EP1384948B1 - Method and device for processing wastes, in particular wet wastes in a combustion furnace - Google Patents

Description

The invention relates to a method for waste processing, in particular of wet waste in a combustion furnace according to the preamble of claim 1.

A further aspect of the invention relates to a device which is suitable in particular for carrying out the method according to claim 10.

The invention is particularly concerned with the problem of wet waste combustion, which is understood to mean a waste having a water content of over 75% by mass. Such wastes are, for example, food or biosludge.

The incineration of such waste presupposes a prior drying, which is usually carried out externally, independently of the combustion in a preceding process step and outside a combustion furnace. The external drying requires extra space as well a complication of the entire process and may even cause a risk of explosion.

More generally, the invention addresses the problem of increasing the efficiency of drying and wet waste combustion. However, it is not limited to the processing of wet waste.

The prior art already includes a device for waste processing, in which a feed device, a degassing and a high-temperature reactor are arranged successively, wherein in the degassing at least one transport screw is arranged (DE 43 30 788 A1). In particular, the degassing is surrounded by a jacket heating, which can be operated with steam or gas. Trash is continuously transported from the feeder to the high temperature reactor by the screw conveyor, the waste being heated to a temperature of about 600 ° C and degassed. A resulting solid residue and the gas are fed to the high-temperature reactor in which synthesis gas and a melt arise, which are further treated externally. - In a variant, air can be supplied to a central portion of the degassing, whereby carbon monoxide and residual carbon are burned in the degassing and thus the waste is heated directly. Also, the screw conveyor may be formed hollow to be charged for heating with steam or gas. In any case, only the output of the degassing, ie the end of the garbage transport path, which is essentially realized by the screw conveyor, with the interior of the high-temperature reactor in connection whose heat is thus practically not transported into the degassing. This is especially true when the screw conveyor ends before the end of the degassing and at the end of a plug is formed from the transported Good. The heat supply to the material in the degassing duct over the surrounding jacket is relatively inefficient. A direct heating of the waste in the degassing can only occur if this sufficient is dry to allow partial combustion. Waste with a moisture content above 30% can not be processed in this way.

Also known is a process for the treatment of sewage sludge, in which the sewage sludge is first dried in successive stages of treatment in a continuous run, then subjected to conversion under anaerobic conditions at about 250 to 350 ° C and finally fired at at least 1250 ° C, the Material to be treated between the individual treatment stages, eg with a screw conveyor, forcibly conveyed (EP 0 474 890 B1). It is therefore not a uniform screw conveyor, which extends over the individual treatment stages. In particular, a drying stage comprises a plurality of treatment units, each with a conveying tube, in which a screw conveyor is rotatably arranged, wherein the conveying tube is surrounded by a jacket tube and the space between the conveying tube and jacket tube is heated by heating gas. The drying process that can be realized with it is similarly inefficient as in the prior art discussed above. In addition, there is a great technical effort to realize the system.

Also known is a process for producing heat energy from carbonaceous fuels after the fuel is heated in at least a first zone to a sufficiently high temperature to be pyrolyzed, after which coal produced by the pyrolysis is transferred to a second separate zone in which the coal is gasified with the supply of combustion air, optionally steam and / or recirculated exhaust gases (WO 97/15641). The resulting in the second zone gases and the pyrolysis gases of the first zone are then subjected to a secondary combustion. Thus, the first zone is to be heated by radiant heat, which is obtained directly from the secondary combustion. - Here, however, the material to be pyrolyzed - fuel - not directly with the atmosphere of the secondary combustion in connection, but this good is heated by radiant heat, the only starting from directly heated pipes. According to this method, although better use is made of the heat produced by the secondary combustion of the pyrolysis gases and gases of the degassing zone, it is achieved only imperfectly.

According to another known method waste is transported via a plug screw into a pyrolysis reactor designed as a Schweltrommel, wherein the carbonization drum is indirectly heated by passing therethrough heating tubes and the thus cooler heating gas is also used to heat a transport channel in which the plug screw is arranged (DE 43 27 633 A1). It is therefore an indirect heating, which is particularly weak and inefficient, especially in the area of the transport channel, as in the prior art discussed above. Processing wet waste with a moisture content of more than 75% is also not effective.

Also known are a device and a method for heat treatment of waste by drying and dry distillation, in which the waste is transported by a screw continuously through a drying chamber whose outer wall is surrounded by a heating furnace, so that here also only an indirect heat transfer occurs (WO 00/13811). The heated dried material is then separated in an evaporation chamber in the absence of air into solid and fluid components of the waste.

It is known to increase the effectiveness of drying and to improve the efficiency of combustion by means of a process in which a screw conveyor for vibrating the fuels is disposed on a drying rack during movement to the upper exhaust end (Patent Abstracts of Japan, Vol. 009 , No. 319 (M439) 1985-12-14 and JP 60152810 A). A free channel through which the exhaust gas produced by a fluidized bed ascends is above one forming the fluidized bed Partly provided. Within the free channel, two upper and lower stages of drying racks are arranged. The upper frame is provided with a screw conveyor for the rotary transport of the fuel to be applied to the frame from a transport end to an insertion end. The lower drying rack is also provided with a screw conveyor for transporting the fuel coming from the injection end to an opening above the fluidized bed. In essence, the racks are designed as frame plates, which can be curved according to the adjacent augers. High hydrous fuels, such as sewage sludge, are fed from an input port to the upper drying rack. With the help of screw conveyors, the kiln is rotated to move against a rising from the fluidized bed exhaust stream, wherein it is dried in good contact with the exhaust gas until the so dried kiln from the opening in the lower drying rack falls into the fluidized bed, where it is burned by it is swirled by a fluidizing gas. The process carried out by the known fluidized bed incinerator thus does not provide a pyrolysis step. In addition, it is not clear if and how the transport end of the upper screw conveyor is so closed that it is prevented that the exhaust gas can escape through the inlet opening for the sewage sludge.

According to another apparatus and method for thermal decomposition of waste, a screw conveyor is housed in a horizontal pipe housing in which the waste is kept in motion and heated gas generated in a reaction zone is moved as a flow in the direction of movement of the waste (US 3 027 854 A). , The waste is treated so that the material is first dried, then dry distilled and finally charred without using up completely. The char is transferred to a vertical chamber in which the combustion of the char is completed and exhaust gas is generated becomes. - The material transported in the tube housing, however, is substantially shielded from the furnace atmosphere. On the other hand, no means appear to be provided which prevent the gas flowing through the pipe casing from escaping through the funnel inlet through which new waste material is introduced.

In another known device for pyrolysis of solid waste, an indirectly heated retort contains a tubular housing in which a screw screw for transporting the solid waste is arranged (US Pat. No. 4,217,175 A). The housing is surrounded by a heating jacket through which hot gas circulates. Adjacent to the entrance of the retort are a feed hopper for the raw material and at its base a reciprocating plunger is provided which forces a compacted batch of new waste material into the feed portion of the retort and thus seals the supply against escape of hot vapors , The screw breaks up the compacted waste into loose particles and brings them into heating contact with the housing, but not with the atmosphere of the furnace.

In a known combustion plant for comminuted fuels runs a supply line in which a screw conveyor is arranged in a flame channel (EP 1 113 223 A1). The supply line opens into a combustion chamber in which burnup takes place. Shielded in the supply line, the combustion material is heated and dried in the region of the flame channel. The dried combustion material is expelled from an opening at the end of the flame channel in the combustion chamber. The combustion gases formed in this and in a Nachverbrennungsraum flow through the flame channel to get to a heat exchanger.

The present invention has for its object to develop a method for waste disposal, with the waste especially high humidity uncomplicated, safe and efficient dried and heated to a temperature required for pyrolysis temperature of the waste.

This object is achieved by the method specified in claim 1.

Thereafter, the processing of the waste takes place along a transport path of the waste realized by a continuously operated transport screw substantially in direct contact with the furnace atmosphere of the incinerator. In this case, in a first phase, a seal to a Beschikkungsstelle by compression of the waste already at the beginning of the transport path instead, so that no entry problem arises at the feed point by gas leakage. However, the sealing stuffing effect can additionally be completed by supplying air at the point of entry, which, in particular as sealing air with an empty screw, prevents heat reflux from the incinerator to the point of loading. The waste will generally be fed batchwise to the point of loading, after which the processing of the waste will be continuous in the subsequent phases.

The first phase of the compression by compression of the waste is followed, as a second phase, by drying of the waste, efficiently and yet safely and without the risk of explosion, with continued heating by direct contact with the furnace atmosphere of the incinerator. The dried waste is continuously heated by the furnace atmosphere to a temperature required for pyrolysis in a third phase. The waste is moved at such a speed over the transport path that is generated in the third phase at a slow expiration of the pyrolysis of waste substantially gas. The total residence time of the waste over the transport line can typically be 15 to 20 minutes.

In a fourth phase, the burnout of the pyrolyzed waste is completed, at the latest following the transport screw in a free area of the furnace interior, in which the pyrolyzed waste falls from the front end of the screw conveyor. It is achieved a complete combustion with little air or oxygen.

It is essential that a large part of the heat flow, the waste receives during its transport along the transport path, is supplied by heat radiation at high temperature without intermediate construction elements, such as walls, pipes, directly from the furnace interior. Thus, it is possible to efficiently process high-moisture waste having a water content of over 75 mass%.

But it is also possible to process waste of low moisture by this method. Low-moisture waste is understood to mean one having a water content of up to 15 percent by mass. For this purpose, if necessary, a change of one or less process parameters is required, for example a variation of the transport speed of the waste to be processed along the transport path.

The inventive method is thus characterized by great universality.

Due to the direct contact with the furnace atmosphere, first at the screw conveyor and then in the free area of the furnace interior, the waste according to claim 3 is exposed to a temperature above 850 to 1200 ° C, which is certainly sufficient for complete pyrolysis depending on the type of waste.

The process according to the invention can be varied in many ways and combined with other procedures. In particular, according to claim 5 alternatively to the processing wet waste in the furnace atmosphere of the incinerator by transport through the special screw conveyor this furnace atmosphere dry waste directly, ie not fed via a screw conveyor via a feed lock from above, so that the waste falls freely into the furnace interior ,

According to claim 6 can further parallel to processing wet waste with a first screw with a first variable speed drive, with the transport speed is set along the transport path, processing low-humidity waste with a second screw with a controlled independently from the first speed-controlled drive second drive also in direct contact with the furnace atmosphere. Different types of waste do not need to be processed in a time-consuming manner.

However, high-moisture waste and low-moisture waste may also be premixed in a blending silo, after which the blended product is further treated with only one feed screw open on one side in direct contact with the furnace atmosphere for residual drying, pyrolysis and burnout.

In a device for carrying out the method according to the invention, according to claim 10, which is open at its end-side section at the top, i. exposed transport screw, which is there thermally unshielded in direct contact with the furnace atmosphere, an essential element. For this purpose, the end-side portion which extends into an interior of the incinerator, taken only at the bottom in a half-shell-shaped shell of refractory material. This ensures that the transported with the screw waste is exposed on the one hand on the top of this section directly the furnace atmosphere and the heat in the furnace interior and nevertheless the transport function of the screw is ensured by the socket on the bottom in the shell-shaped shell, which also for Heat transfer contributes to the transported waste.

The screw conveyor needs to be mounted on one side only at its opposite end to said end portion.

Particularly suitably, the shell-shaped shell is formed under the end-side section of the screw conveyor by a Ofenausmauerung of firebricks, which is both heat-resistant and on the other hand, if necessary, renewable.

With a further arranged according to claims 10 and 11, in particular in the shell of refractory material temperature sensor, the temperature of the transported with the screw conveyor waste can be detected in good approximation. The signal from the temperature sensor can be further processed in a temperature-dependent speed control of a drive of the screw conveyor. With the temperature-dependent speed-controlled drive, the processing, for example, in terms of moisture, density or thermal conductivity of different types of waste, optimized.

Analogous to claim 10, the method according to claim 9 is exercised.

Furthermore, according to claim 13, the temperature of the screw conveyor, which is heated by the furnace atmosphere, be optimized by the formation of a cooling water passage in the screw conveyor in conjunction with a flow-controlled cooling water source. In this case, a temperature outside on wings of the screw higher than 250 ° C has been found to be expedient.

The structural solutions according to claims 14 and 15 serve to realize the method features according to claims 4 and 5.

It should be emphasized in the device according to the invention, the multiple function of an end-side section open at the top, ie exposed screw conveyor which serves along this end-side portion of the efficient drying of the waste and the subsequent pyrolysis and also acts as a stuffing screw in a direction in the transport direction of the waste preceding over the circumference completely closed portion.

Fig. 1

Ein Ausführungsbeispiel einer Einrichtung zur Abfallverarbeitung im wesentlichen in einem vertikalen Schnitt.

The invention is explained below with reference to a drawing with a figure. It shows:

Fig. 1

An embodiment of a device for waste processing substantially in a vertical section.

The device according to the invention, with which the method according to the invention is carried out, generally comprises a screw conveyor 1 in connection with a combustion furnace 2.

In detail, the screw conveyor has a speed-controlled drive 3, which is coupled by a gear mechanism with a substantially horizontal screw conveyor 4. At a loading point 5 of the screw conveyor, a charging device 6 is arranged, which can be fed batchwise or continuously with waste, in particular food waste or biosludge. Between the charging processes, the charging device with a slide 7 or instead by blocking air supply with an air supply port 6a against the environment is lockable.

Starting from the charging point 5, an enclosed or completely covered section 4a of the transport screw extends into the interior of the incinerator 2. This is followed by an end-side section 4b, which projects further into the interior of the incinerator. This end portion 4b is open only at the top and is on its underside of a shell-shaped, approximately U-shaped shell 8 made of refractory material, which is formed from a Ofenausmauerung 9 of firebricks. In FIG. 1, as a result of the sectional view, only the deepest point of the half-shell-shaped jacket 8 is shown, which extends on both longitudinal sides of the transporting screw approximately up to an upper side 10 of the transporting screw or of the screwed tree.

The area of the oven interior which is not occupied by the transport screw 4 and the furnace lining 9 is referred to in the present application as a free area 11 of the incinerator. Above him, an alternative loading lock 15 may be arranged on the combustion furnace, which is only indicated in the drawing. Furthermore, nozzles 12 terminate in the interior space and are used to supply air / oxygen for combustion and heat generation in the interior of the furnace.

The incinerator is closed down in the usual way by an ash bed 14.

For temperature-dependent speed control of the drive 3 at least one temperature sensor 13 is inserted into the Ofenausmauerung 9 in the region of the shell-shaped shell 8, the output signal is a measure of the temperature of the transported in the adjacent area with the screw conveyor waste and is further processed for speed control of the drive 3 ,

In the practice of the method according to the invention, the feeder 6 is supplied with wet waste which may have a water content of over 75% by mass. The waste captured by the screw conveyor under the charging means is compressed in a first phase A in the enclosed section 4a of the screw conveyor, whereby a backflow of heat from the inside of the oven is largely sealed off. The lock can be largely secured by the slider or the charging device supplied sealing air even with empty screw conveyor. In a subsequent phase in which the waste during its further transport along the screw conveyor in particular from the enclosed section 4a of the screw conveyor enters the end, open-topped section of the screw conveyor, takes place, the wet waste in phase B, wherein the Waste on the open top of the transport screw the furnace atmosphere is exposed directly and can absorb heat radiation directly from the inside of the furnace. In addition, in the lower region encompassed by the shell-shaped shell 8, heat transfer can be effected substantially by heat conduction of the furnace lining. In the interior of the furnace there is typically a temperature above 850 to 1200 ° C, to which the waste is already exposed in phase B for drying.

The continuously transported in the longitudinally open-top section and exposed to the hot furnace atmosphere waste is pyrolyzed in the third phase C, wherein substantially pyrolysis gas is formed. Solid pyrolyzed waste falls from the front end of the screw conveyor 4 in the free area 11 of the incinerator 2, in which a burn-out of the waste is completed in a fourth phase D. Residual ash is collected in the ash bed 4 and can be conventionally discharged from there. - But it is also possible in particular with slow helix, that the phase D is completed before the front end of the screw.

It is essential that with the screw conveyor 4 several functions, namely the stuffing of the waste, drying and pyrolysis are each carried out in a largely optimized manner. The screw conveyor is expediently cooled to an outer blade temperature at its wings above 250 ° C, characterized in that cooling water flows through a controlled flow through a cavity in the region of the screw shaft. The cooling is not shown to maintain the clarity of the drawing.

The residence time of the wet waste on the screw conveyor is typically 15 to 20 minutes, ie the internal screw drying and the pyrolysis of the waste take place.

Claims (15)

1. A process for waste processing, particularly of humid waste, in an incineration furnace (2), into which the waste is transported from a feeding station (5) by means of a transportation auger (4) while being heated,
   characterized in
   that the waste is continuously transported by means of a transportation auger (4) with its end-side section (4b) open on top in a plurality of successive phases (A, B, C) in transportation direction viz., in a first phase (A) of filling, towards the feeding station by compressing the waste along an enclosed section (4a) of said transportation auger (4) before the end-side section (4b) thereof,
   a second phase (B) of drying the waste along said end-side section (4b) in the furnace interior, unscreened in direct contact with the furnace atmosphere,
   a third phase (C) of pyrolysis of the waste further along said end-side section (4b) also in the furnace interior, unscreened in direct contact with the furnace atmosphere,
   whereupon, subsequently, the pyrolysed waste drops into a free area of the furnace interior (11) wherein a fourth phase (D) of combustion of the waste is, at the latest, concluded.
2. A process according to claim 1,
   characterized in
   that waste of high humidity is processed, having a water content of more than 75 mass percent
3. A process according to claim 1 or 2,
   characterized in
   that the waste in the furnace interior is subjected, firstly on the transportation auger (4) and subsequently in the free area of the furnace interior (11), to a furnace atmosphere of more than 850 to 1200°C.
4. A process according to at least one of claims 1 to 3,
   characterized in
   that barrier air which avoids heat reflux is fed to the feeding station (5).
5. A process according to one of the foregoing claims,
   characterized in
   that, alternatively to processing humid waste in the furnace atmosphere of the incineration furnace (2), dry waste is fed from above directly to the latter via a feeding lock (15).
6. A process according to at least one of claims 1 to 4,
   characterized in
   that in parallel to the processing of humid waste by means of a first auger having a first speed-controlled drive, waste of low humidity is processed by means of a second auger having a drive controlled independently from the first speed-controlled drive, also in direct contract with the furnace atmosphere
7. A process according to at least one of claims 1 to 4,
   characterized in
   that waste of high humidity and waste of low humidity are premixed in a mixing silo and that the mixed product is fed to the feeding station (5) of transportation auger (4).
8. A process according to claim 6 or 7,
   characterized in
   that the waste of low humanity has a water content of up to 15 mass percent.
9. A process according to at least one of the foregoing claims,
   characterized in
   that processing of the waste, particularly drying and pyrolysis, is optimized by temperature determination of the waste transported on transportation auger (4) by means of a temperature probe (13) disposed within the furnace brick lining (9) in the area of half-shell shaped casing (8) of fire-proof material disposed on the underside of said end-side section (4b) and a temperature-dependent speed control of drive (3) of transportation auger (4), generated by a signal of said temperature probe.
10. Installation for waste processing including an incineration furnace (2) into which the waste can be transported by feeding means (6) via a transportation auger (4) while being heated, particularly for execution of the process according to at least one of the foregoing claims
    wherein an end-side section (4b) of transportation auger (4) extends into the interior of incineration furnace (2), wherein said end-side section (4b) is open on top and is enclosed in a half-shell shaped casing (8) of fire-proof material on the bottom, and wherein transportation auger (4) is coupled to a temperature-dependently speed-controlled drive (3)
11. Installation according to claim 10,
    characterized in
    that in said casing of fire-proof material at least one temperature probe (13) is disposed.
12. Installation according to at least one of claims 10 and 11,
    characterized in
    that the half-shell shaped casing (8) under the end-side section (4b) of transportation auger (4) is formed by a furnace brick lining (9) of fire bricks.
13. Installation according to at least one of claims 10to 12,
    characterized in
    that a cooling water passage is formed in a shaft of the transportation auger (4) which is connected with a passage-controlled cooling water source.
14. Installation according to at least one of claims 10 to 13,
    characterized in
    that an air supply tube (6a) extends into feeding means (6)
15. Installation according to at least one of claims 10 to 14,
    characterized in
    that the incineration furnace (2) includes an alternative feeding lock (15) disposed above a free area (11) of furnace interior which is free from the transportation auger (4).

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