WO2022248233A1

WO2022248233A1 - Stepwise method for continuously producing a combustible material by explosive decompression

Info

Publication number: WO2022248233A1
Application number: PCT/EP2022/062840
Authority: WO
Inventors: Frédéric MARTEL; Adriana QUINTERO-MARQUEZ; Jean-Luc DESPRES
Original assignee: Europeenne De Biomasse
Priority date: 2021-05-25
Filing date: 2022-05-11
Publication date: 2022-12-01
Also published as: FR3123362A1; EP4347749A1

Abstract

The invention relates to a method for continuously producing a combustible material from biomass, comprising: - continuously exposing the biomass introduced into a reactor to the water vapour at a pressure of between 15.3 and 22.9 bars for a sufficient amount of time to cause steam cracking; - continuously extracting, from the reactor, a portion of the biomass contained in the reactor. According to the invention, such a method comprises: - transferring the biomass extracted from the reactor in a conduit to separation means, wherein the vapour pressure is between 7 and 8 bars; - a step of separating a portion of the vapour extracted from the reactor to include the biomass and to exclude the biomass; - a step of reducing the pressure of the biomass separated from the vapour portion to atmospheric pressure.

Description

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

1. Field of the invention

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

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

The invention also finds an application in the manufacture of combustible material for boilers or for industrial furnaces, and for domestic boilers and stoves.

2. State of the art

Biomass, and in particular lignocellulosic biomass from forest exploitation or agricultural production, is in its raw state a material that is not very dense, perishable and which presents 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.

It is known to implement techniques of carbonization, torrefaction, or even by so-called "steam explosion" techniques combining steam cracking with explosive decompression, discontinuous or continuous, to transform lignocellulosic biomass into a stable fuel and substantially constant quality, possessing a significant calorific value.

A drawback of the carbonization technique is that during the transformation a large 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.

The losses of material are also significant, and approximately 10 to 20%, with the torrefaction technique, which moreover has the further disadvantage of being expensive to implement and of requiring implementation under an atmosphere inert to avoid a risk of combustion, which represents a danger. The known techniques of continuous steam cracking or discontinuous “steam explosion” can make it possible to limit the mass losses of material. However, it is noted that a volatile matter rich in energy can be released and lost by this process, which can reduce quite greatly the final calorific value of the final product obtained by these known processes.

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

This known technique has the disadvantage of being complex and costly to implement, because it requires two reactors and an enclosure having an internal volume approximately 13 to 19 times greater than that of the reactors in order to be able to provide expansion and which is capable of withstanding explosive shocks.

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

Also known from document WO 2017/089648 Al 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 one go. only one step, this in order to allow a suitable defibrillation of the treated material. A disadvantage of this known technique is that a quantity of material which is still too great is entrained with the discharged steam.

3. Objects of the invention

The object of the invention is therefore in particular to overcome the disadvantages of the prior art mentioned above. More specifically, the aim of the invention is to provide a technique for the continuous manufacture of combustible material from lignocellulosic biomass by "steam explosion" which makes it possible to improve the calorific value of the combustible material while limiting the losses of material in the form condensable volatile compounds with high carbon content.

An object 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”.

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

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

Another object of the invention is to provide such a technique which is simple to implement and has a reduced cost price.

4. Disclosure of Invention

These objectives, as well as others which will appear subsequently, are achieved using a process 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 part of the biomass contained in the reactor per minute.

In the context of the invention, lignocellulosic biomass is understood to mean 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 shavings, splinters, etc.), treated wood, pallets, biomass from the exploitation of coppice, miscanthus, fescue, bamboo, etc., waste or ligneous co-products from agricultural crops (straw, grass, etc.) or from the food industry ( bagasse, etc.), or green, woody or recycled waste from landfills and any combination thereof.

According to the invention, such a method comprises: 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 separation step in said separation means of 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 vapor until the pressure exerted on the biomass is equal to atmospheric pressure, said biomass at atmospheric pressure forming said combustible material.

Thus, in a novel way, the invention proposes to carry out an 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. Moreover, during the depressurization step, the quantity of residual vapor being reduced, a smaller quantity of recoverable organic compounds of interest is entrained with it.

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

Thus, by providing an additional explosive decompression step, compounds of interest richer in carbon are extracted 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 stage, which again limits the losses of material with high calorific value. These extracted compounds can also be upgraded.

In a particular embodiment of the invention, said depressurization step down 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 separation step in said first additional separation means a portion of the vapor entering said first additional separation means and 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 separation step in said second additional separation means of a portion of the vapor entering said second additional separation means and of said biomass.

Thus an explosive decompression is carried out in four stages, which makes it possible to limit at each stage the losses of material with high power. calorific, 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. In a particular embodiment of the invention, said step of depressurization down 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 up to third additional separation means in which the vapor pressure is equal to 1 bar, and a stage of separation in said third additional separation means of a portion of the vapor entering said third additional separation means and of said biomass.

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.

Advantageously, said means for separating a portion of vapor extracted from said reactor with said biomass extracted from the reactor comprise a cyclone or a centrifugal dynamic separator (turbine). In a particular embodiment of the invention, a method as described above comprises a step of circulating said vapor separated from said biomass in a heat exchanger, such as a condensation heat exchanger.

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

In another particular embodiment of the invention, a method as described above comprises a step of combustion of said portion of vapor separated from said biomass. The steam pressure then makes it possible to diffuse it in the hearth of the boiler to ensure suitable combustion of the volatile organic compounds and to recover the latent heat of the steam.

According to a particular embodiment of the invention, a method as described above comprises a step of condensing at least part of said portion of vapor separated from said biomass and a step of distilling said water vapor condensed 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.

According to a particular embodiment of the invention, a method as described above comprises a step of condensing at least part of said portion of vapor separated from said biomass and a step of purifying said vapor of water condensed by application of an activated sludge treatment or by anaerobic digestion.

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

The acetic acid is thus upgraded to methane.

It should be noted that the implementation of several stages of explosive decompression makes it possible to extract furfuraldehyde or furfural, which is an inhibitor of the methanation reaction of acetic acid, during the first stage or stages of explosive decompression , then proceeding with the methanization of the acetic acid in a subsequent step.

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

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

In a particular embodiment of the invention, said biomass comprises wood chips. 5. List of Figures

Other characteristics and advantages of the invention will appear more clearly on reading the following description of an embodiment of the invention, given by way of a simple illustrative and non-limiting example, and the appended figures, among which: the FIG. 1 represents an installation for manufacturing combustible material from lignocellulosic biomass suitable for implementing a process for manufacturing combustible material according to the invention; FIG. 2 illustrates the steps of another exemplary embodiment of a manufacturing method according to the invention, in the form of a block diagram.

6. Detailed description of the invention

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.

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

This installation 10 comprises a hammer mill 11 supplied with wood chips by means of an endless screw 12 which takes the wood chips from a ladder silo 13. A large wood separator eliminates the oversized elements before the wood chips do not enter the grinder 11. In this wet grinder 11, the wood chips are ground in the form of wood fragments of larger size mainly between 4 and 8 millimeters, up to 16 mm. The silo 13 is filled by a bucket loader which picks up chips from piles formed on storage areas on the ground. These wood fragments flow out of the grinder 11 onto a conveyor belt 14, equipped with a weighing belt, which transports them to the feed hopper of a hot air dryer 15 at low temperature. In this embodiment of the invention, the temperature of the hot air of the dryer is between 75 and 85°C.

This dryer 15 is in this particular embodiment of the invention a double layer belt dryer. The fragments entering the dryer are evenly distributed 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 on 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 top of the first in the dryer. After passing halfway through the dryer a second time, the dried wood fragments, whose moisture content is now below 10%, are separated, unloaded and conveyed to a buffer storage silo 16.

A humidity sensor continuously monitors the humidity content of the wood fragments leaving the dryer and the speed of advancement of the strip is automatically regulated in order to maintain the humidity level of the wood fragments constant at the exit of the dryer.

In the dryer, exhaust fans draw ambient air through heat exchangers in which the air is heated in two stages before blowing it over the wood fragments. Thanks to this air flow, the wood fragments are pressed against the belt and very little dust escapes. 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.

The dried wood fragments are extracted from silo 16 by a planetary screw and deposited on a conveyor belt which transports them to a silo supply 17 of a reactor 18 for treating 500 to 1000 kg per hour of wood fragments continuously.

Reactor 18 is a vertically oriented pressure reactor into the lower part of which 500 to 1000 kg/h of steam is injected at a temperature of 203°C to 250°C. The vapor stream is extracted from the reactor at the top of the reactor. At the reactor outlet, the steam is sent back to the CH boiler in which it was produced.

It will be noted that in the reactor 18 the temperature of the vapor is 203° C. and the pressure 17 bars.

On the bottom of the reactor 18, a scraper mounted pivoting on a vertical axis (not shown in FIG. 1) pushes the fragments of wood, having stayed about 8 minutes in the reactor, towards an endless screw 20 allowing fragments to be extracted. of wood from reactor 18.

This discharge screw 20 pushes the wood fragments out of the reactor towards a valve 21 making it possible to control the flow rate of wood fragments extracted from the reactor continuously.

Under the pressure of the steam present in the reactor and the screw 20, fragments of wood are expelled continuously through the valve 21, at very high speed, in an expansion line 22 and are driven by the flow of steam. exiting with these fragments of wood from the reactor in 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 bar and the temperature is 168°C .

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 can also be envisaged to implement a static cyclone.

It should also be noted that by providing for decompression down to a pressure of 8 bars, the expansion of the steam remains limited to approximately twice the volume of steam leaving the reactor, which allows to implement a pressure-resistant separation unit of reduced size and less cost.

In the separation unit 23, approximately 233m ³ of steam, which correspond to 950 kg/h of steam, is separated per hour from the biomass, entraining 45 kg/h of a first type of volatile organic compounds.

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

Another part of this volume of steam is directed to the boiler CH, where 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.

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 generates a new explosive decompression of the biomass.

This buffer volume 25 feeds, through a second rotary valve 24 ₂ 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.

In this cyclone 26, approximately 22 m ³ of steam per hour, corresponding to 45 kg/h of steam, is separated from the biomass, entraining 4 kg/h of a second type of volatile organic compounds. This vapor 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. By elsewhere, it will be noted that the heat extracted during the condensation of the condensed vapor is used for drying the combustible material at the outlet of the installation 10.

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

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

The vapor pressure in the third separation unit 34 is 1.9 bar and the temperature 117°C. In this cyclone 34, 4m ³ of steam per hour, corresponding to 4 kg/h of steam, are separated from the biomass, entraining 1 kg/h of volatile organic compounds of a third type.

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

The cyclone 44, which is at atmospheric pressure, makes it possible to separate the residual vapor from the biomass. Thus 1 kg/h of steam at 100° C. is extracted from cyclone 44, entraining volatile organic compounds of a fourth type. This vapor is condensed and distilled or purified by a chromatography process in a processing unit 45 to extract fractions of interest, such as 5-hydroxymethylfurfuraldehyde, formic acid, methanol, levoglucosenone or levulinic acid.

At the outlet of the cyclone 44, 450 kg/h of steam-cracked and defibered biomass flow through a discharge conduit 29 into a storage silo 28, in to be processed in the form of pellets with a diameter substantially equal to 7 millimeters and an average length equal to 22 millimeters.

For this they are transported using a chain conveyor, or a pneumatic conveyor, to a pellet mill 210 where they are compacted in the form of pellets.

The pellets obtained, with a density equal to 710 kg/m ³ , are then sent to a bulk loading station for trucks or to a bagging-palletizing station.

FIG. 2 shows the steps of another process for the continuous manufacture of combustible material from lignocellulosic biomass, in synoptic form.

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 steam at a pressure of 17.5 bars.

600 kg/h of lignocellulosic biomass contained in the reactor is continuously extracted from the reactor, after having undergone steam cracking, in a step 203 and propelled under the steam pressure through a valve with controlled opening in an expansion line, in which a first explosive decompression occurs, up to a static cyclone in which the vapor 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 vapor 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).

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 vapor remaining in the first separation unit by controlling the opening of a rotary valve, which generates a new explosive decompression of the biomass. The biomass is then transferred from the buffer volume into a dynamic centrifugal separator in which the steam pressure is 3.8 bars, through a second rotary valve with controlled opening.

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

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).

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

Claims

1. Process for the continuous manufacture of a combustible material, intended in particular for an industrial boiler, from lignocellulosic biomass comprising the following steps:

- continuous extraction from said reactor of part 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 vapor pressure is between 7 and 8 bar;

- a separation step in said separation means of 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 vapor until the pressure exerted on the biomass is equal to atmospheric pressure, said biomass at atmospheric pressure forming said combustible material.

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

4. Manufacturing process according to claim 3, characterized in that said depressurization step down 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 up to to third additional separation means in which the vapor pressure is equal to 1 bar, and a stage 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 process according to claim 1, characterized in that said means for separating a portion of vapor extracted from said reactor with said biomass extracted from the reactor comprise a cyclone or a centrifugal dynamic separator.

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

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

9. Manufacturing process according to any one of claims 1 to 6, characterized in that it comprises a step of condensing at least part of said portion of vapor separated from said biomass and a step of purifying said water vapor condensed by application of an activated sludge treatment or by anaerobic digestion.

10. Manufacturing process according to claim 9, characterized in that said methanization step is an acetoclastic methanization step.

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