EP4136188A1

EP4136188A1 - Method for producing combustible pellets by improved steam cracking using heterogeneous biomass

Info

Publication number: EP4136188A1
Application number: EP21725575.1A
Authority: EP
Inventors: Adriana QUINTERO-MARQUEZ; Jean-Luc DESPRES; Frédéric MARTEL
Original assignee: Europeenne de Biomasse SAS
Current assignee: Europeenne de Biomasse SAS
Priority date: 2020-04-17
Filing date: 2021-04-16
Publication date: 2023-02-22
Also published as: CA3170235A1; JP2023521842A; FR3109390B1; AU2021255991A1; FR3109390A1; BR112022020880A2; CN115698227A; MX2022012988A; KR20230004625A; US20230193149A1; WO2021209725A1

Abstract

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

Description

DESCRIPTION

TITLE: PROCESS FOR THE PRODUCTION OF FUEL PELLETS BY VAPOCRAQUAGE IMPROVED BY USE OF HETEROGENOUS BIOMASS

The invention relates to the production of steam cracked biomass in the form of black pellets in the field of solid biofuels. More particularly, it relates to the production of black granules from a heterogeneous biomass. The objective is to produce black granules with good mechanical strength, good resistance to water and increased calorific value.

Field of the invention

The production of energy (electrical and thermal) of renewable origin can be done from the environment (sun, wind, tide, swell, geothermal energy, hydraulic) or from biomass. River or dam hydraulics, and geothermal energy are renewable energies that are intermittent today, and will remain so as long as energy storage means are not developed. Only biomass constitutes 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.

There are several ways to densify and stabilize lignocellulosic biomass, including carbonization, roasting, and steam cracking. The first, which makes it possible to manufacture charcoal, involves a high price of the material due to a significant loss in yield (of the order of 70 to 80%), and is reserved for uses at high "sales prices". such as home use in a barbecue. Roasting is a technology with an acceptable yield (10% to 20% loss), but the price remains prohibitive, and the technology is not mature. To date, only the Steam cracking seems technically viable, and economically on condition that production costs are contained. This technology makes it possible to manufacture “black pellets” (or “black pellets”). It should be noted that steam cracking cannot be assimilated to hydrothermal pre-treatment or pyrolysis techniques.

Hydrothermal pretreatment, also called aqueous fractionation, solvolysis, hydrothermolysis or hydrothermal treatment, involves the use of high temperature and high pressure water to promote the disintegration and separation of the lignocellulosic matrix. This technique is not suitable for the production of black granules since the products obtained are predominantly liquid. Pyrolysis is the chemical decomposition of an organic compound by intense heating in the absence of oxygen. The compounds obtained after pyrolysis differ in their characteristics from those obtained by steam cracking. Steam cracking cannot be likened to a pyrolysis technique in that it employs a steam explosion and is carried out in the presence of oxygen.

The transformation of lignocellulosic biomass (wood, agricultural residues, co-products from agriculture and agribusiness) into an energetically dense compound, transportable and easily stored makes it possible to develop and consolidate an industrial stationary energy sector (biofuel used at a fixed point, the hearth, unlike biofuels) and reduce environmental impacts ( _{fossil C0 2} emission, with biomass without fertilizers or phytosanitary). The thermal treatment of the biomass by steam cracking allows this energy densification, by homogenizing the biomass into a steam cracked powder according to precise parametric conditions, in particular of particle size, temperature and residence time. The powder is then granulated to facilitate its transport, storage and use.

It is important to ensure that the granulation process is able to ensure a constant and quality product, having a high calorific value and an appropriate mechanical behavior to be stored, transported and used in the boiler, with the best characteristics of mechanical resistance and water resistance, reduced dust formation (fines) during handling, dryness to ensure good calorific value and good combustion, and stability over time and in storage (no self-heating fermentation, gas release, etc.).

Granulation by passing the steam cracked powder through a granulating press makes it possible to form dense and resistant granules. Classically on white granules, softwood sawdust refined (75% between 0.36 and 1 mm, and 50% less than 0.5 mm) and compressed produces granules between 6, 8 and 10 mm in diameter, 2 to 5 cm in length, with a bulk density of 600 at 650 g / L, with a mechanical strength (durability) of 97.5% and a PCI / gross of 4.9 kWh / kg for less than 8% humidity (usually between 5 and 8%). However, it has no resistance to water (it completely disintegrates in water in less than 5 minutes). The black hardwood pellet has a bulk density of 650 to 750 g / L, with a mechanical strength (durability) of 98.5% and a PCI / gross> 5.0 kWh / kg for less than 10% moisture ( usually equal or very close to 10%). It has a resistance to immersion which allows it to reversibly capture less than 10% of its weight in water without noticeable modification of its durability after drying.

However, when granulating a steam cracked powder in which the fibers are too short, this leads to poorer durability, the presence of scales on the granule, a lower bulk density, and more fines produced, especially during handling.

If the severity conditions can be adapted to modulate the steam cracking in order to improve the granulation of the black granules, they make it possible to manufacture longer fibers, but to the detriment of the increase in the expected calorific value and other properties such as resistance. to water or mechanical strength, the drop in cohesion due to the lignin which migrates less at lower severity. This approach is therefore not satisfactory on its own.

There is therefore a need to control the granulation process by new means to improve the quality of granulation of black granules.

Prior art

Patent WO2013 / 191897 describes an installation and a process dedicated to the treatment of biomass using steam explosion methods as a pretreatment before gasification or combustion. The moisture values of the incoming biomass left outside without further drying are between 15% to 60%. The process uses a steam explosion step in which: the biomass is introduced into a unit explosion, low pressure steam is introduced and then steam at at least 10 times atmospheric pressure is finally introduced to heat and pressurize the biomass before rapid depressurization. The produced fine wet biomass particles are then fed to a feed section of the biomass gasifier, which reacts with the biomass particles in a rapid biomass gasification reaction to produce syngas components. The product obtained by this process is a synthesis gas.

Patent WO2019 / 054913A1 relates to a wood pulp production process allowing the production of fuel pellets or briquettes from wood. The process involves debarking tree logs which are then reduced to wood chips. A part of these chips is used to form a paste, while another part undergoes a steam cracking step. The heat-treated bark is discharged from the reactor through an adjustable blow-off valve or a constant diameter discharge port to achieve a vapor explosion discharge of said bark. After the steam explosion step, the chips obtained are granulated with the lignin recovered during the wood pulp production step.

Patent WO2020 / 225504 relates to a powdery carbonaceous substrate of chemical or biochemical reaction obtained by continuous steam cracking of a lignocellulosic biomass at a moisture content of between 5% and 27% without chemical auxiliary by applying a severity factor of included between 3 and 5. The carbonaceous substrate can be in the form of a weakly densified granule. This form can be adopted when packaging the product in order to facilitate handling, but its characteristics are those of a powder when the substrate is impregnated with a solution (enzymatic, acid, etc.).

Disclosure of the invention

The inventors have shown, unexpectedly, that the quality of the black granules is improved when the latter are produced from a steam cracked biomass of heterogeneous particle size. More generally, they have shown that good granulation could be obtained by mixing steam-cracked powders obtained from different biomasses. For example, the powders obtained from soft hardwoods such as poplar, or certain hardwoods such as ash, deliver very fibrous powders which can advantageously be mixed with an oak powder which comprises of the order of 80% fines.

In addition, they demonstrated that the steam cracked powder obtained from coarsely ground biomass (of the order of an average size of 30 mm to 40 mm instead of 10 to 20 mm) made it possible to obtain a powder having a power. more satisfactory calorific value (PCI) thanks to the presence of residual fibers in sufficient quantity (of the order of 20%) capable of agglomerating and ensuring good granulation with the powder and the co-existing fine cotton so as to obtain a black granule having the required specifications.

On the basis of these observations, the inventors have thus established that in order to obtain a quality black granule, it is important to use a heterogeneous steam-cracked biomass having both fibers (of the order of 20% greater than 1 mm) , but also fines in the form of powders or very fine cottony fibers (less than 0.5 mm).

Thus, the invention relates to a process for the production of combustible black granules by continuous steam cracking of biomass at a humidity level of between 5 and 27%, characterized in that the granulation step is carried out on an unwashed steam cracked biomass comprising on the one hand at least 50% of pulverulent compounds with a cross section of less than 0.5 millimeters and on the other hand at least 10% of fibrous compounds having a length greater than 1 mm, said pulverulent and fibrous compounds being linked by the hemicellulose and lignin present in said biomass, without additives.

Advantages of the invention

The process according to the invention has the advantage of ensuring the production of black granules of good quality in a constant manner: good mechanical strength, good resistance to water and increased calorific value. In addition, the use of a heterogeneous steam cracked biomass makes it possible to produce quality granules without adding additives, in which the steam cracked lignin serves as a binder. Additives are expensive and generally unwanted due to their toxicity; To be free from it is therefore advantageous from an economic and ecological point of view.

The heterogeneity of the powders can be obtained in different ways: by using an input biomass whose grinding leads to platelet-type particles of heterogeneous size, by using a heterogeneous input biomass consisting of a mixture of different plant species, in modulating the severity conditions during steam cracking, by mixing biomasses obtained from the same input biomass but treated under different severity conditions during steam cracking by mixing different steam cracked biomasses obtained from different plant species.

A method is thus proposed which allows better management of the biomass: the size of the powder particles can be measured after steam cracking to prepare an appropriate heterogeneous mixture with a view to quality granulation.

Detailed description of the invention

The subject of the invention is a process for the production of fuel granules by continuous steam cracking of biomass at a humidity level of between 5 and 27%, characterized in that the granulation step is carried out on a steam cracked biomass comprising a on the one hand at least 50% of pulverulent compounds with a cross 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 adding additives. In this process, the additives are not necessary because the pulverulent and fibrous compounds of the wood, in particular the lignin and the hemicellulose, are bound in the granules following the chemical and physical modifications induced by the steam cracking.

For the purposes of the invention, the term “additives” is understood to mean the commercial compounds introduced between 0.5% and 10% by weight, such as certain compounds of starch, flour, other plant or petrochemical substances providing a binder.

For the purposes of the invention, the term “biomass” is intended to mean lignocellulosic biomass originating both from agricultural and forestry residues, from wood processing 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 the energy characteristics of the solid combustible material. For example, the most used woods are hardwoods and softwoods.

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

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

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

The biomass comprises in addition to pulverulent compounds and fibrous compounds, cottony compounds.

In a particular embodiment of the invention, the steam cracked biomass is heterogeneous because it comes from different plant species.

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

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

In another particular embodiment, the steam cracked biomass is heterogeneous due to the fact that it comes from several steam cracking of the same initial biomass under conditions of different severity, the powders obtained being mixed before granulation.

The different steam cracking of the same initial biomass under conditions of different severity 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.

To implement the method according to the invention, 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 granulation. This measurement can be made by any means known to those skilled in the art and preferably by a means which can be integrated into the production line, such as measurement by optical diffusion (laser), or even measurement by sieve systems. The result of this analysis allows, where appropriate, an external powder supply so as to comply with the size proportions recommended for quality granulation.

Thus, in a particular embodiment, the method comprises a step in which the particle size of the steam cracked biomass is analyzed before granulation.

The density of the steam cracked powder is also an indicator of its heterogeneity and therefore of its granulability.

In a particular embodiment, the method further comprises a step of adding lignin originating from a steam cracked biomass before granulation. The method can also comprise a step in which the various powders constituting the heterogeneous biomass are pre-granulated separately and then mixed before granulation. The pre-granulation of the powders facilitates their handling and transport. 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 platelets or other form of the initial biomass. This parameter can be easily modulated by adapting the grinding screens. Thus, the method can comprise a step in which the particle size of the biomass crushed before steam cracking is heterogeneous.

This invention finds its application in manufacturers who seek to optimize the production of biofuels by standardizing the final product according to a variable supply which becomes desirable instead of being suffered; the advantage is also to be able to arbitrate thanks to a mixture of variations in availability and price of biomass, in the interest of the final granulated product.

Claims

1. Process for the production of combustible black granules by continuous steam cracking of biomass at a humidity level of between 5 and 27%, characterized in that the granulation step is carried out on a steam cracked biomass comprising on the one hand at least 50 % of pulverulent compounds with a cross 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 adding additives.

2. The method of claim 1 wherein said steam cracked biomass is heterogeneous because it comes from different plant species.

3. The method of claim 2 wherein the steam cracking of different plant species is carried out in a single step.

4. The method of claim 1 wherein said steam cracked biomass is heterogeneous due to the fact that it comes from several steam cracking of the same initial biomass under conditions of different severity, and mixing before granulation.

5. The method of claim 4 wherein said several steam cracking are carried out in parallel.

6. Method according to one of the preceding claims, in which the particle size of the steam cracked biomass is analyzed before granulation.

7. Method according to one of the preceding claims further comprising a step of adding lignin obtained from steam cracked biomass before granulation.

8. Method according to one of claims 2 to 5 wherein the various powders constituting the heterogeneous biomass are pre-granulated separately and then mixed before granulation.

9. Method according to one of the preceding claims, in which the particle size of the biomass crushed before steam cracking is heterogeneous.