Low-temperature rapid calcination process of high-activity magnesium oxide

Abstract

The invention relates to a low-temperature rapid calcination process of high-activity magnesium oxide, and belongs to the technical field of calcination processes, the low-temperature rapid calcination process comprises the following steps: S1, raw material pretreatment: sequentially carrying out coarse crushing, fine grinding and magnetic separation iron removal pretreatment on raw ore; s2, neutral oxygen-controlled first-stage roasting: feeding the pretreated powder into a suspension roasting furnace through a pneumatic conveying system, introducing oxygen-limited mixed gas, staying at 620 + / -10 DEG C for 7 + / -0.5 minutes, and carrying out partial decomposition; s3, carrying out self-reduction second-stage roasting; and S4, deep iron removal and quenching. According to the method, the problems that MgO crystals are coarsened and the specific surface area is smaller than 30 m < 2 > / g due to the fact that high-temperature calcination is needed for several hours at the temperature of 800-1000 DEG C in a traditional calcination process are solved, and according to the scheme, through segmented calcination at the low temperature of 620 DEG C and the total duration is smaller than or equal to 15 min, the energy consumption is reduced, meanwhile, a porous intermediate phase is formed through limited oxygen decomposition, crystal growth is effectively inhibited, and the specific surface area is effectively increased; the problem of impurity removal of the low-grade ore is solved, and the low-grade ore with Fe2O3 larger than 1.5% is subjected to circulating reduction iron removal through self-produced gas.

Description

Technical Field

[0001] This invention relates to the field of calcination technology, and in particular to a low-temperature rapid calcination process for highly active magnesium oxide. Background Technology

[0002] High-activity magnesium oxide refers to magnesium oxide with high specific surface area, porous structure, small grain size, and strong chemical reactivity. Low-temperature rapid calcination is an energy-saving process that avoids excessive growth of MgO crystals by controlling temperature and time. Its core is low temperature and short time. Compared with traditional processes, it can significantly improve activity and reduce energy consumption. The essence of high-activity magnesium oxide is to retain the amorphous structure and enhance surface reactivity by inhibiting crystal growth. Both of these factors work together to promote the high-value utilization of magnesite resources. It is especially suitable for processing low-grade ore or powder that is discarded by traditional processes, and it has both economic and environmental benefits.

[0003] Traditional calcination requires high temperatures of 800–1000℃, which is energy-intensive and leads to excessive growth of MgO crystals, resulting in a specific surface area of ​​<30m². 2 Magnesium oxide with low activity and CAA > 25s, and low-grade or fine ore cannot be directly utilized due to high iron impurities (Fe2O3 > 1.5%), requires additional reducing agents to remove iron before magnetic separation, increasing costs. The existing hydration-secondary calcination method has a process time of up to 4 hours and low efficiency. Suspension roasting still has a temperature > 750℃, with limited improvement in activity. To address this, a low-temperature rapid calcination process for highly active magnesium oxide is proposed. This process replaces the traditional high-temperature long-time calcination at 800-1000℃ with a 620℃ low-temperature segmented oxygen-controlled roasting. While reducing energy consumption, it utilizes oxygen-limited decomposition to form a porous mesophase to inhibit crystal growth, effectively increasing the specific surface area and overcoming the industry bottleneck of crystal coarsening caused by high temperature. Through self-produced CO gas circulation reduction iron removal technology, the first stage roasting generates 6-8% CO concentration for the second stage fluidized bed directional reduction of iron impurities. Combined with 1.4T high-pressure magnetic separation, this reduces Fe2O3 residue and improves the utilization rate of low-grade ore. Summary of the Invention

[0004] This invention provides a low-temperature rapid calcination process for highly active magnesium oxide, which solves the problems of energy consumption and activity being mutually exclusive in the industrial production of highly active magnesium oxide, limited utilization of low-grade ore, and poor activity stability.

[0005] The solution of the present invention to solve the above-mentioned technical problems is as follows: a low-temperature rapid calcination process for highly active magnesium oxide, the process flow of which includes the following steps:

[0006] S1, raw material pretreatment, the raw ore is subjected to coarse crushing, fine grinding and magnetic separation to remove iron in sequence;

[0007] S2, neutral oxygen-controlled first-stage roasting: the pretreated powder is fed into the suspension roasting furnace via a pneumatic conveying system, and an oxygen-limited mixed gas is introduced and held at 620±10℃ for 7±0.5 minutes, during which partial decomposition occurs;

[0008] S3, self-reducing two-stage roasting, the hot material from the first stage is fed into the second stage fluidized bed reactor by a sealed screw feeder, CO mixed gas and N2 protective gas are injected, and the reaction is carried out at 470±10℃ for 5±0.5 minutes for reduction reaction. After the reaction is completed, the material is discharged and cooled to 200℃ by a water-cooled screw conveyor.

[0009] S4, deep iron removal and rapid cooling, after two-stage roasting and reduction, the material is separated into Fe3O4 by a high-pressure magnetic separator, the clean material enters a nitrogen-blown rapid cooling tower for cooling, the cooled finished product is packaged, and the active magnesium oxide is stored in the warehouse.

[0010] Based on the above technical solution, the present invention can be further improved as follows.

[0011] Furthermore, in step S1, during the coarse crushing stage, the magnesite ore is crushed to ≤20mm by a jaw crusher. During the fine grinding stage, a vertical roller mill is used to grind the ore to a particle size D90≤0.074mm, 200 mesh. During the magnetic separation and iron removal stage, a permanent magnet drum separator is used for pre-removal of iron. The magnetic field strength of the permanent magnet drum separator is 0.8T, which makes Fe2O3≤1.2%, creating a raw material basis for low-temperature reduction. The quantitative matching of fine grinding particle size and magnetic field strength increases the utilization rate of traditional waste Fe2O3>1% ore powder from 40% to 95%, and avoids energy waste caused by over-grinding.

[0012] Furthermore, in step S2, the partial decomposition reaction is: MgCO3 → MgO·0.3MgCO3 (porous mesophase) + CO↑. The flue gas is treated by a cyclone separator to collect dust, and the gas then enters the CO enrichment system, achieving material recycling. The nanopores (50-100 nm) of the mesophase MgO·0.3MgCO3 result in a high specific surface area (>80 m²). 2 / g) provides support; the self-produced CO concentration reaches 6-8%, eliminating the cost of purchased reducing agents, and the gas utilization rate is >90%.

[0013] Furthermore, in step S2, the suspension roasting furnace is equipped with an oxygen concentration sensor to monitor the O2 concentration in real time, and the suspension roasting furnace is equipped with a temperature-oxygen concentration coordinated control module. The control target is to maintain the decomposition temperature at 620±5℃ and the O2 concentration at 6±0.2%. The oxygen-limited environment inhibits the complete growth of MgO crystals, and the temperature fluctuation is <±0.5% to avoid over-decomposition of the mesophase. The fluctuation of the product CAA value is reduced from ±5s to ±0.8s.

[0014] Furthermore, in step S3, the concentration of the CO mixture is 6-8%, which is produced by the first-stage roasting. The fluidized bed reactor is equipped with a CO concentration monitor to monitor the concentration of the CO mixture. The second-stage fluidized bed reactor is equipped with a reduction time adaptive control module. The control objective is to dynamically adjust the reaction time according to the Fe2O3 content of the raw material. The adaptive algorithm optimizes the reaction time of high-impurity ore (Fe2O3 = 1.5%) to 5.6 minutes, which reduces iron residue by 60% and energy consumption by 15% compared with the fixed-time process.

[0015] Furthermore, in step S4, the magnetic separation tailings separated by the high-pressure magnetic separator are discarded, the jet quench tower cools the material to 80°C at a rate of ≥100°C / s, and it is packaged by the micro powder packaging machine. The nitrogen quench tower forces a cooling rate of ≥100°C / s, and the water-cooled spiral pre-cools the material to 200°C to achieve a final temperature control of 80°C. The magnetic separation tailings (Fe2O3>20%) are directly discarded.

[0016] The beneficial effects of this invention are: This invention provides a low-temperature rapid calcination process for highly active magnesium oxide, which has the following advantages:

[0017] 1. This solves the problem that traditional calcination processes require high-temperature calcination at 800-1000℃ for several hours, leading to coarsening of MgO crystals and a specific surface area of ​​<30m². 2 Regarding the issue of / g, this solution employs a low-temperature segmented calcination process at 620℃, with a total duration of ≤15 minutes. This reduces energy consumption while utilizing oxygen-limited decomposition to form a porous mesophase, effectively inhibiting crystal growth and increasing the specific surface area.

[0018] 2. Solved the problem of removing impurities from low-grade ores. For low-grade ores with Fe2O3 > 1.5%, a self-produced gas circulation reduction method is used to remove iron. The first stage of roasting produces 6-8% CO gas, while traditional processes require purchasing reducing agents. Directional reduction is achieved in the second stage fluidized bed: 3Fe2O3 + CO → 2Fe3O4. Combined with 1.4T high-pressure magnetic separation, the Fe2O3 residue is ≤ 0.25%, breaking through the application limitations of low-grade ores.

[0019] 3. This solution solves the problem of low cooling rate and inability to lock amorphous structure in traditional quenching processes. It adopts a nitrogen vortex jet quenching tower to stabilize the product CAA value at 10-13 seconds, which effectively improves the cooling efficiency.

[0020] 4. Set up an energy-material synergistic cycle system, where the CO from the first stage flue gas is directly used for the second stage reduction, reducing external energy input, and the waste heat is used for raw material drying, which can effectively reduce energy consumption;

[0021] 5. The system features a dual closed-loop intelligent control design with coordinated temperature and oxygen concentration control to prevent over-decomposition from causing pore collapse. It also incorporates an adaptive reduction time algorithm to dynamically optimize reaction time and address fluctuations in ore composition.

[0022] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it according to the contents of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings. Specific embodiments of the present invention are given in detail below with reference to the accompanying drawings. Attached Figure Description

[0023] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, illustrate exemplary embodiments of the invention and, together with their description, serve to explain the invention and do not constitute an undue limitation thereof. In the drawings:

[0024] Figure 1 This is a system architecture diagram of a low-temperature rapid calcination process for highly active magnesium oxide provided in an embodiment of the present invention;

[0025] Figure 2 This is a process flow diagram of a low-temperature rapid calcination process for highly active magnesium oxide provided in an embodiment of the present invention. Detailed Implementation

[0026] The following is in conjunction with the appendix Figure 1-2 The principles and features of the present invention are described below. The examples given are for illustrative purposes only and are not intended to limit the scope of the invention. The invention is described more specifically in the following paragraphs by way of example with reference to the accompanying drawings. The advantages and features of the invention will become clearer from the following description. It should be noted that the drawings are in a very simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of the invention.

[0027] It should be noted that when a component is described as "fixed to" another component, it can be directly on the other component or may have a component in between. When a component is considered "connected to" another component, it can be directly connected to the other component or may have a component in between. When a component is considered "set on" another component, it can be directly set on the other component or may have a component in between. The terms "vertical," "horizontal," "left," "right," and similar expressions used in this document are for illustrative purposes only.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0029] like Figure 1-2As shown, this invention provides a low-temperature rapid calcination process for highly active magnesium oxide, the process flow of which includes the following steps:

[0030] S1, raw material pretreatment, the raw ore is subjected to coarse crushing, fine grinding and magnetic separation to remove iron in sequence;

[0031] In the coarse crushing stage, the magnesite ore (MgCO3≥70%) is crushed to ≤20mm by a jaw crusher. In the fine grinding stage, a vertical roller mill is used to grind the ore to a particle size D90≤0.074mm (200 mesh). In the magnetic separation and iron removal stage, a permanent magnet drum separator (magnetic field strength 0.8T) is used to pre-remove iron, so that Fe2O3≤1.2%.

[0032] S2, neutral oxygen-controlled first-stage roasting: the pretreated powder is fed into the suspension roasting furnace via a pneumatic conveying system, and an oxygen-limited mixed gas is introduced and held at 620±10℃ for 7±0.5 minutes, during which partial decomposition occurs;

[0033] Reaction formula: MgCO3 → MgO·0.3MgCO3 (porous mesophase) + CO↑;

[0034] Dust is collected by a cyclone separator (for reuse) in the flue gas, and the gas then enters the CO enrichment system.

[0035] The suspension roasting furnace is equipped with an oxygen concentration sensor to monitor the O2 concentration in real time.

[0036] The suspension roasting furnace is equipped with a temperature-oxygen concentration coordinated control module, with the control target being to maintain the decomposition temperature at 620±5℃ and the O2 concentration at 6±0.2%.

[0037] PID feedforward-feedback control

[0038] def control_oxygen_temp(current_temp,current_O2,set_temp=620,set_O2=6):

[0039] #PID parameters (set according to furnace type)

[0040] Kp_temp,Ki_temp,Kd_temp=1.2,0.05,0.3

[0041] Kp_O2,Ki_O2,Kd_O2=0.8,0.01,0.2

[0042] #Temperature control (adjusting the opening degree of the natural gas valve)

[0043] temp_error=set_temp-current_temp

[0044] gas_valve=Kp_temp*temp_error+Ki_temp*integral(temp_error)+Kd_temp*derivative(temp_error)

[0045] #Oxygen concentration control (adjusting N2 dilution gas flow rate)

[0046] O2_error = set_O2 - current_O2

[0047] N2_flow=Kp_O2*O2_error+Ki_O2*integral(O2_error)+Kd_O2*derivative(O2_error)

[0048] return gas_valve, N2_flow;

[0049] S3, self-reducing two-stage roasting, the first stage hot material is fed into the second stage fluidized bed reactor through a sealed screw feeder, and a first stage self-produced CO mixed gas and N2 protective gas with a concentration of 6-8% are injected. The reduction reaction is carried out at 470±10℃ for 5±0.5 minutes. After the reaction is completed, the material is discharged and cooled to 200℃ by a water-cooled screw conveyor.

[0050] Reaction equation: 3Fe₂O₃ + CO → 2Fe₃O₄ + CO₂;

[0051] The fluidized bed reactor is equipped with a CO concentration monitor to monitor the concentration of the CO mixture.

[0052] The two-stage fluidized bed reactor is equipped with a reduction time adaptive control module, the control objective of which is to dynamically adjust the reaction time according to the Fe2O3 content of the raw material.

[0053] Algorithm formula:

[0054] t = t base +k·(C Fe -C base )

[0055] T base = 5 minutes (baseline time);

[0056] C base =1.0% (reference iron content);

[0057] k = 2.0 min / %.

[0058] Execution example:

[0059] If Fe2O3 = 1.3% is detected, then the reaction time t = 5 + 2.0 × (1.3 - 1.0) = 5.6 min;

[0060] S4, deep iron removal and rapid cooling, the reduced material is separated into Fe3O4 by a high-pressure magnetic separator (1.4T), the magnetic separation tailings (Fe2O3≤0.25%) are discarded, the clean material enters the nitrogen-blown rapid cooling tower, and is cooled to 80℃ at a rate of ≥100℃ / s. The finished product is packaged by a micro powder packaging machine, and the active magnesium oxide is put into storage.

[0061] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Content not described in detail in this specification is prior art known to those skilled in the art.

[0062] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Those skilled in the art can readily implement the present invention based on the accompanying drawings and the above description. However, any modifications, alterations, or variations made by those skilled in the art without departing from the scope of the present invention, utilizing the disclosed technical content, are equivalent embodiments of the present invention. Furthermore, any equivalent changes, alterations, or variations made to the above embodiments based on the essential technology of the present invention are still within the protection scope of the present invention.

Claims

1. A low-temperature rapid calcination process for highly active magnesium oxide, characterized in that, The process flow includes the following steps: S1, raw material pretreatment, the raw ore is subjected to coarse crushing, fine grinding and magnetic separation to remove iron in sequence; S2, neutral oxygen-controlled first-stage roasting: the pretreated powder is fed into the suspension roasting furnace via a pneumatic conveying system, and an oxygen-limited mixed gas is introduced and held at 620±10℃ for 7±0.5 minutes, during which partial decomposition occurs; S3, self-reducing two-stage roasting, the hot material from the first stage is fed into the second stage fluidized bed reactor by a sealed screw feeder, CO mixed gas and N2 protective gas are injected, and the reaction is carried out at 470±10℃ for 5±0.5 minutes for reduction reaction. After the reaction is completed, the material is discharged and cooled to 200℃ by a water-cooled screw conveyor. S4, deep iron removal and rapid cooling, after two-stage roasting and reduction, the material is separated into Fe3O4 by a high-pressure magnetic separator, the clean material enters a nitrogen-blown rapid cooling tower for cooling, the cooled finished product is packaged, and the active magnesium oxide is stored in the warehouse.

2. The low-temperature rapid calcination process for highly active magnesium oxide according to claim 1, characterized in that, In step S1, during the coarse crushing stage, the magnesite ore is crushed to ≤20mm by a jaw crusher. During the fine grinding stage, a vertical roller mill is used to grind the ore to a particle size D90≤0.074mm, 200 mesh. During the magnetic separation and iron removal stage, the ore is pre-removed by a permanent magnet drum separator with a magnetic field strength of 0.8T and Fe2O3≤1.2%.

3. The low-temperature rapid calcination process for highly active magnesium oxide according to claim 1, characterized in that, In step S2, the partial decomposition reaction is: MgCO3 → MgO·0.3MgCO3 + CO↑. The flue gas is separated into dust by a cyclone separator and the gas enters the CO enrichment system.

4. The low-temperature rapid calcination process for highly active magnesium oxide according to claim 1, characterized in that, In step S2, the suspension roasting furnace is equipped with an oxygen concentration sensor to monitor the O2 concentration in real time, and the suspension roasting furnace is equipped with a temperature-oxygen concentration coordinated control module. The control target is to maintain the decomposition temperature at 620±5℃ and the O2 concentration at 6±0.2%.

5. The low-temperature rapid calcination process for highly active magnesium oxide according to claim 1, characterized in that, In step S3, the concentration of the CO mixture is 6-8% produced by the first stage roasting. The fluidized bed reactor is equipped with a CO concentration monitor to monitor the concentration of the CO mixture. The second-stage fluidized bed reactor is equipped with a reduction time adaptive control module, and the control objective is to dynamically adjust the reaction time according to the Fe2O3 content of the raw material.

6. The low-temperature rapid calcination process for highly active magnesium oxide according to claim 1, characterized in that, In step S4, the magnetic separation tailings separated by the high-pressure magnetic separator are discarded, and the jet cooling tower cools the material to 80°C at a rate of ≥100°C / s, and then it is packaged by a micro powder packaging machine.

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