Biomass dealkalization method and prepared low-alkali biomass fuel

Abstract

According to the biomass dealkalization method and the prepared low-alkali biomass fuel, the cavitation effect formed by propagation of high-frequency ultrasonic waves in liquid is utilized, instant high pressure of hundreds of atmospheres can be generated in microseconds, and along with the local high temperature phenomenon, the biomass structure can be rapidly destroyed, and the low-alkali biomass fuel can be used for dealkalization of biomass. The internal alkali metal and alkaline earth metal elements are promoted to be quickly released; the catalyst interacts with carbon dioxide to form a dissolved or precipitated state, so that the removal efficiency of alkali metal and alkaline earth metal is greatly improved. Compared with the prior art, the method effectively solves the problem that a conventional method is low in efficiency under the conditions of short time and large solid-to-liquid ratio; and a large amount of acid solution is not needed, so that the dealkalization cost and the equipment corrosion risk are reduced. Therefore, the technological process is simplified, an efficient and environment-friendly technical choice is provided for large-scale industrial application, and the method has a wide application prospect.

Description

Technical Field

[0001] The invention belongs to the field of biomass fuels, and in particular relates to a method for dealkalization of biomass and prepared low-alkali biomass fuel. Background Art

[0002] Against the backdrop of global warming and the energy crisis, low-carbon renewable fuels are attracting widespread attention. Currently, direct combustion of biomass as a fuel is the primary method. However, the high alkali metal content in biomass can lead to problems such as coking, dust accumulation, and corrosion, which can affect the operation of thermal equipment. Consequently, metallurgical blast furnaces and power boilers have strict requirements for biomass fuels entering the furnace, requiring the biomass to undergo dealkalization pretreatment before combustion. Therefore, developing rapid biomass dealkalization methods is crucial for achieving biomass resource utilization.

[0003] The main methods for biomass dealkalization include soaking, flushing, and stirring. However, these methods require large amounts of water, take a long time to wash, and have limited effectiveness. For agricultural and forestry biomass such as straw and sawdust, the alkali metals are mostly distributed in the cell walls and cytoplasm. Although most alkali metals K and Na, as well as a small amount of Ca and Mg, exist in water-soluble forms, under conditions of a large solid-to-liquid ratio and short washing time, the alkali metals within the biomass diffuse slowly into the solution. Long washing times or a reduction in the solid-to-liquid ratio are required to achieve a high alkali metal removal rate. Therefore, large amounts of water are required, washing times are long, and the effectiveness is limited. Adding acid solutions such as hydrochloric acid, nitric acid, and phosphoric acid to the solution can also increase the efficiency of biomass dealkalization, but acid washing is costly. On the one hand, strong acids can cause severe hydrolysis of the biomass, resulting in a decrease in biomass quality and significant mass loss. On the other hand, they produce a large amount of acidic wastewater, leading to very high wastewater treatment costs and serious environmental pollution.

[0004] The patent with publication number CN111842310A published on October 30, 2020, proposes a method for pretreatment of biomass cascade deashing, in which water, organic acid, and inorganic acid are used in sequence to stir and wash the biomass in a cascade manner, thereby obtaining biomass with low ash content and low alkali metal content. Although the acid concentration required in the pickling process is very low, it still causes damage to the equipment. In addition, since water, organic acid, and inorganic acid are used in sequence to stir the biomass for a long time to deash and dealkalize, the organic components in the biomass will be lost in large quantities, and the efficiency of biomass dealkalization will also be reduced.

[0005] Therefore, it is very necessary to develop a biomass dealkalization technology that is simple to operate, mild in conditions, efficient and economical. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for dealkalization of biomass and a low-alkali biomass fuel prepared therefrom, which can achieve rapid dealkalization of biomass by destroying the biomass structure and promoting the hydrolysis process of alkali metals and alkaline earth metals in the biomass.

[0007] The specific technical solutions of the present invention are as follows:

[0008] A method for dealkalization of biomass, specifically comprising:

[0009] The biomass powder is placed in water, ultrasonically treated, separated, and dried.

[0010] The biomass powder is selected from biomass that can be used as fuel, preferably waste bamboo boards;

[0011] Crushing the biomass to obtain biomass powder with a particle size mainly distributed in the range of 0.1-0.5 mm;

[0012] The mass ratio of the biomass powder to water is: 1:5≤mass ratio≤1:20; preferably 1:10≤mass ratio≤1:20;

[0013] Furthermore, during ultrasonic treatment, the biomass is pressed into water using a pressing plate to ensure that the water level is higher than the biomass powder to be dealkalized.

[0014] The ultrasonic treatment has an ultrasonic frequency of 28kHz-100kHz and an ultrasonic time of 15min-60min;

[0015] When the mass ratio of the biomass powder to water is 1:5, the ultrasonic time is ≥30 min;

[0016] Preferably, carbon dioxide is introduced during ultrasonic treatment, and the carbon dioxide gas flow rate is controlled at 0 mL / min-200 mL / min, preferably 50-200 mL / min;

[0017] Furthermore, after ultrasonic treatment, the obtained biomass suspension is subjected to solid-liquid separation, and the obtained solid is the dealkalized biomass after drying.

[0018] After treatment by the method, the K removal rate of the biomass is more than 72%, the Ca removal rate is more than 14%, the Na removal rate is more than 71%, and the Mg removal rate is more than 47%; preferably, when carbon dioxide is introduced during ultrasound, the K removal rate of the biomass is more than 84%, the Ca removal rate is more than 26%, the Na removal rate is more than 84%, and the Mg removal rate is more than 64%.

[0019] In the present invention, the waste bamboo boards are crushed to the submillimeter level, which greatly increases the specific surface area of ​​the biomass and fully exposes the alkali metals (K, Na) and alkaline earth metals (Ca, Mg) bound inside. The ion diffusion distance is shortened to the millimeter level. Combined with ultrasonic cavitation, the liquid-solid mass transfer rate is increased by dozens of times, breaking the boundary layer limitation, improving the dealkalization efficiency, and shortening the dealkalization time. The collapse of high-frequency ultrasonic cavitation bubbles produces microjets and shock waves, which strongly scour the surface of the biomass and strip off the adsorbed metal compounds. The shear force generated destroys the biomass fiber structure, releasing the encapsulated metal ions, and the ultrasound generates local high temperatures, which can decompose metal-organic complexes (such as Ca bound to lignin). 2+ ), improve the dealkalization effect; cavitation accelerates the dissolution of CO2 and the dissociation of carbonic acid, and quickly generates H + and HCO3 - . H + Replaces alkali metal ions, HCO3 - With Ca 2+ / Mg 2+ Forming soluble bicarbonate, improving the dealkalization rate, solving the problem that traditional water washing only removes water-soluble K + 、Na + , for bound Ca 2+ Mg 2+ (such as calcium oxalate) is ineffective. And the weak acidic environment obtained by introducing carbon dioxide inhibits the redeposition of metal ions, while strong acid easily destroys the biomass structure and releases more impurities. Through the pressing plate, the biomass powder is forced to be completely immersed, avoiding the loss of ultrasonic energy at the gas-liquid interface and ensuring that the cavitation effect acts evenly on the material. Therefore, the present invention improves the dealkalization rate without using acid solution and with less water consumption through ultrasonic treatment, control of particle size and pressing plate setting; and synergistically acts with carbon dioxide to further improve the dealkalization rate.

[0020] The present invention provides a low-alkali biomass fuel, which is prepared by utilizing the above-mentioned biomass dealkalization method.

[0021] The ultrasonic cavitation technology of the present invention utilizes the cavitation effect generated by the propagation of high-frequency ultrasonic waves in liquids, which can generate instantaneous high pressures of hundreds of atmospheres within microseconds, accompanied by localized high temperatures. This physical effect can quickly destroy the biomass structure, prompting the rapid release of alkali and alkaline earth metal elements within it. It interacts with carbon dioxide to form a dissolved or precipitated state, significantly improving the removal efficiency of alkali and alkaline earth metals. The present invention achieves a fast and efficient biomass dealkalization process, instantly breaking down the biomass structure, greatly shortening the diffusion time of alkali and alkaline earth metals, and significantly improving dealkalization efficiency. This effectively solves the problem of low efficiency of conventional methods under short time and high solid-to-liquid ratio conditions. Furthermore, the present invention does not require the use of large amounts of acidic solutions, reducing dealkalization costs and equipment corrosion risks, making it suitable for large-scale industrial applications. The use of carbon dioxide promotes the hydrolysis and dissolution of alkali and alkaline earth metals, increasing the removal rate of alkali and alkaline earth metals such as K, Na, Ca, and Mg, enhancing biomass combustion performance, reducing the risk of slagging, and reducing potential environmental hazards. Furthermore, the present invention simplifies the process flow, providing an efficient and environmentally friendly technical option for large-scale industrial applications, with broad application prospects.

[0022] Compared to existing technologies, the ultrasonic cavitation technology of the present invention utilizes the cavitation effect created by the propagation of high-frequency ultrasonic waves in liquids. This technology can generate instantaneous high pressures of hundreds of atmospheres within microseconds, accompanied by localized high temperatures. This rapidly destroys the biomass structure, prompting the rapid release of alkali and alkaline earth metal elements within it. These elements interact with carbon dioxide, dissolving or precipitating them, significantly improving the removal efficiency of alkali and alkaline earth metals. This technology addresses the difficulty of existing technologies in achieving high alkali and alkaline earth metal removal rates from biomass at high solid-to-liquid ratios and in short washing times. It provides a simple and efficient method for biomass dealkalization, promising broad industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 These are SEM images of the biomass before and after dealkalization pretreatment in Example 1;

[0024] Figure 2 This is the XRD pattern of the biomass before and after dealkalization pretreatment in Example 9. DETAILED DESCRIPTION

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0026] Unless otherwise specified, the test materials and reagents used in the following examples can be obtained from commercial sources.

[0027] If no specific techniques or conditions are specified in the examples, they can be carried out according to the techniques or conditions described in the literature in the field or according to the product instructions.

[0028] Example 1

[0029] A method for dealkalization of biomass, comprising the following steps:

[0030] (1) Crushing waste bamboo boards to obtain biomass powder with a particle size mainly distributed in the range of 0.1-0.5 mm, soaking the dried biomass powder in water at a solid-liquid ratio of 1:10 (mass ratio), and pressing the biomass into the water with a pressing plate to ensure that the water level is higher than the biomass powder to be dealkalized.

[0031] (2) The biomass powder and water in step (1) were placed in an ultrasonic cleaning device, the ultrasonic frequency was adjusted to 28 kHz, the carbon dioxide flow rate was 0 mL / min, and ultrasonic treatment was carried out at room temperature for 30 min.

[0032] (3) A vacuum filtration device is used to separate the biomass sample. The separated biomass sample is dried to obtain a low-alkali biomass sample, which is labeled as BB-1.

[0033] Example 2

[0034] A method for dealkalization of biomass, comprising the following steps:

[0035] (1) Crushing waste bamboo boards to obtain biomass powder with a particle size mainly distributed in the range of 0.1-0.5 mm, soaking the dried biomass powder in water at a solid-liquid ratio of 1:10 (mass ratio), and pressing the biomass into the water with a pressing plate to ensure that the water level is higher than the biomass powder to be dealkalized.

[0036] (2) The biomass powder and water in step (1) were placed in an ultrasonic cleaning device, the ultrasonic frequency was adjusted to 40 kHz, the carbon dioxide flow rate was 0 mL / min, and ultrasonic treatment was carried out at room temperature for 30 min.

[0037] (3) A vacuum filtration device is used to separate the biomass sample. The separated biomass sample is dried to obtain a low-alkali biomass sample, which is labeled as BB-2.

[0038] Example 3

[0039] A method for dealkalization of biomass, comprising the following steps:

[0040] (1) Crushing waste bamboo boards to obtain biomass powder with a particle size mainly distributed in the range of 0.1-0.5 mm, soaking the dried biomass powder in water at a solid-liquid ratio of 1:10 (mass ratio), and pressing the biomass into the water with a pressing plate to ensure that the water level is higher than the biomass powder to be dealkalized.

[0041] (2) The biomass powder and water in step (1) were placed in an ultrasonic cleaning device, the ultrasonic frequency was adjusted to 100 kHz, the carbon dioxide flow rate was 0 mL / min, and ultrasonic treatment was performed at room temperature for 30 min.

[0042] (3) A vacuum filtration device is used to separate the biomass sample. The separated biomass sample is dried to obtain a low-alkali biomass sample, which is labeled as BB-3.

[0043] Example 4

[0044] A method for dealkalization of biomass, comprising the following steps:

[0045] (1) Crush the waste bamboo board to obtain biomass powder with a particle size mainly distributed in the range of 0.1-0.5 mm, soak the dried biomass powder in water at a solid-liquid ratio of 1:5 (mass ratio), and press the biomass into the water with a pressing plate to ensure that the water level is higher than the biomass powder to be dealkalized.

[0046] (2) The biomass powder and water in step (1) were placed in an ultrasonic cleaning device, the ultrasonic frequency was adjusted to 40 kHz, the carbon dioxide flow rate was 0 mL / min, and ultrasonic treatment was carried out at room temperature for 30 min.

[0047] (3) A vacuum filtration device is used to separate the biomass sample. The separated biomass sample is dried to obtain a low-alkali biomass sample, which is labeled as BB-4.

[0048] Example 5

[0049] A method for dealkalization of biomass, comprising the following steps:

[0050] (1) The waste bamboo board is crushed to obtain biomass powder with a particle size mainly distributed in 0.1-0.5 mm. The dried biomass powder is soaked in water at a solid-liquid ratio of 1:20 (mass ratio), and the biomass is pressed into the water with a pressing plate to ensure that the water level is higher than the biomass powder to be dealkalized.

[0051] (2) The biomass powder and water in step (1) were placed in an ultrasonic cleaning device, the ultrasonic frequency was adjusted to 40 kHz, the carbon dioxide flow rate was 0 mL / min, and ultrasonic treatment was carried out at room temperature for 30 min.

[0052] (3) A vacuum filtration device is used to separate the biomass sample. The separated biomass sample is dried to obtain a low-alkali biomass sample, which is labeled as BB-5.

[0053] Example 6

[0054] A method for dealkalization of biomass, comprising the following steps:

[0055] (1) The waste bamboo board is crushed to obtain biomass powder with a particle size mainly distributed in 0.1-0.5 mm. The dried biomass powder is soaked in water at a solid-liquid ratio of 1:10 (mass ratio), and the biomass is pressed into the water with a pressing plate to ensure that the water level is higher than the biomass powder to be dealkalized.

[0056] (2) The biomass powder and water in step (1) were placed in an ultrasonic cleaning device, the ultrasonic frequency was adjusted to 40 kHz, the carbon dioxide flow rate was 0 mL / min, and ultrasonic treatment was carried out at room temperature for 15 min.

[0057] (3) A vacuum filtration device is used to separate the biomass sample. The separated biomass sample is dried to obtain a low-alkali biomass sample, which is labeled as BB-6.

[0058] Example 7

[0059] A method for dealkalization of biomass, comprising the following steps:

[0060] (1) The waste bamboo board is crushed to obtain biomass powder with a particle size mainly distributed in 0.1-0.5 mm. The dried biomass powder is soaked in water at a solid-liquid ratio of 1:10 (mass ratio), and the biomass is pressed into the water with a pressing plate to ensure that the water level is higher than the biomass powder to be dealkalized.

[0061] (2) The biomass powder and water in step (1) were placed in an ultrasonic cleaning device, the ultrasonic frequency was adjusted to 40 kHz, the carbon dioxide flow rate was 0 mL / min, and ultrasonic treatment was carried out at room temperature for 60 min.

[0062] (3) A vacuum filtration device is used to separate the biomass sample. The separated biomass sample is dried to obtain a low-alkali biomass sample, which is labeled as BB-7.

[0063] Table 1 Alkali metal and alkaline earth metal removal rate (%) of Example 1 to Example 7

[0064] element K Ca Na Mg Original biomass wt% 0.512 0.276 0.785 0.070 BB-1 removal rate% 83.12 20.87 82.14 60.58 BB-2 removal rate% 81.05 22.83 85.35 60.00 BB-3 removal rate% 77.48 19.54 79.62 55.73 BB-4 removal rate% 72.48 14.53 71.23 47.52 BB-5 removal rate% 82.21 23.12 86.1 61.35 BB-6 removal rate% 76.82 20.24 72.13 55.64 BB-7 removal rate% 81.10 23.50 85.45 60.10

[0065] Figure 1This is an electron microscope scanning image of the biomass sample BB-1 before and after ultrasound treatment in Example 1. The instantaneous collapse of the ultrasonic bubble nucleus converts the absorbed energy into other forms of energy release, generating extreme physical conditions such as high temperature, high pressure, and impinging jets. This extreme physical change destroys plant cell walls and lignin fiber structures. Electron microscope scanning images show numerous holes on the surface of the biomass after ultrasound treatment, disrupting its microstructure. Combining analysis with Examples 1, 2, 3, 4, 5, 6, and 7, Table 1 shows that at high solid-to-liquid ratios and short cleaning times, ultrasound disrupts the biomass microstructure, achieving high alkali and alkaline earth metal removal rates. Further extending the ultrasound time significantly increases the Ca removal rate, but the leaching of K, Na, and Mg essentially reaches its upper limit. The solid-to-liquid ratio, ultrasonic frequency, and ultrasound time significantly influence the alkali and alkaline earth metal removal rates, with the order of influence being solid-to-liquid ratio, ultrasonic frequency, and ultrasound time.

[0066] Example 8

[0067] A method for dealkalization of biomass, comprising the following steps:

[0068] (1) The waste bamboo board is crushed to obtain biomass powder with a particle size mainly distributed in 0.1-0.5 mm. The dried biomass powder is soaked in water at a solid-liquid ratio of 1:10 (mass ratio), and the biomass is pressed into the water with a pressing plate to ensure that the water level is higher than the biomass powder to be dealkalized.

[0069] (2) The biomass powder and water in step (1) were placed in an ultrasonic cleaning device, the ultrasonic frequency was adjusted to 28 kHz, the carbon dioxide flow rate was 50 mL / min, and ultrasonic treatment was carried out at room temperature for 30 min.

[0070] (3) A vacuum filtration device is used to separate the biomass sample. The separated biomass sample is dried to obtain a low-alkali biomass sample, which is labeled as BB-8.

[0071] Example 9

[0072] A method for dealkalization of biomass, comprising the following steps:

[0073] (1) The waste bamboo board is crushed to obtain biomass powder with a particle size mainly distributed in 0.1-0.5 mm. The dried biomass powder is soaked in water at a solid-liquid ratio of 1:10 (mass ratio), and the biomass is pressed into the water with a pressing plate to ensure that the water level is higher than the biomass powder to be dealkalized.

[0074] (2) The biomass powder and water in step (1) were placed in an ultrasonic cleaning device, the ultrasonic frequency was adjusted to 28 kHz, the carbon dioxide flow rate was 200 mL / min, and ultrasonic treatment was performed at room temperature for 30 min.

[0075] (3) A vacuum filtration device is used to separate the biomass sample. The separated biomass sample is dried to obtain a low-alkali biomass sample, which is labeled as BB-9.

[0076] The removal rates of alkali metals and alkaline earth metals in Example 1, Example 8-Example 9 are shown in Table 2.

[0077] Table 2 Alkali metal and alkaline earth metal removal rates of Example 1, Example 8-Example 9

[0078] element K Ca Na Mg Original biomass wt% 0.512 0.276 0.785 0.070 BB-1 removal rate% 83.12 20.87 82.14 60.58 BB-8 removal rate% 84.70 26.46 84.38 64.47 BB-9 removal rate% 86.78 35.98 86.51 68.82

[0079] Combining the above-mentioned examples 1, 8, and 9, as shown in Table 2, the introduction of carbon dioxide produces carbonic acid, which reacts with alkali metal and alkaline earth metal compounds related to Ca and Mg, creating an acidic environment and promoting the hydrolysis of salts. The removal rates of Ca and Mg increased significantly, and the removal rates of K and Na also increased slightly. Figure 2 XRD spectra of low-temperature ash samples of biomass indicate that minerals such as K, Ca, Na, and Mg in the waste bamboo board biomass are likely mostly present as amorphous substances at low temperatures. Alkali and alkaline earth metal minerals were not detected in the XRD patterns. After ultrasonic water washing, the sample ash content decreased, and a distinct CaCO3 diffraction peak appeared in the ash. This CaCO3 diffraction peak was enhanced after CO2-enhanced water washing, indicating that CO2 reacted with some calcium compounds in the waste bamboo board biomass sample to form CaCO3 or unstable Ca(HCO3)2. Therefore, ultrasonic cavitation and carbon dioxide have a synergistic effect, enhancing the dealkalization effect. Figure 2 In the figure, U+CO2 is Example 9, which represents ultrasonic treatment in combination with CO2; U is Example 1 (representing ultrasonic treatment only); RAW refers to untreated biomass raw materials.

[0080] Comparative Example 1

[0081] A method for dealkalization of biomass, comprising the following steps:

[0082] (1) Crush the waste bamboo board to obtain biomass powder with a particle size mainly distributed in the range of 0.1-0.5 mm, soak the dried biomass powder in water at a solid-liquid ratio of 1:5 (mass ratio), and press the biomass into the water with a pressing plate to ensure that the water level is higher than the biomass powder to be dealkalized.

[0083] (2) The biomass powder and water in step (1) were placed in an ultrasonic cleaning device, the ultrasonic frequency was adjusted to 100 kHz, the carbon dioxide flow rate was 0 mL / min, and ultrasonic treatment was performed at room temperature for 15 min.

[0084] (3) A vacuum filtration device is used to separate the biomass sample. The separated biomass sample is dried to obtain a low-alkali biomass sample, which is labeled as BB-10.

[0085] Table 3 Alkali metal and alkaline earth metal removal rates of Example 1 and Comparative Example 1

[0086] element K Ca Na Mg Original biomass wt% 0.512 0.276 0.785 0.070 BB-1 removal rate% 83.12 20.87 82.14 60.58 BB-10 removal rate% 64.28 10.64 63.88 42.22

[0087] Table 3 shows the alkali and alkaline earth metal removal rates for biomass. Due to the excessively high solid-to-liquid ratio, the leaching of alkali and alkaline earth metals quickly reaches dissolution equilibrium. At the same time, the ultrasonic cavitation effect and corrosion capacity at a 100 kHz ultrasonic frequency are weak, resulting in minimal damage to the biomass microstructure. This results in inadequate leaching of alkali and alkaline earth metals. At this point, the removal rates of K, Ca, Na, and Mg from the biomass were only 64.28%, 10.64%, 63.88%, and 42.22%, respectively, falling short of the results achieved in Examples 1-9.

[0088] Comparative Example 2

[0089] A method for dealkalization of biomass, comprising the following steps:

[0090] (1) The waste bamboo board is crushed to obtain biomass powder with a particle size mainly distributed in 0.1-0.5 mm. The dried biomass powder is soaked in water at a solid-liquid ratio of 1:10 (mass ratio), and the biomass is pressed into the water with a pressing plate to ensure that the water level is higher than the biomass powder to be dealkalized.

[0091] (2) The biomass powder and water in step (1) were placed in an ultrasonic cleaning device. No ultrasonic treatment was performed, and only carbon dioxide was introduced at a carbon dioxide flow rate of 100 mL / min. The treatment was carried out at room temperature for 30 min.

[0092] (3) A vacuum filtration device is used to separate the biomass sample. The separated biomass sample is dried to obtain a low-alkali biomass sample, which is labeled as BB-11.

[0093] Table 4 Alkali metal and alkaline earth metal removal rates of Example 9 and Comparative Example 2

[0094] element K Ca Na Mg Original biomass wt% 0.512 0.276 0.785 0.070 BB-9 removal rate% 86.78 35.98 86.51 68.82 BB-11 removal rate% 3.24 5.24 2.95 6.89

[0095] It can be seen from the alkali metal and alkaline earth metal removal rates of biomass in Table 4 that since no ultrasound was applied, there was no ultrasonic stirring effect and cavitation effect, and only the stirring effect of carbon dioxide bubbles was relied upon. At this time, due to the dense stacking of biomass particles, internal air gaps and hydrophobic effects, the biomass was difficult to be infiltrated by the solution, and the leaching of alkali metals and alkaline earth metals was difficult. At this time, the removal rates of K, Ca, Na, and Mg elements in the biomass were only 3.24%, 5.24%, 2.95%, and 6.89%, respectively, which were far below the effects of Examples 1 to 9 (using ultrasonic treatment).

[0096] Comparative Example 3

[0097] A method for dealkalization of biomass, comprising the following steps:

[0098] (1) Crush the waste bamboo board to obtain biomass powder with a particle size mainly distributed in the range of 0.1-0.5 mm, soak the dried biomass powder in water at a solid-liquid ratio of 1:5 (mass ratio), and press the biomass into the water with a pressing plate to ensure that the water level is higher than the biomass powder to be dealkalized.

[0099] (2) The biomass powder and water in step (1) were placed in an ultrasonic cleaning device, the ultrasonic frequency was adjusted to 100 kHz, the carbon dioxide flow rate was 50 mL / min, and ultrasonic treatment was performed at room temperature for 15 min.

[0100] (3) A vacuum filtration device is used to separate the biomass sample. The separated biomass sample is dried to obtain a low-alkali biomass sample, which is labeled as BB-12.

[0101] Table 5 Alkali metal and alkaline earth metal removal rates of Example 1 and Comparative Example 3

[0102] element K Ca Na Mg Original biomass wt% 0.512 0.276 0.785 0.070 BB-1 removal rate% 83.12 20.87 82.14 60.58 BB-10 removal rate% 68.87 17.24 66.63 43.56

[0103] It can be seen from the alkali metal and alkaline earth metal removal rates of biomass in Table 5 that although CO2 was introduced to enhance the ultrasonic dealkalization process, the solid-liquid ratio was too large, the ultrasonic cavitation effect at an ultrasonic frequency of 100 kHz was weak, and the ultrasonic treatment time was short, so that the biomass powder did not have time to fully contact with the aqueous solution. Therefore, the leaching of alkali metals and alkaline earth metals was insufficient. At this time, the removal rates of K, Ca, Na, and Mg elements in the biomass were only 68.87%, 17.24%, 66.63%, and 43.56%, respectively, which did not reach the effects of Examples 1 to 9.

[0104] Combined with the implementation effect of the embodiment, it can be seen that the ultrasonic cavitation effect of the present invention destroys the biomass structure, shortens the diffusion time of alkali metals and alkaline earth metals, realizes rapid dealkalization, and effectively solves the problem of low dealkalization efficiency of conventional stirring and soaking water washing dealkalization methods under short time and large solid-liquid ratio conditions, thereby realizing rapid and efficient dealkalization. Unlike the pickling method, the present invention requires the use of an acidic solution, and strengthens the dealkalization process by using carbonic acid generated by dissolving carbon dioxide in water, thereby greatly reducing the dealkalization cost and the corrosion risk of equipment, and reducing the potential harm to the environment during the dealkalization process, which is suitable for large-scale industrial applications. While ultrasonic cavitation destroys the biomass structure, carbon dioxide dissolving in water can create an acidic environment, which can promote the hydrolysis and dissolution efficiency of alkali metals and alkaline earth metals, significantly improve the removal rate of alkali metals and alkaline earth metals (such as K, Na, Ca, Mg), and reduce the risk of slagging in subsequent applications.

[0105] The above embodiments are described to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A method for dealkalization of biomass, characterized in that The method specifically comprises the following steps: placing the biomass powder in water, ultrasonically treating the powder, separating the powder, and drying the powder.

2. The method according to claim 1, characterized in that The biomass powder is selected from biomass that can be used as fuel.

3. The method according to claim 1 or 2, characterized in that The biomass powder has a particle size distribution of 0.1-0.5 mm.

4. The method according to claim 1 or 2, characterized in that The mass ratio of the biomass powder to water is: 1:5≤mass ratio≤1:

20.

5. The method according to claim 1 or 2, characterized in that During ultrasonic treatment, use a pressing plate to press the biomass into the water to ensure that the water level is above the biomass powder to be dealkalized.

6. The method according to claim 1, characterized in that The ultrasonic treatment has an ultrasonic frequency of 28kHz-100kHz and an ultrasonic time of 15min-60min.

7. The method according to claim 1 or 6, characterized in that During ultrasonic treatment, carbon dioxide is introduced, and the flow rate of carbon dioxide gas is controlled at 0 mL / min-200 mL / min.

8. The method according to claim 1, characterized in that After treatment by the method, the K removal rate of the biomass is above 72%, the Ca removal rate is above 14%, the Na removal rate is above 71%, and the Mg removal rate is above 47%.

9. The method according to claim 7, characterized in that The biomass K removal rate is over 84%, the Ca removal rate is over 26%, the Na removal rate is over 84%, and the Mg removal rate is over 64%.

10. A low-alkali biomass fuel prepared by the biomass dealkalization method according to any one of claims 1 to 9.

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