A drying and consolidation method for roasting pellets and its system and pellets

Abstract

The present invention discloses a drying and consolidation method for roasting pellets, a system and pellets thereof. Aiming at the phenomenon that the drying efficiency, drying cost and strength of the dried pellets cannot be taken into account at the same time in the hot air drying and microwave drying in the prior art, the present invention innovatively adopts hot air selective pre-drying + microwave electromagnetic field drying and consolidation technology to prepare pellets for low-temperature reduction roasting. The pellets are pre-dried to a low moisture content using hot air drying as a basis, and then the pellets are quickly consolidated to improve the strength by using microwave drying and consolidation as the core. The hot air and microwave are efficiently coupled to achieve green production while the obtained dried and consolidated pellets have high strength. The pellets can be directly put into a kiln for low-temperature reduction roasting without pretreatment such as high-temperature preheating and roasting, which greatly improves the drying and reduction efficiency of the pellets and reduces the production input cost.

Description

Technical Field

[0001] The invention relates to a production method of reduction roasted pellets, in particular to a drying and consolidation method for roasted pellets and a system and pellets thereof, belonging to the technical field of metallurgy. Background Art

[0002] Drying process is an important process in the metallurgical industry. Most of them are heated by hot air, gas, steam (superheated steam), electric heating, etc. For example, when using vertical furnace, chain grate machine-rotary kiln, belt roaster, etc. for oxidation pellet production, it is necessary to dry the green balls. When using rotary kiln, rotary hearth furnace, etc. to dispose of metallurgical and municipal solid waste, it is also necessary to dry the solid waste lumps. The temperature of the drying process is generally 200-400℃, which is mainly the evaporation of water in the green balls and the removal of some crystal water in the material. The traditional heating and drying method is to heat from the surface to the inside through conduction, convection and radiation. It has a significant temperature gradient, low heating efficiency, and uneven temperature distribution. In order to ensure the uniformity and qualified rate of the product, it is usually necessary to extend the calcination time and increase the calcination temperature, which leads to the defects of long cycle and high energy consumption in the conventional calcination process.

[0003] At present, the iron and steel metallurgical industry mainly adopts hot air drying technology. During the drying process of iron-containing materials, the surface of the iron-containing materials is usually heated first, and then the heat is transferred to the free water and bound water inside. The required temperature is high and the time is long. There are disadvantages such as uneven heating inside and outside the pellets, low drying efficiency, and high energy consumption. At the same time, the drying equipment used, such as chain grates, has a complex structure, occupies a large area, and has high equipment cost. In the direct reduction process, fine-grained iron-containing materials undergo multiple processes such as pelletizing-drying / preheating-reduction roasting, which requires the dried pellets to have a certain drop and compressive strength. Low strength will cause the pellets to break during transportation or when they rotate in the kiln, affecting smooth production.

[0004] Studies have shown that microwave drying technology has the characteristics of overall heating, selective heating, fast heating speed, high dehydration efficiency, low environmental pollution, and good controllability. For example, patent 201110429400.0 invented a microwave and steam mixed heating belt drying kiln, which can be widely used for drying and dehydrating materials; patents CN201921085336.7 and CN202022137976.7 respectively invented microwave hot air combined drying devices for microwave drying of lignite and minerals; many literature studies have shown that microwave technology can be applied to the drying and dehydration of typical metallurgical materials such as limonite, titanium concentrate, anthracite and high-purity quartz sand, highlighting the advantages of high dehydration efficiency and high thermal energy utilization. Microwave heating, as a new heating method, is different from traditional heating. Microwave heating relies on the thermal effect generated by the dielectric loss of the material in the microwave field, and is closely related to the polarization of the material. The material is heated by microwave heating. The microwave irradiates the material. After the material absorbs the microwave, the molecules vibrate and rub violently to generate heat. The heating speed is fast, the material reaction is completed quickly, and the energy utilization rate is high. However, microwave heating technology is rare in the actual application of metallurgy and mineral drying. The reason is that microwave heating will cause the moisture inside the pellet to dissipate quickly, and the rapid loss of moisture between the molecular gaps of the material inside the pellet makes the gaps inside the pellet dry and consolidate before it shrinks, which seriously reduces the consolidation strength of the pellet. In addition, the fixed investment and pure production cost of pure microwave heating are higher than other heating methods. Therefore, it is of great significance to find a method that can quickly achieve pellet drying and improve pellet strength, so that it can directly participate in roasting without high-temperature preheating. Summary of the invention

[0005] Aiming at the deficiencies of the prior art: the existing single hot air drying has the problems of long drying time, uneven drying inside and outside the pellets, and low drying efficiency, while the single microwave drying has the problems of high investment cost and low strength of the dried pellets. In addition, the existing hot air + microwave joint drying has the problems of low strength of the dried pellets, and it is difficult to balance the strength of the dried pellets with the production efficiency, and has not been applied in the steel industry. The present invention provides a drying and consolidation method for roasting pellets, a drying and consolidation system, and a drying and consolidation pellet. The drying and consolidation method first pre-dries the raw pellets by hot air, reduces the moisture content of the raw pellets, and reduces the gap between the molecules of the materials inside the pellets, and increases the force between the molecules of the materials inside the pellets. Then, the residual moisture in the pellets is further removed by microwave drying and consolidation. While the residual moisture disappears, the particles of the materials inside the pellets are further brought closer and bonded by the action of molecular forces, thereby making the materials inside the pellets more dense, thereby playing the role of pellet consolidation. In addition, by adding a micro-area hot spot welding agent to the raw pellets, it has the effect of absorbing waves and heating up quickly, and promoting local high-temperature liquid phase consolidation.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] According to a first embodiment of the present invention, a drying and consolidation method for calcining pellets is provided:

[0008] A drying and consolidation method for roasting pellets, the method comprising the following steps:

[0009] 1) Using pelletizing ore, binder, with or without welding agent and water as pelletizing raw materials to obtain green pellets.

[0010] 2) Use hot air to dry the green pellets to a low moisture content.

[0011] 3) Using microwaves to dry and consolidate the raw pellets with low moisture content to obtain dry consolidated pellets.

[0012] Preferably, in step 1), the pelletizing ore material is iron-containing ore powder and / or metallurgical and municipal solid waste, and the metallurgical and municipal solid waste is one or more of vanadium-extracting tailings, zinc-containing dust, steel slag, garbage fly ash, and organic solid waste, preferably vanadium-extracting tailings.

[0013] Preferably, in step 1), the binder is an organic binder and / or an inorganic binder, preferably one or more of calcium oxide, calcium hydroxide, calcium carbonate, and high molecular hydrocarbon binders (such as humic acid binders: sodium humate, ammonium humate, potassium humate, and high viscosity PAC binders, etc.).

[0014] Preferably, the welding agent is one or both of carbon powder and iron powder, preferably a mixture of carbon powder and iron powder.

[0015] Preferably, the amount of the binder is 0.5-30% of the total mass of the pelletizing raw material, preferably 1-25%, and more preferably 2-20%.

[0016] Preferably, the amount of the welding agent is 0.5-5% of the total mass of the pelletizing raw material, preferably 0.8-4.5%, more preferably 1-4%.

[0017] Preferably, in step 2), the hot air is electrically heated hot air and / or hot waste gas from a steel plant process. The temperature of the hot air is 100-500°C, preferably 150-400°C, and more preferably 200-300°C.

[0018] Preferably, the drying of the green pellets to a low moisture content is drying the green pellets to a moisture content lower than 4.5%, preferably 0.5-3%, more preferably 1-2%.

[0019] Preferably, in step 2), the temperature of drying and consolidating by microwave is 400-800°C, preferably 450-700°C, more preferably 500-600°C. The power density of drying and consolidating by microwave is 10-50kw / m 3 , preferably 15-40kw / m 3 , more preferably 18-30kw / m 3 .

[0020] Preferably, the particle size of the green pellets is 2-15 mm, preferably 2.5-12 mm, and more preferably 3-8 mm.

[0021] Preferably, the average particle size of the pelletizing raw material is no greater than 80 μm, preferably no greater than 75 μm, and more preferably no greater than 70 μm.

[0022] Preferably, the moisture content of the green pellets is not less than 5wt%, preferably not less than 8wt%, and more preferably not less than 10wt%.

[0023] Preferably, the drop strength of the dried consolidated pellets is 3-15 times / 0.5m, preferably 6-12 times / 0.5m.

[0024] Preferably, the compressive strength of the dried consolidated pellets is 180-400 N / P, preferably 200-350 N / P.

[0025] According to a second embodiment of the present invention, a dry consolidated pellet is provided:

[0026] A dry consolidated pellet is prepared by the method according to the first embodiment.

[0027] According to a third embodiment of the present invention, a drying consolidation system is provided:

[0028] A drying and consolidation system or a system used for the drying and consolidation method described in the first embodiment: the drying and consolidation system comprises a pelletizing device, a hot air drying device and a microwave drying and consolidation device. The feed port of the pelletizing device is connected to a pelletizing raw material adding device, and the discharge port of the pelletizing device is connected to the feed port of the hot air drying device through a raw pellet conveying device. The discharge port of the hot air drying device is connected to the feed port of the microwave drying and consolidation device. The discharge port of the microwave drying and consolidation device is connected to a drying and consolidation pellet conveying device.

[0029] Preferably, the hot air drying device is provided with a hot air inlet duct and a hot air exhaust duct. A blower is provided on the hot air inlet duct and / or an exhaust fan is provided on the hot air exhaust duct.

[0030] Preferably, the system further comprises a reduction roasting device, the feed inlet of which is connected to the drying and consolidation pellet conveying device.

[0031] In the prior art, hot air is generally used to dry the pellets. During the drying process, the surface of the raw pellets is usually heated first, and then the heat is transferred to the free water and bound water inside the pellets. The required temperature is high and the time is long. Since the heat is slowly conducted from the outside to the inside, the water inside and outside the pellets is heated unevenly, resulting in a difference in the quality of the inside and outside of the pellets, making the drying efficiency low and the pellets poor in quality. At the same time, the drying equipment used, such as chain grate machines, has a complex structure, occupies a large area, and has a high equipment cost. In addition, microwave drying is used alone, and the investment cost of microwave drying equipment is huge. Since water is a highly polar molecule, microwave energy can be quickly converted into internal energy, so that the overall water in the raw pellets heats up quickly, and the water migrates and evaporates quickly. In this way, the capillary inside the pellets fails to shrink effectively in time, and the capillary force and the contact capillary force are reduced, resulting in weak bonding between the particles of the material inside the pellets and poor strength of the dried pellets. In addition, the existing hot air + microwave drying technology is just a simple and rough superposition of the two, and no coupling is performed for the strength of the dried pellets. In the direct reduction process, fine-grained iron-containing materials undergo multiple steps such as pelletizing, drying / preheating, and reduction roasting. The dried pellets are required to have certain falling and compressive strengths. Low strength will cause the pellets to break during transportation or when they rotate in the kiln, affecting smooth production.

[0032] In the present invention, based on the purpose of providing high-quality dry and consolidated pellets for low-temperature reduction roasting, the present invention innovatively adds a binder and a micro-area hot spot welding agent during the pelletizing process to respectively enhance the quality of raw pellets and dried pellets; adopts a hot air / microwave drying-microwave consolidation-cooling / direct kiln drying and consolidation process, first using hot air for pre-drying to dry the raw pellets to a low moisture content (the moisture content of the pellets is reduced to below 4.5%, for example 0.5-3%, preferably 1-2%), and then uses microwave thermal energy for drying and consolidation, with high evaporation efficiency of residual water and enhanced molecular forces between particles. In addition, the micro-area hot spot welding agent absorbs waves and heats up quickly, promoting local high-temperature liquid phase consolidation inside the pellets. The compressive strength of the dried and consolidated pellets obtained by the method of the present invention can be as low as 200N·P -1 Around or even higher, it can directly enter the kiln for low-temperature reduction roasting without high-temperature roasting. This method efficiently utilizes the coupled hot air and microwave thermal energy. Microwaves promote the diffusion of heat and moisture from the center of the pellet from the inside to the outside, without the diffusion restriction in the unreacted core model, increasing the temperature of the micro-area, promoting the growth of grains, and forming a loose porous structure. It is beneficial to the internal diffusion of reducing gas during low-temperature reduction roasting, thereby reducing the reduction temperature and time.

[0033] In the present invention, the inventors have found through years of research that, compared with the method of using hot air drying and consolidation alone or using microwave magnetic field drying and consolidation alone, the method of using hot air selective pre-drying + microwave electromagnetic field drying and consolidation is particularly effective. If the hot air drying and consolidation method is used alone, the pellets are dried and consolidated by physical heat transfer, and there is a technical problem of uneven temperature inside and outside the raw pellets, which makes the consolidation strength inside the pellets low. If the microwave electromagnetic field drying and consolidation method is used alone, the moisture inside the pellets is lost too quickly, and the moisture in the gaps between the material molecules in the pellets is suddenly lost, which also affects the consolidation effect between the material molecules in the pellets. Through experiments, it was found that the raw pellets were first dried selectively to a low moisture content by hot air drying and consolidation, so that the moisture in the gaps between the material molecules in the pellets evaporated at a slower rate, so that the material molecules in the pellets slowly gathered together, reducing the distance between the molecules in the material; and then the overall heating effect of the microwave electromagnetic field made the thermal motion of the material particle molecules inside the pellets more intense, prompting the rapid evaporation of the residual moisture inside the pellets, further increasing the interaction between the material molecules, forming a consolidation structure between the material molecules, and making the material inside the pellets denser. That is, the present invention uses a drying and consolidation method that combines hot air selective pre-drying and microwave electromagnetic field drying and consolidation to obtain a composite pellet with greatly improved strength, and can be directly sent to a kiln for reduction roasting without high-temperature roasting preheating.

[0034] In the present invention, it is found through experiments that by adding carbon powder and / or metal iron powder to the inside of the raw pellets to act as micro-area hot spot welding agents, and utilizing the characteristics of the micro-area hot spot welding agents in absorbing waves and rapidly heating up, a local liquid phase bonding bridge can be provided inside the pellets during microwave drying and consolidation, thereby promoting close interconnection of particles and growth of grains, thereby making the pellets have a fast consolidation speed, a short consolidation time, and high strength.

[0035] In the present invention, fine-grained iron-containing ore powder, such as ordinary iron ore, low-grade and complex iron ore, and metallurgical and municipal solid waste, such as vanadium tailings, zinc-containing dust, steel slag, garbage fly ash, organic solid waste resources, etc., are used to prepare green pellets, and optional inorganic and / or organic and / or composite binders (preferably calcium-based binders, polymer hydrocarbon binders, etc.) are added during the pelletizing process. By also adding trace amounts of carbon powder, metal iron powder, etc. as micro-area hotspot welding agents, the binder plays a role in enhancing the quality of the green pellets, and the micro-area hotspot welding agent plays a role in enhancing the quality of the dried pellets. The prepared green pellets have a particle size of 2-15 mm, preferably 2.5-12 mm, and more preferably 3-8 mm.

[0036] In the present invention, high-moisture green pellets (the moisture content of the green pellets is not less than 5wt%, preferably not less than 8wt%, and more preferably not less than 10wt%) enter the hot air drying area, and the hot air is electrically heated hot air or multi-source metallurgical hot exhaust gas. Electric heating comes from green electricity such as solar energy and wind energy, and multi-source metallurgical hot exhaust gas comes from hot exhaust gases from various processes, such as vertical furnaces, rotary kilns, sintering machines, ring coolers, etc. It has been verified through experiments that the drying efficiency and drying effect are most compatible when the wind temperature of hot air drying is 100-500°C, preferably 150-400°C, and more preferably 200-300°C. The free water and part of the bound water of the green pellets are selectively removed by blowing and / or exhaust drying, so that the moisture content of the high-moisture green pellets is reduced to below 4.5%. During the drying process, the process parameters such as air volume, wind temperature and material layer thickness need to be accurately controlled to enhance the overall dehydration effect of the pellets and achieve efficient utilization of waste heat from the exhaust gas.

[0037] In the present invention, the low-moisture raw pellets after selective hot air drying directly enter the microwave drying consolidation area (microwave power density is 10-50kw / m 3 , preferably 15-40kw / m 3 , more preferably 18-30kw / m 3 ), under the overall heating effect of microwaves, the molecular thermal motion of the material particles inside the pellets is more intense, and the heat and moisture of the pellets diffuse from the inside to the outside (center-surface), without being restricted by the diffusion in the unreacted core model, and the residual moisture evaporates quickly; the micro-area hot spot welding agent inside the dry pellet absorbs waves and heats up quickly, providing a local liquid phase bonding bridge, promoting the close interconnection of particles and the growth of grains, so that the pellets are consolidated quickly, in a short time, and with high strength.

[0038] In the present invention, the dried and consolidated pellets obtained by hot air selective pre-drying + microwave electromagnetic field drying and consolidation do not need to be preheated and roasted at high temperature, and can directly enter the kiln for low-temperature reduction roasting; the dried and consolidated pellets have a loose porous structure, which is conducive to the internal diffusion of the gas in the reduction process. By controlling the atmosphere and temperature of the kiln, metallic iron is produced on the surface and inside of the pellets as early as possible, so as to reduce the decrease in pellet strength and the length of the strength trough zone.

[0039] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0040] 1: The present invention innovatively proposes a hot air selective pre-drying + microwave electromagnetic field drying and consolidation technology to prepare pellets for low-temperature reduction roasting, making full use of hot air drying such as green electric hot air and waste gas waste heat as the basis (pre-drying raw pellets to low moisture content), microwave drying and consolidation as the core (making the pellets quickly consolidate and improve strength), efficiently coupling hot air and microwaves, achieving green production while obtaining high-strength dried and consolidated pellets, and no need for high-temperature preheating and roasting and other pretreatments, and can directly enter the kiln for low-temperature reduction roasting. It greatly improves the drying and reduction efficiency of the pellets and reduces the production input cost.

[0041] 2: The present invention adds micro-area hot spot welding agent to the raw pellets, and utilizes the characteristics of the micro-area hot spot welding agent to absorb waves and heat up quickly in the microwave area, so as to strengthen the particle connection and grain growth in the local area of ​​the material inside the pellets and increase the strength of the pellets; the dry consolidated pellets are provided with a loose porous structure, which is conducive to the diffusion of reducing gas during low-temperature reduction roasting, and metallic iron is produced from the surface to the inside as early as possible, so as to reduce the decrease in pellet strength and the length of the strength trough area. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 The present invention is a process flow chart of the drying and consolidation method for roasting pellets.

[0043] Figure 2 This is an example diagram of the state transition of the green pellets of the present invention after hot air selective pre-drying + microwave electromagnetic field drying and consolidation.

[0044] Figure 3 This is an example diagram of the state transition of the microwave drying and consolidation of the raw pellets containing welding agent of the present invention.

[0045] Figure 4 It is a schematic diagram of the structure of the drying and consolidation system used in the method of the present invention.

[0046] Figure numerals: 1: pelletizing device; 2: hot air drying device; 201: hot air inlet duct; 202: hot air exhaust duct; 203: blower; 204: exhaust fan; 3: microwave drying and consolidation device; 4: pelletizing raw material adding device; 5: raw pellet conveying device; 6: drying and consolidation pellet conveying device; 7: reduction roasting device. DETAILED DESCRIPTION

[0047] The technical solution of the present invention is illustrated below by way of example, and the scope of protection requested by the present invention includes but is not limited to the following embodiments.

[0048] A drying and consolidation method for roasting pellets, the method comprising the following steps:

[0049] 1) Using pelletizing ore, binder, with or without welding agent and water as pelletizing raw materials to obtain green pellets.

[0050] 2) Use hot air to dry the green pellets to a low moisture content.

[0051] 3) Using microwaves to dry and consolidate the raw pellets with low moisture content to obtain dry consolidated pellets.

[0052] Preferably, in step 1), the pelletizing ore material is iron-containing ore powder and / or metallurgical and municipal solid waste, and the metallurgical and municipal solid waste is one or more of vanadium-extracting tailings, zinc-containing dust, steel slag, garbage fly ash, and organic solid waste, preferably vanadium-extracting tailings.

[0053] Preferably, in step 1), the binder is an organic binder and / or an inorganic binder and / or a composite binder, preferably one or more of calcium oxide, calcium hydroxide, calcium carbonate, and a high molecular weight hydrocarbon binder.

[0054] Preferably, the welding agent is one or both of carbon powder and iron powder, preferably a mixture of carbon powder and iron powder.

[0055] Preferably, the amount of the binder is 0.5-30% of the total mass of the pelletizing raw material, preferably 1-25%, and more preferably 2-20%.

[0056] Preferably, the amount of the welding agent is 0.5-5% of the total mass of the pelletizing raw material, preferably 0.8-4.5%, more preferably 1-4%.

[0057] Preferably, in step 2), the hot air is electrically heated hot air and / or hot waste gas from a steel plant process. The temperature of the hot air is 100-500°C, preferably 150-400°C, and more preferably 200-300°C.

[0058] Preferably, the drying of the green pellets to a low moisture content is drying the green pellets to a moisture content lower than 4.5%, preferably 0.5-3%, more preferably 1-2%.

[0059] Preferably, in step 2), the temperature of drying and consolidating by microwave is 400-800°C, preferably 450-700°C, more preferably 500-600°C. The power density of drying and consolidating by microwave is 10-50kw / m 3 , preferably 15-40kw / m 3 , more preferably 18-30kw / m 3 .

[0060] Preferably, the particle size of the green pellets is 2-15 mm, preferably 2.5-12 mm, and more preferably 3-8 mm.

[0061] Preferably, the average particle size of the pelletizing raw material is no greater than 80 μm, preferably no greater than 75 μm, and more preferably no greater than 70 μm.

[0062] Preferably, the moisture content of the green pellets is not less than 5wt%, preferably not less than 8wt%, and more preferably not less than 10wt%.

[0063] Preferably, the drop strength of the dried consolidated pellets is 3-15 times / 0.5m, preferably 6-12 times / 0.5m.

[0064] Preferably, the compressive strength of the dried consolidated pellets is 180-400 N / P, preferably 200-350 N / P.

[0065] like Figure 4 As shown, a drying and consolidation system includes a pelletizing device 1, a hot air drying device 2, and a microwave drying and consolidation device 3. The feed port of the pelletizing device 1 is connected to a pelletizing raw material adding device 4, and the discharge port of the pelletizing device 1 is connected to the feed port of the hot air drying device 2 through a raw pellet conveying device 5. The discharge port of the hot air drying device 2 is connected to the feed port of the microwave drying and consolidation device 3. The discharge port of the microwave drying and consolidation device 3 is connected to a drying and consolidation pellet conveying device 6.

[0066] Preferably, the hot air drying device 2 is provided with a hot air inlet duct 201 and a hot air exhaust duct 202. A blower 203 is provided on the hot air inlet duct 201 and / or an exhaust fan 204 is provided on the hot air exhaust duct 202.

[0067] Preferably, the system further comprises a reduction roasting device 7. The feed inlet of the reduction roasting device 7 is connected to the drying and consolidation pellet conveying device 6.

[0068] Example 1

[0069] The raw materials for pelletizing are iron ore powder, calcium hydroxide, carbon powder, iron powder and water, and green pellets with an average particle size of 6.6 mm and a water content of about 12.7 wt % are obtained.

[0070] The green pellets were dried to a moisture content of about 1.0 wt% using electric hot air at a temperature of 330°C (drying time was about 57 min). 3 The raw pellets are dried and consolidated by microwaves at 550°C, and dried and consolidated pellets are obtained when the moisture content is lower than 0.1wt%.

[0071] Example 2

[0072] The raw materials for pelletizing are iron ore powder, calcium hydroxide, carbon powder, iron powder and water, and green pellets with an average particle size of 6.1 mm and a water content of about 13.2 wt % are obtained.

[0073] The green pellets were dried to a moisture content of about 1.2 wt% using electric hot air at a temperature of 330°C (drying time was about 48 min). 3 The raw pellets are dried and consolidated by microwaves at 550°C, and dried and consolidated pellets are obtained when the moisture content is lower than 0.1wt%.

[0074] Example 3

[0075] The raw materials for pelletizing are iron ore powder, calcium hydroxide, carbon powder, iron powder and water, and green pellets with an average particle size of 6.8 mm and a water content of about 12.5 wt % are obtained.

[0076] The green pellets were dried to a moisture content of about 1.5 wt% using electric hot air at a temperature of 330°C (drying time was about 40 min). 3 The raw pellets are dried and consolidated by microwaves at 550°C, and dried and consolidated pellets are obtained when the moisture content is lower than 0.1wt%.

[0077] Example 4

[0078] The raw materials for pelletizing are iron ore powder, calcium hydroxide, carbon powder, iron powder and water, and green pellets with an average particle size of 6.3 mm and a water content of about 13.0 wt % are obtained.

[0079] The green pellets were dried to a moisture content of about 1.8 wt% using electric hot air at a temperature of 330°C (drying time was about 35 min). 3 The raw pellets are dried and consolidated by microwaves at 550°C, and dried and consolidated pellets are obtained when the moisture content is lower than 0.1wt%.

[0080] Example 5

[0081] The raw materials for pelletizing are iron ore powder, calcium hydroxide and water, and green pellets with an average particle size of 6.9 mm and a water content of about 12.2 wt % are obtained.

[0082] The green pellets were dried to a moisture content of about 1.2 wt% using electric hot air at a temperature of 330°C (drying time was about 50 min). 3 The raw pellets are dried and consolidated by microwaves at 550°C, and dried and consolidated pellets are obtained when the moisture content is lower than 0.1wt%.

[0083] Example 6

[0084] The raw materials for pelletizing are iron ore powder, calcium hydroxide and water, and green pellets with an average particle size of 6.8 mm and a water content of about 12.6 wt % are obtained.

[0085] The green pellets were dried to a moisture content of about 1.5 wt% using electric hot air at a temperature of 330°C (drying time was about 45 min). 3 The raw pellets are dried and consolidated by microwaves at 550°C, and dried and consolidated pellets are obtained when the moisture content is lower than 0.1wt%.

[0086] Example 7

[0087] The raw materials for pelletizing are iron ore powder, calcium hydroxide, carbon powder, iron powder and water, and green pellets with an average particle size of 6.5 mm and a water content of about 12.9 wt % are obtained.

[0088] The green pellets were dried to a moisture content of about 0.8 wt% using electric hot air at a temperature of 330°C (the drying time was about 94 min, which was significantly longer). 3 The raw pellets are dried and consolidated by microwaves at 550°C, and dried and consolidated pellets are obtained when the moisture content is lower than 0.1wt%.

[0089] Example 8

[0090] The raw materials for pelletizing are iron ore powder, calcium hydroxide, carbon powder, iron powder and water, and green pellets with an average particle size of 6.9 mm and a water content of about 13.3 wt % are obtained.

[0091] The green pellets were dried to a moisture content of about 0.5 wt% using electric hot air at a temperature of 330°C (the drying time was about 113 min, which was significantly longer). 3 The raw pellets are dried and consolidated by microwaves at 550°C, and dried and consolidated pellets are obtained when the moisture content is lower than 0.1wt%.

[0092] Example 9

[0093] The raw materials for pelletizing are iron ore powder, calcium hydroxide, carbon powder, iron powder and water, and green pellets with an average particle size of 8.0 mm and a water content of about 10.4 wt % are obtained.

[0094] The green pellets were dried to a moisture content of about 2.0 wt% using electric hot air at a temperature of 380°C (drying time was about 29 min). 3 The raw pellets are dried and consolidated by microwaves at 550°C, and dried and consolidated pellets are obtained when the moisture content is lower than 0.1wt%.

[0095] Example 10

[0096] The raw materials for pelletizing are iron ore powder, calcium hydroxide, carbon powder, iron powder and water, and green pellets with an average particle size of 8.5 mm and a water content of about 9.2 wt % are obtained.

[0097] The green pellets were dried to a moisture content of about 2.2 wt% using electric hot air at a temperature of 330°C (drying time was about 26 min). 3 The raw pellets are dried and consolidated by microwave at 520°C, and dried and consolidated pellets are obtained when the moisture content is lower than 0.1wt%.

[0098] Embodiment 11

[0099] The raw materials for pelletizing are iron ore powder, calcium hydroxide, carbon powder, iron powder and water, and green pellets with an average particle size of 8.4 mm and a water content of about 9.7 wt % are obtained.

[0100] The green pellets were dried to a moisture content of about 2.5 wt% using electric hot air at a temperature of 350°C (drying time was about 24 min). 3 The raw pellets are dried and consolidated by microwaves at 550°C, and dried and consolidated pellets are obtained when the moisture content is lower than 0.1wt%.

[0101] Example 12

[0102] The raw materials for pelletizing are iron ore powder, calcium hydroxide, carbon powder, iron powder and water, and green pellets with an average particle size of 8.7 mm and a water content of about 9.9 wt % are obtained.

[0103] The green pellets were dried to a moisture content of about 3.5 wt% using electric hot air at a temperature of 330°C (drying time was about 16 min). 3 The raw pellets are dried and consolidated by microwaves at 550°C, and dried and consolidated pellets are obtained when the moisture content is lower than 0.1wt%.

[0104] Embodiment 13

[0105] The raw materials for pelletizing are iron ore powder, calcium hydroxide, carbon powder, iron powder and water, and green pellets with an average particle size of 8.8 mm and a water content of about 9.4 wt % are obtained.

[0106] The green pellets were dried to a moisture content of about 4.5 wt% using electric hot air at a temperature of 330°C (drying time was about 11 min). 3 The raw pellets are dried and consolidated by microwaves at 550°C, and dried and consolidated pellets are obtained when the moisture content is lower than 0.1wt%.

[0107] Embodiment 14

[0108] The raw materials for pelletizing are iron ore powder, calcium hydroxide, carbon powder, iron powder and water, and green pellets with an average particle size of 9.0 mm and a water content of about 10.2 wt % are obtained.

[0109] The green pellets were dried to a moisture content of about 1.2 wt% using electric hot air at a temperature of 330°C (drying time was about 44 min). 3 The raw pellets are dried and consolidated by microwaves at 450°C, and dried and consolidated pellets are obtained when the moisture content is lower than 0.1wt%.

[0110] Embodiment 15

[0111] The raw materials for pelletizing are iron ore powder, calcium hydroxide, carbon powder, iron powder and water, and green pellets with an average particle size of 9.3 mm and a water content of about 11.1 wt % are obtained.

[0112] The green pellets were dried to a moisture content of about 1.5 wt% using electric hot air at a temperature of 330°C (drying time was about 41 min). 3 The raw pellets are dried and consolidated by microwaves at 450°C, and dried and consolidated pellets are obtained when the moisture content is lower than 0.1wt%.

[0113] Example 16

[0114] The raw materials for pelletizing are iron ore powder, calcium hydroxide, carbon powder, iron powder and water, and green pellets with an average particle size of 9.7 mm and a water content of about 11.5 wt % are obtained.

[0115] The green pellets were dried to a moisture content of about 1.2 wt% using electric hot air at a temperature of 330°C (drying time was about 46 min). 3The raw pellets are dried and consolidated by microwaves at 600°C, and dried and consolidated pellets are obtained when the moisture content is lower than 0.1wt%.

[0116] Comparative Example 1

[0117] Example 2 was repeated, except that only electric hot air at a temperature of 330° C. was used to dry the green pellets until the moisture content was approximately less than 0.1 wt % (drying time exceeded 120 min) to obtain dried consolidated pellets.

[0118] Comparative Example 2

[0119] Example 2 was repeated, except that the green pellets were first dried using electric hot air at a temperature of 330° C. to a moisture content of about 1.2 wt % (drying time was about 47 min). Then, the green pellets were dried using electric hot air at a temperature of 550° C. to a moisture content of less than 0.1 wt % to obtain dried consolidated pellets.

[0120] Comparative Example 3

[0121] Repeat Example 2, except that the power density is 20 kW / m 3 The raw pellets are dried and consolidated by microwaves at 550°C until the moisture content is less than 0.1 wt% to obtain dried consolidated pellets.

[0122] Comparative Example 4

[0123] Repeat Example 2, except that the power density is 15kw / m 3 The raw pellets were dried at 330°C with microwaves to a moisture content of about 1.2 wt% (drying time was about 17 min). 3 The raw pellets are dried and consolidated by microwaves at 550°C, and dried and consolidated pellets are obtained when the moisture content is lower than 0.1wt%.

[0124] Comparative Example 5

[0125] Repeat Example 2, except that the power density is 15kw / m 3 The raw pellets were dried by microwave at 330°C to a moisture content of about 1.2 wt% (drying time was about 15 min). Then, the raw pellets were dried and consolidated by electric hot air at 550°C until the moisture content was less than 0.1 wt%, and dried and consolidated pellets were obtained.

[0126] Comparative Example 6

[0127] Repeat Example 2 except that the power density is 20 kW / m 3The raw pellets are dried by microwave at 550°C to a moisture content of about 1.2wt% (drying time is about 10 minutes). Then, the raw pellets are dried and consolidated by electric hot air at 330°C until the moisture content is less than 0.1wt% (drying time is more than 120 minutes).

[0128] Comparative Example 7

[0129] Example 2 was repeated except that the green pellets were dried to a moisture content of about 1.2 wt% using electric hot air at a temperature of 330°C (drying time was about 48 min). 3 The raw pellets are dried and consolidated by microwaves at 330°C, and dried and consolidated pellets are obtained when the moisture content is lower than 0.1wt%.

[0130] Comparative Example 8

[0131] Example 2 was repeated except that the green pellets were dried to a moisture content of about 1.2 wt% using electric hot air at a temperature of 330°C (drying time was about 50 min). 3 The raw pellets are dried and consolidated by microwave at 300°C, and dried and consolidated pellets are obtained when the moisture content is lower than 0.1wt%.

[0132] Comparative Example 9

[0133] Repeat Example 2, except that the green pellets are dried to a moisture content of about 4.8 wt% using electric hot air at a temperature of 330°C (drying time is about 20 min). 3 The raw pellets are dried and consolidated by microwaves at 550°C, and dried and consolidated pellets are obtained when the moisture content is lower than 0.1wt%.

[0134] Comparative Example 10

[0135] Example 2 was repeated except that the green pellets were dried to a moisture content of about 5.5 wt% using electric hot air at a temperature of 330°C (drying time was about 17 min). 3 The raw pellets are dried and consolidated by microwaves at 550°C, and dried and consolidated pellets are obtained when the moisture content is lower than 0.1wt%.

[0136] Comparative Example 11

[0137] Example 2 was repeated except that the green pellets were dried to a moisture content of about 0.4 wt% using electric hot air at a temperature of 330°C (drying time was about 110 min).3 The raw pellets are dried and consolidated by microwaves at 550°C, and dried and consolidated pellets are obtained when the moisture content is lower than 0.1wt%.

[0138] Comparative Example 12

[0139] Example 2 was repeated except that the green pellets were dried to a moisture content of about 0.4 wt% using electric hot air at a temperature of 650°C (drying time was about 50 min). 3 The raw pellets are dried and consolidated by microwaves at 550°C, and dried and consolidated pellets are obtained when the moisture content is lower than 0.1wt%.

[0140] The performance tests were carried out on the dried consolidated pellets prepared in Examples 1-16 and Comparative Examples 1-12, and the results are shown in the following table:

[0141]

[0142]

[0143] In the present invention, it can be seen from Examples 1-16 that the dried and consolidated pellets obtained by reasonably controlling the moisture content of the pellets after hot air drying and coupling microwaves to continue drying and consolidation meet the quality requirements of the dried pellets required for low-temperature reduction roasting. Figure 2 As shown, the high-water pelletizer relies on the action of capillary force to make the particles stick together. After electric heating and drying, most of the capillary water evaporates, leaving only contact capillary water that is connected to each other at the contact points of the particles, increasing the bonding force. After further microwave heating and drying, the contact capillary water disappears and at the same time, the particles are forced to move closer. With the help of molecular forces, the bonding force between the particles continues to increase. At the same time, with the help of the overall heating effect of microwaves, the thermal motion of the particle molecules is more intense, making the pellets denser and playing a role in consolidating the pellets.

[0144] In the present invention, it can be seen from Examples 5 and 6 that when the green pellets of the present invention do not contain carbon powder or metal iron powder as micro-area hot spot welding agents, the pellets lack the micro-area hot spot welding agents to absorb microwaves and quickly heat up, resulting in local high-temperature liquid phase consolidation, which reduces the strength of the dried and consolidated pellets. However, the quality requirements for direct reduction roasting in the furnace are still met.

[0145] In the present invention, it can be seen from Comparative Examples 1 and 2 that, since only hot air heating and drying are used, the heat is slowly conducted from the outside to the inside, and the moisture inside and outside the pellets is heated unevenly, resulting in a difference in quality inside and outside the pellets, and the quality of the pellets is poor. In addition, the subsequent drying efficiency of the residual moisture inside the pellets is low, which is time-consuming and energy-consuming.

[0146] In the present invention, it can be seen from Comparative Examples 3 and 4 that since only microwave heating and drying are used, because water is a highly polar molecule and can quickly convert microwave energy into internal energy, the water in the pellets heats up quickly as a whole, and the water migrates and evaporates quickly. As a result, the capillaries fail to shrink, and the capillary force and the contact capillary force are reduced, resulting in weak bonding between particles and poor strength of the obtained dried consolidated pellets.

[0147] In the present invention, it can be seen from Comparative Examples 7 and 8 that although hot air is used to dry the raw pellets to a low moisture content (below 4.5%) in the early stage, due to the low temperature of the subsequent microwave heating and drying and the low microwave power density, the microwaves still mainly act on the rapid migration and evaporation of moisture, resulting in the failure of the capillary to shrink, the capillary force and the contact capillary force to decrease, resulting in weak adhesion between particles, and further resulting in poor strength of the dried and consolidated pellets.

[0148] In the present invention, it can be seen from Comparative Examples 9 and 10 that the moisture content of the pellets is still high (more than 4.5%) after hot air drying, resulting in a small increase in the strength of the pellets after short-term microwave heating and drying. Therefore, although the pellets with high moisture content are further subjected to microwave heating and drying, the fall and compressive strength of the obtained dried and consolidated pellets are significantly improved, but still do not meet the quality requirements for direct reduction roasting in the furnace.

[0149] In the present invention, it can be seen from Comparative Examples 11 and 12 that when the electric heating drying time is prolonged or the temperature is too high, the moisture content of the pellets is dried to below 0.5%, and then the pellets are dried and consolidated by microwave heating, but the quality of the pellets is reduced. Therefore, in the initial stage of microwave heating drying and consolidation, the presence of contact capillary water in the pellets is necessary, and the moisture content of the pellets after hot air heating drying should be strictly controlled.

Claims

1. A drying and consolidation method for roasting pellets, characterized in that: The method comprises the following steps: 1) pelletizing with a pelletizing material, a binder, with or without a welding agent, and water as pelletizing raw materials to obtain green pellets, wherein the pelletizing material is iron-containing ore powder; 2) Drying the green pellets to a low moisture content by hot air; the temperature of the hot air is 100-500°C; drying the green pellets to a low moisture content is drying the green pellets to a moisture content of 0.5-3%; 3) Using microwaves to dry and consolidate the green pellets with low moisture content to obtain dry consolidated pellets; the temperature of using microwaves for drying and consolidation is 400-800°C.

2. The drying and consolidation method according to claim 1, characterized in that: In step 1), the pelletizing ore material also includes metallurgical and municipal solid waste, and the metallurgical and municipal solid waste is one or more of vanadium extraction tailings, zinc-containing dust, steel slag, garbage fly ash, and organic solid waste.

3. The drying and consolidation method according to claim 1 or 2, characterized in that: In step 1), the binder is an organic binder and / or an inorganic binder; and / or The welding agent is one or both of carbon powder and iron powder.

4. The drying and consolidation method according to claim 3, characterized in that: The binder is one or more of calcium hydroxide, sodium humate, ammonium humate and potassium humate.

5. The drying and consolidation method according to any one of claims 1 to 2 and 4, characterized in that: The amount of the binder is 0.5-30% of the total mass of the pelletizing raw materials; and / or The amount of the welding agent used is 0.5-5% of the total mass of the pelletizing raw materials.

6. The drying and consolidation method according to claim 3, characterized in that: The amount of the binder is 0.5-30% of the total mass of the pelletizing raw materials; and / or The amount of the welding agent used is 0.5-5% of the total mass of the pelletizing raw materials.

7. The drying and consolidation method according to claim 5, characterized in that: The amount of the binder is 1-25% of the total mass of the pelletizing raw materials; and / or The amount of the welding agent used is 0.8-4.5% of the total mass of the pelletizing raw materials.

8. The drying and consolidation method according to claim 6, characterized in that: The amount of the binder is 1-25% of the total mass of the pelletizing raw materials; and / or The amount of the welding agent used is 0.8-4.5% of the total mass of the pelletizing raw materials.

9. The drying and consolidation method according to claim 7 or 8, characterized in that: The amount of the binder is 2-20% of the total mass of the pelletizing raw materials; and / or The amount of the welding agent used is 1-4% of the total mass of the pelletizing raw materials.

10. The drying and consolidation method according to any one of claims 1-2, 4, 6-8, characterized in that: In step 2), the temperature of the hot air is 150-400°C; and / or The step of drying the green pellets to a low moisture content is drying the green pellets to a moisture content of 1-2%.

11. The drying and consolidation method according to claim 10, characterized in that: The temperature of the hot air is 200-300° C.; the hot air is electrically heated hot air and / or hot waste gas from a steel plant process.

12. The drying and consolidation method according to any one of claims 1-2, 4, 6-8, and 11, characterized in that: In step 3), the temperature of drying and consolidating by microwave is 450-700°C; the power density of drying and consolidating by microwave is 10-50kw / m 3 .

13. The drying and consolidation method according to claim 12, characterized in that: The temperature for drying and consolidation by microwave is 500-600℃; the power density for drying and consolidation by microwave is 15-40kw / m 3 .

14. The drying and consolidation method according to claim 13, characterized in that: The power density of microwave drying and consolidation is 18-30kw / m 3 .

15. The drying and consolidation method according to any one of claims 1-2, 4, 6-8, 11, 13-14, characterized in that: The particle size of the green pellets is 2-15 mm.

16. The drying and consolidation method according to claim 15, characterized in that: The particle size of the green pellets is 2.5-12 mm.

17. The drying and consolidation method according to claim 16, characterized in that: The particle size of the green pellets is 3-8 mm.

18. The drying and consolidation method according to any one of claims 1-2, 4, 6-8, 11, 13-14, 16-17, characterized in that: The average particle size of the pelletizing raw material is not greater than 80 μm; The moisture content of the green pellets is not less than 5wt%.

19. The drying and consolidation method according to claim 18, characterized in that: The average particle size of the pelletizing raw material is not greater than 75 μm; The moisture content of the green pellets is not less than 8wt%.

20. The drying and consolidation method according to claim 19, characterized in that: The average particle size of the pelletizing raw material is not greater than 70 μm; The moisture content of the green pellets is not less than 10wt%.

21. The drying and consolidation method according to any one of claims 1-2, 4, 6-8, 11, 13-14, 16-17, 19-20, characterized in that: The drop strength of the dried consolidated pellets is 3-15 times / 0.5m; and / or The compressive strength of the dried consolidated pellets is 180-400N / P.

22. The drying and consolidation method according to claim 21, characterized in that: The drop strength of the dried consolidated pellets is 6-12 times / 0.5m; and / or The compressive strength of the dried consolidated pellets is 200-350N / P.

23. The drying and consolidation method according to any one of claims 1-2, 4, 6-8, 11, 13-14, 16-17, 19-20, and 22, characterized in that: A drying and consolidation system is used for treatment, the drying and consolidation system comprising a pelletizing device (1), a hot air drying device (2) and a microwave drying and consolidation device (3); the pelletizing raw material adding device (4) is connected to the feed port of the pelletizing device (1), the discharge port of the pelletizing device (1) is connected to the feed port of the hot air drying device (2) via a raw pellet conveying device (5); the discharge port of the hot air drying device (2) is connected to the feed port of the microwave drying and consolidation device (3); and the discharge port of the microwave drying and consolidation device (3) is connected to a drying and consolidation pellet conveying device (6).

24. The drying and consolidation method according to claim 23, characterized in that: The hot air drying device (2) is provided with a hot air inlet duct (201) and a hot air exhaust duct (202); a blower (203) is provided on the hot air inlet duct (201) and / or an exhaust fan (204) is provided on the hot air exhaust duct (202); and / or The system also includes a reduction roasting device (7); a feed inlet of the reduction roasting device (7) is connected to the drying and consolidation pellet conveying device (6).

25. A dry consolidation pellet, characterized in that: The dry consolidated pellets are prepared by the dry consolidation method according to any one of claims 1 to 24.

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