US3509834A - Incinerator - Google Patents

Description

y 1970 R. B. ROSENBERG ET AL 3,509,834

INCINERATOR 2 Sheefs-Sheet 1 Filed Sept 27,

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United States Patent INCINERATOR Robert B. Rosenberg, Evergreen Park, Jack Huebler,

Deerfield, and Esher R. Kweller, Evanston, Ill., as-

signors to Institute of Gas Technology, a not-for-profit corporation of Illinois Filed Sept. 27, 1967, Ser. No. 670,908 Int. Cl. F23g 5/12; F231 15/00 US. Cl. 110-8 19 Claims ABSTRACT OF THE DISCLOSURE The application discloses both wheel-type and checkerbox type regenerators in combination with domestic gasfired incinerators, having both a primary and a secondary combustion chamber. The input ambient air is preheated as it passes through the constantly rotating regenerator wheel or the checker-box, and is then ducted to the charge and gas burner as primary, secondary, or both primary and secondary air. The burning of the materials to be incinerated produces hot gases which are then passed countercurrent through another section of the same wheel and are thereby cooled. The flue products are cooled to below about 250 F., and may be vented into the room wherein the incinerator is situated Without technical or safety problems arising, codes permitting. Masonry chimneys are obviated. The use of the regenerator is in accordance with a process in which the rate of combustion in the primary combustion chamber is controlled.

FIELD AND PRIOR ART The field of this invention is that of gas-fired incinerators particularly useful in domestic applications, although the concept of the invention is equally applicable to commercial size incinerators.

Incinerators per se are known in the art, and the primarily large commercial or industrial types have used stationary tube-type heat exchangers to preheat incoming air. However, the stationary tube-type heat exchangers must be large in order to be reasonably eflicient. Further, prior art incinerators, particularly the domestic type, absolutely require exterior venting of high insulating capacity such as masonry chimneys.

PRESENT INVENTION Objects It is among the objects of this invention to provide an improved gas-fired incinerator useful particularly in domestic situations that will eliminate entirely the need to vent flue products or permit the use of inexpensive ventmg.

It is an object of this invention to provide an improved incinerator and method of incineration that eliminates odors and smoke during operation and permits direct room interior venting.

It is another object of this invention to provide means in combination with an incinerator that lowers the flue gases temperature to below about 250 F. for room interior venting.

It is a further object to provide a process of incineration that eliminates uncontrolled combustion of the charge and high internal temperatures resulting therefrom.

It is also an object of this invention to provide a method of incineration that will reduce the amount of fuel needed to incinerate a given mass of material in a minimum time.

Summary By the present invention, both an apparatus for in cineration of combustible wastes and a method of mcineration are provided, wherein a heat exchanger is used in combination with a standard domestic-type incinerator. More specifically, the preferred type of heat exchanger is the regenerator type, and within that class both wheeltype regenerators and checker-box type regenerators are employed, although the wheel-type regenerator is preferred. The heat regenerator is arranged such that the hot exhaust gases issuing from the incinerator during the incineration are cooled so that such gases may be exhausted directly into the adjacent room space. Alternatively the exhaust gases may be vented exteriorly by means of a common Class C vent, or other conventional low temperature through-the-wall venting means, instead of the more expensive masonry chimney or Class L vents as required by prior art devices. The incoming air, which is to be combusted with the gas and the mass to be incinerated in the incinerator cavity, is preheated by passage through a regenerator wheel in countercurrent relation to the exhaust gases. The wheel is divided into segments such that the gases to be preheated pass through one segment, and the gases which heat the wheel is being exhausted pass through a different segment. The wheel of the wheel-type regenerator is constantly rotating, and the flue gases, as they pass in contact with the regenerator, add substantial amounts of heat energy to the wheel. At a later time, the heat energy accumulated in that part of the regenerator is released to the incoming combustion air, thereby cooling the regenerator back to a temperature where it can continue to cool the exhausting hot gases upon continuation of its cycle of rotation.

A conventional gas-fired incinerator rated at 30,000 B.t.u./hr. input with 950 c.f.h. air flow through the incinerator will exhaust 21,000 B.t.u./hr. to the flue when the incinerator secondary chamber is at about 1400 F. In the device of the present invention With the same total air flow and the same secondary chamber temperature only 3250 B.t.u./hr. is exhausted to the flue. While the total heat input is the same, only 19,000 B.t.u./hr. of that need be gas where a regenerator wheel of appropriate heat resistant material is used, and the remaining 11,000 B.t.u./hr. may be supplied by preheat air. The heat released by the exhaust gases is thus reduced on the order of 70-90%. In addition, the input rate of preheated air is controlled so that there is no run-away combustion in the primary combustion chamber, and thus a more complete burning is achieved. Also, control of the combustion is possible so that it may be completely halted if an unsafe condition should occur.

In the drawings:

FIG. 1 is a schematic view partly in section of a conventional incinerator having a primary combustion chamber, an afterburner in a secondary chamber, and the heat regenerative unit of this invention incorporated therewith;

FIG. 2 is a view partly in section showing details of the heat regenerative unit of FIG. 1;

FIG. 3 is an embodiment of an ignition circuit diagram, primarily for a domestic-type incinerator of this invention;

FIG. 4 is a diagrammatic view partly in section of another embodiment of the invention wherein a checkerbox type regenerator system is employed in combination with the incinerator;

FIG. 5 is a schematic diagram of an embodiment of a complex control primarily for a commercial-type incinerator.

With reference to FIGS. 1 and 2, one embodiment of the incenerator of our invention is a wheel-type heat regenerator unit, indicated generally as 1, shown at the top of an incinerator cabinet 2. The regenerator may be located on the rear of the incinerator, or in any suitable location where the unit geometry permits. The incinerator per se may be any conventional gas-fired in- 3 cinerator whether of the small domestic type of capacity, about 1-4 bushels, or the larger commercial type. The incinerator of our invention has appropriate controls, insulation, and heat-resistant materials of construction.

The wheel-type heat regenerator unit used in conjunction with the incinerator comprising a housing, shown generally at 3, in which is positioned a rotatable, round wheel 4 which serves as a heat sink. The wheel 4 is mounted on a shaft 5 which is adapted to rotate by meansof a small electric motor 6. Alternatively, shaft 5 can be driven by suitable linkage with the motor of forced air fan 7, which fan is used to create a forced draft through the housing 3 and incinerator cavity. The wheel 4 is isolated in a portion of the housing 3 by means of periphery seals 8, 8', and baflle plate 9 which are arranged so as to direct the flow of gases through the wheel as hereinafter described, and to prevent flow of gas around the outside periphery of the wheel and across the faces of the wheel. The housing 3 may be tubular or square in cross section, and where it is square, additional baffle plates between the periphery seals and housing walls will be required to block off the space between the round wheel and the larger square housing. Along the faces of the wheel, there are provided wipers or face seals 10, 10' of tubular or flat configuration, for example, of glass fiber material, which serves to prevent flow of gases across the face of the wheel between the left and right sections.

The right part of housing 3 is a flue 11 containing electric fan 12 adapted to draw combustion products and excess air from the incinerator combustion chambers 13, 14 as shown by the arrows indicating air flow. The left portion of housing 3 comprises air input duct 15. Air coming in through duct 15 is preheated by heat exchange in the regenerator wheel 4, and is then supplied as primary, secondary, or both primary and secondary air to burners in the incinerator cornbustion chambers, and as combustion air to the charge.

The construction of the primary combustion chamber 13 is conventional and contains a gas burner 16, with a grating 17 being spaced above an ash drawer 18 at the bottom of the incinerator. The burner may be of any conventional type and may be placed above, below or integrated with the grate. The burner may be provided with a conventional spark igniter. Located within the input duct 15 is an electric fan 7 adapted to blow air into the duct. Alternatively, the fan 7 .may be located where convenient in association with housing 3 and either it or the exhaust fan 12 may be eliminated, so long as the proper circulation of gases into and out of the incinerator is effected. Where only one fan is used it should be on the flue side in the exhaust ducting 11 so that combustion products will not be blown out of dilution air opening 39.

Regenerator wheel 4 is cylindrical, and is preferably a material of corrugated, or honeycomb or similar surface design, and has a plurality of small axial passages through which the input air and flue gases may pass. It may be made of any heat-rcsistant material, preferably one that has a high heat capacity of substantially non-thermal conductive (i.e., low thermal conductivity) material, such as asbestos, asbestos impregnated with may be on the order of inch. The period and distance will vary somewhat according to the particular chamber temperature sought to be cooled and the exhaust temperature sought to be achieved. The Wheel need not be formed in a spiral configuration, but may be a circular core cut from layers of corrugated asbestos laid together in straight or arcuate rows, as when the wheel would be cut from a segment of a larger roll.

For an incinerator cavity of about 1.5 cubic feet capacity (1 /2 bushels incinerated/hr. is common for a domestic incinerator), the wheel is preferably about 6 inches in diameter and 3 inches thick and rotates at about 5 rpm. The hot exiting flue gases pass through the right half of the wheel, as shown in FIGS. 1 and 2, giving up heat to the wheel. The wheel rotates continuously so that the hot half of the Wheel is then exposed at its left half to incoming combustion air which cools the wheel. It will be understood that the dimensions of the regenerator wheel and its rate of rotation are not critical and are functions of the incinerator cavity size and temperature requirements. Those skilled in the art will recognize that the parameters can be adjusted within the skill of the art to provide the cooling effect desired for any particular incinerator design. Regarding the incinerator size, the conventional maximum for a domestic incinerator is about 4 bushels (5 cubic feet) and is intended to burn a charge of not more than 6 lbs. of waste per hour for each cubic foot capacity.

It should be understood that the incinerator may have additionally in combination a fly ash collector, which may be a perforated or screen, and which is placed preferably between the regenerator wheel and the incinerator cavity so that the apertures of the wheel are not clogged. As seen in FIGS. 1 and 2, the collector is preferably a metal screen 19, of appropriate temperature resistance, which is attached to an extension 20 of the regenerator shaft and rotates with the regenerator wheel. In operation, fly ash is collected on the screen in the flue gases side (right side in FIGS. 1 and 2). Upon rotation of the screen into the inlet air section, the fly ash is blown back into the cavity for further incineration. This type of collector is thus self-cleaning.

Other parts of the incinerator are best described in connection with the operation of the incinerator. Startup is accomplished by charging the primary combustion chamber through door 21 and turning on a timer control switch (FIG. 3). Closing the door latch mechanically closes a door lock switch 76. If the door is opened during operation the door lock switch will be opened and the gas to the burner cut off by gas valve 77. Additionally a positive door lock mechanism may be employed to prevent opening of the door once start-up has occurred. For example the amplified output of a bimetallic thermocouple in the primary combustion chamber is wired to operate a solenoid actuated lock in which a slidable rod associated with the incinerator wall lockingly engages the door when the thermocouple senses,

a hot condition. Alternatively, a bimetallic warp switch can be employed in place of the thermocouple, or a timer-actuated mechanical locking device can keep the door locked during the duration of the cycle.

The timer 75 is set for the desired incineration time, and may have settings for dry and wet loads. The induced air blower (exhaust fan) 12, forced air blower (input fan) 7, and regenerator motor 6 start when the circuit is completed by closing door and timer switches 75 and 76. Air flow through the incinerator ducts and chambers is proven by the sail switch 78, conveniently placed, for example, in input air duct 15. Air pressure closes the sail switch and the circuit is then energized to open the gas solenoid valve 77. A spark igniter 79, including an ignition transformer and electrodes, is disposed adjacent each bnrner in the primary and secondary combustion chambers. When the burner has ignited, a

bimetallic warp switch of a flame sensor 80 switches to the hot side and sparking stops. If the burner fails to ignite within a specified time, usually four seconds, a safety lockout control 81 causes the gas valve to close. All components of this preferred ignition system are standard items and modifications of this circuit can be made to keep the induced air fan on if the loading door is opened, so that flame or smoke does not exhaust through the open door.

Air from outside the incinerator is drawn in through air opening 22 and passes through the duct 15. At the same time the wheel 4 begins to rotate. Hot products of combustion with the air enter the right half of the wheel 4, with the fly ash being caught on the collector screeri 19. The flue products are drawn through the wheel by the circulation of gases caused by induced air exhaust fan 12. The location of baflle 9 and seals 8, 8 and wipers 10, 10 directs the hot gases through the right portion of the wheel and prevents mixing of the exhaust gases with incoming air in the left portion of the wheel. Flue products transfer heat to the wheel 4 and are then discharged through the outlet of fine 11 which communicates with an exterior vent or with the room.

It should be understood that the term flue gases refers to the mixture of hot incineration products and air passing through the afterburner chamber prior to entering the regenerative heat exchanger, and the term exhaust gases refers to the relatively cooler gases in the exhaust duct after having passed through the regenerative heat exchanger.

With the wheel 4 rotating, the hot section of the Wheel rotates out of the flue box portion into the left portion of the housing 3. Ambient room air then passes through the left portion of the hot wheel where it is heated by heat exchange and directed into the incinerator cavity. As the heated air exits from the lower left face of the wheel, it passes through the collector screen and carries with it the ash collected thereon back into the primary combustion chamber. It should be appreciated that the wheel may be placed Wherever convenient with suitable ducting for the input air and flue gases.

The preheated air then passes into the primary combustion chamber, as shown by arrows in FIG. 1, by either or both of two routes. The preheated air may pass, in suitable ducting, partly into the chamber 13 near the top of the charge via opening 23, which alternatively may be placed along the side walls of the chamber 13 as seen in phantom at 24. Part of the preheated air may be directed down duct 25, which may be as shown in FIG. 1 or in the side walls of the chamber at 179, 180 to exit near the bottom of the charge, as at port 26, near the afterburner at 181 or even below the grate. Alternatively the entire side and/or front walls of chamber 13 may be spaced from their insulation 27 to provide a passage for the preheated air to exit out ports 28 shown in phantom lines near the lower end of the primary combustion chamber. Burner 16 shown in schematic in FIG. 1 fires the charge with primary flame 29. Ashes fall through the grate 17 into the ash drawer 18.

In contrast to natural draft conditions, the supply of preheated air is distributed evenly by the fans and ducting to the charge so that insufficient burning which causes soot and tar build-up in the primary combustion chamber is prevented. Air, by-passing the charge to chill the afterburner, is also prevented by the even distribution. By control of distribution and amount of preheated air, the combustion can be regulated so that a flame runaway condition is prevented. In the upper part of chamber 13, natural oxidation, rather than visible flame combustion, may occur. All the combustion products are drawn past vertical grate 30 and below vertical baflle 31 into the afterburner section or secondary combustion chamber 14, the lower portion of which is a settling chamber portion 32 where ash settles through the rear portion of grate 17 into ash drawer 18. The afterburner chamber 14 is under a slightly negative or reduced pressure relative to the primary chamber to insure primary combustion products are drawn into the afterburner chamber.

Any incompletely combusted or oxidized gases, odors, and fumes are completely oxidized to odorless and harmless CO and H 0 in the secondary flame 33 of the afterburner 34, which, for example, may be of the type that impinges on a solid metal target 35 to provide good distribution of the flame in the secondary chamber. The characteristics in the secondary combustion zone 14 that are typical of good practice are a holding time of .03 second at a temperature of 1400 F. and provision of good flame contact.

The then completely oxidized incineration products pass upwardly in zone 14a as shown by solid arrows in FIG. 1, where an asbestos type Wheel as above described is used, it is preferred to use a fixed dilution air damper 36. The preferred embodiment for a domestic incinerator using an asbestos-type wheel employs a fixed opening of predetermined size for room air dilution. As seen in FIG. 1, the damper 36 communicates with the upper portion of zone 14a to admit controlled quantities of ambient air to provide an initial cooling and dilution of the hot, completely oxidized incineration products. Alternatively, a portion of the cooled exhaust gases can be recirculated from duct 11 to damper 36 (not shown), or outside air may be ducted to the damper (not shown) and to the incinerator inlet duct 15, where the room air is contaminated, e.g. as in industrial uses where volatiles.

may contaminate the air. Where a Cercor or other high temperature wheel or checker-box is used, no air damper may be necessary.

The flue gases then pass through the fly ash collector 19, as above described, and thence through the flue box portion of the wheel 4 and exhaust out the flue duct 11. The baffle 31 extends up to the fly ash collector 19 so as to prevent short circuiting of hot flue gases with preheated air. Any blow-back that does occur is relatively harmless since the ash would again collect on the lower face of the right half of the collector screen 19. It should be appreciated that there is a section of bafile 31 provided in the space between the wiper 10 and the upper side of the collector screen 19 to prevent short circuiting of the input air across the wheel face and out the flue box side of the wheel, or vice-versa. Alternatively, the screen or perforated metal plate acting as the fly ash collector may be placed close to or be integral with the wheel face, with appropriate change of wiper design. Also, the collector may be omitted entirely where desired, or a non-rotating collector may be placed in the flue gas stream, e.g. above the dilution air damper 36 of FIG. 1, and adapted for removal and replacement, or for cleaning.

Conventional atmospheric and power burners ranging from non-aerated through totally aerated may be used, in conjunction with suitable ducting, in the primary combustion chamber. In one embodiment, a non-aerated burner arrangement is used in which the preheated air exits directly from the wheel, or is directed, by bafiles, as secondary air to the burner. There is no primary air supply, and thus the flame is of the diffusion type.

In a second embodiment, a partially aerated burner such as a conventional drilled-port burner 16 may be used and is shown in FIG. 1. Optionally, a target-type single port burner, or multi-port burners, may be used. The input fan 7 blows ambient air through the duct 15 and then through the preheat side of the regenerator wheel 4, to be dumped as preheated air, via suitable ducting, to the rear of the drilled-port burner. The air is delivered as both primary and secondary air. Fuel gas is directed via the usual fuel feed tube 16a, to issue into the burner throat through the feed tube orifice. Both primary and secondary flame cones are propagated in this embodiment with gas inspirating the preheated air.

In a third embodiment, a totally aerated burner is employed in the primary combustion chamber. F an 7 blows air through the preheat side of regencrator wheel 4, with all of the preheated air passing via suitable ducting to the burner. The gas inlet tube may have an orifice, and the air is so ducted to the burner as to be all primary.

Power burners have been shown to increase incineration rate due to the higher rate of heat transfer to the charge as compared to inspirating burners. The higher rate of heat transfer is in turn partly due to the higher velocity flame obtained by the increased air-gas mixture pressure. The incineration time and total gas consumption are both reduced. The power burners may use 100% primary air or less, with the higher percentage-s being preferred. The conventional power burner consists of a mechanical air-gas mixer or blower, a pipe or pipes depending on whether it is of the single or multiple tube type, and a flame retention nozzle.

-In the burner embodiments where at least a portion of the air is ducted to the burner as primary air, the rotating type of fly ash collector may be modified so that the blow-back fly ash does not pass into the burner with the primary air, else clogging of the burner ports occurs. A simple form of modification consists of a horizontal, semi--circular baffle 83 extending from the upper end of baflle 31 adjacent screen 19 to shield a portion (40 in FIG. 2) of the screen from the ash. The outer remaining annulus area of the collector screen 19 is not shielded and functions in the usual fashion. Upon rotation of the screen to the preheat side, the air blows back the fly ash only from the outer annulus area into the primary combust-ion chamber. A sidewall duct similar to duct 25 is provided with anextension having an opening 179 opposite the clean central portion 40 of the collector screen 19. The lower terminus of the duct connects directly to the primary air opening of the burner, in the case where all primary air is used, or terminates short of the burner to dump preheated air at 181 at the rear of the burner, in the case where gas inspires the preheated air. Alternatively, the side-wall duct may be re-.

placed by a dip tube 180 placed, for example, between the vertical grate 30 and the vertical bafile 31 with upper and lower terminus openings as above described to direct fiy-ash-free preheated air to or adjacent the burner.

Part of the incoming air, preheated as it passes through the wheel, is directed to the charge via the ducting above described, and the remainder is directed to the burner. The burner may be considered as two sect-ions, primary and afterburner, or as two burners. Air may be directed to each section, or burner, or only to the primary burner in the primary combustion chamber. In the latter case whatever air is not used in the primary chamber will be used to furnish combustion air in the afterburner. By regulation of the air amounts and splitting the air flow, so that controlled amount airis provided to the charge, a run-away condition is prevented. There is also no dependence on a proper chimney draft, controlled, for example, by a barometric damper.

-In the natural combustion of a charge, a spiral runaway may occur. The hot burning gases may provide a vertical air pattern and an increasing amount of air is drawn in at the bottom. The increased air (O supply in turn promotes a faster burning rate and an increase in the vertical air pattern. Each phase promotes the other in the classic spiral run-away pattern. But in the present invention, by the use of a fan or fans to create a preset forced draft, the volume and circulation is controlled so that no spiral run-away can occur.

FIG. 4 shows still another embodiment of the incinerator incorporating a checker-box type of regenerator, the parts numbering corresponding to similar parts in FIG. 1. Ambient room air, drawn by fan 7 enters through ducting 15. The lines A, A and B, B represent vanes, dampers, rotating wheels or other suitable means of closing the ducts to prevent flow in the section of ducting wherein the dampers are located. A preferred type of closure is a rotating wheel or solenoid valve 43. The valves labeled A, A operate in unison as do valves B, B; when valves A, A are open, then both valves B, B are closed and vice-versa. Valves A, A and B, B alternate in opened and closed position at a sufliciently rapid rate to produce a substantially constant exhaust temperature. The opening-closing cycle of the set of valves is preferably set at about 6 seconds for a 1.5 bushel incinerator of about 30,000 B.t.u./hr. input.

In operation, as air passes into duct 15, valve B will be momentarily opened and will pass through the checkerbox C into the incinerator cavity. Since the lower valve A and upper valve A are both closed, there is but one path for the air to flow into the incinerator as shown by solid air flow lines. The heated gases in the incinerator cavity are then drawn out of the cavity by fan 12 placed in the exhaust ducting 11. The flue gases must pass through the second checker-box C and through open valve *B. By the flow pattern, the originally cool second checker-box C is heated and the previously heated first checker-box C is cooled. The heating of the second checker-box C cools the incinerator gases so that they may be passed outwardly as cool exhaust gases. Then the valving switches in unison so that valves A and A are open and valves B and B are closed. The intake fan 7 forces air through the ducting 15 by valve A through the second checker-box C which is the hot checker-box. The exhaust fan continues to operate by drawing air through the ducting 11 after passing through the cool checker-box C past valve A. It will be appreciated that the valve-s A and B may be linked to a thermocouple 37 placed in the exhaust ducting so that when the temperature rises above a predetermined maximum, the valving is tripped in unison to reverse the flow of the gases and air through the checker boxes, and thus maintain a substantially constant maximum exhaust temperature. Stationary fiy-ash collectors are provided that are self-cleaned at each reversal of gases flow. The remaining details of the incinerator are not shown, being similar to that of FIG. 1.

Each checker-box is a heat exchanger of the regenerative type containing staggered rows of fire brick. Gases flow through the openings formed in successive rows of fire brick in intimate contact with the bricks. Hot gases from the afterburner heat the bricks and the gases are in turn cooled until the valving switches for the second half of the cycle. Then cool ambient air passes over the hot bricks and is thereby preheated while the bricks are cooled. The bricks may be arranged in any geometric form and enclosed in the corresponding housing, e.g. cylindrical or cubic.

By way of example and not by way of limitation, the following are presently preferred air and gas input rates, preheat, cavity and exhaust flue temperatures, and B.t.u. outputs, for the regenerative type incinerator.

Preheated air=780 F. (at 750 c.f.h. inlet air rate) Secondary chamber=1400 F.

Flue gases on inlet (lower side) of regenerator=l000 F. (max) Exhaust gases on outlet side of regenerator=200 F.

Based on a refuse consumption of 3 lb. per hour, the rated gas input is at least 19,000 B.t.u./hr., the total air input range is 750 0 c.f.h., and the dilution air rate is at least 350 c.f.h. of the total. Depending on the type of wheel used, the dilution air may not be needed. The gas input depends on the incineration rate desired, and 30,000 B.t.u./hr. gas input is conventional for a domestic incinerator. For the regenerative incinerator of this invention, the preheated air supplies 11,400 B.t.u./hr at 1350 c.f.h. (preheat air temperature of 520 F.), and 10,300 B.t.u./hr. at 750 c.f.h. (percent air temperature of 800 F.). Thus the above presently preferred air input values of our invention permit a reduction of gas input by about 11,000 B.t.u./hr. to 19,000 B.t.u./hr. for a gas 9 saving of about 37%. Since the total B.t.u./hr. input is equivalent, no more than conventional insulation is necessary.

Where an exterior exhaust vent is employed, the amount of insulation needed is negligible since the exhaust gases are relatively very cool, on the order of 250 F., or lower. This low exhaust gases temperature permits a significant reduction in the clearance presently required between flue ducting and combustibles, thus permitting installation of an incinerator of our invention in places where conventional incinerators would not fit. The insulation may be an air gap, and a preferred type employs a concentric pair of ducts one being placed interiorly of the other. The central duct serves as the exhaust duct while the annular space between the inner and outer ducts serves as the incoming air duct. Some small additional degree of preheating incoming air while further cooling exhaust gases is obtained by this construction.

It should be appreciated that for the domestic incinerator all air flow rates are preset, and the gas and air flow rates are constant during the incineration period. Only where an asbestos-type wheel is used is the fixed dilution air opening provided. The flue temperature is kept below a predetermined maximum by the air and gas input rates and the capacity of the regenerator which can be varied by size, as above described. However, for certain applications, where sensing-type controls are required, additional controls may be provided as disclosed in the following alternative embodiments.

Where the flue temperture exceeds the preset maximum, the volume and air flow is cut down to slow the burning. In fact, this inverse control can stop combustion entirely by shutting off the air and gas entirely. Conversely, where the charge is wet, the amount of air and gas will automatically be increased responsive to a preset minimum thermocouple temperature.

Referring to FIGS. 1 and 4, the exhaust flue temperature can be controlled by means of thermocouple 37 which may be linked to the burner, to adjust the rate of incineration in the chamber by controlling gas input. The thermocouple also may be linked to the fans, wheel and dilution air damper to control the rate of air circulation. Thus, a maximum preset exhaust gases temperature may be maintained. Such linkages with the thermocouple provide means of variable control of the volume and circulation of air through the incinerator.

Alternatively, a thermocouple 38 placed just below the collector 19 in the upper portion of chamber 14a can be preset to activate at a maximum temperature of about 1000 F. through a suitable linkage (e.g., a solenoid) the opening of dilution air damper 36. Thus, the maximum temperature of the flue gases, impinging on the inlet (lower) face of the flue box side of the wheel is controlled. This linkage may be independent of that coupling the fans with thermocouple 37.

In a preferred embodiment, when the thermocouple 37 senses that the exhaust gases exceed the preset maximum temperature, say 200 F., louvers located within ducting 23, directing air to the primary combustion chamber, are actuated to close. Air from intake fan 7 continues to be directed to the afterburner chamber via separate ducting. Also, the primary combustion chamber burner is cut back to a pilot condition by its solenoid-type valve linked to the thermocouple through suitable circuitry. This cut-01f of air and gas will starve the flame in the primary combustion chamber, and combustion of the charge ceases. The slowing and starving of combustion produces relatively more smoke, fumes, and odors but these are adequately consumed in the afterburner which remains on.

A simple type of control for the damper 36 employs a bimetallic coil attached to the pivot rod of the damper, which is spring biased. The bimetallic coil extends into the hot flue gas stream in the upper portion of chamber :14a and opens the damper, against the spring force, in proportion to the temperature. The bimetal is selected to fully open at or above a predetermined temperature, and thermocouple 38 may be omitted. Alternatively, the single thermocouple 37 can be linked to close a louver 41 in intake duct 42 while opening the damper 36.

FIG. 5 shows in schematic form one circuit that may be employed to effect control of the incinerator as above described. The output of thermocouple 37 is amplified by amplifier 50, the output of which drives motor speed control circuit 51, which may include, for example, a solid state controlled rectifier for control of the speed of input fan 7. The amplifier output is also directed through threshold switch 52 which in turn activates solenoid 53 to close the louvers 41 in input duct 42 when the temperature of the exhaust gases in duct 11 exceed a preset maximum or detect a runaway condition. The threshold switch 52 may optionally activate, via lead 54 (shown in dashed line), a solenoid controlled valve 55 to turn off burner 16. Control of the dilution air damper 36 is eflected through error amplifier 56 controlling motor 57 in response to the output of thermocouple 38 as compared to driving potential 58. Depending on the sign of the output from error amplifier 56 the motor will open or close damper 36 in proportion to the magnitude of the output. The output of error amplifier 56 is also connected to threshold switch 60' through a diode or equivalent output sign selecting gate 59. The switch 60 activates solenoid valve 55 to turn off burner 16 when temperature in excess of the preset maximum, e.g. 1050 F., or a runaway condition is detected. In place of a thermocouple 38, an error amplifier 56, and a motor 57 being employed to control damper 36, a bimetallic element may be used as above described. In that embodiment, threshold switch 52 may be used to activate solenoid 55 for burner shutofl control.

Those skilled in the art will recognize that the only limitation to the particular heat exchanger used is that the size must be proper to effect the desired cooling function and still be practical for incorporation within the incinerator unit, whether used for domestic or commercial purposes. Having described our invention, those skilled in the art will recognize that various modifications can be made thereto within the spirit of the invention.

What is claimed is:

1. A domestic incinerator comprising in unitary combination:

(a) means defining an incineration chamber for receiving a charge of material to be incinerated,

(b) a first fluid fuel burner disposed withinsaid incineration chamber means and including means for supplying fluid fuel to said first burner,

(0) means defining an afterburner chamber for conbusting flue gases issuing from said incineration chamber means,

(d) means defining a first duct connected to said incineration chamber means,

(e) means defining a second duct connected to said afterburner chamber means,

(f) means for circulating gases through said incineration and afterburner chamber means via said first and second duct means, said circulating means being disposed in communication with one of said duct means,

(g) means for regenerative heat exchange composed of heat-resistant material selected from asbestos, asbestos impregnated with sodium silicate, ceramic material, or a refractory material, said material being of relatively high heat capacity and low thermal conductivity, said regenerative heat exchange means permitting gases passage therethrough and disposed in communication with said first and second duct means, thereby to preheat cool incoming air by heat exchange with hot flue gases produced by combustion of said fuel and said charge, and

(h) means for directing the flow of a portion of said preheated incoming air to said charge in said incineration chamber means,

whereby the burning characteristics of said charge is controlled and said hot flue gases are sufliciently cooled to permit release as exhaust gases into the space immediately adjacent said incinerator.

2. An incinerator of claim 1 wherein said heat sink means comprises a rotatable Wheel having axially disposed apertures therethrough.

3. An incinerator of claim 2 which includes:

(a) means for introducing gases selected from outside air, cooled flue gases and ambient air into said hot flue gases, connected downstream of said afterburner chamber means,

whereby said hot flue gases may be diluted with relatively cool gases prior to passage through said regenerative heat exchange means.

4. An incinerator of claim 3 which includes:

(a) means responsive to temperature of said flue gases disposed downstream of said afterburner chamber means adjacent said regenerative heat exchange means for control of said gases introducing means,

whereby the amount of diluent air may be varied to maintain said flue gases below a predetermined maximum.

5. An incinerator as in claim 2 which includes:

(a) a second fluid fuel burner disposed within said afterburner chamber means,

(b) means for supplying fluid fuel to said second burner,

(c) means disposed in said incineration chamber means for supplying a portion of said preheated incoming air to said first burner.

6. An incinerator as in claim 2 which includes means for retaining fly ash carried in said flue gases disposed adjacent that face of said wheel which communicates with said chamber means, said fly ash retainer means being adapted to be moved from within the path of said flue gases into the path of said preheated air, whereby said fly ash collected on said retainer is blown back into said chamber means.

7. An incinerator of claim 6 wherein said wheel is a cylindrical structure and said material comprises corrugated asbestos and sodium silicate impregnated asbestos, said corrugations providing said axially disposed apertures.

8. An incinerator as in claim 1 wherein:

(a) said regenerative heat exchange means includes a first and a second checker-box containing heat-resistant and substantially nonthermal-conductive materials, and which incinerator includes:

(b) means disposed in said first and said second duct means for (1) changing communication of said first duct means from said first checker-box to said second checker-box, and (2) changing communication of said second duct means from said second checker-box to said first checker-box,

whereby each of said duct means alternately serves as the corresponding duct for incoming air and exhaust gases. so that input air and flue gases pass alternately through said checker-boxes to maintain the exhaust gases temperature below a predetermined maximom.

9. An incinerator as in claim 8 wherein said communication changing means includes:

(a) means for activating said communication changing means in response to predetermined time intervals.

10. An incinerator as in claim 8 which includes:

(a) means responsive to temperature disposed in the path of said exhaust gases exiting from a checkerbox for control of said communication changing means,

whereby communication from said first and second ducts to said checker-boxes is synchronously and correspondingly switched upon said temperature responsive means reaching a predetermined maximum thereby to maintain the exhaust gases temperature below a predetermined maximum.

11. An incinerator as in claim 8 which includes:

(a) means for retaining fly ash carried in said flue gases disposed adjacent those faces of said checker-boxes which communicate with said chamber means,

whereby said fly ash collected on said retainer means is blown back into said chamber means.

12. An incinerator as in claim 8 which includes:

(a) means disposed in said chamber means defining an afterburner chamber,

(b) a second fluid fuel burner disposed within said afterburner chamber and including means for supplying fluid fuel to said burner, and

(0) means disposed in said chamber means for supplying a first portion of said preheated incoming air to said first burner and a second portion of said preheated incoming air to said charge.

13. An incineratorof claim 8 which includes:

(a) means for introducing gases selected from outside air, cooled flue gases, and ambient air into said hot flue gases, connected to said chamber means,

whereby said hot flue gases may be diluted with relatively cool gases prior to passage through said regenerative heat exchange means.

14. A method of incineration of a charge in a nonindustrial type incinerator combustion chamber having a main and an afterburner which comprises:

(a) introducing a stream of incoming air into said combustion chamber,

(b) directing a first part of said incoming air to said charge,

(c) directing a second part of said incoming air to said main burner,

(d) igniting said burners and charge,

(e) directing combustion products produced in said combustion chamber into intimate contact with flame from said afterburner whereby completely combusted flue products are produced,

(f) maintaining the pressure in said afterburner slightly negative relative to said combustion chamber, and

(g) passing said flue products into regenerative heat exchange relationship with said incoming air thereby to preheat said incoming air and produce cool exhaust gases,

whereby complete combustion conditions are maintained in said incinerator to produce odorless and smokeless exhaust gases and the temperature of said exhaust gases is maintained below a predetermined maximum of sufliciently low value that the gases may be safely exhausted into the area immediately adjacent the incinerator.

15. A method as in claim 14 wherein said incoming air is preset in amount and distribution into said first and said second streams thereby preventing a spiral run-away condition.

16. A method as in claim 14 which includes the added step of:

(a) directing a third part of said incoming air to said afterburner.

17. A method of incineration as in claim 14 which includes the added steps of:

(a) diluting said flue gases with ambient air before passing said flue gases in heat exchange relationship with said incoming air, and

(b) removing fly ash from said flue or exhaust gases.

18. An improved method of incineration as in claim 17 wherein said dilution step includes the step of:

(a) controlling the amount of ambient air used for dilution in response to the temperature of said flue gases,

whereby the temperature of said exhaust gases is maintained below a predetermined maximum.

19. An incinerator of claim 2 wherein said flow directing means is linked to means for regulating the flow of preheated air to said charge in response to the temperature in said second duct.

References Cited UNITED STATES PATENTS KENNETH W. SPRAGUE, Primary Examiner US. Cl. X.R.

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