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 resi- dues 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 con-

struction, 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 F1 Pat. Appl. 782,276. Also the embodiments of these publications are hampered by the above-described shortcomings.

It is an object of the present invention to provide a novel type of sealing ar- rangement between the solid-fuel feed system and the combustion space. The sealing arrangement according to the invention is characterized in that the bottom end of the hopper is equipped with a sealing member having a circular edge that is sharpened over its entire pesripheral length.

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 another sealing arrangement according to the invention is characterized in that the seal ring is made from a metallic material.

A still further another sealing arrangement according to the invention is charac- terized in that the actuator mechanism of the gate valve is adapted to first lower the gate valve plate slightly downward from its closed position and thereupon rotate the gate valve plate aside so as to uncover the discharge opening of the feeder hopper and that the closure of the gate valve is adapted to take place in a reverse order.

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 pre- ferred 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 and spirit of the appended claims.