WO2005064236A1

WO2005064236A1 - Inlet valve

Info

Publication number: WO2005064236A1
Application number: PCT/IL2004/001150
Authority: WO
Inventors: Valeri G. Gnedenko; Igor V. Goryachev; Sergei A. Dmitriev; David Pegaz
Original assignee: E.E.R. Environmental Energy Resources (Israel) Ltd.
Priority date: 2003-12-29
Filing date: 2004-12-20
Publication date: 2005-07-14
Also published as: TW200530535A; IL159635A0

Abstract

A sealing door (130) reciprocates in a horizontal manner to close or open an opening. A downwardly-depending sealing gasket (153) is provided along the periphery of the opening, for sealing against the door when the door is pressed upwards against the gasket. For this purpose, wedges (177, 179) are provided to force the door upwards, in a direction essentially orthogonal to the horizontal, at the end of its closing lateral travel. A scraper is provided at one horizontal end of the opening to scrape material off the upper surface of the door to avoid interference with the sealing gaskets. The door may be water cooled.

Description

INLET VALVE

Technical Field

The present invention relates to an improved arrangement for an inlet valve, typically for an inlet valve used to provide material such as waste to a high temperature processing chamber. In particular the present invention is directed to such inlet valves configured to minimize interference with the working thereof by material such as waste.

Background

The processing of waste including municipal waste, medical waste, toxic and radioactive waste by means of plasma-torch based waste processing plants is well known.

One problem commonly encountered in such processing plants is the complete sealing off of the waste within the shaft furnace or processing chamber of the plant from the waste input system, by means of a waste inlet arrangement having one door, and preferably an air lock. Waste material is fed into the processing chamber by means of a single horizontal door, but more commonly via a series of horizontal doors forming an air lock. Waste material thus often rests on one or more of these doors when the doors are in the closed position. When each door is opened in turn, the waste material is fed through the opening made thereby in a descending direction. Often the waste material, comprising mixtures of solids and liquids, may be viscous and/or sticky, and will adhere to the mating edges of the door with the door frame, causing interference between the two and preventing full sealing of the door. Imperfect sealing of the waste inlet may allow product gases to escape via the waste inlet system which can create a fire hazard in the waste inlet system. More importantly, imperfect sealing may enable air to be introduced into the processing chamber which may cause a potential fire or explosion hazard in the processing chamber. While an air lock system having at least two airlock doors reduces the possibility of such gaseous interchange between the processing chamber and the outside, fouling of the doors by waste material can still cause problems. Furthermore, such doors need to operate in a high temperature environment, which can also lead to thermal expansion problems as well as mechanical weakening of the door structure and damage to non-metallic sealing gaskets.

Related problems are also encountered in other high temperature applications where it is necessary to provide material to a high temperature processing chamber via an upper inlet, for example in the provision of metallic ore to a shaft furnace or in processing radioactive waste.

US 5,120,087, US 3,886,685, and JP 08014756 all disclose mechanisms that enable a vertical door leaf to move along a vertical plane (between the open and closed positions), providing insulating contact with the frame. However, none of these references deal with the special problems of a door that moves along a horizontal plane on which waste material, which may foul the sealing mechanism between the door and the frame, may be deposited during operation thereof.

US 4,570,550, US 4,808,205, US 4,182,610 and US 6,415,724 each describe a particular cooling arrangement for a high temperature application door, such as a furnace. However, none of these documents is directed to providing a solution to the problem of ensuring that waste material that is fed vertically into a processing chamber via a door arrangement does not interfere with operation of the door.

It is therefore an aim of the present invention to provide a door or valve arrangement for the inlet which overcomes the limitations of prior art door arrangements.

It is another aim of the present invention to provide such an arrangement that is particularly adapted for high temperature applications including the waste inlet system of a plasma waste converting plant.

It is another aim of the present invention to provide such an arrangement that may be incorporated into a municipal solid waste processing apparatus. It is another aim of the present invention to provide such an arrangement that is relatively simple mechanically and thus is economical to incorporate into a processing plant design.

It is another aim of the present invention to provide such an arrangement that may be incorporated as an integral part of a plasma-torch based type waste converter.

It is also an aim of the present invention to provide such an arrangement that may be readily retrofittable with respect to at least some existing plasma-torch based waste converters.

It is another aim of the present invention to provide such an arrangement the operation of which is substantially unaffected by the thermal conditions within the chamber.

Other purposes and advantages of the present invention will appear as the description proceeds.

Summary of the Invention

This invention relates to a sealing door that reciprocates in a horizontal manner to close or open an upper opening. A downwardly-depending sealing gasket is provided along the periphery of the opening, for sealing against the door when the door is pressed upwards against the gasket. For this purpose, wedges are provided to force the door upwards at the end of its closing lateral travel. A scrapper is provided at one horizontal end of the opening to scrape material off the upper surface of the door to avoid interference with the sealing gaskets. The door may be water cooled.

In a first aspect, the present invention provides a valve arrangement for selectively opening and closing an inlet port. The valve arrangement of the invention comprises a housing having a peripheral frame member associated with the inlet port and a door member comprising motive means for slidingly and reversibly moving the door member from an open position to a closed position with respect to the frame member. The valve arrangement further comprises abutment means for urging the door member against a suitable peripheral gasket comprised in the frame member for forming a seal against a corresponding peripheral portion of the door when in the closed position. The valve arrangement is characterized in comprising scraper means for removing unwanted deposited material from the door when the door is moved with respect to the frame.

In a preferred embodiment of the valve arrangement of the invention, the abutment means provides a motion to the door member that is substantially orthogonal with respect to the motion provided by the motive means. In one embodiment, the abutment means comprises a plurality of pairs of wedges. Each pair of wedges comprises a static wedge that is substantially fixed in relation to the frame and a corresponding lifting wedge mounted onto the door member. The wedges are configured with facing sloping surfaces such that when the door member is slid into the closed position, the lifting wedges are translated towards the frame member by virtue of contact with the static wedges thereby lifting the door into an abutting and sealing position with respect to the gasket, in a preferred embodiment of the invention, at least one pair of wedges is located at a leading edge of the door and at least one pair of wedges at a trailing edge of the door.

In another embodiment of the invention, the abutment means comprises a plurality of suitable wheels on either side of the door and corresponding rails substantially parallel to the direction of motion of the door member. The wheels are preferably operatively connected to a suitable motor, winch system or other motive means such as to provide the required longitudinal motion to the door.

In one embodiment, the wheels are in the form of suitable cams, having a profiled portion such that when the wheels are reversibly rotated until the profiled portions come into contact with the rails, the door is urged into sealing contact with the gasket. In another embodiment, each of the rails comprises a pair of suitably profiled inclined sections that are positioned with respect to the frame such that when the wheels pass over the inclined sections, the door is urged into sealing contact with the gasket.

In a preferred embodiment of the valve arrangement of the invention, the door member is adapted for movement along a substantially horizontal plane.

In a preferred embodiment of the valve arrangement of the invention, the motive means comprises an electric drive operatively connected to a rod to provide reciprocating translational movement to the door member. One end of the rod is connected to the underside of the door member via a suitable link. Preferably, the link allows for vertical movement between the door and the rod.

In the preferred embodiment of the valve arrangement of the invention, the valve is particularly adapted for use in a high temperature environment. In some embodiments, the high temperature environment may comprise a temperature in the range of between about 200 to 400°C. The high temperature environment may be associated with a plasma torch based waste processing plant.

The valve arrangement of the invention may further comprise a cooling system for cooling the door member. The cooling system may comprise a suitable coolant source in communication with the hollow interior of the door member via a suitable pump and radiator means. The cooling system may comprise flexible conduits between the door member and the coolant source adapted for allowing for movement of the door member between the open and closed positions.

In a preferred embodiment, the scraper means of the valve arrangement of the invention comprises at least one forward-facing first scraper mounted to the housing within the frame for scraping accumulated material off a leading edge portion of the door as the door is moved to the open position. Preferably, the first scraper substantially spans the width of the frame substantially orthogonally to the direction of motion of the door member. In some embodiments, a leading edge of the door member has a downwardly sloping upper portion such that any material raked by means of the scraper means is pushed off an upper surface of the door member at least by the time the leading edge comes into proximity with the scraper means. The first scraper is mounted on a suitable arrangement that urges its leading, scrapping edge into contact with an upper surface of the door member when the door member is in the open position, and enables the leading, scrapping edge of the first scraper to be lifted together with the door member when moved to the closed position. Another embodiment of the valve arrangement of the invention further comprises a rearwards-facing, second scrapper longitudinally displaced from the first scraper, for removing any further material that may have accumulated on an upper surface of the door member away from a leading edge of the door member.

In another aspect, the invention presents an air lock system comprising at least two of the valve arrangements of the invention and a chamber therebetween.

Description of the Figures

- Figure 1 shows schematically the general layout and main elements of a typical waste plasma processing apparatus of the prior art;

- Figure 2 shows schematically in transverse cross-sectional view the general relationship between the main elements of a first embodiment of the valve unit of the present invention;

- Figure 3A and Figure 3B show in fragmented view the action of the abutment means of the first embodiment when the door is in the process of being closed;

- Figure 4A and Figure 4B show in fragmented view the action of the scraper means when the door is in the process of being closed; - Figure 5A and Figure 5B show in fragmented view the action of the abutment means of the second embodiment when the door is in the process of being closed; and

- Figure 6A and Figure 6B show in fragmented view the action of the abutment means of the third embodiment when the door is in the process of being closed.

Disclosure of the Invention

The present invention is defined by the claims, the contents of which are to be read as included within the disclosure of the specification, and will now be described by way of example with reference to the accompanying figures. The term "waste converting apparatus" herein includes any apparatus adapted for treating, processing or disposing of any waste materials, including municipal waste (MSW), household waste, industrial waste, medical waste, sewage sludge waste (SSW), radioactive waste and other types of waste, in particular by means of plasma treatment.

Referring to Figure 1, a typical plasma waste processing converting apparatus or plant, designated by the numeral (100), comprises a shaft (vertical) furnace or processing chamber (10). Typically, a solid or mixed waste feeding system (20) introduces waste at the upper end of the chamber (10) via a waste inlet means comprising an air lock arrangement (30). The waste feeding system (20) may comprise any suitable conveyor means or the like, and may further comprise a shredder for breaking up the waste into smaller pieces. The air lock arrangement (30) may comprise an upper valve (32) and a lower valve (34) defining a loading chamber (36) therebetween. The valves (32), (34) are preferably gate valves operated electrically, pneumatically or hydraulically to open and close independently as required. Typically, a closeable hopper arrangement (39) funnels typically solid and/or mixed waste from the feeding system (20) into the loading chamber (36) when the upper valve (32) is open, and the lower valve (34) is in the closed position. Feeding of waste into the loading chamber (36) typically continues until the level of waste in the loading chamber (36) reaches a predetermined point below full capacity, to minimize the possibility of any waste interfering with closure of the upper valve (32). The upper valve (32) is then closed. In the closed position, each of the valves (32), (34) provides an air seal. When required, the lower valve (34) is then opened enabling the waste, accompanied by relatively little or no air, to be fed into the processing chamber (10).

The opening and closing of the valves (32), (34), and the feeding of waste from the feeder (20) may be controlled by any suitable controller (not shown), which may comprise a human controller and/or a suitable computer control system, operatively connected thereto and to other components of the plant (100). Optionally, the hopper arrangement (39) may comprise a disinfectant spraying system (31) for periodically or continuously spraying the hopper and/or its contents with disinfectant, as required, particularly when medical waste is being processed by plant (100).

The processing chamber (10) also comprises a lower part in which pyrolysis takes place. The lower part of the chamber comprises a plurality of plasma torches (40), an oxidizer inlet (75), and a liquid product collection zone (41) having at least one outlet (65) associated with one or more collection reservoirs (60). The processing chamber (10) further comprises at the upper end thereof, and above the top of refuse column 35, at least one gas outlet (50), primarily for channeling away product gases.

The inner facing surfaces of processing chamber (10), at least of the lower part thereof, are typically made from one or more suitable refractory materials, such as for example alumina, alumina-silica, magnesite, chrome- magnesite, chamotte or firebrick. Typically, the processing chamber (10), and generally the plant (100) as a whole, is covered by a metal layer or casing to improve mechanical integrity thereof and to enable the processing chamber to be hermetically sealed with respect to the external environment.

The present invention is directed to a valve or door arrangement that may be used for selectively opening and closing an inlet port, such as, for example, the waste inlet port of a waste processing plant or any other material inlet port used to provide material to a chamber, particularly a high temperature processing chamber. Such high temperature processing chambers may include, for example, shaft furnaces for processing metal ore.

Referring to Figure 2 in particular, a first embodiment of the door or valve arrangement according to the present invention is schematically shown. This embodiment comprises a valve unit (1) that may be integrally or retrofitably mounted via interfacing collar (110) to a waste processing plant, or indeed to any plant or apparatus that requires material to be fed through an upper opening into a reservoir or processing chamber. The valve unit (1) comprises a housing (120) comprising an peripheral frame member (150) and a lid, cover or door (130) that is adapted to slidingly and reversibly move from an open position to a closed position. In the open position, the door (130) is retracted into a chamber (140), and in the closed position, the door is in substantially overlapping arrangement with respect to, and below, the frame (150). The frame (150) comprises a downwardly projecting suitable peripheral gasket (153) for forming a seal against a corresponding peripheral portion of upper surface (132) of the door when the upper surface (132) is urged towards the frame (150) and particularly makes peripheral contact with gasket (153). The gasket (153) is made preferably from a heat resistant material such as, for example, viton or other heatproof plastic.

Preferably, the housing (120) comprises a buffer space (122) at one end thereof opposed to said chamber (140) so as to prevent any waste material that may be present on the door from being trapped between the leading edge (151) of the door and the housing when the door (130) is in the closed position.

Suitable seals (144) are also provided in the chamber (140) for sealing the same with respect to the door (130), and are made preferably from a heat resistant material such as, for example, viton or other heatproof plastics.

Suitable motive means are provided for enabling the door (130) to be reversibly moved between the open and closed positions. In the embodiment illustrated in Figure 2, the motive means comprises an electric drive (116) operatively connected to a rod (107) to provide reciprocating translational movement thereto. One end of rod (107) is connected to the underside (133) of door (130) via a suitable floating link (113). Alternatively, the motive means may comprise any suitable hydraulic, pneumatic, electrical or other arrangement for providing the required selective reciprocating^' motion to the door (130). Suitable seals (146) are provided for sealing the housing with respect to the motive means, and are made preferably from a heat resistant material such as , for example, viton or other heatproof plastics.

Lifting or abutment means (170) are provided for urging the door (130) into an abutting position with respect to the frame (150) when the door (130) is in overlapping relationship therewith. In the first embodiment, and referring also to Figures 3A and 3B, the abutment means (170) comprises a plurality of pairs of cams or wedges, preferably at least one pair of wedges at the leading edge (151) of the door (130), and at least one pair at the trailing edge (152) of the door (130). Each pair of said wedges comprises a static cam or wedge (177) that is fixed in relation to the frame (150), and a corresponding lifting cam or wedge (179) that is mounted onto the door (130). The wedges (177), (179) are configured with facing suitably contoured curved or sloping surfaces (176), (178), such that when the door (150) is moved into the closed position, the lifting wedges (179) are lifted upwards by virtue of contact with the static wedges (177), as illustrated in Figure 3B, lifting the door (150) into an abutting and sealing position with respect to gasket (153). The floating link (113) allows for such vertical movement with respect to the rod (107). Thus, the abutment means provides a motion to the door substantially orthogonal with respect to the motion provided by the motive means.

Preferably, and referring to Figures 4A and 4B in particular, at least one forward-facing first scraper (180) is provided close to the chamber (140) and within the frame (150) for scraping waste off the upper surface (132) preferably starting at the leading edge (151) of the door (130), as the door is moved to the open position. In this manner, the first scraper (180) substantially removes any waste or other material that my have accumulated on the upper surface (132) including the leading edge (151), and prevents waste from interfering with the retraction of the door (130) into the chamber (140). Thus, when the door (130) is subsequently moved to the closed position, any waste that was on the upper surface (132) and which could otherwise become trapped between the upper surface (132) and the gasket (153) is no longer able to interfere and prevent full sealing between the door and the frame. Accordingly, the first scraper (180) substantially spans the width of the frame (150). Preferably, the leading edge (151) of the door has a downwardly sloping upper portion (157) such that any waste raked or otherwise displaced by means of the scraper (180) is easily pushed off the upper surface (132) by the time the leading edge (151) comes into proximity with the first scraper (180).

The first scraper (180) is mounted on a suitable arrangement that provides contact between the leading, scraping edge (182) of the scraper (180) and the upper surface (132), when the door (130) is in the unsealed position, and thus distanced below the gasket (153). Such an arrangement may comprise, for example, a spring (184) or the like, including a jack or any other arrangement that on the one hand provides this required scraping contact, and on the other hand allows the leading edge (182) of the scraper to be lifted together with the door (130) when the latter is lifted or abutted to the closed, sealed position. Optionally, the first scraper may be integrally incorporated into the frame (150). Optionally, the door arrangement (1) may further comprise a rearwards- facing, second scrapper (190), that spans the width of the frame (150) and is longitudinally displaced from the first scraper (180). The second scraper (190) serves to remove any further waste that may have accumulated on the upper surface (132) away from the leading edge (151). It is to be noted that, since the width of the door (130) is less than the interior width of the housing (120), waste that is pushed to the sides by the scrappers will fall into the interfacing collar (110) and will not interfere with the sealing at the side portions of the gasket.

In the preferred embodiment, and referring to Figure 2 showing the door arrangement (1), the door (130) is made of metal, such as stainless steel and further comprises a cooling system for cooling the door (130), particularly when in the closed position. The cooling system typically comprises a coolant inlet (141), leading cooling water into the hollow interior of the door (130), and a larger diameter coaxial pipe that provides a coolant outlet (142). The inlet (141) and outlet (142) pipes are in communication with an external coolant source, including a pump and radiators (not shown), for example, to enable coolant to circulate into the interior of the door (130) and remove heat to an external location. Flexible connectors (not shown) are provided between the coolant source and the door to allow for movement of the door (130) between the open and closed positions. The coolant can be any suitable liquid coolant such as water. Referring to Figures 5A and 5B in particular, a second embodiment of the present invention comprises all of the elements and features of the first embodiment, as described herein mutatis mutandis, with the following difference. In the second embodiment, the abutment means (270) comprises a plurality of suitable wheels (280) on either side of the door (230), running over rails (290) substantially parallel to the direction of motion of the door, the wheels being operatively connected to a suitable motor, winch system or other motive means (not shown) such as to provide the required longitudinal motion to the door (230). The wheels are in the form of cams, having a profiled portion (282) such that when the wheels (280) are rotated until the portions (282) come in contact with the rails (290), the door (230) is urged upwardly into sealing contact with the gasket (153). Conversely, as the door (230) is retracted into the chamber (140), the wheels (280) rotate backwards, and initially lower the door (230) away from the gasket (153) prior to retracting the door into the chamber (140). The essentially elliptically shaped cams must be designed to have a circumference such that when rotating from the location in which the minor axis is essentially vertical to the location at which the major axis is essentially vertical, the door will be moved from its open to its closed position. Alternatively, the cams can be caused to slide without rotating until they reach the required location, at which point they are rotated from their lowest to their highest height. Referring to Figures 6A and 6B in particular, a third embodiment of the present invention comprises all of the elements and features of the first or second embodiments, as described herein mutatis mutandis, with the following difference. In the third embodiment, the abutment means (370) comprises a plurality of suitable wheels (380) on either side of the door (330), running over rails (390) substantially parallel to the direction of motion, the wheels being operatively connected to a suitable motor, winch system or other motive means (not shown) such as to provide the required longitudinal motion to the door (330). Each rail comprises a pair of suitably profiled raised sections (382) that are strategically positioned with respect to the frame (150) such that when the wheels (380) pass over the inclined section (384), the door (330) is urged and translated upwardly into sealing contact with the gasket (153). Conversely, as the door (330) is retracted into the housing (140), the wheels (280) rotate backwards and down the inclined sections (384), and initially lower the door (330) away from the gasket (153).

While the valve unit of the present invention has been described with respect to the feeding of waste into an inlet, particularly of a waste processing plant, the valve unit of the present invention is also directed in a similar manner, mutatis mutandis, to applications in which a material needs to be fed to a chamber via an inlet, particularly when the chamber provides a high temperature environment. The present invention also relates to an air lock system comprising at least two said valve units (1) having a chamber therebetween such that communication between the two sides of the airlock is via the chamber when the corresponding doors are in the open position.

While the foregoing description describes in detail only a few specific embodiments of the invention, it will be understood by those skilled in the art that the invention is not limited thereto and that other variations in form and details may be possible without departing from the scope and spirit of the invention herein disclosed.

Claims

1. A valve arrangement for selectively opening and closing an inlet port, comprising a housing having a peripheral frame member associated with said port and a door member comprising motive means for slidingly and reversibly moving said door member from an open position to a closed position with respect to said frame member, abutment means for urging said door member against a suitable peripheral gasket comprised in said frame member for forming a seal against a corresponding peripheral portion of said door when in the closed position, and scraper means for removing unwanted deposited material from said door when said door is moved with respect to said frame; csharacterized in that said abutment means provides a motion to said door member substantially orthogonal to the motion provided by said motive means.

2. A valve arrangement as claimed in claim 1, wherein the abutment means comprises a plurality of pairs of wedges, each pair of said wedges comprising a static wedge that is substantially fixed in relation to the frame and a corresponding lifting wedge mounted onto the door member.

3. A valve arrangement as claimed in claim 2, wherein the wedges are configured with facing sloping surfaces such that when the door member is slid into the closed position, the lifting wedges are translated towards the frame member by virtue of contact with the static wedges thereby lifting said door into an abutting and sealing position with respect to the gasket.

4. A valve arrangement as claimed in claim 2, comprising at least one pair of wedges at a leading edge of the door and at least one pair of wedges at a trailing edge of the door.

5. A valve arrangement as claimed in claim 1, wherein the abutment means comprises a plurality of suitable wheels on either side of the door and corresponding rails substantially parallel to the direction of motion of said door member, wherein said wheels are in the form of suitable cams, having a profiled portion such that when the wheels are reversibly rotated until the profiled portions come in contact with the rails, said door is urged into sealing contact with the gasket.

6. A valve arrangement as claimed in claim 5, wherein the wheels are operatively connected to a suitable motor, winch system or other motive means such as to provide the required longitudinal motion to the door.

7. A valve arrangement as claimed in claim 1, wherein the abutment means comprises a plurality of suitable wheels on either side of the door and corresponding rails substantially parallel to the direction of motion of the door member, wherein each of said rails comprises a pair of suitably profiled inclined sections that are positioned with respect to the frame such that when said wheels pass over said inclined sections, the door is urged into sealing contact with the gasket.

8. A valve arrangement as claimed in claim 7, wherein the wheels are operatively connected to a suitable motor, winch system or other motive means such as to provide the required longitudinal motion to the door member.

9. A valve arrangement as claimed in claim 1, wherein the door member is adapted for movement along a substantially horizontal plane.

10. A valve arrangement as claimed in claim 1, wherein the motive means comprises an electric drive operatively connected to a rod to provide reciprocating translational movement to the door member, one end of said rod being connected to the underside of said door member via a suitable link.

11. A valve arrangement as claimed in claim 10, wherein the link allows for vertical movement between the door and the rod.

12. A valve arrangement as claimed in claim 1, wherein the valve is particularly adapted for use in a high temperature environment.

13. A valve arrangement as claimed in claim 12, wherein the high temperature environment comprises a temperature in the range of between about 200 to 400°C.

14. A valve arrangement as claimed in any 12, wherein the high temperature environment is associated with a plasma torch based waste processing plant.

15. A valve arrangement as claimed in claim 1, further comprising a cooling system for cooling the door member.

16. A valve arrangement as claimed in claim 15, wherein the cooling system comprises a suitable coolant source in communication with the hollow interior of said door member via a suitable pump and radiator means.

17. A valve arrangement as claimed in claim 16, wherein the cooling system comprises flexible conduits between the door member and the coolant source adapted for allowing for movement of said door member between the open and closed positions.

18. A valve arrangement as claimed in claim 1, wherein the scraper means comprises at least one forward-facing first scraper mounted to the housing within the frame for scraping accumulated material off a leading edge portion of the door as said door is moved to the open position.

19. A valve arrangement as claimed in claim 18, wherein the first scraper substantially spans the width of the frame substantially orthogonally to the direction of motion of the door member.

20. A valve arrangement as claimed in claim 1, wherein a leading edge of the door member has a downwardly sloping upper portion such that any material raked by means of the scraper means is pushed off an upper surface of said door member at least by the time said leading edge comes into proximity with said scraper means.

21. A valve arrangement as claimed in claim 18, wherein the first scraper is mounted on a suitable arrangement that urges the leading, scrapping edge of said first scraper into contact with an upper surface of the door member when said door member is in the open position, and enables said leading, scrapping edge of said first scraper to be lifted together with said door member when moved to the closed position.

22. A valve arrangement as claimed in claim 18, further comprising a rearwards-facing, second scrapper longitudinally displaced from the first scraper, for removing any further material that may have accumulated on an upper surface of the door member away from a leading edge of said door member.

23. An air lock system comprising at least two valve arrangements as claimed in claim 1 and a chamber therebetween.