USE OF A VAPOR CRACKED BIOMASS AS AN ALTERNATIVE FUEL BY DIRECT INJECTION INTO THE COMBUSTION FIRE

Abstract

The invention relates to a powdered biofuel obtained by steam cracking of biomass suitable for direct injection into a combustion chamber. More specifically, the invention concerns the use of steam cracked biomass in dry powder form for use as fuel in a fluid-mode installation, such as, for example, a direct-flow boiler.

Description

Title of the invention: USE OF VA-CRACKING BIOMASS AS AN ALTERNATIVE FUEL BY DIRECT INJECTION INTO THE COMBUSTION HEART

[0001] The invention relates to the field of solid biofuels, particularly to a powder-type fuel obtained by steam cracking of a biomass capable of being injected directly into a combustion chamber. More specifically, the invention relates to the use of a steam-cracked biomass in the form of a dry powder intended to be used as fuel in a fluid mode installation, such as, for example, a direct-line boiler. Field of the invention

[0002] Many industrial facilities, such as factories or thermal power plants using boilers, require the use of fuels to operate. Fuels such as gas, fuel oil or micronized coal are generally used. The use of these fuels has a significant ecological impact on the planet. Indeed, coal is a considerable source of environmental pollution. When burned, it emits many components such as: sulfur, microparticles, ash, heavy metals (mercury, arsenic, selenium, lead). Fuel oil and gas release a large quantity of CO2, massively impacting water and air. In addition to its ecological impact, the use of these types of fuels is often harmful to human and animal health. Finally, these fuels are economically expensive.

[0003] Industrialists are increasingly turning to more ecologically and economically interesting energy production methods. The production of energy (electrical and thermal) from renewable sources can be done from the environment (sun, wind, tide, swell, geothermal, hydraulic) or from biomass. Apart from biomass, river or dam hydraulics, and geothermal, these renewable energies are intermittent unless energy storage methods are developed. And only biomass constitutes a primary energy that can be transported to its place of transformation into heat and / or electricity. But biomass is in fact a low-density, variable and perishable energy.

[0004] The transformation of lignocellulosic biomass (wood, agricultural residues, agricultural and agro-industrial co-products) into an energy-dense, transportable and easily storable compound makes 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). The thermal treatment of biomass by steam cracking allows this densification of energy.

[0005] Steam cracking is a biomass treatment commonly used for the production of biofuels, particularly in the form of pellets ("black pellets" in English). It employs both physical / mechanical and chemical methods to break down the structure of the lignocellulosic material. In general terms, steam cracking is a violent evaporation or flash evaporation of water into steam. Pressure vessels operating above atmospheric pressure can also provide the conditions for rapid boiling, which can be characterized as a steam explosion. Biomass fed into a steam cracking reactor, either continuously or in batches, is rapidly heated with high-pressure saturated steam. The biomass / steam mixture is held for a period of time to promote hydrolysis of hemicelluloses and other chemical and physical changes, this period is then followed by explosive decompression.Steam cracking is typically initiated at a temperature of 160-260 °C for a few seconds to a few minutes before the material is exposed to atmospheric pressure. The powder is then compressed in presses to produce short cylinders called pellets.

[0006] However, the use of this type of fuel requires specific installations allowing the combustion of pellets. However, many industrialists do not have the appropriate installations to use this type of alternative fuel, in particular boilers with grates, steps, or with fuel projectors (spreader stoker).

[0007] The objective technical problem is to propose an ecological and economical solution for the use of a biofuel capable of being injected into conventional boiler installations with direct injection of pulverized material. Prior art

[0008] Patent application FR1905269A1 discloses a process for the continuous manufacture of a combustible material for an industrial boiler. This process comprises the following steps: - obtaining wood fragments from wood chips having a moisture content of between 5 and 25%; - continuously introducing a predetermined volume per minute of said wood fragments obtained into a pressurized reactor, - exposing the wood fragments introduced into said reactor to said water vapor for a time sufficient to obtain steam cracking of between 5 and 9 minutes, - continuously extracting from said reactor the same predetermined volume of wood fragments per minute, through at least one orifice opening into a leads substantially to atmospheric pressure, so as to cause explosive decompression of said wood fragments extracted from said reactor in said conduit - separation of said decompressed wood fragments and the residual steam extracted from said reactor, said wood fragments obtained after separation forming said combustible material.

[0009] Patent application CN108624374A discloses a method for preparing an environmentally friendly fuel, characterized in that it is a method for preparing a bioparticle fuel by using harvest straw and forest waste as raw materials, and the specific steps are as follows: (1) Preparation: selecting the combustible materials, slicing the combustible materials, checking the moisture of the combustible materials and classifying according to different moisture; (2) Drying: the combustible materials classified according to different moisture are pulverized to 10 to 30 mesh, respectively, and sent to an air dryer for drying, so that the moisture of the combustible raw materials after drying is less than 15%;(3) Die casting: Compressing the combustible material after drying in the above step into granules, putting it into a cooling box to cool to room temperature, and then filtering the particles with a diameter of 0.5-2 cm through a vibrating screen; (4) Packing: The granules that meet the requirements of the above step are bagged and packed, the particles that do not meet the requirements are pulverized in step (2), and the following steps are continued until the requirements are met. ; Disadvantages of the state of the art

[0010] The solutions proposed by the prior art are not entirely satisfactory. Indeed, the fuels proposed by the prior art are in the form of pellets. This type of fuel requires a special installation and cannot be used in conventional installations. Statement of the invention

[0011] The present invention proposes a solution for the use of a biofuel which meets the technical problem set out above.

[0012] The objective is to propose an interesting, ecological and economical solution allowing the use of a biofuel as an alternative to conventional fuels, suitable for use in a conventional installation by direct injection into the combustion chamber.

[0013] The invention therefore relates to the use of a vapour-cracked lignocellulosic biomass, suitable for use in a conventional installation and characterized in that said biofuel is of the powder type at the time of injection into the hearth of combustion. Advantages of the invention

[0014] The present invention therefore proposes a new approach in the use of biofuels. It provides a solution making it possible to extend to all industrialists equipped with a boiler operating by injection in fluid mode, the alternative use of a biofuel consisting of steam-cracked biomass in powder form.

[0015] The invention can be implemented either in a direct line boiler, i.e. attached to a steam cracking installation, or in an indirect line by supplying steam cracked powder from a separate production site.

[0016] In a direct line use, the powder, produced by the neighboring steam cracking installation, is directly injected by a conveyor (mechanical or pneumatic system, or other) from the production site to the boiler with possible buffer stocks and returns. It can also be transported in powder form by vehicles.

[0017] In indirect line use, transport can be facilitated by densifying the powdered steam-cracked biomass to form an intermediate product, called a "granulette". These granules have high friability properties and are easy to reduce to powder for direct injection into the combustion chamber in fluid mode. The advantage of granules is that they are an intermediate product in the process for obtaining black granules (densified product) by steam cracking, which does not require the acquisition of new installations. Granules are products obtained during a light or incomplete densification step of the steam-cracked powder. The production of granules therefore represents very low granulation costs, while allowing a transportable form, easily transformed into a powder product by the user.

[0018] In another advantageous embodiment, the steam-cracked biomass used in fluid-mode boilers may come from black pellets. These pellets have a high hydrophobicity, much higher than that of steam-cracked biomass; this form makes it possible to extend the storage life of the steam-cracked biomass and facilitate its transport. These pellets can be transformed into a powdery product by the user by different types of grinding for use in a fluid-mode boiler. The amount of energy required for grinding is greater than that used for pellets, but the pellets are denser and more resistant to transport and storage.

[0019] When using steam-cracked biomass in a direct-line installation, no densification step is necessary. This saves the costs related to the densification of the biomass represented by the granulation step.

[0020] In a particular embodiment, when used in a direct line installation, the evaporates from the steam cracking step can also be injected into the combustion hearth with the steam cracked biomass to optimize energy production, reduce ecological and economic costs.

[0021] Another advantage of using steam-cracked biomass in a direct-line installation is to obtain a standard and controlled flow when injecting the powdered biofuel. DETAILED DESCRIPTION OF THE INVENTION

[0022] The subject of the invention is the use of a steam-cracked lignocellulosic biomass as solid biofuel, intended to be directly injected into the combustion hearth of an installation in fluid mode, characterized in that said biomass is in a powder form at the time of injection into said combustion hearth.

[0023] For the purposes of the invention, the term “lignocellulosic biomass” means any biomass with lignocellulosic characteristics, such as: wood, agricultural residues, agricultural and agro-industrial co-products.

[0024] By "in fluid mode" within the meaning of the invention, it is meant that the finely divided fuel behaves like a liquid or a gas, unlike conventional solid fuels, which are denser and coarser.

[0025] For the purposes of the invention, the term "powdery" means a biomass in powder form. The fact that the biomass is in powder form implies that it is in dry form, the moisture content preferably being between 5% and 27% moisture.

[0026] Thermal treatment of biomass by steam cracking allows the densification of energy, by homogenizing the biomass into a steam cracked powder. When used in a non-direct in-line installation, the powder can be granulated, to facilitate its transport, storage and use.

[0027] During a steam cracking process, the material is chemically modified by a thermal reaction around 200°C, preferably 205-210°C, with a residence time between 5 and 10 minutes, which corresponds to the necessary activation energy allowing the depolymerization and volatilization of low-energy oxygenated compounds (in particular the constituents of the most thermolabile hemicelluloses) while increasing the calorific value of the final compound and preserving the integrity of other macromolecules such as cellulose and lignin, the latter being essential to ensure the cohesion and water resistance of the steam cracked biomass.

[0028] In a preferred embodiment, the steam cracking process is carried out continuously.

[0029] In one embodiment, the use of a steam-cracked biomass takes place in a non-direct line fluid mode installation.

[0030] By "non-direct line" within the meaning of the invention, we mean an installation in which the steam-cracked biomass obtained will undergo a storage and / or transport step before being injected into the combustion chamber.

[0031] When used in a non-direct line, the steam-cracked biomass can be in the form of granules or pellets to facilitate its transport. The granulation step is only intended to optimize the transport logistics, which are more complicated with a powdery product. Indeed, even in powder form, the steam-cracked biomass can be stored and transported; it is stable.

[0032] For the purposes of the invention, the term "granulette" means an intermediate product of the production of granules by steam cracking, i.e. granules with medium compression density. These granules correspond to a form of powder compressed so as to give it the shape of a granule, but which quickly releases a powder by simple mechanical action of the mixing or grinding type (slightly advanced granulation). This form can be adopted during the packaging of the product in order to facilitate handling, but its characteristics are those of a powder.

[0033] For the purposes of the invention, the term "granule" means a product with a high compression density, also called black granules. These granules correspond to a form of compressed powder so as to give it the form of a compact granule with good hydrophobicity, which allows for an increase in storage time.

[0034] In another particular embodiment, the steam-cracked biomass in powder form results from the grinding of granules and / or granules obtained by a steam-cracking process followed by a densification step.

[0035] In another embodiment, the use of a steam-cracked biomass takes place in a direct-line fluid mode installation.

[0036] By "direct line" within the meaning of the invention, we mean an installation in which the steam-cracked biomass obtained will not undergo a storage and / or transport step before being injected into the combustion chamber.

[0037] In a particular embodiment, the steam-cracked biomass is separated from the evaporates, which are produced during the steam-cracking step, before being injected into said combustion hearth of the installation.

[0038] In an alternative embodiment, the evaporates which are produced during the steam cracking step are injected into said combustion hearth of the installation with the steam cracked biomass.

[0039] For the purposes of the invention, the term “evaporates” means a gaseous flow of lower pressure vapor containing volatile organic compounds (VOCs), resulting from the treatment of biomass.

[0040] The advantage of this latter embodiment is that it allows the energy contained in the evaporates and in the water vapor to be recovered in order to conserve / save the overall energy of the process, instead of letting it escape.

[0041] This energy recycling loop is particularly suitable for steam cracking because this combustion method produces a large quantity of water vapor unlike other methods such as torrefaction, pyrolysis, etc. which operate in a dry atmosphere.

Claims

Claims

1. - Use of a steam-cracked biomass as a solid biofuel obtained by a process of steam cracking a lignocellulosic biomass, intended to be directly injected into the combustion hearth of an installation in direct line fluid mode and characterized in that said biomass is in a powder form at the time of injection into said combustion hearth.

2. Use of a steam-cracked biomass according to claim 1, in which said steam-cracked biomass is separated from the evaporates which are produced during the steam-cracking step before being injected into said combustion hearth of the installation.

3. Use of a steam-cracked biomass according to claim 1, in which the evaporates which are produced during the steam-cracking step are injected into said combustion hearth of the installation with the steam-cracked biomass.