AU696437B2

AU696437B2 - Process and apparatus for destroying organic and carbonaceous waste

Info

Publication number: AU696437B2
Application number: AU65572/94A
Authority: AU
Inventors: S. Garry Howell; Martin Krynen; Richard H Scott; Lloyd M Watson
Original assignee: Wabash Inc
Current assignee: Wabash Inc
Priority date: 1993-04-08
Filing date: 1994-04-08
Publication date: 1998-09-10
Anticipated expiration: 2014-04-08
Also published as: AU6557294A; WO1994023802A1; NZ265199A

Description

WO 94/23802 PCT/US94/03912 PROCESS AND APPARATUS FOR DESTROYING ORGANIC AND CARBONACEOUS WASTE I. BACKGROUND OF THE INVENTION: A. Field of the Invention This invention relates to a process and apparatus for destroying the organic or carbonaceous portion of various wastes, including polyhalogenated polyphenyls, paint sludge, chrometannery waste, aluminum pot liners, contaminated soil, hospital waste, hydrocarbon-containing sludges, and mixtures thereof.

B. Description of Related Art The problem of the treatment and disposal of hazardous waste materials continues to plague all sectors of society. Most governments are no longer willing to accept the wholesale release of toxic materials into the environment, and have imposed strict treatment and disposal regulations on nearly every industry. Most of the known solutions to the hazardous waste problem, however, are expensive, dangerous, or have environmental problems of their own. One such method which has become popular in recent years is incineration. Incineration, however, suffers from many drawbacks, especially cost. Incineration units are also often objected to because of the potential for releases of hazardous substances into the environment.

One alternative method for destroying organic waste is shown by U.S.

Patent No. 4,497,782, of which one of the present inventors was a co-inventor. This reference discloses a method of destroying toxic organic chemical products by contacting them with a molten mixture of an alkali -6o,- I, WO 94/23802 PCT/US94/03912 metal hydroxide and an alkali metal nitrate. Apparatus for performing this method is also disclosed in the '782 patent.

Several shortcomings in the process and apparatus of the '782 patent have come to light, however. Since it is well known that sodium hydroxide is hygroscopic, it tends to absorb moisture from the air, flakes or pellets of sodium hydroxide tend to form a solid mass when attempts are made to mechanically feed the material into a molten salt bath. Manual feeding is impractical not only because of danger to the operator, but also due to the fact that the hydroxide absorbs even more moisture from the air, thereby producing large amounts of foam as the water boils off in the molten salt bath. Excessive foaming even occurs when a 50% solution of sodium hydroxide is pumped into the molten salt bath. Additionally, the excess water vapor interferes with contact between the molten salt and the organic material being destroyed, resulting in a significant reduction in the percentage of waste material destroyed.

The apparatus described in Figure 2 of the '782 patent is also not able to operate at sufficiently high flow rates because the nitrogen content of the air which has to be introduced into the column in order to regenerate nitrate dilutes the vaporized waste material. This dilution inhibits mass transfer between the vaporized waste material and the molten salt, thereby limiting the rate of destruction of the waste material. Thus, an extremely large diameter tower would be required to achieve satisfactory destruction of the organic waste material.

Consequently, heretofore there has not been an available process and apparatus for economically destroying organic and carbonaceous wastes to produce materials which are relatively harmless and/or readily disposed of.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a process and apparatus for destroying the organic portion of a waste, which overcome, or at least alleviate, one or more disadvantages of the prior art.

According to the present invention, there is provided a first process for destroying the organic portion of a waste including: maintaining a molten salt solution including an alkali metal nitrate and an alkali metal carbonate; reacting said organic portion of said waste with said molten salt solution in order to form gaseous carbon dioxide, water vapor and gaseous and non-gaseous reaction by-products, and to reduce at least a portion of said nitrate into the corresponding nitrite, thereby destroying said waste; and venting said gaseous carbon dioxide, said water vapor and said gaseous by..products.

The present invention also provides an apparatus when used to carry out the first process, including: a reservoir for maintaining a molten salt solution including an alkali metal nitrate and an alkali metal carbonate in a molten state; i a reaction unit for contacting said waste and said molten salt 20 solution in order to react the waste and the molten salt to form gaseous carbon oo •dioxide, water vapor and gaseous and non-gaseous reaction by-products, and to reduce at least a portion of said molten nitrate into the corresponding molten nitrite, said reaction unit in fluid communication with said reservoir; wherein said reaction unit includes an angled reaction pipe, a screw rotatably attached to said 25 reaction pipe for moving any solid waste or byproducts present along the length of said reaction pipe, and further including: means for feeding said molten salt into said reaction unit; a molten salt outlet in fluid communication with said reservoir, said salt outlet positined on said reaction pipe so as to ensure that a vapor space will be present when said apparatus is operated; and a solids outlet positioned at a higher elevation than said salt outlet such that said solid waste byproducts will be moved by said screw to said solids outlet for removal therethrough, without a significant loss of molten salt through said solids outlet; means for feeding said waste into said reaction unit; and means for venting said carbon dioxide, water vapor and gaseous reaction by-products from said reaction unit.

According to the present invention, there is also provided an apparatus when used to carry out the first process including: a reservoir for maintaining a molten salt solution including an alkali metal nitrate and an alkali metal carbonate in a molten state; a reaction unit for contacting said waste and said molten salt solution in order to react the waste and the molten salt to form gaseous carbon dioxide, water vapor and gaseous and non-gaseous reaction by-products, and to reduce at least a portion of said molten nitrate into the corresponding molten nitrite, said reaction unit in fluid communication with said reservoir; wherein said reaction unit includes a perforated drum rotatably secured within said reservoir such that at least a portion of said drum is submerged beneath said molten salt; means for feeding said waste into said reaction unit; and means for venting said carbon dioxide, water vapor and gaseous reaction by-products from said reaction unit.

20 The present invention further provides an apparatus when used to carry out the first process, including: a reservoir for maintaining a molten salt solution including an alkali metal nitrate and an alkali metal carbonate in a molten state; means for feeding said waste into said reservoir thereby contacting 25 said waste and said molten salt solution in order to react the waste and the molten salt to form gaseous carbon dioxide, water vapor and gaseous and nongaseous reaction by-products, and to reduce at least a portion of said molten nitrate into the corresponding molten nitrite; means for venting said carbon dioxide, water vapor and gaseous reaction by-products from said reservoir; a reaction unit, in fluid communication with said reservoir so that AL2-\ said vented gaseous reaction by-products will enter said reaction unit; and 3b means for feeding a portion of said molten salt to said reaction unit, so that said salt can contact said gaseous reaction by-products thereby further reacting the organic portion of said reaction by-products.

The present invention further provides an apparatus when used to carry out the process of the invention, including: a porous, continuous conveyor belt having an upper flight, a lower flight, and a plurality of compartments: first and second rotatable sprocket wheels about which said conveyor belt passes, such that rotation of said sprocket wheels causes said conveyor belt to move from said first wheel towards said second wheel; a heated upper planar surface upon which said upper flight rides; a lower planar surface upon which said lower flight rides; an inlet for feeding a mixture including said waste material, an alkaline material and an alkali metal nitrate into said compartments of said conveyor belt; and a means for heating said mixture; wherein said upper planar surface will retain said mixture in said compartments "as said upper flight moves across said upper planar surface, and wherein said lower planar surface will retain said mixture in said compartments as said lower flight moves across said lower planar surface.

Also disclosed herein is a second method for destroying the organic portion of a solid waste material having both organic and inorganic portions, including: 25 mixing said waste material with an alkaline material and an alkali metal nitrate to form a reaction mixture; heating said mixture in a reaction unit in order to initiate a reaction between said organic portion, said nitrate and said alkaline material, said reaction causing said organic portion to be destroyed; permitting said reaction to continue until substantially all of said organic portion is converted into gaseous carbon dioxide, water vapor, and gaseous and non-gaseous by-products; IC C:\WINWORD\ILONAWMH\M HSPECI\85572SP.DO I 1 Iventing said carbon dioxide, said water vapor and said gaseous byproducts from said reaction unit; and removing said non-gaseous by-products and said inorganic portion of said waste material from said reaction unit.

Moreover, there is also disclosed an apparatus for carrying out the second method as described in the previous paragraph, including: a reaction unit including a reaction trough having a longitudinal length; means for feeding a mixture including said waste material, an alkaline material and an alkali metal nitrate to said reaction unit; means for moving said mixture along said longitudinal length of said trough; a heater for heating said reaction trough along at least a portion of its longitudinal length in order to initiate a reaction between said waste material, said alkaline material and said alkali metal nitrate, said reaction resulting in the destruction of a portion of said waste, thereby forming gaseous and non-gaseous reaction by-products; means for venting said gaseous by-products from said reaction unit;

C

IC C:\WINWORDULONAWiMH1MHSPECMS5572SP.DOC 1~1 and a solids outlet in fluid communication with said reaction trough for removing unreacted waste material and non-gaseous by-products Still further, there is disclosed an apparatus for carrying out the second method, including: an enclosed reaction unit including a reaction trough having a longitudinal length and a vapor space positioned above said trough; means for feeding a mixture including said waste material, an alkaline material and an alkali metal nitrate to said reaction unit; a screw for moving said mixture along said longitudinal length of said trough, said screw rotatably secured within said trough such that rotation of said screw will move said mixture along said longitudinal length; a fluid jacket disposed about at least a portion of said trough and extending along at least a portion of said longitudinal length, wherein a heated fluid may be circulated through said jacket in order to heat said reaction trough in order to initiate a reaction between said waste material, said alkaline material and said alkali metal nitrate, said reaction resulting in the destruction of a portion of said waste, thereby forming gaseous and non-gaseous reaction by-products; a molten salt bath in fluid communication with said fluid jacket; means for pumping molten salt from said bath into said fluid jacket; S(g) means for venting said gaseous by-products from said reaction unit; and a solids outlet in fluid communication with said reaction trough for removing unreacted waste material and non-gaseous by-products.

on 25 Furthermore, there is disclosed an apparatus for carrying out the second process, including: a porous, continuous conveyor belt having an upper flight, a lower flight, and a plurality of compartments; first and second rotatable sprocket wheels about which said conveyor belt passes, such that rotation of said sprociet wheels causes said conveyor belt to move from said first wheel towards said second wheel; a heated upper planar surface upon which said upper flight rides; -rr a lower planar surface upon which said lower flight rides; an inlet for feeding a mixture including said waste material, an alkaline material and an alkali metal nitrate into said compartments of said conveyor belt; and a means for heating said mixture; wherein said upper planar surface will retain said mixture in said compartments as said upper flight moves across said upper planar surface, and wherein said lower planar surface will retain said mixture in said compartments as said lower flight moves across said lower planar surface.

One advantage of the present invention is the provision of a process which can completely and efficiently destroy the organic or carbonaceous portion of a waste material utilizing a molten salt solution.

Another advantage of the present invention is the provision of an apparatus which can easily and efficiently destroy the organic portion of a waste material by contacting said waste with a molten salt solution.

A further advantage of the present invention is the provision of a method and apparatus which can destroy the organic portion of a solid waste by mixing said waste with a salt blend, and heating said mixture to achieve the desired destruction.

The foregoing advantages can be achieved in accordance with one aspect of the invention by maintaining a molten salt solution comprising an alkali metal nitrate and an alkali metal carbonate, reacting the organic portion of the waste material with said molten salt solution in order to form gaseous carbon dioxide, .water vapor and gaseous and non-gaseous reaction by-products, and to reduce S 25 at least a portion of said nitrate into the corresponding nitrite, thereby destroying said waste; and venting said gaseous carbon dioxide, said water vapor and said gaseous by-products. It is preferred that the nitrate be sodium nitrate and the carbonate be sodium carbonate. It is also preferred that an additional step of regenerating said alkali metal nitrate by converting said alkali metal nitrite into said nitrate be employed, wherein said regeneration is performed by contacting at least a portion of said molten solution containing said nitrite with a gaseous stream containing oxygen. The reaction of the waste and the molten salt may c N,

C)

WO 94/23802 PCT/US94/03912 occur directly in the reservoir itself, or in a reaction unit. The reaction unit can be a packed column, a spray scrubber, a venturi scrubber, or similar gas-liquid contacting device. If the reaction takes place in the reservoir, a packed column is placed in fluid communication with the reservoir, and gaseous reaction by-products will enter the column. Molten salt is then contacted with these by-products within this column to further destroy any organic materials remaining. The waste materials which can be destroyed by this process include paint sludge, chrome tannery waste, contaminated soil, hospital waste, polyhalogenated polyphenyl-containing waste, hydrocarbon-containing sludge, and mixtures thereof.

An alternative embodiment utilizes an angled reaction pipe, having a screw rotatably attached to said reaction pipe for moving any solid waste or by-products present along the length of said reaction pipe, and further comprising a means for feeding said molten salt into said reaction pipe. A perforated drum may also be employed as a reaction unit fo, destroying the organic portion of a waste.

In yet another embodiment, the waste material to be destroyed is mixed with an alkali material and an alkali metal nitrate to form a reaction mixture; this mixture is then heated in a reaction unit in order to initiate a reaction between said organic portion, said nitrate and said alkali material, said reaction causing said organic portion to be destroyed. This reaction is permitted to continue until substantially all of said organic portion is converted into gaseous carbon dioxide, water vapor, and gaseous and nongaseous by-products; said carbon dioxide, said water vapor and said gaseous by-products are then vented from said reaction unit, and said nongaseous by-products and said inorganic portion of said waste material are removed from said reaction unit. The reaction unit for this latter embodiment may be a heated reaction trough having a rotating screw therein, said trough being heated by molten salt flowing through a salt jacket.

-4- WO 94/23802 PCT/US94/0391.2 Ill. BRIEF DESCRIPTION OF THE DRAWINGS: While the specification concludes with claims particularly pointing out and distinctly claiming the present invention, it is believed the same will be better understood from the following description taken in conjunction with the acco:npanying drawings in which: Figure 1 is a schematic of one embodiment of an apparatus for practicing the process of the present invention, wherein the molten salt bath i's shown by cross-sectional view; Figure 2 is a rear view of the embodiment of Fig. 1; Figure 3 is a side-view of the apparatus of Fig's 1 and 2, taken along the line 3-3 of Fig. 2; Figure 4 is a cross-sectional view of the molten salt bath of Fig's 1-3, taken along the 4-4 of Fig. 1, wherein only the drag chain is principally shown and other components have been omitted; Figure 5 is an alternative embodiment for removal of insoluble inorganics from the molten salt bath, and depicts the screw con-eyor arrangement; Figure 6 is a portion of an alternative embodimont of the apparatus shown by Fig. 1; Figure 7 is a schematic of a venturi scrubber which may be employed in practicing the process of the present invention; Figure 8 is a cross-sectional view of yet another apparatus for practicing the process of the present invention; WO 94123802 PCT/US94/03912 Figure 9 is an illustration of another alternative embodiment of an apparatus for practicing the process of the present invention, and is particularly suited for soil; Figure 10 is a cross-sectional view of the embodiment shown in Fig.

9, taken along line 10-10 of Fig. 9; and Figure 11 is an illustration of yet another embodiment of an apparatus for practicing the process of the present invention, and is particularly suited for hospital waste.

Figure 12 is a schematic of another embodiment of the present invention, and is an apparatus suitable for treating solid wastes such as soil.

Figure 13 is a perspective view of a portion of a porous conveyor belt utilized in the apparatus of Figure 12.

Figure 14 is an alternative design for the apparatus of Fig. 12.

IV. DETAILED DESCRIPTION OF THE INVENTION: In contrast to the process disclosed in the previously mentioned U.S.

Patent No. 4,497,782, it has unexpectedly been found that a process using an alkali metul carbonate, instead of hydroxide, is also capable of destroying organic waste and actually provides a more efficient destruction of the organic waste. These carbonates include potassium and sodium carbonate or sesquicarbonate, although sodium carbonate is preferred because of its cost. Carbonates, and in particular sodium carbonate, are considerably less expensive than hydroxides, and, mor. importantly, are significantly less hygroscopic than hydroxides. Sodium carbonate, for example, is available in free flowing granular or powder forms, and since it does not tend to absorb any significant amount of moisture from the air, it can be easily -6- I~'L PP WO 94/23802 PCT/US94/03912 added to a molten salt bath using conventic dry material feeders, such as screw or belt types. This can be significant, since alkali metal carbonate must be continuously fed to the molten salt bath if the waste being destroyed contains sulfates, halogens, phosphates, or similar moieties.

Extensive testing, a portion of which is outlined below, has led to the surprising discovery that the use of alkali metal carbonate in the molten salt solution is actually superior to that which has previously been employed.

EXAMPLE 1 NaNO 3 melts at approximately 308 OC, while the melting point of Na 2

CO

3 is approximately 850 OC. Thus, in order for the process of the present invention to be successful, Na 2

CO

3 must have some appreciable degree of solubility in molten NaNO 3 at the temperatures employed for the process. In order to determine the solubility of Na 2

CO

3 in molten NaNO 3 Na 2

CO

3 was gradually added in one gram increments to 100g of NaNO 3 which had been heated to 500 OC in a steel crucible. Using this procedure it was determined that the solubility of Na 2

CO

3 in NaNO 3 was approximately 12% (on a weight basis).

Likewise, the solubility of salts such as NaCI in the molten mixture is also critical, since it is desired to precipitate out inorganic salts such as NaCI (or s:-lphates, phosphates, etc.) which form during the process. NaCI is particularly significant, since polychlorinated biphenyls (PCB's) will be converted to, among other things, NaCI in the process of the present invention. The solubility of NaCI in a molten solution comprising NaNO 3 and 10% Na 2

CO

3 at 500 OC was determined to be between approximately 10% and 11% by weight, which is advantageous for precipitating NaCI when the present invention is employed to destroy PCB's and similar compounds which form inorganic salts upon destruction.

II

WO 94/23802 PCTfUS94/03912 EXAMPLE 2 A stirred closed laboratory reactor was charged with approximately 900 g of a salt mixture containing about 90% NaNO 3 and 10% Na 2

CO

3 (by weight), placed in a crucible furnace, and heated to 500 The reactor had been fitted with a reflux condenser to condense and recycle unreacted organic starting material, and a stream of air was introduced below the surface of the molten solution. One ml (1.45g) of trichlorobenzene was charged to the reactor by injecting it into the stream of air, and an immediate rise in temperature of 10 OC was observed. Such a temperature increase was surprising, especially considering the amount of molten salt present in the reactor, and clearly indicates that the reaction which occurs is immediate and extremely exothermic.

The gases evolved in this reaction were measured and analyzed by gas chromatography after being passed through a hexane absorber or impinger, and the data thus obtained indicated a destruction efficiency for organic compounds of approximately 85%. While the results indicated that much more than 85% of the trichlorobenzene originally charged to the reactor had been destroyed, other organic by-products from the destruction of the trichlorobenzene remained in the oif gases. The rapidity of the reaction coupled with the reactor configuration resulted in undestructed (and undesirable) gaseous organic compounds being released. Thus, it was evident that more efficient mass transfer was needed in order to ensure the complete destruction of all organic starting material and organic by-products, and thus ensuring the practicability of the process.

EXAMPLE 3 The reactor of Example 2 was modified so that the reactor temperature could be controlled. Ten ml of trichlorobenzene was slowly added (in a stream of air) to a molten solution having the same composition -8-

I

WO 94/23802 PCT/US94/03912 as in Example 2 over a period of 2.9 hours. The reactor temperature was held at 500 ±2 0C over this period. Analysis of the gases released during the reaction period indicated an organic destruction efficiency of greater than 98%Y, which confirms the fact that the reaction efficiency is greatly improved by improving the manner in which the organic waste material and the molten salt solution are contacted. While most of the trichlorobenzene is immediately destroyed, it is also necessary that the organic by-products from this initial destruction be converted into non-hazardous compounds such as CO2 and water vapor. Thus, these organic by-products must also be contacted with the molten salt solution to ensure an efficient destruction of all organics.

The molten solution remaining in the reactor was also analyzed using a pH meter having a specific ion electrode, and it was found that the chloride content was approximately 98% of that theoretically present in the trichlorobenzene charged to the reactor. Thus, it is clear that when the process of the present invention is used to destroy organic materials containing halogens and similar compounds, relatively innocuous inorganic salts, such as NaCI, are produced.

The reaction described above was then repeated using the same molten salt solution, and nearly identical results were obtained. This demonstrates that the Na 2

CO

3 I aNO 3 melt is able to continually destroy organic material, at least until the carbonate supply has been exhausted (assuming that the nitrate is being regenerated by the introduction of air or pure oxygen).

EXAMPLE 4 In order to examine the effect of omitting the carbonate from the molten solution, the experiment of Example 2 was repeated using molten NaNO 3 alone. A large amount of smoke appeared in the reflux condenser, -9- L- WO 94/23802 PCTIUS94/03912 and liquid, later identified as trichlorobenzene, was observed flowing back into the reactor from the condenser. In addition, only a small increase in temperature (less than 2 was observed, further indicating that very little of the trichlorobenzene was destroyed (oxidized).

A small amount of Na 2

CO

3 was added to the same molten solution employed above, and the concentration of Na 2

CO

3 in the reactor was approximately 2% (by weight). When trichlorobenzene was added in the same manner as in Example 2, an immediate temperature increase of 8 'C was observed, cearly indicating that the trichlorobenzene was being oxidized. This clearly demonstrates the unexpected synergistic effect achieved by using even a small amount of Na 2

CO

3 in combination with NaNO 3 EXAMPLE As demonstrated previously, inorganics such as NaCI are only partially soluble in the molten solution of the present invention, and thus can generally be readily removed from the solution as they are formed. Many organic wastes also contain an inorganic moiety which one desires to recover. Such is often the case with organic wastes obtained from paint manufacturing, for example, where valuable pigments are presen in the "sludge" found on the bottoms of many of the vessels. While these sludges have a significant organic component, heavy metals may also be present, and it is of course imperative that they not enter the environment.

A paint manufacturing sludge consisting of various paint resins (alkyds, urethanes, epoxies, etc.) and inorganic pigments was charged to a reactor containing the molten solution of the present invention. The molten salt (at 500 OC) consisted of approximately 90% NaNO 3 and 10% Na 2

CO

3 by weight. The resins were rapidly oxidized, and a corresponding significant increase in temperature of the molten solution was observed. When the reactor was opened and the molten salt solution poured off, reusable WO 94/23802 PCTJUS94/03912 pigment solids remained.

Based upon the foregoing testing, a preferred method for destroying organic waste comprises intimately contacting the waste material with a molten solution of an alkali metal nitrate and an alkali metal carbonate.

Preferably the nitrate is sodium nitrate, and the carbonate is sodium carbonate. The molten solution s& ,uld be maintained at a temperature of 450 OC or greater, and preferably about 550 IC to ensure that the reaction occurs rapidly while also ensuring that the molten solution will not decompose. The molten salt solution should preferably comprise about 8 to carbonate by weight, however lesser amounts can certainly be employed. The upper preferred limit ensures that the carbonate will remain soluble at the temperatures at which the molten salt is maintained, while the lower preferred limit provides for more efficient destruction.

The organic waste material can be in any form, solid, liquid, or gaseous, and various contacting means may be employed. The organic waste material is rapidly oxidized by the molten salt solution and converted into various reaction by-products. These by-products may include other organics, inorganic salts, C0 2 H20, and N 2 depending upon the organic waste material being destroyed. Organic by-products are further oxidized by the molten salt solution so that eventually the overall process byproducts will primarily include only CO 2

H

2 0, N 2 and inorganics. The composition of the inorganics will vary greatly depending upon the type of waste material being destroyed, and may include inorganic sodium salts such as NaCI. Other possibilities include pigments (when the waste material being destroyed is paint sludge), and material such as heavy metals.

It has also been found that the reaction of the present invention can be employed for the destruction of carbonaceous materials such as aluminum pot liners. While the carbon itself does not create disposal problems, carbonaceous materials often contain other hazardous materials -11 WO 94/23802 PCT/US94/03912 thereby creating a large mass of hazardous waste. For example, aluminum pot liners are predominantly carbon, however trace amounts of NaCN and NaF are also generally present. The process of the present invention will oxidize both the carbon and the NaCN, and the remaining NaF will settle to the bottom of the reactor where it can later be removed. NaCN is oxidized to C0 2 Na 2

CO

3 and N 2 while the carbon is oxidized to CO 2 In this fashion, the mass of the hazardous waste is almost entirely eliminated (other than the NaF). Thus, the process of the present invention can be utilized to treat carbonaceous materials also.

Applicants have also found that certain catalysts can be employed to improve the destruction process, and are usually necessary for the destruction of carbonaceous materials. These catalysts include any oxidation promoting heavy metal salts or heavy metal oxides, and can be used in conjunction with one another. Two preferred catalysts are MnO 2 and CuO, and these are preferably employed in a ratio of 3:2 by weight, respectively. These catalysts can be added to the molten salt bath at a concentration of between about 0.05% and about and preferably about While the oxides are generally preferred, salts of the same heavy metal compounds may be employed since these salts will form their respective oxides when added to the molten salt solution.

While the oxidation reaction which takes place is not completely understood, it is believed that the carbonate and nitrate react with the organic (or carbonaceous) material in a synergistic fashion to ensure complete oxidation of any organic material. During this process, if halides, sulfates, phosphates, or similar moieties are present, the carbonate material is slowly exhausted, and therefore must be continually added in order that the reaction can be operated in a continuous fashion. The nitrate in the molten salt solution is reduced into the corresponding nitrite during the reaction process sodium nitrate is reduced to sodium nitrite). Nitrate can be regenerated, however, from the nitrite thus formed merely by contacting the molten salt solution with an oxygen source such as air, 12-

LI

WO 94/23802 PCT/US94/03912 thereby providing a continuous process when carbonate is also added as needed. While batch processing is certainly possible, provided a sufficient amount of carbonate and nitrate are present, continuous processing is obviously preferred.

If a pure oxygen stream is utilized to regenerate nitrate, the gaseous by-products from the reaction will be almost exclusively CO2 and H 2 0. Such a gaseous mixture is relatively easy to separate, and thus can provide a relatively inexpensive source of CO 2 as an added benefit. If air is used to regenerate nitrate, it is preferable to employ an oxygen sensor in the gaseous by-product stream in order to maintain nitrate regeneration stoichiometry. In this fashion, the gaseous by-products will primarily include only C0 2 H20 and N 2 It is also preferred that the nitrate regeneration be performed outside of the reaction zone in which the oxidation of the organic waste material takes place if air is Laing used for nitrate regeneration. This ensures that the presence of the oxygen-containing stream used to regenerate nitrate will not interfere with mass transfer between the molten salt solution and the organic waste being destroyed.

As mentioned previously, most inorganic materials are only partially soluble in the molten salt solution. Furthermore, when material such as chloride ions are present in the waste material, inorganic salts such as NaCI will be formed, with the sodium ions being contributed by the sodium carbonate in the molten salt solution. When material such as paint sludge is to be destroyed, reusable pigments will also settle to the bottom of the molten salt solution. Proper design of the apparatus in which the waste destruction takes place can ensure that these insoluble inorganics can be easily recovered and either reused or properly disposed of. In some instances, the waste material being destroyed 3y even be primarily inorganic in nature, such as the case with cor,,aminated soil or hospital waste. The process of the present invention enables one to readily destroy the organic portion of this waste material while also permitting the recovery of the inorganic portion for proper disposal.

13- WO 94/23802 WO 9423802PCT/US94/0391.2 While the foregoing has provided an overview of the process according to the present invention, the Applicants have also developed a number of apparatus for performing this same process, and the process itself will be better understood once these apparatus have been discussed. Fig's 1-4 depict one preferred embodiment of an apparatus for performing the process of the present invention. The apparatus shown in Fig. 1 is particularly suitable for destroying material such as paint sludge, PCB solutions, carbonaceous materials, and similar wastes. The molten salt solution is maintained in molten salt bath 1, and salt bath 1 also contains a heating means so that the salt solution may be heated to, and maintained at its proper temperature. The heating means may, for example, be a gas furnace or electric heater (not shown). The oxidation reaction which takes place between the molten salt solution and the waste being destroyed is extremely exothermic, and thus once the unit is operational it is normally not necessary to further heat molten salt bath 1. In fact, heat exchangers 2 and 3 are provided in order to remove the excess heat of the reaction so that the proper salt bath temperature can be maintained.

Heat exchangers 2 and 3 are provided at the base of columns 4 and 5, respectively, in order to remove the heat of reaction. Preferably, oil is pumped through exchangers 2 and 3 by pump 46 from hot oil expansion tank 47. Oil coolers 48 and 49 dissipate the heat removed from columns 4 and 5 by the oil circulating through exchangers 2 and 3. The excess heat can optionally be utilized for any of a number of other uses, and an additional or alternative exchanger could even be placed in bath 1 in order to remove excess heat of reaction.

As further shown in Fig. 1, dual multi-stage packed columns 4 and are positioned directly above molten salt bath 1 in fluid communication with said bath. Both columns can be packed with any suitable packing material having a high surface area, such as raschig rings, however a structured packing material such as Koch Flexipack (Koch Engineering, Wichita, KS) is 14- WO 94123802 PCT[US94/03912 preferred. Reactor column 4 comprises the reaction zone in which oxidation of the waste material takes place. As will be discussed shortly however, a portion of the oxidation of the waste material might actually take place in molten salt bath 1 depending upon where the waste material is fed into the unit. Regeneration column 5 is also positioned directly above molten salt bath 1, and is utilized to regenerate nitrate in the molten salt solution from the nitrite formed by the reaction of the present invention.

Both reaction column 4 and regeneration column 5 preferably operate in a counter-current fashion, and subrmnerged pump 6 transports molten salt from molten salt bath 1 to the top of both columns. Obviously, individual pumps could be provided for each column, however, it is preferred that a single pump be utilized, with the discharge 40 from pump 6 being split between column 4 and column 5 (see rear view shown in Fig. Waste material can be fed to the unit in a number of locations, and is depicted in Fig. 1 as being fed into molten salt bath 1 through feed inlet 7. It is preferred that when the material being destroyed is primarily liquid, that inlet 7 is a static mixer (shown in Fig. 1) such as those commonly employed.

This ensures efficient contact between the waste and the molten salt.

As the organic waste material is fed through inlet 7 into molten salt bath 1, almost all of the waste material is immediately oxidized and gaseous reaction by-products will rise into reaction column 4 which is located directly above inlet 7. Baffle plate 8, extending well below the surface of the molten salt, is provided in molten salt bath 1 to ensure that these gaseous by-products will only enter reaction column 4, and are not able to enter regeneration column 5. These gaseous by-products will include primarily CO2, H 2 0, other organic compounds, and possibly N 2 depending upon the waste material being destroyed. The organic by-products which rise through reaction colunimn 4 are further oxidized as they travel upward through the column since molten salt is simultaneously passing through reaction column 4 in the opposite direction. In this fashion, complete oxidation of all organic material will be ensured, resulting in only C0 2

H

2 0, and possibly N 2 exiting WO 94/23802 2PCTIUS94103912 at the top of reaction column 4. In fact, one result of this process is that pure CO2 can, if desired, be produced merely by separating it from the overhead gases from reaction column 4 by well-known methods.

Depending upon the organic material fed to the unit, various inorganics (such as NaCI) will remain in molten salt bath 1, and will settle to the bottom. The insoluble inorganics can be removed by a number of mechanical means, or alternatively may simply remain in molten salt bath 1 until a suitable time at which the unit can be cooled and opened for cleaning. As shown in Fig. 1, and more particularly in Fig. 4, drag chain 42 having scraper blades attached thereto in a manner known in the art is provided. Motor 43 drives chain 42, which picks up material which settles to the bottom of bath 1 and deposits the same in hopper 10. Bottom 43 of bath 1 is also preferably sloped to form channel 44 into which insolubles will collect for easier removal.

Screw conveyor 9 shown in Fig. 5 may alternatively be provided in order to remove inorganics which settle to the bottom of molten salt bath 1, provided that the bottom 41 of molten salt bath 1 is appropriately sloped.

The inorganics are removed along the path of screw conveyor 9 in the direction shown, and are deposited into waste hopper 10. Of course, any of a number of alternative mechanical means may be utilized to remove the organics from molten salt bath 1.

As previously discussed, the nitrate contained in the molten salt solution is converted into the corresponding nitrite during the course of the oxidation reaction. In order to regenerate nitrate, the molten salt solution containing nitrite is pumped to the top of regeneration column 5. At the same time, air is fed through air inlet 11 located near the base of regeneration column 5. In this fashion, the air flows counter-current to the molten salt solution, and is intimately contacted therewith. The oxygen contained in the air will thus regenerate nitrate from nitrite, and the molten -16- WO 94/23802 PCTIUS9403912 salt solution now containing the regenerated nitrate will fall back into molten salt bath 1. In addition, an oxygen sensor may be placed in the overhead gas stream from regeneration column 5, and this sensor will ensure that a stoichiometric amount of oxygen is being provided to regeneration column 5. In this fashion, pure N 2 will be produced by regeneration column If desired, pure oxygen may be utilized instead of air in order to regenerate the nitrate from nitrite, which would permit regeneration column to be reduced in size. In fact, when pure oxygen is utilized, oxygen spargers can be placed in molten salt bath 1, thereby eliminating entirely the need for a regeneration column. By placing spargers in the bath, regeneration of nitrate from nitrite takes place in the bath itself. The mass transfer inhibiting dilution discussed previously does not occur since, if properly controlled, all of the oxygen injected into the bath is consumed in the regeneration reaction.

The overhead gases from both -eaction column 4 and regeneration column 5 can be combined, and optionally pass through scrubber 12 (entering near its base as shown in Fig. 2) in order to ensure that no organics remain in these vent gases. Scrubber 12 can be of any typical design utilized for this purpose. Induced draft fan 13 may also be employed to maintain a negative pressure on reaction column 4, regeneration column and optional scrubber 12, thereby ensuring that any leakage will be inward. Induced draft fan 13 (in fluid communication with outlet 45 of scrubber 12) also ensures that the gaseous by-products will eventually be vented to the atmosphere. Since the overhead gases from reaction column 4 and regeneration column 5 will obviously be at an elevated temperature, heat exchangers may also be provided to recover some of this heat and even preheat the air being fed to regeneration column In some instances, it may also be desirable to pretreat the organic waste material to be destroyed. Thus, organic waste material may be optionally fed to a scraped-surface still in which any solvents in the waste -17- I L WO 94123802 PCT/R94/03912 material may be removed through simple distillation. The heat needed for this distillation may even be provided by the heat exchangers previously mentioned for removing the heat of reaction from the oxidation of waste material. Obviously the means by which the waste material to be destroyed is fed into the unit will vary greatly depending upon the type of material one wishes to destroy, however a simple feed pump will suffice for most liquid wastes.

An alternative design for this process unit is shown in Fig. 6, wherein the reaction column and regeneration column previously discussed are combined into a single structure. The overall configuration of the unit is essentially the same other than this distinction. Single packed column 16 comprises lower reaction section 17 and upper regeneration section 18.

Molten salt is pumped from molten salt bath 1 by means of pump 6 to the top of upper regeneration section 18. A portion of a typical distributor arrangement is shown in Fig. 6, however any of a number of alternative configurations can be employed. In the configuration of Fig. 6, the molten salt enters regeneration section 18 through perforated distributor pipe Overhead gases from regeneration section 18 exit through vent line 25, and may one again be directed to an optional scruboer. Packing 72 is support9d by grid 73 which permits both upflowing vapors and downflowing molten salt to pass through. The molten salt solution flows downward through regeneration section 18, and is contacted with air, or alternatively oxygen, which has been fed into the base of regeneration section 18 (below grid 73) through air inlet 11. As discussed previously, any nitrite contained in the molten salt solution is contacted with the upflowing air, and nitrate is thus regenerated.

The molten salt solution continues to flow downward through grid 73, and thus enters lower reaction section 17. Here the molten salt solution flows countercurrent to either the waste material being destroyed or the gaseous reaction by-products, depending upon the feed location for the 18wo 9423802 PCTUS94/03912 waste material. Once again, the organic waste material may be fed into either the base of lower reaction section 17, or alternatively directly into molten salt bath 1 which is located beneath lower reaction section 17. In this manner, the organic waste material is oxidized by the down flowing molten salt solution, as previously discussed.

In order to employ the configuration of Fig. 6, it is necessary that a means fr ensuring that the by-product gases from lower reaction section 17 cannot enter upper regeneration section 18 be provided. As shown in Fig. 6, lower reaction section 17 and upper regeneration section 18 are separated by perforated plate i9 which also contains a downcomer 75 and accompanying cap 74 which permits the molten salt solution to flow from upper regeneration section 18 into lower reaction section 17, while preventing gaseous reaction by-products from entering regeneration section 18. A distributor weir 20 is also provided in lower reaction section 17 to ensure proper distribution of the molten salt solution across the packing material.

The operation of the unit shown in Fig. 6 is essentially identical to that shown in Fig. 1, as the gaseous reaction by-products (primarily C02 and

H

2 0) are vented through vent line 24, and any inorC~nics, such as inorganic salts or pigments will accumulate in molten salt bath 1. In upper reaction section 18, the vent gases exit through vent line 25, and may be combined with those from vent line 24 for further treatment as needed.

As an alternative to the packed columns of Fig's 1-6, a spray scrubber or venturi scrubber may be employed in place of the packed columns for gas-molten salt contacting. Either of these apparatus may replace the reaction column and/or the regeneration column, however they are generally not as efficient as packed columns.

Figure 7 depicts a typical venturi scrubber 33 which may be utilized 19-

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WO 94/23802 PCT/US94/03912 in place of the reaction column and/or the regeneration column. Venturi scrubber 33 comprises gas inlets 34, liquid inlet 36 and gas/liquid outlet 37.

The molten salt solution is fed through liquid inlet 36, contacts the gaseous material entering through gas inlet 34, and the resulting mixture is dispersed and mixed by nozzle 38. The gaseous material entering gas inlet 34 may be the organic waste material to be destroyed, gaseous reaction by-products, or air (or oxygen) which is being utilized to regenerate nitrate. The molten salt solution and gaseous components entering venturi scrubber 33 are carried into separation chamber 39 wherein both the gaseous by-products and molten salt solution exit through outlet 37. The gaseous portion may be vented overhead, and the molten salt removed from below its surface.

Both venturi scrubber 33 and spray scrubbers offer viable alternatives for ensuring intimate contact between the molten salt solution and the organic waste material to be destroyed (or alternatively the air being used to regenerate nitrate). Additionally, a stirred tank reactor may replace the venturi scrubber for any of the uses described herein for venturi scrubbers.

Such reactors may, for example, be of the type described in the chapter entitled Gas-Liquid Reactors, of Mass Transfer Operations, by Traybal, and in Perry's Chemical Engineers' Handbook, pages 4-24 to 4-27 (6th Ed.).

Figure 8 shows yet another embodiment of an apparatus suitable for performing the process of the present invention. Once again molten salt bath 1 is provided for maintaining the molten salt solution at the desired temperature. Bath 1 is placed in fluid communication with angled reaction pipe 50, and a means (such as pump 90) is provided for pumping molten salt from molten salt bath 1 into angled reaction pipe 50 through salt inlet 51. Salt outiot 52 is also provided, and is located along the length of angled reaction pipe 50, just prior to solids exit 53 of reaction pipe 50. In this fashion, the molten salt solution wil! not fill the entire length of angled reaction pipe 50, thereby ensuring that a vapor spac3 54 will be present in the vicinity of solids exit 53 of reaction pipe WO 94/23802 PCT/US94/03912 Hollow cylindrical shaft 55 is contained within reaction pipe 50, and screw 56 is attached around the circumference of shaft 55. Shaft 55 is rotatably attached to end wall 57 of reaction pipe 50, and thereby permits screw 56 to rotate within reaction pipe 50. Rotation of screw 56 is accomplished merely by providing a means for rotating shaft 55, such as an electric motor. If a diesel engine is employed for this purpose or for electricity generation for the process, the diesel exhaust can be directed down the length of shaft 55. As shown in detail in Fig. 8, shaft 55 may actually comprise concentric tubes 58 and 59, with inner concentric tube 58 open at the end of shaft 55 which is rotatably attached to end wall 57. In this manner, the diesel exhaust flows along the length of shaft 55 through inner concentric tube 58, and then returns in the opposite direction through outer concentric tube 59 after the exhaust has travelled to a point adjacent end wall 57. The purpose of running the diesel exhaust through shaft is to provide a means for economically heating the molten salt solution contained in reaction pipe As shown in Fig. 8, the organic waste to be destroyed enters reaction pipe 50 through inlet 60, located beneath the surface of molten salt contained within pipe 50, where it contacts the molten salt solution contained therein. The organic material is immediately oxidized and gaseous by-products flow along angled reaction pipe 50 with the rotation of screw 56 until they enter vapor space 54. By selecting a sufficient length for reaction pipe 50, complete destruction of any organic material present in the waste can be assured, since the gaseous by-products remain in contact with the molten salt until they reach vapor space 54. Gaseous by-products which enter vapor space 54 exit reaction pipe 50 through vent 61, and may thereafter be vented to the atmosphere. Optionally, a packed column 62 similar to those described previously may be pelaced in fluid communication with vent 61 in order to further oxidize any organics remaining in the gaseous by-product stream. Molten salt solution may also be pumped into packed column 62, in order to oxidize any organic vapors present in the -21 WO 94/23802 PCT/US94103912 stream being vented from reaction pipe 50. The operation of packed column 62 will not be discussed in detail here, since its operation is identical to that of the reaction columns previously discussed. Obviously, the spray scrubber or venturi scrubber previously discussed may also be employed in place of packed column 62 if desired. In addition, an induced draft fan may be placed in fluid communication with the gas outlet 64 from packed colurnn 62 to provide a slight negative pressure throughout the system, thereby ensuring that the gaseous by-products will be drawn through packed column 62.

In order to regenerate nitrate in molten salt bath 1, sparger 65 may be placed in molten salt bath 1. Air or pure oxygen is fed through sparger and thereby regenerates nitrate within the molten salt solution. The air or oxygen entering through the sparger will also act to cool the molten salt solution as needed. Additionally, a heat exchanger may be placed between salt outlet 52 and molten salt bath 1 in order to remove the excess heat of reaction.

Since the apparatus depicted in Fig. 8 is particularly suited for destroying paint sludges, liquid PCB's and hospital waste, there will obviously be a significant amount of insoluble inorganics present in reaction pipe 50. In order to ensure that these inorganics are effectively removed from reaction pipe 50, wire brushes 66 are attached to the flights of screw 56. Wire brushes 66 act to clean the inside surface of reaction pipe ensuring that the insoluble inorganics are carried along the length of reaction pipe 50 by screw 56 as shaft 55 rotates. In this fashion, these insoluble inorganics are moved along the length of reaction pipe 50 and eventually urged towards solids outlet 53. Since the liquid level 68 of the molten salt solution within reaction pipe 50 lies below solids outlet 53, primarily only solids will be discharged into solids outlet 53. Although a small amount of the molten salt solution will exit through solids outlet 53, carbonate and nitrate can be added to the molten salt solution as needed to replace that -22-

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WO 94/23802 PCT/US94/03912 which is lost.

Figures 9 and 10 depict a modification of the apparatus of Fig. 8, and is particularly suited for materials such as hospital waste and contaminated soil. In this design, it is not necessary to utilize a molten salt solution, as it has quite surprisingly been found tht a blend of an alkaline material such as an alkali metal carbonate CaO or MgO) or lime, and alkali metal nitrate can accomplish the desired oxidation of organics. The preferred alkaline material is sodium carbonate due to its water solubility, however even lime is acceptable for some soils. In this method, the soil or hospital waste is pre-mixed with either a dry blend of the carbonate (or lime) and nitrate, or a water solution containing the carbonate and nitrate. Mixing of the waste and the salt blend can be accomplished in a concrete mixer or similar device. It is preferred that the pre-mixed waste/salt blend contain approximately 20% moisture, and this can be accomplished by first adding the nitrate to a water and carbonate or lime slurry. The resulting solution is then mixed with the solid waste material in a ratio of approximately five times the stoichiometrically required amount. It has been found that when this organic waste/salt mixture is heated to at least about 3500 C, and preferably at least about 4500 C, the desired oxidation takes place and the organic component of the waste is thereby destroyed. Since the reaction is exothermic, it is also possible to recover heat from the process, however significant amounts of heat can only be recovered if there is a large amount of organic material present in the soil or hospital waste.

In the apparatus shown in Fig. 9, once again a shaft 55, with attached screw 56, preferably having wire brushes 66 attached thereto, is provided. Instead of a reaction pipe as previously employed, however, shaft is placed within reaction trough 80, and the lower portion of screw 56 will rest against the inner surface of reaction trough 80. As shown in the end view of Fig. 10, a vapor space 81 is also provided above screw 56.

This can be accomplished by providing a rectangular enclosure 82 above -23- WO 94/23802 PCT/US94/03912 reaction trough 80. Obviously, alternative designs equivalent to this structure may be employed, and the apparatus shown in Fig's 9 and 10 is merely a preferred embodiment.

As further shown by Fig. 9, the pre-mixed organic waste/salt mixture is added through inlet 83 near one end of reaction trough 80. Any type of feed means may be employed and may for example be a hopper in fluid communication with inlet 83 or a rotary air-lock type feeder. Since shaft is once again rotatably attached to end 84 of reaction trough 80, as shaft 55 is rotated, the solid mixture is carried along the length of reaction trough As shown in Fig.'s 9 and 10, a salt jacket 85 extends along the length of reaclion trough 80, and thereby provides heat to the dry mixture contained therein (of course alternative means for heating reaction trough could be employed. It is preferred that the unit is operated such that the mixture achieves the desired temperature prior to reaching the end of reaction trough 80. Means for heating the salt jacket is also provided, and may, for example, be electric Firebar heaters 86 (manufactured by Watlow Electric Manufacturing, St. Louis, Missouri) placed along the length of salt jacket 85, thereby enabling the salt contained in the salt jacket to be melted.

Molten salt bath 1 is once again provided, and is placed in fluid communication with salt jacket 85, and heaters 79 are also contained therein. A means for pumping the molten salt solution from molten salt bath 1 is provided, and may for example be pump 87. Pump 87 preferably pumps molten salt to the top portion of salt jacket 85, and it is preferred that salt outlet 78 (see Fig. 10) be similarly located. Salt inlet 77 is also located accordingly (see Fig. This ensures that the salt will not drain from salt jacket 85 when pump 87 is turned off. It is also preferred that the flow of salt through salt jacket 85 be countercurrent to the movement of solids through reaction trough As the pre-mixed organic waste/salt mixture is carried along the length of reaction trough 80, the mixture is heated thereby causing the -24-

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WO 94/23802 PCT/US94/03912 oxidation reaction to occur. The gaseous by-products of this reaction enter vapor space 81 and are carried through vent 88. Once again an induced draft fan may employed to ensure that the gaseous by-products are removed. The solid inorganic material is carried along reaction trough and eventually is urged into solids outlet 67. If, for example, contaminated soil is being treated, the material ejected through solids outlet 67 will comprise primarily the treated soil, and will be essentially free of all organics. In the case of soil, another advantage of this process is that the addition of lime and nitrates to the soil has added benefits when, for example, the treated soil is later utilized as fill, as these components act as soil fertilizers.

Since it is possible that the gaseous by-products leaving through vent 88 may contain some organics, depending upon the nature of the organic waste being treated, once again a packed column or other means for oxidizing these organics may optionally be provided. The design of these units is identical to that described previously for the angled reaction pipe design, and will not be dealt with in detail here. The molten salt bath of Fig's 9 and 10 may even be employed for this purpose, in addition to its heating function. Obviously, it might also be possible to merely employ a scrubber of the type known to those skilled in the art if the organic gaseous by-products are such that they can be effectively removed in this manner.

Figure 11 depicts yet another embodiment for practicing the process of the present invention, and is particular suitable for hospital waste and the like. In this embodiment, molten salt bath 101 is provided, and any suitable means for heating bath 101 (such as those described previously) is also provided. This heating means could, for example, comprise heat exchanger tubes passing through bath 101, or even an electric heating element placed within bath 101. The destruction reaction takes place in perforated or screen drum 102 which is rotatably secured within molten salt bath 101.

Rotation of drum 102 may be accomplished, for example, by motor 104 attached thereto. Drum 102 is typically of the type commonly used in degreasing or deburring small parts, such as drums manufactured by the 25 WO 94/23802 PCT[US94/03912 Ransohoff Co. of Hamilton, Ohio. Perforated drum 102 permits molten salt to enter its interior, and as shown in Fig. 11 the lower portion of drum 102 is positioned slightly belovw salt level 110. Spiral ridges 106 are provided along the interior of drum 102 in order to ensure that solid material contained therein is moved along the length of drum 102 as it is rotated.

The material to be destroyed is fed into hopper 103, from which it enters drum 102 through feed chute 111. Once the waste contacts the molten salt presen'. in the lower portion of drum 102, the organic portion is immediately destroyed in the same fashion as before. Gaseous by-products enter vapor space 112, and eventually escape through vent 105. Once again a packed column or other means a venturi scrubber) for destroying any organic by-products exiting through vent 105 may be employed if necessary. The design of these units is identical to those described previously, and will not be dealt with in detail here. It is even possible that salt from molten salt bath 101 be utilized for this purpose in the manner described previously. The solid inorganic portion of the waste remaining in drum 102 (syringes, etc. when hospital waste is being destroyed) is carried along the length of drum 102 by spiral ridges 106, thereby complete destruction of any organic material. At the end of drum 102, these ridges are typically arranged, as is well-known in the art, such that the solids are deposited into discharge chute 107 and deposited in waste hopper 108. Obviousl/ if it is desired, although not preferred, to operate the apparatus of Fig. 11 in a batch mode, this latter feature may be eliminated. The apparatus would merely be opened periodically to remove any solids accumulating at the end of drum 102 or in bath 101.

In order to regenerate nitrate from the nitrite which forms in molten salt, sparger 109 is preferably provided in bath 101. In this fashion, air or oxygen may be pumped into bath 101 to regenerate nitrate. Of course a regeneration column or the like (as described previously) may optionally be employed for the same purpose. Since it is likely that some of the molten -26- WO 94/23802 PCT[US94/03912 salt may be carried out with the solid inorganics, and since a portion of the carbonate present in the molten salt may be consumed as described previously, it will also be necessary to replenish the molten salt periodically.

This could be accomplished through feed chute 111, although other means may certainly be employed.

Figures 12 14 depict yet another apparatus particularly suited for destroying material such as hospital waste and contaminated soil. The apparatus shown in these figures is preferably employed with the process desc ibed for the apparatus of Figures 9 10, using a blend of an alkaline material and an alkali metal nitrate to accomplish the desired oxidation of organics. The entire apparatus of Figure 12 or Figure 14 may be provided in any suitable enclosure 112. The pre-mixed waste/salt mixture is added through inlet 101, and thereafter falls upon a porous, continuous conveyor belt 102. While the construction of porous conveyor belt 102 can vary, one preferred design is shown by Figure 13. The conveyor shown in Figure 13 is comprised of connecting rods 125 and transverse elements 126, each of the transfers elements having convolutions which interdigitate with adjacent convolutions so that connecting rods 125 may penetrate the adjacent convolutions thereby permitting the transverse elements to rotate about the connecting rods. These porous conveyors, or grate-type conveyors, are commonly employed in various industries for such uses as bottle washing.

Bottles can be placed atop the conveyor and water cascaded down upon the bottles for washing purposes. The water is there then permitted to pass through the conveyor to a suitable collection system.

In the apparatus of Figure 12 and 14, however, the advantage of the conveyor shown in Figure 13 is that the organic waste/salt mixture will be held within the compartments 127 (see Figure 13) of the porous conveyor.

Conveyor belt 120 is further defined by ,,pper flight 130, and lower flight 131, and belt 120 passes around first and second sprocket wheels 104 and 103, respectively. Rotation of first and second sprocket wheels will thereby -27- WO 94/23802 PCT/US94/03912 cause belt 120 to move, preferably from the first wheel towards the second wheel, as shown in Fig. 12. The conveyor belt moves atop an upper planar surface, namely support plate 107, and thus the waste/salt mixture will loosely rest within compartments 127 atop, and retained by, plate 107.

Preferably the porus conveyor employed has a height of approximately one half to three quarters inches, and provides compartments 127 having a volume of approximately 0.5 cubic inches.

As stated previously, porous conveyor belt 102 is driven by sprocket wheels 103 and 104. These wheels are of a typical construction for such a u;e, and the sprockets are not shown in Figures 12 and 14 for the sake of simplicity. A plurality of sprocket wheels may also be provided to ensure uniform and smooth movement of the conveyor, with successive sprocket wheels connecting to one another by a common axle. One or more of the sprocket wheels are mechanically driven, and the remainder are free spinning. In the apparatus of Fig. 12, however, second sprocket wheel 103 preferably comprises a substantially solid drum of substantially the same width as belt 102.

In order to provide the temperatures necessary for the oxidation reaction to occur, a number of heating means are provided. Radiant heater 105 is positioned above porous conveyor 102, and heats the waste/salt mixture from above. Radiant heater 105 may be powered by any suitable means, including gas, oil, electricity, or even molten salt. Since support plate 107 is preferably of a conductive material such as metal, a plurality of heaters 106 are also preferably provided beneath support plate 107. These may likewise be fired by any suitable means such as those previously described, including molten salt. In this manner, the salt/waste mixture, which preferably is soil and the appropriate salt combination, will be heated from both above and below, This will ensure a relatively uniform temperature throughout the mixture, and will quickly initiate the oxidation reaction.

-28-

I

WO 94/23802 PCT/US9403912 As porous conveyor 102 passes across support plate 107 carrying the waste/salt mixture in its compartments 127, the conveyor passes around sprocket wheel 103 to reach lower support plate 108. In order to ensure that the waste/salt mixture remains within compartments 127 of porous conveyor 102, substantially arcuate reversing guide 109 is provided adjacent sprocket wheel 103. In this manner, belt 102 will pass between the second sprocket wheel and the reversing guide, and the mixture will be retained within the compartments by the guide and the solid, drum-shaped sprocket wheel. As the conveyor passes around sprocket wheel 103, however, some mixing of the waste/salt mixture will occur as this mixture is rotated through 180 degrees. After the path of the belt has been reversed, lower flight 131 rides atop lower planar surface, or lower support plate, 108, and the mixture is retained within the compartments 127 by support plate 108. Once again a plurality of heaters 106 may be provided beneath lower support plate 108 in order to continue heating of the reacting mixture. In addition, radiant heat from heaters 106 located above lower support plate 108 will provide further heat to the mixture. Conveyor 102 passes along lower support plate 108 until reaching a point preferably near sprocket wheel 104 where lower support plate 108 terminates. At this point, the solid inorganic material remaining is discharged from compartments 127 of conveyor 102, and falls into solids outlet 110.

As described previously, the heating of the waste/salt mixture to the required temperatures will cause oxidation to take place and the organic component of the waste thereby destroyed. Thus in the apparatus of Figure 12, the material leaving through solids outlet 110 will be free from organic material. As also described previously, however, gaseous by-products will evolve, and therefore vent 111 is provided. As stated previously, an induced draft fan may also be employed to be ensured that the gaseous byproducts are removed. The previous means described for further treating the gaseous by-products leaving through vent 111 may once again be employed in the designs of Figure 12 and 14, including the use of molten -29- WO 94/2380( PCT/US94/03912 salt to remove any organic material remaining in the gaseous by-products.

Figure 14 depicts a modification of the apparatus of Figure 12, and provides for an increased residence time for the waste/salt mixture. The apparatus of Figure 14 generally comprises a plurality of porous conveyor belt systems, with the waste/salt mixture constantly reversing directions as it moves within each belt. Support plate 122 has also been modified, as the plate terminates a predetermined distance from second sprocket wheel 121.

In this case, however, the sprocket wheels employed preferably do not extend across the entire width of belt 102. Rather, sprocket wheel is preferably only a fraction of the width of belt 102, and must merely be thick enough to support belt 102. Of course a plurality of second sprocket wheels upon a single axis could be distributed across the width of the belt.

In this manner, when plate 122 terminates prior to sprocket wheel 121i, the waste/salt mixture will fall from compartmerts 127 of the upper flight of porous conveyor 102 onto the lower flight of porous conveyor 102 which is moving along lower support plate 123. This falling action will provide for further mixing of the waste/salt mixture, thereby improving the destruction process. As also shown in Figure 14, lower support plate 123 terminates well before first sprocket wheel 120, thereby permitting the waste material to fall onto the next porous conveyor moving along a support plate. In this fashion, the waste/salt mixture will cascade from the compartments of one conveyor to the next. Eventually, the inorganic solid material will exit from the apparatus in the manner as described before, and gaseous by-products will exit through a vent. Suitable heaters, as described previously, are likewise provided throughout the app iratus of Fig. 14. Obviously it would certainly be possible to employ only one of the assemblies shown in Fig. 14, thereby providing a structure identical to Fig. 13 except for the manner in which the reaction mixture was moved from the upper flight to the lower flight. In addition, the plurality of assemblies shown by Fig. 14 could be staggered from one another, and the direction of movement of one or more WO 94/23802 PC'T/US94/03912 of the conveyor belts reversed.

It will be understood that modifications may be made in the present invention without departing from the spirit of it. For example, various apparatus other than that which has been described herein may be effectively employed to practice the process of the present invention. Thus, the scope of the present invention should be considered in terms of the following claims, and is understood not to be limited to the details of structure and operation shown and described in the specification and drawings.

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Claims

1. A process for destroying the organic portion of a waste including: maintaining a molten salt solution including an alkali metal nitrate and an alkali metal carbonate; reacting said organic portion of said waste with said molten salt solution in order to form gaseous carbon dioxide, water vapor and gaseous and non-gaseous reaction by-products, and to reduce at least a portion of said nitrate into the corresponding nitrite, thereby destroying said waste; and venting said gaseous carbon dioxide, said water vapor and said gaseous by-products.

2. The process of Claim 1, wherein said alkali metal nitrate is sodium nitrate or potassium nitrate and said alkali metal carbonate is sodium carbonate or 15 potassium carbonate.

3. The process of Claim 1 or Claim 2, wherein said molten salt solution comprises about 8 to 10% alkali metal carbonate by weight. f

4. The process of any one of Claims 1 to 3, wherein said molten salt solution is maintained at a temperature of at least 450C. The process of any one of Claims 1 to 4, further includes the step of adding a catalyst system having one or more oxidation promoting heavy metal salt or heavy metal oxide.

6. The process of Claim 5, wherein said catalyst system includes MnO 2 and CuO.

7. The process of Claim 6, wherein said catalyst system includes about 3 parts MnO 2 and about 2 parts CuO by weight, and said catalyst system is present in said molten salt solution at a concentration of between about 0.05 and about VT OD 4 weight percent.

8. The process of any one of Claims 1 to 7, further including the step of regenerating said alkali metal nitrate by converting said alkali metal nitrite into said nitrate, wherein said regeneration is performed by contacting at least a portion of said molten solution containing said nitrite with a gaseous stream containing oxygen.

9. The process of any one of Claims 1 to 8, wherein said molten salt solution is maintained in a heated reservoir, arid the reacting step includes pumping said molten salt from said reservoir into a reaction zone while simultaneously feeding said waste into said reaction zone.

10. The process of any one of Claims 1 to 8, wherein said molten salt solution is maintained in a heated reservoir, and said reacting step is performed in said reservoir. e

11. The process of Claim -9 wierein said reaction zone is chosen from the group consisting of: a packed column, a spray scrubber, a venturi scrubber, and a stirred tank reactor.

12. The process of Claim 8, or of any )ne of Claims 9 to 11 when appended to Claim 8, wherein said regenerating step is performed in a regeneration unit chosen from the group consisting of: a packed column, a spray scrubber, a venturi scrubber, and a stirred tank reactor.

13. The process of any one of Claims 1 to 12, further including the step of removing non-gaseous by-products which are insoluble in the molten salt arid insoluble unreacted waste from said molten salt solution.

14. The process of Claim 10, further including the step of further reacting said -v r gaseous by-products with said molten salt solution in a reaction unit so as to destroy any organic gaseous by-products, said reaction unit in fluid communication with said reservoir. The process of Claim 14, wherein said reaction unit is chosen irom the group -,,,slishinig of: a packed column, a spray scrubber, a venturi scrubber, and a stirred Lr ,k ,,,actor.

16. The process of any one of Claims 1 to 15, wherein said waste is chosen from the group consisting of: paint sludge, chrome tannery waste, contaminated soil, hospital waste, polyhalogenated polyphenyl-containing waste, aluminum pot liners, hydrocarbon-containing sludge, and mixtures thereof.

17. An apparatus when used to carry out the process of claim 1, including: a reservoir for maintaining a molten salt solution including an alkali metal nitrate and an alkali metal carbonate in a molten state; a reaction unit for contacting said waste and said molten salt solution in order to react the waste and the molten salt to form gaseous carbon dioxide, water vapor and gaseous and non-gaseous reaction by-products, and to reduce at least a portion of said molten nitrate into the corresponding molten nitrite, said reaction unit in fluid communication with said reservoir; wherein said o:reaction unit includes an angled reaction pipe, a screw rotatably attached to said reaction pipe for moving any solid waste or byproducts present along the length of said reaction pipe, and further including: S means for feeding said molten salt into said reaction unit; a molten salt outlet in fluid communication with said reservoir, said salt outlet positioned on said reaction pipe so as to ensure that a vapor space will be present when said apparatus is operated; and a solids outlet positioned at a higher elevation than said salt outlet such that said solid waste byproducts will be moved by said screw to said solids outlet for r smoval therethrough, without a significant loss of molten salt through said solids outlet; means for feeding said waste into said reaction unit; and I Sy 4 \0 00u "r 0 means for venting said carbon dioxide, water vapor and gaseous reaction by-products from said reaction unit.

18. The apparatus of Claim 17, further including a sparger positioned within said reservoir for feeding air or oxygen into said reservoir in order to regenerate nitrate.

19. The apparatus of Claim 17 or Claim 18, wherein said reaction unit is chosen from the group consisting of: a packed column, a spray scrubber, a venturi scrubber, and a stirred tank reactor. The apparatus of any one of claims 17 to 19, further including a plurality of brushes attached to said screw for removing solid materials from the interior of said angled reaction pipe.

21. The apparatus of any one of claims 17 to 20, further including a hollow rotating shaft about which said screw rotates, and wherein heated fluid may be circulated through said shaft in order to provide additional heat to said reaction unit. oe 2 0 22. An apparatus when used to carry out the process of claim 1, including: *o a reservoir for maintaining a molten salt solution including an alkali metal nitrate and an alkali metal carbonate in a molten state; a reaction unit for contacting said waste and said molten salt 25 solution in order to react the waste and the molten salt to form gaseous carbon dioxide, water vapor and gaseous and non-gaseous reaction by-products, and to reduce at least a portion of said molten nitrate into the corresponding molten nitrite, said reaction unit in fluid communication with said reservoir; wherein said reaction unit includes a perforated drum rotatably secured within said reservoir such that at least a portion of said drum is submerged beneath said molten salt; means for feeding said waste into said reaction unit; and means for venting said carbon dioxide, water vapor and gaseous 36 reaction by-products from said reaction unit.

23. The apparatus of Claim 22, further including spiral ridges positioned on the interior of said drum for moving solid material along the interior length of said drum as said drum is rotated.

24. An apparatus when used to carry out the process of claim 1, including: a res-"voir for maintaining a molten salt solution comprising an alkali metal nitrate and an alkali metal carbonate in a molten state; means for feeding said waste into said reservoir thereby contacting said waste and said molten salt solution in order to react the waste and the molten salt to form gaseous carbon dioxide, water vapor and gaseous and non- gaseous reaction by-products, and to reduce at least a portion of said molten nitrate into the corresponding molten nitrate; means for venting said carbon dioxide; water vapor and gaseous reaction by-products from said reservoir, a reaction unit, in fluid communication with said reservoir so that said vented gaseous reaction by-products will enter said reaction unit; and means for feeding a portion of said molten salt to said reaction unit, S 20 so that said salt can contact said gaseous reaction by-products thereby further reacting the organic portion of said reaction by-products.

25. The apparatus of claim 24, further including a regeneration unit in fluid communication with said reservoir, a means for feeding a portion of said molten 25 salt to said regeneration unit, and a means for feeding a gaseous stream containing oxygen into said regeneration unit, such that the molten salt will be contacted with said oxygen-containing gaseous stream, thereby regenerating nitrate from any nitrite present in said molten salt, and such that said molten salt will return to said reservoir after said regeneration has occurred.

26. The apparatus of claim 25, wherein said reaction unit and said S--V R, regeneration unit are each separate packed, multi-stage columns positioned directly above, and in fluid communication with, said reservoir, and wherein molten salt enters at the top of each of said columns, such that said gaseous reaction by-products will rise from said reservoir into said reaction unit, and such that molten salt will exit from the base of each of said columns and fall back into said reservoir.

27. The apparatus of Claim 25, wherein said reaction unit includes the lower section of a packed, multi-stage column, said regeneration unit includes the upper section of said column, and molten salt enters at the top of said column, such that in operation molten salt will flow downward through both sections of said column, gaseous reaction by-products will rise from said reservoir into the lower section of said column, and molten salt will exit from the base of said column and fall back into said reservoir.

28. The apparatus of any one of Claims 24 to 27, further including a means for removing insoluble organics from said reservoir. R.A a S. o: 2: ,C I• ,o '?I -38-

29. An apparatus when used to carry out the process of the claim 1, including: a porous, continuous conveyor belt having an upper flight, a lower flight, and a plurality of compartments: first and second rotatable sprocket wheels about which said conveyor belt passes, such that rotation of said sprocket wheels causes said conveyor belt to move from said first wheel towards said second wheel; a heated upper planar surface upon which said upper flight rides; a lower planar surface upon which said lower flight rides; an inlet for feeding a mixture including said waste material, an alkaline material and an alkali metal nitrate into said compartments of said conveyor belt; and a means for heating said mixture; wherein said upper planar surface will retain said mixture in said compartments as said upper flight moves across said upper planar surface, and wherein said lower planar surface will retain said mixture in said compartments as said lower flight moves across said lower planar surface.

30. The apparatus of claim 29, wherein said upper planar surface terminates a 9* 20 predetermined distance from said second sprocket wheel so that said mixture will fall from said compartments at the termination point of said upper planar surface onto said lower flight.

31. The apparatus of claim 29, wherein said second sprocket wheel comprises 25 a substantially solid wheel, and further including a substantially arcuate reversing guide located -'djacent said second sprocket wheel, whereby said conveyor belt will pass between said second sprocket wheel and said guide, and whereby said mixture will be retained within said compartments by said guide anld said second sprocket wheel. IC C,\WINWORDJLONAIWMMHIMMHSPECII85572.DOC -39-

32. The apparatus of any one of claims 29 to 31, wherein said heating means includes at least one heater located beneath said upper planar surface, whereby said heater will heat said upper planar surface and will heat said mixture contained within said compartments of said lower flight.

33. A process for destroying the organic portion of a waste according to claim 1, substantially as herein described with reference to any one of the Examples.

34. A process for destroying the organic portion of a waste according to claim 1, substantially as herein described with reference to any one of the embodiments of the accompanying drawings. An apparatus for destroying the organic portion of a waste when used to carry out the process of claim 1, substantially as herein described with reference to any one of the embodiments of the accompanying drawings. DATED: 7 July, 1998 0 ,PHILLIPS ORMONDE FITZPATRICK Attorneys for: WABASH, INC. 00 i: co oRi •e Vr ce•- s o• ~c