METHOD AND APPARATUS FOR INCINERATING DIFFERENT KINDS OF SOLID AND POSSIBLY LIQUID WASTE MATERIAL

Abstract: Solid and possibly liquid waste material is incinerated by a) partial combustion on the stepped grates (9, 10, 11) of the solid waste material, the latter being delivered to the rotary kiln (2) at such a high temperature, that a liquid slag is formed at the inlet of the rotary kiln, b) possibly adding liquid waste material to the solid waste material being incinerated on the stepped grates (9, 10, 11), and c) collecting the ash products from the combustion process, such as grate screenings, boiler ash, fly ash, and residual products from flue-gas cleaning, and returning these products to the input end (12) of the rotary kiln (2), at which input end these products are introduced into the liquid slag. In this manner, it is achieved that the slag, fly ash and other harmful residual products from the combustion process are fused into a glass-like mass, from which salts and heavy metal cannot be leached out.

Description: METHOD AND APPARATUS FOR INCINERATING DIFFERENT KINDS OF SOLID AND POSSIBLY LIQUID WASTE MATERIAL TECHNICAL FIELD The present invention relates to a method of the kind set forth in the preamble of claim 1. BACKGROUND ART With the steadily increasing quantities of waste material and the increasingly strict environmental requirements to the incineration of this material, the use of flue-gas cleaning results in the production of increasingly greater quantities of harmful residual products. In the waste incineration plants known at the present moment, the temperature of combustion is held below 1100 β C, e.g. at approximately 875°C, in order to avoid the formation of liquid slag at the side walls of the grate section and in the rotary kiln, this slag having a tendency to solidify at the sides of the furnace and obstruct the exit end of the rotary kiln. These plants are so adapted and designed that the slag and the ash are discharged as a dry or moistened inho ogenous mixture respectively in as many as three different discharge assemblies. Thus, boiler ash is obtained from the boiler assembly, e.g. being of the impact-descaling type, and fly ash from an electrical filter. Further, flue-gas cleaning is performed by adding e.g. lime, after which the flue gas passes through a filter or a flue-gas washing arrangement, in which a residual product is separated out. Further, "small waste" falls through the grate, and such grate screenings are taken to a slag outlet. It is, however, necessary that less than 3% of the slag is un-combusted. These known plants do, of course, suffer from the dis¬ advantages that the salts and heavy metals atthached to the slag, the fly ash and the residual products from the flue-gas washing arrangement may be leached out, and some heavy metals evaporate during the process. For this reason, these products must be deposited in a safe manner, e.g. by being placed in controlled waste-disposal sites, thus producing a percolate of a kind causing a considerable damage to the environment, or in salt mines. DISCLOSURE OF THE INVENTION It is the object of the present invention to make the slag, fly-ash and other harmful residual products produced by the combustion of solid and/or liquid waste material harmless, and this object is achieved with a method of the kind referred to initially, which according to the present invention is characterized by the features set forth in the characterising clause of claim 1. In this manner, it is achieved that the substances in question are encapsulated in the relatively hot, liquid slag when passing through the rotary kiln, so that the product from the incineration of the waste material becomes a harmless, glassified slag incapable of giving off harmful substances, such as heavy metals, for which reason this slag may be deposited without problems. This incineration of waste material can be carried out in a plant, in which types of waste material being fed in, possibly through a number of feeding arrange- ments, are dried, ignited, and combusted. The solid waste material is burnt to form a not completely burnt-out slag, the latter being plunged into a rotary kiln in direct-line communication with the grate section, in which rotary kiln this slag mixture and the separately fed residual products from the flue-gas cleaning arrangement are fused together so as to form a glass-like mass. The rotation of the rotary kiln enhances the burning-out and fusing of the mass to form a homogenous substance. With the embodiment set forth in claim 2 it is achieved that the slag does not solidify in the rotary kiln. The embodiment set forth in claim 5 makes it possible, if necessary, to ensure maintaining such a high temperature, that the slag does not solidify in the rotary kiln. This causes variations in the calorific value of the waste material to be reduced, and a continuous supply of molten material is ensured. The present invention also relates to an apparatus for use in carrying out the method, said apparatus being of the kind set forth in the preamble of claim 6. According to the present invention, the apparatus is constructed in the manner set forth in the charac¬ terizing clause of claim 6. With the embodiment set forth in claim 8, the advantage is achieved that the least possible amount of air is added, at the same time as the oxygen supplied to the combustion process is utilized to a maximum extent. The atmosphere produced in this manner, partly having reducing properties, lowers the melting point for various indifferent materials without the need of adding reducing agents. With the embodiment set forth in claim 9 it is achieved that the liquid slag remains in a pocket at the lowermost part of the rotary kiln, until it has been completely glassified. BRIEF DESCRIPTION OF THE DRAWINGS In the following specification, the present invention will be explained in more detail with reference to the drawings, in which Figure 1 diagrammatically shows the principle of functioning of the apparatus according to the present invention, Figure 2 is a diagrammatical sectional view through an apparatus constructed according to the present invention, and Figure 3 is a sectional view along the line III-III in Figure 2, showing the feeding-in of the residual products. DESCRIPTION OF THE PREFERRED EMBODIMENT The plant shown in Figure 2 consist of a grate section 1, a rotary kiln 2, a burner assembly 3, a residual- product silo 4, an after-burning chamber 5, a boiler assembly 6, and a residual-product conveyor 7. Waste material 21 to be burnt, mainly consisting of household refuse, bark, industrial waste, hospital refuse, and in part chemical waste material in a relatively inhomogenous mixture, is supplied to the plant through a hopper 20 and a feed chute 8 shown to the left in Figure 2. The material having been fed in is distributed on grates 9, 10 and 11, these grates also receiving any liquid waste material, and air 31 for combustion is supplied from below. Grate screenings, i.e. small pieces of waste material, possibly containing unburnt material and having fallen through the grates 9, 10 and 11, are conveyed to the residual-products silo 4 by a belt conveyor 17 and the conveyor 7. The incompletely burnt slag formed during the burning in the grate section is discharged in a manner known per se into the rotary kiln 2. At the transition 12 from the grate section 1 to the rotary kiln 2, the residual products collected in the intermediate silo 4 are fed in through a dosing worm conveyor 13, and the residual products are mixed with each other and burned-out forming a melting mass in the rotary kiln 2. The rotary kiln 2 may have conically converging ends, thus ensuring that the liquid slag is retained. At the exit end 15 of the rotary kiln 2, the burner assembly 3 is placed, preferably in the form of an oxygen/gas-burner system, adapted to provide continous temperature control at the slag outlet. The slag is removed from the slag outlet 15 by means of a belt conveyor 22. The flue gases are conducted from the rotary kiln 2 through the after-burning chamber 5 to the boiler assembly 6. In the latter, boiler ash 28 is separated out in a tail-end boiler (impact descaling boiler), and fly ash 29 is separated out by means of an elec- triσal filter 23. The boiler ash 28 and the fly ash 29 are conveyed to the residual-products silo 4 by means of a belt conveyor 18 and the conveyor 7. Downstream of the electrical filter 23, the flue gases pass into, the reactor 24 in a flue-gas cleaning plant, in which lime 25 is added. The reaction products from this plant are conveyed to a filter 26, in which a residual product 30 is separated out. This residual product 30 is conveyed by belt conveyors 19 and 32 to the conveyor 7 and further to the residual-products silo 4, whilst the flue gases, from which the residual product 30 has been removed, are discharged through a chimney 27. The present invention is not limited to exactly what has here been shown and described, and it should be noted that for a skilled person, it will be possible to make a number of modifications, e.g. by altering a number of rotary kilns or incinerating grates. As mentioned above, the main principle of the invention consists in that combustion slag and residual products, such as grate screenings, fly ash and reaction products, are melted together in a process step without intermediate cooling, i.e. the energy once having been produced in the slag is utilized for the melting process. LIST OF PARTS 30 residual product 31 air for combustion 32 belt conveyor

Claims: CLAIMS: 1. A method of incinerating solid and possibly liquid waste material in a plant, in which a rotary kiln (2) is being used, said kiln being situated downstream from an incinerating section (1) with stepped grates (9, 10, 11), c h a r a c t e r i z e d in a) the solid waste material is partially combusted on the stepped grates (9, 10, 11) and delivered to the rotary kiln at such a high temperature, that the burning-out in the rotary kiln produces a liquid slag, b) that any liquid waste material is added to the waste material being combusted on the stepped grates (9, 10, 11), and c) that the ash products from the combustion, such as grate screenings, boiler ash, fly ash, and residual products from flue-gas cleaning, are collected and returned to the input end (12) of the rotary kiln (2), at which point these products are introduced and fused together with the liquid slag. 2. A method according to claim 1, c h a r a c- t e r i z e d in that the slag is melted in the grate furnace space (1) at temperatures of approximately 1100°C or above. 3. A method according to claim 1 or 2, c h a ¬ r a c t e r i z e d in that the temperature in the grate furnace space (1) is controlled by opening and closing a damper (14) in a bypass duct (16) between the grate furnace space (1) and the flue-gas duct (5). 4. A method according to any one or any of the claims 1-3, c h a r a c t e r i z e d in that the waste material delivered for combustion in the grate section (1) is utilized as the energy source for the melting. 5. A method according to any one or any of the claims 1-4, c h a r a c t e r i z e d in that the exit end (15) of the rotary kiln (2) is supplied with heat from a burner (3). 6. An apparatus for use in carrying out a method according to any one or any of the claims 1-5 and being of the kind comprising a) a grate section (1), b) a rotary kiln (2), said two components being situated in successive positions in the direction of movement of the waste material, c h a r a c t e r i z e d by a feed assembly (13) adapted for continuously dosing slag and ash products collected from the incinerating plant at the input end (12) of the rotary kiln (2) in order to cause these substances to be fused together with the liquid slag forming a glass-like product being dis¬ charged at the exit end (5) of the rotary kiln (2). 7. An apparatus according to claim 6, c h a ¬ r a c t e r i z e d by a burner (3), preferably in the form of an oxygen/gas-burner assembly, being situated at the exit end (15) of the rotary kiln. 8. An apparatus according to claim 6 or 7, c h a r a c t e r i z e d by a collecting container (4) situated upstream of the feed assembly (13). 9. An apparatus according to any one or any of the claims 6-8, c h a r a c t e r i z e d in that the rotary kiln, adapted to rotate about a downwardly inclined axis, comprises conically converging or constricted end portions.

Inventors: BINNER SIEGFRIED, BINNER, SIEGFRIED
Applicants: VOELUND MILJOETEKNIK, VOELUND MILJOETEKNIK A/S
Application year: 1991
Main classification: F23G5
IPC codes: F23G5