CA2056194A1

CA2056194A1 - Process and device for cleaning waste materials containing harmful substances

Info

Publication number: CA2056194A1
Application number: CA 2056194
Authority: CA
Inventors: Hans-Klaus Schott
Original assignee: Kuettner GmbH and Co KG
Current assignee: Kuettner GmbH and Co KG
Priority date: 1991-03-20
Filing date: 1991-11-26
Publication date: 1992-09-21
Also published as: MX9101507A; JPH04295507A; RU2062796C1; EP0504502A1; BR9104441A

Abstract

ABSTRACT OF THE DISCLOSURE

The present invention concerns a process and a device for removing harmful substances from waste materials (such as industrial dust and sludge, roll scale, used foundry sand etc.) in which a heated bulk material bed is formed into a fluidized bed by the introduction of a gas at least in the upper portion of the bulk material, whereby the fluidized bed, which consists (at least in part) of materials to be cleaned, is heated from above, whereby the heating intensity is controllable or adjustable, so that the solid material temperature, on the one hand, and the gas temperature prevailing in the gas chamber located above the fluidized bed, on the other hand, are adjustable, and that the thermal requirements for the cleaning process and the flow-technological requirements for the material systems can be adjusted independent of one another.

Description

2 ~ 9 ~

The present invention concerns a process and appaxatus for the removal of harmful substances from waste materials (such as industrial dust and sludge of the type occurring, for example, in ferrous and non-ferrous metallurgy, 5 roll scales, used foundry sand and similar materials,) in filtering facilities, scrubbers, clarifying basins etc., in which a bulk material bed is heated from above and formed into a fluidized bed at least in the upper portion of the bed, by introducing a gas.
The present invention further concerns a device for carrying out the above-mentioned process by means of a bed-forming container, within which a bed is to be formed which consists at least partly of material to be cleaned. A
fluidizing device introduces a fluidizing gas into the bed for 15 the purpose of creating a fluidized bed. A heater is located above the bed for heating the fl~idized bed, and a waste/exhaust gas line removes burned gases.
Waste materials of the above-mentioned type are generated in large quantities during a wide variety o~
20 technological processes, and were formerly (in some cases until very recently) deposited as such at waste storage sites.

In response to the ~act that the available waste storage spa e has become scarce (and correspondingly 25 expensive), and in view of the fact that it has become imperative (for ecological reasons) to at least partly clean such "waste materials" and make them into reusable materials, several cleaning processes have recently been developed.
However, these processes are not as efficient as would be 30 desirable, in that they partially lead to considerable environmental stresses etc.
A typical example of this is the used sand which is continuously generated, in relatively large ~uantities, in foundries. The original molding sand contains, as molding 35 materials, inorganic bonding agents ~for example bentonite, and referred to as "inorganic used sand") and~or organic bonding agents (such as phenolic and/or furan resins, and 2 ~ 9 ~

referred to as "organic used sand"). In inorganically bonded molding sands, the bonding agent bentonite or similar substances is - dependent on the degree o~ heating during the casting process - fixed in a shell-like manner on the surface 5 of the sand grains by oolithization. In the case of organic molding sands, the organic bonding agents are thermally decomposed during the casting process and thus create adhering residues of carbon-rich derivatives of the organic bonding agents on the surface of the sand grains. In addition, the 10 used sand is often polluted by other additives such as sizing materials, lustrous carbons etcO
For the cleaning of used sand, a number of special pneumatic or mechanical cleaning processes are known which separate the sand into a reusable material fraction and an 15 non-reusable waste fraction, which is enriched with harm~ul substances.
An objective of the process of the invention is the decontamination of the waste fraction and the recovery of usable material from the otherwise non-reusable waste. ~ s~e 20 cases the used sand can be cleaned with conventiQnal mechanical or mechanical/pneumatic means to such an extent that a waste fraction results which contains such a small part of potentially reusable material that it would be too costly to recover. In such cases, the waste ~raction is typically 25 an especially fine-grained, highly contaminated material which must be decontaminated. During decontamination o~ this material the complete burn-out of the organic substances must be assured by corresponding long dwell times in the reactor.
Another problem involving the decontamination of 30 waste materials involves the occurrence, or cleaning, of roll scale, which typically consists of a mixture of FE and/or FEO
and/or FE304 and FE203, along with water and oilO I Roll scale generally is produced with differing granulations (predominantly smaller than 500 ~m) and greatly varying oil 35 and water content. On the other hand, roll scale typically contains only relatively small quantities of other types o~
contaminants, such as Zn, P~ and alkalies. Once it has been ~os~

properly cleaned, roll scale can be returned to a metallurgical pxoduction process as a very valuable raw material.
Decontamination of roll scale has up to now been 5 done with a rotating cylindrical kiln, in whi~h the roll scale is heated directly or indirectly, so that oil is converted or burned up by direct burning-off or smouldering, and the water evaporates. This so-called rotating kiln process tends to be energy inefficient, and usually requires a subsequent 10 treatment with gas.
Other cases of the type being discussed here involve the cleaning of waste products such as clearing basis sludge;
sludge from wet cleaning of kilns etc.; contaminated soil;
residues from production processes in the paint industries 15 etc.; as well as other contaminated pasty (or at least partially liquid) substances such a~ fine-grained solids of various types.
It is therefore an object of the present invention to provide a process (and a device suitable for its 20 implementation) with which a wide variety of waste materials can be decontaminated and thus regenerated into reusable raw materials in a technically, economically and ecologically satisfactory manner by substantially separating or destroying the harmful substances they contain.
According to an aspect of the invention, there is provided a process for cleaning bulk materials containing harmful contaminants, said process comprising; forming a fluidised bed composed at least partially of said bulk 30 material by introducing a flow of gas at least into the upper portion of thereof; heating said fluidised bed; and providing a controlled source of heating in the gas above said bed;
whereby the heating intensity of the material within the fluidised bed, and the heating intensity in the gas above the 35 fluidised bed are adjustable; and wherein the thermal conditions required for decontamination of said bulk materials, and the gas flow requirements for maintaining a 2 ~ 9 ~

fluidis~d bed and bulk material flow, are independently adjustable.
According to another aspect of the invention, there is provided a device for decontaminating bulk materials 5 containing harmful substances, said device comprising: a container adapted to contain therein a bed composed at least partially of said bulk material: means for introducing a fluidising gas into said container so as to ~orm a fluidis~d bed of said bed composed at least partially of the bulk lO material; means for heating the fluidised bed, said heating means being adjustably positioned within said contain~r above said fluidised bed; an exhaust gas line adapted to conduct gases, which have previously passed through said fluidised bed, away frQm said container; and bulk material inlet and 15 discharye openings adapted to facilitate supply of bulk material to said fluidised bed, and subsequent removal o~ said bulk material therefrom.

The material systems subject to cleaning ha~e 20 varying material properties, which must be taken into account for material conversion (incineration, drying etc.) and material movsment in the fluidizing bed. Thus, solids must be cleaned at varying critical temperatures, while the highest permissible temperature is derived from the properties of the 2~ respecti~e solid substance. Likewise, the dwell time of the solid material in the fluidizing bed, until th~ desired degree o~ material conversion is attained, depends on the ~olid material and its grain structure.
It is therefore preferable to have a reactor where 30 the amount of fuel and combustion air required for the necessary reaction heat does not burden the fluidizing bed, so that the amount of ~luidising gas which is required for the dif~erent solid materials can be adapted to the ~low conditions in the fluidizing bed without affecting the 35 heating, and vice versa.
The process portion of the invention is generally characterised in that the fluidizing bed, which consists at 2~s~

least partially of material to be cleaned, is heated from above, if necessary, wherein the heating intensity can be controlled or regulated so that the solids temperature and the gas temper~ture prevailing in the gas chamber above the 5 fluidizing bed are adjustable (pre~erably separately).
Preferably, the fluidising gas volume required for generating the optimal fluidization condition is adjustable, independently o~ the heating intensity. This is especially true for particularly fine-grained materials to be cleaned.
During this process, the fluidizing bed can consist essentially completely of materials to be cleaned, or, in a different embodim nt of the invention, it may contain a granular carrier material. In the latter case, the materials to be cleaned are preferably added to the carrier material in 15 the lower third of the fluidizing bed.
In the process using carriar materlal, the grain size o~ at least the predominant portion of the carrier material should preferably be greater than the particle size of the materials to be cleaned, in order to ensure that the 20 materials to be cleaned can be separated from the carrier material in no less time than the required dwell time in the reactor.
For the same reason, the gross density o~ the carrier material should preferably be greater than the gross 25 density of the materials to be cleaned, while, among other things, the choice o~ the relative gross densities can also be used to adjust the dwell time of the materials to be cleaned in the carrier layer during cleaning.
It has been shown to be especially practical for a 30 majority of materials to be ~leaned if the carrier material is at least essentially globular.
In another embodiment of the invention, the fluidized bed can be at least partially operated in a circulating fashionO In addition, either an oxidizing or 35 reducing environment can be maintained within the reactor (as opposed to a conventional, neutral environment). However, in this case, the exhaust gas must be subsequently treated.

~6~.9~

In accordance with a further embodiment of this invention, the fluidising gas may consist essentially of air (i.e. not of fuel), in which case the fluid gas volume, which is introduced into the fluidized bed on a per unit time basis, 5 must be proportioned in such a way that the oxygen it contains is sufficient to convert or burn the fual (for example oil, hydrocarbon compounds etc.) contained in the materials to be cleaned within a predetermined time inkerval, provided that the fluid gas volume determined in this manner is sufficient lo for the fluidiæation of the fluidized bed. The fluidizing speed of said fluidized bed can be adjustable ovex a wide range in yet another much preferred embodiment of this invention.
If the oxygen (in the supplied air volume) required 15 for the conversion of the combustible materials (for example, oil, hydrocarbons etc.) contained in the materials to be cleaned exceeds the air volume required for the optimal fluidization condition in the fluidized bed, then the materials to be cleaned (which in that case are generally very 20 fine-grained) can be agglomerated to a suitable grain size by the addition of water. This prevents excess temperature in the fluidized bed and, at the same time, the required dwell time of the Eine particles in the ~luidizing bed is maintained at the time re~uired for dissolving the agglomerates. In 25 these cases, it is preferable that the ~luidizing bed is made up of the coarse portion contained in the materials to be cleaned.
In order to bond sulphur components of the materials to be cleaned, it can be of practical advantage to add 30 limestone or similar material to the fluidizing bed in a conventional manner.
Furthermore, it must be pointed out that the addition of air during the generating o~ reaction heat can be graduated, and is preferably adjusted in such a way that 35 essentially no significant formation of NOX occurs.
According to the invention, the ~luidized bed is heated most preferably from above, preferably with high-speed ~0~9~

burners. Gaseous Euels have proven to be especially advantageous for this purpose as auxiliary fuels (i.e. in addition to the combustible components already contained in the materials to be cleaned).
The fluidized bed is pre~erably maintained at a steady temperature of approximately 750 to 950C.
According to further preferxed embodiments of this invention, the temperature in the solid material, on the one hand, and in the gas chamber above the fluidized bed, on the 10 other hand, can be variably adjusted. Similarly, the dwell time of the materials to be cleaned in the fluidized bed can be adjusted. It is also preferable for the fluidizing speed of the fluidized bed to be adjustable over a wide range, in order to be able to adapt the operating conditions to the 15 respective requirements of the materials to be cleaned as optimally as possible.
Furthermore, it can be advantageous to separate solid materials in a separator or similar equipment placed behind the fluidized bed. In this case it can then also be 20 most advantageous to return the separated solids at least partially to the fluidized bed.
In the case of cleaning roll scale, according to the invention, the roll scale is placed into a heated fluidized bed having a high heating capacity. The ~luidized 25 bed is, in thls case, operated with a carrier material tor with coarse roll scale). The fine grains of the roll scale can be practically removed from the gas stream above the fluidised bed, while the coarse roll scale can be removed at the foot of the fluidized bed. Regardless o~ whether coarse 30 roll scale or, for example, steel shot is used as the carrier material, the moisture contained in the roll scale to be cleaned evaporates spontan~ously as the roll scale is fed in~o the fluidized bed. As a result o~ this, the oil (and other hydrocar~ons) contained in the roll scale is finely atomized, 35 and any oil (and other hydrocarbons adhering to the roll scale grains is spontaneously gasified, so that it can be completely ~ 0 ~

oxidized with the fluidizing gas air (or oxygen) which is continuously fed into the fluidizing bedO
In the case of wet cleaning sludge, contaminated soil, residues from the paint-producing industry, etc., one 5 ~an likewise also worX with a fluidized bed with or without separate carri~r materialr In this case thare generally occurs an "after burning" above the fluidized bed in the so-called gas chamber and even the finest flying dust particles are completely decontaminated.
The same is true for cleaning pasty or liquid substances according to the invention. In this case a carrier material is used in the fluidized bed, and by this means organic components are completely converted ("burned up") and any possible sulphur components can be bonded by the addition 15 of limestone.

An embodiment of the invention wlll now be described by way of example, with reference to the accompanying drawing which diagrammatically illustrates a system according to the 20 invention for decontaminating waste materials from a mechanical sand cleaning process.
The drawing shows in a diagrammatic representation, a bin 1 in which waste material is collected. The waste material is fed to a wetting and agglomerating device 2, and 25 the agglomerates which are formed here are moved into the fluidized bed 3.
As a result of the extremely fast heat transfer (and the good mixture in the ~luidized bed), the outer layers o~ the agglomerates are virtually instantaneously heated to 30 an operating temperature of approximately 800 to 850C, and the harm~ul inorganic contaminants are completely converted (by combustion~ with the aid of atmospheric oxygen. As a result of the movement of the materials in the ~luidiæed bed 3, the agglomerates are slowly dissipated.
Fine-grained solids are removed from the fluidizing bed 3 by the upward flow of fluidising gas. These solids are separated from the gas flow in a separator 6/ in order to 2 ~ 9 ~

protect th~ subsequent heat exchanger 5 against wear and tear.

LargQr grain solids ~i.e. those which are not carried upwards by the gas stream) leave the fluidized bed 5 through lateral discharge openings 7a or 7b. The upper discharge opening 7a is used to discharge the majority of the solids, whereas the lower discharge opening 7b i5 used only occasionally to remove material which is too heavy to be fluidi7able, and which therefore sinks to the bottom of the 10 fluidised bed.
ThP kiln gas is cooled in a heat exchanger 5 with the heat removed from the kiln gas being used to preheat the fluidizing air.
The solids which are separated from the gas stream 15 in the separator 6, and the solids which are removed laterally from the fluidized bed through the discharge openings 7a and 7b are cooled in a cooler 8.
A high-speed burner 10 is shown in the fluidizing kiln 9 above the fluidized bed 3. The burner 10 can be 20 adjusted with respect to its heating performance, and the position of burner nozzle ll can be adjustable with r~spect to the wall 12 of the fluidizing kiln 9, as well as with i respect to the surface of the fluidized bed 3~ This high-speed burner 10 is generally placed centrally within the 25 fluidising kiln 9 and attached to the roof of the fluidized bed by means of a mounting support (not shown).

Claims

1. A process for cleaning bulk materials containing harmful contaminants, said process comprising;
forming a fluidised bed composed at least partially of said bulk material by introducing a flow of gas at least into the upper portion of thereof; and heating said fluidised bed from above;
the heating intensity being adjustable so that the temperature of the material in the fluidised bed, and the temperature of the gas above the fluidised bed may be controlled; and wherein the thermal conditions required for decontamination of said bulk material, on the one hand, and the gas flow requirements for maintaining a fluidised bed and for bulk material flow, on the other, are independently adjustable.

2. A process according to claim 1, wherein the temperature of the solids within the fluidised bed, and the gas temperature are separately adjustable.

3. A process according to claim 1, wherein the heating intensity is adjusted independently of the flow-technological requirements of the material system.

4. A process according to claim 1, wherein the materials movement is adjustable independent of the heating.

5. A process according to claim 1, wherein the fluidized bed consists essentially completely of said bulk material.

6. A process according to claim 1, wherein the fluidized bed contains a granular carrier material.

7. A process according to claim 6, wherein said bulk material is fed into the fluidized bed from above.

8. A process according to claim 1, wherein the bulk material is fed into the lower third of the fluidized bed.

9. A process according to claim 6, wherein very fine-grained bulk material is wet-agglomerated before being fed into the fluidized bed.

10. A process according to claims 6, wherein the grain size of at least a predominant proportion of the carrier material is greater than the particle size of the bulk material.

11. A process according to claim 6, wherein the gross density of the carrier material is greater than the gross density of the bulk material.

12. A process according to claim 6, wherein the carrier material is essentially spherical.

13. A process according to claim 1, wherein the fluidized bed is operated at least partly in a circulating manner.

14. A process according to claim 1, wherein the fluidized bed is operated in an oxidizing gas.

15. A process according to claim 1, wherein the fluidized bed is operated in a reducing gas, said gas being subsequently subjected to secondary burning.

16. A process according to claim 1, wherein the fluidising gas comprises of air and inert gas, which components are proportioned such that the amount of oxygen in the gas flow is just sufficient to ensure complete combustion of any combustible substances contained in the bulk material within the fluidised bed.

17. A process according to claim 1, wherein the fluidizing speed of the fluidized bed is adjustable over a wide range.

18. A process according to claim 1, wherein the supply of combustion air is controlled in such a way as to substantially prevent the formation of significant amounts of NOx.

19. A process according to claim 1, wherein the fluidizing gas comprises a gaseous fuel as auxiliary fuel.

20. A process according to claim 1 r wherein the oxygen content of air is used as an oxidizing agent for fuels and other combustible substances.

21. A process according to claim 1, wherein the fluidized bed is maintained at a steady temperature in the range of approximately 700 to 950°C.

22. A process according to claim 1, wherein a portion of the bulk materials which have been discharged from the fluidised bed are subsequently returned to the fluidized bed.

23. A process according to claim 1, wherein the fluidizing gas is preheated, prior to entering the fluidised bed, by the stream of heated gases which have previously passed through the fluidised bed.

24. A process according to claim 1, wherein the gas which has passed through the fluidised bed is subsequently quenched with water so as to reduce its temperature from approximately 450 to 150°C.

25. A process according to claim 1, wherein the heating is done in a near-stoichiometric manner.

26. A device for decontaminating bulk materials containing harmful substances, said device comprising:
a container for a bed composed at least partially of said bulk material;
means for introducing a fluidising gas into said container so as to convert said bed to a fluidised bed;
heating means adjustably positioned within said container above said fluidised bed, for heating the fluidised bed;
an exhaust gas line for removing gases which have passed through said fluidised bed; and bulk material inlet and discharge openings for supplying of bulk material to said fluidised bed, and removing bulk material therefrom.

27. A device according to claim 26, wherein said heating means comprises a burner, the burner orifice of which is located essentially centrally above the fluidised bed.

28. A device according to claim 26, further comprising a secondary burner located in said exhaust line.

29. A device according to claim 26, further comprising a secondary combustion chamber located in said exhaust line.

30. A device according to claim 26, further comprising a flue gas after-treatment device is located in the exhaust gas line.

31. A device according to claim 30, wherein the flue gas after-treatment device is equipped with a separator adapted to remove fine-grained solids from the gas stream.

32. A device according to claim 30 or 31, wherein the flue after-treatment device contains a water-operated quenching stage.

33. A device according to claim 30, wherein the flue gas after-treatment device is equipped with a filter.

34. A device according to claim 33, wherein the filter is a cloth filter.

35. A device according to claim 26, wherein said fluidised bed is at least partially comprised of a granular fill material, the grain size of which is essentially greater than the grain size of the bulk material.

36. A device according to claim 35, wherein the grains of said filler material are generally spherical is shape.

37. A device according to claim 35, wherein the gross density of the fill is greater than the gross density of the bulk material.

38. A device according to claim 26, further comprising at least one nozzle, said at least one nozzle being adapted to direct a flow of gas into the region of the fluidised bed.

39. A device according to claim 38, wherein the penetration depth of each of said at least one nozzle is individually adjustable.

40. A device according to claim 26, further comprising a control device by means of which the fluidising gas volume flow rate is controlled.

41. A device according to claim 31, further comprising a control device responsive to volume rate at which fine grain solids are separated in the separator, by means of which control device a non-circulating operating mode of the fluidized bed is at least partially switched over to a circulating mode.