EP0118455B1

EP0118455B1 - Pulverized solid fuel burning apparatus

Info

Publication number: EP0118455B1
Application number: EP83901967A
Authority: EP
Inventors: William H. Sayler; Justin Chad White
Original assignee: T A S Inc
Current assignee: T A S Inc
Priority date: 1982-05-14
Filing date: 1983-04-11
Publication date: 1987-06-03
Also published as: CA1203435A; DE3371938D1; EP0118455A4; AU7715487A; WO1983004085A1; ZA833054B; AU1604983A; AU566176B2; AU7715387A; EP0118455A1; KR840004566A; AU601469B2; KR910006233B1; AU601470B2

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 as least one to fifteen, includes a unique pulverizer (12) capable of both impact and autogenous pulverizing, and a unique burner (14) which includes a valve firing nozzle having a firing conduct (48) with firing orifice (49) and controlled secondary air supply (16, 16a, 54, 59). A movable valve element (50), preferably in the form of double-taper-ended body, positioned downstream from the firing orifice (49) passes a turbulent stream of mixed primary and secondary, in which are suspended particles of the pulverized fuel, into an ignition chamber (55) and controls flame shape.

Description

The invention relates to a solid fuel pulverizing and burning system, including a staged impeller 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, staged impeller means, and discharge means for passing a stream of the primary air and autogenously pulverized solid fuel to a burner for firing into a combustion chamber of a furnace or other heating structure; the burner having means defining an ignition chamber, a firing conduit connected at one end to a conduit leading from the pulverizer and having a firing orifice defined at the downstream end and directed into said ignition chamber, an element within said firing conduit being formed with slanted vanes for imparting swirl to material flowing through said firing conduit; means for introducing a controlled quantity of swirling secondary air into said stream which consist of a secondary air conduit concentric with and surrounding said firing conduit and opening into said ignition chamber of the burner, wherein said firing conduit is slidable longitudinally relative to said secondary air conduit and to said ignition chamber, so as to permit selective positioning of said firing orifice relative thereto, and wherein means are provided for securing said firing conduit in the selected position; means for igniting the turbulent air and pulverized solid fuel in said ignition chamber; and means for observing conditions within said ignition chamber.
The system of the present invention is usable for burning pulverized fuels such as coal or other fossil fuels suspended in a stream of air in industrial furnaces, such as those used to heat gypsum-processing kettles, steam boilers, rotary kilns and metallurgical furnaces.
Various kinds of burner systems for pulverized fuel using air as a transport medium have been described. The carrier air is often referred to as "primary" air and the main combustion air is referred to as "secondary" air. Various problems arise in connection with the control of fuel flow rates and fuel/air ratios necessary to control the shape, size, and oxidizing or reducing characteristics of the flames needed for particular applications. The achievable turndown ratio, i.e. the ratio of maximum to minimum firing rate, is about 3 to 1. Attempted uses of commercially available equipment with greater turndown ratio result in unstable combustion or in flame-out.
The document GB-A-329 963 relates to a system of the kind initially described. Air discharged from a heater is divided into two portions, one of which is the primary air supply and the other the main air supply. The primary air is pressurized by a fan and introduced into a pulverizing apparatus, in which fan plates secured to a vertically driven shaft are mounted within a casing having a fuel hopper at its upper end. Fuel discharge from the hopper to the inner portion of the upper fan member is thrown outwards against the casing wall and pulverized, then guided downwards by baffles to the lower fan members. From the lower part of the casing the mixture of air and pulverized fuel is distributed to fuel tubes of a furnace. Each fuel tube penetrates a plate of a hollow front for a furnace and has a burner tube or sleeve slidably mounted thereon and passing slidingly into an ignition chamber through an opening in an inner partition or wall of the hollow front. Angled vanes are located on a control boss, which is slidingly disposed within the burner sleeve and carried by a sliding rod extending axially through the fuel tube and operable from the outside. Main air for combustion is supplied into the ignition chamber from a conduit which coaxially surrounds the front end of the burner sleeve and is spaced therefrom. The air enters through a ring of angled vanes producing a whirling movement and is supplied in radial direction towards the open end of the burner sleeve.
Control of the burning of the fuel/air mixture is made by adjusting the position of the exit end of the slidable burner sleeve relative to the furnace opening and the position of the angled vanes in the burner sleeve relative to the exit end of the fuel tube, as well as by varying the amount of the mixture of fuel and primary air and the amount of secondary air supplied to the ignition chamber.
This burner arrangement may be expected to provide a good combustible fuel/air mixture within the ignition chamber or furnace at some distance from the burner sleeve opening, nevertheless, the achievement of a flame of controlled shape near the burner orifice and easy initial ignition of the mixture at a point located at the input side of the combustion chamber appears difficult.
The document US-A-4221 174 describes a burner which utilizes 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 in order to diffuse a discharging stream of air and pulverized coal which is mixed with oxygen and an inert gas at varying ratios to provide optimum conditions for ignition of the discharged fuel mixture.
A burner for pulverized fuel furnaces which is arranged to discharge the incoming stream of fuel and air in the shape of a spirally whirling hollow cone is described in the document US-A-1 676 511. Pulverized fuel is introduced into an air conduit from a second conduit having its discharge opening concentrically positioned with respect to the air conduit. In order to allow alterations of the discharge area into a furnace with changes of furnace capacity, whilst maintaining desired gas flow conditions, the mixture is passed into the furnace through a widening conical outer shell, within which an inner double-taper-ended inner cone is disposed. An adjustment rod is slidably supported by spiders within the air conduit and is connected to the rear end of the inner cone. The adjacent sides of the outer shell and the inner cone are substantially parallel, wherein the outer shell is provided with spiral vanes projecting inwardly toward the cone and the cone is provided with similar vanes projecting outwardly. Movement of the cone in axial direction increases or decreases the discharge area, wherein the overlapping spiral vanes coact to rotate the cone. The cone evidently serves to assist the mixing of the pulverized fuel with the air and no provision is made for a supply of secondary air into the furnace. Because of the shaping requirements of the vanes of the conical outer shell and the inner cone, the range of adjustment of the cross- sectional area of the discharge opening is limited.
The document GB-A-795 887 describes a combustion device for burning powdered or liquid fuels, including a combustion chamber, a centrally arranged inlet pipe for supplying fuel and air to the combustion chamber, means disposed within the pipe for imparting a whirling motion to the fuel/air mixture flowing through the pipe, a pipe chamber surrounding the pipe and having an inlet for secondary air, an annular outlet from the secondary air chamber which is formed between the outlet opening of this chamber and a mouthpiece on the inlet pipe for the fuel/air mixture and opens directly into the combustion chamber, wherein at least a portion of the combustion chamber has an annular cross- section wider than the outlet opening of the secondary air chamber and a constricted outlet, so that a stationary eddy is formed in the annular portion of the combustion chamber from secondary air flowing back along the wall of the annular portion towards the annular outlet from the secondary air chamber. The mouthpiece on the inlet pipe narrows toward the opening thereof and the mixture of fuel and air is ejected through the mouthpiece in the form of a conical jet into the combustion chamber. The combustion device is provided with igniting means, an inspection opening, and an opening for additionally injecting combustible dust, liquid or gas into the annular portions. Possibilities of controlling the shape of the flame formed within the combustion chamber appear to be limited.
It is the object of the present invention to provide a solid fuel pulverizing and burning system of the kind initially described, which allows substantially instantaneous ignition of the pulverized fuel in the burner and rapid heating to operating temperature for effective flame propagation, the achievement of much higher turndown ratios than possible with presently available equipment, and desired flame shapes to be obtained easily for particular purposes.
In a system of the kind initially described, these objects are achieved by said secondary air conduit having an annular discharge orifice at its end, by said firing orifice being defined by an inturned circumferential lip sloping so as to direct the outflowing stream of carrier air and suspended solid fuel particles against a double-taper-ended valve element movably mounted downstream of said firing orifice for adjustment closer thereto or farther therefrom, and by mutually spaced spiders, that slidably support within the firing conduit an elongate operating rod having said valve element secured to one end thereof and extending backwardly through said firing conduit, defining said element having said slanted vanes.
The double-taper-ended valve element, which is positioned movably at the discharge end of the firing conduit for the pulverized fuel and in line with the stream flow therethrough, creates turbulence and controls the quantity of the stream of air-suspended, pulverized, solid fuel fired into the ignition chamber of a furnace and the shape and 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.
A pulverizer may be employed which exerts a drying action on the solid fuel as it is being pulverized inside the pulverizer by the inherent operating conditions therein.
Setting of the burner valve is determined for maximum operative effectiveness under actual operating conditions by observation of such operating conditions. Substantially instantaneous ignition is achieved on the basis of an initial valve setting in conjunction with a fluid-fueled pilot ignitor, and rapid flame propagation is ensured by a heat retaining and reflecting ignition chamber of refractory material, which is cast to form as an integral block and through which flame-observation peep holes extend from the front of the burner. Observation of flame characteristics enable setting of the valve for optimum operation.
The pulverized coal may be consumed at the selected rates, and the plume of the flame may have a wide range of shapes and sizes and may have oxidizing or reducing characteristics and temperatures to meet the requirements of various industrial processing or space heating uses.
Whilst eliminating or substantially alleviating disadvantages of present solid fuel pulverizing and burning systems, the invention provides for turndown ratios of fifteen to one or higher, in comparison with turndown ratios of three to one of presently available equipment.
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 a fragmentary top plan view of an installation of a coal pulverizing and burning system of the invention in connection with a gypsum-processing kettle;
Fig. 2, a front elevation of the system of Fig. 1;
Fig. 3, a vertical section partly in elevation as taken on the line 3-3 of Fig. 1;
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 5-5 of Fig. 4;
Fig. 6, a vertical section taken on the line 6-6 of Fig. 4;
Fig. 7 a vertical 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 drawn to a larger scale;
Fig. 9, a horizontal section through the respective coal and air inlet conduits of the pulverizer portion of the system as taken on the line 9-9 of Fig. 3;
Fig. 10, 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 11-11 of Fig. 8; 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.

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 11, enabling such furnace to be fired with finely pulverized coal, about eighty percent of which is of forty 11m particle size and all of which will pass a standard two hundred mesh screen (screen opening: 74 pm).
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 forwardly protruding part 10a of the furnace 10 by means of a plate 14a which may or may not be provided as a part of burner 14. A blower 15 supplies ambient secondary air to burner 14 through a conduit 16, primary air carrying the pulverized coal in suspension being supplied by pulverizer 12 through conduit 13.
Ambient primary air is supplied to pulverizer 12 through a conduit 17, Fig. 3, and run-of-the-mine coal (maximum size about two inches or 51 mm) is supplied through a conduit 18.
Tertiary air for helping to support combustion at and beyond the burner may be supplied through a series of openings 19, Figs. 2,3, and 4, provided in the front of the furnace circumferentially of the burner proper.
The pulverizer component of the present system is unique in a system of this kind in that, although machine impact is a factor, fineness of grind is achieved largely autogenously under drying conditions by particle-to-particle attrition. However, other pulverizers of this general kind can be employed in this system so long as they perform in accordance with the teachings hereof. Although vertical orientation is preferred to utilize the effect of gravity, other orientations are possible.
The details of down-draft pulverizer 12 are shown in Figs. 8-12. A diametrically split, cylindrical housing 20, having bottom and top walls 21 and 22, respectively, is supported in vertical position by a stand 23. The two semicircular sections of such housing are secured together by means 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 rotatable impeller shaft 26 to which are affixed, in mutually spaced relationship, a series of impellers 27, 28, 29, 30 and 31 representing successive pulverizing stages from the upper inlet end of the housing to the lower discharge end thereof. The impellers are preferably all imperforate, circular plates of uniform diameter, leaving respective, relatively narrow, annular spaces 32 between their circumferences and the inside cylindrical wall of the housing. They are mounted on shaft 26 by means of respective splined collars 33 and set screws (not shown). A series of horizontal, annular partitions 34 extend inwardly between mutually adjacent impellers of respective sets of same from circumferential securement 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 sections, as illustrated in Fig. 10. Bars 27a extend from the circumference of the plate inwardly toward, but short of, its 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 top 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 utilized in any given instance. They are preferably provided at diametrically opposite sides of impeller shaft 26. For best distribution of the air entering 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 interchangeable, both of the openings and conduits leading thereinto are preferably identical. Where, as here, the opening 41 and supply conduit 43 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 tramp iron detector (not shown) to avoid damage to the pulverizer.
The spacings between the several 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. 11, instead of four, and impellers 29 and 30 of the third and fourth stages have four bars each, 29a and 30a, respectively, Fig. 8, the same as impeller 27 of the first stage.
The fifth, i.e. final, stage effects discharge of the pulverized solid fuel suspended in air through a tangential discharge conduit 45, Fig. 12, which is connected by conduit 13 to burner 14. Impeller 31 of such fifth stage 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 particles to settle. The height of vanes 31 a extends over much of the height of the discharge outlet so as to sweep the pulverized fuel and carrier air 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 spaced, 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 annular partition 34.
In descending through the pulverizer, the turbulent air and solid fuel particle mix is funneled from the first stage onto the second stage, 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 through 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 135 and 150 miles per hour, 146 miles per hour being optimum (217, 241 and 235 km/h, respectively).
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 49 is advantageously defined by an inturned lip 48a sloping downstream, so as to direct the outflowing stream of carrier air and suspended solid fuel particles against a valve element 50, which is preferably double-taper-ended, as at 50a and 50b, and positioned in-line with flow of material to impart maximum turbulence to the emerging stream. The angles of the tapered ends of the valve element 50 may be varied for particular applications.
Valve element 50 is secured to one end of an operating rod 51, which extends backwardly through firing conduit 48 and outwardly thereof through a packing gland 51a in the wall of an elbow 52 in the conduit. A handle 51 b on the exposed end of rod 51 provides for convenient manipulation in either pushing or pulling such rod to position valve element 50 either farther away from or closer to firing orifice 49 to change flame shape for particular purposes and to otherwise control operating characteristics. A set screw 51c provides for locking valve element 50 in adjusted position.
Operating rod 51 is slidably supported by mutually spaced spiders 53 within firing conduit 48, which have vanes 53a angled to impart swirl to the stream of carrier air and suspended solid fuel particles.
Concentric with and surrounding firing conduit 48 is a secondary air conduit 54 extending in cantilever fashion from securement to burner plate 14a and having conduit 16 connected in flow communication therewith. The downstream end, i.e. firing orifice 49, of conduit 48 and the downstream end 54a of conduit 54 open into an ignition chamber 55 of the burner, which is defined by heat retaining and reflecting refractory material 56, to provide a divergent inlet portion 55a in which valve element is positioned, and a discharge portion 55b of uniform diameter. Such material is advantageously a commercial refractory produced in powder form under the proprietary name of "Krusite" by A. P. Green Refractories Co., and is mixed with water and cast into final form as an integral block.
Firing conduit 48 is slidable within and along secondary air conduit 54 to place firing orifice 49 at variable distances from, or right at, the downstream end of secondary air conduit 54. A section of flexible pipe 57 in conduit 13 accommodates the movement of the firing conduit 48, and a set screw 58 provides for locking it in its adjusted position. The flow velocity in firing conduit 48 is sufficient to suspend enough pulverized coal particles to render the primary mixture in such conduit too fuel-rich for effective combustion, or at least sufficiently rich in coal particle content relative to air content for a low flame propagation rate such as will prevent flashback.
In practice, the weight of air in the primary mixture may range from 10% to 30% of the mixture weight, but should be maintained constant for any particular application.
Introducing secondary air into the primary fuel feed mixture adjusts the coal/air ratio of such primary mixture for ignition and combustion. The amount of secondary 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 16 into conduit 54 for selective angular orientation, so that an adjustable swirling component of velocity is imparted to the secondary air as it enters conduit 54. This swirling component persists through ignition 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 to produce correspondingly more full, but shorter plumes, and vice versa.
For start-up of the furnace, the position of 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 effect ignition, the flame from an igniter torch 60, Fig. 4, is directed into the highly turbulent mixture of air and pulverized solid fuel in ignition chamber 55 by way of an ignition passage 61, which extends from the front of the burner 14 through plate 14a and the block of refractory material 56 and opens into the ignition chamber 55. Ignition should take place instantaneously.
Following ignition, torch 60 is kept burning for about five minutes while the refractory material 56 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 14 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 strategically located for substantially complete viewing of conditions in the ignition chamber 55. Based on such observation, the operating position of valve element 50 is established 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 relocate its firing orifice 49 relative to the annular discharge orifice of secondary air conduit 54 at its end 54a, that can be done if found expedient in order to establish optimum 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°F (1094 to 1650°C), and serves as a continuing source of ignition heat for the fuel feed to the burner 14.
To adjust the coal feed rate, i.e. turndown ratio, for or during operation of the furnace, valve element 50 is positioned, as previously indicated, by manipulation of rod 51 to adjust flow of the primary fuel mixture into the ignition chamber 55. The supply of secondary air is then adjusted by means of valve 16a for the desired coal to air ratio. It should be noted that the combustion energy provided by the system is controlled and maintained by input offuel and air. In practice, the operator usually first adjusts the flame in this manner 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 flame 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 14 to accommodate large variations in coal consumption for achieving various desired results in the operation of a furnace or boiler is believed to come largely from thorough mixing of pulverized coal and air in both the pulverizer 12 and the firing nozzle of the burner 14 and by the reliability of continuing ignition. Coal feed rates to the burner 14 can be successfully adjusted over a turndown range of 15:1, or higher, with stable combustion and without flameout or flashback. Within the range, 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 the lower coal firing rates, the flow of secondary air being adjusted for relatively rapid combustion. The 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 mixture ratio and coal consumption rate.
For firing rates of 1/4 to 1/2 ton per hour (254 to 508 kg/h), the firing conduit 48 of the firing nozzle may be four inches (10.2 cm) in diameter, recirculation conduit 54 six inches (15.2 cm) in diameter, firing orifice 49 three and one-half inches (8.9 cm) in diameter, portion 55b of ignition chamber 55 fourteen inches (35.6 cm) in diameter, and the overall length of the ignition chamber twenty-four inches (61 cm).
The illustrated embodiment may be varied without departing from the essential features of the invention heretofore set forth. Thus, the firing nozzle may incorporate manifolding to accommodate two or more burners 14 simultaneously utilizing a single pulverizer 12, or more than one firing nozzle may be served by a single pulverizer 12.
For observation purposes, an ultraviolet scanner, such as a Honeywell "Mini Peeper", No. C7027A-1023, is 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 setting or settings can be carried out instead of manual.
In the continued operation of the furnace after start-up, standard automatic controls normally employed to govern the firing of fluid fuels, such as gas and oil, are employed, with feed of the solid fuel and of primary air being based on the turndown ratio desired at any given time.

Claims

1. A solid fuel pulverizing and burning system, including:

- a staged impeller pulverizer (12) for impacting relatively coarsely sized solid fuel and autogenously pulverizing it in turbulent air, said pulverizer (12) having a housing (20) with means for introducing solid fuel to be pulverized, means for introducing ambient primary air, staged impeller means, and discharge means for passing a stream of the primary air and autogenously pulverized solid fuel to a burner (14) for firing into a combustion chamber of a furnace (10) or other heating structure,

- the burner (14) having means defining an ignition chamber (55), a firing conduit (48) connected at one end to a conduit (13) leading from the pulverizer (12) and having a firing orifice (49) defined at the downstream end and directed into said ignition chamber (55), an element within said firing conduit (48) being formed with slanted vanes (53a) for imparting swirl to material flowing through said firing conduit (48),

- means for introducing a controlled quantity of swirling secondary air into said stream which consist of a secondary air conduit (54) concentric with and surrounding said firing conduit (48) and opening into said ignition chamber (55) of the burner (14), wherein said firing conduit (48) is slidable longitudinally relative to said secondary air conduit (54) and to said ignition chamber (55), so as to permit selective positioning of said firing orifice (49) relative thereto, and wherein means are provided for securing said firing conduit (48) in the selected position,

- means for igniting the turbulent air and pulverized solid fuel in said ignition chamber (55), and

- means for observing conditions within said ignition chamber (55),
characterized in that

- said secondary air conduit (54) has an annular discharge orifice at its end (54a),

- said firing orifice (49) is defined by an inturned circumferential lip (48a) sloping so as to direct the outflowing stream of carrier air and suspended solid fuel particles against a double-taper-ended (50a, 50b) valve element (50) movably mounted downstream of said firing orifice (49) for adjustment closer thereto or farther therefrom, and

- mutually spaced spiders (53), that slidably support within said firing conduit (48) an elongate operating rod (51) having said valve element (50) secured to one end thereof and extending backwardly through said firing conduit (48), define said element having said slanted vanes (53a) for imparting swirl to material flowing through said firing conduit (48).

2. A system according to claim 1, characterized in that the pulverizer (12) includes

- a shaft (26) rotatably mounted in the housing (20),

- a series of impellers (27 to 31) fixed to said shaft (26) in mutually spaced arrangement defining respective pulverizing stages and terminating short of said housing (20) to provide circumferential flow space therearound, said impellers (27 to 31) being provided with air-motivating, solid particle impact members thereon,

- air inlet means adjacent to one end of said housing (20) 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 (20) as the means for introducing solid fuel to be pulverized,

- discharge conduit means adjacent to the other end of the housing (20) and connected to the firing conduit (48) as the means for passing the carrier stream of air and pulverized solid fuel to the burner (14), and

- means for rotating the impeller shaft (26).

3. A system according to claim 2, characterized in that the pulverizer (12) additionally includes a series of annular partitions (34) fixed to the housing and extending peripherally thereof and between mutually adjacent impellers of respective sets of mutually adjacent impellers (27 to 31) to direct flow toward the impeller axis in opposition to centrifugal force exerted by the impellers (27 to 31).

4. A system according to claim 3, characterized in that the air inlet means and the fuel inlet means are arranged to discharge directly against the first stage impeller (27), and in that the second stage impeller (28) is provided with a greater number of impact members than is said first stage impeller (27).

5. A system according to claim 4, characterized in that the annular partition (34) between the first and second stage impellers (27 and 28, respectively) has additionally a discharge lip (34a) turned inwardly toward the axis of the impellers (27 to 31) to funnel material from said first stage to said second stage.

6. A system according to claim 2, characterized in that the inside face of the housing (20) is provided with impact bars (47) spaced peripherally thereof and positioned within the said flow space.

7. A system according to claim 3, characterized in that the housing (20) is cylindrical and it and the impeller shaft (26) are positioned vertically, with the upper end of the housing (20) closed by a top wall, in that the impellers (27 to 31) and annular partitions (34) extend horizontally, and in that the primary air inlet means and the solid fuel inlet means are located in said top wall.

8. A system according to claim 7, characterized in that the primary air inlet means and the solid fuel inlet means include respective elongate, substantially rectangular openings (40, 41) through the top wall of the housing (20) at diametrically opposite sides of the impeller axis, and flow conduits (42, 43) leading to the respective openings.

9. A system according to claim 8, characterized in that the long sides of the rectangular, elongate, air inlet opening (40) are substantially uniformly concavely curved toward the impeller axis.

10. A system according to claim 9, characterized in that both the primary air inlet opening (40) and conduit (42) and the fuel inlet opening (41) and conduit (43) are similarly formed so as to interchangeably used, and in that deflector skirts (44) are provided in the one selected as the solid fuel inlet opening (41) so as to reduce its size relative to that of said air inlet opening (40).

11. A system according to claim 7, characterized in that the discharge conduit means opens substantially tangentially into the lowest impeller stage through the cylindrical side wall of the housing (20) and the impeller (31) of said stage has vanes (31 a) 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.

12. A system according to claim 1, characterized in that the construction and arrangement of the pulverizer (12) and the means for operating it are such that the energy input during operation is sufficient to generate solid-fuel-drying heat internally of the housing (20) during operation with ambient air input.

13. A system according to claim 7, characterized in that the inside cylindrical wall of the housing (20) is lined with ceramic.

14. A system according to claim 11, characterized in that the impeller (31) 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 (20).

15. A system according claim 1, characterized in that the means for observing conditions within the ignition chamber (55) of the burner (14) include at least one peep passage (62) extending through the front of the burner (14) and opening into said ignition chamber (55).

16. A system according to claim 1, characterized in that the igniting means of the burner is a passage (61) extending through the front of the burner(14) and opening into the ignition chamber (55), said passage (61) being adapted to have an igniter (60) directed therethrough and into said ignition chamber (55).

17. A system according to claim 1, characterized in that provision is made for the inflow of tertiary air to the furnace (10) so as to surround the means defining the ignition chamber (55) with a flow of said tertiary air.

18. A system according to claim 1, characterized in that the ignition chamber (55) is an integral block of heat retaining and reflecting refractory material (56) cast to shape.