Note: Descriptions are shown in the official language in which they were submitted.
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The invention relates to a process for the disposal of toxic
and/or infectious waste according to the pre-characterising
part of claim 1. The inven-tion also relates to an installation
for carrying out the process.
Processes for the disposal of household and/or industrial waste
by pyrolysis with a degassing drum are already known, e.g. from
DE-A 33 47 554, DE-A 35 29 445 and DE-A 37 27 004.
However, only waste containing only a small quantity of
ecologically harmful or noxious matter can be disposed of,
further processed or treated for the recovery of fuels by means
of these processes.
This involves in particular highly halogenated solids and
containers for hospital materials with toxic and/or infsctious
contents, and for various plastics, e.g. PVC and plastics
containing superchlorinated or superbrominated additives, e.g.
flameproofing agents (decabromo biphenyl ether) and the like.
If this waste were to be treated by pyrolysis with the high
temperatures prevailing in this process, the high chlorine
content would cause problems in the resulting carbonisation
gas. In addition, e.g. highly toxic dioxins and furans with
more than three chlorine atom bonds would be contained in
relatively large quantities in the carbonisation gas, the
complete destruction oP which in the subsequent treatment
process would be difficult. In addition, the risk of accidents
would be increased. In addition, poisonous gases, e.g.
fluorocarbons from styropor of refrigerators and the like are
already released when crushing and granulating waste of this
kind. Similarly, infectious waste cannot be simply crushed
il~mediately for reasons of hygiene.
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Autoclaves for degassing products are already known (see, e.g.
EP-B 0 007 620).
However, the autoclaving of waste has hitherto been regarded as
uneconomical, particularly on account of the necessary
batchwise operation of the autoclave and the associated
intermittent and there~ore irregular flow of waste gases.
A further disadvantage o~ the known process consists in that
temperatures of approximately 450 are provided for in the
autocla~e, the resulting gas being advanced to a subsequent
burner of a heat generator. However, with high degassing
temperatures of t~is kind, environmentally harmful and
poisonous substances are formed and are released by the
subsequent carbonisation gas combustion, so that, e.y. highly
halogenated solids and other special waste cannot be treated by
a process of this kind.
The object of this invention is to provide a process and an
installation for the disposal of waste by means o~ which toxic
and/or infectious waste can also be disposed of and possibly
made recyclable without causing problems for the environment
and/or the health of humans and animals.
This problem is solved according to the invention by the
features specified in the characterising part o~ claim 1~
Tests have in ~act surprisingly shown that by coupling an
autoclave as a first degassing stage for carrying out partial
degassing with subsequent residue pyrolysis, the problems
mentioned at the outset can be solved in a hygienic, economical
and ecological manner.
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In temperature-controlled autoclave partial degassing for the
disinfection of the feed material, the halogens can split off
~rom plastics simultaneously at a temperature of approximately
310C, for which dwell times of approximately 20 minutes to 6
hours are required, according to t:he type.
The oil and coal tar-like intermediate product of autoclave
partial degassing at be:Low 320C no longer contains any
aromatics and therefore has no mutagenic or carcinogenic
properties. It can therefore be further processed without
difficulty, giving the particular advantage wi.th respect to the
subsequent treatment thereof that, if it is introduced into the
autoclave in advance, the active carbon-like pyrolysis residue
from the pyrolysis absorbs the fluid components and thus allows
for the discharge o~ a solid from the autoclave.
Residual solid structures of the intermediate product can be
granulated without any difficulty once they have been cooled
and discharged from the autoclave, so that -they can then be
completely degassed in a second degassing stage in a degasser,
e.g. a rotary drum degasser, at approximately 600C, together
with the pyrolysis residue enriched with oily and tarry matter.
It has been ~ound to be advantageous in thls connection to mix
the feed material in the degassing drum with other waste
material having such a high carbon content that the degassing
product pyrolysis residue contains more than 30 % by weight of
carbon. In this case, it has been surprisingly shown that, if
it is pressed through a water bath before contact with air, the
hot pyrolysis residue forms an active carbon structure with
such a great pore surface that its absorption and adsorption
properties correspond to approximately 70 % of those o~ active
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carbon produced normally. As a result of this property, this
pyrolysis residue can then be used, inter alia, ~or filtering
waste containing harmful substances, especially for absorbing
the waste produced when washin~ the pyrolysis cracked gas
(prior to oxidation), or when wet scrubbing carbonisation gas
waste gases. Unless there is complete absorption of the waste
as a medium of the water bath for the formation of the active
carbon structure by evaporation, the excess water is almost of
drinking water quality.
It is also advantageous that the process according to the
invention is virtually free o~ waste, i.e. no waste is
produced. The water required in the process can be
recirculated.
The carbonisation gas produced intermittently in the autoclave
can be mixed directly with the carbonisation gas from the
continuously operating pyrolysis degasser for further
processing thereof. The intermittently produced carbonisation
gas from the autoclave, which led to corresponding problems
according to the prior art, especially with respect to
economical treatment, can then be further treated without
difficulty in that it is advanced to the second degassing
stage. In this case, it is simply necessary for the
continuously operating second degassing stage to have a maximum
load such that it can handle the intermittent operation, i.e.
the batchwise delivery of the granulated waste.
If, in an advantageous development of the invention, several
autoclaves are provided and these are operated staggered over
time in a corresponding manner, load peaks are further
established and, if desired, a subsequent second degassing
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stage can also be operated continuously ~y means of pyrolysis
degassing via aukoclaves. This means that in a case of this
kind, normal household waste or industrial waste does not
necessari].y have to be mixed, but the special waste can also be
disposed of separately in an economical manner.
It may be advantageous to free the carbonisation gas o~
hydrochloric acid before mixing w:ith the carbonisation gas ~rom
the second degassing stage via a cooling path by condensation,
in order to reduce the load of the subsequent washing stage.
In this case, the carbonisation gas is then heated again to
over 300C, preferably approximately 450C, in order to prevent
it cooling when it is mixed with the carbonisation gas of the
second degassing stage and thus to prevent the condensation of
tarry substances resulting in blocking in the pipeline network.
In ordér to improve the method of operation,and the efficiency
of the autoclave and to reduce the quantity of waste gas of the
entire process, it has been found to be advantageous to use the
hot waste gases from the carbonisation drum as a heating medium
from their indirect heating by combustion of self-produced
pyrolysis cracked gas or other fuels. For rapid heating, part
of the even hotter (approximately 9~0C~ cracked gas after the
gas converter before the washer can be removed by means of a
separate pipeline network and can then be returned to the
washer after passage through the autoclave.
A cooling medium which must be oxygen-free is required for
temperature control and for cooling the feed chamber in
connection with the required batchwise feed of the autoclave.
To this end, it is advantageous to use cold pyrolysis cracked
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gas, which is removed at approximately 35C after the gas
washer and can then be returned to the gas converter enriched
with carbonisation gas for disposal and reuse or can be
advanced to the combustion chamber of the carbonisation drum
for direct combustion.
Once the feed chamber has b4en cooled to an internal
temperature below the minimum spontaneous ignition temperature
and the deg~ssing termination temperature (approximately 45C),
the feed chamber of the autoclave can then be flooded with cold
air for the purposes of accessibility, said cold air being
sucked out ~or its disposal as combustion air for the gas
converter or other burners of the disposal system. It is
therefore possible to achieve accessible temperatures without
having to reduce the autoclave casing temperature of
approximately 310C if, as in one embodiment of the invention,
a double-walled autoclave is used, a flow channel being
provided between the wall of the feed chamber and the outer .
wall of the autoclave, through which the hot gases ~low. In
this manner, the fsed interval and thus the flow rate and thus
the efficiency of the autoclave can be considerably improved.
In order to further reduce the climate-related trace gases,
such as C02, CO, NOx produced upon the disposal and energy
conversion processes and to increase the thermal value of the
pyrolysis cracked ~as by reducing the nitrogen content thereo~,
in so far as this originates as atmospheric nitrogen from the
supply of combustion air to the gas converter for the
temperature control thereof by substoichiometric carbonisation
gas combustion, it has been found to be possible and
advantageous to split oxygen with a purity of more than 80 %
from the atmospheric air by means of a pressure swing
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adsorption .installation and then to mix the waste gas partial
flows from the carbonisation drum in such a manner that the
mixing product has an oxygen content of more than 25 % by
volume and to return this mixture in order to cover the oxygen
requirement of the gas converter and the combustion chambers
and the gas motors used to drive generators ~or generating
current.
In the case of the gas converter feed, ox~gen enrichment of up
to 45 % may be advantageous, as this considerably reduces the
cracked gas mass and means that it i.s possible to increase the
thermal value of the cracked gas by more than 10 ~.
In order to work the pyrolysis residue from the second
degassing stage into a completely inert final product for
disposal, which can then be sent to normal dumps or can be used
as a building material aggregate, it has been found to be
advantageous to mix a certain quantity of puzzolana, i.e.
silicate and aluminate materials, with the wet pyrolysis
residue, together with calcium-~ontaining compounds such as
lime, lime hydrate or lime hydrate waste, wherein it must be
ensured that the mole ratio of Sio2, A12O3, CaO, ZnO, Fe2O3
and/or MgO, on the one hand, to the entire mole content of the
metals lead, chromium, manganese, cadmium, beryllium, barium,
selenium, arsenic, vanadium, antimony, bismuth, strontium
and/or zircon is at least 6:1, and similarly that the mole
ratio of calcium, magnesium and so~ium, on the one hand, to the
entire sulphur, chlorine and fluorine content is at least 2:1.
If this mixture is pressed into ovoid-shaped pellets at between
200 and 550 kg/cm2 and is hardened at normal temperatures for a
period of at least ~ days, compounds such as calcium silicate
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hydrate, calcium aluminate hydrate and calcium ferrite hydxate
are produced, these being slishtly water-soluble and having
hydraulic properties such that the structure is dimensionally
stable and can be used without di~ficulty for carrying out an
annealing process, e.g. in a direct-current shaft furnace, in
order to be annealed therein at approximately 1200-1250C using
the carbon energy content. This means that the heavy metals
are incorporated into the mineralogical structure of complex
calcium silicates, ~or which reason the waste gas flow is
substantially ~ree of heavy metals, and the sand-like solid
residue corresponding to its ceramic structure is almost
unleachable and thus can be used a building material.
If it is ensured that the carbon content in the pyrolysis
residue is more than 30 % by weight, its thermal value is
sufficient to ensure temperatures of up to 1300C in the
direct-current shaft furnace, taking account of tha required
mixing described hereinbefore when supplying sufficient
combustion air, in order to make the annealing residue
relatively insoluble. In leaching tests, all of the completely
burnt out briquette residue of the type described hereinbefore
displayed cadmium values of less than 0.2 ppm, chromium values
of less than 0.4 ppm and lead values of less than 0.3 ppm, even
when the maximum metal content in the briquette was in excess
of 8000 ppm in the case of cadmium and in excess of 6000 ppm in
the case of lead. No measurable losses of lead or cadmium
could be established in the waste gas flow, so that the hot
waste gases can also be used without purification for heating
the autoclave and carbonisation drum and for drying moist waste
before it is introduced into the degassers.
By virtue o the invention, industrial residue, components or
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the like and waste displaying great inhomogeneity, possibly
with interstitial, attached and structural water, etc., which
are toxic or become toxic upon thermal conversion, can be
sub~ected without difficulty to the desired pyrolytic
treatment, thereby producing useful gases for an energy use
without special waste and sewage beiny produced. Inorganic
materials of composite materials can thus be recovered in some
cases, so that real recycling of useful basic materials and the
like is poissible in that, after khe pyrolytic coating removal,
e.g. metal components are subjected to suitable coating once
again and can be used as ~inished components.
Further advantages and developments according to the invention
will be clear ~rom further subclaims and an installation
according to the invention for carrying out the process, which
will now be described in diagrammatic form with reference to
the accompanying drawings.
The material to be disposed of or recycled is advanced from an
autoclave pre-chamber 1 to an autoclave 2, e.g. via an
appropriate feeding apparatus in the form of a manually
operable sliding platform having correspondingly track-bound
special wagons. The conveying can take place, e~g. in metal
skeleton containers, below which a metal tank is fitted,
previously filled with active carbon-like pyrolysis residue
from the second degassing stage, in order to absorb the heavier
degassing products, oils and tars. The metal wagons loaded
with pallets or baskets described hereinbefore ara advanced
from the pre-chamber 1 into the reaction chamber of the
autoclave 2. A rontinuously adjustable temperature limit
between 250C and 320C can be selected and provided. The
charge times depend on the organic portions in association with
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the magnitude of the heat trans~er. When loadiny per autoclave
and pe.r charge with pallets or wir~ baskets, there are
dif~erent charge times accordincJ to the introduction o~ the
organic substances. As mixed loading is possible, average
charge times can be kept constant. The pre-chamber 1 can be
supplied with air for purification and cooling via a pipe 4,
removed via a discharge pipe 3A. A flow channel 6 o.f the
autoclave 2 is supplied via a pipe 5 with hot waste gases from
a carbonisation drum combustion chamber 16A for heating the
casing thereof, in order to heat the walls thereo~. After the
addition of heat to the internal chamber of the autoclave, the
substantially cooled waste gases are reused via a discharge
pipe 3C for reheating in the carbonisation drum or, enriched
with oxygen from a pressure swing absorber 7, are reused as
combustion air for a gas converter 8 or the burner of a
carbonisation drum 16.
Hotter cracked gas from the gas converter 8 can be added via a
pipe 10 for rapid heating of the cracking chamber, said gas
leaving the gas converter at approximately 920C.
Once the autoclave 2 has been charged with the material to be
degassed the degassing chamber is first flooded via a pipe 9
with inert gas (hot waste gas) and is withdrawn via a discharge
pipe 3B in order to remove the oxygen from the reaction chamber
of the autoclave 2. Subsequently, the reaction chamber of the
autoclave 2 is flooded with hot cracked gas via a pipe 10A in
order to accelerate the commencement of the degassing of the
feed material. The pipe 10A can be a branch of the pipe 10
with the hot cracked gases of the gas converter ~. This hot
cracked gas is discharged via the pipe 3B. Removal from the
pipes 3A and 3B is effected via the pipes 3 and 33 by supplying
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the gas converter B or the burner oE a carbonisation drum 16.
After the commencement of degassing, the discharge pipe 3B is
closed. The carbonisation gas is advanced via a heak exchanger
11 to a carbonisation discharge pipe 17 a~ter the carbonisation
drum 16. Condensable contents such as aqueous hydrochloric
acid from the carbonisation gas flow can be separated if
necessary in the heat exchanger 11 and collected in a container
12. Subsequently, the carbonisation gas i5 heaked again by
means of a heat exchanger 13 to at least 450C, in order then
to be mixed via a pipe 17A with the pipe 17. The carbonisation
gas is then advanced via the pipe 17 to the high-temperature
gas converter 8. At the end of the degassing process below
320C in the reaction chamber of the autoclave 2, in order to
prevent the ~ormation of aromatics, for discharge of the feed
material, the autoclave 2 is flooded via a pipe 2B with cold
cracked gas which is removed after a gas washer 21 and 24.
Discharge is again ef~ected via the pipe 3B. Flooding is
effected unkil the temperatures in the internal chamber fall to
below 80C, in spite of the autoclave casing being at a
temperature of approximately 300C. Subsequently, the
autoclave 2 is flooded with fresh air before the autoclave
doors are unlocked and the wagon with the degassed material is
removed. New feeding can be effected simultaneously during
this removal via the points.
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The degassed solid material including the pyrolysis residue
enriched with oils and tars in the discharged tank of the wagon
is then advanced via a path 67 into a shredder or a granulating
means 14 where it is mixed if necessary with other carhon-
containing waste from the supply pipe 70. If necessary, metals
coated in plastic or metal plastic composite materials already
present can first be removed, in order to return them for
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recyclinq.
The only partially degassed but now disinfected and crushed
material in the reaction chamber o~ the autoclave 2, mixed with
other granulated waste from the supply pipe 70, can then be
advanced via a rotary vane feeder or a similar ~eeding
apparatus, such as a filling screw 15, to the carbonisation
drum 16, in which carbonisation ~as is produced in the known
manner by pyrolysis at temperatures o~ 550 - 600C, said
carbonisation gas being fed via a discharge pipe~17B and a dust
removing apparatus 18 into the pipe 17 leading to the high-
temperature gas converter 8. The carbonisation gas is treated
or converted in the yas converter 8 over a coal or coke bed.
A gas converter of this type is described, e.g. in DE-A 33 17
977, for which reason it will not be described in more detail
here. The design of the carbonisation drum 16, the gas
converter 8 and the subsequent gas purification means is such
that these can be operated continuously by the degassing of the
waste flow fed via the supply pipe 70 and the intermittently
produced carbonisation gas flow and the solid waste from the
batchwise degassing by the autoclave 2 serve as a peak load,
wherein it is also possible to use several autoclaves 2 out of
phase in parallel operation in order to guarantee more uniform
feeding of the installation module. After passage through a
heat exchanger 20, the cracked gas from the gas converter 8
arrives at a gas washing installation consisting essentially of
a water spray tower 21, a blower 22 and a purifying cyclone 23
and a drop separator 24. ~he purified gas is advanced via a
gas pipe 25 to a gasometer 26 in which, i~ too much gas is
supplied, excess gas can be advanced via a by-pass 27 to a
flaring apparatus 28. The gas ~rom the gasometer 26 is
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normally advanced to a gasometer 29 which is connected to a
generator 30~ the burnt waste ~ases being fed via a waste gas
pipe 31 to a chimney 32. However, these waste gases or a
partial waste gas flow 75 can also be advanced to a mixiny
chamber 76, which is mixed with air enriched with oxygen by the
pressure swing absorber 7, which again can be returned as
combustion air for the gasometer 29 and via the pipe 33 to the
gas converter for maintainin~ its crack temperature by
substoichiometric carbonisation gas combustion. The qas
converter 8 receives coke via a coke inlet 34~ and water via a
pipe 34B. Ash and slag are withdrawn via an outlet pipe 35.
If desired, a coke return pipe 36 can also be provided for the
coke freed of slag in order to save energy. The coke is
returned to the carbonisation drum 16 together with the solid
residue from the washing water settling tank of a gas
purification means 41. A by-pass 37 branches off from the gas
pipe 25 and leads to a gas burner 38 serving to supply heat to
the carbonisation drum 1~. During the start-up phase of the
installation, an oil burner 39 or even a separate gas ~urner
serves to heat the carbonisation drum 16. Subsequently,
however, in khe course of operation, the heat required for the
carbonisation drum 16 can be supplied entirely by the burner
38.
The washing water resulting from the gas purification arrives
at a washing water tank 40 and subsequently at a filtering
apparatus 41, which is generally a settling tank. Solids
separated in the filtering apparatus are introduced via a pipe
42 into an ash container 43. The residue from the ash
container 43 is carried away via an outlet pipe 44 and is
returned to the carbonisation drum 16 via a feeding apparatus,
e.g. the filling screw 15~
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The purified washing water is led from the filtering apparatus
41 via a return pipe 45, after passage through a cooling tower
46, back into the spray tower 21 of the gas-washing
installation. Part of the purifiled washing water is fed into a
washing water neutralising plant 47/48. From the washing water
neutralising plant 47/48, the washing water is advanced via a
return pipe 53 ~or recycling treatment to the spray tower 21,
while part of it is advanced via a removal pipe to the batch
treatment plant of the water neutralising plant 47/48. Here,
the washing water is chemically purified in the known manner by
appropriate chemicals which are supplied via a chemical pipe
49, unless the chemical oxid,ation is ef~ected by ozonisation
means 54, as a result of which the quantity of residue
increasing additives added can be sharp]y reduced. The washing
water is partly guided via a recycle pipe 50 through an air
filter 51 for the removal of foam, waste gases being blown off
through a pipe 52 via the chimney 32, and is partly returned
via a pipe 52B to the spray tower 21. The excess water from
the gas purification collected in the container 48 is advanced
via a pipe 55 to a water bath 57 for the discharge of the
pyrolysis residue after khe carbonisation drum 16. During the
evaporation process taking place there, this excess quantity o~
washing water is absorbed by the pyrolysis residue as
interstitial and attached water, the harmful substances
contained therein being adsorbed and absorbed by the active
carbon. The washing water is disposed of in this manner.
If more excess water should be produced from the gas washing
than is absor~ed by the pyrolysis residua, it is discharged via
a pipe 58. However, as a result of the filtering action of the
active carbon-like pyrolysis residue, this excess water is
almost of drinking water quality. However, as a rule, there is
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no excess water. The wet pyrol~sis resiclue can be advanced via
a pipe 56 to a mixing apparatus 60 in which silicate and
aluminate materials are mixed, together with calcium-containing
compounds. Subsequently, it is ~ed to a briquetting press 61,
in which dimensionally stable ovoid-shaped pressed piec~s are
produced from the mixing product. These are then annealed in a
direct-current shaft furnace 62 a.t approximately 1250C.
The resulting hot waste gases at a temperature of more than
1000C can then be advanced via the pipe 74 as a partial ~low
pipe for heating the carbonisation drum or as a partial flow
pipe 71 ~or drying other waste to a drier 72. The paxtial Plow
not required to this end is advanced via the pipe 65 to the
chimney 32. The fresh air required for the direct-current
shaft furnace 22 is advanced via a heat exchanger 64 via the
pipe 63.
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The annealing residue from the shaft furnace 62 is rendered
completely inert and can be advanced ~ia a discharge means 66
for reuse as a building material.
As an alternatiYe to the carbonisation gas cracking described
hereinbefore via a gas converter l9 with subsequent cracked gas
washing, in which case purification of the gas prior to
oxidation is e~fected at approximately 40C and ~hus only a
very small volume of gas has to be puri~ied, the carbonisation
gas from the pipe 17 can also be advanced ~o a combustion
chamber 77 directly via the connecting pipe 170 indicated only
by a dotted line, followed by a boiler plant 78, a mixing
chamber 79 which is supplied with lime via a nozzle means 80
via an air pipe 85, and a filtering installation 81. The
residue from the filtering apparatus can be removed via a line
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59A in the mixing chamber 60. The waste gas puri~ied or
filterad in the ~iltering installation 81 is returned via a
waste gas pipe 82 to the chimney 32B or, optionally, after
passage through a condensation installation 83, via a pipe 8~
for heating or drying purposes into the installation, e.g. to
the partial flow pipe 71.
An air pipe 86 leads in the conventional manner into the
combustion chamber 86 and optionally also a secondary fuel line
87. A feed water pipe 88 leads to the boiler plant 78 and a
steam pipe 89 leads therefrom. Compressed air is blown into
the filtering installation 81 via a compressed air pipe 89 for
purification.
Whereas the autoclave 2 and the carbonisation drum 16 must be
operated together, the installation unit 60-62 can also be
operated in another manner if an appropriate energy consumer is
present.
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