A method for preparing a blast furnace injection biomass fuel

Abstract

The present application relates to a kind of methods for preparing blast furnace injection biomass fuel, including biomass raw material pretreatment, biomass pre-treatment, hydrothermal carbonization treatment, carbon slurry delivery, refining, separation treatment, process water treatment and hydrothermal carbon drying treatment etc., by the equipment, step and parameter of each step are specifically set, so that energy and resources are optimized in preparation process Configuration, and the properties of the hydrothermal carbon obtained can be more in line with blast furnace injection, greatly improve the rationalization of resource allocation level.

Description

Technical Field

[0001] This invention relates to the field of industrial environmental protection, and specifically to a method for preparing biomass fuel injected into blast furnaces. Background Technology

[0002] The benchmark level for energy consumption in the blast furnace process of ironmaking in the steel industry is 361 kgce / tFe. The comprehensive energy consumption of blast furnaces in some steel enterprises, especially small and medium-sized blast furnaces, is higher than this value. If the energy consumption of existing blast furnace processes cannot be reduced, they may face production restrictions or even shutdowns in the future.

[0003] Compared with traditional fossil fuels such as coal, biomass resources are a clean energy source with large capacity, wide distribution, and renewable properties. The carbon-neutral nature of biomass resources means that they do not release additional greenhouse gases into the atmosphere during industrial use, which plays a positive role in mitigating the increasingly serious global greenhouse effect. The application of biomass resources in ironmaking is of great significance in reducing coal consumption and carbon emissions. As a renewable resource, biomass resources will play an even more prominent role in the steel industry's efforts to control energy consumption.

[0004] Blast furnace tuyere fuel injection technology is currently a major technical means to reduce costs and pollutant emissions in blast furnace ironmaking. This process primarily replaces metallurgical coke, requiring the injected fuel to have high calorific value, good combustibility, and low ash and harmful element content. Currently, anthracite, bituminous coal, heavy oil, or natural gas are mainly used for blast furnace tuyere fuel injection. Biomass, due to its high moisture content, low energy density, and low crushing efficiency, cannot be directly used for blast furnace tuyere fuel injection. Conventional biomass pyrolysis technology solves these problems, but it is energy-intensive, heavily polluting, and the ash and harmful elements such as sodium and potassium in biomass accumulate in the pyrolysis char, limiting the application of biomass pyrolysis char in blast furnace fuel injection.

[0005] Currently, biomass hydrothermal carbonization technology is mainly still in the experimental research stage, and in the industrial field, it is mainly used for the harmless treatment of sludge. If it is used to prepare blast furnace injection fuel, there are still many engineering problems in terms of system continuous operation rate, system energy / water consumption, waste heat recovery and utilization rate, and product quality optimization, and there is considerable room for improvement.

[0006] Biomass hydrothermal carbonization refers to the process of simulating and accelerating the natural coal formation process in a subcritical water environment under moderate pressure (1–5 MPa) and temperature (180–280℃). Biomass undergoes a series of complex chemical reactions, including hydrolysis, dehydration, decarboxylation, and condensation, to form hydrothermal carbon similar to coal. Compared to conventional biomass pyrolysis, water does not undergo a phase change during hydrothermal carbonization, resulting in lower energy consumption. Organic matter with any water content can be used as raw material, and there are no emissions during the reaction process, making it a cutting-edge technology in biomass treatment. After hydrothermal carbonization, the increased hydrophobicity of biomass facilitates dehydration and drying, and the calorific value of the hydrothermal carbon can reach 23–28 MJ / kg, comparable to coal. For the steel industry, biomass hydrothermal carbon has a high calorific value, low content of harmful elements such as ash, potassium, sodium, and sulfur, and excellent grindability, combustibility, and transportability. It can be used directly as a substitute for coal and coke in sintering, pelletizing, ironmaking, and steelmaking processes, significantly reducing carbon emissions during production.

[0007] Chinese invention patent publication CN110218826B discloses a method for injecting biomass hydrothermal char into a blast furnace and a method for preparing biomass hydrothermal char. The method involves preparing hydrothermal char through a high-temperature hydrothermal carbonization reactor. However, the production process is costly and uses an extensive preparation method, which is not very environmentally friendly.

[0008] Chinese invention patent publication CN105861003A discloses a pre-pressurized hydrothermal carbonization method for biomass. By using heating carbonization and pre-pressurization, the reaction time is shortened by more than 100% and energy is saved by more than 100%. However, it does not address the effective utilization of energy in the overall preparation process. Summary of the Invention

[0009] This invention addresses the shortcomings of traditional biomass pyrolysis processes, such as high energy consumption, heavy pollution, and product quality that fails to meet the requirements of blast furnace injection processes. It provides a clean, environmentally friendly, and efficient method for preparing blast furnace injection fuel using biomass hydrothermal carbonization, which meets the requirements of blast furnace injection processes.

[0010] Specifically, this is achieved through the following technical solution:

[0011] A method for preparing blast furnace injected biomass fuel includes the following steps:

[0012] (1) Biomass raw material pretreatment: The biomass raw material is crushed by a crushing device to a maximum particle size of 28-35 mm. The crushed biomass particles are then transported to a mixing device, and water with a weight of 3-6 times that of the biomass particles is added. The mixture is then stirred to obtain a biomass raw material slurry with a water content of 73-85 wt%.

[0013] (2) Biomass preheating treatment: The biomass raw material slurry obtained in step (1) is pressurized to 2-4 MPa, and then the pressurized biomass raw material slurry is discharged into the preheating pipeline. The preheating pipeline is a shell structure with inner and outer tubes. The heating liquid and the biomass raw material slurry are located in the shell side and the tube side, respectively. The preheating pipeline preheats the biomass raw material slurry to 150-200℃.

[0014] (3) Hydrothermal carbonization treatment: The biomass raw material slurry after pressurization and preheating in step (2) enters the hydrothermal reactor of the hydrothermal reaction device through the pipeline. The biomass raw material slurry is mixed with high-temperature subcritical water at 255-270℃ at the top of the hydrothermal reactor, so that the temperature of the mixed slurry rises to 190-230℃. The heated and mixed slurry undergoes hydrothermal carbonization reaction in the hydrothermal reactor. The temperature in the hydrothermal reactor is controlled at 205-245℃, the reaction pressure is 2.8-4.2MPa, and the water content of the slurry in the hydrothermal reactor is maintained at 80-90wt%. The hydrothermal carbonization reaction time is 2.5-4h, and a high-temperature hydrothermal carbon slurry with a temperature of 230-250℃ is obtained.

[0015] (4) Carbon slurry transportation, refining and separation treatment: The high-temperature hydrothermal carbon slurry obtained in step (3) is discharged into the shell structure of the preheating pipeline mentioned in step (2). The biomass raw material slurry in step (2) is preheated by heat exchange through the pipe wall. The high-temperature hydrothermal carbon slurry is cooled to 40-60°C. Then, the obtained hydrothermal carbon slurry is depressurized to reduce the pressure to atmospheric pressure. Then, the hydrothermal carbon slurry is placed in a crushing and grinding device for crushing to below 0.3-0.8 mm. Then, the crushed hydrothermal carbon slurry is floated and then filtered to obtain process water and hydrothermal carbon cake with a water content of 28-35 wt%.

[0016] (5) Process water treatment: 35-65% of the volume of the process water discharged in step (4) is discharged into the stirring device in step (1) as part of the water added to the biomass pellets for slurry formation, and the remaining part is discharged into the process water treatment device for harmless treatment.

[0017] (6) Hydrothermal carbon drying treatment: The mud-like hydrothermal carbon cake obtained in step (4) is placed into a drying device for drying treatment. After drying, the air-dried basis moisture content of the obtained biomass hydrothermal carbon is less than 3wt%, the sulfur content is less than 0.5wt%, the alkali metal content is less than 0.1wt%, the Hardgrove grindability index is greater than 60, and the lower heating value is 22-26MJ / kg.

[0018] Preferably, in step (3), the hydrothermal reaction device includes a hydrothermal reactor and a temperature and pressure control device. The temperature and pressure control device includes a high-pressure control tank, a low-pressure control tank, an atmospheric pressure water tank, a cooling tower, and a thermal oil furnace. The hydrothermal reactor is provided with a material inlet, a material outlet, a gas outlet, and a high-temperature subcritical water inlet. The low-pressure control tank is provided with a gas inlet, a gas outlet, and a subcritical water outlet. The high-pressure control tank is provided with a subcritical water outlet, a high-temperature subcritical water outlet, a gas outlet, a cooling water inlet, a heat exchange liquid inlet, and a heat exchange liquid outlet. The atmospheric pressure water tank is provided with a cooling water outlet and an atmospheric pressure water outlet. The cooling tower is provided with a reaction gas inlet, a cooling water spray component, and a spray water outlet. The gas outlet of the hydrothermal reactor and the gas outlet of the low-pressure control tank are connected. The inlet is connected via a pipeline. Biomass raw material slurry is discharged into the hydrothermal reactor through the material inlet. The treated high-temperature hydrothermal carbon slurry is discharged through the material outlet. The gas outlet of the low-pressure control tank and the gas outlet of the high-pressure control tank are respectively connected to the reaction gas inlet of the cooling tower through pipelines. The subcritical water outlet of the low-pressure control tank is connected to the subcritical water outlet of the high-pressure control tank through a pipeline. The high-temperature subcritical water outlet of the high-pressure control tank is connected to the high-temperature subcritical water inlet of the hydrothermal reactor through a pipeline. The spray water outlet of the cooling tower is connected to the cooling water outlet of the atmospheric pressure water tank through a pipeline. The atmospheric pressure water outlet of the atmospheric pressure water tank is connected to the cooling water inlet of the high-pressure control tank through a pipeline. The thermal oil furnace is connected to the heat exchange liquid inlet and heat exchange liquid outlet of the high-pressure control tank through pipelines.

[0019] Preferably, in step (3), a high-pressure water pump is installed on the pipeline between the subcritical water discharge port of the low-pressure control tank and the subcritical water discharge port of the high-pressure control tank, the pipeline between the high-temperature subcritical water discharge port of the high-pressure control tank and the high-temperature subcritical water inlet of the hydrothermal reactor, and the pipeline between the atmospheric water discharge port of the atmospheric water tank and the cooling water inlet of the high-pressure control tank; a heat transfer oil circulation pump is installed on the pipeline between the heat transfer oil furnace and the heat exchange liquid inlet of the high-pressure control tank; a vent valve is installed on the top of the atmospheric water tank; the cooling water spray component includes one or more nozzles installed in the cooling tower, a cooling pipe connected to the nozzle, and a cooling water pump installed on the cooling pipe.

[0020] Preferably, in step (3), the excess subcritical water after heat exchange is discharged as water vapor along with the gas generated by the hydrothermal reaction from the gas outlet at the top of the hydrothermal reactor. Then, it enters the low-pressure control tank through the gas inlet. The temperature inside the low-pressure control tank is set 10-20°C lower than the temperature in the hydrothermal reactor. When the pressure inside the low-pressure control tank exceeds the set threshold, the gas generated by the reaction and some water vapor are discharged through the gas outlet and into the cooling tower through the reaction gas inlet. When the liquid level in the low-pressure control tank exceeds the set liquid level threshold, the excess subcritical water is pumped through a high-pressure water pump and discharged into the high-pressure control tank through the subcritical water outlet. The excess gas in the high-pressure control tank also enters through the reaction gas inlet. The gas is discharged into the cooling tower, where it is cooled by a cooling water spray system. The sprayed water is then discharged through the spray water outlet and into the atmospheric pressure water tank through the cooling water inlet. The cooling water in the atmospheric pressure water tank is discharged through the atmospheric pressure water outlet and then into the high-pressure control tank via a high-pressure water pump and a cooling water inlet. The water in the high-pressure control tank is heated by the heat transfer oil between the heat transfer oil furnace and the high-pressure control tank. The heating temperature is such that the water temperature in the high-pressure control tank is 20-40°C higher than the temperature in the hydrothermal reactor. Then, the high-temperature, high-pressure subcritical water in the high-temperature control tank is discharged through the high-temperature subcritical water outlet and pumped into the hydrothermal reactor for hydrothermal carbonization treatment.

[0021] Preferably, in step (5), the process water discharged into the process water treatment device is first sent to the neutralization reactor, where alkali solution is added to adjust the pH value to 6-7. Then, the pH-adjusted process water is discharged into the comprehensive equalization tank to dilute it to a maximum COD volumetric load of 18-22 kg COD / (m³). 3·d) Then, nutrients are added to the process water, and the pH is adjusted to 6.5–7.5. The process water, after being adjusted in the equalization tank, is then discharged into the anaerobic reactor for anaerobic digestion. The temperature of the anaerobic reactor is controlled at 30–38°C, the mixed liquor suspended solids concentration is 30–90 g / L, and the hydraulic retention time is 55–65 h (preferably 60 h). Through anaerobic digestion, 88–95% of the COD, BOD, and nitrogenous compounds in the process water are removed. The apparatus produces treated water, biogas, and sludge. The biogas is connected to a thermal oil heater or the drying device in step (6) via a pipeline and is used as fuel for the thermal oil heater or the drying device in step (6). The treated water after anaerobic digestion is discharged into an intermediate water tank, cooled to 20-30°C (preferably 25°C), and then discharged into an aerobic biochemical tank for aerobic digestion. The concentration of suspended solids in the mixed liquor of the aerobic digester is controlled at 8-10 g / L, the hydraulic retention time is 115-125 h, and it is maintained at a constant temperature. The dissolved oxygen concentration in the aerobic tank is 0.05-0.3 g / L. Aerobic digestion produces treated water and sludge. The treated water produced after aerobic digestion is discharged into the Fenton reaction tank for advanced oxidation via the Fenton reaction. The hydraulic retention time is controlled to be 1.5-2 h. The treated water after the Fenton reaction undergoes solid-liquid separation. The separated sludge is concentrated together with the sludge produced by anaerobic digestion and aerobic digestion. The solid content of the concentrated sludge is 2-3.6 wt%. It is discharged into the stirring device in step (1) as a diluent (the amount of diluent added is to maintain the biomass raw material slurry with a water content of 73-85 wt% obtained by stirring in step (1), that is, the amount of diluent added is to replace 96.4-98% of the water and 2-3.6 wt% of the dry basis in the biomass. The amount of water added in step (1) is adjusted according to the amount of sludge produced). The water obtained from solid-liquid separation is used as reclaimed water in the steel plant or sent to a secondary wastewater treatment plant for treatment and discharge after meeting the standards.

[0022] Preferably, the biogas produced by anaerobic digestion has a CH4 content of 55-65 vol%; the solid-liquid separation is carried out by an air flotation machine, and the flocculent material at the top of the air flotation machine enters the sludge thickener.

[0023] Preferably, in step (2), the biomass raw material slurry obtained in step (1) is pressurized to 2-4 MPa using a plunger pump.

[0024] Preferably, in step (4), the high-temperature hydrothermal carbon slurry flows from the shell side of the preheating pipeline, and the biomass raw material slurry flows from the tube side of the preheating pipeline. The two flow in opposite directions and exchange heat without direct contact.

[0025] Preferably, in step (5), the pH-adjusted process water is discharged into the integrated equalization tank and diluted until the COD volumetric load is less than or equal to 20 kg COD / (m³).3 ·d); In step (5), the nutrient salt is one or a mixture of two of potassium dihydrogen phosphate or urea; In step (5), the solid content of the concentrated sludge is 3 wt%.

[0026] As a preferred embodiment, the advanced oxidation of the Fenton reaction in step (5) is specifically as follows: first, the pH of the treated water discharged into the Fenton reaction tank is adjusted to 3-4, and then 1.6-2.5 kg / (kgCOD) (preferably 2 kg / (kgCOD)) of hydrogen peroxide and 1.1-1.5 kg / (kgH2O2) (preferably 1.2 kg / (kgH2O2)) of ferrous sulfate are added to carry out the advanced oxidation of the Fenton reaction, and the hydraulic retention time is controlled to be 1.5-2 h.

[0027] The technical advantages of this invention are as follows:

[0028] (1) This invention, through specific settings of steps and parameters, especially the continuous production process and temperature and pressure control system, preheats the biomass raw material slurry with high-temperature hydrothermal carbon slurry after reaction, and then further heats the raw material with high-temperature subcritical water. Through two different stages of preheating, energy is utilized in a tiered manner. This tiered heating method not only makes full use of heat, but more importantly, it makes the microparticle structure in the high-temperature hydrothermal carbon slurry obtained by hydrothermal carbonization more uniform and stable, improves hydrophobicity, and makes the final hydrothermal carbon more suitable for blast furnace injection. Thus, it promotes the specific process of hydrothermal carbon for specific purposes. This invention returns part of the process water to the raw material treatment stage as part of the water raw material, which not only reuses water resources, but also returns the usable biomass microparticles in the process water back to the process flow, making fuller use of biomass. The biogas generated in the process water treatment process is used for the preparation of high-temperature subcritical water and the drying of hydrothermal carbon, which also greatly reduces the amount of fuel supplied to the outside world by the entire process and greatly improves environmental friendliness.

[0029] (2) This invention makes specific arrangements for the hydrothermal reaction device, including components such as a low-pressure control tank, a high-pressure control tank, an atmospheric pressure water tank, a cooling tower, and a thermal oil furnace (temperature and pressure control device), and combines high-pressure water pumps set in different locations to reasonably control the pressure and temperature at different stages, so that the water in the hydrothermal reaction process can flow efficiently. Through such specific arrangements, the hydrophobicity of solid materials in the biomass hydrothermal reaction process is enhanced, and the carbonization efficiency is improved. The principle of hydrothermal carbonization is used to discharge the water in the biomass in a liquid form as comprehensively as possible, reducing the energy consumed by the phase change of water during the evaporation and drying process of biomass.

[0030] (3) This invention, through detailed settings of the temperature and pressure control systems in the hydrothermal reactor, enables rapid and precise adjustment of the temperature and pressure of the hydrothermal reactor, contributing to the stable operation of the hydrothermal carbonization process. To meet the requirements of different types of biomass raw materials and product quality, the temperature and residence time of the hydrothermal reactor can be flexibly changed within the scope of this invention, thereby achieving control over the properties of the hydrothermal carbon products. This invention uses high-temperature subcritical water to supplement the heat of the hydrothermal reactor and achieves temperature control. Compared with existing heat exchangers, this method has higher thermal efficiency and faster control speed. The specific settings for discharging high-temperature subcritical water into the hydrothermal reactor and the overall water circulation method of this invention, compared with the existing direct injection of medium- and high-temperature steam, can reduce disturbance to the flow field within the hydrothermal reactor, thus facilitating the sedimentation and separation of unreacted substances and products within the hydrothermal reactor, greatly improving reaction efficiency. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the process flow of the hydrothermal reaction device of the present invention.

[0032] Figure 2 This is a process flow diagram of the method for preparing blast furnace injected biomass fuel according to the present invention.

[0033] In the diagram: 11-Hydrothermal reactor, 12-Low-pressure control tank, 121-High-pressure water pump 2, 13-High-pressure control tank, 131-High-pressure water pump 1, 14-Thermal oil furnace, 141-Thermal oil circulation pump, 15-Atmospheric pressure water tank, 151-High-pressure water pump 3, 16-Cooling tower, 161-Cooling water pump, A-Cooling water. Detailed Implementation

[0034] Example 1

[0035] Methods for preparing biomass fuel injected into blast furnaces, such as Figure 1 As shown, it includes the following steps:

[0036] (1) Biomass raw material pretreatment: The biomass raw material is first crushed to below 50mm by a coarse crusher, and then crushed to below 30mm by a fine crusher. It is then conveyed to a mixing tank and mixed with water to produce a biomass raw material slurry with a moisture content of 80%.

[0037] (2) Biomass preheating treatment: The biomass feedstock slurry is fed to a plunger pump via a screw feeder. The plunger pump pressurizes the slurry to 3.5 MPa before it enters the preheating pipeline. The preheating pipeline has a shell-and-tube structure, with the biomass feedstock slurry in the tube side and the high-temperature hydrothermal carbon slurry after reaction in the shell side. The biomass feedstock slurry stays in the preheating pipeline for 45 minutes and is preheated to 200°C.

[0038] (3) Hydrothermal carbonization treatment: The pressurized and preheated biomass slurry enters the hydrothermal reactor through pipelines, where it is mixed with high-temperature subcritical water at 260°C at the top of the reactor and heated to 220°C. The biomass hydrothermal carbonization process is an exothermic reaction. The temperature of the hydrothermal reactor is controlled at 240°C, the reaction pressure at 3.3 MPa, and the water content of the slurry in the reactor is maintained at 85%. After heat exchange, the excess subcritical water is discharged from the top of the reactor as water vapor along with the hydrothermal reaction gas and enters the low-pressure control tank. The temperature of the low-pressure control tank is 230°C. When the pressure in the low-pressure control tank is too high, the reaction gas and some water vapor will be discharged from the top; when the liquid level in the low-pressure control tank is too high, the excess subcritical water will be transported to the high-pressure control tank by a high-pressure water pump. The reaction gas, water vapor, and excess gas in the high-pressure tank are cooled by cooling water spray in the cooling tower, and then enter the atmospheric pressure water tank together. The reaction gas is discharged through the vent valve at the top of the atmospheric pressure water tank. Cooling water from the atmospheric pressure tank is injected into the high-pressure control tank via a high-pressure water pump. Water from both the atmospheric and low-pressure control tanks is heated in the high-pressure tank by heat transfer oil in a heat exchanger, maintaining the high-pressure tank temperature at 260°C. High-temperature subcritical water is then pumped to the hydrothermal reactor for heating. The biomass feedstock remains in the hydrothermal reactor for 2.5 hours, generating high-temperature hydrothermal carbon slurry.

[0039] (4) Hydrothermal slurry conveying, refining, and separation: The high-temperature hydrothermal slurry, after hydrothermal carbonization at 240°C, is first heated in a preheating pipeline to recover residual heat and reduce the temperature to 50°C. After the pressure is reduced to atmospheric pressure by a depressurization device, the hydrothermal carbon particles are crushed to below 0.5 mm by a colloid mill and then enter the flotation column for flotation. The hydrothermal carbon concentrate with high carbon content is enriched with the foam at the top of the flotation column and sent to the foam storage tank by a foam scraper. The rich ore foam in the foam storage tank is transported to a plate and frame filter press by a foam pump for filtration to obtain hydrothermal carbon cake with a moisture content of 30% and process water.

[0040] (5) Process Water Treatment: A portion of the process water (e.g., 50% in this embodiment) is directly transported to the mixing tank of the pretreatment system for slurry formation, while the other portion enters the process water treatment system. In the process water treatment system, the process water is first pumped to the neutralization reactor, where alkali is added to adjust the pH to 6-7. Then, it enters the general conditioning tank for dilution, nutrient salts are added, and the pH is adjusted to approximately 7. The process water, after its composition has been adjusted in the general conditioning tank, first enters the anaerobic reactor for anaerobic digestion, removing 90% of COD, BOD, and nitrogenous compounds. It then enters the intermediate water tank 1 for cooling before entering the aerobic biochemical tank for aerobic digestion. The biogas produced by the anaerobic reactor contains approximately 60% CH4 and is used as fuel for the thermal oil heater or drying system. The process water treated in the aerobic biochemical tank undergoes advanced oxidation in the FENTON reactor before entering the flotation unit for solid-liquid separation. The flocculent material from the top layer of the dissolved air flotation (DAF) unit enters the sludge thickener, where it is thickened together with the sludge discharged from the anaerobic reactor and aerobic biological treatment tank. The thickened sludge is then sent to the mixing tank of the raw material processing system for hydrothermal treatment to render it harmless. The water separated from the DAF unit and the sludge thickener can be used as reclaimed water in the steel plant or sent to a secondary wastewater treatment plant in the city for treatment before being discharged in compliance with standards.

[0041] (6) Hydrothermal charcoal drying: The muddy charcoal cake enters a rotary dryer for drying. The heat source for the drying system is the flue gas from the thermal oil furnace and the biogas from anaerobic fermentation. The final biomass hydrothermal charcoal has an air-dried moisture content of less than 1%, an ash content of less than 6%, a sulfur content of less than 0.5%, an alkali metal (Na+K) content of less than 0.1%, a Hardgrove grindability index of greater than 60, and a lower heating value of greater than 24 MJ / kg.

[0042] Comparative Example 1

[0043] The other settings of this comparative example are the same as those of Example 1, except that a flash evaporation method is used to recover energy from the high-temperature slurry after the reaction, and the resulting high-temperature steam is used to preheat the raw material slurry. The specific temperature and pressure control system and raw material preheating pipeline of this invention are not used. Other settings are the same, and hydrothermal carbon is prepared using the same raw materials and other conditions as in Example 1. Compared to Example 1, although Comparative Example 1 can also obtain hydrothermal carbon of the same quality, it uses a flash evaporator to recover waste heat from the high-temperature carbon slurry. The upper limit of the temperature of the obtained high-temperature steam is 100°C, therefore the preheating temperature of the biomass raw material slurry does not exceed 100°C. At this time, since the temperature of the high-temperature subcritical water remains constant, and the heat required to raise the temperature of the biomass raw material slurry from 100°C to 220°C is much higher than that required to raise the temperature from 200°C to 220°C in the comparative example, it is necessary to increase the amount of high-temperature subcritical water and the amount of water vapor discharged from the top of the hydrothermal reactor to ensure sufficient heat supply within the reactor. In this scenario, the flow rate of high-temperature subcritical water in Comparative Example 1 is six times that of Example 1. This large flow rate of high-temperature subcritical water disrupts the flow field within the hydrothermal reactor, hindering the separation of unreacted substances and products. Simultaneously, the volumes of the high-pressure control tank and the low-pressure control tank are six and 23 times larger than those in Example 1, respectively, increasing the heat load on the thermal oil heater by 82.6%, requiring more fuel for heating. Furthermore, the flash tank of the flash evaporation system requires additional space and investment, and the valves and fittings are more prone to damage, resulting in poorer system stability and higher maintenance costs.

[0044] Comparative Example 2

[0045] The setup of Comparative Example 2 is the same as that of Example 1, except that the hydrothermal reactor uses an existing intermittent high-temperature reactor. To improve reactor utilization efficiency, the reactor is emptied as soon as possible after heat preservation. Therefore, flash evaporation is typically used to recover energy from the high-temperature slurry after the reaction. The resulting high-temperature steam is used to preheat the raw material slurry. Other setups are the same, and hydrothermal carbon is prepared using the same raw materials and other conditions as in Example 1. Compared to Example 1, although Comparative Example 2 can also obtain hydrothermal carbon of the same quality, the intermittent operation of the hydrothermal reactor requires a significant amount of time for heating and cooling the reactor, resulting in low operating efficiency. To achieve the same production scale as in Example 1, the reactor volume and floor space must be increased. Furthermore, similar to Comparative Example 1, flash evaporation is used to recover waste heat from the high-temperature carbon slurry. Since the preheating temperature of the biomass raw material slurry is no higher than 100°C, the heat required to raise the biomass raw material slurry from 100°C to the preset reaction temperature must be entirely provided by external energy input (fuel, electricity, or steam). In this case, the energy consumption of the hydrothermal reactor is 5 to 6 times that of Example 1.

[0046] Comparative Example 3

[0047] The other settings in this comparative example are the same as in Example 1, except that the temperature of the low-pressure control tank is set to 200°C, meaning that the temperature setting of the low-pressure control tank is outside the temperature relationship range defined by this invention within the hydrothermal reactor. Other settings are the same, using the same raw materials and other conditions as in Example 1 to prepare hydrothermal carbon. However, because the temperature of the low-pressure control tank is lower, the temperature of the low-temperature subcritical water injected from the low-pressure control tank into the high-pressure control tank is also lower. To maintain the temperature of the high-pressure control tank, the load on the thermal oil furnace will increase by approximately 3.4%, requiring more fuel consumption.

[0048] Comparative Example 4

[0049] The other settings in this comparative example are the same as in Example 1, except that the temperature of the high-pressure control tank is set to 240°C, meaning that the temperature setting of the high-pressure control tank is outside the range defined by this invention regarding its relationship with the temperature inside the hydrothermal reactor. Other settings are the same, using the same raw materials and other conditions as in Example 1 to prepare hydrothermal carbon. However, since the enthalpy of the high-temperature subcritical water at 240°C is lower than that of the subcritical water at 260°C in Example 1, to ensure the raw materials are heated to the same temperature, the flow rate of the high-temperature subcritical water needs to be increased to twice that of Example 1, and the flow rate of the top-discharged steam needs to be 5.4 times that of Example 1. Consequently, the volumes of the high-pressure control tank and the low-pressure control tank also need to be increased accordingly to twice and 5.4 times that of Example 1, respectively, increasing the investment and footprint of the equipment. At the same time, the increased flow rates of the high-temperature subcritical water and the top-discharged steam are also detrimental to the stability of the flow field inside the hydrothermal reactor, affecting the separation of unreacted substances and products within the reactor.

[0050] Comparative Example 5

[0051] The other settings in this comparative example are the same as in Example 1, except that the temperature of the high-pressure control tank is set to 280°C. This means the temperature setting of the high-pressure control tank is outside the range defined by this invention regarding its relationship with the temperature inside the hydrothermal reactor. Other settings are the same, using the same raw materials and other conditions as in Example 1 to prepare hydrothermal carbon. However, since the enthalpy of the high-temperature subcritical water at 280°C is higher than that of the subcritical water at 260°C in Example 1, ensuring the raw materials are heated to the same temperature, the flow rate of the high-temperature subcritical water can be reduced to 66.7% of that in Example 1, and the volume of the high-pressure control tank can be correspondingly reduced to 66.7% of that in Example 1. Meanwhile, the heat load of the thermal oil furnace will increase by 1.8% compared to Example 1. Increasing the temperature of the high-pressure control tank can reduce the flow rate of high-temperature subcritical water (reducing disturbance to the flow field within the hydrothermal reactor), reduce the volume of the high-pressure control tank, and decrease the corresponding investment. However, this leads to an increase in system energy consumption. Furthermore, the high-pressure control tank is heated by heat transfer oil. To ensure the heat exchange efficiency of the heat transfer oil, its temperature is typically 30°C higher than that of the high-pressure control tank, meaning the operating temperature of the heat transfer oil needs to be between 310°C and 340°C. This requires the selection of special high-temperature resistant heat transfer oil, and carbon buildup and blockages are prone to occur during operation, affecting the stable operation of the system.

[0052] Comparative Example 6

[0053] The other settings in this comparative example are the same as in Example 1, except that 50% of the process water is not returned to the raw material mixing device; instead, all process water is directly treated to render it harmless. Other settings are the same, using the same raw materials and other conditions as in Example 1 to prepare hydrothermal carbon. The water consumption in this comparative example is 6 times that of Example 1, and the process water treatment volume is 2 times that of Example 1. The volume of all equipment and the consumption of chemicals in the process water treatment process are also 2 times that of Example 1. In addition, during the hydrothermal carbonization reaction, on the one hand, large molecular organic matter in the solid phase decomposes and enters the aqueous phase; on the other hand, small molecular organic matter in the aqueous phase polymerizes and deposits into the solid phase. Since the makeup water in the biomass raw material slurry in Comparative Example 6 is all fresh water with a very low organic matter content, more organic matter will enter the aqueous phase during the hydrothermal carbonization reaction, leading to a decrease in the yield of biomass hydrothermal carbon.

[0054] Comparative Example 7

[0055] The other settings in this comparative example are the same as in Example 1, except that the cooled hydrothermal char slurry was not floated; instead, solid-liquid separation and drying were performed directly. All other settings are the same, using the same raw materials and other conditions as in Example 1 to prepare the hydrothermal char. When the biomass hydrothermal char ash content in Comparative Example 7 is approximately 12%, the lower heating value is approximately 23.2 MJ / kg. In Example 1, the biomass hydrothermal char ash content is less than 5%, and the lower heating value is greater than 25 MJ / kg. This shows that the biomass hydrothermal char of Example 1 is more suitable for blast furnace injection.

Claims

1. A method for preparing a blast furnace injection biomass fuel, characterized by, It comprises the following steps: (1) biomass raw material pretreatment: the biomass raw material is crushed by a crushing device to a maximum particle size of 28-35 mm, and then the crushed biomass particles are transported into a stirring device, 3-6 times the weight of the biomass particles of water is added, and then stirring is performed to obtain a biomass raw material slurry with a moisture content of 73-85 wt%; (2) biomass preheating treatment: the biomass raw material slurry obtained in step (1) is pressurized to 2-4 MPa, and then the pressurized biomass raw material slurry is discharged into a preheating pipeline, the preheating pipeline has a shell-and-tube structure, the heating liquid and the biomass raw material slurry are in the shell side and the tube side respectively, and the preheating pipeline preheats the biomass raw material slurry to 150-200℃; (3) hydrothermal carbonization treatment: the pressurized and preheated biomass raw material slurry in step (2) is transported into a hydrothermal reactor of a hydrothermal reaction device through a pipeline, the biomass raw material slurry is mixed with high-temperature subcritical water at 255-270℃ at the upper part of the hydrothermal reactor, so that the temperature of the mixed slurry is raised to 190-230℃, the raised and mixed slurry is subjected to hydrothermal carbonization reaction in the hydrothermal reactor, the temperature in the hydrothermal reactor is controlled to 205-245℃, the reaction pressure is 2.8-4.2 MPa, the moisture content of the slurry in the hydrothermal reactor is maintained at 80-90 wt%, the hydrothermal carbonization reaction time is 2.5-4 h, and a high-temperature hydrothermal carbon slurry with a temperature of 230-250℃ is obtained; (4) carbon slurry transportation, refining, and separation treatment: the high-temperature hydrothermal carbon slurry obtained in step (3) is discharged into the shell-and-tube structure of the preheating pipeline in step (2), the biomass raw material slurry in step (2) is preheated by heat exchange through the tube wall, the high-temperature hydrothermal carbon slurry is cooled to 40-60℃, then the obtained hydrothermal carbon slurry is depressurized to reduce the pressure to normal pressure, then the hydrothermal carbon slurry is placed in a crushing and grinding device for crushing to below 0.3-0.8 mm, then the crushed hydrothermal carbon slurry is subjected to flotation, and then pressure filtration is performed to obtain process water and hydrothermal carbon cake with a moisture content of 28-35 wt%; (5) process water treatment: 35-65% of the process water discharged in step (4) by volume is discharged into the stirring device in step (1) as part of the water added to the biomass particles for slurry preparation, and the remaining part is discharged into a process water treatment device for harmless treatment; (6) hydrothermal carbon drying treatment: the muddy hydrothermal carbon cake obtained in step (4) is placed in a drying device for drying treatment, and after drying, the obtained biomass hydrothermal carbon has an air-dry basis moisture content of less than 3 wt%, a sulfur content of less than 0.5 wt%, an alkali metal content of less than 0.1 wt%, a Hardgrove grindability index of greater than 60, and a low heating value of 22-26 MJ / kg.

2. The method for preparing a blast furnace injection biomass fuel according to claim 1, characterized by, In step (3), the hydrothermal reaction device comprises a hydrothermal reactor and a temperature and pressure control device, the temperature and pressure control device comprises a high-pressure control tank, a low-pressure control tank, a normal-pressure water tank, a cooling tower and a heat-conducting oil furnace; the hydrothermal reactor is provided with a material inlet, a material outlet, a gas outlet and a high-temperature subcritical water inlet; the low-pressure control tank is provided with a gas inlet, a gas outlet and a subcritical water discharge port; the high-pressure control tank is provided with a subcritical water inlet, a high-temperature subcritical water outlet, a gas discharge port, a cooling water inlet, a heat exchange liquid inlet and a heat exchange liquid outlet; the normal-pressure water tank is provided with a cooling water discharge port and a normal-pressure water discharge port; the cooling tower is provided with a reaction gas inlet, a cooling water spraying part and a spraying water discharge port; the gas outlet of the hydrothermal reactor is communicated with the gas inlet of the low-pressure control tank through a pipeline, the biomass raw material slurry is discharged into the hydrothermal reactor through the material inlet, the treated high-temperature hydrothermal carbon slurry is discharged through the material outlet, the gas outlet of the low-pressure control tank and the gas discharge port of the high-pressure control tank are respectively communicated with the reaction gas inlet of the cooling tower through pipelines, the subcritical water discharge port of the low-pressure control tank is communicated with the subcritical water inlet of the high-pressure control tank through a pipeline, the high-temperature subcritical water outlet of the high-pressure control tank is communicated with the high-temperature subcritical water inlet of the hydrothermal reactor through a pipeline, the spraying water discharge port of the cooling tower is communicated with the cooling water discharge port of the normal-pressure water tank through a pipeline, the normal-pressure water discharge port of the normal-pressure water tank is communicated with the cooling water inlet of the high-pressure control tank through a pipeline, and the heat-conducting oil furnace is communicated with the heat exchange liquid inlet and the heat exchange liquid outlet of the high-pressure control tank through pipelines.

3. The method for preparing a blast furnace injection biomass fuel according to claim 2, characterized by, In step (3), high-pressure water pumps are arranged on the pipeline between the subcritical water discharge port of the low-pressure control tank and the subcritical water inlet of the high-pressure control tank, the pipeline between the high-temperature subcritical water outlet of the high-pressure control tank and the high-temperature subcritical water inlet of the hydrothermal reactor and the pipeline between the normal-pressure water discharge port of the normal-pressure water tank and the cooling water inlet of the high-pressure control tank; a heat-conducting oil circulating pump is arranged on the pipeline between the heat-conducting oil furnace and the heat exchange liquid inlet of the high-pressure control tank; the top of the normal-pressure water tank is provided with a vent valve; the cooling water spraying part comprises one or more nozzles arranged in the cooling tower, a cooling pipeline connected with the nozzles and a cooling water pump arranged on the cooling pipeline.

4. The method for preparing a blast furnace injection biomass fuel according to claim 3, characterized by, In step (3), the supercritical water is discharged from the gas outlet at the top of the hydrothermal reactor after heat exchange, and then enters the low-pressure control tank through the gas inlet. The temperature in the low-pressure control tank is set to be 10-20℃ lower than that in the hydrothermal reactor. When the pressure in the low-pressure control tank is higher than the set threshold, the generated gas and part of the water vapor are discharged through the gas outlet and then discharged into the cooling tower through the reaction gas inlet. When the liquid level in the low-pressure control tank is higher than the set liquid level threshold, the excess supercritical water is transported by the high-pressure water pump and then discharged into the high-pressure control tank through the supercritical water discharge inlet. The excess gas in the high-pressure control tank is also discharged into the cooling tower through the reaction gas inlet. The gas entering the cooling tower is cooled and sprayed by the cooling water spraying component. The sprayed water is discharged through the spraying water discharge outlet and then discharged into the normal-pressure water tank through the cooling water inlet. The cooling water in the normal-pressure water tank is discharged through the normal-pressure water discharge outlet and then transported into the high-pressure control tank through the high-pressure water pump and the cooling water inlet. The water in the high-pressure control tank is heated by the heat-conducting oil between the high-pressure control tank and the heat-conducting oil furnace. The heating temperature is set to be 20-40℃ higher than the temperature in the hydrothermal reactor. Then, the high-temperature and high-pressure supercritical water in the high-temperature control tank is discharged through the high-temperature supercritical water discharge outlet and then transported into the hydrothermal reactor by the high-pressure water pump for hydrothermal carbonization treatment.

5. The method for preparing a blast furnace injection biomass fuel according to claim 1, characterized by, In step (5), the process water discharged into the process water treatment device is first delivered to the neutralization reactor, the pH value is adjusted to 6-7 by adding lye, and then the process water with adjusted pH value is discharged into the comprehensive conditioning tank to be diluted to a maximum COD volume load of 18-22 kgCOD / (m 3 ·d), then nutrients are added to the process water, and the pH value is adjusted to 6.5-7.5; the process water with adjusted composition in the comprehensive conditioning tank is discharged into the anaerobic reactor for anaerobic digestion, the temperature of the anaerobic reactor is controlled at 30-38℃, the mixed liquor suspended solids concentration is 30-90 g / L, and the hydraulic retention time is 55-65 h, through anaerobic digestion treatment, 88-95% of COD, BOD and nitrogen-containing compounds in the process water are removed; the anaerobic digestion treatment produces treated water, biogas and sludge, the biogas is connected to the heat conduction oil furnace or the drying device of step (6) through a pipeline and is used as fuel for the heat conduction oil furnace or the drying device of step (6); the treated water after anaerobic digestion treatment is discharged into the intermediate tank, cooled to 20-30℃, and then discharged into the aerobic biochemical tank for aerobic digestion, the mixed liquor suspended solids concentration of the aerobic digestion tank is controlled at 8-10 g / L, the hydraulic retention time is 115-125 h, and the dissolved oxygen concentration in the aerobic tank is maintained at 0.05-0.3 g / L, aerobic digestion produces treated water and sludge, the treated water after aerobic digestion is discharged into the Fenton reaction tank for Fenton reaction advanced oxidation, and the hydraulic retention time is controlled at 1.5-2 h, the treated water after Fenton reaction is subjected to solid-liquid separation, the sludge after separation is concentrated together with the sludge produced by anaerobic digestion treatment and aerobic digestion treatment, the solid content of the concentrated sludge is 2-3.6 wt%, and the concentrated sludge is discharged into the stirring device in step (1) for use as a diluent, and the water obtained by solid-liquid separation is used as reclaimed water in the steel plant or is sent to a secondary sewage treatment plant for treatment and then discharged in accordance with the standard.

6. The method for preparing a blast furnace injection biomass fuel according to claim 5, characterized by, The CH4 content in the biogas produced by anaerobic digestion is 55-65 vol%; the gas floatation machine is used for solid-liquid separation, and the flocculation on the top layer of the gas floatation machine enters the sludge thickener.

7. The method for preparing a blast furnace injection biomass fuel according to claim 1, characterized by, In step (2), the biomass raw material slurry obtained in step (1) is pressurized to 2-4 MPa by using a plunger pump.

8. The method for preparing a blast furnace injection biomass fuel according to claim 1, characterized by, In step (4), the high-temperature hydrothermal carbon slurry flows in the shell side of the preheating pipeline, and the biomass raw material slurry flows in the tube side of the preheating pipeline. The flow directions of the two are opposite, and they exchange heat without direct contact.

9. The method for preparing a blast furnace injection biomass fuel according to claim 5, characterized by, In step (5), the process water having the adjusted pH is discharged into the combined adjustment tank to be diluted to a COD volumetric loading of less than or equal to 20 kg COD / (m3.d) and a pH of 6.5 to 8.

5. 3 d); in step (5), the nutrient salt is one or a mixture of both of potassium dihydrogen phosphate or urea; in step (5), the solid content of the concentrated sludge is 3 wt%.

10. The method for preparing a blast furnace injection biomass fuel according to claim 5, characterized by, In step (5), the Fenton reaction advanced oxidation is specifically as follows: the pH of the treatment water discharged into the Fenton reaction tank is adjusted to 3-4, then 1.6-2.5 kg / (kgCOD) of hydrogen peroxide and 1.1-1.5 kg / (kgH2O2) of ferrous sulfate are added for Fenton reaction advanced oxidation, and the hydraulic retention time is controlled to be 1.5-2 h.

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