Apparatus for processing solid wastes to produce a fuel

An apparatus for processing of residential or industrial solid wastes, including first grinding means, magnetic separation means, first screening means, whose screenings are directed to second grinding means, drying means comprising a hot air generator, gravity separation means, cyclone separation means, second screening means, and press granulating means. The apparatus is used for production of solid fuels in granules, whose net calorific value can be modified by causing the mesh size of the first and second screening means to vary.

FIELD OF THE INVENTION 
This invention relates to an apparatus and process for processing of solid 
wastes, such as residential wastes, industrial wastes and the like, to 
produce a storable solid fuel. It relates more particularly to an 
apparatus and a process aimed at producing a solid fuel with preset 
characteristics from wastes freed of their fermentable organic fraction. 
BACKGROUND OF THE INVENTION 
There are already known in the field numerous apparatus for processing 
wastes, for example, of the residential waste type, to obtain a solid 
fuel. 
There are already known in particular, as disclosed in French Pat. Nos. 2 
265 457 and 2 322 660, processing apparatus in which means are provided to 
subject the wastes to the action of an acid such as an inorganic acid. 
However, this type of apparatus is both complex and costly. 
Further, there is shown in French Pat. No. 2 487 221, an apparatus for 
processing residential wastes to produce fuel agglomerates and a compost 
in which a ventilation separation is performed with output gases from a 
cyclone separator, the solid fraction availale at the output of this 
separator being subjected to screening followed by shredding. 
SUMMARY OF THE INVENTION 
This invention aims at simplifying such a processing without compromising 
the quality of the resulting solid fuel, and at proposing a processing 
apparatus in which specific means are closely combined to assure drying 
simply and effectively, and separation of inorganic heavies and fines, the 
product delivered by said means being advantageously suitable for shaping 
into granules or other agglomerates, without additional grinding. 
Another object of the invention is to make it possible in a simple way at 
this stage to vary the net calorific value of the resulting fuel. 
For this purpose, this invention relates to an apparatus for obtaining a 
solid fuel from residential wastes or the like, characterized in that it 
comprises, in combination, and successively from upstream to downstream: 
(a) first grinding means to reduce the particle size of the initial wastes; 
(b) magnetic separation means to eliminate ferrous metals; 
(c) first screening means to separate smaller-sized fermentable organic 
materials from the rest of the wastes, or combustible fraction, able to be 
transformed into fuel; 
(d) second grinding means designed to reduce the particle size of the fuel 
fraction still further; 
(e) pneumatic drying means designed to reduce the water content of the fuel 
fraction and outputting a gas stream charged with said fuel fraction; 
(f) gravity separation means designed to separate from the gas stream the 
heavy products contained in the fuel fraction; 
(g) cyclone separation means designed to separate from the gas stream the 
fuel fraction freed of said heavy products; 
(h) second screening means designed to eliminate the inorganic fines having 
a high ash content; and 
(i) press granulating means designed to transform the fuel fraction on 
coming from the second screening means into fuel granules; 
DETAILED DESCRIPTION OF THE INVENTION 
The net calorific value of the resulting fuel granules can be modified to 
meet fuel requirements by varying the mesh sizes of the first and second 
screening means.

With reference to the drawings, raw residential wastes contained in bulk in 
a hopper 10 are brought into a grinder 12, in the present case with a 
grappling transfer mechanism 14 and a conveyor 15. Grinder 12, which 
suitably has a shredding capability, is designed to shred the plastic bags 
in which residual wastes are most often collected, and to give said wastes 
a relatively fine texture suitable for their further processing. In 
particular, and as will be seen in more in detail below, such a grinding 
will give the ground organic materials a texture that will promote their 
fermentation (composting), and to the fuel fraction a particle size that 
will promote its transformation into fuel. 
After their passage in grinder 12, the wastes are routed, in the present 
case by a belt conveyor 16 to a standard magnetic separator, 
diagrammatically indicated as 18, which is designed to assure the 
elimination of ferrous metals. Actually, this type of material is, of 
course, unsuitable both for composting and for obtaining fuel. The metals 
recovered at the output of separator 18 can be recycled, as applicable. 
The available ground material on coming from magnetic separator 18 and 
freed of ferrous metals is then subjected to a screening in a screen 20. 
The object of this screening is to separate the material into a 
fermentable organic fraction and a fuel fraction. It should be noted here 
that such a separation is made possible by screening because the fuel 
products, after grinding in 12, prove to exhibit a considerably coarser 
particle size than that of the fermentable organic materials. Thus, the 
fuel products are available in the form of screenings, while the 
fermentable organic materials, which are finer, are recovered after having 
gone through the meshes of screen 20. By way of illustration, a mesh size 
of screen 20 between 10 and 25 mm has proven satisfactory. 
After this screening stage, the fermentable organic materials can be dumped 
or processed by composting, in a standard way. 
The screenings which, as has been said, are able to be converted into fuel, 
are then subjected to fuel production process itself. 
It should be noted that at the screening stage in 20, there is a 
possibility of adjustment, i.e., the capability of favoring one or other 
of said fractions. Thus, by reducing the mesh size of screen 20, the 
amount of fuel screenings is increased while reducing the amount of 
fermentable material, which makes it possible to obtain a larger amount of 
fuel from residential wastes. On the other hand, by increasing the mesh 
size of screen 20, the amount of fermentable organic materials is 
increased, while reducing the amount of fuel product. 
However, it will be noted that, regardless of what happens, undesirable 
materials for fuel production, such as glass, porcelain, etc., are ground 
in grinder 12 to be eliminated with the fermentable fraction in screen 20. 
Thus, it is possible to increase the fuel fraction without, however, 
increasing in it the presence of such "parasite" materials. 
The fuel production process itself is described in detail below. 
The fraction with high net calorific value provided at the output of screen 
20 in the form of screenings, as a result of the physical processing 
described above, is brought by means not shown and along arrow 21 into a 
surge hopper 22; this latter, of course, gives the installation a greater 
flexibility in use. 
The materials contained in hopper 22 are brought, in the present example, 
by a grapple 24 or the like and a conveyor 25 to a shredder grinder 26. 
The object of the grinding and shredding operation performed in 26 is to 
reduce the particle size of the product, particularly textile materials 
that it contains, often left intact by the preprocessing described, to 
facilitate its later drying, its transport all along the processing line, 
and its granulation at the end of processing, as will be seen below. Tests 
have shown that a particle size on the order of 30 to 50 mm is 
satisfactory for the processing sequence. 
After shredding and grinding in 26, the product is dried in a drying unit 
28. Actually, it has been found that at this processing stage, the product 
intended to be transformed into solid fuel has a water content most often 
between 25 and 40%. Thus, by eliminating at least a part of this water by 
drying, to bring it to proportions less than 15%, there are obtained a 
notable increase in the net calorific value, a better mechanical strength 
of the fuel product once ground as described below at the end of the 
processing, as well as a possibility of storage of the product by 
minimizing the risks of variations of the latter, particularly by 
fermentation. 
In the present embodiment, drying unit 28 is of the pneumatic type. More 
specifically, the product provided at the output of shredder grinder 26 
and routed to the input of dryer 28 is transported in this latter by a 
drying fluid. It can be noted here that the prior grinding of the product 
in 26 promotes its transport by such a drying liquid. 
This drying fluid, in the present embodiment, consists of inert hot gases 
at a temperature on the order of 500.degree. to 600.degree. C., supplied 
by a generator indicated overall as 30. As will be seen more in detail 
below, these hot gases are obtained by combustion of a part of the fuel 
produced in the present installation. 
As FIG. 2 shows more in detail, pneumatic dryer 28 is in the form of a 
horizontal cylindrical housing 31 provided at its opposite ends, 
respectively, with an input 32 for the product to be dried, a coaxial hot 
gas input 34, and a coaxial output 36 located at the free end of a 
narrowing 38. On the inside of housing 31 are formed radial baffles 40 
forming a single central passage, in a standard way. 
On coming from housing 31, the product is in the form of a solid phase in 
suspension in a gas phase. The necessary separation of these two phases is 
performed as follows. First, at the lowest point of the product output, 
i.e., as shown by FIG. 2, in the lower wall of output 36, sealing device 
such as isolation trap 42 or equivalent is located. Isolation trap 42 is 
designed to extract by gravity at this site the heavy elements unsuited 
for fuel production, such as nonferrous metals (not eliminated by the 
magnetic separator mentioned above), leather, rubber, etc. Actually, it is 
found that this type of product, because of its density, cannot be 
pneumatically entrained by the hot gases, which is used to perform the 
separation. In an experimental installation it was found that more 
generally all products of a density greater than 0.6 were evacuated by 
isolation trap 42. 
After this stage of separation of the heavies by isolation trap 42, the hot 
gases routing the rest of the fuel product are introduced into a standard 
cyclone separator 44, at the lower end of which the dry product is 
recovered, as said above, free of heavy bodies. 
The hot gases, recovered at the top of cyclone separator 44, are introduced 
into a dust removal unit 46, for example of the multicyclone type, to be 
rejected into the atmosphere (by a stack indicated as 48), with or without 
additional processing, in compliance with existing standards and 
regulations, or also for an optional recycling. 
The dry product available at the output of separator 44 and of dust remover 
46 is then subjected to a fine screening in a screen 50. The object of 
this screening is to eliminate the last inorganic fines with a high ash 
content, which are, of course, undesirable because they are inert and are 
still in the product. 
Such a fine screening at this stage of processing offers the following 
advantages: the product to be screened is in the dry state at this stage, 
which particularly facilitates its screening; as already said, the ash 
content is advantageously lowered; and finally, it offers the possibility 
of adjustment of the net calorific value of the final fuel. Actually, if 
the mesh size of the screen is made to vary, it is possible to obtain as 
output (the waste side of screening) a more or less pure product. More 
precisely, the greater the proportion of inorganic fines eliminated, the 
higher the net calorific value of the fuel, and vice versa. 
Thus, tests have shown that it was possible, with the installation of this 
invention, to obtain fuels with a net calorific value varying between 3600 
and 5000 kcal/kg, depending on the above-mentioned adjustment. 
In this embodiment, but optionally, on coming from screen 50 the product, 
at an intermediate point of a conveyor 52, is subjected to an additional 
separation in a magnetic separator, indicated diagrammatically as 54, to 
eliminate the last particles of ferrous metals that may have escaped 
magnetic separator 18 at the beginning of the processing. 
It can be noted that the fuel used in generator 30 to obtain hot drying 
gases can advantageously consist of a small part of the product taken from 
various sites in the line, by adapting the hot gas generator to the nature 
of the product. 
The rest of the product is delivered, at the output end of conveyor 52, to 
an input of a granulating unit, indicated overall as 56. First of all, the 
unit comprises a mixer, indicated diagrammatically as 58, in which the 
product is initially homogenized. Such a mixer will also be useful in the 
optional case where another fuel, such as wood, charcoal, plants in the 
dry state, is added to the fuel product to be granulated, which has been 
obtained from residual type wastes in the way described above. It should 
be noted that the consistency of the fuel product at this processing stage 
advantageously allows such a mixing with this other fuel. Finally, the 
object of mixer 58 is to perform the distribution of the product on 
associated granulating presses, indicated as 60. Preferably, presses 60 
are of the roller or die type, standardly used in granulating plant or 
other products. 
On coming from the presses, the granules, still relatively high 
temperature, are cooled in the present case by going through an air cooler 
62. The hot air recovered in this cooler, if necessary, can be recycled to 
generator 30 to improve its efficiency. Also, the fines recovered at the 
cooler can be recycled to mixer 58. 
The granules coming from cooler 62 can be subjected to a sieving (not 
shown) to eliminate the last fines, which will also be recycled to mixer 
58, before being deposited in a storage hopper 66 by standard conveyor 
means. 
The apparatus according to the present embodiment of the invention was 
tested and provided the following results: for 100 tons of standard 
residential wastes at the start there was obtained 28 tons of solid fuel 
granules of an apparent density on the order of 600 kg/M.sub.3, with a 
moisture content less than 10%, an ash content on the order of 18 to 20%, 
with a net calorific value between 3600 and 3800 kcal/kg. The fuel product 
was odorless, not fermentable, free of pathogenic germs, and its storage 
proved to be quite easy (simply protection from water). 
Further, by increasing the mesh size, particularly in second screen 50, 
there was obtained, still for 100 tons of wastes at the start, 20 tons of 
granules of an apparent density on the order of 600 kg/M.sub.3 
(unchanged), with a moisture content less than 10% (also unchanged), but 
an ash content on the order of 15 to 18%, with a considerably increased 
net calorific value between 4600 and 4800 kcal/kg. 
Of course, this invention is not limited to the embodiment described, but 
includes any variant or modification that a person skilled in the art can 
bring thereto.