Process for separating salts from biomass

Abstract

Method for separating salts from biomass. This description relates to a salt separator (100) for separating salts from a carbonaceous material comprising: - a chamber including a side wall (101), a lid (102) and a bottom (103), delimiting an inner chamber (105), - a precipitation structure (140), for example rough, alveolar, particulate, perforated or porous, positioned in the inner chamber (105), on which, when biomass is injected into the inner chamber (105), the salts contained in the biomass precipitate, - an ultrasonic probe (120), positioned in the inner chamber (105) or outside the chamber against the side wall (101), the bottom (103) or the lid (102), configured to detach the salts precipitated on the precipitation structure (140) when it emits ultrasound,- heating means (130) configured to heat at least the precipitation structure (140) to a temperature above 374°C. Figure for the abstract: Fig. 1,

Description

Title of the invention: Process for separating salts from biomass. Technical field

[0001] The present description relates in general to the field of energy recovery from biomass.

[0002] The invention relates to a method for separating salts contained in biomass. The invention also relates to a salt separator. The invention is particularly interesting because it allows for the easy separation of inorganic salts from organic matter containing them, for example, biomass, thereby increasing gasification yields and reducing fouling.

[0003] The invention has applications in many industrial fields, and in particular for the recovery of waste from the paper industry such as black liquor but also for the recovery of sludge from wastewater treatment plants. Previous technique

[0004] Hydrothermal gasification (or supercritical water gasification) is a thermochemical process for producing renewable gas from wet organic matter. Wet organic matter has a dry matter content of between 5 and 20% by mass, or even up to 50% by mass. Wet organic matter can originate, for example, from agri-food industry waste, industrial effluents such as black liquor, non-spreadable digestate from methanization, and sewage sludge.

[0005] By placing itself under supercritical conditions (temperature above 374°C and pressure above 221 bar), the medium is very reactive and leads to the obtaining of excellent rates of conversion of carbon from biomass into biogas (around 70-90%).

[0006] The process generates a high energy synthesis gas, composed of a mixture rich in methane, hydrogen, carbon dioxide, and other light hydrocarbons.

[0007] One of the major limitations of this type of process is salt precipitation. Indeed, in the vicinity of the critical point, the properties of water change (a significant decrease in density and dielectric constant, among other things). Under these conditions, the atoms of the inorganic components that could be dissolved / transported in the water below the critical point are no longer so. Thus, the evolution of the dielectric constant and the ionic product of water in the supercritical state leads to the precipitation of the salts contained in the resource.

[0008] The salts precipitate and then agglomerate on the hot surfaces, causing blockages in the reactors. Managing the precipitation and its location is a key element for the development of hydrothermal gasification.

[0009] This phenomenon of salt precipitation in solid or liquid form can lead to reactor blockages and cause intermittent process shutdowns. It is essential to avoid such phenomena, which not only hinder the proper functioning of the installation but also risk damaging it.

[0010] To prevent the risk of clogging during the hydrothermal gasification process, some solutions have already been proposed.

[0011] For example, a vertical scraper can be used to separate the salt that has precipitated on the hot inner walls of the reactor, as shown, for example, in document WO 2024 / 008691 AL. The vertical movement scrapes the precipitated salt and causes it to fall by gravity to the bottom of the reactor in the cold zone, where it is then removed. However, integrating moving mechanical parts into a reactor is complex in terms of maintenance, sealing, and durability.

[0012] It is also possible to use a deformable porous structure as described in document WO 2024 / 008757 AL. When heated by its environment, the salts precipitate on its surface. Successive stresses on this heated porous structure allow the salts to be evacuated by gravity to the bottom of the reactor in the cold zone. They can then be removed. However, as before, it is necessary to integrate a moving mechanical part inside a reactor. Furthermore, the parts often need to be coupled to a motor, which poses problems of high-pressure and high-temperature sealing, as well as maintenance, wear, and cost. Summary of the invention

[0013] There is a need for a process that allows for the efficient separation of inorganic salts from an organic material containing them, while avoiding clogging problems, the process having to be able to be used sustainably over time.

[0014] This goal is achieved by a process for separating inorganic salts from biomass comprising an organic part and inorganic salts, the process comprising the following steps: a) provide a salt separator comprising: - an enclosure comprising a side wall, a lid and a base, delimiting an inner chamber, - a precipitation structure being positioned in the inner chamber of the enclosure, - heating means arranged and configured to heat at least the precipitation structure to a temperature above 374 °C, - an ultrasonic probe, positioned either inside the inner chamber or outside the enclosure against the side wall, lid or bottom, b) bringing the biomass and the precipitation structure heated to a temperature above 374°C into contact in the inner chamber of the enclosure, at a pressure exceeding 22.1 MPa, thereby causing the organic part of the biomass to be at least partially gasified, in the form of an organic effluent, and the inorganic salts to precipitate on the precipitation structure, c) apply ultrasound, so as to detach the inorganic salts from the precipitation structure and cause them to fall to the bottom of the inner chamber, the bottom being at a temperature below 374°C, thereby dissolving the inorganic salts at the bottom of the inner chamber.

[0015] According to a particular embodiment, the ultrasonic probe is positioned within the precipitation structure.

[0016] According to one embodiment, the ultrasonic probe is positioned outside the enclosure, against the side wall.

[0017] According to one embodiment, the ultrasound has a frequency between 25 and 40 kHz.

[0018] According to one embodiment, the precipitation structure is a rough, alveolar, particulate, perforated or porous structure.

[0019] According to one embodiment, the pressure in the inner chamber of the enclosure is between 250 and 300 bars.

[0020] This objective is also achieved by a salt separator for separating salts from a carbonaceous material containing them, the salt separator comprising: - an enclosure comprising a side wall, a lid and a bottom, delimiting an inner chamber that can be subjected to a pressure exceeding 22.1 MPa, - a precipitation structure, positioned in the inner chamber of the enclosure, onto which, when the solution is injected into the inner chamber, the salts contained in the solution precipitate on its surface, - an ultrasonic probe, positioned either inside the inner chamber or outside the enclosure against the side wall, lid or bottom, and capable of detaching the salts precipitated on the precipitation structure when it emits ultrasound, - heating means configured to heat at least the precipitation structure to a temperature above 374°C.

[0021] According to a particular embodiment, the precipitation structure is made of stainless steel, for example 3161 or 304L stainless steel, a nickel-chromium alloy, aluminum or ceramic.

[0022] According to a particular embodiment, the precipitation structure is a rough, alveolar, particulate, perforated or porous structure.

[0023] According to a particular embodiment, the precipitation structure is a foam, a bed of beads, a perforated sheet, a rough tube or a grid, the precipitation structure being able to be arranged on a grid.

[0024] According to a particular embodiment, the precipitation structure corresponds to a rough part of the side wall of the inner chamber.

[0025] This objective is also achieved by a biomass gasification plant comprising: - a salt separator as defined previously, - a gasification reactor connected to the salt separator to be supplied with biomass free of inorganic salts.

[0026] This goal is also achieved by a biomass gasification process comprising the following steps: - provide an installation as defined above, - to implement the process of separating inorganic salts from biomass comprising an organic component and inorganic salts, as defined previously, in the salt separator, - gasify the biomass devoid of inorganic salts in the gasification reactor. Brief description of the drawings

[0027] These features and advantages, as well as others, will be described in detail in the following description of particular embodiments, given by way of non-limiting example, in relation to the accompanying figures, among which:

[0028] Fig. 1 and Fig. 2 represent, schematically and in cross-section, a salt separator according to different particular embodiments of the invention;

[0029] [Fig.3] represents, schematically and in cross-section, a biomass gasification installation comprising a salt separator according to another particular embodiment of the invention.

[0030] The different elements are not necessarily represented at a uniform scale to make the figures more legible. Description of the implementation methods

[0031] The same elements have been designated by the same reference numerals in the different figures. In particular, the structural and / or functional elements common to the different embodiments may have the same reference numerals and may have identical structural, dimensional and material properties.

[0032] For the sake of clarity, only the steps and elements useful for understanding the described embodiments have been represented and are detailed.

[0033] Unless otherwise specified, when referring to two elements connected together, this means directly connected without intermediate elements other than conductors, and when referring to two elements connected (in English "coupled") together, this means that these two elements can be connected or linked through one or more other elements.

[0034] In the following description, when reference is made to absolute positional qualifiers, such as the terms "top", "bottom", etc., or relative positional qualifiers, such as the terms "above", "below", "superior", "inferior", etc., or to orientational qualifiers, such as the terms "horizontal", "vertical", etc., reference is made, unless otherwise specified, to the orientation of the figures.

[0035] Unless otherwise specified, the expressions "approximately", "roughly", and "on the order of" mean at 10%, preferably at 5%.

[0036] By between X and Y, we mean that the bounds X and Y are included.

[0037] By critical point of water, we mean a temperature above 374 °C and a pressure above 221 bars (i.e. 22.1 MPa).

[0038] Biomass is defined as any inhomogeneous material of biological origin, which may be almost dry, such as sawmill residues or straw, or waterlogged, such as household waste. Advantageously, biomass has a moisture content greater than 50%. It may consist of algae (microalgae or macroalgae, for example), agricultural waste (oilseed cake, tree-top waste, etc.) or industrial waste (from the paper industry in particular, black liquor, for example), digestates from methanization, household waste, sludge from wastewater treatment plants, or wastewater.

[0039] Subsequently, biomass refers to any type of natural, industrial or household waste containing a valuable organic part and an inorganic part.

[0040] Biomass contains a significant amount of inorganic matter, typically between 1 and 10% by mass (relative to the raw biomass). The term "between X and Y" hereinafter refers to the inclusion of these limits. The inorganic portion of the biomass may consist of sodium carbonate salts and / or calcium carbonate salts and / or potassium carbonate salts. It may also include, particularly when the biomass is sewage sludge, one or more of the following metals: copper, iron, manganese, magnesium, nickel, lead, titanium, zinc, and silicon.

[0041] Inorganic salts are separated from the organic matter contained in the biomass by means of a salt separator 100 containing a precipitation structure on which the inorganic salts will precipitate.

[0042] The conditions for implementing the separation are close to the critical point of water: the system operates at a pressure higher than the critical pressure of water (for example between 222 bars and 360 bars) and at a temperature above the critical temperature of water (for example above 400°C and preferably above 420°C).

[0043] We will now describe the salt separator 100 in more detail with reference to [Fig.1] and [Fig.2].

[0044] The salt separator 100 includes an enclosure delimiting an inner chamber 105.

[0045] The enclosure includes a side wall 101, a cover 102 and a bottom 103.

[0046] The enclosure can be single-sided wall 101 or double-sided wall 101.

[0047] The enclosure is advantageously made of a material suitable for the operating conditions of temperature and pressure. It can be made of Inconel®, stainless steel or other materials.

[0048] The side wall 101 or the lid 102 is pierced by a first orifice 111 to allow the injection of a solution containing the biomass. The solution is injected into the separator chamber, for example, through a tube, such as an injection lance, capable of reaching the interior of the chamber 105.

[0049] The side wall 101 or the cover 102 is pierced with a second outlet 112 through which the effluents of carbonaceous matter devoid of inorganic salts are intended to be discharged.

[0050] The side wall 101 or the bottom 103 is pierced by a third outlet 113 through which the precipitated salts are intended to be discharged in the form of brine or in solid form. The flow of the salt-depleted solution is discharged through the outlet 113.

[0051] Evacuation is preferably carried out by means of a fluid that drains the precipitated or redissolved salts. The side wall 101 or the bottom 103 may have a fourth injection port 114 through which the draining fluid is intended to be injected. The draining fluid may be water, a solvent, or a carrier gas. The draining fluid is advantageously injected at a temperature between 300°C and 1000°C, for example 300°C, and at a pressure between 222 bar and 1000 bar, for example 250 bar.

[0052] According to an advantageous configuration, the outlet 113 of the salts precipitated in the form of brine is arranged below the fourth injection orifice 114, so that the salts can be discharged by gravity drainage in the form of brine through this outlet 114 made in the lower part of the separator 100.

[0053] A precipitation structure 140 is positioned in the inner chamber 105 of the enclosure. It serves as a support during the precipitation of the salts.

[0054] The precipitation structure 140 is a structure having a large surface area.

[0055] The precipitation structure 140 can correspond to a rough part of the inner surface of the enclosure. The rough part can be positioned at the level of the side wall 101 of the inner chamber 105.

[0056] The precipitation structure 140 can be an element, for example a tube, positioned in the inner chamber 105 and having a rough surface.

[0057] A rough surface is defined as a surface with numerous irregularities. A rough surface has, for example, a roughness Ra (arithmetic mean roughness) greater than or equal to 1.6 pm. The Ra value indicates the average roughness of the surface over the length of the measurement taken, that is, the average difference between the peaks and troughs. This roughness is found in ISO 4287.

[0058] Such a surface is more susceptible to friction, as it offers resistance to the movement of objects on the surface. Salts can then more easily become trapped in the surface's crevices.

[0059] According to other embodiments, the precipitation structure 140 can be a grid, a perforated sheet or plate, a foam, a bed of beads, a honeycomb material or an open-pore porous material.

[0060] The perforated sheet metal can have a thickness of between 1 and 2 mm.

[0061] A foam advantageously has an essentially open porosity, which makes it accessible and allows a high capacity for retaining precipitated salts.

[0062] The open porosity of the pores of the structure defines a very large surface area for the deposition / precipitation of salts.

[0063] The structure preferably has channels within it allowing the circulation of the supercritical fluid. The channels have, for example, a diameter of more than 5 mm.

[0064] Such precipitation structures 140 increase the contact surface area for better salt distribution, while preventing the formation of salt accumulations that are more difficult to separate / crumble later. Such precipitation structures can be manufactured by 3D printing.

[0065] The precipitation structure 140 may or may not be coated with a catalytic coating.

[0066] The precipitation structure 140 can be made of stainless steel, for example 3161 or 304L stainless steel, a nickel-chromium alloy (for example Inconel®), aluminum, or ceramic. Advantageously, a metallic material that resists the corrosive environment at high temperatures (between 400°C and 500°C, or even 600°C) is chosen.

[0067] When the biomass solution is injected into the enclosure of the salt separator 100, the salts contained in the solution precipitate on the surface of the precipitation structure 140.

[0068] The precipitation structure 140 can be arranged on a grid 150 arranged in the inner chamber 105 of the enclosure.

[0069] The grid 150 is preferably positioned above the third outlet orifice 113. The fourth outlet orifice 114 can be positioned below the grid 150, at the level of the grid 150, or at the level of the precipitation structure 140.

[0070] The separator 100 further includes an ultrasonic probe 120. The ultrasonic probe 120 can be positioned inside the inner chamber 105 or outside the inner chamber 105, for example against the side wall 101, the lid 102, or the bottom 103. When the ultrasonic probe 120 is activated, the precipitated salts present on the surface of the precipitation structure 140 are detached. The ultrasound also cleans the precipitation structure 140 by removing any precipitated particles and / or salts.

[0071] The separator 100 also includes heating means 130 for heating the inner chamber 105 of the enclosure.

[0072] Several embodiments can be implemented to heat the solution. The following embodiments can be used alone or in combination with each other: - heating devices 130 arranged around the side wall of the enclosure, - heating elements placed within the thickness of the side wall of the enclosure, - a heat transfer fluid circuit made within the thickness of the side wall of the enclosure.

[0073] Three temperatures coexist within chamber 105: - a first temperature Tl at the level of the precipitation structure 140, - a second temperature T2 in the lower part of the inner chamber 105 (i.e. on the bottom side 103 of the enclosure), - a third temperature T3 in the upper part of the inner chamber 105 (i.e. on the side of the lid 102 of the enclosure).

[0074] The temperatures are such that T2 < T1 and T3 <TL

[0075] Tl is greater than or equal to the precipitation temperature of the salts (typically greater than 374°C) and less than 1000°C, preferably less than 600°C. For example, the temperature is 400°C.

[0076] The precipitation structure 140 is thus heated via the side wall 101 of the enclosure to a temperature between 300°C and 1000°C, for example 400°C. The inorganic salts contained in the solution are trapped / precipitated upon contact with the heated precipitation structure 140.

[0077] T2 and T3 are below 374°C. The salts therefore precipitate only on the precipitation structure 140.

[0078] Preferably, the operating pressure of the enclosure is between 221 bars (22.1 MPa) and 1000 bars (100 MPa).

[0079] The method of operating a salt separator 100 as described above comprises the following successive steps: a) providing a salt separator 100 as described above, b) injecting a solution through the first injection port 111 and heating the enclosure so that, in the inner chamber 105, the precipitation structure 140 is at a temperature greater than or equal to the critical temperature of water, whereby the salts precipitate on the precipitation structure 140, c) starting the ultrasonic probe 120, the ultrasound enabling the salts to be detached from the precipitation structure 140, d) removing the salts in the form of a brine or in solid form, for example by injecting a draining fluid through the fourth port 114 to drain the precipitated salts detached from the structure 140 towards the outlet port 113.

[0080] In step b), the separator 100 is heated and the wet biomass is injected into the inner chamber 105. The upper part of the chamber 105 can be at a temperature T3, typically at 300°C, and at a pressure above the critical pressure, exceeding 222 bar. The precipitation structure 140 is at a temperature T1 above 374°C, for example, 420°C.

[0081] The salts contained in the biomass then precipitate on the precipitation surface 140. The salt-free biomass effluents are discharged from the enclosure through the outlet 112. The effluents can then be gasified.

[0082] The biomass injection can be stopped.

[0083] The ultrasonic probe 120 is then switched on. These ultrasonic stimuli will cause a cavitation effect on the precipitation structure 140 and cause the detachment (i.e. the separation) of the salts previously precipitated in the structure 140. The ultrasounds have, for example, a frequency between 25 and 40 kHz.

[0084] The reactor and precipitation structure 140, as well as the ultrasonic probe 120, are dimensioned and chosen so that the maximum amount of salts precipitate on the precipitation structure 140 and, when the ultrasound is switched on, the precipitated salts detach from the structure 140 and fall by gravity to the bottom of the inner chamber 105 of the reactor 100.

[0085] It is then possible to inject a draining fluid, preferably water, through the injection port 114 to drain the precipitated salts, detached in solid or brine form, towards the outlet port 113. The lower part of the reactor's inner chamber 105 (i.e., the part below the precipitation structure 140) is at a temperature T2 lower than the critical temperature of water. The salts are thus dissolved and removed more easily.

[0086] The inner chamber 105 of the reactor is at the same pressure.

[0087] The inorganic salts recovered at the outlet of separator 100 can be used. In particular, when the inorganic salts, containing phosphorus, potassium, calcium, nitrogen or a mixture thereof, can be used as fertilizer.

[0088] The reactor is particularly interesting for use in a biomass gasification plant.

[0089] The separator 100 can be used upstream of a hydrothermal gasification step to prevent clogging problems in the gasification reactor. Alternatively, it can be used for both the salt separation step and the gasification step.

[0090] For example, as shown in [Fig. 3], the biomass gasification plant comprises: - a 200 biomass tank to supply the 100 salt separator, the biomass being able to be preheated, - a salt separator 100 as described previously, - a gasification reactor 300 connected to the salt separator 100 to be fed with salt-free biomass, - a high pressure separator 400 connected downstream of the salt separator 100 to separate the salts precipitated in solid form from the brine water.

[0091] Advantageously, the operating temperature of the gasification reactor is about 600°C and the operating pressure of the gasification reactor is about 300 bars.

[0092] The installation can operate continuously.

[0093] Various embodiments and variations have been described. A person skilled in the art will understand that certain features of these various embodiments and variations could be combined, and other variations will become apparent to a person skilled in the art.

[0094] Finally, the practical implementation of the embodiments and variants described is within the reach of a person skilled in the art, based on the functional indications given above.

Claims

Demands

1. A process for separating inorganic salts from biomass comprising an organic part and inorganic salts, the process comprising the following steps: a) providing a salt separator (100) comprising: - an enclosure comprising a side wall (101), a lid (102) and a bottom (103), delimiting an inner chamber (105), - a precipitation structure (140) being positioned in the inner chamber (105) of the enclosure, - heating means (130) arranged and configured to heat at least the precipitation structure (140) to a temperature above 374 °C, - an ultrasonic probe (120), positioned either in the inner chamber (105) or outside the enclosure against the side wall (101), the lid (102) or the bottom (103), b) bringing into contact in the inner chamber (105) of the enclosure, at a pressure above 22.1 MPa, the biomass and the precipitation structure (140) heated to a temperature above 374°C, whereby the organic part of the biomass is at least partially gasified, in the form of an organic effluent, and the inorganic salts precipitate on the precipitation structure (140), c) apply ultrasound, so as to detach the inorganic salts from the precipitation structure (140) and cause them to fall to the bottom (103) of the inner chamber (105), the bottom (103) being at a temperature below 374°C, whereby the inorganic salts are dissolved at the bottom of the inner chamber (105).

2. Method according to claim 1, wherein the ultrasonic probe (120) is positioned within the precipitation structure (140).

3. Method according to claim 1, wherein the ultrasonic probe (120) is positioned outside the enclosure, against the side wall (101).

4. A method according to any one of the preceding claims, wherein the ultrasound has a frequency between 25 and 40 kHz.

5. A method according to any one of the preceding claims, wherein the precipitation structure (140) is a rough, alveolar, particulate, perforated or porous structure.

6. A method according to any one of the preceding claims, wherein the pressure in the inner chamber (105) of the enclosure is between 250 and 300 bars.

7. A salt separator (100) for separating salts from a carbonaceous material containing them, the salt separator comprising: - a housing including a side wall (101), a lid (102) and a bottom (103), delimiting an inner chamber (105) capable of being pressurized to a pressure greater than 22.1 MPa, - a precipitation structure (140), positioned in the inner chamber (105) of the housing, onto which, when the solution is injected into the inner chamber (105), the salts contained in the solution precipitate, - an ultrasonic probe (120), positioned either in the inner chamber (105) or outside the housing against the side wall (101), the lid (102) or the bottom (103), and capable of detaching the salts precipitated on the precipitation structure (140) when it emits ultrasound, - heating means (130) configured to heat at least the precipitation structure (140) at a temperature above 374°C.

8. Separator according to claim 7, wherein the precipitation structure (140) is made of stainless steel, for example 3161 or 304L stainless steel, a nickel-chromium alloy, aluminum or ceramic.

9. Separator according to any one of claims 7 and 8, wherein the precipitation structure (140) is a rough, alveolar, particulate, perforated or porous structure.

10. Separator according to any one of claims 7 to 9, wherein the precipitation structure (140) is a foam, a bed of beads, a perforated sheet, a rough tube or a grid, the precipitation structure (140) being able to be arranged on a grid (150).

11. Separator according to any one of claims 7 to 9, wherein the precipitation structure (140) corresponds to a rough part of the side wall (101) of the inner chamber (105).

12. Biomass gasification plant comprising: - a salt separator (100) as defined in any one of claims 7 to 11, - a gasification reactor (300) connected to the salt separator (100) to be supplied with biomass free of inorganic salts.

13. A process for gasifying biomass comprising the following steps: - providing an installation as defined in claim 12, - carrying out the process for separating inorganic salts from biomass comprising an organic part and inorganic salts, according to any one of claims 1 to 6, in the salt separator (100), - gasifying the biomass devoid of inorganic salts in the gasification reactor (300).

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