COMBINATION MECHANICAL/PNEUMATIC COAL FEEDER

Abstract: Feeder for feeding particulate fuel into a furnace (10) has a closely coupled hopper (22), fuel metering device (24), rotor (42) and air swept delivery plate (52). Larger particles of fuel of the mix supplied are distributed over the length of the furnace by the action of the rotor whilst fines also are distributed over the length of the furnace by the action of air jets over the delivery plate whereby a usual mix of different particle sized fuel is provided through the furnace.

Description: BACKGROUND AND SUMMARY OF THE INVENTION The present invention relates to a device for feeding fuel to industrial furnaces (including boilers) fired by spreader stokers, fluidized bed combustion, and like technologies, and more particularly to combination mechanical/pneumatic fuel feeders for feeding coal. Most coal feeders in use today are of the mechanical type using a rotating shaft with blades or paddles, in that they propel the coal into the furnace. Although mechanical coal feeders work adequately, they suffer the disadvantage that they comprise many moving parts which are exposed to the heat of the furnace and often to damaging tramp material, all of which can present maintenance problems. Also, pneumatic systems such as air swept spouts have been in use for years, but principally for incineration of refuse. Typically, the metering device for such systems is remotely located with the refuse fuel free falling through a chute onto the air swept plate. Attempts have been made to mix coal with the refuse at the remote metering location and then letting the mixture free fall together, however, such systems have not gained industry acceptance. Combination coal/refuse feeders have been used which consist of a mechanical coal thrower combined with an air swept refuse feeder having remote refuse metering and a free fall chute, using air of variable flow rate to spread the refuse across the furnace grate. Also, coal feeders have utilized steam or compressed air to blow coal off a shelf into a furnace, but these systems did°not use a closely coupled metering conveyor, nor did they vary steam or air flow to spread the coal across the furnace to fully cover the grate with fuel. Mechanical rotors, by themselves, have a difficult time throwing very fine coal to the rear of a long furnace. By the same token, air swept feeders have difficulty in feeding coarse coal past the middle of the furnace. One of the primary objects of the present invention, therefore, resides in the provision of a combination mechanical/pneumatic coal feeder which provides the pneumatic energy to propel finely sized coal particulate as well as the mechanical energy of a rotor assembly to propel coarser sized coal into the furnace. Such a combination provides improved fuel distribution within the furnace. The present invention therefore obviates the aforesaid problems and provides increased reliability and overall performance. Our earlier US-A-4 326 469 discloses a feeder in accordance with the prior art portion of claim 1. This prior machine is typical of the refuse burning machines referred to above, where fuel is mechanically fed into the furnace and the refuse is pneumatically fed. The pneumatic refuse feed is above the mechanical fuel feed and no pneumatic assistance is provided to the fuel feed. While an air jet is provided into the furnace below the fuel feed, this is primarily for cooling purposes. As indicated above, generally pneumatic feeding and mechanical feeding have been used alternatively in feeders for feeding fuel into furnaces. The present invention, as defined in claim 1, provides a pneumatic feed below the mechanical feed so that the mechanical feed rotor itself can act as a separator whereby the larger pieces of fuel are mechanically projected into a furnace with the finer particles of fuel being separated therefrom by being passed from beneath the rotor onto a plate from which they are pneumatically projected into the furnace. This combination of feed means enables the different sized particles of fuel to be fed where required into the furnace and reliably distributed through the length of the furnace. Preferably, in order to control the feeder, the space between the rotor and arcuate surface of the housing surrounding the rotor is variable by varying the position of the housing relative to the rotor in order to vary the space available for feeding fuel to the plate for air delivery, as compared with the fuel delivered mechanically by the rotor blades. By continuously varying the strength of the air jets sweeping across the plate, the air-delivered fuel can be continuously caused to vary the length of discharge into the furnace. Other advances and features will become apparent from the following specification, taken in conjunction with the accompanying drawings. Brief Description of the Drawings Figure 1 is a somewhat diagrammatic vertical cross-sectional view of a combination mechanical/pneumatic coal fuel feeder according to the preferred embodiment of the present invention. Figure 2 is a frontal view of Figure 1 showing the rotor assembly according to the preferred embodiment of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to Figure 1, there is illustrated a furnace 10 having a front wall 12 in which is provided a charging opening 14. The furnace 10 is provided with the normal insulation and refractory 16, tuyeres 18, etc. and in all respects is conventional except as specifically noted. Disposed immediately outside charging opening 14 is a combination mechanical/pneumatic feeder 20 embodying the principles of the present invention. The feeder 20 generally comprises a normally filled coal hopper 22 disposed over and opening downwardly onto a metering device in the form of a chain conveyor 24 which is driven in a clockwise direction as shown. A fuel delivery opening 25 is provided in the side of hopper 22 nearest furnace 10. Fuel delivery opening 25 is disposed adjacent to conveyor 24 with the top of conveyor 24 defining the bottom surface of opening 25. The depth of coal delivered by conveyor 24, which varies with the type and size coal being used, is controlled by a vertically movable adjustable gate 26 which is held in pre-set position within fuel delivery opening 25 and above the top surface of conveyor 24 by means of a threaded fastener 28. It is contemplated that other types of adjustable gating mechanisms could be readily adapted to the present invention. In addition, other types of metering devices may be used, such as, rotary driven or vibrating conveyor-type metering devices. Conveyor 24 is powered by a roller chain 30 driven by a sprocket 32 on an output shaft 34 of a gearbox 36 driven by an electric motor 38. Motor 38 is preferably a variable speed motor, AC or DC, and is controlled in the usual manner by a signal from the combustion control systems (not shown) to vary the coal feed rate to satisfy the output requirements of the boiler or furnace. Metered coal delivered by conveyor 24 drops behind blades 40 of a mechanical rotor assembly 42. Mechanical rotor assembly 42 is disposed below and immediately adjacent the end of conveyor 24 nearest furnace 10 and is arranged to receive coal therefrom. Rotor assembly 42 rotates in a counter clockwise direction, as shown. This direction of rotation is commonly referred to as "underthrow" which specifically provides for improved control of the trajectory of the coal as it is mechanically propelled into furnace 10. Underthrow propulsion alleviates disadvantages associated with clockwise rotation ("overthrow") such as the uncontrollable "spray" of coal thrown into furnace 10. Further, underthrow permits utilization of a smaller charging opening 14 to better optimize furnace efficiency and reduce heat related maintenance problems. Rotor assembly 42 has at least one row of rotor blades 40 and preferably a plurality of four or more rows of blades 40 which are configured to splay the coal sideways in a lateral direction across the furnace grate (not shown) to provide optimum lateral distribution. Also, blades 40 are pivotally secured to pivot posts 44 to inhibit jamming of oversized coal as it passes between rotor assembly 42 and rotor housing 46. Rotor housing 46 has a generally arcuate shaped surface 47 which is disposed a predetermined radial distance away from end 48 of blades 40. This radial distance is preferably adjustable, in any suitable manner, and permits finely sized coal particles to slide onto a coal delivery plate which will be detailed hereafter. Rotor housing 46 also confines the coal as it is propelled radially outwardly by the underthrow rotation of rotor assembly 42 so as to guide the trajectory of the coal into furnace 10 through charging opening 14. Rotor assembly 42 includes a drive shaft 50 extending longitudinally in coaxial relation with blades 40. The speed of rotation of drive shaft 50 directly controls the mechanical energy generated to propel coal into furnace 10. The higher the speed of rotation, the greater the distance into furnace 10 the coal is delivered. Drive shaft 50 is driven by a variable speed motor (not shown) AC or DC, which is controlled utilizing a conventional electronic or mechanical controller (not shown) to selectively vary the speed of rotation. While coal can be variably distributed within the furnace based on variations in the particle coal size, the extremely wide size variability of coal as delivered does not provide optimum distribution with a constant rotor speed. Because of this, the controller will selectively vary the rotor speed above and below a mean rotational speed with the ability to selectively adjust the minimum and maximum speeds as well as the rate of change. Coal which is not mechanically propelled by rotor assembly 42 into furnace 10 drops onto an air-swept coal delivery plate 52. Delivery plate 52 is upwardly angled and is pivotably attached to shaft 91 which can be rotated to increase or decrease the angle of inclination of delivery plate 52. A first portion 54 of delivery plate 52 is disposed immediately below the lower most edge 48 of blades 40 and a second portion 56 extends through charging opening 14. Coal delivery plate 52 provides assistance in controlling the trajectory of coal pneumatically swept into furnace 10. Coal delivery plate 52 and shaft 91 are rotatably adjustable via locking arm 92 which is held in position by fastener 58, so that delivery plate 52 can be selectively adjusted up and down to vary trajectory characteristics. A plurality of closely spaced air jets 62 are provided on a downwardly extending surface 49 of rotor housing 46 along the lateral length thereof. Air jets 62 pneumatically propel finely sized coal particulate delivered by rotor assembly 42 onto coal delivery plate 52 into furnace 10. The air jets 62 may be similarly sized or have variable sizing depending on the requisite feeder application requirements. Air of sufficient pressure, flow rate, and volume from a remote source (not shown) is supplied to air jets 62 via an air plenum 64 which fluidly communicates through passage 66 with chamber 68 so as to directly supply air jets 62. The pressure and volume of air supplied chamber 68, which determines the rate of air flow through air jets 62, can be continuously varied during operation of the feeder by a valve in the form of a damper 70 disposed in passage 66, both of which extend approximately one-half to two-thirds of the width of the feeder as viewed from the front. Damper 70 is mounted on an actuating shaft 74 to which is fixed a lever 76 having at one end a follower 78 engaging a cam 80 driven by output shaft 34 and at the other end a counterweight (not shown) to bias follower 78 toward cam 80. Follower 78 is mounted on lever 76 by means of a fastener 86 and an adjusting screw 88 is provided on lever 76 to fine adjust the angular position of follower 78 with regard to lever 76 to properly define the extreme positions of damper 70. Second adjusting screw 90 is provided to vary the degree of oscillation of lever 76 and hence damper 70. When properly adjusted, the air being delivered to air jets 62 varies continuously between a minimum rate necessary to propel the coal on coal delivery plate 52 to the near end of the furnace grate (not shown) and a maximum rate necessary to propel the coal to the far end of the grate.

Claims: A feeder for feeding particulate fuel into a furnace (10) having a fuel charging opening (14), comprising: a fuel hopper (22) having an open lower end; a metering device (24) for conveying fuel in a direction toward said furnace (10), said metering device (24) being disposed immediately adjacent said hopper (22) and being positioned to receive fuel from the hopper (22), means (38 and/or 26) associated with the metering device (24) to meter the rate of delivery of fuel; a rotor (42) disposed below and immediately adjacent the discharge end of the metering device (24) to receive fuel delivered by the metering device (24) for mechanically propelling the fuel through the fuel changing opening (14) into said furnace (10), said rotor (42) being rotatable about an axis extending transversely of the direction of discharge of the metering device (24) and having at least one row of blades (40) extending therefrom for mechanically propelling large particles of fuel received from the metering device (24) into the furnace (10) whilst rotating in an underthrow direction, such that it is the uppermost portion of the rotor (42) which returns in a direction towards the metering device (24); a rotor housing (46) adjacent the rotor (42) and having an arcuate surface (47) extending part way around the lower periphery of the rotor (42) outwardly of the radial ends (48) of the rotor blades (40); and an air jet (62) directed into the furnace (10) at a location below the outer housing (46); characterised in that a generally horizontally disposed delivery plate (52) is provided having a first portion (54) disposed substantially below both the rotor (42) and the downstream end of the arcuate surface (47) and adjacent to said downstream end to receive finely sized particles of fuel delivered from beneath the rotor (42), and a second portion (56) extending through the charging opening (14), and in that the air jet (62) is disposed above and adjacent the first portion (54) of the plate (52) and below and adjacent the downstream end of the surface portion (47), and is positioned to direct air along the top surface of the plate (52) against fuel delivered to the plate (52) from the rotor (42), pneumatically to propel the finely sized particles of fuel across the plate (52) into the furnace (10). A feeder according to claim 1, further comprising flow control means (70) for supplying air at a continuously varying flow rate to said air jet (62) so that fuel is pneumatically propelled into said furnace (10) over a range of distances. A feeder according to claim 2, wherein said flow control means comprises a valve (70) having an actuating shaft (74) and being disposed in an air supply passage (66), and powered actuating means (76,78,80) connected to said shaft (74) for causing said valve (70) to oscillate between a relatively open position and a relatively closed position when said feeder is operating. A feeder according to claim 3, wherein said powered actuating means comprises a lever arm (76) affixed to said shaft (74), a powered cam (80) engaging said arm (76) to cause it to oscillate and a counterweight on said arm (76) to cause said follower (78) to be biased towards said cam (80). A feeder according to claim 4, wherein said metering device (24) and cam (80) are drivingly interconnected. A feeder according to claim 2, 3, 4 or 5, further comprising means (88) for adjusting said flow control means (70) for changing the maximum and minimum values of said varying flow rate. A feeder according to claim 6, when appendant to claim 4 or 5, further comprising adjustable limit means (90) for limiting the maximum amplitude of oscillation of said lever arm (76). A feeder according to claim 6, when appendant to claim 4 or 5, further comprising means (90) for adjusting the open and closed angular positions of said valve (70) relative to said passage (66). A feeder according to any preceding claim, wherein said metering device includes a generally horizontal conveyor (24) provided with a gate (26) for controlling the depth of fuel delivered by said conveyor (24) to said rotor (42). A feeder according to any preceding claim, further comprising speed control means for variably controlling the speed of rotation of said rotor (42). A feeder according to claim 10, wherein said speed control means comprises a drive shaft (50) coupled to said rotor (42) such that the speed of rotation of said drive shaft (50) is variably controlled by a remote controller device. A feeder according to any preceding claim, wherein said rotor housing (46) comprises means for varying the distance between the arcuate surface of said rotor housing (46) and the outermost edge (48) of said blades (40). A feeder according to any preceding claim, further comprising pivotal means (44) mounting said rotor blades (40) for inhibiting jamming of fuel between said rotor blades (40) and said rotor housing (46). A feeder according to any preceding claim, wherein said air jet (62) comprises a series of similar size bores extending across the lateral length of said delivery plate (52). A feeder according to any one of claims 1 to 13, wherein said air jet (62) comprises a plurality of differently sized bores extending across the lateral length of said plate (52) for pneumatically propelling coal particles over a range of distances into said furnace. A feeder according to any preceding claim, further comprising means (92) for adjusting the position of said plate (52) relative to the rotor (42). A feeder according to any preceding claim, further comprising angular adjustment means (91,92) for selectively adjusting the angular inclination of said delivery plate (52) relative to said air jet (62). A feeder according to claim 17, wherein said angular adjustment means comprises a pivotable shaft (91) coupled to said plate (52), said shaft (91) being rotatable and coupled to a locking arm (92) for selectively rotating said shaft (92) and plate (52).

Inventors: LOVISKA, TIMOTHY ROBERT, RESCHLY, DAVID CHARLES
Applicants: DETROIT STOKER COMPANY
Application year: 1990
Main classification: F23K3
IPC codes: F23K3