Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~Z~73~3
MET~OD AND APP~R~TUS FOR THE DECOMPOSITION
OF H~Z~RDOUS MATERIALS AND THE LIKE
... . . .
This applieation is a division of eo-pendiny patent
applieation serial number 429,593 ~iled June 2, 1983.
B k~round of the Invention
The present invention relates generally to a
;method and apparatus for ~he decomposition of hazardous
materials, such as polychlorobiphenyls (PCBs) and th
like, and, more particularly, to such a method and
appara~us for the pyrolysis of PCBs and other such
hazardous materials utilizing a D.C. arc in a sealed
electric arc furnace.
Description of the Prior Art
Polychlorobiphenyl materials (PCBs) have been used
ex~ensively in the past in electrical equipment such as
transform~rs and capacicors, due in a large part to
their flame retardant characteristic, high temperature
stability, inertness to biodegradation and excellent
dielectric properties. Other uses in mining equipment,
hydraulic systems and heat transfer systems were
prompted by chese same properties.
In the nineteen sixties it was discovered that
PCBs were highly toxic snd the environmental impact of
PCB contamination received a great deal of coverage in
the public press. The fact that PCBs were found to be
c~rcinogenic in mice and are extremely stnble has
resulced in the enactment of legislstion severely
restrictillg the manufacturing, processing ~3nd sale of
PCBs. The storage nnd disposal of existing PCBs and
matcriAls concailling PCBs has nlso been the subject of
le~;isl.l~ioll, as well as reg~ cion by goverllmelltnl
a~;el~cie~, sllcll a~ ch~ Irl~iroll~ncnCal l'rotectioll A~ency.
38
--2--
Th~ exceptional chemical stability which makes PCBs
useful ~s a dielectric fluid and heat transfer agent
also makes it extremely difficult to destroy.
Four basic techniques have been previously
S developed for PCB disposal: landfill; chemic~l
destruction; biological destruction; and
incineration/pyroylsis.
The simplest and lowest cost technique used for
disposal of PCBs has been by landfill. However, at the
present time there is only a relatively small number of
landfill sites which have obtained the requisite
permits from the Environmental Protection Agency and
ot~er government agencies for receiving and disposing
of PCBs. In the present era of increasing public
awareness and with the existing regulatory struct~lre,
it is unlikely that a significant number of new
landfill sites will be approved for disposal of PCBs.
In addition, the existing ~overnmental regulations only
permit the disposal of solid materials contaminated by
PCBs at landfill sites (liquid PCBs must be
incinerated), thereby necessitating the prior draining,
flushing and stora~e of all liquid PCBs. Thus, it is
clear that the disposal of PCBs utilizing landfill
sites is not a viable final solution to the PCB
disposal problem.
Various chemicsl treatment processes have
reportedly been successfully used for the destruction
of small quantities of PCBs in the lnboratory. One
such technique involves the treatment of PCBs with
alkaline 2-propanol solution followed by exposing the
resulting material to ultraviolet light for a
predetermined period of time. Another such chemical
treatment technique involves t~le atepwise removal of
~2~738
electrons from the aromatic ring sys~em of the PCBs,
followed by hydrolysis, solvolysis, oxida~ive coupling
and dimerization utilizing high anodic potentials in
acetonitrile.
While the above-described chemical treatment
process, as well as other chemical treatment processes,
have achieved some success in the decomposition of
PCBs, the techniques have only been employed in
connection with very small quant.ities of PCBs. These
chemical treatment processes would be cumbersome and
extremely expensive to employ in connection with the
decomposition of large quantities of PCBs. In
ad:dition, some of the chemical treatment processes have
resulted in the generation of haæardous by-products,
which require additional special handling and
destruction.
Although PCBs are generally thought to be
extremely resistant to biological or enzyme attnck,
recent studies have shown that some PCBs are degradable
. 20 by certain strains of bacteria and soil fungus. One
such technique involves the use of acromasacter (two
species) pseudomonas sp, acinetrobacter sp strain
y42+33, and acinecobacter sp strain P6 ~o oxidatively
degrade PCBs to chlorobenzoic acids. A second
technique as described in U.S. Patent No. 3,779,866
employs strains of caldosporium cladosporicides,
candidelipoly~ice, nocardia globerola, nocardia rubra
and/or saccharomyces cerevisiae to totally destroy
PCBs.
Again, while the above~described and other
biological techniques have nchieved some success in the
destruction of Pcss in limited quantities, none of
these biological tcchlliques have offered a solution to
7313
~he disposal of large ~uantities of PCBs in an
environmentally sound manner at n reasonable cost.
In regard to incineration of PCBs, it has been
found that PCBs have high thermal stability and
generally require combustion telnperatures on the order
of 1600C for total destruction. Although numerous
prior art attempts have been made to develop a method
or system for the incineration of PCBs utilizing
different variations of conventional combustion
techniques, the prior art methods and processes for the
most part have been unsuccessu] primarily due to the
extreme difficulty involved in maintaining the required
1~00C temperature. The failure to maintain the
requisite temperature generally results in an
incomplete destruction of the PCBs and may result in
the generation of even more toxic by-product materials,
such as hexachlorobenzene or polychlorinated
dibenzo~urans. In addition, the prior art
i~ineration/pyroloysis methods were primarily used for
the destruction of liquid PCBs due to difficulties in
employing such methods in connection with solids.
Furthermore, the prior art techniques resulted in the
~eneration of large volumes of gas which had to be
collected and scrubbed to remove various impurities
2S therefrom.
The present invention was developed to overcome
various problems associated with a number of prior art
destruction processes. More specifically, the present
invention comprises a method and apparatus for the
destruction of PCBs and other hazardous materials
u~ilizing a totally sealed system, which includes a
high current DC arc for maintaining a temperature
considerflbly in excess of 1600C ~nd for providin~
~Z~L738
bond-breaking ultraviolet and other radiation. The use of the DC arc nssures
that the original PCBs are decomposed into relatively harmless gaseous
components and that no dangerous intermediate chemicals remain in the exhaust
gas. The system of the present invention is capable of effective
decomposition of both solid and liquid PCBs and, due to the lack of oxygen or
other atmospheric gases present in the sealed system, the need for excessive
containment and scrubbing equipment for the exhaust gases is effectively
reduced.
Summary of the Invention
Briefly stated, the present invention provides an apparatus for the
decomposition of hazardous mat0rial utilizing a DC arc, comprising:
. a gas-tight ch~mber including a sump which contains a molten bath;
inlet means for introducing the ha%ardous material into the chamber
and the molten bath for initial decomposition of the hazardous material into a
product within the molten bath and a gaseous product within the chamber,
wherein the inlet means comprises a multi-sealed passage having Q closable
entry port for access outside the chamber and a closable exit port providing
communication inside the chamber, the passage further including closable
partition means between the entry port and the exit port for dividing the
passage into a first compartment adjacent the entry port and a second
compartment adjacent the exit port, the sealed passage operating such that
hazardous material is introduced into the first compartment with the partition
means closed, the hazardous material passing from the first compartment into
the second compartment through the partition means with the entry port and the
exit port closed, and the hazardous material passing from the second
compartment into the chamber through the exit port with the partition means
closed;
electrode means for maintainin~ a DC arc within the chamber, the arc
having a current level sufficient to promote the decomposition of the
hazardous material; and
exhaust means within the chamber proximate to the DC arc for the
removal of gnses from the chamber, whereby the gaseous product passes in the
73~
proximity of the arc for undergoing decomposition prior to removal thereof
through the exhaust means.
In another aspect, the invention provides an apparatus for the
decomposition of haæardous material utilizing a DC arc, comprising:
a gas-tight chamber including a sump which contains a molten bath;
inlet means for introducing the hazardous material into the chamber
and the molten bath for initial decomposition of the hazardous material into a
product within the molten bath and a gaseous product within the chamber,
wherein the inlet means comprises a sealable passage having a closable entry
port for access outside the chamber and a closable exit port providing
communication inside the chamber, and puncturin~ means within the passage for
puncturing containers with hazardous material therein;
electrode means for maintaining a DC arc within the chamber, the arc
having a current level sufficient to promote the decomposition of the
ha~ardous mater;al;
exhaust means within the chamber proximate to the DC arc for the
removal of gases from the chamber, whereby the ~aseous product passes in the
proximity of the arc for undergoing decomposition prior to removal thereof
through the exhaust meQns.
srief Description of the Drawin~s
The foregoing summary, as well as the following detailed description of a
preferred embodiment and
~Z~73~3
several alterna~e embodiments of the present invention,
will be better understood when read in conjunction with
the appended drawings, in which:
Fig. 1 is a schematic elevational view, partially
in section, of a preferred embodiment of an appartaus
for the decomposition of ha~ardous material in
accordance with the present invention;
Fig. 2 is a schematic elevational view, partially
in section, of an alternate embodiment of the apparatus
of Fig. l;
Fig. 3 is a fragmentary schematic sectional view
showing a variation of a portion of the apparatus of
Fig~ 2;
Fig. 4 ;s a fragmentary schematic sectional view
showing a different variation of the apparatus of Fig.
2; and
Fig. 5 is a schematic view of a pressure relief
system employed in connection with the apparatus of
Fi~s. 1 or 2.
Description of the Preferred and Alternate
Embodiments
Referring to Fig. 1, there is shown a schematic
view of an apparatus or pyrolytic furnace indicated
generally as 10, for the decomposition of liquid, solid
or gaseous hazardous materials or any combination
thereof, such as polychlorobiphenyls (PCBs)~ PCB
contaminated liquids and solids and the like, into
innocuous gases by pyrolysis employing a D.C. arc. It
ha-s been found that by subjecting PCBs and PCB
contaminated liquids and solids to a two-step process
in which they are initially exposed to a high
cemperature (such as in a molten bath) to promote
~L2~'738
--7--
initial decomposition into a gaseous product and then
eXposing the gaseous product to a high current, high
temperature D.C. arc, the resulting gaseous product
produced comprises C0, C02, H2, CH4 and HCl.
The furnace 10 compr;ses, in this embodimen~, a
generally cylindrical housing 12 having an outer
con~ainmen~ shell 14, which may be comprised of steel
or any o~her similar electrically conductive structural
material, and an inner refractory lining 16, which may
be comprised of any suitable known electrically
conductive furnace lining material, Çor example,
graphite. Because of the high temperatures and
pressures involved in the decomposition process
conducted within the furnace 10, the outer shell 14
and/or ~he inner lining 16 must be capable o~
withstanding an interior pressure of five atmosphere
and may be cooled in any conventional manner, for
example, by circulating cooling ~luid (s~lch as water)
through fluid passages (not shown) which may be
embedded within or adjacent to the outer shell 14
and/or the inne~ lining 16.
Due to the hazardous nature of the PCBs and other
materials which are to be decomposed within the furnsce
10, it is important that the ~urnace 10 be carefully
constructed ~o maintain a completely gas-tight chamber
18 within which the decomposition takes place.
Suitable seals (not shown) are employed where required
to main~ain the chamber 18 in a gas-tight condition.
I~ this Inanner, leakage of unreacted or partially
decomposed toxic gases into the a~mosphere can be
avoided. In addition, in the gas-tight chamber, the
presence of oxy~en in the furnace 10 can be avoided to
thereby provide a reducing environment wllich per;nits
.,
738
the use of unconventional lining material ~such as
graphite which would quickly deteriorate from burning
in the presence of oxygen) for the furnace 10.
The lower portion of the furnace 10 forms an
S annular sump 20 within the chamber 18. The sump 20 has
maintained therein a molten bath 22 comprised of
metals, salts or any other suitable material which, in
its molten state, is a good electrical conductor. The
molten bath 22 serves to promote the initial
decomposition or volitization of the PCBs and other
hazardous materials, which may be introduced into the
furnace 10, into a gaseous product which is liberated
i~to the chamber 18 above the molten bath 22. In
addition, the molten bath 22 serves to melt or
decompose any other organic or inorganic materials
which may be introduced into the furnace and remain in
the molten bath. Such organic or inorganic materials
may include, for example~ the metal, plastic or
cellulose packaging materials which were employed to
contain the PCBs. It is considered necessary to
destroy such container materials since, due to their
`prior contact with the PCBs, they are also considered
to be hazardous.
As will here;nafter be described in more detail,
the temperature of the molten bath 22 is maintained at
a level commensurate with the volitization temperature
of che particular hazardous material being decomposed.
For example, when PCBs are being decomposed, the
temperature level of the molten bath may be on the
order of 1500C, which is lower than the temperature
for complete destruction of PCBs in the prior art, but
lower temperatures are possible in the present system
~Z~17313
due to the use of the arc which significantly aids the
destruction process.
The furnace 10 includes inlet means, shown
generally as 24, for charging or introducing the
S hazardous material from the outside of the housing 12
into the chamber 18. The inlet means 24 comprises a
plurality of individual charging ports positioned at
various locations around the circumference of the
housing 12. By po~itioning the charging ports around
the circumference of the housing 12, the PCBs or other
hazardous material may be immersed into different areas
of the molten bath 22 (perhaps sequentially) ~o thereby
prevent excessive localized cooling of the molten bath
22 which may occur if only a single charging port is
employed. The charging ports must be capable of
introducing PCBs or other hazardous material into the
r~ chamber 18 while maintaining a generally gas-tight
system. In this manner, the furnace 10 has the
capability of operating batch (one charge of hazardous
material at a time) or operating continuously
(continuous addition of hazardous material).
In the present embodiment, two differPnt types of
charging ports 26 and 28 are shown and will hereinafter
be described in some detail. Furnace 10 may include
one or more of each type of the chargin~ ports 26 and
28 or may include one type of charging port or ports.
Charging ports 26 and 28, which each comprise a two
stage air-lock arran~ement, are but two examples of the
ty~es of charging ports which may be employed for
introducing ha~ardous material into the chamber 18.
Therefore, it should be appreciated that the present
invention is not limited to the specific type or
-10-
combination of charging ports disclosed bu~ could
employed any other suitable type or combination of
inlet means which allows for introduction of hazardous
material into the furnace 10 while effectively
S maintaining the chamber 18 in a gas-tight condition to
prevent the escape of any toxic or otherwise hazardous
gas.
Charging port 26 is particularly suited for
introducing, for exa~ple, capacitors designated 29 into
the furnace 10. Capacitors 29 of the type shown may
comprise ceramic, cellulose plastic metal and some form
of generally sealed metalic outer container which
enclose (sometimes under pressure) liquid PCBs as a
dielectric element. Both the PCBs within ~he container
and the container itself must be disposed of as
hazardous materials. The charging port 26 comprises a
:; sealed (gas-tigh~) generally tubular passage 30 having
an entry port 32 on a first or outer end and an exit
pQr~ 34 on the second or inner end. The sealed passage
30 further includes a closable parcition means 36
positioned approximatley halfway between the entry port
32 and ~he exit port 34 to divide the sealed passage
into a first outer compartment 38 adjacent to the entry
port 32 and a s~cond inner compartment 40 adjacent to
the exit port 34. Each of the ports 32 and 34 and
partition 36 are adapted to open and close
independently of each other and to provide tight seals
when closed, so that the charging port 26 has the
c~`pability of continuously charging or introducing
material into the furnace 10 while continuing to
maintain the gas-tight condition of the chamber 18.
In the operation of the inlet device 26, the ports
32 and 34 and partition 36 are initially closed as
sbown. The entry port 32 is then opened and capacitor
29, or other solid or liquid hazardous material to be
decomposed or destroyed, is admitted or inserted into
the first compartment 38 as shown. The entry port 32
is then closed and the first compartment 38 is
evacuated (employing any known suitable means) to
prevent the introduction of oxygen into the chamber 18.
Thereafter, the partition 36 is opened and the
capa~itor 29 is passed from the first compartment 38
into the second compartment 40. In the embodiment
shown on Figo 1, the tubular passage 30 slopes
slightly downwardly so that the capacitor 29 may sîmply
s~ide or roll downwardly from the first co~partment 38
through ~he partition 36 ~o the second compartment 40.
Alternatively, any other suitable means could be
employed for moving the capacitor 29 from ~he first
compartment 38 to the second compartment 40, such as a
push rod (not shown) or a conveyor belt (not shown).
~ Once the capacitor 29 is positioned within the
second compartment 40, the partition 36 is again closed
and the first compartment 38 is evacuated to prevent
the escape (to the atmosphere) of any toxic gas when
the entry port 32 is opened again. The exit port 34 ~s
then opened and the capacitor 29 passes from the second
compartment 40 along the downwardly sloping passage 30
and into the molten bath 22~ As previously mentioned,
any other suitable means may be employed for moving the
capacitor 29 from the second compartment 40 into the
molten bath 22.
While in some cases it is desirable to have entire
capacitors inserted directly into the molten bath 22 as
described above, in other cases this is not an
acceptable procedure. secause of the size and
construction of some capacitors, and particularly large
p~essure sealed capacitors, the immersion of the er.tire
capacitor directly into the molten bath 22 would result
in R build-up in pressure within the capacitor and
5 eventually a violent or uncontrolled explosion which
may result in potential damage to the furnace. In
order to alleviate the potential explosion hazard, the
second compartment 40 may include suitable means 42,
for example the multi-pronged "iron maiden" shown in
10 Figo 1, for puncturing and/or crushing the capacitor 29
in order to prevent the formation of excessive
pressure. In addition, by puncturing or crushing the
capacitor 29 in this manner, the liquid PCBs within the
capacitor 29 are permitted to drain from the capacitor
15 container.
The lower end of the second compartment 40
g includes an opening into a conduit means or drain pipe
44 which communicates with the interior of the chamber
18 as shown. The drain pipe 44 receives liquid PCBs
20 from the punctured or crushed capacitor 29 and allows
liquid PCBs to flow into the molten bath 22. The
liquid PCBs may be preheated utilizing waste heat from
the furnace 10 (not shown) prior to their entering ~he
molten bath 22. A suitable valve means 46, which may
25 be provided by any suitable known control valve, may be
installed within the drain pipe 44 in order to restrict
and control the flow of liquid PCBs into the molten
bath 22. In addition, the liquid PCBs may be
pr~essurized, atomized and sprayed (not shown) against
30 the surface of the molten bath 22 to provide more
intimate contact between the PCBs and the molten bath
and to avoid localized cooling of the bath.
As discusscd briefly above, each of the
compartments 38 and 40 of tlle charging por~ 26 also
~ -13-
includes a suitable evacuation system (not shown) for
removing any ~ses which may enter ei~her compartment
from the chamber 18 or from the a~mosphere. The
evacuated gas from the compartments 38 and 40 is
preferably recycled back into the chamber 18 by any
suitable means (not shown) to provide for the
processing of any hazardous gas which may be present.
Such an evacuation system may be of any suitable known
type and need not be described in detail for a complete
understanding of the present invention.
Charging port 28 is similar to charging port 26,
in that, it comprises a generally tubular sealed
(gas-tight) passage 48 having an entry port 50, an exit
port 52 and a partition means S4 to divide the passage
48 into a first outer compartmen~ 56 and a second inner
compartment 58. Both of the compartments 56 and 58
include an evacuation system (not shown) for the
purposes described in connection wi~h charging port 26.
}lowever, unlike charging port 26, the second
compartment 58 of charging port 28 includes a
conventional motor driven screw conveyor or auger 60.
The screw conveyor 60 transports the PCBs and the PCB
containers received within compartment 58 to the exit
port 52 and for the reasons as stated above, punctures
or c~ushes the capacitors or containers.
The second compartment 58 of the inlet device 28
also includes a conduit means or drain pipe 62 for
conveying the li~uid PCBs from punctured capacitors
(not shown) within the second compartment 58 to the
molten bath 22. However, unlilce the prèviously
discussed arrangemcnt of drain pipe 44, drain pipe 62
empties directly into the molten bath 22 below the
surface tllereof. ~ ~suit~ble pump 64 is employed to
provide cnough plcssurc to "bubblc" thc liquid PCBs
~Z1~38
-14-
directly into the molten bath 22 as well as to control
the flow rate of liq~id PCBs into the bath.
As discussed above, the immersion of the PCBs into
the high temperature molten bath 22 results in the
S decomposition of the PCBs into gases which remain
within the chamber 18 above the molten bath 22. As the
gases come into contact with the high temperature upper
surface of the molten bath 22, the chemical bonds are
further broken. By controlling the quantity of PCBs
which are immersed into the molten bath 22 (i.e.,
through the use of valve 46 and pump 64), the quantity
of the gases subsequently released into the chamber 18
and thus, the gas pressure within the chamber 18, may
be controlled. The housing 12 should be strong enough
lS to withstand a gas pressure of five atmospheres within
the chamber 18 with no uncontrolled leakage of gas to
the atmosphere.
The furnace 10 also includes electrode means,
generally designated 66, for maintaining a direct
current (DC) electric arc within the chamber 18. The
electrode means 66 comprises in part an elongated
tubular electrode 68 movably mounted to the furnace
cover 70. The electrode 68 is moved vertically with
respect to the molten bath 22 for the purpose of
establishing and maintaining ~he desired elec~rical arc
(shown generally as 72) extending from the arcing tip
82 to the molten bath 22. Any suitable means may be
employed for the vertical movement of the electrode 68.
For example, a rack 74 may be fixed to the electrode
and a suitable pair of motor-driven pinions 76 may be
employed to engage the electrode rack 74 for movement
thereof in either vertical direction.
.
73~
The furnace 10 also includes exhaust means,
generally designated 78, for the removal o gases from
the gas-tight chamber 18. In the present embodiment,
the exhaust means 78 comprises the hollow interior of
the tubular electrode 68 which communicates with a
suitable exhaust conduit 80 extending throu~h the
furnace cover 70 to atmosphere. ~oweYer, it should be
appreciated that any other suitable exhaust means
(other than the hollow inter;or of the tubular
electrode 68) could be employed for the removal of
gases from the chamber 18. The only requirement for
the exhaust means 78 is that its entrance be loca~ed
proximate to the ~rcing tip 82 of the electrode 68, so
that all of the gases within the chamber 18 must pass
near or through the arc 72 before being exhausted from
the furnace 10.
The exhaust gas removed from the furnace lO may be
received snd stor~d in suitable containers (not shown)
f~r testing and analysis. If the analyzed gas is found
to be clean enough to comply with existing regulations
or standards, it may be exhausted directly to the
atmosphere. If the analyzed gas is found to be of
unacceptable quality, it may be further processed by a
suitable device such as a bubble tank (not shown) or a
scrubb~r (not shown). An exit gas afterburner (not
shown) may also be employed. In the event that the
exhaust gas from the furnace still contains toxic or
other hazardous material, the gas may be recycled by
any suitable means (not shown) back into the chamber l~
for further processing relative to the electric arc.
Suitable heat exchange means (not shown) may be
provided to lower the temperature of the exhaust gases
from the furnace and to rec1aim or recycle the
recovered therma1 energy.
73~3
-16-
In order to provide a subs~antially continuous DC
arc within the chamber 18 be~ween the arcing tip 82 of
the electrode 68 and the molten bath 22, the outer
shell 14 of the furnace is connected to ground (not
shown) and the electrode is connected to a suitable low
voltage, solid state DC current supply (not shown).
Preferably, the DC current supply is so poled that the
electrode 68 is negative with respect to the outer
shell 1~. The conductive inner lining 16 ~nd the
conductive molten bath 22 are also maintained at ground
potential. Thus, the electrode 68 constitutes the
negative terminal and the molten bath 22 constitutes
the positive terminal of a DC load circuit. As shown,
the two terminsls (the electrode 68 and the molten bath
22) are spaced apart in operation to provide between
them an arc gap of a predetermined distance in which
.~ the arc 72 exists when the circuit is energized. A
current regulator (not shown) m~y be provided to
maintain a substantially constant predetermined arc
level as required for the desired decomposition of the
hazardous material being processed. Arc voltage
sensing equipment (not shown) rnay also be employed to
compare the arc voltage with a preset reference for
comparison and arc length control. A DC choke coil
(not shown) may also be connected in series with the DC
arc current path in order to prevent arc extinction due
to any sudden rise in arc vol~age, any sudden cooling
of the arc due to endothermic chemical reactions, or to
tr.ansient gas pressures which occur during PCB
decomposition.
The arc 72 provides the primary heat to initially
melt and thereafter maintain the material within the
sump in the molten state. The arc 72 also serves as a
source o~ radiation, or example, ultraviolet
-17-
radiation, which assists in bresking the bonds of the
PCBs. In addition, the extreme high temperature of the
arc (10,000C or higher) assures that the gases and any
previously non-decomposed material passing through or
S near the arc toward the exhaust means 78 ~re completely
decomposed into the above-described generally innocuous
gaseous elements.
In order to further insure that the gases from the
chamber 18 obeain maximum exposure to the arc for
complete decomposition, the furnace 10 also includes
means, generally designated 84, for rapidly and
uniformly moving the arc 72 in a predetermined path
around the surface of the arcing tip 82 of the
el~ctrode 68. The rapid rotation of the arc 72 around
the arcing tip 82 also provides a more uniform
distribution of heat to the molten bath 22 and
processing in the chamber 18 which tends to preserve
the inner lining 16. The rotating arc also puts
pressure on the molten bath material where the arc hits
the molten bath 22, this together with the high
temperature of the arc causes the material to boil and
form an indentation in molten bath material. The
rotation of the arc around the arcing tip 82 may be so
fast that the indentation may not be refilled, and high
temperature boiling materiAl is spewed out in the
vicini~y of the indentation. The gases passing
proximate the arc are contacted by the heat and the
super heated bath material to aid in decomposition.
In the present embodiment, the means for moving
the arc around the surfsce of the arcing tip 82 of the
tubular electrode 68 comprises magnetic me~ns in the
form of an annular electromagnetic coil 86 positioned
within the housing 12 beneath the arcing ~ip 82. The
eleccroma~entic coil 86 is connected to a ~suit~ble DC
73i~
-18-
voltage source (not shown) to generate a ma~netic field
having flux lines (not shown) extending generally
perpendicular to the arc 72. In this manner,
well-known magnetohydrodynamics principles are employed
S to move the arc 72 around the surface of the arcing tip
82. The rate of movement of the arc around the arcing
tip 82 is controlled by controlling the location of the
electromagnetic coil 86 and the intensity and
orientacion of the magnetic field generated by the coil
86. The magne~ic field also serves to stir the molten
bath 22 to provide more complete mixing of the molten
bath ma~erial and the hazardous materials which are
being decomposed. In this manner, the upper su~face of
t~e mol~en bath 22 is kept in condition to receive and
react with newly introduced hazardous material.
As hazardous material and the various inorganic
(metallic) containers ~ssociated therewith are added to
the furnace 10, the level of the molten bath 22 tends
to rise. In order to maintain the molten bath 22 at a
p~edetermined depth commensurate with the size of the
chamber, the length of the arc and other such factors,
it is necessary to provide a means for removing some of
the material from the molten bath 22 while still
continuing the decomposition of the hazardous material.
In the present embodiment, the means for maintaining
the molten bath at the desired prede~ermined depth
comprises a generally cylindrical container 88
positioned beoeath the center of the furnace housing
12. ~n annular weir 90 is provided to establish the
predetermined depth of the molten bath. Whenever the
depth of the molten bath exceeds the height of the weir
90~ molten material flows over the weir 90, through a
conduit rncans or drain pipe 92 and into the cylindrical
` ~Z1~738
,9
container 88. The conduit means 92 and the cylindrical
container 88 are provided with suitable sealing mesns
(not shown) in order to maintain the chamber 18 in the
gas-tight condition.
The cylindrical container 88 is removably attached
to the furnace housing 12. In this manner, material
flowing from the molten bath 22 over the weir 90 may be
collected in the cylindrical container 88 until the
cylindrical container is filled. The cylindrical
container may then be removed from the furnace housing
12 and the material collected therein may be suitably
emptied and/or disposed of in a conventional manner.
In order to ensure that the chamber 18 remains
ga3-tight during the period of time when the
cylindrical container 88 is removed for emptying, a
suitable sealing apparatus 94 is provided to close off
the conduit means g2. A suitable evacuation system
(not shown) may also be provided to remove any gases
which may have accumulated within the cylindrical
co~tainer 88. The gases removed from the cylindrical
container 88 are recycled back into the chamber 18. By
first sealing off the conduit means 92 with the sealing
apparatus 94 and then employing the evacuation system
to remove gases accumulated in the cylindrical
container 88, the container 88 may be removed for
emptying without affecting the continued operation of
the furnace 10. Once the empty contaîner is replaced,
the sealing apparatus 94 is again opened and molten
material may again flow through the conduit means 92
for collection in the container 88.
Alternatively, excess material may be removed from
the molten bath 22 by means of a standard tap or drain
(shown in phantom as 96). However, in order to utilize
~Z1~38
-20-
such a tap or drain 96, it is first preferable to halt
the normal operation of the furnace 10. Material
removed through ~he tap 94 may be suitably disposed of
in any conventional manner.
As a variation of the above-described embodiment,
the gases from the chamber 18 may be exhausted through
the conduit means 92, into the cylindrical container 88
and out of an alternate exhaust conduit (shown in
phantom as 81). In this manner, the gases may react
with the material within the container 88 for further
processing.
Referring now to Fig. 2, there is shown an
apparatus or furnace 110 for the decomposition of
h~zardous material which is substantially the same as
the furnace 10 of Fig. 1. In connection with the
description of Fig. 2, the same numbers will be used
for the same components bu~ with the addition of 100
thereto. Viewing Fig. 2, it can be seen that the
furnace 110 comprises a generally cylindrical housing
1~2 which defines a gas-tight, generally cylindrical
~hamber 118. Within the chamber 118 is a molten bath
122 of metal, salt or any other suitable conductive
material. A generally tubular electrode 168 is
similarly movably actached to the furnace cover 170.
As in the furnace shown in Fig. 1 J the center of the
tubular electrode 168 comprises an exhaust means 178
which further includes an exhaust conduit 180 to permit
che removal of gases from the chamber 118 to the
outside of the furnace 110. The furnace 110 further
includes suitable inlet means (not shown in Fig. 2) for
introducing hazardous material into the chnmber 118 in
che same manner as was shown and described in
conneccion with Fig. 1.
73~
-21-
The primary difference between the furnace 10 of
F~g. 1 and the furnace 110 of Fig. 2 is in the manner
in which the excess material is removed from the molten
bath. As shown on Fig. 2, a generally cylindrical
container 188 is provided adjacent to one side of the
furnace housing 112. The adjacent side wall of the
furnace housing 112 includes an opening which forms a
weir 190 to establish the depth level of the material
within ~he molten bath 122. Any material rising above
the level of the weir 190 flows through a conduit means
192 and into the container 188. The con~ainer 188 is
remo~able from the conduit means 192 and both the
container 188 and the condui~ means 192 are provided
with suitable sealing means (not shown) to preserve the
gas-tight integrity of the chamber 118. A suitable
sealing apparatus 194 is provided to close off and seal
the conduit means 192 when the container 188 has been
removed for emptying. A suitable evacuation system 198
co~prising a sui~able pump 200 and a corresponding
check valve 202 is provided to evacuate any gases which
may accumulate in the container 188 prior to emptying
the container. As shown, the gases removed from the
container 188 are recycled back into the chamber 118
for further processing.
A further difference between the furnace 10 of
Fig. 1 and the furnace 110 of Fig. 2 is in the loc~tion
of the nnnular electromagnetic coil 186 which is
employed to cause the rotation of the arc 172 around
the arcing tip 182 of the tubul~r electrode 168. As
shown, the electromagnetic coil 186 is located on the
outside of the housing 112 beneath the electrode 168.
In order to insure that the housing ll2 does not
interfere with the magnetic field generated by the
. ~L2~738
-22-
external electromagnetic coil 186, the lower portion of
~he housing is comprised of non-magnetic material as
shown. As in the embodiment of Fig. 1, the flux lines
from the ma~netic field are perpendicular to the arc
172, thereby causirlg the arc to rotate around the
surface of the arcing tip 182.
Fig. 3 shows a slight variation of the furnace of
Fig~ 2, wherein the same numbers are used as appear in
Fi~. 2 but with the addition of primes thereto. In
Fig. 3, the conduit me~ns 192' for removing material
from the molten bath 122' is positioned beneath the
surface of the molten bath. The conduit 192' further
includes a standard plumber's P-trap arrangement 104'
to effectively prevent gases contained within the
chamber 118' from entering the container 188'. A
sealing apparatus 144' is also provided to facilitate
the emptying of the container 188' without any
interruption of furnace operation.
Fig. 4 shows a different variation of the furnace
of Fig. 2 in which a different means is provided for
moving ehe arc 472 around the arcing electrode tip 482.
Referring to Fig. 4~ the same numbers are used as in
Fig. 1 but with the addition of 400 thereto. In Fig.
4, instead of employing an electromagnetic coil, as was
done in connection with the embodiment of Fig. 2,
first generally cylindrical ferrous member 406 is
positioned within the hollow interior of the tubular
electrode 468 adjacent to the arcing tip 482.
Similarly, a tubular ferrous member 407 surrounds the
tubular electrode 468 edjacent to ehe arcing eip 482.
Both of the ferrous members 406 and 407 may be cooled
employing a suitable known cooling system (not shown)
which uses a heat transfer fluid such as water (not
-~ ~Z1~738
shown). The ferrous members 406 and 407 interact with
the arc current to generate a magnetic field having
flux lines (not shown) which extend generally
perpendicular to the arc 472. In this manner, ~he arc
S is made to rotate around the surface of the arcing tip
482 in the same manner as was discussed in detail in
relation to the apparatus of Fig. 1.
~ eferring now to ~ig. S, there is shown a
schematic representation of a pressure relief system
ge~erally designated SOO which may be employed in
connection with furnace 10 of the type described in
Fig. 1 or any of the above-described alternative
furnace embodiments. The pressure relief system
comprises a sealed (gas-tight~ container or surge tank
502 located proximate to the furnace 10. A suitable
first conduit means 504 extends between the furnace 10
and the sealed container 502 and provides communication
between ~he interiors thereof. A pressure relief valve
506 is positioned within the first conduit means 504 to
conerol and effectuate relief of the pressure within
the furnace lO, if necessary. As described above, the
furnace lO should be constructed to withstand an
internal gas pressure of five atmosphere without
leaking any gas therefrom. The pressure relief valve
506 should be designated to relieve the furnace
pressure ~t a preset pressure point slightly less than
the five atmosphere level.
Once the preset pressure point of the pressure
relief valve 506 has been exceeded the excess gas from
the furnace lO flows into the container 502 thereby
lowering the pressure within the furnace. A second
conduit means 508 and a suitable pump S10 are provided
to return gas from the sealed contniner 502 to the
~2~1~38
-24 -
furnace 10 for further processing when the pressure
within the furnace has decreased to sn acceptable
level.
From the foregoing description and the
accompanying figures, it can be seen that the present
invention provides a method and npparatus for the
decomposition of PCBs and o~her hazardous material
which is efficient, relatively easy to control and is
very effective in operaeion. It will be recognized by
those skilled in the art ~hat changes or modifications
may be made to the above-described embodiments without
departing from the broad inventive concepts of the
invention. It is understood, therefore, that this
invention is not limited to the particular embodiments
described9 but it is intended to cover all changes and
modifications which are within ehe scope and spirit of
the invention as set forth in the appended claims.
