EP0465406A2 - Process for the continous melting of solid or viscous products - Google Patents

Abstract

During the continuous melting, heterogeneous solid or viscous residues are first heated to a preheating temperature (T1) in a preheating and fractionation stage (4), volatile components being expelled and being fed as a waste gas (8) for further treatment, then heated (T2) at least to the flow temperature in a melting stage (10) and thereafter brought to an inert solid final state by cooling. A small melt volume and a short residence time (t2) in the melting stage (10) are thus achieved. This ensures better conversion of the residues into an inert state and optimally controllable fractionation of all material components. <IMAGE>

Description

The invention relates to a process for the continuous melting of heterogeneous solid or viscous residues and an apparatus for carrying out the process. Residues are to be understood in the following: residues and residues from industry, trade and household in particular also residues with pollutants that are difficult to inert, e.g. filter ash and slag from energy generation and incineration plants, paint sludge from paint shops, filter press and electroplating sludge and residues from flue gas cleaning. The pollutants contained in the residues have to be converted, rendered inert or recycled, especially heavy metals such as mercury, lead, zinc and cadmium and toxic, organic components such as dioxins and furans. Heavy metals such as zinc and lead, often with a relatively high content, can also be recycled. The harmful components of the residues must be rendered inert to the extent that they can be landfilled. For this purpose, the solubility of inerted harmful components must be negligibly low, so that there is no impairment of the Groundwater can occur. Annoyance from smell and dust from a landfill should also be avoided.

A known process for the inertization of such residues is the inclusion process in which e.g. Filter dust containing heavy metals from coal-fired power plants or other incineration plants is mixed with cement and structural minerals and incorporated into a concrete-like mass. However, this process requires large amounts of additives, it requires correspondingly large landfill volumes, and the long-term stability with regard to washing out integrated, harmful components is at least still unclear.

Another known method for inerting such residues consists in their glazing, which in large tubs of large glass furnaces is slowly heated to high temperatures and glazed as homogeneously as possible. These glass melting processes are e.g. described in waste management journal 1 (1989) No. 7/8, pages 27 to 28. Due to the long dwell times of several hours at the high melting temperatures, the majority of the volatile components, in particular the heavy metals, are inevitably evaporated and must be disposed of or recycled in an additional, subsequent stage. In particular, the flue gas gypsum is decomposed again in the previous slow glass melting process and the SO₂ previously bound therein is released again, which requires a subsequent additional desulfurization stage. So these processes do not form a SO₂ sink.

The object of the present invention is to overcome the disadvantages of the known methods and to provide a method and a device for inerting residues create, which allows an extensive and controllable integration of pollutants, especially heavy metals and which can also form a SO₂ sink.

This object is achieved by the method according to claim 1 and by means of a device according to claim 12.

By selecting the preheating temperature T1, the chemical conversions and physical evaporation of residual material components corresponding to this temperature take place in a controlled manner in the preheating and fractionation stage. Undesired reactions and evaporation of components that occur above the preheating temperature T1 are thus avoided. The remaining residues in the melting stage are then heated relatively quickly to at least their flow temperature, fused and solidified by cooling. This relatively rapid melting process largely prevents undesired further decomposition of the residues (e.g. CaSO4). A substantial proportion of the sulfur contained in the flue gas gypsum is thus rendered inert or incorporated in slag, i.e. it creates a SO₂ sink. The inerting method according to the invention is thus also much more comprehensive and effective than the previously known. A qualitatively and quantitatively larger spectrum of residues can be melted down and converted into an inert, landfill-capable solid final state.

The dependent claims relate to advantageous developments of the invention. The preheating temperature T1 can preferably be between 400 ° C and 1000 ° C, and it can be at least 200 ° C below the melting temperature T2. The preheating temperature T1 can also be selected according to the composition of the residues Exhaust gas fraction and adjusted to the softening temperature of the residues. For the purpose of well-controlled fractionation, the residence time in the fractionation stage can be chosen to be longer than the residence time in the melting stage, often several times longer. For the purpose of rapid and complete integration of all components, the residence time in the melting stage can advantageously be less than 15 minutes, often even less than 5 minutes. Depending on the physical properties and the chemical composition of the residues, the temperatures and dwell times of the preheating stage and melting stage or their heating outputs and feed rates can be set and controlled as operating parameters so that the desired proportions are fractionated in the preheating stage and the remaining residues are melted down completely will. In a subsequent further treatment stage, the hot exhaust gases can be abruptly cooled by blowing in cold gas or solid, so that heavy metal salts can be desublimated and converted into a usable powder form, without having to stay in the critical temperature range of 300 ° C to 400 ° C for a long time Cooling toxic organic substances such as dioxins and furans are formed. Exhaust gases of a relatively low preheating temperature T1 and short dwell time t1 can be subjected to a subsequent high-temperature treatment, for example afterburning, in which any undestroyed toxic organic compounds are completely decomposed. The device according to the invention can have a plurality of preheating stages, each with a material inlet, a heater and an exhaust pipe, with individually adjustable and controllable operating parameters of the preheating stages, so that different material inlets can each be optimally treated. Preferably, the volume of the melt in the crucible or melting vessel must be at least five times smaller than the volume of the preheating stage in order to achieve a relatively short residence time in the melting stage. In order to set optimal operating conditions for different inputs of residual materials, the crucible can also have an adjustable or adjustable discharge siphon.

Crucibles made of ceramic materials or electrically conductive crucibles made of refractory metals such as molybdenum, tantalum and tungsten or of other electrically conductive materials such as graphite and silicon carbide are suitable for the relatively high temperatures T2 of the melting stage. A ceramic crucible wall can also be surrounded with electrically conductive material. Electric crucible heaters can thus be implemented as inductive or resistance heaters. This results in a quickly and easily controllable heating in the immediate vicinity of the melting material. In the case of inductive heating, electrically conductive internals in the crucible enable very good heat transfer. The conductivity can also be achieved by conductive residues or additives. The crucible can also have indirect gas or oil heating. Gas or oil heating, resistance heating or induction heating are also possible for the preheating stage. As a possible simplification, the heating of the melting stage can also be used to heat the preheating stage 4. The device according to the invention is particularly suitable as an integrated part of disposal systems in general and in particular in combination with a flue gas cleaning device.

• Fig. 1 schematisch das erfindungsgemässe Verfahren an einer Vorrichtung mit mehreren Reststoffeingängen und Vorwärmstufen;
• Fig. 2 eine Vorrichtung mit Vorwärmstufe und Einschmelzstufe;
• Fig. 3 einen Einschmelztiegel mit Induktionsheizung;
• Fig. 4 eine kombinierte Heizung von Einschmelzstufe und Vorwärmstufe;
• Fig. 5 eine Entsorgungsanlage mit Rauchgasreinigung und integrierter Einschmelzvorrichtung;
• Fig. 6 bis 8 verschiedene Beispiele von Temperaturverläufen in Vorwärm- und Einschmelzstufe.

The invention is explained in more detail below with the aid of examples and figures. Show:

• 1 shows schematically the method according to the invention on a device with a plurality of waste material inputs and preheating stages;
• 2 shows a device with preheating stage and melting stage;
• 3 shows a melting crucible with induction heating;
• 4 shows a combined heating of the melting stage and preheating stage;
• 5 shows a disposal system with flue gas cleaning and integrated melting device;
• Fig. 6 to 8 different examples of temperature profiles in the preheating and melting stage.

The melting device according to the invention can have one or more preheating stages. 1 shows three separate preheating and fractionation stages 4, 41, 42, into which various residues 3, 31, 32 are fed (2, 21, 22). The residues are moved through the preheating stages by means of conveying devices 7, 71, 72 in a throughput time t1, t11, t12 and are thereby heated to the preheating temperatures T1, T11, T12 by means of the associated heaters 6, 61, 62. Fractionated exhaust gases are produced in each stage , which are discharged via lines 8, 81, 82 and supplied to any further treatment stages (9). The preheating temperatures T1, T11, T12 can be adjusted separately to the corresponding residue composition and the desired fractionation effect.

All residues of the parallel preheating stages 4, 41, 42 are then passed together into a melting stage 10, where they are heated to a melting temperature T2 which corresponds at least to the flow temperature of the remaining solid phase. In a relatively small crucible 11 with an associated heater 12 and a corresponding possible short throughput time t2, the residues can be melted down completely or to a small extent enclosed by the melt, without undesired decomposition and evaporation occurring, as was unavoidable in previous large and very slow glass furnaces is.

Following the melt outlet 14, the melted phase can be solidified very quickly in a cooling or quenching device 15 or can be converted into a desired shape using controlled temperature gradients. The exhaust gases of this stage 10 are also carried away via an exhaust line 13 and supplied to any further treatment stages.

Fig. 2 shows a melting device with a screw conveyor 7, which is driven by a motor 29. By controlling this motor, the throughput time or the dwell time t1 in the preheating stage 4 can be set. A gas oven 26 serves here as heating for both stages 4 and 10. A heating outlet 27 serves as heating 12 of the melting stage 10 and the heating outlet 28 serves as heating 6 of the preheating stage 4. At the end of preheating stage 4 and screw conveyor 7, the remaining residues fall vertically in a tube down into the crucible 11 of the melting stage. The pipe 13 serves as the exhaust pipe of this stage 10. The preheating stage 4 has two further exhaust pipes 81 and 82, which can accommodate different exhaust gas fractions, for example, with slow heating. Under the exit 14, the melt 17 falls into a water bath as a quenching device 15. The inertized, landfill-capable residues 20 can be supplied for further use via a conveying bath 25.

3 shows a melting stage with induction heating 35, power supply lines 36 and water cooling 37, which heats up an electrically conductive crucible 11 directly. This results in a very concentrated heating, which enables a quickly controllable temperature setting T2. An adjustable outlet siphon 16 determines the desired height H of the melt 17 in the crucible 11. For this purpose, the siphon drain pipe 40 is actuated via an adjusting rod 38 in an adjustment range 39. The desired melting height H can also be set by replaceable inserts of the siphon drain pipe 40. If there is a slight layer of slag on the melt, an additional drain can be installed in the crucible.

4 shows a combined heating of both stages by means of a gas furnace 26. The melting stage 10 is heated directly, the preheating stage 4 indirectly by means of a bypass 45 and adjustable, for example, by a flap 46. The exhaust pipe 8 of the preheating stage is a subsequent high-temperature treatment stage 92 supplied, which is also heated by the gas furnace 26. Toxic organic compounds that are contained in the residue or that arise at low preheating temperatures of 300 ° C to 500 ° C can be completely decomposed in this high temperature stage 92. The high temperature stage can also consist of afterburning, the thermal energy of which can also be used to heat the preheating stage. The inclined arrangement of preheating stage 4 simplifies the conveyance of residues and preheating. The funding can also be provided by a rotary kiln.

5 shows a disposal system with an integrated melting device 4, 10 according to the invention. In a combustion system 47, the flue gases 49 are treated in a dust separation stage 48 and the resulting filter ash 32 together with the furnace ash 33 and the filter cake 34 from a waste water purification system of the preheating and fractionation stage 4 fed. The residue treatment is carried out as described via the melting stages 10 to the resulting inert solid 20. If necessary, a floating slag layer can be removed 66 separately. The exhaust gases 8 and 13 are fed to a quench stage 91 as a further treatment stage 9 and cooled and blown in very quickly by blown-in air 59 solidified. The resulting concentrated heavy metal salts 50 can be used further. An exhaust gas outlet of the quench stage leads into an activated carbon filter 65, in which the toxic mercury and other highly volatile, toxic substances 51 are eliminated. Exhaust gas 58 is then returned to the incinerator. The exhaust gases 55 from the dust separator 48 are fed to a wet flue gas cleaning unit 56. Their outputs are clean gas 54 and waste water, which is separated in a waste water purification system 57 into clean salts 52 (e.g. road salt), clean waste water 60 and a contaminated filter cake residue 34. The filter residue 34 in turn is returned to the preheating stage 4. The method according to the invention is further illustrated on the basis of the temperature profile T (t) over time in FIGS. 6 to 8 and the following examples.

Example 1a: At low preheating temperatures T1 = 400 ° C to 500 ° C and very short residence times t2 in the melting stage of a few minutes or even less than a minute, heavy metals such as zinc and lead can largely remain in the residues and thus become one Improve the melt quality (e.g. lead as an excellent glass former). This is also beneficial if there is no subsequent reprocessing of heavy metals. Curve 71 in Fig. 6 with T1 = 400 ° C and T2 = 1400 ° C shows such a temperature profile that the residues experience.

Example 1b: Conversely, at high preheating temperatures T1 = 1000 ° C and longer residence times t1 and t2, the heavy metals can largely be evaporated and can therefore be used in the concentrate for recycling (curve 73 in FIG. 7).

Example 2: Average preheating temperatures T1 of e.g. 600 ° C. can be used to pyrolyze organic components, for example paint sludge with paint residues (curve 72 in FIG. 7). The correct preheating temperature T1 is important here because, on the one hand, pyrolysis does not take place completely if the temperature is too low, so that violent reactions with abrupt gas formation can then occur at the high melting temperature in the crucible, which residues can be undesirably entrained in the exhaust gas. On the other hand, if the preheating temperatures T1 are too high, rapid reactions can take place and entrain dust into the exhaust gas.

Example 3: For two different inputs of residues with two parallel preheating stages 41 and 42 with separately adjustable preheating temperatures T11 and T12, optimal pretreatment of residues can be achieved, e.g. in the first stage 41 an additive such as bottle glass or borax can be added to the residues to reduce the Flow temperature in the subsequent melting stage to, for example, T2 = 1100 ° C. The preheating stage 41 is then, for example with T11 = 600 ° C, still below the Softening point of the aggregates operated. The residues of the second stage 42, from which heavy metals can largely be evaporated by high heating, for example from fly ash, can be operated at a relatively high temperature of T12 = 1000 ° C. (curves 72 and 73 of FIG. 7).

Example 4: Flue gas gypsum originating from flue gas cleaning contains substantial amounts of heavy metal impurities which have to be rendered inert. However, these heavy metals cannot be evaporated at the necessary high temperatures as is the case in conventional glazing systems, because at these high temperatures above 1000 ° C the calcium sulfate decomposes again and the previously bound SO2 is released again. In the process according to the invention, however, the heavy metal portion in the preheating stage can be at a temperature T1 of e.g. 700 ° C are already largely evaporated without undesired production of SO2 by decomposition of calcium sulfate, and organic substances can also be pyrolyzed in the process. In the subsequent melting stage, the undecomposed calcium sulfate can be melted down quickly together with a suitable residual and / or aggregate thanks to the very short throughput time t2. The sensitive substance then remains inertized in the solidified melt (curve 74 of FIG. 6) or is removed separately as slag.

Example 5: Fig. 8 shows the temperature curve according to curve 75 of a two-part preheating stage, in the first part of which is heated to T15 = 600 ° C (e.g. for pyrolysis) and then in the second part to T16 = 1000 ° C (e.g. evaporating heavy metals). With the preheating stage 4 according to the invention, any desired optimal temperature profile can in principle be set by appropriate subdivision and metering of the heater 6.

Label list

2, 21, 22

Feeder

3, 31, 32

Residues

4, 41, 42

Preheating and fractionation stage

6, 61, 62

Heating of 4

7, 71, 72

Conveyor

8, 81, 82

Exhaust pipe from 4

9

further treatment stage

10th

Melting level

11

crucible

12

Heating from 10

13

Exhaust pipe from 10

14

Melt leakage

15

Cooling, quenching device

16

Discharge siphon

17th

melt

20th

inertized residues

25th

Conveyor belt

26

Gas oven

27th

Heating output for 10

28

Heating output for 4

29

Motor for 7

30th

Recyclables, metal salts

32

Electrostatic precipitator

33

Oven ash

34

ARA filter cake

35

Induction heating

36

Power supply lines

37

water cooling

38

Adjustment rod

39

Adjustment range

40

Siphon drain pipe

45

Bypass of 26

46

Adjustment flap

47

Incinerator

48

Dust removal level

49

Flue gas

50

Metal salts, recyclables

51

Ed

52

Salts (road salt)

53

Furnace slag

54

Clean gas

55

Exhaust gases from 48

56

Wet cleaning

57

Wastewater treatment

58

Exhaust gas

59

Air in 91

60

clean sewage

65

Activated carbon filter

66

additional drainage slag layer

71 to 75

Temperature curves T (t)

91

Quench stage

92

High temperature level

T1, T11, T12, T15, T16

Preheating temperatures

T2

Melting temperature

t1, t11, t12, t15, t16

Residence times in level 4

t2

Dwell time in level 10

H

Melt height 17

Claims (25)

Process for the continuous melting of heterogeneous solid or viscous residues, characterized in that the residues are heated in a preheating and fractionation stage (4) in a controlled manner to an adjustable preheating temperature (T1), volatile components being expelled or split off and discharged as exhaust gas, which Exhaust gases can be fed to a further treatment stage, and that the preheated remaining solid phase is heated in a subsequent melting stage (10) to a temperature (T2) which corresponds at least to its flow temperature and that they then become inert in a glassy or crystalline solid by subsequent cooling or quenching Final state is brought. A method according to claim 1, characterized in that the preheating temperature (T1) is adjusted according to the composition of the residues and matched to the desired exhaust gas fractions. Method according to claim 1 or 2, characterized in that the preheating temperature (T1) is between 400 ° C and 1000 ° C. Method according to one of claims 1 or 3, characterized in that the preheating temperature (T1) is at least 200 ° C below the melting temperature (T2). Method according to one of claims 1 to 4, characterized in that the preheating temperature (T1) is adjusted to the softening temperature and the composition of the residues. Method according to one of claims 1 to 5, characterized in that the residence time (t1) of the residues to be treated in the fractionation stage (4) is greater than the residence time (t2) in the melting stage (10). A method according to claim 6, characterized in that the residence time (t2) in the melting stage is less than 15 minutes. A method according to claim 6, characterized in that the residence time (t2) in the melting stage is at most 5 minutes. Method according to one of claims 1 to 8, characterized in that the operating parameters, depending on the physical properties and the chemical composition of the resulting residues and the desired proportions of substances to be fractionated in the exhaust gas, are adjusted, controlled and regulated, the operating parameters being Temperatures (T1, T2) and the dwell times (t1, t2) of the preheating stage and the melting stage, or the corresponding heating outputs and the delivery rate, can be controlled. Method according to one of claims 1 to 9, characterized in that the hot exhaust gases are suddenly cooled in a further treatment stage (91) by blowing in cold air or another gas or cold solid and desubliming substances are eliminated. Method according to one of claims 1 to 10, characterized in that the exhaust gases are subjected to a subsequent high-temperature treatment (92). Device for the continuous melting of residues according to the method of claim 1, characterized by a feed (2) of the residues (3) into a preheating and fractionation stage (4) with a first heater (6), a conveyor (7) and a first exhaust pipe (8), and by a subsequent melting stage (10) with a crucible (11) receiving the conveyed residues, a second heater (12), a further exhaust pipe (13) and a melt outlet (14). Apparatus according to claim 12, characterized in that a plurality of parallel preheating stages (4, 41, 42) each with a material inlet (3, 31, 32), a heater (6, 61, 62) and an exhaust pipe (8, 81, 82) are provided, the operating parameters (T1, T11, T12, t1, t11, t12) of the preheating stages, matched to different material inputs (3, 31, 32), being individually adjustable and controllable. Device according to claim 12 or 13, characterized in that the volume of the melt in the crucible (11) is at least five times smaller than the volume of the preheating stage (4) for the residues. Device according to one of claims 12 to 14, characterized in that the crucible (11) has an adjustable or adjustable outlet siphon (16) for continuously draining the melt (17). Device according to one of claims 12 to 15, characterized in that the crucible (11) consists of ceramic materials. Device according to one of claims 12 to 15, characterized in that the crucible (11) consists of electrically conductive, high-melting metals such as molybdenum, tantalum, tungsten or their alloys or other electrically conductive materials such as graphite, silicon carbide or clay graphite. Device according to one of claims 12 to 15, characterized in that the crucible wall containing the melt consists of ceramic material and that electrically conductive material is attached to the crucible wall or around the crucible or as internals in the crucible. Device according to one of claims 12 to 15, characterized in that the crucible (11) has a controllable direct or indirect electrical resistance heating. Device according to one of claims 12 to 15, characterized in that an electrically conductive crucible (11) and an inductive heater are provided. Device according to one of claims 12 to 16, characterized in that the crucible (11) has a gas or oil heater. Device according to one of claims 12 to 21, characterized in that the preheating stage (4) has a gas or oil heater, a resistance heater or an induction heater. Device according to one of claims 12 to 16, characterized in that the heater (12) of the melting stage (10) can also be used at least in part for heating the preheating stage (4). Disposal system with a melting device (1) according to one of claims 12 to 23 as an integrated part of the system. Disposal system according to claim 24, which has a flue gas cleaning device combined with the melting device.

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