GB2121927A

GB2121927A - Isolating valve for a pulverised Fuel pipeline

Info

Publication number: GB2121927A
Application number: GB8315875A
Authority: GB
Inventors: Peter Holdsworth
Original assignee: R A J Thomson
Current assignee: R A J Thomson
Priority date: 1982-06-12
Filing date: 1983-06-09
Publication date: 1984-01-04
Also published as: GB8315875D0

Abstract

An isolating valve for a pulverised fuel pipeline comprises a pipeline section (12) in which is mounted an arcuate valve flap (14) pivotal between an open position shown in figure 1 and a closed position wherein the flap blocks the pipeline section and mates with a valve seat (20). In the open position sealing means (28) on the back of the flap (14) close a port (24) for purging air, that port being opened as the flap moves to the closed position. <IMAGE>

Description

SPECIFICATION Isolating valve for a pulverised fuel pipeline This invention relates to an isolating valve for a pulverised fuel pipeline.

Many electrical power generating stations are fueiled by coal. The coal is generally pulverised in a mill adjacent to the power station boiler and fed to the boiler along pipelines in the form of a fine powder, known as pulverised fuel or 'P F'. PF pipelines are fitted with valves, for example non return valves to prevent blow back from the boiler and isolating valves for separating the pulverised mill from the boiler when desired, for instance for maintenance purposes.

Since pulverised fuel can ignite explosively under certain circumstances the pipelines and valves must of necessity be of a robust construction capable of withstanding transient high pressures far in excess of normal operating pressures. Conventional isolating valves have in general consisted of a shutter which is moved across the pipeline to close it off. Such a shutter requires a housing externally of the pipeline in which the shutter may be held in its retracted position and so such valves are both bulky and introduce weaknesses into the pipeline. When a PF pipeline is isolated it is usual to flush out any remaining pulverised fuel by means of a purging stream of air, an operation that needs to be undertaken independently of and in addition to the closing of the isolating valve. Again, this adds to bulk and introduces potential operating difficulties.

This present invention seeks to provide an isolating valve in which the above disadvantages are reduced or eliminated.

According to the present invention there is provided an isolating valve for a pulverised fuel pipeline, comprising an arcuate valve flap pivotally mounted on a pipeline section so that in an open position the flap conforms closely to the inner surface of the pipeline section and in a closed position the flap substantially fills the whole of the cross-sectional area of the pipeline section and mates with a corresponding valve seat located within the pipeline section to produce a substantially gas-tight seal, a port within the pipeline section connectable to a source of purging air and sealing means carried by the flap and acting to close the port when the flap is in the open position.

The flap of the valve of the invention will be actuated by suitable drive means such as an electric motor, or suitable pneumatic or hydraulic means. Thus the valve may be positively held in its open or closed position. In its open position, the shape of the flap is such that it conforms closely to the inner surface of the pipeline and presents very little obstruction to the free flow of the pulverised fuel passing therethrough; it also closes off the supply of purging air. The whole of the operating mechanism of the valve of the invention (with the exception of the drive means) is located within the pipeline itself and no bulky external housing, which can represent a weak point in high pressure conditions, is necessary.As the valve moves to the closed position the port for the purging air is opened, so allowing purging to occur without the need to operate further controls.

It has been found that in order for a good seal to be obtained between the flap and its seating one or the other should preferably carry a layer of a resilient seating material, for example an elastomeric plastics material such as neoprene rubber. Such a seating material has been found to compensate for any irregularities which may exist in the mating surfaces and provide an effective gas-tight seal. Similarly, it is preferred that the port is surrounded by a seating and the sealing means carried by the flap comprises similar resilient seating material compressible onto the seating when the flap is in the open position.

Particular embodiments of valves in accordance with the invention will now be described further, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a sectional side view of a valve constructed in accordance with the invention; Figure 2 is a plan view of the valve of figure 1; Figure 3 is a detail, on an enlarged scale, of the valve seating; Figure 4 its a perspective view of a second embodiment of the valve of the invention; and Figure 5 is a section on line A-A in figure 4.

Referring to the drawings, it can be seen that a valve generally designated 10 in accordance with the invention comprises a tubular pipeline section 12 forming part of a PF pipeline system between a puiverising mill and a boiler. The valve 10 comprises an arcuate flap 14 which in shape conforms closely to the inner surface of the pipeline section 1 2 and is pivotally mounted on a drive shaft 1 6 externally of the pipeline. A valve seat 1 8 is located within the pipeline and fits closely about its inner circumference. The shape of the seating portion 20 of the valve seat 1 8 corresponds closely with the profile 1 5 of the flap 14 so as to mate therewith.The seating portion 20, as can be seen more clearly from figure 3, carries a sealing layer of high temperature fireresistant neoprene rubber cold bonded to the seat.

A purge air port 24 is provided in the pipeline section 12, being connectable to a source of compressed air. The port 24 has a seat 26 which mates with a resilient sealing layer 28 affixed to the back of the flap 14. The sealing layer 28 may conveniently be of high temperature fire resistant neoprene rubber similar to that employed on the seating surface 20.

The operation of the device is as follows. In figure 1 the flap is in the fully open position where it may be held by a bias being applied to the drive shaft 1 6 by suitable drive means (not shown). In this position neither the seat 18 nor the flap 14 present substantial resistance to flow of pulverised fuel through the pipeline section 12.

The sealing layer 28 mates with the seat 26 of the port 24 thus preventing ingress of compressed purging air through the port 24. Should it be desired to isolate the pipeline, the drive means is employed to turn the shaft 1 6 thereby moving the flap 14 in an anti-clockwise direction as viewed in figure 1 until it mates with the valve seating 20 forming a gas-tight seal therewith, by virtue of the resilient layer 22. Again bias applied by the drive means to the shaft 1 6 maintains the flap tight against the valve seating 20. As the valve closes so as to shut off the pipeline section 12, the flap 14 moves away from the port 24, which is thus opened to compressed air to allow compressed air to pass into the pipeline section 1 2 in order to purge the pipeline.

The device is simple and effective, and being located almost wholly within the tubular pipeline 12, is not bulky and presents the minimum of interruption to the pipeline which can be sources of weakness under high pressure.

It is more reliable and cheaper to manufacture than isolating valves hitherto employed in PF piplines and automatically ailows the entry of purging air as the valve closes.

Referring now to figure 5 and 6, it can be seen that the valve illustrated is similar to the embodiment of figure 1. However, in this embodiment, ducting 32 from the compressed air source feeding the purge air port 24 is taken about the outside of the pipeline section 12 in the area of the valve seat sealing layer 22. Air holes 30 communicating with interior of the pipeline section 12 are provided at regular intervals within the ducting 32. The effect of this arrangement is that the continual flow of purged air travels through the holes 30 from the duct 32 and impinges on the valve seat sealing layer 22 thus maintaining it swept clean of any particles of pulverised fuel which may otherwise tend to settle on it. This ensures that when the flap valve 1 4 closes, a good seal is made between the valve 1 4 and the resilient layer 22 of the valve seat 20. The amount of purged air employed in this way need only be slight and will not interfere with the operation of the PF pipeline in any way.

Figure 5 also shows more clearly the preferred assembly of the valve seating 20 within the pipeline section 12, the two being substantially concentric and being spaced apart by a layer 34 of fireproof grouting.

Claims

1. An isolating valve for a pulverised fuel pipeline, comprising an arcuate valve flap pivotally mounted on a pipeline section so that in an open position the flap conforms closely to the inner surface of the pipeline section and in a closed position the flap substantially fills the whole of the cross-sectional area of the pipeline section and mates with a corresponding valve seat located within the pipeline section to produce a substantially gas-tight seal, a port within the pipeline section connectable to a source of purging air and sealing means carried by the flap and acting to close the port when the flap is in the open position.

2. An isolating valve according to claim 1 in which at least one of the flaps and the valve seat -carries a layer of resilient sealing material compressible to form a seal between the flap and the valve seat when the flap is in the closed position.

3. An isolating valve according to claim 1 and claim 2 in which the port is surrounded by a seating and the sealing means carried by the flap comprises resilient sealing material compressible onto the seating when the flap is in the open position.

4. An isolating valve according to any one of the preceding claims and including ducting connectable to the source of purging air and extending around the outside of the pipeline section substantially following the contour of the valve seat, the wall of the pipeline being formed with holes opening therethrough from the ducting and positioned to direct purging air across the valve seat.

5. An isolating valve for a pulverised fuel pipeline, substantially as herein described with reference to figures 1 and 2 or to figures 4 and 5 of the accompanying drawings.