US2251029A - Apparatus for regulating fuel supplied to burners - Google Patents

Description

H. R. BARTON July 29, 1941.

APPARATUS FOR REGULATING FUEL SUPPLIED T0 BURNERS Filed June 1, 1938 3 Sheets-Sheet l FUEL V41 V5 21 70 BURNER M/L L INVENTOR '//0z0a2zZ/z Bar-fan BY L ATTORNEY5 July 29, 1941. H. R. BARTON 2,251,029

APPARATUS FOR REGULATING FUEL SUPPLIED TO BURNERS Filed June 1, 1938 5 Sheets-Sheet 2 570 BUR/V67? INVENTOR fi oward $527232 ATTORNEYS July 29, 1941. H, R, BART ON 2,251,029

APPARATUS FOR REGULATING FUEL SUPPLIED TO BURNERS Filed June 1, 1958 3 Sheets-Sheet 3 5 To sum v5? v [so/LEE EXHAUSTER.

BUEA/[R VALVE REGULATOR M/LL FUEL F5150 ER.

l N V EN TO R flaward f2 50. 72572,

ATTORNEY$ Patented July 29, 1941 STATES OFFIQE APPARATUS FOR REGULATING FUEL SUPPLIED TO BURNERS 9 Claims.

This invention relates to an improved process for the control of the quantity of pulverized fuel supplied to the combustion chamber of boilers, furnaces, kilns and the like. More particularly this invention relates to a delicate method of control to which the amount of pulverized fuel fed to the burner is instantly responsive. The present invention also includes various forms of apparatus which are suitable to accomplish the desired delicate control, as well as various other improvements hereinafter more fully disclosed.

There are currently employed two fundamentally different methods for supplying pulverized fuel to fuel burners. One system, frequently referred to as the storage system, involves the grinding of a fuel such as coal to the desired fineness and delivering it to a convenient storage space from which it is withdrawn and fed to the burners as required. While this method results in comparatively ease of control of the amount of fuel fed to the burners according to varying requirements, it does not afford a completely satisfactory or economically profitable solution to the problem of supplying pulverized fuel to the burners. The cost of the added equipment necessary and the space required to dry, handle and store the fuel in accordance with this system constitute serious disadvantages to its use. There is the further disadvantage that storing such a finely pulverized combustible material in any quantity presents serious explosion hazards and the danger of spontaneous combustion. In the second method of operation commonly termed the unit system the fuel is pulverized as necessitated by the requirements of the burners, and fed from the pulverizing miil directly to the burners. Altho the unit system entails lower costs and smaller space requirements it has not been found to be completely satisfactory due to the fact that it does not provide a sufficiently responsive method of control of the amount of fuel fed to the burners. In such systems the amount of fuel fed to the burner is regulated by varying the amount of unpulverized fuel passed to the mill. When an increased amount of fuel is required it must first be pulverized before it is supplied to the burner. This grinding operation requires time and consequently this method of control has not given entirely satisfactory results. To overcome this difficulty attempts have been made to maintain a reserve of pulverized fuel in the grinding mill, but this has failed to accomplish the desired result. Even in the best of these proposed methods of control there is a substantial tim lag insorbed in the heat absorption apparatus.

volved, so that from a few to many minutes are required to change the amount of fuel actually entering the burner in order to produce the desired change in available heat. There is the further disadvantage that delicate regulation of the flame is diificult if not impossible due to the lack of sensitivity in the means of control.

The primary object of the present invention is to overcome such difficulties, particularly the lack of responsiveness in the control of the amount of fuel fed to the burners thru lack of flexibility and sensitivity of burner control by providing a new and improved process and apparatusoperating generally according to the unit system, but whereby a delicate and responsive control of the fuel feed is attained.

A further object of my invention is to provide a method andmeans whereby operating efflciencies of burners fed with pulverized fuel are increased concurrently with the previously mentioned advantages.

Thus, the apparatus of my invention comprises apparatus for supplying regulated amounts of pulverized fuel to a burner responsive to the quantity of heat units which are absorbed in a heat absorption apparatus and which are provided by combustion of pulverized fuel supplied to the burner. The apparatus comprises agrinding mill adapted toreduce unpulverized fuel to a degree of fineness appropriate for use in a pulverized fuel burner, means for conveying pulverized fuel suspended in a gaseous medium in a stream from the mill to the burner, and a regulator responsive to the quantity of heat ab- Means are provided intermediate the grinding mill and the burner for concentrating at least the coarser particles of at least a portion of the suspension of pulverized fuel together with a portion of the fine particles of pulverized fuel in an amount determined by the regulator. More specifically, this latter means, disposed intermediate the grinding mill and the burner and which is adjustable, may comprise means for imparting whirling centrifugal motion to at least a portion of the stream of pulverized fuel and an adjustable valve disposed in the stream of pulverized fuel for controlling the amount-of fuel to'be returned tothe stream of fuel flowing from the mill to the burner in the form of a stream of fuel concentrated by said centrifugal motion, the controlled amount of fuel being determined by the regulator. Means are further provided for returning the stream of fuel concentrated by the centrifugal motion to a point in the stream of fuel flowing from the mill to the burner located in advance of the adjustable means for concentrating the fuel.

In accordance with my invention, unpulverized fuel is fed in controlled quantities to a conventional grinding mill adapted to reduce the fuel to a particle size suitable to be fed directly to the burner. The comminuted fuel emerges from the grinding mill suspended in a gaseous medium capable of supporting combustion such as, for example, air, and is conveyed through pipes or conduits toward the burner by means of a fan or a similar forcing means. In the foregoing respects, my process resembles the customary unit system of operation, and except for my improvements would be subject to all the defects and shortcomings of such systems. In accordance with my invention, I depart from the previously known methods of operating pulverized fuel burners, by controlling an amount of pulverized fuel and air supplied to the system in such a way as to keep immediately available in a cyclic system an amount of fuel sufficient to meet the maximum immediate requirements of the burner. Under varying operating conditions this amount of fuel may fluctuate materially, and is in time increased or decreased by increasing or decreasing the amount of coal or other fuel fed to the mill and from the mill in a pulverized condition to the fuel stream. The grinding of the fuel, as previously stated, consumes an appreciable time, and this time requirement has been largely responsible for the lag in the response of the previously known unit system to the burner requirements. The reserve supply of pulverized fuel which, in accordance with my invention, is kept immediately available is largely in the form of a circulating stream, but this may be augmented to a greater or lesser degree by additional proportions of fuel which have been deposited at points in the cyclic system by settling out from the circulating stream due to the air in this stream be coming oversaturated with fuel. Any such settled fuel is readily picked up by the circulating stream as the concentration of suspended fuel diminishes, thus remaining immediately available for use at the burners. Since the maximum fuel requirement to supply an increment in the burner requirement until such time as the mill can furnish sufficient added fuel is constantly maintained in suspension or otherwise, as above described, instantly available for feeding to the burner, my invention is not dependent upon variations in the amount of fuel ground in the mill to meet immediate burner requirements. It is to be understood that the terms circulating stream and circulating reserve supply as hereinafter used, are intended to include pulverized fuel thus deposited in the cyclic system as well as that actually in suspension.

In the present system, the greater amount of fuel in suspension than is required by the burner is continuously passed through the pipe leading from the mill toward the burner. Before reaching the burner that portion of the fuel stream not required by the burner is diverted, and with or without separation from the gaseous medium is returned to the system ahead of the forcing means. By the regulation of a valve in the fuel conduit the amount of fuel passed to the burner may be increased or decreased instantly. By the present invention, the burning of powdered fuel may be accomplished with the same flexibility of accurate and immediate control as the burning of gas in a gas burner.

Regardless of whether the variation in fuel requirement is an increase 01' decrease it is readily instantly made by my improved process and apparatus. If a decreased amount of fuel is required one merely diverts a greater portion of fuel into the circulating reserve supply, and conversely if the furnace conditions call for a greater amount of fuel a less amount is so diverted. Accordingly, it is desirable to maintain sufficient fuel in the stream passing toward the burner to meet the immediate burner requirements when the diverting mechanism is in an intermediate position.

It is desirable though not essential to my invention that the means for varying the amount of unpulverized fuel fed to the mill be correlated with the diverting mechanism in the fuel stream. Frequently, the fluctuations are only momentary and can be accommodated solely by the circulating reserve supply of suspended fuel. However, if the changed requirement continues it is necessary to change the rate of supply of additional fuel from the mill to the reserve stream. It is desirable therefore to increase or decrease the supply of fuel to the mill as the burner requirements increase or decrease. By thus controlling the supply of fresh fuel to the system the circulating reserve supply of immediately available suspended fuel is maintained more uniformly and a sufficient supply for long continued increased demands is assured. The time required for pulverizing the fresh fuel fed to the mill is of no consequence, since a supply adequate to accommodate increased demands during this interval is constantly in an immediately available condition.

In addition to the improved process just described the present invention comprehends various forms of apparatus effective to accomplish the desired degree of fuel control together with other important improvements. Essentially the apparatus provided by my invention to accomplish the above described fuel control involves a unit system of fuel supply in which a precisely controlled portion of the fuel stream is fed to a burner, and a further portion is diverted and returned to the system at a point in advance of the point of diversion, thus producing a continuously and immediately available reserve supply of fuel in the form of a circulating stream.

The process and apparatus of the present invention are particularly suited to the use of coal suspended in air, but it is to be understood that the use of other solid fuels than coal and other gaseous media than air are also included in my invention.

The various embodiments of the present invention will be more completely understood by a consideration of the following detailed description supplemented by reference to the drawings in which Fig. 1 represents diagrammatically an elevational View partly in section of one embodiment; Fig. 2 is a horizontal sectional view of the fuel valve 5 of Fig. 1; Fig. 3 represents alternative means for returning the diverted fuel to the system; Fig. 4 represents an alternative means for separating the fuel to be fed to the burner from the circulating reserve supply; Fig. 5 is a detailed horizontal section of the control mechanism of Fig. 4 along the line BB; Fig. 6 represents a further embodiment which employs a variation in the type of control mechanism used to divert the variable reserve supply from the stream of fuel which is passed to the burner; Fig. 7 is a detail of a specific feature shown in Fig. 6; and Fig. 8 is a schematic diagram showing the complete assembly of the apparatus of my invention connected with a burner supplying heat to a boiler with the regulator connected to the boiler. In each of these figures common reference numerals indicate similar parts.

In one embodiment the apparatus provided by the present invention is illustrated diagrammatically in Fig. 1. In this embodiment l represents a grinding mill of a conventional type suitable to grind the unpulverized fuel to a degree of fineness appropriate to be fed to the burners. The mill is supplied by the customary raw fuel feeder 2 adapted to feed such fuel to the mill in variable amounts. A fan 3 forces the fuel from the mill thru connection 4. In the diagrammatic representation of Fig. 1 this fan conveyor is shown as an air blower which exhausts the mill by drawing air thru it. The suspended fuel is conveyed in a stream thru pipe 5 to valve 6 which embodies a means for dividing the suspended fuel stream, one portion of the thus divided stream passing to the burner and the other thru the annular space 1 of variable size into chamber 8, thru connecting pipe 9, and cyclically returning thru connection ID to the mill and thence to connection 4 leading to the fan 3. An alternative arrangement of the return line 9 is shown in Fig. 3 in which the circulating reserve supply is returned to connecting line 4 thru connection Ill. This connection may be placed at any point in advance of the fan. The expedient of returning the circulating reserve supply in such a way that it will again pass thru the mill affords the further advantage of subjecting this fuel to additional grinding action. While this further grinding is not essential to my invention, since the fuel in the cycle has been previously reduced to sufiicient fineness, it is advantageous to reduce the fuel to as fine a condition as possible due to the added combustion eiiiciency attained.

The referred to valve 6 may be any suitable type of valve adapted to divide a stream of suspended fuel into two portions. In one particular advantageous form which is diagrammatically represented in Fig. 1 and shown in greater detail in Fig. 2, this valve comprises a movable pipe I! disposed in such a way that it may be moved parallel to the axis of pipes 5 and i2. Movable pipe H and fixed pipe 5 are equipped with flared ends disposed in such a way that by varying the position of movable pipe H the size of the annular space I may be varied as indicated by dotted lines in Fig. 2.

The size of the annular space i is thus regulated in order to permit a controlled amount of suspended fuel to pass thru pipe ll into connecting pipe 52 and thence to the burner. The amount of fuel permitted to pass thru said connecting pipe H is determined by the immediate requirements of the burner. When an increased amount of heat is required the valve 6 is partially closed thus immediately causing a larger proportion of the suspended reserve fuel supply, which would otherwise be circulated back to the mill, to enter the burner via pipes H and I2 by decreasing the amount of suspended fuel which is permitted to circulate. Conversely when a lesser amount of heat is desired the valve is opened further and an increased proportion of fuel is diverted and recirculated. While I have referred herein to a single burner it will be understood that any number of burners consistent with the capacity of the apparatus may be fed thru a single fuel valve.

The fuel valve 5 is regulated by any suitable means of control. In the diagrammatic representations I have illustrated one advantageous method of control which may be used when the apparatus of the instant invention is employed to regulate the heat developed in a boiler. Thus, in Fig. 1, valve 6 is actuated by control lever l3 whose motion is governed by an automatic combustion regulator M which in turn is automatically controlled by the amount of steam drawn from the boiler. The control means l5 for regulating the unpulverized or raw coal feeder is with advantage also connected to regulator [4, thus making. possible a correlated control of the amount of unpulverized fuel fed to the mill and of the amount of pulverized fuel fed to the burner. It is to be noted that an interconnection between control means i3 and I5 is not essential. If there is no such actual connection, a fairly close coincidence of operation should be maintained between the two control means in order that the circulating reserve supply of fuel is not exhausted or overloaded.

While the above described embodiment provides a successful means of regulation, I prefer to incorporate in connecting pipe 5, a means (l6) for inducing centrifugal force on the stream of suspended fuel thereby producing a greater concentration of the fuel in the vicinity of the perimeter of the tube. This effect may be accomplished by mounting in the tube a fixed spiral, or twisted blade suitably supported by being attached to a rod or tube as an axis, or supported directly by the walls of pipe 5, such as illustrated in Fig. 1, at it. By the incorporation of such a centrifugal separator which increases the density of the fuel at the outside of the tube, the diversion of the excess fuel is more readily accomplished. Thus a much smaller annular area 7 in valve 6 is necessary to produce a larger effect on the amount of fuel diverted from the stream since the variable annular opening is located adjacent the periphery of the tube. The blades or vanes on the centrifugal separator are given the proper inclination to impart a maximum amount of swirling motion to the stream of suspended fuel consistent with the passage of the normally required volume of fuel thru the center H of the control valve. A further advantage of incorporating such a device in the connecting pipe is that the coarser particles will tend to concentrate at the outside thus permitting the finer and more desirable fuel to be passed to the burners, and the heavier particles, altho of sufficient fineness to be used toremain suspended in the circulating reserve supply. The arrangement of the return pipe illustrated in Fig, 1 is of particular utility Where a separator is used, since the coarser particles are returned to the mill for further grinding during the course of their circulation.

In the alternative embodiment, the apparatus of the present invention is illustrated diagrammatically in Figs. 4 and 5. In this embodiment the means for regulating the amount of suspended fuel fed to the burners, and concurrentl the amount circulated in the reserve siupply assumes the form of a damper valve pivoted at one end as shown at H, in Fig. 5. This damper is represented in a normal position by solid lines. The suspended stream of fuel con veyed thru pipe 5 will be split by this damper, a portion passing thru opening I8 into pipe [9 which connects directly with pipe l2 leading to the burner or burners. The portion passing thru opening 28 enters a centrifugal separator 2I where the suspended fuel is largely separated from the air in which it is suspended. The fuel so separated which constitutes a portion of the immediately available reserve supply of the present invention is cyclically returned to the system at a point in advance of the circulating means. This is illustrated in Fig. 4 where the separated fuel is returned thru connection 9, and, a here illustrated, may advantageously be returned directly to the mill. The air or other gaseous medium from which the fuel has been largely separated, together with minor proportions of the finest fuel, the proportion of this latter being dependent on the efliciency of the centrifugal separator and thespeed at which it is operated, passes out of the separator thru pipe 22 and enters pipe l2 which feeds the burners. While I have described and illustrated a centrifugal separator, it will be understood that any conventional type of separater suitable to separate a substantial amount of solid material suspended in a gaseous medium from such gaseous medium, may be employed in this embodiment of my invention. By the proper control of Valve H it will be apparent that the amount of fuel fed to the burners may be instantly varied in a manner similar to that involved in the previous embodiment illustrated in Figs. 1-3. The valve I1 and the control mechanism for the amount of unpulverized fuel fed to the mill may be controlled by mechanisms similar to those discussed in connection with Figs. 1-3.

As represented in Figs. 6 and '7, one means of control for regulating the amount of pulverized fuel fed to the burners and circulated in the reserve supply may assume still another form. In this embodiment the suspended stream of fuel conveyed thru pipe 5 by the fan 3 passes into chamber 23 at 25, which point is situated opposite the outlet pipe i2 which leads to the burner. Compartment 23 is connected to a point in the system in advance of the fan by return pipe 9. The fuel supplied to the burners passes directly thru compartment 23 into pipe i2. The control means for regulating the proportion of the fuel passing thru pipe [2 to the burners, and that being circulated in the reserve supply comprises a variable centrifugal separator disposed in pipe 5. This separator consists of a flexible vane 24 disposed longitudinally within the pipe 5. One end of this vane is attached on a diameter of the pipe 5 at the outlet end 25. The opposite end of the vane is fixed on a diameter of a movable ring 26 located in advance of diameter 25, said ring being rotatable about the common axis of the pipe 5 and the ring. When the ring 26 is rotated about its axis by means of mechanism l3 which corresponds to similar mechanisms in previously described embodiments, the flexible vane is twisted about its longitudinal axis. When the vane is in a flat position, that is, when the two ends are in the same plane there is no resistance offered to the passage of the stream of fuel, and substantially all of the stream flows directly across chamber 23 into pipe l2 and thus to the burners. However, when a twist is imparted to the flexible vane a swirling motion of the fuel is instituted and a proportion of the suspended fuel, depending on the degree of twist in the vane, is caused by centrifugal force to pass outside of the opening of pipe I2. The proportion which does not enter pipe I2 is returned to the system through return pipe 9 and constitutes the immediately available reserve supply. It will be apparent that the amount of centrifugal action and consequently the amount of fuel fed to the burners may be varied by varying the degree of twist imparted to the flexible vane and that by varying the twist of this vane an instantaneous control of the fuel fed to the burners is attained. The other features in the apparatus of this embodiment are similar to those represented in the discussion of the above alternative types of apparatus useful for carrying out my invention. It will be understood that the mechanism for simultaneously controlling the degree of twist in the vane by turning the movable ring 26 and concurrently regulating the feed of unpulverized fuel to the grinding mill, as well as the centrifugal separator itself are illustrated in Figs. 6 and 7 in diagrammatic form, and this as well as other portions of the apparatus may be altered in detail without departing from the spirit and scope of the present invention. It may also be desirable to incorporate a damper 9 in return pipe 9, which may advantageously be operated in conjunction with flexible vane 24, in order to reduce the suction on chamber 23 when it is desired to feed a substantially higher proportion of the fuel stream to the burner.

While I have illustrated in diagrammatic form several specific embodiments of my invention it is to be understood that the invention is not limited to the precise forms or arrangements shown but comprehends other alternatives and mechanical equivalents of the apparatus herein illustrated and falling within the scope of the appended claims.

I claim:

1. An apparatus for supplying regulated amounts of pulverized fuel to a burner responsive to the quantity of heat units which are absorbed in a heat absorption apparatus and which are provided by combustion of pulverized fuel supplied to the burner comprising a grinding mill adapted to reduce unpulverized fuel to a degree of fineness appropriate for use in a pulverized fuel burner, means for conveying pulverized fuel suspended in a gaseous medium in a stream from said mill to the burner, a regulator responsive to the quantity of heat absorbed in the heat absorption apparatus, adjustable means disposed at a point between the mill and the burner comprising means for imparting whirling centrifugal motion to the stream of pulverized fuel and an adjustable valve disposed in the stream of pulverized fuel in the path of the fuel concentrated by said centrifugal motion for diverting a variable proportion of the pulverized fuel stream in concentrated form in an amount determined by said regulator, and means for returning said diverted portion of the fuel stream to a point in the stream of fuel flowing from the mill to the burner located in advance of the first said point.

2. An apparatus for supplying regulated amounts of pulverized fuel to a burner responsive to the quantity of heat units which are absorbed in a heat absorption apparatus and which are provided by combustion of pulverized fuel supplied to the burner comprising a grinding mill adapted to reduce unpulverized fuel to a degree of fineness appropriate for use in a pulverized fuel burner, means for supplying a controlled quantity of unpulverized fuel to said grinding mill, a forcing means for conveying pulverized fuel suspended in a gaseous medium in a stream from said mill to the burner, a regulater responsive to the quantity of heat absorbed in the heat absorption apparatus, adjustable means disposed at a point between the mill and the burner comprising means for imparting whirling centrifugal motion to the stream of pulverized fuel and an adjustable valve disposed in the stream of pulverized fuel in the path of the fuel concentrated by said centrifugal motion for diverting a variable proportion of the pulverized fuel stream in concentrated form in an amount determined by said regulator, and means for returning said diverted portion of the fuel stream to a point in the stream of fuel flowing from the mill to the burner in advance of said forcing means.

3. An apparatus f o r supplying regulated amounts of pulverized fuel to a burner responsive to the quantity of heat units which are absorbed in a heat absorption apparatus and which are provided by combustion of pulverized fuel supplied to the burner comprising a grinding mill adapted to reduce unpulverized fuel to a degree of fineness appropriate for use in a pulverized fuel burner, means for supplying a controlled quantity of unpulverized fuel to said grinding mill, a fan for conveying pulverized fuel suspended in a gaseous medium in a stream from said mill to the burner, a conduit extending from a point between the mill and the burner to a point in advance of the fan, a regulator responsive to the quantity of heat absorbed in the heat absorption apparatus, and adjustable means for diverting a variable proportion of the pulverized fuel stream in concentrated form through the conduit from said first named point, said means including means for imparting whirling centrifugal motion to the stream of pulverized fuel and an adjustable valve controlled by said regulator disposed in the stream of pulverized fuel in the path of the fuel concentrated by said centrifugal motion.

4. Apparatus for supplying regulated amounts of pulverized fuel to a burner substantially immediately responsive to variations in the quantity of heat units which are absorbed in a heat absorption apparatus and which are provided by combustion of pulverized fuel supplied to the burner which comprises a grinding mill for producing pulverized fuel, means for conveying pulverized fuel suspended in a gaseous medium from the grinding mill to the burner, means intermediate the grinding mill and the burner for imparting whirling centrifugal motion to the suspension of pulverized fuel for concentrating at least a portion of the suspension of pulverized fuel, a regulator responsive to the quantity of heat absorbed in the heat absorption apparatus, means comprising an adjustable valve disposed in the stream of pulverized fuel in the path of the fuel concentrated by said centrifugal motion for withdrawing a variable proportion of the concentrated fuel in an amount determined by said regulator, and means for returning the withdrawn portion of the concentrated fuel to said conveying means at a point intermediate the mill and said means for concentrating the suspension of pulverized fuel.

5. Apparatus for supplying regulated amounts of pulverized fuel to a burner substantially immediately responsive to variations in the quantity of heat units which are absorbed in a heat absorption apparatus and which are provided by combustion of pulverized fuel supplied to the burner which comprises a grinding mill for producing pulverized fuel, means for conveying pulverized fuel suspended in a gaseous medium from the grinding mill to the burner, a regulator re'-' sponsive to the quantity of heat absorbed in the heat absorption apparatus, means intermediate the grinding mill and the burner for concen trating at least the coarser particles of at least a portion of the suspension of pulverized fuel together with a portion of the fine particles of pulverized fuel in an amount determined by said regulator, means for withdrawing a variable pro portion of the concentrated fuel from the apparatus, and means for returning said withdrawn portion of the fuel to the grinding mill.

6. Apparatus for supplying regulated amounts of pulverized fuel to a burner substantially immediately responsive to variations in the quantity of heat units which are absorbed in a heat absorption apparatus and which are provided by combustion of pulverized fuel supplied to the burner which comprises a grinding mill for producing pulverized fuel, means for conveying pul verized fuel suspended in a gaseous medium from the grinding mill to the burner, means intermediate the grinding mill and the burner for imparting whirling centrifugal motion to the sus pension of pulverized fuel for concentrating at least a portion of the suspension of pulverized fuel, a regulator responsive to the quantity of heat absorbed in the heat absorption apparatus, means for withdrawing a variable proportion of the concentrated fuel in an amount determined by said regulator, said means comprising an adjustable valve having an annular opening of variable size disposed in the path of flow of the concentrated fuel, and means for returning the withdrawn portion of the concentrated fuel to said conveying means at a point intermediate the mill and said means for concentrating the pulverized fuel.

7. Apparatus for supplying regulated amounts of pulverized fuel to a burner substantially immediately responsive to variations in the quantity of heat units which are absorbed in a heat absorption apparatus and which are provided by combustion of pulverized fuel supplied to the burner which comprises a grinding mill for producing pulverized fuel, means including a cylindrical conduit for conveying pulverized fuel suspended in a gaseous medium from the grinding mill to the burner, means intermediate the grinding mill and the burner for imparting whirling centrifugal motion to the suspension of pulverized fuel for concentrating at least a portion of the puverized fuel adjacent the outer confining sur face of the cylindrical conduit, said conduit terminating in an end portion of reduced cross-section, a movable conduit having a flared end disposed within said cylindrical conduit and adapted to provide in the path of the fuel concentrated by said centrifugal motion an annular opening of variable size depending upon the position of the flared end of the movable conduit with respect to the reduced end portion of the cylindrical conduit, a regulator responsive to the quantity of heat absorbed in the heat absorption apparatus, means for controlling the size of the annular opening responsive to said regulator, and means for returning the portion of concentrated fuel passed through said annular opening to the cylindrical conduit at a point intermediate the mill and said means for concentrating the pulverized fuel.

8. An apparatus for supplying regulated amounts of pulverized fuel to a burner responsive to the quantity of heat units which are absorbed in a heat absorption apparatus and which are provided by combustion of pulverized fuel supplied to the burner comprising a grinding mill adapted to reduce unpulverized fuel to a degree of fineness appropriate for use in a pulverized fuel burner, means for conveying pulverized fuel suspended in a gaseous medium in a stream from said mill to the burner, a regulator responsive to the quantity of heat absorbed in the heat absorption apparatus, adjustable means disposed at a point between the mill and the burner comprising means for imparting whirling centrifugal motion to at least a portion of the stream of pulverized fuel and an adjustable valve disposed in the stream of pulverized fuel for controlling the amount of fuel to be returned to the stream of fuel flowing from the mill to the burner in the form of a stream of fuel concentrated by said centrifugal motion, said controlled amount of fuel being determined by said regulator, and means for returning the stream of fuel concentrated by said centrifugal motion to a point in the stream of fuel flowing from themill to the burner located in advance of the first said point.

9. An apparatus for supplying regulated amounts of pulverized fuel to a burner responsive to the quantity of heat units which are absorbed in a heat absorption apparatus and which are provided by combustion of pulverized fuel supplied to the burner comprising a grinding mill adapted to reduce unpulverized fuel to a degree of fineness appropriate for use in a pulverized fuel burner, a regulator responsive to the quantity of heat absorbed in the heat absorption apparatus, adjustable means for supplying a controlled quantity of unpulverized fuel to said grinding mill, a forcing means adapted to force a stream of pulverized fuel suspended in air through a pipe connected to the outlet of the grinding mill, a connecting pipe between said forcing means and the burner, means situated in said connecting pipe for diverting a portion of the pulverized fuel stream in an amount determined by said regulator, a centrifugal separator for separating a substantial portion of the suspended fuel from the gaseous medium of said diverted portion of the fuel stream, a connection for returning the thus separated fuel to a point in the stream of fuel flowing from the mill to the burner located in advance of the forcing means, and a connection for conveying to the fuel burner the gaseous medium from which a substantial portion of the suspended fuel has been separated. HOWARD R. BARTON.

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