A method for producing high-density, roasted biomass particles.

Abstract

A method for producing high-density and roasted biomass particles is disclosed. The method includes at least: a roasting step of roasting particulate biomass material under roasting conditions; a densification step of densifying the roasted particulate biomass material from the roasting step to obtain high-density and roasted biomass particles; and a post-heat treatment step of heat-treating the density and roasted biomass material particles from the densification step under roasting conditions. The post-heat treatment step improves the durability of the high-density and roasted biomass particles.

Description

[Technical Field]

[0001] The present invention relates to a method for torrefying biomass materials, and particularly to a method for producing densified torrefied biomass particles. [Background Art]

[0002] Technical Background Torrefaction of biomass can be described as a mild form of pyrolysis under low-oxygen conditions, typically at torrefaction temperatures ranging from a low temperature such as 180 to 200°C up to 340°C or even higher. Biomass subjected to torrefaction is converted into a hydrophobic, decay-resistant material that can be used for various applications, such as fuel for combustion or gasification. During torrefaction, moisture and light volatile substances are removed from the biomass material, while biopolymers including cellulose, hemicellulose and lignin are partially decomposed, thereby forming additional volatile substances. Accordingly, torrefaction involves mass loss and chemical energy loss with respect to the solid material. Torrefaction is often combined with densification, such as pelletization or briquetting, to increase energy density and hydrophobic properties. Densified torrefied biomass is more convenient to handle and transport than the original biomass from which it is derived.

[0003] Production of densified torrefied products is generally carried out according to one of the following processes. In one such process, biomass is torrefied, and subsequently the torrefied biomass is densified. In another process, the received biomass is densified, and thereafter the densified biomass is subjected to torrefaction. Hybrid processes are also known from the patent literature.

[0004] For example, US2020 / 0181516A1 discloses a method for producing a water-resistant compressed biomass product. This known method includes: sizing and optionally milling roasted biomass to provide particulate matter having an average particle size typically of 0.1–5 mm; adjusting the moisture content of the particulate matter by adding water to provide humidified biomass having an average moisture content typically of 5–15% by weight, based on the total mass of roasted biomass and the water present; adjusting the temperature of the humidified biomass to have an average bulk temperature of at least 80°C, typically in the range of 80–140°C; compressing the humidified and finely crushed roasted biomass to provide compressed biomass having a density typically of 1.0–1.4 g / cm³; reheating the compressed biomass to a temperature higher than 120°C, typically in the range of 120–230°C, for a period of at least 5 minutes, typically about 30–60 minutes; and cooling the biomass to ambient temperature.

[0005] EP4186589A1 discloses a plant and method for producing hydrophobic biomass granules, which includes pelletizing biomass at a first predetermined temperature T1 to obtain biomass granules, placing the biomass in an oven at the first temperature T1, roasting the biomass granules in the oven at a second temperature T2 while simultaneously transporting them to achieve a predetermined residence time, and discharging the biomass granules thus processed.

[0006] US2016 / 244686A1 discloses a method and system for forming densified lignocellulose biomass. In one embodiment, lignocellulose biomass is roasted, and then the roasted lignocellulose biomass is fed into a compression die, where it is densified and extruded. Following compression, the lignocellulose biomass can be maintained under high temperature and pressure conditions for a certain period of time, for example, by transport through a series of extension dies directly downstream of the compression die. Water can be added to the compression die to improve the lubrication of the densified lignocellulose. The densified lignocellulose can then be cooled under pressure to a temperature below the Tg of lignin in the biomass. A disadvantage of simultaneous roasting and densification is that severe defoliation occurs (PCA Bergman, Combined torrefaction and pelletisation The TOP process (July 2005)).

[0007] When densely packed biomass, such as pellets, is roasted under high pressure, the resulting gases will remain in the gaps within the densely packed biomass. When the pressure is released, these gases escape from the pellets, causing them to burst and crack, which degrades the quality of the pellets, including their integrity and strength.

[0008] Furthermore, the addition of water for lubrication is thought to degrade the efficiency of roasting due to its hydrolysis instead of the desired repolymerization of hydrocarbons.

[0009] Hydrophobicity is an important characteristic of roasted biomass products, which improves during roasting and densification compared to untreated biomass. However, this hydrophobic property is limited. This is significant when roasted biomass products are stored in humid environments, for example, outdoors where they are exposed to typical weather conditions. This exposure to moisture, such as (rain)water, can cause damage to the roasted biomass products and their disintegration, for example, during storage and, for the most part, during handling and transport, resulting in the formation of dust and particulate matter, and thus the loss of biomass material. In fact, roasted biomass products may still possess some hydrophilic properties, absorbing water and thereby reducing their energy density. Also, upon exposure to water, some organic compounds may leach from the roasted product to some extent and, accompanied by (rain)water, pose a potential environmental hazard.

[0010] The present invention aims to produce roasted biomass products that at least partially reduce the above disadvantages. More specifically, an object of the present invention is to improve the durability of high-density roasted products. Another object is to improve water resistance with low water absorption. [Overview of the project]

[0011] Brief description of the invention According to the invention, a method for producing high-density, roasted biomass particles is: A roasting process in which particulate biomass material is roasted under roasting conditions; A densification step to increase the density of the roasted particulate biomass material from the roasting step to obtain high-density roasted biomass particles; and A post-heat treatment process in which the densified and roasted biomass particles from the densification process are heat-treated under roasting conditions, typically at atmospheric pressure. Includes.

[0012] In the method according to the invention, the biomass material is optionally subjected to a pre-drying step followed by roasting to obtain roasted biomass material. In a subsequent step, the roasted biomass material is typically subjected to a densification step, such as pelletizing or briquetting, after cooling, to obtain densified and roasted biomass particles such as pellets or briquettes. These densified and roasted biomass particles are then again subjected to heat under mild roasting conditions, typically at atmospheric pressure.

[0013] Experimentally, it has been demonstrated that the durability of roasted and densified biomass products (particularly their resistance to disintegration in humid environments) can be improved by additional heat treatment under roasting conditions. [Brief explanation of the drawing]

[0014] The invention is illustrated by the accompanying drawings, and hereby, [Figure 1] Figure 1 is a diagram of one embodiment of the method according to the invention; [Figure 2] Figure 2 is a series of photographs of wood pellets of various origins, with and without post-treatment according to the invention; [Figure 3] Figure 3 is a series of photographs of wood pellets of various origins, with and without post-treatment according to the invention; [Figure 4] Figure 4 is a series of photographs of wood pellets of various origins with and without post-treatment according to the invention; and [Figure 5] Figure 5 schematically shows a system for implementing one embodiment of the invention. [Modes for carrying out the invention]

[0015] Detailed description of the invention The method according to the invention comprises at least three process steps, including a roasting step of a biomass material, a densification step of the roasted biomass material, and a post-heat treatment step of the densified and roasted biomass particles.

[0016] In this technical domain, the term "biomass" should be understood as all organic matter derived from photosynthesis, and may include wood, plants, vegetable oils, green waste, fertilizers, sewage sludge, or any other form of material of an organic nature.

[0017] The received biomass material may contain varying moisture content from batch to batch. Taking this into consideration, in one embodiment, the biomass material is subjected to a drying process, typically under relatively mild conditions, with a dry gas, such as preheated ambient air, to remove water adhering to the outer surface of the biomass, as well as intracellular and intercellular water, using a dryer having, for example, the basic design disclosed in WO2020 / 190135A1. Optionally, after drying, the biomass material subjected to a roasting process typically has a moisture content of up to 15% by weight, preferably 10% by weight or less. The optionally dried biomass material is then roasted under roasting conditions. Typical roasting conditions include roasting temperatures in the range of 180–320°C or even higher. In one embodiment, the roasting temperature is 230–320°C, such as 260–300°C. In one embodiment, the biomass material is kept at the desired roasting temperature for 3–30 minutes. In one embodiment, the biomass material is heated indirectly. Alternatively, the biomass material is heated directly by an inert gas flow, which then heats it indirectly. Optionally, the heat source is exhaust gas from the combustion of volatile gases released during the roasting process. For example, volatile substances released from the biomass material during roasting can be combusted. The combustion exhaust gas can be used to indirectly heat the roasting reactor in which the roasting is carried out. An example of a roasting reactor is a vertical tubular reactor with a screw conveyor configured to transport the biomass material from an inlet for supplying the biomass material to an outlet for discharging the roasted biomass material. Generally, the roasting atmosphere is a low-oxygen (less than 3 volume% O2) atmosphere. A substantially oxygen-free inert atmosphere can also be applied.

[0018] Generally, roasted biomass material from the roasting process is cooled. The end temperature of such a cooling process depends on the characteristics of densification. In one embodiment, the roasted particulate biomass material is cooled from the roasting exit temperature to a densification feed temperature of 80°C or higher, preferably 90 or 100°C or higher. In one embodiment, the moisture content of the roasted particulate biomass material when entering the densification process is in the range of up to 12% by weight. Typically, the moisture content will be about 0% when the densification feed temperature is above 100°C. In the densification process, the roasted biomass material is densified, for example, by pelletizing or briquetting, thereby obtaining densified, roasted particulate biomass. The shape of the polymerized and roasted biomass particles can and are not limited. For example, cylindrical pellets may have a length on the order of 10 to 50 mm and a diameter of 4 to 20 mm. In one embodiment, the roasted biomass is extruded under pressure through a plate having at least one, generally more, orifices. During densification, the presence of heavier volatile substances on the roasted biomass material can act as a kind of lubricant. Typically, friction-induced densification will raise the temperature of the roasted biomass to, for example, 130°C or higher. The higher the exit temperature of the densified and roasted biomass particles, the less heat will be supplied to the downstream post-heat treatment process.

[0019] In one embodiment, the method further includes a cooling step for cooling the densified and roasted biomass particles from the densification step. Sometimes, when the densified and roasted biomass particles are left hot from the densification step, they may be fragile and brittle, and may have insufficient mechanical strength to withstand the roasting conditions in the post-heat treatment step, thereby posing a risk of some undesirable collapse. By cooling the densified and roasted biomass particles from the densification step, the mechanical properties of the densified and roasted biomass particles are improved, which allows for subsequent post-heat treatment under roasting conditions without degradation of the biomass particles. The final temperature of this cooling step depends on the sufficient recovery of these mechanical properties. For example, the densified and roasted biomass particles may be cooled to a final cooling temperature of 100°C or less. In one embodiment, cooling to a final temperature of 60°C or less may be required, preferably below 40°C.

[0020] In the post-heat treatment step, the densified and torrefied biomass particles are subjected to an additional heat treatment under mild torrefaction conditions with respect to temperature, such as 235 to 300°C, preferably 240 to 290°C, more preferably 240 to 265°C, at atmospheric pressure, and in a low-oxygen atmosphere (less than 3% by volume of O2), advantageously in the absence of oxygen, for example in an inert nitrogen stream. In one embodiment, the reheating of the densified and torrefied biomass particles is carried out in the apparatus disclosed in WO2020 / 190135A1, followed by a post-heat treatment in a separate apparatus. Typically, the post-treatment step, like all process steps, is carried out on free-flowing, densified and torrefied particulate biomass. Typically, the post-heat treatment is carried out in an indirectly heated reactor similar to the torrefaction reactor described above. Alternatively, the post-treatment can be carried out using direct contact with a heated gas stream. Exhaust gas derived from the combustion of volatile gases released during the torrefaction process can be used as a heat source. Generally, the torrefied and densified biomass material is kept at the post-treatment temperature for a period ranging from 2 to 15 minutes. Typically, the post-treatment conditions are milder than the torrefaction conditions in the torrefaction step preceding the densification step. For example, the post-treatment temperature is lower and / or the residence time is shorter.

[0021] The dispersion of total degassing / mass loss across the roasting and post-heat treatment processes offers the advantage that the densification following roasting is improved and requires less energy, as the amount of carbonization in the roasting process is reduced compared to a process where the same total degassing / mass loss is achieved in a single roasting process before densification. Typically, the total degassing / mass loss based on the dry biomass material supplied to the roasting process ranges from 10-35% to 40%, corresponding to a mass yield of 60% or more, such as 65-90%, based on the dry material supplied to roasting. Typically, the operating window for mass yield in the inventive method ranges from 70-90%, based on the dry starting biomass material. Lower and higher percentages are achievable depending on the required specifications, such as the fixed carbon content of the final pellets, energy balance, and the efficiency of the equipment used. For example, if the starting biomass is wet and the energy required for drying is to be obtained from the combustion of volatile substances and heat exchange with air for drying, more degassing may be required in the case of drier starting materials. The operation of inefficient equipment used may also require additional energy, which may be obtained from the combustion of additionally released volatile substances, thus requiring more degassing. A higher degree of degassing may also be beneficial when the volatile substances can be used for energy production, for example, by burning them to produce steam through heat exchange with a water stream of exhaust gas resulting from combustion.

[0022] In a specific embodiment, the degree of degassing / mass loss in the post-heat treatment step is less than 35% by weight of the total degassing / mass loss, more preferably in the range of 10 to 30% by weight of the total degassing / mass loss, based on the dry biomass material fed to the roasting step. For example, if a desired total mass loss is set at 25%, about 80% thereof (total mass loss of about 20%) can be achieved in the roasting step by setting an appropriate average roasting temperature and residence time for the biomass material, while in the post-heat treatment step, an additional mass loss of 5% by weight (combined loss of about 20%) occurs in the post-heat treatment step through appropriate setting of temperature and residence time. After the post-heat treatment, the biomass particles thus obtained are cooled to ambient temperature for further processing such as storage, transportation, or final application in combustion and / or gasification.

[0023] In one embodiment, the method further comprises recycling condensable volatiles released during the roasting step and / or the post-heat treatment step to the biomass particles.

[0024] In one embodiment, the method further comprises combusting volatiles released during the roasting step and / or the post-heat treatment step.

[0025] In one embodiment, (light) condensable materials volatilized in the drying step before roasting and / or during roasting are advantageously at least partially recycled (other portions can be used for combustion) to the roasted biomass material or to the densified roasted biomass material after any cooling and / or preheating thereof, such that these condensable materials deposit thereon, and repolymerize and densify during the subsequent post-heat treatment step, and devolatilize into the solid component of the roasted biomass, thereby improving the strength and hydrophobicity throughout the densified roasted biomass material. Deposition of the released condensable materials onto particulate biomass is also beneficial for the energy content per unit mass.

[0026] In one embodiment, the released condensable material, or at least a portion thereof, is deposited on the roasted biomass material and acts as a lubricant, which reduces energy consumption during the subsequent densification process.

[0027] The cooling of roasted biomass material can be carried out in two steps. The first step involves quenching with water to a certain temperature, typically above 100°C, to a final biomass temperature, so that the water used is converted to steam and the biomass material does not get wet. This substantially reduces the stickiness of the roasted biomass particles, as well as their adhesion to equipment surfaces and thus contamination. In the second cooling step, the thus quenched biomass particles are cooled using a forced flow of gas, such as air. The forced gas flow also contributes to stopping the roasting reaction, which is thought to stop completely at temperatures below 100°C.

[0028] Detailed description of the drawing Figure 1 shows a process diagram of one embodiment of the method according to the invention, in which the received biomass is dried in a drying step 10, then heated and roasted in a roasting step 20, partially cooled in an optional cooling step 30, densified in a densification step 40, cooled in an optional cooling step 50, reheated and roasted in an additional heat treatment step 60, and finally cooled to the ambient temperature in a final cooling step 70.

[0029] Figure 2 shows, from left to right, 1A: Class A waste wood pellets from the Netherlands, roasted (roasting conditions: 300°C, 4 minutes, conditioning, and 6% moisture content in pellets after pelletizing), after 30 hours of stagnant immersion in water and no post-heat treatment; 2A: Roasted Dutch waste wood Class A pellets, subjected to heat post-treatment (conditions: 250°C, 10 minutes, <1% moisture after post-treatment and cooling) after 30 hours of stagnant immersion in water; roasting conditions: 300°C, 4 minutes, 6% moisture in pellets after adjustment and pelletizing. 3W: Willow pellets that have been roasted (roasting conditions: 285°C, 4 minutes, adjusted and pelletized, with 6% moisture content after 30 hours of stagnant immersion in water and no heat post-treatment) and; 4W: Roasted willow pellets (roasting conditions: 285°C, 4 minutes, 6% moisture content in pellets after adjustment and pelletizing) after 30 hours of immersion in water and heat post-treatment (conditions: 250°C, 10 minutes, <1% moisture content after post-treatment and cooling). This indicates.

[0030] Figure 3, from left to right, Dutch waste wood class A pellets that have been roasted (roasting conditions: 300°C, 4 minutes, adjusted and pelletized, with 6% moisture content in the pellets) after 30 hours of stagnant immersion in water and no post-heat treatment; and Dutch waste wood class A pellets that were subjected to a heat post-treatment (conditions: 250°C, 10 minutes, <1% moisture after post-treatment and cooling) after 30 hours of stagnant immersion in water, followed by roasting (roasting conditions: 300°C, 4 minutes, 6% moisture in pellets after adjustment and pelletizing). This indicates.

[0031] Figure 4, from left to right, After 30 hours of stagnant immersion in water, the EFB was subjected to heat post-treatment (conditions: 250°C, 10 minutes, <1% moisture after post-treatment and cooling), and then roasted (roasting conditions: 275°C, 4 minutes, 6% moisture in pellets after adjustment and pelletization). Empty Fruit Bunches (a type of biomass waste from the palm oil industry (Asia)) pellets, and After 30 hours of stagnant immersion in water, the EFB (Earth-Filtrated Blast) was roasted without post-heat treatment (roasting conditions: 275°C, 4 minutes, adjustment and pelletization, resulting in 6% moisture content in the pellets). This indicates.

[0032] As shown, samples that were roasted and then pelletized retained their surface shape and showed less discoloration than samples prepared by the method of the invention, exhibiting greater disintegration, as evidenced by the presence of fine particles in water, and leaching, as evidenced by discoloration of the water. [Examples]

[0033] Example 1 Biomass of various origins was dried to a moisture content of 6–10% by weight and then roasted at 265–310°C for 4 minutes. The roasted biomass was cooled to 20°C and then pelletized into cylindrical pellets with lengths of 5–25 mm and diameters of 5.8–6.0 mm. At the time of entry into the pelletizer, the roasted biomass had a moisture content of 9–11% by weight. The roasted pellets thus obtained were subjected to post-heat treatment at the temperatures and times shown in Table 1.

[0034] Durability was qualitatively and quantitatively evaluated after immersion in water for different durations (PDI = Pellet Durability Index). The results are summarized in the table below.

[0035] [Table 1]

[0036] These test results suggest that the immersed pellets showed only a very limited decrease in pellet strength (PDI) compared to the unimmersed pellets, and thus appear to demonstrate a strong hydrophobic characteristic.

[0037] Example 2 Samples of roasted Douglas fir pellets (roasting conditions: 300°C, 4 minutes - no post-treatment) were subjected to a water absorption test according to ISO 23343, followed by a durability test according to ISO 17831. Table 2 below shows the results.

[0038] [Table 2]

[0039] Example 3 Samples of roasted pine wood pellets (roasting conditions: 300°C, 4 minutes - no post-treatment) were subjected to a water adsorption test according to ISO 23343, followed by a durability test. In this example, the durability test was performed by manually tumbling the pellets for 30 seconds, followed by sieving them on a 3.15 mm sieve for 30 seconds. Table 3 below shows the results.

[0040] [Table 3]

[0041] Figure 5 shows one embodiment of a preferred process according to the invention. Particulate biomass is subjected to pretreatment (pretreatment step 100), such as size reduction and / or sieving, in order to obtain particulate biomass having physical properties, such as dimensions, within a predetermined range. The pretreated particulate biomass is dried / preheated to a temperature of approximately roasting temperature in a drying / preheating step 110, typically in an apparatus disclosed in WO 2020 / 190135A1. In the roasting step 120, the particulate biomass is roasted under atmospheric pressure roasting conditions, typically in an indirectly heated screw reactor. The roasted particulate biomass is cooled in a cooling step 130, for example in a pellet mill, to a temperature suitable for densification in the subsequent densification step 140. Subsequently, the densified and roasted particulate biomass is optionally cooled in a cooling step 150 to enhance the densified and roasted particulate biomass, and then again in a preheating step 160 to a post-heat treatment temperature, which is typically carried out in a post-heat treatment step 170 under atmospheric pressure roasting conditions in an apparatus disclosed in WO 2020 / 190135A1. After post-heat treatment, the thus post-heat treated particulate biomass is cooled to a temperature above 100°C by rapid cooling with water in a cooling step 180, and then cooled to ambient temperature in a cooling step 190, for example by (forced) air cooling.

[0042] In this embodiment, any volatile substances released during the drying / preheating step 110 and during the roasting step 120 are recovered, and a portion of them is burned with air in the combustion step 200. The exhaust gas resulting from the combustion is used in the heat exchange step 210 to reheat another portion of the condensable volatile substances released during the drying / preheating step 110 and the roasting step 120, and the heat-exchanged volatile substances are recycled back to the drying / preheating step 110. In the heat exchange step 210, air used for drying is also typically heated to the operating temperature. A similar loop is provided over the post-heat treatment step 170. A portion of the volatile substances released during the heat post-treatment is burned with air in the combustion step 220, and the exhaust gas resulting from the combustion is heat-exchanged in the heat exchange step 230 with another portion of the condensable volatile substances released during the post-heat treatment, which is recycled back to the post-heat treatment step 170. Generally, the air required for the preheating process 160 is also heated by heat exchange in the heat exchange process 230. Volatile substances released during post-heat treatment can also be directly recycled into the densified and roasted particulate biomass that enters the post-heat treatment process 170.

[0043] Some of the volatile substances released in the roasting process 120 are also recycled into the roasted particulate biomass that enters the densification process 140.

[0044] In Figure 5, heat exchange processes 210 and 230 are shown operating simultaneously. Typically, they would be arranged in counterflow. It is also feasible to combine combustion processes 200 and 220 into a single unit operation. The same applies to heat exchange processes 210 and 230.

[0045] Generally, processes other than the densification process are carried out on freely flowing biomass particles at atmospheric pressure (without any additional pressure applied).

Claims

1. A roasting process in which particulate biomass material is roasted under roasting conditions; A densification step of increasing the density of the roasted particulate biomass material from the roasting step to obtain high-density roasted biomass particles; and A post-heat treatment process in which the densified and roasted biomass particles from the densification process are heat-treated under roasting conditions. A method for producing high-density, roasted biomass particles containing [a specific substance].

2. The method according to claim 1, wherein, in the post-heat treatment step, the high-density and roasted biomass particles are heat-treated at atmospheric pressure under roasting conditions.

3. The method according to claim 1 or 2, wherein the degree of degassing / mass loss in the post-heat treatment step is less than 35% by weight of the total degassing / mass loss, based on the dry biomass material supplied to the roasting step.

4. The method according to claim 3, wherein the degree of degassing / mass loss in the post-heat treatment step is in the range of 15 to 30% by weight of the total degassing / mass loss, based on the dry biomass material supplied to the roasting step.

5. The method according to any one of the preceding claims, wherein the post-heat treatment step is carried out under roasting conditions in the range of 235 to 300°C, preferably in the range of 240 to 290°C, more preferably in the range of 240 to 265°C.

6. The method according to any one of the preceding claims, wherein, in the post-heat treatment step, the densified and roasted biomass particles are maintained at a post-treatment temperature for a period of 2 to 15 minutes.

7. The method according to any one of the preceding claims, wherein the post-heat treatment step is carried out in the absence of oxygen.

8. The method according to any one of the preceding claims, wherein the roasted particulate biomass material has a supply temperature to the densification step in the range of 80°C or higher, preferably in the range of 100°C or higher.

9. The method according to any one of the preceding claims, wherein the roasted particulate biomass material has a feed moisture content to the densification process in the range of up to 12% by weight.

10. The method according to any one of the preceding claims, wherein the roasting process is carried out at a roasting temperature in the range of 180 to 320°C.

11. Furthermore, the method according to any one of the preceding claims, further comprising a cooling step of cooling the densified and roasted biomass particles from the densification step before the post-heat treatment step.

12. The method according to any one of the preceding claims, further comprising recycling condensable volatile substances released during the roasting process and / or post-heat treatment process into biomass particles.

13. The method according to any one of the preceding claims, further comprising burning volatile substances released during the roasting and / or post-heat treatment steps into biomass particles.

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