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Title:
ELIMINATION OF PRODUCTS OF INCOMPLETE COMBUSTION
Document Type and Number:
WIPO Patent Application WO/1996/032609
Kind Code:
A1
Abstract:
Water is introduced into the flue gas effluent leaving the flame zone (12) of any type of thermal destruction device (1) (such as an incinerator, boiler, or cement, aggregate or rotary kiln) being fed any kind of waste (such as hazardous, medical, municipal, mixed (radioactive) or mixtures thereof). The water provides both atomic oxygen radicals and hydroxyl radicals which attack the organic molecules of the waste feed stream (2) that survive the flame environment, thereby essentially eliminating the organic products of incomplete combustion (PICs) that would otherwise result.

Inventors:
MALANCHUK, Myron HUFFMAN, George, L.
Application Number:
PCT/US1996/004942
Publication Date:
October 17, 1996
Filing Date:
April 10, 1996
Export Citation:
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Assignee:
ENVIRONMENTAL PROTECTION AGENCY.
International Classes:
F23G5/16; F23L7/00; (IPC1-7): F23G5/16; F23L7/00
Foreign References:
US4198384A1980-04-15
EP0541194A21993-05-12
EP0487052A21992-05-27
US4950309A1990-08-21
US3556024A1971-01-19
DE2950526A11981-06-19
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Claims:
WHAT IS CLAIMED IS:
1. A twostep method for destroying or eliminating the products of incomplete combustion that result from burning, combustion, incineration and thermal destruction of waste feed streams containing at least some halogenated organic feed material, said method comprising: (a) subjecting said waste feed streams to temperatures of from 10001500°C in a flame zone for at least one millisecond; and (b) treating the effluent from step (a) in a secondary zone at a temperature of from about 7001000°C for from one to four seconds by injecting water or water vapor at the point the effluent enters said secondary zone to quantitatively convert the halogen content of the halogenated organic feed material to hydrogen halide and to quantitatively convert the carbon content of the halogenated organic material to carbon dioxide.
2. The method according to claim l wherein the temperature of the secondary zone ranges from about 750850°C and the residence time of the waste feed stream in the secondary zone is about two seconds.
3. The method according to claim 1 wherein the products of incomplete combustion are halogenated hydrocarbons.
4. The method according to claim 3 wherein the halogenated hydrocarbons are chlorinated hydrocarbons.
5. The method according to claim 1 wherein the feed stream is a liquid or a solid and the water is injected directly into the feed stream.
6. The method according to claim 1 wherein the concentration of halogenated organic feed material is up to at least about 100,000 ppm of organic vapor.
7. The method according to claim 1 wherein said waste feed is selected from the group consisting of hazardous wastes, medical wastes, municipal wastes, radioactive wastes, and mixtures thereof.
Description:
ELIMINATION OF PRODUCTS OF INCOMPLETE COMBUSTION Field of the Invention

The present invention relates to methods for eliminating the products of incomplete combustion from incinerators and all types of combustion devices handling organic wastes. Backσrc""^ "f the Invention

Waste halogenated organic materials, such as halogenated organic residues from halogenation processes, have in the past presented a difficult disposal problem. These materials are toxic to plants and animals, so that they should not be dumped into rivers or lakes, nor should they be dumped onto land where the drainage therefrom would reach water used for drinking. Because these compounds contain a large amount of halogens, normal disposal in furnaces has heretofore been unsuitable because the materials either would not burn easily or the materials produced free halogens in the exit gases which corroded the equipment and contaminated the air.

Disposing of toxic materials in waste requires special treatment of the waste to ensure the effective destruction of all hazardous constituents, particularly halogenated hydrocarbons. High-temperature decomposition offers one way for destroying toxic organic constituents present in hazardous waste. Combustion includes not only a flame zone of very high temperatures (i.e., greater than 1000°C) , but also exposure to a non-flame or post- flame region of lower temperatures (e.g., less than about 850°C) for several seconds for the afterburner-bound effluent stream. The non- flame conditions also exist in pockets of unignited droplet material within the intermediate limits of the flame zone. Regulations set as a result of the Resource Conservation and Recovery Act (RCRA) of 1976 require that an incinerator attain a minimum of 99.99 percent destruction and removal efficiency for the principal organic hazardous constituent (POHC) compounds in the waste feed. A compound that has not been destroyed to that degree in the flame environment must then either undergo additional degradation in the post-flame region or removal, prior to its exiting in the combustion products sent to the open atmosphere.

During the thermal treatment of hazardous organic wastes, such as treatment by incineration, toxic compounds in the feed material are eliminated by decomposition and reaction with other components present in the thermal reactor atmosphere, principally oxygen. At high temperatures, large quantities of atomic oxygen radicals are produced by the dissociation of molecular bonds, not only of oxygen, but also of any water molecules present in the feed. Those radicals of oxygen, as well as radicals of other species which are simultaneously produced, represent a ready source of highly reactive elements that can act upon organic molecules or intermediate products resulting from the thermolysis of the feed organic constituents. Such thermolysis, if limited in intensity and in quantity, can and does produce some quantities of intermediate products of combustion which eventually escape the reaction zone as products of incomplete combustion (PICs) in the effluent emissions. These products are often highly toxic, and may be even more toxic than the organic compounds originally designated as hazardous components of the waste material.

Incineration most often includes a primary zone of exposure of the hazardous waste feed to temperatures as high as 1200-1500°C, for milliseconds of time, resulting in major destruction of the organic waste compounds, usually more than 99%. To meet the requirements of the Resource Conservation and Recovery Act regulations, incineration must destroy and remove 99.99% of the feed components designated as principal organic hazardous constituent. Therefore, further treatment is required. This further treatment may take place in a secondary zone, or post- flame zone, which is a region of lower temperatures, generally about 800°C or less, where a much longer exposure time of 1-2 seconds or more can achieve the additional destruction of the principal organic hazardous constituents that is required. At that point, the required degree of destruction of the principal organic hazardous constituents may have readily been met, while the level of the unregulated products of incomplete combustion may still be quite high. When the products of incomplete combustion

are identified, and their toxicity is known, the concentration of such products in the emissions to the open atmosphere could present an unacceptably hazardous contribution to the atmosphere. Methods and apparatus for increasing the efficiency of combustion of organic waste materials to reduce the amount of hazardous material in the ultimate products have been proposed.

Cull et al., in U.S. Patent No. 3,140,155, disclose a method for converting halogenated organic residue materials to hydrogen halides. The halogenated organic compounds are burned in a furnace at 900-1500°C in the presence of added sources of hydrogen and oxygen. The hydrogen source may be steam, hydrogen gas, hydrocarbon gas and mixtures thereof. If the organic residue contains sufficient burnable hydrogen, no additional hydrogen is needed. The oxygen may be derived from steam, air, oxygen and mixtures thereof. Cull et al. state that the method disclosed therein results in a product having "substantially no free carbon and free halogen and no organics." However, there is no indication that this process results in a gaseous product in which more than 99.99% of the hazardous material is removed or destroyed.

Woodland et al., in U.S. Patent No. 3,305,309, disclose a method for converting halogenated organic residue materials to hydrogen halide, which can be recovered. A halogenated organic material and a gaseous medium such as oxygen or hydrogen sources are mixed and passed through a constricted zone under pressure into an expanded zone to atomize the mixture. The atomized mixture is passed into a combustion zone to effect substantially complete conversion of the mixture to a product comprising carbon dioxide and a hydrogen halide. The temperature of the combustion zone is in the range of about 900 to 1300°C. Among the oxygen sources are air, oxygen and steam. Steam is used to add heat to the halogenated organic material. Woodland et al., require that the feed be atomized prior to combustion. This process requires the addition of special apparatus to atomize the chlorinated organic material with the hydrogen source, as

well as, ideally, a source of steam to be atomized with the product to be treated.

Brainerd et al., in U.S. Patent No. 2,803,669, disclose a method for reducing the chlorine or bromine content of halophenols by converting polyhalogenated phenols to halophenols of lower halogen content, and to converting monohalophenols to phenols. Vapor of a halogenated phenol is contacted with gaseous hydrogen and a solid catalyst of cuprous halide on porous activated alumina. The hydrogen may be generated by feeding methane and steam into the reaction zone to dehalogenate the halogenated phenol. This process requires the use of a catalyst to reduce the halogen content of the halophenols.

Tschantre, in U.S. Patent No. 4,100,255, discloses a method for combustion of refuse containing chlorinated hydrocarbons in which additional combustible substances may be introduced, such as residual oils, used crank-case oils, and the like. The gases resulting from combustion are then detoxified with quicklime, slaked lime, or burned magnesite. Tschantre assumes that combustion gases arising from the incineration of the chlorinated hydrocarbons will be kept separate from the combustion gases arising from the incineration of the refuse.

Evans, in U.S. Patent No. 4,400,936, discloses a method for disposing of polychlorinated biphenyl (PCB) waste liquids by blending the PCB with fuel and subjecting the mixture to combustion in a self-contained system. A gas scrubber or tower with packing material is provided for adsorbing contaminants. This process is limited to disposal of PCBs from waste liquids rather than to treatment of halogenated organic materials in general.

Gullett, in U.S. Patent No. 5,021,229, discloses a method for reducing the amount of chlorinated organics released to the atmosphere in incinerating wastes by injecting calcium-based sorbents into flue gas at around

700°C to react with HCl; the removal of HCl from the flue gas precludes the downstream formation of chlorinated organics. The sorbent materials, such as calcium oxide or calcium

hydroxide, reacts with HCl in the flue gas to form calcium chloride. This product diminishes the amount of chlorinated organics released to the atmosphere in incinerating wastes. This process deals with treating the effluent from municipal and industrial waste incinerators.

Schulz, in U.S. Patent No. 5,245,113, discloses a method for removal of PCBs or similar refractory organic substances from solid surfaces by volatilizing the PCBs from substrates contaminated therewith by contacting them with carrier gas such as a mixture of hydrogen, carbon monoxide and steam. The carrier gas and volatilized components are introduced into a partial oxidation zone of a gas generator where the PCBs are completely destroyed at a temperature range of 2800- 3500°F. Okazaki et al. , in U.S. Patent No. 5,118,492, disclose a process for the catalytic decomposition of chloro-fluoro alkanes (flons) into harmless substances by using a catalyst comprising iron oxide supported on active carbon at a temperature above 300°F in the presence of steam. In the presence of steam the flons react with water to form HCl, HF, C0 2 , CO, etc., as well as CX 3 C0X (where X is a halogen) in the case of flons having more than one carbon atom. The acids formed are absorbed and neutralized by alkalis such as calcium dihydroxide, sodium hydroxide, etc. This process requires the use of an iron oxide catalyst.

None of these processes addresses the problem of the refractory nature of the products of incomplete combustion that result from the thermal destruction of hazardous organic waste streams (products which themselves can be very toxic and represent a real hazard in the final effluent from the thermal destruction/combustion/incineration operation) . t.nτmτmτ-y pf the Invention

It is an object of the present invention to provide a method for virtually eliminating products of incomplete combustion.

It is another object of the present invention to protect the public health and environment from the threat of dangerous emissions generated during the combustion of

hazardous wastes.

• According to the present invention, water vapor is introduced into the gaseous effluent leaving a flame-zone of a combustor or thermal destructor which has been fed hazardous organic wastes. The water vapor provides both atomic oxygen radicals and hydroxyl radicals which initially attack the organic molecules which have survived the flame environment and thereby virtually eliminate the products of incomplete combustion which would otherwise emanate from the combustion operation.

The process of the present invention can be used regardless of whether destruction of the organic wastes is accomplished in a new or existing incinerator, boiler, cement or aggregate or rotary kiln, or any other type of combustor. By injecting water in the form of liquid or vapor into the feed stream, sufficient oxygen and hydroxyl radicals are provided to substantially eliminate all products of incomplete combustion (PICs) from the flue gas stream that leaves the combustor. The waste that is treated by the method of the present invention can be from any type of source, including hazardous waste, medical waste, municipal waste, mixed waste, radio active waste, etc.

The present invention is featured by way of example as in Figure 1, a schematic diagram of an incineration process or system for handling a feed of organic wastes which may contain highly toxic halogenated compounds. Figure 1, therefore, represents the embodiment of this invention.

The system is comprised of an incinerator or primary combustor (1) which provides a high temperature zone (about 1500°C) , called a "flame zone" (la) for the destruction of the principal organic hazardous constituents, (POHCs) present in the feed (2) . The high temperature is maintained by a regulated control of heat such as that produced by the combustion of an auxiliary fuel (3) entering in a stream along with the supply of combustion air (3a) .

The decomposition products and the PICs immediately enter a "post-flame zone" (4) of lower temperature, i.e.,

about 700-1000°C. The invention provides a port of entry (5) for steam to be injected into the gases exiting the flame- zone region. As the gases cool down, they decrease in volumetric rate of flow so that an extended reaction time of 2-4 seconds overall is obtained before the gases exit the secondary combustion zone (6) following the primary combustor.

A scrubber and/or other type of pollution control device (7) removes HCl from the flue gas exiting the combustion system. From the gas purification system, the effluent gas is sent to the stack (8) for venting to the atmosphere.

From the flue gas entering the stack, a probe adapted to handle the gases at the conditions that exist at that point provides a source of gas sample for the total hydrocarbon (THC) analyzer equipped with a flame ionization detector, FID (9) to provide continuous monitoring of the gases exiting the gas purification system. A gas chromatograph (not shown) is used on an intermittent basis to analyze the gas (sample) at the same point for a "fingerprint" of the composition of the gas. The total hydrocarbon (THC) analyzer (9) is used for the expeditious evaluation of both POHCs and PICs within the combustors at that time and provides an automatic feedback control of the rate of injection of water vapor at site (5) [or of liquid water at site (2)] . A steam generator is needed at those plants or facilities that do not have a ready supply of process steam.

The feedback control enables one to measure continuously the amount of organics entering the stack and, upon increase of the organics, automatically increases the water or water vapor (steam) to be injected into the reaction zones within the combustor(s) , thereby virtually eliminating products of incomplete combustion from the gas exiting the system and entering the environment.

The process of the present invention allows more precise control over the combustion process and more efficient operation, because the products of incomplete combustion are virtually eliminated. The feed requirements for the combustion apparatus are less selective. By using the

process of the present invention, in which water vapor is introduced into the combustion chamber, the combustion chamber can handle more diverse compositions of feed and still reduce and minimize the pollutants exiting from the combustor. No pure oxygen is required; the water vapor supplies all of the oxygen and hydroxyl radicals required for the effective destruction of the feed constituents. The lower operating temperatures of the post-flame zone can thereby be used to lessen the emissions emanating from the combustion operation.

The present invention provides a method for virtually eliminating the products of incomplete combustion as well as the principal organic hazardous constituents exiting a combustion process to a greater degree than has heretofore been possible. There is a direct response of water injection rate to the level of contaminants in the emissions from the flame zone. Brief Description of the Drawings

Figure 1 illustrates the method or process of the present invention (in schematic fashion) .

Figure 2 is a schematic of a thermal decomposition unit- gas chromatograph system.

Figure 3 is a bar graph of emissions from the thermal treatment of chlorinated methanes mixture vapor (Cl/H = 5:1) at t r = 2.0 sec. and Φ = 0.05 (where t r = residence time and Φ = the ratio of stoichiometric oxygen to the actual oxygen available) .

Figure 4 is a bar graph of emissions from the thermal treatment of a chlorinated methanes mixture vapor (Cl/H = 5:1) at t r =2.0 sec, Φ =0.95.

Figure 5 is a bar graph of emissions from the thermal treatment of a chlorinated methanes mixture vapor (Cl/H = 5:1) at t r =2.0 sec, Φ « ∞.

Figure 6 shows the thermal decomposition profiles of carbon tetrachloride for various atmospheres (or for various Φs) .

Figure 7 shows the total organic emissions from the thermal treatment of carbon tetrachloride (vapor feed,

nitrogen carrier gas, t r =2.0 sec).

Figure 8 shows the thermal decomposition profiles of the 5-component Mix #1 of the Combustion Research Facility (CRF) (pyrolysis, nitrogen carrier gas, Φ - ∞) . Figure 9 shows the thermal decomposition profiles of the 5-component CRF Mix #1(nitrogen carrier gas with water vapor, Φ •■ oo) .

Figure 10 shows the total organic emissions from the thermal treatment of the 5-component CRF Mix #1 (vapor feed, t r =2.0 sec) .

Detailed Description of the Invention

Introducing water vapor into the post-flame or flame- zone during the combustion of hazardous organic waste materials, as shown in Figure 1, provides atomic oxygen radicals and hydroxyl radicals for attacking the organic molecules which survive the flame environment. This greatly minimizes the products of incomplete combustion exiting from the combustor or thermal destructor.

The materials which may be converted by the process of the present invention are fluids, solids, and semisolids which are combustible in ordinary waste disposal incinerators, boilers, furnaces, or kilns, as well as highly halogenated organic residues which are normally difficult or impossible to decompose completely in ordinary waste disposal combustors. Examples of such materials are hexachlorocyclopentadiene, hexachlorobutadiene, octachlorocyclopentene, heptachlorocyclopentene, benzene hexachloride, the trichlorobenzenes, the tetrachlorobenzenes, the trichlorophenols, pentachlorophenol, monochlorotoluene, monochlorobenzyl chloride, chlorobenzoyl chlorides, chlorinated aliphatic acids, sulfur-containing chlorinated organics such as the chlorinated thiophenes and thiophene oxides, chlorinated lower aliphatics such as carbon tetrachloride, chloroform, trichloroethylene, perchloroethylene, hexachloroethane, tetrachloroethane, and the like, as well as the fluorinated, brominated and iodinated analogs of the above. In general, the requirement for the fluid-like materials which can be treated by the

process of the present invention is that they be obtainable in a sufficiently fluid form as to be pumpable.

The process of the present invention virtually eliminates the products of incomplete combustion by attacking these products with oxygen and hydroxyl radicals formed from water vapor. Since water vapor is a ready source of oxygen and hydroxyl radicals, there is a direct relationship between the rate of injection of water and to the level of contaminants in the emissions from the secondary combustor. The operating temperature can be lower than with previous systems for destroying halogenated organics. The feed requirements are also less selective, because the use of water vapor as a source of oxygen and hydroxyl radicals for all types of organics in the feed means that the process can handle diverse compositions of feed and still result in reduced levels of pollutants contained in effluent gases.

By using water vapor as a source of oxygen in addition to the oxygen contained in the combustion air, there is less need to introduce large quantities of excess air or oxygen into the combustion zone. Lower operating temperatures in the post-flame zone can be used to effectively destroy the organic emissions coming from the flame zone due to reactions that take place as a result of the increased amount of water present. According to the present invention, water in the form of vapor (steam) is injected into a gas stream of organic compounds as the stream exits the flame zone and before the stream enters into a secondary, "post-flame", zone, or water can be injected into the waste feed itself. Injection of this water provides oxygen and hydroxyl radicals which interact with the organic components of the gas stream and greatly reduces the level of products of incomplete combustion and principal organic hazardous constituents that may have escaped destruction in the flame (primary) zone, all at the relatively low temperature of about 800°C. The temperature of the gas steam into which the steam is injected generally ranges from about 700 - 1000°C.

With the ready availability of water and at the moderate

reaction temperature prevailing in the secondary zone, practically all of the organic compounds, both halogenated and non-halogenated, can be eliminated from the effluent leaving the secondary zone. Where required, an absorption unit can be used to remove the hydrogen compounds of the halogens resulting from the water vapor reactions before releasing the emissions to the open atmosphere.

After the combustion products leave the flame zone, they are combined with water vapor at a reactor or combustor temperature of from 700-1000°C for 1-4 seconds of residence time, at a gaseous concentration of up to about 100,000 ppm organic vapor. The preferred ranges of conditions are 750- 850°C for two seconds residence time with a gaseous concentration of about 1000 ppm. Analysis of Products

A laboratory unit, identified as the Thermal Decomposition Unit-Gas Chromatograph (TDU-GC) , was used to investigate key thermal decomposition factors in the post- flame zone such as temperature and oxygen/waste compound ratios, for their effect upon the effluent decomposition products. During the studies, it was discovered that high excesses of oxygen in the reactor atmosphere as well as quantitative levels of water vapor dramatically reduced the concentrations of various organic compounds that otherwise survived in large quantity through the high-temperature core the thermal reactor. Apparatus and Method for Tests

The TDU-GC apparatus shown schematically in Figure 2 comprised two basic sections: a thermal reactor for exposing the organic compounds of the feed to an elevated temperature, and an analyzer consisting of a gas chromatograph for separating, identifying and measuring the components in the effluent sample drawn directly from the reactor.

The thermal reactor comprised a capillary quartz tube (not shown) of 1.0 mm internal diameter and of sufficient length to provide residence time for the vaporized sample at a prevailing high temperature, within a practical working range of 1/2 to six seconds. The insertion chamber was

fitted with a probe to handle gas, liquid or solid samples. The liquid and solid organic samples were converted to vapors at elevated temperatures produced by a heating jacket. The vapor/gas was conveyed to the reactor by a controlled flow of carrier gas through a heated transfer line. The carrier gas for the feed sample passing through the thermal reactor was selected according to the nature of the atmosphere required in the high-temperature zone of the reactor.

For most runs, an organic vapor supply was prepared in a flask or cylinder which contained a measured amount of air (oxygen) to establish a definite organic/oxygen ratio. An aliquot of that vapor supply was withdrawn by a syringe for introduction into the insertion chamber of the TDU-GC system. The gaseous emissions from the reactor were sent through a heated tube to a collection trap just inside the wall of the gas chromatograph that was maintained at a sub-ambient temperature. Upon injection of the sample into the GC capillary column, as initiated by a switch on a computer, the temperature program for the capillary column controlled the separation of the components of the reactor emissions sample in the GC and their ensuing detection and measurement by the flame ionization detector.

The computer coupled with a recorder provided a means for storing the output of the flame ionization detector (FID) and depicting it in a chromatogram of component peaks on the recorder as well as in a tabulation/measurement of each peak area on the computer tapes.

The compounds tested were reagent grade material obtained either from a commercial supplier or from a quality control laboratory.

Additionally, the various organic compounds used in a calibration procedure to confirm the gas chromatograph retention time identities of solvent compounds and of product of incomplete combustion compounds were also reagent grade material obtained largely from a quality control laboratory. Cylinder gases of the highest purity (>99.999%) were used for transfer of the test gas/vapor through the reactor and for operation of the gas chromatograph. The gas transfer

lines from the nitrogen and helium supply cylinders were provided with gas purifier tubes to remove oxygen and water from the gases supplied to the reactor and the gas chromatograph. Initially, the parameters of atmosphere type, temperature level in the thermal reactor and mean residence time were selected and the necessary steps were taken to set those conditions. The temperature selected was adjusted by the controls on the furnace. A source of the carrier gas required for the reactor atmosphere was regulated by the instrument console control (switching and flow control valve) to provide the necessary flow rate for maintaining the selected residence time of the test gas sample in the high temperature zone of the furnace. The effluent collection trap in the walls of the gas chromatograph was cooled to the sub-ambient temperature selected as the starting point for the gas chromatograph analysis program. The sample was then introduced into the insertion chamber to be mixed in the gaseous state with the carrier gas. There followed a continuous transfer of the test sample (very short period for a gas; much longer for a solid which had to be vaporized) into the thermal reactor during the period of the temperature rise programmed for the insertion chamber. Following exposure of the feed stream to a set temperature at a controlled flow rate, the effluent products from the thermal reactor were collected in the cold trap located just inside the wall of the gas chromatograph which had been cooled to sub-ambient temperature to be used as the starting point for the analytical program. With switching of the carrier gas to helium, the gas chromatograph analysis step followed. The analysis was initiated by pressing the injection switch on the computer at the very same time that the start button of the gas chromatograph temperature programmer was depressed. A complete chromatogram of the product components as well as a tabulation of the component peaks (retention times and peak area counts and area percent) were obtained with the conclusion of the gas chromatograph analytical run.

The thermal exposure test runs made over a series of

temperatures provided data for a thermal decomposition profile of the principal organic hazardous constituents and formation- decomposition profiles for various products of incomplete combustion, within the temperature limits 5 investigated. Example 1

Chlorinated Methanes Mixture as the Feed The apparatus and method of operation described above were used in this series of test runs. 10. A comprehensive study of the thermal treatment of mixes of the four chlorinated methane homologs (methyl chloride, dichloromethane, chloroform, and carbon tetrachloride) demonstrated the strong effect of oxygen upon the thermolysis of the organic compounds. The study involved two different 15 degrees of chlorination in the feed (Cl/H ratios of 1:1 and

5:1) and three different levels (concentrations) of oxygen in the reactor atmosphere (equivalence, Φ, of 0.05, 0.95 and pyrolysis, Φ—∞, where Φ is the ratio of stoichiometric oxygen to the actual oxygen available for reaction with the 20 hydrocarbon compound to form C0 2 and H~0) .

The impact of oxygen in the reactor atmosphere is readily evident in the three bar graphs, Figures 3, 4 and 5, showing the cumulative amounts of the principal organic hazardous constituents (POHCs) and of the products of 25 incomplete combustion (PICs) added together to yield the sums of the total emissions measured by the flame ionization detector--those values being for the common feed Cl/H ratio of 5:1 and a reaction residence time of 2.0 seconds.

It was found that the products of incomplete combustion 30 that were produced accounted for the preponderance of the total emissions at the higher temperatures. A close examination of the cumulative values of the principal organic hazardous constituents at the various temperatures shows that the rate and extent of degradation of the POHCs were nearly 35 the same for all three equivalence conditions of oxygen concentration. However, because of the large production of products of incomplete combustion, the total emissions were mostly PICs at the higher temperatures (above 750°C) . Thus,

at 800°C, there was less than one percent of total principal organic hazardous constituents remaining when the Φ value was 0.05, and about 7.5 percent of equivalent products of incomplete combustion. There was as much as 58 percent of such products of incomplete combustion in the case where Φ was 0.95, and an even greater percent, 86 percent, for the pyrolytic condition in which Φ was approximately infinity. At the much higher temperature of 1000°C, there still was almost 12% of PICs for a Φ of 0.95 and as much as 57% for a Φ of oo. All of the products of incomplete combustion in the highly oxidative condition where Φ was 0.05 had been virtually eliminated at 1000°C, and at 950°C as well.

In industrial applications, the condition of availability of oxygen in the combustion atmosphere at the highly excessive rate defined by Φ=0.05 most likely would not be practical. However, the toxic nature of a particular feed material and of its products of incomplete combustion may justify the use of 100 percent or greater excess of oxygen, i.e., Φ > 0.5. In lieu of the oxygen available to the thermolysis process in the form of "free" (though volumimous) molecular oxygen in the atmosphere, other sources of oxygen may offer a practical alternative. For example, the oxygen in water (vapor) that is heated to the high temperature of a thermal reactor may be activated to the state of highly energized atomic radicals that would readily react with organic compounds to form non-toxic products. In addition, water also presents a source of hydrogen, which in its radical atomic form or in combination with oxygen to form hydroxyl radicals, could strongly react with highly chlorinated/halogenated compounds to render them and their products harmless or easily removable from the emissions. Carbon Tetrachloride as the Single-Component Feed The apparatus and method of operation described above and used in Example 1 were also used in this series of test runs.

Carbon tetrachloride was initially studied because carbon tetrachloride lacks the hydrogen component present in most hydrocarbon derivatives that could produce water

molecules by interaction with oxygen present in the reaction atmosphere. Also, carbon tetrachloride had shown itself in a laboratory study to be particularly difficult to decompose in a pyrolytic environment and it was intended to test the effect of water vapor in an oxygen-free (pyrolytic) atmosphere. The dry pyrolytic condition was repeated in a series that included three other reactor conditions as follows:

(a) dry air with a 100% excess of oxygen, Φ = 0.5; (b) pyrolysis, Φ - oo, but with water vapor added in a small excess above that needed for complete reaction of carbon tetrachloride according to the following equation:

CC1 4 + 21^0 > C0 2 + 4HC1;

(c) 100% excess of oxygen, Φ = 0.5, with water vapor added as in the pyrolysis case of (b) . The results of these four reactor conditions are presented in Figures 6 and 7.

Figure 6 shows the decomposition profiles of the principal organic hazardous constituent itself, i.e., of the carbon tetrachloride present in the feed. While some improvement over the pyrolysis case is shown for the 100% excess of oxygen, Φ = 0.5, there was a notably large improvement for the water vapor/ pyrolysis case. Thus, at 850°C there was no measurable amount (<0.01 mol %) of the principal organic hazardous constituent in the effluent for the water vapor case, whereas 2.5 to 3.5 percent remained in the dry air (Φ = 0.5) and the dry pyrolysis situations, respectively.

More noteworthy is the total emissions picture seen in Figure 7. While the destruction of the principal organic hazardous constituent (POHC) (Figure 6) reached a point of

0.6 mol% remaining at 1000°C for the pyrolysis case and about 0.1 mol% for the dry air (Φ = 0.5) case, the products of incomplete combustion (PICs) presented a more formidable problem. Figure 7 shows that as much as 40 percent of equivalent organics remain in the total emissions at 1000°C for the pyrolysis case and 6 percent for the dry air condition, with an overwhelming concentration of PICs persisting in the emissions. At 850°C, where there was only

one percent or less of total emissions, measured according to the area count of the chromatogram peaks, in the water vapor case, there was a very prominent 45 percent in the dry air case and a manifestly greater 76 percent in the pyrolysis case.

CRF Mix 81. Five Components as the Feed In this series of runs, the method and apparatus were the same as used in Examples 1 and 2.

The addition of water vapor to the reactor atmosphere was studied in a system that involved a mixture of five organic compounds. The feed, identified as CRF Mix #1, included:

Component Volume % in Mix

Monochlorobenzene, C 0 HjCl 17 Toluene, C 6 H 5 CH 3 48

Trichloroethylene, C 2 HC1 3 12

Carbon tetrachloride, CC1 4 11 Freon-113, C 2 C1 3 F 3 12

In an oxygen-deficient atmosphere, all five components appeared to be quite refractory, i.e., very difficult to decompose thermally. Under pyrolysis conditions, where Φ approaches infinity, the results expressed in the component decomposition profiles of Figure 8 showed monochlorobenzene to be the most refractory component, with nearly 22 percent still present in the emissions at a reactor temperature as high as 1000°C and a residence time of 2.0 seconds.

While Figure 9 shows the results obtained with a pyrolytic atmosphere (Φ «■ oo) that was "spiked" with water vapor, the decomposition profiles for each and every one of the five components of the feed were very nearly exact duplicates of the results obtained in an atmosphere that had the highly excessive concentration of oxygen of Φ = 0.05. It is quite evident from comparison of Figure 8 with Figure 9 that a remarkable reduction in the incinerabiltiy of the feed components was achieved by the very feasible introduction of readily available water vapor. It should be noted, however, that up to the temperature of 775°C, Freon- 113 remained just as refractory in the wet vapor-pyrolysis

environment as in the dry pyrolytic one. Beyond 775°C, some specific reaction mechanism in the water vapor atmosphere became effective in destroying the Freon-113 to levels as low as had already been reached by the other four components of the feed. In terms of the ultimate availability of hydrogen atoms to interact with chlorine atoms and form the highly stable hydrogen chloride (HCl) molecule, the conditions in the case of both atmospheres, dry and wet, at a time when Φ approached infinity, were the same, i.e., the same feed composition was used and exposed to the same range of temperatures.

The feed composition overall was close to an atomic ratio of 7 carbon: 7 hydrogen: 2 chlorine. Quantitatively, within the feed itself there were more than sufficient hydrogen atoms to meet the demand for combination with chlorine atoms for the facilitated production of HCl molecules. In that sense, the combination could occur in a pyrolytic environment that was dry, to the same extent as in one that contained abundant water vapor. Whatever intermediate compounds were formed were active agents capable of readily supporting the interaction between the hydrogen atoms and the chlorine atoms to form stable hydrogen chloride at the same time that simpler molecules of organic products were effected. While the four feed compounds in the CRF Mix ftl readily decomposed, the fifth, Freon-113, displayed a more refractory nature. The greater stability of the Freon-113 was due, in part, to the much higher bond dissociation energy of the fluorine atoms present in the molecular structure, and this stability persisted in spite of the more vulnerable associated chlorine atoms of significantly lower energy of bonding with the carbon atoms.

Irrespective of the reaction mechanisms that prevailed during thermal treatment of the organic compounds, the presence of substantial water vapor in the gas fed to the reactor resulted in very significant reduction and/or minimization of both the principal organic hazardous constituent material and the products of incomplete combustion as well.

Mechanisms of Reactions

A test series investigating the simpler, single- component feed of carbon tetrachloride offers a more favorable approach to understanding the impact of water vapor upon the thermolysis process. In terms of the final products of the global reaction, i.e., where carbon dioxide and water and hydrogen chloride/chlorine are considered ultimately to dominate the emissions, the following simplified equations are offered for the principal sets of reactor conditions studied:

CC1 4 > 2C1 2 + C (Pyrolysis)

CC1 4 + 0 2 > C0 2 + 2C1 2 (Oxygen present)

CC1 4 + 2H 2 0 > C0 2 + 4 HCl (Water present)

In addition to the products described above, intermediate products were observed, as represented by the peaks on the chromatograms at the various temperatures applied to the systems. In each of the three reaction systems cited above, considerable amounts of tetrachloroethylene, C_.C1 4) were generated. Along with the C 2 C1 4 were seen significant peaks for lighter (i.e., lower gas chromatograph retention time) molecules in the oxidative (oxygen) reactor condition, very little of the lighter but some definite amounts of heavier molecules in the water vapor condition, and much of the heavier molecules in the pyrolysis case. Based on those general results, it is projected that: (1) In all cases:

CC1 4 > :CC1 2 + 2C1

I C 2 C1 4 (2) In pyrolysis:

CC1 4 > : CC1 2 + 2C1

C 2 C1 4 > C 2 C1 6

( 3 ) With oxygen present : CC1 4 + 0 2 > : CC1 2 + 2C10

1 I C 2 C1 4 > 2 C0C1 2 + Cl 2

(4) With water vapor present:

CC1 4 + HOH > : CC1 2 + 2HC1 + 0

4 4 C 2 C14 > C 2 C1 4 0 Also, CC1 4 + 2HOH > C0 2 + 4HC1;

C 2 C1 4 + HOH > C 2 0C1 2 + 2HC1

C 2 C1 4 0 + HOH > C 2 C1 2 0 2 + 2HC1

The above equations are offered as probable mechanisms of reactions for the various products of incomplete combustion that were formed during the individual test runs. The examples support the general results that were observed, namely:

(1) Tetrachloroethylene, C 2 C1 4 , one of the several products of incomplete combustion identified in the reactor effluent, greatly dominated the organic composition of the emissions under all reactor conditions investigated in the test series with carbon tetrachloride, CC1 4 , as the single organic component in the feed.

(2) During dry pyrolysis, significant quantities of compounds "heavier" than CC1 4 and C 2 C1 4 were observed, as peaks of longer retention time in the gas chromatogram. An abundance of chlorine radicals contributed to the formation of perchlorinated compounds, even hexachlorobenzene, C 6 C1 6 .

(3) With a fairly large excess of oxygen, Φ = 0.5 (100% excess) , the oxygen radicals available in the reaction environment helped to readily form simple oxidation products and with their elimination, prevented the production of higher molecular weight carbon compounds. Also, because of the lack of sensitivity of the flame ionization detector (FID) for such compounds, products such as C0C1 2 were not readily measured. Even so, it is observed in Figures 6 and 7 that considerable total emissions as measured by the FID were present at the high temperatures, i.e., greater than 900°C.

(4) In the presence of water vapor, the chlorine atoms stripped off of the chlorinated molecule actively react with the hydrogen atoms supplied by the water to form the quite stable HCl that exited in the effluent gas. The greatly reduced quantity of C 2 C1 4 as compared to the amounts present

under the other reactor conditions was likely due to the ready production of hydrogen chloride from the initial CC1 4 principal organic hazardous constituent material as well as from the intermediate products of C 2 C1 and C 2 C1 4 0. (5) The difference in results for the different reactor conditions obtained from the single feed component of carbon tetrachloride can be extrapolated to similar reaction modes for the much more complex five-component CRF Mix #1. The general relationship of total emissions for the various reactor conditions appears very much alike for the five- component CRF Mix #1, Figure 10, as for the single-component CC1 4 , Figure 7. The mechanisms of reaction generally must be very similar. A major difference in the two series was that for the single-component CC1 4 case, a maximum of 10-12 products of incomplete combustion were detected and measured for any one test run, whereas for the five-component CRF Mix #1 as many as 130 component peaks were detected by the flame ionization detector (FID) during some temperature runs. Summation No catalysts are required for the decomposition of organic compounds according to the present invention. The only requirement the is introduction of water vapor at the entrance to the non-flame zone or environment of a combustion apparatus. Likewise, no sorbent is required to remove the hazardous chemicals, known as products of incomplete combustion (PICs) from the combustor effluent gas; the only product of the reaction which must be removed is hydrogen chloride or hydrogen halide (which is readily done by conventional scrubbing techniques) . The above results from a study of different reactor conditions used in the thermal treatment of a mixture of chlorinated organics found that the conditions of a high excess of oxygen and of water vapor in the reactor were beneficial when testing either a single-component organic feed or a multi-component organic mixture. Both of these reactor conditions were very favorable in destroying the feed (principal organic hazardous constituent) compounds as well as in minimizing the organic products of incomplete

combustion. The addition of adequate amounts of water vapor at the entrance to the non-flame zone or environment of the combustor offers a more feasible, more effective, and more practical way of destroying organic waste, particularly chlorinated compounds, than does a high excess of oxygen or air. Water or steam is easier to use, destroys trace organics better, and is more cost-effective (because of the large amount of nitrogen that accompanies the oxygen found in atmospheric air) . The foregoing description of the specific embodiments will so fully reveal the general nature of the invention that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and therefore such adaptations and modifications are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation. All references cited in this specification are hereby incorporated by reference.