Method and equipment for preparing washing fly ash hollow microspheres based on electromagnetic kiln sintering

Abstract

The invention relates to a method and equipment for preparing washing fly ash hollow microspheres based on electromagnetic kiln sintering. The method comprises the following steps: batching and grinding washing fly ash; placing the ground material in an aging tank, and adding an adhesive and a foaming agent to obtain slurry for molding and drying; putting the aged slurry into an atomizer at the top of a spray forming tower for spray drying to form a hollow microsphere blank; and sending the hollow microbead blank into an electromagnetic kiln for firing, and cooling to obtain the hollow microbead. The electromagnetic kiln is used for replacing a high-pollution traditional rotary kiln, and the problems of smoke and energy consumption are solved. The electromagnetic kiln directly heats the green body, the heat efficiency is higher than 80%, and the comprehensive energy consumption is reduced by 50% compared with that of a traditional rotary kiln; the material loss rate is less than 3%, the flue gas amount is reduced by 70%, and the flue gas treatment cost is greatly reduced; the green body is sintered from outside to inside through induction heating, the temperature uniformity is + / -5 DEG C, and the problem of microbead breakage caused by temperature fluctuation of a traditional rotary kiln is solved.

Description

TECHNICAL FIELD

[0001] The present application relates to solid waste resource utilization, hazardous waste recycling new materials, inorganic non-metallic material preparation, in particular to the technical field of fly ash resource preparation of light hollow microbeads. BACKGROUND

[0002] Fly ash is a product of municipal solid waste incineration, which belongs to hazardous waste (HW18). The particle size is generally between 1-150 μm, the porosity is high, and it is easy to adsorb pollutants. Fly ash contains heavy metals, carcinogenic dioxins and soluble chlorides and other harmful substances. The leaching of heavy metals pollutes the surrounding soil and groundwater, directly threatening people's health. At present, the disposal of fly ash is faced with the problems of large inventory, secondary pollution and low resource utilization rate. Municipal solid waste incineration fly ash contains heavy metals, chlorides and other pollutants. The resource utilization of fly ash first needs to be pretreated (such as water washing) to reduce its toxicity.

[0003] Hollow microbeads are a kind of small-sized hollow inorganic non-metallic materials with particle size ranging from 20 to 200 μm. They have superior performance in mechanical, physical, chemical and electrical insulation, and are widely used in building materials, mechanical manufacturing, chemical industry, aviation and military fields.

[0004] Combined with the chemical composition characteristics of fly ash, a new material of hollow microbeads with low cost, light weight, heat insulation and good adsorption performance can be developed, and rotary kiln sintering is one of the traditional technologies.

[0005] The existing rotary kiln (natural gas) sintered fly ash microbeads have the following fundamental defects: (1) High sintering energy consumption (>1300℃), natural gas kiln relies on fuel combustion and air convection heat transfer, and high-temperature flue gas carries away most of the heat, with low thermal efficiency (<40%); (2) Forced ventilation, the wind speed in the kiln is large, and the bulk density of hollow microbead blank is only 0.6-0.7 g / cm3, which leads to the loss of micro-fine particles carried away by flue gas (material loss rate >20%); (3) Large amount of flue gas, the cost of tail gas treatment accounts for more than 30% of the total cost; (4) Large wind speed in the kiln, material turbulence leads to collision and breakage; in addition, the temperature uniformity is poor, and the hollow structure of the finished product is not complete (the finished product rate is <70%).

[0006] (5) Uncontrolled pollution: traditional kiln has slow heating, and dioxin is easy to be synthesized again in the low temperature zone of the kiln tail (200-300℃ temperature zone). SUMMARY

[0007] The technical problem to be solved by the present application is to introduce the electromagnetic kiln sintering technology into the preparation of water-washed fly ash hollow microbeads, and to realize energy saving, environmental protection and high finished product rate.

[0008] The technical scheme for solving the above technical problems is as follows: A method for preparing water-washed fly ash hollow microbeads based on an electromagnetic kiln sintering process, comprising the following steps: S1, water-washed fly ash batching and grinding; S2, placing the ground slurry into an aging tank, and adding a binder and a foaming agent to obtain a slurry for molding and drying; S3, placing the aged slurry into an atomizer at the top of a spray molding tower for atomization and drying to form a hollow microbead blank; S4, placing the hollow microbead blank into an electromagnetic kiln for sintering, and obtaining a hollow microbead after cooling.

[0009] The beneficial effects of the present application are: the electromagnetic kiln replaces the high-pollution traditional rotary kiln, solving the problems of flue gas and energy consumption. The electromagnetic kiln directly heats the blank: the thermal efficiency is > 80%, the comprehensive energy consumption is reduced by 50% compared with the traditional rotary kiln; no forced ventilation is required: the material loss rate is < 3%, the flue gas volume is reduced by 70%, and the flue gas treatment cost is greatly reduced; induction heating realizes sintering of the blank from the surface to the inside, the temperature uniformity is ± 5℃, and the problem of microbead rupture caused by temperature fluctuation in the traditional rotary kiln is solved: the microbead yield is > 90%.

[0010] On the basis of the above technical scheme, the present application can also be improved as follows.

[0011] Further, in the step S1: The specific method for batching is: the water-washed fly ash is punched into a buffer bin by a screw conveyor, process water is pumped into a batching tank, the stirring system in the batching tank is started, the water-washed fly ash in the buffer bin is unloaded into the batching tank through a discharge valve, and continuous stirring is performed for 30-50 min to obtain a slurry.

[0012] The beneficial effects of the above further scheme are that a suspension is formed by continuous stirring, the fly ash particles are uniformly distributed in the liquid, and the consistency of the slurry is ensured, thereby avoiding uneven concentration when discharging due to sedimentation.

[0013] Further, in the step S1: The specific method for grinding is: the slurry is pumped from the batching tank into a grinding tank by a diaphragm pump, and then pumped into a grinding machine from the grinding tank by a diaphragm pump, the fly ash particle size distribution is tested by a laser particle size analyzer after grinding for 2-3 h, and the average particle size reaches D50≤5μm.

[0014] The beneficial effects of the above further scheme are that the fineness of D50≤5μm has reached the particle size requirements of many mineral admixtures or fillers in the field of building materials. This makes the treated fly ash can be used as a high-activity admixture in hollow microbeads, not only realizing waste resource utilization, but also improving certain performance of the product.

[0015] Further, the slurry ratio is 1:1-1:5 of washed fly ash: process water.

[0016] The beneficial effect of the above further scheme is to provide a selection space for fly ash with different characteristics, which can meet the washing requirements and ensure that the slurry has good pumpability and stirrability.

[0017] Further, in the step S2: The specific method of aging is: pumping the ground qualified slurry into the aging tank through the diaphragm pump, adding adhesive and foaming agent, continuously stirring and aging for 6-9h, adjusting the viscosity to 400-900CP, and obtaining the slurry for forming and drying.

[0018] The beneficial effect of the above further scheme is to ensure that the added adhesive and foaming agent are absolutely uniformly distributed in the slurry, avoiding performance defects of the final product due to uneven mixing.

[0019] Further, the material ratio in the step S2 is 150-200 parts of slurry, 10-30 parts of adhesive, and 5-15 parts of foaming agent. The adhesive is liquid, and is any one of polyvinyl alcohol, carboxymethyl cellulose, and polyvinyl formal adhesive, with a solid content of 1-5%; The foaming agent is liquid, and is any one of sodium dodecyl sulfate, cetyltrimethylammonium bromide, and calcium carbonate, with a solid content of 15-30%.

[0020] The beneficial effect of the above further scheme is that the amount of adhesive is sufficient to form an effective bonding network between particles, providing the necessary mechanical strength to prevent the product from loosening. The amount of foaming agent introduces an appropriate amount of pores on the basis of the bonding skeleton, significantly reducing the bulk density of the material and achieving lightweight. This proportion range ensures that the material will not collapse in strength due to too much foaming agent, nor become dense and heavy due to too much adhesive.

[0021] Further, the stirring speed is 30-40r / min.

[0022] The beneficial effect of the above further scheme is that low-speed stirring can avoid large bubbles being cut into uneven small bubbles, and also prevent small bubbles from colliding and merging into large bubbles, thereby obtaining a fine and uniform pore structure.

[0023] Further, in the step S3: The aged slurry is continuously pumped into the atomizer at the top of the spray forming tower by a diaphragm pump, and the slurry is atomized into microdroplets by the high-speed rotating centrifugal force of the atomizer, and is fully contacted with the high-temperature flue gas introduced from the top of the tower to form a hollow microsphere blank with a water content of less than 5%, and the hollow microsphere blank is naturally settled to the bottom of the tower and collected, and the tail gas is discharged from the middle of the tower cone and discharged into the atmosphere after flue gas purification treatment. The temperature of the high-temperature flue gas introduced from the top of the spray forming tower is 300-350℃, and the temperature of the tail gas discharged from the middle of the tower cone is 90-150℃. The rotating speed of the atomizer is controlled within 6000-12000r / min.

[0024] The beneficial effect of the above further scheme is that the microdroplets generated by the atomizer will naturally form perfect spherical shape under the action of surface tension. After drying, this spherical shape is retained, and the product obtained is a spherical powder with uniform particle size and excellent flowability.

[0025] Further, in the step S4: The hollow microsphere blank is sent into the electromagnetic kiln by a belt conveyor and / or a bucket elevator for sintering, so that the blank material moves to the kiln head under the action of the slope and rotation of the kiln body, and the hollow microsphere product falls into the air cooler from the kiln head, and the qualified hollow microsphere product is obtained after cooling; The technical parameters of the electromagnetic kiln include: sintering temperature: 1000-1200℃, holding time: 30-90min; The electromagnetic parameters: using medium frequency induction heating with a frequency of 1-10kHz, the eddy current is generated in the blank by the alternating magnetic field to heat, and the power density is 50-200kW / m³; Atmosphere: the kiln head gas pressure is -1Pa or the weak reducing atmosphere with CO concentration <5%; The rotating speed of the electromagnetic kiln: 2-4r / min.

[0026] The beneficial effect of the above further scheme is that compared with the traditional natural gas rotary kiln process, the green electricity ratio of the electromagnetic kiln is >80%, the emission reduction amount jumps to 0.18-0.22 tons of CO2 per ton of microsphere, and the reduction is 70-85%.

[0027] An equipment for preparing water-washed fly ash hollow microspheres based on electromagnetic kiln sintering, characterized by comprising a feeding system, an electromagnetic kiln and a PLC control system; The electromagnetic kiln is inclined and rotatingly arranged, and the inlet end is higher than the outlet end; the feeding system is connected to the inlet end of the electromagnetic kiln, and the inductive coil is wound around the side of the electromagnetic kiln; the PLC control system is electrically connected with the feeding system, the electromagnetic kiln and the inductive coil; The hollow microsphere blank enters the electromagnetic kiln through the feeding system and moves along the inclined surface to the outlet end of the electromagnetic kiln along with the rotation of the electromagnetic kiln.

[0028] The beneficial effects of the present application are: the traditional natural gas rotary kiln firing of water-washed fly ash hollow microspheres often adopts a countercurrent air supply form, resulting in a kiln head temperature of 900-1300℃, while the temperature of the water-washed fly ash just entering the rotary kiln at the kiln tail is 250-300℃, which is the easy synthesis interval of dioxin, resulting in rapid generation of dioxin into the tail gas, increasing the difficulty of subsequent tail gas treatment; while the electromagnetic kiln realizes rapid temperature rise and precise control through the distribution of the coil and the principle of electromagnetic induction, so that the blank entering the rotary kiln directly passes through the 200-300℃ secondary synthesis temperature zone (heating rate > 50℃ / min), the dioxin decomposition rate > 99.99%, and the environmental protection effect is outstanding. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 A flowchart of the method for preparing water-washed fly ash hollow microspheres based on electromagnetic kiln sintering provided by the present application is shown in the figure; Figure 2 An electromagnetic kiln equipment schematic diagram for preparing water-washed fly ash hollow microspheres based on electromagnetic kiln sintering provided by the present application is shown in the figure; In the drawings, the components represented by each reference number are listed as follows: 1, feeding system; 2, induction coil; 3, PLC control system; 4, hollow microsphere blank. DETAILED DESCRIPTION

[0030] The principles and features of the present application are described below, and the examples are only used to explain the present application and are not intended to limit the scope of the present application.

[0031] According to Figure 1 As shown in the figure, the present application provides a method for preparing water-washed fly ash hollow microspheres based on electromagnetic kiln sintering, comprising the following steps: S1, water-washed fly ash batching and grinding; S2, placing the ground slurry into an aging tank and adding a bonding agent and a foaming agent to obtain a slurry for molding and drying; S3, putting the aged slurry into an atomizer at the top of a spray molding tower for atomization and drying to form a hollow microsphere blank; S4, feeding the hollow microsphere blank into an electromagnetic kiln for firing, and obtaining a hollow microsphere after cooling.

[0032] The embodiment solves the problems of flue gas and energy consumption by replacing the high-pollution traditional rotary kiln with an electromagnetic kiln. The electromagnetic kiln directly heats the blank: the thermal efficiency is > 80%, and the comprehensive energy consumption is reduced by 50% compared with the traditional rotary kiln; no forced ventilation is needed: the material loss rate is < 3%, the flue gas volume is reduced by 70%, and the flue gas treatment cost is greatly reduced; induction heating realizes sintering of the blank from the surface to the inside, the temperature uniformity is ± 5℃, the problem of micro-bead rupture caused by temperature fluctuation of the traditional rotary kiln is solved: the micro-bead yield is > 90%. Compared with the traditional natural gas rotary kiln process, if the proportion of green electricity of the electromagnetic kiln is > 80%, the emission reduction amount jumps to 0.18-0.22 tons of CO2 / ton of micro-bead (a decrease of 70-85%).

[0033] Based on the above technical solutions, the application can also be improved as follows.

[0034] Preferably, in the embodiment, in the step S1: The specific method of batching is: the water-washed fly ash is punched into the buffer bin by the screw conveyor, the process water is pumped into the batching tank, the stirring system in the batching tank is started, the water-washed fly ash in the buffer bin is unloaded into the batching tank through the unloading valve, and continuous stirring is carried out for 30-50 min to obtain the slurry.

[0035] The screw conveyor can uniformly and controllably punch the powdered water-washed fly ash into the buffer bin. The buffer bin serves as an intermediate storage unit. The process water is first pumped into the batching tank, and then the fly ash is added. This is beneficial to the full wetting of the fly ash particles by water, reduces dust flying (although it has been water-washed, but dry feeding may still produce dust), and allows the water to better wrap each particle as a dispersion medium. Continuous stirring for 30-50 minutes makes the fly ash solid particles and the process water reach a high degree of uniform mixing. This is the basis for complete and thorough solidification reaction. In addition, the fly ash has a large density and is easy to quickly settle in water. By continuous stirring, a suspension is formed, the fly ash particles are uniformly distributed in the liquid, so that the consistency of the slurry is ensured, and the concentration is uniform when the slurry is unloaded.

[0036] Preferably, in the embodiment, in the step S1: The specific method of grinding is: the slurry is pumped from the batching tank to the grinding tank through the diaphragm pump, and then is punched from the grinding tank to the grinding machine through the diaphragm pump, and the average particle size reaches D50≤5μm after 2-3h of grinding and testing by the laser particle size instrument.

[0037] The grinding of fly ash particles to an average particle size D50≤5 μm (micron level) means that the number of particles increases exponentially and the total specific surface area increases sharply. The fineness of D50≤5 μm has reached the particle size requirement of many mineral admixtures or fillers in the field of building materials. This makes the treated fly ash can be used as a high-activity admixture in hollow microsphere, not only realizes the resource utilization of waste, but also improves the performance of the product. In addition, finer particles can reduce the settling velocity, form a more stable suspension, reduce the risk of blockage during pumping in subsequent steps, and facilitate pumping and subsequent filling and molding. The slurry after grinding can be filled more densely during molding, reducing internal porosity, thereby forming a final solidified body with more uniform structure and fewer defects, further enhancing its physical strength and impermeability.

[0038] Preferably, in the embodiment, the slurry ratio is 1:1-1:5 of water-washed fly ash to process water.

[0039] Sufficient water is a prerequisite for dissolving and flushing soluble salts (such as chloride salts, sulfate salts) and part of the leachable heavy metals in fly ash. Low proportion provides basic water quantity, which can wet fly ash and partially dissolve pollutants. It is suitable for scenarios with low initial pollutant content or not extremely high requirements for subsequent processes, with the advantages of low water consumption and small amount of subsequent wastewater treatment. High proportion provides a large amount of washing medium, creating a larger solid-liquid contact area and concentration difference (driving force), which can more thoroughly "extract" pollutants from the surface and pores of fly ash. Significantly reduces the salt content and soluble heavy metal content of fly ash after washing, laying a good foundation for subsequent stabilization / solidification or resource utilization, and improving the environmental safety and quality of the final product.

[0040] At the same time, the slurry formed by low proportion is very viscous, close to paste. Although water is saved, the stirring resistance is extremely large, the requirements for stirrers and motor power are high, and blockage during piping and pumping is extremely easy to occur, operation is difficult, and production is discontinuous.

[0041] The slurry formed by high proportion has good fluidity and is easy to mix, ensuring uniform washing process; at the same time, it can be reliably transported to the next process (such as pressure filtration dewatering) through a diaphragm pump, a pipeline, etc., realizing the continuous and automatic process. The range of 1:1-1:5 provided by the embodiment provides a selection space for fly ash with different characteristics, which can not only meet the washing requirements, but also ensure that the slurry has good pumpability and stirrability.

[0042] Preferably, in the embodiment, in the step S2: The specific method of aging is: pumping the qualified slurry after grinding into the aging tank through a diaphragm pump, adding an adhesive and a foaming agent, continuously stirring and aging for 6-9 h, adjusting the viscosity to 400-900 CP, and obtaining a slurry for molding and drying.

[0043] At this viscosity, the slurry has good flowability, can be smoothly injected into the mold by pumping, and can fill every corner of the mold, ensuring that the shaped product is complete in shape and dense in structure, without material defects. At the same time, the viscosity is high enough that the slurry does not flow everywhere like water after stopping stirring and pouring into the mold, can maintain the preset shape, and will not collapse or deform severely. For the foaming process, this viscosity is sufficient to wrap and stabilize the bubbles generated by the foaming agent, preventing the bubbles from merging, becoming larger, or escaping, thereby ensuring that the final product obtains a uniform and fine pore structure.

[0044] The binder (such as cement, water glass, resin, etc.) begins to hydrate or cross-link during the aging period, forming a gel that wraps and bonds the fly ash particles. This is the fundamental reason why the final product obtains mechanical strength (compressive and bending resistance). The aging process allows the reaction to proceed initially, forming initial strength, so that the subsequent demolding and drying processes do not damage the product structure. The foaming agent generates uniform and fine bubbles under stirring. Controllable and uniformly distributed pores are formed in the slurry. By continuous stirring, it is ensured that the added binder and foaming agent are absolutely uniformly distributed in the slurry, avoiding performance defects in the final product due to uneven mixing.

[0045] Preferably, in the examples, the material ratio in step S2 is 150-200 parts of slurry, 10-30 parts of binder, and 5-15 parts of foaming agent. The binder is liquid and is any one of polyvinyl alcohol, carboxymethyl cellulose, and polyvinyl formal adhesive, with a solid content of 1-5%. A low solid content means that the binder solution has a low viscosity, like water. This allows it to be very uniformly dispersed throughout the slurry system, fully wrapping each fly ash particle and forming a uniform bonding film, avoiding local clumping or uneven bonding. With a low solid content, even with the addition of 10-30 parts of liquid, the actual amount of solid binder introduced is very small. This avoids the problem of the slurry becoming too thick and having poor flowability due to the addition of too much solid powder.

[0046] The foaming agent is liquid and is any one of sodium dodecyl sulfate, cetyltrimethylammonium bromide, and calcium carbonate, with a solid content of 15-30%. A high solid content of 15-30% means that it is a concentrated foaming agent solution. Only a small amount (5-15 parts) needs to be added to introduce a sufficient concentration of foaming components into the slurry, thereby generating a large amount of stable foam. This also avoids diluting the slurry by adding too much liquid. Surfactant-type foaming agents (SDS, CTAB) not only can foam, but also can reduce the surface tension of the bubbles, stabilize the foam structure, prevent the bubbles from merging or breaking during stirring, pouring, and the initial stage of solidification, and finally form a uniform and closed pore structure.

[0047] The slurry (i.e. the treated fly ash) accounts for the absolute majority of the formulation (about 85-95%). This maximizes the consumption of hazardous waste, in line with the primary principle of solid waste treatment "reduction and resource utilization", while directly reducing the cost of raw materials.

[0048] The amount of binder (10-30 parts) is sufficient to form an effective bonding network between the particles, providing the necessary mechanical strength to prevent the product from becoming loose. The amount of foaming agent (5-15 parts) introduces an appropriate amount of pores on the basis of this bonding framework, significantly reducing the bulk density of the material and achieving lightweight. This proportion range ensures that the material will not collapse in strength due to too much foaming agent, nor become dense and heavy due to too much binder.

[0049] Preferably, in the examples, the stirring speed is 30-40 r / min. By low-speed stirring, large bubbles can be avoided from being cut into uneven small bubbles, and at the same time, small bubbles are also prevented from colliding and merging into large bubbles, thereby obtaining a fine and uniform pore structure. Gentle stirring is conducive to forming an ideal closed pore structure, which can significantly improve the thermal insulation performance of the product, and is also more beneficial to the strength of the final product. The foamed slurry is like a dough filled with countless small balloons. Low-speed stirring (30-40 r / min) is like gently folding and pressing the dough with hands, the purpose is to evenly distribute the balloons in the dough, while not breaking any one, so that the hollow microsphere blank formed in the subsequent atomization and drying process is more in line with the molding requirements.

[0050] Preferably, in the examples, the step S3 is: The aged slurry is continuously pumped into the atomizer at the top of the spray forming tower by a diaphragm pump, and the slurry is atomized into microdroplets by the high-speed rotating centrifugal force of the atomizer, and is fully contacted with the high-temperature flue gas introduced from the top of the tower, to form hollow microsphere blanks with a water content of <5%. The hollow microsphere blanks are naturally settled to the bottom of the tower and collected, and the tail gas is discharged from the middle of the tower cone and discharged into the atmosphere after flue gas purification treatment; all volatile substances and water vapor are concentrated in the tail gas of the spray forming tower, and are discharged from the middle of the tower cone and treated by a set of concentrated flue gas purification system (such as bag dust removal, washing tower, etc.) before being discharged, ensuring the environmental friendliness of the production process and avoiding unorganized discharge of pollutants.

[0051] The temperature of the high-temperature flue gas introduced from the top of the spray forming tower is 300-350°C, and the temperature of the tail gas discharged from the middle of the tower cone is 90-150°C; it ensures that a large amount of water in the mist droplets can be evaporated instantly, realizing rapid drying. The high temperature provides a huge temperature difference driving force, which is the key to achieving extremely low moisture content (<5%). The decomposition temperature of the organic components in the fly ash, such as PVA, CMC, and foaming agent, is usually above 200°C. Controlling the exhaust gas temperature at 90-150°C means that the temperature of the material itself is always controlled at about 100°C (the boiling point of water) by the evaporation cooling effect of water, effectively preventing the thermal decomposition and failure of organic additives, and ensuring the strength and porous structure of the microbeads.

[0052] The rotation speed of the atomizer is controlled within 6000-12000r / min. Within this high rotation speed range, extremely fine mist droplets of tens to hundreds of microns can be produced, which directly determines the particle size of the final hollow microbeads. High rotation speed ensures atomization effect, and the size distribution of the obtained mist droplets is concentrated, thereby ensuring uniform particle size of the final product. The water on the surface of the fine mist droplets evaporates rapidly, and a dense solid shell is formed on the outside, while the internal water vaporizes and expands under heat, but is wrapped by the outer shell, thereby naturally forming a hollow microbead structure.

[0053] The microdroplets produced by the atomizer will naturally form perfect spherical shapes under the action of surface tension. After drying, this spherical shape is preserved, and the obtained product is a spherical powder with uniform particle size and excellent flowability.

[0054] Preferably, in the examples, in step S4: The hollow microbead blanks are sent into the electromagnetic kiln by a belt conveyor and / or a bucket elevator for sintering, so that the blank material moves towards the kiln head under the action of the slope and rotation of the kiln body, and the finished hollow microbeads fall into the air cooler from the kiln head, and the qualified hollow microbead product is obtained after cooling; The technical parameters of the electromagnetic kiln include: sintering temperature: 1000-1200°C, holding time: 30-90min; this temperature range is much higher than the melting point of fly ash, which can make the silicon and aluminum components in the fly ash melt to form a glass liquid phase, fill the interstitial space between particles, and densify the shell of the hollow microbead, greatly improving its strength. At high temperatures, heavy metal elements are firmly solidified or embedded in the formed glass network or crystal phase, achieving permanent stabilization, and the leaching toxicity is reduced to a very low level, and the product has extremely high environmental safety. Long holding time is beneficial to the formation of mullite (3Al2O3·2SiO2) and other high-temperature stable crystal phases, further endowing the product with excellent high-temperature stability, chemical inertness and mechanical strength.

[0055] The electromagnetic parameters: medium-frequency induction heating with a frequency of 1-10kHz is adopted, and eddy current heating is generated in the blank body by alternating magnetic field, and the power density is 50-200kW / m³; The kiln head gas pressure is -1 Pa: ensure the overall airflow in the kiln flows to the kiln head direction, prevent harmful gas or dust from leaking to the kiln tail, and maintain a clean operating environment. At the same time, it is beneficial to discharge the volatile gases released by the green body during the sintering process.

[0056] Weak reducing atmosphere (CO<5%): This is the key to producing light-colored or white hollow microspheres. Iron (Fe2O3) in fly ash will generate gray FeO or Fe3O4 under reducing atmosphere, avoiding the generation of deep red Fe2O3, thereby obtaining lighter and more valuable products. At the same time, the reducing atmosphere helps to reduce certain valence heavy metals and dissolve them in the glass body.

[0057] Electromagnetic kiln rotation speed: 2-4r / min. The rotation speed and the slope together determine the residence time of the material in the kiln. Slow rotation at 2-4r / min, combined with a suitable slope, ensures that the material has sufficient and uniform 30-90 minute holding time to complete the required sintering reaction. Rotation makes the production process continuous (hollow microsphere green body enters from the kiln tail and finished product exits from the kiln head), greatly improving production efficiency and product quality consistency compared to batch kilns. Slow rotation makes the material roll forward gently, avoiding violent collision and wear between hollow microspheres, ensuring high sphericity and intact surface structure of the product.

[0058] Traditional kilns heat from the outside to the inside by convection, resulting in temperature gradients that can cause uneven heating of the product, resulting in problems such as outer core and inner growth, cracking and deformation. The present invention uses electromagnetic induction heating (1-10 kHz medium frequency): the alternating magnetic field makes the green body itself generate eddy current and heat, and the heat is transferred from the inside to the outside. Achieve extremely fast heating rate and extremely uniform heating, eliminate temperature gradient. This makes the sintering degree of each hollow microsphere highly consistent, resulting in uniform product structure and stable performance.

[0059] In addition, the combustion process of traditional gas kilns produces a large amount of flue gas (NOx, SOx, CO2, etc.), which requires a complex flue gas treatment system. The heat source of the electromagnetic kiln in this embodiment is electricity, and there is no combustion process in the kiln. The production of combustion exhaust gas is fundamentally eliminated, and the tail gas only comes from the decomposition of organic matter in the green body and a small amount of volatile matter, with small gas volume and simple composition, which is easy to treat. The production process is clean and environmentally friendly, meeting the requirements of high-end manufacturing.

[0060] Moreover, heat is generated directly inside the material, avoiding the need to heat the furnace body material and a large amount of heat loss. Its thermal efficiency can usually reach 60-80%, which is much higher than the 20-40% of traditional kilns. The power density of 50-200kW / m³ proves its strong heating capacity, enabling rapid sintering, shortening the cycle, and further reducing unit product energy consumption. The electromagnetic kiln method provided by the present application compared with the traditional gas-fired rotary kiln, the specific indicators are shown in Table 1: Table 1: Example 1: 1. Take 100 kg of water washed fly ash (Cl- = 0.6%) and ball mill with 100 L of water until D50 ≤ 5 μm; 2. Add 20 kg of binder with a solid content of 3%, and 10 kg of foaming agent with a solid content of 20%. Adjust the stirring speed to 35 r / min and stir for 7 h; 3. Adjust the speed of the atomizer to 8000 r / min for spray drying, and set the inlet flue gas to 300℃ to obtain the water washed fly ash hollow microsphere blank; 4. Sinter in an electromagnetic kiln at 1150℃ for 60 min (frequency 5 kHz), and then cool to obtain the finished product; 5. Output: 94 kg of hollow microspheres (floatation rate > 95%, bulk density 0.78 g / cm³).

[0061] According to Figure 2 The application also provides a device for preparing water washed fly ash hollow microspheres based on electromagnetic kiln sintering, characterized in that it comprises a feeding system 1 (such as the aforementioned bucket elevator), an electromagnetic kiln, and a PLC control system 3. The electromagnetic kiln is arranged to tilt and rotate, with the inlet end higher than the outlet end. The feeding system 1 is connected to the inlet end of the electromagnetic kiln, and the electromagnetic kiln is wrapped with an induction coil 2 on the side. The PLC control system 3 is electrically connected to the feeding system 1, the electromagnetic kiln, and the induction coil 2. The hollow microsphere blank 4 enters the electromagnetic kiln through the feeding system 1, and moves along the inclined surface to the outlet end of the electromagnetic kiln as the electromagnetic kiln rotates. The direction indicated by the arrow in the figure is the movement direction of the hollow microsphere blank 4.

[0062] Traditional natural gas rotary kiln firing of water washed fly ash hollow microspheres often adopts counterflow air supply form, resulting in a kiln head temperature of 900-1300℃, while the temperature of the kiln tail where the water washed fly ash just enters the rotary kiln is 250-300℃, which is the easy synthesis interval of dioxin, leading to rapid generation of dioxin into the tail flue gas, increasing the difficulty of subsequent tail gas treatment. The electromagnetic kiln, through the distribution of the coil and the principle of electromagnetic induction, realizes rapid temperature rise and precise control, so that the blank entering the rotary kiln directly passes through the 200-300℃ secondary synthesis temperature zone (heating rate > 50℃ / min), with a dioxin decomposition rate > 99.99%, and outstanding environmental protection effect.

[0063] In the description of the application, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the application and simplifying the description, and does not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the application.

[0064] In addition, the terms "first", "second" are only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features defined with "first", "second" can explicitly or implicitly include at least one of the features. In the description of the application, the meaning of "a plurality of" is at least two, such as two, three, etc., unless otherwise explicitly specified and limited.

[0065] In the present application, unless otherwise explicitly specified and limited, the terms "mounting", "connection", "connection", "fixing" and the like should be understood broadly, for example, it can be fixed connection, or detachable connection, or integral; it can be mechanical connection, or electrical connection; it can be directly connected, or indirectly connected through intermediate medium, it can be the internal communication of two elements or the interaction relationship between two elements, unless otherwise explicitly limited. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0066] In the present application, unless otherwise explicitly specified and limited, the first feature is "on" or "under" the second feature, which can be direct contact between the first and second features, or indirect contact between the first and second features through intermediate medium. Moreover, the first feature "above", "above" and "above" the second feature can be directly above or obliquely above the first feature, or only indicate that the horizontal height of the first feature is higher than that of the second feature. The first feature "below", "below" and "below" the second feature can be directly below or obliquely below the first feature, or only indicate that the horizontal height of the first feature is less than that of the second feature.

[0067] In the description of the specification, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are contained in at least one embodiment or example of the present application. In the specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any suitable manner in any one or more embodiments or examples. In addition, the person skilled in the art can combine and combine the different embodiments or examples described in the specification and the features of the different embodiments or examples without contradiction.

[0068] Although the embodiments of the present application have been shown and described above, it is understood that the above-described embodiments are exemplary and are not to be construed as limiting the present application, and those skilled in the art can make changes, modifications, replacements and variations to the above-described embodiments within the scope of the present application.

Claims

1. A method for preparing hollow microspheres from washed fly ash based on electromagnetic kiln sintering, characterized in that, Includes the following steps: S1. Preparation and grinding of water-washed fly ash; S2. Place the ground slurry into an aging tank and add binder and foaming agent to obtain a slurry for molding and drying. S3. The aged slurry is fed into the atomizer at the top of the spray forming tower for atomization and drying to form hollow microsphere blanks. S4. The hollow microsphere blank is fed into an electromagnetic kiln for firing, and after cooling, hollow microspheres are obtained.

2. The method for preparing water-washed fly ash hollow microspheres based on electromagnetic kiln sintering according to claim 1, characterized in that, In step S1: The specific method for batching is as follows: the washed fly ash is pumped into the buffer silo via a screw conveyor, the process water is pumped into the batching tank, the stirring system in the batching tank is turned on, the washed fly ash in the buffer silo is discharged into the batching tank through the discharge valve, and the mixture is stirred continuously for 30-50 minutes to obtain the slurry.

3. The method for preparing water-washed fly ash hollow microspheres based on electromagnetic kiln sintering according to claim 2, characterized in that, In step S1: The specific grinding method is as follows: the slurry is pumped from the batching tank into the grinding tank by a diaphragm pump, and then pumped from the grinding tank into the grinding machine by a diaphragm pump. After grinding for 2-3 hours, the fly ash particle size distribution is tested by a laser particle size analyzer, and the average particle size reaches D50≤5μm.

4. The method for preparing water-washed fly ash hollow microspheres based on electromagnetic kiln sintering according to claim 2, characterized in that, The slurry ratio is 1:1 to 1:5 for washed fly ash and process water.

5. The method for preparing water-washed fly ash hollow microspheres based on electromagnetic kiln sintering according to claim 1, characterized in that, In step S2: The specific aging method is as follows: the qualified slurry is pumped into the aging tank through a diaphragm pump, binder and foaming agent are added, and the mixture is continuously stirred and aged for 6-9 hours. The viscosity is adjusted to 400-900CP to obtain the slurry for molding and drying.

6. The method for preparing water-washed fly ash hollow microspheres based on electromagnetic kiln sintering according to claim 5, characterized in that, The material ratio in step S2 is 150-200 parts slurry, 10-30 parts binder, and 5-15 parts foaming agent; The adhesive is liquid and is any one of polyvinyl alcohol, carboxymethyl cellulose, or polyvinyl alcohol formaldehyde adhesive, with a solid content of 1-5%. The foaming agent is liquid and is any one of sodium dodecyl sulfate, hexadecyltrimethylammonium bromide, and calcium carbonate, with a solid content of 15-30%.

7. The method for preparing water-washed fly ash hollow microspheres based on electromagnetic kiln sintering according to claim 5, characterized in that, The stirring speed is 30-40 r / min.

8. The method for preparing water-washed fly ash hollow microspheres based on electromagnetic kiln sintering according to claim 1, characterized in that, In step S3: The aged slurry is continuously pumped into the atomizer at the top of the spray forming tower via a diaphragm pump. The high-speed rotation of the atomizer atomizes the slurry into micro-droplets, which come into full contact with the high-temperature flue gas introduced from the top of the tower to form hollow microsphere preforms with a water content of <5%. The hollow microsphere preforms naturally settle to the bottom of the tower and are collected. The exhaust gas is discharged from the middle of the tower cone and discharged into the atmosphere after being treated by flue gas purification. The temperature of the high-temperature flue gas introduced from the top of the spray forming tower is 300-350℃, and the temperature of the exhaust gas discharged from the middle of the tower cone is 90-150℃. The atomizer speed is controlled within 6000-12000 r / min.

9. The method for preparing water-washed fly ash hollow microspheres based on electromagnetic kiln sintering according to claim 1, characterized in that, In step S4: Hollow microsphere blanks are fed into an electromagnetic kiln for firing via belt conveyor and / or bucket elevator. The blank material moves towards the kiln head under the action of the kiln slope and rotation. The finished hollow microspheres fall from the kiln head into an air cooler and are cooled to obtain qualified hollow microsphere products. The technical parameters of the electromagnetic kiln include: sintering temperature: 1000-1200℃, holding time: 30-90min; Electromagnetic parameters: Medium-frequency induction heating with a frequency of 1-10kHz is used. Eddy current heating is generated inside the billet through an alternating magnetic field, and the power density is 50-200kW / m³. Atmosphere: The kiln head pressure is -1 Pa or the CO concentration is <5% in a weak reducing atmosphere. Electromagnetic kiln rotation speed: 2-4 r / min.

10. An apparatus for preparing hollow microspheres from washed fly ash based on electromagnetic kiln sintering, characterized in that, Includes a feeding system (1), an electromagnetic kiln, and a PLC control system (3); The electromagnetic kiln is tilted and rotated, with its inlet end higher than its outlet end; the feeding system (1) is connected to the inlet end of the electromagnetic kiln, and an induction coil (2) is wound around the periphery of the electromagnetic kiln; the PLC control system (3) is electrically connected to the feeding system (1), the electromagnetic kiln, and the induction coil (2). The hollow microsphere blank (4) enters the electromagnetic kiln through the feeding system (1) and moves along the inclined surface to the outlet end of the electromagnetic kiln as the electromagnetic kiln rotates.

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