CA1184075A - Grating structure - Google Patents

Abstract

ABSTRACT
A furnace for burning dry or wet wood waste products such as hogged bark and the like is pro-vided with a grating therein comprised of aligned rows of bricks resting on supporting cross beams, with at least some of the rows of bricks maintained a uniform distance from other rows of bricks by spacers disposed between such spaced-apart rows of bricks. The furnace is charged by turbulent air entering both above and below the grating, with a select portion of such air being pre-heated. A
temperature gradient is established between an area immediately beneath the grating and the area above the grating in the range of 2200°F and can be con-trolled by selected initial placement of the bricks and spacers to achieve an optimum cross sectional area for flow of heated, turbulent air through the grating to produce a temperature for efficient heating, drying and burning of wood waste products in an essentially pollution-free manner.

Description

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S P E C I F I C A T I O N
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The present invention relates to wood waste burning systems, and somewhat more particularly to an improved grating structure for use in a furnace means chargea wit~ wet or dry wood waste materials~
Particulate wood waste materials, such as sawdust, hogged bark, wood chips, shavings, green twigs and the like are produced in large quantities in many industries. Disposal of such materials, particularly if it is moist or wet, in an efficient and pollution-free manner is a serious problem in such industries. Because such waste wood materials generally occupy a substantial volume and such materials are a potentially valuable heat source~
disposal is generally undertaken by means of com-bustion.
In order to dispose of a high volume of wood waste materials in an efficient manner, a furnace for burning such materials must be capable not only of accommodating a large volume of material but must also be able to uniform]y raise the temperature of such material to a level at which optimum combustion can occur and be able to supply adequate air or oxygen to allow complete combustion to occur. If the temper-ature achieved is too low to effectuate proper combus-tion, only a portion of the material to be disposed will burn, thereby not only diminishing disposal efficiency, but also requiring that the furnace be cleansed more frequently than if comple-te combustion ~.

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occurred, I~ lnsuffici~nt oxygen or air is supplied to the combustion chamber, a similar problem occurs.
~ further aggravating fact in the dîsposal of waste wood materials is that frequently such materials are green, damp or even wet and thus must first be driedf. then heated and finally ignited before complete combustion of such material can occur.
This requires a relati~ely steep temperatur~ gradient within the combusti~n chamber of a furnace so as to avoid undue delays between drying and ignition.
In addition to achieving a proper temperature in a furnace~ other factors contribute to efficient and pollution-free burning of wood waste material, such as the rate at which such material is fed to the furnace, the material-to~air ratio in the material stream being charged to the combustion chamber and the amount of ai.r turbulence available within the com-bustion chamber for uniformly heating, drying and igniting the material. A controlled wood waste burning system capable of monitoriny and cooperatively adjusting each of these factors is disclosed and cl~i,med in United States Patent No~ 4,311,102. The system disclosed in this application comprises a rotary screw ConYe~Or for bottom unloading of a waste wood material storage bin, a sensor monitoring material levels in the bin, a choke screw device for transferring a select amount o~ the waste material to a transport system ~2-t75 comprising a rotary feed, which transfer a constant amount of the particulate material from the choke screw to a transport conduit, an adjustable blower which pro~ides a select volume of air to the conduit to entrain the material deposited therein at an optimum material-to-air ratioJ a furnace means fed by such conduit and wherein the material is combusted, along with integrated control circuitry for optimum operation of the overall system.
A typical present-day wood waste burning furnace means comprises an enclosed relatively large-volume chamber lined with a fire-resistant material and connected to a chimney stack. A relatively large volume of wood waste material to be burned is either manually or automatically loaded onto the floor of such chamber, doused with a flamable liquid, such as kerosene or oil, ignited and allowed to smolder for an indefinite period of time. This type of operation is ineffective to fully extract the maximum amount of heat energy in the wood material, produces excessive ashes, smoke and other pollutant in the chimney which contaminate the atmosphere and produces large amounts of solid combustion products that require furnace shut-down every one or two loading cycles for manual clean-out thereof. While other furnace systems are known, they typically can-not accommodate large volumes of waste wood products, particularly when such products are moist or damp.
It is an obje~t of the present invention to provide an improved grating structure functioning as a hearth in a fuxnace means, such as a boiler furnace, for efficient and pollution-~xee buxning of all types of particulate wood waste material. It is a further object of the invention to provide a grating structure havin~ initially selectable openings therein to permit flow of turbulent heated air through the grating structure to develop a high-speed hot air stream contacting and/or suspending a mass of particulate wood waste material above an upper surface of the grating structure. In this manner, each parti-culate piece of the waste material is optionally heated, dried and ignited for a substantially smoke- and ash-free operation. During such air-waste material particle contact, the surEace of each wood particle is heated to drive out any volatile matter therein and the moving air stream strips away such volatile matter so that additional matter can exit from the wood particle surface. Once the volatile matter is removed from a wood particle, it is uni-formly heated to its ignition point and, in the presence of excess air or oxygen, combusts substan-tially without smoke or ash residue.
These and other objects, features and ad-vantages are inventively achieved by providing an improved hearth or grating structure comprised o a plurality of parallelly arranged suppor~ beams transversing a boiler furnace floor at a distance above suc~ floo~, with a plurality of fire-bricks arranged in rows on such beams in abutting relation with one another and having a pre-sel~cted size open area between at least some adjacent bricks or rows of bricks to permit flow of turbulent hot air through such open areas or spaces for optimized heating, drying and combustion of particulate wood waste materials pneumatically fed onto the upper sur-face of such grating structure. The support means may be T-beams, H-beams, I-beams, U-~hannels or other types of support having appropriate properties and dimensions. The bricks and/or brick rows are main-tained a select distance apart from adjacent bricks or brick row by spacers which are also supported by the beams disposed beneath select portions of abuttin~
bricks.
When the bricks are initially positioned and arrangea on the support beams with the spacers in a select pattern, the dimension of the space between adjacent bricks or rows thereof can be chosen so as to provide a total cross sectional air flow area through the grating which produces optimum turbulence and temperature for heating, drying and combusting particulated wood waste material, whether wet or dry.
It has been found that by providing a select pattern o~ predetermined size open areas between adjacent bricks or rows thereof, efficient non-polluting com-bustion of wet (containing up to 50-60% moisture) or dr~ wood waste material is achieved. T~e open areas cause the heated air fed ~elow the grating structure to exit through the structure as a high-speed turbulent air stream which not only suspends the particulate material above the grating structure, drying and heati~g such material but also, because of its velocity, actually cools elements of the grating structure, while releasing heat to the particulate material for drying and combustion~
On the Drawings:
Fig. 1 is a partial side elevational, some-what schematic view of a particulate wood wasteburning system utilizing an improved grating structure constructed in accordance with the principles of the invention.
Fig. 2 is a partial sectional view of a furnace of the type utilized in the system of Fig.
1 having an improved grating s-ructure of the inven-tion therein.
Fig. 3 is a partial sectional view taken along line III-III of Fig. 2.
Fig. 4 is a partial sectional view taken along line IV-IV of Fig. 2.
Fig. 5 is an enlarged, perspective view of an embodiment of a grating structure constructed in accordance with the principles of the invention.
A particulate wood waste material burning system is generally illustrated at 10 in Fis. 1.
Brie~ly described, the system 10 comprises a storage bin 11 elevated on bin supports lla and which contains particulate wood waste material 12 to be burned. The material 12 t which may comprise dry, wet ~r green wood was~e, such as ho~ged bark, sawdust, twigs and other l~ke wood was~e material, is unloaded from ~he bin 11 by means of a rotary scxew conveyor 13 which is restrained along the bin floor by a retaining means 13a and is revolved around the base o~ the bin 11 by a motor 14 through a linkage lS, The screw conveyor 13 transfers material 12 through an opening 16 in the base of the bin 11 into an intermediate hopper 17.
The intermediate hopper 17 is equipped with a soni.c transmitter 20 and a sonic receiver 21 to monitor the leYel of material 12 in the hopper 17. The bin 11 may also be equipped with a suitable material monitoring device llb, such as a weight or height sensor. Further de~ails of this unloading system can be obtained from our U.S. patents 3,414,142 and 3,865l053.
The :hopper 17 empties into a trough 18 which paxtially encloses a choke screw conveyor 22, proYided with a shroud-like member 22a at the output end thereof for transferring a controlled amount of particulate wood waste material, from hopper 17 to the particulate material transport system (further details of suc~ choke screw conveyor are disclosed in U.S~ Patent 2,723,021j, The choke screw conveyor feeds the p~rticulate material in~o a rotary feeder 23. The xotary feedex 23 i5 comprised of a generally cylindrical ~7-, .. ...

housing having a plurality of blades mounted on an axis for rotation within such chamber. A constant volume chamber is defined between adjacent blade members. Preferably, each blade terminates in a knife-edge so that any larger pieces of wood waste material protruding beyond such knife edges are sheared and an air seal is formed between the re-spective blade edges and the inner housing wall of feeder 23. Controlled rotation of the blades 24 is effected via mechanical linkage between the axis on which the blades are mounted and motor-pulley means 25. During operation, the rotary feeder 23 transfers a unit constant amount of wood waste matexial to conduit 30 for admixing such material with a proper volume of air for optimized combustion.
The air seal defined between each rotating blade of ~eeder 23 eEfectively separates the material storage and unloading system (elements 11 through 22) from the transport, charging and combustion system (elements 23 through 35~, thereby providing a safe-guard against back flow of gases and heat, such as may occur in the event of a malfunction of one or more elements.
An air flow is developed in the conduit 30 by a blower 26 having an adjustable intake 27 controlled by a motor 28 and linkage 29. Adjustment of the air intake 27 to the blower 26 results in a select volume of air in conduit 30 which entrains the material 12 deposited therein in a pxescribed (37~

material-to air ratio.
The conduit 30 is connected to a furnace means, which may comprise a fire tube or water tube boiler or industrial hot air furnace, industrial incinerator or heat-excha~yer (using a heat-exchange medium, such as thermal oil, water or other suitable medium) and can be primarily or supplementarly fired by coal, gas, oil or other available fuel. The firing system for such furnace means and fuels are known so that further details thereof are unnecessary.
In the embodiment shown, the furnace means is a boiler furnace 35 which, as shown, is connected to conduit 30 via dual conduit branches 32a and 32b. Each branch 32a, 32b is provided with a respective blow back damper 33 and 34 as another safety feature to prevent reverse air or material flow from the fur-nace to the transport-charging system in the event of an explosion or malfunction in the furnace. Branches 32a and 32b, which comprise comhustible material inputs, are aligned relative to one another and to the central area over grating structure 39 for optimum material distribution and for creation of optimum turbulence within the furnace combustion chamber. The boiler furnace 35 is provided with heat-extraction means, such as heat-exchange coils 37 and 41 for extracting heat from the furnace. At least some of the extracted heat can be utilized for heating air fed into the furnace beneath andJor above the grating structure 39 for heating, drying _g_ s and combusting the particulate wood waste material fed to the furnace via branch conduits 32a ~nd 32b.
Of course, some extracted heat may be utilized for other heat applications. Typically, the heat ex-change means within a boilex furnace comprise steamcoils and which can be associated with dry-air coils (not shown) so that the steam heats the dry air and such heated dry air is fed via a conduit 40 tbest seen at Fig. 3) under positive pressure into the furnace for contacting the waste wood material being combusted.
All of the parameters of the charging system, including the rate of unloading from the bin 11, the material levels in the bin 11 and the hopper 17, the feed rate of the choke screw conveyor 22, the feed rate of the rotary feeder 23, the volume of air intake to blower 26 al~d the steam pressure in coils 37 and 41 are all monitored and cooperatively controlled via suitable circuitry operationally interconnected within a control panel 36.
The boiler furnace 35 is provided with a grating structure or grate 39 constructed in accordance with the principles of the invention. The outer periphery of the grating structure 39, which typically is rectangularly-shaped (although other geometrically-shaped str~lctllres may be utili.zed), is comprised of parallel, spaced-apart support beams 44 and 47 having a plurality of pa~allel rows of bricks 45 positioned thereon as shown, and is supported a distance above a base floor of furnace 35 on three outer edges thereof by angle beams 47 attached to the corresponding outer walls 35a of furnace 35 and on the fourth, inner edge by a similar beam attached to a vertical wall 38 positioned within furnace 35, as shown. The wall 38 functions, in addition to a support means, as a guide for directing heated air within the furnace in a sinuous path to maximize contact between the hot air and the heat-extracting means within the furnace. Although the support beams 4~ are shown as T-beams, H-beams r I-beams, U-channels or other support members having a flat upper load-bearing sur~ace can also be used. Positioned below the grate 39 is at least one and preferably two hot air inlet conduits 40a and 40b. The hot air inlet conduits can be arranged in a staggered or off-set fashion relative to each other or in some other fashion for maximizing the amount of air turbulence generated by their respective air stream, keeping in mind the orientation of the material and air feed conduit branches 32a and 32b. Each hot air inlet is provided with an adjust-able intake blower 51 (operated by motor 50) and is selectively connected to a hot air source, such as the heat-extraction means within the furnace via a valve-controlled conduit 40.
A plurality of heat resistant fire bricks, for example composed of a fire or sintered reEractory material~ such as A1203 and typically being of a rectangular shape with dimensions of about 2" x 4" x 8"

(it will be understood that the composition and dimensions of the bricks can vary as desired), are arranged in parallel rows extending across the beams 44 and 47. Each brick is supported at its respective ends by spaced-apart beams. The bricks may be orientated so that a major face (i.e., the top or bottom surface as defined by the length and width of each brick) con-tacts the support beams, as shown at Fig. 5 or some other brick orientation may be utilized. The bricks are merely enplaced, without cement or other anchoring or binding material, on th~ upper beam sur-faces so that individual bricks are in surface contact with adjacent bricks within the row and at least some rows are spaced from at least one adjacent row. Such enplacement provides velocity-generating air flow spaces and allows repositioning and/or replacement of the bricks as necessary or desired.
Each row of bricks 45 can be positioned a select distance 52 from an adjacent row of bricks.
The distance 52 can be uniform throughout the entire grating structure or may vary so that, for example, wider spaces 53a are provided along a central area of the grate and narrower spaces 53b are provided along outer edges of the grate. Of course, other pattersn of open spaces between the brick rows may also be utilized.
The distance 52 between each adjacent row of bricks is defined and maintained by a plurality of spacers 46 positioned on the support beams 4~ and between at least some ad~acent brick rows. The spacers may comprise mild steel bar stock or ~e comprised of a refractory material similar to that of ~he bricks and be fashioned so as to have a select spacing dimensi~n, for example, so as to be 1/4" to 1/8" in thickness, (although another spacing dimension can be used, if desired).
The open spaces or areas Eormed by the pattern of support beams 44, spacers 46 and bricks 45 allow air flow through the grate 39 for improved drying, heating and combustion of wood wast material fed to furnace 35.
~ s best at Fig~ 3, a valve-or damper-controlled conduit 40 is connected to a hot air supply, such as the heat-extraction means within the furnace 35 for selectively feeding hot air to a blower 51 operated by motor 50. rrhe blower 51 can also be provided with a separate ambient air intake so that when relatively dry waste wood material is being combusted, the conduit 40 can be shut-off and only ambient air be fed beneath the grate 39. The air stream provided beneath the yrate 39 flow upwardly at increased speeds because of the reduced flow space and causes turbulence within the combustion chamber. ~n in-stances where a hot air stream is fed beneath thegrate, the turbulent, hot (about 250 to 400~F) air stream initial contacts moist or wet wood waste material and first heats and dries the waste material, then heats it up to its ignition point and thereafter contributes oxygen for sustained combustion~
Since a controlled amount o~ air ~generally in excess of that required for combustion of a given volume of wood waste material) is fed to the combustion chamber of furnace 35 via a primary air source input, such as br~nch c~nduits 32a and 32b, and a controlled auxiliary amount of air is fed through the grate 39, a relatively large excess of oxygen is present within the combustion chamber promoting rapid combustion of any fuel and substantially raising the temperature of the combustion chamber (up to a maximum range of about 2000 to 2500F).
With an exemplary grating structure con-structed in accordance with the principles of the invention and having spacers with a thickness or spacing dimension in the range of about 1/8" to 1/4", approximately 10,000 B.T.U. were produced, when 7.33 pounds of air were introduced, along with an appro-priate amount of a fuel into the combustion chamber of a boiler furnace equipped with such grating struc-ture. With the foregoing parameters, the temperature of the combu~stion chamber above the upper brick surface was in the range of about 2000 to 2500F
while the temperature just below the lower brick 25 surface was in the range of about 400 to 600F and the temperature immediately below the support beams 44 was in -the range of about 200 to 300F. Thus, the temperature gradient developed within the area just below the bottom of beams 44 to just above the ô)s top of the bricks was approximately 2,250F but such steep temperature gradient did not harm the gratin~ structure itself because of the velocity of the gas stream passing the various elements thereof~
As will be appreciated, a moving gas stream, although containing a substantial amount of heat therein, nevertheless tends to cool any stationary structures that it flows past. Such steep temperature gradient, along with the inducea turbulence acts on relatively moist or wet waste material particles by rapidly heating and drying such particles and then further heating them to ignition. The presence of excess air allows substantially complete combustion to occur without ash or smoke.
In a typical furnace provided with the grating structure of the invention and utilizing particulate wood waste material as fuel, continuous operation can occur for substantially extended periods of time without the necessity of furnace shut-down for cleaning-out of solid combustion pxoducts.
The select placement of bricks and spacers, along with the select orientation of the fuel material inputs and the primary and auxiliary air inlets lbranch conduits 32a, 32b and air inlets ~Oa and 40b) provide an improved grating structure operable in a substantially pollution-free manner with wet or dry wood waste m~terials.
The furnace 35 has an outlet 42 connected to a chi~ney stack 43 for emission of exhaust gases.

The stack 43 may be provided with a suitable damper 42a for aid in heat retention. The furnace 35 may be equipped with combustion efEiciency sensors, such as an 2 analyzer, a Co2-analyzer or other combustion analyzers and with pollution c~ntrol devices, such as a fly-ash arrestor, a scrubbed (dry or wet) or other equipment required by local air pollution governing agencies, as are known in the art. Such sensors and controlled devices are operationally interconnected with the integrated control circuitry of the overall system so as to be controlled and monitored by the control panel 36.
As is apparent from the foregoing specifica-tion, the present invention is susceptible of being embodied with various alterations and modifications which may differ particularly from those that have been described in the preceding specification and description. For example, additional air input con-duits, either above or below the grating structure can be utilized for creating additional turbulence if desired. Further, the spacers may be omitted from certain portions of the grate area so thak cer-tain rows of bricks are in contact with one another while others are spaced apart. For these reasons, it is to be fully understood that all of the foregoing is intended to be merely illustrative and is not to be construed or interpreted as being restrictive or otherwise limiting of the present invention, ex-cepting as it is set forth and defined in the hereto -16~

appended ~laims.

Claims (11)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows.

1. A grating structure for a furnace means having at least one air intake and at least one combustible material input in communication with a fire-containing combustion chamber within said furance means, said grating structure comprising: a plurality of spaced parallel beams transversing said chamber in a single plane above said air intake and below said combustible material input, said air intake being spaced from said material input; a plurality of parallel rows of bricks, each of said rows comprised of a plurality of individual bricks arranged in a single plane in surface contact with adjacent bricks and perpendicular to and removeably directly supported by said beams; and a plurality of spacers removeably directly supported on said beams and positioned between at least some adjacent rows of bricks, said spacers maintaining a selected open area between said some adjacent rows of bricks fox permitting flow of air from said air intake through said grating struc-ture.

2. The grating structure of claim 1 wherein said spacers have a spacing dimension in the range of about 1/8 inch to 1/4 inch.

3. A grating structure as defined in claim 1 wherein said air intake comprises at least a pair of air conduits off set relative to one another and positioned below said beams, at least one of said air conduits being selectively connected to a hot air source.

4. A grating structure as defined in claim 3 wherein said one air conduit is selectively con-nected to a heat-extraction means within said furnace means.

5. A grating structure as defined in claim 1 wherein said material input comprises at least a pair of selectively orientated conduits positioned above said bricks and relative to each other so that respective streams of material flowing therefrom at least partially impinge against one another.

6. A furnace for burning particulate waste material comprising: at least one steam coil con-nected to a steam source for heating air surrounding said coil; a means for transferring said heating air to at least one intake disposed at a lower por-tion of said furnace; a means disposed at an upper portion of said furnace for charging said furnace with particulate wood waste material; a plurality of spaced parallel beams supported across a combustion chamber in said furnace in a plane between said upper and lower portions of said chamber; a plurality of spaced parallel rows of bricks, each said row comprised of a plurality of individual bricks arranged in an end-to-end fashion, perpendicular to and sup-ported by said beam; a plurality of spacers supported on said beams and disposed between adjacent rows of bricks, said spacers maintaining a selected open area between said adjacent rows of bricks to permit flow of heated air from said intake through the open areas defined by said beams and bricks to contact particulate wood waste material deposited on said bricks from said charging means; and an exhaust means for disposing of gases formed by combustion of said particulate wood waste material.

7. The furnace of claim 6 wherein said selected open area between said adjacent rows of bricks is in the range of approximately 1/8 inch to 1/4 inch.

8. The furnace of claim 6 wherein said selected open area between said adjacent rows of bricks is uniform for all said rows of bricks.

9. The furnace of claim 6 wherein said plane in said furnace in which said spaced parallel beams lie has a central area and an outer area, said outer area disposed near the edges of said furnace t and wherein said selected open area between said ad-jacent rows of bricks is wider in said central area than said spacing in said outer area.

10. The furnace of claim 6 wherein said means for charging said furnace with particulate wood waste material comprises at least a pair of material inputs in said furnace disposed above said bricks and relative to each other such that respective streams of particulate wood waste material flowing from each input at least partially impinge against one another.

11. The furnace of claim 6 further comprising a heat exchange means including said steam coil for utilizing heat from the burned particulate wood waste material for heating said steam coil.