TECHNICAL FIELD The present invention relates to an incineration plant of the kind set forth in the preamble of claim 1.

BACKGROUND ART

DK-B-154 452 belonging to the applicants discloses a plant of this kind, in which the after-treatment unit is a rotar kiln connected to the exit end of the incineration grate b means of an inclined chute, via which that part of the waste material not yet having been incinerated but merely pre-drie is made to fall down into the rotary kiln, in which it is incinerated so as to form a pure sterile slag.

The more recent DK-B1-168 245 likewise belonging to the ap¬ plicants discloses a method and a plant of a similar kind, in which a rotary kiln is placed immediately downstream o an incineration section with stepped grates, and in which glass-like product is formed in the rotary kiln, and it is evident from this document, perhaps most clearly from it abstract, that the intention is to convert the solid products of combustion resulting from the incineration into a glass like mass, from which salts and heavy metals cannot b leached.

Thus, the problem having been solved with the plant describe in this document is that of providing an after-treatment o these solid products of combustion in such a manner, tha they can be deposited or possibly recycled without placing load upon the environment.

The solution described is, however, in itself problematic, because the infeed end of the rotary kiln must necessaril have a diameter that is greater than the width of the in

cineration grate, the latter again being decisive for the capacity of the incineration plant.

It is, however, for technical reasons difficult to construct rotary kilns with a large diameter, partly because their oval deformation becomes more marked, partly because the wedge-shaped refractory bricks constituting the lining in such a kiln are held in place in the kiln i.a. by a "vault function", and this function sets an upper limit for the diameter of such a lining, i.e. a lower limit for the wedge angle of said refractory bricks. Thus the rotary kiln sets an upper limit for the incineration capacity of the plant.

To this must be added that the solution described cannot be applied to existing older incineration plants, in which space will generally prohibit post-installation of a rotary kiln in extension of the incinerating grate. In order to be able to vitrify the solid combustion products, such as slag and ashes, there is no other way but at some later time to convey these products to a special after-treatment unit, e.g. in the form of an electric melting furnace, which is costly with regard to both energy consumption and labour, partly because in this case, the solid products of combustion are cooled, pos¬ sibly all the way down to room temperature, partly because this procedure requires an additional labour-intensive col¬ lection and transportation of the products of combustion to the after-treatment unit.

DISCLOSURE OF THE INVENTION It is the object of the present invention to provide an in¬ cineration plant of the kind set forth in the preamble of claim 1, with which the above-mentioned problems can be solved, and in which the dimensions of the after-treatment unit, such as the diameter of a rotary kiln, do not set limits for the width of the incineration grate of the plant and hence for its capacity, and in which the measures to be taken

according to the invention, possibly in association with an after-treatment unit, can in most cases be post-installed in an existing older incineration plant.

This object is achieved by means of the features set forth in the characterizing clause of claim 1, said features making it possible to convey the solid products of combustion and possible uncombusted parts of the material to be incinerated leaving the incineration grate directly to the after-treatment unit, so that both the sensible and latent heat contained in the material may be utilized fully for vitrifying slags and ashes in the after-treatment unit. Normally, the conveyor may readily be installed in an older incineration plant in its so-called "slag pit" below the exit end of the incinera- tion grate, and if so, the after-treatment unit may be placed outside of the incineration plant at its side.

The conveyor may be of any type being able to withstand the temperature of the solid products of combustion and possible uncombusted parts of the material leaving the incineration grate, e.g. an endless conveyor of the "caterpillar type", but the embodiment set forth in claim 2 is preferred.

With the embodiment set forth in claim 3, the width of the incineration grate of the plant, and hence its capacity, is completely independent of the diameter of the rotary kiln. With the embodiment set forth in claim 4, the combustion gases from the rotary kiln, from the incineration grate and possibly from the conveyor can be conducted further through the plant. The embodiment set forth in claim 5 facilitates the control of the exit temperature of the vitrified solid pro¬ ducts of combustion. With the embodiment set forth in claim 6, additional heat is supplied to the material fed into the rotary kiln to incinerate uncombusted parts of this material. With the embodiment set forth in claim 7, the vitrified solid products of combustion, being liquid at this location, are

temporarily retained.

Additional embodiments of the incineration plant according to the invention, the effects of which will be evident from the following detailed part of the present description, are set forth in claims 8 and 9.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following detailed part of the present description, the invention will be explained in more detail with reference to the the exemplary embodiments of an incineration plant according to the invention shown in the drawings, in which Fig. 1 is a side view, partly in section, of a first embodi¬ ment, and Fig. 2 is a diagrammatic plan view of a second embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The incineration plant shown in Fig. 1 comprises furnace walls 1, between which is placed a stepped incineration grate, the lowermost grate section 2 of which may be of the kind described in applicants' GB-B-2 120 764, comprising grate blocks placed in alternate reciprocable and stationary rows. A conveyor 3 in the form of a grate section of the same kind as the grate section 2, but with a smaller number of rows of grate blocks, is placed below the lowermost end of the grate section 2. The reciprocable grate blocks in the grate 3 are operated by a motive mechanism 4. The grate 3 leads into the infeed opening of an after-treatment unit in the form of a rotary kiln 5, the rotational axis 6 of which is inclined downwardly in the downstream direction and the exit end 7 of which, being conically narrowed on the inside, debouches into a shaft 8 for collecting the liquid vitrified slags and ashes flowing down from the exit end 7 of the rotary kiln 5. A burner 9 is placed in the wall of the shaft 8 so as to face the exit end 7 of the rotary kiln 5 for controlling the temperature of the vitrified mass. Hot flue gas from the

furnace space and/or air for combustion may be conducted to the exit end 7 of the rotary kiln 5 via the slag shaft 8 by means of suitable ducts (not shown) .

The incineration plant shown in Fig. l operates in the fol¬ lowing manner:

Solid products of combustion and possible uncombusted fuel components leaving the lowermost end of the grate section 2 fall down on the grate 3, by which they are conveyed into the rotary kiln 5, through which they are conveyed in counter- current with the combustion gases, possibly with further combustion taking place, to the internally conically narrowed exit end 7 of the rotary kiln 5, possibly being heated by a flame from the burner 9 to melt into a liquid vitrified mass being temporarily retained by the internal conical restric¬ tion in the exit end 7 before flowing down into the shaft 8.

If, due to considerations of space, it is desired to place the rotary kiln in extension of the furnace grate, this can be achieved with transversely directed grates in the manner shown in Fig. 2. Downstream of the combustion grate 11 there are three conveyors or grates 12, 13 and 14. Of these, two conveyors 12 and 14 placed to the right and the left of the kiln respectively convey the material from the incineration grate 11 towards a conveyor 13 in immediate extension of the incineration grate 11 collecting the material from the latter and from the two transverse conveyors 12 and 14 to discharge it into the rotary kiln or after-treatment unit 15.

It will appreciated that the incineration plants shown and described may be more modified in several ways within the scope of the claims. Thus, the grate 3 could e.g. be replaced by an endless conveyor, and the rotary kiln 5 could be re- placed by an electrically heated furnace suitably constructed as an after-treatment unit.

LIST OF PARTS

1 Furnace wall

2 Lowermost grate section

3 Conveyor or grate 5 4 Motive mechanism

5 Rotary kiln

6 Rotational axis

7 Exit end

8 Shaft 10 9 Burner

11 Incineration grate

12 Conveyor or grate

13 Conveyor or grate 15 14 Conveyor or grate

15 Rotary kiln