METHOD FOR PRODUCING COMBUSTIBLE PELLETS BY IMPROVED STEAM CRACKING USING HETEROGENEOUS BIOMASS

Abstract

The production of steam-cracked biomass in the form of black pellets in the field of solid biofuels. More particularly, the present disclosure relates to the production of black pellets from a heterogeneous biomass. The aim of the present disclosure is to produce black pellets having good mechanical strength, good water resistance and an increased calorific value.

Claims

1. A method for producing combustible black pellets, comprising: continuously steam cracking biomass at a humidity level of between 5% and 27% by weight to form steam-cracked biomass comprising at least 50% by weight of pulverulent compounds with a section of less than 0.5 millimeters, and at least 10% by weight of fibrous compounds having a length greater than 1 millimeter, without additives; and pelletizing the steam-cracked biomass.

2. The method of claim 1, wherein the steam-cracked biomass is heterogeneous and originates from different plant species.

3. The method of claim 2, wherein the steam cracking of biomass comprises steam cracking the different plant species in a single step.

4. The method of claim 1, wherein the steam-cracked biomass is heterogeneous, and wherein the steam cracking of biomass comprises performing a plurality of steam cracking operations of a same initial biomass under different conditions to form a plurality of volumes of differing steam-cracked biomass, the method further comprising mixing the volumes of differing steam-cracked biomass to form the steam-cracked biomass before the pelletizing of the steam-cracked biomass.

5. The method of claim 4, further comprising performing the plurality of steam cracking operations in parallel.

6. The method of claim 1, further comprising analyzing a particle size of the steam-cracked biomass before the pelletizing of the steam-cracked biomass.

7. The method of claim 1, further comprising adding lignin originating from a steam-cracked biomass before the pelletizing of the steam-cracked biomass.

8. The method of claim 2, further comprising separately pre-pelletizing a plurality of powders constituting the heterogeneous steam-cracked biomass and then mixing the pre-pelletized the plurality of powders before the pelletizing of the steam-cracked biomass.

9. The method of claim 1, wherein a particle size of the biomass before the steam cracking is heterogeneous.

Description

DETAILED DESCRIPTION

[0030] The present disclosure relates to a method for producing combustible pellets by continuous steam cracking of biomass at a humidity level of between 5 and 27%, characterized in that the pelletizing step is carried out on a steam-cracked biomass comprising on the one hand at least 50% of pulverulent compounds with a section of less than 0.5 millimeters, and on the other hand at least 10% of fibrous compounds having a length greater than 1 millimeter, without additives.

[0031] In this method, additives are not necessary because the powdery and fibrous compounds of the wood, in particular, lignin and hemicellulose, are bound in the pellets following the chemical and physical modifications induced by the steam cracking.

[0032] Within the meaning of the present disclosure, “additives” means the commercial compounds introduced between 0.5% and 10% by weight, such as certain compounds of starch, flour, or other plant or petrochemical substances providing a binder.

[0033] Within the meaning of the present disclosure, “biomass” means the lignocellulosic biomass originating both from agricultural and forestry residues, from wood transformation by-products and from dedicated crops. It 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 combustible material. For example, the most used woods are hardwoods and softwoods.

[0034] In a preferred embodiment, the humidity level is between 7% and 20%, and even more preferably is between 8 and 14%.

[0035] In another preferred embodiment, the pulverulent compounds with a section of less than 0.5 millimeters represent at least 75% of the steam-cracked biomass.

[0036] In another preferred embodiment, the fibrous compounds having a length greater than 1 millimeter represent at least 20% of the steam-cracked biomass.

[0037] The biomass also comprises powdery compounds and fibrous compounds, cottony compounds.

[0038] In a particular embodiment of the present disclosure, the steam-cracked biomass is heterogeneous because it comes from different plant species.

[0039] The composition of the lignocellulosic biomass varies according to the plant species in these major constituents, i.e., cellulose, hemicellulose and lignin. This is why the powders obtained by steam cracking from the different species are not of equivalent quality.

[0040] In a preferred embodiment, the steam cracking of the different plant species is carried out in a single step.

[0041] In another particular embodiment, the steam-cracked biomass is heterogeneous in that it comes from several steam cracking operations of the same initial biomass under different severity conditions, the powders obtained being mixed before pelletizing.

[0042] The different steam cracking operations of the same initial biomass under different severity conditions can be carried out at different times or in parallel. In a preferred embodiment, they are carried out simultaneously in continuous reactors arranged in parallel.

[0043] To implement the method according to the present disclosure, the particle size of the steam-cracked biomass powders must be known. To do this, the particle size of these powders can be measured before pelletizing. This measurement can be done by any means known to those skilled in the art, and preferably by means that can be integrated into the production line, such as measurement by optical scattering (laser), or even measurement by sieve systems. The result of this analysis allows, if necessary, an external powder supply so as to respect the size proportions recommended for quality pelletizing.

[0044] Thus, in a particular embodiment, the method comprises a step in which the particle size of the steam-cracked biomass is analyzed before pelletizing.

[0045] The density of the steam-cracked powder is also an indicator of its heterogeneity and therefore of its pelletability.

[0046] In a particular embodiment, the method further comprises a step of adding lignin originating from a steam-cracked biomass before pelletizing.

[0047] The method can also comprise a step in which the various powders constituting the heterogeneous biomass are pre-pelletized separately and then mixed before pelletizing. Pre-pelletizing the powders facilitates their handling and transport.

[0048] The particle size of the biomass after steam cracking is also influenced by the particle size of the biomass before steam cracking, that is to say, by the size of the platelets or other form of the initial biomass. This parameter can be easily modulated by adapting the grinding grids.

[0049] Thus, the method can comprise a step in which the particle size of the ground biomass before steam cracking is heterogeneous.

[0050] The present disclosure finds its application with industrialists who seek to optimize the production of biofuels by standardizing the final product according to a variable supply, which becomes desirable instead of being endured; the interest is also to be able to arbitrate owing to a mixture to the variations of availability and price of the biomasses, in the interest of the final pelletized product.