Plasma Gasification System with Improved Heat Transfer

Description

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. provisional application 63/736,755 filed Dec. 20, 2024, and hereby incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates to systems for waste conversion and in particular to the gasification system employing plasma torches.

Gasification is a process where raw materials, such as municipal waste, are broken down at elevated temperatures in the presence of a gasifying agent, such as steam, air, oxygen, or carbon dioxide, to produce synthetic gas, for example, the latter commonly being mixtures of hydrogen and carbon monoxide and carbon dioxide.

A typical gasification system may provide for a high-temperature crucible receiving waste material heated by plasma torches to break it down into synthetic gas and a glassy slag which collects at the bottom of the crucible. The torches may face inwardly from the sides of the crucible to a center portion of the surface of the slag receiving the waste. Electrodes positioned in the lower portion of the crucible may be used to further heat the slag to contribute to the gasification of the newly received waste.

SUMMARY OF THE INVENTION

The present inventors have recognized that the synthetic gas produced by the gasification of received waste can counterproductively dissipate and cool the plasma in its path to the waste and may further combust from contact with the plasma, reducing yield efficiency. Accordingly, the present invention provides a gasification system employing extender tubes to conduct the plasma to a location proximate to the waste bypassing contact with the produced synthetic gas stream. The extender tubes may pass inwardly from the sidewalls of the crucible or upwardly through the molten waste from the bottom of the crucible.

More specifically, in one embodiment, the invention provides a gasifying system having a crucible having a volume adapted to hold a molten slag and receiving a waste stream at a waste reception area on the surface of the slag. A plasma generator generates a plasma outside of the volume and directs it along an introduction axis through a wall of the crucible through an extender tube conducting the plasma through the volume by a distance of at least 25% of a distance between an inner wall of the crucible and a center of the crucible to be released at a point proximate to the waste reception area at the surface of the slag.

It is thus a feature of at least one embodiment of the invention to direct plasma to the site of waste introduction in a way that minimizes contact with generated gas.

The extender tube may extend inwardly from sidewalls of the crucible and angle downwardly to a center region of the surface of the slag.

It is thus a feature of at least one embodiment of the invention to isolate the extender tube from interference by the slag.

Alternatively, the extender tube may pass upward through a lower wall of the crucible through the slag to a central region of the surface of the slag.

It is thus a feature of at least one embodiment of the invention to provide extender tubes that may better resist damage from falling waste.

The extender tube may include inlets for admitting gas from the volume into the extender tube in a swirling pattern to separate the plasma in the extender tube from the inner walls of the extender tube.

It is thus a feature of at least one embodiment of the invention to reduce heat loss from the plasma into the extender tube and volume through the use of a sequestering layer of heated gas centrifugally surrounding the plasma.

In some embodiments, the plasma generator is a microwave plasma generator receiving a carrier gas.

It is thus a feature of at least one embodiment of the invention to allow highly efficient microwave plasma generation shielded from the intense heat inside the crucible.

These particular objects and advantages may apply to only some embodiments falling within the claims and thus do not define the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational cross-section of a simplified gasification system providing a crucible with side-mounted plasma torches using extender tubes to conduct the plasma to the center of the crucible where waste is received;

FIG. 2 is a fragmentary detail of the connection between an extender tube extending into the crucible and a microwave plasma torch positioned outside of the crucible communicating through a thermal barrier with the extender tube;

FIG. 3 is a detailed fragmentary cross-section of the thermal barrier of FIG. 2 limiting heat transfer while providing a sealed connection accommodating thermal expansion of the joined components and a continuation of the plasma gas swirl;

FIG. 4 is a second embodiment of the gasification system showing the extender tubes passing upward from the bottom of the crucible through the molten slag to a position proximate to the received waste stream;

FIG. 5 is a fragmentary perspective view of an upper end of the extender tubes of FIG. 4 providing a deflector cap and side port;

FIG. 6 is a cross-sectional fragmentary view of an alternative embodiment providing multiple radially exiting exhaust ports for positioning directly beneath the waste stream; and

FIG. 7 is a cross-section through an extender tube of FIG. 1 showing angled inlet holes promoting an inner layer of swirling gas around the plasma.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 1, a gasification system 10 may provide for a refractory lined crucible 12 defining an enclosed volume communicating with a waste receipt channel 14 and exit channel 16 for synthetic gas 17.

The waste receipt channel 14 may include a flow control valve or the like (not shown) to control the feed rate of waste material 18, the latter, for example, which may be municipal solid waste or other waste including plastic waste, petroleum waste, hazardous waste, and the like. The waste receipt channel 14 operates to admit waste material 18 into the crucible 12 while minimizing the introduction of outside air that would affect the stoichiometry maintained by the gasification system 10.

The crucible 12 may also include additional ports 20 providing controlled inflow of steam, air, oxygen, or carbon dioxide through valves 21 and preferably positioned to enter through the wall of the crucible 12 at a level proximate to slag material 22. These additional gases provide desired chemistry for producing synthetic gas 17 from decomposition of the waste material 18

An exit port 26 may be provided at the bottom of the crucible 12 allowing for the removal of slag material 22 to maintain its level within the crucible 12 at a substantially constant height. Opening of the exit port 26 may be provided by activation of inductive heater coils 28 liquefying material within the exit port 26 to allow its flow.

The crucible 12 may be formed of any suitable material capable of handling temperatures in excess of about 1500° C. including, for example, ceramics. A lower inner portion of the crucible 12 may support electrodes 24, for example, formed of graphite and placed in contact with the slag material 22 beneath the level of the slag material 22. Direct or alternating electrical current flowing through the electrodes 24 may provide resistive heating of the slag to maintain the slag material 22 in molten form and to introduce heat that will assist in gasifying the waste material 18.

Waste material 18 accumulating on the surface of the slag material 22 may be initially heated by side-mounted, inwardly facing plasma torch assemblies 30. These plasma torch assemblies 30 provide extender tubes 32 communicating through the sidewalls of the crucible 12 to terminate within the crucible 12 at a distal end proximate to the center of the slag material 22 receiving the waste material 18. Generally the extension extender tubes 32 will extend through the volume of the crucible 12 by at least 25% of the distance between the inner wall of the crucible 12 and the center of the crucible 12 so as to substantially bypass the outflowing synthetic gas 17. The diameter of the extender tubes 32 is such as to maintain a concentration of the plasma 42 and to promote a swirling of the gas mixture shielding the extender tube 32 from direct contact with the plasma 42 as much is possible.

The extender tubes 32 may, for example, be a high-temperature refractory material such as a ceramic including but not limited to silicon carbide or aluminum oxide. Other examples of high-temperature refractory materials that would be suitable for the extender tubes 32 include high-melting-point metals, oxides, carbides, nitrides, and borides. Desirably, the extender tubes 32 preserve a degree of swirl in the plasma gases to minimize plasma heating of the extender tubes 32, while still resisting plasma contact and the high temperatures within the crucible 12.

The extender tubes 32 receive plasma 42 from corresponding microwave plasma generators 34 positioned outside of the crucible 12. The microwave plasma generators 34 in turn receive a plasma carrier gas 35 which is then excited by microwave sources 36 to generate the plasma 42. The produced plasma 42 is then passed to the extender tubes 32 through water-cooled thermal barriers 38. The plasma carrier gas may be air, nitrogen, argon, steam, oxygen, methane, carbon dioxide, a combination thereof, and the like and may be switched among different gases, for example, to aid in ignition and may serve to augment the gases used in the chemistry of producing synthetic gas 17.

During operation of the gasification system 10, plasma 42 is conducted through the extender tubes 32 to break down the waste material 18 producing a flow of synthetic gas 17. This synthetic gas 17, having a relatively lower temperature of approximately 1500° Kelvin, may then pass around the extender tubes 32 which shield the internal plasma 42, having a temperature of approximately 3000° Kelvin, from cooling and combusting the synthetic gas 17.

Referring now to FIG. 2, the microwave plasma generators may employ resonantly driven dielectric rings 40 generating a plasma 42 in the carrier gas 35 within a central plasma tube 41, for example, the later constructed of quartz or high-temperature borosilicate glass. The dielectric rings 40 are shielded from the heat of the plasma 42 by a coaxial outer tube 44 through which cooling gases are passed and by a spacing of the outer surface of the coaxial outer tube 44 from the inner surfaces of the dielectric rings 40. The dielectric rings 40 are positioned within a resonant cavity 45 driven by a microwave generator 36. A resonant cavity and waveguide suitable for use with the present invention may follow the teachings of U.S. patent application Ser. No. 17/652,839, assigned to the assignees of the present invention and hereby incorporated by reference. U.S. Pat. No. 9,706,635 and 9,491,841, assigned to the assignee of the present application and hereby incorporated by reference, provide additional details about a suitable microwave plasma generators 34.

The central plasma tube 41 of the microwave plasma generators 34 may connect with the extender tube 32 through a thermal barrier 38 blocking heat from the extender tubes 32 from being conducted to the central plasma tube 41 maintained in the cooler environment outside of the crucible 12. Referring now to FIG. 3, the thermal barrier 38 may provide a collar 52 that may surround a junction 54 between the extender tube 32 and the central plasma tube 41 which may be separated from direct contact by an air gap reducing conductive heat flow therebetween. For this purpose, the collar 52 provides a central bore receiving the plasma tube 41 and extender tube 32 along a common axis but sized to be spaced from those tubes to also prevent direct thermal conduction between the plasma tube 41 and extender tube 32 through the collar 52. The collar 52, for example, may be constructed of a stainless steel and may include water cooling channels 56 receiving circulated water to maintain a cool temperature.

In order to retain the tubes 41 and 32 together in alignment and to prevent the escape of hot plasma, a high-temperature packing material 58 is formed in a ring seal around each of the adjacent ends of the tubes 41 and 32. This packing material 58 fits within respective channels in the collar 52 and may be axially compressed by one movable channel sidewall 60 controllably compressed inwardly against the packing material 58 by machine screws 62 or the like.

As the movable channel sidewalls 60 compress the horizontal dimensions of the packing material 58 (as depicted) the packing material 58 expands radially inwardly toward the plasma tube 41 and the extender tubes 32, respectively. This horizontal inward compression produces a sealing force equalized by the elasticity of the packing material 88 so that the sealing force produces a circumferential compression to the tubes 41 and 32 against which they are highly resistant and which blocks gas flow.

Other gasket materials including carbon fiber, woven ceramic, and mineral materials are also contemplated.

Referring again to FIG. 2 and to FIG. 7, inlet holes 80 may be placed in the sidewalls of the extender tubes 32 inside the crucible 12 but close to an outer stainless steel shell 82 of the crucible 12. Fast-moving plasma 42 through the extender tube 32 draws gas 86 from inside the crucible 12 through an opening in the refractory material 84 lining the inside of the crucible 12 and around the extender tubes 32. This gas flow reduces heat transfer from the extender tube 32 to the refractory material 84, protecting the refractory material 84. The inlet holes 80 may be angled so as to promote a helical swirling of gas 86 near the inner walls of the extender tubes 32 (consistent with the swirling direction generated by the plasma torch assemblies 30) to help shield the extender tubes 32 from the hot plasma 42. The amount of gas 86 so introduced is limited so as to not unduly deplete the production of syngas 17 or to substantially cool the plasma 42 as might occur if the plasma 42 were not contained within the extender tubes 32.

Referring now to FIG. 4, erosion of the extender tubes 32 in the corrosive environment of the crucible and possible damage from the stream of waste material 18 may be reduced by positioning the extender tubes 32 to pass upwardly through this slag material 22 to a point adjacent to the accumulating waste material 18. In one configuration, a set of plasma torch assemblies 30 may be placed in a ring with the microwave plasma generators 34 beneath the crucible 12 and the extender tubes 32 extending vertically upwardly into the crucible 12 so that their upper distal ends encircle about a point of accumulation of the waste material 18. The number of plasma torch assemblies 30 may vary, for example, between three and twenty in a typical application and will be positioned at equal angles about a central axis of the crucible 12. The plasma 42 from each extender tube 32 may exit via a side port 78 (shown in FIGS. 5 and 6) or via a gas-diffuser-style port in the distal ends of the extender tubes 32 directed radially inward toward the center of the crucible 12 where the waste material 18 accumulates. The side port 78 is desirably adjusted to be close to a surface of the slag material 22 which may be ensured by controlling the height of the slag material 22. In one embodiment this control may include a slag height detector 70, for example, a laser or ultrasound rangefinder, directed downwardly toward the surface of the slag material 22 from an upper portion of the crucible 12 providing a height signal. This height signal may be relayed to a controller 72 controlling a valve 74 through actuator 75 limiting a rate of introduction of waste material 18 and/or may control a draining of slag material 22 through the exit port 26 by controlling the heater coils 28.

Referring now to FIG. 5, upper portions of the extender tubes 32 in the embodiment of FIG. 4 may provide for deflector caps 76 of refractory material whose bottom surface covers the upper end of the extender tubes 32 to provide a desired side directed port 78 and whose upper portions provide outwardly sloped surfaces that deflect debris or introduced waste material 18 from falling into the extender tubes 32.

Referring now to FIG. 6 in an alternative embodiment, the central extender tube 32 may be positioned to pass upwardly directly into the center of the accumulating waste material 18. In this case, the deflector cap 76 and extender tubes 32 may provide for multiple radially directed ports to provide plasma exit in many directions within the accumulated waste material 18. A combination of a central extender tube 32 shown in FIG. 6 and the peripheral extender tubes 32 shown in FIG. 4 may also be used.

Certain terminology is used herein for purposes of reference only, and thus is not intended to be limiting. For example, terms such as “upper”, “lower”, “above”, and “below” refer to directions in the drawings to which reference is made. Terms such as “front”, “back”, “rear”, “bottom” and “side”, describe the orientation of portions of the component within a consistent but arbitrary frame of reference which is made clear by reference to the text and the associated drawings describing the component under discussion. Such terminology may include the words specifically mentioned above, derivatives thereof, and words of similar import. Similarly, the terms “first”, “second” and other such numerical terms referring to structures do not imply a sequence or order unless clearly indicated by the context.

When introducing elements or features of the present disclosure and the exemplary embodiments, the articles “a”, “an”, “the” and “said” are intended to mean that there are one or more of such elements or features. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional elements or features other than those specifically noted. It is further to be understood that the method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed.

References to “a controller” can be understood to include one or more processors that can communicate in a stand-alone and/or a distributed environment(s), and can thus be configured to communicate via wired or wireless communications with other processors, where such one or more processor can be configured to operate on one or more processor-controlled devices that can be similar or different devices.

It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein and the claims should be understood to include modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims. All of the publications described herein, including patents and non-patent publications, are hereby incorporated herein by reference in their entireties

To aid the Patent Office and any readers of any patent issued on this application in interpreting the claims appended hereto, applicants wish to note that they do not intend any of the appended claims or claim elements to invoke 35 U.S.C. 112(f) unless the words “means for” or “step for” are explicitly used in the particular claim.