FR3059333A1 - PROCESS FOR PRODUCING PELLETS COMPRISING VAPOR RECOVERY FROM BIOMASS MILLING, ASSOCIATED PLANT - Google Patents

Abstract

The invention relates to a method for producing granules, comprising the following successive steps: a / fine grinding of a wet biomass within a mill, b / recovering the vapors resulting from the milling of the wet biomass, c / condensing the recovered vapors, d / introduce and mix in a pellet press, the particles of biomass ground according to step a / and at least a portion of the condensates from step c /. It also relates to the associated continuous installation.

Description

Technical area

The present invention relates to the general field of the production of granules from a biomass, more particularly lignocellulosic biomass, which is ground.

By "biomass" is meant here and within the framework of the invention, all of the organic materials used for energy or agronomic purposes.

The term “organic matter” means all of the living matter which can be crushed to form granules, whether it is matter of plant origin comprising organic waste from agriculture and forestry: agricultural waste, residues food, wood, roots, leaves ..., organic household or industrial waste, sludge from sewage treatment plants ..., fungi and materials of animal origin (animal manure ...)

The invention relates more particularly to the recovery of vapors from the grinding of wet biomass which leads to the production of a flour or powder from which granules are made.

Although described in relation to the application to a biomass intended to also form biofuel granules, the invention applies to any biomass whose granules which result therefrom can be used for energy purposes (biofuel granules) or agronomic. The granules produced for agronomic purposes can be fertilizer granules, animal food granules.

State of the art

The mechanical treatment of biomass of plant origin containing carbon (tree trunk, straw bales, green waste) conventionally includes a first coarse grinding step, generally at the place of harvest, which in particular facilitates transport and reduce its cost. This first grinding step is carried out using a shredder (English shredder) and leads to particles of centimeter or millimeter dimensions, typically forest chips in the wood industry. It is carried out using mills with proven technology (hammer, knife or scissor mill). The coarsely ground particles thus constitute what are called the inputs of the thermochemical conversion or granulation pathways in order to obtain biofuel granules.

Depending on the desired application, a second mechanical treatment step consecutive to the first, is necessary and consists of fine grinding to give specific properties to the biomass powder. For example, it can be flour or wood powder for the production of biofuels in the form of pellets.

A certain number of studies are devoted to the fine grinding of particles of biomass, in particular of forest chips, to reach particle sizes from millimeter to micron depending on the case. In these studies, the effects of the nature of the biomass, of the type of grinder (s) used, of the desired particle size were characterized on the energy cost of the actual fine grinding operation, and / or the properties of the powder obtained (particle size distribution, shape of the particles).

A new type of fine grinding has recently been implemented: it innovatively combines both grinding and drying of inputs. This process was developed by the Canadian company First American Scientific Corporation. This process is particularly advantageous insofar as it saves the heat energy to be produced compared to a conventional process in which the wet biomass is first dried beforehand, then once dry is ground.

This process as well as the associated mill are described in patent US7481385B2. The grinding as such is carried out by means of metal chains mounted on an axis and which rotate at high speed and thus project by centrifugal force the wet biomass, such as forest chips, on the walls of the mill chamber. The impacts of biomass, such as wood chips, on the walls pulverize them and release heat and water containing residues (dust, tannin, lignin, ...). Under the effect of the heat produced, the water turns into water vapor containing the residues, which is thus mixed with the high air flow which flows through the mill. The crusher can also be equipped at the outlet of the grinding chamber with a particle size classification wheel which makes it possible to select the fine particles having the desired size. The speed of rotation of the classification wheel allows the fineness of the powder to be adjusted.

The essential components of the mill are reproduced in FIG. 1 as disclosed in the aforementioned patent.

This crusher 1 comprises a grinding chamber 10 provided with a supply orifice 12 for wet biomass and air, and with an outlet duct 14 for the crushed biomass. The chamber 10 comprises a lower wall 16, a cylindrical side wall 18 and a set of generally circular covers 20.

A plurality of chains 42 is mounted on a hub 44 which can be rotated in a horizontal plane by a motor 46 via an axis 48. A flywheel can be keyed onto the axis 48 to stabilize the forces exerted by the engine.

Deflector plates 50 and a frustoconical hollow torus 52 are arranged above the chains 42 to confine the wet biomass projected by the chains 42 in rotation.

The outlet duct 14 of the chamber 10 extends towards the upper cylinder of a cyclone separator 22. Thus, the solid biomass particles crushed by bursting against the walls 16, 18, 52 of the chamber 10 are evacuated from it. ci by an air stream and are separated from the air in the cyclone separator 22. The ground particles are substantially drier than they were in the wet biomass at input 12. The solid particles separated from the air inside the separator is collected at the bottom of a cone and is discharged through an exhaust orifice 24.

A fan 30 evacuates the air from the separator to circulate it through a duct 32 to a condenser 34, then in a heating circuit 36 and, finally, to a certain number of ejectors 38 from which the air is injected into the grinding chamber. This air circulates through the chamber then recirculates in the duct 14 where it returns to the cyclone separator 22.

An extraction pipe or vent 40 produced in the cover 20 allows part of the air laden with moisture and containing possible residues to be extracted directly to the atmosphere from inside the grinding chamber 10.

The inventor used such a crusher to produce biofuel pellets from ground particles of extracted wood.

He was thus able to highlight a major drawback which is that significant releases of water vapor, heat and dust are evacuated directly into the open air.

In addition, one of the key parameters to master in the production of biofuels (“pellets”) is the water content.

Thus, a good water content determines whether a granule can be formed in a press provided for this purpose and how the granule can keep its shape afterwards. During the entire granule manufacturing process, therefore, control and adjustment mechanisms are needed to help control the water content. Before the finely ground biomass particles are transformed into granules, they must be humidified again in order to reach the optimum water content for this transformation. There seems to be a consensus on the optimum humidity with a rate between 10% and 15% for wood particles. Outside this range, if the ground particles are too dry in the press, the granules obtained become brittle and the operating state of the press becomes such that it is necessary to carry out more frequent maintenance work with costs. higher related maintenance costs. If the crushed particles are too wet, the press flow decreases as well as the quality of the granules formed.

Intensive use of a pellet press involves significant water consumption.

There is therefore a need to improve the process for manufacturing biofuel granules from biomass, in particular lignocellulosic biomass, in order to overcome the current drawbacks associated with the use of a wet mill and in order to guarantee use. optimal of a pellet press.

In general, there is a need to improve the process for manufacturing all types of granules from a wet raw material which must be ground beforehand, in order to overcome the current drawbacks associated with the use of a wet mill. and to guarantee optimal use of a pellet press.

The object of the invention is to meet this need at least in part.

Statement of the invention

To do this, the invention relates, in one of its aspects, to a process for manufacturing granules, comprising the following successive steps:

a / fine grinding of wet biomass in a grinder, b / recovering the vapors from the grinding of wet biomass, c / condensing the recovered vapors, d / introducing and mixing in a pellet press, the particles of biomass crushed according to step a / and at least part of the condensates from step c /.

The biomass can advantageously be lignocellulosic biomass constituted by forest chips, or green waste having possibly undergone a pre-grinding. The forest chips can advantageously be of the M40 type, with a humidity rate of less than 40%, or of green waste, obtained by prior grinding of the M65 type. In general, when the granules are intended for energy purposes, it can be any type of bio-resource which can be transformed into the form of biofuel granules.

Preferably, the moisture content of the material introduced into the press, obtained by the condensates, is between 5 and 25%, preferably between 10 and 20%, preferably around 15%. It is specified here that this humidity rate is a mass percentage and that it is equal to the ratio between the difference in mass of wet wood and that of dry wood over the mass of wet wood, multiplied by 100.

According to an advantageous embodiment, the method can also comprise a step c1 / of recovering the latent heat from the vapors.

The step cl / is advantageously carried out by means of an air exchanger, the heated air being injected at the inlet of the crusher implementing the step a /.

The temperature of the air entering the exchanger can be ambient temperature, while the temperature of the heated air injected at the inlet of the mill is between 40 and 50 ° C.

Thus, according to this mode, the latent heat from the grinding is advantageously recovered during this condensation step, in order to preheat the bio resource at the input of the mill. Thus, the temperature of the air entering the mill can be increased, which favors its operation because the hot air can absorb more humidity, and therefore the user can inject even more humid resources, typically resources to 40-50% humidity like green waste from recycling centers.

An energy gain is thus obtained in the operation of the mill.

According to an advantageous variant, step d / can be carried out with the addition of an additional binder, preferably containing lignin.

The following temperature ranges are advantageous:

- temperature inside the mill higher than 100 ° C.

- temperature of the vapors at the outlet of the grinding of the wet biomass between 70 and 90 ° C.

- temperature of the condensates introduced into the pellet press being between 30 and 60 ° C.

According to another of its aspects, the invention also relates to a continuous granule manufacturing installation comprising:

- A wet biomass grinder, comprising a wet biomass supply orifice, at least one orifice for extracting the vapors from the grinding of the wet biomass, and an orifice for discharging the crushed biomass particles;

- an air exchanger forming a condenser, a first circuit of which is an ambient air circulation circuit, a second circuit is the circuit of circulation of the vapors extracted from the grinder;

- a pellet press comprising a condensate supply port connected to the second condenser circuit and a supply port of crushed biomass particles connected to the discharge port of the crusher.

According to an advantageous variant, the first condenser circuit is connected to the air supply orifice of the mill.

Thus the invention essentially consists in recovering the vapors extracted during the operation of grinding the biomass (wood or other bio-resources or other biomass) and in forcing their condensation, then in recovering and injecting the condensates within a pellet press to make biofuel pellets or for agronomic purposes (fertilizer pellets, feed pellets for animals).

The condensates recovered at the condenser outlet, which are composed of hot water containing residues (dust, tannin, lignin, ...) advantageously serve as additives to the crushed biomass particles.

The reuse of hot condensates according to the invention can lead to savings in terms of energy and water consumption of a global installation for the production of biofuel pellets.

Indeed, the production of good quality pellets, more particularly biofuels, requires a number of conditions and may require the addition of water (liquid or vapor).

By injecting the condensates from the vapors extracted from the grinding directly into the pellet press, one can dispense with any additional water supply.

In other words, thanks to the invention, the humidity necessary for the production of granules is brought directly from the upstream stage of wet grinding of the biomass, which amounts to not consuming additional water.

In addition, the addition of condensates makes it possible to dispense with any chemical additive or binder usually required in pellet presses.

These binders (or pressing aids) are additives that are incorporated at a low rate, typically 0.5 to 2.5%, for the sole purpose of increasing the yield of the presses and the cohesion of the granules. These substances can be of organic or mineral origin. Among organic substances, lignosulfites are by-products of the paper industry, including organic compounds extracted from wood (lignin).

There are laboratory tests which make it possible to assess the binding or lubricating ability of these pressing aids, depending mainly on the humidity and the type of raw material: [1], Pilot-scale tests generally show an influence positive of the addition of lignosulfites on the mechanical properties of the agglomerates and a tendency towards a reduction in the energy consumed by the press in the case of mixtures rich in cereals and / or in starch. The extremely reliable formulation of lignosulfites ensures high quality pulverization of the ground particles.

However, as mentioned above, the vapors extracted from the grinding contain residues which contain lignosulfites.

Thus, the injection into a pellet press, of condensates from the vapors extracted from the grinding not only has the advantage of allowing the absence of water supply from outside the grinding process but also it allows 'bring in the content of its residues lignosulfites which are very suitable for obtaining the properties sought by the granules.

Furthermore, the recovery and condensation of the vapors extracted from the grinding process prevents their release into the open air.

In view of the processes and installations of the state of the art, recover the vapors extracted from a wet grinding, condense them then inject the condensates, mixture of water vapor, lignocellulosic compounds, dust, in a pellet press is far from obvious to a person skilled in the art.

Indeed, it emerges from the state of the art as a whole, that a person skilled in the art necessarily tends to reject these vapors to the open air, because he considers that the dust which they contain has a systematic tendency to settle and form harmful plugs at the outlet of the mill.

detailed description

Other advantages and characteristics of the invention will emerge more clearly on reading the detailed description of examples of implementation of the invention made by way of illustration and not limitation with reference to the following figures, among which:

- Figure 1 is a schematic view of a wet biomass crusher according to patent US7481385B2;

- Figure 2 is a schematic representation of an installation for manufacturing biofuel pellets comprising a grinder according to Figure 1 and a pellet press.

A wet biomass crusher 1 according to the state of the art and according to the invention includes the numerical references to designate the same elements.

It is specified that the terms “upstream”, “downstream”, “inlet”, “outlet” used with reference to FIGS. 1 and 2 are to be considered with respect to the direction of circulation of the ligno-cellulosic biomass in a crusher and an installation for the continuous production of biofuel granules according to the invention.

Figure 1 has already been described in detail in the preamble. It will therefore not be commented on below.

The inventors have thought of creating a continuous production facility for biofuel pellets, using a wet biomass crusher and a pellet press whose water it needs to carry out the granulation is brought directly by the condensates of the vapors extracted from the grinding process. .

The installation according to the invention therefore comprises a wet crusher 1, such as that described with reference to FIG. 1 and a pellet press 7. It is specified that in the illustrated embodiment, the crusher 1 incorporates a classification wheel which largely allows to select alone the particle size of the crushed biomass particles so that they have dimensions suitable for their granulation by a pellet press. In other words, the classification wheel which can moreover be arranged in the grinder 1, between the input of the biomass and the grinding part proper, makes it possible to select the fine particles having the desired size in order to obtain granulation by the after. The speed of rotation of the classification wheel thus makes it possible to adjust the fineness of the particles crushed at the outlet of the mill.

As shown in FIG. 2, the discharge port 24 for the particles of biomass crushed in the crusher 1 is connected to the supply port 71 of the pellet press 7.

According to the invention, the installation further comprises an air exchanger 6, which forms a condenser. In the example illustrated, the air exchanger 6 is of the fin type.

One of the circuits 60 is an ambient air circulation circuit. The other of circuits 61 is a circuit for circulation of the vapors extracted from the grinder.

As shown in Figure 2, the vapor circuit is open from the extraction port 40 of the vapors from the grinder 1 to a supply port 70 in condensate of the pellet press.

Thus, when the vapors are passed through the circuit 61 of the air exchanger 6, they are cooled by the ambient air forcedly circulating in the circuit 60. The vapors therefore change phase and condense.

The condensates injected through port 70 provide all the water necessary for producing the granules. The humidity level at this entry 70 is controlled to be between 10 and 15%.

Furthermore, the circuit 60 of the condenser 6 is connected to the air supply port 12 for the mill.

Thus, the ambient air circulating in the circuit 60, which is heated by heat exchange with the vapors circulating in the circuit 61, comes directly to preheat the inlet air of the mill 1. Preferably, the temperature at the inlet of the mill is between 40 and 50 ° C.

With this heating of air by the own vapors from the grinding, we recover and use a significant energy, in the form of latent heat, within the grinder 1. Consequently, we reduce the energy consumption of the grinder 1 compared to l 'state of the art where the vapors extracted from wet grinding are directly released into the atmosphere.

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Other variants and advantages of the invention can be achieved without departing from the scope of the invention.

The wet mill used may or may not include a means of classifying the ground particles making it possible to obtain granules in the pellet press. Thus, depending on the type of shredder and / or the nature of the biomass entering the wet shredder, it is necessary to perform a classification or not to obtain the correct particle size. If the grinding as such gives ground particles to dimensions all compatible with the downstream pellet press, no classification as such is necessary.

The invention is not limited to the examples which have just been described; one can in particular combine together characteristics of the examples illustrated within variants not illustrated.

References cited [1]: Melcion, J.P. (1995). "Use of binders for the pressing of animal feed: technological and nutritional aspects. "Productions Animales, 8 (2), 83-96.

Claims (12)

1. Method for manufacturing granules, comprising the following successive steps: a / fine grinding of wet biomass in a grinder, b / recovering the vapors from the grinding of wet biomass, c / condensing the recovered vapors, d / introducing and mixing in a pellet press, the particles of biomass crushed according to step a / and at least part of the condensates from step c /. 2. Method according to claim 1, the wet biomass being constituted by forest chips or green waste having possibly undergone a pre-grinding, the granules obtained at the end of step d / being biofuel granules. 3. Method according to claim 1 or 2, the moisture content of the material introduced into the press, obtained by condensing, being between 5 and 25%, preferably between 10 and 20%, preferably of the order 15%. 4. Method according to one of the preceding claims, further comprising a step cl / recovery of latent heat from the vapors. 5. Method according to claim 4, step c1 / being carried out by means of an air exchanger, the heated air being injected at the inlet of the mill implementing step a /. 6. The method of claim 5, the temperature of the air entering the exchanger being ambient temperature, while the temperature of the heated air injected into the mill is between 40 and 50 ° C. 7. Method according to one of the preceding claims, step d / being carried out with the addition of an additional binder, preferably containing lignin. 8. Method according to one of the preceding claims, the temperature within the mill being greater than 100 ° C. 9. Method according to one of the preceding claims, the temperature of the vapors at the outlet of the grinding of the wet biomass being between 70 and 90 ° C. 10. Method according to one of the preceding claims, the temperature of the condensates introduced into the pellet press being between 30 and 60 ° C. 11. Continuous granule manufacturing plant comprising: - a wet biomass grinder (1), comprising a supply port (12) for wet biomass, at least one extraction port (40) for the vapors resulting from the grinding of wet biomass, and a discharge port ( 24) crushed biomass particles; 5 - an air exchanger (6) forming a condenser, a first circuit (60) of which is an ambient air circulation circuit a second circuit (61) is the circuit for circulation of the vapors extracted from the mill; - a pellet press (7), comprising a condensate supply orifice (70) connected to the second condenser circuit and a supply orifice (71) in 10 particles of crushed biomass connected to the discharge port of the shredder. 12. Installation according to claim 11, the first condenser circuit being connected to the air supply orifice (12) of the mill. 1/2