CA1203435A - Solid fuel pulverizing and burning system and method and pulverizer and burner therefor - Google Patents

Abstract

ABSTRACT
A system for pulverizing and burning solid fuel, such as coal or other fossil fuel, characterized by a possible turndown ratio of up to at least one to fifteen, includes a unique pulverizer capable of both impact and autogenous pulverizing, and a unique burner which includes a valved firing nozzle having a firing conduit with firing orifice and controlled secondary air supply. A
movable valve element, preferably in the form of a donble-taper-ended body, positioned downstream from the firing orifice passes a turbulent stream of mixed primary and secondary air, in which are suspended particles of the pulverized fuel, into an ignition chamber and controls flame shape.

Description

~Z~3~3~ii SPEC:IPICATION

Back~round of the Invention Technical Field:
The invention is concerned with systems and methods for pulverizing solid fuels, such as coal or other ~ossil fuels, And for burning such pulveriz~dfuels suspended in a stream of air.
Background Art:
The combustion of solid fuels in pulverized form in furnaces has been practiced for many decades, probably beginning with the simple blowing of finely divided coal through pipes directly into the furnace combustion chamber to supplement the normal furnace fire for enhanced temperature and heat generation. Ignition of such supplementary coal came from the heat of the main fire9 ~nd little if any consideration was given to the control of fuel flow rates iuel/air ratios necessary to achieve and control the shape, size, and oxidizirig or reducing characteristics of the flame desirable for particular applications.
More recently, burner systems for large ;ndustrial furnaces have been developed to burn pulverized coal fed from grindirg mills using air as a 20 transport medium, sse Crites U.S. Patent No. 1,541,903 of June 16, 1925, entitled "Means for Pulverizing, Feeding, and Burning Fuel'l. The carrier air is often referred ,o as "primary" air. The main combustion air is supplied to the burner as "secondary" air, and some attention has been given flame characteristics in the supply of such air. However, there is a lack of precise 25 control of coal/air ratios in primary mixtures fed to the burner and oî flow - rates of secondary air. Achievable turndown ratio, i.e. ratio of maximum to minimum firing rate, is about three to one, and there ;s no control of flame shape for part,icular purposes. The lack of precise control in the aforementioned respects severely restricts selection and control of flame 30 characteristics. Attempted use of commercial~y available equipment with greater turndown ratio results in unstable combustion or in flameout.
Since coal is usually stored in piles unprotected from the weather, it is of~en wet at the time of use. Pulverizing and burning systems are normally equipped with coal-drying equipment in sdvance of feed to the pulverizing ~5 mill or at least the carrier air is preheated Burners for pulverized solid fuels suspended in air have, in some instances, utilized a conical deflector rigidly mounted in a predetermined fixed position at the discharge end of and extending downstream from the firing conduit of the burner. Thus7 In Smith et aL U.S. Patent No. 4,221,174 S of September 9, L980, entitled "Direct Ignition of a Fluctuating Fuel Stream", such a deflector is employed to diffuse a dischar~ing stream of air-suspended pulverized coal with which is mixed oxygen or an inert gas at varying r~tios said to provide optimum conditions for ignition of the discharged fuel mixture. Again, in Gunnerman l~.S. Patent No. 4,249,471 of Eiebruary 10~
10 1981 entitled "Method and Apparatus for Burning Pellstized Organic Fibrous Fuel", such a deflector is similarly employed to diffuse a stream of air-suspended pulveris~ed sawdust, or similar organic fiber, with which is mixed Q
flammable gas for subsequent ignition and burning.
Pulverizers utili~ing a staged impeller for impacting friable solid 15 material to be ground and for throwing the impacted material outwardly against other stationary impacting members in an environment of turbulent air flow which promotes autogenous attrition of solid particles are well known in the pulverizing of materials such as lithopone, titanium oxide, cocoa, sulfur, talc and the like in instances where impalpable powders of five 20 micron SiZ2 or less are desired. For example, see Lykken et al. U.S. Patent Nos. 2,392,331 and 2,497,088 and Jackering U.S. Patent No. 3,071,330.
However, pulverizers or grinding mills her~tofore used in conjunction with burners for pulverized coal have been impact ~rushers adopted from the metallurgical industry, for example the hammer mill used in the system of 25 the aforementioned Crites U.S. Patent No. 1,541,903.
Disclosure of the Invention:
.
Primary objectives in the making of the present invention were to provide for effective pulverization of even wet coal in a system for pulverizing and burning solid fuels, principally in connection with industrial 30 furnaces such as those used to heat gypsum-processing kettles and steam boilers, and in connection with rotary kilns and metsllurgical furnaces; to enable use of ambient air as the carrier in contrast to the usual preheated air, and to accomplish effective drying of the wet material by means of heat generated internally of thP pulverizer; to provide for subst~ntially 35 instantaneous ignition of the pulverized fuel in the burner and rapid heatingto operating temperature for effective flame propagation; to provide for much higher turndown r~tios than posslble with pr sently av~ilablc equipment; to provide for easily obtaining desired fLqm~ shapes for particular purposes; and to provide for optimum overall operation of such a system by utilizing observation of firing conditions in the ignition chamber of the burner5 to govern firing conditions.
Wlth the foregoing in mind, the invention eliminates or subst~ntially alleviates disadvantages of pressnt solid fuel pulverizing and burning systems and provides for turndown ratios of fifteen to one or higher, as contrasted with the three to one of presently available equipment.
The burner of the invention has valved, fuel-firing nozzle mean~, preferably in the form of a movably positioned, double-taper-ended valve element at the discharge end of a firing conduit for the pulveriæed solid fuel end in line with stream flow therethrough to create turbulence and control the quantity of the stream of ai~suspended, pulYeri~ed, solid fuel fired into 15 the ignition chamber of a furnace and the shape ~nd character of the resulting flame. The quantity and velocity of fuel passed to the burner is largely controlled by the amounts of air and solid fuel material fed to the pulverizer.
Here, the pulverizer ~s unique in the drying action exerted on the solid 20 fuel as it is being pulverized internally of the pulverizer by the inherent operating conditions therein.
Setting of the burner valve is determined for maximum operative ef fectiveness under actual operating conditions by observation of such operating conditions. Substantially instantaneous ignition is achieved on the 25 basis of an initisl valve setting in conjunction with a fluid-fueled pilot igniter, and rapid name propagation is insured by reason of a heat retaining and reflecting ignition chamber of refrQctory material, which, in accordance with the invention, is cast to form as an integral block and through which flame-observation peep holes extend from the front of the burner.
30 Observation of flame characteristics enable setting of the valve for optimum operatior!. ~
Tne pulveri~ed coal may be consumed at selected rates, and the plume - of f~me may have a wide range of shapes and sizes and may have oxidizing or reducing characteristcs and temperatures to met the rec uirements of 35 various industrial processin~ or space heating uses.

~æ~ s 13rief Descrip~lon of Drawin~s:
In the drawings, which illustrate an embodiment of the invention typical of what is presently contemplated as the best mode for carrying it out in actual practice Fig. 1 is ~ fragmentary top plan view of an installation of a coal pulverizing and burning system of the invention in connection with a ~ypsum-processing kettle;
Figr 2~ a front elevation of the system of Fig. l;
Pig. 3, a verticgl section partly in elevation as taken on the line 3-3 of Fig. 19 Fig. 4, a fragmentary, axial, vertical section through the burner portion of the system as taken on the line 4-4 of Fig. 2 and drawn to a larger scale;
Fig. 5, a vertical section taken on the line 5-S of Fig. 4;
Fig. 6, a vertical section taken on the line 6-6 of Pig. 4;
Pig. 7 R vertic~l section taken on the line 7-7 of Fig. 4;
Fig. 8, a vertical section through the pulverizer portion of the system as taken on the line 8-8 of Fig. 3 and dr~wn to a larger scale;
Fig. 9, a horizontal section through the respective coal and air inlet conduits of the pulverizer portion of the system ~s taken on the line 9-9 of 20 Fig. 3, Fig. tO, a horizontal section through the pulverizer portion of the system as taken on the line 10-10 of Fig. 8;
Fig. 11, a similar horizontal section as taken on the line 11-ll of Fig. 3;
and Fig. 12, a similar horizontal section as taken on the line 12-12 of Fig. 8, hidden portions below being shown by broken lines.
Best Modes for Carryin~ Out the Invention:
As illustrated, the system of the invention is applied to the usual furnace portion 10, Figs. 1 and 3, of a conventional gypsum processing kettle 30 11, enabling such furnace to be fired with finely pulverized coal, about eighty percent of which is o~ forty micron particle size and all of which will pass a standard two hundred mesh screen.
Pulverized coal of this fineness is supplied on a continuous basis by a pulverizer 12 through a conduit 13 to a burner 14 attached to a Iorwardly 35 protruding part 1Ua of the furance 10 by means of a plate 14~ which may or may not be provided as a part of burner 14. A blower 15 supplies ambient $

secondary ~ir to burner 14 through a conduit 16, primhry dir carrying the pulverized coal in suspension being supplied by pulverizer 12 through conduit 13.
Ambient primary air 3s supplied to pulYeri7.er 12 through a conduit 17) Fig. 3, and run~f-the-mine co~l (maximum slze ~bout two inches) is supplied through ~ conduit 18.
Tertiary air for helping to support combustion At and beyond the burner may be supplisd through a series of openings 19, Figs 2, 3, ~nd 4, provided in the front of the furnace circumferentially of the burner prsper.
The pulverizer component of the present system is unigue in a system of this kind in th~t, although machine impa~t ls a factor, fineness of grind is ~chieved largely autogenously under drying conditions by particle-t~p~rticle attrition. The downdraft pulverizer 12 herein specifically illustrated and described is believed to be ne~,v in and of itself and is claimed herein per se as a subcombin~tion. However, other pulverizers of this general kind can be employed in this system so long 8S they perf3rm in accordance with the teQchings hereof. Thus, an updraft pulverizer can be used, snd, althou~h verticfll orientRtion is preferred to ut;lize the effect of gravity, other orientations are possible.
The details of down-draft pulverizer 12 are shown in Figs. 8-12. A
diametrically split, eylindrical housing 2û, having bottom and top w811s 21 and 22, respectiYely, is supported in vertical position by a stand 23. The two 3emi-circular sections of such housing Are secured together by rneans of outwardly projecting flanges 20a and bolts 20b. Journaled in the bottom and top walls by bearings 24 and 25 are opposite ends, respectively. of a rotat~ble impeller shaft 26 to which Qre affixed, in mutually spaced relationship9 a series of impellers 27, 28, 29, 30, hnd 31 representing successive pulverizing stages from the upper inlet end of the housing to the lower discharge end thereof. The impellers are preferably aLI imperfor~te9 circular pl~tes of uniforrn diameter, leaving respective, relstiYely narrow, annul~r spaces 32 between their circumferences and the inside cylindrical w~ll of the housing.
They are mounted on shaft 26 by means of respective splined collars 33 ~nd ~et screws (not shown). A series o~ horizontal, annul~r partitions 34 extend inwardly between mutually sdjacent impellers DI respective s~ts of same , from circumferentinl ~ecurement to the inside face of housing 20, to direct flow toward the impeller axis in opposition to centrifugal force exerted by the impellers The impellers are spaced from the respective partitions 34 to provide flow passages 35 therebetween as continuations of the annular spaces 32. An electric motor 36, supported from housing 20 by bracket 37 drives impeller shaft 26 through a belt and pulley drive 38.
Uppermost impeller 27 has four radial bars 27a dividing the upper surface of its plate into quarter sections3 as illustrated in Fig. l0. Bars 27a extend from the circumference of the plate inwardly toward, but short of, its 10 collar 33 so as to leave an annular space 39 surrounding the collar. This impeller is designed to receive, mix and distribute inflowing air and coal, as well as to shatter coal pieces by impact of the bars 27a thereagainst and by impact of the coal pieces against the housing wall and against each other as they are thrown outwardly by centrifugal force.
Inlet openings 40 and 41, Fig. 9, are provided through tcp wall 22 of housing 20 for connection with respective supply conduits 42 and 43, Fig. 3.
One is for the supply of ambient primary air, the other for the supply of run-of-the-mine coal or other solid fuel which may be utili7ed In any given instance. They are preferably provided at diametrically opposite sides of 20 impeller shaft 26. For best distribution of the air enterin~ through its opening, such opening is preferably elongate rectangular in shape, with the longitudinal sides concavely curved toward the impeller axis, as illustrated in Fig. 9. Since it is desirable that the primary air and fuel supplies be interchangeable9 both of the openings and conduits leading thereinto are 25 preferably identical. Where, as her~, the opening 41 and supply conduit ~3 are used to supply the solid fuel, deflector skirts 44 may be provided to reduce the size of the fuel inlet opening relative to that for the air.
Solid fuel is conveyed to its supply conduit through a tr~ mp iron detector (not shown) to avoid damage to the pulverizer.
- The spacings between the sever 1 impellers may be uniform, but in the illustrated instance are varied as shown in Fig. 8.
Second stage impeller 28 has six radial bars 28a, Fig. 1l, instead of four, and impellers 29 and 30 of the third and fourth stages h~ve four bars each, 29a and 30a, respectively, ~ig. 8, the same as impeller 27 of the first 35 stage-~Q~

The fifth, i.e. final~ stage effects discharge of the pulverized solid fuel suspended in air through a tangential discharge conduit 45, Fig. 129 which is connected by conduit 13 to burner 1~. Impeller 31 of such fifth stnge has four relatively thin and tall, air motivating vanes 31a placed radially on the upper surface of its imperforate plate similarly to but instead of the thicker and lower impact bars of the other impellers. Also, it has sets of diametrically opposite, mutually spaced, relatively slender bars 31b on its undersurface to stir up any tendency for solid pnrticles to settle. The height of vanes 31a extends over rnuch of the height of the dis~harge outlet so as to sweep the pulverized fuel and carrier eir therethrough.
The inside cylindrical walls of housing 20 are preferably covered by a thick ceramic lining 46 to resist abrasion and consequent wear, as well as to aid in pulverization, and there are preferably provided mutually ~paced, vertical, impact bars 47 secured to such inside cylindrical walls and projecting into the annular spaces 32 of stages second through fifth In order to funnel material from the first stAge to the second stage, a downwardly-turned lip 34a is preferably provided as an addition to the uppermost snnular partition 34.
In descending through the pulverizer, the turhulent air and solid fuel particle mix is funneled from the first stage onto the second stQge, where it comes under the influence of a greater number of activating bars than in the first StAge and then follows a sinuous or serpentine course as it passes thro~lgh the several succeeding stages It should be noted that the input energy to the pulverizer is normally sufficient to produce operating heat effective to dry even wet fuel fed thereinto along with ambient air. Thus, energy input by motor 36 should provide an RPM for impeller shaft 26 that imposes an outer tip speed for the impeller bars and vanes of between 13S and 150 miles per hour, 146 miles per hour being optimum.
Burner 14 as here illustrated, Figs. 4-7, comprises a firing nozzle which includes a firing conduit 48, connected at one end to conduit 13 leading from pulverizer 12 and having a firing orifice 49 at the downstream end. Such firing orifice is advantageously defined by an inturned lip 48a sloping downstream, so as to direct the outflowing stream of carrier air and suspended solid fuel perticles against a valve element 50, which is prefernbly double-taper~ended) as at 50a and 50b, and positioned in-line with now of ~3gl3~

materisl to Impart msximum turbulence to the emerging stre~m. The angles of the tapered ends of the valve element may be v~ried for particular applications Valve element 50 is secured to one end of an oper~ting rod 51, which 5 extends oackw~rdly through firing conduit 48 and outwardly thereof through a packing glQnd 51~ in the wall of ar; elbow 52 in the conduit. A hRndle 51b on the exposed end of rod 51 provides for convenient manipul~tion in either pushing or pulling such r~d to position valve element 50 either fArther aw~y from or closer to firing orifice 49 to change fl~me shape for particulrlr 10 purposes and to otherwise control operating chsrReteristics A set screw 51c provides for locking valve element 50 in sdjusted position.
Operating rod 51 is slid~bly supported by mutually spaced spiders 53 within firing conduit 483 which h~ve v~nes 53a ~ngled to impart swirl to the stream of carrier air ~nd suspended solid fuel particles.
Concentric with Qnd surrounding firing conduit 48 is 8 second~ ir conduit 54 extending in c~ntilever fashion from securement to burner plste 14a and h~ving conduit 16 connected in flow communication therewith. The downstreHm end, i.æ firing orifice 49, OI conduit 43 and the downstream end 54a of S~onduit 54 ~pen into an ignition chamber 55 of the burner, sqhich is defined by heat retaining and reflecting refractory mQterial 56, to provide n divergent inlet portion 55a in which valve element is positioned, ~nd discharge portion 65b of uniform diameter. Such materisl is advant~geously a commercial refr~ctory produced in powd~r form under tha proprietary n~me OI "l~rusite" by A. P. Green Refractories Co., and is mixed with water ~nd cast into final form as an integral block.
Firing conduit 48 is slidable within ~nd ~long secondary air conduit 5~
to place firing orific~ 49 ~t variable distances from, or right ~t, ~he downstre~m end of secondary air conduit 54. A section of ~exible pipe 57 in conduit 13 Rccommodates the movement of the firirlg conduit, and ~ set screw 58 provides for locking it in its Rdjusted position. The flow velocity in firing conduit 48 is sufficient to suspend enough pulverized coE~l p~rticles to render the primary mixture in such conduit too fuel-rich for effective combusion, or at least sufficiently rich in coal particle content rel~tive to Bir content for a low IlRme propagation rate such as will prevent flashb~ck.
In practice, the weight of ~ir in the prim~ry mixture m~y r~nge rom 10% to 30% of the mixture weight, hut should be m~intained constant îor ~ny p~rticular applicatio~
* Trademark 3~

Introducing secondary air into the primary fuel feed mixture ~djusts the coal/air ratio of such primary mixture for ignition and combustion. The amount of secondQry air supplied is controlled by a valve 16a, Fig. 4, in conduit 16 to produce oxidizing, reducing, or stoichiometric combustible mixtures as desired for the particular application and to at least partially control the shape of the flame plume in the furnace.
A vane 59 may be pivotally mounted at the entrance of secondary air from conduit ï6 into conduit 54 for selective angular orientation, so thet an adjustable swirling component of velocity is imparted to the secondary air as it enters conduit 54. This swirling component persists through i~nition chamber 55 to help shape the flame plume. Making use of valve 16a, the operation may induce more pronounced swirls to aid the valved firing nozzle eo produce correspondingly more full, but shorter plumes, and vice versa.
For start-up OI the furnace, the position OI firing conduit 48 is first adjusted relative to secondary air conduit 54 in accordance with firing conditions, and valve element 50 is positioned about three inches from firing orifice 49. Motor 36 of pulverizer 12 and blower 15 supplying secondary air to burner 14 are energized.
To efe~t ignition, the flame from an igniter torch 60, Fig. 4, is directed into ths highly turbulent mixture of air and pulverized solid fuel in ignition chamber 55 by way of an igniting passage 81, which extends from the front of the burner through plate l ~a and the block of refractory material 56 and opens into the ignition chamber. Ignition should take place instantaneously.
Following ignition, torch 60 is kept burning for about five minutes while the refractory material 5G is being brought to operating temperature and during observation of flame propagation. In the present instance, observation is carried out manually through peep passages 62, Fig. 4, which, like igniting passage 61, extend from the front of the burner through plate 14a and the block of refractory material 56 to open into ignition chamber 55. Although only one such peep passage could serve the purpose, it is preferred to employ two or more stratigically located for substantially complete viewing of conditions in the ignition chamber. Based on such observation, the operating position of valve element 50 is s~:stahlished by movement thereof from its initial position either toward or away from nozzle firing orifice 49. Although it is not usually necessary to readjust the position of firing conduit 48 to ~3~

reloc~te its firing orifice 49 relativ~ to the annular disch~rge orifice of seconddry air conduit 54 at its end 54a, that can be done if found expedient in order to establish optimurn conditions for flame propagation in and beyond ignition chamber 55.
In operation, refractory block 56 becomes heated to a temperature of from about 2000 to 3000 P, and serves as a continuing source of ignition heat for the fuel feed to the burner.
To adjust the coal feed rate, i.e. turndown ratio, for or during operation of the furnace~ valve element S0 is positioned, as previously indicated, by manipulation of rod 51 to adjust flow of the prim~ry fuel mixture into the ignition chamber. The supply of secondary air is then adjusted by means of valve 16a for the desired coal to air ratio. lt should be noted that the combustion energy provided by the system is controlled and maintained by input of fuel and air. In practice, the operator usually first adj-lsts the fl~me in this rnanner and then makes whatever further adjustments therein and to the setting of vane 59 and to valve 16a that may be required to modify flame swirl to achieve shape of fl~me plume suitable for the particular application.
If necessary, he may analyze the furnace exhaust gases to determine the oxidizing or reducing character of the flame.
The capability of the burner of the invention to accommodate large variations in coal consumption for achieving various desired results in the operation of a furnace or boile~ is believed to come largely from thorough mixing of pulverized co&l and air in both the pulverizer Rnd the firing nozzle of the burner and by the reliability of continuing ignition. Coal feed rates to the burner can be successfully adjusted over a turndown range of 15:1, or higher, with stable combustion and without flameout or flashback. Within the rangs, the shape, temperature, and oxidizing or reducing potential of the flame plume may be varied widely and controlled closely. The shorter, more expansive plume preferred for boiler heating is readily achieved with ~he lower coal firing rates, the flow of secondary air being adjusted for relativelyrapid combustion. Thè longer plume preferred in industrial process furnaces is achieved with higher coal firing rates The previously discussed adjustable swirling of injected secondary air provides further flame shape control at the selected mixturè r~tio and coal consumption rate.
For firing rates of 1/4 to 1/2 ton per hour9 the firing conduit 48 of the firing nozzle may be four inches in diameter, recirculAtion conduit 5~ six ~3g~

inches in diameter, firing orifice 49 three and one-half inches in dinmete~, portion 55b of ignition chamber 55 fourtPen inches in diameter, and the overall ler~th of the ignition chamb~r twenty-four inches.
The illustrated emboaiment may be varied without departing from the 5 essential features of the invention heretofore set forthO Thus, the firing nozzle may incorporaee rnanifolding to accommodate two or more burners simultaneously utilizing a single pulverizer, or more than one firing noæzle may be served by a single pulverizer.
For observation puposes, an ultraviolet scanner, such as a Honeywell 10 "Mini Peeper", No. C7027A-10~ installed in each passage 62.
Although manual observation is a convenient procedure, it will be apparent to those skilled in the art that electronic observation and automatic control of valve s~tting or settings can be carried out instead of manuaL
In the continued operation of the furnace after start-up, standard 15 automatic controls normally employed to govern the firing of fluid fuels, such as gas and oil, are employed, with feed o~ ehe solid fuel and of primary air being based on the turndown ratio desired at any given time.
Industrial A~plicability Whereas this invention is here illustrated and described with specific 20 reference eO an embodiment thereof presently contemplated as the best mode of carrying out such invention in actual practice, it is to be understood that various changes may be made in adapting the invention to different embodiments without departing from the broader inventive concepts disclosed herein and comprehended by the claims that follow.

i

Claims (35)

CLAIMS:

1. A solid fuel pulverizing and burning system characterized by a possible turndown ratio of up to at least fifteen to one and comprising a pulverizer for impacting relatively coarsely sized solid fuel and autogenously pulverizing it in turbulent air, said pulverizer having a housing with means for introducing solid fuel to be pulverized, means for introducing ambient primary air impeller means, and discharge means for passing a stream of the primary air and autogenously pulverized solid fuel to a burner for firing into the ignition chamber of a furance or other heating structure; a burner having means defining an ignition chamber, an elongate, firing conduit having one end in communication with said discharge means of the pulverizer and the opposite end in communication with said ignition chamber as n firming orifice; said conduit being adapted to pass said stream from end-to-end thereof and into said ignition chambers through said firing orifice; a valve element movably mounted relative to said firing orifice for adjustment closer thereto or farther therefrom as a primary air and fuel feed control valve, said conduit being relatively long and longitudinally imperforate so as to confine the longitudinally extensive flow of said primary air and fuel stream therethrough;
structural means within said conduit and mutually spaced along the length thereof for imparting turbulence to said longitudinally extensive flow of primary air and fuel prior to its discharge from said conduit and its entering said ignition chamber; means for introducing a controlled quantity of secondary air into the turbulent stream after its discharge through said firing orifice; means for igniting the pulverized solid fuel in said ignition chamber; means for observing conditions within said ignition chamber;
and means for adjusting the position of said valve element relative to said firing orifice in accord with observed conditions in the ignition chamber to control the quantity of primary air and fuel fired into said ignition chamber and to influence flame propagation and flame shape.

2. A system according to Claim 1, wherein the pulverizer comprises n shaft rotatably mounted in the housing; a series of impellers fixed to said shaft in mutually spaced arrangement defining respective pulverizing stages and terminating short of said housing to provide cirumferential flow space therearound, said impellers being provided with air-motivating solid particle impact members thereon; air inlet means adjacent to one end of said housing as the means for introducing primary air, to provide a carrier stream of air; solid fuel inlet means adjacent to said one end of the housing as the means for introducing solid fuel to be pulverized; discharge conduit means adjacent to the other end of the housing and connected to the firing conduit as the means for passing the carrier stream or air and pulverized solid fuel to the burner;
and means for rotating the impeller shaft.

3. A system according to Claim 2, wherein the pulverizer additionally comprises a series of annular partitions fixed to the housing and extending peripherally thereof and between mutually adjacent impellers of respective sets of said mutually adjacent impellers to direct flow toward the impeller axis in opposition to centrifugal force exerted by the impellers.

4. A system according to Claim 3, wherein the air inlet means and the fuel inlet means are arranged to discharge directly against the first stage impeller; and wherein the second stage impeller is provided with a greater number of impact members than is said first stage ampeller.

5. A system according to Claim 4, wherein the annular partition between the first and second stage impellers has additionally n discharge lip turned inwardly toward the axis of the impellers to funnel material from said first stage to said second stage.

6. A system according to Claim 2, wherein the inside face of the housing is provided with impact bars spaced peripherally thereof and positioned within the said flow space.

7. A system according to Claim 3, wherein the housing is cylindrical and it and the impeller shaft are positioned vertically, with the upper end of the housing closed by n top wall; wherein the impellers and annular partitions extend horizontally;
and wherein the primary air inlet means and the solid fuel inlet means are located in said top wall.

8. A system according to Claim 7, wherein the primary air inlet means and the solid fuel inlet means comprise respective elongate, substantially rectangular openings through the top wall of the housing at diametrically opposite sides of the impeller axis; and flow conduits lending to the respective openings.

9. A system according to Claim 8, wherein the long sides of the rectangular, elongate, air inlet opening are substantially uniformly, concavely curved toward the impeller axis.

10. A system according to Claim 9, wherein both the primary air inlet opening and conduit and the fuel inlet spending and conduit are similarly formed so as to be interchangeably used, and wherein deflector skirts are provided in the one selected 85 the solid fuel inlet so as to reduce its size relative to that of said air inlet.

11. A system according to Claim 7, wherein the discharge conduit means opens substantially tangentially into the lowest impeller stage through the cylindrical side wall of the housing, and the impeller of said stage has vanes fixed to and projecting from its upper surface substantially within the height of the opening into said discharge conduit means so as to serve in effect as an ejector the for the carrier stream of primary air and the pulverized fuel entrained therein.

12. A system according to Claim 1, wherein the construction and arrangement of the pulverizer and the means for operating it are such that the energy input during operation is sufficient to generate fuel-drying heat internally of the housing during operation with ambient air input and to produce finely pulverized solid fuel, about 80% of which is 40 microns in size and all of which will pass a standard two hundred mesh screen.

13. A system according to Claim 1, where provision is made for the inflow of tertiary air to the furnace so as to surround the means defining the ignition chamber with a flow of said tertiary air.

14. A system according to Claim 1, wherein the firing orifice is defined by an inturned, circumferential lip sloped toward the ignition chamber.

15. A system according to Claim 1, wherein the valve element of the burner is double-taper ended and is positioned in-line with flow of material through the firing orifice.

16. A system according to Claim 1, wherein the means for introducing secondary air is a conduit concentric with and surrounding the firing conduit and opening into the ignition chamber of the burner, said firing conduit being slidable longitudinally relative to the conduit for the introducing of secondary air and to the ignition chamber so as to permit selective positioning of the firing orifice relative thereto; and wherein means are provided for securing said firing conduit in the selected position.

17. A system according to Claim 1, wherein the valve element is fixed to one end of an elongate rod which extends backwardly through the firing conduit to a location exteriorly thereof; and wherein mutually spaced spiders within said firing conduit slidably support said rod, said spiders being formed with slanted vanes as the means for imparting turbulence to the fuel and primary air flowing through the conduit.

18. A solid fuel pulverizer, comprising a vertical shalt rotatably mounted in a vertically positioned housing having a top wall; a series of horizontal impellers fixed to said shaft in mutually spaced arrangement and terminating short of said housing to provide peripheral flow space therearound, said impellers being provided with air-motivating, solid particle impact members thereon, and the inside cylindrical face of said housing being provided with mutually spaced, substantially vertical, impact bars positioned within said flow space; a series of annular partitions fixed to the housing and extending peripherally thereof and between mutually adjacent impellers of respective sets of said mutually adjacent impellers to direct flow toward the impeller axis in opposition to centrifugal force exerted by the impellers; air inlet means in said top wall of the housing as the means for introducing primary air to provide a carrier stream of air; solid fuel inlet means also in said top wall of the housing as the means for introducing solid fuel to be pulverized; discharge conduit means adjacent to the lower end of the housing; and means for rotating the impeller shaft.

19. A solid fuel pulverizer according to Claim 1, wherein the primary air inlet means and the solid fuel inlet means comprise respective elongate, substantially rectangular openings through the top wall of the housing at diametrically opposite sides of the impeller axis; and flow conduits leading to the respective openings.

20. A solid fuel pulverizer according to Claim 19 wherein the long sides of the rectangular, elongate, air inlet opening are substantially uniformly concavely curved toward the impeller axis.

21. A solid fuel pulverizer according to Claim 19 wherein both the primary air inlet opening and conduit and the solid fuel inlet opening and conduit are similarly formed so as to be interchangeably used, but wherein deflector skirts are provided in the one selected as the solid fuel inlet so as to reduce its size relative to that of said air inlet.

22. A solid fuel pulverizer according to Claim 18 wherein the discharge conduit means opens substantially tangentially into the lowest impeller stage through the side wall of the housing, and the impeller of said stage has vanes fixed to and projecting from its upper surface substantially within the height of the opening into said discharge conduit means, so as to serve in effect as an ejector fan for the carrier stream of primary air and the pulverized fuel entrained therein.

23. A solid fuel pulverizer according to Claim 22 wherein the impeller of the lowest impeller stage also has members on its underside to aid in ejecting any particles that tend to settle on the bottom wall of the housing.

24. A solid fuel pulverizer according to Claim 18 wherein the inside cylindrical wall of the housing is lined with ceramic.

25. A solid fuel pulverizer according to Claim 18 wherein the primary air inlet means and the fuel inlet means are arranged to discharge directly against the first stage impeller; and wherein the second stage impeller is provided with a greater number of impact members than is said first stage impeller.

26. A solid fuel pulverizer according to Claim 25 wherein the annular partition between the first and second stage impellers has additionally a discharge lip turned inwardly toward the axis of the impellers to funnel material from said first stage to said second stage.

27. A solid fuel pulverizer according to Claim 18 wherein the construction and arrangement of the pulverizer and the means for rotating the impeller shaft are such that the energy input during operation is sufficient to generate solid-fuel-drying heat internally of the housing during operation with ambient air input.

28. A pulverized solid fuel burner adapted for attachment to a furnace or other heating structure comprising means defining an ignition chamber; an elongate firing conduit having one end adapted to connect with means for supplying a stream of primary air and pulverized solid fuel and having a fuel firing orifice at the other end for discharge of a stream of the pulverized fuel and primary air that passes through said firing conduit internally and from end-to end thereof, said firing orifice being directed into said ignition chamber; a valve element movably mounted relative to said firing orifice for adjustment closer thereto or farther therefrom as a primary air and fuel feed control valve said conduit being relatively long and longitudinally imperforate so as to confine the longitudinally extensive flow of said primary air and fuel stream therethrough; structural means within said conduit and mutually spaced along the length thereof for imparting turbulence to said longitudinally extensive flow of primary air and fuel prior to its discharge from said conduit and its entering said ignition chamber; means for introducing a controlled quantity of secondary air into the turbulent stream after its discharge through said firing orifice; means for igniting the pulverized solid fuel in said ignition chamber; means for observing conditions within said ignition chamber; and means for adjusting the position of said valve element relative to said firing orifice in accord with observed conditions in the ignition chamber to control the quantity of primary air and fuel fired into said ignition chamber and to influence flame propagation and flame shape.

29. A burner according to Claim 28 wherein the firing orifice is defined by an inturned, circumferential lip sloped toward the ignition chamber.

30. A burner according to Claim 28 wherein the valve element is double-taper-ended and is positioned in-line with flow of material through the firing orifice.

31. A burner according to Claim 28 wherein the means for introducing secondary air is a conduit concentric with and surrounding said firing conduit and opening into the ignition chamber, the firing conduit being slidable longitudinally relative to the secondary air conduit and to the ignition chamber, so as to permit selective positioning of the firing orifice and wherein means are provided for securing said firing conduit in the selected position.

32. A burner according to Claim 28 wherein the valve element is fixed to one end of an elongate rod which extends backwardly through the firing conduit to a location exteriorly thereof; and wherein mutually spaced spiders within said firing conduit slidably support said rod, said spiders being formed with slanted vanes for imparting turbulence to the fuel and primary air flowing through the conduit.

33. A burner according to Claim 28 wherein the ignition chamber is an integral block of heat retaining and reflecting refractory material cast to shape.

34. A method of firing the combustion chamber of a furnace or other heating structure with pulverized solid fuel, comprising pulverizing such a fuel by impact and autogenously under pulverizing conditions, so as to generate sufficient heat to dry the fuel in the presence of a flow of ambient air, to thereby provide a flow of primary air and entrained pulverized fuel capable of substantially instantaneous ignition and rapid flame propagation; passing said flow of primary air and fuel through a burner constructed in accordance with Claim 28 igniting the fuel in the ignition chamber of said burner; observing conditions in said ignition chamber and adjusting the extent of valve opening through the firing orifice of said burner to control the amount of primary air and fuel fed therethrough into said ignition chamber and to establish optimum conditions for flame propagation and desired flame shape; and continuing the pulverizing and delivering of pulverized fuel to the ignition chamber.

35. A method in accordance with Claim 34 wherein about 80% of the solid fuel when pulverized is no more than 40 microns in size.