PLANT AND METHOD FOR THE PRODUCTION OF HYDROPHOBIC BIOMASS PELLETS

Description

Technical field

[0001] The present invention relates to the general field of the manufacture of biofuel pellets from biomass, more particularly lignocellulosic biomass.

[0002] By "biomass" is meant here and within the framework of the invention, all organic materials used for energy or agronomic purposes.

[0003] “Organic matter” means all living matter that can be ground to form granules, namely materials of plant origin including organic waste from agriculture and forestry, agricultural waste, food residues, wood, roots, leaves, household or industrial organic waste, sludge from sewage treatment plants, fungi and materials of animal origin (animal manure).

[0004] The invention relates more particularly to the production of hydrophobic granules, that is to say which will absorb very little water if they are stored in a humid environment.

[0005] To comply with current standards, a granule can be described as hydrophobic within the meaning of the invention if it absorbs less than 10% of its mass in water... Prior art

[0006] In a context where energy consumption continues to increase, the use of biomass is being considered in order to diversify energy resources and reduce greenhouse gas emissions.

[0007] With the aim of standardizing equipment that can use this biomass, packaging this resource in the form of pellets is a major step forward.

[0008] This granulation operation, also called pelletization, consists of assembling or agglomerating fine solid particles of biomass in order to form larger elements (spheres, briquettes or even cylindrical granules).

[0009] To carry out this granulation operation, a pellet press, in particular an annular one, is generally used, as described for example in patent US4838779.

[0010] Other equipment such as a worm screw as described in patent JP2013000940 may be used.

[0011] Many improvements have been made to this equipment. Examples include patent US4711622, which relates to the addition of a deflector directing the powder under a pressure roller, patent FR2359701B1, which relates to the use of rollers of different diameters to improve production capacity, and patent application WO2011 / 50987, which relates to a modular design to facilitate maintenance.

[0012] The general operating principle of these machines remains the same, however, and consists of compressing the biomass powder into dies whose diameter corresponds to that of the pellets produced. The notable common point in all these pellet presses is the heating caused by the compression stage itself. It should therefore be noted that the pellets leaving these presses have a temperature between 80 and 100°C and are cooled before packaging.

[0013] The main advantage of biomass pellets is that they can be easily handled, transported, or stored, provided they are always protected from moisture. They have a high capacity to absorb moisture. A biomass pellet immersed in water can absorb up to 150% of its dry mass. This absorption also has negative consequences on its mechanical strength, which quickly reduces and can lead to its disintegration.

[0014] There is therefore a strong interest in producing hydrophobic granules, i.e. water-resistant, and few solutions have been proposed for this purpose in the state of the art.

[0015] Patent application WO2014 / 152931 describes a method comprising the addition of an additive followed by heat treatment by microwaves in a temperature range between 50 and 230°C. One of the advantages of this process is that it remains at a relatively low temperature and can therefore be carried out in air.

[0016] Torrefaction is also known as another technique to achieve good hydrophobicity without additives, which consists of a different heat treatment at a higher temperature. Torrefaction is a mild heat treatment of biomass at the interface between drying and pyrolysis, and aims to remove water and modify part of the organic matter of the biomass to break its fibers. In other words, this mild heat treatment alters the fibrous structure of the biomass. Torrefaction is carried out in the absence of oxygen, generally at temperatures between 200 and 350°C and its duration is generally 30 to 60 minutes.

[0017] As explained in patent FR302422B1, it is well known that torrefaction improves the properties of biomass, with a view to its storage by giving it a hygrophobic character and resistance to biological degradation.

[0018] Industrial torrefaction units are designed to process a wide variety of biomass, generally in the form of forest chips or agricultural residues. These units can potentially torrefy biomass pellets, but they are often not studied and optimized for this. The level of torrefaction applied in these units, i.e. the temperature and duration of the heat treatment, is rather high because the objective is to produce biomass with a better carbon content, and therefore a better calorific value (LHV). This heat treatment completely dries the biomass, which results in the production of water vapor. There is also a loss of dry mass on the torrefied biomass, compensated by the creation of a torrefaction gas composed mainly of CO 2 and CO . The higher the torrefaction level, the more the torrefaction gas contains combustible gas in the form of CO, or even CH 4 and H 2 in the 300-350°C range.

[0019] Most of the patents on this technology concern the energy integration and valorization of this combustible roasting gas.

[0020] This is for example the case of the aforementioned patent FR3024221B1 which integrates two burners and heat exchangers allowing the operation of a biomass drying unit before torrefaction.

[0021] Patent FR2982273B1 presents a simpler energy optimization with recovery of the heat from the combustion of roasting gases which are directly returned partly to the roasting unit, and the rest to the drying unit.

[0022] The roasting installation implemented in this patent FR2982273B1 consists of tray ovens, with arms that stir and move the biomass from one tray to another. The rotation speed of the arms determines the average residence time but the stirring carried out leads to a strong dispersion on the residence time of the biomass.

[0023] Patent application WO2013 / 03960 describes a torrefaction unit, a rotary drum oven, inclined, in which the biomass is introduced at the top and descends towards the oven outlet driven by gravity and the rotational movement. As in patent FR2982273B1, the torrefaction gases are burned and reintroduced into the torrefaction unit to ensure heating but also to maintain an absence of oxygen in the torrefaction unit. Also, as in patent FR2982273B1, the mixing of the biomass by a rotary drum induces a dispersion of residence time of the treated biomass.

[0024] On the contrary, patent application WO2016 / 116588 describes a method for controlling the residence time by performing batch torrefaction of biomass, i.e. the biomass is introduced into the cold oven in one go and then also removed in one go after heat treatment. This is a method usually used in laboratory studies but the patent application seeks to make it an industrial process. This patent application also describes the use of a vacuum pump to lower the oxygen level before torrefaction and then to extract the gases produced during the heat treatment.

[0025] Such batch biomass processing is used in many laboratory devices such as the one described in patent FR2985043, the objective of which is to be able to carry out rapid torrefaction of a biomass sample. The diameter of the sample is measured and an optimization of the temperature and the torrefaction duration is made from mathematical formulas for the purpose of pretreatment before gasification.

[0026] Thus, a study of the state of the art on torrefaction shows that there are processes for torrefying biomass, and therefore biomass pellets, but there has been no optimization aimed at the specific objective of the hydrophobicity of biomass pellets.

[0027] Rather than torrefying pellets, the publication [1] details the interest of carrying out granulation (pelletization) after the torrefaction operation. If no additives are used to facilitate pelletization, the torrefied biomass pellets obtained must have good hydrophobic properties. Without specifically addressing this subject of hydrophobicity, this laboratory study demonstrates the energy and technical-economic interest of producing torrefied pellets, but it does not provide a technical solution.

[0028] Patent application US2014 / 0082998 discloses an installation comprising a dryer, a roaster connected downstream of the dryer, a grinder downstream of the roaster and downstream, a pelletizing press. In this application, there is a thermal optimization because the roasting gases are recovered for heating, which is only applicable if the roasting level is high so as to have enough CO to make the roasting gas combustible. The oven used is of the rotating drum type which, as mentioned previously, has the disadvantage of not guaranteeing a precise roasting time. In this application also, the air is simply expelled by the water vapor emitted by the heated biomass.

[0029] In addition to this state of the art, the inventors of the present invention carried out a laboratory study specifically dedicated to measuring water absorption by previously torrefied wood pellets. The study consisted of a short, temperature-controlled torrefaction on representative pellet samples. A specific experimental device was created and the results obtained differ from what was commonly estimated by experts in the field.

[0030] Indeed, it is commonly accepted by experts in this technical field that the hydrophobicity of biomass improves continuously with the level of torrefaction and therefore that good hydrophobicity requires a high level of torrefaction. There are also studies that confirm this, such as [2] which analyzes the properties of pine pellets torrefied for 60 minutes at temperatures of 240 to 340°C and shows a continuous improvement in resistance to humidity.

[0031] The authors of the study [3] show that for the same roasting time of 30 minutes, an improvement in hydrophobicity over 4 roasting temperatures (230°C, 250°C, 270°C, 290°C) and conclude that it is advisable to exceed 270°C for a correct result (<15% moisture uptake).

[0032] For the inventors of the present invention, these studies are biased by the difficulty of properly controlling the roasting rate of the samples analyzed. Indeed, if the moisture uptake tests are carried out on samples in which some of the granules have not been well roasted, then the latter will absorb a lot of water, typically up to 150% of their mass. Even if there are very few poorly roasted granules, this has a very strong impact on the average measurement over the entire sample.

[0033] However, as the curve of the figure 1, the study carried out by the inventors on wood pellets shows that the hydrophobicity improves significantly at the start of roasting, reaches an optimum after 20 minutes and then practically no longer improves if roasting is continued for longer.

[0034] The optimum on the curve is the operating point allowing a granule with good hydrophobicity to be obtained while retaining a maximum of its heating capacity because the shorter the roasting time, the less mass and therefore energy the treated granule loses.

[0035] In conclusion, the design of a system installation intended to produce hydrophobic biomass pellets can be optimized because it requires a short torrefaction, typically 20 minutes, at a relatively low temperature, typically 230 to 250°C, and with good control of the residence time. These are particular operating conditions for which the state of the art previously mentioned shows that industrial torrefactors are not suitable.

[0036] On the other hand, it is interesting to note that these optimal conditions are close to those used for roasting coffee, which also lasts around 20 minutes but at a lower temperature, between 160 and 220°C. In addition, this does not need to be carried out in inert conditions and the associated patents therefore describe air roasting systems. For example, patent FR1182626 is a coffee roaster comprising a belt composed of vibrating trays so as to expose all sides of the beans to the heat of infrared radiation. Patent FR2213019 is a system for roasting coffee in the open air with a conveyor belt and infrared or ultrasonic heating. Finally, patent FR2390202 describes a principle of coffee roasting in a fluidized bed (in a flow of hot air) with a belt comprising paddles to carry the beans from the inlet to the outlet.None of these systems would be suitable for torrefying biomass pellets since they are not airtight.

[0037] US patent application 2015 / 275115 A1 describes a biomass torrefaction process in which the biomass is introduced into a fluidized bed or non-fluidized bed reactor and heated to a predetermined temperature in an oxidizing environment.

[0038] US patent application 2020 / 056098 A1 describes a system and method for torrefying a combination of biomass and colloidal dispersion of biochar.

[0039] There is therefore a need to propose an optimized technical solution for the production of hydrophobic biomass pellets.

[0040] The aim of the invention is therefore to respond at least in part to this need. Statement of the invention

[0041] To this end, the invention relates, in one of its aspects, to an installation for producing hydrophobic biomass pellets, comprising: a pelletizing unit comprising an outlet through which biomass pellets are intended to be discharged at a given temperature; a roasting oven comprising an inlet connected to the outlet of the pelletizing unit and an outlet through which the roasted biomass pellets are intended to be discharged, the roasting oven comprising: a sealed and thermally insulated casing, at least one biomass pellet conveying device housed inside the sealed casing and configured to guarantee an identical residence time for all the biomass pellets between the inlet and the outlet, at least one heating system housed inside the envelopesealed, the heating system being configured to maintain the interior of the envelope at a substantially constant roasting temperature, at its outlet, at least one gas-tight device configured to evacuate the roasted biomass pellets while ensuring a gas-tight seal.

[0042] According to an advantageous embodiment, the outlet of the furnace comprises at least one gas-tight device configured to evacuate the torrefied biomass pellets while ensuring a gas-tight seal.

[0043] According to this method, the gas-tight device can advantageously consist of two valves mounted tilting one downstream of the other in the outlet of the furnace, forming an airlock, so as to evacuate the torrefied biomass pellets in batches while ensuring a gas-tight seal. Thus, to carry out the evacuation, the upstream valve is opened so that the volume of the airlock between the two valves is filled with a batch of biomass pellets, the downstream valve being closed. Then, the upstream valve is closed and the downstream valve is opened in order to evacuate the batch of torrefied biomass pellets from the airlock. Advantageously, this evacuation takes place solely by gravity.

[0044] The gas-tight device can also be made up of a rotary valve or any other mechanical device allowing the passage of torrefied pellets while ensuring a gas-tight seal.

[0045] According to another advantageous embodiment, the sealed envelope is pierced with at least one gas outlet through which the gases resulting from roasting are sucked in.

[0046] According to an advantageous configuration, the furnace is arranged below the pelletizing unit, the inlet of the furnace comprising at least one hopper for discharging the granules by gravity from the pelletizing unit to the conveying device(s).

[0047] According to an advantageous variant, the outlet of the furnace comprises at least one hopper for evacuating by gravity the hydrophobic roasted granules from the sealed envelope.

[0048] According to another advantageous embodiment, the installation comprises several conveying devices arranged one after the other in the conveying direction inside the envelopesealed. This mode can allow a reduction in the length of the roasting oven and limit the external surface of the oven, thus reducing heat losses proportional to this external surface of the oven. For example, considering that the oven has a geometric shape of a rectangular parallelepiped, this external surface is minimal if we approach the shape of a cube.

[0049] Each conveyor device advantageously consists of a perforated conveyor belt. Such a device allows for precise control of the residence time of the pellets in the furnace, which is typically desired to be around 20 minutes. Instead of a conveyor belt, any other device whose conveyance allows for a precise residence time can be considered. For example, a bucket conveyor can be considered.

[0050] The invention also relates to a method for producing hydrophobic biomass granules, in particular implemented by an installation as described above, comprising the following steps: i / pelletizing in order to obtain biomass pellets at a first given temperature (T1); ii / injecting the biomass pellets at the first given temperature (T1) into a furnace; iii / roasting at a second given temperature (T2) in the furnace by simultaneously conveying the biomass pellets inside the furnace so as to guarantee a predetermined residence time in the furnace, substantially identical for all the pellets, in order to obtain hydrophobic biomass pellets; iv / removing the hydrophobic biomass pellets from the furnace.

[0051] Advantageously, the first given temperature (T1) is substantially equal to 100°C.

[0052] Advantageously, the second given temperature (T2) is substantially between 230 and 250°C.

[0053] Preferably, the residence time in the oven is approximately between 20 and 25 min.

[0054] According to an advantageous embodiment, the method comprises, simultaneously with step iii / of roasting, a step v / of suction of the gases resulting from the roasting with a view to their treatment or purification before release into the atmosphere.

[0055] Thus, the invention essentially consists of adding, downstream of a biomass pelletization / granulation unit, a torrefaction oven which houses one or more conveying devices so that the biomass pellets remain within the oven for a short and precise time in order to optimize their hydrophobicity.

[0056] Ultimately, a device according to the invention has many advantages, including: obtaining hydrophobic torrefied biomass pellets whose hydrophobicity rate is constant for all pellets; thermal optimization of a hydrophobic biomass pellet production facility by direct torrefaction of pellets whose temperature at the inlet of the furnace and that of the pelletizing unit, typically a temperature between 80 and 100°C. This optimization can save up to 20% of the heating energy required for torrefaction; due to the inlet of the torrefaction furnace being directly connected upstream to the outlet of the pelletizing unit, limitation of the entry of air into the torrefaction furnace and therefore no need to install a complex sealing system such as a double valve or rotary lock at the furnace inlet.

[0057] Other advantages and characteristics of the invention will become more apparent upon reading the detailed description of examples of implementation of the invention given by way of illustration and not limitation with reference to the following figures. Brief description of the drawings

[0058] [ Fig 1 ] there figure 1 illustrates in the form of a curve the time decrease in the moisture uptake of wood pellets subjected to torrefaction at relatively low temperature. Fig 2 ] there figure 2 is a schematic view of a plant for producing hydrophobic biomass pellets according to the invention. Fig 3 ] there figure 3 is a schematic view of an installation according to a variant of the invention. Detailed description

[0059] In the following description and throughout the application, the terms "vertical", "lower", "upper", "bottom", "top", "below" and "above" are to be understood by reference to an installation for producing hydrophobic biomass pellets, as it is in a horizontal operating configuration, with the pelletizing unit arranged above the roasting oven housing a horizontal conveying device.

[0060] Also, the terms “inlet”, “outlet”, “upstream”, “downstream”, are used by reference to the directions of transfer of the biomass, of circulation of the torrefaction gas in the hydrophobic pellet production facility according to the present invention.

[0061] There figure 1has already been briefly commented on in the preamble. To avoid the bias of studies like that of [2], the inventors of the present invention have developed a batch roasting oven allowing the production of conditioned samples, representative of approximately 30g each and with very good roasting homogeneity and above all very rapid temperature rise and fall rates.

[0062] Thanks to these reliable samples, the moisture uptake curve of the figure 1 was plotted and highlighted the notion of roasting optimum for hydrophobicity.

[0063] After achieving this optimum at a low roasting level, around 20 minutes at 250°C for softwood pellets, the inventors looked for a production facility that could achieve such an optimum operating point during roasting. However, by taking inventory of existing roasting units, they concluded that none of them could do so.

[0064] At this level of roasting, the quantity of roasting gas produced is low, it contains less than 15% of combustible CO, hence a very low thermal capacity. It is therefore not economically viable to try to recover it by recovering the heat from its combustion, unlike what is generally implemented in industrial roasting units.

[0065] On the figure 1, the optimum point at 20 minutes and 250°C was obtained for softwood pellets. But depending on the biomass composing the pellets, the inventors found that these optimal conditions can vary slightly. For example, on hardwood pellets, the optimal torrefaction temperature is 230°C for the same duration of 20 minutes. However, this remains in the low range of torrefaction temperature levels and the amount of heating energy to carry out the heat treatment is low, this is one of the advantages of the proposed system.

[0066] As seen previously, controlling the residence time of pellets in a roasting oven is an essential parameter and they therefore tested known roasting units.

[0067] The inventors thus carried out a 25-minute roasting test in a tray drum oven and estimated that 25% of the pellets tested did not have a sufficient degree of roasting. In fact, the moisture uptake measurements on some samples gave an average of 44% water absorption, which is of the order of magnitude of the theoretical calculation where 25% of the pellets take on 150% moisture and 75% of the pellets only take on 12% moisture, i.e. 25 × 1 + 1.5 + 75 × 1 + 0.12 100 = + 46 % .

[0068] The inventors concluded that because of the mixing of the granules that they induce, tray ovens or rotating drums according to the state of the art do not allow homogeneity of hydrophobicity to be obtained in the torrefied granules.

[0069] They then thought of creating a production facility with a roasting oven in which the pellets from a roasting unit would be placed on a conveyor device which would allow each pellet to be heated evenly and to control the residence time of said pellets in the oven.

[0070] There figure 2 illustrates a plant for producing hydrophobic biomass pellets according to the invention, arranged in an environment at temperature T0.

[0071] In this installation, the outlet of a pelletizing unit 1 is directly connected to the inlet E of a roasting oven 2, arranged below the pelletizing unit. More precisely, the inlet E comprises a hopper 3 for discharging the pellets by gravity from the pelletizing unit to the conveying device(s).

[0072] The roasting oven firstly comprises a sealed and thermally insulated casing 2.

[0073] At least one conveying device 4 is housed inside the sealed casing 2. As explained below, the conveying device(s) is(are) configured to guarantee an identical residence time for all the biomass pellets between the inlet E and the outlet S of the furnace. Each device is preferably a perforated metal conveyor belt. Any other equipment that meets the criterion of guaranteeing the residence time in the furnace, which is identical, may be suitable.

[0074] A heating system 5 is also housed inside the sealed casing, the heating system being configured to maintain the interior of the casing 2 at a substantially constant roasting temperature T2. Many technical solutions are possible to ensure this function of maintaining a temperature T2, such as electric heating by means of electric resistors, by gas combustion, by means of a heat exchanger, etc. Similarly, the homogeneity of the heating within the envelope 2 may require mixing by a ventilation device which may be integrated into the heating system 5.

[0075] The quality of the thermal insulation of the casing 2 makes it possible to limit the loss of energy through the furnace but also to avoid condensation of tars. In the context of the invention, the fact that the temperature T2 is in the low range of usual roasting temperatures, typically between 230 and 250°C is a technical advantage because the thermal losses are proportional to the temperature difference T2-T0 and the production of a casing 2 with good thermal insulation of a furnace at 250°C is relatively easy with conventional materials.

[0076] The outlet S of the furnace may comprise an outlet hopper 6 in order to discharge the biomass pellets at the end of the torrefaction heat treatment to an environment at temperature T3. This outlet S may comprise at least one gas-tight device 7 configured to discharge the torrefied biomass pellets while ensuring a gas-tight seal.

[0077] As illustrated, this device 7 may consist of two valves mounted tilting one downstream of the other in the outlet S of the furnace, forming an airlock, so as to evacuate the torrefied biomass pellets in batches while ensuring a gas seal.

[0078] Thus, the device 7 makes it possible to contain the roasting gas in the casing 2 of the oven. This gas is potentially dangerous and polluting, because it contains carbon monoxide CO and tars in vapor form. The evacuation of this gas G can be carried out by a gas outlet orifice 8 made by drilling through the wall of the top of the casing 2. In fact, the gas G can be sucked in through this orifice 8 for further treatment or combustion before release into the atmosphere. The suction must be sufficient to avoid gas release through possible leaks in the casing.

[0079] The operating steps of the production plant to obtain hydrophobic torrefied granules are now described.

[0080] Step i / : pelletization is carried out in unit 1 in order to obtain biomass pellets 9 at a given temperature T1.

[0081] Step ii / : the biomass pellets 9 at temperature T1 in the envelope 2 are discharged by gravity by means of the inlet hopper 3.

[0082] Step iii / : roasting is carried out by the heating system 5 at a given temperature T2 in the oven. Simultaneously with the implementation of the heating, the biomass pellets 9 are conveyed by the conveying device 7 inside the oven so as to guarantee a residence time in the oven. This predetermined residence time is substantially identical for all the pellets, in order to obtain hydrophobic biomass pellets 9.

[0083] Simultaneously with roasting step iii / , a step is carried out to suck up the gases G from roasting through orifice 8 for treatment or purification before release into the atmosphere.

[0084] Step iv / : the hydrophobic biomass pellets 9 are discharged by gravity through the outlet hopper 6. More precisely, the upstream valve of the device 7 is opened so that the volume of the airlock between the two valves is filled with a batch of biomass pellets, the downstream valve of the device 7 being closed. Then, the upstream valve is closed and the downstream valve is opened in order to discharge the batch of torrefied biomass pellets by gravity from the airlock.

[0085] The energy integration of pelletization unit 1 in a roasting oven installation allows a gain on heating which can be estimated by calculation knowing the specific heat of the biomass, typically wood ( Cp wood ), the specific heat of liquid water ( CP water), the specific heat of the steam ( Steam cp ) and the latent heat of vaporization of water ( Lv water ).

[0086] Considering that wood pellets contain HR % humidity at the entrance to the roasting oven 2, energy E torref necessary to bring them from temperature T0 to T2 is given by equation 1: E torref = HR % × Cp eau + 1 − HR % × Cp bois × 100 − T 0 + HR % × Lv eau + HR % × Cp vapeur + 1 − HR % × Cp bois × T 2 − 100

[0087] The energy gained by thermal integration is that contained in the pellet at temperature T1. It is given by equation 2: E granul é = HR % × Cp eau + 1 − HR % × Cp bois × T 1 − T 0

[0088] The percentage gain R can be calculated by the ratio R = E granul é E torref It can vary from 10 to 35% depending on the pellet production conditions. Such a gain constitutes a very significant economic advantage since the cost of heating is the main operating expense of the installation.

[0089] As an illustrative example, the outside temperature T0 = T3 is equal to 20°C, the temperature of the pellets leaving the pelletizing unit T1 is equal to 100°C, the roasting temperature T2 is equal to 250°C, the residence time of the pellets in the oven being between 20 and 25 min.

[0090] The moisture content of a pellet entering roasting oven 2 is considered to be 30%.

[0091] Other numeric values ​​are: Cp wood = 1.5 kJ / kg / K, CP water = 4.0 kJ / kg / K, Cp steam = 4.4 kJ / kg / K And Lv water = 2250 kJ / kg.

[0092] With these values, it is possible to calculate the heating energy gain with the previous equations: E torref = 1210 kJ / kg E granul é = 180 kJ / kg R = 15 %

[0093] In other words, with pellets containing 30% humidity at the inlet of kiln 2, the energy gain R from integrating kiln 2 at the outlet of a pelletizing unit is 15%.

[0094] Extrapolating, this R gain would be 20% for pellets that only contain 14% moisture because the drier the pellets at the input, the greater the gain. It should be noted that this gain is a minimum because the calculation carried out does not take into account the exothermic reactions that take place during roasting.

[0095] There figure 3 illustrates a variant integrating several conveyor systems 7. This makes it possible to reduce the size of the roasting unit and to limit the external surface area of ​​the oven, thus reducing heat losses.

[0096] The invention is not limited to the examples which have just been described; in particular, it is possible to combine characteristics of the illustrated examples within non-illustrated variants.

[0097] Other variants and embodiments may be envisaged without departing from the scope of the invention. List of cited references

[0098] [1]: “Combined roasting and pelletization. The TOP process” by PCA BERGMAN (2005). [2]: JH Peng & al. “Study on density, hardness, and moisture uptake of torrefied wood pellets” (2013). [3]: Maryam Manouchehrinejad, Sudhagar Mani “Torrefaction after pelletization (TAP): Analysis of torrefied pellet quality and co-products”, Biomass and Bioenergy, (2018): 93-104.

Claims

1. Plant for producing hydrophobic biomass pellets, comprising: - a pelletization unit (1) comprising an outlet through which biomass pellets (9) are intended to be discharged at a given temperature (T1); - a torrefaction furnace comprising an inlet (E) connected to the outlet of the pelletization unit and an outlet (S) through which the torrefied biomass pellets (9) are intended to be discharged, the torrefaction furnace comprising: • a fluidtight and thermally insulated casing (2), • at least one conveying device (4) for conveying the biomass pellets (9), which is housed inside the fluidtight casing and configured to ensure an identical residence time for all of the biomass pellets between the inlet (E) and the outlet (S), • at least one heating system (5) housed inside the fluidtight casing, the heating system being configured to maintain the inside of the casing (2) at a substantially constant torrefaction temperature (T2), • at its outlet (S), at least one gastightness device (7) configured to discharge the torrefied biomass pellets while at the same time ensuring gastightness.

2. Plant according to Claim 1, the gastightness device (7) consisting of two valves pivotably mounted one downstream of the another in the outlet (S) of the furnace, forming an airlock, so as to discharge the torrefied biomass pellets in batches while at the same time ensuring gastightness.

3. Plant according to either of the preceding claims, the fluidtight casing (2) being pierced by at least one gas outlet (8) through which the gases resulting from the torrefaction are extracted.

4. Plant according to one of the preceding claims, the furnace being arranged below the pelletization unit, the inlet (E) of the furnace comprising at least one hopper (3) for discharging the pellets by gravity from the pelletization unit to the conveying device(s).

5. Plant according to one of the preceding claims, the outlet (S) of the furnace comprising at least one hopper (6) for discharging the hydrophobic torrefied pellets by gravity from the fluidtight casing.

6. Plant according to one of the preceding claims, comprising a plurality of conveying devices (4) arranged in succession in the conveying direction inside the fluidtight casing (2).

7. Plant according to one of the preceding claims, each conveying device (4) consisting of a perforated conveyor belt.

8. Process for producing hydrophobic biomass pellets, in particular carried out by a plant according to one of the preceding claims, comprising the following steps: i / pelletization in order to obtain biomass pellets at a first given temperature (T1); ii / injecting the biomass pellets into a furnace at the first given temperature (T1); iii / torrefaction at a second given temperature (T2) in the furnace while simultaneously conveying the biomass pellets inside the furnace so as to ensure a predetermined residence time in the furnace, said residence time being substantially identical for all of the pellets, in order to obtain hydrophobic biomass pellets; iv / discharging the hydrophobic biomass pellets from the furnace.

9. Process according to Claim 8, the first given temperature (T1) being substantially equal to 100°C.

10. Process according to Claim 8 or 9, the second given temperature (T2) being substantially between 230 and 250°C.

11. Process according to one of Claims 8 to 10, the residence time in the furnace being substantially between 15 and 30 minutes, preferably between 20 and 25 minutes.

12. Process according to one of Claims 8 to 11, comprising, simultaneously with step iii / of torrefaction, a step v / of extracting the gases resulting from the torrefaction in order to treat or purify them before they are released into the atmosphere.