NO314673B1 - Method and apparatus for the thermal treatment of fly dust from grate incinerators - Google Patents

Description

Technical area

The invention relates to the waste incineration area. It concerns a method and a device for the thermal treatment of flying dust and any fine ash from grate incineration plants.

State of the art

For the thermal treatment of waste/rubbish, many methods are known in which the waste is gasified, low-temperature carbonized by vacuum, or incinerated. The solid reaction products that arise are further processed in different ways, e.g. thermally, and the products that are no longer usable are then deposited. Thereby, the quantities of fly ash to be deposited must be as small as possible, as they contain a high proportion of heavy metals.

Thus, it is e.g. from DE 38 11 820 Al a method is known where the waste is converted into incompletely burned gas and mainly non-volatile pyrolysis residues in a pyrolysis reactor. In addition to this, the incompletely combusted gas is taken to a separate secondary combustion chamber, and likewise the fine part (low-temperature coke and fine dust) of the residues and that in the dust filtration plant, respectively. the waste heat steam boiler obtained fly ash (dust). The airborne dust and particulates are burned in this high-temperature chamber and the solids are fused together. The molten slag is then led out of the combustion chamber to a water container, where it solidifies into a glass-like granule.

However, such a solution requires a treatment of the incompletely burned material and a separate secondary combustion chamber, which results in increased space requirements and high costs.

This also applies to the incineration-smelting plant for waste removal in the cities described in EP 0 446 888 Bl. Here, a melting furnace for melting the ash from the incinerator is connected after the incinerator, whereby the ash is transported to the melting furnace via a drying conveyor. Via special nozzles, filter dust from the dust separator is also brought into the melting furnace, so that both ash from the incinerator and flying dust from the dust separator are fused together in the melting furnace.

A further possibility to reduce the amount of fly ash consists, for example, of in arranging own ash melting facilities after the incineration process at waste incineration plants. Such a method is described in F.-G. Simon and K.-H. Andersson: "In-Rec-Verfahren - Verwertung von Reststoffen aus der termischen Abfallbehandlung", ABB Technik 9/1995, pp. 15 - 20. In this method, called the "AshArc" process, the fine fraction of the grate ash is melted together with the filter ash in a direct current arc furnace. With the help of the high temperatures, organic compounds are immediately decomposed. Metal chlorides evaporate and heavy metal compounds are reduced to elements and then either sink into the metal bath and thus form an alloy, or they leave the furnace in a gaseous state. The exhaust gas undergoes a secondary combustion for CO and a rapid cooling with water and plenty of air to above all prevent the new formation of toxic organic compounds. Vaporized metal chlorides resublimate and are separated on a bag filter. This heavy metal concentrate can be remelted into metal.

As the ash-arc furnace is designed for very large throughput quantities, it is possible to process the fine fraction of the grate ash (approx. 8% of used waste) together with the filter ash from the particle separation of the flue gas cleaning (approx. 2.5% of used waste).

A disadvantage of this state of the art is that an external furnace installation must be built which is heated 100% separately. Moreover, the resulting glassy product is not a component of the rice bag.

Description of the invention

The invention seeks to avoid all these disadvantages. The invention is based on the task of developing a method and a device for the thermal treatment of flying dust and possibly fine ash from waste incineration plants, whereby a product is obtained in a simple way and at low cost that can either be added to the rice bag or used separately, and the remaining amount of fly ash is thereby reduced.

According to the invention, this is achieved by at least part of the flying dust, by a method according to the preamble of claim 1, being returned to the incinerator's high-temperature area, where the temperature in this high-temperature area is above the melting temperature or the flying dust's sintering temperature, and that the flying dust remains sufficiently long in the high temperature range of the incinerator, so that it is at least partially vitrified or sintered. In addition, these products can be added to the rice bag or used separately.

According to the invention, this is achieved by a device according to the preamble of claim 13, in that the ash transport system extends to the vicinity of the incinerator's high temperature area, that there is connected after the ash transport system a dosing device for introducing at least part of the returned flying dust into the incinerator's high-temperature area, and that in the high-temperature area of the incinerator means are arranged to ensure a sufficiently long residence time of the ash.

The invention's advantages consist, among other things, of in that the separate high-temperature combustion chamber or the external furnace installation, which until now has been necessary for melting the fly ash, is eliminated. This will save costs. The product will be able to be added to the grate bag so that the remaining amount of fly ash with a high proportion of harmful substances is reduced, compared to the state of the art. A further advantage of the invention is that existing facilities will be able to be supplemented without problems.

It is particularly appropriate if the entire amount of flying dust is returned to the incinerator's high-temperature area, since in this way a product is formed that will not have to be deposited as special waste.

Furthermore, it is advantageous when the flying dust, in the case of only partial return of this to the incinerator's high temperature area, after it has been taken out from the boiler or the dust filter system, is first divided into a pollutant-rich and a pollutant-free fraction and only the pollutant-poor fraction of the flying dust is returned to the high-temperature area of the incinerator, as a pollutant-rich product is thereby formed and the dangers of corrosion problems due to elevated concentrations of heavy metals in the boiler area are reduced.

Finally, the flying dust is suitably removed, after it has been taken out of the boiler or the dust separation plant, mixed with the fine fraction {< 2 mm) of the sieve bag, which e.g. is processed according to the "DryEx/DryRec" method (dry extraction and dry sorting), and this mixture then returned to the incinerator's high-temperature area. This entails the advantage that the pollutant-free fraction of the rice bag will be able to be processed separately. At the same time, the melting properties are improved, e.g. viscosity, melting temperature, the liquid slag, and a dry but hardly dusty rice bag is obtained.

Further advantageous embodiments of the invention are described in the following independent claims.

Brief description of the drawings

Several embodiments of the invention are shown in the drawings, where fig. 1 schematically shows a first embodiment of a waste incineration plant according to the invention, where the entire quantity of flying dust is returned to the primary combustion chamber,

fig. 2 schematically shows a second design example of a garbage incineration plant according to the invention, where the entire amount of flying dust, after intermediate storage and pelletization, is returned to the secondary combustion chamber,

fig. 3 schematically shows a third embodiment of a waste incineration plant according to the invention, where only part of the flying dust is returned to the primary combustion chamber,

fig. 4 schematically shows a fourth embodiment of a garbage incineration plant according to the invention, where the fly ash together with the fine fraction of the sawdust is returned to the primary combustion chamber,

fig. 5 shows a detail of the furnace's high temperature area with a special design of a means to ensure sufficient residence time of the returned flying dust in this area, and

fig. 6 schematically shows a fifth embodiment of a waste incineration plant according to the invention, where the molten ash is brought out separately from the grate box.

Procedure for carrying out the invention

In the following, the invention will be explained in more detail with the help of design examples with reference to fig. 1-6.

Fig. 1 schematically shows a waste incineration plant according to a first embodiment of the invention.

The waste incineration plant mainly consists of an incinerator 1, after which a boiler 2 and a dust separation plant 3 are connected, e.g. an electrofilter. In the incinerator 1, a combustion grate 4 is arranged on which rubbish 5, e.g. household waste, is incinerated by the supply of primary air 6 in the primary combustion chamber 7. The combustion is further completed in the secondary combustion chamber 8 by the supply of secondary air 9. During the combustion of the household waste, flying dust 10 is formed which is transported with the flue gas 11 via the primary combustion chamber 7, the secondary combustion chamber 8, the boiler 2 radiation path 12 and " contact run 13 into the boiler 2 and into the filter 3. The fly ash 10 (boiler ash and fly ash) is separated on the boiler tube walls and electrofilter plates, not shown here. After knocking, the fly dust is fed to an ash transport system 14, preferably a chain conveyor, a pneumatic conveyor or a screw conveyor, via discharge devices not shown, such as cell wheel shutters or double dampers. According to the invention, the ash transport system 14 extends to the vicinity of the high-temperature area of the incinerator 1. There is a dosing device 15, for example a feed auger or a piston pump connected downstream ash transport facility 14. In this first embodiment of the invention, all discharged flying dust 10 is supplied to the dosing device 15 via the ash transport facility, optionally with the addition of additives 16, e.g. water or melting point depressants.

Via the device 15, flying dust 10, possibly mixed with additives 16, is metered into the high-temperature area of the incinerator 1. If water is added to the ash (flying dust 10) before it is returned to the furnace, the cooling effect of the returned ash on the surrounding refractory stones of the incinerator 1 is further enhanced already before. This provides a contribution to corrosion reduction. As is clear from fig. 1, the fly ash 10 in this first embodiment is returned to the primary combustion chamber 7.

Of course, in a second embodiment it is also possible to return the flying dust 10 to the high temperature area of the secondary combustion chamber 8 {see fig. 2). The difference is that the temperature in this area is higher than the melting temperature or the sintering temperature of the flying dust 10, respectively the mixture of flying dust 10 and additives 16, and that the residence time for the flying dust 10 or the mixture of flying dust 10 and additives 16 in this high-temperature area of the incinerator 1 is so long that vitrification or sintering of at least part of the flying dust 10. It is particularly advantageous when the entire proportion of the returned product is melted or sintered. Should the temperature not be sufficient, a further amount of heat can be supplied via auxiliary burners 17 (not shown here) which are operated by means of oil, gas or waste operation.

According to the invention, means 18 are arranged in the high temperature area of the incinerator to ensure a sufficiently long residence time of the ash. These funds 18 will e.g. could be chutes, crucibles, guiding bodies and/or plates, or also specially designed refractory stones.

In addition, the products that occur during the vitrification/sintering are added to the grate box 19, which is either discharged dry or wet via a water bath, from the incinerator 1. In case of dry discharge, it is important that the ash extraction forms an airtight closure of the boiler room, which in existing facilities are secured using a water lock. The rice bag 19 is then further processed using methods known per se, e.g. dry sorting.

Fig. 2 shows a second embodiment of the invention. This only differs from the first design example in that the flying dust 10, after it has been fed out of the boiler 2 and the filter 3, is temporarily stored in a bunker 20 via the ash transport facility 14, then transported into a pelletizing plant 21, after which the pelletized flying dust 10 , which is optionally again mixed with additives, is metered into the high temperature area of the secondary combustion chamber 8. The external temperature source 17 (burner, burner lance) which is shown schematically in fig. 2, can supply the secondary combustion chamber 8 with additional heat energy. Thereby, a temperature that is above the melting or sintering temperature for the flying dust is ensured in each case, or the mixture of flying dust 10 and additives 16, so that melting/sintering of the ash is supported.

In the third embodiment of the invention, shown in fig. 3, only a part of the flying dust discharged from the boiler 2 and the dust separator 3 is returned to the high temperature area of the primary combustion chamber 7. Before entering the combustion chamber 7, the fly ash 10 enters a separation chamber 22, in which the fly ash 10 is divided into a pollutant-rich fraction 10.1 and a pollutant-rich fraction 10.2. Only the pollutant-poor fraction 10.1 is returned to the high-temperature area of the incinerator 1 via the ash transport facility 14 and the dosing device 15, and added to the grate box 19 after vitrification.

Fig. 4 schematically shows an embodiment of the invention which only differs from that in fig. 1 showed a first embodiment in that the fly ash 10, after discharge from the boiler 2 and the filter 3, is returned to the high-temperature area of the incinerator 1 together with a fraction 19.1 of the grate bag, which is smaller than 2 mm and was separated (e.g. at approx. 2 m particle size) from the rest 19.2 of the rice bag

in the sorting facility 23.

Fig. 5 shows a possible embodiment of the means 18 for ensuring sufficient residence time of the flying dust 10 which are arranged in the primary combustion chamber 7 or the secondary combustion chamber's 8 high-temperature area. The feed auger 15 has a downstream chute 18 in which the flying dust 10 will be able to stay so long under high temperature conditions that it at least partly melts and vitrifies or pre-sintered, and these products can then be added to the grid box, or used separately.

Fig. 6 shows a further design example. Here is an afterburner chamber 26 which is designed in such a way that the molten ash 25 can be fed out separately from the grate ash, connected after the boiler chamber 7, 8. As with the embodiments already described above, a mixture or a single fraction of the ash (boiler ash , filter ash, fine fraction of the grate ash), with or without the addition of additives 16, could also be fed back to the boiler room 7, 8 or the post-combustion room 26 in this embodiment.

A further advantage of this design consists in the possibility of returning the dust to the hot area via the nozzles for secondary air 9 and/or tertiary air 24. Moreover, by means of non-concentric transitions between the boiler room and the afterburner room 26 and/or by tangential feeding of the secondary air 9 or the tertiary air 24 into the post-combustion chamber 26 could achieve a vortex flow in the post-combustion chamber 26. The vortex leads to a better separation of ash particles on the walls of the post-combustion chamber 26. The recycled ash, which is fed into the post-combustion chamber 26 by means of the secondary air 9 or the tertiary air 24, is flung against the walls, where, due to the very high temperatures, an ash melting flow occurs. The molten ash flows down the walls of the high-temperature post-combustion chamber 26 and is removed from the third pre-combustion chamber 26 via a device 27 specially arranged for this purpose.

Claims (16)

1. Method for the thermal treatment of flying dust (10) and possibly parts of the grate box (19) from a waste incineration plant, where the waste is burned on a combustion grate (4) in an incinerator (1), whereby flue gas (11) is formed which contains rice ash (19) and fly ash (10), where the rice ash (19) is fed out from the incinerator (1) which has a primary t (7) and a secondary combustion chamber (8), and is further processed, and where the fly ash (10) which settles in a downstream boiler (2) and a downstream dust filter system (3) is exhausted, and at least part of the flying dust (10) is melted and sintered, characterized in that at least part of the flying dust (10) is fed back to the incinerator's (1) high-temperature area, as the temperature in this high-temperature area is above the flying dust's (10) melting temperature, or sintering temperature, and that at least a part of the flying dust (10) remains sufficiently long in the high temperature area of the incinerator (l), so that at least a part of it is vitrified or sintered. 2. Method according to claim 1, characterized in that the vitrified or sintered flying dust (10) in the high-temperature area of the incinerator (1) is then added to the grate box (19). 3. Method according to claim 1 or 2, characterized in that the entire amount of flying dust (10) is returned to the high-temperature area of the incinerator (1). 4. Method according to one of claims 1-3, characterized in that the flying dust (10) is returned to the primary combustion chamber's (7) high temperature area. 5. Method according to one of claims 1-3, characterized in that the flying dust (10) is fed back to the secondary combustion chamber's (8) high temperature area. 6. Method according to claim 1 or 2, characterized in that the flying dust (10), in the case of a partial return of the flying dust (10) to the high temperature area of the incinerator (1) after discharge from the boiler (2), respectively. the dust filter (3), is first separated into a pollutant-poor fraction (10.1) and a pollutant-rich fraction (10.2) and only the pollutant-rich fraction (10.1) of the flying dust (10) is returned to the high-temperature area of the incinerator (1). 7. Method according to one of claims 1-6, characterized in that the high temperature area of the incinerator (1) is supplied with additional heat via an auxiliary burner (17). 8. Method according to one of claims 1-7, characterized in that the flying dust (10), after discharge from the boiler (2), respectively the dust separator (3), is mixed with a fraction (19.1) of the treated sieve bag (19), preferably < 2 mm, and this mixture is then returned to the high-temperature area of the incinerator (1). 9. Method according to one of claims 1-8, characterized in that the flying dust (10), after discharge from the boiler (2), respectively the dust separator plant (3), is transported by means of an ash transport plant (14), optionally intermediately stored, pelletized and/or moistened, and then fed dosed into the high temperature area of the incinerator (1) via suitable means (18). 10. Method according to one of claims 1-9, characterized in that additives (16), preferably water and/or melting point-reducing substances, are added to the flying dust (10) or the mixture of flying dust (10) and the fine part of the grate dust (19) before feeding it into the high temperature area of the incinerator (1). 11. Method according to one of claims 1-10, characterized in that the ash which has been returned to the high temperature area of the incinerator (1) is fed into the primary combustion chamber (7) or the post-combustion chamber (26) by secondary and/or tertiary air input. ■ 12. Method according to one of the claims 1-11, characterized in that a swirling flow of the flue gases (11) is provided in the afterburning chamber (26). 13. Device for thermal treatment of flying dust (10) and possibly parts of the rice bag (19) from waste incineration plants, mainly consisting of an incinerator (1) with a combustion grate (4) and a discharge device for slag and rice bag (19), which has a primary (7) and a secondary combustion chamber (8), a boiler (2) connected after the incinerator (1) with radiation run (12) and contact run (13), and a dust separation system (3) connected after the boiler (2), where discharge devices for the flying dust (10) are arranged on the boiler (2) and the dust separator system (3), and these discharge devices are assigned to an ash transport system (14), characterized in that a) the ash transport system extends to the vicinity of the incinerator's high temperature area, b) that a dosing device (15) for introducing at least part of the returned fly ash (10) into the high temperature area of the incinerator (1) is connected to the ash transport system (14), and c) that in the high temperature area of the incinerator (1) temperature range means (18) are arranged to ensure sufficient residence time of the ash. 14. Device according to claim 13, characterized in that a traction chain conveyor, a pneumatic conveyor or a screw conveyor is used as the ash transport system (14). 15. Device according to claim 13, characterized in that a stop screw or a piston pump is used as dosing device (15). 16. Device according to claim 13, characterized in that chutes, crucibles, guide members and/or plates are used as means (18) to ensure sufficient residence time of the ash in the incinerator's (1) high-temperature area.