or working fluid from an external source  105 , such as a fan or blower. As best shown in  FIG. 5A , fluid passageways such as holes, apertures or slots  101  are provided in the circular pipe  100  to allow for air, or another working fluid, to be released into the chambers between the respective hearths  406 - 409  with some velocity. As illustrated in  FIG. 4 , air or fluid flow through the apertures  101  results in a plurality of small jets  135  of air (or other working fluid) which are aimed in a downward direction toward the floor of each hearth, and hence, toward the solid materials located thereon.  
         [0034]     As can be seen in  FIG. 6 , an initial benefit of these jets  135  is the impingement  132  of the stream of air (or other working fluid) with the material (not shown) on the hearth floors to create better mixing of the air and solid fuel, resulting in improved heat and mass transfer, and hence, improved drying, heating, cooling, and/or combustion efficiency and improved emissions performance. A secondary benefit is the induced flow field inherently caused by the introduction of a jet or jets  135  of air. The jet or jets  135  entrain the surrounding low velocity air and gases and create an induced flow field as shown in  FIG. 6 . The downward flow (which may be of a high velocity) along with entrainment of the surrounding gases forces a stream of air and gases to impinge in a ring centered around the center shaft  417 , then diverge in two directions, one toward the center of the furnace  400  and the other away from the center of the furnace  400 . Being confined by the outer furnace wall  412 , and the center shaft  417 , the streams of air and gases recirculate back toward the ring of jets and repeat the process. This results in two stable vortex structures, known as “dual donut vortices”, the inside vortex  131 , nearer the center of the furnace and the outside vortex  130 , nearer the external wall  412 . This multiple recirculation is superimposed upon the normal flow field of the furnace shown in  FIG. 3  such that the normal gases moving through the furnace  400  are now forced to repeatedly flow downward, impinge, and mix with the solid fuel or material located on the floors of the hearths in a highly turbulent manner. The gases must now rotate several times in the first vortex, then pass through the impingement region  132 , then rotate several times through the next vortex, then exit the chamber to repeat the process in the next hearth. This greatly improves the mixing as well as the heat and mass transfer between the gases and the solids on the floor of the chamber. In addition, use of the present invention results in improved emissions performance due to the improved combustion performance, and in particular, results in reduced emissions of CO and NOx (carbon monoxide and oxides of Nitrogen NO, NO 2 , NO 3) .  
         [0035]     This same flow field shown in  FIG. 6  also greatly enhances the drying of solids, such as biosolids, inside a similar chamber, such as in a multiple hearth furnace. This is due to the greatly increased convective heat transfer caused by the significantly increased local air and/or gas velocities at the surface of the solid materials as well as the recirculation regions generated by the impingement region and dual vortex flows. For similar reasons, the present invention can also greatly enhance heating or cooling of solids, such as ash or other materials, by introducing jets of air or working fluid at a different temperature into the chamber.  
         [0036]     The apparatus of the present invention can take on many variations in order to produce a beneficial flow field and fluid motion. Some depend on the shape of the device into which it is installed or other limitations or requirements. For example, the embodiment shown in  FIG. 7  creates a flow field very similar as that shown in  FIG. 6 , but with a different arrangement for the apparatus. In the specific embodiment shown in  FIG. 7 , the furnace  400  is provided with an external annular pipe or conduit  103  and a plurality of radial pipes or conduits  108 . In this specific embodiment, the external annular pipe  103  may be disposed around and attached to the furnace  400 . The plurality of radial pipes or conduits  108  may be attached to and in fluid communication with the external annular pipe  103  and extend through the furnace wall  412  and inside the furnace  400  towards the center shaft  417 . The conduits  108  may be connected in fluid communication with the external annular conduit  103  in any conventional manner. For case of maintenance, the radial pipes  108  can be easily extracted from the furnace  400  while the furnace  400  is still operating. The radial pipes  108  arc provided with at least one fluid passageway (e.g. a hole, aperture, slot, etc.)  101  through which air or other working fluid may be fed to create one or more jets in the manner explained above. In a specific embodiment, as shown in  FIG. 7A , the holes or slots  101  may be located at the end of each of the radially inward pipes  108  and may be arranged in this example with two holes straight downward, and two holes angled to each side. The air or working fluid is supplied from the external conduit  103  and fed from an external supply  105 .  
         [0037]     Another variation of the apparatus of the present invention may be the linear arrangement shown in  FIG. 8 . In this specific embodiment, the furnace  400  may be provided with a plurality of straight pipes or conduits  109  (having apertures/holes  101  as discussed above) arranged in multiple lines to create impingement regions below each supply pipe  109 , and also to create linear vortices between each row of jets, thereby creating a similar benefit as the circular vortices. In this specific embodiment, the furnace  400  is also provided with one or more semi-circular conduits  103 , which may be attached on the outside of the furnace  400  to the furnace wall  412 . The conduits  109  are disposed through the furnace wall  412  and connected in fluid communication in any conventional manner to the one or more conduits  103 , much like discussed above in connection with  FIG. 7 .  
         [0038]     While the present invention has thus far been primarily described and illustrated in the context of a multiple hearth furnace, the scope of the present invention is not intended to be limited for use only with multiple hearth furnaces or with furnaces in general. Instead, it may be used and installed in any other type of furnace or device to which the invention is applicable. For example, as shown in  FIG. 9 , the invention is shown installed within a traveling grate furnace  500 . In this specific embodiment, the traveling grate furnace  500  is provided with a plurality of conduits  502  that are shown here disposed in generally parallel alignment and attached to a ceiling  504  of the furnace  500 . While not shown here, the conduits  502  are provided with appropriate passageways (e.g., holes, apertures, slots, etc.) as discussed above, through which air or other working fluid may be fed to create jets  135  which flow downwardly, with some velocity. In this embodiment, the furnace  500  is provided with a hopper or stack  506  for holding waste or other material  508  to be burned in the furnace  500 . The furnace  500  further includes a conveyor  510  that carries the material  508  from the hopper  506  into the heating area of the furnace  500  to be burned. As the waste material  508  moves through the furnace  500  on the conveyor  510 , the jets  135  create impingement regions  132  on the waste material  508  and corresponding recirculation flow fields as indicated by the circular lines and arrows. This results in the enhancement of the rate of heat and mass transfer, and more efficient burning and combustion of the waste material  508 , and reduced emissions, as more fully discussed above.  
         [0039]     It will also be understood that, in addition to heat and mass transfer enhancement, the device can also be used to advantage in several other ways where jets, impingement and recirculation are beneficial. These include applying coatings (such as paint, epoxies, etc.), air or gas mixing, air or gas and particulate mixing, liquid applications, liquid mixing applications, propulsion and propulsion control systems, and other combustion applications.  
         [0040]     It is further intended that any other embodiments of the present invention that result from any changes in application or method of use or operation, method of manufacture, shape, size, or material which are not specified within the detailed written description or illustrations contained herein yet are considered apparent or obvious to one skilled in the art are within the scope of the present invention.