Patent Application
20050230224
The invention relates to an apparatus for controlling the deposition of feed material on a deposition build-up surface of a feed arrangement for feeding feed material from an in-process feed material source to a material handling location.
Stokers are mechanical devices that feed and burn solid fuels in a bed at the bottom of a furnace. The solid fuel is burned on some form of grate, through which passes some or all of the air for combustion. The grate surface in the stationary or moving. Feeder devices continuously project metered amounts of solid fuel into the furnace above an ignited fuel bed on the grate. Fines are burned in suspension while larger particles fall and burn on the grate.
A particular type of coal feeder device for feeding metered amounts of coal from a coal silo onto a stoker includes an underthrow coal distributor having a spaced chain that conveys substantially uniform increments of the coal fed thereto from the coal silo. The spaced chain drops off the coal to fall in between respective pairs of the rotating blades of a distribution rotor and the distribution rotor further conveys the coal to the stoker, which may be, say, a traveling grate stoker.
It has become a common design practice, in connection with this type of coal feeder device, to provide a so-called siftings tray shortly below the lower run of the spaced chain of the underthrow coal distributor and extending to the upstream edge of a cowling partially encircling the distribution rotor. Such siftings trays are subjected to a deposition build-up of coal particles thereon in connection with which an excessive build up of such coal particles interferes with the operation of the spaced chain of the underthrow coal distributor.
While one approach to the deposition build-up of coal particles has been to merely permit such a build-up of the coal particles, whereupon space constraints the inherent instability of the accumulation of the coal particles will eventually limit further deposition build-up of coal particles, the need still exists for an approach that can more reliably ensure the desired operation of the underthrow coal distributor. Such an approach should preferably be inexpensive to manufacture and should be capable of using a power source that is readily available in a typical process plant, in order to keep installation costs to a minimum. Also, the approach should be suitable for use in the relatively harsh environment of the coal feed operation including being subjected to temperature gradients and vibration. The system also should be simple and reliable, in order to keep maintenance costs to a minimum.
Accordingly, it is an object of the present invention to provide an apparatus that addresses the concerns set forth above.
According to the present invention, an apparatus for controlling the deposition of feed material on a deposition build-up surface is provided that advantageously influences the movement of feed material relative to the deposition build-up surface such that the deposition of feed material on the deposition build-up surface is hindered.
According to one aspect of the present invention, the apparatus is configured for use in a feeder arrangement having an endless conveyor for conveying feed material to the rotating blades of a distribution rotor for further conveyance of the feed material, whereby the inventive apparatus controls the deposition of feed material on a deposition build-up surface subjected to deposition loading of feed material that has exited the endless conveyor yet has not been conveyed beyond the distribution rotor. The particular type of feeder arrangement for which the inventive apparatus is suitable is the type of feeder arrangement wherein the endless conveyor moves in a loop having a respective clockwise-denominated handedness with some portion of the endless conveyor always traveling along an upper run while another portion of the endless conveyor travels along a lower run below the upper run with the endless conveyor, as it travels along its upper run, conveying feed material to a drop-off location at which conveyed feed material drops off the endless conveyor for receipt thereof by the rotating blades of the distribution rotor, wherein the rotation of such distributor rotor blades in an opposite clockwise-denominated handedness relative to the endless conveyor causes a portion of the feed material to move towards the deposition build-up surface and thereby disadvantageously promote a deposition build up on the surface.
According to further details of the one aspect of the present invention, the apparatus includes means for influencing the movement of feed material relative to the deposition build-up surface such that the deposition of feed material on the deposition build-up surface is hindered.
According to a variation of the one aspect of the present invention, the means for influencing the movement of feed material relative to the deposition build-up surface includes means for directing a fluid relative to the feed material.
According to another variation of the one aspect of the present invention, the means for influencing the movement of feed material relative to the deposition build-up surface includes a mechanical device for displacing feed material.
Reference is now had to
Referring now more particularly to the fossil fuel delivery arrangement of the combustion chamber 10, coal 24 which may have been optionally subjected to an appropriate particle size reduction treatment such as, for example, grinding thereof by a pulverizer (not shown), is stored in a coal silo 26 and is fed therefrom in a metered manner onto an underthrow coal distributor 28. The underthrow coal distributor 28 spreads or throws out the coal 24 onto a traveling grate stoker 30 that, in turns, supports the coal 24 as the traveling grate stoker 30 travels along its upper run at the lower portion of the combustion chamber 10. The coal 24 is thus combusted as it is supported on the traveling grate stoker 30 while overfire air is supplied through a plurality of nozzles 32 and underfire air is supplied beneath the traveling grate stoker 30 via a plurality of underfire air inlets 34.
The traveling grate stoker 30 is comprised of a continuous “chain” of interconnected laterally elongated bar and key assemblies trained around a stoker idler sprocket 36 and an stoker drive sprocket 38. The traveling grate stoker 30 is driven in a clockwise direction under the driving action of the stoker drive sprocket 38.
Reference is now had to
The hub 48 of the distribution rotor 44 is operatively connected to a conventional rotor drive motor (not shown) that rotates the hub 48, and the blades 46 connected thereto, in a counter-clockwise direction about a distribution rotor axis BDR. The rotating blades 46 of the distribution rotor 44 further convey the coal 24 delivered to the distribution rotor 44 by the endless conveyor 42 to the traveling grate stoker 30.
The endless conveyor 42 is comprised of a spaced chain 50 itself formed of a plurality of feeding bars 52 secured together by a plurality of links 54 in an endless loop. Each feeding bar 52 is spaced from adjacent feeding bars 52 such that the respective spaces thus formed between respective adjacent pairs of the feeding bars 52 can receive and convey coal 24. The spaced chain 50 moves in a loop having a respective clockwise-denominated handedness; with regard to the one embodiment of the deposition control apparatus 40 illustrated in
The spaced chain 50 is trained around a conveyor drive sprocket 56 and a conveyor idler sprocket 58, each of which has an axis of rotation parallel to the distribution rotor axis BDR, whereupon the spaced chain 50 continuously or endlessly travels successively along an upper run extending from the conveyor idler sprocket 58 to the conveyor drive sprocket 56 and a lower run extending from the conveyor drive sprocket 56 to the conveyor idler sprocket 58. Also, a support plate 60 supports the spaced chain 50 along its upper run such that some portion of the spaced chain 50 is always traveling along the upper run while another portion of the spaced chain 50 travels along the lower run below the upper run.
The endless conveyor 42, as it travels along its upper run, thus conveys the coal 24 to the drop-off location DFL at which conveyed coal 24 drops off the endless conveyor 42 for receipt thereof by the rotating blades 46 of the distribution rotor 44. Specifically, the coal 24 falls from the endless conveyor 42 at the drop off location DFL into the gaps between angularly adjacent pairs of the rotating blades 46 of the distribution rotor 44 and the distribution rotor 44 then carries the coal 24 in a counter-clockwise rotational path from approximately the top dead center of the rotational path of the distribution rotor 44 to a throw out location TAH at which the conveyed coal 24 is “spread” or thrown out onto the traveling grate stoker 30. The throw out location TAH is located at approximately two hundred and seventy degrees (270°) from the top dead center of the rotational path of the distribution rotor 44 as measured in the counter-clockwise direction. The “spreading” or throwing out of the coal 24 by the distribution rotor 44 is further assisted by a stream of high pressure air introduced at the throw out location TAH by a high pressure air outlet 62; this stream of high pressure air promotes the transport of the relatively more fine particles of the coal 24 away from the deposition control apparatus 40 and toward the traveling grate stoker 30.
The rotating blades 46 of the distribution rotor 44 rotate in a respective clockwise-denominated handedness that is opposite to that of the endless conveyor 42—for example, with respect to the arrangement shown in
It can be seen in
With respect to the events that lead to the “deposition build-up” on a surface, the concept of the “deposition build-up” on a surface is intended to comprehend all manner and type of mechanisms that result in the disposition of feed material on a respective surface, wherein such mechanisms may include one or all of the following: (a) the release of any coal 24 in the spaces between the feeding bars 52 of the spaced chain 50 that has been retained in the spaced chain 50 as the spaced chain 50 travels around and beyond the conveyor drive sprocket 56, (b) the effect of centrifugal force generated by either the movement of the endless conveyor 42 or the distribution rotor 44 on the coal 24, (c) the effects of collisions between particles of the coal 24 falling into the gaps between the blades 46 of the distribution rotor 44 and the blades themselves, (d) the air sweeping force exerted by the movement of the spaced chain 50 between its upper and lower runs or by the rotational movement of the distribution rotor 44, (e) the surface adhesion forces of the surface on the coal 24, or (f) the surface adhesion forces of particles of the coal 24 already deposited on the surface on other particles of the coal 24. Moreover, the concept of “deposition” with respect to the “deposition build-up” on a surface is intended to comprehend, in addition to the disposition of particles of the coal 24 directly or immediately on the surface itself, the disposition of particles of the coal 24 not directly onto the surface itself but, instead, the disposition of such particles of the coal 24 onto other particles of the coal 24 which themselves are directly or immediately on the surface itself or are disposed on still other particles of the coal 24 which themselves are directly or immediately on the surface itself.
It may be considered that one approach to avoiding deposition build-up is to configure the respective feed arrangement such that no surfaces are presented that would detrimentally promote the deposition of feed material thereon including, especially, no such surfaces in the region of the drop off location DFL. However, the underthrow coal distributor 28 is specifically configured to feed the coal 24 at a uniform feed rate onto the traveling grate stoker 30 for the reason that an operation of the underthrow coal distributor 28 in this manner permits reliable control of the respective output—i.e., steam rate, electrical power generation, etc.—of the combustion chamber 10 and/or any power generation equipment to which the combustion chamber 10 is coupled. For this reason, it can be understood that it is desirable, in many circumstances, to orient the endless conveyor 42 such that the upper run of the spaced chain 50 is as nearly horizontal as possible, whereupon the operation of the spaced chain 50 can be optimally coordinated with the metered dosage of the coal 24 from the coal silo 26 onto the spaced chain 50 such that a substantially uniform increment of the coal 24 is conveyed between each adjacent pair of the feeding bars 52 of the spaced chain 50. An inclined upper run of the spaced chain 50 may lead to spillage of coal between adjacent pairs of the feeding bars 52 of the spaced chain 50, thereby raising the risk of the conveyance of the coal 24 by the spaced chain 50 in non-uniform increments. Additionally, it can be seen that a cowling 66 having a curvature configured with respect to the distribution rotor 44 is mounted relative to the distribution rotor 44 to facilitate the capture and retention of the coal 24 by the distribution rotor 44 and this cowling 66 has an upstream edge (viewed relative to the direction of rotation of the distribution rotor 44) that is positioned to ensure that a portion of the coal 24 that has immediately before entered into a gap between a respective pair of the blades 46 of the distribution rotor 44 remains within the gap as the gap travels toward the throw out location TAH. It has thus become, in connection with the types of coal feed arrangements to which the underthrow coal distributor 28 belongs, a common design practice to provide a so-called siftings tray shortly below the lower run of the spaced chain of the underthrow coal distributor and extending to the upstream edge of the cowling of the distribution rotor. Such siftings trays are subjected to a deposition build-up of coal particles thereon in connection with which an excessive build up of such coal particles interferes with the operation of the spaced chain.
In accordance with the present invention, the deposition control apparatus 40 is provided to hinder at least partially and, preferably, to hinder completely, the deposition build up of coal particles on the deposition build-up surface 64. The deposition build-up surface 64 may be either a conventional siftings tray that is comprised as a component of the original equipment underthrow coal distributor 28 or may be a structure that has been added to the underthrow coal distributor 28 (in this latter instance, the structure can be, for example, a siftings tray that has been added or retrofitted to the underthrow coal distributor 28). The deposition control apparatus of the present invention illustrated in
In the one embodiment of the deposition control apparatus 40 described in connection with
It can be understood that the flow characteristics of the stream of pressurized air directed by the outlet nozzle 70—namely, the orientation of the stream of pressurized air relative to the particles of the coal 24 which are disposed on the deposition build-up surface 64, the mass flow rate of the pressurized air, and the continuous application of the stream of pressurized air or, if applied in a pulse manner, the frequency and duration of the pulses—will pre-determine or govern the particle movement capability of the pressurized air device 68. For example, the flow characteristics of the stream of pressurized air directed by the outlet nozzle 70 can be configured such that the stream of pressurized air completely resists any build up of particles of the coal 24 on the deposition build-up surface 64. Alternatively, the flow characteristics of the stream of pressurized air directed by the outlet nozzle 70 can be configured to promote sufficient movement of coal particles such that a deposition build up on the deposition build-up surface 64 occurs but is of a sufficiently limited magnitude as to not interfere with the operation of the endless conveyor 42. Moreover, the stream of pressurized air directed by the outlet nozzle 70 can be continuously or intermittently operated or can be operated at a relatively lower mass flow rate for a predetermined interval during which a deposition build up may occur until reaching an unacceptable extent and then operated at a relatively higher mass flow rate for a subsequent interval to reduce or completely eliminate the deposition build up on the deposition build-up surface 64.
Reference is now had to
Since the invention is susceptible to various modifications and alternative forms, it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the scope of the invention extends to all modifications, equivalents and alternatives falling within the spirit and scope of the invention as defined by the appended claims.
