Note: Descriptions are shown in the official language in which they were submitted.
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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).
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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.
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129E~l 6~
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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
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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
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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
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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
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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
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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
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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.
EXAMPLE 1
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-
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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.
S EXAMPLE 2
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.
EXAMPLE 3
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
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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.
