DESCRIPTION

Technical Field

The present invention relates to a method for pre-treating biomasses, more particularly for pre-treating biomasses intended for a biorefinery or similar facility for producing biofuels. The present invention further relates to a plant for pre-treating biomasses capable of implementing said method.

Prior Art

Biorefineries in which biofuels are obtained from biomasses through a fermentation process are known.

In particular, it is known to produce bioethanol by fermentation starting from biomasses.

In current biorefineries, bioethanol is obtained starting from biomasses deriving from sugar-rich agricultural products. For example, sugarcane, corn, sunflower and soy are raw materials widely used for the production of bioethanol.

However, use of said crops for producing biofuels is being increasingly criticized as it subtracts resources from the food industry.

In recent times, attempts have been made at obtaining biofuels, particularly bioethanol, starting from the cellulose contained in non-food masses such as for instance wheat straw or rice straw and other agricultural waste materials.

Furthermore, cellulose is a raw material of great interest non only for producing bioethanol, but more generally for the entire field of the so-called "green chemistry". However, at present bioethanol production from cellulose appears to be too expensive and non-competitive from an economic viewpoint when compared with the production starting from agricultural crops.

The main difficulties in producing bioethanol from cellulose lie in the preparatory steps of pre-treatment of raw materials rather than in the process of cellulose fermentation.

Indeed, in order to make cellulose available for the fermentation process and expose it to the microorganisms responsible for such fermentation process, it is necessary to separate cellulose from lignin.

Such separation can take place according to different methods: chemo-physically (for instance by "steam cracking"), thermally (for instance by gasification), enzymatically. Whatever the separation method may be, the raw materials must be homogenized and purified from possible contaminants such as rocks, stones, soil, metal pieces and so on. In currently known plants, non-food biomasses such as wheat straw and/or rice straw fed in bales are freed from straps and shredded, for example by using a hammer shredder. However, this solution of the known type involves a series of drawbacks.

First of all, the presence of foreign bodies (stones, rocks, metal scraps and the like) inside the biomasses involves the risk of jamming and failure, thus limiting plant reliability, and also causes quick wear of the used shredding devices.

Secondly, during shredding, an excessive quantity of dusts is created, which is a remarkable problem during the subsequent processing steps.

Furthermore, the size grade of the material after shredding is non-homogeneous and the presence of unshredded straw stalks (which may be up to 150 cm long) involves problems and inefficiencies in the subsequent processing steps.

The document EP 175 128 describes a method and an arrangement for pre-treating paper in which a step of paper disintegration and a step of removal of foreign bodies are provided upstream of the paper shredding step. However, this step of removal of foreign bodies takes place in dry conditions and cannot effectively remove lighter foreign bodies. In order to limit dust formation during shredding, the method and the arrangement described in EP 175 128 provides for wetting paper by spraying, but this measure does not ensure satisfactory results.

The aforementioned difficulties related to the pre-treatment of biomasses have heretofore strongly limited the production of bioethanol from cellulose.

In this respect it is to be noted that such difficulties are further amplified by the need to treat high flowrates of biomasses, usually comprised between 20 and 50 t h of dry matter.

The main object of the present invention is therefore to overcome the aforementioned drawbacks so that the production of cellulose-derived biofuels - particularly of bioethanol

- becomes more desirable and cost convenient.

In particular, an object of the invention is to provide a method for pre-treating biomasses, especially, though not exclusively, non-food biomasses intended for a biorefinery or similar facility, which allows to provide biomasses in optimum conditions for subsequent processing.

Another object of the invention is to provide a plant for pre-treating biomasses that is capable of implementing the aforementioned method.

These and other objects are achieved by the method and plant for pre-treating biomasses as claimed in the appended claims.

Summary of the Invention

The method for pre-treating biomasses according to the invention comprises a step of shredding the biomasses and, upstream of said shredding step, a step of soaking the biomasses and simultaneously removing foreign bodies from said biomasses.

To this aim, in the method according to the invention, the soaking step takes place by immersing the biomass in a liquid, preferably water.

In particular, during said step of soaking by immersion, which can take place - for instance - in one or more soaking vessel(s), it is possible to obtain removal both of light foreign bodies (dusts), which remain in suspension, and of heavy foreign bodies (wood pieces, rocks, stones, sands, metal scraps), which precipitate.

In particular, thanks to this soaking step very fine foreign bodies, such as for instance dusts, which would be difficult to remove in a dry manner, can be removed from the biomasses.

Specific measures may possibly be further provided for magnetically removing ferrous foreign bodies.

Advantageously, the duration of said soaking step (i.e. the dwelling time in said one or more soaking vessel(s)) is chosen so as to ensure effective separation both of light and heavy foreign bodies from biomasses.

Advantageously, the step of soaking the biomasses, effected with high-temperature water, possibly mixed with appropriate chemical compounds (such as for instance ammonia), allows to separate some substances (such as for instance silica and waxes) that are undesirable for the subsequent processing steps and facilitates destruction of the structure of the biomasses themselves, thus promoting exposure of the cellulose contained therein and facilitating the subsequent step of lignin separation (for example by means of "steam cracking").

In the case where biomasses are provided in bales (for instance in the case of wheat straw and/or rice straw), the soaking step is preferably preceded by a step of disintegrating the bales and spreading the treated biomasses on the belt so as to allow maximum exposure of the materials to the subsequent treatments. In addition, a preliminary step of removing straps from the bales may be provided in a manner known per se.

Advantageously, according to a preferred embodiment of the invention, the step of shredding the biomasses is a step of shredding by cutting, which ensures higher homogeneity in the size of the material exiting said step with respect to the one obtainable with a shredding by means of hammer shredders.

The invention further relates to a plant for pre-treating biomasses which comprises a station for shredding biomasses and a station for soaking biomasses arranged upstream of said shredding station.

Advantageously, inside the soaking station for soaking biomasses there is provided a simultaneous removal of foreign bodies from said biomasses: inside said station, on one hand biomasses are soaked with water and on the other hand foreign bodies - both light and heavy ones - precipitate or remain in aqueous suspension inside the station and are thus removed.

In the case where biomasses are provided in bales, the station for removing foreign bodies is preferably preceded by a preliminary station for removing straps from the bales and by a station for disintegrating the bales.

Advantageously, according to a preferred embodiment of the invention, the shredding station comprises a blade shredder o similar cutting device, which ensures higher homogeneity in the size of the material exiting said station.

Brief Description of the Drawings

Further features and advantages of the invention will become more apparent from the following detailed description of some preferred embodiments of the invention, given by way of non-limiting example with reference to the annexed drawings, in which:

- Figure 1 is a block diagram schematically showing the main steps of the method according to the invention;

- Figure 2 is a perspective view schematically showing a plant according to the invention capable of implementing the method of Figure 1 ;

- Figure 3 is a side view of the plant of Figure 2.

Description of a Preferred Embodiment of the Invention

A preferred embodiment of the invention will be described in detail hereafter.

Such embodiment should not be intended as limiting the scope of protection of the present invention.

In particular, although hereafter reference is made to the pre-treatment of wheat straw and/or rice straw provided in bales, the invention can be equally applied to biomasses of a different nature.

In addition, although hereafter reference is made to the pre-treatment of biomasses for application to biorefineries for producing biofuels (for instance bioethanol), the invention can be equally applied to the pre-treatment of biomasses intended for other purposes, for which it may be deemed necessary or convenient that said biomasses have a homogeneous size and are free from foreign bodies.

Referring to Figure 1, the main steps of the method for pre-treating biomasses according to the invention are schematically illustrated in the form of a block diagram.

Specifically, in the illustrated example reference will be made to the pre -treatment of nonfood biomasses, particularly of wheat straw and/or rice straw provided in bales.

In said example, the illustrated method may therefore comprise an initial step of strap removal 10 for removing the straps wound around the bales.

The thus freed bales are fed to a shredding step 40.

According to the invention, prior to the shredding step 40 the method for pre-treating biomasses comprises a soaking step 30.

Said soaking step 30, during which the biomass is soaked with water preferably having a high temperature and possibly mixed with appropriate chemicals, contributes to destroy the structure of the biomass itself, thus exposing cellulose and promoting subsequent processing thereof, especially for subsequent separation of cellulose from lignin by means of "steam cracking".

Said soaking step 30 further advantageously allows to simultaneously obtain a step of removing foreign bodies 30' in a wet manner.

Said soaking step 30 with simultaneous removal of foreign bodies 30' may for instance take place in a soaking vessel in which the treated biomass is moved forward.

In this way, the biomass, during its passage in the soaking vessel, becomes soaked with water and at the same time foreign bodies, both light and heavy ones, remain in suspension or precipitate and sediment, thus becoming separated from the biomass, which goes to the subsequent step.

The dwelling time in said soaking vessel will therefore be chosen so as to ensure both proper soaking of the biomass (i.e. sufficient to cause destruction of the structure of the biomass itself and exposure of cellulose) and effective removal of foreign bodies.

Said dwelling time will preferably be comprised between 30 seconds and 3 minutes.

Advantageously, said soaking step 30 is preferably preceded by a step of disintegrating bales 20, during which the bales are disintegrated so as to spread the straw and expose the foreign bodies contained therein, thus facilitating removal thereof.

The thus cleaned biomass (straw) is at last subjected to the shredding step 40.

It will be evident to the person skilled in the art that due to the fact that light and heavy foreign bodies have been previously removed, on one hand the production of dusts during the shredding step 40 is drastically reduced and on the other hand the risk of failures or malfunctioning during this shredding step 40 as well as wear of the used devices are remarkably reduced. In this respect, it is to be noted that removal of foreign bodies in a wet manner is particularly effective in removing dusts and other fine foreign bodies.

In addition, the water contained in the biomass can advantageously act as lubricant, thus contributing to further reduce wear of the devices used in the shredding step 40 and to increase process productivity.

Preferably, according to the invention, the biomass shredding step 40 is a step of shredding by cutting.

The fact that the biomass is cut - instead of being for instance subjected to sieving, as happens in commonly used hammer shredders - allows to obtain higher homogeneity in the size of the shredded biomass thus obtained.

In particular, in the case of the pre-treatment of wheat straw and/or rice straw, shredding by cutting allows to prevent very long straw stalks from being left inside the biomass during the subsequent processing steps.

The thus shredded straw is ready for being fed to a plant for subsequent processing, for instance to a biorefinery for producing bioethanol.

In Figures 2 and 3 there is schematically illustrated an example of a plant for treating biomasses 100 according to the invention, and more particularly a plant capable of implementing the method described above with reference to Figure 1.

Said plant for treating biomasses 100 comprises a transport line 102 consisting of one or more conveyor belt(s) and a plurality of working stations 110 - 150 arranged along said transport line.

In this case, too, with particular reference to the pre-treatment of wheat straw and/or rice straw provided in bales, the plant according to the invention may comprise a station for removing straps 110 that comprises one or more strap-removing machine(s) 112.

Downstream, it is possible to provide for the presence of a station for disintegrating bales 120 which is capable of disintegrating the bales and spreading the straw on the transport line 102, thus exposing the foreign bodies contained therein and facilitating subsequent removal thereof. Said disintegration station 120 may comprise for instance one or more suitably arranged screw conveyor(s) 122.

According to the invention, the plant for treating biomasses further comprises a soaking station 130.

Said station comprises for instance one or more soaking vessel(s) 132, through which the treated straw is moved forward.

During passage through the soaking vessel(s) 132, the straw becomes impregnated with water, preferably having a high temperature and possibly mixed with appropriate chemicals, in order to destroy the structure of the biomass itself, thus exposing cellulose and promoting further processing thereof.

Advantageously, inside the vessels 132 of the soaking station 130 an effective removal of the foreign bodies contained in the biomass is simultaneously effected, wherein said bodies, depending on their density, precipitate to the bottom of said soaking vessels 132 or remain in suspension inside said vessels, thus becoming separated from the straw, which is extracted from said soaking vessels 132 and continues to move forward along the transport line 102.

In order to obtain a correct soaking of the biomass and an effective removal of the foreign bodies contained therein, the straw is moved forward through the soaking vessels 132 so that its dwelling time inside said vessels is adequate, and preferably comprised between 30 seconds and 3 minutes.

In this respect the soaking vessels 132 are provided with suitable means (not shown) for removing heavy foreign bodies and light foreign bodies, such as for instance one or more scraper(s) arranged at the bottom of the vessels for removing heavier sedimented foreign bodies and one or more sludge pump(s) for removing lighter suspended foreign bodies.

Suitable magnetic removal means (not shown) may possibly be provided in the soaking vessels 132 for removing ferrous foreign bodies.

As an alternative, it will be possible to provide that one of the conveyor belts of the transport line 102 is a magnetic belt, so as to effect removal of foreign bodies directly during the forward movement of the straw on said transport line.

The thus cleaned straw finally moves forward to the shredding station 140, where it is cut to pieces.

Advantageously, according to a preferred embodiment of the invention, said shredding station 140 comprises one or more blade shredder(s) 142 or similar cutting devices.

Using blade shredders allows a more homogeneous size in terms of dimensions of the obtained shredded biomass and, in particular, it prevents long straw stalks from remaining uncut.

As anticipated above, the water with which the straw exiting the preceding soaking station 130 is impregnated advantageously serves as lubricant, thus contributing to limit wear of the shredding blades and increase productivity of the shredder.

The thus shredded straw is further conveyed by means of conveyor belts of the transport line 102 to the subsequent processing plants, possibly after being stored in an appropriate storage station 150.

Said storage station 150 may comprise for instance a tank provided with suitable means for handling, dosing and extracting the shredded straw.

The plant described in Figures 2 and 3 may comprise an appropriate system for feeding the biomass to the transport line 102.

Said feeding system may for instance include a storage site and handling means for moving the biomass to be treated from said storage site to the pre-treating plant 100.

Preferably said storage site may comprise a simple storage area and an aerated storage area for dehydrating the biomass having a high moisture content, so as to avoid acetic and lactic fermentation thereof.

The handling devices may preferably comprise one or more overhead travelling crane(s) arranged above the storage site and translationally movable along a direction or, even better, along two orthogonal directions. Said travelling cranes can thus move above the storage site and pick up, in a simple and reliable manner, the desired biomass to be fed to the pre-treating plant 100 (independently of the order in which the biomasses arrive at the storage site).

From the above description, it is evident that the method and the plant according to the invention allow to reach the objects set forth above.

Indeed, with the pre-treatment provided in the method and the plant according to the invention, the biomass at the time of shredding is substantially free from foreign bodies, and in particular from dusts and foreign bodies that may cause jamming, failures and malfunctioning of the devices used for shredding the biomass.

In addition, at the end of the pre-treatment provided for by the method and the plant according to the invention, the biomass is shredded in pieces having homogeneous size and with the cellulose contained therein fully available for subsequent treatments, especially for the subsequent fermentation in case said biomass is used for producing biofuels.

It is further evident that what has been described above with respect to the preferred embodiments of the method and plant according to the invention has been provided merely by way of example and that several variants and modifications can be made on the basis of the common knowledges of the person skilled in the art without departing from the scope of protection as defined in the appended claims.

In particular, although reference has been made above to the pre-treatment of wheat straw and/or rice straw, it is evident that the invention can be equally applied both to food and non-food biomasses of different kind.

In addition, although reference has been made above to the pre-treatment of biomasses intended for biorefineries for producing biofuels, it is evident that the invention can be used for pre-treating biomasses intended for other purposes, whenever it is deemed necessary or convenient for the good outcome of the subsequent processing operations to free said biomasses from the foreign bodies contained therein.