A method for producing biofuels by steam cracking

Abstract

The present invention relates to a method for producing biofuel by continuous or discontinuous steam cracking of lignocellulosic biomass, characterized in that: - recording a digital model of the optimal steam cracking parameters depending on the type of plant components of the biomass; - feeding a heterogeneous biomass into a steam cracking reactor; - measuring the type of plant components of the biomass at least once during the treatment; - controlling the adjustment of the steam cracking parameters depending on the measured type of plant components of the biomass and on the digital model.

Description

Detailed Description of the Invention

[0001] [Technical field] The present invention relates to the production of solid biofuels derived from the processing of biomass of various origins, said production being by using steam cracking or steam explosion processes.

[0002] Biomass is a renewable primary energy source that can be transported to a site for conversion, but it is a low-density, variable, and perishable energy source.

[0003] The conversion of lignocellulosic biomass (wood, agricultural waste, agricultural and agro-industrial by-products) into energy-dense, transportable and easily storable compounds makes it possible to develop and enhance the stationary energy industrial sector (biofuels for fixed-point use in homes, as opposed to biofuel oils) and reduce the environmental impact (fossil CO2 emissions from biomass without fertilizers or phytosanitary agents).

[0004] Thermal treatment of biomass by steam cracking allows for this energy densification, modifying the structure of the treated biomass: -Lignocellulosic materials are defibrillated - The crystallinity of cellulose increases as a result of the crystallization of the amorphous part. - Hemicellulose is easily hydrolyzed -Delignification is enhanced as a result of the modification of the lignin structure.

[0005] Steam explosion is a biomass treatment commonly used for the production of biofuels, especially in the form of granules ("black pellets"). It uses both physical / mechanical and chemical methods simultaneously to break down the structure of lignocellulosic materials. Generally speaking, steam explosion is the violent or flash evaporation of water into steam. Pressurized vessels operating at or above atmospheric pressure can also provide conditions of rapid boiling that can be characterized as steam explosion. Biomass introduced into the steam cracking reactor, either continuously or batchwise, is rapidly heated by using saturated steam under high pressure. The biomass / steam mixture is held for a period of time, promoting hydrolysis of hemicellulose, as well as other chemical and physical changes. This period is then followed by explosive decompression. Steam explosion is typically initiated at temperatures of 160-260 °C for a few seconds to minutes before the material is exposed to atmospheric pressure.

[0006] The apparatus for steam explosion consists of an evaporator (steam generator) and a reactor that undergoes rapid decompression. Steam explosion can be described as consisting of two successive stages: steam cracking (i.e., breaking down complex molecules into smaller ones under the influence of steam) and explosive decompression.

[0007] The first stage is to make water vapor penetrate inside the structure of the material under high pressure. Thus, the water vapor condenses and wets the surface of the material. The condensed water initiates the hydrolysis of the acetyl and methylglucuronic acid groups present in the hemicellulose. The acids thus liberated lower the pH of the medium and catalyze the depolymerization of hemicellulose. The application of more drastic conditions allows the formation of monosaccharides, while increasing the concentration of furfural and 5-hydroxymethylfurfural, which are fermentation inhibitors.

[0008] During the second stage, the explosive decompression leads to the instantaneous evaporation of a portion of the condensed water present in the structure. This expansion of water vapor exerts shear forces on the surrounding structure. If the shear forces are high enough, the water vapor causes mechanical failure of the lignocellulosic structure. The combined effect of the two aforementioned stages includes modification of the physical properties of the material (specific surface area, water retention, coloration, crystallinity of cellulose, etc.), hydrolysis of hemicellulose compounds, and modification of the chemical structure of lignin, allowing the opening of the material and facilitating its extraction.

[0009] The two parameters that control steam explosion are the reaction temperature and residence time. The time the biomass spends in the reactor helps determine the extent of hydrolysis of hemicellulose by organic acids. However, long residence times also increase the production of decomposition products, which must be minimized in the following fermentation process. Temperature controls the steam pressure in the reactor. Higher temperatures result in higher pressures, and therefore a greater difference between the reactor pressure and atmospheric pressure. The pressure difference is, in turn, proportional to the shear force.

[0010] The parameters of the process are important and to facilitate the comparison of the different options, a model was developed based on the assumption that the kinetics of the process is first order and follows the Arrhenius law, making it possible to develop the ordinate of the reaction (R0):

[0011]

number

[0012] where Tr is the reaction temperature (°C), Tb is the reference temperature (boiling point of water at atmospheric pressure: 100°C), t is the residence time (min) and 14.75 is the conventional activation energy, assuming that the general process is hydrolytic and that the general conversion is first order. The log10 value of the reaction ordinate gives the severity factor (or severity) used to describe the impact of steam explosion on biomass. Severity=log10(R0) Generally, the production of biofuels by steam cracking is carried out starting from natural biomass, derived from felling or coppicing, or from products resulting from wood utilization, or indeed from other agricultural products, and the operating point is optimized to obtain good energy qualities of the steam cracked powder.

[0013] Steam cracking differs from hydrothermal pretreatment, also known as aqueous fractionation, solvolysis, hydropyrolysis, or hydrothermal treatment, in that the latter involves the use of water at high temperature and pressure to promote the disintegration and separation of the lignocellulosic matrix. This technique is not suitable for the production of black pellets, as the resulting product is largely liquid.

[0014] Pyrolysis is the chemical decomposition of organic compounds by intense heating in the absence of oxygen. The compounds obtained after pyrolysis differ in their properties from those obtained by steam cracking. Steam cracking is not related to pyrolysis techniques in that it uses steam explosion and is carried out in the presence of oxygen.

[0015] [Prior Art] Pyrolysis techniques in which digital models are used to optimize the process parameters are known, for example from document WO 2012 / 109490 or document CN 105806735 A. These known pyrolysis techniques are based on the chemical decomposition of organic compounds by intense heating in the absence of oxygen.

[0016] The document BV BABU “Biomass pyrolysis: a State of the art review” also describes the prior art of pyrolysis. However, these methods are different from the steam pyrolysis technique.

[0017] US patent US2013 / 341569 describes a method for the pretreatment of biomass, including a step of steam cracking to produce synthesis gas. The method also includes a catalytic converter using a control system that regulates the gas conversion rate depending on the composition of the catalytic material. In this patent, a digital model is used for the steam cracking step, so that optimal parameters can be obtained depending on the nature and content of the pollutants. The document discloses a control method related to the catalytic converter, without any mention of the control of the steam cracking.

[0018] Finally, SAGEHASMI ET AL: “Superheated steam pyrolysis of biomass elemental components and Sugi (Japanese cedar) for fuels and Chemicals” discloses a method using a digital model for superheated steam pyrolysis, the application of which is limited to samples of a few individual components of biomass (xylan, cellulose, lignin, etc.) or to a single type of biomass, namely Sugi (Table 1 on page 1273; right column on page 1273, lines 1-5).

[0019] [Disadvantages of the Prior Art] In the case of solutions known in the prior art, the best solution to guarantee the best results of the steam cracking is to have a regular and controlled supply of biomass of the same quality. In the case of wood, the challenge is to select the size of the trees and the diameter of the trunks to provide homogeneous batches of wood of the same species of the same land plot, in particular with regular debarking. In case of fluctuating resources, an attempt should be made to group them by homogeneous batches and to feed these batches to the steam cracker, readjusting the operating parameters of the steam cracking according to each change of batch and quality. This requires traceability and compliance with specifications by the biomass supplier, a high degree of reliability and, at the factory level, the ability to identify changes in batch or quality to correct the implementation of the work. However, this does not prevent some batches from being mixed with other species of biomass, various ages or different qualities.

[0020] Prior art solutions are not entirely satisfactory as they either utilize pyrolysis methods, simply provide parameter control for the catalytic converter, or actually require a uniform biomass supply, which can prove to be limiting.

[0021] In fact, the pyrolysis process does not make it possible to obtain compounds with sufficient properties to manufacture black pellets.

[0022] In the prior art, the use of digital models has been: - pyrolysis systems that are unable to obtain compounds with the properties required to obtain black pellets; - a system that does not include a parameterization of steam cracking in the digital model; Applies only to

[0023] As the severity factor increases, the particle size and energy efficiency decrease.

[0024] Conversely, if the severity factor is insufficient, the heating value of the steam cracked material will be reduced and the product will be more fibrous than powdery, making it difficult to form into pellets.

[0025] When the biomass feed exhibits heterogeneity, prior art solutions require screening of the feed at different stages - at felling or harvesting site, during loading, in the wood or biomass storage, during preparation stages (barking, destoning, crushing) - and therefore the overflow must be used to regroup and remake homogenous batches, resulting in handling, storage and traceability requirements, not preventing different products from passing through said screens.

[0026] Solution provided by the present invention In order to overcome the drawbacks of the prior art related to the lesser availability of uniform and homogeneous natural biomass and the inadequacy of known installations for the processing of heterogeneous biomass, the present invention relates, according to its most general meaning, to a method for the continuous or discontinuous production of biofuels by steam cracking of lignocellulosic plant biomass, said method comprising: - recording a digital model of the optimal steam cracking parameters depending on the type of plant component of the biomass; -Heterogeneous biomass is fed into the steam cracking reactor. The type of plant component of the biomass is determined at least once during the treatment. The adjustment of the parameters of the steam cracking is controlled according to the type of plant components of the biomass and according to the digital model. It is characterized by:

[0027] Within the meaning of the present invention, "type of plant components of biomass" means the combination of different components of biomass (lignin, cellulose, etc.) and their relative proportions that define the nature of the biomass. Each type of biomass has a specific type due to its components and is further defined by indicators, such as the degree of heterogeneity of the biomass or its nature.

[0028] Thus, within the context of the present invention, the biomass to be treated may consist of a mixture of different types of biomass having different indicators; hence the reference to "heterogeneous biomass".

[0029] According to an advantageous embodiment, the lignocellulosic biomass has a moisture content below 27% and is directly subjected to a steam cracking treatment without any other preceding thermal or chemical treatment.

[0030] According to the variant: The adjusted parameters include at least one of the following parameters: severity factor, steam cracking pressure, steam cracking temperature, steam cracking duration, steam cracking stop, steam / solids ratio (washing, stripping), steam cracking tank fill rate, progress rate in the steam cracking tank, compression ratio at the inlet, compression ratio at the outlet of the reactor with an orifice diameter, feed flow rate, humidity, particle size.

[0031] said measuring step consists of taking a sample of the biomass entering the steam cracking tank and applying a physicochemical analysis to said sample to characterize the sampled biomass.

[0032] said measuring step consisting of taking a sample of the waste gas or liquid inside or at the outlet of said steam cracking tank and applying a physico-chemical analysis to said sample to characterise the steam cracked biomass.

[0033] The measuring step consists of taking a sample of the steam cracked product sample inside or at the outlet of the steam cracking tank and applying physico-chemical analyses to the sample to characterize the steam cracked biomass.

[0034] - said measuring step consists of taking a sample of the pellet specimen and applying a physico-chemical analysis to said sample to characterize the pellets made using said steam cracked biomass.

[0035] At least some of the results of the measurements, as well as the results of measurements made on pellet samples obtained during the same cycle, are periodically recorded and time-stamped.

[0036] The results are injected into the blockchain.

[0037] The injection is performed within a supervised learning system to generate the digital model.

[0038] The model is determined by a series of chemical simulations.

[0039] The invention also relates to an installation for carrying out such a method.

[0040] DETAILED DESCRIPTION OF NON-LIMITING EMBODIMENTS OF THE PRESENT EMBODIMENT The invention will be more clearly understood with reference to the accompanying drawings and from reading the following detailed description of non-limiting embodiments of the invention: - [Figure 1] Figure 1 is a schematic diagram of a steam cracking facility.

[0041] [Steam cracking of heterogeneous biomass] The continuous or batch steam cracking process according to the invention provides a method for monitoring and controlling the steam cracking conditions, making it possible to adjust the severity of the treatment (reaction time and temperature) to adapt to the incoming feedstock and its heterogeneity over time, on the scale of years, seasons, storage times and between processes, and of course to the qualitative variations of the incoming biomass. This is based on the fact that the material is chemically modified using a thermal reaction at around 200°C, preferably 205-210°C, with a residence time that is also adjustable, preferably 6-8 minutes, corresponding to the essential activation energy that allows the depolymerization and volatilization of low-energy oxygenated compounds (especially the most thermolabile hemicellulose components), and constituting a balance between a minimal reactor occupancy (economic advantage) and a retained material yield (technical advantage), while increasing the calorific value of the final compound and preserving the integrity of cellulose and other macromolecules such as lignin, the latter being essential to ensure the agglomeration of the final pellets and therefore their resistance to water and mechanical handling.

[0042] Despite the increased flexibility to produce pellets with high calorific value (temperature range can span 180-220°C and durations from 5-30 minutes), steam cracked powders can in any case have a level of inhomogeneity that is detrimental to the downstream pelletizing process. It is therefore necessary to have available means to manage this inconsistency.

[0043] In addition to the known effectiveness of steam cracking to reduce fibers to powder and homogenize biomass, the effectiveness of steaming is measured by the density and size grade of the product. Generally, a product is achieved that is composed mostly (>80%) of particles smaller than 500 μm, with a few percent of particles remaining larger than 1 millimeter, and indeed several millimeters. However, at similar conditions (essentially temperature and residence time), product variations result in the presence of a fraction that is much less explosive, often indicating the preservation of long fibers or flat particles resulting from the comminution before steam cracking. Also, its density is greater than that of the main product.

[0044] Regarding the heterogeneity of the size classes after steam cracking and before pelleting, the "solids" outlet of the separation system between the powder and the steam (static cyclones or dynamic separators such as Perivapor® by Valmet), screens (rotary or vibrating screens) or density measuring tables allow easy separation of the conformable powder from the larger particles that are poorly steam cracked. The overflow is collected and then transported towards storage means before being reintroduced into the steam cracker together with the crushed biomass.

[0045] It is therefore the case that after steam cracking, in a method for transporting the powders, a particle size or density distribution screen is carried out to select the much less explosive fractions, followed by separation of said fractions and returning them to the feed of the steam cracker, with the aim either to immediately reprocess them if their level of disintegration is sufficiently advanced (particles are not fully broken but already reduced in size), or to delay processing under steam cracking conditions more suited to their resistance, which corresponds to the ability to adjust the conditions (severity) of steam cracking to the biomass substrate or screen overflow.

[0046] [Description of the embodiment of the equipment] Figure 1 shows a schematic diagram of an installation for discontinuous steam cracking of biomass, but the general principles apply to a continuous process. The installation for steam explosion consists of an evaporator (100) which generates steam, and a reactor (200) which is subjected to rapid depressurization.

[0047] It comprises a steam cracking reactor (200) and a spark arrestor (300). The reactor (200) is filled with biomass via valve (13). After closing valve (13), steam is introduced into said reactor via charging valve (6). Then, the reactor (200) is allowed to reach the target temperature, after which a period at the desired temperature is started. Typically, about 20 seconds is required to reach the desired temperature. At the end of the desired period, valve (9) is opened to allow explosive decompression. The steam exploded material passes through a connecting pipe and is charged into a collection vessel (300).

[0048] A high pressure pump (1) supplies the water vapor generator (100). Heating bands (2) ensure the thermal stability of the various items of equipment.

[0049] Furthermore, the installation comprises a pressure gauge and sensor (3) for measuring the pressure and temperature in the steam generator (100) and a pressure gauge and sensor (4) for measuring the pressure and temperature in the reactor (200). An isolation valve (5) controls the inflow of steam into the steam generator (200). A safety valve (7) limits the pressure in the steam generator (100). The reactor (200) also comprises a safety valve. The spark arrestor (300) comprises a pressure gauge (12). The feeding of the reactor (200) is achieved by a feed chamber (14) which draws according to a controlled volume of biomass stored in a reservoir (15).

[0050] The facility comprises one or more sampling devices (50-54) for solid, liquid or gas samples for analyzing the properties of the biomass provided. These data are processed by a programmable machine (16) that controls the parameters of the facility depending on the results of the analysis and on the parameters provided by pressure and temperature sensors. Furthermore, the data are stored in a memory (17), which also contains a record of a processing model that determines the parameters to be applied depending on the results of the analysis. This memory (17) is associated with a calculator that applies a supervised learning process to the historical data stored in the memory (17) and also controls the injection of the data into the blockchain.

[0051] [Biomass types and indicators] Types of biomass include: - Wood of different species, either alone or mixed - Different types of agricultural residues, either alone or in mixtures - Different types of by-products of agriculture and agro-industry, either alone or in mixtures - With or without bark - Presence of category A, B or C timber, either alone or in a mixture - A mixture of lignocellulosic materials of various specific median sizes.

[0052] Indicators include, separately or in combination: - the level of heterogeneity of the biomass mixture by determining the variance of the physical or chemical properties measured for a series of samples, such as color, density, median element size, optical recognition of the properties of different types of biomass recorded, etc. The nature of the biomass, in particular by using automatic recognition or by collecting information manually, such as wood type, maturity, nature of the tissue (bark, pith, branches, knots, stumps, etc.).

[0053] Said automatic recognition can be achieved by imaging with an "electronic nose", or indeed by any physico-chemical measurement making it possible to distinguish between types of biomass.

[0054] [Equipment Criticality Factors and Controls] The control measures for the treatment of heterogeneous biomass take into account the optimum steam cracking conditions in the reactor (200).

[0055] Therefore, the control parameters and operating points are selected not only depending on the breakdown process of the lignocellulosic material, but also on the type of heterogeneous biomass that is steam cracked.

[0056] For this purpose, digital models of the biomass types and of the control means suitable for each combination of biomass types are developed, thus making available digital references that allow the parameters to be automatically adapted depending on the nature of the biomass entering the reactor (200).

[0057] The construction of this model can be carried out experimentally, running a series of treatments of various heterogeneous biomasses, with different control measures, and thus retaining the control measures corresponding to the optimization of the steam cracking of the identified biomasses, depending on the quality of the pellets produced.

[0058] The model can also be created by a supervised learning solution from recorded historical data.

[0059] Finally, the model can be developed by simulating the chemical reactions associated with the main types of biomass that can be supplied.

[0060] The model determines, for each class of biomass, the control measures to be selected.

[0061] During the new process, physicochemical analyses provide the properties and composition of the steam-cracked biomass, and the computer automatically determines the control measures of the equipment depending on the results of the analyses and the recorded digital models. [Brief description of the drawings]

[0062] [Figure 1] FIG. 1 is a schematic diagram of a steam cracking facility.

Claims

1. A method for producing black pellet biofuel by continuous or discontinuous steam cracking of lignocellulosic biomass by converting said lignocellulosic biomass to a high energy density, comprising: - recording a digital model of the optimal parameters of said steam cracking depending on the type of plant component of the biomass; - Heterogeneous biomass is fed into the steam cracking reactor the type of plant components of the biomass is determined at least once during the steam cracking process, said step of determining comprising taking samples of waste gases or liquids inside or at the outlet of the steam cracking tank and applying physico-chemical analyses to said samples for characterization purposes; The adjustment of the steam cracking parameters is controlled according to the type of plant components of the biomass and according to the digital model. A manufacturing method comprising:

2. 2. A method for producing biofuel by steam cracking of biomass according to claim 1, characterized in that the adjusted parameters comprise at least one of the following parameters: severity factor, steam cracking pressure, steam cracking temperature, steam cracking duration, steam cracking stop, steam cracking tank filling rate, progress rate in the steam cracking tank, compression rate at the outlet of the reactor with an orifice diameter, humidity, particle size.

3. 3. The method for producing biofuel by steam cracking according to claim 1 or 2, characterized in that the initial biomass has a moisture content of less than 27% during the steam cracking treatment.

4. 4. A method for producing biofuel by steam cracking of biomass according to at least one of claims 1 to 3, characterized in that at least some of the results of the measurements, as well as the results of measurements carried out on pellet samples obtained during the same cycle, are periodically recorded and time-stamped.

5. The method for producing biofuel by steam decomposition of biomass according to claim 4, characterized in that the results are injected into a blockchain.

6. 6. The method of claim 5, wherein the input is performed within a supervised learning system to generate the digital model.

7. A method for producing biofuel by steam cracking of biomass according to claim 1, characterized in that the model is determined by a series of chemical simulations.

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