Claims
- 1. A method of incinerating a fuel containing difficult to remove tramp comprising wire comprising the steps of:
- placing of a fluid bed within a downwardly and inwardly tapered centrally hollow air distributor disposed within a lower portion of a vessel;
- introducing fuel comprising combustible material and tramp comprising wire into the fluid bed;
- incinerating the combustible material in the fluid bed accommodating downward migration within the fluid bed of the wire without any central obstruction to such migration;
- in the course of performing the incinerating step, fluidizing the bed solely by introducing inwardly at several tiered locations directed air into the bed only around the tapered periphery along the lower portion of the vessel from a plurality of inwardly and downwardly parallel sites as causing the bed material and tramp to migrate downwardly and inwardly without central bed obstruction toward a discharge site.
- 2. A method according to claim 1 further comprising the step of cooling the air distributor.
- 3. A method according to claim 1 wherein the introducing step comprises discharging air from each site substantially parallel to the downward and inward taper of the adjacent air distributor.
- 4. A method according to claim 1 wherein the introducing step comprises discharging air as a plurality of downwardly and inwardly streams disposed in a plurality of flow layers.
- 5. A method according to claim 4 wherein each layer is initially directed at an angle on the order of 15 degrees to the horizontal.
- 6. A method according to claim 5 wherein each flow layer is initially directed downwardly and inwardly, but thereafter turns upwardly through the bed.
- 7. A method according to claim 1 further comprising the steps of discharging bed material and wire tramp from the vessel and segregating the wire tramp from the bed material.
- 8. A method according to claim 7 further comprising the step of recycling the segregated bed material to the fluid bed.
- 9. A method according to claim 7 wherein the wire tramp segregation step comprises magnetically separating wire tramp from the bed material and any non-magnetic tramp.
- 10. A method according to claim 3 wherein the introducing step causes a pressure drop per flow layer which progressively decreases in a downward direction from one flow layer to the next.
CONTINUITY
This application is a division of our co-pending U.S. patent application Ser. No. 542,229, filed June 22, 1990, now U.S. Pat. No. 5,060,584.
The present invention relates generally to incineration or pyrolysis of waste and more particularly to smokeless, low pollution fluidized bed combustion of pieces of solid organic waste containing a large amount of difficult to handle noncombustibles and, especially, of waste such as shredded tires which produce tramp in the form of wire which may ball or otherwise cumulate and become immobile in incinerators having central structural impediment beneath the fluid bed inhibiting movement of the tramp from the incinerator. More specifically, the present invention relates to a novel sloping fluidized bed vessel bottom which provides no impediment to tramp moving downwardly toward a removal site at the deepest point of the bed bottom and yet effects airflow adequate to support the fluid bed material while allowing incoming, nozzled airflow and the force of gravity to progressively remove tramp and a small amount of bed material from the bed. In addition, a novel fluidized bed material recovery system separates the removed bed material from the removed tramp and recycle the separated bed material to the vessel for further use.
While low pollution fluidized bed incineration systems are finding ever greater application in eliminating organic waste, there remain numbers of combustible materials for which incineration systems heretofore have been ineffective. The difficulties of disposing of waste tires comprising large amounts of non-combustible wire and other tramp is a prime example. There is some combustion of tires being practiced wherein tires are being used not as the primary fuel but as a fuel supplement. In these cases, however, tires are most often being used where the high temperature slags the wires during combustion or where the tires are de-wired during the shredding process. Unless either of these two processes is used, periodic removal of wires from the incinerator requires significant downtime after incinerator shut down.
It is estimated that over 200 million tires per year are disposed of in some form or recycled for retreading or reuse. Of this 200 million, which equates to nearly one tire per person in the U.S., roughly 36 million are retreaded, 10 million recycled for reclaiming the rubber, and 5 million are currently being used as a fuel supplement in various energy system operations. The remaining 75 percent or nearly 150 million tires per year, are directed to landfill or stored openly, creating unsightly, unsafe and ever growing mounds of waste tires. These tires are currently creating environmental problems which ofttimes are of calamitous proportions. Numerous local communities have experienced acrid pollution of their atmospheres due to nearly impossible-to-extinguish fires which seems to be occurring with increasing frequency. Fire fighters have been imperiled trying to control these fires. Significant mosquito problems have erupted as the result of long dwelling water in tire wells.
The latent energy which can be derived from tire rubbish is enormous. Each tire can supply 300,000 BTU's of energy. Considering the number of tires going to landfall or open storage annually, this equates to 43.5 trillion BTU's per year. On the basis of typical power plant cycle efficiency, this energy is sufficient to generate approximately 3 million megawatt hours of electricity per year. This estimate does not include tires already accumulated in landfill and tire graveyards throughout the country.
As can be appreciated by reference to U.S. Pat. No. 4,576,102, continuously operating fluidized bed incineration systems typically require a fluid bed vessel, a fluidizing air distribution structure, bed material of predetermined depth, a preheater, an ongoing source of fuel distributed throughout the bed, and a means for continuous or regular removal of any non-combustible material or tramp which may collect and hamper operation. When considering the special problems created by fuels having high concentrations of inert materials, most notably, fuels such as tire chips with high concentrations of wire strands, problems not previously solved by prior art becomes evident. These problems are particularly evident when considering vessels which comprise no moving parts.
Wire strands tend to accumulate and form high density masses and bundles which inhibit fluidization. Collecting masses of wire and like tramp are not mobile in the sense of most rocks and other tramp. Any edge or structure upon which a wire may catch can be the point of beginning of a balling mass which ultimately will grow to significantly impede fluidization, forming high density masses and bundles which will not obey removing forces within the vessel. Also wire strands and like tramp tend to ball and collect in stagnant areas of the system. The significance of the problem of wire disposition from fluidized bed systems is evidenced by the fact that wire makes up ten percent of tire mass by weight.
One of the primary problems addressed in prior art has been keeping tramp and fluidizable bed material out of the air plenum while providing uniform supporting airflow below the base of a fluidized bed. Standoff nozzles above a tramp removal system is described in U.S. Pat. No. 4,060,041. A dual cone system comprising holes in the upper cone for downward tramp flow to the lower cone is described in U.S. Pat. No. 4,253,824.
An approach to limiting tramp and fluidizing material which may fall into the air distribution plenum below a bed support structure and otherwise collect in the fluidizing air distribution system is presented in U.S. Pat. No. 4,576,102. Each outlet nozzle, which is orthogonal to the distribution structure, is fitted with a tube which is formed into a "U" similar to that used in a liquid sewer connection to limit the amount of material which may collect and clog the nozzle. The size and depth of the volume in which material may collect is limited to the amount which may be ejected by the force of bed fluidizing airflow provided through each outlet.
In all known prior art which applies to fluidized bed incinerating vessels, provisions for emission of fluidizing air have resulted in structures or areas of stagnation which provide the opportunity for wire and like tramp to accumulate, to form balling masses, and ultimately, to require an otherwise continuous incineration process to undergo periodic termination of operation for cleaning.
A thermal decomposition furnace in which waste tires having their original unaltered shape can be laid horizontally and be thermally decomposed is described in U.S. Pat. No. 4,572,082. While this relates a method for decomposing and removing tramp of whole tires, it does not solve the problems associated with incineration of tire chips and is severely restricted in size and throughput due to a limitation in the combustion portion of the vessel to an internal diameter of less than that of a tire.
Prior art for fluidized bed vessels generally deals with use of airflow primarily directed upward to support the fluidized bed. In U.S. Pat. No. 4,576,102 airflow is directed out of a downwardly sloping bed support structure wherein it is stated, "Fluidizing air and gravity alone gently walk tramp material downwardly along the top of the top of the bed support structure toward a discharge site. Although the discharge of fluidized air through the grid plate into the bed may be non-vertical, the horizontal component of said air discharge is immediately dissipated and the bed turbulence or direction of fluidization is essentially vertical." The discharge of fluidized air through the grid plate is essentially orthogonal to the grid plate and not vertical because the grid plate is sloped. The airflow which originally flows directly upward away from the plane of the discharge plate provides lifting force which "gently" aids gravity in "walking" the material downwardly.
Some non-vertical airflow has been used. For example, horizontal airflow in regions above the discharge plate is used as described in U.S. Pat. No. 4,060,041 to create a vortex to increase the residence time, prevent channeling, and centrifuging airborne solid particles. However, in no known prior art is airflow vectored to directly accommodate tramp displacement toward a disposal means.
Continuous incineration processes also must contend with loss of fluidizable bed material entrapped in tramp and otherwise depleted, such as through the gaseous exhaust system. To recycle fluidizable bed material, wire and large, non-fluidizable tramp must be segregated after removal.
Incineration of tire chips is mentioned above in an exemplary way, since waste comprising auto shredded residue, municipal and industrial waste and the like which contains large amounts of difficult to handle noncombustibles present a similar problem. Nevertheless, heretofore fluid bed incineration of tire segments as a principal fuel has not been possible on a continuing basis, because tramp wire from the tire segments tends to accumulate into a bird's nest ball in the fluid bed and, therefore, continuous removal of the wire was heretofore not achieved. Consequential fluidization of the bed is impaired, creating poor fuel/air distribution and causing eventual shutdown of the fluid bed system.
In brief summary, this invention alleviates all of the known problems related to incineration of waste containing large amounts of difficult to handle noncombustibles, such as tire chips, auto shredded residue and municipal and industrial waste. It provides a system which can operate continuously, receiving fuel having a high, difficult to remove tramp content delivered to the vessel by a combustible material delivery system, controlling and reducing release of undesirable exhaust gases at or below environmentally acceptable levels, moving tramp to a discharge chute without accumulating work-stopping tramp which inhibits fluidizing processes, and discharge noncombustibles (tramp) through a discharge separation system which recycles entrapped fluidizing bed material. The present invention, in a primary way, comprises an air distributor disposed at the bottom of a fluid bed vessel which is centrally hollow and is tapered downwardly and inwardly in steps or tiers whereby a plurality of layers of air are directionally issued peripherally to support and fluidize the bed and displace the tramp toward the hollow center of the distributor.
Restated, major problems related to balling and/or accumulation of wire and like tramp are solved by a novel centrally hollow fluidizing air structure disposed at the bottom of the vessel. The fluidizing air structure is louvered or tiered so that adjacent layers or steps are separated by directionally oriented air discharge gaps by which fluidizing air is communicated from a surrounding plenum to the bed. When the plenum is pressurized, airflow is displaced in a downward and inward direction across the surface of the tiered structure, in combination with the force of gravity, to stimulate progressive removal of tramp from the bed without accumulation thereof. The tiered construction offers no structural impediment to bed material and tramp migrating downward toward a discharge site.
The geometry of the tiers is downwardly convergently tapered, and may comprise an inverted stepped cone or inverted stepped pyramid. The gap between each tier comprises air discharge sites which determine waveform, pressure drop and velocity of the airflow. There is no stagnant area on the surface of each plate, in the central lower region of the vessel or elsewhere, at which tramp could accumulate. Ultimately, each layer of air turns upward to support and fluidize the bed and ultimately passes from the vessel through an exhaust port. The geometry of the upper and lower portions of adjacent tiers and the associated gap are coordinated to nozzle airflow by which the bed is supported and fluidized. Preferably the pressure drop per tier progressively decreases in a downward direction.
Tramp and fluidized bed material, thus progressively delivered to the discharge site, are continuously released. Released material is separated into magnetic and non-magnetic components. The non-magnetic components are further separated into two groups, which comprise recyclable bed material, which is returned to the vessel, and nonmagnetic tramp.
It is a primary object of the present invention to provide a novel fluid bed incinerator, and related methods, which materially overcomes or alleviates the aforementioned problems of the prior art.
It is a paramount object to provide a novel fluid bed incinerator, and related methods, by which waste containing large amounts of difficult to handle noncombustibles or tramp can be processed.
It is another primary object of this invention to provide a novel fluidized bed vessel system, and related methods, for continuously incinerating combustible material comprising pieces of tires and concurrently removing tramp material.
It is a further important object to provide a fluidized bed vessel comprising structure at the bottom of the vessel which is not an impediment to removal of the tramp material through the bottom of the vessel without shut down.
It is a prime object to provide a fluidized bed vessel comprising bottom structure by which the bed is supported upon and fluidized by the cushion of air which also accommodates unencumbered passage throughout of tramp material.
Another paramount object is provision of a novel fluid bed comprising novel louver structure defining directional air ingress gaps which, in combination with the force of gravity, sweep tramp and bed material from the interior surfaces of the bottom.
It is a dominant object to provide bottom structure of a fluid bed vessel comprising an air distribution interior perimeter defining an open region within the perimeter.
Another significant object is the provision of a novel fluidized bed vessel comprising a louvered bottom louvers of which are slightly sloped inwardly and downwardly in respect to the horizontal.
It is a further prime object to provide for bottom air flow in a fluidized bed vessel which is directed from the periphery through the gaps inwardly and downwardly to aid the sweeping of tramp and other material from the surface interior of the bottom and which ultimately turns upward to support and fluidize the bed without the benefit of a centrally disposed air distributor system.
It is an elemental object to provide bottom structure in a fluid bed vessel which provides for unobstructed migration of tramp material which may comprise wire or other difficult to handle noncombustibles.
It is a fundamental object to control and balance airflow in a fluid bed vessel by geometry of the overlapping layers and gap spacing.
It is an important object to provide a plenum and compressor pump in a fluid bed vessel to provide a source of air which flows through the gaps into the vessel.
It is a key object to provide a vessel which has no moving parts.
It is an essential object to provide a combustion initiation system by which fluidized bed material temperature can be elevated to initiate combustion.
It is a further integral object to provide a discharged material handling system for a fluid bed vessel which provides for delivery and further processing of tramp and entrapped fluidizable bed material from the vessel.
It is an important object to provide a discharge chute means in a fluid bed vessel which comprises a lockhopper means to control tramp and exhaust discharge.
It is a significant object to separate magnetic tramp from non-magnetic tramp and to further separate recyclable fluidizable material from non-magnetic tramp.
It is a further key object to provide a system for recycling bed material from a fluid bed vessel, through a segregation site and back to the vessel.
It is a significant object to provide a fluidized bed vessel incineration system which provides sensing and control of the content of exhaust gases.
It is a further significant object to provide for separating particulates from the exhaust gases before release of gases to the atmosphere.
It is a basic object to provide for combustible waste fuel delivery to a fluid bed vessel which allows no exhaust gas leakage from the vessel.
It is a further basic object to provide for delivery of waste fuel to a fluid bed vessel which provides uniform dispersal of fuel to the vessel and which can deliver fuel, recycled fluidizable material, and reclaimed particulates from an exhaust gas particulate separation system.
It is an important object to provide for energy transfer to transform energy produced by combustion to a reusable form.
It is another paramount objective to provide a novel fluid bed apparatus, and related methods, comprising a novel air distributor which is centrally hollow and which supports and fluidizes the bed using a plurality of air layers.
It is a further significant object to provide a novel air distributor for a fluid bed vessel which prevents accumulation of tramp, including wire, and continuously migrates the same to an outlet site and which issues a plurality of downwardly and inwardly directed layers or streams of air which change direction to support and fluidize the bed.
These and other objects and features of the present invention will be apparent from the detailed description taken with reference to accompanying drawings.
US Referenced Citations (10)
Divisions (1)
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Number |
Date |
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542229 |
Jun 1990 |
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Patent Grant
5101742
