Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1 33479~
`.~BACKGROUND OF THE INVENTION
The invention relates to a process for the conversion
of solid, mostly dehydrated waste substances into glass,
wherein the waste substances are mixed with one or several
additives to form a batch to be melted. A major portion of
the batch is melted into a glass melt by supplying heat and
a minor portion is exhausted from the melting batch as an
exhaust gas. Solid vitreous bodies are formed from the
glass melt by means of casting and cooling. Furthermore,
the invention relates to an apparatus for the working of
this process.
It has long been known, to convert toxic and
radioactive waste substances in the form of slurries or
suspensions into glass by means of melting after adding
additives and mixing it into a batch. The formerly loose
waste substances are now tightly incorporated in the glass.
Glass possesses the advantages property that it is difficult
to leach out, thus permitting the release of heavy metal and
other substances contained in the glass only to such a small
extent that the storage or the use of bodies made of such
glass does not cause any problems.
One difficulty regarding the vitrification of waste
substances is their generally high percentage of chlorides
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and calcium sulfate. They are integrated into the glass
melt only to a very small extent during the melting process
even if the chloride and sulphur capacity of the glass melt
is completely saturated, which is due to the large amount of
these substances present. Hence, large amounts of exhaust
gas containing gases of chlorides and sulfate, especially
C1, HC1, SO2, and SO, are a disadvantageous result.
Contrary to that, it is a matter of fact that a sufficient
amount of heavy metal and additional alkali escaping from
the glass melt by means of vaporizztion. The most
aggravating disadvantage of the known process, especially
with regard to its environmental effects, is the formation
or possible formation of dioxin and/or furan when the batch
is heated during the melting process. This occurs when the
waste substances to be converted still contain organic
components, from which these harmful substances are formed
under temperatures occurring during the melting of the
batch.
SUMMARY OF THE INVENTION
Hence, it is the object of the invention to provide a
process which is less harmful to the environment and
excludes especially the emission of dioxin and/or furan even
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if heterogeneous, organic components as well as heavy metal
are employed. Furthermore, it is the object of the
invention to provide an apparatus for the working of this
process.
The first part of the object is achieved in a process
where the waste substance is incineration ash, and hot
exhaust gas is withdrawn under exclusion of surrounding air
and reintroduced into the batch to be melted where it is
cooled down to 20 to 50C. Condensation products resulting
from the cooling process are melted with the batch, and the
cold exhaust gas emerging from the batch to be melted is
purified.
The new process permits the conversion of a so far very
problematic waste substance, i.e. incineration ash, into
glass in an ecologically beneficial way despite the fact
that such ash producls are heterogeneous and consist of high
and unstable percentages especially of carbon, mercury,
lead, tin, zinc, calcium, chlorides, and halides. A major
portion of these harmful substances is directly integrated
into the glass melt, hence, they are tightly incorporated.
Harmful substances escaping as gases are mostly condensed by
cooling within the batch to be molten and then reintroduced
into the melting mass. The remaining, relatively small
amount of cold exhaust gases are neutralized in a subsequent
purification process.
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A further development of the process p--~vides a
reheating of the hot exhaust gas which escapes from the
batch to be molten to at least 1200C for a residence time
of at least 1.5 second. The gas is then pre-cooled under
partial condensation to 200 to 300C and subsequently
reintroduced into the batch to be molten where it is cooled
down to 20 to 50C; the condensation products resulting
from the pre-cooling are reintroduced into the batch to be
molten and/or exhausted. Reheating the exhaust gas
definitely eliminates a possible presence of dioxin and
furan. Hence, the average temperature and residence time
must be selected to ensure the elimination desired. The
subsequently exhausted gas basically contains only
chlorides, sulfates, carbon dioxide, and alkali and heavy
metal vapor. Through a following pre-cooling to 200-300C
the hot exhaust gas is partially condensed, hence reduced in
its quantity as well as in its number of components. The
return pipes provided for the reintroduction of the
condensation products into the batch to be molten keep these
products in a closed circuit; they are gradually converted
into glass. After an initial phase a balanced condition is
reached causing the amount of condensation products to
remain constant. Passing the pre-cooled exhaust gas through
the batch to be molten causes vapors which condense only at
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low temperatures, like heavy-metal vapor and especia''y
mercury vapor, to be deposited on batch particles, thus
being reintroduced to the melting process. Due to the
strong cooling while passing through the batch, the
chlorides and sulfates are practically completely condensed.
If more chlorides and sulfates are vaporized than can be
dissolved in the glass melt after the reintroduction of the
condensed products, these substances are enriched in the
batch. To avoid this, the surplus condensation product
resulting from the pre-cooling is advantageously removed.
These condensation products are for the most part solid.
The remaining cold exhaust gas then contains almost
exclusively hydrogen chloride (HC1) and sulfur dioxide (S02)
in high concentration. The volume of the remaining exhaust
gas is relatively small, compared to the throughput of
incineration ash. Moreover, the relatively high
concentration and the simple composition of the cold exhaust
gas is advantageous to the subsequent final gas
purification. The gas purification requires only a
relatively small capacity and provides comparatively pure
separation products, especially sodium chloride and sodium
sulfate, which can be used, for example, for the manufacture
of soda. The heat energy required for the melting process
is electrically generated, thus avoiding the addition of
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combustion gas of a fossil-fuel-operated heating device to
the exhaust gas resulting from the melting batch, a fact
which would complicate the exhaust gas treatment.
The new process is ecologically very beneficial as well
as economical. On the one hand, the exhaust gas emission is
largely reduced and on the other hand the process provides
raw material for other purposes; for example vitreous
bodies which are employed as construction materials and the
already mentioned sodium chloride and sodium sulfate. The
new process excludes any emission of dioxin and/or furan.
Furthermore, the new process permits a reheating of the
hot exhaust gas in a separate after-burner. This variant of
the process is not as economical with regard to the energy
consumption, however, it does not require a complicated
melting device. Furthermore, it is advantageous that the
entire glass bath can be covered by the batch, permitting a
major portion of the alkali and heavy metal vapor to be
condensed under the batch cover in the ~urnace. An
alternative and particularly energy saving embodiment of the
process suggests that a part of the glass melt surface be
free of batch; the hot exhaust gas escaping from the
melting batch be then passed over the batch-free part of the
glass melt surface and thus reheated by heat absorption from
the glass melt.
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Another alternative suggests that the cold exhaust gas
emerging from the batch to be molten be reheated up to a
temperature of at least 1200C for a period of at least 1.6
seconds and then be subject to purification. The exhaust
gas reheating elim nates dioxin and/or furan, thus ensuring
that there is no escape of these harmful substances.
As a last alternative regarding the reheating of the
exhaust gas, the process suggests that the exhaust gas
emerging from the purification process be reheated to a
temperature of at least 1200C for a period of at least 1.5
seconds. This also ensures an elimination of dioxin and/or
furan. The selection of an appropriate variant is up to the
expert and depends on the requirements and conditions of the
individual case.
With regard to the additives, the process suggests the
use of substances containing SiO2, especially sand and/or
phonolite. These additives are easy to handle and
inexpensive. Alternatively and/or supplementary, cullet can
be employed as an additive containing SiO2. The process
also suggests that the gas escaping from the melting batch
as well as the hot exhaust gas be exhausted under
subatmospheric pressure and pre-cooled and that the
pre-cooled exhaust gas be then put under super atmospheric
pressure. The exhaust gas can then be passed through the
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batch to be molten in a counterflow and the pressure of the
cold exhaust gas escaping from the batch to be molten can be
controlled so that it be basically identical with the
pressure of the surrounding air. On the one hand this
ensures that no exhaust gas resulting from the melting batch
escapes into the environment; on the other hand there is a
sufficient throughput of pre-cooled exhaust gas through the
batch to be molten. Finally, it is also achieved that there
is no major escape of exhaust gas into the environment
during the formation of the batch and that no additional air
infiltrates the exhaust gas.
Apparatus for practicing the process includes a batch
mixer and a closed glass melting furnace. The batch mixer
has an inlet for incineration ash and additives, and an
outlet for the mixed batch, as well as gas inlet and a gas
outlet for passing exhaust gas from the furnace through the
batch. A batch outlet provides charge to one end of the
furnace, which has a molten glass outlet at the opposite
end.
This apparatus permits a safe, continuous, and
ecologically beneficial working of the above described
process.
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BRIEF DESCRIPTION OF THE DRAWINGS
igure l is a diagram.matical cross section view of the
first embodiment,
Figures 2 to 4 show the apparatus in its respective second,
third, and fourth embodiments,
Figure 5 is a schematic of a first embodiment of gas
purification device,
Figure 6 is a schematic of a second embodiment of gas
purification device,
igure 7 is a flow diagram of a system of removing dust
and filtrate slurry from the exhaust gas.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Fisure 1 shows supply vessels 2, batch mixer 3, a glass
melting furnace 4, a glass working machine, an exhaust gas
cooler 6, and a gas purification device 7.
The supply vessels 2 serve to hold and store
incineration ash 80 and additives 81. The bottom end of
each supply vessel 2 is provided with a dosing sluice 20,
for example a cellular wheel sluice. These dosing sluices
end in a common conveyor device 21, in this case a screw
conveyor, which leads to the top of the batch mixer 3. The
batch mixer 3 consists of a funnel-like housing 30 and a
m;~;ng screw 31 disposed in housing 30. The mixing screw 31
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runs parallel to the inner side of the lateral wall of
housing 30; it can be rotated around its own axis as well
as around an axis running vertically through the center of
the housing 30 of the batch mixer. The upper part of
housing 30 is provided with a solid substance inlet which is
connected with the above mentioned conveyor device 21. The
bottom end of housing 30 of the batch mixer 3 is provided
with a solld substance outlet leading to a batch conveyor
46. The batch conveyor 46 is already part of the glass
me'ting furnace 4. The glass melting furnace 4 includes a
tank 41 of fire-proof material covered by a superstructure
42, also made of fire-proof material. The tank 41 and the
superstructure 42 rest on a support configured as steel
girders. The external surface of the superstructure 42 of
the glass melting furnace 4 has a gastight cover 42'
consisting of sheet steel. The cover 42' reaches up to the
top rim of tank 41 to which it is joined in a sealed
connection. From the top downward, heating electrodes 43
pass through the superstructure 42 and the cover 42' into
the interior of the glass melting furnace 4. The interior
of the glass melting furnace is subdivided into two
different areas: a melting area, which is represented on
the right side of Figure 1. A suspended and straight arch
44 subdivides the glass melting furnace into said areas.
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lnis arch 44 protrud~es downwardly and is configured as a
part of the superstructure 42 from which it is suspended.
During operation of the glass melting furnace 4 this arch 44
is close to the surface 84' o a glass melt 84 contained in
the furnace 4, and serves as a perpendicular dividing wall
to form the gas area of furnace 4. Furthermore, under arch
44 there is a coolant tube 45 which runs parallel to this
arch across the glass melting furnace 4. The coolant tube
45 passes exactly at the same level with the surface 84' of
the glass melt 84 and causes the glass melt 84 to solidify
in the area surrounding the tube 45. The right end of the
glass melting furnace is provided with a glass melt outlet
48 where a diagrammatically represented glass working
machine 5 is added. Finally, the right end of the glass
melting furnace 4 is also provided with an upward exhaust
gas outlet 47 passing through the superstructure 42.
A heat insulated gas pipe 60 extends from the exhaust gas
outlet 47 of the glass melting furnace 4 to the gas inlet 61
of the exhaust gas cooler. In addition to the gas inlet 61,
the exhaust gas cooler 6 is also provided with a gas outlet
62 and an outlet 63 for condensation products. Both outlets
are disposed on the bottom end of exhaust gas cooler 6.
Furthermore, the exhaust gas cooler 6 is furnished with a
device 65 for the feeding as well as the supply and the
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discharge of a coolant, e..g., cooling water or cooling air.
On top of the exhaust cooler 6, a mechanical cleaning device
66 is indicated by means of which the gas containing parts
of the exhaust gas cooler 6 are continuously or periodically
cleansed of the condensation products which result from
exhaust gas cooling. The condensation product outlet 63 of
the exhaust gas cooler 6 is connected to the feeding side of
the batch mixer 3, i.e. to the upper part of its interior,
via another conveyor device 64, in this case also a screw
conveyor. For this purpose, the upper part of the housing
30 of the batch mixer 3 is provided with a condensation
product inlet 36. If required, the condensation products
can be discharged either partially or completely via a
switch 69 which is disposed on the upper end of the conveyor
device 64.
A first suction fan 67, whose end is joined to a
connecting pipe 68, is disposed downstream of the gas outlet
62 of the exhaust gas cooler 6. The connecting pipe 68
leads to a gas inlet 34 of the batch mixer 3. The gas inlet
34 in disposed in the bottom part of the housing 30, and is
configured to permit the gas to enter the interior of the
housing 30, but to prevent any batch discharge from the
interior of housing 30 into pipe 38.
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A gas outlet 35, followed by a second downstream
suction fan 70, is disposed on the opposite end of gas inlet
34, i.e. on the upper end of batch mixer 3. The power of
the first suction fan 67 and of the second suction fan 70
can be controlled, preferably by a common control device. A
gas pipe 71 leads from the outlet of the second suction fan
70 to a gas purification device 7 whose components are
generally known and are therefore not listed in detail.
Finally, a chimney 79 is disposed downstream of the outlet
of the gas purification device 7.
The embodiment represented in Figure 2 has a slightly
different configuration than the embodiment as described in
Figure 1. The arch 44 of Figure 1 is omitted in the glass
melting furnace 4 of Figure 2; the superstructure 42 of the
glass melting furnace 4 is con igured as one single
continuous component with the furnace interior forming one
single area. Furthermore, the coolant tube 45 of the glass
melting furnace according to Figure 1 is moved towards the
discharge end of the glass melting furnace 4, i.e. to the
right side. This permits the batch 83, which floats on the
glass melt 84, to cover almost the entire surface 84' of the
glass melt 84. This causes a major part of the gases and
vapor escaping from the glass melt 84 to condense on the
batch resting thereon. Thus, the amount of exhaust gas is
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1 334792
reduced. At the same tim~, the temperature of the gas
emerging from the glass melting furnace 4 through outlet 47
is reduced. At this point, the temperature is between 300
and 500C. In order to ensure a complete elimination of
dioxin and/or furan in the exhaust gas, a separate gas
heater 91 is employed in the gas pipe 60 disposed downstream
of the gas exhaust outlet 47. This gas heater 91 is only
diagrammatically indicated and can be of conventional
design. The incoming gas is heated to a temperature of at
least 1200C for a period of at least 1.5 seconds.
Other details of the apparatus of Figure 2 correspond
to the apparatus of Figure 1, with same parts of the
apparatus being characterized by the same numbers.
In a third embodiment of the apparatus, shown in Figure
3, the exhaust gas cooler 6 inclusive of the mating gas pipe
60 is omitted. The glass melting furnace 4 corresponds in
its essential parts to the glass melting furnace as
represented in Figure 2. It differs from the latter
inasmuch that the gas exhaust outlet 47' is disposed at the
charging end, i.e. on the left end of the glass melting
furnace 4. This exhaust gas outlet 47' is connected to the
intake of the first suction fan 67 via a short gas pipe 60'.
From this point, an already described connection pipe 68
leads to the batch mixer 3.
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Since there are no condensation products fed to the
exhaust gas cooler, the batch is, in its upper part,
configured without the charging inlet 36 as described in the
embodiments of Figures 1 and 2.
The heat necessary for the definite elimination of
dioxin and/or furan is generated by a separate gas heater
91. In the apparatus according to Figure 3 this gas heater
91 is connected to the exhaust gas pipe 71 leading from the
second suction fan 70 to the gas purification device 7.
The embodiment of Figure 4 corresponds mostly to the
embodiment of Figure 3. It differs from the latter in that
the separate gas heater 91 for the heating of the gas and
the elimination of possible dioxin and/or furan is disposed
downstream of the gas purification device 7 and is
incorporated in the gas pipe leading to chimney 79. mhis
embodiment offers the particular advantage that the amount
of gas to be heated after passing the gas purification
device amounts only to about 50% of the original amount of
gas which means saving heating energy.
The following is a description o, how the process
works, based on the apparatus described in Figure l.
Incineration ash 80 from a refuse incinerator or a
garbage disposal plant is fed to the first supply vessel 2.
The remaining supply vessels 2 are charged with the
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necessary additives 81, especially sand and pho~olite and,
if required, cullet. By means of the dosing sluices 20,
premeasured amounts of incineration ash 80 and additives 81
are taken from the supply vessels 2 and fed via conveyor
device 21 to vessel 30 of batch mixer 3, where the
individual components are mixed by a mixer screw 31 in order
to form a homogenous batch 82 which can be molten. The
prepared batch 82 is fed through the solid substance outlet
33 of the batch mixer to the interior of the glass melting
furnace 4 by means of the batch charging device 46. During
operation, the glass melting furnace 4 is filled with glass
melt 84 up to a certain level. The surface 84' of the glass
melt 84 is exactly at the same level with the coolant tube
45 and just below the arch 44.
The batch which is supplied by the batch charging
device floats as a melting batch 83 on the glass melt 84 and
is distributed on the surface 84' of the latter in the
melting area (left part) of the glass melting furnace 4. A
solidification of the glass melt 84 in the area surrounding
the coolant tube caused by a coolant passing through the
latter prevents the melting batch 83 from passing beyond the
arch 44 and the coolant tube 45. The heat energy required
for the melting of the batch 83 is generated as joulean heat
by heating electrodes 43, whose bottom ends protrude into
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the glass melt 84 which, in turn, assumes the function of an
ohmic resistor.
During the melting process, gases escape from the batch
83 with an exhaust gas temperature between 100C and 1000C.
Basically, this exhaust gas can contain SO2, HCl, chloride,
sulfates, carbon dioxide, alkali and heavy metal vapor, and
dioxin and/or furan.
This exhaust gas 85 enters the right side of the
interior of the glass melting furnace 4 through a crack
between the bottom of arch 44 and the coolant tube 45. The
surface 84' of the glass melt 84 in this part of the glass
melting furnace 4 is free of batch. The glass melt 84
contained in this part of the glass melting furnace 4 has a
temperature of approximately 1400C. Hence, the temperature
in the upper part of the glass melting furnace 4 above the
melt 84 amounts to at least 1300-1350C. To achieve the
highest possible temperature it is advantageous to provide
the superstructure 42 of the glass melting furnace 4 with a
best possible insulation. The gas entering this area of the
glass melting furnace 4 is reheated by absorbing heat from
the glass melt. An appropriate adjusting of the flow rate
and a corresponding selection of the dimensions of glass
melting furnace causes the temperature of the hot exhaust
gas to amount to at least 1200C for a period of at least
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1.5 seconds. Thus, the dioxin and/or furan which is
possibly contained in the exhaust gas is definitely
eliminated; consequently the hot exhaust gas contains only
the chlorides, sulfates, carbon dioxide and the alkali and
heavy metal vapors.
This hot exhaust gas is exhausted through the heat
insulated pipe 60. Basically, the insulation serves to
prevent a cooling and thus a subsequent condensation of the
o~ hot exhaust gas 86 within the pipe 60. The hot exhaust
gas is fed through gas inlet 61 to exhaust gas cooler 6,
where it is cooled down to a temperature between 300 and
500C, a process whereby a par. of the exhaust gas is
condensed and deposited within the exhaust gas cooler 6.
The resulting condensation products 88 are removed
continuously or periodically by means of a cleaning device
66 and fed to condensation product outlet 63 which is below
the exhaust gas cooler 6. The condensation products 88 are
fed via conveyor device 64 through condensation product
inlet 36 to the interior of the batch mixer 3 and thus
reintroduced into the batch to be molten. If necessary, the
condensation products cna be removed completely or partially
via outlet 69.
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The pre-cooled exhaust gas 87 exits the exhaust gas
cooler via gas outlet 62 and reaches the first suction fan
67, which generates at its intake, i.e., within the exhaust
gas cooler 6, in the pipe 60 and in the glass melting
furnace 4, a pressure less than the pressure of the
surrounding air. On the side facing towards the conveyor,
the pre-cooled exhaust gas passes through the connecting
pipe 68 towards the batch mixer 3 at a pressure higher than
the pressure of the surrounding air. This pre-cooled
exhaust gas 87, being under a superatmospheric pressure, is
fed into the batch 82 contained in the interior ol the batch
mixer 3 via gas inlet 34. While the exhaust gas 87 is
passing through, it condenses and thereby is cooled down to
approximately 20-50C. It emerges from the surface of the
batch 82 as a cold exhaust gas. In addition to the mixing
of the individual batch components, the mixer screw 31 keeps
the batch loose and permeable to gas. Due to the intense
cooling, even low condensing vapor e.g. heavy metal vapor
condenses within the batch 82 to be molten. The cold
exhaust gas 89 escaping through gas outlet 35 of the batch
mixer 3 contains basically only HCl and SO2.
Interacting with a corresponding control unit and a
pressure sensor, it is the purpose of the second suction fan
70, which is disposed downstream of the gas outlet 3S, to
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maintain the pressure of the cold exhaust gas 89 in the
upper part of the batch mixer at approximately the same
level with the pressure of the surrounding air. This
prevents the intrusion of exhaust gas and additional air
into the system.
The cold exhaust gas 89 which is basically a
concentrated gas consisting of chlorides, S02, and S03 is
fed to the gas purification device 7 via pipe 71 where it is
subject to purification. The remaining exhaust gases 90,
especially N2, C02 and small amounts of oxygen, which escape
from the gas purification device are finally exhausted into
the environment through chimney 79. The relatively harmless
components of the remaining exhaust gas 90 are not hazardous
or pollutant to the environment.
According to the representative embodiments, the
apparatus 1 provides, in addition to the remaining exhaust
gas, a vitreous body 9 which can be reused as a raw material
for further industrial purposes. These vitreous bodies 9
are manufactured continuously from the discharged glass melt
84'' by means of a glass working machine 5. These vitreous
bodies can be used, for example, as ballast or concrete
additives.
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The size of the glass melting furnace 4 and hence the
volume of the glass melt 84 contained therein are
advantageously selected to be large enough so that
deviations in the composition of the incineration ash, which
might occur, do not suddenly change the entire chemistry of
the molten glass. Changes of the glass melt composition 84
can be determined very quickly, e.g. by changes in the
electrical resistance of the glass melt 84 between the
electrodes. These measured values can be used to control
the mixture of the incineration ash 80 and the individual
additives, especially additives with a certain alkali
percentage, e.g. phonolite.
Another possibility for monitoring the composition of
the glass melt 84 is to examine the crystallization of the
final glass product. Glass compositions within certain
limits form certain crystals which can be easily recognized
in the final glass. They indicate if and how the
composition of the glass has been modified. The amount o,
the incineration ash 80 and the additives to be added can
then be correspondingly adapted. Figures 5 and 6 show two
embodiments of the gas purification device 7. Figure 5
represents a wet cleaning device 7, and Figure 6 a dry or
semi-dry cleaning device 7.
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According to Figure 5, the cold exhaust gas 89 is fed
through pipe 71 to a first purification stage 72. This
first purification stage serves to wash out especially HCl
gas from the exhaust gas. In a second purification stage
72' S02 is washed out. A subsequent drop separator 73
separates the water drops which were dragged along. In a
gas reheating stage 74, the gas is reheated to an
appropriate temperature between 30 and 90 5C and subsequently
fed through an activated carbon filter stage 78. After
passing this stage the remaining exhaust gas 90 consists
basically of N2, C02, and small amounts of oxygen which are
exhausted into the environment via chimney 79.
For the HCl separation in the first purification state
72, an acid, preferably of pH less than 1, has to be
selected. For the separation of S02 in the second
purification stage 72', however, a pH of 6-7.5 is preferred.
Preferably, both purification stages 72 and 72' operate on
reversed current, however, direct current is also possible.
Mercury which is possibly present in the exhaust gas 89 is
separated in the activated charcoal filtering stage. The
amount of waste water and slurry resulting from the
purification stages 72 and 72' and from the drop separator
are fed advantageously to a waste-water purifying plant.
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The seco~ embodiment of the gas purification device 7,
shown in Figure 6 has as a first component a saturator 75 to
which the cold exhaust gas 89 is fed, also via pipe 71.
Once the exhaust gas is saturated with water in the
saturator 75, it is introduced to a fluidized bed or a spray
adsorber 76. Preferably, NaOH or Ca(OH) in watery solution
are admitted to the spray adsorber. In a gas temperature
regulating stage 77 the escaping gas is brought to an
optimum temperature for the subsequent activated charcoal
filtering stage 78. The finally remaining exhaust gas which
escaped is exhausted into the environment through chimney
79.
The waste waters and the solid substances resulting
from this process are subject to further purification, e.g.
in a waste-water purification plant or are dumped or reused.
Due to the relatively simple, defined composition of
the exhaust gas 89, the gas purification devices serve to
recover sodium chloride and sodium sulfate in a relatively
pure form. These raw substances, in turn, can be used for
the manufacture of soda.
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Apart from glass, products resulting from the inventive
process are glass gall, dust, and/or slurry which have to be
deposited or further processed if they are not used as a
construction material like the glass.
It is thus a further object of the invention, to solve the
problem of substances resulting from the melting of incineration
ash in glass, which substances have not been deposited at all, or
only to a small extent. The process should operate inexpensively,
by means of conventional industrial apparatus, and should be safe
and troublefree.
This further object is achieved, by adding dust resulting from
gas purification into the batch, which dust may be a filtrate
slurry.
In order to have an absolutely harmless pure gas, the exhaust
gas is fed through an activated charcoal filter after purification.
In order to concentrate the exhaust gas, it is advantageous to cool
it before and after purification.
The total amount of harmful substances discharged from the
process is reduced by those substances resulting from the gas
purification and the heavy metals contained in the melt. Since the
solubility for the heavy metals contained in the glass melt, and
in a broader sense for all metals contained therein, is not
exceeded during the process, all heavy metals are incorporated in
261 3347q2
the glass, where they cannot be leached out, by re-
introduction into the glass melt.
It is further surprising that the glass gall residue is
relatively clean. This is due to the fact that a larger
amount of gall, as compared to the process, permits a more
exact separation and the gall thus reaches also a higher
degree of purity. It is possible to use this glass gall as a
raw material for chemical purposes. The glass gall
percentage amounts to approximately 5-10% of the incineration
ash employed.
In an incinerator 100 waste is burned. This burning
produces ash and exhaust gas, a part of the ash being
transported in the gas as fly ash. In an exhaust gas
purifier 101 the fly ash is divided from the gas. All the
ash is then fed into a mixer 103, together with additives
102, known as raw material for the making of glass, In the
mixer 103 a batch is made, which is fed into a glass melting
furnace 104. From the furnace 104 two liquid products are
separately removed, namely, vitreous material and glass gall.
Further, exhaust gas is removed from the furnace 104 and fed
into a three stage gas cleaning device, The first stage is a
dry dust separator 105 and the second stage is a wet cleaner
106. The dust and filtrate removed from the gas in the dust
separator 105 and in the wet cleaner 106 are fed together
back to the mixer 103 and re-introduced into the batch. The
gas leaving the wet cleaner 106 flows through an activated
charcoal filter 107, which is the third and last stage of the
gas cleaning device. The pure gas leaving the activated
charcoal filter 107 is let out into the atmosphere.
