Apparatus and Method for Enhancing Heat and Mass Transfer

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

This application claims the benefit of United States Provisional Application Ser. No. 60/708,324, filed on Aug. 16, 2005.

BACKGROUND OF THE INVENTION

1. Field of the Invention

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.

2. Description of the Related Art

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.

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.

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.

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

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.

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.

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.

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.

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.

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.

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.

Other features, aspects and advantages of the present invention will become apparent from the following discussion and detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

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.

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.

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.

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.

FIG. 4 is a perspective view of a specific embodiment of the present invention installed within a multiple hearth furnace.

FIG. 5 is a bottom view of a specific embodiment of the present invention installed within a multiple hearth furnace.

FIG. 5A is a magnified diagram of a part of the present invention designated at 5A in FIG. 5.

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.

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.

FIG. 7A is a magnified diagram of a part of the present invention designated at 7A in FIG. 7.

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.

FIG. 8A is a magnified diagram of a part of the present invention designated at 8A in FIG. 8.

FIG. 9 is a side view of traveling grate furnace having a specific embodiment of the present invention installed therein.

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

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.

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 406a-409a and a ceiling 406b-409b. 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 406a-409a 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.

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.

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, NO₂, NO₃₎.

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.

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.

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.

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.

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.

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.

Claims

1. 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 positioned to direct a jet into contact with the material.

2. The apparatus of claim 1, wherein the at least one conduit is circular.

3. The apparatus of claim 1, wherein the at least one conduit is straight.

4. The apparatus of claim 1, wherein the apparatus is a furnace.

5. The apparatus of claim 4, wherein the furnace is a multiple hearth furnace.

6. The apparatus of claim 4, wherein the furnace is a traveling grate furnace.

7. The apparatus of claim 1, wherein the jet is a stream of air.

8. The apparatus of claim 1, wherein the jet is a stream of fluid.

9. The apparatus of claim 1, wherein the surface is a hearth.

10. The apparatus of claim 1, wherein the surface is a conveyor belt.

11. The apparatus of claim 1, wherein the at least one conduit is above the surface and the jet may be downwardly directed into contact with the material.

12. 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 positioned to direct a jet into contact with material on the hearth.

13. The furnace of claim 12, wherein the supply conduit is attached to an exterior surface of a furnace wall, and the at least one conduit is a generally straight section of conduit and disposed through the furnace wall.

14. The furnace of claim 13, wherein the at least one passageway is disposed near an inner end of the straight section of conduit, the inner end terminating within the furnace.

15. The furnace of claim 13, wherein the straight section of conduit is disposed through the furnace wall in two places.

16. The furnace of claim 12, wherein 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.

17. The apparatus of claim 12, wherein the at least one conduit is above the surface and the jet may be downwardly directed into contact with the material.

18. A method 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.

19. The method of claim 18, wherein the fluid is air.

20. The method of claim 18, wherein the jet is directed into contact with a material in a chamber.

21. The method of claim 20, wherein the chamber is in a furnace.

22. The method of claim 21, wherein the furnace is a multiple hearth furnace.

23. The method of claim 21, wherein the furnace is a traveling grate furnace.