EP3963028A1

EP3963028A1 - Method for treating solid biomass by steam cracking integrating the energy of the co-products

Info

Publication number: EP3963028A1
Application number: EP20731914.6A
Authority: EP
Inventors: Jean-Luc DESPRES; Thomas Habas; Adriana QUINTERO-MARQUEZ; Frédéric MARTEL
Original assignee: Europeenne de Biomasse SAS
Current assignee: Europeenne de Biomasse SAS
Priority date: 2019-05-03
Filing date: 2020-04-30
Publication date: 2022-03-09
Also published as: FR3095656B1; WO2020225503A1; FR3095656A1

Abstract

The present invention relates to the field of methods for transforming solid biomass by steam cracking into a substrate for green chemistry and biotechnology. More specifically, the invention relates to a method for treating solid biomass by steam cracking in which the energy contained in the evaporates and in the steam generated is retained within the system or used for other types of industries such as electricity generation.

Description

SOLID BIOMASS TREATMENT PROCESS BY INTEGRATED VAPOCRAQUAGE

THE ENERGY OF CO-PRODUCTS

The present invention relates to the field of processes for transforming solid biomass by steam cracking into a substrate for green chemistry and biotechnologies. More specifically, the invention relates to a process for the treatment of solid biomass by steam cracking in which the energy contained in the evaporates and in the water vapor generated is kept within the system or used for other types of industries such as than electricity production.

Technical area

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 currently intermittent renewable energies, due to a lack of energy storage means. In this context, only biomass constitutes primary energy that can be transported to its place of transformation into heat and / or electricity. However, biomass is a low density, variable and perishable energy.

Indeed, one way of exploiting biomass is to use woodchips, related sawmill products (sawdust) or wood pellets without modification. These renewable materials are very low in density (it takes 5 to 8 volumes of wafers to produce the energy equivalent of a single volume of coal), which involves an oversized supply chain and tools, not to mention the variability of contents of the supplies that impact the operation of the boiler (humidity, ash, heavy metals, organic, nitrogen, chlorine, sulfur, dust). The wood pellet (or “white pellet”) is more standardized, but it is expensive, and does not withstand exposure to water and outdoor conditions. Finally, the production of biogas requires the management of diluted liquid effluents, or wet solids that are difficult to transport, and of localized use, often of small size.

To overcome these problems, lignocellulosic biomass (wood, agricultural residues, agricultural and agro-industrial co-products) can be transformed into an energetically dense compound, transportable and easily stored which would allow the development and consolidation of a stationary energy industrial sector (biofuel used at a fixed point, the home, unlike biofuels) and reduce environmental impacts (emission of fossil C02, with biomass without fertilizers or phytosanitary). This solid biofuel, also called “black pellets” (or “black pellet”) can advantageously replace coal, or even fuel oil and gas in boilers.

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, implies a high material price due to significant loss of yield (of the order of 70 to 80%), and is reserved for uses with high selling price such as 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 steam cracking seems technically viable, and economically, provided production costs are contained. This technology makes it possible to manufacture “black pellets” (or “black pellets”).

Steam cracking differs from hydrothermal pretreatment, also known as aqueous fractionation, solvolysis, hydrothermolysis or hydrothermal treatment, in that the latter involves using water at high temperature and pressure to promote the disintegration and separation of the gas. lignocellulosic matrix. This technique is not suitable for the production of black granules since the products obtained are predominantly liquid.

The process for preparing black granules schematically comprises 3 steps: 1) preparation of the raw material (grinding, drying, etc.), 2) steam cracking and 3) granulation, all of which consume energy.

In the case of a plant manufacturing black pellet of steam cracked biomass, a dried biomass and clean steam of pressurized hot water enter the steam cracker. The two streams leaving after steam cracking are:

• a solid stream of steam cracked biomass which will be granulated, and

• a gaseous vapor stream of lower pressure containing volatile organic compounds (VOCs), called evaporates, resulting from the treatment of biomass.

One of the problems associated with the combustion of biomass by steam cracking is the production of these evaporates loaded with VOCs which can be toxic to the environment. It is therefore necessary to treat the evaporates to remove VOCs before releasing clean water vapor out of the system. To do this, it is usual to burn the evaporates so that the VOCs decompose into CO2 and CO, molecules which can then be released into the atmosphere without endangering the environment, in the form of white fumes (vapor d 'water).

State of the art

Prior art methods disclose the use of co-product energy in biomass condensation methods.

By way of example, document US2014 / 309475 discloses a solid biomass treatment process integrating the energy of the co-products comprising a steam cracking step as well as a step of injecting the volatiles produced into the steam cracking chamber with steam cracking and an external energy source in the boiler to produce clean water vapor for steam cracking. The method further comprises a step according to which the combustion to supply the boiler is carried out using treated biomass and evaporates resulting from steam cracking. The energy for the production of steam cracking being produced at least in part by the combustion of said recycled organic compounds.

Document US2012 / 085023A1 relates to a solid biomass treatment process integrating the energy of the co-products. The disclosed process comprises a biomass steam cracking step in which the volatile organic compounds, produced in the steam cracking chamber, are injected with the steam cracking steam directly into the boiler to produce clean water steam intended for the steam cracking.

Document US2017 / 314758A1 describes a process comprising a biomass steam cracking step in which the volatile organic compounds produced in the steam cracking chamber are injected with the steam cracking steam directly into the boiler to produce water vapor suitable for steam cracking. .

The solutions of the prior art therefore have limitations and it remains desirable to reduce the production costs of black granules to allow their industrial use.

Disclosure of the invention

The inventors propose to optimize the use of the co-products of the transformation process to reduce the production costs of the black granules. More specifically, it is proposed to burn the evaporates in a biomass boiler generating compressed steam used for steam cracking (recycling), and which can also be used by another local consumer (industrialist using steam, or electrician turbining the steam to manufacture electricity).

It is more generally proposed to use the energy associated with the evaporates and the water vapor by introducing volatile organic compounds and at least part of the recycled water vapor into the combustion chamber and condensing the vapor. water vapour.

Other types of fuel production from biomass require dry heat (white pellets or roasting) which often use fossil gas. The environmental balance is therefore degraded for these last two types of solid biofuel production. These processes do not generate water vapor.

Thus, the invention consists of a process for the production of solid combustible material integrating the energy of the co-products comprising a biomass steam cracking step characterized in that:

• the volatile organic compounds produced in the steam cracking chamber are injected, along with the steam cracking steam, directly into the combustion chamber of the boiler to produce clean water vapor intended for steam cracking and possibly another energy consumer;

• the energy for the production of steam cracking is produced at least in part by the introduction directly into the combustion chamber of volatile organic compounds and recycled water vapor.

The efficiency of this process can also be increased by condensing the combustion water vapors from the evaporates to dry the biomass before steam cracking.

In addition, it is possible to debark the wood used as a raw material, or to recover bark from an external source and burn these bark in the boiler.

Advantages of the invention

The method according to the invention makes it possible to use available energy sources that are usually not used to reduce the energy balance of the overall process and make it more ecological. Thus, the reduction in the material yield of the biomass entering the steam cracking (generally between 5% and 15%) is not totally lost because it generates energy.

This process comprises the optimized recovery of the energy available within the device for transforming biomass by steam cracking, namely:

the energy contained in the VOCs of the evaporates generated by steam cracking; this energy is released by combustion of volatile organic compounds;

the energy contained in the water vapor accompanying the evaporates (steam cracking vapor), which is either introduced directly into the combustion chamber or recovered by condensation;

the energy contained in the water vapor produced by the combustion of the evaporates, and recovered by condensation;

and optionally, in the same way, the energy contained in the bark and released by combustion, as well as the water vapor produced during this combustion and recovered by condensation. The originality of the process according to the invention is therefore to use the energy contained in the evaporates and in the water vapor to conserve / save the overall energy of the process, instead of letting it escape.

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

The fact of using the energy internal to the system in particular for drying the granules and in the form of water vapor introduced for the steam cracking increases the efficiency of the process and makes it more ecological.

This process is particularly advantageous when applied to a treatment of biomass producing large amounts of VOCs, for example when the severity of the steam cracking conditions is high. It should be noted that the severity is generally controlled to avoid the production of large quantities of VOCs which reduce the yield of the process since the evaporates are co-products not used in conventional processes. Here, the energy balance incorporates the energy associated with evaporates and water vapor rather than counting it in losses. This process therefore allows the implementation of severe conditions since the losses of combustible materials are in fact compensated since they are used to produce energy.

Advantageously, when the wood introduced into the system is previously treated to remove the bark, these bark are introduced into the boiler. The bark, which is the least interesting fraction for the targeted applications (often less caloric, more mineralized and potentially contaminated by pollutants), then becomes a residual co-product that can be exploited by burning it in the boiler serving in particular to produce steam for steam cracking, or intended for other industrial needs. Such a method of treating solid biomass including the recycling of the evaporates and of the water vapor, or even of the bark, is therefore particularly advantageous from an industrial, economic and ecological point of view since it provides an energy saving which can range from up to 30% compared to a process allowing the energy of the water vapor and the potential of the evaporates to escape.

DETAILED DESCRIPTION OF THE INVENTION

The invention relates to a method for treating solid biomass integrating the energy of the co-products comprising a biomass steam cracking step, characterized in that: the volatile organic compounds produced in the steam cracking chamber are injected with the steam cracking steam, directly in the boiler to produce clean water vapor intended for steam cracking and possibly another energy consumer;

the energy for the production of steam cracking being produced at least in part by the combustion of said recycled volatile organic compounds.

It is specified that the water vapor associated with VOCs produced during steam cracking can also be recycled to produce energy by direct introduction into the combustion chamber of the boiler (just like VOCs).

It is specified that the boiler has two compartments; a first combustion zone in which the hearth with the flame is located (lower part) and a second zone which corresponds to the vapor exchange zone (upper part). Thus, when VOCs and water vapor for combustion are injected “directly into the boiler”, we mean in the combustion zone.

In a particular embodiment, the energy for the production of steam cracking steam is produced in mixed mode comprising the combustion of the recycled VOCs and the combustion of a main external energy source. In one embodiment particularly alternative, the energy for the production of steam cracking steam is produced by the combustion of VOCs as well as by condensation of the water vapor available in the boiler, and possibly an external energy source.

Thus, the invention relates to a method for treating solid biomass integrating the energy of the co-products comprising a biomass steam cracking step, characterized in that: the volatile organic compounds produced in the steam cracking chamber are injected, with the steam from steam cracking, directly in the boiler to produce clean water vapor intended for steam cracking and possibly another energy consumer;

the energy for the production of steam cracking being produced at least in part by the combustion of said recycled volatile organic compounds,

the energy for the production of steam cracking vapor being produced at least in part by introducing into the combustion chamber at least part or all of the vapor accompanying the VOCs; this water vapor is preferably introduced immediately and directly into the combustion chamber of the boiler to minimize energy loss.

In addition, in particular modes of implementation,

the energy for the production of steam cracking vapor can be produced at least in part by the condensation of at least part or all of the vapor accompanying the VOCs;

the energy for the production of steam cracking steam may at least in part come from an external energy source;

the energy contained in the water vapor can be recovered by condensation.

These modes of implementation can be combined with one another.

In a particular embodiment, the biomass thus treated is used for the production of combustible material with a high calorific value, in particular in black granules. In another particular embodiment, the biomass thus treated is used as a pulverulent substrate for applications in green chemistry and in biotechnology.

Thus, the invention relates to the use of the biomass treated according to the process of the invention either to produce combustible material with a high calorific value, or as a pulverulent substrate for applications in green chemistry and in biotechnology.

The term “solid combustible material” within the meaning of the invention is understood to mean a powder (black powder) or black granules (black pellet) obtained by compression of the black powder, this powder and these granules consisting of steam cracked biomass.

Black granules with high calorific value can be obtained thanks to a process for transforming biomass by steam cracking under severe conditions. In a particular embodiment, such a method is implemented as follows:

- Obtaining, from wood chips, fragments of wood whose size is between 0.5 and 14 mm and having a moisture content of between 5 and 27%;

- Continuous introduction of a predetermined volume per minute of said wood fragments into a pressurized reactor, said reactor being supplied with substantially saturated water vapor, the pressure of which is between 10 and 25 bars and the temperature is between 180 and 220 ° C;

exposure of the wood fragments introduced into said reactor to said water vapor for a period sufficient to obtain a steam cracking of between 5 and 30 minutes, the value of said exposure time 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;

- Continuous extraction from said reactor of the same predetermined volume of wood fragments per minute, through a plurality of orifices opening into a duct substantially at atmospheric pressure, so as to cause explosive decompression of said extracted wood fragments from said reactor in said conduit;

- Separation of said decompressed wood fragments and of the residual vapor extracted from said reactor, said wood fragments obtained after separation forming said combustible material in powder form.

The wood fragments collected in powder form at the outlet of the separator are then dried until their 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.

The Treatment Severity Factor is defined by the formula: FS = Log10 (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 material is lost in the evaporates.

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 5.6 MWh / t. It exhibits an increase in mass 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. The condensation of lignocellulosic biomass by steam cracking produces an evaporate which must be cleaned of VOCs and this requires energy and specific washing equipment. The advantage of the process according to the invention is that the energy of the co-products is recycled, namely that the evaporates are burnt and that the energy produced by the combustion VOCs in the form of water vapor is reused as well as other available clean water vapor, in particular that resulting from steam cracking.

It should be noted that the nature of the effluents depends on the method used to condense the biomass. Steam cracking produces energy-rich VOC-laden effluents as well as a significant amount of water vapor (compared to alternative methods of biomass condensation). This specificity fully justifies an interest in recycling this available energy. This is all the more true when the conditions applied for the steam cracking are severe.

On the other hand, in a controlled boiler, the parameters will be adjusted according to the pressure and / or the chemical characteristics of the effluent produced. A boiler backed by a steam cracker will therefore have a specific operating mode.

In a preferred embodiment of the invention, the process further comprises a step of condensing at least part of the combustion water vapors of the evaporates for drying the biomass before steam cracking.

In fact, the vapors of water from the combustion of the evaporates can be condensed: by transferring their heat through hot loops to pulsed air, they supply a current for drying the raw material, which allows a reduction in humidity. Thus, the biomass returns drier to steam cracking. The amount of energy consumed to heat the biomass is then lower because there is much less water to heat (5 to 10% instead of 40 to 50% water). The steam-cracked product leaves between 5 and 10%, therefore granulatable and delivering a black granule which is more energy dense.

In another preferred embodiment, the method further comprises a step of condensing at least part of the steam cracking water vapors for drying the biomass before steam cracking.

If the energy generated in the form of water vapor in the boiler, in particular by combustion of VOCs, is not fully mobilized for the production of steam cracking water or for drying the biomass, it is possible to make it available to another local energy consumer, such as an industrialist using steam or an electrician using steam to produce energy and located near the steam cracking unit. "Nearby" means a distance allowing the transport of energy in the form of steam, therefore via a connected system.

By “biomass” within the meaning of the invention, is meant lignocellulosic biomass originating both from agricultural and forestry residues, by-products of wood processing and from dedicated crops. It may be in particular wood chips, with or without bark. The quality of this raw material will directly influence the quality and characteristics energies of solid combustible material. For example, the most widely used woods are hardwoods and softwoods.

Further energy integrations are possible since by definition the sites for the production of black granules by steam cracking are sites for the production of steam from biomass: we can therefore select the best wood or parts of wood for the manufacture of the pellets, and the less noble are burnt for endogenous energy.

In an advantageous embodiment, the bark obtained from the debarking of the biomass is valorized, as fuel making it possible to supply the boiler for the production of steam. The purpose of the debarking is to reduce the minerals in the black granules (located mainly in the bark) and to extract the least calorific fraction of the wood, the bark, to generate more energetic black granules. In addition, the fact of burning the bark residues in the boiler makes it possible to recover the energy they contain and to increase the overall efficiency of the process by reducing the losses of raw material.

In a particular embodiment, the steam cracked biomass consists of wood and the method according to the invention further comprises:

i) a step of separating the bark from said biomass before steam cracking and ii) a step of burning said bark in said boiler.

It is also possible to introduce into the boiler residual bark and other biomass and co-products that are not very valuable in black granules or coming from another process as a combustible raw material for the production of energy and of condensable water vapor.

Thus, in a particular embodiment, the biomass introduced into the boiler comprises bark.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1: Diagram showing an embodiment of the method according to the invention integrating the recycling of the energy of the co-products.

EXAMPLE

The manufacture of black granules (or black pellet) replaces the grinding-refining used during the manufacture of white granules (or white pellet) by steam cracking which consumes electrical energy and mainly thermal energy from steam. The manufacturing process for manufacturing black granulate produces energy not previously used and which the present process according to the invention makes it possible to use. Indeed, the outgoing product sees the energy of the evaporates (approximately 180 kWh / tonne of black granulate) and bark (approximately 260 kWh / tonne of black granule) recovered in the form of thermal energy, i.e. 440 kWh / tonne of granule. black. In addition, the condensation of the water, brought by the humidity of the bark, as well as that resulting from the combustion of the bark and the evaporates, makes it possible to generate 80 kWh / tonne of black granulate. Finally, the steam cracking, which is a carrier fluid which transfers its sensible heat and retains its latent heat, also generates 290 kWh / tonne of black granulate.

In the end, 810 kWh / tonne of black energy granulate are recovered during the recovery of the evaporates and bark (and 500 kWh / tonne of black granulate for the evaporates alone, specific to the black granulate, without taking into account the recovery of the bark, which can also take place with the white granulate). The energy requirements for the production of black granulate are 830 kWh / tonne of black granulate for drying and 430 kWh / tonne of black granulate for steam cracking, or 1260 kWh / tonne of black granulate.

Thus, the thermal energy needs for the production of black granules are covered at 64% by renewable resources (evaporate co-products and bark) and by thermal integration (combustion and condensation energy, recycling of vapor flows).

In the case of white granules, drying alone (around 830 kWh also) is covered by only 310 kWh of bark recovery, or 37% of thermal energy coverage.

The process for preparing the black granule therefore has an energy saving of 27% compared to that of the white granule, which must use additional exogenous energy resources.

Claims

1. A method of treating solid biomass integrating the energy of the co-products comprising a steam cracking step and characterized in that:

• the volatile organic compounds produced in the steam cracking chamber are injected, along with the steam cracking steam, directly into the combustion chamber of the boiler to produce clean water steam intended for the steam cracking and possibly to another consumer of energy;

• the energy for the production of steam cracking being produced at least in part by the introduction into the combustion chamber of said volatile organic compounds and at least part of the recycled water vapor

and further comprising a step of condensing at least part of the water vapors originating from the steam cracking and resulting from the combustion of the evaporates for drying said biomass before steam cracking.

2. The method of claim 1 wherein the energy for the production of steam cracking steam is also produced by the combustion of an external energy source.

3. Method according to one of claims 1 to 2 wherein said other energy consumer is chosen from an industrialist using steam or an electrician turbining the steam to produce energy.

4. Method according to one of the preceding claims, in which the biomass is a lignocellulosic raw material such as whole wood or wood without bark.

5. Method according to one of the preceding claims wherein said biomass consists of wood and further comprises:

6. Method according to one of the preceding claims wherein said biomass introduced into said boiler comprises bark.