Steam cracking process including a separation step and separate processing of the particles obtained according to a threshold value

Abstract

The present invention relates to the field of solid biofuels obtained by steam cracking. More particularly, the present invention relates to a method for the treatment of lignocellulosic biomass by steam cracking, in which the powder obtained is treated to separate the particles into two categories according to a threshold value, each category being treated differently.

Description

Detailed Description of the Invention

[0001] The present invention relates to the field of solid biofuels obtained by steam cracking. More particularly, the present invention relates to a method for the processing of lignocellulosic biomass by steam cracking, the powder obtained being processed to separate the particles into two categories according to a threshold value, each category being processed separately.

[0002] [Technical field] The production of energy (electricity and heat) of renewable origin can be achieved from the environment (sun, wind, tide, swell, geothermal, hydro) or biomass. With the exception of biomass, river hydro, barrage hydro, and geothermal, these renewable energies are intermittent unless energy storage means are developed. Only biomass is a primary energy and can be transported to the site of conversion to heat and / or electricity. However, biomass is in fact a less dense, variable, and perishable energy. The transformation of lignocellulosic biomass (wood, agricultural waste, co-products of agriculture and agro-industry) into energy-dense, transportable, and easily storable compounds makes it possible to develop and intensify the stationary energy industry sector (biofuels used at fixed points in homes, as opposed to biofuel oil) and reduce the environmental impact (CO2 fossil emissions due to biomass without fertilizers or phytosanitary agents).

[0003] Thermal treatment of biomass by steam cracking allows for energy densification by homogenizing the biomass into a steam cracked powder according to precise parameter conditions, particularly size class, temperature, and residence time. The powder is then pelletized to facilitate its transport, storage, and use.

[0004] It is therefore a question of ensuring that the steam cracking process can guarantee a constant product, i.e. an output powder that is stable in terms of quality and can be converted or used downstream of the process for the desired application, that has a suitable calorific value and composition for use in combustion and that can be pelletized.

[0005] Today, the best solution to guarantee the best results of steam cracking is a regular and controlled supply of biomass of the same quality. However, there also seems to be an interest in being able to process heterogeneous biomass with a view to increasing the throughput of biomass for the purpose of producing solid biofuels.

[0006] The parameters of the steam cracking 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):

[0007]

number

[0008] 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 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) The problem encountered when processing heterogeneous biomass is that the resulting powder is itself heterogeneous, which causes pelleting problems. Indeed, depending on the nature of the initial biomass and the conditions applied, steam cracking does not have the same effect on the breakdown of the material. Therefore, when the input material is heterogeneous, the severity conditions must be adjusted to avoid total destruction of the least resistant material, which would have a negative effect on pelleting. If the severity conditions are adjusted based on the less resistant biomass, steam cracking will produce residual particles originating from the more resistant biomass, which will also interfere with the pelleting process.

[0009] Failure with respect to final quality and pelleting specifications can be catastrophic, either from processing that leaves large particles or from processing that is too aggressive and degrades the product and its behavior when pelletized.

[0010] There is therefore a need to have access to a steam cracking process suitable for the treatment of heterogeneous biomass for the production of black pellets of controlled quality.

[0011] Steam cracking differs from hydrothermal pretreatment in that hydrothermal pretreatment, also called aqueous fractionation, solvolysis, hydrothermal cracking, or hydrothermal treatment, consists of using 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 because the resulting products are mostly liquid.

[0012] 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 similar to the pyrolysis technique in that it uses steam explosion and is carried out in the presence of oxygen.

[0013] It is also necessary to distinguish the torrefaction process, which is characterized by a thermochemical treatment between 100 and 300 ° C, thereby making it possible to modify part of the organic material to break down the fibers, while removing the water.

[0014] [Prior Art] Chinese patent CN102 949 969A discloses a system for pyrolyzing solid carbonaceous materials or materials with increased viscosity using a duvet mixer and a catalytic heat transfer fluid heater, and a method for using the reactor system, which further includes a solid / solid or solid / liquid separator, allowing separation of solid or liquid pyrolysis products from the catalytic heat transfer fluid used.

[0015] US 2012 / 260563 A1 describes a process for the thermochemical conversion of biomass by hydropyrolysis (conventional pyrolysis liquid reaction with hydrogen in the presence of a solid catalyst) to obtain liquid products. The method includes, inter alia, an inertial separator.

[0016] US 2014 / 298716 A1 relates to a method for drying and torrefaction of lignocellulosic biomass. The drying and torrefaction installation comprises two circuits. The second circuit comprises a cyclone separator that allows to remove all large volatile particles.

[0017] Finally, US 2016 / 251611 A1 discloses a method for growing microorganisms comprising culturing the microorganisms in the presence of a hydrolyzed composition obtained from a lignocellulosic feedstock that has been subjected to a process of steam explosion. The treated lignocellulosic biomass further comprises a step of separating fibers according to a threshold value, such as fiber size.

[0018] [Disadvantages of the Prior Art] The prior art solutions are not entirely satisfactory, since they either use techniques or use non-powdered products. In fact, these are the following techniques: Pyrolysis, which leads to obtaining compounds different from those obtained by steam cracking.

[0019] Roasting is a technology that has acceptable yields (10%-20% losses), but the costs are still very high and the technology is not mature.

[0020] DISCLOSURE OF THEINVENTION To meet this need, the inventors have developed a process for steam cracking having a predetermined severity factor, characterized in that it comprises a step of processing a powdered product to separate particles above a threshold from particles below said threshold, and a step of processing a first category of particles and a second category of particles separately.

[0021] Said method makes it possible, on the one hand, to pelletize a homogeneous powder from which resistant particles have been removed, and, on the other hand, to treat the overflow of less degraded material by returning it to the steam cracker or by another subsequent treatment.

[0022] The invention also relates to a steam cracking facility for carrying out this process, including a particle separator.

[0023] Advantages of the Invention The present invention therefore provides a screen for separating resistant particles that are less susceptible to degradation from a pelletizable powder, or a screen for separating powders with a very fine particle size from a pelletizable powder.

[0024] The main advantage of this method is that it allows the production of black pellets of constant quality from any type of biomass, especially from heterogeneous biomass. In fact, the removal of less degraded particles from the powder to be pelleted improves the quality of the pellets, which are therefore more cohesive, more hydrophobic and of higher energy.

[0025] This method allows the overall pelleting process specifications to be met in terms of quality and quality consistency, as well as the specifications of the final product.

[0026] This method makes it possible to recover less degraded particles and reuse them, although the problem of subjecting them to a second steam cracking process or using them for other purposes can arise.

[0027] It is also possible to screen out the finest powders that do not pellet well, and keep only those that can clog, for the purpose of producing pellets. For example, it is possible to envisage using the finest powders in a biotransformation process.

[0028] It should be noted that if an increase in the severity of the treatment were to be attempted to overcome the problem of particles remaining coarse, this would result in degradation of the more unstable wood particles and also in increased material losses due to excessive degradation of the polymeric forms of the molecules into volatile compounds (e.g. hemicellulose, which is most sensitive to temperature and residence time). It is therefore more advantageous to recycle the powder overflow after steam cracking screening to the head of the process than to increase the severity or, indeed, to expose them to more moderate severity conditions, either alone or in a grouped manner.

[0029] Detailed Description of the Invention The present invention relates firstly to a method for steam cracking of lignocellulosic biomass, characterized in that it comprises a step of processing the powdered product to separate particles above a threshold value from particles below said threshold value, and a step of processing the first category of particles and the second category of particles separately.

[0030] The method of the present invention comprises the steps of: steam cracking lignocellulosic biomass; screening the powdered product obtained by steam cracking to separate particles above a threshold value (referred to as the "first category") from particles below said threshold value (referred to as the "second category"); Treating the first category of particles and the second category of particles separately.

[0031] The severity factor applied to the steam cracking process is determined according to the biomass being treated. It is determined from the Log10 value of the ordinate of the reaction.

[0032] Severity = log10 (R0) This is an inherent feature of the steam cracking process and those skilled in the art know how to measure and adapt. Typically, the severity factor is between 4.0 and 4.02, more precisely between 4.05 and 4.15.

[0033] The method performs a screening aimed at separating steam cracking particles into two categories for separate processing. The threshold value can be, for example, the mass, size, cross-sectional area or density of the particles, but also their aerodynamic behavior or any other criterion that allows separating particles, such as being too fine, too large, too dense, etc., compared to the threshold value.

[0034] In a preferred embodiment, one of the two particle categories is pelletized for the preparation of black pellets.

[0035] In certain embodiments, the particles to be pelleted represent a category of particles above a threshold, and the issue is to remove the largest and / or most dense and / or most resistant particles.

[0036] In another embodiment, the particles to be pelletized correspond to a category of particles above a threshold value. Removal of very fine particles that cannot be pelletized becomes an issue.

[0037] Among other expected qualities such as water resistance, mechanical strength, and high calorific value, black pellets can be characterized in a general way by a predominant composition (>80%) of particles smaller than 500 μm in size, and a few percent of particles larger than 1 millimeter, i.e., in practice, a few millimeters.

[0038] The resistance of the pellets to water can be evaluated by soaking, i.e. the product should not absorb much water during soaking and the quality of the product, such as mechanical strength, should not change after soaking. The mechanical strength of the pellets is related to impact resistance and mechanical durability.

[0039] The heating value of the pellets must be increased relative to the heating value of the initial biomass.

[0040] The severity factor of the steam cracking process is fixed depending on the nature of the biomass and the type of powder it is desired to collect.

[0041] The removed particles may be subjected to a process different from pelletization, recovered and recycled, for example, by reintroduction into the steam cracker immediately or later after separation, or reused in other processes.

[0042] There are as many different possibilities for dealing with the removed particles as there are specific embodiments of the invention.

[0043] In certain embodiments, particles above a threshold (e.g., resistant, too large, and / or too dense) are directly reintroduced into the steam cracker to be processed again in a continuous process.

[0044] In other specific embodiments, particles above or below the threshold are collected for recycling in a later process. They can then be reintroduced into the steam cracker under different severity conditions or reused in other processes. Particles too fine to be pelletized can be used as substrates for biotransformation reactions, such as biotechnological processes and green chemistry. Very large particles can be reused by means of local combustion in boilers or incorporated into biological materials.

[0045] This process therefore makes it possible to process heterogeneous biomass and to recycle all of this biomass.

[0046] The heterogeneous biomass may consist of a mixture of young and old wood, a mixture of wood from different species, waste wood, and the like.

[0047] The invention secondly relates to a steam cracking installation comprising at least one steam cracking section, a separator for separating particles into two categories according to a threshold value, and means for conveying the separated particles.

[0048] The steam cracking equipment is conventional in terms of its elements up to the powder recovery device installed at the outlet of the steam cracker. The particle separator can be of any type and depends on the criteria selected for screening. Thus, the screening means can be a rotary screening, a size selection separation such as a perforated or tilting vibrating table, a dynamic density measurement separation such as a ballistic screen, or a centrifugal effect.

[0049] Means for separate transport of the particles allow the overflow powder to be transported to a site for immediate processing or to a storage site for later processing. Such transport means may be conveyors, chutes, screws, chain conveyors, pneumatic devices, etc.

[0050] The facility may further include downstream items of facility associated with handling said overflow.

Claims

1. 1. A method for steam cracking of lignocellulosic biomass, comprising: I) a first step of steam cracking lignocellulosic biomass with a severity factor of 4.05 to 4.15, the first step of steam cracking comprising steam explosion in the presence of oxygen to obtain a powder; II) a second step of screening the powdered product obtained at the end of the steam cracking step to separate the first category of particles above a threshold value and the second category of particles below said threshold value, the second category of particles being pelletized while the first category of particles are removed; and III) A third step of recovering and recycling the removed particles of the first category, wherein the removed particles of the first category are reintroduced into the steam cracker of the first step immediately or later after separation.

2. The method of claim 1 , wherein the threshold value is selected from a mass, a size, a cross-sectional area, and a density of a particle.

3. 3. The method of claim 1 or 2, wherein the particle size of the biomass is non-uniform.

Images