Low specific gravity polymer dry powder automatic feeding device and feeding control method thereof

Abstract

The application discloses a low-specific-gravity polymer dry powder automatic feeding device and a feeding control method thereof, and relates to the technical field of powder material conveying equipment. A fluidization air-permeable plate on a conical hopper wall of a powder storage tank constitutes the only air supplement path under a feeding working condition, and the fluidization gas is used as a conveying carrier gas. The lower part of the upper storage tank is composed of an air-permeable wall and a jacket wall, and the interlayer is a drying cavity. A controller takes the pressure drop across the material suction section as a solid phase load characteristic quantity, calculates the mean value and the standard deviation thereof according to a sliding time window, and judges the material breakage state, the stable state, the unstable state and the over-charging state according to the mean value and the standard deviation, and adjusts the fluidization gas flow online. The flow is synchronously adjusted back when the arch is broken in stages. Meanwhile, different cross-wall pressure difference target values are taken under the feeding, standby and discharging working conditions, so that the drying cavity pressure follows the storage cavity pressure. The application can simultaneously inhibit the bridging, material breakage and over-charging pipe blockage, and reduce the drying gas consumption and the air-permeable surface blind blockage.

Description

Technical Field

[0001] This invention relates to the field of powder material conveying equipment, specifically to an automatic feeding device for low-density polymer dry powder and its feeding control method. Background Technology

[0002] Polyacrylamide, acrylic resin, and other polymer powders typically have a bulk density of only 0.30 g / cm³ to 0.60 g / cm³. Their surfaces are rich in hydrophilic groups, making them highly susceptible to moisture absorption and clumping. This leads to bridging or "rat holes" within the hopper, where material flows only through a central channel while surrounding material remains stagnant. These materials are difficult to transport. Manual loading is labor-intensive and generates significant dust pollution. Screw conveyors exert shearing and frictional heat on the long polymer chains, easily causing a decrease in molecular weight, and still struggle to prevent adhesion and bridging to the hopper walls. Therefore, negative pressure pneumatic conveying has become a common solution for loading these materials.

[0003] CN104261135A discloses a negative pressure feeding device for a dry granulator. The storage tank has a closed space inside, and the bottom of the tank is conical and equipped with a connecting pipe component. The outer wall of the inner connecting pipe component and the inner wall of the outer connecting pipe component form an air inlet channel. When feeding under negative pressure, external air enters the tank through the air inlet channel, passes through the accumulated powder, and is drawn away together with the powder through the flow hole on the powder baffle. The solid-to-gas ratio is related to the size of the flow hole. After the sensor detects a lack of material, it drives the tank to swing left and right to break the arch bridge. For low-density polymer dry powder, this solution has three limitations in application: First, the air replenishment is taken from untreated outside air and passes directly through the powder layer, which is equivalent to continuously introducing moisture into the material layer for hygroscopic materials; Second, the solid-to-gas ratio is determined once by the size of the flow orifice, but the flowability of low-density polymer dry powder varies with the material level, batch moisture content and storage time, and the fixed solid-to-gas ratio is difficult to take into account different working conditions. If the air replenishment is too small, the cone bucket will bridge and break the material, and if the air replenishment is too large, the powder will be over-aerated and rush into the pipeline, causing blockage; Third, relying on the overall swing of the bucket to break the arch is limited by the volume of the bucket and the support method, and it is difficult to implement for powder storage tanks of ten cubic meters.

[0004] CN203544799U discloses a powder silo anti-bridging device and a powder silo. It describes that the working surface of an existing anti-bridging and flow-aiding air cushion is made of porous material with small pores that prevent powdery materials from passing through. However, it is prone to rupture under overpressure, and after rupture, the powder airway system experiences backflow of ash, leading to airway blockage. Therefore, porous permeable surfaces used for flow aids require specialized measures in terms of both pressure resistance and prevention of powder backflow. Furthermore, during long-term operation, powder may become embedded in the pores when the pressure difference disappears or reverses, causing the permeable surface to gradually lose its permeability. This phenomenon is not addressed in the aforementioned literature, nor are any methods provided for actively maintaining the permeability of the permeable surface during operation.

[0005] On the other hand, negative pressure pneumatic conveying typically uses the vacuum level of the conveying pipeline as an indicator of the material flow status. The inventors of this application have discovered that the effectiveness of this indicator depends on the gas supply method. When the gas supply port is open to the atmosphere, the gas supply volume adapts to the total system resistance; as the solid load increases, the gas supply volume decreases, and the vacuum pump draws to a deeper vacuum, thus the vacuum level monotonically increases with the solid load. However, once the gas supply is changed to a metered supply of dry gas via a regulating valve for moisture prevention, the vacuum pump inlet pressure is mainly determined by the mass flow rate of the gas supply. The vacuum level at any single point on the pipeline no longer monotonically changes with the solid load, and the fluidizing gas flow rate itself is also a regulating mechanism. Therefore, its direct impact on the vacuum level is intertwined with the indirect impact generated by the solid load. Therefore, how to obtain a solid load feedback quantity with a definite direction that can be used for closed-loop tuning under quantitative gas replenishment is a problem that must be solved in combining the above-mentioned moisture-proof measures with online solid-gas ratio tuning. Existing solutions do not discuss this issue. The above-mentioned understanding that the vacuum degree loses its monotonicity under quantitative gas replenishment is something that the inventors obtained during the research and development process. It is not common knowledge or existing technology.

[0006] In summary, when using negative pressure pneumatic conveying for low-density polymer dry powder, the following problems still need to be addressed: the air supply source is not dried, which conflicts with the moisture-proof objective; under quantitative air supply conditions, there is a lack of solid phase load feedback with a definite direction, making it difficult to adjust the solid-to-gas ratio online, and it is difficult to simultaneously address the two types of faults: bridging material breakage and overfilling pipe blockage; and porous permeable surfaces used for moisture-proofing or flow aiding lack measures to prevent backflow and blind blockage. Summary of the Invention

[0007] The purpose of this invention is to provide an automatic feeding device for low-density polymer dry powder and its feeding control method, so as to achieve fully enclosed, dry and low-damage conveying of polymer dry powder, simultaneously suppressing bridging and material breakage and overfilling and pipe blockage in the same air circuit, and maintaining the long-term air permeability of the porous air permeable surface.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: An automatic feeding device for low-density polymer dry powder includes a powder storage tank, a drying air source unit, a negative pressure conveying unit, an upper storage tank, and a controller.

[0009] The powder storage tank is a vertical, sealed tank with a conical bottom. A fluidizing and venting plate is embedded in the hopper wall. A suction port with a suction valve is located at the bottom of the conical hopper, and the suction port is connected to the upper storage tank via a conveying pipeline. A vent with a breather valve is located at the top of the storage tank. During the feeding process, the controller closes the breather valve, ensuring that the fluidizing and venting plate forms the sole air supply path for the storage tank during feeding. This means that all the air required for negative pressure conveying is provided by fluidizing gas, which simultaneously serves the functions of aiding flow and breaking arches, as well as conveying the carrier gas.

[0010] The outlet of the drying gas source unit has a fluidizing gas branch, a drying chamber inlet branch, and a backflush gas branch. The fluidizing gas branch is equipped with a first proportional regulating valve and is connected to the fluidizing permeable plate. The pressure dew point of the gas at the outlet of the drying gas source unit is not higher than -40℃.

[0011] The negative pressure conveying unit includes a vacuum pump, conveying pipeline, and a conveying differential pressure transmitter. The positive pressure side of the conveying differential pressure transmitter is connected to the upper gas phase space of the powder storage tank, and the negative pressure side is connected to a pressure tap located 0.5m to 1.5m downstream of the suction port on the conveying pipeline. Its output is the pressure drop p across the suction section. s .

[0012] The upper part of the upper storage tank is a solid-walled cylinder, while the lower part consists of a permeable wall and a jacketed wall covering the outside of the permeable wall. The interlayer between the two forms the drying chamber, and the inner cavity of the upper storage tank forms the storage chamber. The top of the upper storage tank is equipped with a filter chamber and a pulse backflushing device, which is connected to the backflushing air branch. The bottom of the upper storage tank is equipped with a discharge pipe with a discharge valve. The storage chamber is equipped with a stirring device and a level gauge. A second proportional regulating valve is installed on the air inlet branch of the drying chamber and is connected to the drying chamber. A pressure equalization branch connects the upper gas phase space of the drying chamber and the storage chamber, and a third proportional regulating valve is installed on the pressure equalization branch. A transwall differential pressure transmitter is also installed between the two, and its output is the pressure difference between the drying chamber and the upper gas phase space of the storage chamber, i.e., the transwall pressure difference Δp.

[0013] The controller is electrically connected to the conveying differential pressure transmitter, the trans-wall differential pressure transmitter, the level gauge, the first proportional control valve, the second proportional control valve, the third proportional control valve, the suction valve, the discharge valve, the breather shut-off valve, the stirring device, and the vacuum pump. The controller has feeding mode, standby mode, and discharge mode, and is configured to: close the discharge valve and the breather shut-off valve in the feeding mode, and calculate the pressure drop p in the suction section according to the sliding time window. s mean p m And standard deviation σ, and determine the conveying status according to the following rules: p m When the material level is less than the lower limit p1, it is considered a material shortage state. m When the charge level is greater than the overcharge limit p2, it is considered an overcharge state. m When the pressure difference is not less than p1 and not greater than p2, and σ is greater than the upper limit of fluctuation σ2, it is judged as an unstable state; otherwise, it is judged as a stable state. In the material shortage state, the fluidizing gas flow rate Q is increased; in the overcharge state, the fluidizing gas flow rate Q is decreased; in the unstable state, the fluidizing gas flow rate Q is kept constant; in the stable state, the fluidizing gas flow rate Q is proportionally and integrally adjusted with the set value p0 as the target, where p0 is greater than p1 and less than p2. At the same time, the second and third proportional control valves are controlled in a split-range manner to make the cross-wall pressure difference Δp stabilize at the pressure difference target value as the pressure in the storage chamber changes. The pressure difference target value Δp1 under the feeding condition is less than the pressure difference target value Δp2 under the standby condition, and Δp2 is less than the pressure difference target value Δp3 under the discharging condition.

[0014] The four states of the above criteria do not overlap and cover all value combinations, leaving no blind spots in the discrimination. Preferably, in the material-cut-off state, the fluidizing gas flow rate is increased step by step and the arch is broken in stages according to the order of fluidization, vibration, and mechanical loosening, and the fluidizing gas flow rate is adjusted back to the reference flow rate Q0 at the same time as starting the vibrator or loosening rod; in the overcharge state, the fluidizing gas flow rate is reduced and the suction valve is closed if necessary; in the unstable state, the fluidizing gas flow rate is kept constant and short pulse vibration is applied; in the stable state, proportional-integral adjustment is performed with p0 as the set value.

[0015] Preferably, the controller also pre-stores the correspondence between the pressure drop of the suction section and the fluidizing gas flow rate Q under empty tank conditions as an empty load baseline, and uses p m The difference between the current fluidizing gas flow rate Q and the no-load baseline value is used as a solid-phase load characteristic quantity for discrimination, so as to further eliminate the influence of fluidizing gas flow rate changes on the criterion.

[0016] Preferably, the outlet of the second proportional regulating valve on the air inlet branch of the drying chamber is provided with a flow-limiting orifice plate; the air inlet branch of the drying chamber is also provided with a hole-keeping pulse valve, which is connected in parallel with the branch formed by the second proportional regulating valve and the flow-limiting orifice plate connected in series, and its outlet is directly connected to the drying chamber without passing through the flow-limiting orifice plate; the controller increases the cross-wall pressure difference through the hole-keeping pulse valve before each spraying action of the pulse backflushing device, and periodically opens the hole-keeping pulse valve to form a hole-keeping pulse in the standby condition.

[0017] As a preferred option, the outlet of the filter chamber is divided into two paths: one path is connected to the vacuum pump via a vacuum shut-off valve, and the other path is connected to the external dust removal system via a back pressure exhaust valve. In standby and feeding conditions, the vacuum shut-off valve is closed, and the dry gas that seeps into the storage chamber through the ventilated wall is discharged by the back pressure exhaust valve, so that the storage chamber maintains a slight positive pressure.

[0018] Preferably, the powder storage tank has a vibrator on the outer wall of the conical hopper and a loosening rod inside the hopper. The loosening rod includes a cylinder, a guide sleeve passing through the hopper wall, a rigid core rod driven by the cylinder and extending into the hopper through the guide sleeve, and an elastic umbrella-shaped head fixed to the inner end of the core rod. The core rod is a rigid component and is constrained by the guide sleeve, while only the umbrella-shaped head is an elastic component. The arch-breaking action mainly occurs during the retraction stroke. After the umbrella-shaped head opens, it forms a downward peeling action on the arch above it. Two lip-shaped sealing rings are arranged in series along the axial direction of the core rod inside the guide sleeve. The annular cavity between the two lip-shaped sealing rings forms a sealing cavity. The sealing cavity is connected to the drying air source unit through an air inlet branch equipped with a constant flow orifice plate and is kept at a pressure higher than atmospheric pressure. This ensures that the pressure in the sealing cavity is simultaneously higher than the negative pressure inside the hopper and the external atmospheric pressure. A small amount of gas leaks into the tank at the inner lip seal to prevent powder from entering the sealing area, and a small amount of gas leaks into the atmosphere at the outer lip seal, preventing external humid air from being drawn into the tank even after the lip seal wears down.

[0019] Preferably, both the permeable wall and the fluidized bed are made of sintered stainless steel, and the pore size of the permeable wall is smaller than the d of the polymer dry powder. 10 Particle size; Each fluidized bed inlet is equipped with a flow equalization plate and a one-way valve. The flow equalization plate forces a uniform distribution of air volume among the fluidized beds to prevent all airflow from flowing to the section with the least resistance. The one-way valve prevents powder from flowing back into the air path under the static pressure of the material column after shutdown. The stirring device in the storage chamber includes a rotating shaft and a stirring frame mounted on the rotating shaft. The stirring frame rotates at a low blade tip linear velocity, which avoids strong shearing of the polymer long chains on the one hand, and maintains a small gap between its outer edge and the inner surface of the permeable wall on the other hand. During rotation, it scrapes off the powder adhering to the inner surface of the permeable wall, which, together with the pore-preserving pulse, constitutes a micropore anti-blind blockage measure.

[0020] As a preferred embodiment, a dead zone is provided at the split point of the split control to prevent the second and third proportional control valves from operating simultaneously near the split point, causing the drying gas to directly short-circuit into the storage chamber via the pressure equalization branch; in addition to the operation of the orifice pulse valve, the controller will also limit the cross-wall pressure difference to prevent the powder from being excessively fluidized in the conical section and gushing out when the valve is opened.

[0021] As a preferred embodiment, the top of the powder storage tank is also equipped with an air inlet, which is connected to the drying air source unit in sequence via an air inlet shut-off valve and a pressure reducing valve. Both the breathing shut-off valve and the air inlet shut-off valve are soft-seal shut-off valves and are equipped with valve position detection switches. The controller is allowed to start the vacuum pump only after receiving the closed signal output by the breathing shut-off valve, thereby ensuring that the powder storage tank is reliably isolated from the atmosphere during the feeding process in an interlocking manner, and avoiding the intake of outside humid air under negative pressure due to the valve not being closed in place.

[0022] Compared with the prior art, the present invention has the following beneficial effects: 1. A single gas source fundamentally eliminates the introduction of moisture during the gas replenishment process. The powder storage tank is a sealed tank. During the feeding operation, the breather valve at the top of the tank is closed, and its closed-position signal constitutes a necessary condition for the vacuum pump to start. All the replenishment gas required for negative pressure conveying is supplied through the fluidized permeable plate. All gas entering the system is taken from the same dry gas source with a pressure dew point not higher than -40℃. Compared with the scheme in CN104261135A where external air enters through the material layer, this invention avoids direct contact between humid air and powder without sacrificing the solid-to-gas ratio adjustment function.

[0023] 2. By replacing the single-point vacuum degree with the pressure drop across the suction section, the problem of unobservable solid load under quantitative gas replenishment conditions is solved. As described in the background art, when the gas replenishment is quantitatively controlled by the first proportional regulating valve, the vacuum pump inlet pressure is mainly determined by the mass flow rate of the replenished gas. The vacuum degree at any single point on the pipeline no longer changes monotonically with the solid load, and therefore cannot be used as a feedback quantity for solid-gas ratio tuning. This invention uses the pressure drop p between the upper gas phase space of the powder storage tank and the pressure tapping point downstream of the suction port.s As a characteristic of solid load: the pressure drop is mainly caused by the inflow and acceleration of powder at the feed inlet, and increases monotonically with solid load; while the change in fluidizing gas flow rate Q will simultaneously raise or lower the absolute pressure at both pressure taps. This effect occurs in a common-mode manner and is mostly offset by differential pressure measurement, thus making the operating variable Q and the controlled variable p... m The causal relationship between them is singular and the direction is definite, thus enabling closed-loop tuning to be established.

[0024] 3. A two-dimensional criterion is constructed using the mean and pulsation standard deviation to simultaneously suppress two opposing types of faults: bridging and overcharging. For low-density polymer dry powders, the limiting factor for conveying capacity is the flowability of the powder within the cone hopper. Therefore, within the set range, the conveying capacity increases monotonically with the fluidizing gas flow rate. However, when the fluidizing gas flow rate exceeds a critical value, the powder loses internal friction due to over-aeration and rushes into the suction port, leading to a sudden increase in the solid-to-gas ratio and pipe blockage. This optimal window drifts with the material level and batch moisture content, making fixed-value gas replenishment unsuitable. This invention uses p m The solid load inside the pipe is characterized by the standard deviation σ, which characterizes the stability of the material flow: p m The direction of the out-of-bounds movement is given, and σ indicates the stability of the material flow. Only p... m It is impossible to distinguish between stable conveying and intermittent conveying caused by local collapse of the material layer. Introducing σ can separate the two, thereby achieving closed-loop tuning within the window.

[0025] 4. The staged arch breaking and fluidizing gas recirculation are linked, eliminating the risk of overfilling induced by the arch breaking action itself. Vibration or mechanical loosening causes the arch to collapse suddenly. If the fluidizing gas is still at its upper limit at this time, the collapsing powder will be immediately over-inflated, directly jumping from a material shortage state to an over-inflated state and clogging the pipe. This invention recirculates the fluidizing gas flow rate back to the reference flow rate while starting the vibrator or loosening rod, and then gradually increases it after it stabilizes, thus decoupling the arch breaking and aeration actions in terms of timing.

[0026] 5. The drying chamber is controlled by a constant pressure difference following the pressure of the storage chamber, taking into account moisture penetration prevention, drying gas conservation, and prevention of blind blockage in the micropores. If the drying chamber is controlled by a fixed pressure, the storage chamber will be under negative pressure during the feeding process, and the cross-wall pressure difference will rise to over 30 kPa. On the one hand, a large amount of drying gas will enter the storage chamber through the micropores and be drawn away by the vacuum pump, wasting gas resources and weakening the conveying pressure drop at the suction port; on the other hand, the high-speed perforating airflow will blow away the powder that has just fallen in and carry it into the filter chamber, increasing the pulse backflushing load. This invention reduces the target pressure difference value to Δp1 during the feeding process, raises it to Δp2 during the standby process to maintain a slightly positive pressure for moisture prevention, and raises it to Δp3 during the feeding process to aid flow. At the same time, a positive pressure spike will appear in the upper gas phase space of the storage chamber during the pulse backflushing. If not treated, the cross-wall pressure difference may reverse, forcing the powder into the micropores and causing blind blockage. This invention uses feedforward pressure increase to ensure that the cross-wall pressure difference is positive throughout the process.

[0027] 6. The permeable surface is equipped with both backflow prevention and blind blockage prevention measures, ensuring long-term permeability. Firstly, the permeable wall is only located in the lower part of the upper storage tank, while the upper part of the upper storage tank is a solid-walled cylinder, preventing short-circuiting of the drying gas caused by exposed permeable surfaces at low material levels. Secondly, the flow-limiting orifice plate on the air inlet branch of the drying chamber limits the maximum flow capacity of the drying gas, thus constraining the amount of short-circuited gas when partially exposed. Thirdly, the pore-preserving pulse in standby mode blows out powder particles embedded in micropores from the inside out, cooperating with the wall scraping of the stirring frame. Fourthly, each fluidized permeable plate has a one-way valve at its air inlet end, and when feeding ends, the suction valve is closed first, the fluidized gas continues to purge, and then the fluidized gas branch is closed to prevent powder from embedding in the channels or backflowing into the air path under the static pressure of the material column after shutdown.

[0028] 7. The entire process is a closed pipeline conveying system with no dust leakage; the blade tip linear velocity of the low-speed agitator in the storage chamber is no more than 0.5m / s, which avoids the strong shearing and thermal damage to the long polymer chains caused by the screw conveyor. It is suitable for fine chemical and pharmaceutical intermediate powders that require protection of molecular weight. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the overall structure of the feeding device in Example 1; Figure 2 This is a schematic diagram of the structure of the loose rod in Example 1; Figure 3 This is a schematic diagram showing the electrical connections between the controller and each sensor and actuator in Example 1; Figure 4 This is a flowchart of the feeding control method in Example 2; In the diagram: 1-Powder storage tank, 11-Conical hopper, 12-Fluidizing permeable plate, 121-Flow equalization orifice plate, 122-One-way valve, 13-Suction port, 14-Suction valve, 15-Vibrator, 16-Loosening rod, 161-Cylinder, 162-Guide sleeve, 163-Core rod, 164-Umbrella head, 17-Breathing shut-off valve, 18-In-tank pressure transmitter, 110-Maintenance air shut-off valve, 2-Drying air source unit, 21-First proportional regulating valve, 22-Second proportional regulating valve 23-Pulse valve, 24-Dew point meter, 25-Orifice-holding pulse valve, 26-Flow limiting orifice plate, 31-Vacuum pump, 32-Conveying pipeline, 33-Conveying differential pressure transmitter, 34-Vacuum shut-off valve, 4-Upper storage tank, 41-Jacket wall, 42-Storage chamber, 43-Ventilating wall, 44-Drying chamber, 45-Discharge pipe, 46-Discharge valve, 47-Cross-wall differential pressure transmitter, 48-Third proportional regulating valve, 49-Filter chamber, 410-Pulse backflushing device. Detailed Implementation

[0030] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0031] Example 1 like Figures 1 to 3 As shown, this embodiment provides an automatic feeding device for low-density polymer dry powder, including a powder storage tank 1, a drying air source unit 2, a negative pressure conveying unit, an upper storage tank 4, and a controller.

[0032] The drying air source unit 2 includes a screw air compressor, an oil removal filter, a refrigerated dryer, an adsorption dryer, a two-stage precision filter, and an air storage tank connected in sequence. All of the above components are commercially available conventional equipment. The exhaust volume of the drying air source unit 2 is 3.6 m³ / min. The air storage tank outlet is equipped with a dew point meter 24, the outlet pressure is 0.6 MPa, and the pressure dew point is -45℃.

[0033] The outlet of the drying gas source unit 2 leads to three main gas branches: a fluidizing gas branch, a drying chamber inlet branch, and a backflushing gas branch. The fluidizing gas branch is connected to each fluidizing permeable plate 12 via the first proportional regulating valve 21, and its flow rate is adjustable from 60 m³ / h to 150 m³ / h, with a base flow rate Q0 of 100 m³ / h and an upper limit flow rate Q max The flow rate is 150 m³ / h; the air inlet branch of the drying chamber is connected to the drying chamber 44 via the second proportional regulating valve 22. The outlet of the second proportional regulating valve 22 is equipped with a flow limiting orifice plate 26, and the maximum flow capacity of the flow limiting orifice plate 26 is 30 m³ / h. The air inlet branch of the drying chamber is also equipped with a hole-preserving pulse valve 25, which is connected in parallel with the branch formed by the second proportional regulating valve 22 and the flow limiting orifice plate 26 connected in series. The hole-preserving pulse valve 25 is a solenoid pulse valve with a nominal diameter of DN25, and its outlet is directly connected to the drying chamber 44; the backflush air branch is connected to the pulse backflush device 410 via the pulse valve 23.

[0034] The powder storage tank 1 is a vertical, sealed stainless steel tank with a volume of 20 m³ and an inner diameter of 2400 mm. It is designed to withstand an external pressure of no less than -15 kPa. The exterior of the powder storage tank 1 is filled with insulation material. Inside the powder storage tank 1, three layers of pressure-reducing cones are coaxially arranged from top to bottom. Each cone has a half-cone angle of 30°, a maximum outer diameter of 1440 mm, an annular gap of 480 mm between the outer edge of the pressure-reducing cone and the tank wall, and a layer spacing of 1.2 m. Each layer of pressure-reducing cones is fixed to the tank wall of the powder storage tank 1 by support rods. It should be noted that, based on an inner diameter of 2400 mm, a half-cone angle of 25° for the cone 11, and an outlet inner diameter of 150 mm, the volume of the cone 11 is approximately 3.9 m³. The remaining approximately 16.1 m³ is provided by the cylindrical section, whose height is sufficient to accommodate the three layers of pressure-reducing cones with a layer spacing of 1.2 m.

[0035] It should be noted that the function of the pressure-reducing cone is to bear the weight of the material column above it and transfer it to the tank wall of the powder storage tank 1 via the support rod, thereby forming a stress-shielding zone below it. This prevents the material in the cone hopper 11 from bearing the vertical stress of the entire tank's material column, inhibiting the compaction and arching of the material at the bottom. The value of the annular gap must simultaneously meet two conditions: it must not be less than the critical arch span of the material to prevent the gap itself from becoming a new arching point; and it must not be greater than one-quarter of the inner diameter of the powder storage tank 1 to ensure the pressure relief effect. In this embodiment, the critical arch span of the polyacrylamide dry powder was determined to be 320 mm by shear test, so the annular gap is taken as 480 mm.

[0036] The bottom of the powder storage tank 1 is a conical hopper 11 with a semi-conical angle of 25° and an outlet inner diameter of 150mm. It should be noted that the semi-conical angle referred to in this embodiment is the angle between the generatrix of the conical surface and its central axis, i.e., half of the cone apex angle. A semi-conical angle of 25° corresponds to an angle of 65° between the hopper wall and the horizontal plane. This angle is selected based on the friction angle between the material and the sintered stainless steel wall, according to mass flow principles, to ensure that the material moves downwards as a whole without forming a central rat hole.

[0037] Four fluidizing and permeable plates 12 are evenly embedded along the circumference of the hopper wall of the cone hopper 11. The fluidizing and permeable plates 12 are sintered stainless steel plates with a pore size of 30μm, and the effective area of ​​a single plate is 0.25m², with the four plates totaling 1m². Their working surfaces are flush with the inner surface of the hopper wall. It should be noted that the total area of ​​the fluidizing and permeable plates 12 is determined based on the seepage gas velocity: the apparent gas velocity corresponding to a fluidizing gas flow rate of 60m³ / h~150m³ / h is 60m / h~150m / h, that is, 1m³ / (m²·min)~2.5m³ / (m²·min), which is within the normal seepage gas velocity range of the flow-aiding air cushion, thereby ensuring that the drying gas seeps into the wall-mounted material layer in a low-speed and uniform manner without forming local jets; in this embodiment, the side surface area of ​​the cone hopper 11 is approximately 10.6m², and the above-mentioned permeable area accounts for approximately 9% of it. Each fluidizing permeable plate 12 is equipped with a flow equalization orifice plate 121 and a one-way valve 122 at its air inlet end. The flow equalization orifice plate 121 and the one-way valve 122 are located on the fluidizing gas branch of the drying gas source unit 2. The maximum flow capacity of a single flow equalization orifice plate 121 is 40 m³ / h. Its orifice diameter is selected according to the following criteria: Under the upper limit of the fluidizing gas flow rate, the pressure drop of a single flow equalization orifice plate 121 is not less than 20% of the combined pressure drop of the downstream fluidizing permeable plate 12 and the wall-mounted material layer. In this embodiment, the pressure drop is 6 kPa. The opening direction of the one-way valve 122 is from the gas path to the inside of the powder storage tank 1.

[0038] The bottom of the cone hopper 11 is equipped with a suction port 13, and a suction valve 14 is mounted on the suction port 13. The suction port 13 is connected to the upper storage tank 4 via a conveying pipeline 32. The suction valve 14 is a pneumatic pinch valve with no dead zones in its valve body, preventing powder from entering the valve seat, and not shearing the material during opening and closing. It is also full-bore when fully open. It should be noted that a butterfly valve is not suitable here because butterfly valves are always located in the flow channel, and low-density powders are prone to compaction and agglomeration on the back of the butterfly valve, which will increase local resistance and interfere with the measurement of pressure drop in the suction section. The pneumatic actuator of the suction valve 14 is equipped with a valve position detection switch, which is used to send its output switch position signal to the controller.

[0039] It should be noted that the fluidizing and permeable plate 12 performs two functions. Firstly, it aids flow and breaks up arches: the drying gas penetrates the wall-mounted material layer at a low speed, over a large area, and uniformly, forming an air film on the wall to reduce wall friction. Simultaneously, it slightly aerates the powder adhering to the wall, lowering the internal friction angle, thereby breaking up arches and rat holes. Secondly, it has a unique function of this invention: because the powder storage tank 1 is sealed, and the breathing shut-off valve 17 at the top of the powder storage tank 1 is closed during feeding, the carrier gas required for conveying can only enter through the fluidizing and permeable plate 12. Therefore, the fluidizing gas flow rate Q simultaneously determines the degree of fluidization of the powder in the cone hopper 11 and the solid-to-gas ratio in the conveying pipeline 32, unifying both into a single, online adjustable operating quantity. The air supply pipe cannot replace the fluidizing and permeable plate 12 here because point-source air supply will create perforations, or channels, within the material layer. The gas will then short-circuit directly to the suction port 13 along these local channels, failing to aid flow or carry powder. Only large-area uniform permeation can achieve both flow aiding and air carrying functions. It should be noted that the channeling mentioned here refers to the short-circuit channels formed by gas within the material layer, which is different from the "rat hole" mentioned earlier. A rat hole is a through-flow channel formed by the material itself, where powder flows out only along the channel while surrounding material remains stationary. The causes and consequences of the two are different.

[0040] The purpose of setting up the flow equalization orifice plate 121 is to force a uniform distribution of air volume among the fluidized permeable plates 12, preventing the airflow from all flowing towards the plate with the least resistance and causing flow deviation. The principle is that the four fluidized permeable plates 12 are connected in parallel, and the pressure drop in each branch is equal. If the branch resistance comes entirely from the fluidized permeable plates 12 and the material layer outside them, the resistance differences caused by the material layer thickness and local agglomeration will be directly amplified into air volume differences, with the plate with the least resistance taking away the vast majority of the air volume. After the flow equalization orifice plate 121 is connected in series, as long as the pressure drop of the orifice plate dominates the total pressure drop of the branch, the air volume of each branch is mainly determined by the orifice diameter of the orifice plate. The influence of downstream resistance differences on air volume distribution is correspondingly weakened; therefore, the aforementioned pressure drop percentage should not be less than 20%.

[0041] Regarding whether the fluidizing and permeable plate 12 leaks material: There are two conditions for no leakage during operation: first, the aperture is smaller than the material particle size; second, the airflow direction is always from the air side to the material side, the pressure difference is positive, and the powder cannot enter in reverse. After shutdown, the second condition disappears, and the static pressure of the material column acts directly on the plate surface. To prevent powder from embedding in the channels and backflow into the air path, the following measures are taken: First, each fluidizing and permeable plate 12 has a one-way valve 122 at its air inlet end, preventing powder from entering the air path under any circumstances; second, at the end of feeding, first close the suction valve 14, maintain the fluidizing gas flow rate to continue purging for 10 seconds, and then close the fluidizing gas branch, so that the powder remaining on the working surface and in the channels of the fluidizing and permeable plate 12 is blown away.

[0042] A pneumatic piston vibrator 15 is installed on the outer wall of the cone 11, and a loosening rod 16 is also inserted through the wall of the cone 11. Figure 1 , Figure 2 As shown, the loosening rod 16 includes a cylinder 161, a guide sleeve 162, a core rod 163, and an umbrella-shaped head 164. The guide sleeve 162 passes through the wall of the cone hopper 11, and two lip-shaped sealing rings are arranged in series along the axial direction of the core rod 163 inside it. The annular cavity between the two lip-shaped sealing rings forms a sealing cavity. The sealing cavity is connected to the drying air source unit 2 through a constant flow orifice plate and a pressure reducing valve in sequence. The outlet pressure of the pressure reducing valve is set to 0.3MPa, the orifice diameter of the constant flow orifice plate is 0.3mm, the flow rate is 0.5m³ / h, and the pressure in the sealing cavity is maintained at 5kPa higher than atmospheric pressure. The core rod 163 is a stainless steel rigid rod that is driven by the cylinder 161 to extend into the cone hopper 11 through the guide sleeve 162. The umbrella-shaped head 164 is a silicone rubber part fixed to the inner end of the core rod 163, which is in the shape of an upward-opening umbrella with an outer diameter of 80mm.

[0043] It should be noted that the constant flow orifice plate can provide a constant purging flow rate because it operates in a critical flow state. The absolute pressure inside the sealing cavity is approximately 106 kPa, while the absolute pressure at the outlet of the pressure reducing valve is approximately 400 kPa. The latter is 3.8 times the former, which is greater than the critical pressure ratio of air (1.9 times). Therefore, the flow velocity at the orifice of the orifice reaches the local speed of sound. The flow rate is determined only by the outlet pressure of the pressure reducing valve and the orifice diameter, and is independent of the pressure downstream of the orifice. Thus, regardless of how the negative pressure inside the cone hopper 11 fluctuates with operating conditions, or how the leakage changes after the lip seal wears, the purging air volume remains constant, and the pressure in the sealing cavity is stably maintained within the range of 3 kPa to 10 kPa higher than atmospheric pressure.

[0044] It should also be noted that the core rod 163 of the loosening rod 16 is a rigid component and is constrained by the guide sleeve 162, while only the umbrella-shaped head 164 is an elastic component, thus there is no problem of instability under pressure. The arch-breaking effect of the umbrella-shaped head 164 mainly occurs during the retraction stroke: when the core rod 163 extends, the umbrella-shaped head 164 retracts backward due to material resistance, and the extension resistance is small; during retraction, the umbrella-shaped head 164 opens, forming a downward peeling effect on the arch above it, and the core rod 163 is under tension during this stroke. The reason for choosing silicone rubber for the umbrella-shaped head 164 is that it has low surface energy, does not adhere to hygroscopic powders, and its elastic deformation is sufficient to pass through the orifice of the guide sleeve 162.

[0045] It should also be noted that the use of two tandem lip seals and the introduction of dry gas at a pressure higher than atmospheric pressure into the sealing cavity serves two purposes: Firstly, to ensure the sealing cavity is simultaneously above the negative pressure inside the cone hopper 11 and the external atmospheric pressure. Secondly, to prevent a small amount of gas from leaking into the powder storage tank 1 at the inner lip seal, thus preventing powder from entering the sealed area. Thirdly, to prevent a small amount of gas from leaking into the atmosphere at the outer lip seal, ensuring that even after the lip seal wears down, external humid air cannot be drawn into the powder storage tank 1. If the sealing cavity pressure is set based on the pressure inside the cone hopper 11, the sealing cavity may still be under negative pressure during the feeding process, and the outer lip seal will lose its blocking effect.

[0046] The powder storage tank 1 has a breather port on its top, and a dust collector filter element is installed inside the breather port. A breather shut-off valve 17 is installed on the breather port. The breather shut-off valve 17 is a pneumatic soft-seal butterfly valve with a valve seat made of EPDM rubber. Its leakage rate meets the Class A requirements of GB / T 13927, meaning no visible leakage when closed. Its pneumatic actuator has a valve position detection switch; when the valve is fully closed, this switch outputs a closed-position signal to the controller. It should be noted that the dust collector filter element is located inside the breather port, and the breather shut-off valve 17 is downstream of the filter element. No dust-laden gas passes through its flow channel; therefore, the issue of powder accumulation on the back of the butterfly valve at the aforementioned suction valve 14 does not exist.

[0047] The powder storage tank 1 is also equipped with an air supply port at the top. The air supply port is connected to the drying air source unit 2 via an air supply shut-off valve 110 and a pressure reducing valve. The pressure after pressure reduction is 0.05 MPa. The air supply shut-off valve 110 is a pneumatic soft-seal ball valve, and its pneumatic actuator is also equipped with a valve position detection switch. The powder storage tank 1 is equipped with an internal pressure transmitter 18 with a range of -50 kPa to 50 kPa.

[0048] It should be noted that during the feeding operation of adding powder into the powder storage tank 1, the breathing shut-off valve 17 is open, and the gas displaced by the powder in the tank is discharged through the dust removal filter. During the loading operation, both the breathing shut-off valve 17 and the gas replenishment shut-off valve 110 are closed, and the controller only allows the vacuum pump 31 to start after receiving the signal that the breathing shut-off valve 17 is closed. After the loading is completed and the vacuum pump 31 stops, the gas replenishment shut-off valve 110 is opened to replenish dry gas into the tank to break the residual vacuum and maintain a slight positive pressure of 0.5 kPa to 2 kPa. The powder storage tank 1 is isolated from the atmosphere except for the above-mentioned passages. During the loading operation, the replenishment gas above the powder layer in the tank can only enter through the fluidized permeable plate 12, that is, the fluidized gas constitutes the only replenishment gas passage for negative pressure conveying.

[0049] It should be noted that the "unique gas supply path" in this embodiment refers to the fact that all the gas entering the powder storage tank 1 from the outside during the feeding operation is taken from the drying gas source unit 2, and the portion of it that is adjusted according to the operating conditions is all supplied through the fluidizing permeable plate 12. Although a small amount of the purging gas from the sealing cavity of the loosening rod 16 and the purging gas from the pressure tap of the differential pressure transmitter 33 also seeps into the tank, they are taken from the same drying gas source, limited to a constant flow rate by the constant flow orifice plate, and the total flow rate is not greater than 1.5 m³ / h, not greater than 2.5% of the fluidizing gas flow rate, and has been included in the no-load baseline. Therefore, it does not participate in the setting of the solid-gas ratio and does not affect the uniqueness mentioned above.

[0050] The negative pressure conveying unit includes a vacuum pump 31, a conveying pipeline 32, a conveying differential pressure transmitter 33, and a vacuum shut-off valve 34. The vacuum pump 31 is an oil-free rotary vane vacuum pump driven by a frequency converter. The conveying pipeline 32 is a combination of stainless steel pipe and wear-resistant flexible hose. The conveying differential pressure transmitter 33 has a range of 0 kPa to 40 kPa and a sampling frequency of 100 Hz. Its positive pressure side is connected to the upper gas phase space of the powder storage tank 1, and its negative pressure side is connected to the pressure tapping point located 1 m downstream of the suction port 13 on the conveying pipeline 32. Its output is the pressure drop p in the suction section. s The vacuum shut-off valve 34 is a pneumatic butterfly valve. The top of the upper storage tank 4 is equipped with a filter chamber 49, and the vacuum shut-off valve 34 is located on the pipeline from the outlet of the filter chamber 49 to the vacuum pump 31.

[0051] It should be noted that both pressure taps of the differential pressure transmitter 33 are equipped with microporous filters and are respectively connected to a small amount of dry gas limited to 0.5 m³ / h by a constant flow orifice plate to prevent dust from clogging the pressure tapping channels. Since the purge gas volume and filter specifications on both sides are the same, the additional pressure drop generated by the purge gas at the two pressure taps cancels each other out and does not affect the differential pressure measurement value.

[0052] It should also be noted that, in addition to the three main gas branches, the drying gas source unit 2 also has a supplementary gas branch, a purging branch for the sealing cavity of the loosening rod 16, and a purging branch for the pressure tap of the differential pressure transmitter 33. These three branches are either on / off or limited to a constant micro-volume by a constant flow orifice plate and do not participate in the adjustment of operating conditions.

[0053] The upper storage tank 4 is located above the dissolving vessel. The effective volume of the upper storage tank 4 is 1 m³, and its inner diameter is 1000 mm. It is configured to handle 30-60 minutes of downstream equipment usage. The upper part of the upper storage tank 4 is a solid-walled cylindrical body; the lower part of the upper storage tank 4, namely the conical section and the 300 mm high cylindrical section above it, has a double-layer structure. The inner layer is a permeable wall 43, and the outer layer is a jacketed wall 41. The interlayer between the two forms a drying chamber 44 with a thickness of 150 mm. The effective volume of the drying chamber 44 is 0.4 m³. The permeable wall 43 is a sintered stainless steel plate with a pore size of 50 μm, an effective permeable area of ​​2.5 m², a permeability coefficient of 5 m³ / (m²·h·kPa) in a clean state, and a pressure resistance of not less than 50 kPa. The jacketed wall 41 also has an external pressure resistance of not less than 50 kPa. It should be noted that the above air permeability coefficient is the value for a clean empty plate. During operation, the working surface of the permeable wall 43 is covered by a powder layer. The seepage resistance of the powder layer is much greater than that of the plate itself. Therefore, the actual permeation rate is much smaller than the value calculated according to this coefficient. The measured standby rate is no more than 8 m³ / h. The air replenishment rate after flow restriction by the flow-limiting orifice plate 26 is sufficient to maintain the required cross-wall pressure difference. The inner cavity of the upper storage tank 4 constitutes the storage chamber 42. The semi-cone angle of the conical section is 25°, and a discharge pipe 45 is provided at the bottom. A pneumatic slide gate type discharge valve 46 is provided on the discharge pipe 45. The top of the upper storage tank 4 is equipped with a filter chamber 49 and a pulse backflushing device 410. The outlet of the conveying pipeline 32 extends into the upper part of the storage chamber 42, and the upper part of the storage chamber 42 is connected to the filter chamber 49. The outlet of the filter chamber 49 is divided into two paths: one path is connected to the vacuum pump 31 via a vacuum shut-off valve 34, and the other path is connected to the workshop dust removal system via a back pressure exhaust valve. The set opening pressure of the back pressure exhaust valve is 1 kPa. A pressure equalization branch is connected between the upper gas phase space of the drying chamber 44 and the storage chamber 42. A third proportional regulating valve 48 is installed on the pressure equalization branch, and a trans-wall differential pressure transmitter 47 with a range of -5 kPa to 30 kPa is also installed between the two. The storage chamber 42 is equipped with a stirring device and a level gauge. The stirring device includes a vertically arranged rotating shaft, a stirring frame mounted on the rotating shaft, and dividing blades connected to the stirring frame. The gap between the outer edge of the stirring frame and the inner surface of the ventilated wall 43 is 10mm, so the outer diameter of the stirring frame is 980mm. The rotation speed is adjustable in the range of 3r / min to 9r / min. In this embodiment, 6r / min is used. The blade tip linear velocity is 0.31m / s. The level gauge is a radio frequency admittance type and has two level set points, high and low.

[0054] It should be noted that the permeable wall 43 is only located at the lower part of the upper storage tank 4 and does not extend to the upper part. The reason for this is that the condition for triggering feeding is a low material level. If the entire side wall is a permeable wall, the permeable surface above the material level will be exposed. The drying gas will bypass the material layer and directly short-circuit into the storage chamber 42 and be drawn away by the vacuum pump 31, which wastes gas resources and weakens the conveying pressure drop. In this embodiment, the upper edge of the permeable wall 43 is higher than the low material level set point, so it is basically covered by powder under any operating condition. In addition, the flow restrictor plate 26 limits the air supply of the drying chamber 44 to within 30 m³ / h. Even if there is local exposure, the short-circuit gas volume is constrained.

[0055] It should be noted that the small gap between the outer edge of the mixing frame and the inner surface of the ventilated wall 43, in addition to eliminating dead corners for accumulation, also allows the mixing frame to scrape off the powder adhering to the inner surface of the ventilated wall 43 during rotation, thus forming a micropore anti-clogging measure together with the pore-maintaining pulse. It should also be noted that the pore size of the ventilated wall 43, 50μm, is smaller than the d of the conveyed polyacrylamide dry powder. 10 With a particle size of 150μm, it can block most particles; however, extremely fine powders with a particle size smaller than the pore size may still be embedded in the pores, so it is necessary to combine pore-preserving pulses and wall scraping measures, which is the reason why the above measures are set in this invention.

[0056] The controller uses a programmable logic controller (PLC) and is electrically connected to the following sensors and actuators via a fieldbus: (e.g.) Figure 3 As shown, the input side includes a conveying differential pressure transmitter 33, a cross-wall differential pressure transmitter 47, a tank pressure transmitter 18, a level gauge, a dew point meter 24, and valve position detection switches for the suction valve 14, the breathing shut-off valve 17, and the replenishment shut-off valve 110. The output side includes a first proportional regulating valve 21, a second proportional regulating valve 22, a third proportional regulating valve 49, a suction valve 14, a discharge valve 46, a breathing shut-off valve 17, a replenishment shut-off valve 110, a vacuum shut-off valve 34, a pulse valve 23, a hole-holding pulse valve 25, a vibrator 15, a cylinder 161 for the loosening rod 16, a stirring device, and a vacuum pump 31 driven by a frequency converter. The controller performs calculations based on the input signals from the above sensors and outputs signals to drive the above actuators. The human-machine interface displays the material level of each tank, the gas dew point, the system pressure, the pressure drop of the suction section, and the conveying status judgment results. The pressure reducing valve, check valve 122, back pressure exhaust valve, flow equalization orifice plate 121, flow limiting orifice plate 26, and constant flow orifice plate are all self-operated or mechanical components and are not connected to the controller.

[0057] The gas consumption is checked as follows. Under the feeding condition: the fluidizing gas branch consumes 60 m³ / h to 150 m³ / h; the replenishment gas to the drying chamber 44, after being limited by the flow-limiting orifice plate 26, does not exceed 30 m³ / h, with an actual measurement of 6 m³ / h; pulse backflushing is calculated at once every 2 minutes, with each pulse consuming 0.02 m³, equivalent to an average of 0.6 m³ / h; the pulse for maintaining the orifice consumes approximately 0.08 m³ per pulse, calculated at once every 20 minutes, equivalent to an average of 0.24 m³ / h; the combined purging of the sealing of the loosening rod 16 and the purging of the pressure tap of the differential pressure transmitter 33 does not exceed 1.5 m³ / h. The total of the above items does not exceed 185 m³ / h. Under the unloading condition, the fluidizing gas branch is closed, and the gas consumption does not exceed 32 m³ / h. The exhaust volume of the drying gas source unit 2 is 3.6 m³ / min, or 216 m³ / h, which can meet the gas demand under various operating conditions.

[0058] Example 2 like Figure 4 As shown, this embodiment provides a method for controlling the feeding of low-density polymer dry powder, using the feeding device described in Embodiment 1, as follows: Step 1, Standby Condition. The discharge valve 46 is closed, the vacuum pump 31 is stopped, the vacuum shut-off valve 34 is closed, and the target pressure difference is set to Δp2 = 5 kPa. Drying gas slowly seeps into the storage chamber 42 through the permeable wall 43, forming a slightly positive pressure moisture-proof environment within the powder layer. The seeped gas is discharged to the workshop dust removal system through the back pressure exhaust valve, maintaining a slightly positive pressure of 1 kPa in the storage chamber 42. The stirring device runs intermittently for 2 minutes every 30 minutes. When the output of the level gauge falls below the low level set value, the feeding condition is switched to.

[0059] Step 2: Starting the feeding operation. The controller closes the discharge valve 46, the breathing shut-off valve 17, and the replenishment shut-off valve 110, and opens the stirring device, the suction valve 14, and the vacuum shut-off valve 34, switching the pressure difference target value from Δp2 to Δp1=1kPa; after receiving the closing signal of the breathing shut-off valve 17, the vacuum pump 31 is started, and the fluidizing gas branch is opened at the reference flow rate Q0=100m³ / h. At this time, the gauge pressure in the powder storage tank 1 is -3kPa to -8kPa, and the pressure in the storage chamber 42 is -25kPa to -35kPa.

[0060] Step 3: Conveying Status Determination. The controller calculates the pressure drop p in the suction section output by the differential pressure transmitter 33, using a sliding time window of 2 seconds and a sampling frequency of 100Hz. s mean p m The criterion for the sum and standard deviation σ is: When p mWhen the pressure drop is less than the lower limit of material interruption p1 = 6 kPa, it is judged as a material interruption state. At this time, the suction port 13 is almost only sucked in gas, and the pressure drop caused by the inflow and acceleration is minimal. When σ is less than the lower limit of fluctuation σ1 = 0.3 kPa, it is judged as a complete material interruption state. At this time, the cone hopper 11 has been completely arched, and the material flow is completely interrupted. When σ is not less than σ1, it is judged as a rat hole state. At this time, a through-type central channel has been formed in the cone hopper 11, and only a few scattered powder materials collapse along this channel. The overall solid load in the pipe is very low and the pulsation is obvious.

[0061] When p m When the overcharge limit p2 = 16 kPa is exceeded, it is judged as an overcharge state. At this time, excessive powder flows into the feed inlet 13.

[0062] When p m When the value is not less than p1 and not greater than p2, and σ is greater than the upper limit of fluctuation σ2 = 2.5 kPa, it is judged to be in an unstable state. At this time, the material flow is intermittently transported in a sporadic manner, and local collapse and re-accumulation of the material layer occur alternately. The average value still falls within the normal range, only the pulsation is abnormally increased.

[0063] The remaining cases are considered stable states. The four states mentioned above do not overlap and cover p. m Combined with all possible values ​​of σ.

[0064] In addition, the controller has pre-stored p in the empty tank state. s The relationship between the fluidizing gas flow rate Q and the no-load baseline is used, and during operation, p is used as the baseline. m The difference between the current Q and the corresponding no-load baseline value is used as a solid phase load characteristic quantity for discrimination, so as to eliminate the offset caused by the change of gas phase pressure drop with Q.

[0065] Step 4: Fluidizing gas flow rate setting. In the off-flow state, the controller gradually increases the fluidizing gas flow rate Q in steps of 5% of full scale at 3-second intervals; in the overcharge state, Q is decreased in the same step size. If p m If the pressure exceeds the overcharge protection value p3 = 22 kPa, then the suction valve 14 will be closed, and the pressure will be released after p3 = 22 kPa. m The pressure drops below p2 and then reopens. It should be noted that after closing the suction valve 14, the pressure is maintained for a fixed duration (e.g., 5s~15s) before reopening. In the unstable state, Q remains constant while the vibrator 15 operates in a 1.5s pulse pattern. In the rat-hole state, Q is increased in the aforementioned step size while the vibrator 15 operates in a 1.5s pulse pattern. In the stable state, Q is proportional-integral adjustment with p0=11kPa as the setpoint. Furthermore, when the reading of the tank pressure transmitter 18 is below -10kPa, the controller reduces the operating frequency of the vacuum pump 31 to prevent the tank from experiencing excessive external pressure. The adjustment cycle of this protection circuit is 10s~30s, much longer than the 3s of the fluidizing gas setting circuit; the two are decoupled on a time scale and do not interfere with each other.

[0066] Step 5: Staged Arch Breaking and Rebound. When the duration of the complete material cut-off state exceeds t1=25s, the controller starts vibrator 15. This duration is sufficient to allow the fluidizing gas flow rate to increase from the baseline flow rate Q0=100m³ / h to the upper limit Q according to the step size and interval of Step 4. max =150m³ / h, meaning that fluidization methods are first fully tested before mechanical arch breaking is employed; if the material supply remains interrupted for t2=8s, the loosening rod 16 is activated for reciprocating motion. The key is that, simultaneously with activating the vibrator 15 or the loosening rod 16, the controller adjusts the fluidizing gas flow rate from its current value back to the baseline flow rate Q0, and only increases it gradually in steps according to the set increments after the judgment result returns to a stable state. Without this adjustment, the powder falling during the moment of arch collapse will be immediately over-inflated by the fluidizing gas at its upper limit, directly transitioning from a material supply interruption state to an over-inflated state and causing pipe blockage.

[0067] Step Six: Drying Chamber Differential Pressure Follow-up Control. The controller uses the output of the transwall differential pressure transmitter 47 as feedback to control the second proportional regulating valve 22 and the third proportional regulating valve 48 in a split-range manner: when the transwall differential pressure Δp is lower than the target value minus half the dead zone width, the second proportional regulating valve 22 is opened to replenish gas and increase pressure; when it is higher than the target value plus half the dead zone width, the third proportional regulating valve 48 is opened to release pressure into the gas phase space of the storage chamber 42. When within the dead zone, both valves maintain a constant opening degree. In this embodiment, the dead zone width is taken as 0.3 kPa. This allows the pressure in the drying chamber 44 to follow the pressure changes in the storage chamber 42 in real time. The target differential pressure value is taken as Δp1 = 1 kPa under the feeding condition; Δp2 = 5 kPa under the standby condition; and Δp3 = 10 kPa under the unloading condition. Except for the feedforward pressure boosting and orifice-holding pulses described below, the transwall differential pressure Δp is limited to below 15 kPa to prevent the powder from being excessively fluidized in the conical section and gushing when the valve is opened. It should be noted that the purpose of setting the dead zone is to prevent the second proportional control valve 22 and the third proportional control valve 48 from operating simultaneously near the split point. Otherwise, the drying gas will be directly short-circuited from the drying chamber inlet branch through the pressure equalization branch into the storage chamber 42.

[0068] Step 7: Backflushing Feedforward and Orifice Preservation Pulse. 0.5 seconds before each opening of pulse valve 23, the controller opens orifice preservation pulse valve 25 for 0.3 seconds and simultaneously closes the third proportional regulating valve 48, causing the transwall pressure difference Δp to feedforward and increase by approximately 8 kPa. After the injection ends, the controller restores the original target value for 1.5 seconds, ensuring that Δp remains at least 0.3 kPa throughout the injection process. Otherwise, the positive pressure spike in the upper gas phase space of the storage chamber 42 during injection will reverse the transwall pressure difference, forcing powder into the micropores and causing blind blockage. In standby mode, the controller opens orifice preservation pulse valve 25 for 0.3 seconds every 20 minutes, causing the transwall pressure difference Δp to instantaneously rise to 20 kPa, blowing away powder particles embedded in the micropores from the inside out, forming an orifice preservation pulse. It should be noted that a pulse valve must be used here instead of the second proportional regulating valve 22 being fully open: to pressurize the 0.4m³ drying chamber 44 to 20kPa in 0.3s, approximately 0.08m³ of free air needs to be supplied, which translates to an instantaneous flow rate of nearly 1,000 cubic meters per hour. This far exceeds the flow capacity of the second proportional regulating valve 22 after the flow is limited by the flow limiting orifice plate 26. However, a DN25 electromagnetic pulse valve with a 0.6MPa air source can meet this instantaneous flow rate requirement.

[0069] Step 8: Completion of feeding and repressurization. When the output of the level gauge reaches the high level set value, the controller first closes the suction valve 14, keeps the breathing shut-off valve 17 closed, and maintains the fluidizing gas flow rate Q0 to continue purging for 10 seconds. The purging gas blows away the residual powder in the working surface and channels of the fluidizing permeable plate 12 and carries it into the gas phase space inside the tank. At the same time, the pressure in the powder storage tank 1 gradually rises from negative pressure to about 3 kPa. Then, the fluidizing gas branch is closed, the vacuum pump 31 is stopped and the vacuum shut-off valve 34 is closed, and the gas replenishment shut-off valve 110 is opened to replenish the tank with dry gas to a slight positive pressure of 0.5 kPa to 2 kPa.

[0070] It should be noted that during the purging period and when the suction valve 14 is closed, the controller suspends pipeline status determination and fluidizing gas setting, and the fluidizing gas flow rate remains at Q0.

[0071] It should also be noted that the breathing shut-off valve 17 remains closed throughout the entire purging and repressurization process, and the powder storage tank 1 is not connected to the atmosphere, thereby preventing the intake of outside humid air during the repressurization stage. At the same time, the controller opens the second proportional regulating valve 22 and the third proportional regulating valve 48, allowing the drying gas to enter the storage chamber 42 through the drying chamber 44 and the pressure equalization branch. The storage chamber 42 recovers from negative pressure to a slightly positive pressure of 1 kPa, and excess gas is discharged through the back pressure exhaust valve. Then, the pressure difference target value is switched to Δp2 = 5 kPa, and the system enters standby mode.

[0072] Step Nine, Feeding. When the downstream dissolving vessel requests feeding, the controller switches the differential pressure target value to Δp3=10kPa and opens the feeding valve 46. At this time, the drying gas seeps from the permeable wall 43 into the powder layer in the conical section, reducing the wall friction resistance. Combined with the continuous operation of the stirring device, this ensures smooth feeding. It should be noted that the feeding valve 46 is interlocked with the feeding condition. During the feeding condition, the feeding valve 46 must be closed; otherwise, outside air will be drawn back into the storage chamber 42 through the discharge pipe 45, which will both disrupt the conveying vacuum and introduce moisture.

[0073] This invention is not limited to the above embodiments. The conveyed material can also be acrylic resin, cellulose ether, or other easily hygroscopic low-density powders, and nitrogen can also be used as the drying gas. The volume, size, area, flow rate, and power parameters given in the above embodiments are only examples of matching a 20m³ powder storage tank. Adjustments can be made according to the processing capacity, material characteristics, and site conditions during implementation. All modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. An automatic feeding device for low-density polymer dry powder, characterized in that, include: The powder storage tank has a fluidizing and venting plate embedded in the wall of the cone-shaped hopper at the bottom. The suction port at the bottom of the cone-shaped hopper is equipped with a suction valve, and the suction port is connected to the upper storage tank through a conveying pipeline. The top of the powder storage tank is equipped with a breathing shut-off valve. The drying gas source unit has a fluidizing gas branch, a drying chamber inlet branch and a backflush gas branch leading out from its outlet. The fluidizing gas branch is equipped with a first proportional regulating valve and is connected to the fluidizing permeable plate. The negative pressure conveying unit includes a vacuum pump, a conveying pipeline, and a conveying differential pressure transmitter. The positive pressure side of the conveying differential pressure transmitter is connected to the upper gas phase space of the powder storage tank, and the negative pressure side is connected to the pressure tapping point located downstream of the suction port on the conveying pipeline. The output of the conveying differential pressure transmitter is the pressure drop p in the suction section. s ; The upper storage tank has a solid-walled cylindrical upper part and a lower part consisting of a permeable wall and a jacketed wall covering the outside of the permeable wall. The interlayer between these two walls forms the drying chamber, and the inner cavity of the upper storage tank forms the storage chamber. The top of the upper storage tank is equipped with a filter chamber and a pulse backflushing device, which is connected to the backflushing air branch. The discharge pipe at the bottom of the upper storage tank is equipped with a discharge valve. The storage chamber is equipped with a stirring device and a level gauge. A second proportional regulating valve is installed on the air inlet branch of the drying chamber and is connected to the drying chamber. A pressure equalization branch is connected between the upper gas phase space of the drying chamber and the storage chamber. A third proportional regulating valve is installed on the pressure equalization branch. A cross-wall differential pressure transmitter is also installed between the upper gas phase space of the drying chamber and the storage chamber. The output of the cross-wall differential pressure transmitter is the difference between the pressure of the drying chamber and the pressure of the upper gas phase space of the storage chamber, i.e., the cross-wall pressure difference Δp. The controller is electrically connected to each of the aforementioned transmitters, proportional control valves, suction valve, discharge valve, breather shut-off valve, level gauge, mixing device, and vacuum pump. The controller has feeding, standby, and discharge modes, and is configured to: close the discharge valve and breather shut-off valve during feeding, making the fluidized bed the sole air supply path to the powder storage tank; and calculate the pressure drop p in the suction section according to a sliding time window. s mean p m The standard deviation σ and the standard deviation σ are used to jointly determine the conveying state, and the opening of the first proportional regulating valve is adjusted according to the determination result to change the fluidizing gas flow rate Q; the second and third proportional regulating valves are controlled in a split-range manner so that the cross-wall pressure difference Δp follows the change of the pressure in the storage chamber and stabilizes at the pressure difference target value, and the pressure difference target value Δp1 under the feeding condition is less than the pressure difference target value Δp2 under the standby condition, and Δp2 is less than the pressure difference target value Δp3 under the unloading condition.

2. The automatic feeding device for low-density polymer dry powder according to claim 1, characterized in that, The powder storage tank has a vibrator installed on the outer wall of the cone-shaped hopper, and a loosening rod installed inside the cone-shaped hopper. The loosening rod includes a cylinder, a guide sleeve passing through the cone-shaped hopper wall, a rigid core rod driven by the cylinder and extending into the cone-shaped hopper through the guide sleeve, and an elastic umbrella-shaped head fixed to the inner end of the core rod. The guide sleeve has two lip-shaped sealing rings arranged in series along the axial direction of the core rod. The annular cavity between the two lip-shaped sealing rings forms a sealing cavity. The sealing cavity is connected to the drying air source unit in sequence through a constant flow orifice plate and a pressure reducing valve. The pressure of the sealing cavity is 3 kPa to 10 kPa higher than atmospheric pressure. The vibrator and the cylinder are both electrically connected to the controller.

3. The automatic feeding device for low-density polymer dry powder according to claim 1, characterized in that, Both the permeable wall and the fluidizing permeable plate are made of sintered stainless steel. The pore size of the permeable wall is 20μm~50μm, and the pore size of the fluidizing permeable plate is 20μm~40μm. Each fluidizing permeable plate is equipped with a flow equalization plate and a one-way valve at the air inlet end.

4. The automatic feeding device for low-density polymer dry powder according to claim 1, characterized in that, On the air inlet branch of the drying chamber, the outlet of the second proportional regulating valve is equipped with a flow-limiting orifice plate, and the maximum flow capacity of the flow-limiting orifice plate is no more than 30 m³ / h; the air inlet branch of the drying chamber is also equipped with a flow-limiting pulse valve, which is connected in parallel with the branch formed by the second proportional regulating valve and the flow-limiting orifice plate connected in series, and the outlet of the flow-limiting pulse valve is directly connected to the drying chamber without passing through the flow-limiting orifice plate; the flow-limiting pulse valve is electrically connected to the controller.

5. The automatic feeding device for low-density polymer dry powder according to claim 1, characterized in that, The top of the powder storage tank is also equipped with an air inlet, which is connected to the drying air source unit in sequence via an air inlet shut-off valve and a pressure reducing valve. Both the breathing shut-off valve and the air inlet shut-off valve are soft-seal shut-off valves and are equipped with valve position detection switches. The controller is allowed to start the vacuum pump only after receiving the closed signal output by the valve position detection switch of the breathing shut-off valve. The outlet of the filter chamber is divided into two paths: one path is connected to the vacuum pump via a vacuum shut-off valve, and the other path is connected to the external dust removal system via a back pressure exhaust valve. The set opening pressure of the back pressure exhaust valve is 0.5kPa~2kPa.

6. A method for controlling the feeding of low-density polymer dry powder, employing the automatic feeding device for low-density polymer dry powder as described in any one of claims 1 to 5, characterized in that, Includes the following steps: S1. In standby mode, the controller closes the feeding valve, sets the differential pressure target value to Δp2, and the drying gas seeps into the storage chamber through the ventilated wall and forms a slightly positive pressure moisture-proof environment in the powder layer; when the output of the level gauge is lower than the low level set value, it switches to feeding mode. S2. Under the feeding condition, the controller closes the feeding valve and the breathing shut-off valve, opens the suction valve and the stirring device, switches the differential pressure target value from Δp2 to Δp1, starts the vacuum pump, and opens the fluidizing gas branch with the reference flow rate Q0. The fluidizing gas enters the powder storage tank through the fluidizing permeable plate and becomes the only source of supplementary gas for negative pressure conveying. S3. The controller calculates the pressure drop p in the suction section output by the differential pressure transmitter according to the sliding time window. s mean p m And standard deviation σ, and determine the conveying status according to the following rules: p m When the material level is less than the lower limit p1, it is considered a material shortage state. m When the charge level is greater than the overcharge limit p2, it is considered an overcharge state. m The state is considered unstable when the value is not less than p1 and not greater than p2 and σ is greater than the upper limit of fluctuation σ2; otherwise, the state is considered stable. S4. The controller increases the fluidizing gas flow rate Q in the off-state, decreases the fluidizing gas flow rate Q in the overcharge state, maintains the fluidizing gas flow rate Q constant in the unstable state, and performs proportional-integral regulation of the fluidizing gas flow rate Q with a set value p0 as the target in the steady state, where p0 is greater than p1 and less than p2, so that p m It stabilizes between p1 and p2; S5. During the feeding process, the controller controls the second and third proportional regulating valves in a split-range manner to make the cross-wall pressure difference Δp stabilize at Δp1 as the pressure in the storage chamber changes. S6. When the output of the level gauge reaches the high level set value, the controller sequentially closes the suction valve, maintains the fluidizing gas flow rate Q0 to continue purging for 5s~15s, then closes the fluidizing gas branch and stops the vacuum pump. During the above purging, the breathing cut-off valve remains closed. Then, the second proportional regulating valve and the third proportional regulating valve are opened to allow the drying gas to enter the storage chamber through the drying chamber and the pressure equalization branch. The storage chamber is restored from negative pressure to slightly positive pressure, and the pressure difference target value is switched to Δp2, and the system enters the standby mode. S7. When downstream production equipment picks up materials, the controller switches the differential pressure target value to Δp3 and opens the discharge valve. The discharge valve is interlocked with the feeding condition.

7. The feeding control method for low-density polymer dry powder according to claim 6, characterized in that, p1 is 5kPa~8kPa, p2 is 14kPa~20kPa, p0 is the arithmetic mean of p1 and p2, σ2 is 1.5kPa~4kPa, and the length of the sliding time window is 1s~3s. In step S3, the controller further distinguishes the material-cut-off state based on the standard deviation σ: when σ is less than the lower limit of fluctuation σ1, it is judged as a complete material-cut-off state; when σ is not less than σ1, it is judged as a mouse hole state. σ1 is 0.2kPa~0.6kPa.

8. The feeding control method for low-density polymer dry powder according to claim 7, characterized in that, The outer wall of the cone-shaped hopper of the feeding device is equipped with a vibrator, and a loosening rod is installed inside the cone-shaped hopper; in step S4, when the controller determines that the material is completely cut off, it performs graded arch breaking: first, the fluidizing gas flow rate Q is gradually increased to the upper limit Q by a set step size. max If the complete material shortage state lasts longer than t1 and remains in the material shortage state, the vibrator is started. If it continues for another t2 and remains in the material shortage state, the loosening rod is started. t1 is 20s~40s and t2 is 5s~15s. At the same time as starting the vibrator or loosening rod, the fluidizing gas flow rate is adjusted back to the reference flow rate Q0. After the judgment result returns to a stable state, the flow rate is increased again according to the set step size.

9. The feeding control method for low-density polymer dry powder according to claim 6, characterized in that, A hole-preserving pulse valve is installed on the air inlet branch of the drying chamber. This valve is connected in parallel with a branch consisting of a second proportional regulating valve and a flow-limiting orifice plate connected in series. Δp1 ranges from 0.5 kPa to 2 kPa, Δp2 from 3 kPa to 6 kPa, and Δp3 from 8 kPa to 14 kPa. A dead zone of 0.2 kPa to 0.5 kPa is provided at the split-range control point. The controller opens the hole-preserving pulse valve for 0.2 seconds 0.3 to 1 second before each pulse backflushing action of the pulse backflushing device. The controller operates for approximately 0.5 seconds and simultaneously closes the third proportional control valve to ensure that the transwall pressure difference Δp is not lower than 0.3 kPa throughout the entire injection process, and restores the original pressure difference target value 1 to 2 seconds after the injection ends. In standby mode, the controller also opens the orifice-preserving pulse valve for 0.2 to 0.5 seconds every 10 to 30 minutes to instantly raise the transwall pressure difference Δp to 15 to 25 kPa. Except for the action of the orifice-preserving pulse valve, the controller limits the transwall pressure difference Δp to below 15 kPa.

10. The feeding control method for low-density polymer dry powder according to claim 6, characterized in that, In step S3, the controller also pre-stores the correspondence between the pressure drop of the suction section and the fluidizing gas flow rate Q in the empty tank state as an empty load baseline, and uses p m The difference between the current fluidizing gas flow rate Q and the no-load baseline value is used as a solid-phase load characteristic quantity to participate in the determination of the transport state; in step S4, the controller is in p m When the overcharge value exceeds the overcharge protection value p3, the suction valve is closed until p m It falls back below p2, and p3 is greater than p2.

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