Biomass rotary kiln direct reduction process

Abstract

The present application provides a kind of biomass rotary kiln direct reduction process, it relates to metallurgical field, comprising: the oxidation pellet is mixed with coal according to certain proportion uniformly, mixture material is transported to chain grate machine and is dried and is heated;The mixture material of chain grate machine output is fed into the kiln tail inlet of rotary kiln, gradually moves forward along with the rotation of rotary kiln, and continues to heat, pre-reduction, forms the mixture of pre-reduced pellet and residual carbon;When the mixture material enters high temperature zone of rotary kiln, a certain proportion of biomass particles and residual carbon are thrown into kiln head and pre-reduced pellet is deeply reduced, and the mixture of metallized pellet and residual carbon is output;The mixture is discharged from kiln head and enters cooling system, and is cooled to normal temperature;Normal temperature mixture is transported to magnetic separation system, and metallized pellet and residual carbon are output;Residual carbon is mixed with a certain bentonite uniformly, and granulation is completed by water distribution through granulator, and is recycled to the first coal mixing process.The present application improves the productivity, production efficiency and economy of metallurgical rotary kiln process.

Description

Technical Field

[0001] This invention relates to the field of metallurgical technology, specifically to a direct reduction process for biomass in a rotary kiln. Background Technology

[0002] Traditional direct reduction rotary kilns use coking coal or granular coal as reducing agents and heat sources. Both coking coal and granular coal are non-renewable carbon-based energy sources, resulting in high CO2 emissions. In particular, coke production generates large amounts of SO2, ammonia, benzene, benzo[a]pyrene, and other toxic waste gases and wastewater that are harmful to humans and organisms. Furthermore, due to the poor reactivity of coking coal and granular coal, the material remains in the kiln for an excessively long time in traditional direct reduction rotary kilns, typically reaching 8-12 hours. This severely impacts the capacity and efficiency of the metallurgical rotary kiln process, thereby deteriorating the economic viability of the direct reduction rotary kiln process. Summary of the Invention

[0003] This invention provides a direct reduction process for biomass in a rotary kiln to solve the technical problems mentioned in the background section.

[0004] To solve the above-mentioned technical problems, this invention discloses a direct reduction process for biomass in a rotary kiln, comprising:

[0005] Step 1: Mix the oxidized pellets and coal evenly in a certain proportion;

[0006] Step 2: The mixture produced in Step 1 is conveyed to the chain grate machine, where the mixture exchanges heat with the flue gas to dry and heat the mixture.

[0007] Step 3: The preheated mixture produced in Step 2 is fed into the feed port at the tail of the rotary kiln. After entering the rotary kiln, it gradually moves forward as the rotary kiln rotates, and continues to be heated and pre-reduced under the action of high-temperature flue gas to form a mixture of pre-reduced pellets and residual carbon.

[0008] Step 4: When the mixture of pre-reduced pellets and residual char from Step 3 enters the high-temperature zone of the rotary kiln, a certain proportion of biomass pellets and residual char are thrown into the kiln head to deeply reduce the pre-reduced pellets, producing a mixture of metallized pellets and residual char; the furthest throwing point of the biomass pellets is the boundary between the pre-reduction stage and the high-temperature zone.

[0009] Step 5: The mixture of metallized pellets and residual carbon produced in Step 4 is discharged from the kiln head and enters the cooling system to be cooled to room temperature;

[0010] Step 6: The ambient temperature mixture produced in Step 5 is fed to a magnetic separation system to produce metallized pellets and residual carbon;

[0011] Step 7: The residual carbon produced in Step 6 is mixed evenly with a certain amount of bentonite, and then granulated by adding water through a granulator. The granules are then fed back to Step 1 and mixed into the coal.

[0012] Preferably, in step 1, the iron content of the oxidized pellets is ≥62%, the particle size is 10-16mm, and the compressive strength is ≥1500N; the coal addition ratio is 10-20% of the mass of the oxidized pellets, the particle size is 5-30mm, the volatile matter is ≤15%, the ash content is ≤10%, and the calorific value is ≥5000cal / kg.

[0013] Preferably, in step 2, the flue gas entering the chain grate is drawn from the tail of the rotary kiln, with an initial flue gas temperature of 700-900℃ and a final flue gas temperature of 200-300℃. The mixed material enters the chain grate at room temperature and exits at a final temperature of 400-600℃. The flue gas is discharged from the chain grate to the flue gas treatment system and meets emission standards.

[0014] In step 3, the total length of the preheated mixture during heating and pre-reduction is about 1 / 3 to 1 / 2 of the length of the rotary kiln, and the material temperature is increased from 400-600℃ to 800-1000℃.

[0015] Preferably, in step 4, the total length of the high-temperature zone is approximately 1 / 2 to 2 / 3 of the length of the rotary kiln, the material temperature in the high-temperature zone is 800-1200℃, the biomass pellet size is 5-30mm, the hydrogen content is ≥5%, the volatile matter is ≥50%, the ash content is ≤10%, the calorific value is ≥4000cal / kg, and the hourly feed mass of biomass pellets is 20-40% of the hourly feed mass of oxidized pellets; the metallization rate of the produced metallized pellets is ≥90%, and the residual char mass is approximately 1 / 3 to 2 / 3 of the feed mass of oxidized pellets; the feeding temperature of the metallized pellets and residual char is 800-1000℃.

[0016] Preferably, the total restoration time for steps 3 and 4 is 2-3.5 hours.

[0017] Preferably, the cooling system in step 5 is an indirect cooling device containing a cooling medium, which cools an equal amount of metallized pellets and residual carbon exiting the kiln at 800-1000℃ to below 60℃ within 2 hours.

[0018] In step 6, the magnetic separation system is a permanent magnet drum device with a surface magnetic field strength of 0.1-0.2T.

[0019] Preferably, in step 7, the mass of bentonite added is 2-3% of the mass of residual char, and the total mass of water added is 7-9% of the total weight of bentonite and residual char. Mixing and granulation are carried out using a mixer and a disc granulator, respectively, with a particle size of 10-20mm and a granulation strength ≥200N.

[0020] Preferably, step 20 is performed before batch processing step 2 for the current type of material. Step 20 includes:

[0021] Step 201: Obtain the baseline temperature rise rate - baseline equivalent pyrolysis gas concentration mapping table for each temperature rise stage of the current material;

[0022] Step 202: Heat the current batch of material with the reference heating parameters for each temperature rise stage to determine the material temperature rise coefficient, internal temperature gradient coefficient, and thermal diffusion state coefficient for different temperature rise stages; and determine the pyrolysis gas-temperature coupling coefficient for each temperature rise stage based on the detection of pyrolysis gas concentration during the heating test.

[0023] Step 203: Determine the material permeability coefficient based on the pyrolysis gas concentration detection during the heating test and the gas pressure and flow rate detection values ​​in the heating space at each temperature rise stage;

[0024] Step 204: Determine the equivalent thermal inertia coefficient of the current batch of materials based on step 202;

[0025] Step 205: Based on the target time range of the current material passing through the chain grate, determine the first conveying speed range of the chain grate for the current material;

[0026] Step 206: Determine the load factor of the chain grate based on the weight of the current batch of material per unit length in the chain grate and the weight of the current batch of material per unit length in the chain grate at the end of each temperature rise stage, and correct the load factor based on the equivalent thermal inertia coefficient of the current batch of material.

[0027] Step 207: Determine the target conveying speed of the current batch of materials based on the corrected load coefficient of the chain grate and the first conveying speed range of the current batch of materials;

[0028] Step 208: Based on the target conveying speed of the current batch of materials, determine the target heating control parameters of the heating device corresponding to each temperature rise stage, as per Step 202.

[0029] Preferably, when drying and heating the current batch of materials in batches through the chain grate machine, the heating device of the chain grate machine for the corresponding temperature rise stage is controlled based on the target heating control parameters of the heating device for each temperature rise stage.

[0030] Preferably, step 70 is performed before batch processing step 7 for the current type of material. Step 70 includes:

[0031] Step 701: Obtain the water ratio-mixture viscosity fitting curves for the current type of residual char and the current batch of bentonite within the ideal water ratio range;

[0032] Step 702: Conduct a premixing test on the current batch of residual char and the current batch of bentonite to determine the bonding state coefficient and bulk density of the mixture;

[0033] Step 703: Determine the predicted permeability state coefficient of the mixture based on the bulk density and the binding state coefficient of the mixture;

[0034] Step 704: Based on the water addition ratio-mixture viscosity fitting curve, the predicted permeability state coefficient of the mixture, and the mixture bonding state coefficient, determine the target water addition ratio and the mixture bonding-rheological comprehensive coefficient corresponding to the target water addition ratio;

[0035] Step 705: Determine the target extrusion pressure range by combining the combined rheological coefficient and bulk density of the mixture;

[0036] Step 706: Obtain the following fitting curves under the reference conditions for the mixture formed by the current disc pellet mill on the current type of residual carbon and the current batch of bentonite: speed-reference pelletizing rate fitting curve, speed-reference pelletizing strength fitting curve, and speed-reference extrusion pressure fitting curve.

[0037] Step 707: Determine the first screening rotation speed based on Step 705, Step 706, and the target granulation requirement parameters;

[0038] Step 708: Determine the target rotational speed of the disc pellet mill based on the slopes of the rotational speed-reference pelletizing rate fitting curve, the rotational speed-reference pelletizing strength fitting curve, and the rotational speed-reference extrusion pressure fitting curve of the first screening rotational speed.

[0039] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] This invention alleviates the problems of high CO2 emissions and severe pollution associated with traditional direct reduction rotary kilns;

[0042] This invention uses biomass pellets as the main reducing agent and heat source in a direct reduction rotary kiln. Biomass pellets are a renewable resource, significantly reducing CO2 emissions from the process. This invention eliminates the use of coke, thus preventing the generation of large amounts of SO2, ammonia, benzene, benzo[a]pyrene, and other toxic waste gases and wastewater during coke production. It improves the capacity, production efficiency, and economy of the metallurgical rotary kiln process. Biomass pellets have high hydrogen and volatile matter content, exhibiting excellent reactivity, enabling deep reduction of oxidized pellets within 2-3.5 hours, with a reduction efficiency approximately three times that of traditional rotary kilns, significantly improving the reduction and production efficiency of the metallurgical rotary kiln process. Waste heat from the rotary kiln flue gas is used to heat the raw material chain grate, improving energy utilization efficiency and reducing heat loss. With improved reduction efficiency, production efficiency, and energy utilization efficiency, the economics of the metallurgical rotary kiln process are effectively enhanced. Attached Figure Description

[0043] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0044] Figure 1 This is a schematic diagram of the process of the present invention. Detailed Implementation

[0045] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0046] Furthermore, in this invention, the use of terms such as "first" and "second" is for descriptive purposes only and does not specifically refer to any order or sequence, nor is it intended to limit the invention. They are merely used to distinguish components or operations described using the same technical terms and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the technical solutions and features of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. If a combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0047] The present invention provides the following embodiments:

[0048] Example 1: This embodiment of the invention provides a direct reduction process for biomass using a rotary kiln, such as... Figure 1 As shown, it includes:

[0049] Step 1: Mix the oxidized pellets and coal evenly in a certain proportion;

[0050] Step 2: The mixture produced in Step 1 is conveyed to the chain grate machine, where the mixture exchanges heat with the flue gas to dry and heat the mixture.

[0051] Step 3: The preheated mixture produced in Step 2 is fed into the feed port of the rotary kiln tail via a chain conveyor. After entering the rotary kiln, it moves forward gradually as the rotary kiln rotates and continues to heat up under the action of high-temperature flue gas, gradually undergoing carbon gasification reaction and iron oxide reduction reaction, and the oxidized pellets undergo pre-reduction; forming a mixture of pre-reduced pellets and residual carbon.

[0052] Step 4: When the mixture of pre-reduced pellets and residual char from Step 3 enters the high-temperature zone of the rotary kiln, a certain proportion of biomass pellets and residual char are thrown into the kiln head to deeply reduce the pre-reduced pellets, producing a mixture of metallized pellets and residual char; the furthest throwing point of the biomass pellets is the boundary between the pre-reduction stage and the high-temperature zone.

[0053] Step 5: The mixture of metallized pellets and residual carbon produced in Step 4 is discharged from the kiln head and enters the cooling system to be cooled to room temperature;

[0054] Step 6: The ambient temperature mixture produced in Step 5 is transported to the magnetic separation system to produce metallized pellets and residual carbon (the amount of residual carbon is about 1 / 3 to 2 / 3 of the amount fed into the kiln).

[0055] Step 7: The residual carbon produced in Step 6 is mixed evenly with a certain amount of bentonite, and then granulated by adding water through a granulator. The granules are then fed back to Step 1 and mixed into the coal.

[0056] In this process, oxidized pellets and coal are mixed evenly at a mass ratio of 100:(10-20); in step 1, the iron content of the oxidized pellets is ≥62%, the particle size is 10-16mm, and the compressive strength is ≥1500N; the coal addition ratio is 10-20% of the mass of the oxidized pellets, the particle size is 5-30mm, the volatile matter is ≤15%, the ash content is ≤10%, and the calorific value is ≥5000cal / kg.

[0057] In step 2, the flue gas from the chain grate is drawn from the tail of the rotary kiln. After the mixed material enters the chain grate, it exchanges heat with the flue gas in a counter-current manner. The initial temperature of the flue gas entering the chain grate is 700-900℃, and the final temperature of the flue gas exiting the chain grate is 200-300℃. The initial temperature of the mixed material entering the chain grate is room temperature, and the final temperature of the flue gas exiting the chain grate is 400-600℃. The flue gas is discharged from the chain grate to the flue gas treatment system and meets the emission standards.

[0058] In step 3, the total length of the preheated mixture during heating and pre-reduction is about 1 / 3 to 1 / 2 of the length of the rotary kiln, and the material temperature is increased from 400-600℃ to 800-1000℃.

[0059] In step 4, the total length of the high-temperature zone is approximately 1 / 2 to 2 / 3 of the rotary kiln's length, and the material temperature in the high-temperature zone is 800-1200℃. The biomass pellets have a particle size of 5-30mm, a hydrogen content ≥5%, volatile matter ≥50%, ash content ≤10%, and a calorific value ≥4000cal / kg. The hourly feed mass of biomass pellets is 20-40% of the hourly feed mass of oxidized pellets. When the biomass pellets fall to the surface of the material layer, they are covered by the material being turned up as the rotary kiln rotates. When the internal temperature of the material layer rises to 350-1200℃, the internal volatile matter pyrolyzes to produce a large amount of H2 and CO. H2 and CO further reduce the oxidized pellets at 800-1200℃, and the resulting H2O and CO2 re-gasify the carbon in the biomass particles and residual char, forming H2 and CO to further reduce the oxidized pellets, and this process is repeated; finally, H2 and CO or H2O and CO2 are discharged from the material surface, and H2 and CO are burned for heating under the action of oxidizing gases; the metallization rate of the produced metallized pellets is ≥90%, and the residual char mass is about 1 / 3-2 / 3 of the mass of the oxidized pellets entering the kiln; the feeding temperature of the metallized pellets and residual char is 800-1000℃. The high-temperature zone refers to the area with a material temperature of 800-1200℃ in the kiln head direction;

[0060] The total restoration time for steps 3 and 4 is 2-3.5 hours.

[0061] In step 5, the cooling system is an indirect cooling device containing a cooling medium (such as water), which cools an equal amount of metallized pellets and residual carbon that exit the kiln at 800-1000℃ to below 60℃ within 2 hours.

[0062] In step 6, the magnetic separation system is a permanent magnet drum device with a surface magnetic field strength of 0.1-0.2T, producing metallized pellets and residual carbon, respectively.

[0063] In step 7, the bentonite added is 2-3% of the residual carbon mass, and the total water mass is 7-9% of the total weight of bentonite and residual carbon. Mixing and granulation are carried out using a mixer and a disc granulator, respectively, with a particle size of 10-20mm and a granulation strength ≥200N. The mixture is then fed back to step 1 and mixed into the coal to replace an equal amount of coal.

[0064] The iron content of the oxide pellets is 65.59%, the particle size is 10-16mm, and the average compressive strength is 2223N; the coal particle size is 5-30mm, the volatile matter is 12.00%, the ash content is 8.92%, and the calorific value is 5103cal / kg.

[0065] The oxidized pellets and coal were mixed evenly at a mass ratio of 100:18 using a mixer.

[0066] The mixture of oxidized pellets and coal discharged from the mixer is conveyed to the belt conveyor and then to the chain grate machine. After the mixture enters the chain grate machine, the temperature rises from room temperature to 512℃, and the flue gas temperature drops from 880℃ to 227℃. The flue gas is then discharged to the flue gas treatment system and meets the emission standards.

[0067] The 512℃ mixture is fed into the rotary kiln tail feed port via a chain conveyor. After entering the rotary kiln, it gradually moves forward as the kiln rotates and continues to heat up under the action of high-temperature flue gas, pre-reducing the oxidized pellets. The total length of the pre-reduction stage is about 1 / 3 of the length of the rotary kiln. During this period, the material temperature increases from 512℃ to 930-970℃, forming a mixture of pre-reduced pellets and residual carbon.

[0068] The mixture of materials at 930-970℃ enters the high-temperature zone, which occupies 2 / 3 of the length of the rotary kiln. The ratio of the hourly feed rate to the hourly feed rate of oxidized pellets is 100:32. The biomass pellets have a particle size of 5-30mm, a hydrogen content of 7.49%, a volatile matter content of 71.05%, an ash content of 4.32%, and a calorific value of 4080cal / kg. When the mixture of metallized pellets and residual char is discharged from the kiln head, the temperature is 970℃. Among them, the metallization rate of the metallized pellets is 94.25%, the mass is 75.10% of that of the oxidized pellets, and the mass of the residual char is 45.35% of the coal fed into the kiln.

[0069] The mixture of metallized pellets and residual carbon is discharged from the kiln head into a drum-type indirect water cooler via a chute, and cooled to 43°C in 1 hour.

[0070] After cooling, the metallized pellets and residual carbon are lifted by a bucket elevator to a permanent magnet drum device with a surface field strength of 0.1-0.2T to complete the separation of the metallized pellets and residual carbon.

[0071] The residual carbon and bentonite are mixed evenly in a mixer at a ratio of 100:2.3. Then, 7.6% water by weight of the residual carbon is added to the mixture through a pelletizer to make wet carbon balls with a particle size of 10-20mm and a strength of 237N. The wet carbon balls are mixed into the coal to replace an equal amount of coal and are mixed evenly with the oxidized pellets.

[0072] Specific implementation examples are as follows:

[0073] The iron content of the oxide pellets is 65.59%, the particle size is 10-16mm, and the average compressive strength is 2223N; the coal particle size is 5-30mm, the volatile matter is 12.00%, the ash content is 8.92%, and the calorific value is 5103cal / kg.

[0074] The oxidized pellets and coal were mixed evenly at a mass ratio of 100:18 using a mixer.

[0075] The mixture of oxidized pellets and coal discharged from the mixer is conveyed to the belt conveyor and then to the chain grate machine. After the mixture enters the chain grate machine, the temperature rises from room temperature to 512℃, and the flue gas temperature drops from 880℃ to 227℃. The flue gas is then discharged to the flue gas treatment system and meets the emission standards.

[0076] The 512℃ mixture is fed into the rotary kiln tail feed port via a chain conveyor. After entering the rotary kiln, it gradually moves forward as the kiln rotates and continues to heat up under the action of high-temperature flue gas, pre-reducing the oxidized pellets. The total length of the pre-reduction stage is about 1 / 3 of the length of the rotary kiln. During this period, the material temperature increases from 512℃ to 930-970℃, forming a mixture of pre-reduced pellets and residual carbon.

[0077] The mixture of materials at 930-970℃ enters the high-temperature zone, which occupies 2 / 3 of the length of the rotary kiln. The ratio of the hourly feed rate to the hourly feed rate of oxidized pellets is 100:32. The biomass pellets have a particle size of 5-30mm, a hydrogen content of 7.49%, a volatile matter content of 71.05%, an ash content of 4.32%, and a calorific value of 4080cal / kg. When the mixture of metallized pellets and residual char is discharged from the kiln head, the temperature is 970℃. Among them, the metallization rate of the metallized pellets is 94.25%, the mass is 75.10% of that of the oxidized pellets, and the mass of the residual char is 45.35% of the coal fed into the kiln.

[0078] The mixture of metallized pellets and residual carbon is discharged from the kiln head into a drum-type indirect water cooler via a chute, and cooled to 43°C in 1 hour.

[0079] After cooling, the metallized pellets and residual carbon are lifted by a bucket elevator to a permanent magnet drum device with a surface field strength of 0.1-0.2T to complete the separation of the metallized pellets and residual carbon.

[0080] The residual carbon and bentonite are mixed evenly in a mixer at a ratio of 100:2.3. Then, 7.6% water by weight of the residual carbon is added to the mixture through a pelletizer to make wet carbon balls with a particle size of 10-20mm and a strength of 237N. The wet carbon balls are mixed into the coal to replace an equal amount of coal and are mixed evenly with the oxidized pellets.

[0081] The beneficial effects of the above technical solution are as follows:

[0082] This invention alleviates the problems of high CO2 emissions and severe pollution associated with traditional direct reduction rotary kilns.

[0083] This invention uses biomass pellets as the main reducing agent and heat source in a direct reduction rotary kiln. Biomass pellets are a renewable resource, significantly reducing CO2 emissions from the process. This invention eliminates the use of coke, thus preventing the generation of large amounts of SO2, ammonia, benzene, benzo[a]pyrene, and other toxic waste gases and wastewater during coke production. It improves the capacity, production efficiency, and economy of the metallurgical rotary kiln process. Biomass pellets have high hydrogen and volatile matter content, exhibiting excellent reactivity, enabling deep reduction of oxidized pellets within 2-3.5 hours, with a reduction efficiency approximately three times that of traditional rotary kilns, significantly improving the reduction and production efficiency of the metallurgical rotary kiln process. Waste heat from the rotary kiln flue gas is used to heat the raw material chain grate, improving energy utilization efficiency and reducing heat loss. With improved reduction efficiency, production efficiency, and energy utilization efficiency, the economics of the metallurgical rotary kiln process are effectively enhanced.

[0084] Example 2, based on Example 1, involves performing step 20 before batch processing the current type of material in step 2. Step 20 includes:

[0085] Step 201: Obtain the baseline temperature rise rate - baseline equivalent pyrolysis gas concentration mapping table for each temperature rise stage of the current material;

[0086] Step 202: Heat the current batch of material with the reference heating parameters for each temperature rise stage to determine the material temperature rise coefficient, internal temperature gradient coefficient, and thermal diffusion state coefficient for different temperature rise stages; and determine the pyrolysis gas-temperature coupling coefficient for each temperature rise stage based on the detection of pyrolysis gas concentration during the heating test.

[0087] Step 203: Determine the material permeability coefficient based on the pyrolysis gas concentration detection during the heating test and the gas pressure and flow rate detection values ​​in the heating space at each temperature rise stage;

[0088] Step 204: Determine the equivalent thermal inertia coefficient of the current batch of materials based on step 202;

[0089] Step 205: Based on the target time range of the current material passing through the chain grate, determine the first conveying speed range of the chain grate for the current material; based on the effective conveying length of the chain grate and the target time range, determine (e.g., the minimum value of the first conveying range = the effective conveying length of the chain grate ÷ the maximum value of the target time range), this is the prior art;

[0090] Step 206: Determine the load factor of the chain grate based on the weight of the current batch of material per unit length in the chain grate and the weight of the current batch of material per unit length in the chain grate at the end of each temperature rise stage, and correct the load factor based on the equivalent thermal inertia coefficient of the current batch of material.

[0091] Step 207: Determine the target conveying speed of the current batch of materials based on the corrected load coefficient of the chain grate and the first conveying speed range of the current batch of materials;

[0092] Step 208: Based on the target conveying speed of the current batch of materials, and Steps 202 and 203, determine the target heating control parameters of the heating device corresponding to each temperature rise stage.

[0093] When the current batch of materials is dried and heated in batches through the chain grate machine, the heating device of the chain grate machine is controlled to work according to the target heating control parameters of the heating device corresponding to each temperature rise stage.

[0094] The current batch of materials belongs to the current type of materials, that is, "the current batch of materials is determined to be the current type of materials", and the specific conditions for subsequent "same type of materials" must be met.

[0095] The "same type of material" mentioned in step 2 must simultaneously meet the following conditions:

[0096] Material type: A mixture of "oxidized pellets + coal";

[0097] Coal type consistency: Use exactly the same coal type (e.g., all are anthracite of a certain grade, and coal type substitution is not allowed);

[0098] Consistency of proportions: The mixing ratio of oxidized pellets and coal must be strictly the same (e.g., if the benchmark ratio is 7:3, the actual ratio must be precisely matched, or a clear allowable fluctuation range, such as ±0.5%) must be specified).

[0099] Pellet composition consistency: The key components of the pellets are the same or within the same pre-agreed range (if they exceed this range, they are judged to be different materials).

[0100] Temperature rise stage: The entire process of heating the material from its initial temperature to the target temperature, divided into "segments" according to temperature ranges. The initial and final temperatures of each temperature rise stage are fixed.

[0101] Benchmark temperature rise rate: For the "current material", the recommended "temperature rise rate" for each temperature rise stage under ideal conditions (such as precise laboratory control and no interference). This was determined through extensive laboratory testing and process verification: for the "current material" (oxidized pellets + coal with a fixed formula), energy consumption and finished product quality were tested at different temperature rise rates, and the optimal rate (with better finished product quality and lower energy consumption) was selected as the "benchmark".

[0102] Reference heating parameters: In order for the material to reach the "reference temperature rise rate", the operating parameters need to be set for the corresponding temperature rise stage of the chain grate machine. The core is the matching of heating power and time.

[0103] The equivalent pyrolysis gas concentration at the reference temperature rise rate for each temperature rise stage is the reference equivalent pyrolysis gas concentration; the equivalent pyrolysis gas concentration of a certain pyrolysis gas is the average value of the pyrolysis gas concentration of that pyrolysis gas in different regions detected.

[0104] The material temperature rise coefficient in the current temperature rise stage = the actual temperature rise time in the current temperature rise stage ÷ the reference temperature rise time in the current temperature rise stage (the theoretical time under ideal conditions; corresponding to the reference heating rate conditions).

[0105] During the heating test, multiple temperature measuring points are buried inside the material or a temperature measuring device that can be inserted into the material is set up. The difference between the highest and lowest temperatures inside the material at a certain testing moment is recorded, which is the actual temperature gradient at the corresponding moment.

[0106] Obtain the first ratio of the actual temperature gradient at each detection moment to the reference temperature gradient at the corresponding detection moment (ideally, under the reference heating rate condition; that is, for the current material (fixed formula), under ideal laboratory conditions (precise temperature control, no interference), use the reference heating rate to test and record the temperature gradient at multiple moments).

[0107] The temperature gradient coefficient for the current temperature rise phase is the average of all the first ratios obtained for the current temperature rise phase.

[0108] Thermal diffusivity coefficient:

[0109] During the heating test, record the surface temperature and center temperature of the material at different test time points (e.g., at the 10th minute, surface temperature 100℃, center temperature 80℃; at the 20th minute, surface temperature 200℃, center temperature 180℃); the surface temperature minus the center temperature at the current test time point is the temperature difference at the current test time point.

[0110] The average rate of change of temperature difference at different temperature rise stages can be obtained as ((maximum temperature difference - minimum temperature difference) ÷ (time interval between maximum and minimum temperature difference)).

[0111] The thermal diffusivity of the current temperature rise stage = the actual average temperature difference change rate of the current temperature rise stage ÷ the reference average temperature difference change rate of the current temperature rise stage (corresponding to the ideal state and the reference heating rate state).

[0112] pyrolysis gas-temperature coupling coefficient:

[0113] During the heating test, the material temperature and the concentration of pyrolysis gas are measured simultaneously.

[0114] Consult the “Benchmark Mapping Table” to see the benchmark pyrolysis gas concentration at a specific temperature under the benchmark temperature rise rate;

[0115] The pyrolysis gas-temperature coupling coefficient = actual pyrolysis gas concentration ÷ reference pyrolysis gas concentration.

[0116] Material permeability coefficient:

[0117] 1. First calculate the "actual overall ventilation value":

[0118] The actual measured values ​​of pyrolysis gas concentration, pressure, and flow rate are converted into a numerical value that reflects the "ease of ventilation":

[0119] Step 1: Measure the actual pyrolysis gas concentration at the current temperature rise stage (e.g., using a gas analyzer);

[0120] Step 2: Measure the actual air pressure in the heating space (the space where the material to be heated is located, inside the chain grate machine) (e.g., by using a pressure sensor).

[0121] Step 3: Measure the actual flow rate of the heating gas into the material (e.g., using an anemometer).

[0122] Step 4: Calculate the "Actual Overall Ventilation Value" = Actual Pyrolysis Gas Concentration × Actual Gas Pressure ÷ Actual Flow Velocity

[0123] (The larger this value, the worse the air permeability, because when the concentration is high, the gas pressure is high, and the flow rate is slow, it is more difficult for the gas to penetrate the material.)

[0124] 2. Calculate the "ideal overall ventilation value":

[0125] Using the baseline parameters under ideal conditions (standard values ​​measured in the laboratory), calculate using the same logic:

[0126] Step 1: Look up the baseline mapping table to find the baseline pyrolysis gas concentration for the current temperature rise stage;

[0127] Step 2: Look up the reference mapping table to find the reference air pressure for the current temperature rise stage;

[0128] Step 3: Look up the reference mapping table to find the reference flow rate for the current temperature rise stage;

[0129] Step 4: Calculate the "ideal ventilation comprehensive value" = reference pyrolysis gas concentration × reference gas pressure ÷ reference flow rate

[0130] (This value is a standard reference for good ventilation);

[0131] 3. Finally, calculate the "material permeability coefficient":

[0132] By comparing the "actual ventilation comprehensive value" with the "ideal ventilation comprehensive value", a coefficient is obtained:

[0133] Material permeability coefficient = Actual permeability comprehensive value ÷ Ideal permeability comprehensive value.

[0134] Step 206 specifically involves:

[0135] 1. Measure the "weight of material per unit length" (basic data):

[0136] Step 1: Select a temperature rise stage (e.g., 200℃→300℃) and take a fixed length (e.g., a 1-meter long area) on the chain grate machine.

[0137] Step 2: Weigh the material in this 1-meter-long area (e.g., 1-meter-long material weighs 50 kilograms; the fixed paving area and thickness corresponding to this type of material).

[0138] Result: The weight of material per unit length is 50 kg / m (the weight may change due to pyrolysis weight loss at different temperature rise stages, so it must be measured at each stage).

[0139] 2. Calculate the "initial load factor" (ignoring thermal inertia):

[0140] Logic: The load factor is directly proportional to the "weight per unit length" (the heavier the material, the more effort the chain grate needs to pull, and the greater the load).

[0141] Record the "rated weight per unit length" of the chain grate machine design (for example, the equipment is marked as being able to carry a maximum of 60 kilograms per meter).

[0142] Initial load factor = actual weight per unit length ÷ rated weight per unit length;

[0143] →Example: 50 kg / m ÷ 60 kg / m ≈ 0.83 (This means the current load is 83% of the rated load).

[0144] 3. Correct the load factor using the "equivalent thermal inertia coefficient":

[0145] The effect of thermal inertia: If the material has high thermal inertia (such as high moisture content and slow heat conduction), the chain grate machine will require more energy to heat it, and the actual load will be greater than the "weight calculation".

[0146] Measure the "equivalent thermal inertia coefficient" of the current batch of materials (for example, through experiments, we know that the thermal inertia of this material is 1.2, which means that it is more difficult to heat than the standard material).

[0147] Corrected load factor = initial load factor × equivalent thermal inertia factor;

[0148] →Example: 0.83×1.2≈1.0 (After correction, the actual load is close to the rated value, and the equipment pressure needs to be monitored).

[0149] Thermal inertia coefficient = (actual heating power ÷ actual temperature rise rate) ÷ (reference heating power ÷ reference temperature rise rate);

[0150] Where the corrected load K is greater than the corresponding rated value (K 额 ), trigger an alarm;

[0151] If K≤K 额定 (Load not exceeded) → Target speed range = first conveying speed range (keep the original range, efficiency first);

[0152] If K > K 额 (Overload) → Speed ​​needs to be reduced to allow the load to return to a safe range:

[0153] Target speed range upper limit = first speed range upper limit × (K) 额 ÷K);

[0154] →Example: Upper limit of the first speed range = 10 meters / minute, K = 1.2, K 额 =1.0→New speed limit=10×(1÷1.2)≈8.33 meters / minute.

[0155] The target conveying speed is the average of the smallest N (e.g., values ​​from 1 to 5) values ​​within the target speed range.

[0156] If the target conveying speed is greater than the reference conveying speed, then the conveying speed correction factor is equal to the target conveying speed divided by the reference conveying speed (to increase the speed, more energy is required).

[0157] If the target conveying speed is less than the reference conveying speed, then the conveying speed correction factor is equal to the reference conveying speed divided by the target conveying speed (slowing down the speed reduces the amount of energy supplied).

[0158] Joint correction factor: A correction factor that combines the material heating coefficient, the internal temperature gradient coefficient of the material, the thermal diffusion state coefficient, and the pyrolysis gas-temperature coupling coefficient;

[0159] Joint correction factor = material temperature rise coefficient in the current temperature rise stage × temperature gradient coefficient in the current temperature rise stage × pyrolysis gas-temperature coupling coefficient ÷ thermal diffusivity in the current temperature rise stage;

[0160] Target heating control parameter = Reference heating control parameter × × × ;

[0161] , , They are respectively Corresponding heating control parameter correction index The corresponding heating control parameter correction index and the heating control parameter correction index corresponding to the joint correction coefficient (obtained through experimental testing and data fitting: first, simulate different working conditions (changing ventilation, conveying speed, joint correction coefficient, etc.), and collect data on the changes in the target heating control parameters; then, use mathematical methods (such as the least squares method) to fit the data, find the exponential relationship between the coefficient and the parameter, and determine... , , ).

[0162] The heating control parameters can be the wind speed or wind pressure of the hot air output for heating;

[0163] The reference conveying speed is a reference conveying speed parameter set for the current material under ideal working conditions (ideal working conditions refer to the optimal / ideal conveying speed under the conditions of reference heating control parameters, uniform material, no impurities, no equipment wear, and stable ambient temperature and humidity, which is a theoretical reference).

[0164] The beneficial effects of the above technical solution are as follows:

[0165] The temperature rise stage is broken down and dynamically adjusted to adapt the heating process to the material characteristics. For example, in the mixture of oxidized pellets and coal, the heating power is matched by the material's temperature rise coefficient in the "preheating (200-400℃)" and "rapid heating (400-800℃)" stages, and the internal temperature difference is controlled by the temperature gradient coefficient (which can be stabilized within ±5℃). This solves the problem of "overheating of the surface and underheating of the interior" caused by traditional extensive heating, and reduces the defect rate of the finished product.

[0166] The pyrolysis gas-temperature coupling coefficient correlates the pyrolysis gas concentration with the heating parameters in real time. For coal-based pellets, it can accurately capture the "sudden change point of pyrolysis gas concentration" (such as the concentrated release stage of coal volatiles), adjust the heating rate to avoid local overheating, ensure the consolidation strength and composition uniformity of the pellets, and improve the finished product strength qualification rate to over 95%.

[0167] The conveying speed correction coefficient is linked to the "target speed" and the "baseline speed". When the conveying resistance changes due to the humidity or fine adjustment of the material, the speed of the chain grate is automatically adjusted (e.g., if the humidity increases by 5%, the speed will be reduced by 8%-12%). This ensures that the material stays in the machine matches the heating requirements, improves the stability of the production cycle, and avoids batch quality fluctuations caused by speed mismatch.

[0168] The joint correction coefficient integrates multiple factors such as "heating and heat diffusion" to make the heating power output more in line with actual needs.

[0169] The load factor correction combines "weight per unit length + thermal inertia" to monitor the "effective load" of the chain grate in real time. When the thermal inertia coefficient of the material increases due to moisture content (e.g., from 1.0 to 1.3), it automatically triggers a speed reduction to prevent the equipment from operating under overload for extended periods. Calculations show that this extends the lifespan of the chain grate's transmission components by 20%-30%.

[0170] The same material selection criteria (consistency of composition, coal type, and proportion) support rapid formula switching on the production line (e.g., the ratio of oxidized pellets to coal changes from 7:3 to 6:4). Switching can be completed in 1-2 hours simply by recalibrating parameters such as the "reference temperature rise rate and air permeability coefficient," adapting to the needs of multi-variety, small-batch production and improving the production line's flexible manufacturing capabilities by 40%.

[0171] Example 3, based on Example 1 or 2, uses a disc granulator for granulation. Before performing step 7 on the current batch of materials, step 70 is performed. Step 70 includes:

[0172] Step 701: Obtain the water ratio-mixture viscosity fitting curves for the current type of residual char and the current batch of bentonite within the ideal water ratio range;

[0173] Step 702: Conduct a premixing test on the current batch of residual char and the current batch of bentonite to determine the bonding state coefficient and bulk density of the mixture; the mixture is the mixture of the current batch of residual char and the current batch of bentonite.

[0174] Step 703: Determine the predicted permeability state coefficient of the mixture based on the bulk density and the binding state coefficient of the mixture;

[0175] Step 704: Based on the water addition ratio-mixture viscosity fitting curve, the predicted permeability state coefficient of the mixture, and the mixture bonding state coefficient, determine the target water addition ratio and the mixture bonding-rheological comprehensive coefficient corresponding to the target water addition ratio;

[0176] Step 705: Determine the target extrusion pressure range by combining the combined rheological coefficient and bulk density of the mixture;

[0177] Step 706: Obtain the following fitting curves under the reference conditions for the mixture formed by the current disc pellet mill on the current type of residual carbon and the current batch of bentonite: speed-reference pelletizing rate fitting curve, speed-reference pelletizing strength fitting curve, and speed-reference extrusion pressure fitting curve.

[0178] Step 707: Determine the first screening speed based on steps 705 and 706 and the target granulation requirement parameters; the target granulation requirement parameters include: the target granulation rate range and the target granulation strength range; the speed-reference granulation rate fitting curve segment corresponding to the first screening speed meets the target granulation rate range; the speed-reference granulation strength fitting curve segment corresponding to the first screening speed meets the target granulation strength range; the speed-reference extrusion pressure fitting curve segment corresponding to the first screening speed meets the target extrusion pressure range;

[0179] Step 708: Determine the target rotational speed of the disc pellet mill based on the slopes of the rotational speed-reference pelletizing rate fitting curve, the rotational speed-reference pelletizing strength fitting curve, and the rotational speed-reference extrusion pressure fitting curve of the first screening rotational speed.

[0180] When granulating the current type of residual carbon and the current batch of bentonite, the actual rotation speed of the disc granulator is controlled to be the target rotation speed;

[0181] When mixing the current type of residual carbon and the current batch of bentonite with water, the actual water addition ratio should be controlled to the target water addition ratio.

[0182] Step 701 Implementation Path:

[0183] Prepare materials: Take a fixed mass of "current type residual carbon" + "current batch bentonite".

[0184] Set the water addition ratio gradient: Select several ratio points within the "ideal water addition ratio range". The ideal water addition ratio range is determined based on experimental data of the current type of residual carbon and the same type of bentonite in the current batch, or from historical production data, to the water addition ratio range that results in qualified granulation results;

[0185] Mixing + Viscosity Measurement: Add water according to each ratio, mix thoroughly to form a homogeneous material, and measure the viscosity using equipment such as a rotational viscometer.

[0186] Curve fitting: Using "water ratio" as the X-axis and "viscosity" as the Y-axis, use software such as Excel / Origin to generate a continuous curve using methods such as linear regression and multinomial fitting.

[0187] Coefficient of bonding state of mixture ;

[0188] in, The specific surface area of ​​the mixture obtained by premixing the current batch of residual carbon and the current batch of bentonite is measured using a BET analyzer. This represents the specific surface area of ​​the current batch of residual char. When performing a premixing test between the current batch of residual carbon and the current batch of bentonite, the mass ratio of the current batch of residual carbon is (in the premixing test, the mass of the current batch of residual carbon ÷ (the mass of the current batch of residual carbon + the mass of the current batch of bentonite)). This represents the specific surface area of ​​the current batch of bentonite. The mass ratio of the current batch of bentonite to the current batch of residual carbon when performing a premixing test with the current batch of bentonite. This represents the theoretical specific surface area of ​​the mixture.

[0189] The closer E is to 1, the closer the specific surface area after mixing is to the theoretical value, and the worse the affinity; the smaller the value, the better the affinity.

[0190] The predicted permeability state coefficient K of the mixture is calculated as follows: K = (1 - (actual density of the mixture ÷ bulk density of the mixture) ÷ bonding state coefficient of the mixture);

[0191] 1 - (The actual density of the mixture ÷ the bulk density of the mixture corresponds to the porosity;)

[0192] Step 704:

[0193] If the target viscosity of the current type of residual char and the current batch of bentonite granulation is A, and the allowable error is ±B, then the required viscosity range is [AB, A+B].

[0194] First, select the water addition ratio that meets the required viscosity range from the water addition ratio-mixture viscosity fitting curve (this is the first water addition ratio).

[0195] The viscosity evaluation value for the first water addition ratio is determined as follows: |The value corresponding to the viscosity fitting curve of the first water addition ratio and the mixture - the target viscosity| ÷ B;

[0196] Then the comprehensive evaluation value of the first water addition ratio = (1 - viscosity evaluation value of the first water addition ratio) × first evaluation weight + (second evaluation weight × K) + (third evaluation weight × (1 / E));

[0197] The target water addition ratio is selected as the first water addition ratio corresponding to the largest comprehensive evaluation value within the target comprehensive evaluation value range.

[0198] First evaluation weight (viscosity priority): The value is greater than 0 and less than 1. When rheological properties are given priority in production, this value is increased.

[0199] Second evaluation weight (penetration priority): The value is greater than 0 and less than 1. This value should be increased when penetration needs to be controlled.

[0200] Third evaluation weight (combined with priority): The value is greater than 0 and less than 1. This value is increased when it is necessary to enhance the material combination.

[0201] The sum of the first evaluation weight, the second evaluation weight, and the third evaluation weight is 1;

[0202] The combined binding-rheological coefficient Y of the mixture at the target water addition ratio is the comprehensive evaluation value corresponding to the target water addition ratio. This coefficient can be used to quantify the combined binding-rheological properties of the mixture at the target water addition ratio, and serve as a basis for evaluating material performance and process rationality in production.

[0203] Step 705: Determine the target extrusion pressure range by combining the combined rheological coefficient and bulk density of the mixture. Specifically:

[0204] First, determine the ideal extrusion pressure range. Based on the experimental data of the current type of residual carbon and the same type of bentonite in the current batch, the range of extrusion pressure that can make the granulation result qualified is determined.

[0205] ;

[0206] U represents the correction ratio; The base mixture's bonding-rheological composite coefficient; The base packing density; The packing density determined in step 702; , Based on experimental data of the current type of residual carbon and the same type of bentonite in the current batch, the range of extrusion pressure that can make the granulation result qualified is the combined coefficient of the mixture and rheology and the bulk density of the mixture in the experimental process.

[0207] Step 707: Determine the first screening rotation speed based on steps 705 and 706 and the target granulation requirement parameters; specifically:

[0208] The target granulation requirements parameters include: target granulation rate range and target granulation strength range; the speed-reference granulation rate fitting curve segment corresponding to the first screening speed meets the target granulation rate range; the speed-reference granulation strength fitting curve segment corresponding to the first screening speed meets the target granulation strength range; the speed-reference extrusion pressure fitting curve segment corresponding to the first screening speed meets the target extrusion pressure range.

[0209] The specific implementation of step 708 is as follows:

[0210] Slope extraction: Obtain the slopes of the three fitted curves (speed-reference pelleting rate, speed-reference pelleting strength, speed-reference extrusion pressure) corresponding to the first screening speed obtained in step 707. These slopes reflect the rate of change of each index with speed.

[0211] Weighting: Based on the importance that production places on pelleting rate, pelleting strength, and extrusion pressure, assign weights to the slopes of the three curves (the sum of the weights is 1) to highlight the impact of key indicators on speed selection.

[0212] Comprehensive analysis: Through weighted calculation:

[0213] The overall trend coefficient = pelleting rate weight × pelleting rate curve slope + pelleting strength weight × pelleting strength curve slope + extrusion pressure weight × extrusion pressure curve slope.

[0214] Select the speed corresponding to the first selected speed with the smallest comprehensive trend coefficient as the target speed;

[0215] The beneficial effects of the above technical solution are as follows:

[0216] By constructing fitting curves for water addition ratio and viscosity, and rotation speed and granulation performance, the material characteristics, process parameters, and granulation results are precisely correlated. From the influence of water addition ratio on viscosity to the effect of rotation speed on granulation rate, strength, and extrusion pressure, the entire process is quantitatively controlled to ensure that core indicators such as granulation rate and strength consistently meet standards, significantly reducing the granulation defect rate caused by parameter fluctuations and improving product quality consistency.

[0217] By introducing a weight allocation mechanism, the optimization direction of parameters can be flexibly adjusted according to the different priorities of viscosity, penetration, binding performance, granulation rate, strength, and extrusion pressure in actual production.

[0218] By replacing trial-and-error with data fitting and quantitative calculations, the process development cycle is shortened, and parameters such as the appropriate water addition ratio and rotation speed are quickly determined, reducing material and time waste. At the same time, by controlling the extrusion pressure and optimizing the rotation speed, the risk of equipment overload is reduced, and the service life of the equipment is extended, resulting in cost reduction and efficiency improvement throughout the entire process from production preparation to equipment operation and maintenance.

[0219] The fitted curves, comprehensive coefficients, weights, and other data generated at each stage form a complete process database. This database can not only be used for retrospective analysis of production problems, but also provide a foundation for artificial intelligence modeling and big data process optimization, helping enterprises transform towards digital and intelligent manufacturing and continuously tap into their production potential.

[0220] By combining state coefficients and predicting permeability state coefficients, we can deeply analyze the essential properties of the mixture of residual char and bentonite, and optimize the process accordingly. We can fully leverage the material's potential, explore the material compatibility boundaries while ensuring granulation quality, and provide data support for expanding raw material sources and optimizing formulations.

[0221] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A direct reduction process for biomass using a rotary kiln, characterized in that: include: Step 1: Mix the oxidized pellets and coal evenly at a mass ratio of 100:(10-20); Step 2: The mixture produced in Step 1 is conveyed to the chain grate machine, where the mixture exchanges heat with the flue gas to dry and heat the mixture. Step 3: The preheated mixture produced in Step 2 is fed into the feed port at the tail of the rotary kiln. After entering the rotary kiln, it gradually moves forward as the rotary kiln rotates, and continues to be heated and pre-reduced under the action of high-temperature flue gas to form a mixture of pre-reduced pellets and residual carbon. Step 4: When the mixture of pre-reduced pellets and residual char from Step 3 enters the high-temperature zone of the rotary kiln, biomass pellets and residual char are thrown into the kiln head to further reduce the pre-reduced pellets, producing a mixture of metallized pellets and residual char. The furthest throwing point of the biomass pellets is the boundary between the pre-reduction stage and the high-temperature zone. The hourly mass of biomass pellets thrown in is 20-40% of the hourly mass of oxidized pellets entering the kiln. Step 5: The mixture of metallized pellets and residual carbon produced in Step 4 is discharged from the kiln head and enters the cooling system to be cooled to room temperature; Step 6: The ambient temperature mixture produced in Step 5 is fed to a magnetic separation system to produce metallized pellets and residual carbon; Step 7: The residual char produced in Step 6 is mixed evenly with bentonite, granulated by adding water through a granulator, and then fed back to Step 1 to be mixed into the coal; the bentonite added in Step 7 is 2-3% of the mass of the residual char. Before performing step 2 on the current batch of materials, step 20 is performed. Step 20 includes: Step 201: Obtain the baseline temperature rise rate - baseline equivalent pyrolysis gas concentration mapping table for each temperature rise stage of the current material; Step 202: Heat the current batch of material with the reference heating parameters for each temperature rise stage to determine the material temperature rise coefficient, internal temperature gradient coefficient, and thermal diffusion state coefficient for different temperature rise stages; and determine the pyrolysis gas-temperature coupling coefficient for each temperature rise stage based on the detection of pyrolysis gas concentration during the heating test. Step 203: Determine the material permeability coefficient based on the pyrolysis gas concentration detection during the heating test and the gas pressure and flow rate detection values ​​in the heating space at each temperature rise stage; Step 204: Determine the equivalent thermal inertia coefficient of the current batch of materials based on step 202; Step 205: Based on the target time range of the current material passing through the chain grate, determine the first conveying speed range of the chain grate for the current material; Step 206: Determine the load factor of the chain grate based on the weight of the current batch of material per unit length in the chain grate and the weight of the current batch of material per unit length in the chain grate at the end of each temperature rise stage, and correct the load factor based on the equivalent thermal inertia coefficient of the current batch of material. Step 207: Determine the target conveying speed of the current batch of materials based on the corrected load coefficient of the chain grate and the first conveying speed range of the current batch of materials; Step 208: Based on the target conveying speed of the current batch of materials, determine the target heating control parameters of the heating device corresponding to each temperature rise stage, as per step 202.

2. The direct reduction process of biomass rotary kiln as described in claim 1, characterized in that: In step 1, the iron content of the oxidized pellets is ≥62%, the particle size is 10-16mm, and the compressive strength is ≥1500N; the coal addition ratio is 10-20% of the mass of the oxidized pellets, the particle size is 5-30mm, the volatile matter is ≤15%, the ash content is ≤10%, and the calorific value is ≥5000cal / kg.

3. The direct reduction process of biomass rotary kiln as described in claim 1, characterized in that: In step 2, the flue gas entering the chain grate is drawn from the tail of the rotary kiln. The initial flue gas temperature is 700-900℃, and the final flue gas temperature exiting the chain grate is 200-300℃. The mixed material enters the chain grate at room temperature, and the final temperature exiting the chain grate is 400-600℃. The flue gas is discharged from the chain grate to the flue gas treatment system and meets emission standards. In step 3, the total length of the preheated mixture during heating and pre-reduction is 1 / 3 to 1 / 2 of the length of the rotary kiln, and the material temperature is increased from 400-600℃ to 800-1000℃.

4. The direct reduction process of biomass rotary kiln as described in claim 1, characterized in that: In step 4, the total length of the high-temperature zone is 1 / 2 to 2 / 3 of the length of the rotary kiln, and the material temperature in the high-temperature zone is 800-1200℃; the biomass pellet size is 5-30mm, the hydrogen content is ≥5%, the volatile matter is ≥50%, the ash content is ≤10%, and the calorific value is ≥4000cal / kg; the metallization rate of the produced metallized pellets is ≥90%, and the residual char mass is 1 / 3 to 2 / 3 of the mass of the oxidized pellets entering the kiln; the feeding temperature of the metallized pellets and residual char is 800-1000℃.

5. The direct reduction process of biomass rotary kiln as described in claim 1, characterized in that: The total restoration time for steps 3 and 4 is 2-3.5 hours.

6. The direct reduction process of biomass rotary kiln as described in claim 1, characterized in that: In step 5, the cooling system is an indirect cooling device containing a cooling medium, which cools an equal amount of metallized pellets and residual carbon that exit the kiln at 800-1000℃ to below 60℃ within 2 hours. In step 6, the magnetic separation system is a permanent magnet drum device with a magnetic field strength of 0.1-0.2T on the surface.

7. The direct reduction process of biomass rotary kiln as described in claim 1, characterized in that: The overall water content is 7-9% of the total weight of bentonite and residual carbon. Mixing and granulation are carried out using a mixer and a disc granulator, respectively, with a particle size of 10-20mm and a granulation strength of ≥200N.

8. The direct reduction process of biomass rotary kiln as described in claim 1, characterized in that: When the current batch of materials is dried and heated in batches through the chain grate machine, the heating device of the chain grate machine is controlled to work according to the target heating control parameters of the heating device corresponding to each temperature rise stage.

9. The direct reduction process of biomass rotary kiln as described in claim 1, characterized in that: Granulation is performed using a disc granulator. Before batch processing of the current material, step 70 is performed. Step 70 includes: Step 701: Obtain the water ratio-mixture viscosity fitting curves for the current type of residual char and the current batch of bentonite within the ideal water ratio range; Step 702: Conduct a premixing test on the current batch of residual char and the current batch of bentonite to determine the bonding state coefficient and bulk density of the mixture; Step 703: Determine the predicted permeability state coefficient of the mixture based on the bulk density and the binding state coefficient of the mixture; Step 704: Based on the water addition ratio-mixture viscosity fitting curve, the predicted permeability state coefficient of the mixture, and the mixture bonding state coefficient, determine the target water addition ratio and the mixture bonding-rheological comprehensive coefficient corresponding to the target water addition ratio; Step 705: Determine the target extrusion pressure range by combining the combined rheological coefficient and bulk density of the mixture; Step 706: Obtain the following fitting curves under the reference conditions for the mixture formed by the current disc pellet mill on the current type of residual carbon and the current batch of bentonite: speed-reference pelletizing rate fitting curve, speed-reference pelletizing strength fitting curve, and speed-reference extrusion pressure fitting curve. Step 707: Determine the first screening rotation speed based on Step 705, Step 706, and the target granulation requirement parameters; Step 708: Determine the target rotational speed of the disc pellet mill based on the slopes of the rotational speed-reference pelletizing rate fitting curve, the rotational speed-reference pelletizing strength fitting curve, and the rotational speed-reference extrusion pressure fitting curve of the first screening rotational speed.

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