JP2012216133A - Liquid level control device and liquid level control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid level control device and a liquid level control method capable of performing liquid level control with higher accuracy and reducing a useless adjustment.SOLUTION: A liquid level control device 1 comprises: a container 20 where liquid is stored; a supply channel 10; a discharge channel 30; a control valve 12 to control flow rates in the supply channel 10 as well as the discharge channel 30; a discharge pump 32; and level switches 20H and 20L to detect whether a liquid level of the container 20 reaches high liquid levels H or low liquid levels L. The liquid level control device 1 has a control section 40 which calculates a difference ΔW between a supply quantity and a discharge quantity based on detection results of the level switches 20H and 20L and controls the liquid level of the container 20 by adjusting the flow rates in the supply channel 10 as well as the discharge channel 30 so that the difference ΔW converges to zero. Thus, the liquid level control device 1 can perform liquid level control with higher following capability with respect to an external disturbance such as a fluctuation in the supply quantity or the discharge quantity and higher accuracy and thereby enabling a useless adjustment to be reduced.

Description

  The present invention relates to a liquid level control apparatus and a liquid level control method, and more particularly, to a liquid level control apparatus and a liquid level control method for controlling the height of a liquid level stored in a container.

  Techniques have been proposed for controlling the height (liquid level) of the liquid stored in the container. In industrial applications, liquids stored in containers include liquids that are difficult to measure in liquid containers such as medium and high viscosity fluids whose viscosity and specific gravity change depending on temperature and composition. . In some cases, such a liquid is continuously or semi-continuously supplied into the container, and the liquid stored in the container is discharged to control the liquid level of the container. In such a case, if liquid is continuously supplied or discharged using a differential pressure type liquid level gauge or float type liquid level gauge, the liquid level in the container becomes too high because the liquid level detection accuracy is low. There is a concern that the liquid overflows or the liquid level becomes too low and the liquid runs out.

  For the purpose of reliably detecting the liquid level, there is a method of batch supply or extraction in which level switches are installed at the upper and lower limits of the water level of the container, and for example, dispensing is started at the upper limit and dispensing is stopped at the lower limit. However, in this method, the ON / OFF operation is performed at the upper and lower limits, the operation frequency of the pump and the control valve is high, it causes the failure of the device, and the fluctuation of the liquid level is greatly unsatisfactory.

  As a liquid level control method for the purpose of improving these problems, there is a method described in Patent Document 1, for example. In this method, the liquid level in the container is controlled so as to be within a predetermined range, and not only the supply pump is turned ON / OFF, but also the pump rotational speed is controlled to turn the pump ON / OFF. The number of times of OFF is reduced, and the disturbance of the liquid level is suppressed.

Japanese Patent No. 3599790

  However, in the above technique, the rotation speed control of the pump corresponds to the moving average value of the numerical sequence of ON = 1, OFF = 0, which is formed by the ON / OFF signal output by the liquid level detection means every predetermined time. This is a method of obtaining the rotation speed and controlling the pump at the rotation speed, and does not continuously operate the pump at the optimum rotation speed. In other words, even if the liquid level changes suddenly, the ON / OFF state of the switch acquired within a certain time does not change with one, so the amount of change in the liquid level is appropriate for the supply and discharge of the pump. Not reflected in. On the other hand, even if the supply amount and discharge amount of liquid are balanced and a constant liquid level is maintained, if one of the level switches continues to be turned on or off, useless adjustment is performed.

  The present invention has been made in view of the above problems, and it is an object of the present invention to provide a liquid level control device and a liquid level control method that enable liquid level control with higher accuracy and reduce unnecessary adjustment. And

  The present invention includes at least one of a container in which liquid is stored, a supply path for supplying the liquid to the container, a discharge path for discharging the liquid stored in the container, and a supply path and a discharge path. A flow rate adjusting mechanism for adjusting the flow rate of the liquid passing therethrough, a first level switch for detecting whether or not the liquid level of the liquid stored in the container has reached the first height, A second level switch for detecting whether or not the liquid level of the stored liquid has reached a second height lower than the first height, a detection result of the first level switch, and a second level From the detection result of the switch, the calculation means for calculating ΔW, which is the difference between the supply amount of the liquid supplied to the container by the supply path and the discharge amount of the liquid discharged from the container by the discharge path, is calculated by the calculation means. Supply path and discharge path to the flow rate adjustment mechanism so that ΔW converges to 0 And a control means for controlling the height of the liquid level stored in the container by adjusting the flow rate of the liquid passing through at least one of the liquid level control device.

  According to this configuration, at least one of a container in which the liquid is stored, a supply path for supplying the liquid to the container, a discharge path for discharging the liquid stored in the container, and a supply path and a discharge path A flow rate adjustment mechanism for adjusting the flow rate of the liquid passing through the container, a first level switch for detecting whether or not the liquid level of the liquid stored in the container has reached the first height, and the interior of the container And a second level switch that detects whether or not the liquid level of the liquid stored in the liquid level reaches a second height lower than the first height. ΔW, which is the difference between the supply amount of the liquid supplied to the container by the supply path and the discharge amount of the liquid discharged from the container by the discharge path, from the detection result of the level switch of FIG. And the control means sets ΔW calculated by the calculation means to 0. The height of the liquid level of the liquid stored in the container is controlled by adjusting the flow rate of the liquid passing through at least one of the supply path and the discharge path so that the flow rate adjusting mechanism is bundled. For this reason, followability with respect to disturbances such as changes in supply amount and discharge amount is better, liquid level control with higher accuracy is possible, and wasteful adjustment can be reduced.

  In this case, a third level switch that detects whether or not the liquid level of the liquid stored in the container has reached a third height that is higher than the first height, and is stored in the container. And a fourth level switch for detecting whether or not the liquid level of the liquid has reached a fourth height lower than the second height, and the computing means includes a detection result of the first level switch, It is preferable to calculate ΔW from the detection result of the second level switch, the detection result of the third level switch, and the detection result of the fourth level switch.

  According to this configuration, the third level switch that detects whether or not the liquid level of the liquid stored inside the container has reached the third height that is higher than the first height, and the inside of the container And a fourth level switch for detecting whether or not the liquid level of the stored liquid has reached a fourth height lower than the second height, and the computing means includes first to fourth levels. Since ΔW is calculated from the detection result of the switch, liquid level control with higher accuracy becomes possible.

  Further, the calculating means is configured so that one of the level switches with which the liquid level of the liquid is close depends on a time T from the height at which one of the level switches at which the liquid level of the liquid is close to the height at which the other is detected. ΔW = V / T is calculated as a value obtained by dividing the change amount V of the liquid in the container from the height detected by the other until the height detected by the other, and the control means supplies the flow rate adjusting mechanism. It is preferable that ΔW converges to 0 by increasing or decreasing the flow rate of the liquid passing through at least one of the path and the discharge path by ΔW or more.

  According to this configuration, the calculation means is configured so that the liquid level of the liquid is close by the time T from the height detected by one of the level switches to which the liquid level of the liquid approaches to the height detected by the other. ΔW = V / T is calculated as a value obtained by dividing the change amount V of the liquid in the container from the height detected by one of the switches to the height detected by the other, and the control means adjusts the flow rate. By causing the mechanism to increase or decrease the flow rate of the liquid passing through at least one of the supply path and the discharge path by ΔW or more, ΔW converges to zero. For this reason, the divergence of ΔW can be surely prevented.

  Further, when the third level switch detects that the liquid level of the liquid stored in the container has reached the third height, the control means passes the supply path to the flow rate adjusting mechanism. It is preferable to perform at least one of control for adjusting the flow rate of the liquid to be adjusted to the minimum possible value and control for adjusting the flow rate of the liquid passing through the discharge path to the maximum possible value.

  According to this configuration, when the third level switch detects that the liquid level of the liquid stored inside the container has reached the third height, the control means causes the flow rate adjustment mechanism to At least one of control for adjusting the flow rate of the liquid passing through the supply path to the minimum possible value and control for adjusting the flow rate of the liquid passing through the discharge path to the maximum possible value is performed. For this reason, the overflow of the container can be reliably prevented.

  Further, when the fourth level switch detects that the liquid level of the liquid stored in the container does not reach the fourth height, the control means passes the supply path to the flow rate adjusting mechanism. It is preferable to perform at least one of control for adjusting the flow rate of the liquid to be adjusted to the maximum possible value and control for adjusting the flow rate of the liquid passing through the discharge path to the minimum possible value.

  According to this configuration, when the fourth level switch detects that the liquid level of the liquid stored inside the container has not reached the fourth height, the control means causes the flow rate adjustment mechanism to At least one of control for adjusting the flow rate of the liquid passing through the supply path to the maximum possible value and control for adjusting the flow rate of the liquid passing through the discharge path to the minimum possible value is performed. Thereby, it can prevent reliably that all the liquids in a container are discharged | emitted.

Further, the flow rate adjusting mechanism is a pump provided in the discharge passage, and the control means sets the current rotational speed of the pump to R ₀ , the preset minimum rotational speed of the pump to R _MIN , and the preset maximum pump speed. Assuming that the rotation speed is R _MAX , an arbitrary constant satisfying 1 ≦ k ≦ 2 is k, and the liquid discharge amount per rotation of the pump is ω, the target rotation speed R shown in the following equations (i) to (vi) It is preferred to control the pump.
(1) When the current rotational speed R ₀ is in the range of R _MIN <R ₀ <R _MAX and the liquid level of the liquid stored in the container rises, the first level switch is brought into the container. When it is detected that the liquid level of the stored liquid has reached the first height, ΔW> 0,
R = R ₀ + k × ΔW / ω (i)
(2) When the current rotational speed R ₀ is in the range of R _MIN <R ₀ <R _MAX and the liquid level of the liquid stored in the container is lowered, the second level switch is brought into the container. When it is detected that the liquid level of the stored liquid does not reach the second height, ΔW <0,
R = R ₀ + k × ΔW / ω (ii)
(3) When the current rotational speed R ₀ is in the range of R _MIN <R ₀ <R _MAX and the liquid level of the liquid stored in the container rises, the third level switch is brought into the container. When it is detected that the liquid level of the stored liquid has reached the third height,
R = R _MAX (iii)
(4) When the current rotational speed R ₀ is in the range of R _MIN <R ₀ <R _MAX and the liquid level of the liquid stored in the container is lowered, the fourth level switch is brought into the container. When it is detected that the liquid level of the stored liquid does not reach the fourth height,
R = R _MIN (iv)
(5) When the current rotational speed R ₀ is R ₀ = R _MAX and the liquid level of the liquid stored in the container is lowered, the third level switch is moved to the liquid stored in the container. When it is detected that the liquid level no longer reaches the third height, ΔW <0,
R = R _MAX + k × ΔW / ω (v)
(6) When the current rotational speed R ₀ is R ₀ = R _MIN and the liquid level of the liquid stored in the container rises, the fourth level switch When it is detected that the liquid level has reached the fourth height, ΔW> 0,
R = R _MIN + k × ΔW / ω (vi)

According to this configuration, the flow rate adjusting mechanism is a pump provided in the discharge passage, and the control means is preset with the current rotation speed of the pump being R ₀ and the preset minimum rotation speed of the pump being R _MIN . The target rotation shown in the following formulas (i) to (vi), where R _MAX is the maximum rotation speed of the pump, k is an arbitrary constant satisfying 1 ≦ k ≦ 2, and ω is the amount of liquid discharged per one rotation of the pump. Control the pump to a number R.

(1) When the current rotational speed R ₀ is in the range of R _MIN <R ₀ <R _MAX and the liquid level of the liquid stored in the container rises, the first level switch is When it is detected that the liquid level of the liquid stored inside has reached the first height, ΔW> 0 and R = R ₀ + k × ΔW / ω (i). Thereby, when the liquid level rises and reaches the first height, the control means increases ΔW or more by increasing the flow rate of the liquid passing through the discharge path so that ΔW converges to zero. For this reason, the divergence of ΔW can be surely prevented.

(2) When the current rotational speed R ₀ is in the range of R _MIN <R ₀ <R _MAX and the liquid level of the liquid stored in the container is lowered, the second level switch is When it is detected that the liquid level of the liquid stored inside does not reach the second height, it is assumed that ΔW <0 and R = R ₀ + k × ΔW / ω (ii). As a result, when the liquid level drops and does not reach the second height, the control means reduces the flow rate of the liquid passing through the discharge path by ΔW or more so that ΔW converges to 0. . For this reason, the divergence of ΔW can be surely prevented.

(3) When the current rotational speed R ₀ is in the range of R _MIN <R ₀ <R _MAX and the liquid level of the liquid stored in the container rises, the third level switch is When it is detected that the liquid level of the liquid stored inside reaches the third height, R = R _MAX (iii). Thereby, when the liquid level rises and reaches the third height, the control means maximizes the flow rate of the liquid passing through the discharge path. For this reason, the overflow of the container can be reliably prevented.

(4) When the current rotational speed R ₀ is in the range of R _MIN <R ₀ <R _MAX and the liquid level of the liquid stored in the container is lowered, the fourth level switch is When it is detected that the liquid level of the liquid stored inside does not reach the fourth height, R = R _MIN (iv). As a result, when the liquid level drops and does not reach the fourth height, the control means minimizes the flow rate of the liquid passing through the discharge path. For this reason, it can prevent reliably that all the liquids in a container are discharged | emitted.

Further, (5) the current rotation speed R ₀ is R ₀ = R _MAX and the liquid level stored in the container is lowered, so that the third level switch is stored in the container. When it is detected that the liquid level does not reach the third height, ΔW <0 and R = R _MAX + k × ΔW / ω (v). As a result, when the liquid level drops due to the maximum rotational speed and does not reach the third height, the control means reduces the flow rate of the liquid passing through the discharge path by ΔW or more, so that ΔW is To converge to zero. For this reason, the divergence of ΔW can be surely prevented.

(6) The current level R ₀ is R ₀ = R _MIN , and the liquid level stored in the container rises, so that the fourth level switch is stored in the container. When it is detected that the liquid level has reached the fourth height, ΔW> 0 and R = R _MIN + k × ΔW / ω (vi). Thereby, when the liquid level rises to reach the fourth height by the minimum rotation speed, the control means increases the flow rate of the liquid passing through the discharge path by ΔW or more, so that ΔW becomes 0. To converge to. For this reason, the divergence of ΔW can be surely prevented.

  Further, the liquid stored in the container can have a viscosity of 100 cP or more.

  The present invention has better followability to disturbances such as changes in the supply amount and discharge amount, enables more precise liquid level control, and can reduce wasteful adjustment, so that the viscosity is 100 cP or more. Is effective against high liquids.

  The level switch is preferably a capacitance meter.

  According to this configuration, since the level switch is a capacitance meter, it is advantageous when detecting the liquid level of highly viscous liquid.

  The level switch is preferably a gas purge type thermometer.

  According to this configuration, the level switch is a gas purge thermometer, which is advantageous when detecting the liquid level of highly viscous and high temperature liquid.

  The present invention also includes at least one of a container in which liquid is stored, a supply path for supplying the liquid to the container, a discharge path for discharging the liquid stored in the container, and a supply path and a discharge path. A flow rate adjusting mechanism for adjusting the flow rate of the liquid passing through the first level switch, a first level switch for detecting whether or not the liquid level of the liquid stored in the container has reached the first height, In a device comprising a second level switch for detecting whether or not the liquid level of the liquid stored inside has reached a second height lower than the first height, the liquid is stored inside the container. A liquid level control method for controlling the liquid level of a liquid, wherein the supply of liquid supplied to a container through a supply path from the detection result of a first level switch and the detection result of a second level switch ΔW, which is the difference between the amount of liquid discharged from the container through the discharge path By calculating the flow rate of the liquid passing through at least one of the supply path and the discharge path so that the ΔW calculated in the calculation step and ΔW calculated in the calculation step converge to 0, the inside of the container And a control step for controlling the height of the liquid level of the stored liquid.

  In this case, the apparatus includes a third level switch that detects whether or not the liquid level of the liquid stored in the container has reached a third height that is higher than the first height, A fourth level switch for detecting whether or not the liquid level of the stored liquid has reached a fourth height lower than the second height, and in the calculation step, the first level switch is detected. It is preferable to calculate ΔW from the result, the detection result of the second level switch, the detection result of the third level switch, and the detection result of the fourth level switch.

  Further, in the calculation step, one of the level switches with which the liquid level of the liquid is close depends on the time T from the height at which one of the level switches at which the liquid level of the liquid is close to the height at which the other is detected. ΔW = V / T is calculated as a value obtained by dividing the change amount V of the liquid in the container from the height detected by the other until the height detected by the other, and in the control step, the supply path to the flow rate adjusting mechanism It is preferable that ΔW converges to 0 by increasing or decreasing the flow rate of the liquid passing through at least one of the discharge paths by ΔW or more.

  When the third level switch detects that the liquid level of the liquid stored in the container has reached the third height, the control step passes the supply path to the flow rate adjusting mechanism. It is preferable to perform at least one of control for adjusting the flow rate of the liquid to be adjusted to the minimum possible value and control for adjusting the flow rate of the liquid passing through the discharge path to the maximum possible value.

  In addition, when the fourth level switch detects that the liquid level of the liquid stored in the container has not reached the fourth height, the control means passes the supply path to the flow rate adjusting mechanism. It is preferable to perform at least one of control for adjusting the flow rate of the liquid to be adjusted to the maximum possible value and control for adjusting the flow rate of the liquid passing through the discharge path to the minimum possible value.

The flow rate adjusting mechanism is a pump provided in the discharge passage. In the control step, the current rotation speed of the pump is R ₀ , the preset minimum rotation speed of the pump is R _MIN , and the preset maximum pump speed is set. Assuming that the rotation speed is R _MAX , an arbitrary constant satisfying 1 ≦ k ≦ 2 is k, and the liquid discharge amount per rotation of the pump is ω, the target rotation speed R shown in the following equations (i) to (vi) It is preferred to control the pump.
(1) When the current rotational speed R ₀ is in the range of R _MIN <R ₀ <R _MAX and the liquid level of the liquid stored in the container rises, the first level switch is brought into the container. When it is detected that the liquid level of the stored liquid has reached the first height, ΔW> 0,
R = R ₀ + k × ΔW / ω (i)
(2) When the current rotational speed R ₀ is in the range of R _MIN <R ₀ <R _MAX and the liquid level of the liquid stored in the container is lowered, the second level switch is brought into the container. When it is detected that the liquid level of the stored liquid does not reach the second height, ΔW <0,
R = R ₀ + k × ΔW / ω (ii)
(3) When the current rotational speed R ₀ is in the range of R _MIN <R ₀ <R _MAX and the liquid level of the liquid stored in the container rises, the third level switch is brought into the container. When it is detected that the liquid level of the stored liquid has reached the third height,
R = R _MAX (iii)
(4) When the current rotational speed R ₀ is in the range of R _MIN <R ₀ <R _MAX and the liquid level of the liquid stored in the container is lowered, the fourth level switch is brought into the container. When it is detected that the liquid level of the stored liquid does not reach the fourth height,
R = R _MIN (iv)
(5) When the current rotational speed R ₀ is R ₀ = R _MAX and the liquid level of the liquid stored in the container is lowered, the third level switch is moved to the liquid stored in the container. When it is detected that the liquid level does not reach the third height, ΔW <0,
R = R _MAX + k × ΔW / ω (v)
(6) When the current rotational speed R ₀ is R ₀ = R _MIN and the liquid level of the liquid stored in the container rises, the fourth level switch When it is detected that the liquid level reaches the fourth height, ΔW> 0,
R = R _MIN + k × ΔW / ω (vi)

  Further, the liquid stored in the container can have a viscosity of 100 cP or more.

  The level switch is preferably a capacitance meter.

  The level switch is preferably a gas purge thermometer.

  According to the liquid level control device and the liquid level control method of the present invention, more accurate liquid level control is possible, and wasteful adjustment can be reduced.

It is a block diagram which shows the structure of the liquid level control apparatus which concerns on embodiment of this invention. It is a flowchart which shows the outline of operation | movement of the liquid level control apparatus which concerns on embodiment of this invention. It is a flowchart which shows the detail of the operation | movement which controls the rotation speed of the discharge pump of the liquid level control apparatus which concerns on embodiment of this invention. It is a graph which shows an example of the change of the rotation speed of a payout pump, and the height of a liquid level. It is a graph which shows an example of the change of the rotation speed of a payout pump, and the height of a liquid level.

  Hereinafter, a liquid level control device and a liquid level control method according to an embodiment of the present invention will be described with reference to the drawings.

  The liquid level control device and the liquid level control method according to the present embodiment are, for example, discharging the highly viscous tar generated in the resorcinol production process to the outside of the container while continuously or semi-continuously supplying the tar, By storing tar at a predetermined liquid level in the container, the inside of the container is kept at a pressure lower than atmospheric pressure, and tar supplied from the upstream of the manufacturing process overflows the container and flows out to other processes or outside. It is a device to prevent. In addition to this, the liquid level control device and the liquid level control method according to the present embodiment can be applied to control the height of the liquid level stored in the container.

  As shown in FIG. 1, the liquid level control device 1 according to this embodiment includes a supply path 10, a control valve 12, a container 20, level switches 20HH, 20H, 20L, and 20LL, a payout path 30, a payout pump 32, and a control unit 40. It has.

  The supply path 10 is a path for supplying a high-viscosity tar of 100 cP or more generated in the resorcinol production process into the container 20 continuously or semi-continuously. The supply path 10 is provided with a control valve 12 for adjusting the flow rate of tar flowing in the supply path 10.

  The container 20 stores high-viscosity tar generated in the production process of resorcinol. In the container 20, four level switches 20HH, 20H, 20L, and 20LL are provided in the order of the liquid level from the top to the locations HH, H, L, and LL at different heights of the container 20, respectively. The level switches 20HH, 20H, 20L, and 20LL output an ON / OFF signal according to whether or not the level of tar stored in the container 20 has reached the height of the level switch 20HH or the like. The level switch 20HH or the like outputs an ON signal when the level of the liquid in the container 20 reaches the height of the level switch 20HH or the like, and the level switch 20HH or the like outputs the signal in the container 20 to the height of the level switch 20HH or the like. When the liquid level has not reached, an OFF signal is output. For example, a capacitance meter or a gas purge type thermometer is applied to the level switch 20HH or the like.

  The payout path 30 is a path for discharging the tar stored in the container 20 from the container 20 continuously or semi-continuously. The payout path 30 is provided with a payout pump for adjusting the flow rate of tar flowing through the payout path 30.

  The control unit 40 controls the operation of the control valve 12 and the discharge pump 32 based on the ON / OFF signal from the level switches 20HH to 20LL by a method as will be described later, whereby tar stored in the container 20 is stored. This is for controlling the liquid level.

  Hereinafter, the operation of the liquid level control apparatus 1 of the present embodiment will be described. In the liquid level control device 1 of the present embodiment, the optimal supply amount or optimal discharge amount of liquid is sequentially calculated from the ON / OFF time intervals of the four level switches 20HH to 20LL, and the difference between the supply amount and the discharge amount is calculated. The supply amount or the payout amount is controlled so that ΔW converges to zero.

  First, the outline | summary of operation | movement of the liquid level control apparatus 1 of this embodiment is demonstrated. As shown in FIG. 2, the control unit 40 of the liquid level control apparatus 1 receives ON / OFF signals of the level switches 20HH to 20LL (S11).

  The control unit 40 controls the level switch 20HH etc. that are closest to each other among the level switches 20HH to 20LL after the liquid level rises and one level switch 20HH etc. turns from OFF to ON. Measures the time interval from turning OFF to ON, or the time interval T from when the liquid level is lowered and one level switch 20HH etc. turns from ON to OFF until the other level switch 20HH etc. turns from ON to OFF (S12).

  The control unit 40 determines the difference ΔW = V / T between the supply amount and the discharge amount from the measured time interval T and the volume V of the liquid held between the closest level switches 20HH and the like in the container 20. Is calculated (S13).

  The control unit 40 calculates the opening degree of the control valve 12 in the supply passage 10 and the rotation speed of the discharge pump 32 in the discharge passage 30 so that ΔW converges to 0 according to the calculated ΔW. The discharge pump 32 is controlled (S14).

Hereinafter, the details of the operation of the liquid level control device 1 of the present embodiment will be described. In the following description, it is assumed that the liquid level control is performed only by the operation of the discharge pump 32 of the discharge path 30, and the opening degree of the control valve 12 is made constant. In the following description, the current rotation speed of the discharge pump 32 is R *, the minimum rotation speed of the discharge pump 32 set in advance is R _MIN , the maximum rotation speed of the discharge pump 32 is set to R _MAX , 1 Assume that an arbitrary constant satisfying ≦ k ≦ 2 is k, and the liquid discharge amount per one rotation of the discharge pump 32 is ω.

As shown in FIG. 3, when the current rotational speed R * of the dispensing pump 32 is R _MIN <R * <R _MAX (S21), the control unit 40 of the liquid level control device 1 uses the level switches 20HH to 20LL. From the ON / OFF signal, the rise and fall of the liquid level of the liquid stored in the container 20 and its height are determined (S22).

Until the level of the liquid stored in the container 20 rises, the level switch 20H changes from OFF to ON, and the level switch HH changes from OFF to ON (between the level switch 20H and the level switch 20HH), the control unit 40 Calculates the target rotational speed R of the discharge pump 32 by the following equation (1).
R = R * + k × ΔW / ω (where ΔW> 0) (1)

Until the liquid level of the liquid stored in the container 20 is lowered, the level switch 20L is turned from ON to OFF, and the level switch LL is turned from ON to OFF (between the level switch 20L and the level switch 20HH), the control unit 40 Calculates the target rotational speed R of the discharge pump 32 by the following equation (2).
R = R * + k × ΔW / ω (where ΔW <0) (2)

When the level of the liquid stored in the container 20 rises and the level switch 20HH is turned from OFF to ON, or when a predetermined time has passed after the level switch 20HH is turned from OFF to ON (level switch 20HH The control unit 40 calculates the target rotational speed R of the discharge pump 32 by the following equation (3).
R = R _MAX (3)

When the liquid level of the liquid stored in the container 20 drops and the level switch 20LL is turned from ON to OFF, or when a predetermined time has passed since the level switch 20LL was turned from ON to OFF (level switch 20LL The control unit 40 calculates the target rotational speed R of the dispensing pump 32 by the following equation (4).
R = R _MIN (4)

In the case where the current rotation speed R * of the discharge pump 32 is R * = R _MAX (S21), the level of the liquid stored in the container 20 is lowered and the level switch 20HH is turned from ON to OFF. When the liquid level is between the level switch 20H and the level switch 20HH (S27), the control unit 40 calculates the target rotational speed R of the discharge pump 32 by the following equation (5) (S28). However, in the case where the current rotation speed R * of the discharge pump 32 is R * = R _MAX (S21), the level of the liquid stored in the container 20 is maintained while the level switch 20HH remains ON. When it is higher than the level switch 20HH, the control unit 40 sets R = R _MAX R = R _MAX + k × ΔW / ω (where ΔW <0) (5)

In the case where the current rotation speed R * of the discharge pump 32 is R * = R _MIN (S21), the level of the liquid stored in the container 20 rises and the level switch 20LL is turned from OFF to ON. When the liquid level is between the level switch 20LL and the level switch 20L (S29), the control unit 40 calculates the target rotational speed R of the discharge pump 32 by the following equation (6) (S30). However, in the case where the current rotation speed R * of the discharge pump 32 is R * = R _MIN (S21), the level of the liquid stored in the container 20 remains unchanged while the level switch 20LL remains OFF. When it is higher than the level switch 20LL, the control unit 40 sets R = R _MIN R = R _MIN + k × ΔW / ω (where ΔW> 0) (6)

(Experimental example 1)
FIG. 4 shows the relationship between the rotational speed of the dispensing pump 32 and the liquid level when the liquid level control apparatus 1 of the present embodiment is operated. In this example, when the level switch 20HH is switched from OFF to ON, the control unit 40 sets the rotational speed R of the discharge pump 32 to R = R _MAX, and when the level switch 20LL is switched from ON to OFF, R = _RMIN .

Further, the control unit 40 calculates the rotational speed _RL of the discharge pump 32 when the level switch 20L is turned from OFF to ON and the level switch 20H is turned from OFF to ON according to the following equation (7). Further, the control unit 40 calculates the rotational speed _RH of the discharge pump 32 when the level switch 20H is turned from ON to OFF and the level switch 20L is turned from ON to OFF according to the following equation (8). However, T _HL is a time interval until the level switch 20H is turned from ON to OFF and the level switch 20L is turned from ON to OFF. T _LH is the level switch 20L from OFF to ON, and the level switch 20H is turned on. This is the time interval from OFF to ON.
R _L = R _MAX -2 (V / ωT _HL ) (7)
R _H = R _L +2 (V / ωT _LH ) (8)

  As shown in FIG. 4, it can be seen that the liquid level is maintained between the level switch 20HH and the level switch 20LL.

(Experimental example 2)
FIG. 5 shows the relationship between the rotation speed of the dispensing pump 32 and the liquid level when the liquid level control apparatus 1 of the present embodiment is operated. In this example, the control unit 40 includes a section from the level switch 20L to the level switch 20H, a section from the level switch 20H to the level switch 20HH, a section from the level switch 20H to the level switch 20L, and from the level switch 20L. For the section reaching the level switch 20LL, the rotational speed R of the discharge pump 32 was controlled based on the above formulas (1) to (6). The control unit 40 sets the target rotational speed R of the dispensing pump 32 to R = R _MAX = 400 rpm when 10 minutes have elapsed since the level switch 20HH was turned from OFF to ON. Further, the control unit 40 sets the target rotational speed R of the dispensing pump 32 to R = R _MIN = 60 rpm when 10 minutes have elapsed since the level switch 20LL was turned from ON to OFF.

  As shown in FIG. 5, it can be seen that the liquid level is smoothly controlled in each section of the level switch 20HH and the level switch 20LL.

  In the present embodiment, the container 20 in which the liquid is stored, the supply path 10 that supplies the liquid to the container 20, the payout path 30 that discharges the liquid stored in the container 20, the supply path 10 and the payout A control valve 12 and a discharge pump 32 for adjusting the flow rate of the liquid passing through the passage; a level switch 20H for detecting whether or not the liquid level of the liquid stored in the container 20 has reached H; In the liquid level control device 1 including the level switch 20L that detects whether or not the liquid level of the liquid stored inside has reached L, the control unit 40 detects the detection result of the level switch 20H and the level switch 20L. From the detection result, ΔW that is the difference between the supply amount of the liquid supplied to the container by the supply path 10 and the discharge amount of the liquid discharged from the container by the discharge path 30 is calculated, and the calculated ΔW is 0. The liquid level of the liquid stored in the container 20 is controlled by allowing the control valve 12 and the discharge pump 32 to adjust the flow rate of the liquid passing through the supply path 10 and the discharge path 30 so as to converge. To do. For this reason, followability with respect to disturbances such as changes in supply amount and discharge amount is better, liquid level control with higher accuracy is possible, and wasteful adjustment can be reduced.

  In the present embodiment, the level switch 20HH that detects whether or not the liquid level of the liquid stored in the container 20 has reached HH, and the liquid level of the liquid stored in the container 20 is LL. The controller 40 further includes a level switch 20LL that detects whether or not the level has been reached, and the control unit 40 calculates ΔW from the detection results of the level switches 20HH to 20LL, so that liquid level control with higher accuracy is possible.

  The control unit 40 determines the level switch 20HH, etc., where the liquid level of the liquid is close by the time T from the height detected by one of the level switches 20HH, etc., where the liquid level of the liquid is close to the height detected by the other. ΔW = V / T is calculated as a value obtained by dividing the amount of change V of the liquid inside the container 20 from the height detected by one of the two to the height detected by the other, and the control valve 12 and the dispensing pump By increasing or decreasing the flow rate of the liquid passing through the supply path 10 and the payout path 30 by ΔW or more in 32, ΔW converges to zero. For this reason, the divergence of ΔW can be surely prevented.

  Further, in this embodiment, when the level switch 20HH detects that the liquid level of the liquid stored in the container 20 has reached HH, the control unit 40 controls the control valve 12 and the dispensing pump 32. Then, at least one of control for adjusting the flow rate of the liquid passing through the supply path 10 to the minimum possible value and control for adjusting the flow rate of the liquid passing through the discharge path 30 to the maximum possible value is performed. For this reason, the overflow of the container 20 can be reliably prevented.

  Further, in the present embodiment, when the level switch 20LL detects that the liquid level of the liquid stored in the container 20 has not reached LL, the controller 40 controls the control valve 12 and the dispensing pump 32. At least one of control for adjusting the flow rate of the liquid passing through the supply path 10 to the maximum possible value and control for adjusting the flow rate of the liquid passing through the discharge path 30 to the minimum possible value is performed. Thereby, it can prevent reliably that all the liquids in the container 20 are discharged | emitted.

Further, in the present embodiment, when the current rotational speed R * is in the range of R _MIN <R * <R _MAX and the liquid level of the liquid stored in the container 20 rises, the level switch 20H is When it is detected that the liquid level of the liquid stored inside 20 reaches H, ΔW> 0 and R = R * + k × ΔW / ω (1). Thereby, when the liquid level rises and reaches H, the control unit 40 increases the flow rate of the liquid passing through the discharge path 30 by ΔW or more so that ΔW converges to 0. For this reason, the divergence of ΔW can be surely prevented.

Further, in the present embodiment, when the current rotational speed R ₀ is in the range of R _MIN <R * <R _MAX and the liquid level of the liquid stored in the container 20 is lowered, the level switch 20L is When it is detected that the liquid level of the liquid stored inside 20 does not reach L, ΔW <0 and R = R * + k × ΔW / ω (2). As a result, when the liquid level drops and does not reach L, the control unit 40 reduces the flow rate of the liquid passing through the discharge path 30 by ΔW or more so that ΔW converges to zero. For this reason, the divergence of ΔW can be surely prevented.

Further, in the present embodiment, when the current rotational speed R * is in the range of R _MIN <R * <R _MAX and the liquid level of the liquid stored in the container rises, the third level switch is When it is detected that the liquid level of the liquid stored in the container has reached the third height, R = R _MAX (3). Thereby, when the liquid level rises and reaches HH, the control unit 40 maximizes the flow rate of the liquid passing through the discharge path 30. For this reason, the overflow of the container 20 can be reliably prevented.

Further, in the present embodiment, when the current rotational speed R * is in the range of R _MIN <R * <R _MAX and the liquid level of the liquid stored in the container 20 is lowered, the level switch 20LL is moved to the container. When it is detected that the liquid level of the liquid stored inside 20 does not reach LL, R = R _MIN (4). As a result, when the liquid level drops and does not reach LL, the control unit 40 sets the flow rate of the liquid passing through the dispensing path 30 to the minimum value. For this reason, it can prevent reliably that all the liquids in the container 20 are discharged | emitted.

In the present embodiment, the current rotational speed R * is R * = R _MAX and the liquid level of the liquid stored in the container 20 is lowered, so that the level switch 20HH is stored in the container 20. When it is detected that the liquid level of the applied liquid does not reach HH, ΔW <0 and R = R _MAX + k × ΔW / ω (5). As a result, when the liquid level drops due to the maximum rotational speed and does not reach HH, the control unit 40 reduces the flow rate of the liquid passing through the discharge path 30 by ΔW or more, so that ΔW becomes 0. To converge. For this reason, the divergence of ΔW can be surely prevented.

Further, in the present embodiment, at the current rotational speed R * R * = R _MIN, and by the liquid level of the pooled liquid into the container 20 rises, the reservoir level switch 20LL within the interior of the container 20 When it is detected that the liquid level of the applied liquid has reached LL, ΔW> 0 and R = R _MIN + k × ΔW / ω (6). Thereby, when the liquid level rises and reaches LL at the minimum rotational speed, the control unit 40 increases the flow rate of the liquid passing through the discharge path 30 by ΔW or more, so that ΔW converges to 0. To do. For this reason, the divergence of ΔW can be surely prevented.

  Further, in the present embodiment, the followability to disturbances such as changes in supply amount and discharge amount is better, more accurate liquid level control is possible, and wasteful adjustment can be reduced, so that the viscosity is 100 cP or more. It is effective against liquids with high viscosity.

  In the present embodiment, the level switches 20HH to 20LL are capacitance meters, which is advantageous when detecting the liquid level of a highly viscous liquid. Alternatively, in the present embodiment, the level switches 20HH to 20LL are gas purge type thermometers, which is advantageous when detecting the liquid level of highly viscous and high temperature liquid.

  It should be noted that the present invention is not limited to the above-described embodiment, and it is needless to say that various modifications can be made without departing from the gist of the present invention. For example, in the above example, the liquid level control device 1 has mainly been described with respect to a mode in which the highly viscous tar generated in the resorcinol production process is stored in the container 20, but the present invention is not limited to this. The present invention can be applied to all modes in which the liquid level on the liquid surface is controlled while storing the liquid in the container.

DESCRIPTION OF SYMBOLS 1 ... Liquid level control apparatus, 10 ... Supply path, 12 ... Control valve, 20 ... Container, 20HH, 20H, 20L, 20LL ... Level switch, 30 ... Discharge path, 32 ... Discharge pump, 40 ... Control part.

Claims (18)

A container in which liquid is stored,
A supply path for supplying the liquid to the container;
A discharge path for discharging the liquid stored in the container;
A flow rate adjusting mechanism for adjusting the flow rate of the liquid passing through at least one of the supply path and the discharge path;
A first level switch for detecting whether or not the liquid level of the liquid stored in the container has reached a first height;
A second level switch for detecting whether or not the liquid level of the liquid stored in the container has reached a second height lower than the first height;
From the detection result of the first level switch and the detection result of the second level switch, the supply amount of the liquid supplied to the container by the supply path and the liquid discharged from the container by the discharge path A calculating means for calculating ΔW which is a difference from the liquid discharge amount;
By causing the flow rate adjustment mechanism to adjust the flow rate of the liquid passing through at least one of the supply path and the discharge path so that the ΔW calculated by the calculation means converges to 0, the inside of the container Control means for controlling the height of the liquid level of the liquid stored in
A liquid level control device. A third level switch for detecting whether or not the liquid level of the liquid stored in the container has reached a third height higher than the first height;
A fourth level switch for detecting whether or not the liquid level of the liquid stored in the container has reached a fourth height lower than the second height;
Further comprising
The calculation means is configured to calculate the first level switch detection result, the second level switch detection result, the third level switch detection result, and the fourth level switch detection result from the first level switch detection result. The liquid level control device according to claim 1, wherein ΔW is calculated. The calculation means includes the level switch in which the liquid level of the liquid approaches by the time T from the height detected by one of the level switches adjacent to the liquid level of the liquid to the height detected by the other. The value ΔW = V / T is calculated as a value obtained by dividing the amount of change V of the liquid inside the container from the height detected by one of them to the height detected by the other,
The control means causes the ΔW to converge to 0 by increasing or decreasing the flow rate of the liquid that passes through at least one of the supply path and the discharge path to the flow rate adjusting mechanism by the ΔW or more. The liquid level control apparatus according to 1 or 2. When the third level switch detects that the liquid level of the liquid stored inside the container has reached the third height,
The control means causes the flow rate adjusting mechanism to adjust the flow rate of the liquid passing through the supply path to a minimum possible value and to adjust the flow rate of the liquid passing through the discharge path to a maximum possible value. The liquid level control device according to claim 2, wherein at least one of the controls is performed. When the fourth level switch detects that the liquid level of the liquid stored in the container does not reach the fourth height,
The control means causes the flow rate adjustment mechanism to adjust the flow rate of the liquid passing through the supply path to the maximum possible value and to adjust the flow rate of the liquid passing through the discharge path to the minimum possible value. The liquid level control apparatus according to claim 2, wherein at least one of the control is performed. The flow rate adjusting mechanism is a pump provided in the discharge path,
The control means is configured such that the current rotation speed of the pump is R ₀ , the preset minimum rotation speed of the pump is R _MIN , the preset maximum rotation speed of the pump is R _MAX , 1 ≦ k ≦ 2. 6. The pump is controlled to a target rotational speed R shown in the following formulas (i) to (vi), where k is an arbitrary constant and ω is a discharge amount of the liquid per one rotation of the pump. The liquid level control apparatus according to any one of the above.
(1) When the current rotational speed R ₀ is in the range of R _MIN <R ₀ <R _MAX and the liquid level of the liquid stored in the container rises, the first level switch is When it is detected that the liquid level of the liquid stored in the container has reached the first height, ΔW> 0,
R = R ₀ + k × ΔW / ω (i)
(2) When the current rotational speed R ₀ is in the range of R _MIN <R ₀ <R _MAX and the liquid level of the liquid stored inside the container is lowered, the second level switch is When it is detected that the liquid level of the liquid stored in the container does not reach the second height, ΔW <0,
R = R ₀ + k × ΔW / ω (ii)
(3) When the current rotational speed R ₀ is in the range of R _MIN <R ₀ <R _MAX and the liquid level of the liquid stored in the container rises, the third level switch is When it is detected that the liquid level of the liquid stored inside the container has reached the third height,
R = R _MAX (iii)
(4) When the current rotational speed R ₀ is in the range of R _MIN <R ₀ <R _MAX and the liquid level of the liquid stored in the container is lowered, the fourth level switch is When detecting that the liquid level of the liquid stored inside the container does not reach the fourth height,
R = R _MIN (iv)
(5) When the current rotational speed R ₀ is R ₀ = R _MAX and the liquid level of the liquid stored in the container is lowered, the third level switch is stored in the container. When it is detected that the liquid level of the liquid does not reach the third height, ΔW <0,
R = R _MAX + k × ΔW / ω (v)
(6) When the current rotational speed R ₀ is R ₀ = R _MIN and the liquid level of the liquid stored in the container rises, the fourth level switch is stored in the container. When it is detected that the liquid level of the liquid has reached the fourth height, ΔW> 0,
R = R _MIN + k × ΔW / ω (vi)   The liquid level control device according to claim 1, wherein the liquid stored in the container has a viscosity of 100 cP or more.   The liquid level control apparatus according to claim 1, wherein the level switch is a capacitance meter.   The liquid level control apparatus according to any one of claims 1 to 7, wherein the level switch is a gas purge thermometer. At least one of a container in which liquid is stored, a supply path for supplying the liquid to the container, a discharge path for discharging the liquid stored in the container, and the supply path and the discharge path A flow rate adjusting mechanism for adjusting the flow rate of the liquid passing through the first level switch, and a first level switch for detecting whether or not the liquid level of the liquid stored in the container has reached a first height; A second level switch for detecting whether or not the liquid level of the liquid stored in the container has reached a second height lower than the first height; A liquid level control method for controlling the height of the liquid level of the liquid stored in the interior,
From the detection result of the first level switch and the detection result of the second level switch, the supply amount of the liquid supplied to the container by the supply path and the liquid discharged from the container by the discharge path A calculation step for calculating ΔW which is the difference from the liquid discharge amount;
By causing the flow rate adjustment mechanism to adjust the flow rate of the liquid passing through at least one of the supply path and the discharge path so that the ΔW calculated in the calculation step converges to 0, the inside of the container A control step of controlling the height of the liquid level of the liquid stored in
A liquid level control method. The apparatus includes a third level switch that detects whether or not the liquid level of the liquid stored in the container has reached a third height that is higher than the first height; A fourth level switch for detecting whether or not the liquid level of the liquid stored inside reaches a fourth height lower than the second height;
In the calculation step, from the detection result of the first level switch, the detection result of the second level switch, the detection result of the third level switch, and the detection result of the fourth level switch, The liquid level control method according to claim 10, wherein ΔW is calculated. In the calculation step, the level switch in which the liquid level of the liquid approaches by the time T from the height detected by one of the level switches adjacent to the liquid level of the liquid to the height detected by the other The value ΔW = V / T is calculated as a value obtained by dividing the amount of change V of the liquid inside the container from the height detected by one of them to the height detected by the other,
In the control step, the flow rate of the liquid that passes through at least one of the supply path and the discharge path is increased or decreased by ΔW or more to the flow rate adjusting mechanism so that the ΔW converges to 0. The liquid level control method according to 10 or 11. When the third level switch detects that the liquid level of the liquid stored inside the container has reached the third height,
In the control step, the flow rate adjusting mechanism controls the flow rate of the liquid passing through the supply path to a minimum possible value, and controls the flow rate of the liquid passing through the discharge path to a maximum possible value. The liquid level control method according to claim 11 or 12, wherein at least one of the controls is performed. When the fourth level switch detects that the liquid level of the liquid stored in the container does not reach the fourth height,
The control means causes the flow rate adjusting mechanism to adjust the flow rate of the liquid passing through the supply path to the maximum possible value and to adjust the flow rate of the liquid passing through the discharge path to the minimum possible value. The liquid level control method according to any one of claims 11 to 13, wherein at least one of the controls is performed. The flow rate adjusting mechanism is a pump provided in the discharge path,
In the control step, the current rotation speed of the pump is R ₀ , the preset minimum rotation speed of the pump is R _MIN , and the preset maximum rotation speed of the pump is R _MAX , 1 ≦ k ≦ 2. The pump is controlled to a target rotational speed R represented by the following formulas (i) to (vi), where k is an arbitrary constant and ω is a discharge amount of the liquid per one rotation of the pump. The liquid level control method according to any one of the above.
(1) When the current rotational speed R ₀ is in the range of R _MIN <R ₀ <R _MAX and the liquid level of the liquid stored in the container rises, the first level switch is When it is detected that the liquid level of the liquid stored in the container has reached the first height, ΔW> 0,
R = R ₀ + k × ΔW / ω (i)
(2) When the current rotational speed R ₀ is in the range of R _MIN <R ₀ <R _MAX and the liquid level of the liquid stored inside the container is lowered, the second level switch is When it is detected that the liquid level of the liquid stored in the container does not reach the second height, ΔW <0,
R = R ₀ + k × ΔW / ω (ii)
(3) When the current rotational speed R ₀ is in the range of R _MIN <R ₀ <R _MAX and the liquid level of the liquid stored in the container rises, the third level switch is When it is detected that the liquid level of the liquid stored inside the container has reached the third height,
R = R _MAX (iii)
(4) When the current rotational speed R ₀ is in the range of R _MIN <R ₀ <R _MAX and the liquid level of the liquid stored in the container is lowered, the fourth level switch is When detecting that the liquid level of the liquid stored inside the container does not reach the fourth height,
R = R _MIN (iv)
(5) When the current rotational speed R ₀ is R ₀ = R _MAX and the liquid level of the liquid stored in the container is lowered, the third level switch is stored in the container. When it is detected that the liquid level of the liquid does not reach the third height, ΔW <0,
R = R _MAX + k × ΔW / ω (v)
(6) When the current rotational speed R ₀ is R ₀ = R _MIN and the liquid level of the liquid stored in the container rises, the fourth level switch is stored in the container. When it is detected that the liquid level of the liquid has reached the fourth height, ΔW> 0,
R = R _MIN + k × ΔW / ω (vi)
  The liquid level control method according to claim 10, wherein the liquid stored in the container has a viscosity of 100 cP or more.   The liquid level control method according to claim 10, wherein the level switch is a capacitance meter.   The liquid level control method according to claim 10, wherein the level switch is a gas purge type thermometer.

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