EP2809447A1

EP2809447A1 - Method for finely grinding a carbonated material load with additives added, and associated continuous biomass processing installation and gasification application

Info

Publication number: EP2809447A1
Application number: EP13712911.0A
Authority: EP
Inventors: Thierry Chataing; Clément BAUW; Thierry MELKIOR
Original assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Current assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 2012-02-03
Filing date: 2013-02-01
Publication date: 2014-12-10
Anticipated expiration: 2033-02-01
Also published as: FR2986443B1; DK2809447T3; WO2013114328A1; FR2986443A1; EP2809447B1

Abstract

The invention relates to a method for finely grinding a carbonated material load, wherein the carbonated material load in the form of millimeter-size or micron-size particles is introduced into the inlet of a first vibrating mill chamber (5) the outlet of which is connected to the inlet of a second vibrating mill chamber (7), the first and second vibrating mill chambers each comprising grinding media freely accommodated therein and designed to grind particles. In said method, the first and second chambers are made to vibrate so as to crush the introduced particles between the grinding media and between the grinding media and the peripheral inner wall of each chamber. According to the invention, additives of mineral materials and/or additives of plant materials and/or additives of materials of plant origin are also introduced into the inlet of the second vibrating mill chamber, the additives being in the form of a micron-size powder.

Description

FINE GRINDING PROCESS OF A CARBON FUEL LOAD WITH ADDITIVE ADDITIVES, BIOMASS CONTINUOUS PROCESSING FACILITY

AND APPLICATION TO GASIFICATION

Technical area

The present invention relates to the mechanical treatment of carbonaceous material feedstock and more particularly to a process for the fine grinding of such a feedstock, in particular biomass feedstock.

It is specified here that fine grinding is understood to mean grinding the particles of the carbonaceous material charge to obtain micron or millimetric dimensions, that is to say up to hundreds of microns or even up to dimensions less than 5 millimeters. Of course, the crushed carbonaceous material filler particles are smaller in size than the millimetric or micron-sized carbonaceous material filler particles that feed the inlet of the first chamber of the vibratory mill in accordance with the invention.

In the case of lignocellulosic biomass, a first stage of mechanical treatment is conventionally performed and consists of coarse grinding (shredding for forest chips). Depending on the desired application, a second mechanical treatment step subsequent to the first is necessary and consists of fine grinding to confer specific properties on the biomass powder. For example, it may be wood flour for the manufacture of biofuels in the form of granules.

The invention therefore relates more particularly to this second step of mechanical treatment of biomass, for injection in powdered form in a downstream conversion reactor (gasification) or in a combustion or so-called co-combustion reactor (biomass and coal) in a coal-fired power plant or for granulation to produce biofuels.

The invention is advantageously applied to the gasification of biomass for the production of biofuels from the synthesis gas widely known under the name Syngaz. In this application, the fine biomass crushing method according to the invention is preferably carried out upstream of a powder conditioning / storage unit itself upstream of a gasification reactor to subsequently produce biofuels. State of the art

The mechanical treatment of biomass (tree trunk, straw bales) typically comprises a first step of coarse grinding, usually at the place of harvest, which in particular facilitates transport and reduce its cost. This first step of grinding is carried out by means of shredder (in English "shredder") and leads to centimetric or millimeter-sized particles, typically wood chips in the wood dies. It is made using grinders with proven technology (hammer mill, knife or scissors). The particles thus coarsely ground thus constitute what are called inputs in the gasification or biomass combustion pathways (heat and electricity cogeneration, heat production, biofuel production).

For an application of thermochemical conversion of the biomass by gasification, in a reactor type flow driven reactor, the size required for the biomass particles is of the order of a few hundred microns.

For biomass combustion applications, numerous studies show that particle size plays a key role: as indicated in the publication [1], the micronisation of the powder promotes combustion and reduces particulate emissions.

A number of studies are devoted to the fine grinding of biomass particles, especially wood chips, to reach millimeter to micron granulometries depending on the case. In these studies, the effects of the nature of the biomass, the type of mill (s) used, the desired grain size were characterized on the energy cost of the actual operation of fine grinding, and / or properties of the powder obtained (granulometric distribution, particle shape).

From these studies, he has identified a number of trends that can be summarized as follows.

For the grinding of lignocellulosic biomass, knife mills and hammer mills are well suited: here we can cite the publications [1], [2] which highlight this. This operation is of low energy cost if the size of the particles does not fall below the millimeter. Each of these technologies has advantages and disadvantages, as highlighted in the publication [3]. Thus, the major advantage of the so-called hammer mill technology is its robustness and a lower maintenance cost. On the other hand, the energy consumption is greater for a hammer mill, typically of the order of 130 kWh / ton (kWh / t), than for a knife mill, typically of the order of 60 kWh / t: see publication [4]. In addition, the powder obtained with a hammer mill has a more spreading particle size distribution (publication [5]), which is a major drawback for the flowability, that is to say the ability to flow, the powder as highlighted in the publications [6], [7]. Hammer mill grinding occurs mainly by impact and attrition, which induces an elongated and deformed particle geometry, showing hook-like projections along the fiber, called fibrils, which promote the interlace effect between particles, cohesion between the grains and through this the accentuation of the effect known as the effect of vault in storage containers (silos): see publication [8]. It should also be noted that a longer mechanical treatment induces a high energy cost without fundamentally modifying the shape of the particles, because they always undergo crushing by hammers.

Similarly, ball mills conventionally used for grinding coal work by attrition and produce elongated particles and many fines on fibrous materials.

In addition to these proven grinding technologies for grinding carbonaceous material feedstock, it is known to use a vibrating type mill to grind hard and friable materials, such as limestone, metal oxides. Reference can be made to publications [9] and [10] which respectively describe the theoretical aspect of the fragmentation of these materials and the different mill technologies used. Thus, in a vibratory mill, fragmentation takes place by impact and attrition at a variable frequency. The team of Kobayashi et al thought to use a vibrating mill technology in order to achieve a fine grinding (micronisation of the bio mass) for a combustion application: see publication [6]. It has been found that fragmentation by impact makes it possible on the one hand to solve the problem of the presence of fibrils on the biomass particles obtained and on the other hand to shorten the length of the particles by promoting the propagation of the cracks present in the particles. biomass fibers. The tests carried out by Kobayashi et al were carried out directly from millimeter-sized (22 mm) wood chips introduced at the entrance of vibrating mill chamber and required a relatively long powder treatment time to achieve the desired characteristics (d <30 μιη), which resulted in a high energy cost (800kwh / t).

It emerges from these studies that the major problem of fine biomass crushing lies in the energy cost of the operation itself, because of the fibrous nature of the biomass particles.

In addition, the biomass powders obtained, that is to say finely ground, are difficult to transport, handle, inject into a downstream conversion reactor, because they tend to form agglomerates which generates the effect of arch , poor flowability ...

It is known from US Pat. No. 6,833,185 and patent application US 2008/0116118 that it is possible to improve the flowability properties of a fine powder, by mixing it with an additive powder of nanometric or submicron dimension, of which the average apparent particle density is lower than that of the fine powder.

Beyond the actual grinding operation itself, two pathways are currently envisaged for the global treatment to reduce the size of biomass particles in energy applications (cogeneration, heat production, production of combustion products, production of biofuels ).

The first route consists of a mixed solution of thermal pre-heat treatment called roasting combined with mechanical grinding by the milling technology already proven and mentioned above: hammer mills for fibrous ball mill materials for coal. Roasting is a gentle thermal treatment of biomass at the interface between drying and pyrolysis, usually carried out at temperatures between 200 and 350 ° C and aimed at removing water and modifying some of the organic matter bio mass to break its fibers. In other words, this mild heat treatment alters the fibrous structure of the biomass, thus facilitating its grinding. This makes it possible to reduce the energy cost of grinding and to obtain less fibrous particles, thus easier to transport, store and inject into a downstream reactor: see publication [11]. The powder obtained for a high roasting of the biomass, that is to say leading to a loss of mass greater than 30% by the operation, has characteristics close to those obtained with coal. This allows to use the solution conventionally adopted for the grinding and for the powder injection which is the pneumatic conveying (dense phase). Indeed, as already mentioned, the intrinsic characteristics of the biomass (fibrous and elastic material) are at the origin of the difficulties of storage, transport and injection in thermochemical conversion reactors. Thus, the thermal pre-treatment of roasting solves the problem, but for an energy cost that could prove prohibitive. Evaluations are currently underway.

The second way is to optimize either grinders given according to the type of biomass or complete chains of mechanical grinding.

Thus, in the publication [4], already tested mechanical grinding technology solutions are studied according to the type of biomass with the main objective of reducing the energy cost of the grinding operation and adapting it to the intended application.

It has also been proposed to use two grinders in series to finely grind biomass.

The Esteban team explicitly proposes the serialization of two grinders in order to optimize the energy cost of grinding: see publication [12]. Here again, the choice fell on the implementation of two grinders of the same type, namely hammer mills. The authors then worked on the integration of the whole to optimize the energy cost of the chain and the granulometry of the final product. They thus determined the granulometric threshold at the outlet of the first mill, optimized the types of recirculation of the product. On the basis of their tests, the authors estimate that the cost of grinding on an industrial scale, that is to say for a flow rate of the order of 10 t / h, amounts to 120 to 150 kWh / t for wood chips (poplar or pine respectively). However, the authors specify in the publication [12] that it was not possible to use a sieve size sieve smaller than 1.5 mm at the output of the second mill, because of stuffing problems. In other words, with the solution according to Esteban, it appears impossible to finally obtain finely ground particles.

The team of Siyi Luo et al. proposes a grinding chain capable of mechanically treating both wood (pine) and softer biomass (straw, stems ...): see publication [13]. The proposed chain makes it possible to reduce the dimensions of the particles up to values of 250μιη fixed by a cyclone downstream so that they can be used in a burner. More precisely, the proposed chain comprises two crushers in series, with identical technology called blades (in English "crushers"). In operation, the first mill, that is to say the one upstream, has its axis which extends horizontally while the axis of the second mill extends to the vertical. The energy cost is estimated at 87 kWh / t for pine chips. The effect of this grinding chain on the flowability and injection properties of the powder in a reactor is not studied by the team of Siyi Luo et al. In addition, it should be noted that the chain incorporates an initial drying of the biomass, whose energy cost is not integrated into the evaluated value. On the other hand, if the particle size of the powder is given, the particle shape of the powder has not been characterized.

The general object of the invention is to overcome at least some of the disadvantages of the state of the art of biomass treatment and more generally of carbonaceous material charge for its injection in powder form in a conversion reactor. downstream (gasification) or in a combustion or so-called co-combustion reactor (biomass and coal) in a coal-fired power station or for granulation to produce biofuels.

A particular aim is to propose a process for the fine grinding of biomass, and more generally of carbonaceous material feedstock, which improves the properties (flowability, fluidization ability) of the powder obtained and at a lower energy cost. In other words, it is sought according to the particular object to avoid agglomerates of finely ground biomass powder to improve their ability to be transported, manipulated, and injected into a downstream conversion reactor.

Presentation of the invention

To do this, the subject of the invention is a process for the fine grinding of a charge of carbonaceous material according to which the charge of carbonaceous matter, in the form of particles of millimeter or micron dimensions, is introduced at the inlet of a first chamber of vibrating-type mill whose output is connected to the inlet of a second vibrating-type mill chamber, the first and second vibrating mill chambers each comprising grinding bodies freely housed therein and adapted to grind particles, a method according to which the first and second chambers are vibrated so as to crush the particles introduced on the one hand between the grinding body and secondly between them and the peripheral inner wall of each chamber.

According to the invention, at the inlet of the second chamber of the second vibrating mill, additives of mineral matter and / or additives of vegetable matter and / or additives of material of plant origin are introduced, the additives being in the form of a micron-sized powder.

The term "micron-sized powder" means a powder whose particles have unit dimensions of less than 1 mm with, where appropriate, elementary particles of nanometric size, typically of the order of 100 nm.

According to a preferred embodiment, the charge of carbonaceous material is biomass. Thus, to carry out a fine biomass crushing operation, the inventors have thought of putting in series two chambers or stages of vibratory mills, which is advantageous from an energy cost point of view, and to introduce into that the most downstream, that is to say the one in which the biomass particles are already finely ground on the submillimeter scale, additives of mineral matter and / or plant material and / or material of plant origin, in the form of a micron-sized powder, preferably less than 5 μιη. Thus, with such dimensions, at least a partial coating of the biomass particles is carried out in the dry process, which makes it possible to improve the flowability properties and the fluidization ability of the powder finally obtained. In other words, the very fine particles of additives of mineral matter and / or plant material and / or material of plant origin, are brought into direct and close contact with the relatively larger biomass particles, by application of mechanical forces. shear and impact for example. Depending on the biomass used, the additives may be chosen from magnesium stearate (C36H70MgO4), silica in the form of microbeads, such as that marketed under the brand name New reach SilicaFume NR950 and which contains 95% of SiO2 or else marketed by Rhodia under the trade name Tixosil®68 and which contains 90% of the amorphous silica or under the name Tixosil®331. The additives may also be based on silicon oxide particles SiO ₂ or containing CaCO 3. In other words, according to the invention is incorporated additives that allow proper operation of a downstream gasification reactor. Thanks to the fine biomass crushing method according to the invention, it is now possible to envisage carrying out, on an industrial scale and continuously, a gravity injection directly in thermo-chemical conversion reactors, which was not envisaged. to date, due to the poor flowability and / or fluidization ability of known biomass powders, with the undesirable vault effect that could occur.

It is specified here that "flowability of the powder" is understood to mean the definition given in the publication [14], namely the ability to flow freely in a regular and constant manner in the form of individual particles.

The mineral composition of the additives is advantageously chosen to be a chemical mineral supplement required for ash management in a downstream gasification reactor. Indeed, it is known that the ash content of the biomass is very variable and of very different composition. The publication [15] indicates that wood typically contains 0.5-1% ash with mostly calcium and potassium, whereas wheat straw contains 8% ash with mostly potassium and silica. two types of biomass, there are significant differences in ash content and very different compositions. These differences directly impact the operation of a gasification reactor: the operation with wood generates a very high ash melting temperature required, which requires the addition of additives (silica in this case) to adjust this temperature to the operation reactor, typically at about 1300-1400 ° C. Conversely, the operation with straw results in a melting temperature required too low for the operation of a gasification reactor requiring the addition of different additives (calcium) to raise this temperature value. Thus, preferably, the micron powder of mineral additives is rich in silicon or calcium (greater than 10% by weight). If the biomass treated is wood, the additive is for example based on particles of silicon oxides SiO ₂ or silica-based microbeads. If the treated biomass is derived from agricultural residues with a low calcium content, the additives making it possible to control the gasification operation are preferably derived from lime, that is to say a mixture of calcium CaCO ₃ and magnesium oxide.

According to a preferred embodiment, a pre-grinding step is advantageously carried out using a knife mill which produces a powder with particles. shorter (reduced length / diameter ratio) and a reduced fine particle ratio (<30 μιη). Particle calibration by sieving also significantly improves the efficiency of fine grinding and particle shaping. The sieving operation can be carried out so as to have particles smaller than 500 μιη. Thus, advantageously, pre-grinding particles of unit dimensions of the order of a millimeter and the vibrating mill is used to adjust the shaping of the particles (remove the fibrils, round the corners and shorten their length).

The plant material additives are advantageously based on charcoal, such as charcoal and / or cereal straw charcoal. The plant material additives may also be advantageously based on roasted biomass, such as roasted wood, or roasted agricultural products, that is to say having previously undergone such as cereal straw, the bark, shells (cherry stones, walnut shells ...).

Preferably, the amount of added plant material additives is between 0.5 and 20% by weight of the carbonaceous material feed, more preferably between 5 and 10%. It has been found that the greater the quantity of additives added, the better the flowability obtained at the output of the vibratory mill. Thus, the preferred range is advantageous because it is a good compromise between, on the one hand, improving the flowability according to the invention and the cost of carrying out the process.

The plant material additives may advantageously be based on fossil coal. It is specified here that fossil coal (charcoal) comes from the degradation of the organic organic matter and that it contains minerals whose content may vary according to the geographical area of coal extraction.

According to an advantageous variant, the particle dimensions of the carbonaceous material feed introduced into the first vibrating mill chamber are substantially between 1 and 2 mm.

According to an advantageous variant, the dimensions of the micronic additive powder introduced into the second vibrating mill chamber are substantially less than 5 μιη.

Preferably, the particle size of the carbonaceous material charge obtained at the outlet of the second vibratory mill chamber is less than 800 μιη, preferably less than 200 μιη. According to an advantageous variant, the vibratory mill grinding bodies freely housed inside the chamber consist of several sets of cylindrical bars of unit diameter different from each other.

The invention also relates to a method for treating biomass in which the mass of biomass is dried in the raw state, and then the fine grinding process as described above is carried out by introducing the biomass into the first vibrating mill chamber. at least dried. Preferably, the dried biomass feed is made with a water content thereof in a range of 10 to 15%.

According to an advantageous embodiment, a pre-grinding of the dried biomass is carried out upstream of the fine grinding process by introducing it into a chamber of a knife or scissors-type grinder. A knife or scissors mill comprises, for example, notches on a central shaft rotatably mounted in the chamber, the notches being adapted to pull the dried biomass particles against the peripheral inner wall of the chamber. According to an advantageous variant, the particle size of the pre-milled biomass is substantially greater than 1 mm.

According to an advantageous embodiment, a sieving of the pre-milled biomass is carried out upstream of the fine grinding process, and downstream of the pre-grinding of the dried biomass. According to an advantageous variant, the sieving of the pre-milled biomass is carried out so as to carry out the fine grinding process from particles of millimeter dimensions less than 2 mm or micron dimensions less than 500 μιη. Preferably, the millimeter-sized particles greater than 2 mm are reintroduced into the knife mill.

According to an advantageous embodiment, at the outlet of the second vibratory mill chamber, the particles obtained are selected according to their dimensions so that they are less than 800 μιη, preferably less than 200 μιη.

According to an advantageous embodiment, a roasting heat treatment is carried out with biomass, and then the fine grinding process as described above is carried out by introducing into the first chamber of the vibrating mill the roasted bio mass.

The subject of the invention is also a continuous bio mass treatment plant intended to implement the method as described above, comprising:

a first vibrating-type grinding chamber, a second vibrating-type mill chamber whose inlet is connected to the outlet of the first vibrating mill chamber;

- A micronization mill for grinding additives of mineral material and / or plant material and / or material of plant origin, in the form of a micron-sized powder, the output of the micronization mill being connected to the entrance to the second chamber vibrating mill.

The plant may further include a drying apparatus upstream of the first vibrating mill chamber. It can also further comprise immediately downstream of the drying apparatus and upstream of the second vibrating mill chamber, a knife mill. It can also further include immediately downstream of the knife mill and immediately upstream of the first vibrating mill chamber, a sieving apparatus. Finally, it may further comprise a dynamic variable speed selector immediately downstream of the second vibrating mill chamber, said dynamic selector being adapted to extract at the output of the second vibrating mill chamber particles smaller than a desired diameter. The vibratory mill grinding bodies freely housed inside the chamber advantageously consist of several sets of cylindrical bars of unit diameter different from each other.

detailed description

Other advantages and features of the invention will emerge more clearly from a reading of the detailed description of the invention, given by way of illustration and without limitation with reference to the following figures among which:

FIG. 1 is a diagrammatic view of a first embodiment of a continuous biomass treatment plant incorporating a vibratory mill with two stages and making it possible to implement the method of fine grinding of the biomass according to FIG. invention;

FIG. 1A is a schematic view of an alternative embodiment of an installation according to the first illustrated mode of FIG. 1;

FIG. 2 is a schematic view of a second embodiment of a continuous biomass treatment plant incorporating a vibratory mill with two stages and making it possible to implement the method of fine grinding of the biomass according to FIG. invention; FIG. 3 is a graph of test records which shows the number of measurements at a given avalanche angle value, the tests being carried out with a wood powder (beech) as a carbonaceous material feedstock of the process fine grinding according to the invention and with or without mineral additives;

FIG. 4 is a graph of test records which shows the avalanche angle value as a function of the type of wood powder as carbonaceous material feed of the fine grinding process according to the invention and with or without additives of mineral matter;

FIG. 5 is a graph of test records which shows the number of measurements at a given avalanche angle value, the tests being carried out with a wood meal (sawdust) as a carbonaceous material feedstock of the process fine grinding according to the invention and with or without additives of material of plant origin;

FIG. 6 is a graph of test records which translates the number of measurements to a given avalanche angle value, the tests being carried out with a wood powder (beech) as a charge of carbonaceous material of the process fine grinding according to the invention and with or without additives of material of plant origin;

In the description which follows the terms "input", "output" "upstream", "downstream", "first", "second" are used by reference with the direction of transfer of biomass and the powder of additives to both in the vibrating mills according to the invention, and in the installation incorporating the mills.

In the embodiment of FIG. 1, the plant firstly comprises upstream a dryer 1 fed with treated raw biomass to carry out its drying. For example, the treated raw biomass consists of forest chips, typically a few mm thick and a few cm in length. By way of example also, the flow rate of treated raw mass is of the order of 1 t / h and the dryer 1 used is a rotary kiln dryer, marketed by Maguin. This drying step makes it possible to have a reduced energy consumption of the pre-grinding operation immediately downstream on the one hand and allows the optimal operation of the grinding operation according to the invention on the other hand. We can consider all types of dryers available on the market (rotary kiln, belt dryer etc. ...) to achieve this step.

Once the biomass has dried at the outlet of the dryer 1, it is introduced into a knife mill 2 which therefore performs a step of mechanical pre-grinding of the particles dried biomass. For example, the knife mill 2 may be monorotor type (FL / FNG / FNV) also operating at a rate of 1 t / h and marketed under the trade name Poittemill Forplex. To reduce the energy cost of this pre-grinding operation, care is taken to obtain advantageously at the output of the knife mill particles of dimensions at least equal to one millimeter.

To optimize the pre-grinding operation and to reduce the particle size distribution of the particles, a sieving operation is carried out continuously using a sieving apparatus 3. For example, it may be a vibrating sieve marketed by the company RITEC, under the name of MC type.

As shown in FIG. 1, the particles of dimensions greater than 2 mm are preferably reinjected into the knife mill 2. During this continuous sieving step, it is advantageous to extract the very fine particles of smaller diameter. at 30 μιη, using a dynamic selector not shown: according to this variant, the fraction thus taken can be used as a fuel for supplying energy to the dryer 1. Thus, at the outlet of the sieving apparatus, obtains particles of dimensions substantially between 1 and 2 mm. This sieving operation can also be carried out with an apparatus for sieving mesh openings of micrometric (micron) dimensions so as to obtain, at the outlet of the apparatus, micron sized dried biomass particles, typically between 0 and 500 μιη. or between 0 and 200 μιη.

Finally, fine grinding of the dried, pre-milled and sieved biomass particles is carried out continuously. To do this, these particles are first introduced at the inlet of a first chamber 5 of a vibratory mill. The output of this first vibrating mill chamber 5 is connected directly and immediately downstream to the inlet of a second vibrating mill chamber 7.

According to the invention, at the inlet of the second vibrating mill chamber 7 concomitantly passes biomass particles already finely ground in the first vibrating mill chamber 5, a micron powder of additives 4 (CaCO ₃ + SiO 2 or silica microbead ...).

As shown in this FIG. 1, the additives 4 may be continuously micronised to a diameter of less than 20 μιη, preferably less than 5 μιη by means of a micronization mill 6. The first and second chambers, respectively 5 and 7, of vibrating mill can be carried out in the same apparatus. For example, it may be the one marketed by the company RITEC under the name Palla 50U (90 kW) which incorporates two grinding stages or in other words two rooms in the same device. As grinding bodies freely housed inside the vibrating mill chamber, steel bodies can be used, preferably in the form of solid cylindrical bars. More preferably, the cylindrical bars used may have a diameter of between 10 and 60 mm, preferably between 20 and 50 mm. The grinding bodies can also be in the form of balls or in the form of cylpebs. Preferably, the grinding bodies are of different unit sizes to each other. According to an advantageous variant, it is possible to advantageously use several sets of cylindrical bars of different unit diameters between them, housed freely in the same chamber of the vibratory mill 5. This further improves the efficiency of the grinding because compared to cylindrical bars of same unit diameter, it reduces statistically the clearances between bars of different unit diameter.

By way of example also, the micronization mill 6 of the additives 4 can also be a vibrating type mill, marketed by the company RITEC, under the name lab / pilot (2.2 kW), and its operating flow can be equal at 10 kg / h. Fine grinding according to the invention then advantageously combines the effect of the second chamber 7 vibrating mill and finely milled additives 4 (micron powder). In this way, at least a partial coating of the biomass particles already ground in the first vibratory mill chamber 5 is carried out in a certain way. This improves the flowability and fluidization properties of the powder. At the very least, the vault effect of such a powder conventionally observed in storage silos is considerably reduced. Preferably, the additives 4 have a mineral composition best chosen to control the ash melting temperature in a downstream gasification reactor.

At the outlet of the second vibrating mill chamber 7, particles of unit dimensions smaller than 30 μιη are extracted using a dynamic selector 6. For example, the dynamic selector 6 may be the one marketed by the company RHEWUM under the name of type AQ. This extraction is advantageous because the very fine particles reduce the flow property of the powder. This extracted fraction can be used as a combustion product directly in a reactor downstream conversion and / or as a product of combustion directly in the dryer 1 upstream, which further reduces the energy cost.

In the variant illustrated in FIG. 1A, the dried, pre-milled, and sieved bio-mass particles are introduced concomitantly with particles of abrasive mineral material 4 'entering the chamber of a vibrating mill 5. The fine grinding according to FIG. The invention is thus advantageously supplemented by the effect of the first vibrating mill chamber 5 and the injected inorganic abrasive particles 4 'by coating the biomass particles with the additives. In other words, the first vibratory mill chamber 5 operates in semi-autogenous operation with the mineral abrasive grinding powder 4 'of particle size equal to 3 mm. Preferably, the mineral abrasive particles 4 'injected are based on SiO ₂ silicon oxide particles. Preferably, they have a chemical composition with an SiO 2 content greater than 80%. Thus, it may be silica (sand) or quartz for example.

The amount of the abrasive powder 4 'can be advantageously adjusted with the micronised additive powder 4 injected to have an ash melting temperature adjusted to the operating temperature of the downstream gasification reactor. Thus, it is preferable to choose relative proportions between additives 4 containing CaO and abrasive powder 4 'containing at least 80% of SiO 2 in a range which may vary between 35% o and 65% o of each of these two constituents, namely CaO and SiO ₂ , in order to have an operating temperature of a downstream gasification reactor of between 1436 and 1460 ° C.

In the mode illustrated in FIG. 2, instead of drying, pre-grinding and continuously sieving the particles as in the embodiment illustrated in FIGS. 1 and 1A, the inlet of the first vibratory mill chamber 5 of the biomass having previously undergone a roasting heat treatment step. It can be forest chips previously shredded to unit sizes of 50 mm and roasted.

To optimize the energy cost of the installation which has just been described, care is taken to find an optimum between the dimensions of the particles targeted between the pre-grinding step by the knife mill 2 and fine grinding by the first and second chambers 5 and 7 vibrating mill and the total energy consumed. Various tests were carried out on samples to corroborate the effect of better flowability of the crushed carbon material feedstock thanks to the additives introduced at the inlet of the first vibrating mill chamber according to the invention.

In order to quantitatively evaluate the flowability, we measure what is called the avalanche angle, which is a characteristic of a powder flow: the lower the angle, the better the powder flows. The avalanche angle of each sample was measured using a device marketed under the name REVOLUTION by MERCURY SCIENTIFIC. This apparatus comprises a drum rotating on itself and inside which the powder is placed whose avalanche angle is to be measured.

First of all, a first series of tests was carried out with silica additives in the form of microbeads, which is the one marketed by RHODIA under the trademark Tixosil®331.

This first series of tests is carried out with a natural beech wood powder with particle sizes between 0 and 500 μιη to which a greater or lesser percentage of Tixosil®331 additives has been added. It is specified here that in Figures 3, 4 and 6 the abbreviation% m means the percentage by mass of the additives in relation to the quantity of the bio mass concerned.

FIG. 3 illustrates the number of occurrences (measurements) for a given avalanche angle for the natural beech wood powder respectively without additive, with 1% by mass of Tixosil®331 added and with 2% by mass of Tixosil added ®331. It is clear that the measured average avalanche angle is lower for a larger amount of Tixosil®331 added. In other words, the flowability of the natural beech powder under free flow conditions is improved by the addition of Tixosil®331 mineral additives. This improvement is even greater than the amount of additive is important.

A second series of tests was carried out again with the same Tixosil®331 mineral additives, with a natural beech wood powder but with particle sizes between 0 and 200 μιη and for two different batches.

A third series of tests were also carried out with the same Tixosil®331 mineral additives, but with a spruce wood powder with particle sizes between 0 and 200 μιη and for a single batch. The graph in Figure 4 illustrates the results obtained for these second and third series of tests: it appears that the avalanche angle measured is lower for a larger quantity of Tixosil®331 added for each batch and whatever the nature of the wood (natural beech or spruce). In other words, the flowability of the wood powder under free flow conditions is improved by the addition of Tixosil®331 mineral additives regardless of the nature (natural beech or spruce) of the wood. For natural beech or spruce powder, the improvement in flowability is greater the greater the amount of Tixosil®331 mineral additive. For example, for batch No. 1 of natural beech powder, an added quantity of Tixosil®331 mineral additives of 2% by weight decreases the value of the avalanche angle by 58 ° (without additive ) at 50 °.

Other tests have been carried out with additives of plant material as additives to wood.

FIG. 5 illustrates the number of occurrences (measurements) for a given avalanche angle for wood flour (sawdust) with particle sizes between 0 and 200 μιη, respectively without additive and with about 10% by weight ( D50%) added fossil coal ("coal"). It is clear that the average avalanche angle measured is lower when fossil coal is added. In other words, the flowability of the wood flour powder in free flow condition is improved by the addition of fossil coal additives.

Finally, trials were carried out with additives of vegetable matter as additives to wood.

FIG. 6 illustrates the number of occurrences (measurements) for a given avalanche angle for natural beech powder of particle sizes between 0 and 200 μιη, respectively without additive and with 10% by weight of added coal. wood. It is clear that the average avalanche angle measured is lower when adding charcoal. In other words, the flowability of the natural beech powder under free flow conditions is improved by the addition of charcoal additives.

From all these tests, it can be concluded that the flowability of a powder or wood flour of micron particle size under free flow conditions is improved by the addition of additives in the form of a powder. of dimension micron, these additives can be of mineral matter, plant material or plant material. This improvement of flowability is all the more marked as the amount of additives added to the powder or wood flour is important.

Although described with reference only to bio mass, the plant can be used for the fine grinding of other charges of carbonaceous material (coal, petcoke ...).

References cited

[1]: Partial and handling characteristics of wood fuel powder: ejfects of different mills, by Susanne Paulrud, Jan Erik Mattsson and Calle Nilsson, December 2001 (Fuel Processing Technology 76 (2002) pp 23-39);

[2]: Ist Int. Symp. Partial Size Reduction, by Mr. A. Heimann May 1983, Manhattan;

[3]: Mozammel Hoque, Shahab Sokhansanj, Ladan Naimi, Xiaotao Bi, and Jim Lim, June 2007 (Meeting Presentation of the American Society of Agricultural and Biological Engineers (Paper Number 076164));

[4]: Biomass Size Reduction Machines for Enhancing Biogas Production, by Lukas Kratky and Tomas (Eng Eng Technolpgy 2011, 34, No. 3, pp 391-399);

[5]: Comminution Energy consumption of biomass in Knife Mill and its Particle Size Characterization of Venkata SP Bitra Alvin R. Womac, Igathinathane Cannayen Petre I. Miu, Yuechuan T. Yang and Shahab Sokhansanj, June 2009 (Meeting Presentation of the American Society of Agricultural and Biological Engineers (Paper Number 095898));

[6]: A new pulverized biomass utilization technology, by Nobusuke Kobayashi, Piao Guilin, Jun Kobayashi, Shigenobu Hatano, Yoshinori Itaya, Shigekatsu Mori (Powder Technology 180 (2008) pp 272-283);

[7]: Flow Properties of Biomass and Coal Blends, by Mohammad Zulfiqar, Behdad Moghtaderi, Terry F. Wall Fuel Processing Technology 87 (2006) pp 281-288);

[8]: Mixing and segregation in powders by JC Williams (Chapter 4 - Principles of Powder Technologies edited by M.J. Rhodes);

[9] -.Fragmentation - Theoretical Aspects Engineering Techniques [J 3050];

[10] -.Fragmentation - Technology Engineering Technology [J 3 051];

[11]: Influence of Roasting on the Grindability and Reactivity of Woody Biomass by B. Arias, C. Pevida, J. Fermoso, MG Plaza, F. Rubiera, JJ Pis (Fuel Processing Technology 89 (2008) pp. 169-175) ;

[12]: Evaluation of different strategies for pulverization of forest Montasses, Esteban and Carrasco (Powder Technology 166 (2006) pp 139-151);

[13]: A novel biomass pulverization technology, by Siyi Luo, Chang Liu, Xiao Bo, Lei Xiao (Renewable Energy 36 (2011) pp 578-582)

[14]: Characterization and analysis of powders, Techniques of the Engineer [J2 252]; [15]: Bioenergy II: Suitability of Wood Chips and Varions Biomass Types for Use in Plant Production by Gasification of Dupont, Capucine; Red, Sylvie; Berthelot, Alain; Perez, Denilson; Da Silva, Graffin; Ambroise, Labalette; Françoise Laboubee; Céline, Mithouard; Jean-Claude, Pitocchi; Sophie (INTERNATIONAL JOURNAL OF CHEMICAL REACTOR ENGINEERING (2010) Volume: 8 Article Number: A74).

Claims

1. Process for the fine grinding of a carbonaceous material charge according to which the charge of carbonaceous material, in the form of millimetric or micron-sized particles, is introduced at the inlet of a first vibrating-type milling chamber (5) whose outlet is connected to the inlet of a second vibrating-type milling chamber (7), the first and second vibrating mill chambers each comprising grinding bodies freely housed therein and adapted to grind particles, method according to which the first and second chambers are vibrated so as to crush the particles introduced on the one hand between the grinding bodies and on the other hand between them and the peripheral inner wall of each chamber, characterized in that at the inlet of the second vibrating mill chamber (7), additives (4) of mineral material and / or additives of plant material and / or additives of original material are introduced. plant, the additives being in the form of a micron-sized powder.

2. Fine grinding process according to claim 1, wherein the carbonaceous material is biomass.

3. Fine grinding process according to claim 1 or 2, wherein the mineral additives are based on silicon oxide particles Si0 ₂ or containing CaCO 3, or silica-based microbeads.

4. Fine grinding method according to one of the preceding claims, wherein the plant material additives are based on coal, such as charcoal and / or cereal straw coal.

5. Fine grinding process according to one of the preceding claims, wherein the plant material additives are based on roasted biomass, such as roasted wood, or roasted agricultural products.

6. Fine grinding process according to one of the preceding claims, wherein the additives of plant material are based on fossil coal.

7. Fine grinding process according to one of the preceding claims, wherein the amount of added plant material additives is between 0.5 and 20% by weight of the carbonaceous material charge, preferably between 5 and 10% .

8. Fine grinding process according to one of the preceding claims, wherein the particle size of the carbonaceous material feedstock introduced into the first chamber (5) vibrating mill is substantially between 1 and 2 mm.

9. The method of fine grinding according to one of the preceding claims, wherein the dimensions of the micron powder additives introduced into the second chamber (7) vibrating mill are substantially less than 5 μιη.

10. A method of fine grinding according to one of the preceding claims, wherein the particle size of the carbonaceous material charge obtained at the outlet of the second chamber (7) vibrating mill is substantially less than 800 μιη, preferably less than 200 μιη.

11. A method of fine grinding according to one of the preceding claims, wherein the grinding bodies of the vibrating mill freely housed inside the chamber consist of several sets of cylindrical bars of unit diameter different from each other.

12. Process for treating biomass according to which the mass of the mass is dried in the raw state, then the fine grinding method according to one of Claims 2 to 11 is carried out by introducing into the first chamber (5) vibrating mill the biomass at least dried.

The biomass treatment method of claim 12, wherein the dried biomass feed is made with a water content thereof in a range of 10 to 15%.

14. A method of treating biomass according to claim 12 or 13, wherein is carried out upstream of the fine grinding process, a pre-grinding of the dried biomass by introducing it into a chamber of a grinder type to knives or scissors.

The method of treating biomass of claim 14, wherein the particle size of the pre-milled biomass is substantially greater than 1 mm.

16. A method of treating biomass according to claim 14 or 15, wherein is carried out upstream of the fine grinding process, and downstream of the pre-grinding of the dried biomass, sieving the pre-milled biomass.

The method of treating biomass according to claim 16, wherein the sieving of the pre-milled biomass is carried out so as to carry out the fine grinding process from particles of millimeter dimensions smaller than 2 mm or micron dimensions smaller than 500 μιη.

18. Process for treating biomass according to claim 17, wherein particles of millimeter dimensions greater than 2 mm are reintroduced into the knife mill.

19. Process for treating biomass according to one of claims 12 to 18, wherein at the output of the second chamber (7) vibrating mill is selected particles obtained according to their dimensions so that they are lower than at 800 μιη, preferably less than 200 μιη.

20. Process for treating biomass according to which a roasting heat treatment is carried out with biomass, then the fine grinding process according to one of Claims 2 to 11 is carried out by introducing into the first chamber of the vibrating mill the roasted biomass. .

A continuous biomass treatment plant for carrying out the method of any one of claims 12 to 20 comprising:

a first chamber (5) of a vibrating type mill,

- A second chamber (7) vibrating type mill whose input is connected to the output of the first vibrating mill chamber;

- A micronization mill (6) for grinding additives (4) of mineral material and / or plant material and / or material of plant origin, in the form of a micron-sized powder, the output of the grinding mill. micronization being connected to the inlet of the second vibrating mill chamber (7).

Continuous biomass treatment plant according to claim 21, comprising a drying apparatus (1) upstream of the first vibrating mill chamber (5).

23. Continuous biomass treatment plant according to claim 22, further comprising immediately downstream of the drying apparatus and upstream of the second vibrating mill chamber, a knife mill (2).

24. Continuous biomass treatment plant according to claim 23, further comprising immediately downstream of the knife mill and immediately upstream of the first vibrating mill chamber a sieving apparatus (3).

25. Continuous biomass treatment plant according to one of claims 21 to 24, further comprising a variable speed dynamic selector (6). immediately downstream of the second vibrating mill chamber, said dynamic selector being adapted to extract at the output of the second vibrating mill chamber particles smaller than a desired diameter.

26. Continuous biomass treatment plant according to one of claims 21 to 25, wherein the vibrating mill grinding bodies freely housed inside the chamber consist of several sets of cylindrical bars of unit diameter different from each other.