Furnaces – Fuel feeders – Feeder responsive to fuel bed height
Reexamination Certificate
2000-02-16
2001-07-17
Ferensic, Denise L. (Department: 3749)
Furnaces
Fuel feeders
Feeder responsive to fuel bed height
C110S297000, C110S182500, C110S106000, C110S10400A, C110S147000, C126S28500B, C251S172000, C251S159000, C251S302000, C251S327000, C251S231000
Reexamination Certificate
active
06260490
ABSTRACT:
FIELD OF THE INVENTION
This invention is in the field of equipment for delivering pulverized coal to coal-fired combustion chambers of the type used in power generating plants, and more particularly relates to the gate or shutoff valve structure commonly found in the delivery pipes between a pressurized coal supply and the combustion chamber.
BACKGROUND OF THE INVENTION
Power plants using coal-fired combustion chambers are typically supplied with coal from an on-premises coal mill or pulverizer. Ground coal “fines” are delivered from the pulverizer to the combustion chamber, often by means of an exhauster fan or some other source of suction or pressure sufficient to pneumatically carry the dust-like fines from the mill through delivery pipes to the combustion chamber.
Occasionally it is necessary to isolate a section of delivery pipe to allow work on a mill, pulverizer, or exhauster fan. Common sense and certain codes require that the system being worked on be isolated from the combustion chamber to prevent a reverse “puff” of positive pressure (and heat, gas or coal dust) from the combustion chamber in reverse through the pipe.
At the present time, it is believed that the National Fire Protection Agency applies certain standards and requirements to such shutoff valves, for example NFPA Valve Requirements 2-5.1.2.1 (Pulverized Fuel Systems):
“2-5.1.2.1 For a suction furnace that can be fired by other main fuels or is connected to two or more pulverizers or exhausters, valves shall be installed to isolate all burner lines. This requirement can be met with one dust tight and one barrier valve or two dust tight valves. A dust tight valve shall be installed in the burner pipe as close to the furnace as practicable. The second valve shall be installed as close to the pulverizer as practicable. The valves shall be closed prior to entering a pulverizer, exhauster, or fuel piping.”
Such valves are not only used for temporarily closing off sections of coal delivery pipe for maintenance, but they may be used to close down certain sections of the piping for as long as several years. They accordingly must be robust, and yet in the case of dust tight valves maintain a tight seal relative to the isolated section of pipe. Other difficulties encountered in the manufacture and installation of such valves include: the release of pressurized fines from the conduit when the valve is opened and closed; the entrapment of fines within various parts of the shutoff valve mechanism; and the need to maintain a dust tight seal around the valve housing or enclosure when the valve is open.
SUMMARY OF THE INVENTION
The present invention is a burner isolation valve and sealing arrangement with a novel pivoting-type opening/closing mechanism for the valve plate; a novel sealed housing for the valve plate as it moves between the open and closed positions; and an improved sealing arrangement in which a built-in seal can be inflated/deflated into and out of sealing engagement with the conduit in the valve-open position and with the valve plate in the valve-closed position.
In a preferred form the valve plate is pivot-mounted in a sealed housing which bisects the coal delivery pipe. The valve plate pivots between open and closed positions while contained entirely within the housing, riding on a pivot point controlled by an external lever or actuator accessible from outside the housing. In one embodiment the valve plate is a novel tear drop-shape which lends itself particularly well to the pivot actuation of the invention.
In a further preferred form of the invention, the housing includes a built-in sealing arrangement associated with the delivery pipe, comprising an annular, inflatable seal mechanism positioned to engage the housing around the perimeter of the delivery pipe in the valve-open position, and to engage the perimeter of the valve plate in the valve-closed position. In this manner the delivery pipe can be sealed from the remainder of the housing in both the valve-open and valve-closed positions. In a first form, the inflatable seal can be pressurized by the same source that supplies pressure to the housing around the conduit. In a second form the seal can be inflated/deflated by a separate pressure source, for example an air/fluid accumulator attached to the housing.
In a further preferred form the housing is sealed dust tight, and is optionally pressurized around the delivery pipe and inflated seal as a backup to the seal to keep coal fines out of the housing, thereby ensuring that the valve plate moves freely and seats properly in the housing in the valve-open and valve-closed positions.
The invention is useful for both dust-tight and barrier valve installations, through use of an optional gasket on the side of the valve plate opposite the inflatable seal.
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Nardi John Anthony
Wark Rickey E.
Ferensic Denise L.
Rinehart K. B.
Sure Alloy Steel Corporation
Young & Basile P.C.
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