US2955879A

US2955879A - Ash feed control

Info

Publication number: US2955879A
Application number: US728990A
Authority: US
Inventors: Edgar B Tolman
Original assignee: United Conveyor Corp
Current assignee: United Conveyor Corp
Priority date: 1958-04-16
Filing date: 1958-04-16
Publication date: 1960-10-11
Anticipated expiration: 1977-10-11

Description

Oct. 11, 1960 E. B. ToLMAN ASH FEED CONTROL Filed April 1s. 1958 atet ge l 2,955,379

Patented Oct. 11, 1960 ASH FEED CONTROL Edgar B. Tolman, Winnetka, DI., assigner to United Conveyor Corporation, a corporation of Iliinois Files Apr. 16, 195s, ser. No. 728,990

9 claims. (ci. 3oz-s2) This invention relates to apparatus for feeding ash from a furnace to a storage bin, and in particular it relates to mechanism for controlling the rate of flow of ash into a vacuum or other pneumatic conveyor system.

Ash from high efficiency coal furnaces of the type used in electric power generating plants is exremely tine, and presents special problems in handling and disposition. A modern electric generating plant produces several tons of ash per hour, and this is conveniently handled in vacuum conveyor systems. Because the ash is eX- trernely tine, it is quite diflcult to handle due to arching, slumping of large masses of ash into the conveyor conduit, and other phenomena which produce uneven flow through the vacuum system and into a storage bin.

The ash handling system for a high capacity electrtic power plant commonly has severalA hoppers which receive ash from each furnace, and these hoppers act as temporary receptacles from which the ash is fed into the vacuum conveyor conduit for transmission to the storage bin. Conveniently, the system is arranged to handle ash from one boiler, or furnace, until all of the hoppers serving that furnace are exhausted; after which the system is switched so that ash is fed from the hoppers serving another furnace. The present system provides relatively even flow of ash from all of the hoppers serving a single furnace so as to minimize clogging ofthe vacuum conveyor conduit, and also permits all the associated hoppers to remain in communication with the vacuum conduit even though one hopper may empty sooner than another. This, of course, simplies the control mechanism by making it unnecessary to close o the discharge opening of an empty hopper while the associated hoppers are still discharging. A group of associated hoppers may be put intoV the ash discharging cycle at the same time, and the control mechanism need not provide for segregating one or more hoppers of the group while the others are feeding. Feed of ash from the entire group of hoppers is terminated at one time, and the system may then be switched to another group of hoppers serving another furnace.

The operation of a vacuum conveyor system requires that the rate of flow of ash into the vacuum conduit remain fairly uniform. A certain negative pressure is required in the vacuum conduit merely to overcome the internal resistance of the system. The vacuum, of course, must be increased to overcome the added resistance to ow which results from introducing ash into the conduit. Accordingly, a system which has an air exhauster adapted to produce a particular negative pressure in the system will clog if a large quantity of ash suddenly enters the conduit. As long as the ash load remains constant at the optimum for the particular conveyor system, the vacuum remains constant. -If excess material enters the conduit, the iiow of air through the system is inhibited, and this increases the negative pressure in the conduit between the air exhauster and the excess load of ash. Conversely, if the volume of ash entering the conveyor conduit is reduced, the vacuum ahead of the air exhauster becomes less. This fact is utilized in the present system to control the feed of ash into Vthe conduit by means of suitable vacuum controlled valves.

Each hopper in the present system is provided with an ash feed-opening, and associated with the ash feed opening is a conventional mechanism for fluidizing the ash so that it flows readily through the opening. The feed of ash is not controlled by opening and closing the feed openings, but instead is controlled by starting and stoppin-g the flow of iiuidizing air to the fluidizing units associated with the feed openings. The Vacuum controlled valves admit fluidzing air until such time as au increase in the vacuum of the system results from excessive ash in the conduit; and this increase in vacuum is utilized to suspend the aerating air until the vacuum in the system again decreases to the point where the system can handle additional ash, at which point the ow of aerating air is resumed.

The present disclosure deals only with pressures which are below atmospheric, so in the specification and claims the word minimum is used to refer to a pressure nearest to atmospheric, while maximum refers to a pressure farther from atmospheric. p Intermediate refers to a pressure -between maximum and minimum, reduction of vacuum means that the vacuum system approaches atmospheric pressure.

The invention is illustrated diagrammatically in the accompanying drawing, which illustrates the control for two hoppers which feed into the vacuum conduit simultaneously. When. thetwo illustrated hoppers are empty, they are segregated from the conduit and a similar group of hoppers (not illustrated) is placed in communication with the conduit under a similar control system.

Referring to the drawing in greater detail, the system includes hoppers,-indicated generally at 1 and Z, which are provided respectively, with outfeed mechanisms, indicated generally at 3 and 4. Each hopper is the bottom portion of a centrifugal or electrostatic separator of conventional design, which separates ash from the hot air coming out of a furnace. Outfeed mechanisms 3 and 4 have discharge pipes 5 and 6, respectively, which are connected to a vacuum` conduit 7; and the conduit 7 feeds through a conventional centrifugal separator S where the ash is removed from the conveying air stream for deposit in a storage bin 9. From the separator 8, the air passes through a suction conduit 16; and air iiow through the system is provided by conventional fluid operated air exhauster, indicated generally at 1i.

The flow of ash into the conduit 7 from the feed mechanisms `3 and L- is controlled by a vacuum system indicated generally at 12, which includes a vacuum control pipe i3 connected to the vacuum conduit 1?.

The two ash hoppers and their associated ash feed mechanisms are identical, so only the hopper l and the feed mechanisms, 3 are described in detail. Each hopper has a continuous upright side wall 14 which is the lower part of a separator, and which merges into a frustopyramidal bottom f5 provided with a discharge throat 16 through which ash enters the feed mechanism 3. in the bottom portion 1S of the hopper is an arrangement of fluidizing stones i7 which are spaced apart to aiford a passage 18 through which ash flows to the throat i6. The hopper construction here disclosed is disclosed and claimed in my copending application, S.N. 728,989, filed April 16, 1958.

The ash feed mechanism 3 consists of VaV chamber 19 having an inclined fluidizing stone 2l), and a feed opening 21 in one Vwall of the chamber 19 has its lower margin ush with the surface of the uidizing stone 20 so that uidized ash in the chamber 19 may ow through the pipe reached, valve 29 again opens.

obvious to those skilled in the Y Vfor the uidizing stones 17 inithe hopper 1-,7' a branch line 26 forV theiluidizing stone 20 in ythe feed mechanism 3, and

similarbranch lines

27 and 28 for the corresponding parts Yof the hopper 2 and feed mechanism 4. Y

Flow of iluidizing air toV the branch lines to 28, 'inelusive, is controlled by a solenoid valve 29, which in turn is opened and closed bya vacuum switch inthe vacuum control Vpipe 13. When the system is first started,

The feed mechanism 3 also Y 2,955,879 Y. c 'Y feed opening of sufficiently small area in proportion to the area of all of said openings thatthe reduction of vacuum thereV must Vbe a vacuum Within the conduit 7 before any ash is fed out of the hoppers. Accordingly, y Y v the vacuum switch 30 is set to open the solenoid Vvalve 29 at a predetermined minimum pressure which is suitable for the Vparticular installation. This admits low pressure air 'from the supply line 24 to the uidi'zing stones 17 and Zt? and so lluidizes, Vor aerates, the ash in the lower portions fof the hoppers Vand the associated feed mechanisms that the ash may ilow freely through the feed openings 21 into theconduit 7. As the ash load'in conduit 7 increases, the pressure in the vacuuml control pipe 13 approaches the maximum which can be properly utilized with the particular air exhausterY 11 in the system.V In

' a typical system the maximum negative pressure might be 18 inches Hg, or greater in certain types of systems.

in said conduit resulting from'the free flow of air through a hopper produces only aY small reduction in the ashmoving characteristics of the apparatus; aerating means for simultaneously aeratingV the ash in all said chambers; a solenoid valve for controlling said air supply; and a vacuum controlled electric switch in said vacuumV systemV for operating Ysaid valve in accordance with predetermined pressures in said system,wwhereby the aerating means operates to facilitate flow of ash from thehoppers'to the conveyor system when the pressure in said system is within a predetermined range.

2. Apparatus for feeding ash at aeontrolled rate; comprising: a plurality of ashV receiving hoppers; a vacuum conveyor conduit; an outfeed mechanismV for each hopper, eachsaid mechanism including an Yaerating chamber having a constantly open feed opening through which ash passes from the hopper to said conduit, the area of each opening being sufficiently small in proportion to the total area of all said openings that the reduction of vacuum in said conduit resulting from freeflow of air through a hopperproduces only a small reduction in the ash moving characteristics of the apparatus;` means for aerating ash in each of said chambers to facilitate theow of ash from said hoppers to said conduit; and means controlled by the amount of ash in saidconduit for selectively actuating said aerating means.

If the ratevofilow of ash into the conduit 7 is heavy Y enough to bring the negative pressure in the vacuum control pipe 13 above the optimum of 18 inches Hg, the pressure acts upon the vacuum switch'30 lto close the solenoid valve 29 and'thus suspend the ow of aerating air to the stones 17 and 20.1-A Flow of ash into conduit 7 is thereby `suspended and the pressure -in the control pine 13l approaches an intermediate pressure at'which efficient operation of the system Yrequires that the ow of ash be resumed. ,When the intermediate pressure is The pressure difference between the suspension of flow and resumption of flow may be 3 or 4 inchesHg. Thus uidizer 20 constitutes ow control means positioned between hopper 1 and conduit 7 to control the movement of ash from the hopper to the conduit and varies rapidly between a first condition which permits no movementof ash into therconduit and a second condition Ywhich permits maximum movement of ash into the conduit'.

A great advantage of the present system is'that it permits the use of feed openings 21 from the feed mechanisms which are lsmall enough that the valve 22 need not still feeding.V The ash owis controlled entirely by fluidi izing it, andthe valves 22 are closed only when allthe hoppers of a group are emptied.' The system is illus- Y trated with only 2 hoppers in a group, but a typical large ness of understanding only and no unnecessary limitations should be understood therefrom, as modifications will be I claim: Y

l. Apparatus for feeding ash at a controlled vrate com- 70 ,Y A Y Y Y 'prlslngz Yan ash receiving hopper; an ash outfeed mechapr'ising: a pluralityof ash `receiving hoppers; a vacuum being one such mechanism in communication between `be closed if the Vhopper 1 is Vempty and the hopper 2 is V3. Apparatus for feeding Vash at af controlled rate, comprising: a -vacuum conveyor conduit; vacuum means for drawing air through'said conduit to move a predeter- I mined volume of ash per unit time; dust,collector means to receive ashmoved through said conduit; a pluralityV of ashreceiving hoppers; a separate aerating chamberin direct communicationvwith each of said hoppers,V each f said aerating `chamber having an outlet orifice' in communication with said conduit, the area ofA a singleoriiice being so Vsmall in proportion to the total area of al1 said oricesthat the reduction of vacuum Vin said conduit resulting from free flow of airthrough a'hopper produces only a small reduction inthe ash moving characteristics of the apparatus;,means for aeratingrthe ashV in all said aeratingV chambers; and control meansrto limit the operation of said aerating means in accordance with the level of vacuum in the conduit.V I

4. AApparatus for feeding ash'at acontrolledrate, comprising: a vacuum conveyor conduit; vacuum means for drawing air through said conduit to move a predetermined Y Y volume of ash per unit time;V dust collector means to receive ash moved through said conduit; a plurality of ash receiving hoppers; a separate aerating chamber in direct communication with each of said hoppers, each Ysaid aerating chamber having an outlet orifice in communication with said conduit, the area'of a single oriice beings'o small in proportion to the .total area of all said orifices Y that' the, reduction of vacuum in said conduit resulting each of said hoppersjand said vacuum system, eachoutfrom exhaustion ofthe ash from any oneihop'per produces only a small reduction in the-ash moving characteristics of the apparatus; means-forV aerating the ash in allrsaid aerating chambers; a valve controlling ,the flow of air to 'said aerating meanvsfand vacuum'operated control means 'for said valve in'communication with said Vacuum conveyor system to open and close said valve when the conduit is under vacuum, lsaid control means being'constructed' andgarranged to stop the ilow of aerating air 'when the pressure in the system reaches a predetermined vmaximum, and torresume the flow of said. aerating air Vwhen said-pessurereaches a predetermined intermediate level.Y Y 1' Y' 5. uApparatus for feeding yash at aV controlled rate, comnism connected with the bottom of said hopper, said outtrolling the ow of air to said aerating means, said valve being of a type which has only a fully open and a fully closed position; a vacuum conveyor system to transport ash discharged through said feed opening, said system including a dust collector and means for discharging ash from said collector to a storage bin; means for producing a negative pressure in said vacuum `ssytem; starting means for fully opening said valve when the negative pressure in the system reaches a predetermined minimum; and control means which responds to variations in the negative pressure in said vacuum system to fully open and fully close said valve while the conveyor system is under vacuum, said control means being constructed and arranged to fully close said valve when the negative pressure in the system reaches a predetermined maximum, and to fully reopen said valve when said pressure reaches a predetermined intermediate level between said minimum and maximum pressures.

6. Apparatus for feeding ash at a controlled rate, comprising: an ash receiving hopper; a pneumatic conveyor conduit; air moving means for producing in said conduit an air pressure different from atmospheric pressure; flow control means positioned between said 'hopper and said conduit to control the ow of ash from the hopper to the conduit, said flow control means including a chamber having a feed opening of restricted size in a side wall, said chamber being providing with aerating means to iluidize material for free ow through the opening, iand a movable valve for selectively closing said opening, and said flow control means varying rapidly between a first condition permitting no ow of ash and a second condition permitting maximum ilow of ash through said opening; and control means which responds to the pressure in the conveyor conduit to control said ow control means by varying it between said rst and second conditions, said control means being constructed and arranged to place said flow control means in said second condition when pressure in the conduit reaches a rst level close to atmospheric pressure at which flow of ash into the conduit is desired, to return said ilow control means to said first condition when excessive ash in the conduit causes pressure to reach a second level a maximum distance from atmospheric pressure, and thereafter to restore said flow control means to said second condition when reduction of the quantity of ash in the conduit has caused pressure in the conduit to reach a predetermined intermediate level between said rst and second pressures.

7. Apparatus for feeding ash at a controlled rate, comprising: an ash receiving hopper; a pneumatic conveyor conduit; air moving means for producing in said conduit an air pressure different from atmospheric pressure; flow control means positioned between said hopper and said conduit to control the flow of ash from the hopper to the conduit, said flow control means including a chamber having a feed opening of restricted size in a side wall, said chamber being provided with aerating means to fluidize material for free flow through the opening, and said flow control means varying rapidly between a rst condition permitting no ow of ash and a second condition permitting maximum flow of ash; an air valve which closes to place said flow control means in s'aid first condition and which opens to place said means in said second condition; and control means which responds to the pressure in the conveyor conduit to open and close said air valve, said control means being constructed and arranged to completely open said air valve when pressure in the conduit reaches a rst level close to atmospheric pressure at which flow of ash into the conduit is desired, to completely close said valve when excessive ash in the conduit causes pressure to reach a second level a maximum distance from atmospheric pressure, and thereafter to again completely open said valve when reduction of the quantity of ash in the conduit has caused pressure in the conduit to drop to a predetermined level between said rst and second pressures.

8. Apparatus for feeding ash at a controlled rate, comprising: an ash receiving hopper; a pneumatic conveyor conduit; air moving means for producing in said conduit an air pressure dilferent from atmospheric pressure; flow control means positioned between said hopper and said conduit to control the flow of ash from the hopper to the conduit, said yflow control means including a chamber having a feed opening of restricted size in a side wall, said chamber being provided with aerating means to fluidize material for free flow through the opening, and said flow control means varying rapidly between a rst condition permitting no flow of ash and a second condition permitting maximum flow of ash; starting means for placing said i'low control means in said second condition when pressure in the conduit reaches a rst level close to atmospheric; and control means constructed and arranged to place said low control means in said first condition when excessive ash in the conduit causes pressure to reach a second Ilevel a maximum distance from atmospheric pressure, and thereafter to restore said ow control means to said second condition when reduction of the quantity of ash in the conduit has caused pressure in the conduit to reach a predetermined intermediate level between said rst and second pressures.

9. Apparatus for feeding ash at a controlled rate, cornprising: an ash receiving hopper; a vacuum conveyor conduit; air moving means for producing a negative pressure in said conduit; flow control means positioned between said hopper and said conduit to control the flow of ash from the hopper to the conduit, said flow control means including a chamber having a feed opening of restricted size in a side wall, said chamber being provided with aerating means to iluidize material for free flow through the opening, and said -ow control means varying rapidly between a lirst condition permitting no flow of ash and a second condition permitting maximum flow of ash; an yair valve which closes to place said flow control means in said first condition and which opens to place said means in said second condition; starting means for opening said air valve when the negative pressure in the conduit reaches a predetermined minimum; and control means which responds to variations in the negative pressure in the conduit to open and close said valve while the conduit is under vacuum, said control means being constructed and arranged to close said valve when the negative pressure in the conduit reaches a predetermined maximum, and to reopen said valve when said pressure reaches a predetermined intermediate level between said minimum and maximum pressures.

References Cited in the le of this patent UNITED STATES PATENTS Oetiker Mar. 11, 1958