JPH0259416B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical field of the invention] The present invention is useful for preventing tank rollovers.
This article relates to a temperature difference measuring device for an LNG storage tank. [Technical Background of the Invention] Liquid LNG stored in an LNG storage tank has a low boiling point and is composed of several components with different boiling points, which causes problems when a peculiar phenomenon occurs during storage. In other words, when LNG is stored in a tank, the tank is warmed by the outside air and vaporization progresses gradually. If this vaporized gas is left as it is, there is a risk of exceeding the withstand pressure of the tank, so the vaporized gas is vented to the outside to keep the pressure below a certain level. on the other hand,
The components of LNG are shown in Table 1 below, and the main component is methane, which has a low specific gravity and a low boiling point.

【table】

[Problems with background technology]

However, according to the above conventional method, the liquid temperature of LNG is in the cryogenic region of -160℃, which is far from 0℃, so it is difficult to obtain high resolution and it is not possible to accurately capture the temperature difference in each part. There was a risk that a rollover would occur. [Object of the invention] The present invention solves the problems of the above-mentioned prior art,
Accurately captures temperature differences in each part of the LNG storage tank,
The purpose of the present invention is to provide a temperature difference measuring device for an LNG storage tank that can reliably prevent tank rollover. [Summary of the Invention] Therefore, the present invention provides a plurality of liquid temperature measuring devices spaced apart in the height direction inside the LNG storage tank.
Place the RTD. On the other hand, a float is placed on the LNG liquid surface and an RTD for reference temperature measurement is placed there. Each of the RTDs is connected in series to a constant current source, and a plurality of capacitors are provided to hold the voltage of each RTD for measuring liquid temperature. Paired with these capacitors are a plurality of capacitors that hold the voltage of the reference temperature measurement RTD. By connecting the two capacitors paired in this way in reverse, the difference voltage between the holding voltages is input to the amplifier one pair at a time, and after amplification, it is digitized and taken out via an A/D converter. It is something. [Embodiments of the Invention] The present invention will be described below with reference to embodiments shown in the drawings. FIG. 1 shows an overall configuration diagram of a temperature difference measuring device according to an embodiment of the present invention, in which 1 is a tank for storing LNG, 2 is an LNG liquid part stored in tank 1, and 3 is a tank for storing LNG. This is a gas layer filled with gas vaporized from the LNG liquid part 2. Sensors 4A to 4N are installed at equal intervals from the bottom to the ceiling inside the tank 1, and are used to measure the temperature of the LNG liquid. 5 is a float floating on the LNG liquid surface, and there are LNG liquid part 2 and gas layer 3.
The number of sensors 6A to 6N that measure the temperature at the boundary surfaces of the two sensors 4A to 4N are provided in a number corresponding to the number of sensors 4A to 4N. 7
is a processing device consisting of a scanner, an amplifier, and an A/D converter. Figure 2 shows the inside of the processing device 7 and the sensors 6A to 6N.
In this figure, 8 is a constant current source, 9 is a scanner having capacitors 10A to 10N and 11A to 11N, 12 is an amplifier, and 13 is an A/D converter. With the above configuration, the temperature at the interface between the LNG liquid part 2 and the gas layer part 3 is not affected by the external temperature, and the LNG temperature remains constant once the LNG components and the pressure in the gas layer are determined.
It can be considered as a kind of reference temperature. Sensors 6A to 6 for measuring this reference temperature
N and the sensors 4A to 4N installed at equal intervals in the tank 1 form a current loop that receives current from the constant current source 8. Therefore, the low resistance values of the RTDs of sensors 4A to 4N and 6A to 6N change depending on their respective temperatures, and when current flows through these sensors, a voltage drop corresponding to their respective resistance values is generated. . This voltage is led to the scanner 9 via a cable, and the charge is stored in a capacitor.
When a sampling command is issued, the scanner capacitor is separated from the sensor side and connected to the amplifier side. The scanner capacitor is charged to the same voltage as the sensor voltage and connected to the amplifier, so the moment a sampling command is issued, it is as if the amplifier were directly connected to the sensor. Such a method is generally called a flying capacitor method. In this case, the capacitors of the scanner 9 are 10A and 11A, 10B and 11B, . . . 10N and 11N, which form pairs, and are sequentially switched from the sensor side to the amplifier side one pair at a time in response to a sampling command. As a result, sensors 6A to 6N and sensors 4A to 4N
Each voltage is reverse biased and read, and a temperature difference voltage between each reference temperature and the LNG liquid temperature is output to the amplifier 12. For example, regarding the voltages of the sensors 6A and 4A, when the capacitor 10A is connected to the sensor side, the upper side thereof is charged to a negative polarity, and the lower side thereof is charged to a positive polarity. On the other hand, the capacitor 11A is charged with positive polarity on the upper side and negative polarity on the lower side. Next, when the capacitors 10A and 11A are connected to the amplifier side in accordance with the sampling command, the lower side of the capacitor 10A and the upper side of the capacitor 11A are connected, and the upper side of the capacitor 10A and the lower side of the capacitor 11A are connected to the input terminal of the amplifier 12. Ru. As a result, the amplifier 12 has the voltage E _A of the sensor 6A and the voltage E _B of the sensor 4A = E _A +
The temperature difference voltage ΔE = E _B − E _A is input. This temperature difference voltage ΔE is a value that is 0V if the temperatures of sensors 6A to 6N and sensors 4A to 4N are the same.Even if there is a slight temperature difference, if you increase the gain of the amplifier 12, the temperature difference will be reduced. can be enlarged and read. This makes it possible to measure temperature with higher precision than in the past. That is, as before
If the sensor output voltage in the LNG liquid is directly input to the amplifier and processed by the A/D converter, the LNG liquid temperature is -160°C, which is quite far from 0°C, as mentioned above. Naturally, the resolution will be lower. On the other hand, if processing is performed using the temperature difference voltage ΔE as in this embodiment, the resolution will be extremely high, allowing highly accurate temperature measurement. Also, regarding the current fluctuation of the constant current source 8, for example, if the fluctuation rate is α, when processing at absolute temperature, E _B × α,
Since E _B ≫ΔE, the fluctuation becomes large, but when processing with a temperature difference, the influence can be suppressed to a small level. Similarly, the influence of gain fluctuations in the amplifier system and variations in the A/D converter can be reduced compared to processing using absolute temperature. In this way, each sensor 6A-6N and 4A-4
After taking out the temperature difference voltage ΔE of N, amplifying it with the amplifier 12, and digitizing it with the A/D converter 13, the difference between each temperature difference voltage ΔE is taken out, and the tank is stirred according to the temperature difference between the sensors. By automatically performing this, tank rollover can be prevented. Alternatively, the inside of the tank may be stirred by directly displaying and monitoring each temperature difference voltage ΔE. At this time, if you want to know the absolute temperature as well as the temperature difference voltage ΔE, you can easily do this by attaching one additional sensor to the float 5 and adding this sensor output to each temperature difference voltage ΔE in the processing device 7. can be obtained. Alternatively, the signals may be taken out directly from each sensor 4A to 4N to the amplifier 12 as in the conventional case. In the above embodiment, the reference temperature and the liquid temperature to be measured are connected to the capacitor 1 from the sensors 6A to 6N and 4A to 4N.
0A to 10N and 11A to 11N, and sampled pair by pair in order to extract each temperature difference voltage ΔE. However, as shown in Fig. 3, only one 6A sensor was used for reference temperature measurement, and sensor 6A Even if the generated voltage is charged to the capacitors 10A to 10N, the same effects as in the above embodiment can be obtained. [Effects of the Invention] As described above, according to the present invention, it is possible to measure the temperature difference inside an LNG storage tank with high resolution and high precision, and as a result, it is possible to measure the temperature difference inside an LNG storage tank with high resolution and precision, which previously was dependent on the careful attention of the LNG storage tank monitor. Monitoring of LNG storage tanks, which had previously been monitored, can now be performed based on accurate data, reducing the burden on monitors and enabling safe management of LNG storage tanks.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram of a temperature difference measuring device for an LNG storage tank showing one embodiment of the present invention, Fig. 2 is an electric circuit diagram of Fig. 1, and Fig. 3 is a temperature diagram showing another embodiment of the present invention. FIG. 3 is an electrical circuit diagram of the difference measuring device. 1...tank, 2...LNG liquid part, 3...gas layer part, 4A~4N, 6A~6N...sensor, 5...
Float, 7... Processing device, 8... Constant current source, 9
...Sukiyana, 10A~10N, 11A~11N
...Capacitor, 12...Amplifier, 13...A/
D converter.

Claims (1)

[Claims] 1. A plurality of resistance temperature sensors installed at predetermined intervals from the bottom to the ceiling inside the LNG storage tank, a reference resistance temperature measurement object installed on a float floating on the liquid level in the tank, and the Compatible with a circuit consisting of multiple resistance temperature detectors and a reference resistance temperature detector connected in series with a constant current source, multiple capacitors that hold the voltage generated in the multiple resistance temperature detectors, and these multiple capacitors. and a plurality of reference capacitors for holding the voltage generated in the reference resistance temperature sensing element, the plurality of capacitors and the plurality of reference capacitors are each sequentially scanned as a pair, and the difference voltage between them is sequentially scanned. A scanner to take out the data, an amplifier to amplify the difference voltages outputted from the scanner, and an A/D converter to digitize the output of the amplifier.
LNG characterized by comprising a D converter.
Storage tank temperature difference measuring device. 2. The LNG according to claim 1, wherein the reference resistance temperature sensing elements are present in a number corresponding to the plurality of resistance temperature sensing elements, and generate a holding voltage to the plurality of capacitors. Storage tank temperature difference measuring device.