Process for producing biofuels by steam cracking

Abstract

The invention relates to a method for producing biofuels by continuous or discontinuous steam cracking of lignocellulosic biomass, characterized by: - ​​recording a digital model of optimal steam cracking parameters according to the typology of the plant components of the biomass; - supplying a steam cracking reactor with heterogeneous biomass; - measuring the typology of the plant components of the biomass at least once during the treatment; - controlling the regulation of the steam cracking parameters according to the typology of the plant components of the biomass and said digital model.

Description

Technical Field

[0001] The present invention relates to the production of solid biofuels derived from the treatment of biomass from various sources by steam cracking or steam explosion processes.

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

[0003] The conversion of lignocellulosic biomass (wood, agricultural waste, by-products of agriculture and agro-industry) into energy-dense, transportable and easily storable compounds makes it possible to develop and consolidate a stationary energy industry sector (biofuels used in households, at fixed points, as opposed to biofuel oils) and reduce the environmental impact (CO2 fossil emissions, use of biomass without fertilizers or phytosanitary agents).

[0004] Thermal treatment of biomass by steam cracking allows this densification of energy and changes the structure of the treated biomass:

[0005] - Defiberization of lignocellulosic raw materials

[0006] - Due to the crystallization of the amorphous part, the crystallinity of cellulose increases

[0007] - Hemicellulose is easily hydrolyzed

[0008] - Promotes delignification due to changes in lignin structure.

[0009] Steam explosion is a biomass treatment commonly used for the production of biofuels, especially in the form of pellets ("black pellets"). It uses both physical / mechanical methods and chemical methods to destroy the structure of lignocellulosic materials. In general, steam explosion is the violent evaporation or flashing of water into steam. A pressurized vessel operating at a pressure higher than atmospheric pressure can also provide conditions for rapid boiling, which can be characterized as steam explosion. Biomass introduced into a steam cracking reactor continuously or in batches is rapidly heated by saturated steam at high pressure. The biomass / steam mixture is maintained for a period of time to promote hydrolysis of hemicellulose and other chemical and physical changes. Then, explosive decompression is performed after this period of time. Steam explosion is usually initiated at a temperature of 160°C to 260°C for a few seconds to a few minutes, after which the material is exposed to atmospheric pressure.

[0010] The apparatus used for steam explosion consists of an evaporator (steam generator) and a reactor subjected to rapid decompression. Steam explosion can be described as consisting of two sequential stages: steam cracking (i.e. the breaking of complex molecules into smaller molecules under the action of steam) and explosive decompression.

[0011] The first stage consists in penetrating steam under high pressure into the interior of the material structure. As a result, the steam condenses and wets the surface of the material. The condensed water triggers the hydrolysis of the acetyl and methyl glucuronic acid groups present in the hemicellulose. The acids thus released lower the pH of the medium and catalyze the depolymerization of the hemicellulose. The application of more drastic conditions makes it possible to form monosaccharides while increasing the concentration of furfural and 5-hydroxymethylfurfural, which are fermentation inhibitors.

[0012] In the second stage, the explosive decompression causes some of the condensed water present in the structure to evaporate instantaneously. This expansion of the water vapor exerts shear forces on the surrounding structure. If the shear forces are high enough, the steam will cause a mechanical breakage of the lignocellulosic structure. The combined effects of these two stages include modification of the physical properties of the material (specific surface area, water retention, coloring, 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.

[0013] The two parameters that control steam explosion are 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 will also increase the production of degradation products, which must be minimized in the subsequent fermentation process. Temperature controls the steam pressure in the reactor. Higher temperatures result in higher pressures, thus increasing the difference between the reactor pressure and atmospheric pressure. The pressure difference, in turn, is directly proportional to the shear force.

[0014] The parameters of the method are critical and in order to facilitate the comparison of the different options, a model has been developed based on the assumption that the kinetics of the method are first order and follow the Arrhenius law, making it possible to develop the ordinate of the reaction (R0):

[0015] R0=∫ t exp[(Tr-Tb) / 14.75]dt

[0016] Where Tr is the reaction temperature (°C), Tb is the baseline 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 hydrolysis and the general conversion is first order. The log10 value of the reaction ordinate gives the depth factor (or depth) used to represent the effect of steam explosion on biomass:

[0017] Depth = log10(R0)

[0018] Typically, the production of biofuels by steam cracking is carried out starting from natural biomass originating from wells or overburden, or products from wood mining, or other agricultural products, and the operating point is optimized to obtain a good energy quality of the steam cracked powder.

[0019] Steam cracking differs from hydrothermal pretreatment (also known as aqueous fractionation, solvolysis, hydrothermal cracking 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 technology is not suitable for the production of black pellets because the product obtained is mostly liquid.

[0020] 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 cannot be compared to the pyrolysis technique, since it uses steam explosion and is carried out in the presence of oxygen. Prior art

[0021] Pyrolysis techniques which use numerical models to optimize the parameters of their process 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.

[0022] The document BV BABU "Biomass pyrolysis: a state of the art review" also describes a prior art of pyrolysis technology. However, these methods are different from steam cracking technology.

[0023] US Patent US2013 / 341569 describes a method for pre-treating biomass, which includes a steam cracking step to produce synthesis gas. The method also includes a catalytic converter using a control system that adjusts the gas conversion rate according to the composition of the catalyst material. In this patent, a digital model is used for the steam cracking step to obtain optimal parameters according to the nature and content of the pollutants. The document discloses a control method involving a catalytic converter, but does not mention steam cracking control.

[0024] Finally, SAGEHASMI et al. disclose a method for producing fuels and chemical products by pyrolyzing biomass components and Sugi (Japanese cedar) with superheated steam in "Superheated steam pyrolysis of biomass elemental components and Sugi (Japanese cedar) for fuels and chemicals". This document discloses a method for superheated steam pyrolysis using a numerical model, and its application is limited to samples of some individual components of biomass (xylan, cellulose, lignin, etc.), or to a single type of biomass, namely Japanese cedar (Table 1 on page 1273; lines 1-5 in the right column of page 1273).

[0025] Disadvantages of existing technology

[0026] In the case of solutions known in the prior art, the best solution for ensuring the best results of steam cracking is to supply biomass of the same quality in a regular and controlled manner. In the case of wood, the problem is to provide uniform batches of wood of the same species of the same plot, with the selection of tree size and trunk diameter, in particular in order to have regular debarking. In the case of variable resources, attempts should be made to group these in uniform batches and supply these batches to the steam cracker, and readjust the steam cracking operating parameters each time the batch and quality change. This requires traceability and specification compliance, high confidence, and the ability to identify batch or quality changes at the plant level to change operating behavior of the biomass supplier. However, this cannot avoid that some batches are mixed with biomass of other species, different ages, or different qualities.

[0027] Prior art solutions are not entirely satisfactory as they either utilize pyrolysis methods, providing only parameter control for the catalytic converter, or require a supply of homogenous biomass which can prove to be restrictive.

[0028] In fact, the pyrolysis process does not allow obtaining compounds with satisfactory characteristics for the production of black granules.

[0029] In the prior art, digital models are only applied to:

[0030] - Impossibility to obtain a pyrolysis system for compounds with the properties required to obtain black pellets

[0031] - Systems for which steam cracking parameterization is not involved in the numerical model.

[0032] As the depth factor increases, the particle size and energy efficiency decrease.

[0033] Vice versa, if the depth factor is insufficient, the calorific value of the steam cracked material is reduced and the product is more fibrous than powdery, which makes it difficult to form it into pellets.

[0034] When the supply of biomass exhibits inhomogeneity, prior art solutions require sorting the supply at different stages - at the logging or collection site, during charging, at the wood or biomass storage, during the preparation phase (peeling, degranulating, grinding). It is therefore necessary to regroup and regenerate homogeneous batches using overflows, which leads to requirements in terms of handling, storage, traceability, and it is impossible to avoid different products passing said screening.

[0035] The solution provided by the present invention

[0036] In order to overcome the disadvantages of the prior art regarding the lower availability of homogeneous and natural biomass and the inadequacies of known devices for processing heterogeneous biomass, the present invention in its most general sense relates to a process for the continuous or discontinuous production of biofuels by steam cracking of lignocellulosic plant biomass, characterized in that:

[0037] - Numerical model recording the optimal steam cracking parameters according to the typology of the plant components of the biomass

[0038] - Supplying heterogeneous biomass to the steam cracking reactor

[0039] - Typology of plant components of biomass measured at least once during processing

[0040] - Controlling the regulation of steam cracking parameters according to the typology of the plant components of the biomass and the numerical model.

[0041] In the sense of the present invention, "typology of the plant components of biomass" refers to the combination of the different components of biomass (lignin, cellulose, etc.) and their relative proportions, which define the properties of this biomass. Each type of biomass has a specific typology due to its components and is defined by indicators. The indicators are, for example, the level of heterogeneity of the biomass or its properties.

[0042] Thus, in the context of the present invention, the biomass being treated may consist of a mixture of different types of biomass having different specifications; hence the term "heterogeneous biomass".

[0043] According to an advantageous embodiment, the lignocellulosic biomass has a moisture content of less than 27% and is directly subjected to a steam cracking treatment without any other prior thermal or chemical treatment.

[0044] According to the change mode:

[0045] The adjusted parameters include at least one of the following parameters: depth factor, steam cracking pressure, steam cracking temperature, steam cracking duration, stop of steam cracking, steam / solid ratio (washing, stripping), filling rate of the steam cracking tank, forward speed in the steam cracking tank, compression ratio at the inlet, compression ratio at the effluent outlet of the reactor and pore diameter, supply flow rate, humidity, particle size.

[0046] - The measuring step comprises obtaining a sample of the biomass entering the steam cracking drum, and performing a physicochemical analysis on the sample to characterize the sampled biomass.

[0047] - The measuring step comprises taking a sample of the waste gas or waste liquid in or at the outlet of the steam cracking drum and performing a physicochemical analysis on the sample to characterize the steam cracked biomass.

[0048] - The measuring step comprises taking a sample of a sample of the steam cracking product in or at the outlet of the steam cracking drum and performing a physicochemical analysis on the sample in order to characterize the steam cracked biomass.

[0049] - The measuring step comprises taking a sample of a pellet sample and performing a physicochemical analysis on the sample in order to characterize the pellets produced using the steam cracked biomass.

[0050] - Periodically recording and time-stamping at least some of the measurement results and the results of measurements performed on pellet samples obtained during the same cycle.

[0051] - Introduce the results into the blockchain.

[0052] - said introduction is carried out in a supervised learning system in order to generate said digital model.

[0053] - The model was determined by a series of chemical simulations.

[0054] The invention also relates to a device for implementing such a method.

[0055] DETAILED DESCRIPTION OF NON-LIMITING EMBODIMENTS OF THE INVENTION

[0056] The invention will be more clearly understood by reading the following detailed description, which refers to the accompanying drawings and relates to non-limiting embodiments of the invention, in which:

[0057] -[ Figure 1 ] Figure 1 is a schematic diagram of a steam cracking plant.

[0058] Steam cracking of heterogeneous biomass

[0059] The continuous or batch steam cracking process according to the invention provides a means for monitoring and controlling the steam cracking conditions, making it possible to adjust the depth of the treatment (reaction time and temperature) to the raw material introduced and to its heterogeneity over time (on the scale of years, seasons), storage time and during the process, and of course to the qualitative changes of the biomass introduced. This is based on the fact that the material is chemically modified by a thermal reaction at about 200° C., preferably between 205° C. and 210° C., which corresponds to the activation energy required to allow the depolymerization and volatilization of low-energy oxygenated compounds (especially the most thermolabile hemicellulose components), while the residence time is also adjustable, preferably between 6 and 8 minutes, and this constitutes a balance between minimal reactor occupancy (economic advantage) and a preserved material yield (technical advantage), while increasing the calorific value of the final compound and maintaining the integrity of other macromolecules such as cellulose and lignin, the latter being essential to ensure the cohesiveness of the final pellet and therefore its resistance to water and mechanical treatments.

[0060] Although this increased adaptability of the process (temperature range can also be between 180°C and 220°C for a duration of 5 to 30 minutes) is intended to produce pellets with a high calorific value, this may particularly result in steam cracked powders having levels of heterogeneity that are detrimental to downstream pelletizing processes. It is therefore necessary to have available means for managing such differences.

[0061] In addition to the known effects of steam cracking that pulverizes fibers into powder and homogenizes biomass, the effect of steam treatment is measured by the density and size classification of the product. Typically, the majority (>80%) of the product obtained consists of particles smaller than 500 μm, and a few percentages of particles remain larger than 1 mm, or are several mm. However, for similar conditions (mainly temperature and residence time), the change in product results in the presence of a fraction that is much less blasted, usually showing that long fibers or flat particles from the grinding before steam cracking are retained. Its density is also greater than that of the main product.

[0062] Regarding the inhomogeneity of the size fractionation after steam cracking and before granulation, the separation system between powder and steam (static cyclone separator or dynamic separator, such as Valmet's ) a "solids" outlet, a screen (rotating or vibrating) or a density meter makes it easy to separate the pliable fines from the large particles that are not sufficiently steam cracked. The overflow is collected and then conveyed to a storage device before being reintroduced into the steam cracker together with the pulverized biomass.

[0063] Therefore, after steam cracking, one scenario is to use a particle size or density meter sieve for the method of transferring the fines, which selects the fractions that are much less exploded, and then separates and returns the fractions to the supply source of the steam cracker, with the purpose of either immediate reprocessing if their level of disintegration is high enough (particles without sufficient structure but size has been reduced), or delayed processing under steam cracking conditions more suitable for their resistance, which means adjusting the steam cracking conditions (depth) to the capacity of the biomass matrix or the overflow of the sieve.

[0064] Description of Embodiments of the Device

[0065] Figure 1 is a schematic diagram of an apparatus for discontinuous steam cracking of biomass, but the general principles apply to continuous processes. The apparatus for steam explosion comprises an evaporator (100) for generating steam and a reactor (200) which is subjected to rapid decompression.

[0066] It comprises a steam cracking reactor (200) and a flame arrester (300). The reactor (200) is filled with biomass via valve (13). After valve (13) is closed, steam is introduced into the reactor via a feed valve (6). The reactor (200) is then brought to a target temperature, after which the time period is started at the desired temperature. Typically, it takes about 20 seconds to reach the desired temperature. At the end of the desired time period, valve (9) is opened to allow explosive decompression. The steam exploded material passes through the connecting pipe and fills the collection container (300).

[0067] The high pressure pump (1) supplies the steam generator (100). The heating belt (2) ensures thermal stability of the various items of the equipment.

[0068] The device also includes a pressure gauge and a sensor (3) for measuring the pressure and temperature in the steam generator (100), and a pressure gauge and a sensor (4) for measuring the pressure and temperature in the reactor (200). An isolation valve (5) controls the entry of steam into the generator (200). A safety valve (7) limits the pressure in the steam generator (100). The reactor (200) also includes a safety valve. The flame arrester (300) is equipped with a pressure gauge (12). The supply of the reactor (200) is achieved through a supply chamber (14), which draws a controlled volume of biomass stored in a reservoir (15).

[0069] The device comprises one or more sampling devices (50 to 54) for solid, liquid or gaseous samples for analyzing the properties of the biomass provided. According to the results of the analysis and the parameters provided by the pressure and temperature sensors, these data are processed by a programmable machine (16) that controls the parameters of the device. The data are further stored in a memory (17), which also contains a record of a processing model that determines the parameters to be applied according to the results of the analysis.

[0070] The memory (17) is associated with a computer that applies a supervised learning process to the historical data stored in the memory (17) and also controls the introduction of data into the blockchain.

[0071] Biomass types and indicators

[0072] Types of biomass include:

[0073] - Wood of different species, either singly or mixed

[0074] - Different types of agricultural residues, either alone or mixed

[0075] - Different types of by-products of agriculture and agro-industry, either singly or in combination

[0076] - Presence of bark

[0077] - Presence of wood of type A, B or C, either singly or in combination

[0078] - A mixture of lignocellulosic materials having variable median particle sizes.

[0079] Indicators include (alone or in combination):

[0080] - The level of heterogeneity of a biomass mixture by determining the variation in a physical or chemical characteristic measured over a series of samples, such as colour, density, median size of elements, optical identification of characteristics of different types of biomass recorded, etc.

[0081] - the nature of the biomass, in particular information such as the species of wood, maturity, nature of the tissue (bark, core, branches, knots, stumps, etc.), either through automatic identification or by operator acquisition.

[0082] Automatic identification can be achieved by imaging, with the help of an "electronic nose", or by any physicochemical measurement, which makes it possible to distinguish the type of biomass.

[0083] Depth Factor and Device Control

[0084] The control measures for processing heterogeneous biomass allow for optimal steam cracking conditions in the reactor (200).

[0085] Therefore, the selection of control measures for parameters and operating points depends not only on the method of destruction of the lignocellulosic material but also on the typology of the heterogeneous biomass being steam cracked.

[0086] For this purpose, a digital model of control measures adapted to the biomass type and to each combination of biomass types was developed in order to have available a digital reference which allows the automatic adjustment of parameters according to the properties of the biomass entering the reactor (200).

[0087] The construction of the model can be carried out experimentally, carrying out the successive treatment of various heterogeneous biomasses with different control measures in order to retain the optimized control measures corresponding to the steam cracking of the identified biomass according to the quality of the pellets produced.

[0088] The model can also be derived from recorded historical data by a supervised learning solution.

[0089] Finally, it can be derived by simulating the chemical reactions associated with the main types of biomass available.

[0090] The model determines the control measures to be selected for each type of biomass.

[0091] In the new process, physicochemical analysis provides the properties and composition of the steam cracked biomass, and the computer automatically determines the control measures of the equipment based on the analysis results and the recorded digital model.

Claims

1. A method for producing solid biofuels from heterogeneous lignocellulosic biomass by continuous or discontinuous steam cracking, characterized in that: - A numerical model recording the optimal steam cracking parameters according to the typology of the plant components of the biomass; - supplying heterogeneous biomass to a steam cracking reactor; - measuring the typology of the plant components of said biomass at least once during the treatment, wherein the measuring step comprises obtaining a sample of the waste gas or waste liquid in or at the outlet of the steam cracking reactor, and performing a physicochemical analysis on the sample for characterization; - Controlling the regulation of steam cracking parameters according to the typology of the plant components of the biomass and the numerical model.

2. The method according to claim 1, characterized in that The adjusted parameters include at least one of the following parameters: depth factor, steam cracking pressure, steam cracking temperature, steam cracking duration, filling rate of the steam cracking reactor, forward speed in the steam cracking reactor, compressibility at the inlet, compressibility at the outlet of the effluent of the steam cracking reactor, and pore diameter, supply flow rate, humidity, particle size.

3. The method according to claim 1 or 2, characterized in that: The initial biomass had a moisture content of less than 27% when subjected to the steam cracking process.

4. The method according to claim 3, characterized in that At least some of the measurements and the results of measurements on pellet samples obtained in the same cycle are recorded periodically and time-stamped.

5. The method according to claim 4, characterized in that The results are introduced into the blockchain.

6. The method according to claim 5, characterized in that The introduction is performed in a supervised learning system to generate the digital model.

7. The method according to claim 1, characterized in that The model was determined through a series of chemical simulations.

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