Low-temperature microwave pelletizing method for improving bulk density of biomass coal

Abstract

The invention relates to a low-temperature microwave pelletizing method for improving the bulk density of biomass coal, which comprises the following steps: 1) mixing: drying and screening biomass charcoal, pulverized coal and an additive, and uniformly mixing to obtain a mixed material; 2) pelletizing: adding water to wet the mixed material, feeding the mixed material into a pelletizer for pelletizing when the water addition amount does not exceed 2% of the weight of the mixed material, and performing low-temperature heating by adopting microwaves at the same time; and 3) drying the pellets obtained in the step 2) at the temperature of 105-115 DEG C for 2-3 hours to obtain the biomass briquette. According to the method, microwave heating is utilized, the temperature can be rapidly increased, the pellet preparation time is remarkably shortened, pellet preparation can be conducted within 2-3 h, microwave heating directly acts on the interior of a substance, heat loss in a traditional heating mode is reduced, and therefore energy consumption is remarkably reduced.

Description

Technical Field

[0001] The invention relates to the field of pelletizing, in particular to a low-temperature microwave pelletizing method for improving the pile density of biomass coal. Background Art

[0002] The application of biomass-based fuels to the steel industry instead of fossil fuels is an important measure to alleviate the dual pressures of resources and the environment. Biomass energy is an environmentally friendly energy source. Biomass energy accounts for 10% to 14% of the world's primary energy. In the context of global energy resource shortages, it has important development potential and is also the only renewable carbon source. By 2050, depending on the source, the proportion of biomass energy in the energy consumption structure will reach more than 30-40%. Biomass can be used to obtain carbon, but it is not a fossil fuel-derived material. It can be used in electricity, heat energy, transportation and other fields. Therefore, it has more advantages than fossil energy in terms of environmental and socio-economic benefits. After different treatment methods, biomass can be further decomposed to produce CO and H2, both of which can be used as reducing agents for the reduction of iron oxide. Less CO2 is produced after complete combustion of biomass. According to the calculation of the combustion reaction, the CO2 produced after biomass combustion will be reduced by 58%. However, due to the low energy density, limited combustion efficiency, high moisture content, more volatile substances, and large volume of biomass, the utilization of biomass energy is limited to a certain extent.

[0003] Compared with fossil fuels, biomass has the highest oxygen-carbon ratio (O:C) and hydrogen-carbon ratio (H:C). Higher oxygen and hydrogen content will reduce the calorific value of solid fuels because the energy of C-O bonds and C-H bonds is lower than that of C-C bonds. Based on this, raw biomass cannot be used directly and needs to be pre-treated and upgraded to meet the requirements. Biomass energy is mainly converted into solid, liquid and gaseous fuels through physical conversion (solid molding fuel), chemical conversion (direct combustion, gasification, liquefaction), biological conversion (such as fermentation into methane), etc. At present, the yield of biomass coal is very low, only about 20%. The existing biomass conversion methods in industrial production include direct combustion, thermochemical conversion and biological conversion to obtain the final biomass coal. The limiting factor for the use of biomass coal in ironmaking is still the energy density problem. The energy density of biomass is relatively low, which to a certain extent limits its application in the ironmaking process.

[0004] There are many methods to increase the bulk density of coal in the existing coking process, including ramming coking, blended coal coking, preheating coking, etc. Foreign countries mainly use methods such as graded crushing, heating, ramming of coal materials and increasing the height of the carbonization chamber to increase the bulk density of coal charged to the furnace. At the same time, studies have found that with the increase of bulk density, the porosity and specific surface area of ​​coke will decrease, and correspondingly, the reactivity of coke will also decrease. The improvement of biomass coal bulk density can refer to these technologies. Ramming coking is an unconventional coking method, which mainly uses a mechanical ramming hammer outside the carbonization chamber of the coke oven to pound the blended coal into coal cakes, and then pushes it into the carbonization chamber from the machine side of the coke oven for high-temperature carbonization. This technology can add more high-volatile coal and weakly caking coal according to the different uses of coke. In the ramming coking process, the bulk density of the blended coal is 0.75t / m 3 Increased to about 1.1t / m 3 . Coal blending is a method of coking by blending coking coal of different metamorphic degrees in appropriate proportions. At the end of coking, the briquettes and coal powder fuse with each other to form a whole coke. The advantages of this method include: expanding the range of coking coal resources, improving the strength of coke, and using existing coking equipment without building new coking ovens. In addition, by applying coal blending technology, not only can the quality of coke be guaranteed, but also the coal resources can be reasonably utilized and high-quality coking coal can be saved. Preheating coking is a technology that preheats the coking coal to about 200°C outside the furnace and then loads it into the coke oven for coking. This method has the following advantages: first, it can improve the quality of coke; second, it can increase the production capacity of the coke oven; in addition, without reducing the quality of coke, more weakly caking coal can be used in the coking coal; finally, it also helps to extend the service life of the coke oven.

[0005] However, the existing technologies only involve various types of coal, but fail to take biomass coal into consideration. Therefore, it is necessary to find a method to increase the bulk density of biomass coal. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a method for low-temperature microwave pelletizing for improving the bulk density of biomass coal, utilizing the characteristic that coal tar precipitates adhesive colloids after being heated in a medium-low temperature region, and loading the biomass coal and coal tar into a pelletizing machine with low-temperature microwave heating to make pellets.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A method for low-temperature microwave pelletizing for increasing the pile density of biomass coal, comprising the following specific steps:

[0009] 1) Mixing: drying and screening the biochar, coal powder and additives, and then mixing them to obtain a mixed material;

[0010] 2) Balling: The mixed material is moistened with water, the amount of water added does not exceed 2% of the weight of the mixed material, and is sent into a balling machine for balling, while microwaves are used for low-temperature heating;

[0011] 3) The pellets obtained in step 2) are dried at 105° C. to 115° C. for 2 to 3 hours to obtain biomass coal pellets.

[0012] The biochar in step 1) is obtained by pyrolysis or hydrothermal carbonization of biomass raw materials, and the biomass raw materials include organic waste and energy plants.

[0013] Step 1) The particle size of the biochar after drying and screening is less than 3 mm.

[0014] The additive in step 1) includes one or both of asphalt and coal tar, and the added mass fraction is 1-12% of the mixed material.

[0015] Step 1) The drying temperature is 105° C. to 115° C., and the drying time is 4 h to 6 h.

[0016] Step 2) The microwave heating temperature is controlled at 100-300° C., and the heating time is 2-3 hours.

[0017] Step 2) The ball diameter of the ball is 15 to 30 mm.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] This application uses microwave heating, which can quickly heat up, thereby significantly shortening the preparation time of the pellets, which can be prepared in 2 to 3 hours. This high-efficiency and rapid preparation makes the production process more efficient and can meet market demand in a timely manner. Compared with traditional pelletizing preparation methods, bio-microwave pelletizing technology reduces the use of organic solvents, thereby reducing the risk of environmental pollution. Microwave heating acts directly on the inside of the material, reducing heat loss in traditional heating methods, thereby significantly reducing energy consumption. By adjusting the microwave power, heating time and raw material ratio, the particle size, shape and structure of the biomass coal balls can be accurately controlled.

[0020] The present invention improves the bulk density of the product coal by pelletizing, and increases the bulk density of the coal charged to the furnace to 0.75-0.95 ton / m 3 The above meets the requirements of top-loading coke and ramming coke during coking, which can reduce the volume of fuel, reduce transportation and storage costs, and at the same time increase the heat output during combustion and improve the overall energy utilization efficiency.

[0021] By using biomass as a substitute for coking coal, the present invention can reduce the dependence of steel enterprises on traditional coal resources, thereby reducing production costs and improving resource sustainability. As a clean energy source, the carbon dioxide produced by the combustion of biomass can be absorbed by plants to form a carbon cycle, thereby reducing greenhouse gas emissions and having little impact on the environment. Appropriate substitution of coke powder or coal powder for iron ore powder sintering can produce significant emission reduction effects. The calorific value, characteristic combustion temperature and combustion rate of biomass can affect the injection effect of biomass mixed coal, thereby improving the ironmaking process. The use of biomass resources can promote the optimization of the energy structure of steel enterprises, improve energy utilization efficiency and reduce energy consumption. The use of biomass energy can be combined with industries such as agriculture and forestry to provide additional sources of income for rural areas and promote the sustainable development of the rural economy. By adopting biomass energy, steel enterprises can demonstrate their commitment to environmental protection and sustainable development, and enhance their sense of social responsibility and image. DETAILED DESCRIPTION

[0022] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood by specific circumstances.

[0023] A method for low-temperature microwave pelletizing for increasing the pile density of biomass coal, comprising the following specific steps:

[0024] 1) Mixing: The biochar, coal powder and additives are dried and screened, and then mixed to obtain a mixed material; the biochar is obtained by pyrolysis, hydrothermal or gasification carbonization of biomass raw materials, and the biomass raw materials include organic waste and energy plants.

[0025] 2) Pelletizing: The mixture is moistened with water, the amount of water added does not exceed 2% of the weight of the mixture, and is fed into the pelletizing machine for pelletizing. At the same time, microwaves are used for low-temperature heating; the microwave heating temperature is controlled at 100-300°C, and the heating time is 2-3 hours. This step is the key to improving the density and strength of biomass coal pellets. Microwave roasting can heat the inside and outside of the pellets at the same time in a short time. The pelletizing process also makes microwave sintering more uniform, thereby improving heating efficiency and pellet quality.

[0026] 3) The pellets obtained in step 2) are dried at 105° C. to 115° C. for 2 to 3 hours to obtain biomass coal pellets.

[0027] Step 1) The preparation process of biochar comprises:

[0028] Pyrolysis carbonization: Heat the biomass at 350-650℃ under oxygen-deficient or oxygen-limited conditions to cause thermal decomposition of the biomass to form biochar.

[0029] Hydrothermal carbonization: With the participation of water, biomass is pyrolyzed at 150-350°C to form biochar.

[0030] Gasification and carbonization: Biomass reacts at 600-800℃ in the presence of oxygen to generate combustible gas and biochar.

[0031] Step 1) The particle size of the biochar after drying and screening is less than 3 mm.

[0032] The additive in step 1) includes one or both of asphalt and coal tar, and the added mass fraction is 1-12% of the mixed material.

[0033] Step 1) The drying temperature is 105° C. to 115° C., and the drying time is 4 h to 6 h.

[0034] Step 2) The diameter of the ball in step 2) is 15 to 30 mm.

[0035] In order to make the purpose, technical scheme and technical effect of the present invention clearer, the technical scheme in the embodiment of the present invention is now clearly and completely described. However, the embodiments described below are only part of the embodiments of the present invention, not all of the embodiments. In combination with the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] Example 1

[0037] A method for low-temperature microwave pelletizing for increasing the bulk density of biomass coal is as follows:

[0038] Step 1: Sieve the coal powder and biomass charcoal through a 2mm sieve, and put the above raw materials into a 105℃ oven for drying for 2h. Weigh each raw material with an electronic balance (accuracy 0.01g), totaling 500g. The mass of biomass charcoal in the raw materials is 70%, the mass of coal powder is 30%, and asphalt is selected as an additive, adding 4% of the total material mass.

[0039] Step 2: Mixing ingredients: Mix the weighed biochar, coal powder and asphalt evenly using a planetary ball mill for 60 minutes.

[0040] Step 3: Make balls of the evenly mixed materials in a ball making machine and perform microwave low-temperature heating at a heating power of 900w, a heating temperature of 280℃, and heating for 2.5 hours.

[0041] Step 4: The pellets obtained in step 3 are dried at 105°C for 3 hours. Stir several times during the process to make it dry more evenly. After drying, take out the sample to obtain raw pellets with a particle size of about 10 mm. Use a 10 mm sieve to sieve the raw pellets. The raw pellets with a particle size of +10 mm are qualified.

[0042] Example 2

[0043] A method for low-temperature microwave pelletizing for increasing the bulk density of biomass coal is as follows:

[0044] Step 1: Sieve the coal powder and biochar through a 3mm sieve, and put the above raw materials into a 110℃ oven for drying for 4 hours. Weigh each raw material with an electronic balance (accuracy 0.01g), with coal powder accounting for 50% and biochar accounting for 50%, totaling 300g. Coal tar is selected as an additive, adding 3% of the total material mass.

[0045] Step 2: Mixing ingredients: Mix the weighed biochar, coal powder and coal tar evenly using a planetary ball mill for 30 minutes.

[0046] Step 3: The uniformly mixed material is pelletized in a pelletizing machine and simultaneously subjected to microwave low-temperature heating with a heating power of 800w, a heating temperature of 260°C and a heating time of 2.2 hours.

[0047] Step 4: The ball material obtained in step 3 is dried at 108°C for 5 hours. Stir several times during the process to make it dry more evenly. After drying, a raw ball with a particle size of about 10 mm is obtained. The raw balls are sieved with a 10 mm sieve, and the raw balls with a particle size of +10 mm are qualified.

[0048] Although 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 the embodiments without departing from the principles and basic spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for low-temperature microwave pelletizing to increase the bulk density of biomass coal, characterized in that: The specific steps include: 1) Mixing: drying and screening the biochar, coal powder and additives, and then mixing them to obtain a mixed material; 2) Balling: The mixed material is moistened with water, the amount of water added does not exceed 2% of the weight of the mixed material, and is sent into a balling machine for balling, while microwaves are used for low-temperature heating; 3) The pellets obtained in step 2) are dried at 105° C. to 115° C. for 2 to 3 hours to obtain biomass coal pellets.

2. The method for low-temperature microwave pelletizing for increasing the bulk density of biomass coal according to claim 1, characterized in that: The biochar in step 1) is obtained by pyrolysis or hydrothermal carbonization of biomass raw materials, and the biomass raw materials include organic waste and energy plants.

3. The method for low-temperature microwave pelletizing for increasing the bulk density of biomass coal according to claim 1, characterized in that: Step 1) The particle size of the biochar after drying and screening is less than 3 mm.

4. The method for low-temperature microwave pelletizing for increasing the bulk density of biomass coal according to claim 1, characterized in that: The additive in step 1) includes one or both of asphalt and coal tar, and the added mass fraction is 1-12% of the mixed material.

5. The method for low-temperature microwave pelletizing for increasing the bulk density of biomass coal according to claim 1, characterized in that: Step 1) The drying temperature is 105° C. to 115° C., and the drying time is 4 h to 6 h.

6. The method for low-temperature microwave pelletizing for increasing the bulk density of biomass coal according to claim 1, characterized in that: Step 2) The microwave heating temperature is controlled at 100-300° C., and the heating time is 2-3 hours.

7. The method for low-temperature microwave pelletizing for increasing the bulk density of biomass coal according to claim 1, characterized in that: Step 2) The ball diameter of the ball is 15 to 30 mm.