The process of the present invention consists in collecting and storing biomass residues of various types, be it natural or cultivated, from land or from the sea, all the vegetable organisms, such as agricultural residues, residues and products from reforestation and discarded from the food industry, even indirectly organic product derived from biological activity of animals and humans, these residues being thus stored in large amounts. Such residues are subjected to processing steps that beneficiate them by drying, refining, separation and peptization.

The final product is thus obtained in compacted form with a high density index, herein called pellets, a sort of cylindrical capsule of small diameter (about 6 to 25 mm). These pellets may be used in furnaces of any type and provide a high calorific value, advantageously replacing fissile combustion materials, mainly in various heating system that would only be guaranteed by methane gas and fuel oil. These compacted pellets become one of the most ecological fuels ever produced by man industrially. PRIOR ART

Today, the demand for and development of industrialized proc- esses that respect and do not harm the environment is great, mainly when it comes to combustible materials. In this case, what is involved is not only the environment, but also renewable sources. The demand has increased the tireless researches and, in most cases, the solutions are found in nature itself, as was the case of alcohol, extracted from a plant organism, as well as another much commented case at present, which is still the object of various researches, the so-called biodiesel, also extracted from a plant organism. These are alternative fuels found in nature itself and used mainly and with an

advantage in replacing fossil fuels as a renewable source, and said to be ecologically correct. The world is gradually changing with respect to the aggression to the environment, seeking alternatives for continuing the industry, but without river, air and sound pollutions, thanks to the awareness thereof by the public and organizations.

Patent US 4,314,825 discloses a process for preparing combustible solid fuel from grain residue which includes the steps of passing the grain residue through a pelletizing zone wherein the residue is subjected to compaction pressure of greater than about 100 psi while passing live steam therethrough for a period sufficient to cause the in-situ cellulose to form a cohesive pelletized mass. The pellets are thereafter permitted to cool and dry and are then ready for use as solid fuel.

Patent US 4,828,573 describes a method of manufacturing a pel- ietized fuel including the steps of hydrolizing cellulose containing material to form a binder, mixing the binder with combustible fines including preferably coal fines and wood chips or saw dust in which the binder is about two percent to eight percent by weight of the mixture, and forming the mixture into pellets. The pellets are dried by subjecting them to a temperature sufficient to drive off substantially the water content thereof. Patent US 4,561 ,860 discloses a process of producing refuse derived fuel by taking raw refuse, pulverizing it and then screening it to remove fines and oversize material, the screened residue being passed to an air classifier where the light fraction, rich in paper and plastics, is separated. This light combustible refuse fraction is then passed to a densifying machine, either directly or via a secondary shredder, to produce partially compacted material which is then dried in a rotary dryer. The dried material can be passed to a second densifying machine which produces pellets in the form of small dense cylinders or blocks having a calorific value equal to about half that of coal. Coal dust or other combustible particulate material can be added to and mixed with the combustible fraction between the two densifying machines.

Patent DE 196 39 330 provides an apparatus and a method for

producing a substitute fuel from waste materials by using a pre-grinder and a pelletising press for finer grinding. The pelletising press has a ring counter die with openings extending radially from the inside to the outside. The openings have a passage section with an inlet diameter of 6-25mm on their end on the inside. There is a further opening section after the first one with an outlet diameter larger than that of the first section.

Patent EP 247,285 discloses an apparatus and a process for the preparation of briquettes from moist waste, wherein the comminuted moist waste is to be pressed to give briquettes without drying. For this purpose, the moist waste is mixed with a dry, moisture-absorbing and preferably combustible material of small particle size, especially likewise consisting of waste, and then pressed to give briquettes. The apparatus comprises a mixing device which is associated with feeding devices for moist wastes and for a dry, preferably combustible material (14), and is connected via a conveyor to a pellet press and/or briquette press. OBJECTIVE OF THE INVENTION

According to the present invention, a process has been developed which aim at using one more renewable source of fuel, as well as the utilization of residues that are often discarded or thrown away without a cor- rect destination, thus generating environmental passives. These residues are utilized, processed and transformed into a compacted biomass (called pellets) to be used in combustion to feed furnaces with great advantages. Besides the fact that organic substances of various kinds and also biological ones are reused, one creates thereby an ecological fuel, since the produc- tion thereof does not require any kind of chemical aggregating agent, except for those naturally found in the residues themselves, that is to say, the burning thereof does not generate any substance or gas harmful to the environment, depending only upon the amount of CO ₂ equivalent to the amount absorbed during their life time. By way of comparison of the calorific value of the thus formed pellets, ordinary wood, sawdust, bagasse and other plant organisms in natural conditions, especially with their high moisture, can reach a calorific value of 2,000 Kcal/kg, whereas the combustible pellets of the pre-

sent invention can reach a value of 3,500 to 5,000 Kcal/Kg. This calorific value is directly linked to the maximum moisture, which ranges from 8 to 14%, with compaction between 550 and 750 Kg/m ³ . The present invention comprises the use of biomass residues of the most varied types, such as sawdust, bagasses, wastes from agricultural activities, industrial food refuse and from reforestation processes, and others, which can be used in a single matter or mixed in percentages, depending on previous studies for the sake of safety of the process and quality of the pellet.

Thus, this raw material comprising biomass residues is charged into a deposit and from there it follows to processing steps. The material is then led to a drying system that uses hot air produced in a hot-air generator. They can be used as a drying system, for example, a rotary-drum drying system or a conduit drying system (pipeline-type). In such drying systems, one can use hot air with a temperature gradient between the entry and the exit of the system or hot air at a constant temperature throughout the system.

The drying system and the hot-air generator are preferably controlled by temperature and pressure measuring devices. They also have emergency deviation devices. The drying system preferably works at a temperature of up to 45O ⁰ C, containing inside it a mixture of hot gases, so as to keep all the natural characteristics of the residues, without letting off volatile substances found naturally in them.

Depending on the type of biomass residues charged into the deposit, a separation step may become necessary before the drying step. This step aims at separating larger non-usable contaminating residues such as plastics, paper, fabrics and others, from those usable by means of a separator, preferably a separator comprising a disc system with speed variations.

The still crude raw material may further be led to the drying system through a conveying and feeding conduit, preferably by a screw- conveyor or "Redler", which guarantees, by means of a "PLC" panel control, a continuous feeding to the drying step.

During this drying step, there may optionally be a second separation step using a system that preferably functions as a siphon, that is to say,

contamination residues that are not removed in the first step are deposited on the bottom by gravity action, since they are heavy, such as sand, glass, metal and others.

Thus, after the raw material had been duly dried and is free from non-usable residues, it follows to a refining step. If the material to be fed to the refiner contains coarser residues, for example, residues with a size bigger than or equal to 2 cm, a step of separating and grinding these coarser residues becomes necessary. The thus ground residues follow to the refining step. After the refining step, the residues pass through a separating step in a separator, preferably a vibratory separator. At this step, fine contaminants such as silica and other inorganic impurities are separated. Silica, particularly, is abrasive for the pelletizer and, therefore, it would reduce its useful working life if it is not withdrawn. In addition, if silica remains in the pel- let formed, it will crystallize in the burning of the pellet as a fuel, thus reducing the efficiency of the combustion. The fine residues separated in this step may be used as fuel in the hot-air generator used in the drying system.

Then, one goes on to the pressing and extruding steps, wherein one uses a pelletizer to form the pellets. Preferably, such a pelletizer com- prises a roller system to press the residues on a circular rotary surface provided with orifices ranging from 6 to 25 mm in width. One then extrudes the material, which, after being pressed through the orifices, is cut by blades, whereby the pellets are obtained.

In addition to the extremely low moisture contents, another great advantage of the pellets produced according to the present invention is directly linked to the logistic sector. Due to its high density, a charge of a number of cubic meters may contain much more biomass by weight and consequently in Kcal than other similar charges, such as wood, sawdust, bagasse and others, thus bringing about a great economy in transport per kilocalorie. DESCRIPTION OF THE FIGURE

Figure 1 represents a schematic block diagram of the process of the present invention, showing the passage of the raw material comprising

biomass residues through the steps of producing and obtaining the pellets.

It should be noted that the essential and necessary steps for carrying out the process of the present invention are indicated in the blocks and arrows with continuous line and the optional or preferred steps indicated in the blocks and arrows are drawn with dashed line. DESCRIPTION OF THE INVENTION

The present invention relates to a process for preparing pellets from biomass residues, which comprises the following steps. a) charging the biomass residues into a deposit (1); b) drying the biomass residues in a drying system (3) by means of hot air from a hot-air generator (2); c) refining the biomass residues dried in step b) in a refiner (4); d) separating, in a separator (5), the biomass residues refined in step c) into 2 fractions: fines residues and residues suitable for the produc- tion; and e) pressing and extruding the residues suitable for the production separated in step d) in a pelletizer (6), thus forming the pellets.

The present invention also relates to the pellets prepared by the process described above, which may be used as fuel. DETAILED DESCRIPTION OF THE INVENTION

According to Figure 1, the process of preparing the pellets according to the present invention comprises a step of charging the biomass residues into a deposit (1 ); a step of drying the residues in a drying system (3) by means of hot air from a hot-air generator (2); a refining step in a refiner (4); a step of separation into fine residues and residues suitable for the production in a separator (5); and a step of pressing and extruding the residues suitable for the production in a pelletizer (6).

Thus constituted, the process begins by charging the biomass residues into a deposit (1). The residues are then led to a drying system (3), which uses hot air produced in a hot-air generator (2). Preferably, the drying system (3) is a rotary-drum drying system or a conduit drying system (pipeline-type). Particularly , the drying system (3) uses either hot air with a tern-

perature gradient between the inlet and the outlet thereof or hot air at a constant temperature throughout the system.

The drying system (3) and the hot-air generator (2) are preferably controlled by pressure and temperature measuring devices, and have emer- gency deviation devices. The drying system works preferably at a temperature of up to 45O ⁰ C.

Optionally, if necessary, the process may further comprise, prior to the drying step, the step of separating larger non-usable contaminating residues from usable residues by means of a separator (7). Preferably, such a separator (7) comprises a disc system with speed variations, so as to separate the larger non-usable contaminating residues such as plastics, paper, fabrics and others.

In a preferred embodiment of the present invention, the biomass residues may be led to the drying system (3) through a conveying and feed- ing conduit, which can function as a screw-conveyor or "Redler". By means of a "PLC" panel control, this conveying and feeding conduit guarantees a continuous feeding to the drying system (3).

Optionally, is necessary, the process may further comprise, during the drying step, the step of separating the heavier residues from less heavy residues in a separator (8). Preferably, such a separator (8) comprises a system working like a siphon and a lower reservoir for holding the heavier residues, such as small solid grains. These contaminating residues, which may not have been removed in the previous separation step, are deposited in a reservoir on the bottom by gravity action, since they are heavy residues, such as sand grains, glass, metal and others.

After the biomass residues have been duly dried by the drying system (3) and, as the case may be, free from non-usable residues by means of the separators (7) and (8), they follow to the refining step in a refiner (4). Optionally, if the material to be fed to the refiner (4) contains coarser residues, for example, bigger than or equal to 2 cm, the biomass residues are subjected to a step of separating these coarser residues in a

separator (9) and grinding them in a grinder (10). The residues ground in the grinder (10) follow then to the refiner (4).

After the refining step, the biomass residues pass through a separation step in a separator (5), preferably a vibratory separator. The bio- mass residues are thus divided into 2 fractions: fine residues and residues suitable for the production. Examples of fine residues separated by the separator (5) are silica and other inorganic impurities. Preferably, the fine residues separated in this step are used as fuel in the hot-air generator (2) used in the drying system (3). The residues suitable for the production separated by the separator (5) are subjected to a pressing and extruding step in a pelletizer (6) for the formation of pellets. Preferably, such a pelletizer (6) comprises a roller system against a wall that has small orifices ranging from 6 to 25 mm. The external part of said wall has rotary blades that cut the biomass residues into small pieces, giving rise to the pellets.

The pellets formed according to the process of the present invention, as described above, have preferably a diameter of 6 to 25 mm. They come out of the pelletizer (6) preferably at a temperature lower than or equal to 9O ⁰ C. These pellets may be used as fuel and have a calorific value be- tween 3,500 and 5,000 Kcal/Kg, a maximum moisture between 8 and 14%, a compaction between 550 and 750 Kg/m ³ and ash contents lower than 1%.

There are numberless advantages of the process for preparing pellets from biomass residues according to the present invention. The steps employed bring about better operation control over the process, for instance, enabling one to control the moisture between 8 and 14% ± 0.5. The processing steps prior to the pressing and extrusion cause the biomass residues to exhibit characteristics of their own, thus enabling one not to use vapor or ag- glutinants, such as maize starch, molasses, and agglutinant chemical produces, in the pelletizer, unlike the processes known from the prior art. In addition, the pellets according to the present invention come out of the pelletizer at a temperature lower than or equal to 9O ⁰ C, a cooling step being unnecessary, which is commonly used in the processes known

from the prior art. So, the pellets of the present invention can follow directly to a storage silo.

Another advantage of the process of the present invention is that there is no need to use conditioners that employ agglutinants, vapor and wa- ter to prepare the biomass residues for entry into the pelletizer. This pre- pelletizing step, employed in prior-art processes, is not employed in the process of the present invention, since the biomass residues have characteristics of their own, conferred by the processing steps preceding the pressing and extruding step. The process of the present invention enables one to obtain pellets with a calorific value between 3,500 and 5,000 Kcal/Kg, a maximum moisture between 8 and 14%, a compaction between 550 and 750 Kg/m ³ and ash contents lower than 1%. These characteristics make the pellets of the present invention suitable for use as fuel. The illustrative example given below will serve to describe better the present invention. However, the process described therein merely refers to an embodiment of the present invention and, therefore, the example given below should not be take as being limitative of the scope thereof. EXAMPLE 3000 Kg of biomass residues from sugar-cane bagasse was charged into a deposit. The charge was divided into 2 parts of 1500 kg each to follow by different drying systems.

1500 Kg of biomass residues was dried in a rotary-drum drying system through hot air from a hot-air generator. In this drying system, the hot air had an inlet temperature of 45O ⁰ C and an outlet temperature of 60 ⁰ C.

1500 Kg of biomass residues was dried in a conduit drying system (pipeline-type) through hot air from a hot-air generator. In this system, the hot air had a constant temperature of about 25O ⁰ C.

After the biomass residues from both drying systems had been dried, they were subjected to a refining step, using a 5 mm-mesh refiner.

The thus refined biomass residues followed to a pneumatic vibratory separator to remove fine contaminants, such as silica and other inor-

ganic impurities. A 1 mm-mesh separator was used, thus separating 2 fractions: fine residues of a size equal or smaller than 1 mm and residues suitable for the production with a size ranging from 1 to 5 mm. The percentage of fine residues was of 13-15%, a sufficient amount to feed the hot-air genera- tor.

The residues suitable for the production having size between 1 and 5 mm followed then to a pelletizer, without the use of agglutinant or vapor. The compaction was of 700 Kg/m ³ and the pellet diameter was of 6 mm.

The thus formed pellet exhibited 10% moisture, ash contents lower than 1 % and temperature of 6O ⁰ C, a cooling step being unnecessary, and it could follow directly to a storage silo.

An embodiment of the invention having been described, one should understand that the present invention embraces other embodiments, being limited only by the scope of the accompanying claims.