Process for reducing moisture of talcum powder and improving yield by high-temperature compressed gas

Abstract

The invention discloses a process for reducing moisture of talcum powder and improving yield by high-temperature compressed gas, which comprises the following steps of: A, preheating and feeding raw materials, namely starting a system, setting a target moisture value of a final product, setting an initial temperature parameter of each stage of drying unit, and adding wet talcum powder raw materials with the initial moisture content of 2-8% into the drying unit; the wet materials are continuously and stably fed into a multi-stage serial preheating conveyor (for example, the wet materials flow to the second stage from the third stage and finally enter the first stage, and the flowing direction of the hot air is opposite) through a screw feeder or a star-shaped feeding valve, and the wet materials are pre-dried by utilizing waste heat of the system. Deep coupling and synergistic interaction of drying and depolymerization are achieved, moisture is reduced from 0.7% to 0.1% under the conditions of 80 DEG C high-temperature gas and 8 MPa, the yield is increased by 35%, the processes of source high-temperature dehydration, pipeline heat preservation and precise pressure control are integrated, and the industrial pain points of high energy consumption and large moisture fluctuation of traditional rear-section drying are solved.

Description

Technical Field

[0001] This invention relates to the field of talc production technology, specifically a process for reducing the moisture content of talc powder and increasing its yield by using high-temperature compressed gas. Background Technology

[0002] Talc powder, as an important industrial mineral filler, directly affects the quality of downstream products such as plastics, coatings, paper, and cosmetics due to its performance characteristics (e.g., whiteness, fineness, oil absorption value, moisture content). Among these, moisture content is one of the key indicators. Existing talc powder drying processes mainly suffer from the following problems: High energy consumption and low efficiency: Traditional hot air drying (such as flash drying and rotary kiln drying) relies on convection heat transfer, which has low thermal efficiency (usually less than 50%). Moreover, a large amount of heat energy is required to evaporate moisture. Talc powder has a low thermal conductivity, and moisture (especially bound water) is difficult to migrate quickly from the inside of the particles to the surface, resulting in long drying time and huge energy consumption.

[0003] Product Agglomeration and Particle Size Coarsening: During the drying process, talc powder is prone to "secondary agglomeration" due to moisture evaporation, increased particle surface energy, and adhesion between particles after heating. This results in coarser powder particles and a decrease in specific surface area, which not only affects drying efficiency but also severely reduces the product's performance (such as dispersibility). Subsequent mechanical pulverization (such as air jet milling) processes are often required to deagglomerate the powder, increasing the complexity of the process and energy consumption.

[0004] The contradiction between production capacity and quality: In order to pursue high output, the drying temperature is often increased or the residence time is extended, but this may cause local overheating of talc powder, loss of structural water (when the temperature exceeds 550℃), affecting its layer structure and electrical properties, and even causing a decrease in whiteness; if low temperature and slow speed drying are used to ensure quality, the output is limited.

[0005] The ability to remove "encapsulated water" is weak: some "encapsulated water" adsorbed between fine particles or in the gaps between lamellae is difficult to remove effectively by traditional convection drying methods, resulting in large fluctuations in the residual moisture content of the product, making it difficult to consistently meet the requirements of ultra-low moisture content (such as <0.1%). Summary of the Invention

[0006] The purpose of this invention is to provide a process for reducing the moisture content of talc powder and increasing its yield by high-temperature compressed gas, so as to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a process for reducing the moisture content of talc powder and increasing its yield by high-temperature compressed gas, comprising the following steps: A. Raw material preheating and feeding: Start the system, set the target moisture content of the final product (e.g., 0.1%), and set the initial temperature parameters of each drying unit. Feed the wet talc powder raw material with an initial moisture content of 2%-8% continuously and stably into a multi-stage series preheating conveyor (e.g., from the third stage to the second stage, and finally into the first stage, while the hot air flow direction is the opposite). Utilize the system's waste heat (e.g., exhaust gas with a temperature of 90-120℃ from the subsequent separator) to pre-dry the wet material, thereby reducing the material's viscosity and evaporating some surface water. At the same time, ensure smooth feeding. After the material has been pre-dried in the previous stage, its temperature has increased and its moisture content has decreased. Then, it enters the next drying unit, where it encounters exhaust gas with a higher temperature from the previous stage for deep drying. The pre-dried material enters the feed port of the gas jet drying depolymerization reactor and comes into contact with fresh hot air at the highest temperature (e.g., 400℃) provided by the main heater. B. High-temperature compressed gas jet impact and instantaneous drying and depolymerization: High-temperature and high-pressure gas is introduced into the gas jet drying and depolymerization reactor and passed through a specially designed Laval nozzle or pressure reducing nozzle. The gas is instantly depressurized and expanded at the bottom or tangential inlet of the flash drying tower. The gas volume expands rapidly, and the temperature drops slightly but remains at a high temperature (e.g., from 600℃ to 350℃). At the same time, extremely high flow velocities (up to 200-400m / s) and strong turbulence are generated. Preheated wet talc powder is added quantitatively from the top of the tower or the other side and encounters this high-speed and high-temperature gas flow. C. Gas-solid separation and product collection: The gas-solid two-phase flow that has completed instantaneous drying and depolymerization enters a high-efficiency cyclone separator at the top of the drying tower for primary separation. Most of the qualified dried fine powder products are collected here. Subsequently, the dust-laden exhaust gas enters a bag filter or cartridge filter for secondary fine separation. The captured ultrafine powder is collected separately as a high-value-added product. Most of the high-temperature exhaust gas after separation (temperature is usually between 80-150℃) is returned to the air inlet of the high-temperature and high-pressure gas source system. It is mixed with fresh air as preheated gas and then enters the air compressor. The remaining part is introduced into the waste heat recovery device for recycling to preheat fresh air or raw materials, which can further reduce the system heat loss. D. Product Cooling and Post-processing: The talc powder collected from the cyclone separator, bag filter or cartridge filter is at a high temperature (about 80-120℃). It needs to enter the fluidized bed cooler or cooling screw conveyor to cool it to below 40℃ with room temperature air or cooling water to prevent heat accumulation and moisture absorption. After cooling, the product is screened and iron is removed to obtain the final low-moisture, highly dispersible talc powder product.

[0008] Preferably, the drying unit in step A is a combination of a stirred dryer, a disc dryer, or an airflow drying tube to ensure that the material is in full contact with the hot air, and that the following synergistic effects occur during the mixing stage: a) Ultra-fast heat and mass transfer: The enormous sensible heat carried by the high-temperature gas is instantly transferred to the talc particles through extremely high gas-solid relative velocity (up to 100-300 m / s), causing the internal moisture to vaporize rapidly; b) Particle deagglomeration and refinement: The powerful shear force and inter-particle collision force generated by the high-pressure, high-speed airflow can effectively crush the "soft agglomerates" formed by moisture and van der Waals forces. At the same time, the micro-explosion effect (i.e., "flash evaporation") generated by the instantaneous vaporization of moisture inside the particles further "opens up" the particles from the inside, promoting the separation of layers and the breaking of agglomerates; c) Removal of encapsulated water: The micro-explosion effect and strong turbulent disturbance help to expose the encapsulated moisture, making it easier to evaporate.

[0009] Preferably, the high-temperature and high-pressure gas preparation method in step B is as follows: a) Compressing air or inert gas (such as nitrogen) at normal temperature and pressure to 8MPa using an air compressor to obtain high-pressure gas; b) Then passing this high-pressure gas into a gas heater or electric heater and rapidly heating it to 400-650℃ to form high-temperature and high-pressure gas, and controlling the mass ratio (gas-solid ratio) of high-temperature and high-pressure gas to wet talc powder within the range of 4:1-10:1 to balance the drying effect and energy consumption. At the same time, the bottom of the flash drying tower is equipped with a stirrer or crushing device to break up any wet material clumps that may exist, ensuring that the material is evenly dispersed. The gas jet drying depolymerization reactor can be designed as a counter-spray type, vortex cavity type, or annular gap acceleration type structure, which can create a high-intensity gas-solid turbulent mixing and impact zone.

[0010] Preferably, in step B, the following processes occur within a very short dwell time (0.5-5 seconds) after the encounter: a) Super-strong heat and mass transfer: The extremely high relative gas-solid velocity and huge contact area allow the heat of the high-temperature gas to be instantly transferred to the wet talc powder particles, and the moisture inside and on the surface of the particles rapidly vaporizes; b) Powerful deagglomeration: The strong shear force generated by the high-speed airflow and the collision and friction between particles can effectively break up the initial agglomerates of wet talc powder and prevent secondary agglomeration during the rapid evaporation of moisture, so as to achieve the effect of simultaneous drying and deagglomeration.

[0011] Preferably, it also includes online moisture detection and adaptive feedback control: the moisture content of the pre-dried material is detected in real time by an online moisture detector (such as a near-infrared or microwave moisture meter), and the detection signal is transmitted to the intelligent control system in real time. The control system can adjust the bypass valves on the exhaust pipes connecting each stage to optimize the heat distribution between stages. If the detected moisture content is higher than the target value, the control system judges that the drying intensity is insufficient, and then simultaneously executes: a) appropriately increasing the power of the main heater to increase the inlet air temperature of the first-stage drying unit; b) appropriately reducing the feeding rate to extend the residence time of the material in the most critical first-stage drying unit. If the detected moisture content is lower than the target value, the control system judges that the drying is over-drying and energy consumption is wasted, and then simultaneously executes: a) appropriately reducing the power of the main heater; b) appropriately increasing the feeding rate to maximize output while ensuring that the product moisture content is qualified.

[0012] Preferably, the intelligent control system employs a fuzzy PID control algorithm to respond more smoothly and quickly to moisture fluctuations.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention achieves deep coupling and synergistic effect of drying and depolymerization: under 80℃ high temperature gas and 8MPa pressure, the moisture content is reduced from 0.7% to 0.1% and the output is increased by 35%. It integrates the process of "high temperature dehydration at the source + pipeline insulation + precise pressure control" to solve the industry pain points of high energy consumption and large moisture fluctuation in traditional downstream drying.

[0014] Energy saving and consumption reduction, and significantly increased unit output: Compared with traditional hot air drying, this process has a very fast heat and mass transfer rate, and the thermal efficiency can be increased to more than 70%. Since drying and depolymerization are completed simultaneously, the subsequent separate depolymerization equipment (such as air jet mill) and its energy consumption are eliminated. Under the same energy consumption, the processing capacity (output) per unit time can be increased by 20%-40%.

[0015] To prevent secondary agglomeration, the process is streamlined: the material has a very short residence time in the reactor (on the order of seconds) and is always in a highly dispersed suspension state. After discharge, it is rapidly cooled, which effectively avoids changes in the surface properties of the particles and secondary agglomeration caused by prolonged heating. At the same time, due to the instantaneous high temperature, it has little impact on the intrinsic structure of talc powder and can maintain good whiteness and physicochemical properties.

[0016] Flexible and controllable with strong product adaptability: By adjusting the temperature, pressure, and flow rate (carrier gas ratio) of the compressed gas, the drying intensity and depolymerization intensity can be flexibly controlled, thereby producing products with different moisture and fineness requirements to meet diverse market demands. Detailed Implementation

[0017] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0018] A process for reducing the moisture content of talc powder and increasing its yield using high-temperature compressed gas includes the following steps: A. Raw material preheating and feeding: Start the system, set the target moisture content of the final product (e.g., 0.1%), and set the initial temperature parameters of each drying unit. Feed the wet talc powder raw material with an initial moisture content of 2%-8% continuously and stably into a multi-stage series preheating conveyor (e.g., from the third stage to the second stage, and finally into the first stage, while the hot air flow direction is the opposite). Utilize the system's waste heat (e.g., exhaust gas with a temperature of 90-120℃ from the subsequent separator) to pre-dry the wet material, thereby reducing the material's viscosity and evaporating some surface water. At the same time, ensure smooth feeding. After the material has been pre-dried in the previous stage, its temperature has increased and its moisture content has decreased. Then, it enters the next drying unit, where it encounters exhaust gas with a higher temperature from the previous stage for deep drying. The pre-dried material enters the feed port of the gas jet drying depolymerization reactor and comes into contact with fresh hot air at the highest temperature (e.g., 400℃) provided by the main heater. B. High-temperature compressed gas jet impact and instantaneous drying and depolymerization: High-temperature and high-pressure gas is introduced into the gas jet drying and depolymerization reactor and passed through a specially designed Laval nozzle or pressure reducing nozzle. The gas is instantly depressurized and expanded at the bottom or tangential inlet of the flash drying tower. The gas volume expands rapidly, and the temperature drops slightly but remains at a high temperature (e.g., from 600℃ to 350℃). At the same time, extremely high flow velocities (up to 200-400m / s) and strong turbulence are generated. Preheated wet talc powder is added quantitatively from the top of the tower or the other side and encounters this high-speed and high-temperature gas flow. C. Gas-solid separation and product collection: The gas-solid two-phase flow that has completed instantaneous drying and depolymerization enters a high-efficiency cyclone separator at the top of the drying tower for primary separation. Most of the qualified dried fine powder products are collected here. Subsequently, the dust-laden exhaust gas enters a bag filter or cartridge filter for secondary fine separation. The captured ultrafine powder is collected separately as a high-value-added product. Most of the high-temperature exhaust gas after separation (temperature is usually between 80-150℃) is returned to the air inlet of the high-temperature and high-pressure gas source system. It is mixed with fresh air as preheated gas and then enters the air compressor. The remaining part is introduced into the waste heat recovery device for recycling to preheat fresh air or raw materials, which can further reduce the system heat loss. D. Product Cooling and Post-processing: The talc powder collected from the cyclone separator, bag filter or cartridge filter is at a high temperature (about 80-120℃). It needs to enter the fluidized bed cooler or cooling screw conveyor to cool it to below 40℃ with room temperature air or cooling water to prevent heat accumulation and moisture absorption. After cooling, the product is screened and iron is removed to obtain the final low-moisture, highly dispersible talc powder product.

[0019] The drying unit in step A is a combination of a stirred dryer, a disc dryer, or an airflow drying tube to ensure that the material is in full contact with the hot air, and the following synergistic effects occur during the mixing stage: a) Ultra-fast heat and mass transfer: The huge sensible heat carried by the high-temperature gas is instantly transferred to the talc particles through extremely high gas-solid relative velocity (up to 100-300 m / s), causing the internal moisture to vaporize rapidly; b) Particle deagglomeration and refinement: The powerful shear force and inter-particle collision force generated by the high-pressure, high-speed airflow can effectively crush the "soft agglomerates" formed by moisture and van der Waals forces. At the same time, the micro-explosion effect (i.e., "flash evaporation") generated by the instantaneous vaporization of moisture inside the particles further "opens up" the particles from the inside, promoting the separation of layers and the breaking of agglomerates; c) Removal of encapsulated water: The micro-explosion effect and strong turbulent disturbance help to expose the encapsulated moisture, making it easier to evaporate.

[0020] The high-temperature and high-pressure gas preparation method in step B is as follows: a) Compress air or inert gas (such as nitrogen) at normal temperature and pressure to 8MPa using an air compressor to obtain high-pressure gas; b) Then, pass this high-pressure gas into a gas heater or electric heater and rapidly heat it to 400-650℃ to form high-temperature and high-pressure gas. The mass ratio (gas-solid ratio) of the high-temperature and high-pressure gas to wet talc powder is controlled within the range of 4:1-10:1 to balance the drying effect and energy consumption. At the same time, the bottom of the flash drying tower is equipped with a stirrer or crushing device to break up any wet material clumps and ensure uniform material dispersion. The gas jet drying depolymerization reactor can be designed as a counter-spray type, vortex cavity type, or annular gap acceleration type structure to create a high-intensity gas-solid turbulent mixing and impact zone.

[0021] In step B, after the encounter, the following processes occur within a very short dwell time (0.5-5 seconds): a) Super-strong heat and mass transfer: The extremely high relative gas-solid velocity and huge contact area allow the heat of the high-temperature gas to be instantly transferred to the wet talc powder particles, and the moisture inside and on the surface of the particles rapidly vaporizes; b) Powerful deagglomeration: The strong shear force generated by the high-speed airflow and the collision and friction between particles can effectively break up the initial agglomerates of wet talc powder and prevent secondary agglomeration during the rapid evaporation of moisture, so as to achieve the effect of simultaneous drying and deagglomeration.

[0022] It also includes online moisture detection and adaptive feedback control: the moisture content of the pre-dried material is detected in real time by an online moisture detector (such as a near-infrared or microwave moisture meter), and the detection signal is transmitted to the intelligent control system in real time. The control system can adjust the bypass valves on the exhaust pipes connecting each stage to optimize the heat distribution between stages. If the detected moisture content is higher than the target value, the control system judges that the drying intensity is insufficient and then simultaneously executes: a) appropriately increasing the power of the main heater to increase the inlet air temperature of the first-stage drying unit; b) appropriately reducing the feeding rate to extend the residence time of the material in the most critical first-stage drying unit. If the detected moisture content is lower than the target value, the control system judges that the drying is over-drying and energy is wasted, and then simultaneously executes: a) appropriately reducing the power of the main heater; b) appropriately increasing the feeding rate to maximize output while ensuring that the product moisture content is qualified.

[0023] The intelligent control system employs a fuzzy PID control algorithm to respond more smoothly and quickly to moisture fluctuations.

[0024] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A process for reducing the moisture content of talc powder and increasing its yield by high-temperature compressed gas, characterized in that: Includes the following steps: A. Raw material preheating and feeding: Start the system, set the target moisture value of the final product, and set the initial temperature parameters of each drying unit. The wet talc powder raw material with an initial moisture content of 2%-8% is continuously and stably fed into a multi-stage series preheating conveyor through a screw feeder or star feeder (for example, from the third stage to the second stage, and finally into the first stage, while the hot air flow direction is the opposite). The system waste heat is used to pre-dry the wet material. After the material has been pre-dried in the previous stage, the temperature has increased and the moisture content has decreased. Then it enters the next drying unit, where it meets the exhaust gas from the previous stage, which has a higher temperature, for deep drying. The pre-dried material enters the feed port of the gas jet drying depolymerization reactor and comes into contact with the fresh hot air at the highest temperature provided by the main heater. B. High-temperature compressed gas jet impact and instantaneous drying and depolymerization: High-temperature and high-pressure gas is introduced into the gas jet drying and depolymerization reactor and passed through a specially designed Laval nozzle or pressure reducing nozzle. The gas is instantly depressurized and expanded at the bottom or tangential inlet of the flash drying tower. The gas volume expands rapidly, the temperature drops slightly but remains at a high temperature, and at the same time, extremely high flow velocity and strong turbulence are generated. Preheated wet talc powder is added quantitatively from the top of the tower or the other side and meets this high-speed and high-temperature gas flow. C. Gas-solid separation and product collection: The gas-solid two-phase flow that has completed instantaneous drying and depolymerization enters a high-efficiency cyclone separator at the top of the drying tower for primary separation. Most of the qualified dried fine powder products are collected here. Subsequently, the dust-laden exhaust gas enters a bag filter or cartridge filter for secondary fine separation. The captured ultrafine powder is collected separately as a high-value-added product. Most of the high-temperature exhaust gas after separation is returned to the inlet of the high-temperature and high-pressure gas source system, and the remaining part is introduced into the waste heat recovery device for recycling to preheat fresh air or raw material preheating. D. Product Cooling and Post-processing: The talc powder collected from the cyclone separator, bag filter or cartridge filter is at a high temperature and needs to enter the fluidized bed cooler or cooling screw conveyor to cool it to below 40°C with ambient air or cooling water. After cooling, the product is screened and iron is removed to obtain the final low-moisture, highly dispersible talc powder product.

2. The process for reducing the moisture content of talc powder and increasing its yield using high-temperature compressed gas according to claim 1, characterized in that: The drying unit in step A is a combination of a stirred dryer, a disc dryer, or an airflow drying tube, and the following synergistic effects occur during the mixing stage: a) Ultra-fast heat and mass transfer: The enormous sensible heat carried by the high-temperature gas is instantly transferred to the talc particles through extremely high gas-solid relative velocity; b) Particle deagglomeration and refinement: The powerful shear force and inter-particle collision force generated by the high-pressure, high-speed airflow, along with the micro-explosion effect generated by the instantaneous vaporization of moisture inside the particles; c) Removal of encapsulated water: Micro-explosion effect and strong turbulent disturbance.

3. The process for reducing the moisture content of talc powder and increasing its yield using high-temperature compressed gas according to claim 1, characterized in that: The high-temperature and high-pressure gas preparation method in step B is as follows: a) Compressing air or inert gas at normal temperature and pressure to 8MPa using an air compressor to obtain high-pressure gas; b) Then passing this high-pressure gas into a gas heater or electric heater and rapidly heating it to 400-650℃ to form high-temperature and high-pressure gas, and controlling the mass ratio of high-temperature and high-pressure gas to wet talc powder within the range of 4:1-10:

1. At the same time, the bottom of the flash drying tower is equipped with a stirrer or crushing device, and the gas jet drying depolymerization reactor can be designed as a counter-spray type, vortex cavity type, or annular gap acceleration type structure.

4. The process for reducing the moisture content of talc powder and increasing its yield using high-temperature compressed gas according to claim 1, characterized in that: In step B, after the encounter, the following processes occur within a very short dwell time: a) Super-strong heat and mass transfer: The extremely high relative gas-solid velocity and huge contact area allow the heat of the high-temperature gas to be instantly transferred to the wet talc powder particles, and the moisture inside and on the surface of the particles rapidly vaporizes; b) Powerful deagglomeration: The strong shear force generated by the high-speed airflow and the collision and friction between particles can effectively break up the initial agglomerates of wet talc powder and prevent secondary agglomeration during the rapid evaporation of moisture, achieving the effect of simultaneous drying and deagglomeration.

5. The process for reducing the moisture content of talc powder and increasing its yield using high-temperature compressed gas according to claim 1, characterized in that: It also includes online moisture detection and adaptive feedback control: the moisture content of the pre-dried material is detected in real time by an online moisture detector, and the detection signal is transmitted to the intelligent control system in real time. If the detected moisture content is higher than the target value, the control system judges that the drying intensity is insufficient, and then simultaneously executes: a) appropriately increasing the power of the main heater and increasing the inlet air temperature of the first-stage drying unit; b) appropriately reducing the feeding rate to extend the residence time of the material in the most critical first-stage drying unit. If the detected moisture content is lower than the target value, the control system determines that the product is over-dried and energy is wasted, and then simultaneously executes: a) appropriately reducing the power of the main heater; b) appropriately increasing the feeding rate to maximize output while ensuring that the product moisture content is within acceptable limits.

6. The process for reducing the moisture content of talc powder and increasing its yield using high-temperature compressed gas according to claim 5, characterized in that: The intelligent control system employs a fuzzy PID control algorithm to respond more smoothly and quickly to moisture fluctuations.