Patent Application
20110239915
The present invention relates generally to systems and assemblies for controlling the flow of air and fuel in conduits supplying coal-fired furnaces and boilers. More particularly, the present invention relates to an adjustable, diffusing damper assembly for use in such systems.
A coal-fired furnace used in electrical power generation typically employs multiple burners in a single combustion chamber, each burner fed by a mixture of pulverized coal and air supplied through a network of conduits originating from one or more pulverizer mills. It is well known that balancing the fuel supply among the burners is essential to good performance, since imbalances in the flow of coal from the furnace's burner nozzles can cause problems such as NOx formation, incomplete combustion (loss-on-ignition), erosion and contamination of the combustion chamber, and the like. It is also well known that the two-phase flow of air and coal through the various conduits supplying the furnace is affected by a number of factors, including the dimensions and configurations of the conduits themselves, the characteristics of the fuel, and the design and installation of various distribution system components.
A variety of devices have been employed or proposed to balance the distribution of coal as it flows from a single pulverizer, through several branches, to the burner nozzles. These devices include so-called riffle boxes and various damper valves and orifice restrictor devices. For instance, Ohtani et al., U.S. Pat. No. 6,976,440, discloses an adjustable damper deployed within a conduit branch to balance fuel distribution between the two outlets of the branch. Other devices have been proposed specifically to combat problems caused by “roping,” or “laning,” which is the tendency of the solid particles in the air-coal stream to become concentrated, forming a rope-like strand. For example, Wark et al., U.S. Pat. No. 6,234,090 describes linear diffuser elements deployed across the inside of a coal conduit for diffusing the coal flow across the interior of the conduit. Similarly, Wark, U.S. Pat. No. 6,840,183 describes a diffuser insert, with a combination of radial and axial diffusion elements, for use near an elbow connection to a burner nozzle.
However, some of these devices, such as the riffle box, are not adjustable, thus providing no means for variably regulating coal and air flow through the system. Other devices, such as orifice restrictors, may suffer from clogging or wear caused by the coal flow, while others can actually cause wear, by diverting all or part of the flow of the pulverized coal against interior walls of the conduit. Furthermore, some of these devices are difficult to install. Accordingly, improved devices that are uncomplicated to install and that simultaneously provide for diffusing and balancing coal flow are needed.
Disclosed herein is an adjustable, diffusing coal valve for use in controlling flow of air and pulverized fuel to a burner. The device can be constructed for easy installation, and includes a perforated damper blade to diffuse the flow of coal and reduce roping and pipe erosion. The disclosed coal valve can be installed at any of several points in a coal distribution system, such as at a mill outlet, before and/or after one or more riffle boxes, and just before a burner inlet, to facilitate balancing of pulverized coal between multiple distribution conduits and the corresponding burners while avoiding roping, clogging, and erosion problems.
In an exemplary embodiment, an adjustable, diffusing coal valve assembly comprises a conduit section and a diffusing damper plate mounted within the conduit section and movable between an open position and a closed position. The diffusing damper plate has a periphery dimensioned to occupy a majority, but less than all, of said inner cross-sectional area when in the closed position. In some embodiments, the diffusing damper plate's periphery is dimensioned to occupy less than about 80% of the conduit's inner cross-sectional area when in the closed position, thus ensuring a gap between damper plate periphery and the interior walls of the conduit.
The diffusing damper plate also includes a plurality of perforations distributed within an outer region of the plate, thus allowing coal particles to flow through the damper plate when it is in a closed or partly-closed position. In some embodiments, the diffusing damper plate and its perforations are dimensioned so that between about 40% and about 60% of the inner cross-sectional area of the conduit is obstructed when the diffusing damper plate is in the closed position. The cumulative cross-sectional area of the perforations in some embodiments is between about 10% and about 20% of the area defined by the diffusing damper plate's periphery. In other embodiments, for instance where more diffusing but less damping is required, the cumulative cross-sectional area of the perforations may comprise as much as about 40% of the area defined by the diffusing damper plate's periphery.
In several embodiments, the diffusing damper plate is rotatably mounted within the conduit section to rotate between the open and closed positions, although other configurations are possible. The diffusing damper plate may be constructed in various ways—in some embodiments, for example, the diffusing damper plate comprises two planar sections rigidly attached to opposite sides of a central shaft. In others, the diffusing damper plate instead comprises a single planar section connected to a shaft to form a substantially planar rotatable plate. In some embodiments, the diffusing damper plate may be coated with an abrasion resistant material, such as tungsten carbide, to resist wear.
In some embodiments, a diffusing damper plate is rotatably mounted within a spoolpiece for installation in new or existing coal distribution systems. In other embodiments, a diffusing damper plate may be connected to a mounting flange configured to be disposed against the outside surface of a conduit, so that the diffusing damper plate is rotatable within an inner region of the conduit between an open and closed position when the mounting flange is disposed against the outside surface of the conduit. The latter embodiments may be installed without removal of a pipe section, in many instances.
Of course, those skilled in the art will appreciate that the present invention is not limited to the above contexts or examples, and will recognize additional features and advantages upon reading the following detailed description and upon viewing the accompanying drawings.
As discussed above, various devices are presently known for balancing the distribution of coal in a pulverized coal distribution system. Other known devices are designed to encourage a diffuse flow of coal through the system. However, none of the existing devices provide a solution that adequately provides for balancing coal distribution, by means of variably restricting the coal and air flow through a pipe, while simultaneously diffusing the coal throughout the pipe, thus reducing the potential for coal roping and pipe erosion.
A novel diffusing damper apparatus 10, according to some embodiments of the present invention, is thus pictured in
As will be discussed in further detail below, diffusing damper plate 15 has a periphery generally dimensioned to occupy a majority of the inner cross section of conduit 11 when in its closed position. However, the periphery of damper plate 15 is also dimensioned to provide for a gap between the conduit walls and the damper plate, to avoid clogging and excessive erosion of the walls of conduit 11. Diffusing damper plate 15 further comprises a plurality of perforations distributed within an outer region of damper plate 15, while the inner region is generally free of perforations. The perforations permit a substantial portion of the flowing coal particles to pass through the diffusing damper plate 15, rather than around it, when the damper plate 15 is in a closed or partially closed position, thus providing for a diffuse flow of coal without roping.
In
In some embodiments, a handle 18 is securely attached to shaft 14, allowing an operator to manually rotate the diffusing damper plate. Locking pin assembly 12 may also be provided to allow the diffusing damper plate 15 to be locked into any of several positions between fully closed, in which the generally planar surface of damper plate 15 is substantially orthogonal to the air flow through conduit 11, and fully open, in which the diffusing damper plate is substantially planar to the air flow through the conduit. Those skilled in the art will appreciate that the assembly illustrated in
Diffusing damper plate 15 is a generally planar plate, connected to a rotating shaft, with a periphery dimensioned so as to substantially, but not completely, occupy the interior cross section of conduit 11 when in a closed position. As pictured, diffusing damper plate 15 is generally circular, although other shapes may be used. For instance, a rectangular damper plate may be preferred for installations in a rectangular conduit. Alternatively, appropriately dimensioned hexagonal or other multi-sided shapes may be used in conduits of various shapes.
A typical conduit 11 may have a nominal diameter of between about twelve and twenty-four inches, although diameters ranging eight to twenty-eight inches are well known. As noted above, the periphery of diffusing damper plate 15 is dimensioned to substantially, occupy the interior cross-sectional area of conduit 11 when closed. Accordingly, a diffusing damper plate configured for use in a pipe having an interior diameter of fourteen inches, for example, might have a diameter of about 10.5 inches, thus providing a gap of about 1.75 inches around the periphery of the damper plate when the valve is in a closed position. Damper plates according to various embodiments of the present invention have a periphery dimensioned to occupy less than about 80% of the inner cross-sectional area of the conduit when closed, although a somewhat larger periphery may be acceptable in some cases. For example, a generally round damper plate having a diameter of 10.5 inches has a cross section of about 87 square inches. This constitutes about 56% of the cross section of a 15-inch conduit (with an inner diameter of about 14 inches). The same damper plate may be suitable for use in a conduit having a 12-inch inner diameter as well, in which case the damper's cross section constitutes about 76% of the conduit's cross-sectional area.
The gap between the damper plate and the wall reduces erosion of the pipe due to coal particles forced around the damper plate and into the pipe's interior walls. This erosion is a particular problem with prior art damper devices having solid blades. However, this problem is reduced with the diffusing damper devices discussed herein, since a substantial portion of the coal flow is permitted to pass through the damper plate when in the closed position, rather than around it. Thus, diffusing damper plate 15 also includes several perforations 22 distributed within the outer portion of the plate, as shown in
Perforations 22 permit the flow of air and pulverized coal through the damper plate as well as around it, scattering the pulverized particles and preventing the formation of coal “ropes,” which can cause burner performance problems, fuel balancing problems, and excessive erosion of the pipes. The inner region of the plate is generally free of perforations, breaking up any pre-existing ropes of pulverized coal and forcing a more even distribution of the pulverized coal fines. This can be seen in
When in a closed position, the effective cross section of damper plate 15 is defined by its periphery as well as the number and dimensions of the perforations. For example, the 10.5-inch damper plate discussed above may include approximately 20 circular perforations one inch in diameter, having a cumulative area of about 15.7 square inches. Thus, the effective cross section of the 10.5-inch damper plate is about 71.3 square inches (87−15.7=71.3). This represents about 46% of the interior cross section of a 14-inch inner-diameter pipe—thus, 46% of the pipe's cross section is obstructed by the damper plate when in a fully closed position. Those skilled in the art will appreciate that damper plates may have effective cross sections, compared to the interior cross section of the conduit, that vary from this figure. Accordingly, some embodiments of the present invention have diffusing damper plates and perforations that are dimensioned so that between about 40% and about 60% of the inner cross-sectional area of the conduit is obstructed when the diffusing damper plate is in the closed position.
The number, shape, and dimensions of the perforations 22 may vary, provided that the perforations cumulatively allow a substantial quantity of the coal flow to pass through the perforations, rather than around the damper, when the diffusing damper plate is fully closed. Perforations having diameters between three-fourths inch and one inch have been found to be suitable in a damper plate configured for use in a 14-inch conduit. A broader range of perforation sizes is also possible, depending at least in part on the size of the damper plate. The perforations may also be have any of a variety of cross sections (i.e., they need not be circular) and shapes (e.g., the perforations may be tapered, or penetrate the damper plate at an angle, or the like). In some embodiments the cumulative cross-sectional area of the perforations is between about 10% and 20% of the area defined by the periphery of the diffusing damper plate. For instance, the 10.5-inch damper plate described above has twenty one-inch perforations, which cumulatively account for about 18% of the area defined by the damper plate's periphery. Those skilled in the art will appreciate that the cumulative area of the perforations and the gap around the damper plate determines the maximum damping effect of the diffusing damper plate. Accordingly, in instances where more diffusing but less damping is desired, the cumulative cross-sectional area of the perforations may comprise as much as about 40% of the area defined by the diffusing damper plate's periphery.
In any event, in many embodiments the cumulative effect of the diffusing damper plate and its perforations is to obstruct roughly one-half of the interior cross section of the conduit when in a fully closed position. In some embodiments, therefore, the diffusing damper plate and its perforations are dimensioned so that between about 40% and about 60% of the conduit's inner cross section is obstructed when the damper is fully closed. In a fully open position, on the other hand, the diffusing damper plate's obstruction of the conduit is negligible. Accordingly, the damping effect of the diffusing damper plate may be varied by simply rotating the plate, facilitating balancing of coal distribution between several conduits supplying a furnace.
Those skilled in the art will also appreciate that various approaches to installing the diffusing damper apparatuses discussed herein. One approach is to construct a “spoolpiece” comprising a section of appropriately sized conduit and the damper plate rotatably mounted within it. The spoolpiece may be installed into an existing pipe by removing a length of pipe and replacing it with the spoolpiece, using conventional methods for joining the spoolpiece.
To facilitate easier installation, some embodiments of the present invention may comprise a diffusing damper plate, as described above, coupled to a mounting flange configured for disposal against the outside surface of the target conduit. (In some embodiments, the interior side of the mounting flange may be curved, with a radius matching the outer radius of the target pipe. In others, a flat flange may be used, perhaps with a suitable gasket.) A shaft connected to (or forming part of) the damper plate extends through the mounting flange, and may be rotatably secured to the mounting flange using conventional means, such as a bearing and a retaining handle, or the like. The diffusing damper assembly may be installed in an existing conduit by simply cutting a slot in a conduit wall, along the axis of the conduit. The slot need only have a width slightly larger than the widest part of the damper plate assembly (including the shaft), and a length slightly longer than the diameter of the damper plate. Those skilled in the art will appreciate that the damper plate may thus be fitted through the slot, and the mounting flange then secured to the exterior conduit wall using conventional means. In some embodiments, a hole may be drilled in the conduit wall opposite the mounting flange to accommodate an extension of the shaft at least partly into the conduit wall, for additional support.
Those skilled in the art will appreciate that
Indeed, the present invention may be carried out in other specific ways than those set forth without departing from the scope of the inventive techniques illustrated by the specific embodiments illustrated herein. Thus, the present invention is not limited to the features and advantages detailed in the foregoing description, nor is it limited by the accompanying drawings. Indeed, the present invention is limited only by the following claims and their legal equivalents.
This application is a divisional of U.S. patent application Ser. No. 12/186930, filed 6 Aug. 2008.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12186930 | Aug 2008 | US |
| Child | 13160823 | US |
