The waste infeed chute is generally directed vertically in order that the waste can slide downwards through the chute by gravity, while the waste infeed means in the bottom of the chute removes, advances and feeds the waste lying at the bottom into the combustion chamber, possibly through an infeed sluice.

Known waste infeed means at the bottom of the waste infeed chute are e. g. one or more hydraulic pistons, apron feeders, moving grates or actual combustion grates, known e. g. from US patent No. 4,494,469 and DK patent No. 170,493.

Characteristic for the known waste infeed means is e. g. that complete filled waste bags and waste of similar bulk size easily and undivided can be fed into the combustion chamber, potentially via an infeed sluice, after having passed down through the waste infeed chute, in which the waste functions as a relatively dense plug, securing only small amounts of combustion air following the waste into the combustion chamber, avoiding propagation of the combustion back into the waste infeed chute.

In the oven system, to which the invention relates, the combustion takes place in the oven chamber at a pressure lower than ambient pressure, e. g. secured by placing an induced draft fan for the flue gas immediately in front of the chimney of the incineration plant.

Sludge from waste water cleaning facilities has previously to a great extent been disposed of by spreading on fields as a fertilizer, but stricter environmental rules lead to a demand that sludge of this kind, like many other liquid waste materials, is disposed of by other means, e. g. by combustion.

Special sludge ovens for combustion of waste water sludge are known, but will normally require supply of supplementary fuel, e. g. in the form of oil or gas.

Combustion of waste water sludge in combination with other types of waste in a waste incineration plant is known, in which the sludge has continuously been fed in directly in the hot combustion chamber through the ceiling thereof, or by infeeding via the waste infeed chute on top of the chute. The former of these infeed methods is relatively cumbersome due to infeed sluices, flaps or nozzles in the very hot ceiling of the oven, and both infeed methods will inevitably lead to odour problems and unhygienic working conditions in connection with the infeed of the sludge.

From US-patent No. 4,724,776 it is known to forcedly feed waste and sludge through the wall of the oven directly into the hot combustion chamber using a motorized charging screw or a motorized conveyor, so that waste and sludge falls down on a combustion grate placed at the bottom or higher up in the combustion chamber. The object is stated to be the burning of waste and sludge by a method, which aims at a concurrent good gas combustion before the flue gas is delivered to the chimney. Nothing is mentioned about seeking to eliminate the odour and hygienic problems and the complete oven system described is furthermore an overpressure system, not only giving odour and hygienic problems but also dust and escape of poorly combusted flue gases to the surroundings or the working environment in which the personnel of the plant is working. Furthermore, the infeed screw means that the waste has to be subjected to a cumbersome, expensive and unhygienic disintegration before feeding to the combustion chamber.

When feeding the sludge through the ceiling as well as through the wall of the oven, directly into the waste combustion chamber, the sludge falls through a flue gas stream at a temperature of approximately 1000°C, drying out and carrying

away many of the fine-grained sludge particles, so that the content of dust in the flue gas is raised remarkably, which is unconvenient, the boiler after the combustion oven being further smudged and the flue gas cleaning demand being increased.

It is the object of the present invention to provide a waste incineration plant as mentioned in the introduction, in which the above-mentioned odour problems are minimized and the hygienic working conditions are optimized.

This is achieved by an incineration plant as mentioned in the introduction, by providing the waste infeed chute or sluice with at least one infeed tube for adding sludge to the waste in the chute or sluice, and at least one pressure-feed appliance for feeding the sludge through the at least one infeed tube into the waste.

Hereby it is achieved that the sludge is fed into the waste infeed chute or infeed sluice, at a position in which there exists a pressure lower than ambient pressure, when the plant is working so that unhygienic dust is sucked into the cold waste and the odour materials are sucked into the combustion chamber, whereby they are burned and removed. At the same time the sludge is fed into the combustion chamber in such a way that the development of dust during the combustion process is minimized and the infeed of waste is still performed optimally with respect to combustion, as normally, without any cumbersome, expensive and unhygienic comminution of the waste.

Preferably the infeed is performed close to the bottom part of the waste infeed chute or in the infeed sluice, so that generally all of the time waste is present in the infeed chute or infeed sluice at the level of the mouth of the infeed tube.

By providing the infeed tube for sludge in the wall of the waste infeed chute facing the combustion chamber or in the ceiling of the infeed sluice, the sludge will always be positioned on top of the waste being fed into the waste combustion chamber and thus being dried out immediately when entering the combustion chamber.

Preferably, there are several infeed tubes evenly distributed over the width of the waste infeed chute or sluice, respectively, whereby the sludge can be distributed evenly over the waste.

By having the infeed tube or tubes debouching in a downwardly slanted angle into the waste infeed chute or forwardly slanted into the sluice, respectively, the sludge will be dragged with the waste onwards through the chute or sluice, whereby possible clogging problems at the mouth of the infeed tube or tubes are avoided.

In order to avoid odour problems the infeed tube or tubes are preferably connected to a pipeline for the supply of sludge from a pressure-feed appliance upstream connected to a silo for temporary storage of sludge. Thus, the infeed of sludge can be performed almost hermetically closed with respect to the surroundings.

In order to make it possible to transport sludge over greater distances in connection with sludge with a relatively high content of dry matter, e. g. 30-40%, the pipeline for supply of sludge may be provided with one or more ring nozzles, for lubricating the inner wall of the pipeline with e. g. a polymer for reduction of the sliding friction between sludge and pipeline.

The sludge to be incinerated in the plant in accordance with the invention may be selected from the group consisting of sludge from waste water cleaning, crude oil sludge, petrochemical waste products, animal sludge, liquid waste, slurry and liquid manure or mixtures thereof, possibly with admixture of materials selected from the group consisting of grate screanings, boiler ash, filter ash, flue gas cleaning products, other waste products from waste incineration plants, shredded waste, plastic waste, car fluff, and stabilizers reducing dust and/or vapour generation and/or unwanted chemical reactions in the combustion chamber.

As can be seen, many different waste products can be disposed of in this way. By a suitable composition of the sludge and the admixed materials, it is possible to achieve a stabilization with respect to dust, vapour, chemical reactivity, viscosity of the mixture, etc.

By providing several separate pressure-feed appliances and pipelines for supply of different mixtures of sludge etc., the pipelines debouching in separate infeed tubes or in common infeed tubes via a manifold, it is possible to control the infeed speed for the different mixtures, thereby controlling the combustion in the combustion chamber. The control can be relatively fast reacting as the infeed of the sludge is placed very close to the combustion process in the combustion chamber.

It is a further object of the invention to provide a method for incinerating industrial and household waste and sludge in an incineration plant of the above-mentioned type, in which the above-mentioned odour problems are minimized and the hygienic working conditions are optimized.

This is achieved by a method comprising pressure-feeding the sludge into the waste immediately in front of the infeed means.

Preferably the sludge is supplied to the incineration plant via a hermetically closed supply system.

The infeed quantity of the sludge can be used as one parameter for controlling the burning of waste in the combustion chamber. The method preferably comprises pressure-feeding of sludge of varying composition, possibly with admixture of further material to be disposed of or material providing stabilization of the sludge mixture.

The advantages of the method in accordance with the invention correspond to the advantages described above in connection with the incineration plant in accordance with the invention.

In the following detailed portion of the present description, the present invention will be explained in more detail with reference to the exemplary embodiments of an incineration plant according to the invention shown in the drawings, in which Fig. 1 shows an incineration plant comprising infeed tubes for adding sludge to the waste in accordance with the present invention,

Fig. 2 shows an arrangement comprising four infeed tubes, via a manifold connected to a pipeline for supply of sludge, and Fig. 3 shows a rough outline of a plant comprising a waste incineration plant and corresponding pipeline for sludge and a pressure-feed appliance provided to transport the sludge and a silo for temporary storage of sludge.

The incineration plant shown in Fig. 1 comprises a waste infeed chute 1 for industrial and household waste and a grate system 2 for advancing the waste through the inlet to the combustion chamber and for advancing the waste in the combustion chamber 3, positioned downstream of the chute 1. The waste infeed chute 1 comprises an infeed tube 4 for supply of sludge. In the embodiment shown, the infeed tube is placed close to the bottom part of the waste infeed chute 1 and in the wall in the waste infeed chute 1 facing the combustion chamber 3.

Thus, sludge being supplied to the shown waste incineration plant through the infeed tube 4 will end up lying on top of the industrial and household waste on the grate system 2 in the combustion chamber 3.

In order to avoid possible clogging problems at the infeed of sludge into the waste infeed chute 1, the infeed tube 4 for supply of sludge is, as shown in the drawing, positioned to debouch in a downwardly slanted angle into the waste infeed chute 1.

Fig. 2 shows how four infeed tubes 4 are connected to a pipeline 5 for supply of sludge via a manifold 6, intended to provide a uniform distribution of the added sludge across the four infeed tubes 4, the sludge being equally distributed across the feeding direction for the grate system 2 in the waste combustion chamber 3.

Fig. 3 shows how sludge can be supplied from a storage silo 7 for temporary storage of the sludge, forward to the infeed tube 4 in a hermetically closed system.

Between the silo 7 and the infeed tube 4, a pressure-feed appliance 8 is provided close to the silo 7, and a pipeline 5 is connected between the pressure-feed appliance 8 and the infeed tube 4, the pipeline 5 potentially comprising a ring nozzle 9, for lubricating the inner wall of the pipeline 5 with e. g. a polymer for reduction of the sliding friction between sludge and pipeline 5.