Process for the continuous manufacture of a combustible material by explosive decompression operating in stages

Abstract

The invention relates to a method for the continuous production of a combustible material from biomass comprising: - exposing the biomass continuously introduced into a reactor to said steam at a pressure of between 15.3 and 22.9 bars for a time sufficient to obtain steam cracking; - continuously extracting from said reactor a portion of the biomass contained in the reactor. According to the invention, such a method comprises: transferring said biomass extracted from said reactor in a conduit to separation means in which the steam pressure is between 7 and 8 bars; a step of separating a portion of the steam extracted from said reactor with said biomass and from said biomass; - a step of depressurizing said biomass separated from said portion of steam to atmospheric pressure. Figure to be published: 1

Description

Title of the invention: Process for the continuous production of a combustible material by explosive decompression operating in stages Field of invention

[0001] The field of the invention is that of the production of biomass-based fuels.

[0002] More specifically, the invention relates to a process for the continuous production of a combustible material from lignocellulosic biomass.

[0003] The invention also finds application in the manufacture of combustible material for boilers or for industrial furnaces, and for domestic boilers and stoves. Prior art

[0004] Biomass, and in particular lignocellulosic biomass from forestry or agricultural production, is in its raw state a low-density, perishable material with great disparities. It is therefore necessary to transform it in order to be able to use it in boilers or industrial furnaces, but also to facilitate its transport and storage.

[0005] It is known to implement carbonization techniques, roasting, or even so-called “steam explosion” techniques combining steam cracking with explosive decompression, discontinuous or continuous, to transform lignocellulosic biomass into a stable fuel of substantially constant quality, possessing a high calorific value.

[0006] A disadvantage of the carbonization technique is that during the transformation a significant mass quantity, generally of the order of 70 to up to 80%, of material is lost, which makes the fuels obtained by this technique expensive.

[0007] Material losses are also significant, and around 10 to 20%, with the roasting technique, which also has the disadvantage of being expensive to implement and requiring implementation under an inert atmosphere to avoid a risk of combustion, which represents a danger.

[0008] Known techniques of continuous steam cracking or discontinuous steam explosion can limit mass losses of material. However, it is noted that energy-rich volatile material can be released and lost by this process, which can significantly reduce the final calorific value of the final product obtained by these known processes.

[0009] Document WO2006 / 006863 A1 describes a “steam explosion” technique in batch in which explosive decompression is carried out in two stages. In a first stage, part of the water vapor contained in the reactor is transferred to a second reactor, in order to limit energy losses and in a second stage, the biomass having undergone steam cracking is evacuated with the residual water vapor into a drain chamber, under the effect of expansion.

[0010] This known technique has the disadvantage of being complex and expensive to implement, due to the fact that it requires two reactors and an enclosure having an internal volume approximately 13 to 19 times greater than that of the reactors to be able to ensure expansion and which is capable of resisting explosive shocks.

[0011] Furthermore, the productivity of this known production technique is limited, because it is necessary to empty the drain chamber after the treatment of each batch of material, before introducing new material to be treated into the reactors.

[0012] Also known from document WO 2017 / 089648 A1 is a technique for treating biomass by continuous “steam explosion”, in which the material leaving the reactor undergoes explosive decompression during which the pressure is lowered below 5 bars in a single step, in order to allow suitable defibrillation of the treated material. A disadvantage of this known technique is that too much material is still entrained with the discharged steam. Objectives of the invention

[0013] The invention therefore aims in particular to overcome the drawbacks of the prior art cited above.

[0014] More specifically, the invention aims to provide a technique for the continuous production of combustible material from lignocellulosic biomass by "steam explosion" which makes it possible to improve the calorific value of the combustible material while limiting losses of material in the form of condensable volatile compounds with a high carbon content.

[0015] An objective of the invention is also to provide such a technique which makes it possible to obtain a combustible material capable of being transformed into granules, also commonly called “pellets”.

[0016] Another objective of the invention is to provide such a technique which makes it possible to reduce the particle size of the combustible material.

[0017] An objective of the invention is also to propose such a technique which makes it possible to increase the cohesion and water resistance of the combustible material.

[0018] Another objective of the invention is to provide such a technique which is simple to implement and has a reduced cost. Statement of the invention

[0019] These objectives, as well as others which will appear subsequently, are achieved using a process for the continuous production of a combustible material, intended in particular for an industrial boiler, from lignocellulosic biomass comprising the following steps:

[0020] - continuous introduction of a predetermined mass per minute of said biomass in a pressurized reactor, said reactor being supplied with substantially saturated steam, the pressure of which is between 15.3 and 22.9 bars and / or the temperature is between 200 and 220°C once introduced into the reactor;

[0021] - exposure of the biomass introduced into said reactor to said water vapor for a sufficient time to obtain steam cracking;

[0022] - continuous extraction from said reactor of a portion of the biomass contained in the reactor per minute.

[0023] In the context of the invention, lignocellulosic biomass means biomass of agricultural or forestry origin comprising cellulose, hemicellulose and lignin, such as raw wood, forest residues, waste or co-products from the wood processing industry (sawdust, wood chips, splinters, etc.), treated wood, pallets, biomass from the exploitation of coppices, miscanthus, fescue, bamboo, etc., woody waste or co-products from agricultural crops (straw, grass, etc.) or from the agri-food industry (bagasse, etc.), or green, woody waste or waste intended for recycling from waste disposal sites and any combination thereof.

[0024] According to the invention, such a method comprises:

[0025] - an explosive decompression step comprising a transfer of said biomass extracted from said reactor in a conduit to separation means in which the vapor pressure is between 7 and 8 bars; - a step of separation in said separation means of a portion of the steam extracted from said reactor with said biomass and of said biomass;

[0026] - a step of depressurizing said biomass separated from said portion of steam until the pressure exerted on the biomass is equal to atmospheric pressure, said biomass at atmospheric pressure forming said combustible material.

[0027] Thus, in a novel manner, the invention proposes to carry out explosive decompression of the material leaving the reactor in several stages, including a first in which the pressure is brought back to between 7 and 8 bars, which allows suitable defibrillation of the biomass while substantially limiting the losses of material to losses of volatile compounds of low calorific value. Furthermore, during the depressurization stage, the quantity of residual steam being reduced, a smaller quantity of valuable organic compounds of interest is carried along with it.

[0028] In an advantageous embodiment of the invention, said step of depressurization to atmospheric pressure comprises at least one additional explosive decompression step comprising a transfer in a conduit of said biomass from the separation means to additional separation means in which the vapor pressure is less than or equal to 4 bars and a step of separation in said additional separation means of a portion of the vapor entering said additional separation means and of said biomass.

[0029] Thus, by providing an additional explosive decompression step, compounds of interest are extracted that are richer in carbon than those extracted during the first explosive decompression step up to 7 to 8 bars, but in a limited quantity, approximately 10 times lower than that of the compounds extracted during the first step, which again limits the losses of material with high calorific value. These extracted compounds can also be recovered.

[0030] In a particular embodiment of the invention, said step of depressurization to atmospheric pressure comprises:

[0031] - a first stage of additional explosive decompression comprising a transfer in a conduit of said biomass from the separation means to first additional separation means in which the steam pressure is between 3.5 and 4 bars and a step of separation in said first additional separation means of a portion of the steam entering said first additional separation means and of said biomass,

[0032] - a second additional explosive decompression stage comprising a transfer in a conduit of said biomass from the first additional separation means to second additional separation means in which the steam pressure is between 1.8 and 2 bars, and preferably is equal to 1.9 bars, and a step of separation in said second additional separation means of a portion of the steam entering said second additional separation means and of said biomass.

[0033] Thus, explosive decompression is carried out in four stages, which makes it possible to limit the losses of material with high calorific value at each stage, and the volatile organic compounds obtained in the last stages can be condensed and distilled or separated by other means such as membrane filtration techniques to extract molecules of interest.

[0034] In a particular embodiment of the invention, said step of depressurization to atmospheric pressure further comprises a third step of additional explosive decompression comprising a transfer in a conduit of said biomass from said second additional separation means to third additional separation means in which the vapor pressure is equal to 1 bar, and a separation step in said third additional separation means of a portion of the steam entering said third additional separation means and of said biomass.

[0035] Thus, a final separation is carried out at atmospheric pressure, which makes it possible to recover volatile compounds richer in energy which can be recovered.

[0036] Advantageously, said means for separating a portion of steam extracted from said reactor with said biomass extracted from the reactor comprise a cyclone or a centrifugal dynamic separator (turbine).

[0037] In a particular embodiment of the invention, a method as described above comprises a step of circulating said steam separated from said biomass in a heat exchanger, such as a condensation heat exchanger.

[0038] It is thus possible to recover the sensible heat and the latent heat of the portion of steam separated from the biomass, for example to dry the biomass before introducing it into the reactor.

[0039] In another particular embodiment of the invention, a method as described above comprises a step of combustion of said portion of steam separated from said biomass.

[0040] The steam pressure then allows it to be diffused into the boiler hearth to ensure proper combustion of the volatile organic compounds and to recover the latent heat of the steam.

[0041] According to a particular embodiment of the invention, a method as described above comprises a step of condensation of at least a part of said portion of steam separated from said biomass and a step of distillation of said condensed water vapor making it possible to obtain a purified fraction of interest, such as furfural or furfuraldehyde, 5-hydroxymethylfurfuraldehyde, acetic acid, formic acid, methanol, levoglucosenone, levulinic acid, resinous or terpenic derivatives, for example.

[0042] According to a particular embodiment of the invention, a method as described above comprises a step of condensation of at least a part of said portion of steam separated from said biomass and a step of purification of said condensed water vapor by application of an activated sludge treatment or by methanization.

[0043] According to a particular aspect of the invention, said methanization step is an acetoclastic methanization step.

[0044] Acetic acid is thus converted into methane.

[0045] It should be noted that the implementation of several explosive decompression stages makes it possible to extract furfuraldehyde or furfural, which is an inhibitor of the acetic acid methanization reaction, during the first stage(s) of explosive decompression, and then to carry out the methanization of the acetic acid. in a later stage.

[0046] According to a particular aspect of the invention, said conduit has at least one of its ends a rotary valve or dynamic sealing means.

[0047] Preferably, said biomass introduced into the reactor has a humidity level of between 5 and 25%.

[0048] In a particular embodiment of the invention, said biomass comprises wood chips. List of figures

[0049] Other characteristics and advantages of the invention will appear more clearly on reading the following description of an embodiment of the invention, given as a simple illustrative and non-limiting example, and the appended figures among which:

[0050] [Fig. 1] represents an installation for manufacturing combustible material from lignocellulosic biomass suitable for implementing a method for manufacturing combustible material according to the invention;

[0051] [Fig.2] illustrates the steps of another exemplary embodiment of a manufacturing method according to the invention, in the form of a block diagram. Detailed description of the invention

[0052] [Fig. 1] illustrates an installation for manufacturing combustible material from wood chips intended to implement an exemplary embodiment of a manufacturing method according to the invention.

[0053] In this particular embodiment of the invention, the wood chips used are hardwood or softwood chips. In variants of this embodiment of the invention, it may be envisaged to use natural wood chips of any suitable species, such as hardwoods, softwoods, for example spruce, etc. and / or reclaimed wood, such as class A or class B wood.

[0054] This installation 10 comprises a hammer mill 11 fed with wood chips using a worm screw 12 which takes the chips from a scale silo 13. A large wood separator removes the oversized elements before the chips enter the crusher 11. In this wet crusher 11, the wood chips are crushed in the form of larger wood fragments, mainly between 4 and 8 millimeters, up to 16 mm. The filling of the silo 13 is ensured by a bucket loader which takes chips from piles formed on storage areas on the ground.

[0055] These wood fragments are discharged at the outlet of the crusher 11 onto a conveyor belt 14, equipped with a weighing belt, which transports them to the feed hopper of a low-temperature hot air dryer 15. In this embodiment of the invention, the temperature of the hot air from the dryer is between 75 and 85°C.

[0056] This dryer 15 is in this particular embodiment of the invention a double-layer belt dryer. The fragments entering the dryer are distributed homogeneously by a first feed screw on a belt. The layer of wood fragments formed is transported through the dryer on the belt before being discharged onto the first discharge screw. By means of an additional screw conveyor, the wood fragments are transferred to a second feed screw which deposits a second layer on the first in the dryer. After having traveled halfway through the dryer a second time, the dried wood fragments, the moisture content of which is now less than 10%, are separated, discharged and conveyed to a buffer storage silo 16.

[0057] A humidity sensor continuously monitors the moisture content of the wood fragments leaving the dryer and the belt feed speed is automatically regulated to maintain the moisture content of the wood fragments constant at the dryer outlet.

[0058] In the dryer, exhaust fans draw ambient air through heat exchangers in which the air is heated in two stages before blowing it onto the wood fragments. Thanks to this air flow, the wood fragments are pressed against the belt and very little dust escapes. The heat exchangers are condensation exchangers in which part of the water vapor separated from the biomass during the explosive decompression of the biomass is condensed to recover its latent heat.

[0059] The dried wood fragments are extracted from the silo 16 by a planetary screw and placed on a conveyor belt which transports them to a feed silo 17 of a reactor 18 allowing 500 to 1000 kg per hour of wood fragments to be processed continuously.

[0060] Reactor 18 is a vertically oriented pressure reactor into the lower part of which 500 to 1000 kg / h of steam are injected at a temperature of 203°C to 250°C. The steam flow is extracted from the reactor at the upper part of the reactor. At the outlet of the reactor, the steam is returned to the CH boiler in which it was produced.

[0061] It will be noted that in reactor 18 the steam temperature is 203°C and the pressure is 17 bars.

[0062] On the bottom of the reactor 18, a scraper mounted pivoting on a vertical axis (not shown in [Fig.l]) pushes the fragments of wood, having remained for approximately 8 minutes in the reactor, towards an endless screw 20 making it possible to extract fragments of wood from the reactor 18.

[0063] This discharge screw 20 pushes the wood fragments out of the reactor towards a valve 21 for controlling the flow of wood fragments extracted from the reactor continuously.

[0064] Under the thrust of the steam present in the reactor and of the screw 20, fragments of wood are continuously expelled through the valve 21, at very high speed, into an expansion line 22 and are entrained by the flow of steam leaving with these fragments of wood from the reactor into the expansion line 22, in which they undergo a first explosive decompression, up to a first separation unit 23, in which the pressure is 8 bars and the temperature is 168°C.

[0065] In this particular embodiment of the invention, the separation unit 23 consists of a centrifugal dynamic separator. In a variant of this particular embodiment of the invention, it may also be envisaged to implement a static cyclone.

[0066] It should also be noted that by providing decompression up to a pressure of 8 bars, the expansion of the steam remains limited to substantially double the volume of steam leaving the reactor, which makes it possible to implement a pressure-resistant separation unit of limited size and less cost.

[0067] In the separation unit 23, approximately 233m3 of steam, which corresponds to 950kg / h of steam, is separated per hour from the biomass, entraining 45kg / h of a first type of volatile organic compounds.

[0068] A part of this volume of steam is, as already specified above, directed towards a condensation heat exchanger ECHC which makes it possible to provide a part of the heat necessary for the preliminary drying of the wood fragments before their introduction into the reactor. After condensation, the organic compounds in aqueous solution resulting from the condensation of the volatile organic compounds contained in the steam are distilled in order to extract the first compounds of interest, such as furfural for example at this stage.

[0069] Another part of this volume of steam is directed towards the boiler CH, in which the organic compounds entrained with this part are burned and where the latent heat of this volume of steam is used to heat the steam introduced into the reactor.

[0070] The opening at regular intervals of a rotary valve 24i mounted at the base of the separation unit makes it possible to empty the biomass from the separation unit 23 into a buffer volume 25 under the pressure of the residual steam remaining in the separation unit, which causes a new explosive decompression of the biomass.

[0071] This buffer volume 25 feeds, through a second rotary valve 242 with controlled opening, a second separation unit 26, consisting of a static cyclone, in which the vapor pressure is 4 bars and the temperature is equal to 141°C.

[0072] In this cyclone 26, approximately 22 m3 of steam per hour, corresponding to 45 kg / h of steam, is separated from the biomass, carrying with it 4 kg / h of a second type of volatile organic compounds. This steam is condensed and then distilled in a distillation column 27, which makes it possible to extract furfural from the condensed organic compounds of the second type. Furthermore, it will be noted that the heat extracted during the condensation of the condensed steam is used for drying the combustible material at the outlet of the installation 10.

[0073] In this particular embodiment of the invention, a third and then a fourth explosive decompression and separation stage are mounted at the outlet of the second separation unit 26.

[0074] This third and fourth stage of explosive decompression and separation comprise a buffer volume 31, 41 between two controlled-opening rotary valves 32 and 33 or 42 and 43, in which a new defibrillation of the biomass takes place, which feeds a third separation unit 34, respectively a fourth separation unit 44.

[0075] The steam pressure in the third separation unit 34 is 1.9 bar and the temperature is 117°C. In this cyclone 34, 4m3 of steam per hour, corresponding to 4kg / h of steam, are separated from the biomass, entraining 1kg / h of volatile organic compounds of a third type.

[0076] This steam is condensed and the acetic acid present in the condensed organic compounds of the third type is transformed into methane in a methanizer 35 by the acetoclastic route. The methane produced is then stored in a storage tank 36 used to supply burners of the boiler CH. Just as in the previous stage, the heat from the condensation of the steam is recovered and used for drying the combustible material at the outlet of the installation 10.

[0077] The cyclone 44, which is at atmospheric pressure, allows the residual steam to be separated from the biomass. Thus, 1 kg / h of steam at 100°C is extracted from the cyclone 44, entraining volatile organic compounds of a fourth type. This steam is condensed and distilled or purified by a chromatography process in a treatment unit 45 to extract fractions of interest, such as 5-hydroxymethylfurfuraldehyde, formic acid, methanol, levoglu-cosenone or levulinic acid.

[0078] At the outlet of the cyclone 44, 450 kg / h of steam-cracked and defibrated biomass is discharged via a discharge conduit 29 into a storage silo 28, with a view to being transformed into pellets with a diameter substantially equal to 7 millimeters and an average length equal to 22 millimeters.

[0079] For this they are conveyed using a chain conveyor, or a pneumatic conveyor, to a granulating press 210 where they are compacted in the form of pellets.

[0080] The pellets obtained, with a density equal to 710 kg / m3, are then directed to a bulk truck loading station or to a bagging-palletizing station.

[0081] [Fig.2] shows the steps of another process for the continuous production of combustible material from lignocellulosic biomass, in synoptic form.

[0082] In a first step 201, 600 kg / h of lignocellulosic biomass is continuously introduced into a reactor and exposed for 7.5 minutes, during a step 202, to water vapor at a pressure of 17.5 bars.

[0083] 600 kg / h of lignocellulosic biomass contained in the reactor is extracted in continuous from the reactor, after undergoing steam cracking, in a step 203 and propelled under steam pressure through a controlled opening valve in an expansion line, in which a first explosive decompression occurs, to a static cyclone in which the steam pressure is equal to 7.2 bars (step 204). In this first separation unit, approximately 1150 kg / h of steam is separated per hour from the biomass, entraining 54 kg / h of a first type of volatile organic compounds (step 205). This steam enriched with a first type of volatile organic compounds passes through a heat exchanger and is then directed into a boiler where the volatile compounds are burned (step 206).

[0084] In a step 207, the biomass contained in the first separation unit is expelled at regular intervals into a buffer volume under the pressure of the residual steam remaining in the first separation unit by controlling the opening of a rotary valve, which causes a new explosive decompression of the biomass. The biomass is then transferred from the buffer volume into a centrifugal dynamic separator in which the steam pressure is 3.8 bars, through a second rotary valve with controlled opening.

[0085] In this second separation unit, approximately 54 kg / h of steam is separated from the biomass, carrying with it 4.8 kg / h of a second type of volatile organic compounds (step 208), the quantity of steam extracted then being condensed and then distilled in a distillation column (step 209).

[0086] The residual biomass contained in the second separation unit is then transferred under the residual vapor pressure into an expansion line along which the pressure gradually decreases to atmospheric pressure (step 211).

[0087] In a final step 212, these 540 kg of steam-cracked and defibrated biomass obtained per hour are transformed into pellets.

Claims

Claims

1. A method for the continuous manufacture of a combustible material, intended in particular for an industrial boiler, from lignocellulosic biomass comprising the following steps: - continuous introduction of a predetermined mass per minute of said biomass into a pressurized reactor, said reactor being supplied with substantially saturated steam, the pressure of which is between 15.3 and 22.9 bars and / or the temperature is between 200 and 220°C once introduced into the reactor; - exposure of the biomass introduced into said reactor to said steam for a time sufficient to obtain steam cracking; - continuous extraction from said reactor of a portion of the biomass contained in the reactor per minute;characterized in that it comprises: - an explosive decompression step comprising a transfer of said biomass extracted from said reactor in a conduit to separation means in which the steam pressure is between 7 and 8 bars; - a step of separation in said separation means of a portion of the steam extracted from said reactor with said biomass and of said biomass; - a step of depressurization of said biomass separated from said portion of steam until the pressure exerted on the biomass is equal to atmospheric pressure, said biomass at atmospheric pressure forming said combustible material.;

2. Manufacturing method according to claim 1, characterized in that said depressurization step to atmospheric pressure comprises at least one additional explosive decompression step comprising a transfer in a conduit of said biomass from the separation means to additional separation means in which the vapor pressure is less than or equal to 4 bars and a separation step in said additional separation means of a portion of the vapor entering said additional separation means and of said biomass.

3. Manufacturing method according to claim 2, characterized in that said step of depressurization to atmospheric pressure comprises: - a first additional explosive decompression step comprising a transfer in a conduit of said biomass from the separation means to first additional separation means in which the vapor pressure is between 3.5 and 4 bars and a step of separation in said first additional separation means of a portion of the vapor entering said first additional separation means and of said biomass.- a second additional explosive decompression step comprising a transfer in a conduit of said biomass from the first additional separation means to second additional separation means in which the vapor pressure is between 1.8 and 2 bars, and preferably is equal to 1.9 bars, and a step of separation in said second additional separation means of a portion of the vapor entering said second additional separation means and of said biomass.

4. Manufacturing method according to claim 3, characterized in that said step of depressurization to atmospheric pressure further comprises a third step of additional explosive decompression comprising a transfer in a conduit of said biomass from said second additional separation means to third additional separation means in which the vapor pressure is equal to 1 bar, and a step of separation in said third additional separation means of a portion of the vapor entering said third additional separation means and of said biomass.

5. Manufacturing method according to claim 1, characterized in that said means for separating a portion of steam extracted from said reactor with said biomass extracted from the reactor comprise a cyclone or a centrifugal dynamic separator.

6. Manufacturing method according to any one of claims 1 to 5, characterized in that it comprises a step of circulating said steam separated from said biomass in a heat exchanger, such as a condensation heat exchanger.

7. Manufacturing method according to any one of claims 1 to 6, characterized in that it comprises a step of combustion of said portion of steam separated from said biomass.

8. Manufacturing method according to any one of claims 1 to 6, characterized in that it comprises a condensation step of at least a portion of said steam portion separated from said biomass and a step of distillation of said condensed water vapor making it possible to obtain a purified fraction of interest, such as furfural.

9. Manufacturing method according to any one of claims 2 to 4, characterized in that it comprises a step of condensation of at least part of said portion of steam separated from said biomass and a step of purification of said condensed water vapor by application of an activated sludge treatment or by methanization.

10. Manufacturing method according to claim 9, characterized in that said methanization step is an aceto-clastic methanization step.

11. Manufacturing method according to any one of claims 1 to 10, characterized in that said conduit has at least one of its ends a rotary valve or dynamic sealing means.

12. Manufacturing method according to any one of claims 1 to 11, characterized in that said biomass introduced into the reactor has a humidity level of between 5 and 25%.

13. Manufacturing method according to any one of claims 1 to 12, characterized in that said biomass comprises wood chips.

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