Integration of lignin-rich material into biomass before steam cracking for the production of fuel pellets

Abstract

The present invention relates to the field of lignocellulosic biomass recovery, in particular for the production of "black pellet" type fuels with high calorific value. More specifically, the invention is a pellet production process comprising a step of integrating a lignin-rich material or a lignocellulosic material into the biomass before the steam cracking step.

Description

Title of the invention: Integration of a lignin-rich material into a biomass before steam cracking for the production of fuel pellets

[0001] The present invention relates to the field of the valorization of lignocellulosic biomass, in particular for the production of fuels of the "black pellet" type with high calorific value. More specifically, the invention relates to a method for producing pellets comprising a step of integrating a lignin-rich material or a lignocellulosic material into the biomass before the steam cracking step. Technical field

[0002] The transformation of lignocellulosic biomass (wood, agricultural residues, co-products of agriculture and agro-industry) into an energy-dense, transportable and easily storable compound would make it possible to develop and consolidate an industrial stationary energy sector (biofuel used at a fixed point, the hearth, unlike biofuels) and to reduce environmental impacts (fossil CO2 emissions, with biomass without fertilizers or phytosanitary products).

[0003] Black pellets are moisture-resistant cylinders 1 to 3 cm long with good mechanical strength allowing storage and handling similar to that of coal. They have a lower calorific value (LCV) close to 18 to 20 joules / gram of dry matter.

[0004] Black pellets are produced from lignocellulosic biomass that has undergone steam cracking. This involves a heat treatment followed by a sudden depressurization to provide a waterproof material when formed into pellets or briquettes. The raw material is actually steam-exploded, releasing finer particles, allowing the material to have strong cohesion during the aggregation or molding phase.

[0005] Steam cracking differs from hydrothermal pretreatment, also called aqueous fractionation, solvolysis, hydrothermolysis or hydrothermal treatment, in that the latter involves using water at high temperature and high pressure to promote the disintegration and separation of the lignocellulosic matrix.

[0006] The black pellet solution is very promising. However, it has limitations, notably the amount of energy provided per volume of pellet, which although higher than biomass in the form of chips or white pellets, is still 30 to 40% lower than coal for the same volume or weight.

[0007] To overcome this problem, the prior art teaches that an enrichment in lignocellulosic material, in particular in lignin, allows an increase in the quantity of energy provided. Lignin is a co-product naturally present in the biomass which represents 20% to 30% of its mass, for a unit calorific value more than 50% higher than that of the initial biomass, and which also has good hydrophobicity and cohesion properties.

[0008] Patent FR3095655B1 describes a process for the recovery of biomass comprising the mixing, after steam cracking, of an intermediate powdery product resulting from steam cracking and a powdery material with a high lignin content, prior to the granulation step.

[0009] The main problem with enriching lignin-rich material is that it is naturally rich in mineral elements. Products obtained from mineral-rich lignin have the disadvantage of creating a lot of ash and producing more gaseous emissions. In a context of ecological transition, manufacturers cannot afford to increase the rate of gaseous emissions, as this is strictly regulated by law.

[0010] There is therefore a need to obtain black pellets with improved calorific value without negative ecological impact. Statement of the invention

[0011] The inventors propose a process for obtaining black granules with a high calorific value by enriching them with lignin or lignocellulosic material, while controlling the quantity of ash and toxic gas emissions produced. This process consists of introducing the lignin or lignocellulosic material before the steam cracking stage. The granule thus obtained has a higher calorific value than a conventional black granule, without being less environmentally friendly.

[0012] Lignin from industry is a material rich in non-carbon elements (nitrogen, sulfur, chlorine) and minerals. Its combustion results in the emission of toxic gaseous emissions due to the presence of these elements. This particularity creates constraints during the enrichment of fuels in lignin due to environmental standards which regulate the quantity of toxic gaseous emissions authorized. In order to overcome this constraint, it is proposed here to enrich the biomass in lignin or in lignocellulosic material before proceeding to the steam cracking stage; the undesirable components responsible for the high production of ash and toxic gaseous emissions are thus eliminated during the steam cracking which “washes” the lignin and the final product obtained is rich in lignin but depleted in major undesirable elements (non-carbon elements) and in minerals. Black granules obtained by this process are therefore enriched in energy thanks to the presence of added lignin while complying with environmental expectations.

[0013] Thus, the invention consists of a process for valorizing biomass comprising a steam cracking step to produce a fuel product enriched in lignin without increasing the quantity of undesirable elements, characterized in that said process comprises a step of adding a lignin-rich material to said biomass prior to the steam cracking step.

[0014] The invention also relates to a process for preparing black granules having a unit calorific value at least 6% higher than the initial biomass, comprising a step of adding a lignin-rich material to the biomass followed by a steam cracking step, characterized in that the material to be steam cracked obtained at the end of said addition comprises 4 to 60% of a lignin-rich material, without excessive increase in the quantity of undesirable elements.

[0015] Advantages of the invention

[0016] The process according to the invention makes it possible to obtain granules with improved calorific value. The granules obtained by the process according to the invention have a higher calorific value than conventional granules. It is known from the state of the art that conventional processes for obtaining granules make it possible to generate products having a calorific value (PCI) increased by 4%.

[0017] The black pellets obtained by the present process also have retained or improved qualities of water resistance and mechanical strength. In addition, they meet environmental standards favorably since their combustion does not generate more ash and / or toxic gas emissions than conventional black pellets. This amounts to an improvement in the calorific yield. Indeed, the unit calorific value of the pellets obtained is increased by at least 2% compared to that of a conventional pellet. In other words, the unit power of the pellets obtained is at least 6% higher than that of the initial biomass.

[0018] There is a barrier to entry for coal substitution: a lower calorific value (LCV) of at least 5300 kWh / tonne, for an initial biomass of 5000 kWh / tonne. Steam cracking increases this LV by extracting the energy-poor oxygenated volatile molecules from the solid residue, which arithmetically increases its LV, to reach at least 5200 kWh / tonne. Increasing the lower calorific value (LCV) between 5200 and 5300, or even more, means a loss in efficiency that may become economically intolerable to secure a low LV limit value of 5300 kWh / tonne. It is proposed here to relax this situation by adding lignin having a PCI of 7500 kWh / tonne, at a level of approximately 4% by weight or more, in particular at 5%, 6% and up to 30, 40, 50 or 60% of the product leading to a PCI of at least 5300 kWh / tonne of mixture.

[0019] When enriching with lignin, the main difficulty lies in obtaining good quality lignins for boiler makers, in accordance with regulations. Thus, paper mill lignins can be excluded if they are too rich in sulfur compounds depending on the paper mill process from which they are derived. The only lignins that would be ideally compatible are derived from recent lignocellulosic biomass transformation processes, which use polymeric sugars (cellulose and hemicellulose) and leave the lignin for direct energy recovery in boilers, often to produce the steam or electricity necessary for their own operation. However, auxiliaries in transformation processes, such as biological catalysts (enzymes and microorganisms) can be considered as hindering the production of a good quality final product.

[0020] In addition, certain elements naturally present in lignin, such as major elements (nitrogen (N), sulfur (S), chlorine (CL)...) or even minerals, have a disadvantageous effect on the final product. Indeed, the presence of major elements has the effect of generating a product whose combustion produces a large quantity of toxic smoke. The presence of minerals has the effect of generating a product whose combustion produces a lot of ash. The elimination of these undesirable elements therefore makes it possible to obtain an improved final product that is more ecologically interesting.

[0021] The applicants propose to address this problem using a process that allows the "washing" of lignin to remove undesirable elements, ultimately resulting in a good quality granule. Thus, lignins of various origins could be used for the enrichment step. A higher level of lignin could also be introduced into the biomass.

[0022] The objective is also to reduce production costs, for example by removing from the process potential additional lignin treatment steps intended to remove undesirable elements, namely major elements and minerals.

[0023] Costs can also be reduced through process optimization, for example, a portion of the steam-cracked biomass can also be used to produce a source of lignin, suitable for reuse in the process.

[0024] It is interesting to add a lignocellulosic or lignin-rich material before steam cracking, in particular if the origin of the latter requires volatilization of certain compounds in the gas phase (nitrogen, sulfur or chlorine), or if this lignin is too dried or compressed, and the explosion gives it better dispersion within the main biomass.

[0025] Steam cracking also helps soften compounds such as lignin and break down cellulose, which promotes their integration. These bring cohesion and calorific value to the final product.

[0026] At the end of the steam cracking step, the steam cracked biomass enriched in lignin can be used to obtain a lignin depleted in undesirable elements, such as major elements and minerals. This process has the advantage, in addition to providing improved black granules, of giving access to a lignin depleted in undesirable elements (intermediate product) which can be used in other processes.

[0027] Indeed, the process proposed by the inventors allows the recovery of a “cleaned” lignin in that the lignin obtained according to the process is depleted of undesirable elements. The lignin obtained is suitable for use in processes for obtaining white granules or black granules. It can also be used in biomass treatment processes, bioenergy production processes or biomaterials or bioproducts. Description of the embodiments

[0028] A first subject of the invention relates to a process for the recovery of a biomass comprising a steam cracking step to produce a fuel product enriched in lignin without increasing the quantity of undesirable elements, characterized in that said process comprises a step of adding a lignocellulosic or lignin-rich material to said biomass prior to the steam cracking step.

[0029] For the purposes of the invention, the term "biomass" means lignocellulosic biomass originating from agricultural, forestry and silvicultural residues, wood processing by-products and dedicated crops. This may in particular be wood chips, with or without bark. The quality of this raw material will directly influence the quality and energy characteristics of the solid fuel material. For example, the most commonly used woods are hardwoods and softwoods.

[0030] By "a lignin-rich material" within the meaning of the invention, we mean a material containing at least 30% lignin, or even 50% or 70%.

[0031] By “a lignocellulosic material” within the meaning of the invention, we mean a material containing at least 50% cellulose, or even 60 or 70%.

[0032] For the purposes of the invention, the term "undesirable elements" means minerals and non-carbon elements. By way of non-limiting example, the undesirable elements may be major elements (nitrogen (N), chlorine (Cl), sulfur (S)) and / or minerals or a mixture thereof.

[0033] The inventors have, quite surprisingly, discovered that the introduction of lignin into a biomass followed by a steam cracking step had the effect to clean the lignin of unwanted elements. The lignin obtained is of better quality. This characteristic has the effect of allowing an increase in the calorific value of the pellets produced by reducing, or at least without increasing, the quantity of ash and gaseous emissions produced by their combustion.

[0034] In a preferred embodiment, the lignin is added at a rate of 4 to 60% by weight of the initial biomass to be steam cracked. In an even more preferred embodiment, the lignin is added at a rate of at least 4% by weight of the initial biomass to be steam cracked.

[0035] A second subject of the invention relates to a process for preparing black granules having a unit calorific value at least 6% higher than that of the initial biomass, comprising a step of adding a lignin-rich material to said biomass followed by a steam cracking step characterized in that the material to be steam cracked obtained at the end of said addition comprises 4 to 60% of a lignin-rich material.

[0036] The black granules obtained by this process have a unit calorific value at least 6% higher than that of the initial biomass and at least 2% higher than a black granule obtained by a conventional process.

[0037] In a particular embodiment, such a method is implemented as follows: - obtaining a biomass, for example from wood chips, from wood fragments whose dimensions are between 0.5 and 14 mm and having a humidity level maintained by drying between 5 and 27%, preferably between 5 and 10%; - addition of a lignin-rich material to said biomass obtained in the previous step - continuous introduction of a predetermined volume per minute of said biomass into a pressurized reactor, said reactor being supplied with substantially saturated steam whose pressure is between 10 and 25 bars and whose temperature is between 180 and 220°C; - exposure of said biomass introduced into said reactor to said water vapor for a duration sufficient to obtain steam cracking of between 5 and 30 minutes, the value of said exposure duration and the value of the temperature of said substantially saturated vapor being selected so that the severity factor is between 3 and 5, preferably between 3.5 and 4.2; - continuous extraction from said reactor of the same predetermined volume of biomass per minute, through a plurality of orifices opening into a conduit substantially at atmospheric pressure, so as to cause a explosive decompression of said biomass extracted from said reactor in said conduit; - separation of said decompressed biomass and the residual steam extracted from said reactor, said biomass obtained after separation forming said combustible material in powder form. - the said biomass collected in powder form at the outlet of the separator is then optionally dried until its humidity level reaches 10%, before being optionally compacted in the form of granules intended to be used as fuel. It is possible to humidify the wood fragments obtained after separation in order to facilitate granulation.

[0038] The Treatment Severity Factor is defined by the formula: FS=Logl0(time(min)*exp((T°C-100) / 14.75)). The higher the temperature and the longer the treatment time, the more the severity increases, the more transformation is observed in the product, the more carbonaceous matter is lost in the evaporates.

[0039] The steam cracking conditions can be adapted according to the composition of the initial biomass and the rate of incorporation of lignin before steam cracking.

[0040] It is known to those skilled in the art that conventional processes for preparing black granules make it possible to obtain products whose PCI is increased by 4% compared to that of the initial biomass.

[0041] For the purposes of the invention, the term "conventional processes" means processes for obtaining black granules by thermal treatments, such as steam cracking or steam explosion, without adding lignin before steam cracking.

[0042] In a preferred embodiment, the lignin added has a PCI of at least 7500 kWh / tonne and is introduced at a rate of 4 to 60% by weight to the initial biomass, leading to the production of a mixture whose PCI is at least 5300 kWh / tonne of mixture.

[0043] An addition of lignin at a level of at least 4% by weight to the initial biomass leads to the production of a mixture whose PCI is increased by at least 2% compared to the PCI of a black granule obtained by a conventional process of the state of the art. In other words, the unit power of the granules obtained is at least 6% higher than that of the initial biomass.

[0044] For the purposes of the invention, the term "maintained by drying" means an optional step of drying the raw material, in the case where the biomass has a humidity level greater than 27%, in order to reach a humidity level of between 5 and 27%, preferably between 5 and 10%.

[0045] The solid combustible material with high calorific value (black granules) obtained by implementing the process as defined above has a calorific value greater than or equal to 5 MWh / t, preferably greater than or equal to 5.2 or 5.3 or 5.4 or even 5.5 or 5.6 MWh / t. It has a mass increase of less than or equal to 10% after complete immersion in a container of water for one hour and draining for 30 minutes. This combustible material can be used in industrial furnaces, and domestic boilers and stoves.

[0046] In a particular embodiment of the invention, the material to be steam cracked obtained at the end of said addition comprises between: 4 to 50%; 4 to 40%; 10 to 60%; 10 to 50%; 10 to 40% of a material rich in lignin.

[0047] In another particular embodiment, a portion of the steam-cracked biomass obtained according to the process for preparing black pellets - in which the lignin is depleted of undesirable elements by means of steam cracking - is used to produce a lignin-rich material. In other words, the process according to the invention allows the production of a steam-cracked “intermediate” product enriched in lignin, but without increasing the quantity of undesirable elements compared to the quantity present before steam cracking.

[0048] In a preferred embodiment, the lignin-rich material obtained after steam cracking is capable of being reintroduced (i) at the step of adding lignin to the biomass according to the process for preparing black granules, or (ii) before granulation in the processes for producing black or white granules.

[0049] A third subject of the invention relates to the use of lignin depleted in undesirable elements, obtained from steam-cracked biomass enriched in lignin from the process for preparing black granules, in processes for producing granules or treating biomass, processes for producing bioenergy or bioplastics or bioproducts or substrates intended for the chemical and / or biological industry. Indeed, the steam-cracked material is enriched in lignin but without increasing the quantity of undesirable elements, it has new intrinsic properties and whose applications in the field of biofuels are extensive.

Claims

Claims

1. Process for the preparation of black granules having a unit calorific value at least 6% higher than that of the initial biomass, comprising a step of adding a lignin-rich material to said biomass followed by a steam cracking step, said added lignin being rich in non-carbon elements (nitrogen, sulfur, chlorine) and in minerals, characterized in that the material to be steam cracked obtained at the end of said addition comprises 4 to 60% of a lignin-rich material.

2. A method for preparing black pellets according to claim 1, wherein the lignin-rich material added has a PCI of at least 7500 kWh / tonne and is introduced at a rate of 4 to 60% by weight to the initial biomass, resulting in a mixture having a PCI of at least 5300 kWh / tonne of mixture.

3. A method according to claim 1 or 2 wherein at least a portion of the steam-cracked biomass is used as lignin-rich material.

4. A method according to claim 3 wherein said lignin-rich material obtained from steam-cracked biomass is introduced in the step of adding a lignin-rich material to the biomass according to the method described in one of claims 1 or 2.

5. Use of a lignin-rich material, obtained according to the process of claim 4, in processes for producing white granules or black granules or for treating biomass, processes for producing bioenergy or biomaterials or substrates intended for the chemical and / or biological industry.