US2427903A - System for regulating the density of air-fuel mixture supplied by airswept pulverizing mills - Google Patents

Description

IITTORNEY a, m 7. 1i. H N 2 E 4. W 2 1..

foe $1 4155 IR-FUEL MIXTURE J. CRITES TING THE DENSITY OF A Y AIR-SWEPT PULVERIZING MILL Filed May 3, 1944 SUPPLIED B SYSTEM FOR REGULA Sept. 23, 1947.

Patented Sept. 23, 1947 SYSTEM FOR F AIR-FUE nnoum'rmo THE nnusrrr r. MIXTURE SUPPLIED BY AIR- SWEPT PULVERIZING MILLS Joe Crites, Evanston,

Compa y, -r

Ill., assignor to Combustion New York, N. Y.

Application May 3, 1944, Serial No. 533,974

4 Claims. (01- 241-33) coal and air than is ordinarily required is constantly circulated through the main ducts. The

excess provides a fuel reserve so that several fur-- naces may be fired simultaneously while having good control over the amount of coal going to each furnace by drawing upon the reserve.

An object of this invention is to improve such a system for supplying pulverized fuel to furnaces.

A second object is to provide novel control means in a system of the type described for maintaining the proper density of the fuel and air in the main duct from which the furnaces are supplied. l

Another object is to provide in a system of the type described improved means for causing fuelfree air to be recirculated through the pulvermen In the accompanying drawing the single figure is a diagrammatic representation of a system for supplying pulverized fuel to a plurality of furnaces in accordance with the invention.

Raw fuel is fed into a pulverizing mill III by a feeder II and air for carrying fuel is delivered to the mill through a conduit l2. The fuel-laden air leaves the mill through a conduit l3 and then fiows into the part of the main fuel delivery duct 2| and through a Venturi metering device is. Just ahead of metering device l8 additional pulverized fuel is introduced into duct l5 from a storage bin l5 through a duct II. The enrichened fuel-air mixture then passes from metering device l8 to a fan by which it is delivered-into the main duct 2!. Coal from the main duct 2! is taken off through valved branch pipes 22, 23 and 24 to supply the individual furnaces. The coal and air mixture not used by the furnaces is delivered by the main duct 2! to a cyclone collector 25 and is therein separated, the coal passing downwardly into bin i6 and thence through the power operated feeder or air lock 26 into duct E5. The separated air from cyclone 25 passes into H so as to maintain a a duct 21 and is returned therethrough to mill inlet duct l2. In return duct 21 is a metering device 28. A hot air supply pipe 30 connects into return duct 21 just ahead of metering device 28. Dampers 3i and 32 are provided in ducts 21 and 30 as shown. I

The metering devices l8 and 28 control a regulating device for varying the speed of the drive shaft 33 of the feeder II for the mill III.

In the main' duct 2! there is provided a pressure responsive device which actuates a motor 5| to regulate a damper 52 in'the inlet of fan 20. A thermostat 53 is provided .in the outlet of mill In which controls motors .5, to regulate the dampers 3| and 32 in the returned air duct 21 and fresh hot air duct 30.

It will be appreciated that various types of apparatus may be employed for measuring the flow of air to the mill and the amount of coal and air moving inrthe main supply duct 2| and then utilizing these measurements to regulate the speed of operation of the raw coal feeder determined density in the coal and airmixture in duct 2|. Therefore, it is to be understood that the particular mechanism shown in the drawings and described hereinafter is purely illustrative. As shown, variations in the amount of air flowing through the metering device 28 control a diaphragm motor 35 connected to the arm 36 of a lever having its fulcrum at 31 intermediate its ends. The metering device I 8 that measures the flow of the coal and air mixture controls another diaphragm motor 40 connected to the lever arm 38 at the other side of the fulcrum. The outer end of the arm 33 carries a pawl shield ll whose position with reference to a ratchet 42 determines the effective stroke of a pawl 43 movable through a predetermined are by a constant speed motor 44. The ratchet 42 is associated with the drive shaft 33 for the feeder H so that as the volume of coal and air mixture flowing through the metering device It increases the motor 40 tends to move the pawl shield ll so as to obscure a greater number of teeth on ratchet 42 so that the pawl 43 is effective toturn the ratchet 42 a lesser distance andthereby drive the mill feeder it during a smaller part of the effective stroke of the pawl. Conversely, as the volume of coal and air decreases the shield ll is positioned to obscure fewer of the teeth of the ratchet 42 and thereby increase the rate of operation of the feeder H. Inasmuch as the motor 35 associated with the air metering device 28 is connected to the lever arm 35 at the opposite side of the'fulcrum. an

3 increase in the amount of air flowing to the mill tends to increase the rate of operation of the feeder Conversely, a decreased amount of air decreases the rate of operation of the raw coal feeder.

The net result of the control imposed by the metering devices I. and 28 on the feeder II is to increase the rate of operation of the feeder as the differential between the amount of coal andair passing through the metering device it and the volume of air flowing through the meter 28 becomes less and vice versa. Expressed differently the two metering devices serve to control the feeder II in response to fluctuations in the density of the coal and air mixture flowing through the duct 2|, increasing the feed as the density falls and vice versa.

Since all of the air that passes through metering device It with the coal both from mill i and bin I 6 must first pass through metering device 28. the reactions or indications of the former compared with those of the latter represent the differential between air supplied and the total of coal and air mixture. Consequently their opposite reactions upon lever 26, 28 tend to establish a condition of equilibrium representing a desired ratio of coal to air, or the density of the coal-air mixture, and this may be varied by adjustment of the force of a spring 60 connected to the arm 24 of the lever so as to tend to move it counterclockwise. Recapitulated, the pressure responsive device 54 causes the rate of fuel, circulation to increase or decrease with demand by the furnaces while the metering devices i8, 22 act to increase or decrease the rate of raw coal supply by feeder l| so as to maintain a predetermined density of coal and air mixture at various loads.

In operation coal pulverized in the mill III is circulated by fan 24 through the main duct 2| and any of the mixture not withdrawn by furnace connections 22-22-24 is discharged into separator 25. The clean air separated in cyclone 25 flows through return ducts 21 and I2 to the mill from which it carries the pulverized coal back into the main duct. The coal separated in cyclone 25 is fed back into the main duct l5, 2| through the bin II and air lock 22. The quantity of air flowing in the system is measured before it enters the mill II by metering device 22. The quantity of coal and air mixture circulating in the system is measured by metering device I! after the returned coal from the separator 25 and bin It has been added to thatsupplied by mill I 0. The amount oi coal circulating in the system is then regulated in response to the differential between the air metering device 28 and the coal and air mixture metering device It, which in the case of Venturi meters would be the differential of their difl'erential pressures. If this differential increases the rate of feed to the mill is reduced and if the differential decreases the rate of feed to the mill is increased.

The mill outlet temperature is regulated by a thermostat 52 to insure a sufficient drying of the coal in the mill, the dampers 2| and 22 which proportion the amount of returned air to hot air being automatically responsive to thermostat 52. The pressure responsive device duct 2| controls the fan inlet damper means of motor II and thereby maintains 52 by a sub- 50 in the main.

stantially constant pressure in the system for a given rating of the system.

The rotary air lock or feeder 22 is preferably operated at such a speed that the amount of excess coal does not build up too fast in the system 4 during the starting up period but would accumulate in the bin it with all of the fuel branch outlets 22. 22 and 24 for the furnaces shut 01!. However, when all of these fuel outlets are opened, less coal is returned to the bin and the bin preferably remains empty, merely forming part of the coal duct. During normal operation it is preferable that no fuel be stored in the bin ll.

Suppose, for example, that during operation of one or more furnaces at a predetermined rate the valves in the fuel lines to the furnaces 22, 22 or 24 which are already open are opened further or additional furnaces are started up. This is reflected by a reduction of pressure in the main duct 2| and the pressure responsive device ll opens the damper 52 at the inlet Ila of fan 24 and causes the pressure in the main duct 2i to return to normal thereby correspondingly increasing the air flow through the system. More coal now taken out of the system results in reducing the differential pressure between metering devices 28 and It so that the regulating device speeds up the feeder thereby increasing the amount of the coal fed to the mill It. With more coal going in the mill the temperature drops and is registered on the thermostat 82 which in turn acts to close damper 2| and open damper 22 permitting more hot air to enter the system.

In shutting down the system the mill feeder II is stopped. then the mill it. When the mixture to the furnace becomes too lean the valves in the furnace ducts 22, 22 and 24 are closed and the rotary air lock 26 stopped. The small amount of coal that remains in the system is stored in bin l6 and is available for starting up.

An additional metering device 2| may be installed between mill iii and duct I! as shown so that the reading on this meter can be compared with the reading on metering device II to determine the amount of coal being returned to the system from the surge bin ll.

When there is an excess amount of air in the system it escapes through the vent 02 for separator 25. This occurs for example when all the valves to the furnaces are closed.

While I have shown and described a preferred embodiment of my invention, it is to be understood that many changes in the construction, combination and arrangement of parts may be made without departing from the spirit and scope of the invention as claimed.

What I claim is:

1. In a fuel pulverizing system comprising an air-swept pulverizing mill, means for feeding raw fuel into the mill, a first conduit for admitting clean air into the mill, a distributor duct conveying freshly pulverized fuel from the mill in fluent mixture with said air, fan means for moving said fuel-air mixture through the duct, and utilizer means connected with the duct and withdrawing varying portions of said moving fuel-air mixture therefrom, the combination of a separator receiving from the duct the unwithdrawn portions of said fuel-air mixture and functioning to dlsentrain the received pulverized fuel from the received air, a surge bin for collecting the pulverized fuel disentrained by said separator, means connected with said surge bin for returning that collected fuel at a controlled rate into said distributor duct at a point between the mill and said utilizer means connection, means responsive to internal pressure in the utilizer-connection portion of said duct for admitting fuelair mixture into that portion at a rate which keeps said pressure substantially constant, metering means in said distributor duct for measuring the total flow therethrough of freshly pulverized and returned fuel and air mixture, other metering means in said first conduit for measuring the total flow of clean air into said mill, and means jointly responsive to both of said metering means for so governing the rate of said raw fuel feed into the mill as to keep within given limits the ratio of fuel to air in the mixture supplied as aforesaid to the utilizer connection portion of the distributor duct.

2. In a fuel pulverizing system comprising an air-swept pulverizing mill, means for feeding raw fuel into the mill, a first conduit for admitting heated fuel-free air into the mill, a distributor duct for conveying freshly pulverized fuel from the mill in fluent mixture with said air, fan means for moving said fuel-air mixture through the duct, and utilizer means connected with the duct and withdrawing varying portions of said moving fuel-air mixture therefrom, the combination of a separator receiving from the duct the unwithdrawn portions of said fuel-air mixture and functioning to disentrain the received pulverized fuel from the received air, means for introducing a portion of the fuel-free air from said separator into said first conduit for re-use as mill sweeping air, surge bin means for collecting the pulverized fuel disentrained by said eparator and for returning that fuel at a controlled rate into said distributor duct at. a point between the mill and said utilizer means connection, means responsive to internal-pressure in the utilizer-connection portion of said duct for admitting fuel-air mixture into that portion at a rate which keeps said pressure substantially constant, metering means in said distributor duct fL measuring the total flow there-through of freshly pulverized and returned fuel and air mixture, other metering means in said first conduit for measuring the total flow of fuel-free air into said mill, and means jointly responsible to both of said metering means for so governing the rate of said raw fuel feed into the mill as to keep within given limits the ration of fuel to air in the mixture supplied as aforesaid to the utilizerconnection portion of the distributor duct.

3. In a fuel pulverizing system comprising an air-swept pulverizing mill, means for feeding raw fuel into the mill, a distributor duct for conveying a. mixture of freshly pulverized fuel and air from the mill, fan means for moving said fuelair mixture through the duct, and utilizer means 6 connected with the duct and withdrawing varying portions of said moving fuel-air mixture therefrom, the combination of a separator receiving from the duct the unwithdrawn portions of said fuel-air mixture and functioning to disentrain the received pulverized fuel from the received air, a surge bin for collecting the pulverized fuel disentrained by said separator, means connected with said surge bin for returning that collected fuel at a controlled rate into said distributor duct at a point between the mill and said utilizer connection whereby same recirculates through the duct with said mixture of freshly pulverized fuel and air from the mill, and a conduit for carrying a portion of the fuel-free air from said separator back into said mill for re-use as mill sweeping air.

4. In a fuel pulverizing system comprising an air-swept pulverizing mill, means of feeding raw fuel into the mill, a distributor duct for conveying a mixture of freshly pulverized fuel and air from the mill, fan means for moving said fuelair mixture through the duct, and utilizer means connected with the duct and withdrawing varying portions of said moving fuel-air mixture therefrom. the combination of a separator receiving from the duct the unwithdrawn portions of said fuel-air mixture and functioning to disentrain the received pulverized fuel from the received air, a surge bin for collecting the pulverized fuel disentrained by said spearator, and means connected with said surge bin for returning that collected fuel at a controlled rate into said distributor duct at a point between the mill and said utilizer connection whereby same recirculates through the duct with said mixture of freshly pulverized fuel and air from the mill.

JOE CRI'I'ES.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,541,903 Crites June 16, 1925 2,292,243 Schwartz Aug. 4, 1942 1,365,663 Covert Jan. 18, 1921 551,098 Russell Dec. 10, 1895 1,627,766 Bergman May 10, 1927 861,514 Hassan July 30, 1907 2,012,934 Hardgrove Aug. 27, 1935 1,898,086 Frisch Feb. 21, 1933 2,403,976 Harvey July-16, 1948

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