EP0117765A2

EP0117765A2 - Incinerators, and gasifiers and burners forming part of same

Info

Publication number: EP0117765A2
Application number: EP84301358A
Authority: EP
Inventors: Malcolm D. Lefcort
Original assignee: HEURISTIC ENGINEERING Inc
Current assignee: HEURISTIC ENGINEERING Inc
Priority date: 1983-03-01
Filing date: 1984-03-01
Publication date: 1984-09-05
Also published as: ZA841506B; CA1226173A; EP0117765A3

Abstract

A gasifier for generating a producer gas output from a cellulosic waste material input has an axially aligned top fuel feed (20) down onto a conical grate (40) with provision for removing fuel pile ash from around the base perimeter (46) of the grate. A preferred embodiment includes means (20, 30, 32) for adjusting the fuel feed above the level of the grate and to control underfire admission air through plenums 50A to 50E from beneath the grate so as to control the fuel pile size. An annular top opening 16 is provided for guiding producer gas from the chamber. A producer gas burner 300 has a cyclonic combustion chamber 320 with an upper inlet 352 for spirally directing producer gas down into the chamber and secondary combustion air inlet means 342 at the lower end of the chamber for directing secondary air tangentially and upwardly into the chamber. An exhaust outlet 334 is disposed at the lower end of the chamber with an exhaust inlet 330 axially aligned with the chamber. In a preferred embodiment, the gasifier and burner are combined using a double scrolled duct 400 to transport producer gas from the gasifier to the burner, and the gasifier and burner share a common ash removal system 500.

Description

This invention relates to improvements in the design of gasifiers and producer gas burners, and to two-stage incinerators combining gasifiers and producer gas burners to produce useful exhaust heat from fuels such as cellulosic waste material.
There is a body of known technology relating to the design of incinerators, including the design of two-stage incinerators which are fuelled with cellulosic waste materials. Considerable effort has been directed to the development of incinerators which burn such fuels efficiently with minimal pollution. These efforts have often led to designs which are considered to be relatively complicated in their structure thereby attracting increased costs for construction and maintenance. In addition, it is considered that known designs do not address sufficient attention to the question of ash removal as part of the structural and operating arrangement of incinerators, or their gasifier or producer gas burner portions. Further, it is considered that known designs do not sufficiently take into account the impact on overall performance that may result from variations in the moisture content of the fuel.
One aspect of the present invention is particularly directed to improvements in the design of gasifiers so as to better accommodate cellulosic waste material fuel. Typical fuels include wood waste, peat, rice hulls, sewage sludge and the like, the gasification of which generates a producer gas that, in a two-stage incinerator, effectively serves as an intermediate fuel ultimately to be combusted in a producer gas burner.
According to the gasifier aspect of the present invention, there is provided a gasifier comprising a gasification chamber, a feed tube for feeding cellulosic waste material fuel to the chamber, a generally conical grate contained within the chamber for supporting a fuel pile on its upper side, underfire air admission means, and ash removal means for transporting fuel pile ash away from the gasifier.
The gasification chamber has an enclosing side wall which is cylindrical about a vertically extending axis of the chamber. The feed tube is axially aligned with this axis and extends downwardly from an inlet which receives the waste material fuel, through a top opening in the chamber, to a discharge outlet which is in communication with the chamber. The extension of the feed tube through the chamber's top opening forms an axially aligned upper outlet for guiding producer gas from the chamber.
The conical grate has a base perimeter which is spaced inwardly from and concentric with the side wall of the chamber to define an annular base region therebetween, and is aligned with the feed tube such that waste material entering the chamber tends to form a conical fuel pile on the grate. The lower side of the grate defines a generally conical envelope beneath the grate above the plane of its base perimeter, and it is from this envelope region that gasification air is directed through the grate and the fuel pile from the lower side of the grate. Fuel pile ash transported away from the gasifer is captured by the ash removal means from the annular base region between the base perimeter of the grate and the side wall of the chamber.
The foregoing gasifier configuration advantageously enables not only a continuous but also a balanced flow of non-gaseous material from the time raw fuel enters the feed tube to the time fuel pile ash is removed from the annular base region. The axially aligned top feed of fuel onto a conical grate together with ash removal from the annular base region between the grate and the gasification chamber wall tends to maintain a uniform spread of the fuel pile (including ash at the bottom) above the plane of the grate's base perimeter.
In addition, the foregoing gasifier configuration admits itself to the use of a relatively simple and effective ash removal system. Although various means may be devised for removing ash from the base annular region, the ash removal means preferably comprises a plurality of rabble arms and means for rotating the rabble arms to transport (by ploughing) ash inwardly to an ash collection hopper extending downwardly beneath the grate below the plane of the grate's base perimeter. Such an arrangement maintains the balance and continuity of flow and, as will become apparent, can be made compact relative to the overall radial dimensions of the gasifier.
Further, the foregoing gasifier configuration admits itself to the inclusion of particularly effective means for accomodating fuels ranging from the very dry to the very wet. Typical fuels such as those referred to above may have a moisture content ranging from zero to substantial amounts such as 60% or higher on a wet basis. Since the size of the fuel pile will be determined by the required pile residence time (the time required to evaporate all the moisture, pyrolyze all the volatiles and consume all the char), the drier the fuel the smaller the operating pile and vice-versa. In those applications where substantial variations in the moisture content of the fuel may be encountered, the gasifier preferably will include means for adjusting the vertical position of the feed tube relative to the grate - the closer the feed tube to the grate the smaller the pile (and this may include positions where the apex of the grate projects part way up the feed tube); the more distant the feed tube from the pile the deeper the pile. To work in cooperation with the adjustable feed tube feature, the gasifier includes (as part of the underfire air admission means) means for controllably restricting the flow of underfire air through at least a portion of the grate while concurrently permitting the free flow of such air through a remaining portion of the grate. For this purpose, the underfire air admission means preferably comprises a plurality of horizontally disposed plenums stacked vertically with respect to each other within the envelope beneath the conical grate. Each plenum has an associated means for controllably delivering gasification air to the plenum, and an outlet contiguous with an associated segment of the lower side of the grate for delivering gasification air from the plenum through the segment. This arrangement takes into account that a smaller fuel pile will have a smaller base diameter (at the upper level of the ash). Air flow to the plenums can be throttled back or closed off entirely, depending on pile size - any closed off section of the grate becoming an ash reservoir.
Preferably, a gasifier in accordance with the present invention also includes overfire air admission means which directs overfire air at high velocity downwardly and tangentially into the gasification chamber. The general purpose of such air is to burn some of the producer gas so as to raise its temperature to a level such that its ignition upon entry to a producer gas burner will be spontaneous. However, a further purpose of such overfire (or "preignition") air is to centrifugally separate particulate matter from the producer gas stream thereby minimizing the amount of particulate matter leaving the gasifier. This effect will be most pronounced on wetter fuels: more overfire or preignition air is required because there will be an increased cooling effect with greater percentages of water vapour.
A variety of producer gas burner designs may be utilized to combust the producer gas output of the gasifier described above. However, in accordance with another aspect of the present invention, there is provided a new and improved producer gas burner which comprises a cyclonic combustion chamber having an enclosing side wall cylindrical about a vertically extending axis of the combustion chamber, and producer gas inlet means disposed at the upper end of such chamber for spirally directing producer gas downwardly into the chamber. A primary combustion air inlet means is provided for directing primary combustion air into the chamber and for guiding such combustion air to mix with the producer gas as the latter spirally enters the chamber. A secondary combustion air inlet means is disposed at the lower end of the combustion chamber for directing secondary air at high velocity tangentially and upwardly into the chamber. In addition, an exhaust outlet means is provided for transporting products of combustion away from the chamber. Such products may be used for a variety of heating purposes. The exhaust outlet means includes an axially aligned exhaust inlet end disposed at the lower end of the combustion chamber, and extending downwardly therefrom; an exhaust outlet end; and an exhaust duct extending between the inlet and outlet ends. The exhaust inlet end is spaced radially inwardly in relation to an enclosing side wall of the cyclonic combustion chamber.
The foregoing design for the producer gas burner is considered to be advantageous because it introduces spiralling or swirling action from both the top and from the bottom of the combustion chamber thereby contributing to combustion efficiency and enhancing the centrifugal separation of particulate matter within the chamber. Further, the overall structure is considered to be relatively simple - and it may be noted that the use of tuyeres as is common with known cylconic chambers is not specified.
For the purpose of generating the spiralling action from the top of the combustion chamber, the producer gas inlet means preferably comprises a cylindrical plug extending downwardly through an axially aligned upper opening of the chamber. The opening has an inwardly facing perimeter surface, and the plug has a vertically extending outer surface spaced inwardly away from the perimeter surface to define an annular region between the surfaces. At least one spiral vane leads downwardly through the annular region for spirally directing producer gas downwardly into the combustion chamber. The vane preferably forms part of the plug and extends outwardly from the outer surface of the plug.
Advantageously, the primary combustion air inlet means may be incorporated with the plug itself. An inlet chamber or plenum is provided within the plug for receiving primary combustion air. A plurality of openings spaced circumferentially around a lower periphery of the plug, each extending between the inlet chamber and the combustion chamber, direct primary combustion air into the chamber and guide the air to mix with producer gas which is spirally entering the chamber.
The secondary combustion air inlet means preferably comprises a plurality of nozzles spaced circumferentially around the exhaust inlet end disposed at the lower end of the combustion chamber - and each such nozzle is oriented to direct combustion air tangentially and upwardly into the chamber. Advantageously, the secondary combustion air which is being directed to the nozzles is directed by means of a duct or plenum through which the exhaust outlet means extends for the purpose of heating the secondary combustion air.
Generally, it is contemplated that the exhaust inlet means of the producer gas burner will have its outlet end displaced below and laterally away from the combustion chamber. Thus, the exhaust duct will have an elbow section to redirect air products of combustion received downwardly at the exhaust inlet end outwardly towards the exhaust outlet end. The lateral disposition of the outlet end is to facilitate coupling to some device (for example, a rotary dryer) which utilizes the hot air exhaust.
The configuration of the producer gas burner advantageously enables the inclusion as part of its structure of an ash-collecting hopper which extends downwardly from the lower end of the combustion chamber, and which is axially aligned with the combustion chamber. To better enable centrifugally separated particulate matter to be directed past the exhaust inlet end of the exhaust outlet means, the side wall of the combustion chamber expands radially outwardly around the exhaust inlet end.
The gasifier and the producer gas burner which have been described may be advantageously combined to form an efficient and structurally compatible two-stage incinerator. Producer gas generated by the gasifier is transported to the burner by an elongated duct extending from the upper outlet of the gasification chamber to the producer gas inlet means of the burner. Preferably, the elongated duct has a scrolled inlet leading from the outlet of the gasification chamber, and a scrolled outlet leading into the producer gas inlet means (viz. a "double-scroll"). The scrolled inlet is for recovering static pressure from producer gas tangential velocity as producer gas leaves the gasification chamber. Also, it straightens the producer gas flow before the gas travels down the elongated duct, thereby minimizing static pressure loss in the duct. The scrolled outlet is for converting the static pressure of the producer gas at the outlet to producer gas tangential velocity. By this arrangement and with the provision for spirally directing producer gas downwardly into the combustion chamber, the upwardly swirling action of producer gas in the gasification chamber is efficiently converted into downwardly swirling action in the cyclonic combustion chamber.
The fact that the gasifier and the producer gas burner are separated better enables the optimization of each stage. The first stage of gasification tends to be optimized by:

(a) maintaining low gasification air velocities: this minimizes off-the-pile particle elutriation and hence maximizes first-stage ash retention;
(b) maintaining low first-stage temperatures: this minimizes slag formation and hence facilitates ash removal.

The second stage of combustion in the producer gas burner tends to be optimized by:

(a) maintaining vigorous mixing of gas and air;
(b) maintaining low percentages of excess combustion air to maximize combustion temperatures.

Advantageously, a common ash removal means may be used for transporting ash produced by the gasifier and the burner away from the incinerator. For this purpose, there may be provided first, second and common conveyor means. The first conveyor means extends upwardly and outwardly from a lower extension of the gasifier ash collecting hopper to the common conveyor means. The second conveyor means extends upwardly and outwardly from a lower extension of the burner ash collecting hopper to the common conveyor means.
The foregoing and other features of the present invention will now be described in more detail with reference to the drawings.

FIGURE 1 is a front elevation view partially in section of an incinerator, including a gasifier and a producer gas burner, in accordance with the present invention. Some elements have been rotated into view for purposes of illustration.
FIGURE 2 is a section-top view of the incinerator shown in Figure 1.
FIGURE 3 is a top and side elevation view showing in more detail the rabble arm assembly forming part of the gasifer portion of Figure 1.
FIGURE 4 is a functional drawing of the incinerator of Figure 1, showing means for supplying fuel and showing an associated control system diagram.

The incinerator shown in the Figures includes a gasifier generally designated 1 and a producer gas burner generally designated 300, both of which are supported on a common skid 200. As is described in more detail hereinafter, a double-scrolled duct structure designated 400 is provided to transport producer gas from the gasifier to the burner. Further, as part of an overall ash removal system, there is provided a common ash removal conveyor 500.
Figure 1 includes the depiction of a rotary dryer generally designated 900. However this dryer is not part of the incinerator and is shown merely to illustrate an example of an apparatus which may utilize the exhaust output of the incinerator from producer gas burner 300.
Figure 4 includes the depiction of a means for supplying waster material fuel to the gasifier. Such means includes metering bin 600, and associated screw conveyers 610, 620 and 630. As well, Figure 4 illustrates in block diagram an associated control system for the incinerator.

Gasifier

Gasifier 1 has a generally cylindrical configuration around axis 2. For purposes of assembly and disassembly, the structure is sectionalized into three major sections 3, 4 and 5 which are coupled together and collectively suspended from upright supporting beams 205 which extend upright from skid 200. The lower section, section 3, essentially carries the bottom and interior portion of the gasifier. By means of flanged brace structure 110, section 3 is coupled by suitable means such as bolts (not shown) to mating flange 120 around the outer lower periphery of central section 4. Similarly, by means of flange 130 around the outer upper periphery of section 4 and mating flange 140 around the outer lower periphery of upper section 5, section 4 is coupled to section 5. Upper section 5 also includes a flange 150 around its outer upper periphery which is designed for coupling with lower flange 490, the latter of which forms part of the duct structure 400.
Gasifier 1 comprises a gasification chamber 10 having an enclosing side wall 12 formed from refractory and an outer metal shell. A vertically disposed fuel feed tube 20, surrounded by refractory 22 extends downwardly through an upper opening of the chamber to form an annular upper outlet 16 in the region between the tube and wall 18.
As can be seen in Figure 1, tube 20 has a slight outward expansion from its top inlet at 24 to its lower outlet at 26. While not essential, this outward expansion is considered desirable in order to reduce the possibility that the fuel feed may jam in the tube.
Fuel, in the form of cellulosic waste material, is fed into the tube 20 through rotary air lock 28 and falls through the tube "dutch-oven" like onto the upper side 42 of conical grate 40 contained within chamber 10. Conical grate 40 is in axial alignment with tube 20, hence a conical fuel/ash pile P tends to form on the grate upwardly from the grate's lower base perimeter 46. (There will be a fuel pile on top of ash, and the size of the ash reservoir and hence the size of the active fuel pile will depend on how the supply of underfire admission air is controlled - as described hereinafter.)
The lower side 44 of grate 40 defines a generally conical envelope within which is contained a plurality of horizontally disposed plenums 50A - 50E which are stacked vertically with respect to each other. As can be seen in Figure 1, each plenum has a truncated conical configuration, and is associated with a corresponding truncated conical segment of the lower side 44 of grate 40. The plenums are defined by horizontally disposed circular divider plates 52A - 52E, each of which is supported at its outer perimeter by flanges 72 on a bracing structure 70 and at its inner perimeter by the upper flanged end of an associated one of the cylindrical concentrically arranged conduits 54A - 54E. The uppermost plenum is capped at its top by circular plate 52F.
Bracing structure 70 also provides support for grate 40, and is an open structure so as not to interfere with the flow of air from plenums 50A - 50E up through the grate and fuel pile P.
Plenums 50A - 50E and their associated vertical conduits 54A - 54E are all part of an underfire air admission means for the gasifier. Such means also includes horizontal cylindrical conduits 56A - 56E, each of which leads from a common input plenum 60 to one of vertical conduits 54A - 54E. Each horizontal conduit includes a throttle valve 58 by means of which underfire air flow from input plenum 60 (driven by blower 62) may be controlled. Throttle valves 58 may be independently adjusted from fully open positions to completely closed positions. Thus, the flow of underfire air to any desired ones of plenums 50A - 50E may be fully or partially restricted, or not restricted at all. As is described in more detail hereinafter, such means for controlling underfire air admission facilitates the ability of gasifier 1 to accommodate fuels having a range of moisture contents.
The ability of gasifier 1 to accommodate fuels having a range of moisture contents is further facilitated by means for adjusting the vertical position of feed tube 20 relative to upper side 42 of grate 40. Feed tube 20, with the surrounding refractory 22, may be raised or lowered from the position shown in Figure 1, and it may be lowered to a point where the apex of grate 40 actually projects part way into the lower end of the tube. As will readily be appreciated from viewing Figure 1, the raising or lowering of feed tube 20 will effectively control the size of fuel pile P on grate 40.
To enable tube 20 to be raised and lowered, top plate 21 of the tube is threadably engaged with three shafts 30 rotably mounted with suitable bearings at 120° intervals into the top of duct structure 400. Each shaft 30 has at its top a chain gear 32 which is engaged by a chain 34. In order to raise or lower tube 20 chain 34 is driven clockwise or anticlockwise, as the case requires, by motor 36 and chain drive gear 38 mounted to the output shaft of the motor. The motor assembly itself is mounted by suitable means to duct structure 400. A packing gland seal 33 between tube 20 and duct structure 400 prevents pressure loss from the duct.
Thermocouples, positioned above the lower regions of grate 40, can be used to monitor the demarcation line between ash and fuel in ash/fuel pile P. In Figure 1, only one of such thermocouples (thermocouple 41) is shown. Air admitted to an ash zone will not cause a rise in temperature. However, air admitted to a fuel zone will result in an increase in fuel bed temperature.
Gasifier 1 includes means for directing overfire or preignition air downwardly and tangentially into chamber 10. Such means includes a plurality of tuyeres or nozzles 74, each serviced by and leading into chamber 10 from annular plenum 75 carried by upper section 5 of the gasifier. The overfire air is driven at high velocity by blower 77. As will be appreciated, the position of plenum 75 enables the preheating of air passing through the plenum.
Gasifier 1 also includes an ash removal system which includes four rotable rabble arms 180 (only two of which are shown in Figure 1). Each rabble arm includes a number of blades 182 which are angled to progressively work fuel pile ash across gasifier floor 13 from the annular region between base perimeter 46 of grate 40 and side wall 12 to ash collecting hopper 195. Ash is pushed onto floor 13 from the action of fresh fuel falling down onto grate 40 from feed tube 20.
As best seen in Figure 3, each rabble arm 180 extends inwardly from a cylindrical drum support 184 to a common supporting ring 185. (Ring 185 enables passage of conduits 54A - 54E). A shoulder 183 is provided towards the bottom of the drum to be carried on wheels 186 which are rotatably mounted at spaced intervals to floor support structure 112 (see Figure 1). Thus, drum 184 may be rotated thereby rotating the rabble arms to plough ash towards hopper 195. To enable rotation of drum 184, the drum includes a chain rack 187 which extends around its outer perimeter and which, as shown in Figure 1, is engaged by drive train 188 from rabble arm drive motor 189.
Ash falling into hopper 195 is removed from a lower extension 196 of the hopper by water sealed screw conveyor 197 which elevates the ash above the water seal to common ash removal conveyor 500. Ash removal conveyor 500 is also a screw conveyor.
Gasifier 1 further includes a gas burner 88 which is used to light the fuel pile at start-up in a conventional manner using propane, natural gas or other fuel to generate a suitable flame. Air supply to burner 88 is provided by valve controlled supply line 89 branching from the output of blower 77.
In the operation of gasifier 1, fuel is supplied from metering bin 600 (where the fuel has previously been dumped) to feed tube 20 via screw conveyors 610, 620, 630 and rotary air lock 28, the latter of which provides pressure isolation. Metering bin 600 includes variable stroke hydraulically driven blade pushers 601 which are connected to hydraulic reservoir 602 via variable volume hydraulic pump 603. Flowmeter 604 monitors the volume of flow. Pushers 601 push fuel from the bin into the track of screw conveyor 610 depending upon demand from BTU Demand Controller 700 the output of which on line 701 is a signal representative of desired BTU output.
The signal to Controller 700 can be a manifold pressure (steam, hot gas), a temperature, an rpm or any other signal that is representative of the BTU's/hour that the incinerator is expected to supply. For both gasifier 1 and producer gas burner 300, demand establishes the fuel feed and gasification air flows directly. Overfire or preignition air flow and combustion (primary and secondary) air flows are also controlled by demand, with a strong trim by the exit temperatures of the gasifier and the combustion chambers, respectively.
In relation to gasifier 1, the output on line 701 serves as an input to Fuel Feed Controller 705 which in turn controls the volume output of pump 603 via actuator 706 in a conventional manner. Feedback from Flowmeter 604 to Fuel Feed Controller 700 is used to measure when the actual volume output of pump 603 is what it should be as a function of the demand.
The demand signal on line 701 to Fuel Feed Controller 700 may be overridden by Fuel Pile Control 710. If fuel backs up in feed tube 20 or in the conduit between air lock 28 and screw conveyor 630, the event will be sensed by level sensors 711 or 712, as the case may be, and an override signal is directed to Fuel Pile Control 710.
The demand signal on line 701 also serves as an input to Drive Circuit 715 to power rabble arm drive motor 189 in a conventional manner. Ordinarily this circuit will be held off until ash has accumulated - and, as described above, the accumulation of ash can be sensed by thermocouples such as thermocouple 41.
The supply of underfire air is conventionally controlled by the positioning of damper 720 (at the output of blower 62) depending on the output of Gasification Air Flow Controller 725 through damper actuator 721. Feedback representative of the actual air flow as measured at the input of blower 62 is balanced against the demand derived from line 701 to determine the control signal output from Controller 725 to actuator 721.
The supply of overfire or preignition air is controlled by the positioning of damper 740 (at the output of blower 77) depending on the output of Preignition Air Flow Controller 750 through damper actuator 741. This output is determined in a conventional manner from the temperature trimmed demand signal on line 702 combined with feedback representative of the actual flow as measured at the input of blower 77. The demand signal is trimmed by the output from Preignition Temperature controller 755. This output is determined by the difference between a set point temperature and the temperature at the outlet of gasifier 1 as measured by thermcouple 756. The set point temperature is selected to give stable ignition in producer gas burner 300. The gasifier is operated sub-stoichiometrically, hence in order to raise the temperature in the gasifier the control must operate to add more preignition air -- and vice-versa.
In the operation of gasifier 1, gasification air reacts with fixed carbon in the fuel and generates heat for the pyrolizing of volatile matter in the fuel. The producer gas liberated percolates up through the fuel pile, drying the downward flowing fuel in its upward passage. At the surface of the pile, the producer gas is exposed to the tangentially and downwardly admitted overfire or preignition air.
The purpose of the preignition air is to burn some of the producer gas and raise its temperature to a level such that ignition occurs spontaneously in producer gas burner 300. As noted in the introductory portion of the application a further purpose is to centrifugally separate particulate matter from the producer gas stream thereby minimizing the amount of particulate matter which leaves the gasifier through outlet 16.
At the fuel pile, when the downward flowing fuel reaches the grate, its moisture evaporated and its volatile matter pyrolized, it does so as char - the fixed carbon residue. Mixed with the char is the mineral matter - the ash. The char is consumed by the gasification air and the ash is left to collect on the grate from where it is removed in the manner described above.

Producer Gas Burner

Producer gas burner 300 has a generally cylindrical configuration around vertical axis 301. For the purpose of assembly and disassembly, its structure is sectionalized into two major sections 303 and 304 which are coupled together and supported by upright supporting beams 208 which extend upright from skid 200. Each beam 208 has an upper flange 209 to which are coupled flanged footings 307 forming part of lower section 303 of the burner. Upper section 304 is coupled with lower section 303 by means of flange 310 around the lower periphery of the upper section and flange 308 arond the upper periphery of the lower section. Upper section 304 also includes a flange 312 around its upper periphery which is designed for coupling with lower flange 495 forming part of duct structure 400.
Burner 300 comprises a cyclonic combustion chamber 320 having an enclosing side wall 327 formed from refractory and an outer metal shell. At its upper end, burner 300 includes a spiral vaned plug 350 which is sealed into the upper portion of duct structure 400 and which extends downwardly through an upper opening into chamber 320. Spiral vanes 352 on plug 350 provide a means for spirally directing producer gas into chamber 320 through the annular region 322 between the plug and the opposed refractory wall 324 of the upper opening.
Plug 350 includes a sight glass 351 extending downwardly along axis 301 and through which one may view the combustion process within the. Otherwise, however, the interior of the plug is essentially a hollow chamber which serves as an inlet chamber or plenum for receiving primary combustion air via conduit 353 from plenum 340, the latter of which serves as a source of both primary and secondary combustion air. A plurality of openings 354 are spaced circumferentially around the lower periphery of plug 350 and extend from the plug's inlet chamber to combustion chamber 320 substantially at the level where producer gas spirally enters chamber 320.
Burner 300 also includes an exhaust outlet means comprising exhaust inlet end 330, exhaust outlet end 332, and elbow-shaped exhaust duct 334 extending therebetween. As can be seen in Figure 1, the inlet end 330 is axially aligned with axis 301 of the chamber and is spaced radially inwardly from wall 327. In fact, the chamber wall steps radially outwardly at shoulder 328 to provide increased space around inlet end 330. Shoulder 328 is conveniently at the division between lower section 303 and upper section 304 of the burner. Its purpose, as will become more evident hereinafter, is to better enable centrifugally separated particulate matter in chamber 320 to be directed past inlet 330 and into ash collecting hopper 380.
Secondary combustion air is provided to chamber 320 at its lower end by means of a conduit 341 which extends from plenum 340 to a plurality of nozzles 342 spaced circumferentially around exhaust inlet end 330. Nozzles 342 are used to impart high velocity to the secondary combustion air, and they are oriented to direct the air tangentially and upwardly into the chamber, the purpose being to create a strong swirling action up the walls of chamber 320 and to aid the centrifugal separation of particulate matter within the chamber. It will be noted from Figure 1 that the exhaust outlet means passes along the length of conduit 341. This feature permits preheating of the secondary combustion air.
Plenum 340 is supplied by blower 345 and, as indicated above, acts as a common source for both primary and secondary combustion air. As well, plenum 340 serves as a source of air for start-up burner 348 along valve-controlled line 349.
Referring to Figure 4, the supply of primary and secondary combustion air is controlled by the positioning of damper 775 (at the output of blower 345) depending on the output of Combustion Air Flow Controller 780 through damper actuator 776. This output is determined in a conventional manner from the temperature trimmed demand signal on line 703 combined with feedback representative of the actual flow as measured at the input of blower 345. The demand signal is trimmed by the output from Combustion Temperature Controller 790. This output is determined by the difference between a set point temperature and the temperature at exhaust outlet end 332 as measured by thermocouple 791. The set point temperature will depend upon the requirements of the process using the exhaust. Burner 300 is operated above stoichiometric. Hence, in order to raise the temperature in chamber 320 (and the exhaust), the control operates to cut back on the supply of air -- and vice-versa.
In the operation of burner 300, producer gas enters combustion chamber 320 by spiralling down the vaned annular region 322 around plug 350. The producer gas, together with primary combustion air admitted to the combustion chamber in the manner previously described, mix and burning ensues. A core of high temperature, swirling, burning gas results. The core is centred on the bottom of plug 350 and extends along axis 301 down into combustion chamber 320.
Secondary combustion air spirals up wall 327 of chamber 320 to the region of the bottom of plug 350. As the air rises it convectively removes heat radiated to wall 327 by the burning gas core. In so doing, the wall is cooled and the air is preheated.
At plug 350, the secondary air reverses its upward axial component of direction and then corkscrews down around the core of the burning producer gas. The two streams mix, combustion is completed, and the resulting stream of low excess air products of combustion leaves chamber 320 through exhaust inlet 330.
The swirling and spiralling motion within chamber 320 creates a centrifugal action which will throw particulate matter which may have entered the chamber with the producer gas out to the chamber wall. As indicated above, such particulate will be directed down into hopper 380.
Hopper 380 is part of the ash removal means for burner 300. Particulate or ash falling into the hopper is removed from lower extension 381 of the hopper by water sealed screw conveyor 397 which operates in the same way as screw conveyor 197 to elevate ash above the water seal to common ash removal conveyor 500.

Double Scrolled Duct Structure

Duct structure 400 is provided to transport producer gas from upper outlet 16 of gasification chamber 10 to upper inlet 322 of combustion chamber 320. As previously described, it is also used to support some elements of the incinerator associated primarily with gasifier 1 (e.g. feed tube 20) and to support some elements of the incinerator primarily associated with burner 300 (e.g. plug 350).
Duct structure 400 breaks down into two major sections - a lower section 405 having flanges 490 and 495 which couple with gasifier 1 and burner 300 in the manner already described; and an upper section 410 having a lower flange 411 for coupling with upper flange 406 of lower section 405. When sections 405 and 410 are coupled a refractory-lined duct 450 is formed.
As can best be seen in Figure 2, duct 450 includes a scrolled inlet 445 leading from gasifier 1, and a scrolled outlet 455 leading into burner 300. The purpose of scrolled inlet 445 is to recover static pressure from producer gas tangential velocity as the gas leaves gasification chamber 10 through outlet 16. The purpose of scrolled outlet 455 is to convert producer gas static pressure in the duct at outlet 455 to producer gas tangential velocity as the gas enters combustion chamber 320 through upper inlet 322. There is thus an efficient conversion of producer gas tangential velocity in gasifier 1 to producer gas tangential velocity in burner 300; and the spiral vanes of plug 350 assist the effectiveness of the conversion.
The overall output of the incinerator is a stream of hot gas. The gas temperature and volume (viz. the weight flow) determine the BTUs / hr. that are released. The incinerator may be rated by assuming that an "ideal" process is available to use the output - one that will cool the products of combustion down to 77°F. All the water vapour is assumed to be in the vapour state. The difference between the actual discharge temperature and 77°F represents a "loss".
Since most processes do not cool the products of combustion to 77°F, it is important in practice to size the incinerator by taking into account the actual process discharge temperature. For example, an incinerator burning hog fuel, coupled to a process which takes in heat at 1900°F, and discharges at 350°F will need to burn approximately 23% more fuel than one coupled to an "ideal" process discharging at 77°F and supplying the same amount of heat. Similarly, one coupled to a process discharging at 700°F will need to burn approximately 46% more fuel. Stated another way, at 350°F the stack "loss" is typically 23% (for hog fuel and a 1900°F inlet temperature to the process) - while at 700°F the stack "loss" is 46%.
Various modifications to the particular structures which have been illustrated are possible without departing from the spirit and scope of the invention as expressed in the following claims.

Claims

1. A gasifier for generating a producer gas output from a cellulosic waste material input, said gasifier comprising:

(a) a gasification chamber having:

(i) an enclosing side wall cylindrical about a vertically extending axis of the chamber; and,

(ii) an axially aligned cylindrical top opening;

(b) a feed tube axially aligned with said axis, said feed tube extending downwardly:

(i) from an inlet for receiving said waste material,

(ii) through said top opening,

(iii) and to an outlet in communication with said chamber for discharging said waste material into said chamber,

the extension of said feed tube through said top opening forming an annular upper outlet aligned with said axis for guiding producer gas upwardly from said chamber;

(c) a generally conical grate contained within said chamber, said grate having:

(i) a base perimeter spaced inwardly from and concentric with said side wall to define an annular base region therebetween;

(ii) an upper side for supporting a fuel pile;

(iii) a lower side defining a generally conical envelope beneath said grate above the plane of said base perimeter,

said grate being aligned with said feed tube such that waste material entering said chamber from said tube tends to form a conical fuel pile on said upper side of said grate;

(d) underfire air admission means for directing gasification air through said grate and said fuel pile from said lower side of said grate; and,

(e) ash removal means for capturing fuel pile ash from said annular base region, and for transporting such ash away from said gasifier.

2. A gasifier as defined in Claim 1, wherein said ash removal means comprises a plurality of rabble arms and means for rotating said rabble arms to transport said ash inwardly to an ash collection hopper extending downwardly beneath said grate below the plane of said base perimeter.

3. A gasifier as defined in Claim 1, including overfire air admission means for directing overfire air at high velocity downwardly and tangentially into said chamber.

4. A gasifier as defined in Claim 1, 2 or 3, including:

means for adjusting the vertical position of said feed tube relative to said grate;

and wherein:

said underfire air admission means includes means for controllably restricting the flow of underfire air admission air through at least a portion of said grate while concurrently permitting the free flow of such air through a remaining portion of said grate.

5. A gasifier as defined in Claim 1, 2 or 3, including:

means for adjusting the vertical position of said feed tube relative to said grate,

and wherein:

said underfire air admission means comprises a plurality of horizontally disposed plenums stacked vertically with respect to each other within said envelope, each plenum having:

(i) an associated means for controllably delivering gasification air to the plenum; and,

(ii) an outlet contiguous with an associated segment of said lower side of said grate for delivering gasification air from the plenum through such segment.

6. A producer gas burner, comprising:

(a) a cyclonic combustion chamber having an upper end, a lower end, and an enclosing side wall cylindrical about a vertically extending axis of the chamber;

(b) producer gas inlet means disposed at said upper end for spirally directing producer gas downwardly into said chamber;

(c) primary combustion air inlet means for directing primary combustion air into said chamber and for guiding same to mix with said producer gas as it spirally enters said chamber;

(d) secondary combustion air inlet means disposed at said lower end for directing secondary combustion air at high velocity tangentially and upwardly into said chamber; and,

(e) exhaust outlet means for transporting products of combustion away from said chamber, said outlet means including:

(i) an axially aligned exhaust inlet end disposed at said lower end of said chamber, and extending downwardly therefrom;

(ii) an exhaust outlet end; and,

(iii) an exhaust duct extending between said inlet end and said outlet end,

said exhaust inlet end being spaced radially inwardly in relation to said side wall.

7. A producer gas burner as defined in Claim 6, wherein said exhaust outlet end is displaced below and laterally away from said combustion chamber, and wherein said exhaust duct includes an elbow section to redirect products of combustion received downwardly at said -exhaust inlet end outwardly towards said exhaust outlet end.

8. A producer gas burner as defined in Claim 6, wherein said producer gas inlet means comprises:

(a) a cylindrical plug extending downwardly through an axially aligned upper opening of said chamber, said opening having an inwardly facing perimeter surface, said plug having a vertically extending outer surface spaced inwardly away from said perimeter surface to define an annular region between said surfaces; and,

(b) at least one spiral vane leading downwardly through said annular region for spirally directing producer gas downwardly into said chamber.

9. A producer gas burner as defined in Claim 8 having a plurality of spiral vanes leading downwardly through said annular region for spirally directing producer gas downwardly into said chamber.

10. A producer gas burner as defined in Claim 9, wherein said spiral vanes form part of said plug and extend outwardly from said outer surface thereof.

11. A producer gas burner as defined in Claim 8, 9 or 10, wherein said primary combustion air inlet means comprises:

(a) an inlet chamber within said plug for receiving primary combustion air from a source thereof; and,

(b) a plurality of openings spaced circumferentially around a lower periphery of said plug, each extending between said inlet chamber and said combustion chamber for directing primary combustion air into said combustion chamber from said inlet chamber and for guiding same to mix with said producer gas as it spirally enters said combustion chamber.

12. A producer gas burner as defined in Claim 6, wherein said secondary combustion air inlet means comprises a plurality of nozzles spaced circumferentially around said exhaust inlet end at the lower end of said chamber, each such nozzle for directing secondary combustion air at high velocity tangentially and upwardly into said chamber.

13. A producer gas burner as defined in Claim 6, 7 or 8, wherein said secondary combustion air inlet means- comprises:

(a) A plurality of nozzles spaced circumferentially around said exhaust inlet end at the lower end of said chamber, each such nozzle for directing secondary combustion air at high velocity tangentially and upwardly into said chamber; and,

(b) a duct for receiving and transporting secondary combustion air from a source thereof to said nozzles,

at least a substantial portion of said exhaust outlet means extending within said duct for heating secondary combustion air being transported by said duct.

14. A producer gas burner as defined Claim 6, 7 or 12, including an ash-collecting hopper extending downwardly from said lower end of said combustion chamber and axially aligned with said combustion chamber, said side wall of said combustion chamber expanding radially outwardly around said exhaust inlet end for better enabling centrifugally separated particulate matter to be directed past said exhaust inlet end and into said hopper.

15. A two-stage incinerator, comprising:

(a) a gasifier for generating a producer gas output from a cellulosic waste material input, said gasifier comprising:

(i) a gasification chamber having:

A. an enclosing side wall cylindrical about a vertically extending axis of the chamber; and,

B. an axially aligned cylindrical top opening;

(ii) a feed tube axially aligned with said axis, said feed tube extending downwardly:

A. from an inlet for receiving said waste material,

B. through said top opening,

C. and to an outlet in communication with said chamber for discharging said waste material into said chamber,

(iii) a generally conical grate contained within said chamber, said grate having:

A. a base perimeter spaced inwardly from and concentric with said side wall to define an annular base region therebetween;

B. an upper side for supporting a fuel pile;

C. a lower side defining a generally conical envelope beneath said grate above the plane of said base perimeter,

(iv) underfire air admission means for directing gasification air through said grate and said fuel pile from said lower side of said grate; and,

(vi) overfire air admission means for directing overfire air at high velocity downwardly and tangentially into said chamber; and,

(v) gasifier ash removal means for capturing fuel pile ash from said annular base region, and for transporting such ash away from said gasifier;

(b) a burner disposed laterally away from said gasifier, said burner comprising:

(i) a cyclonic combustion chamber for burning said producer gas, said combustion chamber having an upper end, a lower end, and an enclosing side wall cylindrical about a vertically extending axis of the chamber;

(ii) producer gas inlet means disposed at said upper end for spirally directing producer gas downwardly into said combustion chamber;

(iii) primary combustion air inlet means for directing primary combustion air into said combustion chamber and for guiding same to mix with said producer gas as it spirally enters said chamber;

(iv) secondary combustion air inlet means disposed at said lower end for directing secondary combustion air at high velocity tangentially and upwardly into said chamber; and,

(v) exhaust outlet means for transporting air products of combustion away from said combustion chamber, said outlet means including:

A. an axially aligned exhaust inlet end disposed at said lower end of said chamber, and extending downwardly therefrom;

B. an exhaust outlet end; and,

C. an exhaust duct extending between said inlet end and said outlet end,

said exhaust inlet end being spaced radially inwardly in relation to said side wall;

(vi) burner ash removal means communicating with said combustion chamber for capturing burner ash and transporting such ash away from said burner;

and,

(c) an elongated duct communicating between said upper outlet of said gasification chamber and said producer gas inlet means of said burner for transporting said producer gas therebetween.

16. An incinerator as defined in Claim 15, wherein said gasifier ash removal means comprises a plurality of rabble arms and means for rotating said rabble arms to transport said ash inwardly to a gasifier ash collection hopper extending downwardly beneath said grate below the plane of said base perimeter.

17. An incinerator as defined in Claim 16, wherein said burner ash removal means comprises a burner ash collecting hopper extending downwardly from said lower end of said combustion chamber and axially aligned with said combustion chamber, said side wall of said combustion chamber expanding radially outwardly around said exhaust inlet end for better enabling centrifugally separated particulate matter to be directed past said exhaust inlet end and into said burner hopper.

18. An incinerator as defined in Claim 17, including first, second and common conveyor means:

(a) said first conveyor means extending upwardly and outwardly from a lower extension of said gasifier hopper to said common conveyor means for transporting fuel pile ash therebetween;

(b) said second conveyor means extending upwardly and outwardly from a lower extension of said burner hopper to said common conveyor means for transporting burner ash therebetween; and,

(c) said common conveyor means for transporting ash collected from said gasifier hopper and said burner hopper away from said incinerator.

19. An incinerator as defined in Claim 18 wherein said first and second conveyor means are water-sealed screw conveyor means.

20. An incinerator as defined in Claim 15, wherein said elongated duct comprises:

(a) a scrolled inlet leading from said upper outlet of said gasification chamber for recovering static pressure from producer gas tangential velocity as producer gas leaves said gasification chamber; and,

(b) a scrolled outlet leading into said producer gas inlet means of said burner for converting the static pressure of producer gas in said duct at said scrolled outlet to producer gas tangential velocity.

21. An incinerator as defined in Claim 20, wherein said producer gas inlet means of said burner comprises:

(a) a cylindrical plug extending downwardly through an axially aligned upper opening of said combustion chamber, said opening having an inwardly facing perimeter surface, said plug having a vertically extending outer surface spaced inwardly away from said perimeter surface to define an annular region between said surfaces; and,

(b) at least one spiral vane leading downwardly through said annular region for spirally directing producer gas downwardly into said combustion chamber.

22. An incinerator as defined in Claim 21, having a plurality of spiral vanes leading downwardly through said annular region for spirally directing producer gas downwardly into said combustion chamber.

23. An incinerator as defined in Claim 20, 21 or 22, including:

and wherein:

24. An incinerator as defined in Claim 20, 21 or 22, including:

and wherein: