JP2014097873A - Powder transport method and powder transporting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably perform a change in a powder flow rate causing a pressure change in a tank, when sending out powder.SOLUTION: When reducing pressure in a tank 2 up to second pressure from first pressure and also reducing a flow rate of powder up to a second flow rate from a first flow rate during sending out of the powder, a powder transport method performs: a first step of interrupting opening-closing control of a pressurization control valve 10 and changing the opening of the valve to predetermined opening corresponding to the second pressure; a second step of opening a pressure relief valve 11 to predetermined opening determined in accordance with a residual quantity of the powder in the tank 2 and maintaining the opened state for a predetermined time, thereby reducing the pressure in the tank 2 up to the second pressure from the first pressure, the second step being performed together with the first step; and a third step of interrupting opening-closing control of a sending-out flow control valve 6 and gradually changing the opening up to the predetermined opening corresponding to the second flow rate by taking a predetermined time, the third step being performed together with the second step. The opening-closing control of the pressurization control valve 10 and the sending-out flow control valve 6 is resumed after finishing the first step and the second step.

Description

  The present invention relates to a powder conveying method and a powder conveying apparatus for delivering powder together with gas from a tank storing powder.

  2. Description of the Related Art There is known a powder conveyance device that fluidizes powder stored in a tank by blowing gas and sends the powder together with gas from a tank to a pipe. When delivering the powder, the tank is pressurized and kept at a higher pressure than the piping. Patent Document 1 discloses a technique for stabilizing the flow rate of powder to be delivered and improving the responsiveness when changing the powder flow rate by keeping the pressure in the tank constant in such a powder conveyance device. Is described.

  However, in the conventional powder conveying apparatus as described above, the range in which the flow rate of the powder can be changed is limited. When the pressure in the tank is constant, the flow rate of the powder is adjusted by changing the opening degree of the delivery flow rate control valve provided at the outlet of the tank. The opening of the delivery flow control valve decreases as the powder flow decreases, but if the opening is too small, the behavior of the powder when passing through the valve becomes unstable, and the powder is delivered. It disappears or the amount is not stable even if it is sent out.

  Therefore, the range in which the flow rate of the powder can be changed in the conventional powder conveyance device is limited to about 2: 1 in terms of the ratio between the maximum flow rate and the minimum flow rate. If it is desired to change the flow rate of the powder beyond this range, it is necessary to temporarily stop the powder delivery and change the set pressure in the tank. For example, if you want to further reduce the flow rate of the powder, if you lower the set pressure in the tank and then send the powder again, the opening of the delivery flow control valve that delivers the powder can be increased, so it passes through the valve Instability of the behavior of the powder at the time and the fact that the powder is not delivered are eliminated, and stable delivery becomes possible.

Japanese Utility Model Publication No. 61-38128

  However, it has been difficult to execute the same control while continuing the powder delivery. When lowering the set pressure in the tank, the pressure relief valve provided in the tank is opened to discharge the gas in the tank. However, if the pressure relief valve is opened during powder delivery, a large amount of gas may be discharged from the pressure relief valve. As a result, the tank is rapidly depressurized, and the gas is not released from the delivery flow rate control valve, so that the powder stays in the pipe and becomes clogged. If a pressure reducing valve with a small diameter is used, the pressure reduction in the tank can be moderated, but this time it takes too much time to reduce the responsiveness when changing the powder flow rate.

  Accordingly, the present invention has been made in view of the above problems, and an object of the present invention is to stably execute a change in powder flow rate accompanied by a pressure change in the tank during the delivery of powder. It is an object of the present invention to provide a new and improved powder conveying method and powder conveying apparatus that can be used.

  In order to solve the above problems, according to an aspect of the present invention, the pressure in the tank storing the powder, the pressure control valve for adjusting the supply amount of the pressurized gas to the tank, and the gas in the tank are adjusted. There is provided a powder conveying method in which the flow rate of the powder delivered together with the gas from the tank is adjusted by the delivery flow rate control valve while being adjusted by the pressure relief valve to be discharged. In the powder conveying method, the pressure in the tank is reduced from the first pressure to the second pressure and the powder flow rate is decreased from the first flow rate to the second flow rate. The first step of interrupting the opening / closing control of the pressure control valve and changing the opening of the pressurization control valve to a predetermined opening corresponding to the second pressure, and the pressure relief valve in the tank together with the first step A second step of opening the tank at a predetermined opening set in accordance with the remaining amount of the body and reducing the pressure in the tank from the first pressure to the second pressure by maintaining the open state for a predetermined time. The opening / closing control of the delivery flow rate control valve is interrupted, and the opening degree of the delivery flow rate control valve is gradually changed over a prescribed time to a prescribed opening degree corresponding to the second flow rate together with the second step. And after the first step and the second step, the pressurization control valve and the delivery Resume closing control quantity control valve.

  In the above powder conveying method, the opening of the pressure relief valve in the second step may be set so that a predetermined time is constant regardless of the remaining amount of powder in the tank. Further, the supply amount of the fluidizing gas for fluidizing the powder in the tank is adjusted by the fluidization control valve, and the opening degree of the fluidization control valve is set to a predetermined opening corresponding to the second pressure together with the first step. You may perform the 4th process changed every time.

  In order to solve the above problems, according to another aspect of the present invention, a tank for storing powder, a pressurization control valve for adjusting the supply amount of pressurized gas to the tank, and a gas in the tank There is provided a powder conveying device including a pressure relief valve for discharging the gas and a delivery flow rate control valve for adjusting the flow rate of the powder delivered together with the gas from the tank. The powder conveying device includes control means for controlling a pressurization control valve, a pressure relief valve, and a delivery flow rate control valve, and the control means changes the pressure in the tank from the first pressure to the second pressure during powder delivery. In order to reduce the flow rate of the powder from the first flow rate to the second flow rate, the open / close control of the pressurization control valve is interrupted and the opening degree of the pressurization control valve corresponds to the second pressure. The first control for changing to a predetermined opening, and the pressure release valve together with the first control are opened at a predetermined opening set according to the remaining amount of powder in the tank, and the open state is The second control for lowering the pressure in the tank from the first pressure to the second pressure by maintaining the time and the opening / closing control of the delivery flow control valve are interrupted, and the delivery flow control valve is opened together with the second control. The degree is gradually changed over a predetermined time to a predetermined opening corresponding to the second flow rate. Run a third control after the end of the first control and the second control resumes opening and closing control of the pressure control valve and the delivery flow control valve.

  In the above-described powder conveyance device, the opening degree of the pressure relief valve in the second control may be set so that a predetermined time is constant regardless of the remaining amount of powder in the tank. The powder conveying device further includes a fluidization control valve for adjusting a supply amount of fluidizing gas for fluidizing the powder in the tank, and the control means opens the fluidization control valve together with the first control. You may perform 4th control which changes a degree to the predetermined opening degree corresponding to 2nd pressure.

  According to said structure, the opening degree of a pressure relief valve is determined according to the residual amount of the powder in a tank so that pressure reduction in a tank may advance over predetermined time. Therefore, it is possible to avoid problems caused by the pressure inside the tank being suddenly reduced, or conversely, it takes too much time for pressure reduction. In addition, by gradually changing the opening degree of the delivery flow rate control valve according to the predetermined time during which the pressure reduction in the tank proceeds, pressure reduction is achieved while preventing instability of the powder flow due to a sudden change in opening degree. Thereafter, it is possible to quickly start the powder delivery at the changed flow rate.

  As described above, according to the present invention, it is possible to stably change the powder flow rate accompanying the pressure change in the tank during the delivery of the powder.

It is a figure which shows the structure of the powder conveying apparatus which concerns on one Embodiment of this invention. It is a figure for demonstrating the change control of the powder flow rate in the powder conveying apparatus shown in FIG. It is a figure which shows the example of the relationship between the powder residual amount in a tank, and the depressurization time. It is a graph which shows the example of a setting of the regulation opening degree of the pressure relief valve in one Embodiment of this invention. It is a flowchart which shows change control of the powder flow rate in one Embodiment of this invention. It is a graph which shows the result of the change control of the powder flow volume in the Example of this invention.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In the present specification and drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is a diagram illustrating a configuration of a powder conveyance device according to an embodiment of the present invention. In the powder conveying device 1, the powder stored in the tank 2 is fluidized by the fluidizing gas supplied from the fluidizing gas line 3 and sent to the conveying pipe 4 together with the gas in the tank 2. Here, the supply amount of the fluidizing gas is adjusted by the fluidization control valve 5, and the flow rate of the powder to be delivered is adjusted by the delivery flow rate control valve 6. In the transfer pipe 4, the transfer gas is supplied from the transfer gas line 7 to transfer the powder. The amount of carrier gas is adjusted by the blow control valve 8.

  On the other hand, the pressure in the tank 2 is maintained at a predetermined pressure by the pressurized gas supplied from the pressurized gas line 9. The supply amount of the pressurized gas is adjusted by the pressurization control valve 10. The tank 2 is further provided with a pressure relief valve 11 that, when opened, discharges the gas in the tank 2 to reduce the pressure. In this embodiment, the pressure relief valve 11 is a valve whose opening degree can be adjusted. Each valve (fluidization control valve 5, delivery flow rate control valve 6, blow control valve 8, pressurization control valve 10, and pressure relief valve 11) is controlled by the control unit 12. The control part 12 is implement | achieved as a control circuit which outputs a control signal to each valve, for example. The control circuit may include a computer. The control unit 12 uses the remaining amount of powder in the tank 2 detected by the load cell 13 for valve control in addition to operation input and a timer.

FIG. 2 is a flowchart showing change control of the powder flow rate in the powder conveying apparatus shown in FIG. In the powder flow rate change control described below, the pressure in the tank 2 is decreased from P ₁ to P ₂ (P ₁ > P ₂ ), and the powder flow rate is decreased from Q ₁ to Q ₂ (Q ₁ > Q ₂ ).

Powder flow rate changing control before the powder transfer device 1, maintaining the pressure in the tank 2 to P _1, is sending the powder to the transport pipe 4 at a flow rate Q ₁ (step S101). At this time, the control unit 12 controls the opening degree of the pressure control valve 10 so that the pressure in the tank 2 is maintained at P _1, sends the flow control valve as powder flow rate Q ₁ is sent The opening degree of 6 is controlled. Note that control in a state where the pressure in the tank 2 and the powder flow rate are kept constant is a known technique, and thus detailed description thereof is omitted here.

  The control unit 12 starts powder flow rate change control in accordance with, for example, an operation input by an operator or a flow rate change start instruction by a timer or the like. When the flow rate change start instruction is acquired (step S103), the control unit 12 interrupts the control of the pressurization control valve 10 and the delivery flow rate control valve 6 (step S105), and starts the powder flow rate change control. To do.

When the change control of the powder flow rate is started, the control unit 12 sets the opening degree of the pressurization control valve 10 to the specified opening degree, and fixes this value during the change control (step S107). Here, provisions opening of the pressure control valve 10, for example pressure after the pressure in the tank 2 changes, i.e. in the case of controlling so as to maintain the pressure P _2, the opening degree of the pressure control valve 10 It can be a set value.

Along with the above step S107, the control unit 12 opens the pressure relief valve 11 at a specified opening degree (step S109), and reduces the pressure in the tank 2. Here, in this embodiment, the pressure relief valve 11 is a valve whose opening degree can be adjusted, and the control unit 12 sets the opening degree to a specified opening degree when the pressure relief valve 11 is opened. As will be described later, the specified opening degree of the pressure relief valve 11 is determined according to the remaining amount of the powder in the tank 2 detected by the load cell 13 for a predetermined time from the pressure P ₁ in the tank 2 to the pressure P ₂ . It is set to complete at Δt. The control unit 12 monitors the pressure in the tank 2 with, for example, a pressure gauge installed in the tank 2, and determines whether or not the pressure in the tank ₂ has reached P2 (step S111). If the pressure in the tank 2 has reached the _{P 2,} the controller 12 closes the pressure relief valve 11 (step S113). A method for determining the specified opening of the pressure relief valve 11 to be set will be described later with reference to FIGS. 4 and 5.

Further, along with the steps S107 and S109, the controller 12 gradually opens the delivery flow rate control valve 6 (step S115). Opening of the delivery flow control valve 6 is multiplied by the decompression time and the same predetermined time Δt in the tank 2 by the depressurization valve 11 described above, open the corresponding from opening degree corresponding to the flow rate Q ₁ to a flow Q ₂ It is gradually changed to degrees (target opening). Thereby, it is possible to prevent the powder flow from becoming unstable due to a sudden change in the opening degree of the delivery flow rate control valve 6. Further, after the time Delta] t, for allowing delivery of the powder flow rate Q ₂ is at a reduced pressure the end of the tank 2, it is possible to quickly implement a change in powder flow rate. The control unit 12 monitors the control value of the opening degree of the delivery flow rate control valve 6 and determines whether or not the opening degree of the delivery flow rate control valve 6 has reached the target opening degree (step S117). The delivery flow rate control valve 6 is gradually opened until the opening is reached.

When the control of each valve in steps S107 to S117 is completed, the control unit 12 resumes control of the valve, specifically, control of the pressurization control valve 10 and the delivery flow rate control valve 10 (step S119). Thus, the powder conveying device 1 keeps the pressure in the tank 2 to _{P 2,} at a flow rate _{Q 2} sends a powder conveying pipe 4 (step S121). Note that the control of each valve in steps S107 to S117 does not necessarily have to be executed at the same time, and may be executed with a time difference.

Here, the pressure reducing process by the pressure relief valve 11 in step S109 and the opening degree changing process of the delivery flow rate control valve 6 in step S113 may be terminated due to, for example, an error in the measured value of the load cell 13 or the like. Therefore, for example, as shown in steps S111 and S117, the control unit 12 detects that the pressure in the tank 2 and the opening degree of the delivery flow rate control valve 6 have reached the set values, and the step is performed on this condition. In S119, the control of the valve at the pressure P ₂ and the flow rate Q ₂ may be resumed. Alternatively, for example, using a timer, each step of the pressure reducing step (steps S109 to S113) by the pressure relief valve 11 and the opening degree changing step (steps S115 to S117) of the delivery flow rate control valve 6 is performed over time Δt. The valve control may be resumed in step S119 after the time Δt has elapsed from the start of each process. Thereby, the start time of step S119 can be determined, and the powder flow rate can be adjusted in accordance with the blowing start time at the changed powder flow rate.

FIG. 3 is a diagram for explaining an example of control of each valve in the change control of the powder flow rate shown in FIG. In the illustrated example, the change control of the powder flow rate is started at time t _1, (a) pressurized control valve 10, (b) depressurizing valve 11, and (c) sending a flow control valve 6 is controlled respectively . The symbols (a) to (c) shown in FIGS. 1 and 3 correspond to each other.

(A) the change control of the powder flow rate control time t ₁ of the pressure control valve is initiated, provisions opening of the pressure control valve 10 by the control unit 12 matches the powder blowing conditions after change The opening is changed. At this time, the opening / closing control of the pressurization control valve 10 is also interrupted. When the time t ₂ change control of powder flow rate is completed, the control unit 12, as the pressure in the tank 2 is maintained at P _2, it resumes control of the opening degree of the pressure control valve 10.

(B) control with the control above of the pressure control valve 10 of the pressure release valve, the control unit 12, the time Δt only depressurization valve 11 from time t ₁ to time t ₂ is opened at a specified opening degree, in the tank 2 reducing the pressure from the pressure _{P 1} to a pressure _{P 2.}

(C) together with the control of the control above the depressurization valve 11 of the delivery flow control valve, the control unit 12 interrupts the opening and closing control of the delivery flow control valve 6 receives the start of powder flow rate changing control at time t _1. Then, the controller 12 gradually changes the opening degree of the delivery flow rate control valve 6 to the target opening degree corresponding to the changed flow rate Q ₂ over time Δt from time t ₁ to time t ₂ .

As an additional step that is not essential in the embodiment of the present invention, the control unit 12 may control the opening degree of the fluidization control valve 5. For example, along with the control of the pressurization control valve 10, the control unit 12 may change the opening degree of the fluidization control valve 5 from the opening degree corresponding to the pressure P ₁ to the opening degree corresponding to the pressure P _2. Good. By changing the opening degree of the fluidization control valve 5 in accordance with the opening degree of the pressurization control valve 10, the balance between the pressurized gas supplied to the tank 2 and the fluidizing gas can be maintained, and the pressurization control is performed. In some cases, pressurization control of the tank 2 by the valve 10 can be further stabilized. Note that the control of the fluidization control valve 5 does not necessarily have to be executed, and even if executed, it need not be performed simultaneously with the control of the pressurization control valve 10 described above.

  Next, with reference to FIG. 4 and FIG. 5, the specified opening degree of the pressure relief valve 11 in the powder flow rate change control according to the embodiment of the present invention will be further described. FIG. 4 is a diagram showing an example of the relationship between the residual amount of powder in the tank and the pressure relief time, and FIG. 5 is a graph showing a setting example of the specified opening of the pressure relief valve in one embodiment of the present invention. is there.

FIG. 4 shows time-series changes in pressure in the tank 2 when the pressure relief valve 11 having a nominal diameter of 80A is fully opened when the volume of the tank 2 is 31.8 m ³ . As shown in the figure, the time taken for the pressure in the tank 2 to drop due to the opening of the pressure relief valve 11 (pressure relief time) becomes shorter as the amount of powder remaining increases. This is because the larger the residual amount of powder, the smaller the gap in the tank 2 and the smaller the volume of gas filled therein. For example, if no powder remains in the tank 2 (powder remaining amount 0 ton), the volume 31.8 m ³ of the tank 2 becomes the gas volume as it is. On the other hand, if a large amount of powder remains in the tank 2 (powder remaining amount: 30 ton), the gas volume decreases to 4.8 m ³ .

Therefore, for example, when the pressure release valve 11 is fully opened and the pressure in the tank 2 is reduced from P ₁ = 0.6 MPa to P ₂ = 0.4 MPa, the pressure release time is 25 seconds if the powder remaining amount is 0 ton. If the remaining amount of powder is 20 tons, it will vary such as 10 seconds. That is, when the pressure relief valve 11 is opened at the same opening, the time taken for the pressure in the tank ₂ to decrease from P ₁ to P ₂ varies greatly depending on the amount of powder in the tank 2.

  Therefore, even if the depressurization valve 11 is opened at the same opening degree to reduce the pressure in the tank 2, if the remaining amount of powder in the tank 2 is large, the inside of the tank 2 is rapidly depressurized and the gas is stored in the tank. 2 may not flow to the transfer pipe 4 (because the fluid flows in a direction with less pressure loss). This is one of the reasons why it is difficult to change the pressure in the tank 2 and change the powder flow rate while continuing the powder delivery.

  Therefore, in this embodiment, as shown in FIG. 5, the control unit 12 sets the specified opening degree of the pressure relief valve 11 according to the remaining amount of powder in the tank 2 detected by the load cell 13. In the illustrated example, the specified opening degree of the pressure relief valve 11 is set to be smaller as the residual amount of powder in the tank 2 is larger. As a result, when the amount of powder remaining is large, the opening of the pressure relief valve 11 is suppressed to prevent the tank 2 from being rapidly depressurized, and when the amount of powder remaining is small, the degree of opening of the pressure relief valve 11 is reduced. Can be increased to quickly complete the pressure change.

  In FIG. 5, the specified opening of the pressure relief valve 11 is shown to be inversely proportional to the remaining amount of powder, but these relationships are not necessarily proportional. Actually, the specified opening degree of the pressure relief valve 11 for each remaining amount of powder can be set based on the result of a trial run, for example. Further, the specified opening degree of the pressure relief valve 11 is set so as to prevent sudden pressure reduction in the tank 2 as described above, and to allow the pressure change to be completed quickly. The time required for the change, that is, the time Δt may be set so as to be constant regardless of the amount of powder remaining in the tank 2. If the time Δt is constant regardless of the remaining amount of powder, for example, setting of a timer when the control unit 12 changes the opening degree of the delivery flow rate control valve 6 is simplified. In addition, it is preferable that the time required for the change control of the powder flow rate is constant also from the side of the equipment that uses the delivered powder.

  Next, examples of the present invention will be described. In this example, the above-described embodiment of the present invention was applied to a powder conveyance device for sending CaO blown into hot metal in the hot metal pretreatment process. In CaO blowing in the hot metal pretreatment process, the reaction amount per unit time becomes smaller as blowing is continued. Therefore, if the amount of CaO matched to the initial reaction amount of blowing is continuously blown, CaO is excessive in the latter half of blowing, that is, a waste blowing state occurs.

  Therefore, in this embodiment, the amount of CaO to be blown is changed in accordance with the reaction amount per unit time. In this case, an appropriate amount of CaO is 300 kg / min in the first half of blowing and 100 kg / min in the second half. However, in this case, the ratio of the delivery flow rate before and after the change in the powder conveyance device is 3: 1. The ratio of the delivery flow rate that can be changed by the conventional powder conveyance device with a constant pressure in the tank (for example, before and after the change) When the ratio of the delivery flow rate exceeds about 2: 1), it is difficult to realize such a change in the delivery flow rate while continuing the powder delivery. On the other hand, in the powder conveyance device 1 according to the embodiment of the present invention, the pressure in the tank 2 can be changed while the powder is continuously delivered. A change in flow rate can be realized.

In this example, the powder conveyance device 1 (tank volume 31.8 m ³ ) according to the embodiment of the present invention is used, the powder flow rate Q ₁ before change is 300 kg / min, and the powder flow rate Q ₂ after change is 100 kg / min, the pressure was set _{P 1} before the change 0.6 MPa, at 0.4MPa at the pressure _{P 2} after the change. Further, the required time Δt for depressurization in the tank 2 due to opening of the pressure relief valve 11 and change of the opening degree of the delivery flow rate control valve 6 was set to 20 sec.

With the above settings, the powder flow rate change control was performed. At the start of the change control, the remaining amount of the powder in the tank 2 was 20 t, and the volume of the gas filled in the gap was 13.8 m ³ . In the change control, the opening degree of the pressurization control valve 10 is set to a prescribed opening degree (10%) corresponding to the changed pressure (0.4 MPa), and the pressure relief valve 11 is set to a prescribed opening degree (38%) for 20 sec. The inside of the tank 2 was depressurized from 0.6 MPa to 0.4 MPa by opening for a period of time. Further, together with the pressure reduction in the tank 2 by the pressure relief valve 11, the opening degree of the delivery flow rate control valve 6 is changed from an opening degree corresponding to 300 kg / min (56%) to an opening degree corresponding to 100 kg / min (20 sec). 22%).

  FIG. 6 is a graph showing the results of the change control of the powder flow rate in the example of the present invention. As shown in the figure, when the change control of the powder flow rate is performed according to the above-described embodiment, the CaO delivery flow rate is changed from 300 kg / min within 20 seconds from the start of the change control of the powder flow rate while the blowing is continued. It could be changed to 100 kg / min. As a result, the powder conveyance device according to the embodiment of the present invention stably executes a change in the flow rate of the powder delivery in a wider range, which is difficult with the conventional powder conveyance device in which the pressure in the tank is constant. It can be said that it was proved possible to do.

  The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Powder conveying apparatus 2 Tank 5 Fluidization control valve 6 Delivery flow control valve 8 Blow control valve 10 Pressurization control valve 11 Depressurization valve 12 Control part 13 Load cell

Claims (6)

The pressure in the tank that stores the powder is adjusted by a pressurization control valve that adjusts the supply amount of the pressurized gas to the tank and a pressure release valve that discharges the gas in the tank, and together with the gas from the tank In the powder conveying method of adjusting the flow rate of the powder to be delivered by a delivery flow rate control valve,
In reducing the pressure in the tank from the first pressure to the second pressure during the delivery of the powder and reducing the flow rate of the powder from the first flow rate to the second flow rate,
A first step of interrupting the opening / closing control of the pressurization control valve, and changing the opening of the pressurization control valve to a predetermined opening corresponding to the second pressure;
The pressure in the tank is opened by opening the pressure release valve at a predetermined opening set according to the remaining amount of the powder in the tank together with the first step, and maintaining the open state for a predetermined time. A second step of reducing the first pressure from the first pressure to the second pressure;
The opening / closing control of the delivery flow rate control valve is interrupted, and the opening degree of the delivery flow rate control valve is gradually changed over the prescribed time to the prescribed opening degree corresponding to the second flow rate together with the second step. A third step of
And the opening / closing control of the pressurization control valve and the delivery flow rate control valve is resumed after completion of the first step and the second step.   The opening of the pressure relief valve in the second step is set so that the predetermined time is constant regardless of the remaining amount of the powder in the tank. The powder conveyance method as described. Adjusting a supply amount of fluidizing gas for fluidizing the powder in the tank by a fluidization control valve;
The fourth step of changing the opening degree of the fluidization control valve to a predetermined opening degree corresponding to the second pressure is performed together with the first step. The powder conveyance method as described. A tank for storing powder, a pressure control valve for adjusting a supply amount of pressurized gas to the tank, a pressure release valve for discharging the gas in the tank, and the powder sent together with the gas from the tank A powder transfer device including a delivery flow rate control valve for adjusting the flow rate of
Control means for controlling the pressurization control valve, the pressure relief valve, and the delivery flow rate control valve, wherein the control means changes the pressure in the tank from the first pressure to the second pressure during delivery of the powder. In reducing the flow rate of the powder from the first flow rate to the second flow rate while lowering to the pressure,
A first control for interrupting the opening / closing control of the pressurization control valve and changing the opening of the pressurization control valve to a predetermined opening corresponding to the second pressure;
Along with the first control, the pressure release valve is opened at a predetermined opening set in accordance with the remaining amount of the powder in the tank, and the open state is maintained for a predetermined time. A second control for lowering the pressure from the first pressure to the second pressure;
The opening / closing control of the delivery flow rate control valve is interrupted, and the opening degree of the delivery flow rate control valve is gradually changed over the prescribed time to the prescribed opening degree corresponding to the second flow rate together with the second control. And the opening / closing control of the pressurization control valve and the delivery flow rate control valve is resumed after completion of the first control and the second control. apparatus.   The opening degree of the pressure relief valve in the second control is set so that the predetermined time is constant regardless of the remaining amount of the powder in the tank. The powder conveying apparatus as described. A fluidization control valve for adjusting a supply amount of fluidizing gas for fluidizing the powder in the tank;
The said control means performs 4th control which changes the opening degree of the said fluidization control valve to the predetermined opening degree corresponding to a said 2nd pressure with the said 1st control. Item 6. The powder conveying apparatus according to Item 4 or 5.

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