Environment-friendly biomass fuel particle

Abstract

Belonging to the technical field of fuel particle preparation, the invention discloses an environment-friendly biomass fuel particle, which is composed of the following raw materials by weight: 25-40 parts of agriculture and forestry straw powder, 50-70 parts of recycled waste wood, 5-8 parts of modified dolomite, 1-3 parts of calcium dihydrogen phosphate, and 1-3 parts of boric sludge. Wherein the modified dolomite is prepared by compounding activated citric acid with formylated calcium alginate, so that the structural strength and hydrophobicity of the particles are remarkably improved, heavy metals, potassium, chlorine and other fusible elements can be adsorbed, and the generation of low-melting-point ash in the combustion process is reduced. The boric sludge and the monocalcium phosphate have a synergistic effect, coking and slagging are inhibited by generating high-melting-point borate and silicon phosphate, soot oxidation is promoted, and the burn-off rate is increased. And crushing the raw materials to a specific particle size, controlling the water content to be 12-18%, and mixing and granulating to form cylindrical particles with the diameter of 6-12mm. The biomass particles prepared by the invention have the characteristics of high structural strength, low water absorption, stable combustion, high calorific value, less coking and slagging, and less emission of flue gas pollutants.

Description

Technical Field

[0001] The present invention belongs to the technical field of fuel particle preparation, and in particular relates to an environmentally friendly biomass fuel particle. Background Art

[0002] Oil, natural gas, and coal are non-renewable energy sources. With long-term, large-scale exploitation and consumption, their reserves are gradually decreasing, and they face the severe challenge of resource depletion. In stark contrast, biomass energy, as a renewable energy source, is essentially solar energy stored in the form of chemical energy within biomass. Biomass energy is widely available and offers significant advantages such as sustainability and environmental friendliness, making it an increasingly important energy source.

[0003] The processing of agricultural products generates a significant amount of waste, such as straw and rice husks. Furthermore, municipal waste sorting also produces a significant amount of biomass materials, such as waste wood. In theory, these abundant biomass resources can be converted into biomass fuel, achieving resource recycling. However, practical applications present numerous challenges. Pellets made from a single plant generally have a low flash point, posing a safety hazard during storage and transportation and prone to spontaneous combustion due to factors such as temperature fluctuations. These fuels also have a high ash content, producing large amounts of ash after combustion, which not only requires frequent disposal but also reduces energy efficiency. During combustion, single-plant pellets are prone to incomplete combustion, resulting in the emission of large amounts of unburned carbon particles, which wastes energy and exacerbates environmental pollution. Furthermore, their flue gas emissions are highly polluting, releasing large amounts of pollutants such as sulfur and nitrogen oxides and dust, which pose a serious threat to the atmospheric environment. Furthermore, their low fuel efficiency prevents the full realization of the potential of biomass energy.

[0004] At present, there are attempts to prepare biomass pellet fuel by directly mixing a variety of biomass waste materials. However, due to the lack of reasonable formula design, problems such as unstable fuel combustion, large fluctuations in heat output, and difficulty in meeting the stable energy demand in actual production and life often occur. At the same time, the current biomass pellet fuel is also faced with problems such as coking and the formation of white scale on the heating surface of the boiler during combustion. The coking phenomenon will cause the combustion efficiency of the combustion equipment to drop sharply. In severe cases, it will even block the combustion channel, affect the normal operation of the equipment, and greatly increase the equipment maintenance cost and downtime. The white scale formed on the heating surface of the boiler will seriously hinder heat conduction, reduce the heat exchange efficiency of the boiler, and cause a huge waste of energy. In summary, it is necessary to develop a biomass fuel pellet with excellent performance, environmental protection and high efficiency. Summary of the Invention

[0005] In view of the above situation, in order to overcome the defects of the existing technology, the present invention uses agricultural and forestry straw powder to compound with recycled waste wood, modified dolomite, calcium dihydrogen phosphate and boron mud to prepare biomass fuel, wherein the modified dolomite is prepared by citric acid activation treatment and then combined with formaldehyded calcium alginate. It can reduce the formation of low-melting point ash during combustion, improve the structural strength of fuel particles, inhibit water absorption of fuel particles, reduce flue gas emissions, and inhibit coking and slagging.

[0006] In order to achieve the above-mentioned purpose, the following technical solution is adopted: The present invention provides an environmentally friendly biomass fuel pellet, which is characterized in that it is composed of the following raw materials in parts by weight: 25-40 parts of agricultural and forestry straw powder, 50-70 parts of recycled waste wood, 5-8 parts of modified dolomite, 1-3 parts of calcium dihydrogen phosphate and 1-3 parts of boron mud.

[0007] The agricultural and forestry straw powder is crop straw and / or forestry prunings.

[0008] The crop straw is the stems, leaves and other parts left after the crops are harvested. It is an important by-product in the agricultural production process. It mainly consists of cellulose, hemicellulose and lignin. The cellulose content is usually around 30%-50%. It is a macromolecular polysaccharide composed of glucose and is the main component of plant cell walls. Its molecular structure is tight, which provides a certain strength and toughness for the straw. Hemicellulose accounts for about 20%-30%. It is a heteropolysaccharide composed of several different types of monosaccharides. Its degree of polymerization is relatively low and it is easier to decompose than cellulose. Hemicellulose is tightly combined with cellulose to form a complex network structure of the plant cell wall. The lignin content is about 10%-20%. It is a complex organic polymer with a three-dimensional network structure. It can enhance the hardness and compression resistance of the plant cell wall, and also make the straw have a certain resistance to decomposition.

[0009] In an embodiment of the present invention, the crop straw includes but is not limited to a combination of one or more of wheat straw, corn straw, rice straw, sorghum straw, rice husk, and peanut shell.

[0010] In an embodiment of the present invention, the forestry prunings are plant residues produced during landscaping and maintenance, including dead branches, fallen leaves, shrub branches, grass clippings, etc., the main part of which is similar to crop straw.

[0011] In an embodiment of the present invention, the recycled waste wood includes but is not limited to one or more combinations of wood solid wood floors, wood demolition materials, wood construction site formwork waste, and old wood packaging boards.

[0012] The chemical composition of the dolomite is CaMg(CO3)2, which is a carbonate mineral. In terms of building materials, it can be used to produce glass, ceramics, cement, etc.; in the chemical field, it can be used as a raw material for the production of calcium magnesium phosphate fertilizer, magnesium sulfate, etc.; in terms of refractory materials, it can be used as alkaline refractory materials, slag-forming agents, etc. It is also used in environmental protection and energy conservation, as an adsorbent or catalyst carrier, etc.

[0013] The boron mud is the waste residue generated by the production of boric acid, borax and other products. It is a grayish white or yellowish white powdery solid, alkaline, and contains components such as boron oxide, magnesium oxide, total iron, silicon dioxide, and sodium oxide. Since boron is a trace element required for plant growth, boron mud can be used to produce compound fertilizers such as boron magnesium phosphate fertilizer and boron magnesium calcium fertilizer. Boron mud can also be used in the building materials industry, such as the production of refractory bricks, microcrystalline glass, ceramic pipes and basins, etc. It can be used as an additive in ironmaking sintered pellets, as a filler for plastics and rubber, etc., or as a wastewater treatment agent for treating certain specific types of wastewater.

[0014] Furthermore, the modified dolomite is prepared by the following steps:

[0015] S1. Dolomite pretreatment: crush the dolomite raw material into particles with a particle size range of 0.5-2 mm, and pass through 10 mesh and 20 mesh sieves in sequence;

[0016] S2. Activation treatment: adding the pretreated dolomite to a citric acid solution, stirring at 20-30°C for 2-5 hours, then filtering, washing with clean water until neutral, and drying in an oven at 80-100°C for 6-12 hours to obtain activated dolomite;

[0017] S3. Preparing formaldehyded calcium alginate: dissolving sodium alginate in ethanol to obtain a sodium alginate ethanol solution, adding sodium periodate as an oxidant, stirring and reacting at 25-35° C. in the dark for 4-8 hours, then adding ethylene glycol, reacting at 50-60° C. for 2-4 hours, filtering the precipitate, and drying to obtain formaldehyded sodium alginate, dissolving the formaldehyded sodium alginate in ethanol to obtain a formaldehyded sodium alginate ethanol solution, then adding the solution to a calcium chloride solution, reacting for 30-100 minutes, washing the resulting gel with deionized water, and freeze-drying to obtain the formaldehyded calcium alginate;

[0018] S4. Dolomite grafting modification: The activated dolomite and formaldehyded calcium alginate are mixed, and then sodium cyanoborohydride solution is added for moistening. The mixture is mixed at 40-60° C. for 4-6 hours. The mixture is then washed with deionized water and ethanol, respectively, and dried in an oven at 80-100° C. for 6-12 hours. The mixture is crushed, ground, and passed through a 20-mesh sieve to obtain the modified dolomite.

[0019] Furthermore, in step S1, the concentration of the citric acid solution is 5-15 wt%.

[0020] Furthermore, in step S3, the concentration of the sodium alginate ethanol solution is 1-3 wt %, the molar ratio of sodium periodate to sodium alginate is 1:1-3:1, and the amount of ethylene glycol added is 5-15% of the total mass of the reaction system.

[0021] Furthermore, in step S3, the concentration of the aldehyded sodium alginate ethanol solution is 1-3 wt %, the concentration of the calcium chloride solution is 0.5-2 mol / L, and the mass ratio of the aldehyded sodium alginate ethanol solution to the calcium chloride solution is 1:1-1:3.

[0022] Furthermore, in step S4, the mass ratio of activated dolomite to formaldehyded calcium alginate is 1:0.5-1:2, the concentration of the sodium cyanoborohydride solution is 0.1-0.5 mol / L, and the amount of sodium cyanoborohydride solution added is 5-30% of the total mass of the activated dolomite and formaldehyded calcium alginate.

[0023] Furthermore, in step S3, the freeze-drying temperature is -80°C to -50°C, and the drying time is 12-24 hours.

[0024] Furthermore, the mesh size of the dolomite raw material is 80-200 mesh.

[0025] Furthermore, the environmentally friendly biomass fuel particles are prepared by the following steps: agricultural and forestry straw powder and recycled waste wood are crushed and then mixed with modified dolomite, calcium dihydrogen phosphate, and boron mud, ensuring that the powder above 10 mesh before pelletizing is ≥25%, and all particles are ≤3 mesh, and drying to a moisture content of 12-18% before pelletizing. After mixing the components evenly, cylindrical particles with a diameter of 6-12 mm, a length of 15-50 mm, and a moisture content of 6-10% are prepared, which are the environmentally friendly biomass fuel particles.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The present invention increases the porosity and specific surface area of dolomite through citric acid activation treatment, and combined with the coating of formaldehyded calcium alginate, it can adsorb fusible elements such as potassium and chlorine in the fuel, reducing the formation of low-melting-point ash during the combustion process;

[0028] Aldehyde-calcium alginate combines with the surface of activated dolomite through a Schiff base reaction to form a three-dimensional network structure, which improves the structural strength of the fuel particles. The aldehyde groups of the aldehyde-calcium alginate can form a covalent cross-linked network with the hydroxyl and amino groups in the biomass raw materials, acting as a physical binder. The porous structure of the aldehyde-calcium alginate and activated dolomite can adsorb heavy metals and reduce the emission of sulfur and nitrogen oxides. The hydrophobic nature of the aldehyde-calcium alginate can also inhibit water absorption by the fuel particles.

[0029] Boron mud decomposes to form a glassy substance. When coexisting with dolomite and phosphate, it can capture potassium and sodium alkali metals to form high-melting-point borates, reduce coking, and prevent potassium and sodium from reacting with silicates to form low-melting-point eutectics. During the decomposition of boron mud, water vapor and boric acid gas are released, causing volume expansion and forming a porous structure. The electron-deficient property of boron can also promote the oxidation of carbon soot and improve the burnout rate of biomass fuel.

[0030] Calcium dihydrogen phosphate decomposes into calcium pyrophosphate and calcium phosphate, releasing water vapor and phosphoric acid gas. Calcium pyrophosphate can react with silicon dioxide to form high-melting-point silicon phosphate, inhibiting coking and slagging. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The calorific value of the biomass fuel particles prepared in each embodiment of the present invention and the comparative example and the calorific value after storage for 30 days;

[0032] Figure 2 The slagging rate of the biomass fuel particles prepared in various embodiments and comparative examples of the present invention;

[0033] Figure 3 The softening temperature of the ash after combustion of the biomass fuel particles prepared in each embodiment of the present invention and the comparative example;

[0034] Figure 4 The smoke emission concentration of the biomass fuel particles prepared in various embodiments and comparative examples of the present invention;

[0035] Figure 5 The compressive strength of the biomass fuel particles prepared in various embodiments and comparative examples of the present invention.

[0036] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. They are used to explain the present invention together with the embodiments of the present invention and do not constitute a limitation of the present invention. DETAILED DESCRIPTION

[0037] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meanings as those familiar to those skilled in the art. Furthermore, any methods and materials similar or equivalent to those described herein can be applied to the present invention. The preferred embodiments and materials described herein are for illustrative purposes only and are not intended to limit the scope of this application.

[0039] The experimental methods in the following examples, unless otherwise specified, are all conventional methods, and the experimental materials used in the following examples, unless otherwise specified, are all purchased from commercial channels.

[0040] In all embodiments of the present invention, the agricultural and forestry straw powder includes crop straw and / or forestry prunings, the forestry prunings are plant residues produced during landscaping maintenance, the recycled waste wood is wood demolition materials, and the mesh size of the dolomite raw material is 80-200 mesh; in Examples 1-3 of the present invention, the agricultural and forestry straw powder is a combination of crop straw and forestry prunings in a mass ratio of 2:1, and the crop straw is wheat straw.

[0041] Example 1

[0042] An environmentally friendly biomass fuel pellet is composed of the following raw materials in parts by weight:

[0043] 40 parts of agricultural and forestry straw powder, 70 parts of recycled waste wood, 8 parts of modified dolomite, 3 parts of monocalcium phosphate and 3 parts of boron mud;

[0044] The modified dolomite is prepared by the following steps:

[0045] S1. Dolomite pretreatment: crush the dolomite raw material into particles with a particle size range of 0.5-2 mm, and pass through 10 mesh and 20 mesh sieves in sequence;

[0046] S2, activation treatment: adding the pretreated dolomite to a 15wt% citric acid solution, stirring at 30°C for 5h, then filtering, washing with clean water until neutral, and drying in an oven at 100°C for 12h to obtain activated dolomite;

[0047] S3. Preparation of formaldehyded calcium alginate: Sodium alginate was dissolved in ethanol to obtain a 3 wt % sodium alginate ethanol solution, sodium periodate was added as an oxidant at a molar ratio of sodium periodate to sodium alginate of 3:1, the mixture was stirred and reacted at 35°C in a dark environment for 8 h, ethylene glycol was added at 15% of the total mass of the reaction system, the mixture was reacted at 60°C for 4 h, the precipitated precipitate was filtered and dried to obtain formaldehyded sodium alginate, the formaldehyded sodium alginate was dissolved in ethanol to obtain a 3 wt % sodium alginate ethanol solution, the mixture was then added to a 2 mol / L calcium chloride solution, the mass ratio of the formaldehyded sodium alginate ethanol solution to the calcium chloride solution was 1:3, the reaction was carried out for 100 min, the generated gel was washed with deionized water, and freeze-dried at -80°C for 24 h to obtain the formaldehyded calcium alginate;

[0048] S4. Dolomite grafting modification: The activated dolomite and formaldehyded calcium alginate are mixed in a mass ratio of 1:2, and then a 0.5 mol / L sodium cyanoborohydride solution is added to moisten the mixture at a concentration of 30% of the total mass of the activated dolomite and the formaldehyded calcium alginate. The mixture is mixed at 60°C for 6 hours, and then the mixture is washed with deionized water and ethanol respectively, dried in an oven at 100°C for 12 hours, crushed, ground, and passed through a 20-mesh sieve to obtain the modified dolomite.

[0049] The environmentally friendly biomass fuel pellets are prepared by the following steps: agricultural and forestry straw powder and recycled waste wood are crushed and then mixed with modified dolomite, calcium dihydrogen phosphate, and boron mud, ensuring that the powder of the material above 10 mesh before pelletizing is ≥25% and all particles are ≤3 mesh, and drying the material to a moisture content of 18% before pelletizing. After uniformly mixing the components, cylindrical pellets with a diameter of 12 mm, a length of 50 mm, and a moisture content of 10% are prepared, namely the environmentally friendly biomass fuel pellets.

[0050] Example 2

[0051] An environmentally friendly biomass fuel pellet is composed of the following raw materials in parts by weight:

[0052] 25 parts of agricultural and forestry straw powder, 50 parts of recycled waste wood, 5 parts of modified dolomite, 1 part of monocalcium phosphate and 1 part of boron mud;

[0053] The modified dolomite is prepared by the following steps:

[0054] S1. Dolomite pretreatment: crush the dolomite raw material into particles with a particle size range of 0.5-2 mm, and pass through 10 mesh and 20 mesh sieves in sequence;

[0055] S2, activation treatment: adding the pretreated dolomite to a 5 wt% citric acid solution, stirring at 20°C for 2 h, then filtering, washing with clean water until neutral, and drying in an oven at 80°C for 6 h to obtain activated dolomite;

[0056] S3. Preparation of formaldehyded calcium alginate: Sodium alginate was dissolved in ethanol to obtain a sodium alginate ethanol solution with a concentration of 1 wt%, sodium periodate was added as an oxidant according to a molar ratio of sodium periodate to sodium alginate of 1:1, and the mixture was stirred and reacted for 4 h at 25°C in a dark environment, and then ethylene glycol was added at 5% of the total mass of the reaction system, and the mixture was reacted at 50°C for 2 h. The precipitated precipitate was filtered and dried to obtain formaldehyded sodium alginate, and the formaldehyded sodium alginate was dissolved in ethanol to obtain a sodium alginate ethanol solution with a concentration of 1 wt%, and then the mixture was added to a calcium chloride solution with a concentration of 0.5 mol / L, the mass ratio of the sodium alginate ethanol solution to the calcium chloride solution being 1:1, and the mixture was reacted for 30 min. The generated gel was washed with deionized water and freeze-dried at -50°C for 12 h to obtain the formaldehyded calcium alginate;

[0057] S4. Dolomite grafting modification: The activated dolomite and formaldehyded calcium alginate are mixed in a mass ratio of 1:0.5, and then a 0.1 mol / L sodium cyanoborohydride solution is added to moisten the mixture at a concentration of 5% of the total mass of the activated dolomite and the formaldehyded calcium alginate. The mixture is further mixed at 40°C for 4 hours, and then the mixture is washed with deionized water and ethanol respectively, dried in an oven at 80°C for 6 hours, crushed, ground, and passed through a 20-mesh sieve to obtain the modified dolomite.

[0058] The environmentally friendly biomass fuel pellets are prepared by the following steps: agricultural and forestry straw powder and recycled waste wood are crushed and then mixed with modified dolomite, calcium dihydrogen phosphate, and boron mud, ensuring that the powder of the material above 10 mesh before pelletizing is ≥25% and all particles are ≤3 mesh, and drying the material to a moisture content of 12% before pelletizing. After uniformly mixing the components, cylindrical pellets with a diameter of 6 mm, a length of 15 mm, and a moisture content of 6% are prepared, namely the environmentally friendly biomass fuel pellets.

[0059] Example 3

[0060] An environmentally friendly biomass fuel pellet is composed of the following raw materials in parts by weight:

[0061] 32 parts of agricultural and forestry straw powder, 60 parts of recycled waste wood, 1 part of modified dolomite, 2 parts of monocalcium phosphate and 2 parts of boron mud;

[0062] The modified dolomite is prepared by the following steps:

[0063] S1. Dolomite pretreatment: crush the dolomite raw material into particles with a particle size range of 0.5-2 mm, and pass through 10 mesh and 20 mesh sieves in sequence;

[0064] S2, activation treatment: adding the pretreated dolomite to a 10 wt% citric acid solution, stirring at 25°C for 3.5 hours, then filtering, washing with clean water until neutral, and drying in a 90°C oven for 9 hours to obtain activated dolomite;

[0065] S3. Preparation of formaldehyded calcium alginate: Sodium alginate was dissolved in ethanol to obtain a 2 wt % sodium alginate ethanol solution, sodium periodate was added as an oxidant at a molar ratio of sodium periodate to sodium alginate of 2:1, the mixture was stirred and reacted at 30°C in a dark environment for 6 h, ethylene glycol was added at 10% of the total mass of the reaction system, the mixture was reacted at 55°C for 3 h, the precipitated precipitate was filtered and dried to obtain formaldehyded sodium alginate, the formaldehyded sodium alginate was dissolved in ethanol to obtain a 2 wt % sodium alginate ethanol solution, the mixture was then added to a 1.25 mol / L calcium chloride solution, the mass ratio of the formaldehyded sodium alginate ethanol solution to the calcium chloride solution being 1:2, the reaction was carried out for 65 min, the generated gel was washed with deionized water, and freeze-dried at -60°C for 18 h to obtain the formaldehyded calcium alginate;

[0066] S4. Dolomite grafting modification: The activated dolomite and formaldehyded calcium alginate are mixed in a mass ratio of 1:1.25, and then a 0.3 mol / L sodium cyanoborohydride solution is added to moisten the mixture at a concentration of 17.5% of the total mass of the activated dolomite and the formaldehyded calcium alginate. The mixture is further mixed at 50°C for 5 hours, and then the mixture is washed with deionized water and ethanol respectively, dried in an oven at 90°C for 9 hours, crushed, ground, and sieved through a 20-mesh sieve to obtain the modified dolomite.

[0067] The environmentally friendly biomass fuel pellets are prepared by the following steps: agricultural and forestry straw powder and recycled waste wood are crushed and then mixed with modified dolomite, calcium dihydrogen phosphate, and boron mud, ensuring that the powder of the material above 10 mesh is ≥25% and all particles are ≤3 mesh before pelletizing, and drying the material to a moisture content of 15% before pelletizing. After uniformly mixing the components, cylindrical pellets with a diameter of 9 mm, a length of 30 mm, and a moisture content of 8% are prepared, namely the environmentally friendly biomass fuel pellets.

[0068] Example 4

[0069] The difference between this embodiment and embodiment 3 is that the crop straw is a combination of corn straw and rice straw in a mass ratio of 1:1, and the other components, contents, and preparation methods are the same as those in embodiment 3.

[0070] Example 5

[0071] The difference between this embodiment and embodiment 3 is that the agricultural and forestry straw powder only contains crop straw, and the remaining components, contents, and preparation methods are the same as those in embodiment 3.

[0072] Example 6

[0073] The difference between this embodiment and embodiment 3 is that the agricultural and forestry straw powder only contains forestry prunings, and the remaining components, contents, and preparation methods are the same as those in embodiment 3.

[0074] Comparative Example 1

[0075] The difference between this comparative example and Example 3 is that an equal amount of activated dolomite is used in place of modified dolomite in the environmentally friendly biomass fuel particles, and the remaining components, contents, and preparation methods are the same as those in Example 3.

[0076] Comparative Example 2

[0077] The difference between this comparative example and Example 3 is that the boron mud component is removed from the environmentally friendly biomass fuel particles, and the remaining components, contents, and preparation methods are the same as those in Example 3.

[0078] Comparative Example 3

[0079] The difference between this comparative example and Example 3 is that the calcium dihydrogen phosphate component is removed from the environmentally friendly biomass fuel particles, and the remaining components, contents, and preparation methods are the same as those in Example 3.

[0080] Comparative Example 4

[0081] The difference between this comparative example and Example 3 is that the modified dolomite component is removed from the environmentally friendly biomass fuel particles, and the remaining components, contents, and preparation methods are the same as those in Example 3.

[0082] Comparative Example 5

[0083] The difference between this comparative example and Example 3 is that the modified dolomite, calcium dihydrogen phosphate and boron mud are removed from the environmentally friendly biomass fuel particles, and sodium lignin sulfonate is used as a binder instead of modified dolomite, calcium dihydrogen phosphate and boron mud. The other components, contents and preparation methods are the same as those in Example 3.

[0084] Experimental example

[0085] The calorific value of the biomass fuel particles prepared in each embodiment and comparative example was measured with reference to GB / T 30727-2014 "Determination of Calorific Value of Solid Biomass Fuels", and the calorific value was measured after the biomass fuel particles were stored for 30 days at a temperature of 30°C and a relative humidity of 60%. The calorific value is the core indicator of the energy density of biomass fuel and directly determines the combustion efficiency and economy of the fuel. By measuring the calorific value of the biomass fuel particles after storage for 30 days, the hydrophobicity and water resistance of the biomass fuel particles can be characterized. The above results are shown in Figure 1 .

[0086] The slagging rate of the biomass fuel particles prepared in each embodiment and comparative example was measured with reference to NB / T 34025-2015 "Test method for slagging of biomass solid fuels". The slagging rate is the proportion of unburned carbon in the ash after combustion, which is used to evaluate the tendency of ash melting and agglomeration after fuel combustion. A high slagging rate can easily lead to blockage of the boiler heating surface and reduce the heat transfer efficiency. The results are shown in Figure 2 .

[0087] The softening temperature (ST) of the ash of the biomass fuel particles prepared in each example and comparative example after combustion was measured with reference to GB / T 30726-2014 "Determination of Ash Fusibility of Solid Biomass Fuels" to characterize the ash fusibility of the biomass fuel particles. The softening temperature (ST) is defined as the temperature at which the ash cone bends until the cone tip touches the support plate or the ash cone becomes spherical. This temperature indicates that the ash begins to soften significantly and loses its original structural strength. It is the key turning point for the ash fusibility to transition from solid to liquid, which directly affects the slagging tendency and operational stability of combustion equipment (such as boilers). The results are shown in Figure 3 .

[0088] The smoke emission concentration of the biomass fuel particles prepared in each embodiment and comparative example was measured with reference to GB / T 5468-1991 "Test Method for Boiler Smoke". The smoke emission concentration can directly reflect the emission of particulate matter after fuel combustion. The lower the value, the more complete the fuel combustion and the better the pollutant control effect. The results are shown in Figure 4 .

[0089] The compressive strength of the biomass fuel particles prepared in each example and comparative example was measured with reference to NY / T 1881.7-2010 "Test Methods for Biomass Solid Molded Fuels Part 7: Density". The compressive strength reflects the mechanical stability of the fuel particles during transportation and storage, and directly affects the ease of use. The higher the value, the denser the particle structure and the stronger the wear resistance. The results are shown in Figure 5 .

[0090] From the above test results, it can be seen that the calorific value of Examples 1-6 is significantly higher than that of the comparative example due to the addition of modified dolomite and boron mud, and the calorific value decreases less after storage, indicating that the hydrophobic effect of formaldehyded calcium alginate effectively inhibits water absorption. The slagging rate of Examples 1-6 is also lower than that of the comparative example, among which Example 3 has the lowest slagging rate and the highest softening temperature of the ash. This is due to the modified dolomite adsorbing potassium, chlorine and boron mud to generate high melting point borates. The smoke emission concentration of each embodiment is low, far below the national standard (≤200mg / m 3 ), which is related to the adsorption of heavy metals by formaldehyde-calcium alginate and the inhibition of sulfur oxide formation by phosphate. The compressive strength of each embodiment is high because formaldehyde-calcium alginate forms a covalent cross-linked network with biomass hydroxyl groups, thereby enhancing particle density. Comparative Example 5 has the lowest compressive strength due to the absence of additives, indicating that the modifier plays a leading role in improving mechanical strength.

[0091] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

[0092] The present invention and its embodiments are described above. Such description is not restrictive. The drawings show only one embodiment of the present invention, and actual applications are not limited thereto. In short, if a person skilled in the art is inspired by the above, and does not deviate from the purpose of the present invention, any method and embodiment similar to the technical solution without creative design shall fall within the scope of protection of the present invention.

Claims

1. An environmentally friendly biomass fuel particle, characterized by: The method is composed of the following raw materials in parts by weight: 25-40 parts of agricultural and forestry straw powder, 50-70 parts of recycled waste wood, 5-8 parts of modified dolomite, 1-3 parts of calcium dihydrogen phosphate and 1-3 parts of boron mud; The modified dolomite is prepared by the following steps: S1. Dolomite pretreatment: crush the dolomite raw material into particles with a particle size range of 0.5-2 mm, and pass through 10 mesh and 20 mesh sieves in sequence; S2. Activation treatment: adding the pretreated dolomite to a citric acid solution, stirring at 20-30°C for 2-5 hours, then filtering, washing with clean water until neutral, and drying in an oven at 80-100°C for 6-12 hours to obtain activated dolomite; S3. Preparing formaldehyded calcium alginate: dissolving sodium alginate in ethanol to obtain a sodium alginate ethanol solution, adding sodium periodate as an oxidant, stirring and reacting at 25-35° C. in the dark for 4-8 hours, then adding ethylene glycol, reacting at 50-60° C. for 2-4 hours, filtering the precipitate, and drying to obtain formaldehyded sodium alginate, dissolving the formaldehyded sodium alginate in ethanol to obtain a formaldehyded sodium alginate ethanol solution, then adding the solution to a calcium chloride solution, reacting for 30-100 minutes, washing the resulting gel with deionized water, and freeze-drying to obtain the formaldehyded calcium alginate; S4. Dolomite grafting modification: The activated dolomite and formaldehyded calcium alginate are mixed, and then sodium cyanoborohydride solution is added for moistening. The mixture is mixed at 40-60° C. for 4-6 hours. The mixture is then washed with deionized water and ethanol, respectively, and dried in an oven at 80-100° C. for 6-12 hours. The mixture is crushed, ground, and passed through a 20-mesh sieve to obtain the modified dolomite.

2. The environmentally friendly biomass fuel particles according to claim 1 are characterized by: In step S1, the concentration of the citric acid solution is 5-15 wt%.

3. The environmentally friendly biomass fuel particles according to claim 2, characterized in that: In step S3, the concentration of the sodium alginate ethanol solution is 1-3 wt %, the molar ratio of sodium periodate to sodium alginate is 1:1-3:1, and the amount of ethylene glycol added is 5-15% of the total mass of the reaction system.

4. The environmentally friendly biomass fuel particles according to claim 3 are characterized by: In step S3, the concentration of the aldehyded sodium alginate ethanol solution is 1-3 wt %, the concentration of the calcium chloride solution is 0.5-2 mol / L, and the mass ratio of the aldehyded sodium alginate ethanol solution to the calcium chloride solution is 1:1-1:

3.

5. The environmentally friendly biomass fuel particles according to claim 4 are characterized by: In step S4, the mass ratio of activated dolomite to formaldehyded calcium alginate is 1:0.5-1:2, the concentration of the sodium cyanoborohydride solution is 0.1-0.5 mol / L, and the amount of sodium cyanoborohydride solution added is 5-30% of the total mass of the activated dolomite and formaldehyded calcium alginate.

6. The environmentally friendly biomass fuel particles according to claim 5, characterized in that: In step S3, the freeze-drying temperature is -80°C to -50°C, and the drying time is 12-24 hours.

7. The environmentally friendly biomass fuel particles according to claim 6, characterized in that: The agricultural and forestry straw powder is crop straw and / or forestry prunings; the crop straw includes but is not limited to a combination of one or more of wheat straw, corn straw, rice straw, sorghum straw, rice husk, and peanut shell; the forestry prunings are plant residues produced during landscaping maintenance.

8. The environmentally friendly biomass fuel particles according to claim 7, characterized in that: The recycled waste wood includes but is not limited to one or more combinations of wood solid wood floors, wood demolition materials, wood construction site formwork waste, and old wood packaging boards.

9. The environmentally friendly biomass fuel particles according to claim 8, characterized in that: The mesh number of the dolomite raw material is 80-200 mesh.

10. The environmentally friendly biomass fuel particles according to claim 9, characterized in that: The preparation method is prepared by the following steps: crushing agricultural and forestry straw powder and recycled waste wood, mixing them with modified dolomite, calcium dihydrogen phosphate, and boron mud, ensuring that the powder above 10 mesh in the material before pelletizing is ≥25%, and all particles are ≤3 mesh, and drying the material to a moisture content of 12-18% before pelletizing. After uniformly mixing the components, cylindrical particles with a diameter of 6-12 mm, a length of 15-50 mm, and a moisture content of 6-10% are prepared, namely the environmentally friendly biomass fuel particles.

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