Method for preparing biomass charcoal injection material by utilizing waste heat steam co-production of steel mill

Abstract

The invention relates to a method for co-producing and preparing a biomass charcoal injection material by utilizing waste heat steam of a steel mill, which comprises the steps of raw material preparation, acid mixing, carbonization, unloading, distillation, biomass charcoal injection material preparation and the like, each step is specifically set, particularly, the waste heat steam of the steel mill is introduced into the process, and the internal material circulation is set, so that the biomass charcoal injection material is prepared. The biomass charcoal injection material and byproducts with high economic benefits are obtained, no wastewater is produced in the whole process, and the whole process which takes agricultural waste as a raw material to obtain the injection material capable of reducing carbon emission of a steel plant and the byproducts with high additional values, does not generate secondary pollutants and is high in environmental friendliness is realized. And harm is really turned into benefit.

Description

Technical Field

[0001] This invention relates to the field of biochar preparation technology, and in particular to a method for preparing biochar injection material by co-producing waste heat steam from steel plants. Background Technology

[0002] China's crude steel production in 2024 was approximately 1.01 billion tons, accounting for more than half of the world's total. As a resource- and energy-intensive industry, steel production consumes about 16% of the nation's total industrial energy consumption annually and accounts for about 15% of the nation's total industrial carbon emissions, making it the manufacturing sector with the highest carbon emissions. The steel industry was included in the national carbon emissions trading market in 2025, and "carbon reduction" has become the focus of the steel industry's next phase of work.

[0003] my country's steel production is mainly based on the blast furnace-converter long process, emitting approximately 2.35 tons of CO2 per ton of crude steel produced. The blast furnace process accounts for over 70% of the carbon emissions from this long process. Replacing fossil fuels with renewable and clean resources is a key pathway to achieving deep decarbonization. Biomass energy, which is solar energy fixed by plants through photosynthesis, is widely distributed, abundant, and environmentally friendly. my country's agricultural and forestry waste production is approximately 900 million tons per year, equivalent to about 460 million tons of standard coal per year, indicating significant development potential. According to current carbon emission accounting rules, CO2 emissions from biomass energy utilization can be considered zero or excluded from fossil carbon emission accounting. Given the current immaturity of hydrogen smelting technology, using biomass in blast furnace smelting can reduce CO2 emissions without significantly altering the blast furnace smelting system. This approach requires less investment, yields quick results, and is of great significance for reducing carbon emissions in blast furnaces.

[0004] Due to its high moisture content, low energy density, and low crushing efficiency, biomass cannot be directly used for blast furnace tuyeres injection. Traditional biochar production processes, such as biomass pyrolysis, suffer from drawbacks such as high energy consumption, low char yield, heavy pollution, and high cost. Furthermore, while traditional agricultural waste (straw, rice husks, fruit shells, etc.) is widely available, its high seasonality, complex composition, high impurity content, and dispersed collection systems lead to high costs for raw material collection, transportation, and storage, making biochar significantly more expensive than pulverized coal injection and limiting the widespread adoption of blast furnace biochar injection technology.

[0005] The steelmaking process generates a large amount of low- to medium-grade waste heat steam. This steam, especially saturated steam, has virtually no power-generating capacity and extremely low power generation efficiency. It is usually used for preheating and heating, and a small amount can be used for material drying. Often, due to its low grade and difficulty in utilization, factories do not recover waste heat from some processes, resulting in the waste of this waste heat resource.

[0006] Chinese invention patent publication CN119824155A discloses a method for preparing blast furnace pulverized fuel using furfural residue, achieving the technical requirements for blast furnace pulverized fuel through specific processing steps. However, this technical solution directly uses furfural residue that has already formed biochar as raw material, without proposing how to convert biomass into biochar that meets the requirements for blast furnace pulverized fuel.

[0007] Therefore, there is an urgent need to propose a highly environmentally friendly method for preparing biomass materials suitable for blast furnace injection using specific agricultural waste. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of the prior art. In view of the disadvantages of high energy consumption, heavy pollution and high price of traditional biochar preparation process, this invention provides a method for producing biochar that can meet the requirements of blast furnace injection using waste heat steam from steel plants, while simultaneously producing high value-added chemicals.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing biomass char injection material by co-producing waste heat steam from a steel plant includes the following steps: (1) Biomass raw material pretreatment: Biomass rich in hemicellulose (biomass with hemicellulose content of more than 30 wt.%) is crushed to a particle size of 15-30 mm and then transported (preferably by conveyor) to a mixer.

[0010] (2) Acid mixing: The acid solution is mixed with water in the acid mixing tank to obtain dilute acid. The dilute acid is mixed with the biomass raw material crushed in step (1) at a mass ratio of (0.3~0.7):1 and mixed evenly in a stirrer.

[0011] (3) Carbonization: The material after mixing in step (2) is fed into the carbonization reactor. After the material is loaded, the reactor is sealed and steam is introduced. After pressurizing to 0.2~0.4MPa, venting, pressurizing to 0.6~1.2MPa and stabilizing for 2~3 hours, carbonization is completed to obtain biomass charcoal. The flow rate of secondary steam during the stabilization stage is 135~165kg / min, and the top steam is discharged through the steam outlet during the stabilization stage.

[0012] (4) Unloading: After carbonization in step (3), the carbonization reactor is depressurized to 0.1~0.2MPa (preset value), the unloading port is opened and the biomass carbon is discharged through the unloading port using the residual pressure in the reactor. During the depressurization stage, the top steam of the tower is discharged through the steam outlet.

[0013] (5) Distillation: The top steam obtained in step (3) is discharged into the condenser to obtain condensate. The condensate is added to the distillation tower from the middle of the distillation tower for distillation. The distillate at the top of the distillation tower is cooled and enters the separator for stratification. The upper water layer is returned to the distillation tower for circulation, and the lower layer is crude by-product. The bottom waste liquid at the bottom of the distillation tower is discharged into the waste liquid evaporator. The waste liquid evaporator is heated and evaporated by the waste heat steam of the steel plant to obtain secondary steam and concentrated waste liquid. The secondary steam is discharged into step (3) as steam and fed into the carbonization reactor. The concentrated waste liquid is fed into the acid mixing tank in step (2) as raw material for acid mixing, so that no wastewater is discharged throughout the process (the condensate generated after the waste heat steam of the steel plant is softened water, which will return to the steam pipeline system of the steel plant to generate steam again and will not be discharged, so no wastewater will be generated).

[0014] (6) The biomass char obtained in step (4) is mixed with pulverized coal injected into the blast furnace at a mass ratio of (5~12): (88~95), and then the whole mixture is ground (in a mill) to a particle size of less than 0.074 mm (i.e. less than 200 mesh) to obtain biomass char injection material for blast furnace injection (the ratio of dry biomass powder to coal is (3~7): (93~97), but since the moisture content of biomass char is about 50% and the moisture content of coal is about 10%, the mass ratio of the two is (5~12): (88~95)).

[0015] Biomass char and coal are fed together into a medium-speed mill and crushed into powder smaller than 200 mesh, then fed into the blast furnace tuyeres via a pulverized coal injection system. The medium-speed mill uses hot flue gas for material transport and has its own drying function. Although the moisture content of biomass char is higher than that of coal, the amount of biomass char added in this invention is small (approximately 5% on a dry basis, and approximately 5-12% on a wet basis). Therefore, it has little impact on the overall moisture content of the material entering the medium-speed mill and will not affect the moisture content of the mill output. Excessive addition of biomass char will result in insufficient calorific value and excessive alkali metals carried into the blast furnace, affecting the stable operation of the blast furnace.

[0016] Preferably, the hemicellulose-rich biomass in step (1) is one or more of corn cobs, sugarcane bagasse or rice husks (or corn stalks with a hemicellulose content higher than 30 wt.%, depending on the variety of corn stalks, the hemicellulose content can be higher than 30 wt.%).

[0017] Preferably, the acid in step (2) is a mixture of concentrated waste liquid returned to the acid mixing tank in step (5) and sulfuric acid or acetic acid; the dilute acid is dilute sulfuric acid containing concentrated waste liquid with a sulfuric acid concentration of 4~7 wt.% or dilute acetic acid containing concentrated waste liquid with a acetic acid concentration of 5~10 wt.%.

[0018] Preferably, the following steps are included after step (6): (7) By-product purification: The crude by-product obtained in step (5) is neutralized to remove acid impurities, and then high-boiling substances are removed by distillation to obtain the distillate discharged from the top of the distillation column. The distillate is condensed to obtain high-purity furan derivative by-products (e.g., 2-furan carbaldehyde).

[0019] Preferably, the neutralizing agent used in step (7) is one or more of Na2CO3, Ca(OH)2 or NaOH alkaline solution; the distillation pressure is -0.09 to -0.07 MPa.

[0020] Preferably, the height-to-diameter ratio of the carbonization reactor in step (3) is 7~9, and the maximum allowable working pressure is 0.8~1.5MPa.

[0021] Preferably, the steam in step (3) is the secondary steam obtained in step (5); the pressurization time is 10~20 min.

[0022] Preferably, the venting in step (3) is as follows: after pressurization is completed, the venting valve is opened while steam is continuously supplied to vent the air in the carbonization reactor. The opening degree of the venting valve is such that the pressure gauge reading at the top of the carbonization reactor remains unchanged, and the venting time is 1~2 minutes.

[0023] As a preferred option, the pressurization in step (3) specifically involves: closing the vent valve after venting is completed, keeping steam continuously supplied, and continuing to increase the pressure for 20 to 40 minutes until the pressure reaches 0.6 to 1.2 MPa.

[0024] Preferably, the pressure stabilization in step (3) specifically involves continuously controlling the pressure to 0.6~1.2MPa and maintaining it for 2~3 hours.

[0025] Preferably, in step (3), the total mass of the steam discharged into the carbonization reactor during the pressure stabilization stage and the steam discharged from the top of the tower through the steam outlet is 1.6 to 2 times the total mass of the raw materials in the carbonization reactor, so as to reduce the high-value-added small molecule compounds of by-products in the carbonization process from staying in the carbonization reactor for a long time and undergoing secondary reactions.

[0026] Preferably, in step (3), the steam introduced after sealing is the depressurization steam from other carbonization reactors. After pressurization and venting, the secondary steam generated by the waste liquid evaporator is used to increase the pressure.

[0027] Preferably, in step (3), the secondary steam flow rate is controlled at 140~160 kg / min.

[0028] Preferably, multiple carbonization reactors are provided. In step (4), when one of the carbonization reactors is depressurized, the discharged top steam is discharged into other carbonization reactors that have been loaded and sealed, so as to realize waste heat recovery.

[0029] Preferably, the depressurization time in step (4) is 10~20 min, and the pressure at the end of the depressurization is 0.1~0.2 MPa.

[0030] Preferably, in step (5), the top vapor obtained in step (3) is first discharged into the reboiler at the bottom of the distillation column for waste heat recovery to provide heat for the distillation column, and then discharged into the condenser to obtain condensate.

[0031] Preferably, in step (5), the pressure of the waste heat steam from the steel plant used to heat and evaporate the waste liquid in the evaporator is 1.2~1.8MPa, and the waste heat steam is obtained by the steel plant through waste heat recovery to heat the boiler softened water (boiler softened water is usually prepared using ion exchange resin, and the production cost is usually 20~30 yuan / ton). Using waste heat steam to heat the waste liquid at the bottom of the distillation tower to generate secondary steam can not only achieve zero wastewater discharge, but also, since it is obtained by heating softened water, the condensate generated after the waste heat steam heat exchange can be directly returned to the steam circulation system, saving boiler softened water and reducing operating costs).

[0032] Preferably, the concentration ratio of the waste liquid evaporator in step (5) is 15~20:1.

[0033] As an alternative, step (6) is replaced by: first removing and drying the alkali metals from the biomass char obtained in step (4) to obtain low-alkali metal biomass char, then mixing the low-alkali metal biomass char with coal powder at a mass ratio of (7~20):(80~93), then grinding the whole mixture into powder with a particle size of less than 0.074 mm, and then obtaining biomass char injection material for blast furnace injection.

[0034] The alkali load of a blast furnace refers to the total load of alkali metal elements (mainly K₂O and Na₂O) fed into the furnace, typically required to be 3 kg / t of molten iron. The national standard requires the alkali metal content of pulverized coal injected into the blast furnace to be ≤0.25%. If the pulverized coal injection rate is 170 kg / t of molten iron, the corresponding total alkali metal content is 0.425 kg, which can be considered the upper limit of the alkali metal content brought in by the injected fuel when producing 1 ton of molten iron. If the pulverized coal injection rate is 170 kg / t Fe, the alkali metal content in the dry-basis biochar is calculated at 1.5%, and the alkali metal content of the coal is 0.15%, then the amount of biochar that can be added (dry-basis) is 12.6 kg, corresponding to 7.5% of the total fuel of 170 kg. This roughly indicates that the upper limit of biochar addition is 7.5%. Of course, if the alkali metal content of the injected coal is higher than 0.15%, then the amount of biochar added should be reduced accordingly to avoid excessive alkali load on the blast furnace. To be on the safe side, the amount of untreated dry biochar added should not exceed about 5%.

[0035] However, if the biochar undergoes dealkalization treatment, and is pre-dried to avoid insufficient drying capacity of the medium-speed mill, the amount of refined biochar after dealkalization and drying can reach 20%. This is mainly because the calorific value of biochar is only 70-80% of that of pulverized coal. Excessive addition will result in insufficient total heat of the fuel entering the blast furnace. It is difficult to make up for this heat gap by means of blast dehumidification and oxygen-enriched injection, requiring a complete overhaul of the injection system. In addition, biochar has a strong combustion performance, and if the addition exceeds 20%, there may be a risk of explosion. Therefore, to increase the amount of refined biochar added to the pulverized coal, its upper limit is usually set at 20% (and this is after drying). Additions below 7% generally do not require dealkalization and drying treatment. Therefore, the amount of refined biochar after dealkalization and drying is set at 7-20 wt.% in this case.

[0036] Preferably, the removal and drying of alkali metals specifically involves: washing the biochar obtained in step (4) with water 3 to 5 times, filtering the washed biochar, and drying the filter material to a moisture content of 8 to 12 wt.% to obtain biochar with low alkali metal content.

[0037] Preferably, 3 to 4 carbonization reactors are connected in series. After the loading, sealing, pressurization and venting operations are completed in steps (3) and (4), each carbonization reactor goes through several stages in sequence, including pressurization, pressure stabilization, series steam discharge, pressure relief and unloading. The operation cycle of a single carbonization reactor from the start of loading to the completion of unloading is 4 to 6 hours.

[0038] Preferably, the carbonization reactor is provided with a charging port, a steam outlet, an vent, a safety valve and a pressure gauge at the top, and a steam inlet and a discharge port at the bottom; the charging port is sealed with a flange, and the steam outlet, vent, steam inlet and discharge port are controlled by valves.

[0039] On the other hand, the present invention proposes a biochar injection material prepared by the above method, wherein the biochar injection material contains 3-8 wt.% of the biochar material, wherein the biochar material contains 20-25 wt.% cellulose, 51-55 wt.% lignin, and 2.9-3.8 wt.% hemicellulose; and according to industrial analysis, it contains 65-69 wt.% volatile matter, 21-25 wt.% fixed carbon, and 6.9-6.9 wt.% ash. 8.1 wt.%; Elemental analysis shows it contains C: 48.12~51.01 wt.%, H: 4.85~5.62 wt.%, O: 35.21~38.02 wt.%, N: 0.48~0.59 wt.%, and S: 0.66~0.92 wt.%. The biochar has a calorific value of 20~24 MJ / kg, a Hardgrove grindability index of 70~85, and a dry basis bulk density of 0.39~0.50 g / cm³. 3 .

[0040] Compared with the prior art, the technical solution of the present invention has the following beneficial technical effects: (1) In the process of preparing biomass char injection material, this invention directly utilizes the surplus low-grade waste heat steam of the steel plant (i.e., the production line is built directly inside or near the steel plant) as a heat source to provide heat for the heating and carbonization process of biomass. Since this process is similar to biomass hydrothermal carbonization, but the heat required for the carbonization process is provided by external steam, unlike traditional pyrolysis carbonization which relies on the combustion of pyrolysis gas generated by biomass to provide heat for the pyrolysis process, the yield of biomass char material can reach about 90%. Furthermore, since the waste heat steam raw material of the steel plant is softened water, it utilizes the waste heat of high-temperature materials, and there are no pollutant emissions during the production process. In contrast, traditional biomass boilers produce air pollutants such as dust, sulfides, and nitrogen oxides during combustion, requiring supporting environmental protection facilities for pollutant treatment. Therefore, the process of this invention is more environmentally friendly. The biomass char obtained by the above process can meet the fuel requirements of blast furnace injection and can be directly fed into the existing pulverization (directly mixed with existing pulverized coal according to a set specific ratio) and injection system of the blast furnace, thereby greatly reducing carbon emissions in the blast furnace production process.

[0041] (2) By specifically limiting the raw materials and pressure control at each stage during the preparation of biomass char, this invention achieves the simultaneous production of furan derivative byproducts while obtaining biomass char injection material. These byproducts only require simple subsequent refining and can be sold as high-value products. This achieves the simultaneous production of high-value chemicals while producing biomass char injection material, thereby reducing the overall production cost of biomass char. Specifically, the raw materials of this invention are specifically selected agricultural waste, the heat is the surplus waste heat steam from steel plants, and acid is used. However, sulfuric acid does not volatilize and is directly discharged from the system with the biomass char. Acetic acid is produced during the reaction. Through the specific steps of this invention, this part of the acid can be reused for acid preparation (which can be obtained after concentration in the waste liquid evaporator), achieving zero wastewater discharge. Steam circulates within the entire process, ultimately obtaining biomass char injection material for reducing blast furnace carbon emissions and high-value-added byproducts. Thus, by precisely setting the raw materials, energy sources, and specific parameters, this invention can completely turn harm into benefit (eliminating agricultural waste, making full use of the surplus heat of steel plants, and not generating secondary pollutants). That is, the technical effect of this invention is not necessarily to obtain a high-performance final product, but a completely environmentally friendly process that can also produce economically beneficial products.

[0042] (3) If the present invention does not use the waste heat steam of the steel plant, but directly uses the generated biomass char to heat the boiler to generate steam, not only will burning biomass generate air pollutants and increase the investment and operating costs of environmental protection facilities, but the added value of biomass char will also be greatly reduced (it is only used as combustion heat, rather than as a blast furnace injection material to reduce carbon dioxide emissions). Therefore, the present invention does not use biomass char to heat the boiler to generate steam, but uses waste heat steam of the steel plant, which improves the environmental friendliness from all aspects (no gaseous pollutants are generated, more biomass char injection material is obtained, and the surplus waste heat steam of the steel plant is directly utilized). The present invention specifically defines the application of the waste liquid evaporator in the whole process, so that the waste liquid evaporator is not only more compatible with the waste heat steam of the steel plant, but also its secondary steam is returned to the carbonization reactor as steam to achieve zero discharge of wastewater. At the same time, the concentrate is returned to the acid tank as a subsequent acid source, so that no waste is discharged externally as a whole. Attached Figure Description

[0043] Figure 1 This is a process flow diagram of the method for preparing biomass char injection material using waste heat steam from steel plants according to the present invention.

[0044] Figure 2 This is a schematic diagram of the structure of a carbonization reactor according to one embodiment of the present invention.

[0045] In the diagram: 1-mill, 2-agitator, 3-acid mixing tank, 4-carbonization reactor, 5-medium speed mill, 6-blast furnace, 7-distillation tower, 8-waste liquid evaporator, 9-neutralization reactor, 10-rectification tower, 11-by-product storage tank, 12-feeding port, 13-steam outlet, 14-vent, 15-safety valve, 16-pressure gauge, 17-reactor body, 18-steam inlet, 19-discharge port; A-biomass feedstock, B-concentrated acid, C-tap water, D-dilute acid, E-mixed feedstock, F-top steam, G-biochar, H-biochar ultrafine powder, I-bottom waste liquid of distillation tower, J-top distillate of distillation tower, K-steel plant steam, L-condensate, M-secondary steam, N-concentrated liquid from waste liquid evaporator, O-neutralizing agent, P-top distillate of rectification tower. Detailed Implementation

[0046] To better illustrate the objectives, technical solutions, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments. The specific implementation methods, structures, features, and effects of the present invention will be described in detail below with reference to the accompanying drawings and preferred embodiments. Those skilled in the art should understand that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention.

[0047] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0048] Unless otherwise specified, all raw materials used in this invention are commercially available.

[0049] Example 1 This embodiment adopts... Figure 2 The apparatus shown is in accordance with Figure 1 The process shown in this embodiment is carried out by directly setting up the entire equipment and production line within the steel plant. It is an example of producing biomass char injection material and by-products using corn cobs as raw material and dilute sulfuric acid as a catalyst (dilute acid). The process includes the following steps: (1) Raw material preparation Weigh 11 tons of corn cobs (dried basis), and feed them into a crusher (mill 1) via a conveyor to break them into irregular blocks with an average length of about 20mm. Then, feed them into a mixer 2 (e.g., an acid mixer).

[0050] (2) Mixing acid Concentrated sulfuric acid in use such as Figure 1 The acid mixing tank 3 shown contains diluted sulfuric acid (containing some returned acetic acid) at a concentration of 4%~6% obtained by diluting tap water and waste liquid evaporator concentrate. This diluted sulfuric acid is then uniformly mixed with corn cobs in an acid mixing machine. The mass ratio of corn cobs to diluted sulfuric acid is 1:0.4.

[0051] (3) Carbonization The raw materials, after acid mixing, are conveyed into carbonization reactor 4 by a conveyor. The carbonization reactor has a diameter of 1.8 meters, a height of 9 meters, and a nominal volume of 20 m³. 3 After loading, the reactor is sealed, and then depressurized steam from other carbonization reactors is introduced to pressurize it to 0.35 MPa over 15 minutes. The vent valve is then slowly opened, maintaining the top pressure of the carbonization reactor at 0.3~0.35 MPa for 1.5 minutes. The vent valve is then closed, and secondary steam generated by the waste liquid evaporator is introduced to pressurize it to 0.8 MPa over 30 minutes. At this point, the temperature inside the carbonization reactor reaches the preset value (0.8 MPa saturated steam corresponds to a temperature of 170℃). The steam outlet at the top of the reactor is then slowly opened, and the secondary steam flow rate is increased to ensure the pressure inside the carbonization reactor is maintained between 0.8~0.85 MPa. The pressure stabilization process lasts for 120 minutes, with the secondary steam flow rate controlled at 140~160 kg / min. During the pressure stabilization stage, the top steam is discharged through the steam outlet. After the pressure stabilization stage is complete, the secondary steam inlet valve is closed.

[0052] (4) Unloading After the pressure stabilization stage is completed, the secondary steam inlet valve is closed, and the steam from the steam outlet is introduced into other carbonization reactors that have completed loading (i.e., during the pressure relief stage, the steam from the top of the tower is discharged through the steam outlet, and the discharged steam is discharged into other carbonization reactors), thus increasing the pressure in other reactors while reducing the pressure. After 15 minutes, when the pressure inside the reactor drops to 0.14 MPa, the steam outlet is closed, the discharge valve is opened, and the biomass char is discharged using the residual pressure inside the reactor.

[0053] (5) Distillation The overhead steam from the carbonization reactor's pressure stabilization stage, after being slag-removed by a slag remover, first enters the reboiler of distillation column 7 for waste heat recovery, and then enters the condenser to obtain a condensate at 60-90°C containing 7-10 wt.% of the byproduct 2-furancarbaldehyde (furfural). Distillation utilizes the principle of the azeotropic lowering of 2-furancarbaldehyde with water (furfural azeotropic with water is 97.9°C). During distillation, the bottom temperature is controlled at 102-106°C, the top temperature at 96-99°C, and the pressure inside the column is ≤0.018 MPa. After the distillate from the top of the distillation column is cooled to 40-45°C, it enters the separator for phase separation. The upper layer is mainly water, containing 9% furfural and other low-boiling-point fractions, and can be refluxed to the top of the distillation column; the lower layer is crude 2-furancarbaldehyde with a concentration of over 90%. Most of the water and organic waste acid are discharged from the bottom of the distillation tower as waste liquid. After solid-liquid separation, the waste liquid is heated by the waste liquid evaporator 8 (the heat source is 1.2MPa steel plant steam K provided by the steel plant. The condensate L generated here is returned to the steel plant's steam pipeline system to generate steam again and is not discharged externally). The generated secondary steam is used to heat the carbonization reactor to achieve recycling. The concentrated liquid from the waste liquid evaporator is discharged from the bottom of the waste liquid evaporator, cooled and used for sulfuric acid dilution to achieve zero wastewater discharge.

[0054] (6) Prepare biomass char injection material The physicochemical properties of the biochar obtained in step (4) are shown in Table 1. 8.6 parts by weight of biochar (50% moisture content) and 91.4 parts by weight of pulverized coal (10% moisture content) were mixed and then fed into a medium-speed mill 5 for pulverization (hot air was present during the pulverization process to dry the wet material, forming a dry-based material), resulting in a 5% replacement of injected fuel (i.e., the mass ratio of biochar (dry basis) to injected pulverized coal (dry basis) was 5:95). This fuel was then used in the pulverized coal injection process of blast furnace 6 through an injection system. Table 1 shows the physicochemical properties of the biochar obtained in Example 1.

[0055] Table 1 The data in Table 1 shows that the obtained biomass char meets all the requirements for blast furnace pulverized fuel.

[0056] (7) By-product refining The crude 2-furan carbaldehyde contains approximately 90% furfural, such as... Figure 1As shown, firstly, a 10% Na₂CO₃ solution is added to the neutralization tank (neutralization reactor 9) for neutralization and settling to remove organic acids from the crude 2-furan carbaldehyde. The lower layer of liquid from the neutralization tank enters the distillation column 10 for vacuum distillation. The bottom temperature of the distillation column is controlled between 100 and 110°C, and the working pressure is -0.085 MPa. The distillate from the top of the distillation column, after cooling, enters the by-product storage tank 11 as furfural. The high-boiling-point substances at the bottom of the distillation column undergo solid-liquid separation. The liquid phase is sent to the distillation column to recover furfural, and the solid residue (approximately 25 kg of solid residue is produced from 11 tons of corn cobs; this solid residue is mainly condensed organic matter, and the combustion products are carbon dioxide and water) can be used as boiler fuel (i.e., virtually no waste is generated).

[0057] In this embodiment, one production cycle uses 11 tons of corn cobs (air-dried basis) as raw material, which can produce 20 tons of biochar with a moisture content of approximately 50%. The 20 tons of biochar with 50% moisture content and 210 tons of coal (with a moisture content of approximately 10%) are then fed together into a medium-speed mill for crushing and drying, ultimately yielding approximately 200 tons of pulverized fuel for blast furnace injection. One ton of 2-furan carbide with a purity ≥98.5% is also produced as a byproduct. The steel plant's waste heat steam consumption during the production process is approximately 18 tons, and no wastewater is generated throughout the entire process. Furthermore, because the steel plant's steam is used for heating, excess steam from the steel plant is utilized.

[0058] Example 2 This example illustrates the use of acetic acid as a catalyst. The difference from Example 1 is that the mixture with crushed corn cobs is an 8% acetic acid solution, with a corn cob to acetic acid solution mass ratio of 1:0.4. Other setups are the same as in Example 1. After using acetic acid as a catalyst, the consumption of raw materials and steam, as well as the yields of biochar and furfural, are essentially the same as in Example 1. Most of the physicochemical properties of the biochar are essentially the same as in Example 1, except that due to the avoidance of sulfuric acid use, the sulfur content is reduced from 0.83 wt.% in Example 1 to 0.14 wt.%, reducing the sulfur load on the blast furnace and facilitating subsequent treatment of the blast furnace gas. Furthermore, although acetic acid can be partially recycled through a waste liquid evaporator, the catalyst cost when using acetic acid is approximately 5-6 times that when using sulfuric acid, increasing the production cost of biochar compared to Example 1.

[0059] Example 3 This embodiment is used to illustrate the relevant device involved in embodiment 1. The carbonization reactors in this embodiment are arranged in series with four. After the charging, sealing, pressurizing and venting operations are completed in steps (3) and (4), each carbonization reactor goes through several stages in sequence: pressurization, pressure stabilization, series steam discharge, pressure relief and unloading. The operation cycle of a single carbonization reactor from the start of charging to the completion of unloading is 4 to 6 hours (for example, it is set to about 5 hours in this embodiment).

[0060] The general process is as follows: charging for 15 minutes, pressurizing for 15 minutes, venting for 1-2 minutes, pressurizing for 30 minutes, stabilizing for 120 minutes, passing through multiple reactors for 100 minutes, depressurizing for 15 minutes, and discharging for 15 minutes. This "passing through multiple reactors" refers to the process where, as the reaction progresses, the hemicellulose content decreases, the production rate of furan derivatives slows down, and the furan derivative content in the overhead steam decreases. At this point, the overhead steam containing a small amount of furan derivatives can be used as secondary steam and fed into other reactors that have just completed pressurization to improve the yield of furan derivatives.

[0061] Adding the tandem boiling process increases the amount of furfural produced from 11 tons of corn cobs from 1 ton to 1.15 tons, but it also increases the time required for the furfural production cycle and reduces the efficiency of the equipment.

[0062] Comparative Example 1 This comparative example demonstrates a comparative experiment using corn stalks with a relatively low hemicellulose content as raw material. The difference from Example 1 is that corn stalks with a hemicellulose content of 20-25 wt.% are used as raw material for biochar production; other settings are the same as in Example 1. In one production cycle, this comparative example uses 11 tons of corn stalks to produce 21.1 tons of biochar with a moisture content of approximately 50%, but only 0.4 tons of furfural. That is, this comparative example yields 1.1 tons more biochar than Example 1, but 0.6 tons less furfural. This is because 2-furan carbide is mainly converted from hemicellulose in the raw material, and the hemicellulose content in corn stalks is only 20-25%, far lower than the 35-40% in corn cobs. Furthermore, the ash content of corn stalks is approximately 13.5%, much higher than the 3.5% in corn cobs. The ash in the raw material can react with the acid catalyst to form acid salts, unnecessarily consuming the acid solution (catalyst), reducing the hemicellulose conversion rate, and further affecting the furfural yield. Although this comparative example yielded more biochar, from an economic perspective, it only increased the amount of biochar by 1.1 tons while obtaining 60% less furfural (the price of furfural is much higher than that of biochar). Compared to Examples 1 and 2, this comparative example significantly reduced the economic benefits of the present invention.

[0063] Comparative Example 2 This comparative example illustrates a test conducted without an acid catalyst. The difference from Example 1 is that 40 wt.% water (by weight of corn cob) is used instead of dilute sulfuric acid; other settings are the same as in Example 1. This comparative example uses 11 tons of corn stalks per production cycle to produce 21.0 tons of biochar with a moisture content of approximately 50%, but only 0.4 tons of furfural. That is, the byproduct yield of this comparative example is only 40% of that of Example 1. This is because the hemicellulose in the biomass feedstock decomposes very slowly without acid catalysis. However, as the carbonization process proceeds, acetic acid is produced during biomass decomposition. Acetic acid catalyzes the hydrolysis of hemicellulose and the dehydration of pentoses, thereby producing a certain amount of furfural. Therefore, the overall economic benefits of this comparative example are far lower than those of Example 1.

[0064] Comparative Example 3 This comparative example is a test to increase the carbonization reaction temperature. The difference from Example 1 is that the pressure inside the reactor was increased to 1.25 MPa during the pressurization stage of the carbonization reaction (i.e., the temperature of the material inside the reactor was 190°C). Other settings were the same as in Example 1. In this comparative example, 11 tons of corn cob raw material produced 20.5 tons of biochar and 0.7 tons of furfural. That is, compared to Example 1, although only the pressure inside the reactor was increased, the yield of by-products was reduced by 30%, thus reducing economic benefits by more than 30%.

[0065] This is because the side reactions of furfural decomposition intensify with increasing temperature. Maintaining a higher temperature inside the reactor causes some of the generated furfural to decompose, thus reducing the furfural yield. Furthermore, higher reaction temperatures place greater demands on the reactor's pressure resistance and relatively increase energy consumption, further increasing costs and reducing environmental friendliness.

[0066] Comparative Example 4 This comparative example is a test to reduce the secondary steam flow rate. The difference from Example 1 is that the secondary steam flow rate was reduced from 140-160 kg / min to 90-110 kg / min during the pressure stabilization stage of the carbonization reaction. Other settings are the same as in Example 1. In this comparative example, 11 tons of corn cob raw material produced 20.7 tons of biochar and 0.8 tons of furfural. This represents a 20% reduction in byproducts compared to Example 1, thus reducing economic efficiency. This is because reducing the secondary steam flow rate resulted in a steam pressure of 0.8 MPa (170°C). Under these conditions, the formation and decomposition of furfural occur simultaneously. While reducing the steam flow rate can decrease energy consumption in the carbonization process, it also increases the residence time of furfural in the reactor, leading to increased decomposition and thus affecting furfural yield. Therefore, a certain steam flow rate needs to be maintained to remove the generated furfural in a timely manner. (In other comparative examples, increasing the steam flow rate slightly increases furfural yield, but the increased steam consumption actually reduces the overall efficiency of the system.) Comparative Example 5 This comparative example illustrates a comparative test without using waste heat steam from a steel plant. The difference between this comparative example and Example 1 is that, instead of introducing waste heat steam, the biomass discharged through the unloading port is directly fed into a separately installed boiler for combustion. The steam generated by the boiler then heats and evaporates the waste liquid in an evaporator. Other setup methods are the same as in Example 1. In this comparative example, 11 tons of corn cob feedstock produced 8 tons of biochar and 1 ton of furfural. Compared to Example 1, this reduces the production of biochar by 12 tons and the input of waste heat steam by 18 tons. However, from an economic perspective, 18 tons of waste heat steam costs approximately 2160 yuan, while the reduced cost of 12 tons of biochar is approximately 5040 yuan, resulting in a total reduction of 2880 yuan in revenue. More importantly, it reduces biochar production by 60%, meaning a 60% reduction in blast furnace fuel containing biochar, thereby increasing blast furnace carbon consumption and emissions. From a technical perspective, the steam generated by a boiler using biomass charcoal as fuel is obtained through the combustion of biomass charcoal. This process produces air pollutants such as dust, sulfides, and nitrogen oxides. In contrast, waste heat steam from steel plants is generated by recovering the waste heat from high-temperature materials, with no pollutant emissions during the production process. Therefore, the current comparative method wastes the value of biomass charcoal and significantly reduces its environmental friendliness. This demonstrates that the present invention, by introducing waste heat steam from steel plants and utilizing its high calorific value, further reduces energy consumption.

[0067] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing biomass char injection feedstock by co-producing waste heat steam from a steel plant, characterized in that, Includes the following steps: (1) Biomass raw material pretreatment: The biomass raw material rich in hemicellulose is crushed to a particle size of 15~30mm and then conveyed into a mixer; (2) Acid mixing: The acid solution is mixed with water in the acid mixing tank to obtain dilute acid. The dilute acid and the crushed biomass raw material in step (1) are mixed in a stirrer at a mass ratio of (0.3~0.7):

1. (3) Carbonization: The material after mixing in step (2) is fed into the carbonization reactor. After the material is loaded, it is sealed and then steam is introduced. After being pressurized to 0.2~0.4MPa, vented, pressurized to 0.6~1.2MPa and stabilized for 2~3 hours, carbonization is completed to obtain biomass charcoal. The flow rate of secondary steam during the stabilization stage is 135~165kg / min, and the steam at the top of the tower is discharged through the steam outlet. (4) Unloading: After carbonization in step (3), the carbonization reactor is depressurized to 0.1~0.2MPa, the unloading port is opened and the biomass char is discharged through the unloading port using the residual pressure in the reactor. During the depressurization stage, the top steam of the tower is discharged through the steam outlet. (5) Distillation: The top steam obtained in step (3) is discharged into the condenser to obtain condensate. The condensate is added to the distillation tower from the middle of the distillation tower for distillation. The distillate at the top of the distillation tower is cooled and then enters the separator for stratification. The upper water layer is returned to the distillation tower for circulation, and the lower layer is crude by-product. The bottom waste liquid at the bottom of the distillation tower is discharged into the waste liquid evaporator. The waste liquid evaporator is heated and evaporated by the waste heat steam of the steel plant to obtain secondary steam and concentrated waste liquid. The secondary steam is discharged into step (3) as steam and fed into the carbonization reactor. The concentrated waste liquid is fed into the acid mixing tank in step (2) as raw material for acid mixing, so as to achieve no wastewater discharge in the whole process. (6) Preparation of materials: The biomass char obtained in step (4) is mixed with pulverized coal injected into the blast furnace at a mass ratio of (5~12):(88~95), and then the mixture is ground into powder with a particle size of less than 0.074 mm to obtain biomass char injection material for blast furnace injection.

2. The method for preparing biomass char injection material by co-producing waste heat steam from a steel plant according to claim 1, characterized in that, The hemicellulose-rich biomass raw material mentioned in step (1) is one or more of corn cobs, sugarcane bagasse, or rice husks.

3. The method for preparing biomass char injection material by co-producing waste heat steam from a steel plant according to claim 1, characterized in that, The acid in step (2) is a mixture of concentrated waste liquid returned to the acid mixing tank in step (5) and sulfuric acid or acetic acid; the dilute acid is dilute sulfuric acid containing concentrated waste liquid with a sulfuric acid concentration of 4~7 wt.% or dilute acetic acid containing concentrated waste liquid with a acetic acid concentration of 5~10 wt.%.

4. The method for preparing biomass char injection material by co-producing waste heat steam from a steel plant according to claim 1, characterized in that, The following steps are included after step (6): (7) By-product purification: The crude by-product obtained in step (5) is neutralized to remove acid impurities, and then high-boiling substances are removed by distillation to obtain the distillate discharged from the top of the distillation column. The distillate is condensed to obtain high-purity furan derivative by-products.

5. The method for preparing biomass char injection material by co-producing waste heat steam from a steel plant according to claim 4, characterized in that, The neutralization in step (7) uses one or more of Na2CO3, Ca(OH)2 or NaOH alkaline solution as the neutralizing agent; the distillation pressure is -0.09 to -0.07 MPa.

6. The method for preparing biomass char injection material by co-producing waste heat steam from a steel plant according to claim 1 or 2, characterized in that, In step (3), the height-to-diameter ratio of the carbonization reactor is 7~9, and the maximum allowable working pressure is 0.8~1.5MPa; The steam in step (3) is the secondary steam obtained in step (5); the pressurization time is 10~20 min; The venting in step (3) specifically refers to: after pressurization is completed, the venting valve is opened while steam is continuously supplied to vent the air in the carbonization reactor. The opening degree of the venting valve is such that the pressure gauge reading at the top of the carbonization reactor remains unchanged, and the venting time is 1~2 minutes. The pressurization in step (3) specifically involves: closing the vent valve after venting, maintaining continuous steam supply, and continuing to increase the pressure for 20-40 minutes until it reaches 0.6-1.2 MPa; The pressure stabilization in step (3) specifically involves: continuously controlling the pressure at 0.6~1.2MPa and maintaining it for 2~3 hours; In step (3), the total mass of the steam discharged into the carbonization reactor during the pressure stabilization stage and the steam discharged from the top of the tower through the steam outlet is 1.6 to 2 times the total mass of the raw materials in the carbonization reactor, so as to reduce the high-value-added small molecule compounds of by-products in the carbonization process from staying in the carbonization reactor for a long time and undergoing secondary reactions.

7. The method for preparing biomass char injection material by co-producing waste heat steam from a steel plant according to claim 1 or 2, characterized in that, The carbonization reactor is provided in multiple ways. In step (4), when one of the carbonization reactors is depressurized, the steam discharged from the top of the tower is discharged into other carbonization reactors that have been loaded and sealed, so as to realize the recovery of waste heat. The depressurization time in step (4) is 10~20 min, and the pressure at the end of the depressurization is 0.1~0.2 MPa.

8. The method for preparing biomass char injection material by co-producing waste heat steam from a steel plant according to claim 1 or 2, characterized in that, In step (5), the top steam obtained in step (4) is first discharged into the reboiler at the bottom of the distillation column for waste heat recovery to provide heat for the distillation column, and then discharged into the condenser to obtain condensate. In step (5), the pressure of the waste heat steam from the steel plant used to heat and evaporate the waste liquid in the evaporator is 1.2~1.8MPa, and the waste heat steam from the steel plant is obtained by heating the softened water in the boiler of the steel plant. In step (5), the concentration ratio of the waste liquid evaporator is 15~20:

1.

9. The method for preparing biomass char injection material by co-producing waste heat steam from a steel plant according to claim 1 or 2, characterized in that, As an alternative, step (6) is replaced by: first removing and drying the biomass char obtained in step (4) to obtain low-alkali-metal biomass char, then mixing the low-alkali-metal biomass char with coal powder at a mass ratio of (7~20):(80~93), and then grinding the whole mixture into powder with a particle size of less than 0.074 mm to obtain biomass char injection material for blast furnace injection; The removal and drying of alkali metals is specifically as follows: the biochar obtained in step (4) is washed with water 3 to 5 times, the washed biochar is filtered, and the filter material is dried to a moisture content of 8 to 12 wt.% to obtain biochar with low alkali metal content.

10. The method for preparing biomass char injection material by co-producing waste heat steam from a steel plant according to claim 1 or 2, characterized in that, The carbonization reactors are connected in series in 3 to 4 stages. After the loading, sealing, pressurizing and venting operations are completed in steps (3) and (4), each carbonization reactor goes through several stages in sequence, including pressurization, pressure stabilization, series steam discharge, pressure relief and unloading. The operation cycle of a single carbonization reactor from the start of loading to the completion of unloading is 4 to 6 hours. The top of the carbonization reactor is equipped with a charging port, a steam outlet, an vent, a safety valve, and a pressure gauge, while the bottom is equipped with a steam inlet and a discharge port. The charging port is sealed with a flange, and the steam outlet, vent, steam inlet, and discharge port are controlled by valves.

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