Low Pollution Incineration Of Solid Waste

Abstract

An incinerator system and method wherein pieces of solid waste, such as fragments of wood, are conveyed to an influent vertical feed tube where an air jet pump injects them into an incinerating chamber or vessel and at the same time providing influent air for aiding combustion of volatile matter. The falling waste particles are horizontally distributed by striking a cone shaped spreader and secondary air directed horizontally and radially from the spreader may or may not be used to aid in the particle distribution. The particles are "pre-dried" as they pass through the high temperature vapor space before reaching a fluidized bed. A fluidized bed, situated immediately above an air delivery chamber at the bottom of the vessel, supports combustion of the solid wastes in the top layer of fine granular material. The top layer is supported by coarse stone and a perforated plate with cover caps in that order. The air delivery system channels high temperature air into the fluidized bed until operating temperature is reached and so channels ambient air thereafter. Volatile matter given off by combustion of the solid waste in the fluidized bed is burned smokelessly in the vapor space immediately above the bed. The temperature of the vapor space and the bed are set by one or more controlled water spray nozzles. The vessel exhaust is processed through a cyclone separator to remove small particles. A fog nozzle spray system cools the exhaust before it reaches the cyclone.

Description

BACKGROUND

1. Field of Invention

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, such as wood waste, municipal refuse, industrial solid waste and livestock refuse, and volatile matter given off by the solid waste and, if desired, incineration of carbonaceous residual produced by combustion of the solid waste. Recovery of heat energy and/or marketable by-products, e.g. the carbonaceous material, may be obtained.

2. Prior Art

The known prior art comprises expensive incineration of solid waste which results in substantial atmospheric pollution and which are difficult and costly to maintain. Substantial supervision is required.

BRIEF SUMMARY AND OBJECTS OF THE INVENTION

An essentially pollution-free fluidized bed incineration or pyrolysis system and method wherein solid pieces of waste are continually fed into the top of a combustion vessel, by an air jet pump and distributed throughout the vessel cross section by a novel spreader mechanism. The solid pieces of waste are pre-dried as they fall through the high temperature vapor space thereby enabling the combustion of high moisture content feed materials. Water spray is used to control the operating temperature of bed and the vapor space above the bed where volatiles given off by solid waste in the bed are burned. Uniquely the bed from top down, comprises a layer of fine granular particulate material, a layer of coarse stone and a perforated metal plate with hole covers whereby the plate is thermally insulated, backflow of the particulate material is prevented, air flow into the bed through the plate perforations is evenly distributed, and erosion of the grid plate by the particulate material is prevented. Initially, temperatures within the system may be set by a start up heater and elevated to full incineration capacity by combustion of the volatiles within the vapor air space. Either complete incineration or recovery of a carbonaceous residue is accomplished depending on temperature of operation. A cyclone separator processes the vessel exhaust to remove small solid particles.

Accordingly, it is a primary object of the present invention to provide a novel incinerating or pyrolysis system and method.

It is another paramount object of the present invention to novelly distribute pieces of solid waste in a combustion vessel.

An additional important object is to provide a novel feed material drying process to permit combustion of high moisture bearing feed materials.

An additional important object is to provide a novel fluidized bed arrangement for use in incineration and pyrolysis.

A further significant object is provision of a novel water spray system for controlling temperature in a combustion vessel.

It is also an important object to provide a novel method of obtaining operating temperatures in an incineration system.

These and other objects and features of the present invention will be apparent from the following detailed description, taken with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front elevation, with parts shown in cross-section, of a presently preferred embodiment of the present invention;

FIG. 2 is a plan view of the incineration system of FIG. 1;

FIG. 3 is an enlarged cross-sectional view taken along line 3--3 of FIG. 1;

FIG. 4 is an enlarged fragmentary cross-sectional view taken along line 4--4 of FIG. 3;

FIG. 5 is an enlarged fragmentary cross-sectional view taken along line 5--5 of FIG. 3;

FIG. 6 is an enlarged fragmentary section of one grid support member;

FIG. 7 is an enlarged vertical cross-sectional view taken along line 7--7 of FIG. 2;

FIG. 8 is an enlarged fragmentary cross-sectional view taken along line 8--8 of FIG. 2;

FIG. 9 is an enlarged cross-sectional view taken along line 9--9 of FIG. 2;

FIG. 10 is a cross-sectional view taken along line 10--10 of FIG. 1; and

FIG. 11 is a cross-sectional view taken along line 11--11 of FIG. 1.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT

Reference is now made to the Figures wherein like numerals are used to designate like parts throughout. Broadly, the solid organic waste low pollution incinerator, generally designated 10, comprises apparatus for delivering pieces of solid waste 12 to an incineration or pyrolysis site. While any suitable device may be used to deliver the pieces of solid waste 12, FIG. 1 depicts a box chain conveyor 14, comprising a chain 16 supported upon drive sprockets and power driven by means not shown, the upper end of the conveyor 14 comprising a feed slide gate 250 for controlled metering of feed and return of the feed material not metered to the incinerator. As a consequence, the pieces of solid waste 12, which, by way of example, may comprise wood waste and livestock refuse, are gravity fed into the upper intake opening 20 of a feed tube 22 and injected downward by an air jet pump 251 in a generally vertical direction through the tube, out the tube discharge opening 24 into the interior of a fluidized bed vessel or chamber 26. The amount of waste actually introduced into the vessel 26 for incineration or pyrolysis purposes may be metered by, for example, using a conventional return conveyor and a known valve air lock, or slide gate 250 between conveyor 14 and vessel 26.

The pieces of solid waste 12 are horizontally distributed by a momentum spreader mechanism 28 into a vapor space where they fall through the vapor space and are pre-dried before contacting a fluidized bed 30 disposed immediately above an air delivery system 32. The partially dried solid pieces of waste 12 fall in a well distributed pattern and sink into the fluidized bed 30 where they are subjected to high temperature combustion, with or without carbonaceous residue, depending upon operating temperature, oxygen available and mode.

A vapor 34 immediately above the fluidized bed comprises a site where volatile matter, released by the pieces of solid waste 12 during combustion 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 the combustion in the vapor space complement each other so that operating temperatures are readily maintained, once established.

The air delivery system 32 drives air under pressure as indicated by arrows 40 (FIG. 7) from the source of pressurized air upward into the fluidized bed 30 adequate to establish and sustain requisite combustion. Initially, high temperature air under pressure is used, being obtained from an 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 off and a high capacity squirrel cage blower 44 or the like continues to directly deliver ambient air to the fluidized bed.

Gaseous exhaust passes from the vessel 26 through an effluent conduit 50 either directly into the atmosphere, as shown in dotted lines at stack 52 (FIG. 1), where the parts per million of solid particles in the exhaust do not exceed maximum limits permitted for the operating location in question, on through a cyclone separator 60.

Where removal of small solid particles from the exhaust is required or desirable, the effluent conduit 50 is connected to the intake opening 62 of the cyclone separator 60. Such devices are conventional and the one illustrated comprises said intake tube 62 joined to a generally cylindrical body 64 which terminates at its lower end in a funnel shaped dump 66 through which the small solid particles of the exhaust fall into a suitable container 68. Alternatively, the small solid particles can be recycled to the vessel 26 by a second air jet pump 252 and a converting conduit 253. The particle-free exhaust gas then proceeds upward through an exhaust tube 70, which is anchored to a cover plate 72 of the cyclone separator 60 so that the tube 70 is axially aligned with the body 64 and comprises an intake opening 74 centrally disposed within the body 64 and an effluent opening 76 situated outside the body 64 well above the cover plate 72. The exhaust from cyclone separator 60 may be processed through a conventional wet scrubber, if necessary or advisable, particularly in respect to pollution standards.

Exhaust from the vessel 26 is delivered to the cyclone separator 60 by the positive pressure existing in the main vessel 26. However, other suitable air displacement means could include a blower 49 of known type shown as being disposed within conduit 50. In addition, blower 49 may be placed at the influent to the vessel 26, the influent to separator 60 and/or at the gas effluent of the separator.

Heat may be recovered by a suitable heat exchange system which is depicted for purposes of illustration as boiler 80 in FIGS. 1, 2 and 7.

The temperatures within the vessel 26 are preferably controlled by selecting the amount of moisture introduced into the vessel. Specifically, as illustrated in FIG. 7, the moisture within the waste, if any, is supplemented by one or more fog nozzles 90 which may be mounted in the vicinity of the influent opening 20 of the feed tube 22, the spray of water from nozzle 90 being gauged by a conventional water control 92. When only nozzles 90 are used, the combined moisture content of the pieces of solid waste 12 and the spray emanating from nozzle 90 together will appropriately influence the temperatures within the vessel so that the desired amount and type of combustion occurs. Notwithstanding the foregoing, spray from nozzles 90 may be augmented or replaced by spray from one or more fog nozzles 94 disposed within the vessel or by one or more fog nozzles 96 situated adjacent the exhaust effluent of the vessel 26, the nozzles 96 also serving to precipitate small solid exhaust particles back into the vessel, to create aggregates of particles for easier removal by the cyclone 64 and to control stack off-gas temperatures. As can best be seen in FIG. 7, each nozzle 90 and 94 may be mounted by suitable bracket 116 to the cone shaped exterior of waste influent end 20 of the feed pipe 22. Undried wood, for example, typically has 20-60 percent moisture content.

With greater specificity, the fluidized bed vessel 26 comprises a right circular cylinder of sheet metal 100, interiorly insulated by a layer of refractory 102, which is preferably cast into its annular configuration in place using conventional techniques. Refractory 102 together with the control of vessel temperatures by water spray permits the vessel 26 to be fabricated from mild steel.

A horizontal outwardly extending radial top flange 104 of the vessel is welded or otherwise secured to the top edge of the annular sheet of steel 100 to form a lip which supports a top plate 106. It is preferred that an asbestos or other insulating gasket be placed between flange 104 and the adjacent portion of disc shaped top plate 106. Bolts (not shown) preferably secure the top plate 106 to flange 104 in air tight relation, in a conventional manner. Top plate 106 is heat insulated by an interior layer of refractory or the like.

A centrally disposed hole exists at 108 in the plate 106 through which the feed tube 22 extends, being anchored in position by a flanged collar 110 which is welded to the plate 106 and an annular flange 112, which is welded to the central linear portion 114 of the feed tube above the plate 106, the flange of collar 110 and the flange 112 being preferably bolt secured one to another to permit, upon removal of the bolts, removal of the feed pipe 22 from the vessel.

As can be appreciated by inspection of the Figures, particularly FIG. 7, boiler pipes and air conduits connect to the steel cylindrical body 100 of the vessel 26 in well known ways so as to effect a sealed realtion. Specifically, air blower 44 discharges air through vessel intake air conduits 120 and 122 to the central interior of the vessel at the waste spreader site 28. Thus, air conduits 120 and 122 comprise part of the solid waste spreader system 28, which also comprises a vertically oriented metal cone 124 disposed on the central axis of the feed tube 22 immediately beneath its delivery opening 24. Alternatively, air jet pump 251 together with metal cone 124 comprise the solid waste spreader system 28. Thus, the pieces of solid waste 12 falling generally vertically through the tube 22 strike the angular surface of the cone 124 and are deflected substantially horizontally out from the cone 124 causing the pieces to be distributed throughout the interior of the vessel 26. In other words, the vertical momentum of the falling particles is converted into horizontal momentum upon striking the cone 124. The horizontal distribution of waste pieces is materially aided by air passing from blower 44 through conduits 120 and 122. Alternatively, the horizontal distribution of waste is aided by the air jet from air jet pump 251 supplied by blower 254. This air merges at a central, upwardly directed tube 130, which supports the cone 124 upon spaced columns 132, the air passing outward from beneath the cone 124 through the slots between the columns 132 in horizontal, radial directions as indicated by arrows in FIG. 7. Thus, the spreader mechanism 28 has no moving parts and uses two features for spreading the waste over the surface of the fluidized bed 30.

Also, the air emitted by spreader mechanism 28 into the vessel produces a vena cava effect at the mouth of the feed tube 22, resulting in a negative pressure in the feed tube and a downward flow of air through the feed tube. The pneumatic spreader air together with the air flowing down the feed tube serve as overfire or secondary air for combustion of volatile matter emitted from the fluidized bed 30 into the vapor space 34, when the unit is used as an incinerator. Naturally, the amount of air issued from the pneumatic spreader will be regulated to optimize the feed distribution within the vessel as a function of the waste material size and density. Alternately, air jet pump 251 provides the air necessary to spread the feed material and supply overfire air.

Fully automatic control of the process, (no full time generator is required) is achieved by a control system employing a vapor temperature sensor 255, a linear actuator 256 positioning slide gate 250 or other feed metering valve or metering device, a smoke detection sensor 257 and control and logic unit 258. A preselected combustion chamber temperature is demanded by the control and logic unit 258, which in turn positions the feed gate 250 by activating the linear actuator 256. The smoke detection sensor 257 monitors the opacity of exhaust effluent from opening 76. When the exhaust gas opacity reaches a pre-set valve as determined by smoke detector 257, the control and logic unit 258 will reduce the feed rate by activating linear activator 256 and partially closing feed gate 250.

The previously mentioned annular layer of refractory 102 is supported against gravity by an annular flange 140 situated near the bottom of the vessel 26 and welded contiguously to the interior of steel cylinder 100.

A grid plate 142 comprising part of the fluidized bed assembly 30 is situated immediately below the annular flange 140 and is maintained in the indicated position by a number of suitable structural support members. More specifically, the required support, at the edge, is provided by a number of spaced pedestals 144, each of which comprise a small horizontal plate 146 and a central vertical web 148, each pedestal 144 being welded to the interior of the annular steel cylinder 100, as best illustrated in FIG. 7.

The central portion of the plate 142 is maintained in its illustrated horizontal position against the load of the fluidized bed 30 by a plurality of parallel I beams 150. The plate 142 provides four parallel slots 152, one immediately above each I beam 150. A plurality of vertical bars 154, welded to the top flange of the adjacent I beam 150, extend through each slot 152, as best illustrated in FIGS. 3 and 5. The top flange of each I beam 150 is not attached to the grid plate 142. Each bar 154 extends through an aperture in and is welded to a plate 156 which is almost co-extensive with the adjacent I beam, is immediately above the top surface of the grid plate 142 but is not attached to grid plate 142. This arrangement helps allow for heat expansion of the I beams.

Referring now to FIG. 4, each plate 156 is welded at both ends 158 to a bridge plate 160, each bridge plate 160 resting upon the inner extension of annular ring 140. Thus, part of the weight of the beams 150 and the load supported by the beams is transferred to the cylindrical shell 100. Each beam 150 extends beneath ring 140 a distance beyond the end of its corresponding plate 156 to a position immediately adjacent the cylindrical shell 100, each end of each beam 150 being slidably fitted into and resting upon a short length of box beam 170. Each box beam 170 is oriented horizontally and secured, as by welding to the outer end thereof to the interior of the shell 100, as best illustrated in FIG. 4. Thus, each beam 150 and each associated plate 156 are permitted to contract and expand with the temperature changes in the vessel 26 without imparting displacement or deflection to other associated components, particularly the grid plate 142.

As can best be appreciated by inspection of FIG. 3, the grid plate 142, preferably of mild steel, is uniformly perforated by a plurality of apertures 172, which are arranged in evenly spaced X and Y rows. Apertures 172 are sized so as to readily permit influent air from the air delivery system 32 to pass through the plate 142 and into the remainder of the fluidized bed 30, causing an even distribution of air. Cover caps 180 are placed over each aperture as to prevent passage therethrough of the material in the fluidized bed.

A layer of crushed coarse stone 182 is located immediately above and rests upon the grid plate 142 and may be of any desired vertical thickness, a thickness of 1 to 5 inches being suitable for a vessel 20 feet tall and 10 feet in diameter. The size of stone is preferably 1/2 inch to 1 1/4 inch crushed material. A bed 190 of fine granular particulate matter, such as 8 to 30 mesh sand, rests upon the coarse crushed stone 182 and receives therein the previously mentioned pieces of solid waste 12, causing incineration or pyrolysis thereof depending upon selected operating temperatures and other variables. It is preferred that .alpha. phase spherical alumina particles of 8 to 30 mesh size range comprise bed 190. The bed is usually on the order of 9 inches to 18 inches deep. The purpose of the coarse stone layer 182 is four fold: (1) to thermally insulate the grid plate, permitting it to be fabricated of mild steel, (2) to prevent the back flow of the particulate bed 190 through the grid plate when the system is not operating, (3) to provide uniform distribution of the air from the delivery system 32 into the particulate matter 190, and (4) to prevent the sand particles from reaching erosion velocities in the vicinity of the grid plate which would otherwise cause harmful erosion of the grid.

The top of the fluidized bed may be inspected through a window 192 which is preferably fabricated of quartz and held within an assembly 192 as is conventional.

The air delivery system 32 comprises the previously mentioned air heater 42, air blower 44, air influent conduit 200 and an air plenum chamber 202 situated at the bottom of the vessel 26. Air plenum chamber 202 is bounded on the bottom by a bottom plate 204 which is integral, as by welding, with the cylindrical plate 100 and, at the top, by the grid plate 142. The vertical portion of cylindrical shell 100 extending between the bottom plate 204 and the grid plate 142 also defines the air delivery chamber 202. Inspection of the chamber is permitted by a quartz window 206 held in a conventional frame 208 and bolted in a conventional manner to a flanged opening 210 in the cylindrical plate 100.

In like manner, air influent conduit 200 is secured to a flanged opening 212 opposite the window 206, permitting air from either the heater 42 or the blower 44 or both to be introduced into the air delivery chamber 202. Influent conduit 200 is preferably of mild steel exterior 214 and an interior layer of refractory insulation. Thus, air of any desired temperature may be delivered under pressure to chamber 202 and from there evenly distributed up through the apertures 172 of grid plate 142, the voids of the coarse crushed stone layer 182 and into the body of the particulate matter 190.

Heater 42 may be of any suitable type capable of elevating, at the commencement of operations, the temperature of the fluidized bed 30 to on the order of about 700.degree. F. - 1,200.degree. F. Air under pressure from squirrel cage blower 44 may be channeled to the heater 42 using air line 220 (FIG. 2), heated and issued to the air delivery chamber 202 through influent conduit 200.

With particular reference to FIGS. 2, 8 and 9, it is presently preferred that the blower 44 be driven by an electric motor M, which belt drives, at 222, a shaft 224 on which is disposed a squirrel cage (not shown), contained within and toward the rear of the housing 226 of the blower, all of which is conventional.

The squirrel cage effluent is confined in an enclosure 228, the walls of which diverge outwardly in a direction away from the squirrel cage. The air under pressure may be directed into air line 220 at a selected metered rate using a manual damper valve 230. In like manner, the damper valves 232 and 234 may be manually set to selectively control the quantity of air received into previously mentioned spreader air influent conduits 122 and 120, respectively. Damper valves 232 and 234 are snugly situated in vertical chimneys 236 which extend above and open into the enclosure 228.

Also, the amount of air issued from enclosure 228 into the interior of conduit 200, with which it is connected for air passage, is controlled by a rectangular damper valve 238 and may be (a) manually set using its handle to essentially prevent air flow from the blower 44 directly into the conduit 200 (as for example, when the bulk of the air is being diverted through conduit 220, through the heater 42 and then into the conduit 200), (b) set at an angle to meter the amount of air issuing to conduit 200 (as, for example, when some air from the blower 44 and some air from the heater 42 are being combined in conduit 200 and thereafter introduced into the fluidized bed), or (c) set in a fully open position, where essentially all air from blower 44 is issued directly into conduit 200. Naturally, the settings of damper valves 230, 232, 234 and 238 will depend upon the material being incinerated, the kind of incineration desired and other variables. In any event, the operator may manually adjust each until efficient operation results, each being mounted so as to create a substantial amount of frictional resistance to rotation which can be overcome manually but will withstand the force of air impinging thereon.

In operation, incineration or pyrolysis of solid organic waste, using the present invention, will depend upon the operating temperature selected and available oxygen. It has been determined that at bed temperatures slightly greater than 700.degree. F., 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 will burn smokelessly at about 1,100.degree. F. or greater; the carbonaceous residue volatizer at 1,000.degree. F. and burns completely at temperatures of 1,200.degree. F. or greater. Thus, when total incineration is desired, the temperature in the vapor space 34 is maintained above 1,100.degree. F. and that of the bed at 1,000.degree. F. or above, producing energy which can be recovered using boilers or the like.

On the other hand, if it is desired to recover the carbonaceous material as a by-product, the bed is maintained at about 1,000.degree. F. and, under these conditions, the volatile species will, as before, burn smokelessly in the vapor space 34. Also, if the operating temperature of the bed is between 700.degree. F. and 1,100.degree. F., and oxygen availability limited to less than 5 percent concentration the carbonaceous residue and the volatile species will result and each may be utilized, thereafter, as a raw material in organic synthesis or other processes.

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 facilitate this end result. To be certain of bed and space temperatures, it is preferred that temperature sensor of known design be appropriately placed within the interior of 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.degree. F., the volatile species issuing to the vapor space 34 are or can be ignited, increasing the vapor space and bed temperatures to beyond the 1,200.degree. F. level. Smoke free combustion of the volatile species results and total consumption of 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 about 800.degree. F. and is completely shut off by the time the 1,200.degree. F. or higher operating temperatures are reached, thereby not using any of the available oxygen in the fluidizing air. For low moisture content, high heat value feed materials, the bed and vapor space temperatures are prevented from substantially exceeding the desired levels by issuing water spray into the vessel, using the heretofore described nozzles. Stack gas temperatures are controlled and pollution reduced with a water fog spray located at the base of the effluent exhaust stack.

With the present invention (embodying a vessel 10 feet in diameter and 20 feet high), throughput rates of 20 to 150 tons of solid organic waste per day may be processed to pyrolysis or through complete incineration, whichever is desired and, it should be appreciated, that the subject matter of this application and the claims thereof are intended to encompass both objectives in an essentially pollution-free manner.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims

What is claimed and desired to be secured by United States letters Patent is:

1. A method of low pollution incineration, the steps of:

elevating the temperature of a confined fluidized bed to on the order of about 700.degree. F.;

continuously distributing pieces of solid waste from an elevated site on the top surface of the confined fluidized bed;

causing the solid waste to sink into the fluidized bed;

combusting the solid waste within the fluidized bed initially leaving a solid carbonaceous residue in the bed and volatilizing the volatile matter contained within the solid waste into the vapor space immediately above the fluidized bed;

combusting the volatile matter above the fluidized bed thereby;

increasing, first the temperature of the vapor space and then the temperature of the fluidized bed to on the order of about 1,200.degree. F. or more;

thereafter, accomplishing smoke free total incineration of the solid waste, the carbonaceous residue and the volatile matter.

2. A method of low pollution incineration, the steps of:

elevating the temperature of a confined fluidized bed to a first order of magnitude capable of supporting combustion;

continuously causing pieces of solid waste to become imbedded within the confined fluidized bed;

combusting the solid waste within the fluidized bed initially leaving a solid carbonaceous residue in the bed and volatilizing the volatile matter contained within the solid waste into the vapor space immediately above the fluidized bed;

combusting the volatile matter above the fluidized bed thereby;

increasing, first the temperature of the vapor space and then the temperature of the fluidized bed to a higher order of magnitude;

accomplishing smoke free total incineration of the solid waste, the carbonaceous residue and the volatile matter.