A method for drying isostatic dry-process electric porcelain solid particles by using waste heat for self-adjusting humidity in stages

Abstract

The application discloses a kind of isostatic pressing dry method electric porcelain solid particle afterheat step self-regulation wet drying method, after extruding mud strip, fine mud strip is sent into multilayer mesh belt kiln, three-stage hot flue gas is extracted in turn in kiln cooling zone, 120 ℃±5 ℃, 90 ℃±5 ℃, 70 ℃±5 ℃ stable voltage hot air is formed after dust removal and air mixing;Mud strip passes through gradient according to setting time, and mesh belt speed is adjusted by on-line capacitance humidity probe and PID linkage, and the controllable decrease of moisture content 15%→1.5-2.5% is realized.Dried mud strip is kept in hot state by pulse air conveying groove, that is, broken, and then atomized and sprayed into 0.3-0.5 wt% polyethylene glycol 400 to form 3-5 nm film in 90 ℃ afterheat air flow state, and qualified particles of solid, low fine powder and moisture resistance are obtained.All heat sources come from kiln afterheat, and tail gas is recovered to assist combustion, without additional natural gas.The application cancels spray drying, with short process and low energy consumption, and the solid particles are solid without pores, meeting the requirements of isostatic pressing automatic material distribution.

Description

Technical Field

[0001] This invention relates to a waste heat-based self-humidifying drying method for isostatic pressing solid electrical porcelain particles. Background Technology

[0002] In traditional isostatic pressing dry process electrical porcelain manufacturing technology, raw material granulation employs spray drying technology. The resulting granules generally contain pores, which cannot be completely eliminated during the pressing process. This results in high porosity and low strength in the green body (the product before sintering); simultaneously, the sintered porcelain product also exhibits high porosity and low strength. Furthermore, because spray drying dehydration requires boiling and vaporizing the slurry moisture (approximately 60% of the dry weight) using the heat from natural gas combustion, a large amount of gas exceeding 100°C is released into the atmosphere while the moisture vaporization absorbs a significant amount of heat, thus consuming a large quantity of natural gas and resulting in high manufacturing costs. Summary of the Invention

[0003] This invention provides a waste heat-based, stepwise self-humidifying drying method for isostatic pressing solid ceramic granules to address the problems existing in the prior art. This invention replaces the traditional spray drying with a three-step process of "squeezing mud - extruding strips - waste heat drying - wheel crushing". The process is short, the equipment is mature, there is no additional fuel, and the granules are solid and without air holes, thus achieving low-cost, high-flowability isostatic pressing powder preparation.

[0004] The technical solutions adopted in this invention are as follows:

[0005] A waste heat-based self-humidifying drying method for isostatic pressing solid electrical porcelain particles includes:

[0006] a) The ceramic clay strips after pressing and extrusion are fed into a multi-layer mesh belt kiln;

[0007] b) In the kiln cooling zone, multiple stages of hot flue gas are sequentially extracted along the temperature decreasing direction. After dust removal and air mixing, at least three stages of hot air with decreasing temperature gradient and fluctuation ≤ ±5℃ are formed.

[0008] c) The ceramic clay strips are passed through the three-stage hot air zones in sequence, and the speed of the conveyor belt is adjusted by PID control using the online moisture detection signals in each zone to achieve a gradient decrease in the moisture content of the clay strips.

[0009] d) The dried clay strips are directly crushed to obtain solid ceramic particles whose loose density, tapped density and Hausner ratio meet the flowability requirements of isostatic pressing automatic feeding.

[0010] e) The dried low-temperature hot air is recovered to the kiln combustion system to form a closed-loop waste heat utilization.

[0011] Furthermore, the temperatures of the three-stage hot air are 120℃±5℃, 90℃±5℃, and 70℃±5℃, respectively.

[0012] Furthermore, the online moisture detection unit is a capacitive humidity probe, with at least three probes equidistantly arranged along the belt running direction, and the PID control cycle is ≤2s.

[0013] Furthermore, after the ceramic clay strips have completed the tiered drying process and before entering the roller mill crusher, they first pass through a pulse air conveying trough. This trough uses low-temperature waste heat air at 70℃±5℃ as the air source, and generates an instantaneous airflow of 50-80Hz with a duty cycle of 30% through a pulse valve of 0.3-0.5MPa.

[0014] Furthermore, the length of the pulse air conveying trough is 0.6-1.0m, and the mud strip passage time is 3-5s.

[0015] Furthermore, the crushed particles enter a fluidized bed, where 0.3-0.5wt% of polyethylene glycol 400 is atomized and sprayed in using medium-temperature waste heat air at 90℃±5℃ as a carrier.

[0016] Furthermore, the atomized polyethylene glycol 400 forms a 3-5 nm organic thin film on the particle surface.

[0017] Furthermore, the dust removal is a cyclone dust removal system.

[0018] Furthermore, the volumetric flow mixing ratio of the third-level hot air and the ambient air is 1:0.6-1:1.2, and the mixed air residence time is ≥3s.

[0019] Furthermore, the closed-loop waste heat utilization involves sending low-temperature hot air at 70℃±5℃ back to the end of the kiln cooling zone via an induced draft fan as combustion air.

[0020] The present invention has the following beneficial effects:

[0021] (1) The granules obtained by pressing mud-extrusion-low temperature step-drying are solid structures with no macroscopic pores inside. After isostatic pressing, the density distribution of the green body is uniform, and the porosity of the fired ceramic parts is significantly lower than that of traditional spray-dried granules.

[0022] (2) The low-temperature flue gas of 300-150℃ in the kiln cooling zone is used as the entire heat source, eliminating the need for additional natural gas combustion. The spray drying process is eliminated, and the natural gas consumption per unit of dry powder is reduced accordingly.

[0023] (3) After the three-stage air intake and mixed air temperature stabilization, the drying exhaust gas is still returned to the kiln for combustion, forming a closed loop. The exhaust gas temperature drops to below 120℃, realizing the on-site recovery of low-temperature waste heat.

[0024] (4) Pulsed hot air keeps the surface of the mud strip at 45-50℃, and immediately crushes it in a hot state to reduce surface moisture regain; after crushing, the particles are coated with a low-temperature fluidized film, which can suppress moisture absorption and rebound during storage and reduce the fluctuation range of particle size distribution.

[0025] (5) The online capacitive humidity probe is linked with PID speed regulation, which can correct the conveyor belt speed in real time, reduce the moisture content drift caused by day and night temperature difference and raw material batch change, and make the raw material quality of the first shift of the night shift more consistent with that of the day shift. Attached Figure Description

[0026] Figure 1 This is a flowchart of the present invention. Detailed Implementation

[0027] The invention will now be further described with reference to the accompanying drawings.

[0028] like Figure 1 As shown, the specific implementation steps of the waste heat-based self-humidifying drying method for isostatic pressing solid electrical porcelain particles of the present invention are as follows:

[0029] (1) The mud cake is extruded into thin mud strips.

[0030] The porcelain slurry (solid content approximately 40 wt%), after ball milling and iron removal by sieving, is fed into a high-pressure sludge press and dehydrated to a moisture content of 14–16% under a pressure of 15–25 MPa, forming a dense sludge cake. This sludge cake is free of macroscopic cracks, has good plasticity, and can be directly fed into a twin-screw extruder.

[0031] The extruder die diameter is controlled at 1.8–2.2 mm, and the extrusion speed is 0.8–1.2 m / min, resulting in continuous, uniform, and smooth cylindrical clay strips. The diameter deviation of the clay strips is ≤ ±0.1 mm, the length is continuous, and the standard deviation of the moisture content distribution is <0.5%, meeting the consistency requirements for subsequent drying.

[0032] This step avoids the hollow or porous structure formed by droplet vaporization in traditional spray drying, ensuring the solidity of the particles from the source.

[0033] (2) The residual heat of the fine clay strips is used for step-by-step self-humidification drying.

[0034] The above-mentioned clay strips are laid flat on the upper feed end of the multi-layer mesh belt kiln. The mesh belt is made of heat-resistant 310 stainless steel, and the initial running speed is set to 0.6m / min.

[0035] The flue gas temperature at the outlet of the kiln cooling zone is approximately 300–150℃. Three air intakes are set sequentially along the flue gas flow direction to extract flue gas from the high-temperature section (280℃), the medium-temperature section (220℃), and the low-temperature section (160℃), respectively.

[0036] Each flue gas stream first passes through a cyclone dust collector to remove dust (dust removal efficiency ≥90%), and then is mixed with ambient air at volume ratios of 1:0.8, 1:1.0, and 1:1.2 respectively. The mixed air resides in the buffer chamber for ≥3 seconds to ensure uniform and stable temperature. After mixing, three stages of drying hot air are formed, with target temperatures of:

[0037] Level 1: 120℃±5℃;

[0038] Level 2: 90℃±5℃;

[0039] Level 3: 70℃±5℃.

[0040] The clay strips pass sequentially through the three independent temperature-controlled zones, each approximately 3–4 m long. Each zone's inlet and outlet are equipped with at least three capacitive online moisture detection probes (arranged equidistantly along the conveyor belt) to monitor the surface and near-surface moisture content of the clay strips in real time, with a sampling frequency ≥1 Hz.

[0041] The detection signal is input to the PLC control system, which uses a PID algorithm (proportional-integral-derivative control) to dynamically adjust the speed of the conveyor belt motor, with a control cycle of ≤2s. For example, if the moisture content at the outlet of the first zone is higher than the set value (e.g., 8.5%), the conveyor belt speed will be automatically reduced to extend the drying time; conversely, the speed will be increased if the moisture content is lower.

[0042] This closed-loop control achieves a gradient decrease in the moisture content of the clay strips from an initial 15% to 8% to 4% and finally to 1.5% to 2.5%, avoiding cracking or stress concentration caused by rapid dehydration.

[0043] After drying, the clay strips are brittle, uniform in color, and without any soft core or charring.

[0044] (3) Roller crushing to obtain solid powder with graded properties.

[0045] After drying, the clay strips first enter a pulse air conveying trough, which is 0.8m long and is filled with low-temperature waste heat air (from the exhaust gas of the third-stage drying process) at 70℃±5℃. An electromagnetic pulse valve (operating pressure 0.4MPa) installed at the bottom of the trough generates instantaneous airflow pulses with a frequency of 60Hz and a duty cycle of 30%. The clay strips remain in this trough for approximately 4 seconds, their surface is slightly disturbed and maintained in a slightly warm state (surface temperature approximately 45–50℃), effectively preventing the adsorption of ambient moisture and preserving their "hot brittleness," creating ideal conditions for subsequent crushing.

[0046] The clay strips then enter a roller crusher. This equipment consists of a pair of carbide rollers and a rotating chassis. The roller linear velocity is controlled at 1.2–1.8 m / s, and the gap is adjusted to 0.3–0.5 mm. Under the action of rolling and shearing, the brittle clay strips are crushed into irregular polyhedral particles.

[0047] The crushed product was graded through a 100-mesh (0.15mm) standard sieve, with the undersize material accounting for ≥95%, and the particle size distribution being concentrated (D50≈80–100μm), and the loose bulk density ≥0.95g / cm³. 3 Tap density ≥ 1.35 g / cm³ 3The Hausner ratio (tap density / loose packing density) is between 1.35 and 1.45, which fully meets the requirements of isostatic pressing automatic feeding for powder flowability.

[0048] To further improve storage stability, the crushed particles were then introduced into a fluidized bed, into which medium-temperature waste heat air (from the exhaust gas of the second-stage drying process) at 90℃±5℃ was introduced to keep the particles in a suspended fluidized state. At the same time, a 0.4wt% polyethylene glycol 400 (PEG400) aqueous solution was uniformly sprayed in through a two-fluid atomizing nozzle.

[0049] PEG400 is rapidly dried under hot air, forming an organic film approximately 3–5 nm thick on the particle surface. This film is hydrophobic, significantly inhibiting moisture absorption and reabsorption by the powder during storage, thus maintaining stable flowability.

[0050] Finally, all the drying exhaust gas (final temperature of about 70°C) is collected by the induced draft fan and sent back to the end of the kiln cooling zone as combustion air supplement, realizing closed-loop utilization of waste heat. The system exhaust gas temperature is reduced to below 120°C, significantly reducing heat loss.

[0051] Through the above process, the obtained electrical porcelain powder is a solid, non-porous, low-hygroscopic, and highly fluid particle. After isostatic pressing, the green body has a uniform density, and the sintered product has a high density (specific gravity 2.72–2.78 g / cm³). 3 It has excellent mechanical strength (flexural strength 150–180 MPa), and the entire granulation process does not require additional combustion of natural gas, resulting in significant energy savings.

[0052] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements without departing from the principle of the present invention, and these improvements should also be considered within the scope of protection of the present invention.

Claims

1. A method for waste heat-based self-humidifying drying of isostatically pressed solid electrical porcelain particles, characterized in that: include: a) The ceramic clay strips after pressing and extrusion are fed into a multi-layer mesh belt kiln; b) In the kiln cooling zone, multiple stages of hot flue gas are sequentially extracted along the temperature decreasing direction. After dust removal and air mixing, at least three stages of hot air with decreasing temperature gradient and fluctuation ≤ ±5℃ are formed. c) The ceramic clay strips are passed through the three-stage hot air zones in sequence, and the speed of the conveyor belt is adjusted by PID control using the online moisture detection signals in each zone to achieve a gradient decrease in the moisture content of the clay strips. d) The dried clay strips are directly crushed to obtain solid ceramic particles whose loose density, tapped density and Hausner ratio meet the flowability requirements of isostatic pressing automatic feeding. e) The dried low-temperature hot air is recovered to the kiln combustion system to form a closed-loop waste heat utilization.

2. The waste heat-based self-regulating humidity drying method for isostatic pressing solid electrical porcelain particles as described in claim 1, characterized in that: The temperatures of the three levels of hot air are 120℃±5℃, 90℃±5℃, and 70℃±5℃, respectively.

3. The waste heat-based self-regulating humidity drying method for isostatic pressing solid electrical porcelain particles as described in claim 1, characterized in that: The online moisture detection unit is a capacitive humidity probe, with at least three probes arranged at equal intervals along the belt running direction, and the PID control cycle is ≤2s.

4. The waste heat-based self-regulating humidity drying method for isostatic pressing solid electrical porcelain particles as described in claim 1, characterized in that: After the ceramic clay strips have completed the tiered drying process, before entering the roller mill crusher, they first pass through a pulse air conveying trough. This trough uses low-temperature waste heat air at 70℃±5℃ as the air source, and generates an instantaneous airflow of 50-80Hz with a duty cycle of 30% through a pulse valve of 0.3-0.5MPa.

5. The waste heat-based self-humidifying drying method for isostatic pressing solid electrical porcelain particles as described in claim 4, characterized in that: The pulse air conveying trough is 0.6-1.0m long, and the mud strip passes through in 3-5 seconds.

6. The waste heat-based self-regulating humidity drying method for isostatic pressing solid electrical porcelain particles as described in claim 1, characterized in that: The crushed particles enter a fluidized bed, where 0.3-0.5wt% of polyethylene glycol 400 is atomized and sprayed in using medium-temperature waste heat air at 90℃±5℃ as a carrier.

7. The waste heat-based self-humidifying drying method for isostatic pressing solid electrical porcelain particles as described in claim 6, characterized in that: The atomized polyethylene glycol 400 forms a 3-5 nm organic thin film on the particle surface.

8. The waste heat-based self-humidifying drying method for isostatic pressing solid electrical porcelain particles as described in any one of claims 1-7, characterized in that: The dust removal method is cyclone dust removal.

9. The waste heat-based self-humidifying drying method for isostatic pressing solid electrical porcelain particles as described in any one of claims 1-7, characterized in that: The volumetric flow rate mixing ratio of the third-level hot air and the ambient air is 1:0.6-1:1.2, and the mixed air residence time is ≥3s.

10. The waste heat-based self-humidifying drying method for isostatic pressing solid electrical porcelain particles as described in any one of claims 1-7, characterized in that: Closed-loop waste heat utilization involves sending low-temperature hot air at 70℃±5℃ back to the end of the kiln cooling zone via an induced draft fan as combustion air.

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