US2780186A - Feeding pulverized fuel for combustion - Google Patents

Description

Feb. 5, 1957 L v ANDREWS 2,730,186

FEEDING PULVERIZED FUEL FOR COMBUSTION FiledApril 14, 1950 L J/ANDREWJ ATTORNEY United States Patent FEEDING PULVERIZED FUEL FOR COMBUSTION L V Andrews, Worcester, Mass., assignor to Riley Stoker (ilorporation, Worcester, Mass., a corporation of Massac usetts Application April 14,1950, Serial No. 155,959

1 Claim. (Cl. 110-106) This invention relates to the feeding of pulverized fuel for combustion, and more particularly to an improved apparatus for preparing pulverized fuel and transporting it on a current of air directly to a furnace for combustion therein.

It is a common practice to grind coal or similar fuel to a fine powder in a suitable pulverizer, viz. a machine of the rotary beater type, such apparatus usually including a fan arranged to produce a current of so-called primary" air which carries the fine coal in suspension to a furnace burner. The rate of combustion is controlled by regulating the supply of coarse coal to the pulverizer. An increase in the rate of coal feed tends to reduce the rate of primary air flow through the pulverizer, and at high rates of coal feed the air flow may be insufficient to remove fine coal from the pulverizer fast enough to prevent congestion in the pulverizer and overloading thereof. A further difficulty is encountered in installations having two burners both of which are connected to a single pulverizer to receive fuel and primary air therefrom. If such an installation is adjusted to operate properly with both burners in service, and an attempt is made to operate with only one of the burners, it often is very diflicult to maintain ignition of the fuel at the single burner.

It is accordingly one object of the invention to provide an improved apparatus to prevent congestion and overloading in a pulverizer which supplies fine fuel to a furnace.

It is a further object of the invention to provide a simple and dependable apparatus to ensure proper ignition of fuel in an installation having two burners either or both of which may receive fuel from a single pulverizer.

With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.

In accordance with the invention, the conduit through which the stream of pulverized fuel and primary air leaves the pulverizer is fitted with an adjustable valve, and the valve adjustment is varied as required to maintain a predetermined pressure in the conduit beyond the valve. The value of Lhis pressure is increased and decreased as the rate of fuel feed to the pulverizer is increased and decreased, so that when more fine fuel is being produced there will be an increased flow of primary air through the pulverizer to prevent congestion therein. Furthermore, this will ensure the correct flow of primary air to each burner whether one or two burners are in service.

Referring to the drawings illustrating one embodiment of the invention, and in which like reference numerals indicate like parts,

The single figure is an elevation of a steam generating furnace fired with pulverized coal and provided with certain automatic control apparatus.

The embodiment illustrated comprises a steam generating furnace having two burners 1112 through which pulverized coal and air are delivered to the furnace for combustion therein to generate steam in a well-known manner, the steam being conducted by a steam outlet pipe 14 to a place of use. The coal is ground to a fine powder in a suitable pulverizer 15 having its delivery pipe 16 2,780,186 Patented Feb. 5, 1957 connected to the burners 11-12 by two branch pipes 18-19 respectively. The pipes 18-19 are provided with suitable valves 2021 respectively, so that either burner may be taken out of service if desired. The pulverizer is provided with a suitable feeding mechanism 23 which is supplied with coarse coal from an overhead bunker 24 through a downspout 25. The feeding mechanism 23 is driven by a variable-speed electric motor 27 which is supplied with electric current from a source 28 by means of wires 29. A rheostat 31 is connected into the electrical circuit to control the motor speed, the rheostat having a pivotally supported operating arm 32.

The pulverizer 15 is preferably of the rotary beater type adapted to reduce the coal to a fine powder and to deliver the powder, entrained in a current of primary air, through the pipe 16. One suitable pulverizer construction is disclosed in the prior United States patent to Craig, No. 1,714,080, granted May 21, 1929. By suitably controlling the flow of the primary air, highly beneficial results are obtained. For this purpose a valve 34 is mounted in the pulverizer discharge pipe 16 and provided with an operating arm 35, this arm being actuated by automatic regulating apparatus responsive both to the pressure within the pipe 16 beyond the valve 34 and to the rate at which coal is supplied to the pulverizer.

The particular apparatus illustrated comprises a regulator 37 of the type disclosed in the prior United States patent to Temple No. 1,992,048, granted February 19, 1935. This regulator comprises a pilot valve mechanism 38 supplied with fluid under pressure from a suitable source through a pipe 39, the valve mechanism being connected by tubes 40 to a hydraulic motor 42 which is connected by a link 43 to the arm 35 of the valve 34. The pilot valve mechanism is actuated by a lever 44 which in turn is controlled by a flexible diaphragm 45, the diaphragm being loaded by means of a coiled tension spring 47. The upper end of the spring is supported by a nut 48 mounted on a vertical screw 49 which can be raised and lowered by means of a lever 50. The pressure in the pulverizer discharge pipe 16, beyond the valve 34, is transmitted to the upper side of the diaphragm 45 by means of a pipe 52. In order to prevent this pipe from becoming blocked with coal dust, a fine screen or filter 53 of any suitable construction is mounted in the pipe 52, near its junction with the pipe 16. To facilitate cleaning of this screen, a valve 54 is provided in the pipe 52 near the screen, and a pipe 56 having a valve 57 therein is connected to the pipe 52 intermediate the valve 54 and the screen. This pipe 56 may lead from a suitable source of fluid under pressure, such as compressed air. With the valve 54 closed, the valve 57 may be opened to blow air through the screen 53 into the pipe 16, thereby clearing accumulated coal dust from the screen.

The regulator lever 50 and the rheostat arm 32 are both controlled by a regulator 59 which is responsive to the demand for heat from the furnace 10, as indicated for example by changes in the pressure of steam in the pipe 14. This regulator 59 is of the type disclosed in the United States patent to Temple No. 2,049,549, granted August 4, 1936, and it comprises a diaphragm chamber 60 and a motor 61. The diaphragm chamber 60 is connected by a pipe 63 to the steam pipe 14. The motor 61 is connected by a link 64 to a cam lever 65 which engages one end of the lever 50 to adjust the same. A link 66 connects the upper end of the link 64 to the rheostat arm 32.

The operation of the invention will now be apparent in the light of the above disclosure. With both of the valves 20 and 21 open, the pulverizer 15 will supply pulverized coal and primary air to both the burners 11 and 12, the rate of coal supply being dependent upon the speed of the feeder motor 27 which in turn will be under the control of the rheostat 31. So long as the demand for steam is steady, the pressure in the steam outlet pipe 14 will remain constant at a desired value, and this pressure will be transmitted through the pipe 63 to the diaphragm chamber 60 of the regulator 59, which will hold the cam lever 65 and the rheostat arm 32 in fixed positions. With the valve 57 closed and the valve 54 open, the pipe 52 will transmit the pressure in the pipe 16 (beyond the valve 34) to the diaphragm 45 of the regulator 37. Consequently this regulator will act in known manner, through the motor 42, to control the valve 34 as required to maintain a predetermined pressure beyond the same. If now there is an increase in the demand for heat, as evidenced by a drop in the steam pressure in the pipe 14, the regulator 59 will respond by moving the links 64 and 66 downwardly, thereby readjusting the rheostat arm 32 to increase the speed of the feeder motor 27 and also readjusting the cam lever 65 to raise the screw 49 and increase the tension of the diaphragm loading spring 47. Thus more coarse coal will be supplied to the pulverizer 15 by the feeder 23, and more pulverized coal will be supplied to the burners 11-12 to take care of the increased demand for steam. As the tension of the spring 47 increases, the diaphragm 45 and the lever 44 will be moved slightly upward, actuating the pilot valve mechanism 38, and admitting fiuid to the motor 42 so that the latter will open the valve 34 slightly further. This will increase the rate of air flow through the pulverizer, and increase the pressure in the pipe 16 as required to counterbalance the increased spring tension and restore the regulator 37 to a balanced condition. This increase in the air flow will avoid any possibility of congestion in the pulverizer, as might otherwise occur with the increased feed of coarse coal. Consequently the pulverizer will operate satisfactorily even at very high loads, without danger of blocking or plugging thereof by accumulations of coal within the machine.

If the load on the furnace becomes so low that the operator wishes to carry the entire load on a single burner, say the burner 12, he will close the valve 20 and thereby 7 will operate under these conditions to close the valve 34 cause the entire stream of coal and primary air from the sufiiciently to prevent any appreciable increase in the pressure within the pipe 16 beyond this valve, so that the air flow through the burner 12 will remain substantially constant, and ignition will be maintained without difficulty.

It will be apparent that the invention provides a simple and effective solution for certain problems which have heretofore caused considerable difficulty in the burning of pulverized fuel.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

A control system for a furnace of a steam generating unit having a plurality of burners of pulverized fuel, a conduit feeding each of said burners, a main conduit supplying the feed conduits, and a pulverizer supplied with coarse fuel by an adjustable feeding means, said control system comprising: a hydraulic motor whose piston is connected to and responsive to the output of the steam generating unit, the piston being connected to the said adjustable feeding means for control thereof, a diaphragmtype regulator connected to said piston in order that the normal diaphragm position is determined thereby, means for obtaining the static pressure in the main conduit, said means being connected to said regulator for impressing said pressure on one side of the diaphragm, a valve for controlling the flow through the main conduit, a second hydraulic motor connected to said valve for actuation thereof, a pilot valve connected for controlling the hydraulic pressure in said second hydraulic motor, said pilot valve being controlled by connection to the diaphragm of said regulator.

References Cited in the file of this patent UNITED STATES PATENTS Re. 20,156 Hardgrove Nov. 3, 1936 1,787,407 Peebles Dec. 30, 1930 1,951,763 Mittendorf et a1. Mar. 20, 1934 1,992,048 Temple Feb. 19, 1935 2,000,270 Andrews et al May 7, 1935 2,003,985 Wallene June 4, 1935 2,172,317 Dickey Sept. 5, 1939 2,212,125 Peebles Aug. 20, 1940 2,404,937 Anderson July 30, 1946 2,409,002 Smith Oct. 8, 1946 2,530,117 Dickey Nov. 14, 1950

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