CA1065193A - Low pollution incineration of solid waste - Google Patents

Abstract

Abstract of Disclosure An incinerator system and method wherein pieces of solid waste, such as fragments of wood, are disposed within a fluidized bed of an incinerator vessel, preferably the solid waste particles homogeneously. The fluidized bed is situated above a high temperature air delivery chamber at the bottom of the vessel and supports combustion or gasification of the solid waste particles in the fine granular material, preferably olivine, comprising the fluidized bed. Volatile matter given off by combustion is burned smokelessly in the vapor space immediately above the bed. All air flow is vortical being caused at least in part by the heat of the bed. Thus, fine particles comprising the bed and small pieces of solid waste are centrifuged back to the bed. Any solid waste retained within the vapor space are ultimately consumed.
Special bed nozzles to which air is selectively channeled aids in improved combustion by defining a region in which tramp material is either trapped and stored, or trapped and removed. A novel fluidizing air system comprising parallel, spaced air ducts, creating uniform air distribution and nozzle discharge, accommodates continuous recirculation and purification of bed material during normal burner operation is provided.

Description

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BACKGROUND
Field of Invention The present invention relates generally to incineration, pyrolysis or gasification o~ waste and more particularly to smokeless, low pollution fluidized bed combustion of pieces of solid organic waste, such as wood waste, municipal refuse, industrlal solid waste including agricultural residues, and livestock refuse, and volatile matter given off by the solid waste and, if desired, incineration of carbonaceous residue produced by combustion of the solid waste.

Prior Art The known prior art comprises expensive incineration of solid waste which results in substantial atmospheric pollution and which are difflcult and costly to maintain.
Substantial supervision is required and combustion is often incomplete due to a number of factors including inadequate residence time. Also, the fine particles from the fluidized bed are often carried away in the exhaust or other discharge.

BRIEF SUMMARY AND OBJECTS OF THE INVENTION
An essentially pollution-free fluidized bed incineration, pyrolysis or gasification system and method wherein solid pieces of waste a~e continually fed, preferably by an air ~et in~ection system in a homogeneous pattern, into a fluidized bed preferably uniquely comprising olivine near the bottom of a combustion vessel. A novel vortex generator system with or without vertical stagnation columns is . - - r~

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provided causing air to vortically lift from the fluidized bed, which increases the residence time of solid waste particles disposed in the vapor space allowing for the same to be consumed or returned due to centrifugal force to the becl. Fine particles from the fluidized bed are also returned to the bed. Bed nozzles are above air ducts and nozzles to which fluidizing air i3 uniformly channeled and the fluidized bed is above the air distribution system, creating a zone at the bottom of the fluidized bed which receives tramp materlal.
The tramp material may be continuously removed from said zone.
Either complete incineration or recovery of a carbonaceous residue and generation of a combustible gas may be accomplished depending upon temperatures of operation and oxygen availability. The exhaust from the vessel may be processed to other mechanisms for removal of any residual solid particles in one or more known ways.
In accordance with one broad aspect, the invention relates to an incineration pyrolysis and gasification system comprising: a vessel; structure for introducing fuel into the vessel; a fluidized bed of non-agglomerated sand particles disposed within the vessel; a source of heat for elevating the temperature of the bed to in the order of above 1200F to 1900F an assembly for introducing air into the fluidized bed comprising a source of air under pressure, an air distribution system disposed beneath the fluidized bed and comprising a plurality of ducts, a manifold interposed between the source of air under pressure and the ducts and a plurality of nozzles located within the fluidized bed, the nozzles being mounted to and receiving air from the ducts, said ducts being spaced one from the next; generally vertical passageways of substantial width between said spaced ducts defining regions through which undesirable material migrate downwardly from the fluidized bed.
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Accordingly, it is a primary object of the present in~ention to provide a novel incinerating, pyrolysis or gasification system and method.
Another paramount object of the present invention is to provide a novel fluidized bed arrangement including bed nozzles for use in incineration, pyrolysis and gasification.
A further dominant object is the provision of a novel vortex generator system to increase residence time of solid waste particles in a vapor zone above a fluidized bed thereby accommodating full combustion of waste while preventing loss of fine particles from the fluidized bed.
An additional prinicpal object is the provision of a novel air jet fuel injection system for use in solid waste incineration, pyrolysis or gasification.

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1~5~3 Another primary ob~ect is the provision of a unique system for isolating and removal of tramp material from a fluidized bed.
A further important ob~ect is the provision of a novel system for recycling and purifying bed material.
One more significant ob~ect is the provision of a novel fluidized bed material comprised of olivine for incineration, pyrolysis or gasification.
These and other ob~ects and features of the present invention will be apparent from the following detailed description taken in reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is an elevational schematic view of an incinerator in accordance with the present invention, with parts broken away for the purpose of clarity;
Figure 2 is a plan view of the auxlliary air and nozzle system for creating an overfire air vortex;
Figure 3 is a view taken along line 3-3 of Figure

2;
Figure 4 is an enlarged elevational view of a presently preferred nozzle, four of which are shown in Figure 2;
Figure 5 shows an enlarged fragmentary elevation of one presently preferred fluidized bed nozzle configuration for isolation of tramp material;
Figures 6-9 show in elevation with parts broken away for clarity various fluidlzed bed nozzles which may be used in conjunction with the configuration of Figure 5;

10~5~3 Flgure 10 is a vertical cross-sectional view of a second presently preferred embodiment of the present invention;
Figure 11 is a cross-sectional view in plan of the embodiment of Figure 10 taken along lines 11-11 of Figure 10;
Figure 12 is a cross-sectional view taken along lines 12-12 of Figure 11; and Figure 13 is an enlarged elevational view of the fuel in~ection system of the embodiment of Figure 10.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Reference is now made to the embodiment illustrated in Figures 1-9 wherein like numerals are used to designate like parts throughout. Broadly, the solid organic waste low pollution incinerator, generally designated 10, comprises apparatus for continually deliverlng fuel which may comprise pieces of solid waste 12 to an incineration, pyrolysis or gasification site. The pieces of solid waste 12 are caused to become somewhat homogeneously distributed within a fluidized bed 30, disposed near the bottom of an incineration vessel 26. While any conveyance may be used, including the direct in~ection of the pieces into the bed, a box conveyor 14 is illustrated ln Figure 1. Conveyor 14 comprises a conveyor belt 16 conventionally driven and displaced around either roller 17 whereby the solid waste pieces 12 fall into the vessel and are distributed by an impact cone 19 whlch is mounted on a column 21 and in turn supported by a cross member 23. Mechanisms may be used in con~unction with the box conveyor 14 to meter the rate at which solid waste pieces are fed into the incinerator. Thus, the solid waste is caused to be evenly distributed and embedded within the fluidized bed 30.

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~OtjS1~3 Depending upon the particular material and circumstances, pieces of solid waste 12 may be pre-dried before being fed into the incinerator, or water may be added thereto prior to or simultaneously with displacement into the lncinerator.
A vapor zone 34, immediately above the fluidized bed 30 comprises a site where volatile matter, released by the pieces of solid waste 12 during combustion occurring in the fluidized bed, are in turn combusted spontaneously or by separate ignition means. Since the process is continuous, the heat of combustion within the fluidized bed and the heat of combustion in the vapor space complement each other so that operating temperatures are readily maintained, once established.
~ n air delivery system 32 drives air under pressure as indicated by arrow-~40 from the source of pressurized air 25 upward into the fluidized bed 30. Initially, high temperature air under pressure is used, being obtained from a conventional air heater 42. Once the fluidized bed 30 has reached the desired operating temperature or slightly below that temperature, the air heater 42 is switched o~f and a high capacity squirrel cage blower 25 or the like continues to deliver ambient air to the fluidized bed. Blower 44 is driven by motor Ml.
Gaseous exhaust passes from the vessel 26 through an effluent conduit 50 either directly into the atmosphere, where and to the extent permitted, or through auxiliary mechanisms where such solid particle content is adequately reduced.

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With gr~ater specificity, the fluidized bed vessel 26 comprises a rlght circular cylinder of sheet metal which is preferably insulated by refractory material along the lnside thereof. A horizontally disposed top 27, also preferably insulated in the same fashion, seals the vessel except for influent air, influent solid waste pieces and effluent exhaust.
Openlngs 29, 31 and 33 accommodate introduction of solid waste pieces, introduction of influent air, and expulsion of exhaust, respectively.
The air delivery system 32 discharges air under pressure received from blower 25 along conduit 35 through opening 37 into air feed chamber 39. The air under pressure from chamber 39 is forced through apertures 41 and 43 in grld plate 45 directly into the fluidized bed and through bed nozzles 47, respectively. Preferably, adequate structural support for grid plate 45 is provided by conventional structural steel members (not shown). The grid plate 45, preferably of mild steel, is uniformly perforated by said apertures 41 and 43 in evenly arranged X and Y rows. The apertures are sized so as to readily permit influent air from the air delivery system 32 to pass through the plate 45 into the remainder of the fluidized bed 30, causing an even distribution of air. Cover caps 51 of the nozzles 47 are disposed essentially at the interface between the materials comprising the fluidized bed 30 and a tramp zone 53 whereby passage of the particulate matter of the fluidized bed through apertures 43 is prevented. In like fashion, plates 55 are preferably used to cover the apertures 41 for the same purpose as some of the tramp zones 53 will comprise particulate matter from the fluidized bed.

... ,.. ~, . ., . . r--10~5193 The fluidized bed 30 comprises a layer 59 Or fine granular particulate matter, whlch uniquely comprises eight to thirty mesh olivine sand, rests upon the perforated plate 45 and receives therein the prevlously mentioned solid waste pieces 12, causing incineration, pyrolysis or gasification thereof, depending upon selected operating temperatures and other variables.
Suprisingly, research and development has established that a bed material comprising olivine sand results in superior performance both in reducing the tendency to fuse and cake and in the rate of particle breakdown and elutriation of the bed material, when compared with bed materials heretofore used. Olivine sand is a mineral of small particle size identified by the chemical compound (Mg,Fe) SiO4.
More specifically, olivine sand is available from the Olivine Corporation o~ 1015 Hilton Avenue, Bellingham, Washington 98225 and has either of the following compositions:

Mountai_ Quarry Reef Point Quarr~
Silica (SiO2) 40.08% 42.2Iron (Fe~O3) 8. 82 6 . 4 Alumina ~A123) 2. 22 -__ Calcium Oxide (CaO) .24 18.4Magnesia (MgO) 48. 39 31. 2 Sodium (Na2) -Potassium ~K2O) 5 Chromite 0. 2 .
99.89 98.4 The size analysis of olivine sand is reported as follows:

Retained on Weight U.S. Screen Size Percent #16 34.1%
#20 56.o #30 9.2 #40 0.4 pan 0.3 . ,.~.. ,. ~, .

lO~Sl~;3 The specific gravlty of olivine ls 3.22 to 4.39 and with a hardness rating of 6.5 to 7Ø It is a rhombic crystalline form and will vary in color from olive green to grayish green to a yellowlsh brown. The materlal in a particle slze varying from a twelve mesh to thirty mesh material ls preferred, (U.S. standard gauge screens).
It has been found to have a low coefflcient of thermal expansion and is highly fracture reslstant to the mechanical and thermal conditlons to whlch lt is sub~ected in the fluidized bed combustion process.
The entire bed, excluding tramp layer 55, may be on the order of nine inches to eighteen lnches deep.
In respect to the bed nozzles 47 (Figure 5), it has, surprisingly, been found that suitable bed nozzles, each disposed upon a stand pipe 61 (defining the height of the inactlve zone 53) causes non-combustible larger sized material to be continuously removed from the active fluidized bed 30 thereby maintaining good quality bed properties at all times. It has been found that the apertures 43 in the grld plate 45 must permit enough air flow to allow the particulate matter of the bed to move upwardly under the force of said alr. The apertures 41 are preferably of smaller slze and serve fundamentally to purge a substantial part of the particulate matter of the fluldlzed bed from the tramp zones 53.
It is to be appreciated that any one of a number of different types of bed nozzles may be used. Some suitable bed nozzles are illustrated in Figures 5-9. Each is mounted upon the stand pipe 61 and comprises a horizontal top or cover 51.
In Figure 5, the cover 51 is disc shaped, is mounted upon a base plate 63 uslng columns 65, whlch in combination define a plurality of radially disposed, horizontally directed air effluent _g _ ~ ................................. .
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10~5193 port 67. The stand plpe 61 is welded to the base plate 63 at site 69. Each stand pipe 61 is likewise welded at sites 71 t;o the top of the grid plate 45.
Wlth reference to Figure 6, the cover plate 51 is clownwardly configurated to create the horizontally extending lip 73, which is welded to the bottom plate 63 and interrupted at two locations 180 from each other to create air discharge ports 75.
In reference to Figure 7, the square cover plate 51 is mounted directly to the top of the stand pipe 61 by four spacers 79 located at each corner and secured at weld sites 77, with four radially disposed air discharge ports 79' between the four corner spacers 79. Air escaping from the ports 79' is channeled between the bottom surface of top cover plate 51 and the top surface of a lower square plate 63', the latter having a central aperture through which the stand pipe 61 extends and being welded to the stand pipe at sites 81.
Figure 8 is a further bed nozzle embodiment wherein the stand pipe 61 is closed at its upper end by plug 83 whlch is welded or otherwise suitably secured in position.
An external cap 85 fits around the upper end of the stand pipe 61 and is likewise secured thereto by welding or the like. The cap 85 has a plurality of outwardly and down-wardly extending bores 87, which are sized and shaped to match apertures 89 disposed in the upper end of the stand pipe gl. Thus, air emitted from the bed nozzle of Figure 8 will be directed radially at an acute angle to the hori-zontal from the bores 87.

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;S19;3 The bed nozzle embodiment of Figure 9 illustrates the cover plate 51 beln~ supported upon and welded to a plurality o~ posts 91, the lower end of each post being welded to the interior of the stand pipe 61 The stand pipe 61 is flaired at its upper end 93, causing air expelled therefrom to be displaced generally radially in a horizontal plane beneath the cover plate 51.
A novel vortex generator system is best illustrated in Figures 2-4. The system provides a source 101 of air under pressure which may be a squirrel cage blower driven by a variable speed motor M2. Air issuing from the source 101 passes through main conduit 103 issuing into the incinerator vessel 26 through a plurality of discharge sites.
The ma~ority of the air from main conduit 103 is displaced into the vessel 26 through nozzle 105 which downwardly extends into the vessel tightly through opening 31 in the top 27 thereof. Air discharge from the nozzle 105 proceeds as indicated by arrows 107, coming on contact with the top surface of the fluidized bed 30 as a vertical column and being displaced essentially radially outward thereafter. Said influent air, which may be preheated as desired, is elevated in temperature once it reaches the vicinity of the fluidized bed 30 causing the same to commence to elevate along an annulus disposed between the cylindrical vertical wall of the vessel 26 and the column of influent air shown at arrows 107.
Air from the main conduit pipe 103 is channeled, as best illustrated in Figures 1 and 2, by auxiliary conduits 109, 111 and 113 to supply a plurality of vortex nozzles 115. The nozzles 115 may be of any suitable type, the configuration shown in Figure 4 being acceptable. hach 10~;5193 nozzle ls fitted through the vertical wall of the vessel 26 at sltes 117 at an acute angle in regard to the radius thereof such that air issulng from each nozzle 115, while not tangentlal initially becomes tangential immediately upon merging with the annulus of air being circulated between the interior sur~ace of the vertical wall of the vessel 26 and the downwardly directed column of influent air 107. This phenomenon is best illustrated in Figure 2. Preferably, as illustrated in Figure 3, the nozzles 115 are directed at a very slight angle downward from the horizontal to restrict the rate at which the elevating vortex permits air to be discharged through outlet conduit 50.
Thus, air flow elevating from the fluidized bed is collected in an annular ring &d~acent the walls of the vessel with the vortex nozzles discharging air at high velocity which intersects the annular gas stream causing rapid clockwise or counterclockwise rotation of the annulus of air, depending upon the direction in which the nozzles are directed, each nozzle being situated to complement the other nozzles in the rotation of the annular ring of air. There is interface mixing with the vertical column of influent air 107 and the conservation of momentum prevails resulting in vortical flow. Thus, fine particulate matter from the fluidized bed is centrifuged and returned to the bed. Also, the high velocity rotation prevents vertical channeling of air directly to the output 50 resulting in a far greater residence time for unburnt combustible particles. As a result, such small waste particles which are not otherwise centrifuged back into the fluidized bed are preserved in the _,,, .,., . ~
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vapor space above the bed until they are consumed.
With additional reference to Figure 2, it is to be observed that stagnation columns ll9, at any desired location and in any desired numbers may be used to create a stagnation zone interfering with the otherwise high rotational velocity of small combustible particles aiding in their being returned to the fluidized bed.
In operation, incineration, pyrolysis or gasification of solid organic waste will depend upon the operating temperature selected and available oxygen It has been determined that at bed temperature slightly greater than 700 Fahrenheit, the volatile species emanating from the solid waste being consumed in the fluidized bed, are volatized, leaving a carbonaceous residue resembling charcoal in the bed. The reaction is slightly exothermic. The volatile species wlll burn smokelessly at about 1100 Fahrenheit or greater; the carbonaceous residue volati~es at 1000 Fahrenheit and burns completely at temperatures of 1200 Fahrenheit or greater. Thus, when total incineration is desired, the temperature in the vapor space 34 is ma~ntained above 1100 Fahrenheit than that of the bed at 1000 Fahrenheit or above, producing energy which can be recovered using boilers or the like. Temperatures in and above the fluidized bed up to a maximum of 1900 Fahrenheit may be used without causing the bed material to react, either physically or chemically.
On the other hand, if it is desired to recover the carbonaceous material as a by-product, the bed is maintained at about 1000 Fahrenheit and, under these conditions, the volatile species will, as before, burn smokelessly in the ,.... . r~--`` 1()~5i'3~3 vapor space 34. Also, if the operating temperature Or the bed ls between 700 Fahrenheit and 1100 Fahrenheit~ an oxygen availability limited to less than five percent (5%) concentration of the carbonaceous residue, the volatile species will result and each may be utilized, thereafter, as a raw material in organic synthesis or other processes, or burned in a separate combustion process.
It is to be appreciated that if spontaneous ignition of the volatile species in the vapor space 34 does not occur, an auxiliary burner may be used to facilltate this end result.
To be certain of bed and space temperatures, it is preferred that temperature sensors of known design be appropriately placed within the interior of the vessel.
It has also been found that once the fluidized bed 30 has been preheated using heater 42 to a temperature on the order of 700 Fahrenheit, the volatile species issuing to the vapor space 34 are or can be ignited, increasing the vapor space and the bed temperatures to beyond the 1200 Fahrenheit level. Smoke free combustion of the volatile species results and total consumption of the carbonaceous solid residues, when total incineration is sought. The direct combustion air heater 42 is normally gradually shut down once the bed temperature reaches a level of 800 Fahrenheit and is completely shut off by the time a 1900 Fahrenheit operating temperature is reached, thereby not using any of the available oxygen in the fluidizing air.
Reference is now made to Figures 10-13, which illustrate a system generally designated 150. Only those portions of the embodiment 150 which are materially the same as the corresponding . .

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portlon Or the already described embodiment 10 will not hereinafter be descrlbed The solid organic waste low pollution incinerator 150 comprises a unique fuel feed system 152 which operates on the principle of an air ~et pump. The fuel feed conveyor 16 turning at roller 17 dispatches by force of gravity solid waste particles 12 through an opening 154 in a fuel feed chute 156 comprising a side port of the bifurcated fuel influent mechanism 158. The bifurcated fuel influent mechanism 158 passes through the top 160 of the refractory lined vessel 162 at aperture 164. Air is fed from blower 101 through the main conduit pipe 103 as heretofore described, to a fuel in~ection air ~et nozzle 166 (Figure 13). Air under pressure emitted through nozzle 166 in a downward direction increases the air velocity at the output of the nozzle. The increased velocity results ln a decreased static pressure in the region where the fuel feed chute 156 inter-sects the inlet air tube 168 of the bifurcated fuel in~ection mechanism 158. The decreased static pressure, in effect, creates a partial vacuum at the inlet to the fuel chute 154, thus virtually "sucking" the fuel into the chute 156. The outlet tube 170 is directed to the center of the active bed region within the vessel 162 and is at an acute angle in respect to the inlet air tube 168. The action of the high velocity air entering with the fuel tends to spread the fuel evenly over the surface of the bed within the vessel 162.
The fluidized bed 172 of the embodiment 150 is comprised of olivine sand.

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lO~iS1~3 The embodiment 150 also comprises a new fluidizing air system 180 that allows continuous reclrculation and purification of the bed material during normal burning operation in a fashion such that uncombustible "tramp"
material, carried into the burner with the fuel, is continuously removed and eliminated. Fluidizing air is generated at main fluidizing blower 182, the squirrel cage or the like of which is caused to be rotated by motor M3 through a conventional V belt drive or the like. The fluidizing air is displaced f`rom the blower 182 into a main fluidizing air manifold 184. As can be seen from Figure 11, the manifold 184 extends over approximately 105 of the periphery ad~acent the vessel 162 and is progressively constricted in both directions so as to create an even distribution of air into a plurality of rectangular ducts 186. The fluidizing air exitlng from the manifold 184 is displaced into the parallel arrangement of rectangular ducts 186 which extend entirely across the bottom of the active bed area and are spaced one from the next such that the fluidizing nozzle pattern previously described in con~unction with the embodiment 10 is achieved without the use of a grid plate. The ducts 186 are properly shaped and sized to insure a uniform air flow to each duct and are of uniform width and spacing one to another so that the rate at which bed material and tramp material migrates between said ducts is a predetermined known magnitude. The parallel duct arrangement provides several advantages over the prior art including the grid plate technique, i.e. (a) the narrow duct widths allows free passage of the active bed material and tramp material to the cone shaped extraction bin below, (b) a relatively .''~ " ' .

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hot bed material pass~ng between the ducts is cooled by the air within the ducts to a temperature compatlble with the preferred carbon steel extraction bins, ducts, manifold iand screen and at the same time the fluidizing air is preheated, and (c) the vibration of the ducts, caused by the flow of fluidizing air, insures the continuous, uniform passage of the entire contents of the bed to the cone shaped extraction bin and screen conveyors below. The length of the ducts varies from duct to duct because of the circular configuration of the illustrated refractory vessel 192.
The free end of each duct is capped and preferably supported upon an expansion mechanism to accommodate thermal expansion and contraction lengthwise while securing against lateral displacement. With the indicated arrangement, essentially the same magnitude of air is discharged from each nozzle 47. The influent to manifold 184 may be heated if desired by an auxiliary burner 188 (Figure 11).
The granular bed material and tramp material passing ad~acent the ducts fills the space created by and is supported by a cone shaped bin 190, having a ma~or diameter equal to the diameter of the active bed of the vessel 162 and a minor diameter which terminates in a vertical pipe or spout 192. The cone may be either a static cone or a dynamic vibrating cone or a two section cone having both a static and a dynamic section. The spout discharges vertically onto a vibrating screen conveyor 194, which is driven by motor M4 so as to oscillate. The screen conveyor 194 separates reusable bed material from tramp material with the tramp material proceeding up the conveyor 194, off the elevated end 196 and discarded. The reusable bed material passes through the mesh of the conveyor 194 onto a lower 10~;51~3 conveyor 198 and ls discharged from the elevated end 200 thereof into a bed material storage bin 202 into a bed material return conduit 204 along which the return bed materially is displaced and ultimately out effluent end 206 thereof onto the fluidized bed 172 within the vessel 162 under force of blower 208 driven by motor M5. Thus, tramp material is removed and the bed material is continuously recirculated for reuse. The bin 202 also provides a convenient point for the addition of new "makeup" bed material which is required from time to time during normal operation of the embodiment 150, due to particle elutriation and attrition caused by particle fracture and abrasive wear. In this way, the bed inventory is maintained at the optimum level for proper fluidization.

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Claims (5)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An incineration pyrolysis and gasification system comprising:
a vessel;
structure for introducing fuel into the vessel;
a fluidized bed of non-agglomerated sand particles disposed within the vessel;
a source of heat for elevating the temperature of the bed to in the order of above 1200°F to 1900°F
an assembly for introducing air into the fluidized bed comprising a source of air under pressure, an air distribution system disposed beneath the fludized bed and comprising a plurality of ducts, a manifold interposed between the source of air under pressure and the ducts and a plurality of nozzles located within the fluidized bed, the nozzles being mounted to and receiving air from the ducts, said ducts being spaced one from the next;
generally vertical passageways of substantial width between said spaced ducts defining regions through which undesirable material migrate downwardly from the fluidized bed.

2. A system according to Claim 1 wherein said contaminated bed material comprises tramp material and further comprising a system for recycling the contaminated bed material, the recycling system comprising channels beneath the ducts passing the contaminated bed material to a segregation site, a segregater at said site for segregating the contaminated bed material into tramp material and rejuvenated bed material and a transporter for returning the rejuvenated bed material to the fluidized bed in the vessel.

3. A system according to Claim 2 wherein said channels comprises a cone-shaped contaminated bed material extraction bin and a moving vibrating cone.

4. A system according to Claim 2 wherein said segregater comprises a vibrating screen retaining thereon larger tramp material and passing rejuvenated bed material therethrough.

5. A system according to Claim 2 wherein said transporter further comprise bed influent structure for causing new bed material to be co-mingled with the rejuvenated bed material whereby the inventory of bed material within the vessel may be maintained at optimum quantity for efficient fluidization.