A pulse assisted feeder for pneumatic conveying of food powder and method

Abstract

The present application relates to food powder conveying technical field, especially to a small powder periodic feeding structure suitable for unattended food processing equipment, specifically to a pulse auxiliary feeding device and method for low-density food powder such as flour, which adopts PLC control and is suitable for continuous or intermittent accurate feeding of small unattended equipment. The whole system does not need traditional weighing system and complex valves and mechanical transmission, only needs to determine the material characteristics and conveying capacity, obtain gas flow, pressure and other related parameters through experiment, then carry out PLC programming to obtain time integral data, so as to obtain a conveying accuracy less than 5%. The whole system has good sealing property and is suitable for small unattended food processing machinery. The present application solves the problem of flour feeding of small unattended machinery, and the whole powder feeding system has the advantages of simple structure, low cost and high reliability.

Description

Technical Field

[0001] This invention relates to the field of food powder conveying technology, and more particularly to a small-scale periodic powder feeding structure suitable for unattended food processing equipment. Specifically, it relates to a pulse-assisted feeding device and method for low-density food powders such as flour. This conveying method is PLC controlled and is suitable for continuous or intermittent precise feeding in small, unattended equipment. The entire system does not require a traditional weighing system or complex valves and mechanical transmissions. It only requires determining the material characteristics and conveying volume, obtaining relevant parameters such as gas flow rate and pressure through experiments, and then using PLC programming to obtain time integral data to achieve a conveying accuracy of less than 5%. The entire system has good sealing performance and is suitable for small, unattended food processing machinery. This invention solves the problem of flour feeding in small, unattended machinery. The entire powder feeding system has the advantages of simple structure, low cost, and high reliability. Background Technology

[0002] Currently, food powder, especially flour, is typically conveyed using screw conveyors, fluidized bed conveyors, rotary feeder valves, and Venturi pneumatic conveyors. These methods are commonly used in large food processing plants, and flour conveying systems for small, unattended food processing equipment are relatively rare. Furthermore, these systems cannot meet the specific requirements of unattended food processing equipment. Achieving precise small-batch conveying and distribution faces several limitations in existing technologies. Screw conveyors suffer from residue and contamination issues, and powder easily accumulates inside the screw, leading to clumping, moisture absorption, and contamination over long-term operation, which is detrimental to the hygiene maintenance of food equipment and results in significant mechanical wear. Traditional fluidized bed structures have high energy consumption, requiring continuous air supply to maintain powder fluidization, resulting in large air volume demands, significant fluctuations in powder concentration, insufficient conveying stability, and potential clogging of the permeable structure over long periods. Using a mature Venturi powder pump for direct powder intake can easily lead to powder bridging, instantaneous material collapse, drastic fluctuations in the powder-to-air ratio, and unstable conveying volumes due to powder lumps entering the system. Existing small-scale Venturi powder conveying systems (such as electrostatic spraying) are not suitable for unattended food processing equipment, and these devices are generally large in size, complex in structure, require frequent maintenance, and cannot meet food hygiene requirements. Based on the characteristics of existing small-scale unattended equipment (see patent number: 2026103509783) and the need for small-volume, intermittent, short-cycle conveying, we have invented a mechanical structure and method that is simple in structure, highly stable, and capable of both continuous and periodic feeding. Summary of the Invention

[0003] The present invention provides a pneumatic pulse-assisted feeding device and method for food powders, in order to solve the problems existing in the prior art, such as powder bridging, conveying fluctuations, powder clumping and blockage, unstable powder-to-air ratio, complex mechanical structure, and poor food hygiene.

[0004] To achieve the above objectives, the present invention employs a pulse-assisted feeding device for pneumatic conveying of food powders, comprising the following four functional modules (see appendix). Figure 1 The components are a powder storage tank module (1), a discharge pipe pulse bridge breaking module (2), a buffer mixing chamber (3), and a venturi pump conveyor (4).

[0005] The main innovations of this invention are the pulse breaking bridge module in the feed pipe and the buffer mixing chamber (see attached document). Figure 2 The principle is to fully utilize the bridging effect of powder in the storage tank and feed pipe to act as the valve closing function in the conveying system, and to use gas bridging to act as the valve opening function in the conveying system. After bridging, the powder falling by gravity and the bridging gas are premixed in the buffer chamber below to form a stable gas-powder mixture. The premixed gas-powder mixture is then transported to the distributor by the Venturi powder pump below for distribution.

[0006] To ensure that the flour can bridge and form a continuous powder and column after bridging, the main powder storage tank of the gas circuit unit has a conical transition section at the bottom. The semi-cone angle of the conical transition section is generally less than 45 degrees. Below the conical transition section is a feed pipe with symmetrical air inlets at the bottom. The symmetrical air inlets are connected to a pressure-stabilized drying gas source. The pulse frequency and duty cycle of the drying gas source are controlled by a PLC-controlled solenoid valve. By controlling the pressure, flow rate, frequency, and duty cycle of the pulse bridging gas, precise control of the powder falling flow rate is achieved.

[0007] The pulsed gas bridging is achieved within the feed tube (1). The feed tube (1) has two symmetrical, upward-sloping pulsed bridging gas ports at its bottom. Each bridging gas port has a downward-sloping baffle (2) above it. In addition to preventing falling flour from entering the bridging gas pipeline (3), the baffle also provides an additional bridging effect for the flour above. Furthermore, the baffle (2) prevents the pulsed airflow from blowing directly onto the top of the storage tank, guiding the airflow to the center of the "bridging" powder.

[0008] After the bridge is broken, the powder and airflow are still in a non-uniform contact state in the feed tube (1). They need to enter the buffer mixing chamber (4) at the lower end for secondary mixing to form a fluidized and stable powder-air mixture. In order to maintain a constant internal pressure in the buffer mixing chamber (4), at least one natural vent (5) is provided at the upper part of the chamber. This vent is connected to the atmosphere through a filter, which plays a dual role of pressure relief and auxiliary air replenishment.

[0009] To ensure that the powder achieves sufficient flow in the buffer mixing chamber (4), this device introduces a symmetrically distributed rotating airflow group. The rotating airflow pipe (6) is located at the bottom of the chamber and is embedded in the cylindrical cavity wall of the buffer mixing chamber in a horizontal tangential manner, thereby forming a high-speed swirling flow in the cavity and entraining the falling powder into the center of the airflow.

[0010] The buffer mixing chamber (4) is shaped like a gyroscope (or an inverted cone), and its bottom is connected to the Venturi powder pump below through a transition pipe (7). In order to prevent the powder from "collapsed" and rushing in when the Venturi powder pump starts, the transition pipe (7) has been structurally modified: the transition pipe (7) extends upward and penetrates into the interior of the buffer mixing chamber (4). The extension section is not a closed pipe wall, but a multi-column support structure (8) is formed by precision machining (such as laser cutting). Specifically, 2 to 4 rectangular arc grooves are symmetrically machined at the end of the stainless steel pipe, and the remaining pipe wall forms vertically distributed support columns. The top of the support column is provided with an uncut ring, and an umbrella-shaped baffle cap (9) is welded or fixed at the upper end of the ring. The umbrella-shaped baffle cap (9) has a semi-cone angle of less than 45 degrees and its surface is mirror polished to reduce the powder adhesion and prevent the powder from accumulating at this location. The vertical distance between the umbrella-shaped baffle cap (9) and the discharge port of the feed pipe can be preset or adjusted according to the physical properties of the flour (such as the angle of repose). When the system is in a non-conveying state, the umbrella-shaped baffle cap (9) uses the angle of repose of the powder to achieve physical self-locking, preventing the powder from leaking under gravity. When the system starts the pulse bridge breaking and rotating airflow, the powder overflows from the edge of the umbrella cap and is quickly carried away by the surrounding swirling flow.

[0011] This pulse-assisted feeding device achieves food powder conveying and control through powder bridging and breaking. This method eliminates easily clogged valves and mechanical moving parts, using pulsed airflow to periodically break up powder bridges, significantly reducing the instability problems caused by traditional continuous fluidization. Gravity is used to create a continuous powder flow, reducing feeding fluctuations. A buffer mixing chamber and an umbrella-shaped baffle prevent large powder clumps from directly entering the Venturi conveyor. Furthermore, rotating airflow premixes the powder, reducing powder accumulation in the buffer mixing chamber and improving conveying stability. The entire powder conveying system has no moving mechanical parts, reducing mechanical wear and maintenance costs, making it ideal for small food processing equipment, especially for automated feeding in unattended food processing equipment.

[0012] When the system is working, the pulsed airflow periodically breaks up the flour bridging, and the flour forms a continuous flow under the action of gravity. The continuously falling flour enters the buffer mixing chamber, and some of the flour falls onto the surface of the umbrella-shaped structure below. It is dispersed in all directions through the umbrella and dispersed into the transition tube below under the dual action of the vacuum generated by the venturi pump below and the rotating airflow. The powder enters the venturi conveyor below through the transition tube.

[0013] The present invention will be further illustrated below with reference to examples.

[0014] Example: A 304 stainless steel main powder silo with a diameter of 200mm and a height of 400mm. The inner wall of the stainless steel silo is polished to a surface finish of less than 0.4. The lower part of the stainless steel main powder silo has a conical structure with a taper of 25 degrees. The lower part of the cone is a feed pipe with an inner diameter of 16mm and a length of 60mm. 20mm from the bottom of the feed pipe, there are two symmetrical air inlet pipes with an inner diameter of 0.6mm. The air inlet pipes are embedded into the pipe wall at a 60-degree angle upwards. 8mm above the air inlet is a baffle plate tilted downwards at a 45-degree angle (all angles are horizontal). The air inlet pipes and baffle plate are inserted into the feed pipe after being laser-grooved at an angle, and then spot-welded by laser or cold welding. Below the feed pipe, a gyroscope-shaped buffer mixing chamber with an inner diameter of 40mm and a height of 50mm is fixed via a sanitary quick-connect fitting. The upper surface of the buffer mixing chamber has two symmetrical 1.2mm natural air inlet pipes, with PTFE filters nested inside the air inlet pipes. Two symmetrical 1mm holes are laser-drilled at a 30-degree angle on the horizontal plane at a depth of 6mm from the bottom of the cylindrical tube wall of the buffer mixing chamber. A stainless steel tube with an outer diameter of 1mm and an inner diameter of 0.5mm is inserted and welded to form a rotating fluidizing gas path. A 16mm diameter hole is located at the center of the bottom of the gyro-shaped buffer mixing chamber. A 16mm outer diameter feed pipe is inserted into this hole, with four support rods at the end. A 16mm diameter stainless steel umbrella-shaped baffle cap is welded to each support rod. After the feed pipe is inserted into the mixing chamber, the four stainless steel supports of the umbrella-shaped baffle cap extend just beyond the bottom plane of the buffer mixing chamber. The other end of the feed pipe is connected to the main inlet of the venturi powder pump. Attached Figure Description

[0015] Figure 1 A schematic diagram of the overall structure of the conveying system.

[0016] Figure 2 Schematic diagram of pulse bridge breaking and buffer gas mixing chamber structure.

Claims

1. A pulse-assisted feeding device and method for pneumatic conveying of food powder, characterized in that... From top to bottom, it includes a powder storage tank, a feed pipe, a buffer mixing chamber, and a Venturi powder conveying pump.

2. The pulse-assisted feeding device and method for pneumatic conveying of food powder according to claim 1, characterized in that... The powder storage tank includes a cylindrical body and a conical discharge section at the bottom of the body, wherein the semi-cone angle of the conical discharge section is less than 45 degrees.

3. The pulse-assisted feeding device and method for pneumatic conveying of food powder according to claim 1, characterized in that... The feed tube is equipped with pulse bridging nozzles arranged obliquely upwards, and a downward-sloping baffle is provided above the nozzles. The injection axis of the pulse bridging nozzles corresponds to the last edge of the baffle.

4. The pulse-assisted feeding device and method for pneumatic conveying of food powder according to claim 1, characterized in that... The upper part of the buffer mixing chamber is provided with a pressure balance breathing port, and the lower part is provided with a horizontal oblique rotating fluidizing gas inlet; the buffer mixing chamber is provided with an umbrella-shaped material distribution mechanism, which includes multiple vertically distributed thin tubes and an umbrella-shaped baffle cap set on the top of the thin tubes. The umbrella-shaped baffle cap is set above the outlet of the central connecting pipe of the buffer mixing chamber, and the horizontal projection of the umbrella-shaped baffle cap covers the outlet.

5. The pulse-assisted feeding device and method for pneumatic conveying of food powder as described in claim 1, characterized in that... The Venturi powder pump is connected to the bottom of the buffer mixing chamber and has a main air inlet, an auxiliary air inlet, a powder inlet and a conveying outlet, wherein the powder inlet is connected to the buffer mixing chamber.

6. A pulse-assisted feeding device and method for pneumatic conveying of food powder according to claim 3 or 4, characterized in that... The pulse bridge-breaking nozzle and the horizontal oblique rotating fluidizing gas inlet are connected in parallel to the same pulse control gas valve through a gas path; or the two are respectively connected to independent gas sources and are independently driven by their respective pulse control valves.

7. A pulse-assisted feeding device and method for pneumatic conveying of food powder according to claim 4, characterized in that... The pressure-balanced breathing port is equipped with a micron-level filter element or a one-way air intake valve to prevent dust from overflowing while maintaining a slight negative pressure in the buffer chamber.

8. A method for quantitatively conveying powder based on the apparatus according to any one of claims 1-7, characterized in that... The process includes the following steps:

1. Establishing a baseline flow field: Turn on the Venturi main gas and normally open auxiliary gas, and adjust the pressure in the buffer chamber through the pressure balance breather to establish a slightly negative pressure equilibrium state; 2. Pulse synchronous feeding: Open the pulse gas valve to trigger the bridge-breaking airflow in the feed tube and the rotating fluidizing airflow in the buffer chamber, causing the powder to overflow from the edge of the umbrella-shaped baffle and enter a suspended fluidized state; 3. Differential pressure suction conveying: Utilize the vacuum suction generated by the Venturi powder conveying pump to draw in the fluidized powder and send it out through the conveying outlet; 4. Flow compensation and shutdown: Control the conveying volume by adjusting the duty cycle of the pulse gas valve or the slightly positive pressure value of the auxiliary air inlet. When stopping the conveying, first close the pulse gas valve and then close the Venturi main gas after a delay.

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