The invention relates to a seal mechanism for a gate valve operable between a solid fuel feed system and a combustion space, such as a gasifier combustion chamber, the fuel feed system comprising a hopper having at least its bottom end portion shaped substantially cylindrical, whereby the gate valve controls the discharge opening of the feeder hopper bottom end, and the gate valve open/closed positions being controllable by means of a gate valve actuator mechanism in such a fashion that a seal is provided between the hopper bottom end and the gate valve.

In power plants and heating installations having direct feed of solid fuels into the combustion space, the combustion space such as the combustion chamber of a gas generator and the portion of the fuel feed system downstream of the fuel feed point generally need to be isolated from each other for process control and safety reasons. This kind of isolation is frequently complicated since fuel residues such as chips, peat clumps or the like objects may remain on the sealing surfaces, whereby safe sealing is problematic. Also the high temperature in the combustion chamber sets high demands on the sealing arrangement.

Conventional gate valves generally operate hingedly so that the gate plate is rotated downward to open and respectively upward to close the gate valve. Then, at the closure of the gate valve, residues of solid fuel may remain between the gate valve and its seat surface. As a result, the gate valve fails to close tightly.

In the art are also known gate valve constructions in which a sliding gate valve is pushed laterally into guide slots accommodating the gate valve plate, Also this arrangement, however, suffers from the same problem as the former construction, namely, that clumps of the solid fuel can prevent safe closure of the gate valve.

Prior-art sealing mechanisms are disclosed, e.g., in patent publications DE-AS 1132676, DE-PS 671726 and Fl Pat. Appl. 782,276. Also the embodiments of these publications are hampered by the above-described shortcomings.

Document GB-A-1447628 discloses a slide valve plate below a hopper for regulating the flow material from it. The valve is held in position by upward pressure using a P-actuated switch with release of pressure being used to open the slide valve. Also the lower end of the hopper is provided with a scrabing member which makes contact with the sliding plate to close the hopper. This sealing arrangement could not be used with combustion spaces, because the sealing member consists of a polyurethane rubber moulding. The seal would not last the very hot conditions of combustion spaces.

It is an object of the present invention to provide a novel type of sealing arrangement between the solid-fuel feed system and the combustion space. The sealing arrangement according to the invention is characterized in that the lower edge of hopper is provided with a sealing member whose edge facing the gate valve plate is annular and is sharpened substantially over its entire circumferential length, and that when opening the gate valve plate it is first lowered slightly downward from its closed position and thereupon rotated aside so as to uncovered the discharge opening at the feeder hopper and that the closure of the gate valve plate is adapted to take place in reverse order, and that the sealing member is made from a metal.

Another sealing arrangement according to the invention is characterized in that the sealing member is a seal ring detachably mounted to the bottom portion of the hopper.

A still further another sealing arrangement according to the invention is characterized in that the movement of the gate valve plate, is carried out with the help of its actuator mechanism.

The invention is further characterized in that, in the opening direction of gate valve, in a close vicinity of the seal ring is mounted a doctor blade adapted to sweep the top surface of the gate valve plate clean from debris as the gate valve plate passes under the doctor blade.

A benefit of the invention is that any fuel residue possibly remaining between the gate valve plate and the sealing member edge is cut into pieces by the sharp edge of the sealing member, whereby the gate valve can close tightly. Advantageously, the gate valve plate is moved hydraulically thus allowing a sufficient force to be imposed thereon for cutting any solid fuel clumps possibly jamming the gate valve.

In the following, the invention is examined in more detail with the help of a preferred exemplary embodiment by making reference to the attached drawings in which

• FIG 1 shows schematically a solid fuel hopper, a gate valve located thereunder and a combustion space below the gate valve in a closed position of the gate valve;
• FIG, 2 shows the same view now with the gate valve driven slightly open; and
• FIG. 3 shows schematically a view taken from below the fuel hopper, now the gate fully opened, that is, rotated aside from below the hopper.

Referring to FIG 1, therein is shown designated by reference numeral 1 a solid fuel hopper that has its bottom portion made at least partially cylindrical and is adapted to feed fuel further into a combustion space 2. Between hopper 1 mounted on a feeder system frame 8 and combustion space 2 is placed a gate valve 3 that can be driven closed so as to cover the cylindrical bottom opening of the hopper. The function of gate valve 3 is to provide sealed isolation of the fuel feed system from the combustion space.

To the bottom portion of the hopper is made or attached an annular seal member whose lower edge tapers downward so as to form a sharp annular cutting rim in cooperation with gate valve plate 3. As the seal member 4 is metallic, it offers an extremely good service life in regard to conventional seals. By way of using a dismountable annular seal as the seal member, the seal can be removed for resharpening when necessary.

In the diagrams, reference numerals 5 and 6 designate the actuator mechanism of gate valve plate 3 employed for opening and closing the gate valve. In FIG. 1, gate valve 3 is shown in its closed position in which the sharp edge of the annular seal member 4 faces gate valve plate 3. To open the gate valve, the gate valve plate is first lowered by the gate valve actuator mechanism 5, 6 slightly apart from the annular seal member 4 as shown in FIG. 2. In the next phase, the same mechanism performs the rotation of the gate valve into the position shown in FIG 3, wherein the gate valve is entirely removed from below hopper 1 thus allowing the solid fuel to fall from hopper 1 into combustion space 3. Simultaneously as gate valve plate 3 is rotated aside, its top surface meets a doctor blade 7 that sweeps the gate valve plate 3 clean from debris.

To close gate valve 3, the gate valve plate is rotated from the horizontal position of FIG. 2 to a closing position below feeder hopper 1. Also during this movement, doctor blade 7 cleans the top surface of gate valve plate 3. At the instant the gate valve plate is in its correct closing position below hopper 1, the gate valve plate is elevated against the annular sealing member 4 applying a vigorous force exerted by hydraulical means, for instance, such that any possible debris still adhering to the gate valve plate top surface is cut apart by the sharp edge of the annular sealing member thus permitting sealed closure of the gate valve.

To a person skilled in the art it is obvious that the invention is not limited to the exemplary embodiment described above, but rather, can be varied within the scope of the appended claims.