CH680656A5 - Continuous melting of solid or viscous waste - by controlled preheating and fractionating, melting and cooling to form inert prod. - Google Patents

Abstract

Continuous melting of heterogeneous solid or viscous residual materials is carried out by (a) controlled heating to a preheat temp. (T1) in a preheating and fractionating stage (4) so that volatile matter is evolved or decomposed to form waste gas which is fed to a further treatment stage; (b) heating in an adjoining melting stage (10) to a temp. (T2) corresponding to at least the material flow temp.; and (c) cooling or quenching to a vitreous or crystalline solid inert final state. Also claimed are appts. and a disposal plant for carrying out the process. USE/ADVANTAGE - The process is used esp. in the disposal of residues such as filter ash and slag from energy prodn. and combustion plants, lacquer sludge, filter press and electroplating sludges, and flue gas cleaning residues. The residues are converted to a dumpable inert final state in which noxious material (esp. including heavy metals) are immobilised and in which SO2 is trapped.

Description

1

CH 680 656 A5

2nd

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 power 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, inertized 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 can be no impairment of the groundwater caused by washing out. Annoyance caused by 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 processes and the SO2 previously bound therein is released again, which requires a subsequent additional desulfurization step. 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 residual materials, which enables extensive and controllable integration of pollutants, in particular also heavy metals, and which can also form an S02 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. CaS04). A substantial proportion of the sulfur contained in the flue gas gypsum is thus rendered inert, i.e. an S02 sink is created. The inerting method according to the invention is thus also much more comprehensive and effective than the previously known ones. 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 adjusted according to the composition of the residues to a desired exhaust gas fraction and to the softening temperature of the residues. For the purpose of well-controlled fractionation, the residence time in the fractionation stage can be selected 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 delivery 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 matter, e.g. Heavy metal salts are desublimated and converted into a recyclable powder form without toxic organic substances such as dioxins and furans being formed during long periods of time in the critical temperature range of 300 ° C to 400 ° C when cooling

5

10th

15

20th

25th

30th

35

40

45

50

55

60

65

3rd

CH 680 656 A5

4th

will. Exhaust gases of a relatively low preheating temperature T1 and a short residence time t1 can be used for a subsequent high-temperature treatment e.g. Are subjected to afterburning, in which any arisen or. 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. The volume of the melt in the crucible or melting vessel can preferably 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 outlet 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. However, 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.

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;

6 to 8 different examples of temperature processes 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 an exhaust pipe of this stage 10. The preheating stage 4 has two further exhaust pipes 81 and 82, which e.g. can absorb various exhaust gas fractions with slow heating. Under the outlet 14, the melt 17 falls into a water bath as a quenching device 15. The inertized, landfillable residues 20 can be supplied for further use via a conveyor 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 spout

5

10th

15

20th

25th

30th

35

40

45

50

55

60

65

3rd

5

CH 680 656 A5

6

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.

Fig. 4 shows a combined heating of both stages by a gas furnace 6. The melting stage 10 is heated directly, the preheating stage 4 indirectly via a bypass 45 and adjustable e.g. through a flap 46. The exhaust gas line 8 of the preheating stage is here fed to a subsequent high-temperature treatment stage 92, 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 31 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. The exhaust gases 8 and 13 are fed to a quench stage 91 as a further treatment stage 9 and are rapidly cooled and solidified by blown air 59. The resulting concentrated heavy metal salts 50 can be used further. An exhaust gas outlet of the quench stage leads further into an activated carbon filter 65, in which the toxic mercury and other highly volatile, toxic substances 51 are separated out. Exhaust gas 58 is then returned to the incinerator. The exhaust gases 55 from the dust separator 48 are fed to a flue gas cleaning device 56. Their outputs are clean gas 54 and wastewater, which is separated in a wastewater treatment plant 57 into clean salts 52 (e.g. road salt), clean wastewater 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 can cause heavy metals e.g. Most of the zinc and lead remain in the residues and thus contribute to an improvement in 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 T1 = 1400 ° C. shows such a temperature profile that the residues experience.

Example 1 b:

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 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 residues inputs with two parallel preheating stages 41 and 42 with separately adjustable preheating temperatures T11 and T12, an 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 e.g. T2 = 1100 ° C. The preheating stage 41 is then e.g. operated with T11 = 600 ° C still below the softening point of the aggregates. The residues of the second stage 42, of which high heating, e.g. from fly ash, heavy metals can be largely evaporated, 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 temperatures5

10th

15

20th

25th

30th

35

40

45

50

55

60

65

4th

7

CH 680 656 A5

8th

tures 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 residue and / or additive, thanks to a very short throughput time 12. The sensitive substance then remains inertized in the solidified melt (curve 74 of FIG. 6).

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.

Claims (24)

Claims 1. A process for the continuous melting of heterogeneous solid or viscous residues, characterized in that the residues are heated to a preheating temperature T1 in a preheating and fractionation stage (4), 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 it is brought into a glassy or crystalline solid, inert final state by subsequent cooling or quenching . 2. The method according to claim 1, characterized in that the preheating temperature T1 is set below the flow temperature of the residues such that the volatile fractions are expelled or split off in a predetermined sequence and within a predetermined period of time. 3. The method according to claim 1, characterized in that the preheating temperature T1 is between 400 ° G and 1000 ° G. 4. The method according to claim 1, characterized in that the preheating temperature T1 is at least 200 ° C below the melting temperature T2. 5. The method according to claim 1, characterized in that the preheating temperature T1 is adjusted to the softening temperature of the residues. 6. The method according to claim 1, 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). 7. The method according to claim 1, characterized in that the residence time t2 in the melting stage is less than 15 minutes. 8. The method according to claim 1, characterized in that the residence time t2 in the melting stage is at most 5 minutes. 9. The method according to claim 1, characterized in that the operating parameters are tuned, controlled or regulated depending on the physical properties and the chemical composition of the residual materials and on the predetermined proportions of substances to be fractionated in the exhaust gas, the 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, are controlled. 10. The method according to claim 1, 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 excreted. 11. The method according to claim 1, characterized in that the exhaust gases are subjected to a subsequent high-temperature treatment (92). 12. Device for the continuous melting of residues according to the method of claim 1, characterized by a feed (2) of the residues (3) in a preheating and fractionation stage (4) with a first heater (6), a conveyor (7) and one first exhaust pipe (8) and through 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). 13. The 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 being individually adjustable and controllable for adjustment to different material inputs (3, 31, 32). 14. The apparatus according to claim 12, 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. 15. The apparatus according to claim 12, characterized in that the crucible (11) has an adjustable or adjustable outlet siphon (16) for continuously draining the melt (17). 16. The apparatus according to claim 12, characterized in that the crucible (11) consists of ceramic materials. 17. The apparatus according to claim 12, characterized in that the crucible (11) made of electrically conductive, high-melting metals such as molybdenum, tantalum, tungsten or their alloys or 5 10th 15 20th 25th 30th 35 40 45 50 55 60 65 5 G CH 680 656 A5 other electrically conductive materials such as graphite, silicon carbide or clay graphite. 18. The apparatus according to claim 12, characterized in that the crucible wall containing the melt consists of ceramic material and 5 that electrically conductive material is attached in the crucible wall or around the crucible or as internals in the crucible. 19. The apparatus according to claim 12, characterized in that the crucible (11) has a controllable 10 direct or indirect electrical resistance heating. 20. The apparatus according to claim 12, characterized in that an electrically conductive crucible (11) and inductive heating are provided. 15 21. The apparatus according to claim 12, characterized in that the crucible (11) has a gas or oil heater. 22. The apparatus according to claim 12, characterized in that the preheating stage (4) has a gas or oil heater, a resistance heater or an induction heater. 23. The device according to claim 12, characterized in that the heater (12) of the melting stage (10) is at least partially usable for heating the preheating stage (4). 24. Disposal system with a melting device (1) according to one of claims 12 to 23 as an integrated part of the system. 25 Disposal system according to claim 24, which additionally has a flue gas cleaning device combined with the melting device. 35 40 45 50 55 60 65 6