A stirring device for a dry powder fire extinguishing system storage tank

Abstract

This utility model discloses a mixing device for a dry powder fire extinguishing system storage tank, belonging to the field of fire extinguishing technology. It includes a storage tank, a drive motor, and a transmission rod. A spiral blade is fixed on the transmission rod, and a dry powder lifting pipe is sleeved around the spiral blade. The dry powder lifting pipe has a trumpet-shaped powder inlet at the bottom and symmetrical powder outlets at the top. The drive motor is a 24V explosion-proof motor connected to the transmission rod via a coupling. The device is configured for a periodic start-up mode, where the driven spiral blades transport the dry powder from the bottom of the storage tank through the lifting pipe to the upper powder outlets for dispersion. This utility model actively breaks the powder lamination structure through closed-loop circulating fluidization, blocking the conditions for agglomeration from the source. It is suitable for long-term static storage scenarios in fire extinguishing tanks, solving the defect of traditional mixing devices that cannot prevent agglomeration during static storage.

Description

Technical Field

[0001] This utility model relates to the field of fire extinguishing technology, specifically to a mixing device for a dry powder fire extinguishing system storage tank. Background Technology

[0002] When a fire-fighting storage tank has a volume exceeding 100L and remains stationary for an extended period, the dry powder will gradually compact under its own weight. This compaction begins at the bottom of the tank, and as the dry powder accumulates, the porosity of the bottom layer decreases significantly. Reduced porosity means smaller gaps between powder particles, making it easier for moisture to accumulate in these tightly packed particles. This moisture intrusion causes the dry powder particles to stick together, forming a relatively hard caking. This caking phenomenon differs from the instantaneous agglomeration that may occur during production; it forms gradually after a long period of standing, significantly impacting the normal use of the dry powder in the fire-fighting storage tank.

[0003] For outdoor fire-fighting storage tanks, the environmental conditions are complex and variable. During the day-night cycle, temperature and humidity constantly change. During the day, temperatures rise and humidity is relatively low, causing the dry powder to absorb some moisture; at night, temperatures drop and humidity increases, causing the powder to release some moisture and dry again. This repeated moisture absorption and drying process accelerates the gelation of the dry powder. From the perspective of chemical engineering theories on powder agglomeration, the physical and chemical properties of powder change under such cyclical temperature and humidity conditions, leading to the formation of a gel-like structure between powder particles. This causes the dry powder to gradually lose its good flowability, ultimately resulting in agglomeration.

[0004] In firefighting scenarios, the safety requirements for equipment are extremely stringent. For example, fire-fighting motors must be explosion-proof, and considering factors such as safety and stability, they typically use a 24V low-voltage power supply. Furthermore, to balance energy consumption and equipment lifespan, motors in firefighting equipment are prohibited from continuous operation. However, most existing mixing devices are designed for non-firefighting applications and do not fully consider these specific safety constraints in firefighting scenarios. This makes it difficult to find a mixing device in fire-fighting storage tanks that can effectively prevent dry powder agglomeration while simultaneously meeting the requirements of low pressure and intermittent operation. This further exacerbates the problem of dry powder agglomeration in fire-fighting storage tanks, posing a potential threat to the reliability and effectiveness of the fire protection system.

[0005] Based on this, the present invention designs a mixing device for a dry powder fire extinguishing system storage tank to solve the above problems. Utility Model Content

[0006] In view of the above-mentioned shortcomings of the existing technology, the present invention provides a stirring device for a dry powder fire extinguishing system storage tank.

[0007] To achieve the above objectives, this utility model provides the following technical solution:

[0008] A mixing device for a dry powder fire extinguishing system storage tank includes a storage tank, a drive motor, and a transmission rod. A spiral blade is fixed on the transmission rod, and a dry powder lifting pipe is sleeved on the outside of the spiral blade.

[0009] The dry powder lifting pipe is provided with a funnel-shaped powder inlet at the bottom and symmetrical powder outlets at the top.

[0010] The drive motor is a 24V explosion-proof motor, which is connected to the transmission rod via a coupling.

[0011] The device is configured for periodic start-up mode, driving the spiral blades to transport the dry powder at the bottom of the storage tank through the lifting pipe to the upper powder outlet for dispersion.

[0012] Furthermore, the inclination angle of the trumpet-shaped powder inlet is 45-60°.

[0013] Furthermore, the inner wall of the dry powder lifting pipe is provided with spiral guide protrusions, the height of which decreases along the lifting direction.

[0014] Furthermore, the side wall of the horn-shaped powder inlet is provided with an air hole for connecting to an external compressed air source interface.

[0015] Furthermore, the drive motor is connected to the control module and configured to start in real time according to a preset temperature and humidity threshold or a fire extinguishing signal.

[0016] Furthermore, the control module integrates a temperature and humidity sensor, which adaptively adjusts the startup cycle based on environmental data.

[0017] Furthermore, the powder outlets are radially symmetrically distributed, and the outlet direction is inclined downward at 30-45°.

[0018] Furthermore, the pitch of the helical blades is 0.8-1.2 times the diameter of the storage tank.

[0019] Compared with the prior art, this utility model has at least the following advantages:

[0020] 1. This utility model actively breaks the powder lamination structure through closed-loop circulating fluidization, blocking the conditions for agglomeration from the source. It is suitable for long-term static storage scenarios of fire-fighting storage tanks and solves the defect of traditional stirring devices that cannot prevent static agglomeration.

[0021] 2. This utility model physically isolates external moisture through a closed-loop riser tube, and combines it with pulsed airflow to break up arches and block the liquid bridge force caused by capillary action, thus significantly reducing the risk of moisture absorption and clumping in high humidity environments.

[0022] 3. The horn-shaped inclination angle and the spiral guide protrusion of this utility model work together to ensure that the powder enters the riser pipe without resistance, avoids bridging, and is suitable for high-density dry powder, allowing for continuous operation without clogging. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of this utility model or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a three-dimensional sectional view of the mixing device for a dry powder fire extinguishing system storage tank according to the present invention;

[0025] Figure 2 This utility model Figure 1 A magnified structural diagram at point A;

[0026] Figure 3 For the present utility model Figure 1 A magnified structural diagram at point B;

[0027] Figure 4 This is a schematic diagram of the circulation process of the mixing device for a dry powder fire extinguishing system storage tank according to the present invention.

[0028] The labels in the diagram represent:

[0029] 1. Storage tank; 2. Drive motor; 3. Transmission rod; 4. Spiral blade; 5. Dry powder lifting pipe; 6. Coupling; 7. Control module; 501. Horn-shaped powder inlet; 502. Powder outlet; 503. Spiral guide protrusion; 504. Air hole. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the embodiments of this utility model clearer, the technical solutions of the embodiments of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this utility model. All other embodiments obtained by those skilled in the art based on the embodiments of this utility model without creative effort are within the scope of protection of this utility model.

[0031] This embodiment discloses a stirring device for a dry powder fire extinguishing system storage tank, comprising:

[0032] A sealing flange is opened at the center of the top of the storage tank 1. The drive motor 2 (24V explosion-proof motor) is fixed to the flange with bolts. The output shaft extends downward into the interior of the storage tank 1. The transmission rod 3 is directly connected to the output shaft of the drive motor 2 through the coupling 6. The length of the transmission rod is customized according to the height of the storage tank (extending to 100mm above the bottom of the tank). Spiral blades 4 are welded on the transmission rod 3. The gap between the outer edge of the blade and the inner wall of the dry powder lifting pipe 5 is ≤5mm to prevent powder from getting stuck.

[0033] The dry powder riser 5 is installed outside the spiral blade 4. The upper and lower ends of the dry powder riser 5 are fixed to the inner wall of the storage tank 1 by the support frame. The lower part of the dry powder riser 5 is connected to the trumpet-shaped powder inlet 501, the edge of which is 50-100mm from the bottom of the tank. The upper part has two radially symmetrical powder outlets 502, the center of which is 200mm from the top of the tank.

[0034] The pitch of the spiral blades is set to 0.8-1.2 times the tank diameter. Taking 0.8 times the tank diameter (small pitch) as an example:

[0035] When the pitch is small (0.8D), the helix angle of the spiral blade 4 decreases. According to the theory of powder fluidization, a smaller helix angle can enhance the axial conveying force of the powder, reduce radial spillage loss, and thus improve the vertical conveying efficiency. This also reduces the internal friction angle of low-viscosity dry powders (such as sodium bicarbonate). The screw pitch is relatively small (approximately 30-35°), resulting in high powder flowability. A small pitch prevents powder slippage due to gravity, ensuring continuous conveying. According to Jenike's flow function, the screw pitch and the internal friction angle of the powder must satisfy... A pitch of 0.8D can meet this condition. A small pitch leads to an increased contact area between the blade and the powder, resulting in localized pressure concentration. However, the shear resistance of the low-viscosity powder on the blade is relatively small. (A is the contact area,) The radius is still controllable, and the motor power requirement is moderate;

[0036] Taking 1.2 times the tank diameter (large pitch) as an example:

[0037] At high filling rates (>80%), the powder lamination effect is significant, and the axial pressure... Increasing the screw pitch (1.2D) reduces the frequency of contact between the blades and the powder, lowering the risk of powder compaction and preventing bridging blockage. According to the Beverloo model, a larger screw pitch reduces the ineffective friction area between the powder and the pipe wall, increasing the effective conveying capacity. With a larger screw pitch, the helix angle increases, the proportion of axial motion of the powder increases, and radial compression decreases. In the driving torque formula, the frictional resistance torque... Significantly reduced due to decreased contact area ( (where the coefficient of friction is ), suitable for energy-saving operation under high filling rates;

[0038] A large screw pitch can reduce the eddy current effect generated when the screw blades rotate, preventing powder from accumulating on the pipe wall due to centrifugal force. This is based on the critical speed formula for vertical screw conveyors. (where the helix radius is the radius of the helix), and the large pitch corresponds to... Increase the critical speed to prevent the powder from spinning idly with the blades;

[0039] In summary, 0.8 times is suitable for the internal friction angle. Low-viscosity powders (such as dry powder extinguishing agents), 1.2 times more suitable for For high-viscosity or easily hygroscopic powders (such as ammonium phosphate), the pitch-to-diameter ratio in screw conveyor design is typically 0.5-1.5 times, with 0.8-1.2D being a commonly used optimized range. The experimental results are as follows:

[0040]

[0041] The spiral guide protrusion 503 is welded to the inner wall of the riser 5. The height of the protrusion decreases from the powder inlet to the powder outlet (for example, 20mm at the bottom and 5mm at the top). The protrusion is spirally distributed, and the pitch is consistent with the spiral blade 4 (the center line of the protrusion coincides with the lead line of the blade). The material is polytetrafluoroethylene (anti-stick).

[0042] When the spiral blades rotate and push the powder upward, the guide protrusions simultaneously apply a lateral force to the powder to prevent the powder from sticking to the wall and stagnating due to centrifugal force.

[0043] For example, when the pitch of the helical blade is s = 0.8D (D is the diameter of the storage tank), the pitch of the guide protrusion is also 0.8D. In this case:

[0044] Small pitch (0.8D) powder has a high axial movement frequency, and the flow guide protrusions destroy the powder adhesion layer by increasing local turbulence (Reynolds number Re > 4000);

[0045] With a large pitch (1.2D), the powder conveying speed is reduced, and the height of the guide protrusion needs to be reduced accordingly to reduce energy consumption. This is suitable for easily fluidized powders (such as sodium bicarbonate). The matching relationship between the pitch and the guide protrusion needs to meet the powder Froude number to ensure that the powder is neither over-spread nor deposited.

[0046] The spiral guide protrusions 503 decrease in height (high protrusion at the bottom, for example, 20mm). The powder at the bottom of the tank is subjected to the greatest static pressure. The high protrusions generate strong shear force, which destroys the powder bridging structure. For example, when the ratio of protrusion height to pitch (h / s) is set to 0.25-0.3, local vortices can be formed, which can increase the initial velocity of the powder entering the riser pipe and reduce the flow resistance.

[0047] The spiral guide protrusions 503 have decreasing heights (lower protrusion at the top, e.g., 5mm). The powder is already fluidized when it rises to the top. The lower protrusion reduces the contact area with the tube wall, thus lowering the coefficient of friction. The concentration was reduced from 0.3 (metal-powder) to 0.1 (PTFE-powder). The low protrusion at the top prevents fine powder from agglomerating due to van der Waals forces through micro-disturbance (amplitude <0.5mm), which is particularly effective for powders with a particle size <50μm and prevents secondary agglomeration.

[0048] Based on the simulation results of the powder dynamics model of the screw conveyor and the measured data of lithium battery material conveying, the results are as follows:

[0049]

[0050] As shown in the table above, the pitch of the spiral guide protrusion 503 is strictly consistent with that of the spiral blade 4. For example, the bottom 20mm protrusion corresponds to a pitch of 0.8D, and the top 5mm protrusion corresponds to a pitch of 1.2D, forming a progressive flow channel optimization.

[0051] Control module 7 consists of a temperature and humidity sensor, a main control unit, and a communication interface.

[0052] The temperature and humidity sensor (not shown in the figure) uses a DHT11 module (accuracy ±5%RH, temperature range 0-50℃) and is installed on the top of storage tank 1 away from the powder outlet to avoid airflow interference.

[0053] The main control unit is a microcontroller (not shown in the figure), which integrates a PID algorithm module to calculate the rate of change of temperature and humidity in real time and adjust the motor start-up cycle.

[0054] The communication interface (not shown in the figure) is an RS485 bus connected to the fire control system to receive fire extinguishing signals (dry contact input).

[0055] The inclination angle of the funnel-shaped powder inlet 501 is set at 45-60°. The purpose is to balance powder feeding efficiency and bridging prevention. Taking an inclination angle of 45° as an example:

[0056] According to powder mechanics theory, when the inclination angle of the inclined plane is 45°, the gravity acting on the dry powder can be decomposed into a downward force along the inclined plane and a normal force perpendicular to the inclined plane. At this time, the ratio of the downward force to the normal force is 1, which provides sufficient driving force for the powder to slide down while avoiding adhesion between the powder and the inclined plane due to insufficient normal force. For dry powders with good flowability (such as sodium bicarbonate), the internal friction angle is usually small (about 30-40°). According to Jenike's silo design theory, the inlet inclination angle must meet the following requirements. The design ensures that the powder overcomes internal frictional resistance and achieves continuous flow;

[0057] The Beverloo model points out that when powder passes through the orifice, an ineffective flow zone (empty ring) is formed. A 45° inclined plane can reduce the contact area between the powder and the wall, reduce the frictional resistance of the wall, and thus improve the powder feeding efficiency. For low-viscosity powders, a 45° inclination angle can avoid agglomeration between particles caused by van der Waals forces or electrostatic effects.

[0058] Taking a tilt angle of 60° as an example:

[0059] High-density powders (such as ammonium phosphate) are susceptible to lamination effects when left to stand. A steep 60° slope can increase the powder's downward acceleration, shorten its residence time on the slope, and reduce the risk of compaction. Hygroscopic powders are prone to forming liquid bridge forces on slopes. A 60° inclination angle increases the vertical component of the force, disrupting the liquid bridge force balance and preventing moisture absorption and agglomeration. For powders with larger particle sizes, their free settling velocity is higher. According to the Brown and Richards model, a 60° inclination angle can match their critical gas velocity, preventing particles from being stuck due to insufficient kinetic energy. A 60° inclination angle is similar to "inverted cone fluid conversion," which can force the powder to concentrate towards the center, forming a whole flow and eliminating dead corners caused by funnel flow.

[0060] The experimental results, obtained by comparing the flow rate and agglomeration rate of simulated dry powder extinguishing agents at different nozzle angles, are shown in the table below.

[0061]

[0062] As shown in the table above, at an inclination angle of 45-50°, the flow rate remains at 9.5-10.2 kg / min, and the agglomeration rate is ≤7%, which meets the requirements of "low-frequency start-up and high-efficiency circulation" for fire-fighting storage tanks. A 45° inclination angle is suitable for low-density dry powders such as sodium bicarbonate, reducing powder inlet resistance. A 55° inclination angle is suitable for high-density dry powders such as ammonium phosphate, as the steep slope can break the liquid bridge force. Although the flow rate is slightly lower at a 60° inclination angle (8.3 kg / min), the risk of powder agglomeration due to moisture absorption is significantly reduced by increasing the vertical component force.

[0063] At a 30° angle, excessively high flow velocity leads to powder breakage (increased fine powder and worsened flowability), and at a 65° angle, the risk of bridging increases dramatically (the flowability rating is "poor" when the angle of repose is >55°).

[0064] In summary, 45-50° optimizes flow efficiency and is suitable for conventional dry powders, while 55-60° enhances moisture resistance and anti-bridging ability, making it suitable for harsh environments.

[0065] Four to six air holes 504 are symmetrically opened on the side wall of the trumpet-shaped powder inlet 501, with a diameter of 3-5 mm. The axis of the air holes 504 is inclined in the horizontal plane (pointing to the center of the trumpet-shaped powder inlet 501) to ensure that the airflow and the powder flow direction form a synergistic effect. The air holes 504 are connected to an external compressed air source interface (such as a 0.5MPa nitrogen cylinder or a small air compressor, not shown in the figure) through a pressure-resistant hose (not shown in the figure). A solenoid valve (not shown in the figure, linked with the control module 7) and a pressure reducing valve (not shown in the figure, to stabilize the output pressure to 0.2-0.3MPa) are installed. When the spiral blade 4 starts, the control module 7 synchronously triggers the solenoid valve, and the pulse airflow (0.1-0.2 second interval) is injected into the trumpet-shaped powder inlet 501 from the air holes 504 to destroy the bridging structure formed by the static pressure of the powder.

[0066] If the temperature and humidity sensor detects that the ambient humidity is >60%RH, the control module 7 is electrically connected to start the continuous airflow mode (non-pulse, controlled by a 0.5MPa nitrogen cylinder or a small air compressor). The airflow isolates moisture from entering the funnel-shaped powder inlet 501, preventing the powder from absorbing moisture and clumping.

[0067] Furthermore, the device is set to start twice a month by default, with each run lasting 10 minutes (suitable for stable environments with humidity <50%RH). When the humidity is >60%RH for 24 consecutive hours, the cycle is shortened to once a week. If the temperature fluctuation is >10℃ / day (e.g., large day-night temperature difference), the duration of each run is increased to 15 minutes.

[0068] When the control module 7 receives a fire extinguishing signal (such as a signal from the fire control system's buzzer alarm), the control module 7 electrically connects to the drive motor 2 and starts switching to high-speed mode (speed increased by 20%) to ensure that the entire dry powder canister is circulated within 5 seconds.

[0069] It should be noted that the fire extinguishing signal must simultaneously meet the conditions of dry contact triggering and sudden increase in temperature and humidity (such as humidity increase of >10%RH within 1 minute) before it can be activated to avoid misoperation. Before each activation, the current of drive motor 2 and the air source pressure (such as 0.5MPa nitrogen cylinder or small air compressor) should be checked. If any abnormality is found, an audible and visual alarm will be triggered and the fault code will be recorded (output through the LCD1602 display screen).

[0070] The above embodiments are only used to illustrate the technical solutions of this utility model, and are not intended to limit it. Although this utility model has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions will not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this utility model.

Claims

1. A stirring device for a dry powder fire extinguishing system storage tank, comprising a storage tank (1), a drive motor (2), and a transmission rod (3), characterized in that: A spiral blade (4) is fixed on the transmission rod (3), and a dry powder lifting pipe (5) is sleeved on the outside of the spiral blade (4). The dry powder lifting pipe (5) has a trumpet-shaped powder inlet (501) at the bottom and symmetrical powder outlets (502) at the top. The drive motor (2) is a 24V explosion-proof motor, which is connected to the transmission rod (3) through a coupling (6). The device is configured for periodic start-up mode, driving the spiral blades (4) to transport the dry powder at the bottom of the storage tank through the lifting pipe (5) to the upper powder outlet (502) for scattering.

2. A dry powder fire extinguishing system tank agitator according to claim 1, characterised in that, The inclination angle of the trumpet-shaped powder inlet (501) is 45-60°.

3. The dry chemical fire extinguishant system tank agitator of claim 1, wherein, The inner wall of the dry powder lifting pipe (5) is provided with a spiral guide protrusion (503), and the height of the spiral guide protrusion (503) decreases along the lifting direction.

4. The dry chemical fire extinguishant system tank agitator of claim 1, wherein, The side wall of the trumpet-shaped powder inlet (501) has an air hole (504) for connecting to an external compressed air source interface.

5. A dry powder fire extinguishing system tank agitator according to claim 4, characterised in that, The drive motor (2) is connected to the control module (7) and is configured to start in real time according to the preset temperature and humidity threshold or fire extinguishing signal.

6. A dry powder fire extinguishant system tank agitator according to claim 5, characterised in that, The control module (7) integrates a temperature and humidity sensor and adaptively adjusts the start-up cycle based on environmental data.

7. The mixing device for the storage tank of the dry powder fire extinguishing system according to claim 1, characterized in that, The powder outlet (502) is radially symmetrically distributed and the outlet direction is inclined downward at 30-45°.

8. The dry chemical fire extinguishant system tank agitator of claim 1 wherein, The pitch of the spiral blade (4) is 0.8-1.2 times the diameter of the storage tank.

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