Patent Application
20080190335
This invention relates to a variable orifice for a conduit used to deliver a stream of particulate coal to a burner and more particularly to a variable orifice of simple design and to a method of retrofitting the variable orifice in a conduit which is already in place.
It is well known to feed burners, for turbine generator boilers with fuel in the form of airborne particulate coal; structures for carrying out this function are commonly found in electric utility plants throughout the United States and Canada. It is typical in these structures to use a main supply conduit to receive finely pulverized coal from a pulverizer/classifier. It is also typical to divide the main supply conduit into several parallel branches which are connected to individual nozzles or injectors arranged at spaced points around the burner so as to project a stream of particulate coal toward a fireball which is essentially centralized within the burner.
A problem which arises in systems of the type described above is insuring that the branch conduits provide at least approximately equal coal flow rates so that the fireball is stabilized as to size and location and receives essentially equal inputs of fuel from all of the nozzles. The branch conduits are of different lengths and the longer ones present greater resistance to flow. Therefore a variety of devices, hereinafter referred to as “variable orifice” devices, have been created to introduce some additional flow resistance into shorter branches thereby to balance the flows of particulate coal as between parallel branch conduits feeding a single burner. Examples of variable orifices are found in U.S. Pat. Nos. 5,873,156, 6,055,914, 6,186,079, 6,257,415 and 6,234,090.
According to a first aspect, the present invention provides a variable orifice or valve for varying the effective cross-sectional flow area of a conduit which is used to deliver a stream of particulate coal to a burner. In accordance with the invention, the variable orifice comprises a first plate which is fixably mounted within and extending across the supply conduit such that its plane lies parallel to the direction of flow. In the typical installation, the conduit is essentially round in cross-section and the first plate extends across a diameter of the conduit.
Further in accordance with the invention, a second plate is mounted within and extending across the conduit closely adjacent the first plate but, by means of a mechanical structure such as a rotatable shaft attached to the second plate and to the conduit wall, can be selectively varied in its angular relationship with the first plate. When the second plate is parallel and adjacent the first plate, the effective flow area of the conduit is only minimally reduced. However, when the second plate is rotated toward a position in which it extends at right angles to the flow direction, the effective cross-sectional flow area of the conduit is maximally reduced. In the preferred form, means are provided for selectively fixing the movable plate in any of a number of intermediate positions between the unextended or parallel position and the fully extended, right angle position.
In the preferred form, as hereinafter described, the mechanism further comprises an indicator mechanism such as a lever arm is mounted to the shaft externally of the conduit such that its angular position indicates directly or indirectly the angular position of the second plate in the orifice. As hereinafter described, a locking mechanism is provided in the form of a locking plate with an arcuate arrangement of holes formed in it, the plate being fixed in its position relative to the conduit. The lever arm which rotates with the shaft is provided with a spring-loaded pull-to-release pin which can be fitted into any one of the various holes to lock the variable position plate in the desired angular position.
The typical range of motion for the movable blade is 90 degrees, but additional range of motion of up to about 180 degrees can also be provided.
While the invention is described herein with reference to a manually operable device, it would be apparent to those skilled in the art that the device may also be fixed with a motive power source such as a pneumatic or hydraulic actuator and/or a motor.
Referring to the figures, a round, steel conduit 10 is provided for the purpose of delivering an airborne stream of pulverized, particulate coal to a burner (not shown). In the figures, the conduit ranges in size anywhere from about 14 to 19 inches in diameter and the direction of flow is from bottom to top in each of
The conduit 10 is provided with a variable orifice 12 for flow rate regulation purposes as generally described above. The variable orifice 12 comprises a first fixed plate 14, a second, angularly movable plate 16, and a mechanical structure including a shaft 18 and an external assembly 20 for varying the angular position of the plate 16 relative to the plates 14. Whether parallel or defining an included angle, the upper or downstream edges of the plates 14 and 16 are always contiguous. The action of the plates 14, 16 is similar to that of a “butterfly” valve wherein only one “wing” moves.
Going now into greater detail, the plate 14 is mounted diametrically across the conduit 10 with its principal plane parallel to the direction of air stream flow in the conduit 10 so as to provide in and of itself a minimal obstruction to flow. The plate 14 has a longitudinal dimension corresponding substantially to the inside diameter of the conduit 10 and an axial dimension of from 6-12 inches. It may be made of high hardness ¼ inch steel alloy plate. The leading edge may be protected with carbide if desired.
The plate 16 is substantially of the same overall dimensions as the plate 14, but has beveled outside edges 17, to provide clearance with the inside wall of the conduit 10 when its angular position is changed; i.e., when it is rotated up toward a more blocking orientation as shown in the plan view of
The external mechanism 20 for adjusting and indicating the angular position of the plate 16 comprises a rectangular steel frame 22 which is welded to the outside wall of the conduit 10 around an elongate slot 24 which is cut into the conduit 10 in the process of installing the variable orifice device 12 as hereinafter described. Attached to the frame 22 is a bearing box 26 which is capped with an arcuate steel locking plate 28 held in place by means of screws 30 which extend through the plate and into tapped holes in the frame 22 as shown. A collar 31 on the shaft 18 is trapped between plates 28 and 33 to provide a thrust bearing.
Optionally a bearing 32 may be mounted by screws or welding to a plate 36 on the diametrically opposite side of the conduit 10 to receive and support as well as to provide for rotation of the distal end of the shaft 18 as it extends through a round hole 34, also cut into the outside wall of the conduit 10.
As best shown in
As shown in the figures, the plate 16 can be rotated between a fully opened or minimally interfering position in which it is directly parallel to the plate 14 and a fully extended or maximally blocking position in which the plate 16 is essentially at right angles to the plate 14 across the diameter plane of the conduit 10. The plate 28, shown in the figures to provide for only 90 degrees of rotation of plate 16, can be extended upwardly to provide for nearly 180 degrees of rotation as desired.
Tests have shown that the variable orifice device 12 provides a flow resistance which varies nearly linearly with angular position of plate 16. While it appears that particulate coal might flow continuously into the crevice between the plates 14 and 16, under actual flow conditions, a pressure bubble builds rapidly within the angularly enclosed area, thereby increasing flow resistance and reducing the rate of flow in proportion to the angular position of plate 16.
Installation of the device 12 is typically carried out by way of the following steps, assuming that the conduit 10 is already in place and that a retrofit installation is necessary.
First, the slot 24 is cut into the conduit wall with the long axis of the slot parallel to the flow direction. The hole 34 is cut as needed directly diametrically across from the upper end of the slot 24 to receive the distal end of the shaft 18 and the bearing block 32.
Next, the frame 22 is welded in place. Note that the slot in the frame overlies the slot formed in the conduit wall and is of sufficient length and width to accommodate passing therethrough the parallel combination of the two plates 14 and 16 and the shaft 18. The combination is pushed through the slot in the frame 22 across the conduit 10 until the opposite or far end of the shaft 18 fits through the hole 34 and into the pre-installed bearing block 32.
The mechanism 20 is now attached to the frame 22, the clamp 42 is adjusted to correspond with the unblocked position of the plate 16 and the device is thereafter fully operable in the manner described above. As previously mentioned, the manual device shown in the drawings may be supplemented with a device having a motive power source such as a fluid cylinder or motor with appropriate remote control.
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiments but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as is permitted under the law.
