This invention relates to rotary heat-treatment apparatus of the kind in which material is indirectly heated while passing through a rotating container.

In one known form of such apparatus, a fuel burner discharges into a central firing duct which is arranged on the rotational axis of the container. This arrangement, however, has a number of potential disadvantages, including the relatively large diameter of the container in proportion to the quantity of material which it can handle as a result of the central firing duct, difficulties in mounting the container as a result of thermal expansion, and difficulties in making provision for interchangeable containers for the treatment of different materials at different times.

The present invention seeks to provide a new and improved rotary heat-treatment apparatus having various advantages as will hereinafter be apparent.

According to the invention we provide rotary heat- treatment apparatus comprising a casing defining a generally cylindrical heating chamber, means for heating the interior of said chamber and rotatably mounted within the casing an assembly comprising a plurality of tubular members each spaced from and substantially parallel to the longitudinal axis of the chamber, means being provided for feeding material to be treated into and through said tubular members.

The heating chamber may afford an inlet and c-.-.let for the passage of a fluent heating medium therethrcαgh, and in such a case the heating medium may comprise combustion gases from a fluid fuel burner attached to the casing. In accordance with one feature of the invention means are provided for feeding into such burner or into the heating chamber any volatiles from material heated within

said tubular members so as to provide an after burner for such volatiles

Alternatively the heating chamber may be provided with internal heating means, such as gas or oil fired radiant plaque or other burners, or electrical radiant heating elements for example wire-wound elements or silicon carbide hot rods.

The tubular members may each extend between a pair of mounting plates which effectively close the opposite ends of the casing, one end of each tubular member being fixedly secured to one of said mounting plates and the other end of each tubular member being loosely supported by the other of said mounting plates.

Preferably, the mounting plates are themselves carried by a shaft which extends through the casing on the longitudinal axis thereof.

The shaft may carry at one or more positions along its length supporting members which engage the tubular members at one or more intermediate positions. Conveniently, each supporting member comprises a ring which loosely engages the exterior of the corresponding tubular member and a spacer whereby the ring is mounted on the shaft.

The shaft may be formed as a hollow tube and the tubular members may also comprise circular-section tubes. Preferably, however, each of the tubular members is of non- round section at least internally in order to provide for agitation of material therein during rotation of the assembly of tubular members. For this purpose, circular section tubes may be formed or provided with longitudinally extending internal ribs, for example three in number, spaced equally around the inner face thereof. Alternatively, the tubular members may be of lobed shape in cross-section, for example trefoil shape, as disclosed in British Patent Specifications 1600372 and 1600373.

The apparatus may further include end members spaced axially from the mounting plates to define in combination therewith input and output chambers for the material to be treated, the tubular members opening into such chambers. A duct may be provided between said output chamber and the heating chamber to feed any volatile component from the treated material into the heating chamber, or alternatively such duct may convey volatiles to any suitable external treatment plant.

The external surface of the shaft is preferably covered by a layer of thermal insulation, and similarly a layer of thermal insulation is preferably provided inside the casing.

According to a particularly preferred feature of the invention, the casing comprises two separable components whereby the rotatable assembly can be removed and replaced.

,These and other features of the invention will now be described by way of example with reference to the accompanying drawings wherein:-

FIGURE 1 shows one embodiment of rotary heat- treatment apparatus in side view;

FIGURE 2 is a corresponding end view;

FIGURE 3 is a transverse section on the line 3 - 3 of Figure- 1; and

FIGURE 4 is a longitudinal section on the line 4-4 of Figure 3.

In the embodiment as illustrated, a supporting framework 10 carries a casing 11 comprising a lower shell 12 and upper shell 13, and bearings 14, 15 for a rotatable assembly 20.

The casing 11 defines a cylindrical heating chamber, as most clearly seen in Figure 3. The lower shell 12 is formed or provided with an inlet duct 16 at which a burner assembly may be attached so as to direct combustion

gases substantially tangentially into the chamber at one end thereof. The upper shell 13 is formed or provided with an outlet duct 17 at the opposite end of the chamber.

Adjacent to the inlet duct 16, the shells 12, 13 are provided with extension portions 12a,13a which together define an outlet chamber 18, as hereinafter described, with a discharge opening 19 at the underside. A fume duct 16a extends from the outlet chamber 18 to the inlet duct 16 for the purpose hereinafter described.

The rotatable assembly 20 comprises a tubular shaft 21 with end plates 22 which are apertured for ventilation and carry stub shafts 23 supported in the bearings 14,15. The tubular shaft 21 carries respective mounting plates 24,25 at its opposite ends. Each mounting plate is formed with a plurality (e.g. six) of apertures 24a,25a arranged at equal spacings in a ring concentric with the shaft 21. Open-ended tubes 26 extend between the mounting plates 24,25 and through aligned pairs of the apertures 24a,25a as shown. Each tube is formed with longitudinally extending internal ribs 26a at equal spacings around its inner surface. The tubes 26 are fixedly secured to the mounting plate 25 as by welding or by means of bolted flanges for example, but are loosely supported in the apertures 24a of the other mounting plate 24, so as to allow for thermal expansion. The tubular shaft 21 also carries at spaced intervals along its length a series of supporting members 27 each comprising rings 28 which loosely engage the tubes 26 and spacer members 29 which support the rings 28.

The mounting plate 25 also carries an end-cap member 30 which defines therewith an input chamber 31 for material • to be fed through the apparatus. For this purpose, the end-cap member 30 is formed with an annular inlet opening 32 through which material may be fed, for example from a hopper (not shown) , and inclined baffle

plates 33 associated with the end of each tube 26 act to scoop material from the chamber 31 as the assembly rotates.

In use, the apparatus is mounted with the shaft 21 inclined to the horizontal at an angle of up to about 10° with the input end highest. The assembly 20, comprising shaft 21, mounting plates 24,25, tubes 26, supporting members 27 and end-cap member 30, is rotated for example by means of a variable speed chain drive 34. Combustion gases are provided by a burner attached to the inlet duct 16 and material to be treated is supplied to the input chamber 31.

As the assembly 20 rotates, the material is picked up by the baffles 33 and fed into the tubes 26. The material is tumbled within the tubes and progresses gravitationally towards the outlet chamber 18 whilst being indirectly heated by the combustion gases circulating through the chamber defined by the casing 11. The heated material is then discharged through the outlet 19.

.Volatiles driven off from the material are drawn through the fume duct 16a. into the inlet duct 16 so as to be subjected to an after-burning operation within the heating chamber before being vented through the exhaust duct 17 with the combustion gases.

Stationery seals S may be interposed between the rotating mounting plates 24,25 and the casing as illustrated, but any flow of gases from the interior of the outlet chamber 18 to the interior of the heating chamber, for example through the apertures 24a, can be tolerated in the illustrated embodiment since the fume duct 16a in any event provides for such transfer of the gases.

Insulating material I is provided on the exterior surface of the shaft 21, on the interior surface of the shells 12,13 and on the interior faces of the mounting plates 24,25.

By virtue of the such insulation, and its ventilated construction, the shaft 21 can be maintained at

a low temperature so as to obviate problems with its mounting in the bearings 14,15.

The external burner may produce combustion gases within the heating chamber with a temperature typically up to some 800 or 900°C and up to a maximum of 1200°C. and the operating temperature of the process being performed on the material within the tubes 26 may typically be up to some 800°C and up to a maximum of 1200°C. The tubes 26 are adequately supported through their length by the members 27 and are free to expand longitudinally away from their fixed attachment to the mounting plate 25.

By varying the rate of operation of the burner and the rate of rotation of the assembly 20, the treatment time of material, and its treatment temperature, can be varied.

Returning any volatiles discharged from the material being treated into the heating chamber provides an after-burning process which can be carried out at a temperature sufficient to degrade environmentally detrimental compounds before discharge from the apparatus.

The split construction of the casing 11 makes it possible for the rotatably assembly 20 to be removed and replaced easily. In this way, where necessary interchangeable rotating assemblies can be used to carry out different processes in the same apparatus.

The various components of the apparatus may be constructed from conventional metal alloys suited to the temperature requirements and to the materials to be processed.

Instead of employing an external burner as the source of heat, it is alternatively possible to employ internal burners within the casing 11. For example gas or oil fired radiant plaque type burners may be arranged along the length of the casing and around its inner surface. In such a case it may be convenient for the casing shells to be of flat-faced, i.e. polygonal form so as to afford flat

surfaces on which such burners may be mounted. In a further alternative, internal electric radiant heating elements may be employed, including wire-wound elements or silicon carbide hot rods, within the shells.

Apparatus in accordance with the invention can be used to carry out simple drying processes at a relatively low temperature, and where only water or other non- deleterious substances are driven off from the material to be treated, the fume duct 16a may be omitted if desired.

The apparatus may also be used to carry out such processes as soil reclamation and sterilisation in order to drive off organic spillages such as petrol and oil.

The apparatus may also be used to carry out calcining processes at process temperatures up to about 1200°C.

A further use of such apparatus is for the drying of metallic particles (especially swarf) under reducing or oxygen free conditions. For this purpose an appropriate atmosphere would be introduced into the input chamber 31. Combustible products driven off and any combustible constituent of the treatment atmosphere would then be burned in the heating chamber, thereby reducing the fuel requirement at the burner. The swarf or other material would not be oxidised in the treatment process and would have low oxide weight loss.

Such apparatus may also be used in the treatment of pelletized sludges as a primary burn-out kiln and many other industrial and environmental applications are possible.

The features disclosed in the foregoing description, or the accompanying drawing, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, may, separately or in any

combination of such features, be utilised for realising the invention in diverse forms thereof.