CA1298064C - Process for the thermal decomposition of toxic refractory organic substances - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Toxic refractory organic substances are decomposed by exposing them to an oxidizing medium and steam at a temperature in the range of 2500°F to 3200°F
for a period of 5 to 500 milliseconds in a reaction chamber. The toxic refractory organic substance can be dioxins, polyhalogenated biphenyls, organophosphates, halogenated biocides, waste streams from the production of said toxic substances, and mixtures thereof.

Description

1%g~

The present invention relates to a process for the therlmal decomposition of toxic refractory organic substances.

There are a number of toxic organic substances that are so resistant to both thermal degradation and biological degrada-tion that their improper disposal results in severe environmental pollution problems. These toxic organic substances usually un-dergo only partial destruction in conventional incinerators with the result that unreacted or partially oxidized toxic compounds are discharged with the stack gases into the atmosphere and may subsequently cause pollution of the air, soil, and waterways.

The U.S. Environmental Protection Agency has listed hundreds of toxic and hazardous organic substances that must be disposed of in an environmentally acceptable manner to safeguard the public health. These include such highly toxic chlorinated cyclic hydrocarbons as the dioxins and the polychlorinated biphenyls tPCB'S). They comprise a host of pesticides and pesticide residues, lncluding the carbamates and the organophos-phates. In addition, large quantities of chemical waste productsare produced in the course of the manufacture of organic chemi-cals and in the refining of crude oil. Thus, the refinery bottoms frequently contain carcinogenic poly-cyclics that must be safely destroyed.

Incineration has been a traditional mode of disposal.
However, there is an increasing awareness that conventional incineration frequently results in the emission of partial combustion or recombination products that constitute a serious air pollution hazard. The present invention affords an environ-mentally superior disposal means in that it assures quantitative destruction and produces no stack emissions whatever. In addition it converts the toxic or hazardous organic substances or waste materials into a clean, medium-sTu fuel or synthesis gas, that can readily be converted to methanol, high-octane gasoline, or natural gas (methane).

~b ~z~

According to the present invention there is provided a proc:ess for the noncatalytic decomposition of toxic refractory organic substances selected from the group consisting of halogenated organic biocides, organic organophosphates, waste streams from the production of said toxic substances, and mixtures thereof which comprises reacting a feed stream consisting essentially of combustible components including at least one of said toxic refractory organic substances with oxygen and steam at an autogenous temperature in the range of 2500F to 3200F for a period of 5 to 500 milliseconds in a refractory lined reaction chamber wherein the amounts of oxygen and steam supplied to the reaction zone are at least sufficient to convert all of the toxic refractory organic substances to gaseous reaction products comprising carbon monoxide and hydrogen, contacting said gaseous reaction products at a temperature in the range of 2500F to 3200F with an incandescent solid, and recovering a product gas comprising carbon monoxide and hydrogen substantially completely free from halogenated hydrocarbons.

Thus, the invention relates to a process for the decomposition of toxic organic substances that are unusually resistant to thermal degradation. The process for the destruction of toxic refractory organic substances may be superimposed on an efficient, energy-producing gasification process that operates at temperatures substantially higher than those of air-supported incinerators. In this way the quantitative thermal destruction of toxic refractory organic substances is accomplished at a negligible increase in the cost of producing a clean, medium BTU fuel or synthesis gas.

~.

129E~l 6~

- 2a -While the process of this invention can be used to destroy any organic substance that is resistant to thermal and biological degradation, it is of particular value in the destruction of those refractory organic substances that are toxic to living organisms and that when subjected to heating in conventional incinerators yield toxic degradation products that when released into the atmophere cause serious pollution 6Z.~

l2~sa64 problems. Such toxic materials include dioxins; poly-halogenated biphenyls; organophosphates, such as Parathion; halogenated biocides, such as hexachloro-benzene, Chlordane, DDT, and 2,4,5-trichlorophenoxy-acetic acid; and waste streams from the production ofthese toxic substances.
In the process of this invention, the toxic refractory organic substance is reacted with an oxidiz~
ing medium under conditions so controlled as to main-tain a flame or combustion temperature in the range of2500F to 3200F, preferably in the range of 2800F to 3100F, for a period of from 5 to 500 milliseconds in a reaction chamber that may have a refractory lining and that contains incandescent carbon or inc,andescent re-fractory oxides, such as alumina or zirconia. The hightemperature environment is created and maintained by the partial oxidation of the refractory organic sub-stance.
The refractory organic substance that is introduced into the combustion chamber may be a liquid, a gas, or a solution or suspension of a solid in a combustible organic liquid.
The oxidizing medium used in this process may be a gas, such as oxygen, oxygen-enriched air, or air that has been sufficiently preheated to sustain the desired flame temperature; or a liquid, such as nitro-gen tetroxide. It is preferably oxygen or oxygen-en-riched air.
Steam is fed to the gasification chamber to maintain the reaction temperature in the desired range, that is, between 2500F and 3200F, and to provide a reducing atmosphere beyond the partial combustion zone or flame.

12~9~

The amount of oxygen or other oxidizing medium that is fed into the reaction chamber is depen-dent upon such factors as the properties of the toxic refractory organic substance and the apparatus in which the degradation of ~he refractory substance is to be effected. Excellent results have been obtained using the amount of oxidizing medium that is required stoichiometrically for complete combustion of the re-fractory material as well as more or less than this amount. When the refractory substance is destroyed in a gasifier or in a combination of a torch and a gasifi-er, the amount of oxidizing medium used is that re-quired for the partial oxidation of the refractory substance and the gasification of the carbonaceous fuel so as to generate a temperature of at least 2500F.
The relative amounts of steam and oxidizing medium that are used are so regulated as to maintain the desired reaction temperature.
The mixture of partial and complete combustion products leaving the gasifier is passed through a heat exchanger for the recovery of heat and into a conventional scrubber for the removal of noxious inorganic decomposition products, such as hydrogen chloride, hydrogen sulfide, ammonia, or phosphine. The scrubbed product gas may be used as a synthesis gas or fuel. Any solid inorganic impurities introduced with the carbonaceous feed material may be withdrawn from the hearth of the gasifier in the form of a molten slag.
The process of ~his invention may be carried out in an~ suitable and convenient apparatus in which the refractory organic material can be exposed to an oxidizing medium and steam at a temperature in the range of 2500F to 3200F for a period of 5 to 500 lZ~ 4 milliseconds. It is preferably carried out in a torch, a slagging gasifier, or a combination thereof. For example, it may be carriéd out in an alumina-lined reaction chamber having inlets for steam and oxidizing medium; an oxypropane torch may be provided as a pilot light. The chamber may be fitted with zirconia cylin~
ders, bricks, rods, saddles, or bars. The thermal decomposition may also be carried out in a slagging, moving-burden gasifier, such as the gasifiers described in detail in U.S. Patent No. 4,340,397 and U.S. Patent No. 4,052,173; or in a combination of a refractory-lined torch feeding into a gasifier.
In one of the preferred embodiments of the invention, the refractory organic substance is intro-duced into a reaction chamber that is designed to pro-vide a residence time of 5 to 500 milliseconds wherein it is reacted with an oxidizing medium and steam at a temperature of 2500F to 3200F. The partial combus-tion products are then contacted with refractory inor-ganic surfaces that comprise the walls and internalpacking of the reaction chamber which have been heated to incandescence by the reaction products. Steam is fed to the partial combustion zone of the reaction chamber to maintain the temperature in the desired range and to provide a reducing atmosphere beyond this zone. The complete and partial combustion products leaving the reaction chamber are passed through a heat exchanger and into a scrubber. The scrubbed product which contains substantially no toxic compounds may be employed as a synthesis gas or fuel.
In another preferred embodiment of the invention, the process is carried out in an apparatus that comprises a slagging, moving-burden gasifier. The gasifier which is preferably of the type disclosed in 1~?8(~64 U.S. Patent No. 4,052,173 or U.S. Patent No. 4,340,397, and consist of a vertical shaft furnace surmounted by a conventional lock hopper. It may be operated at pressures of 1 to 100 atmospheres but is preferably operated at atmospheric pressure. The carbonaceous fuel that is intro-duced through the lock hopper may be, for example, anthracite coal, petroleum coke, metallurgical coke or wood char. An oxygen-rich gas and steam are fed to the hearth zone of the shaft furnace in a ratio so regulated as to maintain the hearth temperature in the range of 2500F to 3200F while at the same time a toxic refractory organic substance is introduced into the hearth zone.

When employing a gasifier of the type described in U.S. Patent No. 4,340,397, the raw gaseous products reaching the top of the gasifier are recycled to the partial combustion zone through an internal or external conduit by means of a steam jet. At the same time, at least a portion of the resultant tar-free gas leaving the partial combustion zone is withdrawn as product at a point below the pyrolysis and coking zone of the shaft furnace.

The toxic organic substance may be introduced to the partial combustion zone in the form of a liquid, a solution, a slurry or a vapor by means of a torch or tuyere which simultaneously admits the regulated flows of oxygen-rich gas and steam to form a flame. The resultant reaction products issuing from the flame are then brought ~n contact with a bed of incandescent coke or char and/or refractory oxide where they are further pyrolyzed and reduced so that all higher-boiling organic molecules are cracked to non-condensible gases, predominantly carbon monoxide, car-bon dioxide, hydrogen and methane. The flow of oxygenand steam may be so regulated that the consumption of the gravitating bed of metallurgical coke, petroleum coke, or char may be slow or rapid. In either case, the solid carbonaceous substrate will be maintained at incandescent heat by the upward flow of the partial combustion products.
The process of this invention is preferably carried out in a vertical shaft furnace, surmounted by a lock hopper through which the coke is admitted to the furnace. The torches or tuyeres through which the reactants are fed to the partial combustion zone are mounted just above the hearth floor of the furnace.
The hearth floor contains a taphole through which the molten slag resulting from inorganic components in the coke is continuously withdrawn into a connecting quench chamber in which the molten slag is quenched with wa-ter, and from which the fritted slag is withdrawn through a lock hopper.
The flows of reactants, and the flame temperature are so regulated as to secure destruction efficiencies of the toxic organic substances being processed of 99.9999% or better. Depending on the heat stability of the toxic organic substances being pro-cessed, a residence time in the range of 50 to 500 milliseconds is required.
In another embodiment, the destruction of the toxic organic substance by reaction with oxygen and steam may be carried out in a refractory-lined combus-tion chamber so designed that the partial combustion products issuing from the torch or tuyere are caused to traverse a checkerwork of inorganic refractory oxides 129~}64 such as alumina, silica, zirconia, or combinations of these. Again the residence time is controlled to as-sure destruction efficiencies of the toxic organic substances being processed of 99.9999% or better. In this embodiment, the need for consumable carbonaceous substrate is obviated. Upon issuing from the shaft furnace or the refractory-packed reaction chamber, the product gas is cooled by heat exchange in conventional equipment and then scrubbed in a venturi scrubber for the removal of liberated hydrogen chloride and other acidic impurities. The pH of the scrubber water is maintained on the alkaline side through the addition of a base such as milk of lime to insure the efficient removal of these liberated inorganic components. The scrubbed gas is then further treated for the removal of hydrogen sulfide, if sulfur is introduced with the toxic organic substance or with the carbonaceous sub-strate. The sulfur removal and recovery are accom-plished by well-known commercial processes.
The process of this invention employs a combination of high temperature chemical reactions that occur in parallel or in rapid sequence to produce fi-nally a product gas comprised of simple molecules such as hydrogen, carbon monoxide, methane, carbon dioxide, nitrogen, hydrogen chloride, and hydrogen sulfide. The noxious acidic gases are quantitatively removed from the product gas by well-established commercial process-es. The principal reactions occurring in the shaft furnace or the refractory packed reaction chamber in-clude the following:
1. C + 1/202 = CO

2. C + 2 C2 3. C2 + C = 2CO

4. C + H2O = CO + H2 ~zs~a~

5. CO + H2O = CO2 + H2 6. C 1 2H2 CH4 7- CO + 3H2 = CH4 + H20 8- 2CO + 2H2 = CH4 ~ 2 9. S + H2 = H2S
lO. RClx + nO2 + mH2O = xHCl + yCO + zH2 In a preferred embodiment, the reactions are carried out by injecting the toxic organic substances or waste products into the partial combustion zone of a refractory-lined shaft furnace through one or more tuyeres or torches that enter the shaft furnace just above the hearth floor of said shaft furnace. Each tuyere or torch is fed simultaneously with oxygen and steam so that a well-mixed stream of these three reac-tants is injected into the hearth section of the shaftfurnace to form a flame having a temperature in the range of 2500F to 3200F. The flame impinges upon a gravitating bed of incandescent coke or char which provides a strongly reducing atmosphere as well as active reaction sit-es which promote the further pyrolysis of partial combustion and decomposition prod-ucts. To the extent that there is any unreacted oxygen or steam present in the partial combustion products issuing from the flame, these will react with the in-candescent carbon according to reactions l and 4. Byincreasing the flow of oxygen and steam above that required to react with the toxic organic chemicals being processed, the consumption of coke may be arbi-trarily increased to augment the production of synthe-sis gas comprised principally of carbon monoxide andhydrogen. In operating the process, the ratio of oxy-gen to steam is so controlled that the desired flame or reaction temperature is maintained. The temperature may be observed through a view port built into each 1298(~64 tuyere. A recording pyrometer may be focused on the flame or the incandescent coke particles upon which it impinges. This reading may in turn be used to control the flow of oxygen, given a fixed flow rate of steam and toxic feed stream.
The shaft furnace may consist of a water-cooled steel shell lined with an acid-resistant refrac-tory. The furnace is surmounted by a lock hopper through which the coke or pe~roleum coke is fed to the furnace. The product gas is withdrawn through a heat exchanger to an alkaline scrubber to a convention gas clean-up train. There are no stacks associated with the operation of the shaft furnace, and the resultant product gas is scrubbed free of all air-polluting con-taminants, so that it may be used as fuel in a gasturbine or in a public utility boiler, where it burns as cleanly as natural gas.
The inorganic impurities or ash present in the carbonaceous substrate forms a molten slag which collects on the hearth floor from which it is continu-ously withdrawn through a tap hole and quenched in water. The resulting slag granules are withdrawn from the connecting quench vessel through a lock hopper.
In another embodiment the reactants may be introduced through tuyeres or torches mounted in the top head of a cylindrical combustion chamber to flow downwardly over a refractory structure or packing. The structure may be in the form of a brick checkerwork, vertically or horizontally mounted tubes or rods, a series of truncated cone-shaped baffles, or refractory saddles. The refractory lining and the packing materi-al are preferably of an acid resistant composition rich in alumina, silica, or zirconia. The free volume of the combustion chamber and the flow rates are so chosen 1298(~64 as to afford destruction efficiencies of the toxic organic substance being processed of 99,9999~ or bet-ter. This normally requires a residence time of 50 to 500 milliseconds.
After passing through the packed combustion chamber, the resultant product gas passes downwardly through a radiant cooling section into a convective heat exchanger and finally into an alkaline venturi scrubber.
This invention is further illustrated by the following examples.

The following procedure was carried out in a slagging, moving burden gasifier of the type that is disclosed in U.S. Patent No. 4,340,397. This gasifier is a vertical shaft furnace that comprises, successive-ly from top to bottom, a preheating and drying zone, a pyrolysis and coking zone, a high temperature reaction zone, and a partial combustion zone.
Sized coke was charged through a lock hopper on top of the gasifier and gasified by partially oxi-dizing it with oxygen in the presence of steam at a hearth temperature of 2900F to 3100F. This was ac-complished by controlling the amounts of oxygen and steam introduced into the partial combustion zone so that the exothermic partial combustion reaction was balanced by the endothermic watergas reaction.
When steady-state operation of the gasifier had been established, a hot stream of hexachlorobenzene dissolved in toluene was fed directly into the partial combustion zone at the rate of 500 kg/m2/hr.
The product gas issuing from the gasifier was analyzed for unreacted hexachlorobenzene and hydro-lZ9~ 4 gen chloride. These analyses, which were confirmed by gas chromatographic analysis of the off-gas, indicated that 99.99993% of the hexachlorobenzene had been de-stroyed.

The following procedure was carried out in an alumina-lined reaction chamber fitted with an inter-nal structure of zirconia rods, which was provided with a torch and a steam/oxygen tuyere. The chamber was sized to afford a residence time of the order of 100 milliseconds at the feed rates employed.
A 55% solution of Malathion (0,0-dimethyl dithiophosphate of diethyl mercaptosuccinate) in xylene was fed as fuel to the torch which used oxygen and steam as the reaction medium. The oxygen was fed in an amount that was less than the stoichiometric amount required for complete combustion of the Malathion solu-tion, and the steam flow was regulated to maintain the combustion temperature in the range of 2900F to 3100F.
The off-gas was quenched with a~ueous milk of lime in a spray scrubber to remove acidic decomposi-tion products.
Gas chromatographic analysis of the scrubbed gas indicated that 99.99992% of the Malathion had been destroyed.

The following procedure was carried out in a reaction chamber of the type described in Example 2 which fed into the high temperature reaction zone of a slagging, moving burden gasifier of the type disclosed in U.S. Patent No. 4,340,397 which is a vertical shaft 129~

furnace comprising successively from top to bottom, a preheating and drying zone, a pyrolysis and coking zone, a high temperature reaction zone, and a partial combustion zone.
Polychlorinated biphenyl (a mixture of tetrachlorobiphenyl isomers) was burned in the torch, which used oxygen and steam as the reaction medium.
Less than the stoichiometric amount of oxygen required for complete combustion of the polychlorinated biphenyl was fed to the torch. The steam flow was regulated to maintain the flame tempera-ture of the torch at about 3000F.
The combustion products issuing from the reaction chamber were brought into contact with the incandescent coke in the partial combustion and high temperature reaction zones of the gasifier. During this process, the partial combustion zone of the gas-ifier was maintained at about 2~00F. The residence time of the polychlorinated biphenyls in the torch and partial combustion zone of the gasifier was 50 to 100 milliseconds.
Analysis of the product gas issuing from the gasifier showed that 99.99998% of the polychlorinated biphenyls had been destroyed.

Claims (15)

1. A process for the noncatalytic decomposition of toxic refractory organic substances selected from the group consisting of halogenated organic biocides, organophosphates, waste streams from the production of said toxic substances, and mixtures thereof which comprises reacting a feed stream consisting essentially of combustible components including at least one of said toxic refractory organic substances with oxygen and steam at an autogenous temperature in the range of 2500°F to 3200°F for a period of 5 to 500 milliseconds in a refractory lined reaction chamber wherein the amounts of oxygen and steam supplied to the reaction zone are at least sufficient to convert all of the toxic refractory organic substances to gaseous reaction products comprising carbon monoxide and hydrogen, contacting said gaseous reaction products at a temperature in the range of 2500°F to 3200°F
with an incandescent solid, and recovering a product gas comprising carbon monoxide and hydrogen substantially completely free from halogenated hydrocarbons.

2. A process according to Claim 1 wherein the incandescent solid consists essentially of carbon.

3. A process according to Claim 1 wherein the toxic refractory organic substance is a halogenated biocide and the incandescent solid is coke.

4. A process according to Claim 1 wherein the toxic refractory organic substance is polychlorinated biphenyl.

5. A process according to Claim 4 wherein the refractory solid is coke.

6. A process according to Claim 1 wherein the toxic refractory organic substance is dioxin as a solution or suspension in a combustible organic liquid.

7. A process according to Claim 1 wherein the toxic refractory organic substance is hexachlorobenzene.

8. A process according to Claim 2 wherein the residence time in the reaction chamber prior to contact with incandescent carbon is in the range of 5 to 500 milliseconds.

9. A process according to Claim 1 wherein the incandescent solid consists of a checkerwork of shaped packing of refractory inorganic oxide.

10. A process according to Claim 1 wherein the amount of oxygen supplied to the reaction zone as free and combined oxygen is at least sufficient for conversion of all of the carbon in said toxic refractory organic substances feedstream to carbon monoxide.

11. A process according to Claim 1 wherein the amount of oxygen supplied to the reaction zone is that required stoichio-metrically for complete combustion of the toxic refractory organic substance.

:

12. A process according to Claim 1 wherein the feed stream of toxic refractory organic substances consists of a solution or suspension of O, O-dimethyl dithiophosphate of diethyl mercaptosuccinate (malathion) in a combustible organic liquid, the amount of oxygen supplied to the reaction chamber is less than the stoichiometric amount required for complete combustion of the feedstream, and the reaction zone temperature is in the range of 2900°F to 3100°F.

13. A process according to Claim 1 wherein said toxic refractory organic substance is parathion.

14. A process for the non-catalytic decomposition of incombus-tible toxic refractory organic substances selected from the group consisting of polyhalogenated hydrocarbons and organo-phosphates which comprises reacting a feed stream consisting essentially of the toxic refractory organic substance with oxygen and steam at a temperature in the range of 2500°F to 3200°F for 5 to 500 milliseconds in a refractory lined reaction chamber in the presence of sufficient hydrocarbon fuel to autogenously maintain said temperature wherein the amounts of oxygen and steam supplied to the reaction zone are at least sufficient to convert all of the toxic refrac-tory organic substance and hydrocarbon fuel to gaseous reaction products comprising carbon monoxide and hydrogen, contacting said gaseous reaction products at a temperature in the range of 2500°F to 3200°F with an incandescent solid, and recovering a product gas comprising carbon monoxide and hydrogen substantially completely free from toxic refractory organic substances.

15. A process for the decomposition of combustible toxic refractory halogenated organic biocides which comprises reacting a feed stream consisting essentially of at least one toxic refractory halogenated biocide with oxygen and steam at an autogenous temperature in the range of 2500°F to 3200°F for 5 to 500 milliseconds in a refractory lined reaction chamber wherein the amounts of oxygen and steam supplied to the reaction zone are at least sufficient to convert all of the toxic refractory halogenated biocide to gaseous reaction products comprising carbon monoxide and hydrogen, contacting said gaseous reaction products at a temperature in the range of 2500°F to 3200°F with an incandescent solid, and recovering a product gas comprising carbon monoxide and hydrogen substantially completely free from halogenated hydrocarbons.