The disposal of waste material in this manner is an environmentally attractive proposition as energy can be recovered from the combustion gases. However, it is difficult to achieve reasonable efficiency whilst restricting the emission of pollutants to atmosphere to an acceptable level.

It is known to control the flow of combustion gases exiting the combustion apparatus by employing a damper in the exhaust conduit. Such dampers are generally cast in ceramic and are designed to withstand the high temperatures (e. g. 1000°C or more) of the exhaust gases but are prone to failure as a result of thermal shock and the thermal gradients to which they are subjected. In order to ensure longevity of such a damper it is necessary for the apparatus to be subject to a warm-up procedure in which the temperature is increased in increments prior to full operation. A similar cool-down procedure is required after the apparatus has been used.

It is to be understood that the term"combustion"is used hereinafter in the description and the claims to include starved-air combustion (also known as gasification).

It is an object of the present invention to obviate or mitigate the aforesaid problem and to provide for combustion apparatus with an improved damper.

According to a first aspect of the present invention there is provided combustion apparatus comprising a combustion chamber, an exhaust conduit for the products of combustion and a damper in said exhaust conduit, the damper comprising a body that is movable on a mounting member so as to control the flow of exhaust gases, at least a portion of said damper body interior periphery being hollow, wherein the mounting member has a passage for cooling fluid that is in communication with the hollow portion of the body, the passage being connectable to a supply of cooling fluid.

This arrangement provides for a damper in which the heat of the damper body is removed by the flow of cooling fluid through the mounting member and the body.

Preferably the mounting member is hollow so as to define said passage.

The mounting member may pass through the body and may have apertures that provide communication with the passage and the hollow interior of the body.

Preferably the interior of the body is divided into outer and inner portions the apertures in the mounting member being in communication with the outer portion of the body.

The damper is preferably substantially circular in outline.

Preferably the mounting member has deflector members adjacent to said apertures, the deflector members serving to direct at least a part of the flow of fluid out of the mounting member into the outer portion of the body.

The passage in the mounting member preferably has a restriction that reduces the volumetric flow of fluid along the passage. The restriction is preferably a plate with a fluid bleed aperture.

The damper preferably has an outer skin of ceramic.

The mounting member is preferably a rotary member and more preferably a shaft.

According to a second aspect of the present invention there is provided a damper for controlling the flow gases into or out of a combustion chamber of combustion apparatus, the damper comprising a body mounted on a mounting member, wherein the mounting member has a passage for cooling fluid that is in communication with a hollow portion of the periphery of the interior of the body.

A specific embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a diagrammatic representation of combustion apparatus of the present invention; Figure 2 is a longitudinal cross section through a damper of the combustion apparatus of figure 1; and Figure 3 is a cross section view of the damper along line X-X of figure 2 Referring first to figure 1 of the drawings, the combustion apparatus comprises a combustion chamber 1 and an exhaust conduit 2 in the form of a stack.

At the base of the chamber 1 there is a grate 3 on which the waste material 4 to be combusted is supported. Air may be supplied to the combustion chamber through an appropriate inlet (not shown).

A damper 5 is rotatably mounted in the exhaust conduit 2 and serves to control the flow of exhaust gases (the products of combustion).

Referring now to figures 2 and 3, the damper 5 comprises a generally disc- shaped hollow body 6 supported on a central hollow shaft 7. In operation the damper is rotated in the exhaust conduit 2 on the shaft 7.

The body 6 of the damper comprises an inner structure of upper and lower convex walls 8,9 of stainless steel that are joined together (by, for example, welding) at their peripheries by an annular end wall 10, and an outer skin 11 of hardened ceramic fibre felt. The inner structure defines a hollow interior that is penetrated only by the central shaft 7 that passes through the skin 11 and the end wall 10 at diametrically opposed locations. The upper and lower walls 8,9 are welded to the shaft as indicated at reference numeral 12 and the shaft is welded to the end wall at 13, although other fixing means may be used in both cases. The outer skin 11 is applied by laying a known ceramic fibre felt over the inner structure, wetting with ceramic hardener, shaping the felt to cover the inner structure adequately and then curing the assembly for four hours at 600°C.

The shaft 7, which is fabricated from stainless steel, is hollow and defines a fluid flow passage 20 having inlet and outlet ends 21,22. Mid-way along the length of the shaft 5 the diameter of the passage 20 is restricted by a plate 23 with an air bleed aperture 24. On each side of this plate 23, towards the inlet and outlet 21, 22 ends, the shaft has a pair of transverse slots 25,26 and 27,28 that are offset along the longitudinal axis of the shaft and are at diametrically opposed locations. The slots 25 to 28 provide communication between the shaft passage 20 and the interior of the damper body 6.

Each slot 25,26 of the first pair that are disposed proximal the inlet end 21 of the shaft 7 has a deflector plate 29 extending radially into the shaft passage 20. This plate 29 serves to deflect some of the flow of fluid out of the shaft passage.

The hollow interior of the body 6 to each side of the shaft 7 is divided into pairs of radially inner and outer chambers 30,31 by guide members 32,33. Each guide member 32,33 is formed by bending a thin disc-shaped sheet of stainless steel so that it has an approximately U-shaped cross-section, fixing it to the upper and lower walls 8,9 by riveting or bolting and fixing it to the shaft by welds 34 to form an fluid-tight seal.

The connections between the walls 8,9, guide members 32,33 and shaft 7 provide sealing so that the outer chambers 30,31 are each fluid-tight except for the communication with the passage in the shaft 7.

In operation, a source of pressurised cooling fluid such as, for example, air or water is connected to the inlet end 21 of the shaft 7. A fan or pump (not shown) directs a stream of fluid along the shaft interior into the body 6 of the damper as indicated by arrows A. Inside the damper shaft 7 the fluid stream is incident upon the deflector plates 29 which serve to divert portions of the stream out of the shaft 7 through the slots 25,26 and into the two outer chambers 31. The respective diverted streams pass around the periphery of the damper body 6 and re-enter the shaft passage 20 at the slots 27,28 before passing out of the damper through outlet 22.

Concurrently, a small portion of the fluid stream continues along the shaft passage 20 and passes through the bleed hole 24 in the plate 23.

The flow of fluid through the shaft 7 and the extremity of the damper body 6 interior cools the damper body and the shaft. This ensures that the damper 5 is able to operate in the very high temperature environment of the combustion apparatus over a long period of time without failure. Moreover, if water is used as the cooling fluid, the temperature of the water emerging from the outlet 22 is significantly greater than that at the inlet 21. This hot outlet water may be used in other processes. The provision of the ceramic skin 11 provides protection against high temperature heat radiation It will be appreciated that numerous modifications to the above described design may be made without departing from the scope of the invention as defined in the appended claims. For example, the damper may be of any convenient shape and its components may be constructed from any suitable material. Moreover, the shaft may be replaced by any suitable mounting member that allow movement of the damper body in such a way as to move between open and closed positions in the exhaust conduit. Furthermore the mounting member may be disposed at any convenient location relative to the damper body. Such a damper may also be used on an air inlet of the combustion chamber if necessary.