CONTROL OF STEAM CRACKING TO IMPROVE THE PCI OF BLACK PELLETS

Abstract

The present invention relates to a method for the continuous preparation of a powdered material having a higher calorific value than the calorific value of the initial biomass, comprising a steam cracking stage, characterized in that the initial biomass consists of elements having a particle size distribution between P25 and P100, having a moisture content of less than 27%, directly subjected to a steam cracking treatment

Description

CONTROL OF STEAM CRACKING TO IMPROVE THE PCI OF BLACK PELLETS The present invention relates to the field of valorization of lignocellulosic biomass, in particular for the production of fuels of the black pellet type with a high calorific value. Technical area The transformation of lignocellulosic biomass (wood, agricultural waste, co-products of agriculture and agro-industry) into an energy-dense, transportable and easily storable compound would allow the development and consolidation of a stationary industrial energy sector (biofuel used at a fixed point, the home, compared to fossil biofuels) and reduce the environmental impact (CO2 emissions from fossil fuels with a biomass free of fertilizers and phytosanitary products). Black pellets are moisture-resistant cylinders, 1 to 3 cm long, with good mechanical strength, allowing for storage and handling similar to coal. Their combustion produces little ash, with a lower heating value (LHV) of approximately 18 to 20 joules per gram of dry matter. Black pellets are produced from lignocellulosic biomass that undergoes heat treatment, followed by sudden depressurization, to obtain an impermeable material for pellet or briquette production. In reality, the raw material is steam-treated, which releases finer particles, allowing the material to have strong cohesion during the aggregation or molding phase. Steam cracking differs from hydrothermal pretreatment, also known as aqueous fractionation, solvolysis, hydrothermolysis, or hydrothermal treatment, in that the latter uses high-temperature, high-pressure water to promote the disintegration and separation of the lignocellulosic matrix. This technique is not suitable for the production of black pellets, as the resulting products are mostly liquid. Hydrothermal pretreatment, also known as aqueous fractionation, solvolysis, hydrothermolysis, or hydrothermal treatment, is a hot water liquid pretreatment process that uses high temperature and pressure water to promote the disintegration and separation of the lignocellulosic matrix. Q7RI I 0 / 7707 3 / YILI Steam cracking cannot be equated with any of the hydrothermal pretreatment methods, since it employs steam penetration followed by explosive decompression. The invention described in the referenced patent application uses the steam cracking system to carry out this process without reference to a hydrothermal pretreatment system. State of the art In the state of the art, European patent EP2373767B1 describes a process for the batch production of black pellets from a lignin-containing material. This process comprises the following stages: (a) passing the lignin-containing material with a relative moisture content of 0 to 20% by weight through a reactor; (b) heating the lignin-containing material to 180-235°C by injecting steam into the reactor; (c) holding the material in the reactor at the temperature reached for 1 to 12 minutes to soften the material and release the lignin; (d) reducing the pressure in the reactor in at least one stage; and (e) forming the processed material into pellets or briquettes. The lignin-containing material is a lignocellulosic material, comprising wood, bamboo, bagasse, straw, or grass, in the form of 25 mm long chips. The final reduction of the reactor pressure is achieved suddenly by means of a steam explosion to defibrate the material. Alternatively, U.S. patent LJS2016 / 251611A1 describes a process for cultivating a microbial organism comprising a steam cracking heat treatment step of an initial lignocellulosic biomass. The steam cracking heat treatment comprises the following steps: (a) The initial biomass is subjected to hydrothermal pretreatment by subjecting the cellulosic material to at least one soaking operation, pzRLLn / zznza / γALA (b) The cellulosic material is then conveyed through at least one pressure reactor. The cellulosic material is then heated to a temperature between 170 and 230 °C. Also known in the prior art are US patents US2016 / 153010A1 and US2012 / O 06320A1, which describe processes for converting lignocellulosic biomass into ethanol and other products based on a constant hydrothermal pretreatment followed by enzymatic hydrolysis, fermentation, and ethanol recovery. The processes describe a steam cracking stage comprising: (a) contacting the acid-impregnated lignocellulosic biomass feedstock with H2O at a temperature between 140 and 230 °C and a pressure between 75 psig and approximately 250 psig for a period of 1 to approximately 15 minutes in a contact zone to produce a steam-treated feedstock; (b) subjecting the steam-treated raw material to a depressurization zone to produce a volatilized fraction of the steam-treated raw material for a period of approximately 2 to 30 minutes; (c) finally release at least a portion of the volatilized fraction from the depressurization zone to allow control of temperature and pressure in the depressurization zone. Disadvantages of the previous technique The solutions of the previous technique for producing black pellets are promising. However, they have limitations, particularly the amount of energy supplied per volume of pellet, which, although higher than biomass in the form of wood chips or white pellets, is still between 30 and 40% lower than coal for the same volume or weight. Furthermore, the solutions of the previous technique propose batch processes with sequential treatment of biomass volumes, which limits the immediate effects of controlling steam cracking conditions. Finally, the prior art solutions offer various applications for the processes described, such as microbial cultivation or biomass-to-ethanol conversion processes. They have no application for the production of black pellet fuels. Solution provided by the invention To remedy these disadvantages, the present invention relates, in its most general sense, to a process for the continuous preparation of a powdered material having a higher calorific value than the initial biomass, comprising a steam cracking stage, characterized in that the initial biomass consists of elements of particle size class between P16 and P100, having a moisture content of less than 27%, and is directly subjected to a steam cracking treatment. In a particular embodiment, the initial biomass consists of elements of particle size class between P25 and P100. Thus, the invention relates to a process for the continuous preparation of a powdered material having a higher calorific value than the calorific value of the initial biomass, comprising a steam cracking stage, characterized in that the initial biomass is made up of elements of granulometry class between P16 and P100, having a moisture content of less than 27%, and which is directly subjected to a steam cracking treatment. In one embodiment, the gravity factor of the steam cracking stage is greater than 3.7 and less than 4.2. In another embodiment, the gravity factor of the steam cracking stage is controlled based on the carbon content in a sample of steam-cracked biomass. In another embodiment, the gravity factor of the steam cracking stage is controlled based on the carbon content in the outlet gas. Preferably, the gravity factor of the steam cracking stage is controlled based on the carbon content of a sample of steam-cracked biomass. In one particular implementation mode, the severity of the steam cracking stage is controlled by the signal generated by a pH sensor. In one embodiment, the pH is adjusted by adding lime, carbon dioxide, or dissociated forms of carbon dioxide. Q7RI I 0 / 7707 3 / YILI The invention also relates to the application of the process for preparing a powdered material according to the invention for the preparation of granulated fuels. Detailed description of a non-limiting example of the invention The present invention will be better understood by reading the following detailed description of a non-limiting example of the invention, where the single figure represents a schematic view of a continuous production plant according to the invention. Description of an example installation Figure 1 is an example of a steam cracking plant 10, in particular for the manufacture of a fuel material according to the invention from chopped biomass to have a particle size between P16 and P100. In a preferred embodiment, the biomass will have a particle size between P20 and P100, or even between P25 and P100. Figure 2 is a table showing the characteristics of the different particle size classes according to the nature of the elements that make up the material. The steam cracking plant is fed with biomass composed of elements with a particle size class between P16 and P100, with a moisture content of less than 27%. Particle size distribution is defined by the size of the particles in the main fraction (P) and the size of the particles that define the coarse fraction (G). Particles smaller than one millimeter are considered to belong to the fine fraction. The main fraction P must represent at least 80% of the fuel by mass. Based on the size and percentage of the components in the main fraction (P), the coarse fraction (G), and the fine fraction, the particle size distribution of the biomass components is defined according to reference classes. The European Committee for Standardization (CEN / TS 14961) predefines these classes in the Technical Specification (CEN / TS), which serves as a normative document in areas where the current state of the art is not yet sufficiently stable for a European standard. The CEN / TS also specifies that 80% (by mass) of the fuel must pass through a sieve corresponding to the particle size class and be retained on the sieve corresponding to a particle size of 3.15 mm. The coarse fraction (G) must not exceed 1% by mass. The fine fraction must not exceed 5% by mass. Q7RI I 0 / 7707 3 / YILI - P16 corresponds to a granulometry of 3.15 mm < P < 16 mm, and G > 45 mm - P25 corresponds to a granulometry with 3.15 mm < P < 25 mm, and G > 63 mm - P100 corresponds to a granulometry with 3.15 mm < P < 100 mm, and G > 200 mm The granulometry of a platelet sample can be determined using an oscillating sieve system, a rotating sieve, or an imaging measurement system. The biomass is crushed with sharp tools (crushing blades) and is directly subjected to a steam cracking process without wetting it or subjecting it to any other treatment. The Severity Factor of the treatment is defined by the formula: FS=LoglO(time(min)*exp( (T°C-100) / 14.75)) The higher the temperature and the longer the treatment time, the greater the severity and the more transformation is observed in the product. The lower heating value in dry wood increased on average by 0.7 joules per gram, with a variation of 0.25 to 2 joules per gram depending on the severity of the heat treatment, from 17 to 19 joules per gram of dry wood initially, that is, between 2 and 12% gain in LHV, around 4% on average. Depending on the severity of the heat treatment, material losses ranged from a few percent to 24%. The higher the gravity, the greater the loss and the greater the gain in Lower Heating Value. During steam cracking, hemicelluloses are primarily attacked. The main soluble volatiles generated are furfural, acetic acid, and formic acid. These soluble volatiles are found in the escaping steam (which evaporates). Depending on the type of gasoline tested, the nature of the condensates varied. Thus, for oak, furfural is more significant (up to 60% of the VOCs), while for pine, acetic acid is the most prevalent (up to 50% of the VOCs). Q7RI I 0 / 7707 3 / YILI Installation description The installation (10) comprises a hammer mill (11) that is fed with biomass via a screw conveyor (12). A separator removes oversized material before the chips enter the mill (11). In the wet mill (11), the biomass is ground to a particle size of between P25 and P100. The silo (13) is filled by a front-end loader that collects the biomass from the piles formed in the ground storage areas. The biomass is discharged from the shredder (11) onto a conveyor belt (14), equipped with a weighing belt, which transports it to the feed hopper of a hot air dryer (15). A humidity sensor continuously monitors the moisture content of the biomass. The biomass fragments are extracted from the silo (16) by a planetary screw conveyor and deposited onto a conveyor belt that transfers them to a feed silo (17) of a reactor capable of continuously processing 15 tons per hour of biomass. The reactor (18) is a pressure reactor into which superheated steam at a pressure of 18 bar and a temperature of 250 °C is injected from its bottom. This vertically oriented reactor has a conical shape to prevent the formation of plugs. The steam flow is extracted from the reactor at the top. At the reactor outlet, the steam is returned to the CH boiler where it was produced. Note that in the reactor (18) the steam temperature is 203 °C and the pressure is 16.7 bar. The silo (17) is shaped like a truncated ellipsoid to facilitate the flow of biomass fragments. Furthermore, a rotating scraper in the silo (17) pushes the biomass fragments toward an extraction screw (19). This conical screw (19), whose cross-section narrows as it enters the reactor (18), continuously draws a predetermined quantity of biomass fragments from the silo (17), pre-compresses them, and pushes them through a screw passage orifice into the reactor (18) under pressure. The dimensions of the conical passage orifice and the screw have been selected to minimize pressure loss in the reactor and expel air contained within the biomass fragments. It should be noted that the compressive force exerted by the screw on the biomass fragments advantageously allows the expulsion of some of the wastewater present in the biomass fragments. qzri in zznz -i / YiAi At the end of the screw (19), the compacted biomass fragments form a compact block that is dispersed in the reactor by the steam flow. The dispersed biomass fragments then fall by gravity into the reactor, where they are heated by the steam flow and deposited on top of the fragments that have accumulated at the bottom of the reactor, where they are further heated by the steam flow. It should be noted that in the reactor (18), the retention time of the biomass fragments is controlled according to the level of biomass fragments that have accumulated at the bottom of the reactor. In this particular embodiment of the invention, it is set at 7 minutes, which corresponds to a gravity factor of 3.8. At the bottom of the reactor (18), a scraper mounted to pivot on a vertical axis (not shown in Figure 1) pushes the biomass fragments towards a screw conveyor (20) that allows the biomass fragments to be extracted from the reactor (18). This discharge screw (20) pushes the biomass fragments out of the reactor toward a controlled-opening valve (21). The opening of this valve is continuously adjusted to control the flow of biomass fragments exiting the reactor. Under the pressure of the steam in the reactor and / or the screw (20), the biomass fragments are continuously expelled through the valve openings (21) at very high speed into an expansion line (22) and are carried by the steam flow exiting the reactor, along with these biomass fragments, in the expansion line (22) to a separation unit (23). It should be noted that the pressure in the expansion line gradually decreases to approximately 1.1 bar in the separator. This causes an explosive decompression of the biomass fragments due to the re-vaporization of some of the condensation water present in the fragments. This sudden expansion of water vapor causes shear forces to appear in the biomass fragments, leading to the mechanical rupture of the biomass structure. In the separation unit (23), the mixture of biomass fragments and steam enters tangentially into a rapidly rotating vane. Under the centrifugal force generated by this vane, the biomass fragments are thrown into a discharge chute (24), while the steam is discharged from the separator through a valve. qzri in zznz -i / YiAi In an alternative embodiment of the invention, a pressurized cyclone can be used to separate the biomass fragments from the waste steam. It should be noted that the spent steam contains volatile matter that can be advantageously burned in a boiler. The biomass fragments projected into a discharge tube (24) are discharged into a storage silo (25), to be transformed into pellets of approximately 7 mm in diameter and 22 mm in average length in a pellet press (26). Adjustment of steam cracking conditions The continuous operation of the steam cracker allows for real-time monitoring of operating conditions, including - The gravity factor - The pH of the biomass. To do this, the chemical characteristics of the effluents or the chemical characteristics of the solubilized samples of the steam-cracked biomass can be measured. Real-time analysis of effluents Real-time measurement of the effluent's chemical characteristics allows for the assessment of material losses from the steam-cracked biomass, which translates into an increase in the effluent's carbon content. This information can be acquired in real time using an infrared probe placed in the effluent discharge pipe. The real-time signal provided by the probe is representative of the variations in carbon content in the effluent. This signal is used by a computer to modify the parameters of the steam cracker, particularly the gravity rate, according to a function predetermined by the desired objectives: for example, maximizing the lower heating value (LHV). The probe can also be used to analyze other organic compounds, especially oxygenated ones, and provide mapping information on the organic compounds in the effluents to monitor the parameters of the steam cracker. Q7RI I 0 / 7707 3 / YILI Real-time analysis of a sample of steam-cracked biomass The steam cracking plant may also include a real-time sampling system of the steam-cracked biomass, with solubilization of this sample to collect information on the chemical composition using one or more physicochemical probes, for example, a pH measurement or a measurement of the composition of organic compounds. This information is used by a computer to automatically optimize the parameters of the steam cracking installation in real time. Application of granulation For the production of pelleted fuels with a moisture content of less than 10%, the moisture content of the final product must be controlled before pelleting. For this purpose, the initial biomass, before steam cracking, has a low moisture content, in particular less than 14% and preferably less than 10%. Alternatively, the initial biomass can be steam cracked with a moisture content above 14% but below 27%. In this case, a drying stage of the steam cracked biomass is carried out after the steam cracking plant, either before or after granulation.

Claims

NOVELTY OF THE INVENTION Having described the present invention as above, the following is considered novel and, therefore, is claimed as property: CLAIMS 1 - Process for the continuous preparation of a powdered material having a calorific value higher than the calorific value of the initial biomass, comprising a steam cracking stage, characterized in that the initial biomass is made up of elements with a particle size class between P16 and P100, with a moisture content of less than 27%, directly subjected to a steam cracking treatment. 2 - Process for the continuous preparation of a powdered material according to claim 1, characterized in that the gravity factor of the steam cracking stage is greater than 3.7 and less than 4.

2. 3 - Process for the continuous preparation of a powdered material according to claim 1 or 2, characterized in that the gravity factor of the steam cracking stage is controlled based on the carbon content in the gaseous effluents. 4 - Process for the preparation of a powdered material according to claim 1 or 2, characterized in that the gravity factor of the steam cracking stage is controlled as a function of the carbon content in a sample of steam-cracked biomass. 5 - Process for the continuous preparation of a powdered material according to claim 1 or 2, characterized in that the gravity factor of the steam cracking stage is controlled as a function of the pH of a sample of steam-cracked biomass. 6 - Process for the continuous preparation of a powdered material according to claim 1 or 2, characterized in that the pH is adjusted by the addition of lime, carbon dioxide or dissociated forms of carbon dioxide. 7 - Application of the procedure according to claim 1, comprising a biomass granulation step for the preparation of granulated fuels.