WO1996025202A1

WO1996025202A1 - Refractory barrier layer and method of formation

Info

Publication number: WO1996025202A1
Application number: PCT/US1996/001675
Authority: WO
Inventors: Cathy M. Shaw; James E. Johnston
Original assignee: Molten Metal Technology, Inc.
Priority date: 1995-02-14
Filing date: 1996-02-07
Publication date: 1996-08-22
Also published as: AU4917796A; TW283195B; ZA961145B

Abstract

A barrier layer on a refractory lining is formed. The method includes providing a refractory-lined vessel containing a combination of aluminum oxide and calcium oxide that can form a precipitate when exposed to chlorine. The combined aluminum oxide and calcium oxide is exposed to chlorine, whereby the precipitate is formed and deposited on the refractory lining, thereby forming the barrier layer on the refractory lining. In a preferred embodiment, the method includes injecting chlorine or a chlorine-containing compound at a point beneath a surface of a molten bath in said vessel to form the precipitate, whereby the precipitate accumulates on a surface of the lining, thereby forming the barrier layer.

Description

REFRACTORY BARRIER LAYER AND METHOD OF FORMATION

Background of the Invention

Many types of hazardous wastes are continuously being generated. These wastes often include organic materials that are chlorinated, such as pesticides, polychlorinated biphenyls (PCBs) , paints and solvents. Also, other hazardous wastes include inorganic material, such as oxides of iron, zinc, aluminum, copper and magnesium and the salts of ferrous chloride (FeCl₂) , ferric chloride (FeCl₃) , aluminum chloride (A1C1₃) , etc.

Current methods of hazardous waste disposal generally include dumping in designated landfills and incinerating. However, despite capping and other containment attempts, the integrity of dumps can be breached, thereby causing materials to leach into surrounding water tables. The other alternative of incineration typically results in only partial disposition of hazardous substances, thereby leaving residue, such as ash and emissions, which themselves are pollutants that are subject to environmental regulatory restrictions. Halogenated wastes are of particular concern because both dumping and incineration are especially susceptible to loss of water soluble and volatilizable contaminants, such as halogens leaching to the soil or escaping to the atmosphere. Therefore, disposal of hazardous wastes and, in particular, halogen-containing hazardous wastes, can cause release of harmful contaminants to the environment, thereby diminishing the quality of life in surrounding populations. To minimize the environmental effects of waste disposal, alternative methods are being developed to convert wastes into benign, and preferably, useful substances. Among the most promising new methods are those described in U.S. Patents 4,574,714 and

4,602,574, issued to Bach and Nagel . These methods dissociate materials, such as organic materials, to their atomic constituents in a molten metal bath and reforms the atomic constituents into environmentally acceptable products, including hydrogen, carbon monoxide and/or carbon dioxide gases.

Waste materials are often injected through tuyeres beneath the surface of molten baths employed to destroy the wastes. However, many wastes include chlorine, which causes accelerated wear of the tuyeres and of the surrounding refractory materials. Wear of refractory reactor linings in contact with vitreous layers that contain chlorine is of particular concern. Rapid wear can require that operation of reactors be terminated prematurely, which often increases the cost and frequency of reactor repair.

Therefore, a need exist for a method to form a barrier layer to eliminate or substantially reduce the rate of wear of reactor linings and of tuyeres caused by injection of chlorine-containing wastes into molten baths .

Summary of the Invention

The present invention relates to a method for forming a barrier layer on a refractory lining, and to a refractory lining barrier, such as a skull, formed by the method.

The method includes providing a refractory-lined vessel containing a combination of aluminum oxide and calcium oxide that can form a precipitate when exposed to chlorine. The combined aluminum oxide and calcium oxide are exposed to chlorine, whereby the precipitate is formed and deposited on the refractory lining, thereby forming the barrier layer on the refractory lining. In a preferred embodiment, the method includes injecting chlorine or a chlorine-containing compound at a point beneath a surface of a molten bath in said vessel to form the precipitate, whereby the precipitate accumulates on a surface of the lining, thereby forming the barrier layer.

A barrier layer is formed on a refractory lining, such as a skull, by providing a refractory-lined vessel containing a combination of aluminum oxide and calcium oxide that can form a precipitate when exposed to chlorine. The combined aluminum oxide and calcium oxide are exposed chlorine, whereby the precipitate is formed and deposited on the refractory lining, thereby forming the barrier layer on the refractory lining.

This invention provides several advantages. For example, one advantage is that the chlorine can react with the vitreous layer to form a composition that deposits on the refractory lining that can provide an added layer of protection to the refractory lining. This is particularly important at the refractory lining and vitreous layer interface. This barrier layer can help increase the wear resistance of the refractory while in the presence of chlorine, particularly for the area around a tuyere for injecting a waste composition. The barrier layer can be in the form of a skull, which is an accretion formed over the refractory lining that provides for added protection to the refractory. The composition can also be deposited on the surface of a refractory-covered lance or baffle.

Brief Description of the Drawing

The Figure is a schematic representation of a system suitable for employing the method of the invention for forming a barrier layer on a refractory lining in the presence of chlorine.

Detailed Description of the Invention

The features and other details of the method and apparatus of the invention will now be more particularly described with reference to the accompanying drawing and pointed out in the claims. It will be understood that the particular embodiments of the invention are shown by way of illustration and not as limitations of the invention. The principal features of this invention can be employed in various embodiments without departing from the scope of the invention. All parts and percentages are by weight unless otherwise specified. The present invention relates generally to a method for forming a barrier layer on a refractory lining, which can be used in a vessel having a molten bath for treating a chlorine-containing material, particularly, a waste. A process and apparatus for dissociating waste in molten metal baths are disclosed in U.S. Patents 4,574,714 and 4,602,574, issued to Bach et al . The method and apparatus can destroy polychlorinated biphenyls and other organic wastes, optionally together with inorganic wastes. The teachings of U.S. Patents 4,574,714 and 4,602,574 are hereby incorporated by reference. Another apparatus and method for dissociating waste in a molten metal bath and for forming gaseous, vitreous and molten metal product streams from the waste are disclosed in U.S.

Patent 5,301,620, issued to Nagel et al . The teachings of which are hereby incorporated by reference.

An example of a suitable system for carrying out the method of the invention is shown in the Figure. Therein, system 10 includes reactor 12. Examples of suitable reactors include appropriately modified steelmaking vessels known in the art as K-BOP, Q-BOP, argon-oxygen decarbonization furnaces (AOD) , BOF, etc. Reactor 12 includes upper portion 14 and lower portion 16. Off-gas outlet 18 extends from upper portion 14 and is suitable for conducting an off-gas composition out of reactor 12. Reactor 12 has a refractory lining, which is, preferably, aluminum oxide. The refractory lining can also include magnesium oxide (MgO) , calcium oxide (CaO) , silicon dioxide (Si0₂) or other material that is known in the art.

Chlorine-containing material inlet tube 20 includes chlorine-containing material inlet 22 and extends from lower portion 16 of reactor 12. Line 24 extends between chlorine-containing material source 26 and chlorine-containing material inlet tube 20. Pump 28 is disposed in line 24 for directing waste material from chlorine-containing material source 26 through chlorine-containing material inlet tube 20 and into the molten bath contained in reactor 12. Tuyere 30 is disposed at lower portion 16 of reactor 12. Tuyere 30 includes oxidizing agent tube 32 for injection of a separate oxidizing agent at oxidizing agent inlet 34. Line 36 extends between oxidizing agent tube 32 and oxidizing agent source 38. Outer tube 40 of tuyere 30 is disposed concentrically about oxidizing agent tube 32 at oxidizing agent inlet 34. Line 42 extends between outer tube 40 and shroud gas source 44 for conducting a suitable shroud gas from shroud gas source 44 through the concentric opening between outer tube 40 and oxidizing agent tube 32 to oxidizing agent inlet 34.

It is to be understood, however, that more than one chlorine-containing material tube or more than one oxidizing agent tube, or combinations thereof, can be disposed at the lower portion of reactor 12 for introduction of chlorine-containing material and an oxidizing agent into reactor 12. Suitable chlorine- containing material can also, optionally, be introduced into reactor 12 through port 46 and/or conducted from chlorine-containing material source 26 through line 47 to reactor 12. Other means, such as an injection lance (not shown) can also be employed to introduce chlorine- containing material into the molten bath in reactor 12. Bottom tapping spout 48 extends from lower portion 16 of reactor 12 and is suitable for removal of molten bath from reactor 12. Induction coil 50 is disposed at lower portion 16 for heating molten bath 56 in reactor 12. It is to be understood that, alternatively, reactor 12 can be heated by other suitable means, such as by oxyfuel burners, electric arcs, etc. Trunions 52 are disposed at reactor 12 for manipulation of reactor 12. Seal 54 is disposed between off-gas outlet 18 and port 46 and is suitable for allowing partial rotation of reactor 12 about trunions 52 without breaking seal 54. Molten bath 56 is formed by at least partially filling reactor 12 with a suitable metal. Molten bath 56 can include metals or salts or combinations thereof. In one embodiment, the molten bath can be formed substantially of elemental metal. Examples of suitable metals include iron, copper, nickel, zinc, etc. Also, molten bath 56 can comprise a metal having a free energy of oxidation, at operating conditions of system 10, which is greater than the free energy for conversion of atomic carbon to carbon monoxide. Examples of suitable metals include iron, chromium and manganese. Molten bath 56 can also include more than one metal. For example, molten bath 56 can include a solution of miscible metals, such as iron and nickel. Alternatively, molten bath 56 can be formed substantially of metal salts. Examples of suitable salts include sodium chloride, potassium chloride, etc. Molten bath 56 is then heated to a suitable temperature by activation of means for heating.

In many cases for a molten metal phase, it is also preferred to have the viscosity of molten bath 56 in reactor 12 less than about ten centipoise at the operating conditions of reactor 12.

The metal is then heated to a suitable temperature by activation of induction coil 52 or by other suitable means, not shown. Suitable operating conditions of system 10 include a temperature such that it is sufficient to maintain a molten bath and have a catalytic nature that can provide activation for converting at least partially the chlorinated material by dissociation to elemental chlorine and other elemental constituents. Generally, a temperature in the range of between about 1,300 and 1,700°C is suitable.

Molten bath 56 has vitreous layer 62, which can also be called a ceramic layer or slag layer. Vitreous layer 62, which is disposed on molten bath 56, is substantially immiscible with molten bath 56. Vitreous layer 62 can have a lower thermal conductivity than that of molten bath 56. Radiant heat loss from molten bath 56 can thereby be reduced to significantly below the radiant heat loss from molten bath where no vitreous layer is present.

The vitreous layer can include a combination of aluminum oxide (Al₂0₃) and calcium oxide (CaO) that can form a precipitate and deposit to form a barrier layer on a refractory lining during exposure to chlorine. The molten bath can cause the chlorine, which can be dissociated from a chlorine-containing compound, to interact with the combined aluminum oxide and calcium oxide to form a precipitate from the molten bath. If silicon dioxide is present, the molar ratio of aluminum oxide to silicon dioxide should be greater than about one in order to form the precipitate in the presence of chlorine. The precipitate deposits on the refractory to form a barrier layer. The barrier layer can act as an added protective layer on the refractory lining to enhance the wear characteristics of the lining during submerged injection.

In another embodiment, the refractory lining can be formed of a combination of aluminum oxide and calcium oxide that interact with chlorine in the molten bath to form a precipitate, which forms a barrier layer on the exposed lining. The refractory lining is often porous, thereby causing the molten bath, and consequently the chlorine, to partially infiltrate into the refractory lining and interact with the combined aluminum oxide and calcium oxide therein at the operating conditions of the molten bath to form the barrier layer.

In still another embodiment, the refractory lining can be formed of a combination of aluminum oxide and calcium oxide along with a sufficient amount of a chlorine-containing compound, such as calcium chloride, to cause the chlorine contained in the chlorine- containing compound to interact with the aluminum oxide and calcium oxide. When exposed to chlorine at the operating conditions of the molten bath, it is believed that the combination the aluminum oxide and calcium oxide form an aluminum-calcium composition which acts as a barrier layer in the refractory lining. In another embodiment, a skull is formed on a refractory surface by injecting chlorine or a chlorine- containing compound at a point beneath a surface of a molten bath in a refractory-lined vessel. The vessel contains a combination of aluminum oxide and calcium oxide that can form a precipitate when exposed to chlorine, whereby the precipitate accumulates on a surface proximate to the point of injection, thereby forming the skull .

A wide variety of chlorine-containing materials, including a waste material, is suitable for causing the precipitate to form. An example of a suitable waste material is a chlorinated hydrogen-containing carbonaceous material, such as oil, which includes organic waste compounds containing chlorine. For example, the chlorinated waste includes a chlorinated alkane or a chlorinated aromatic, such as a polychlorinated biphenyl or a dioxin. It is to be understood that the chlorine-containing material can include chlorinated inorganic compounds. These chlorinated inorganic compounds can include volatile heavy metal chlorides, such as those of lead, mercury and zinc. Also, the chlorinated inorganic compounds can include transition metal chlorides, such as those of nickel, iron and manganese. In a preferred embodiment, the metal chloride is either ferrous chloride (FeCl₂) or ferric chloride (FeCl₃) . Also, chlorine gas is suitable for causing the precipitate to form.

Chlorine-containing material is directed from chlorine-containing material source 26 through line 24 by pump 28 and is injected into molten bath 56 through waste material tube 20. In one embodiment, the chlorine-containing material is a fluid which can include chlorine-containing material components dissolved or suspended within a liquid. In another, solid particles of chlorine-containing material components are suspended in an inert gas, such as argon.

Chlorine-containing material directed into molten bath 56 is converted to chlorine, carbon, hydrogen and its other atomic constituents. A suitable oxidizing agent is directed from oxidizing agent source 38 through line 36 and is injected through oxidizing agent tube 32 into molten bath 56. In one embodiment, the oxidizing agent is directed into molten bath 56 when the carbon, which is dissolved in the molten metal, approaches saturation in the molten metal . Examples of suitable oxidizing agents include oxygen, air, iron oxide, etc., with the preferred oxidizing agent being oxygen gas.

Molten bath 56 has conditions sufficient to cause the chlorine-containing material injected into molten bath 56 to be converted to chlorine, carbon, hydrogen and other atomic constituents and to cause chlorine in molten bath 56 to form a chlorinated gas, such hydrogen chloride. Oxidizing agent, which oxidizes carbon contained in the molten metal, is directed into molten bath separately or concurrently to form a carbon oxide gas.

An example of a vitreous composition is one that includes calcium oxide and aluminum oxide that can cause a portion of the vitreous composition to form a precipitate when exposed to chlorine. In one embodiment, a concentration of calcium oxide is in the range of between about 20 and 65 percent, by weight, and a concentration of aluminum oxide is in the range of between about 25 and 70 percent. The vitreous composition can also include silicon dioxide. In a preferred embodiment, the silicon dioxide is up to about 35 percent. In a particularly preferred embodiment, the molar ratio of aluminum oxide to silicon dioxide is greater than about one. It is believed that the dissociated chlorine interacts with the vitreous composition, including the aluminum oxide and calcium dioxide, to cause an inorganic composition to form. The composition can be a complex that can include one or more solidified compositions that are a calcium-aluminate, calcium-aluminosilicate or aluminosilicate. In one embodiment, the calcium- aluminate composition includes a crystalline Ca₁₂Al₁₄0₃₃ phase. Also, the composition can be a chloride and oxide complex of aluminum and calcium. In one embodiment, a solidified portion of the composition can precipitate from the molten bath and deposit on the refractory lining. The precipitate can be directed towards the refractory lining by the circulation formed in the molten bath by the injection of the chlorine- containing material from the bottom of the molten bath toward the top of the reactor.

In another embodiment, the refractory lining having sufficient aluminum oxide present can react with the calcium oxide in the vitreous layer and the dissociated chlorine to form a deposit on the refractory lining. The invention will now be further explained by the following example of various applications of the method of the invention for forming a barrier layer on a refractory lining.

Example

Chloride additions, in the form of calcium chloride were investigated for the melt behavior and properties of several glass compositions in a CaO- Al₂0₃-Si0₂ system with an iron melt in a reactor lined with ninety-seven percent alumina (Al₂0₃) refractory material. In general, chloride additions to the low alumina compositions (Al₂0₃/Si0₂ molar ratio less than 1.0) produced a fluid melt which showed glass stability, forming clear, pale yellow glasses upon cooling. Chloride additions to high alumina compositions (Al₂0₃/Si0₂ molar ratio greater than 1.0) , however, resulted in the formation of a viscous, sintered mass, which partially crystallized upon cooling. X-ray diffraction analysis of the high alumina compositions disclosed the presence of a Ca₁₂Al₁₄0₃₃ crystalline phase in a residual glassy matrix, while x-ray diffraction analysis of a chlorinated low alumina composition showed no presence of crystallinity. It appeared that chloride additions to high alumina compositions result in precipitation of Ca₁₂Al₁₄0₃₃ in the melt, leaving a substantial portion of the chloride in the higher Si0₂ glassy phase. Precipitation of the crystalline phase in the melt resulted in a substantial increase in the melt viscosity. This change in behavior appeared to happen as the Al₂0₃/Si0₂ molar ratio approaches about one or is greater than one.

The addition of chlorides to high alumina CaO- Al₂0₃-Si0₂ mixtures resulted in the precipitation of a calcium aluminate crystalline phase, producing a mixture that remained solid at high temperatures (up to about 1,650°C) . It appeared that this high temperature mixture, or reaction layer, can be utilized as a protective layer on the refractory bricks. The experiments with high chloride concentrations resulted in the following observations : minimal ceramic penetration into a 97% alumina crucible with the reaction layer, a visual appearance of a reaction layer between the crucible and the slag, i.e. a crystallized layer between the crucible and the glass, and a ceramic phase that remained fluid throughout the run, and cooled to a clear glassy sample.

Microanalysis of the reaction layer indicated that there was a transition in the composition as the electron probe was stepped from the crucible across the barrier layer and into the glass. Microanalysis indicated a transition from the aluminum oxide crucible to a CaO-Al₂0₃ barrier layer to a chlorinated CaO-Al₂0₃- Si0₂ glass. A local high alumina concentration in the chlorinated ceramic at the ceramic/refractory interface appeared to lead to the formation of a reaction layer. This reaction layer appeared to prevent further penetration of the vitreous layer into the crucible, which enhanced the performance of the crucible. E uivalents

Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to specific embodiments of the invention described specifically herein. Such equivalents are intended to be encompassed in the scope of the following claims.

Claims

A method for forming a barrier layer on a refractory lining, comprising the steps of: a) providing a refractory-lined vessel containing a combination of aluminum oxide and calcium oxide that can form a precipitate when exposed to chlorine; and b) exposing the combined aluminum oxide and calcium oxide to chlorine, whereby the precipitate is formed and deposited on the refractory lining, thereby forming the barrier layer on the refractory lining.

The method of Claim 1 wherein the combined aluminum oxide and calcium oxide is exposed to chlorine by injecting chlorine or a chlorine- containing compound beneath a surface of a molten bath in said vessel, whereby a precipitate accumulates on a surface of the lining, thereby forming the barrier layer.

The method of Claim 2 wherein the refractory lining of the vessel provided further includes calcium oxide.

The method of Claim 3 wherein the concentration of calcium oxide in the refractory lining provided is in a range of between about 20 and 65 percent, by weight .

5. The method of Claim 4 wherein the refractory lining of the vessel provided further includes aluminum oxide.

6. The method of Claim 5 wherein the concentration of aluminum oxide in the refractory lining provided is in a range of between about 25 and 70 percent, by weight .

7. The method of Claim 6 wherein the refractory lining of the vessel provided further includes silicon dioxide.

8. The method of Claim 7 wherein the silicon dioxide in the refractory lining provided has a concentration up to about 35 percent, by weight.

9. The method of Claim 8 wherein the molar ratio of aluminum oxide to silicon dioxide is greater than about one .

10. The method of Claim 2 wherein the molten bath provided includes a molten metal phase which includes iron.

11. The method of Claim 2 wherein the molten bath provided includes nickel .

12. The method of Claim 10 wherein the molten bath provided has a temperature in a range of between about 1,400 and 1,700°C.

13. The method of Claim 12 wherein the chlorine is included in a chlorine-containing compound.

14. The method of Claim 13 wherein the chlorine- containing compound includes an organic chlorinated compound.

15. The method of Claim 14 wherein the organic chlorinated compound includes a chlorinated aromatic .

16. The method of Claim 15 wherein the chlorinated aromatic includes a polychlorinated biphenyl .

17. The method of Claim 15 wherein the chlorinated aromatic includes a dioxin.

18. The method of Claim 14 wherein the organic chlorinated compound includes a chlorinated alkane.

19. The method of Claim 13 wherein the chlorine- containing compound includes an inorganic chlorinated compound.

20. The method of Claim 19 wherein the inorganic chlorinated compound is a heavy metal chloride.

21. The method of Claim 20 wherein the heavy metal chloride is a lead chloride.

22. The method of Claim 20 wherein the heavy metal chloride is a mercury chloride.

23. The method of Claim 20 wherein the heavy metal chloride is a zinc chloride.

24. The method of Claim 19 wherein the inorganic chlorinated compound is a transition metal chloride.

25. The method of Claim 24 wherein the transition metal chloride is a nickel chloride.

26. the method of Claim 24 wherein the transition metal chloride is a manganese chloride.

27. The method of Claim 24 wherein the transition metal chloride is an iron chloride.

28. The method of Claim 27 wherein the iron chloride is ferrous chloride.

29. The method of Claim 27 wherein the iron chloride is ferric chloride.

30. The method of Claim 1 wherein the precipitate formed is a calcium-aluminate.

31. The method of Claim 30 wherein the calcium- aluminate precipitate includes Ca₁₂Al₁₄0₃₃.

32. The method of Claim 30 wherein the precipitate further includes a calcium-aluminosilicate.

33. The method of Claim 30 wherein the precipitate includes a aluminosilicate.

34. The method of Claim 1 wherein the combination of aluminum oxide and calcium oxide further includes silicon dioxide.

35. The method of Claim 1 wherein the molar ratio of aluminum oxide to silicon dioxide is greater than about one .

36. The method of Claim 1 wherein the chlorine is injected at a point beneath a surface of a molten bath in said vessel, whereby a precipitate accumulates on a surface proximate to the point of injection, thereby forming a skull.

37. The method of Claim 36 wherein the point of injection is at a vitreous layer.

38. A barrier layer formed by the method of Claim 1.

39. A method for forming a barrier layer on a refractory lining, comprising the steps of: a) providing a refractory-lined vessel containing a vitreous phase having a combination of aluminum oxide and calcium oxide that can form a precipitate when exposed to chlorine; and b) exposing the vitreous layer to chlorine, whereby the precipitate is formed and deposited on the refractory, thereby forming the barrier layer on the refractory.

40. The method of Claim 39 wherein the vitreous phase provided further includes silicon dioxide.

41. The method of Claim 40 wherein the molar ratio of aluminum oxide to silicon dioxide is greater than about one .

42. The method of Claim 41 wherein the precipitate formed includes a calcium aluminate.

43. The method of Claim 42 wherein the calcium aluminate precipitate includes Ca₁₂Al₁₄0₃.

44. A method for forming a barrier layer on a refractory lining, comprising the steps of: a) providing a refractory-lined vessel, wherein the refractory lining has a combination of aluminum oxide and calcium oxide that can form a precipitate when exposed to chlorine; and b) exposing the refractory lining to chlorine, whereby the precipitate is formed on the refractory lining, thereby forming the barrier layer on the refractory lining.

45. The method of Claim 44 wherein the refractory lining provided further includes silicon dioxide.

46. The method of Claim 45 wherein the molar ratio of aluminum oxide to silicon dioxide is greater than about one .

47. The method of Claim 46 wherein the precipitate formed includes a calcium aluminate.

48. The method of Claim 47 wherein the calcium aluminate precipitate includes Ca₁₂Al₁₄0₃₃.

49. A skull on a refractory lining, formed by a method comprising injecting chlorine or a chlorine- containing compound into a molten bath having a vitreous phase in a refractory-lined vessel containing a combination of aluminum oxide and calcium oxide that can form a precipitate when exposed to chlorine, whereby the precipitate accumulates on said lining proximate to the point of injection, thereby forming the skull.