Plant for the treatment of waste

A plant comprising a post combustion chamber (1) connected to the combustion chamber of a household rubbish incineration furnace whose hot gases it uses in order, by means of suitable burners (2, 3), to heat sewage sludges and industrial liquids and a circuit for the treatment of the smoke and residues coming from said post combustion. This circuit, which is held under vacuum by a blower (27), comprises a dry cooling tower (7) employing semi-liquid sludges as cooling agent, an absorption tower (15) employing a solution adapted to combine the predominantly acid gases of the smoke, and a separating tower (22) in which the liquids in suspension are removed. A recycle circuit (190) for the solution and liquid separated and means of recovering metallic particles and compounds (10, 12, 29) complete this plant.

The object of the present invention is a plant for the treatment of waste 
which is intended to solve certain technical and economic problems raised 
by the elimination of the smoke liberated by household rubbish 
incineration furnaces and by the purification and elimination of slightly 
contaminated industrial liquors and sewage sludges. 
At present, the smoke given off by household rubbish incineration furnaces 
is cooled and then eliminated in annexed installations comprising fragile 
and expensive electrofilters which poorly withstand the chlorinated 
compounds resulting from the combustion of plastics, which have the effect 
of corroding them rapidly. 
Slightly contaminated industrial liquids, such as for instance liquors of 
the galvanic industries, spent solvents and resinous residues cannot be 
treated in purification stations since their degree of contamination is 
still too high for this type of treatment. Therefore, these industrial 
liquids must be stored and then transported for destruction after having 
undergone prior lengthy and complicated filtration and settling. 
Finally, the liquid or semi-liquid sewage sludges which are normally 
treated in the purification stations rapidly clog the latter and thereby 
result in the necessity of effecting frequent cleaning. 
The plant defined in Claim 1 provides the solution for these problems by 
the fact that it combines in a single operating cycle the treatment of 
industrial liquids and of sewage sludges and the treatment of the smoke 
coming from the combustion of both this waste and of rubbish burned in the 
incineration furnace with which it is associated, doing so in an 
economical manner, without the contribution of expensive external energy, 
the energy being provided by the hot gases coming from this furnace. 
The accompanying drawing shows, by way of example, one embodiment of the 
object of the invention.

The sole FIGURE of this drawing is a diagrammatic overall view. 
The plant shown comprises: 
A post-combustion chamber 1 equipped with two burners 2 and 3, arranged 
vertically opposite each other with an inlet 4 intended to be connected to 
the combustion chamber of a household rubbish incineration furnace of any 
existing known type (not shown) in order to recover the hot combustion 
gases directly therefrom via this inlet 4. 
An expansion conduit 5 following and communicating with the post-combustion 
chamber 1 and equipped with a conical bottom with discharge valve 6. 
A dry cooling tower 7 connected to the expansion conduit 5 and equipped 
with an inlet 8 communicating with a feed vat 9, with a conical bottom 
with discharge valve 10 and with an outlet conduit 11. 
A centrifugal separator 12 connected to the cooling tower 7 and equipped 
with an outlet conduit 13 and with a conical receptacle with discharge 
valve 14. 
A wet cooling and absorption tower 15 connected to the centrifugal 
separator 12 by the conduit 13 and equipped with injectors 16, 17 and 18, 
with a conical bottom which discharges into a receptable 19, with an 
evacuation conduit 20, and with a connecting conduit 21. 
A treatment and cooling liquid feed and recycle circuit 190. 
A separating tower 22 connected to the absorption tower 15 by the conduits 
20 and 21 and equipped with a feed container 23 and with an outlet conduit 
24. 
An absorber 25 connected to the separation tower 22 by the conduit 24. 
A filter device 26. 
A blower 27. 
This equipment, which forms a treatment circuit, has the following 
characteristics: 
The two burners 2 and 3 of the post-combustion chamber 1 are of a type 
capable of treating liquid, gaseous or pasty residues, such as for 
instance the high-frequency burner described in Swiss Patent No. 579 238. 
Waste of high heating power such as, for instance, spent solvents and 
resinous residues is injected into the lower burner 2 and waste which on 
the other hand requires a large contribution of heat such as, for 
instance, sewage muds laden with metallic hydroxides, silt, and mud is 
injected into the upper burner 3. Under the effect of the hot gases 
introduced into this chamber via the inlet 4 and which normally reach 
1100.degree. to 1200.degree. C., this waste ignites by itself, burns and 
then passes through the chamber 5 at the bottom of which the heavy 
metallic residues and compounds coming from their combustion, such as 
slags and clinkers accumulate and are evacuated through the outlet valve 
6. 
In order to obtain a good mass transfer between the waste introduced into 
the post-combustion chamber and the combustion air, said chamber is 
arranged preferably vertically, as shown in the drawing, in such a manner 
as to produce a turbulent flow and a sufficiently long average holding 
time, for instance on the order of two seconds. This effect, combined with 
the temperature of the hot gases introduced of 1100.degree. to 
1200.degree. C. assures the decomposition of the most harmful organic 
waste, such as dichlorodiphenyl trichlorethane. 
The use of two burners arranged opposite each other and fed with waste of 
different heating powers is advantageous since this arrangement makes it 
possible to regulate the temperature of the post-combustion chamber 
without the addition of supplementary air, but this arrangement is not 
indispensable and a single burner can assure adequate operation. 
In the dry cooling tower 7 the hot gases are sprayed with semi-liquid 
sludges which are injected via the inlet 8 and come from the vat 9 into 
which they have been previously poured. These sludges, used here as 
cooling agent, will preferably be sewage sludges without appreciable 
heating value and of low content of harmful heavy metals so that they are 
potentially reusable, such as for instance muds, silts, and sludges 
containing metallic hydroxides or other inorganic compounds. 
The metallic particles and compounds contained in these sludges are 
recovered in dried form either via the discharge 10 from said tower 7 for 
the heavier particles and compounds or via the discharge 14 from the 
centrifugal separator in the case of the lighter particles and compounds. 
Parallel to these semi-liquid sludges, metallic particles and compounds 
coming from the separation effected in the absorption tower 15 after 
settling as will be explained further below are injected via the inlet 8 
of said tower. These metallic particles and compounds, dried in this 
cooling tower 7, are also recovered at the outlets 10 and 14 mentioned 
above. 
In the absorption tower 15, the gases which are still hot are again cooled 
by spent solutions, introduced, in the example described, on three levels 
via injectors 16, 17, 18, before being dried in the separation tower 22. 
These spent cooling solutions prior to their injection are conditioned as 
a function of their origin, for instance by oxidation and hydrolysis in 
order to eliminate the cyanide or deadly elements. Their second mission is 
to act as absorbent for the predominantly acid gases, such as for instance 
the sulfurous anhydride or the nitrogen oxides formed upon the primary 
incineration and combustion of the sewage sludges. 
These solutions, acting as coolant and absorbent, are maintained constantly 
in suitable condition in a feed and recycle device 190 coming from a 
container 34 into which there are introduced appropriate reagents, 
depending on the acidity of the gases emitted, primarily sodium hydroxide, 
lime waters or other spent solutions of alkaline content. Depending on the 
pH of the cooling agent, most of the heavy metallic compounds are 
precipitated as their hydroxides. 
At the bottom of the absorption tower 15, this solution is recovered in the 
receptable 19, which stabilizes its flow, and it is recycled in the 
circuit 190, in which it is first of all introduced into a settling tank 
28; at the bottom of this tank the metallic particles and compounds 
contained in the recovered solution accumulate whereupon these wet 
particles and compounds are directed via a conduit 29 equipped with a 
first pump 30 into the vat 9 where they are mixed with the sewage sludges 
for their recovery in dry form, as explained previously, or else into the 
post-combustion chamber 1 via the extension 290 of the conduit 29 for 
their removal or else as additional contribution. 
This solution, which has been clarified in the settling tank 28 overflows 
into a distribution tank 31 after which it is pumped by a second pump 32 
through a conduit 33 also connected to the container 34 which is fed with 
solution. The resultant solution constitutes the feed of the injectors 16, 
17 and 18 to which it is transferred from the pump 33 via a conduit 35. 
The residual metallic particles and compounds still suspended in the 
distribution tank 31 are carried along at the bottom of the latter by a 
continuous flow into a final receptacle 36, after which they are taken up 
by a third pump 3 and reintegrated via a conduit 38 in the receptacle 19 
for drying and recovery in the cooling tower 7. 
In this way all risk of external pollution by the recovered metals is 
avoided, the circuit 190 in which they are cooled and settled being a 
closed circuit. In this way also the solution is continuously reused and 
renewed after settling and clarification. 
In case of need, an addition of dilution liquid in the last receptacle 36 
can be effected from a container 39 provided for this purpose. 
The gases cooled and freed of their metallic particles and compounds in the 
tower 15 are directed via the conduit 20 into the separation tower 22 in 
which all the drops of liquid contained in these gases are removed. For 
this purpose, this tower can be filled with coarse pieces of limestone 
which, furthermore, have the advantage of reducing the residual amount of 
HCl and SO.sub.2 still possibly contained in these gases. 
Via the bottom conduit 21 the condensates are recycled by the circuit 190 
into which they flow via the bottom of the tower 15, so that no liquid 
leaves the plant. 
The absorber 25 contains wood bark which eliminates the malodorous 
components of the gases which, dried in the separation tower 22 and 
deodorized in this absorber 25 are finally filtered in the filtration 
device 26 and then released through the blower 27. 
This blower 27 has the additional important effect of maintaining a vaccum 
throughout the gas treatment circuit of the plant so that any possible 
leak of gases is avoided at the discharge outlets 6, 10 and 14 of this 
circuit. 
Finally, two safety bypass conduits are provided, one 40 connecting the 
inlet 4 of the post combustion chamber 1 to the cooling tower 7, and the 
other 41 connecting the separation tower 22 to the filtering device 26. 
This filtering device 26 may be of any nature whatsoever but the fact that 
the gases emerging from the separating tower 22 are dried, cooled and 
freed of their harmful particles affords the advantage of permitting the 
use of a filtering device known as a "tube filter," which constitutes a 
simple and economical solution. 
Furthermore, the gases are already sufficiently purified upon emergence 
from said separating tower 22 to permit their release at this level and 
thus avoid the addition of the absorber 25 and of the filtering device 26, 
the vacuumizing device 27 being in this case directly connected to the 
outlet conduit 24 of the separating tower 22.