Carbonaceous reducing agent pellet mainly composed of low-rank non-caking coal, and use thereof

Abstract

The present invention belongs to the technical field of efficient and clean utilization of resources, and relates to a carbonaceous reducing agent pellet mainly composed of low-rank non-caking coal, and the use thereof. The carbonaceous reducing agent pellet is mainly composed of low-rank non-caking coal, and a composite organic binder, silica fume and a reinforcing agent are used in combination; same are mixed and subjected to compression molding, and then placed in a sintering furnace and roasted at 450-650°C in a protective atmosphere; and furnace cooling is performed until the carbonaceous reducing agent pellet is obtained. The pellet developed by the present invention has the characteristics of a high fixed carbon content, high pellet strength, high crushing resistance, a good static spheroidization index, a low content of introduced impurities and high reaction activity, such that the pellet is particularly suitable for industrial silicon smelting. In the present invention, low-rank non-caking coal is used in a large proportion, and the silica fume produced by a submerged arc furnace is recycled, such that the present invention is clean and environmentally friendly, and can be completely used for smelting and production of industrial silicon, thereby reducing smelting unit consumption and production cost; and the carbonaceous reducing agent pellet can replace or partially replace charcoal to become a carbonaceous reducing agent for industrial silicon smelting.

Description

Carbonaceous reducing agent pellet taking low-rank non-caking coal as main body and application thereof TECHNICAL FIELD

[0001] The present application relates to a kind of carbonaceous reducing agent pellet taking low-rank non-caking coal as main body and application thereof, belong to resource efficient clean utilization technical field. BACKGROUND

[0002] At present, the production of industrial silicon is mainly to place silica and carbonaceous reducing agent in electric arc furnace for smelting. In actual production, various carbonaceous reducing agents (petroleum coke, charcoal, coal, etc.) are reasonably mixed and proportioned, so that different materials can be fully burned and utilized. China is rich in coal, poor in oil and gas, and the energy structure makes coal resources still support the main energy of domestic economic construction in the foreseeable future. In the coal resources production and reserves of China, the proportion of high-quality anthracite and coking coal is relatively low, while the reserves of low-rank coal with high volatile content are abundant, accounting for about 48% of China's coal resources reserves. Low-rank coal is a low-value resource in industrial silicon smelting, with very low utilization rate and low price. It is of great significance to study how to more effectively apply low-rank coal to industrial silicon smelting.

[0003] The carbonaceous reducing agent accounts for 25%-30% of the production cost in the industrial silicon industry. At present, low-rank coal is not used in large proportions in the industrial silicon industry. The main reason is that, compared with existing carbonaceous reducing agents such as charcoal, petroleum coke and clean coal, the fixed carbon content of low-rank coal is relatively low, the volatile content is high, and the cohesiveness is weak. The production cost of low-rank non-caking or weakly caking coal is extremely low. If it can be optimized and improved to meet the requirements of industrial silicon smelting and replace part of the existing carbonaceous reducing agents, it will have great significance for the efficient use of low-rank coal and the field of industrial silicon smelting. Low-rank coal is a low-value resource in industrial silicon smelting, with very low utilization rate and low price. It is of great significance to study how to more effectively apply low-rank coal to industrial silicon smelting.

[0004] Microsilica is the dust formed by the oxidation of Si and SiO gas in the flue during the production of metallic silicon in a submerged arc furnace, also known as silica fume. The main chemical composition of microsilica is SiO2, of which SiO2 mainly exists in non-crystalline phase (or amorphous SiO2), with a content of ≥80%, few impurities, a specific surface area of 20-28 m 2 / g, and more than 80% of particles with a particle size of less than 10 μm, high chemical activity, easy reaction with alkali, and characteristics of light weight, high refractoriness and strong activity. In recent years, with the strengthening of environmental protection, the production of microsilica has increased year by year. If it is directly discharged or discarded, it will cause environmental pollution and waste of resources. At present, the utilization rate of microsilica is less than one-third. From the perspective of cost saving, returning microsilica to the smelting process of submerged arc furnace is one of the best choices for easy operation and reducing economic losses. Technical issues

[0005] Currently, the utilization of low-rank non-caking coal is limited. Patent 202211156507.7 involves mixing biomass binder and low-rank non-caking coal powder, while simultaneously spraying alkali metal or alkaline earth metal solutions, water, and inorganic binder solutions onto the mixture in sequence and uniformly. The mixture is then cold-pressed into pellets, calcined at low temperature under anaerobic conditions, and cooled to room temperature in the furnace to obtain composite carbonaceous reducing agent pellets for industrial silicon smelting. However, carbonaceous reducing agents have strict requirements for ash content, while biomass binders have high ash content, which is detrimental to subsequent industrial silicon smelting. Patent CN202311453081.6 utilizes different binding coals to coat charcoal powder, petroleum coke, and low-rank non-caking coal, then combines them with water, binder, and alkali metal additives to press them into pellets, and finally prepares the product through microwave calcination. However, this method utilizes low-rank non-caking coal extensively, only covering the inner layer, resulting in low utilization. Currently, there are no patents or papers that directly combine low-rank non-caking coal and microsilica powder to prepare carbonaceous reducing agent pellets for industrial silicon smelting. At the same time, the composite organic binder selected in this invention avoids the introduction of impurity elements such as Fe, Al, Ca, P, Ti and B. In order to actively respond to the green development of traditional energy and realize the transformation of low-value resources into "treasures", the efficient utilization of resources in the smelting process is of great practical significance for reducing the production cost of industrial silicon, improving the efficiency of resource and energy utilization and environmental protection. Technical solutions

[0006] To address the problem of low utilization rates of low-rank non-caking coal and microsilica powder in existing technologies, this invention proposes a carbonaceous reducing agent pellet with low-rank non-caking coal as the main component and its application. Specifically, it includes a carbonaceous reducing agent pellet with low-rank non-caking coal as the main component coupled with microsilica powder, its preparation method, and its application in industrial silicon smelting. The industrial silicon carbonaceous reducing agent pellet of this invention mainly uses low-rank non-caking coal as the main carbonaceous material, which is mixed uniformly with a composite organic binder and microsilica powder to obtain mixture A; a reinforcing agent is added to water to make it a wetting medium, and then added to mixture A for wet milling to obtain mixture B; then it is pressed and shaped into cylindrical pellet precursor C under a pressure of 10-20 MPa; then the pellet precursor C is placed in a microwave tube furnace with argon gas and calcined at a temperature of 450-650℃ for 60-90 min, and then cooled to room temperature with the furnace to obtain the industrial silicon carbonaceous reducing agent pellet. The composite organic binder mainly consists of a starch matrix and a binder. The binder is composed of at least one or more of the following two categories: sodium carboxymethyl cellulose and hydroxypropyl cellulose, which improve thermoplasticity; and sodium lignosulfonate, sodium dodecylbenzene sulfonate, polyacrylamide, and sodium humate, which improve surface activity and formability. The reinforcing agent mainly consists of one or two of sodium hydroxide and potassium hydroxide combined with alkali metal additives. The pellets prepared by this invention have high fixed carbon content, high pellet strength, high breakage resistance, good static spherical index, low impurity content, and high reactivity. It can be widely used for low-rank non-caking coal, and can recycle the microsilica powder produced by submerged arc furnaces. It is clean and environmentally friendly, and can be fully used in the smelting and production of industrial silicon, reducing smelting unit consumption and production costs. It can replace or partially replace charcoal as a carbonaceous reducing agent for industrial silicon smelting.

[0007] The present invention discloses a carbonaceous reducing agent pellet based on low-rank non-caking coal. The preparation of the carbonaceous reducing agent pellet includes the following steps:

[0008] (1) Dry low-rank non-caking coal is crushed and ground to a particle size of less than 5 mm and the particle size of 1-3 mm accounts for 30-60% to obtain micro spherical particles of low-rank non-caking coal; the caking index of low-rank non-caking coal is less than 50, which of course includes non-caking coal with a caking index of less than 5, and preferably non-caking coal with a caking index of less than 2.

[0009] (2) Using low-rank non-caking coal microspheres as the main carbonaceous material for pellets, a composite organic binder and microsilica powder are added, and then mixed evenly to obtain a mixture A with an average particle size of 0.75-1.5 mm; the composite organic binder is composed of D and a binder, the microsilica powder has SiO2 greater than 80 wt% and a particle size less than 1.5 mm; D is a polysaccharide and / or a polysaccharide polymer; the binder is selected from at least one of lignin sulfonate, dodecylbenzene sulfonate, polyacrylamide, and humate.

[0010] (3) Add the reinforcing agent to water to prepare an alkaline wetting medium containing alkali metal additives, and then add it to mixture A for wet grinding and uniform mixing to obtain mixture B with an average particle size of 0.5-1mm; the reinforcing agent is an alkaline substance containing alkali metal elements;

[0011] (4) The mixture B is pressed under a pressure of 10~20MPa to obtain the precursor C;

[0012] (5) Place the pellet precursor C in a microwave tube furnace with argon gas and microwave roast it at a temperature of 450~650°C. Then cool it to room temperature with the furnace to obtain the industrial silicon carbonaceous reducing agent pellets.

[0013] As a preferred method, the drying temperature of low-rank non-caking coal is 105~110℃ for 12~36h.

[0014] In step (1), the fixed carbon content of the low-rank non-caking coal is ≥55wt.%, the ash content is <5wt.%, and the caking index n is less than or equal to 1, which of course includes a caking index of 0.

[0015] In step (2), the proportion of the main carbonaceous material, low-rank non-caking coal, in mixture A is 84-92 wt.%, the amount of composite organic binder added is 4-8 wt.%, and the amount of microsilica powder added is 4-8 wt.%.

[0016] In step (2), the composite organic binder is composed of starch and adhesive aids. The starch content in the composite organic binder is 50-65 wt.%, and the remainder is adhesive aids. The adhesive aids are composed of at least one or more of the following two categories: sodium carboxymethyl cellulose and hydroxypropyl cellulose, which improve thermoplasticity; and sodium lignosulfonate, sodium dodecylbenzene sulfonate, polyacrylamide, and sodium humate, which improve surface activity and formability. The adhesive aid that improves thermoplasticity accounts for 10-20 wt.% of the total mass of the composite organic binder, and the adhesive aid that improves surface activity and formability accounts for 25-30 wt.% of the total mass of the composite organic binder.

[0017] As a further preferred option, if there are multiple combinations of the two types of adhesives (i.e., adhesives that improve thermoplasticity and adhesives that improve surface activity and formability), then the proportions of various organic substances in the same type of adhesive are the same.

[0018] The microsilica powder in step (2) is taken from the flue of the submerged arc furnace, with a SiO2 content of 85-95% and a mass density of 500-670 kg / m³. 2 .

[0019] In step (3), the reinforcing agent is mainly composed of one or two of sodium hydroxide and potassium hydroxide and alkali metal additives, and the alkali metal additives are one or more of K2CO3, Na2CO3 and NaHCO3 powders; the addition ratio of the alkali wetting medium is 8-12 wt. of the mixture A.

[0020] In step (3), the proportions of hydroxide, alkali metal additive and water added to the alkaline wetting medium are 4-6 wt.%, 6-9 wt.% and 85-90 wt.%, respectively. If the hydroxide and alkali metal additive are not the same, then the proportion of each is the same.

[0021] In step (4), the mixture B is pressed under a pressure of 10~20MPa to obtain a cylindrical pellet precursor C with a diameter of 60~70mm and a height of 85~100mm.

[0022] In step (5), the microwave roasting time is 60-90 min and the microwave power is 3-5 kW.

[0023] In step (5), the final pellets have a fixed carbon content ≥70wt.%, cold pressing strength ≥12MPa, breakage resistance ≥85%, hot pressing strength ≥8MPa, static sphericity index ≥0.7, and reactivity ≥90% at 1100℃.

[0024] The carbonaceous reducing agent pellets disclosed in this invention are used in silicon smelting. This includes their use in industrial silicon smelting.

[0025] Selection principles for binders: In the industrial silicon production process, the impurity content in raw materials must be strictly controlled. During the refining process of industrial silicon, Na oxides are reduced to gaseous metallic elements at around 1000℃ and escape; therefore, there are no specific requirements for Na content in binders. While Al, Ca, P, Ti, and B can be reduced through refining, the maximum removal efficiency is only 70%, therefore binders cannot contain large amounts of Al, Ca, P, Ti, and B. Currently, there is no effective method for removing Fe; therefore, the control of Fe content in raw materials is the most stringent in industrial silicon production, requiring the lowest possible Fe content. The composite organic binder selected in this invention consists of a starch matrix and a binder aid, neither of which involves Fe, Al, Ca, P, Ti, or B.

[0026] The relevant principles involved in the interaction between reinforcing agents, microsilica powder, and composite organic binders are as follows: The addition of alkali metal additives in the reinforcing agent promotes the structural rearrangement and crystallization effect of low-rank non-caking coal, increases porosity, and thus increases the contact area, thereby improving reaction efficiency. At the same time, K and Na also have a promoting effect on industrial silicon smelting. Meanwhile, the hydroxide in the reinforcing agent combines with water to form an alkaline solution, which modifies the starch and adhesion promoter in the composite organic binder, reacts with the organic matter, changes the physical and chemical properties of the organic matter, and alters the chemical structure to generate new chemical bonds and functional groups. In addition, the alkaline solution can also neutralize protons in the reaction system, act as an acid-binding agent, activate molecular ions, and generate negative charges. The mutual repulsion of like charges causes molecules to straighten and form a network structure, thereby locking in water and increasing its interaction with water molecules. After the alkaline solution combines with water molecules, it causes the coiled molecules to unwind and form a network structure. These changes help improve the bonding performance of the binder. Microsilica powder is finer, and its addition to pellets enhances intermolecular movement, strengthens atomic migration, and increases interparticle bonding, promoting the fusion of all particles within the pellets and significantly increasing the degree of polymerization of the internal network structure. Furthermore, the surface of microsilica particles contains numerous irregularly shaped molecules and atoms with high chemical reactivity, exhibiting a strong reactivity with alkaline solutions (nSiO2 + 2NaOH → Na2O·nSiO). 2 + H2O), where Na2O·nSiO2 is the main component of water glass, which is a gel. Moreover, excessive microsilica powder will fill the tiny pores of the microspheres, which can improve the overall performance of the pellets. Beneficial effects

[0027] (1) This invention utilizes low-rank non-caking coal resources on a large scale and in a high efficiency, expands the field of coking coal, and can effectively alleviate the contradiction between some resource shortages and the direct production needs of industry and economic development. At the same time, from the perspective of cost saving, since the microsilica powder comes directly from the silicon plant, returning the microsilica powder to the electric arc furnace smelting process is one of the simplest and easiest options to operate and reduce economic losses, thus realizing the recycling and reuse of microsilica powder resources.

[0028] (2) The fine particles of microsilica powder result in a large number of voids inside the pellets, which helps to reduce the burn-off rate during smelting, ensure full utilization, and guarantee the efficient use of carbonaceous materials. At the same time, it appropriately improves the stability of combustion. In addition, it can improve the bonding performance and high-temperature consolidation performance when combined with alkaline solution. The microsilica powder can be reintroduced into the furnace to improve the recovery rate of silica, reduce silica consumption, and lower production costs.

[0029] (3) After microwave roasting and activation, the reinforcing agent and the high volatile matter of low-rank non-caking coal can increase the porosity of the pellets and improve their reactivity. At the same time, microwave-assisted roasting of the pellets reduces the dielectric loss of the carbon material, causing the carbon material to be heated to the sintering temperature as a whole, thereby achieving densification and improving the strength of the pellets. Meanwhile, the intake of alkali metals K and Na plays an important role in saving smelting power consumption, reducing process energy consumption, improving the production efficiency of the submerged arc furnace, reducing SiC deposition at the furnace top, and slowing down the rise of the furnace bottom.

[0030] (4) The composite organic binder in this invention has the characteristics of long-chain molecules and high viscosity after hydration. The main starch can be combined with alkaline solution to modify and improve the bonding ability. At the same time, it avoids the introduction of impurity elements such as Fe, Al, Ca, P, Ti and B, which is conducive to bonding fine powder into agglomerates, reducing the amount of binder used and the introduction of impurities. At low temperature, it can increase the low temperature strength of the pellets. At high temperature, it has good stability. Under high temperature conditions, it acts as the pellet skeleton, weakening the adverse effect of the decrease in pellet strength after the loss of organic matter. At the same time, it fully considers the characteristics of industrial silicon smelting, reduces unnecessary impurities, inhibits the pulverization of powder agglomerates in the electric arc furnace, and further improves the utilization rate of resources.

[0031] (5) The present invention adopts wet grinding and mixing. During the grinding process, the wetting medium can effectively penetrate and promote the bonding of powder, increase the contact area and improve the porosity, so that the mixed carbon material has high reactivity and improves the reaction efficiency of industrial silicon smelting. Attached Figure Description

[0032] Figure 1 is a photograph of the precursor and calcined product in Examples 1 and 2 and Comparative Example 1.

[0033] Figure 2 shows a photograph of the pellets during the wax sealing process.

[0034] In Figure 1, the white and grayish-white parts on the surface of the pellets represent the composite organic binder and microsilica powder. Figure A shows the pellet precursor obtained in step 4 of Example 1, Figure B shows the precursor obtained in step 4 of Comparative Example 1, and the pellets on the left and right sides of Figure C are the pellet precursor obtained in step 4 of Example 2 and the industrial silicon carbonaceous reducing agent pellets obtained after microwave calcination in step 5, respectively. It can be seen that the pellets are significantly smaller after calcination, and the fixed carbon content of the pellets increases, which is due to the release of volatiles. At the same time, some substances in the composite organic binder are carbonized, which also makes the fixed carbon content in the comparative example containing the composite organic binder higher than that without the composite organic binder under the same conditions.

[0035] Figure 2 shows the basic situation of the pellets when they are sealed with wax. Embodiments of the present invention

[0036] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the content described.

[0037] The microsilica powder described in this embodiment of the invention was taken from the flue of a submerged arc furnace in a silicon plant in Yunnan Province. It has a SiO2 content of 91% and a mass density of 617 kg / m³. 2 .

[0038] In this invention, the fixed carbon content of the carbonaceous reducing agent pellets is measured according to GB / T 212-2008. First, the mass percentages of moisture, volatile matter, and ash are measured. Then, the mass percentage of the three components is subtracted from 100% to obtain the mass percentage of fixed carbon.

[0039] In this invention, the reactivity at 1100℃ was measured according to GB / T 220-2001. First, the pellets were dry-distilled to remove volatiles. Then, they were placed in a reaction tube and heated, while a certain flow rate of carbon dioxide was introduced to react with the pellets. The carbon dioxide content in the gas after the reaction was measured, and the percentage of carbon dioxide reduced to carbon monoxide relative to the amount of carbon dioxide introduced, i.e., the carbon dioxide reduction rate (%), was used as an indicator of the chemical reactivity of the pellets.

[0040] In this invention, the breakage resistance of the pellets is tested according to GB / T 15459-1995. The pellets are dropped from a height of 2m onto a 3mm thick steel plate three times, and then sieved using a sieve with a 25mm aperture. The mass of the fragments on the sieve is weighed, and the breakage resistance is calculated by dividing the mass of the fragments on the sieve by the total mass of the pellets and then multiplying by 100%.

[0041] In this invention, the cold compressive strength is determined by drying the pressed pellets at 100°C to remove moisture, then placing the pellets on a strength testing machine. The testing machine applies pressure to the pellets at a uniform speed until the pellets rupture. The maximum pressure reading on the testing machine is the cold compressive strength of the pellets.

[0042] In this invention, the hot-compression strength is determined by placing the pressed pellets in an atmosphere furnace at 800°C for 1 hour while simultaneously introducing inert gas such as Ar into the furnace. After the heat preservation is completed, the pellets are removed and allowed to cool to room temperature before being placed on a strength testing machine. The testing machine applies pressure to the pellets at a uniform speed until the pellets rupture. The maximum pressure value on the testing machine is then read as the hot-compression strength of the pellets.

[0043] In this invention, the static sphericity index K is a parameter that comprehensively reflects the particle size, particle size distribution, specific surface area, and hydrophilicity of the material. It is calculated using the ratio of maximum molecular water to (maximum capillary water - maximum molecular water).

[0044] The maximum molecular water content of the pellets was measured by pressure filtration. The pellet powder sample was moistened with water until saturated and allowed to stand for 2 hours to ensure thorough wetting of the particle surface. Then, the lower stopper was placed in a mold, and 20 sheets of filter paper (60 mm in diameter) were placed on the lower stopper. The prepared pellet powder sample was then spread evenly on the filter paper inside the mold. The mold containing the sample was placed on a hydraulic press at 65 kg / cm². 2 The pressure was applied for 5 minutes, and the sample was then removed and weighed to obtain G1. The sample was then dried at 110℃ to constant weight to obtain G2. The maximum molecular water content can be calculated using (G1-G2) / G1×100%.

[0045] The maximum capillary water content of the pellets was measured using a volumetric method and a wax sealing method. The mass of the dried pellets was recorded as G3. The pellets were placed in a beaker containing paraffin wax, ensuring that the wax completely submerged the pellets. The beaker was heated to allow the paraffin wax to penetrate the pellets through the pores. Once no more bubbles were generated on the surface of the pellets, they were removed, cooled to room temperature, and weighed, which was recorded as G4. The mass of water was converted using the density of water and paraffin wax, which was then converted to G5. The maximum capillary water content of the pellets was calculated using G5 / (G5-G3)×100%. The reason why the saturated water method could not be used and the wax sealing method had to be used was that the main body of the pellets was low-rank non-caking coal, which is porous and absorbent. When subjected to the impact and pressure of water, the internal structure could not remain stable, resulting in the pellets breaking apart.

[0046] Example 1: A method for preparing carbonaceous reducing agent pellets based on low-rank non-caking coal coupled with microsilica powder for industrial silicon smelting, the specific steps of which are as follows:

[0047] Low-rank non-caking coal, after being vacuum dried at 110℃ for 24 hours, was crushed and ground to a particle size of less than 5 mm, with 30% of the particles being 1-3 mm, to obtain micro-spherical particles of low-rank non-caking coal; the fixed carbon content of the low-rank non-caking coal was 59.14 wt.%, the ash content was 4.07 wt.%, the remainder was volatile matter, and the caking index n was 0.

[0048] (2) Low-rank non-caking coal particles are used as the main carbonaceous material of the pellets. Composite organic binder and microsilica powder are added and then mixed evenly to obtain a mixture A with an average particle size of 0.75 mm. The proportion of low-rank non-caking coal as the main carbonaceous material is 92 wt.%, the amount of composite organic binder added is 4 wt.%, and the amount of microsilica powder added is 4 wt.%.

[0049] The composite organic binder is composed of starch and a binder, wherein the starch content is 55 wt.% and the remainder is a binder; the binder is composed of 17 wt.% sodium carboxymethyl cellulose to improve thermoplasticity and 28 wt.% sodium dodecylbenzene sulfonate to improve surface activity and formability.

[0050] (3) Prepare an alkaline wetting medium by mixing 6 wt.% sodium hydroxide, 9 wt.% K2CO3 and 85 wt.% water. Add 8 wt.% alkaline wetting medium to the mixture A based on 100 wt.% of the mixture A and wet grind and mix evenly to obtain a mixture B with an average particle size of 0.5 mm.

[0051] (4) The mixture B was pressed under a pressure of 10 MPa to obtain a cylindrical pellet precursor C with a diameter of 60 mm and a height of 90 mm;

[0052] (5) Place the pellet precursor C in a microwave tube furnace with argon gas introduced, and microwave roast at a temperature of 450°C, a roasting time of 90 min, and a microwave power of 4 kW. After roasting, cool the pellet to room temperature with the furnace to obtain the industrial silicon carbonaceous reducing agent pellet.

[0053] The carbonaceous reducing agent pellets prepared in this embodiment have a fixed carbon content of 72.37 wt.%, a cold compressive strength of 12.24 MPa, a breakage rate of 87.64%, a hot compressive strength of 8.97 MPa, a static sphericity index of 0.72, and a reactivity of 92.74% at 1100℃.

[0054] Comparative Example 1: The difference between this comparative example and Example 1 is that no microsilica powder and composite organic binder are added;

[0055] The carbonaceous reducing agent pellets prepared in this comparative example have a fixed carbon content of 71.24 wt.%, a cold compressive strength of 10.56 MPa, a breakage rate of 80.12%, a hot compressive strength of 5.61 MPa, a static sphericity index of 0.25, and a reactivity of 81.25% at 1100℃.

[0056] Comparative Example 2: The difference between this comparative example and Example 1 is that no microsilica powder and reinforcing agent are added;

[0057] The carbonaceous reducing agent pellets prepared in this comparative example have a fixed carbon content of 71.98 wt.%, a cold compressive strength of 10.91 MPa, a breakage rate of 81.57%, a hot compressive strength of 6.14 MPa, a static sphericity index of 0.34, and a reactivity of 83.56% at 1100℃.

[0058] Example 2: A method for preparing carbonaceous reducing agent pellets based on low-rank non-caking coal coupled with microsilica powder for industrial silicon smelting, the specific steps of which are as follows:

[0059] (1) The low-rank non-caking coal dried under vacuum at 110℃ for 24h was crushed and ground to a particle size of less than 5mm and 60% of the particles were 1-3mm, to obtain micro spherical particles of low-rank non-caking coal; the fixed carbon content of the low-rank non-caking coal was 58.91wt.%, the ash content was 4.13wt.%, the remainder was volatile matter, and the caking index n was 0.

[0060] (2) Low-rank non-caking coal particles are used as the main carbonaceous material of the pellets. Composite organic binder and microsilica powder are added and then mixed evenly to obtain a mixture A with an average particle size of 1 mm. The proportion of low-rank non-caking coal as the main carbonaceous material is 90 wt.%, the amount of composite organic binder added is 6 wt.%, and the amount of microsilica powder added is 4 wt.%.

[0061] The composite organic binder is composed of starch and a binder, wherein the starch content is 50 wt.% and the remainder is a binder; the binder is composed of 20 wt.% hydroxypropyl cellulose to improve thermoplasticity and 30 wt.% polyacrylamide to improve surface activity and formability.

[0062] (3) Prepare an alkaline wetting medium by mixing 5 wt.% sodium hydroxide, 7 wt.% NaHCO3 and 88 wt.% water. Add 10 wt.% of the alkaline wetting medium to the mixture A based on 100 wt.% of the mixture A and wet grind and mix evenly to obtain a mixture B with an average particle size of 0.6 mm.

[0063] (4) The mixture B was pressed under a pressure of 15 MPa to obtain a cylindrical pellet precursor C with a diameter of 64 mm and a height of 85 mm;

[0064] (5) Place the pellet precursor C in a microwave tube furnace with argon gas introduced, and microwave roast at a temperature of 650°C, a roasting time of 60 min, and a microwave power of 4 kW. After roasting, cool the pellets to room temperature with the furnace to obtain the industrial silicon carbonaceous reducing agent pellets.

[0065] The carbonaceous reducing agent pellets prepared in this embodiment have a fixed carbon content of 72.15 wt.%, a cold compressive strength of 12.77 MPa, a breakage rate of 89.21%, a hot compressive strength of 9.11 MPa, a static sphericity index of 0.78, and a reactivity of 93.45% at 1100℃.

[0066] Comparative Example 3: The difference between this comparative example and Example 2 is that no microsilica powder and composite organic binder are added;

[0067] The carbonaceous reducing agent pellets prepared in this comparative example have a fixed carbon content of 70.17 wt.%, a cold compressive strength of 10.89 MPa, a breakage rate of 81.76%, a hot compressive strength of 5.81 MPa, a static sphericity index of 0.27, and a reactivity of 81.69% at 1100℃.

[0068] Comparative Example 4: The difference between this comparative example and Example 2 is that no microsilica powder and reinforcing agent are added;

[0069] The carbonaceous reducing agent pellets prepared in this comparative example have a fixed carbon content of 70.45 wt.%, a cold compressive strength of 11.21 MPa, a breakage rate of 83.69%, a hot compressive strength of 6.07 MPa, a static sphericity index of 0.37, and a reactivity of 83.74% at 1100℃.

[0070] Example 3: A method for preparing carbonaceous reducing agent pellets based on low-rank non-caking coal coupled with microsilica powder for industrial silicon smelting, the specific steps of which are as follows:

[0071] Low-rank non-caking coal, after being vacuum dried at 110℃ for 24 hours, was crushed and ground to a particle size of less than 5 mm, with 40% of the particles being 1-3 mm, to obtain micro-spherical particles of low-rank non-caking coal; the fixed carbon content of the low-rank non-caking coal was 55.74 wt.%, the ash content was 4.81 wt.%, the remainder was volatile matter, and the caking index n was 0.

[0072] (2) Low-rank non-caking coal particles are used as the main carbonaceous material of the pellets. Composite organic binder and microsilica powder are added and then mixed evenly to obtain a mixture A with an average particle size of 1.2 mm. The proportion of low-rank non-caking coal as the main carbonaceous material is 87 wt.%, the amount of composite organic binder added is 7 wt.%, and the amount of microsilica powder added is 6 wt.

[0073] The composite organic binder is composed of starch and a binder, wherein the starch content is 58 wt.% and the remainder is a binder; the binder is composed of 15 wt.% sodium carboxymethyl cellulose to improve thermoplasticity and 27 wt.% sodium lignosulfonate to improve surface activity and formability.

[0074] (3) Prepare an alkaline wetting medium by mixing 4 wt.% sodium hydroxide, 6 wt.% Na2CO3 and 90 wt.% water. Add 12 wt.% of the alkaline wetting medium to the mixture A based on 100 wt.% of the mixture A and wet grind and mix evenly to obtain a mixture B with an average particle size of 0.75 mm.

[0075] (4) The mixture B was pressed under a pressure of 15 MPa to obtain a cylindrical pellet precursor C with a diameter of 70 mm and a height of 100 mm;

[0076] (5) Place the pellet precursor C in a microwave tube furnace with argon gas introduced, and microwave roast at a temperature of 550°C, a roasting time of 80 min, and a microwave power of 5 kW. After roasting, cool the pellet to room temperature with the furnace to obtain the industrial silicon carbonaceous reducing agent pellet.

[0077] The carbonaceous reducing agent pellets prepared in this embodiment have a fixed carbon content of 70.49 wt.%, a cold compressive strength of 12.98 MPa, a breakage rate of 90.45%, a hot compressive strength of 8.83 MPa, a static sphericity index of 0.81, and a reactivity of 91.89% at 1100℃.

[0078] Comparative Example 5: This comparative example differs from Example 3 in that it does not contain microsilica powder or composite organic binder;

[0079] The carbonaceous reducing agent pellets prepared in this comparative example have a fixed carbon content of 68.53 wt.%, a cold compressive strength of 11.27 MPa, a breakage rate of 82.06%, a hot compressive strength of 6.49 MPa, a static sphericity index of 0.29, and a reactivity of 81.98% at 1100℃.

[0080] Comparative Example 6: This comparative example differs from Example 3 in that no microsilica powder or reinforcing agent is added;

[0081] The carbonaceous reducing agent pellets prepared in this comparative example have a fixed carbon content of 68.94 wt.%, a cold compressive strength of 11.49 MPa, a breakage rate of 82.98%, a hot compressive strength of 6.87 MPa, a static sphericity index of 0.38, and a reactivity of 83.47% at 1100℃.

[0082] Example 4: A method for preparing carbonaceous reducing agent pellets based on low-rank non-caking coal coupled with microsilica powder for industrial silicon smelting, the specific steps of which are as follows:

[0083] (1) The low-rank non-caking coal dried under vacuum at 110℃ for 24h was crushed and ground to a particle size of less than 5mm and 50% of the particles were 1-3mm, to obtain micro spherical particles of low-rank non-caking coal; the fixed carbon content of the low-rank non-caking coal was 57.82wt.%, the ash content was 4.54wt.%, the remainder was volatile matter, and the caking index n was 0.

[0084] (2) Low-rank non-caking coal particles are used as the main carbonaceous material of the pellets. Composite organic binder and microsilica powder are added and then mixed evenly to obtain a mixture A with an average particle size of 1.5 mm. The proportion of low-rank non-caking coal as the main carbonaceous material is 84 wt.%, the amount of composite organic binder added is 8 wt.%, and the amount of microsilica powder added is 8 wt.%.

[0085] The composite organic binder is composed of starch and a binder, wherein the starch content is 65 wt.% and the remainder is a binder; the binder consists of 10 wt.% hydroxypropyl cellulose to improve thermoplasticity and a total of 25 wt.% sodium lignosulfonate and sodium dodecylbenzenesulfonate to improve surface activity and formability (each accounting for 12.5 wt.%).

[0086] (3) Prepare an alkaline wetting medium by mixing 5 wt.% sodium hydroxide, 4 wt.% K2CO3, 4 wt.% NaHCO3 and 87 wt.% water. Add 11 wt.% of the alkaline wetting medium to the mixture A based on 100 wt.% of the mixture A and wet grind and mix evenly to obtain a mixture B with an average particle size of 1 mm.

[0087] (4) The mixture B was pressed under a pressure of 20 MPa to obtain a cylindrical pellet precursor C with a diameter of 68 mm and a height of 95 mm;

[0088] (5) Place the pellet precursor C in a microwave tube furnace with argon gas introduced, and microwave roast at a temperature of 600°C, a roasting time of 70 min, and a microwave power of 3 kW. After roasting, cool the pellet to room temperature with the furnace to obtain the carbonaceous reducing agent pellet for industrial silicon.

[0089] The carbonaceous reducing agent pellets prepared in this embodiment have a fixed carbon content of 71.84 wt.%, a cold compressive strength of 13.11 MPa, a breakage rate of 91.78%, a hot compressive strength of 8.27 MPa, a static sphericity index of 0.74, and a reactivity of 91.27% at 1100℃.

[0090] Comparative Example 7: This comparative example differs from Example 4 in that it does not contain microsilica powder or composite organic binder;

[0091] The carbonaceous reducing agent pellets prepared in this comparative example have a fixed carbon content of 69.84 wt.%, a cold compressive strength of 11.21 MPa, a breakage rate of 81.85%, a hot compressive strength of 6.17 MPa, a static sphericity index of 0.31, and a reactivity of 82.46% at 1100℃.

[0092] Comparative Example 8: This comparative example differs from Example 4 in that no microsilica powder or reinforcing agent is added;

[0093] The carbonaceous reducing agent pellets prepared in this comparative example have a fixed carbon content of 70.28 wt.%, a cold compressive strength of 11.69 MPa, a breakage rate of 83.69%, a hot compressive strength of 6.59 MPa, a static sphericity index of 0.40, and a reactivity of 84.15% at 1100℃.

[0094] Example 5: A method for preparing carbonaceous reducing agent pellets based on low-rank non-caking coal coupled with microsilica powder for industrial silicon smelting, the specific steps of which are as follows:

[0095] (1) The low-rank non-caking coal dried under vacuum at 110℃ for 24h was crushed and ground to a particle size of less than 5mm and 55% of the particles were 1-3mm, to obtain micro spherical particles of low-rank non-caking coal; the fixed carbon content of the low-rank non-caking coal was 56.89wt.%, the ash content was 4.61wt.%, the remainder was volatile matter, and the caking index n was 0.

[0096] (2) Low-rank non-caking coal particles are used as the main carbonaceous material of the pellets. Composite organic binder and microsilica powder are added and then mixed evenly to obtain a mixture A with an average particle size of 1.2 mm. The proportion of low-rank non-caking coal as the main carbonaceous material is 85 wt.%, the amount of composite organic binder added is 8 wt.%, and the amount of microsilica powder added is 7 wt.%.

[0097] The composite organic binder is composed of starch and a binder, wherein the starch content is 60 wt.% and the remainder is a binder; the binder consists of 13 wt.% of sodium carboxymethyl cellulose and hydroxypropyl cellulose (each accounting for 6.5 wt.%) to improve thermoplasticity and 27 wt.% of sodium dodecylbenzenesulfonate, polyacrylamide and sodium humate (each accounting for 9 wt.%) to improve surface activity and formability;

[0098] (3) Prepare an alkaline wetting medium by mixing 2 wt.% sodium hydroxide, 2 wt.% potassium hydroxide, 4 wt.% Na2CO3, 4 wt.% NaHCO3 and 88 wt.% water. Add 11 wt.% of the alkaline wetting medium to the mixture A based on 100 wt.% of the mixture A and wet grind and mix evenly to obtain a mixture B with an average particle size of 0.65 mm.

[0099] (4) The mixture B was pressed under a pressure of 18 MPa to obtain a cylindrical pellet precursor C with a diameter of 66 mm and a height of 93 mm;

[0100] (5) Place the pellet precursor C in a microwave tube furnace with argon gas introduced, and microwave roast at a temperature of 620°C, a roasting time of 70 min, and a microwave power of 4 kW. After roasting, cool the pellets with the furnace to room temperature to obtain the carbonaceous reducing agent pellets for industrial silicon.

[0101] The carbonaceous reducing agent pellets prepared in this embodiment have a fixed carbon content of 70.94 wt.%, a cold compressive strength of 13.03 MPa, a breakage rate of 92.14%, a hot compressive strength of 8.73 MPa, a static sphericity index of 0.76, and a reactivity of 93.49% at 1100℃.

[0102] Comparative Example 9: This comparative example differs from Example 5 in that it does not contain microsilica powder or composite organic binder.

[0103] The carbonaceous reducing agent pellets prepared in this comparative example have a fixed carbon content of 68.68 wt.%, a cold compressive strength of 10.95 MPa, a breakage rate of 82.24%, a hot compressive strength of 5.98 MPa, a static sphericity index of 0.33, and a reactivity of 82.15% at 1100℃.

[0104] Comparative Example 10: This comparative example differs from Example 5 in that it does not contain microsilica powder or reinforcing agents.

[0105] The carbonaceous reducing agent pellets prepared in this comparative example have a fixed carbon content of 69.65 wt.%, a cold compressive strength of 11.26 MPa, a breakage rate of 84.12%, a hot compressive strength of 6.31 MPa, a static sphericity index of 0.42, and a reactivity of 84.56% at 1100℃.

[0106] Example 6: A method for preparing carbonaceous reducing agent pellets based on low-rank non-caking coal coupled with microsilica powder for industrial silicon smelting, the specific steps of which are as follows:

[0107] Low-rank non-caking coal, after being vacuum dried at 110℃ for 24 hours, was crushed and ground to a particle size of less than 5 mm, with 55% of the particles being 1-3 mm, to obtain micro-spherical particles of low-rank non-caking coal; the fixed carbon content of the low-rank non-caking coal was 59.68 wt.%, the ash content was 3.97 wt.%, the remainder was volatile matter, and the caking index n was 0.

[0108] (2) Low-rank non-caking coal particles are used as the main carbonaceous material of the pellets. Composite organic binder and microsilica powder are added and then mixed evenly to obtain a mixture A with an average particle size of 1.3 mm. The proportion of low-rank non-caking coal as the main carbonaceous material is 86 wt.%, the amount of composite organic binder added is 8 wt.%, and the amount of microsilica powder added is 6 wt.%.

[0109] The composite organic binder is composed of starch and a binder, wherein the starch content is 54 wt.% and the remainder is a binder; the binder consists of 14 wt.% of sodium carboxymethyl cellulose and hydroxypropyl cellulose (each accounting for 7 wt.%) to improve thermoplasticity and 32 wt.% of sodium lignosulfonate, sodium dodecylbenzene sulfonate, polyacrylamide and sodium humate (each accounting for 8 wt.%) to improve surface activity and formability;

[0110] (3) Prepare an alkaline wetting medium by mixing 6 wt.% sodium hydroxide, 3 wt.% Na2CO3, 3 wt.% K2CO3, 3 wt.% NaHCO3 and 85 wt.% water. Add 12 wt.% of the alkaline wetting medium to the mixture A based on 100 wt.% of the mixture A and wet grind and mix evenly to obtain a mixture B with an average particle size of 0.55 mm.

[0111] (4) The mixture B was pressed under a pressure of 20 MPa to obtain a cylindrical pellet precursor C with a diameter of 70 mm and a height of 98 mm;

[0112] (5) Place the pellet precursor C in a microwave tube furnace with argon gas introduced, and microwave roast at a temperature of 640°C, a roasting time of 65 min, and a microwave power of 4 kW. After roasting, cool the pellets with the furnace to room temperature to obtain the carbonaceous reducing agent pellets for industrial silicon.

[0113] The carbonaceous reducing agent pellets prepared in this embodiment have a fixed carbon content of 72.58 wt.%, a cold compressive strength of 13.37 MPa, a breakage rate of 92.87%, a hot compressive strength of 8.95 MPa, a static sphericity index of 0.82, and a reactivity of 94.38% at 1100℃.

[0114] Comparative Example 11: This comparative example differs from Example 6 in that it does not contain microsilica powder or composite organic binder.

[0115] The carbonaceous reducing agent pellets prepared in this comparative example have a fixed carbon content of 70.68 wt.%, a cold compressive strength of 11.19 MPa, a breakage rate of 81.64%, a hot compressive strength of 6.27 MPa, a static sphericity index of 0.31, and a reactivity of 83.74% at 1100℃.

[0116] Comparative Example 12: This comparative example differs from Example 6 in that it does not contain microsilica powder or reinforcing agents.

[0117] The carbonaceous reducing agent pellets prepared in this comparative example have a fixed carbon content of 71.25 wt.%, a cold compressive strength of 11.67 MPa, a breakage rate of 82.61%, a hot compressive strength of 6.38 MPa, a static sphericity index of 0.41, and a reactivity of 85.74% at 1100℃.

[0118] Comparative Example 13: Other conditions are the same as in Example 1, except that:

[0119] Low-rank non-caking coal, after being vacuum dried at 110℃ for 24 hours, was crushed and ground to a particle size of less than 5 mm, with 30% of the particles being 1-3 mm, to obtain micro-spherical particles of low-rank non-caking coal; the fixed carbon content of the low-rank non-caking coal was 59.14 wt.%, the ash content was 4.07 wt.%, the remainder was volatile matter, and the caking index n was 0.

[0120] (2) The microspheres of low-rank non-caking coal were pressed into cylindrical pellet precursors with a diameter of 60 mm and a height of 90 mm under a pressure of 10 MPa.

[0121] (3) Place the pellet precursor in a microwave tube furnace with argon gas, and microwave roast at 450°C for 90 min and microwave power of 4kW. After cooling to room temperature with the furnace, the industrial silicon carbonaceous reducing agent pellets can be obtained.

[0122] The carbonaceous reducing agent pellets prepared in this comparative example have a fixed carbon content of 75.19 wt.%, a cold compressive strength of 10.32 MPa, a breakage rate of 79.89%, a hot compressive strength of 5.48 MPa, a static sphericity index of 0.23, and a reactivity of 80.46% at 1100℃.

[0123] Comparative Example 14: Other conditions are the same as in Example 1, except that:

[0124] (2) Low-rank non-caking coal particles are used as the main carbonaceous material of the pellets. Organic binder and microsilica powder are added and then mixed evenly to obtain a mixture A with an average particle size of 1.5 mm. The proportion of low-rank non-caking coal as the main carbonaceous material is 84 wt.%, the amount of organic binder added is 8 wt.%, and the amount of microsilica powder added is 8 wt.%.

[0125] The organic binder is starch;

[0126] The carbonaceous reducing agent pellets prepared in this comparative example have a fixed carbon content of 71.89 wt.%, a cold compressive strength of 12.99 MPa, a breakage rate of 91.08%, a hot compressive strength of 8.53 MPa, a static sphericity index of 0.75, and a reactivity of 87.46% at 1100℃.

[0127] Example 7: Other conditions are the same as in Example 1, except that:

[0128] (2) Low-rank non-caking coal particles are used as the main carbonaceous material of the pellets. Composite organic binder and microsilica powder are added and then mixed evenly to obtain a mixture A with an average particle size of 1 mm. The proportion of low-rank non-caking coal as the main carbonaceous material is 90 wt.%, the amount of composite organic binder added is 6 wt.%, and the amount of microsilica powder added is 4 wt.%.

[0129] The composite organic binder is composed of starch and a binder, wherein the starch content is 50 wt.% and the remainder is a binder; the binder is hydroxypropyl cellulose, which improves thermoplasticity.

[0130] The carbonaceous reducing agent pellets prepared in this comparative example have a fixed carbon content of 72.18 wt.%, a cold compressive strength of 12.85 MPa, a breakage rate of 90.98%, a hot compressive strength of 9.34 MPa, a static sphericity index of 0.73, and a reactivity of 88.88% at 1100℃.

[0131] The specific embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A carbonaceous reducing agent pellet based on low-rank non-caking coal, characterized in that: The preparation of the carbonaceous reducing agent pellets includes the following steps: (1) Dry low-rank non-caking coal is crushed and ground to a particle size of less than 5 mm and the particle size of 1-3 mm accounts for 30-60% to obtain micro spherical particles of low-rank non-caking coal; the caking index of low-rank non-caking coal is less than 50, which of course includes non-caking coal with a caking index of less than 5, and preferably non-caking coal with a caking index of less than 2. (2) Using low-rank non-caking coal microspheres as the main carbonaceous material for pellets, a composite organic binder and microsilica powder are added, and then mixed evenly to obtain a mixture A with an average particle size of 0.75-1.5 mm; the composite organic binder is composed of D and a binder, the microsilica powder has SiO2 content greater than 80 wt% and a particle size less than 1.5 mm; D is a polysaccharide and / or a polysaccharide polymer; the binder is selected from at least one of lignin sulfonate, dodecylbenzene sulfonate, polyacrylamide, and humate. (3) Add the reinforcing agent to water to prepare an alkaline wetting medium containing alkali metal additives, and then add it to mixture A for wet grinding and uniform mixing to obtain mixture B with an average particle size of 0.5-1mm; the reinforcing agent is an alkaline substance containing alkali metal elements; (4) The mixture B is pressed under a pressure of 10~20MPa to obtain the precursor C; (5) Place the pellet precursor C in a microwave tube furnace with argon gas and microwave roast it at a temperature of 450~650°C. Then cool it to room temperature with the furnace to obtain the industrial silicon carbonaceous reducing agent pellets.

2. The carbonaceous reducing agent pellets based on low-rank non-caking coal according to claim 1, characterized in that: The drying temperature for low-rank non-caking coal is 105~110℃ for 12~36 hours.

3. The carbonaceous reducing agent pellets based on low-rank non-caking coal according to claim 1, characterized in that: In step (1), the fixed carbon content of the low-rank non-caking coal is ≥55wt.%, the ash content is <5wt.%, and the caking index n is less than or equal to 1, which of course includes a caking index of 0.

4. The carbonaceous reducing agent pellets based on low-rank non-caking coal according to claim 1, characterized in that: In step (2), the proportion of the main carbonaceous material, low-rank non-caking coal, in mixture A is 84-92 wt.%, the amount of composite organic binder added is 4-8 wt.%, and the amount of microsilica powder added is 4-8 wt.%.

5. The carbonaceous reducing agent pellets based on low-rank non-caking coal according to claim 1, characterized in that: In step (2), the composite organic binder is composed of starch and adhesive aids. The starch content in the composite organic binder is 50-65 wt.%, and the remainder is adhesive aids. The adhesive aids are composed of at least one or more of the following two categories: sodium carboxymethyl cellulose and hydroxypropyl cellulose, which improve thermoplasticity; and sodium lignosulfonate, sodium dodecylbenzene sulfonate, polyacrylamide, and sodium humate, which improve surface activity and formability. The adhesive aids that improve thermoplasticity account for 10-20 wt.% of the total mass of the composite organic binder, and the adhesive aids that improve surface activity and formability account for 25-30 wt.% of the total mass of the composite organic binder.

6. The carbonaceous reducing agent pellets based on low-rank non-caking coal according to claim 1, characterized in that: The microsilica powder in step (2) is taken from the flue of the submerged arc furnace, with a SiO2 content of 85-95% and a mass density of 500-670 kg / m³. 2 .

7. The carbonaceous reducing agent pellets based on low-rank non-caking coal according to claim 1, characterized in that: In step (3), the reinforcing agent is mainly composed of one or two of sodium hydroxide and potassium hydroxide and alkali metal additives, and the alkali metal additives are one or more of K2CO3, Na2CO3 and NaHCO3 powders; the addition ratio of the alkali wetting medium is 8-12 wt. of the mixture A.

8. The carbonaceous reducing agent pellets based on low-rank non-caking coal according to claim 1, characterized in that: In step (3), the proportions of hydroxide, alkali metal additive and water added to the alkaline wetting medium are 4-6 wt.%, 6-9 wt.% and 85-90 wt.%, respectively. If the hydroxide and alkali metal additive are not the same, then the proportion of each is the same.

9. The carbonaceous reducing agent pellets based on low-rank non-caking coal according to claim 1, characterized in that: In step (5), the microwave roasting time is 60~90min and the microwave power is 3~5kW.

10. The application of carbonaceous reducing agent pellets based on low-rank non-caking coal as described in any one of claims 1-9, characterized in that: The carbonaceous reducing agent pellets are used in silicon smelting.

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