Adjustable orifice for coal supply conduit

A variable orifice for use in connection with a conduit designed to convey particulate material comprising a set of semi-circular plates mounted on respective concentric shafts so that they may be rotated in opposite directions between a first position in which they extend across the interior of the conduit for maximum flow resistance to a second folded condition where they are adjacent and parallel to one another to present minimum flow resistance. An actuator is connected through the concentric shafts to the plates and mounts on the outside of the conduit surface. The unit is operated by hand crank and has a position indicator. The size of the valve plates is such that, even when fully extended relative to one another and lying across the cross-section of the conduit, only about a 30% restriction is produced.

FIELD OF THE INVENTION

This invention relates to variable orifices for use in combination with conduits designed to convey particulate material such as pulverized coal or metal ore.

BACKGROUND OF THE INVENTION

It is common to use metal pipe as a conduit for the conveyance of particulate matter from one point to another. An example is the transportation of finely crushed coal from a pulverizer to a combustion chamber or “firebox” where the pulverized coal is ignited and the heat used to make steam which powers a turbine. Metal conduits are also used to transport mineral ore and many other materials in extraction and refining operations.

In some conduit arrangements, it is essential to be able to regulate the flow of material through the conduit; for example, it is often desirable to balance the flow of pulverized coal flowing through multiple, parallel conduits to supply points around a combustion chamber thereby to control the shape and location of the fireball within a the combustion chamber.

Various types of valves or variable orifices have been designed for this purpose. Some such devices are gate type valves in which a blade structure is set up to slide variably across the interior cross-section of the conduit. There are numerous disadvantages associated with gate valves of this type. Other orifices use variable angle blades.

SUMMARY OF THE INVENTION

A first aspect of the present invention is an improved variable orifice of the variable angle type for use in combination with conduits designed to convey particulate material, such as pulverized coal or metal ore from one point to another. In accordance with the first aspect of the invention, a fabricated variable orifice comprises first and second plates, preferably of semi-circular shape, mounted in a contiguous fashion for coordinated angular movement between a first position in which the plates are adjacent along their diametric edge and are substantially co-planar, to a second position to which the plates are in a folded, substantially adjacent and parallel condition. In the preferred device, the dimensions are such that, when mounted within the conduit for which they are intended, a clearance exists entirely around the outer edges of the plates and inner surfaces of the conduit when the plates are co-planar; i.e., fully extended to the maximum restriction position.

In a preferred embodiment hereinafter described in detail, the invention further comprises an actuator connected to a pair of concentric shafts, each shaft in the concentric arrangement being attached to a respective plate, such that rotation of the two shafts in opposite directions moves the plates in the fashion of butterfly wings between the folded and extended positions described above. The actuator permits multiple intermediate positions of the blades between the maximum and minimum restriction positions.

Also in the preferred embodiment, a mechanism for rotating the shafts and including a position indicator is fabricated in such a way as to be attached to the outer surface of the conduit wall, with the shafts holding the blades extruding through the conduit wall.

In accordance with the second aspect of the invention, a method of installing a variable orifice of the type described above is provided. In general, the method comprises forming an elongate slot in the sidewall of the conduit for which the variable orifice is intended, folding the plates of the variable orifice to the adjacent parallel (minimum restriction) condition, inserting the plates through the slot, attaching a mounting plate to the outer surface of the conduit wall and thereafter operating the orifice in the intended manner.

A more complete understanding of the invention can be obtained by reading the following specification which describes an illustrative and preferred embodiment thereof.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENT

Referring to the figures, the variable orifice10comprises first and second semi-circular metal valve plates12,14mounted on a concentric shaft arrangement16which is connected to an actuator gearbox18in such a way that the relative positions of the two plates12,14can be changed by rotation of a manual crank handle20. An indication of the position of the valve plates12,14within a conduit24as hereinafter described in greater detail is provided by the external dial22with a pointer55.

In this case, the conduit24is circular in cross-section and is made of cylindrical steel having internal and external surfaces. As best shown inFIG. 4, the concentric shaft arrangement comprises a central shaft26which extends through the gearbox18and is welded to one of the two plates12,14along an edge thereof so that rotation of the shaft26also changes the angular position of the plate to which it is attached within the interior of the conduit24. The shaft26is connected to a drive gear28which meshes with satellite gears30,32to rotate a second drive gear34which is attached to an external shaft36concentric with the shaft26. The shaft36, thus, rotates in the opposite direction as shaft26. Shaft36is welded along the edge of the other of the two plates12,14so that the two plates12,14, when the shafts26,36are rotated, rotate in angularly opposite directions.

The structure for mounting the variable orifice to the conduit24comprises plates38,42and a gasket40. The plates38and42are drilled and the holes in plate42are tapped to receive bolts41which extend through the gasket into the plate42. A surface of plate42is contoured to fit flush against the circular exterior surface contour of the conduit24and is molded to the conduit sidewall.

For installation purposes, an elongate, key-shaped slot48is cut into the sidewall of the conduit24, and plate42is welded in place, The plates12,14are rotated to the fully folded position shown inFIG. 6Cand are inserted through the plate42and the gasket40, through the aperture or slot48and into the center of the conduit24. It will be noted particularly with reference toFIGS. 3 and 4that the overall diameter of the plates12,14in the fully extended position is substantially less than the interior diameter of the conduit24. Thus, the maximum restriction condition in this illustrative embodiment is approximately 30% of the overall cross-sectional area of the conduit24. The crank20may be operated with the help of the indicator22to place the plates12,14in an intermediate position shown inFIG. 6Bor in the fully extended position shown inFIG. 6Aor in the fully folded (minimum restriction) position shown byFIG. 6C. Multiple intermediate positions are preferably provided by a detent plate46.

The crank20is connected through a shaft in the gearbox44with a worm gear connection to the shaft26so as to rotate the indicator pointer55relative to the indicator dial22so that the pointer always illustrates or represents the angular position of the plates12,14and the degree of restriction created.

For abrasion resistance purposes, collars50,52are welded to the shafts and plates to protect them from abrasion due to the flow of particulate matter through the conduit24. It should be noted that the flow direction in the drawings ofFIGS. 1,6A,6B and6C is from bottom to top; i.e., into the included angle between the plates12,14as shown inFIG. 6B.

It has also been found desirable to mount or form a plug56on the outside of the plate38, which plug extends through slots58,60and into the notch or slot48formed in the sidewall of the conduit24to plug the conduit and prevent both abrasion and leakage. The fit of plug56into slot40should be close, but with enough tolerance to allow for installation.

It will be understood that the invention has been described with reference to an illustrative but preferred embodiment and that a number of variations from the structure illustrated are possible. It will also be understood that the plates12,14and all other elements which are exposed to the abrasive action of particulate flow are preferably made of a wear-resistant material such as high hardness alloys and/or are made of softer metals but protected with either heat-treating or welded on abrasion-resistant materials or both.