JP3141773B2 - Liquid level detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid level detecting device in a device provided with a container into which a liquid or a substance which is liquefied by heating is charged, and a heating means for heating the container from outside.

[0002]

In this kind of liquid level detection device, since the substance put into the container is generally solid at room temperature and a stirrer is usually mounted in the container, for example, A method of detecting with a load cell (a method of detecting with a load) and a method of taking out and detecting with a pipe outside are adopted. However, in the former method, it is difficult to remove the influence of the load on the piping connected to the container,
In the latter method, it is necessary to heat the communication pipe and the chamber to make them liquid, and it is necessary to control the temperature.

[0003]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has a container for containing a liquid or a substance to be liquefied by heating, and a heating device for heating the container from outside. Means, a large number of wall temperature detection sensors disposed at predetermined pitches vertically on the wall surface of the container, a liquid temperature detection sensor for detecting a liquid temperature in the container, and each of the wall temperature detection sensors and searches a non-contiguous portions of the temperature difference between the liquid temperature sensor, comprising a determining liquid level judgment means the liquid level in the vessel based on the search result, the heating hand
Heating state and hot gas where the stage supplies hot gas to heat the vessel
And a scavenging state in which the liquid is not supplied.
Sensor search result and scavenging condition in the heated state
Collating with the sensor search result in a state
You.

[0004]

[0005]

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a liquid level detecting apparatus according to the present invention includes a container for containing a liquid or a substance to be liquefied by heating, and a heating means for heating the container from outside. A large number of wall temperature detection sensors vertically arranged on the wall surface of the container at a predetermined pitch, a liquid temperature detection sensor for detecting a liquid temperature in the container, each of the wall temperature detection sensors and a liquid temperature detection sensor, And a liquid level determining means for determining the liquid level in the container based on the search result.

This embodiment will be described in detail below. The liquid or the substance liquefied by heating includes plastics and animal oils having a high pour point which are liquefied by heating in a solid state at normal temperature, but may be liquid at normal temperature. The container containing this substance is usually made of metal, and is heated from outside by a heating means such as a combustion device. As the heating means, a high-temperature heat medium is supplied between the inner container and the outer container as a double structure of the inner container and the outer container that contains a substance and a combustion device that generates a hot gas (high-temperature gas). The heating means may be configured to heat the substance in the inner container by using the heating means. As the combustion device, one that burns gaseous fuel, one that burns liquid fuel, or the like is employed. The wall temperature detection sensor is directly attached to the outer wall of the container and directly detects the temperature of the outer wall, or the temperature of the outer wall of the container is detected by interposing some member between the wall and the outer wall, or the wall temperature is attached to the inner wall of the container. For detecting the temperature, for example, a thermocouple or a resistance temperature detector (such as a thermistor) is used. A large number of the wall temperature detecting sensors are arranged on the wall surface of the container at a predetermined pitch (e.g., several mm pitch) at equal or irregular intervals. The large number is a number by which a change in a temperature difference described later can be determined, and the number is determined by a fluctuation range of the liquid level. The liquid temperature detection sensor is inserted at a position where the liquid level can always be detected in consideration of the liquid level fluctuation in the container, and a thermocouple or temperature measuring resistor (thermistor, etc.)
Is used.

The liquid level determining means calculates a temperature difference between each wall temperature detecting sensor and the liquid temperature detecting sensor, and a portion where the difference is discontinuous, in other words, a portion where the difference greatly changes (wall temperature). Sensor), and the liquid level is determined based on the search result. The determination that the temperature difference is discontinuous is determined to be large when the absolute value of the temperature difference is equal to or greater than a predetermined value (determination based on an absolute value comparison), or the temperature difference between a certain wall temperature sensor and another wall temperature sensor is determined. For example, a method (e.g., determination based on a relative comparison) based on a difference or ratio with respect to the temperature difference is used. By determining that the temperature difference is discontinuous, a sensor close to the liquid level can be specified and searched, and the liquid level in the container is estimated based on the search result .

Further, in the present embodiment, it is assumed that the heating means can take a heating state in which the container is heated by supplying a hot gas and a scavenging state in which the heating gas is not supplied. It is assumed that the sensor search result is compared with the sensor search result in the scavenging state.

As described above, when the heating means can be in a heating state in which the heating gas is supplied to heat the container and in a scavenging state in which the heating gas is not supplied, in the heating state, the liquid level in the container is above the liquid level. Since saturated steam is present, heat transfer from the outside is not sufficient, and the relationship of liquid layer temperature <gas phase temperature holds, whereas heating is not performed in the scavenging state. On the basis of the finding that liquefaction progresses in the gas phase and heat of condensation is released at that time, a liquid film is formed, and the relationship of liquid layer temperature> gas phase temperature holds. The liquid level is determined by the liquid level determining means at both the time and the scavenging time, and the results of both determinations are compared and collated to accurately determine the liquid level. Whether a scavenging state or a heating state can be determined by monitoring a control signal from a control unit that controls the heating unit. In addition, this implementation
In the embodiment , when the temperature difference of the sensor is preferably in the heating state, if the temperature of the liquid layer portion is smaller than the temperature of the gas phase portion, it is determined that the temperature is correctly detected. If the temperature difference of the liquid layer part temperature> the gas phase part temperature, a means for determining that the temperature is correctly detected is provided. If the temperature difference is not correct, the liquid level determination based on the result of the temperature difference calculation is performed. Processing such as not performing the processing is performed. The scavenging state means scavenging before starting combustion (so-called pre-purge) or scavenging after stopping combustion (so-called post-purge) when the heating means is a combustion device, and the heating state means combustion of the combustion device. I do. Further, in a stopped state in which neither combustion nor scavenging is performed, the liquid level is not determined by the liquid level determining means, and the liquid level determination result in the heating or scavenging state is held and output. good.

[0011]

[0012]

[0013] In the implementation according to the above, preferably includes the following means. First, it is desirable to provide a stirring means for stirring the liquefied substance in the container. This stirring means is for equalizing the temperature in the liquid layer portion in the container, for example, a stirring blade for performing mechanical stirring, or forming a circulation path outside the container for the substance, and using this circulation path. Stirring means for circulation are used. Further, it is desirable to have a pour point detecting means for detecting that the temperature of the substance in the container has become equal to or higher than the pour point. Thus, by limiting the determination of the liquid level to after the substance is fluidized, unnecessary liquid level determination can be prevented. When the pour point detecting means is not used, the liquid level determination may be started after heating for a predetermined time by the heating means. Further, it is desirable to have an arithmetic means for obtaining an initial liquid level position from the amount of the substance put into the container, and to have an initial liquid level determining means for determining whether the initial determination by the liquid level determining means is appropriate. Thereby, the validity of the determination by the liquid level determining means can be verified.

[0014]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a plastic cracking apparatus in which a heating means is used as a combustion device according to the first and third embodiments. 1 and 2, reference numeral 1 denotes a container for dissolving (dissolving and vaporizing) a plastic decomposing device for heating and melting a plastic (synthetic resin) and vaporizing the same, which is usually made of steel. The container 1 is heated from outside by a hot gas (combustion gas in this case) generated when the combustion device 2 burns. The combustion device 2 is controlled to any of a scavenging state, a heating (combustion) state, and a non-stop state by a control signal output from a controller 3 including a microcomputer or the like.

K ₁ , K ₂ , K ₃ ... K _N (N is a positive integer) are mounted on the outer wall of the container 1 so as to detect the wall temperature of the container 1 at a predetermined pitch of about several mm up and down. In many of the wall temperature detection sensors described above, thermocouples are used as sensors. K
Reference numeral ₀ denotes a liquid temperature detection sensor inserted in the container so as to constantly detect the temperature of the liquid layer portion L in the container 1, and is located below a lower limit of an assumed liquid level fluctuation range in the container 1. And a thermocouple is used as the sensor. Reference numeral 4 denotes a stirring blade for stirring the liquid layer portion L in the container 1, and a driving means (not shown).
Is driven to rotate. The controller 3 receives signals from the wall temperature detection sensors K ₁ ... K _N and the liquid temperature detection sensor K ₀ and controls the combustion device 2 and the like according to processing procedures stored in a memory (not shown) in advance. At the same time, control is performed to determine the liquid level position in the container 1 and display the result on the display 5.
FIG. 3 shows an example of the processing procedure of the liquid level determination by the controller 3.

The control configuration and operation of the controller 3 according to the present embodiment will be described below with reference to FIG. In step S1 (hereinafter, S ○ means step S ○), a plastic in a solid state at room temperature is charged into the container 1, the heating device 2 is heated, and after the plastic is fluidized, the stirring blade 4 is driven. Start disassembling the plastic. The temperature detected by the liquid temperature sensor K ₀ Next in S2, it is determined whether the pour point T _X or more. In the case of NO, S1 → S2 is repeated, and YE
S is determined, that is plastic flow of the container 1, when it is possible to determine the liquid level, of each wall temperature sensor K ₁ · · · K _N proceeds to step S3 detected temperature T ₁ · · · T _N Is calculated, and a temperature difference T _N -T ₀ between the detected temperature of each wall temperature sensor and the detected temperature of the liquid temperature sensor is calculated and stored in the memory. Next, in S4, it is determined whether the combustion device 2 is heating, scavenging, or otherwise (stop). If it is determined that the heating is being performed, the process proceeds to S6. If T _N -T ₀ is positive, that is, if it is determined that the wall temperature of the container 1 is higher than the liquid temperature, it is determined that the temperature detection is normal, and the process proceeds to S5. I do. If not all are positive in the determination in S5, it is determined in advance whether to make the determination by majority decision or to determine that it is abnormal. Next, in S6, the temperature difference T _N −
T ₀ is searched, and a portion where the value is large and discontinuous, that is, a portion larger than a predetermined value obtained in advance by an experiment or the like is searched. For example, assuming that the temperature difference is about 20 ° C. below the liquid level, but about 30 ° C. in the gas phase near the liquid level, the predetermined value is set to, for example, 25 ° C. It is determined that the temperature difference is large, and the sensor is specified as a sensor near the liquid level. Then, the flow shifts to S9, where the liquid level is determined and output. That is, if the identification of the sensor in S5 is the first, the position of the specific sensor is taken as the liquid level,
Output to the display 5 and return to S1. The display on the display 5 displays the position of the liquid level by a numerical value or a picture.

If it is determined in S4 that scavenging is being performed, the process proceeds to S7, and if T _N -T ₀ is negative, that is, if it is determined that the wall temperature of the container 1 is lower than the liquid temperature, it is determined that the temperature detection is normal. Then, the process proceeds to S7. In addition, when all are not negative in the judgment of S7,
It is determined in advance whether to make the determination by majority decision or to determine that it is abnormal. Next, in S8, the temperature difference T _N -T ₀ is searched, and a portion where the value is large and discontinuous, that is, a portion where the value is smaller than a predetermined value obtained by an experiment or the like in advance is searched. For example, if the temperature difference is −15 ° C. below the liquid level and −30 ° C. in the gas phase near the liquid level, the temperature difference becomes −3 ° C.
The sensor at 0 degrees C is specified as a sensor near the liquid surface. Upon completion of the process in S8, the process proceeds to S9. Here, assuming that the sensor at the liquid level portion being heated is specified, the specific sensor being heated is compared with the specific sensor being scavenged this time, that is, whether or not both sensors are the same, It is determined whether the distance between the middle sensor and the scavenging sensor is within a predetermined range. When this determination is YES, the determination of the liquid level is determined to be normal, and the previous display is displayed on the display 5.

In FIG. 3 of the present embodiment, the processes S6 and S8 may be combined into one, and may be arranged after the process S3.

[0019]

[0020]

[0021]

[0022]

According to the present invention, as described above, the liquid level can be determined and detected without worrying about solidification in the pipes and conduits, and the liquid level detecting device can be configured simply and inexpensively. There is an effect that can be done.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of a plastic decomposition apparatus according to one embodiment of the present invention.

FIG. 2 is a diagram showing an electrical schematic configuration of the embodiment of the present invention.

FIG. 3 is a flowchart showing a control procedure by a controller according to the embodiment of the present invention.

Claims (1)

(57) [Claims] 1. A container comprising a container for containing a liquid or a substance to be liquefied by heating, and a heating means for heating the container from the outside, wherein a plurality of the containers are vertically arranged on a wall surface of the container at a predetermined pitch. A wall temperature detection sensor, a liquid temperature detection sensor for detecting a liquid temperature in the container, and a discontinuous portion of a temperature difference between each of the wall temperature detection sensors and the liquid temperature detection sensor, and based on the search result, Liquid level determining means for determining the liquid level in the container , wherein the heating means supplies a hot gas.
Heating conditions and the scavenging without hot gas supply
And the liquid level determination means is in a heating state.
Search results in a state of scavenging and sensor search in a scavenging state
A liquid level detection device for collating with a search result .