JP2000171592A - Liquid level calculating method for operating evaporator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain exact and stable liquid level with small fluctuation and contrive the reduction of a maintenance work by eliminating a density meter and the like and omitting welding inspection. SOLUTION: Processed liquid in a supply tank 10 is supplied to a evaporator 16 and evaporation-processed in the evaporator and the processing liquid quantity is controlled with a flow control valve 32 so as to maintain the evaporator liquid level constant. The generated vapor sent through a condenser 20 is stored in a condensate liquid tank 22 and the condensed liquid in the evaporator is batch-processed by draining at the time reaching a specific concentration. The evaporator liquid level in operation is obtained by such an operation process that evaporator liquid level in operation = evaporator liquid level before operation start + (evaporator total inflow - evaporator total outflow)/evaporator area. The evaporator total inflow is obtained from the measured value of a supply tank liquid level meter 24 and the like, and the evaporator total outflow is obtained from the measured value of a condensed liquid tank liquid level meter 28 and the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the liquid level of an evaporator during operation. More specifically, it measures the evaporator liquid level before operation and the total inflow and outflow of evaporator during operation. The present invention relates to a method capable of obtaining a stable evaporator liquid level with a small fluctuation range during operation by arithmetic processing. This technique is useful, for example, in a system for concentrating and separating radioactive waste liquid generated in a nuclear power plant using an evaporator.

[0002]

2. Description of the Related Art In a system for concentrating and separating a processing solution using various types of evaporators, the level of the evaporator during operation is determined, and the supply amount of the processing solution is controlled so that the level remains substantially constant. While performing the evaporation process. This is because when the liquid level rises, the effective gas-phase height in the can decreases, and for example, when the radioactive waste liquid is subjected to evaporative concentration, a predetermined decontamination coefficient cannot be obtained. In this type of concentration / separation system by evaporation, the liquid level is determined by a differential pressure type (diaphragm type) liquid level meter due to the measurement object and installation environment.

However, in a calandria natural circulation evaporator, an externally heated forced circulation evaporator for crystallization, or other evaporators, an accurate liquid level during operation is required by the above-mentioned differential pressure level gauge. I can't. This is because as the evaporative concentration process proceeds, the density of the processing liquid gradually increases, so that the evaporator liquid level during operation is detected to be higher than the actual liquid level.

Therefore, a sensor such as a density meter is incorporated in the evaporator, and the liquid level is corrected using the measured liquid density to obtain the evaporator liquid level during operation (for example, Japanese Patent Laid-Open No. Hei 2 232600).

[0005]

The processing liquid inside the evaporator during operation generates bubbles due to boiling, and the bubbles boil out of the liquid to give buoyancy to the liquid. The generated bubbles vary in size and size, and their generation time and location are also irregular. In the method of measuring the liquid level of the evaporator using the head pressure, the buoyancy greatly changes due to bubbles generated at irregular size, time and place, and the liquid level measurement value by the differential pressure level meter fluctuates greatly. I will.

Therefore, even if the above-described density correction method is adopted, the fluctuation width of the correction liquid level remains large in principle in order to perform the density correction for the measurement liquid level that constantly fluctuates greatly. . Since only a certain width is corrected (shifted) in the evaporator liquid level measurement value according to the measured density, the state in which the liquid level fluctuates greatly is the same as the case without correction.

In addition, since the density meter is attached to a part of the evaporator, which is a pressure vessel, the attachment portion is subjected to welding inspection.
You have to pass strict inspections. Further, since the densitometer is in direct contact with the processing liquid in the evaporator, which is gradually concentrated, dust and the like easily adhere to the sensor unit, and frequent maintenance is required to prevent malfunction. In this way, costs are increased in both manufacturing (assembly) and maintenance.

An object of the present invention is to provide a method for calculating the liquid level of an evaporator during operation, which can obtain a stable liquid level with accuracy and a small fluctuation range. Another object of the present invention is to
An object of the present invention is to provide a concentration processing system using an evaporator, which can eliminate welding inspection and the like by eliminating the need for mounting a density meter or the like and can reduce maintenance work.

[0009]

According to the present invention, a processing liquid stored in a supply tank is supplied to an evaporator, and the processing liquid in the evaporator is subjected to an evaporating process. The amount of the processing liquid from the supply tank is controlled by the flow control valve so as to maintain the pressure, and the generated vapor is discharged to the condensate tank through the condenser and stored, and the concentrated liquid in the evaporator reaches the predetermined concentration. It assumes a batch processing system that discharges at the time. Here, in the present invention, the evaporator liquid level before the start of operation, the total evaporator inflow amount and the total evaporator outflow amount during operation are obtained, and the evaporator liquid level during operation = evaporator liquid level before operation start + (during operation) This is a method for calculating the liquid level of the evaporator during operation by calculating the evaporator liquid level during operation by the calculation process of (evaporator inflow total amount-evaporator outflow amount) / evaporator area.

In the present invention, the total evaporator inflow during operation is obtained from a measured value of a supply tank level meter or a measured value of a supply liquid flow meter provided in a pipe connecting the supply tank and the evaporator. Further, the total amount of the evaporator flowing out during the operation is obtained from the measured value of the condensate tank level meter or the measured value of the condensate flow meter provided in the pipe connecting the condenser and the condensate tank. In order to further improve the liquid level calculation accuracy, the volume of the condensed liquid remaining in the condenser can be corrected in addition to the total amount of the outflow of the evaporator.

[0011]

FIG. 1 is a block diagram showing an example of a batch-type evaporative concentration system used in the method of the present invention. The processing liquid stored in the supply tank 10 is supplied to the evaporator 16 by the pump 14 through the supply pipe 12. The processing liquid inside is evaporated by the evaporator 16, and the generated vapor passes through the discharge pipe 18, passes through the condenser 20, and is discharged and stored in the condensate tank 22. The supply tank 10 is provided with a supply tank level gauge 24, the evaporator 16 is provided with a differential pressure type (diaphragm type) evaporator level gauge 26, and the condensate tank 22 is provided with a condensate tank level gauge 28. . Those measurement data are sent to the arithmetic and control unit 30. In addition, a flow control valve 32 whose degree of opening and closing is controlled based on the calculation result in the calculation control device 30.
Into the supply pipe 12. In FIG. 1, a solid line represents a piping system, and a dotted line represents a signal system. In addition,
Here, the evaporator 16 is a device using steam as a heating source.

FIG. 2 is a block diagram showing another example of a batch-type evaporative concentration system used in the method of the present invention. Since the basic configuration is the same as that of FIG. 1, the corresponding portions are denoted by the same reference numerals for easy understanding of the description. Supply tank 10
Is supplied to the evaporator 16 by the pump 14 through the supply pipe 12. The internal processing liquid is evaporated in the evaporator 16, and the generated steam is discharged to the discharge pipe 18.
Through the condenser 20 and discharged to the condensed liquid tank 22 for storage. A supply liquid flow meter 34 is provided in the supply pipe 12, a differential pressure type (diaphragm type) evaporator liquid level meter 26 is provided in the evaporator 16, and a condensate flow rate is provided in the discharge pipe 18 from the condenser 20 to the condensate tank 22. A total of 36 are provided. Those measurement data are sent to the arithmetic and control unit 30. The arithmetic and control unit 3
A flow control valve 32 whose degree of opening and closing is controlled based on the calculation result of 0 is incorporated in the supply pipe 12.

In these, in the arithmetic and control unit 30,
Based on each measurement data, the liquid level of the processing liquid in the evaporator 16 is calculated, and the amount of the processing liquid supplied from the supply tank 10 is controlled by the flow control valve 32 so that the calculated liquid level keeps a substantially constant value. As described above, the evaporator liquid level during operation is obtained from the following equation: evaporator liquid level during operation = evaporator liquid level before operation + (total evaporator inflow during operation-total evaporator outflow) / evaporator area. calculate.

Here, the evaporator liquid level before the start of operation is obtained by a differential pressure type (diaphragm type) evaporator liquid level meter 26. In the case of FIG. 1, the total amount of evaporator inflow during the operation is the supply tank level meter 24.
(That is, from the product of the liquid level change amount and the tank inner diameter), and in the case of FIG. 2, from the measurement value of the supply liquid flow meter 34 (that is, from the integrated flow rate). Further, the total amount of the evaporator flowing out during operation is the condensate tank level gauge 28 in FIG.
(That is, from the product of the liquid level change amount and the inner diameter of the tank), and in the case of FIG. 2, from the measurement value of the condensate flow meter 36 (that is, from the integrated flow rate).

The method for calculating the total amount of evaporator inflow and the total amount of evaporator outflow may be a combination of the method shown in FIG. 1 and the method shown in FIG. The method of obtaining from the tank liquid level meter is inexpensive (usually, since the liquid level meter is installed in the tank, its signal can be used), but the accuracy decreases as the diameter of the tank increases. The method of obtaining the flow rate is high in accuracy because the flow rate is directly measured, but it is expensive in some cases (the flow meter may not be provided as an equipment, and the cost increases due to addition). Therefore, it is desirable to select an appropriate method in consideration of these points.

In the course of the evaporative concentration process, some condensate remains inside the condenser 20. The amount of retained condensate can be estimated from the capacity of the condenser 20. Therefore, the amount of the condensate remaining inside the condenser 20 is calculated from the measured value of the condensate tank level meter 28 or the total amount of the evaporator outflow during operation obtained from the measured value of the condensate flow meter 36. , And a more accurate evaporator liquid level can be calculated. However, when the capacity of the condenser 20 is relatively small, the evaporator liquid level can be calculated with necessary and sufficient accuracy without performing correction.

In the present invention, the evaporator level gauge 26 uses only the measured values before the start of operation, but does not use the measured values during the operation at all. In the present invention, the evaporator liquid level during operation is calculated using the values of the liquid level meter and the flow meter originally provided in the supply tank and the condensate tank. Therefore, it is not necessary to additionally mount a sensor such as a density meter as in the prior art, and it is possible to omit the accompanying welding inspection and reduce the maintenance work.

[0018]

EXAMPLE Using the evaporative concentration system shown in FIG. 3, the evaporative concentration (evaporation separation) of the radioactive waste liquid was performed by an evaporator using steam as a heating source. On the basis of batch processing every day, the concentrated liquid in the evaporator is discharged when a predetermined concentration is reached. The basic configuration of the system is a combination of the systems shown in FIGS. 1 and 2, and the corresponding parts are denoted by the same reference numerals and detailed description thereof will be omitted. In the system of this embodiment, a supply tank level meter 24 is provided in the supply tank 10, a differential pressure type (diaphragm type) evaporator level meter 26 is provided in the evaporator 16, and the condenser 20 reaches the condensate tank 22. The discharge pipe 18 is provided with a condensate flow meter 36. The total amount of evaporator inflow is the supply tank liquid level meter 2.
4 and the total amount of evaporator outflow was calculated from the measured value of the condensate flow meter 36.

The process control was performed in the following two items.
The opening degree of the heating steam inlet flow rate control valve is automatically adjusted in accordance with the set condensate flow rate. The opening of the heating steam inlet flow rate control valve was gradually increased until the condensate flow rate reached the rated flow rate. The opening of the supply liquid flow control valve was automatically adjusted according to the set evaporator liquid level. The evaporator liquid level before the start of operation was detected by a differential pressure type (diaphragm type) liquid level meter.

The evaporator liquid level during operation is calculated by the arithmetic and control unit 30.
Was calculated as follows. Evaporator liquid level L before starting operation
The _S, by adding the value obtained by dividing the difference between the evaporator inlet flow (integrated value) [sigma] v _I and evaporator runoff (cumulative value) [sigma] v _O in evaporator area S, and the evaporator liquid level L _R during operation I do. _{That, L R = (ΣV I -ΣV} O) / S + L S

The evaporator inflow amount (integrated value) ΣV _I is obtained by inputting a liquid level signal of the supply tank liquid level meter 24 to the arithmetic and control unit 30. However, since the liquid level of the supply tank 10 constantly fluctuates due to agitation, the liquid level signal is filtered and smoothed. The evaporator outflow amount (integrated value) ΣV _O is obtained by inputting a flow rate signal of the condensate flow meter 36 to the arithmetic and control unit 30. In the arithmetic and control unit 30, from these signals,
The liquid level is corrected by the above equation, and the amount of the processing liquid supplied by the flow control valve 32 is controlled by the corrected liquid level signal so that the actual liquid level of the evaporator 16 is kept constant.

When the concentration process is performed using the measured value of the evaporator liquid level meter without performing any liquid level correction, the evaporation during operation depends on the buoyancy of bubbles in the liquid in the evaporator. The can level is detected lower than the actual level. For this reason, the operation is actually performed at a liquid level higher than the set value, and a predetermined decontamination coefficient cannot be obtained because the effective height of the gas phase portion in the evaporator decreases. The density correction method merely corrects (shifts) a certain width in consideration of the density of the measured liquid level of the evaporator, so that irregular fluctuations due to bubbles generated by boiling appear as they are, that is, the fluctuation width is large. On the other hand, in the liquid level correction method of the present invention, a stable and accurate liquid level can be obtained.

As a concentration system using an evaporator,
In some cases, continuous operation is performed over a long period of time instead of batch processing (short-term operation). The error in the total amount of inflow into the evaporator and the total amount of outflow from the evaporator increases with the passage of time. Therefore, when operating continuously for a long period, the liquid level should be corrected with the density that is the current value (instantaneous value). However, in the operation method by the batch processing, the method of the present invention is more advantageous because the error can be reset (accurate liquid level measurement) before the operation and the error is small.

[0024]

The present invention is based on the premise that a batch process is operated for a relatively short period of time. Before starting the operation, an accurate evaporator liquid level is measured. Because the method calculates the evaporator liquid level from the total flow rate and the total amount of outflow, a stable and accurate liquid level can be obtained even during operation, and precise liquid level control in the evaporator can be performed. Especially in the treatment of radioactive liquid waste,
By controlling the liquid level accurately, the effective height of the gas phase in the evaporator can be kept constant, and there is an effect that a predetermined decontamination coefficient can be secured. Further, in the present invention, it is not necessary to attach a sensor such as a density meter to the evaporator, so that welding inspection becomes unnecessary and maintenance work can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an example of a batch evaporation concentration system used in the method of the present invention.

FIG. 2 is a configuration diagram showing another example of a batch evaporation concentration system used in the method of the present invention.

FIG. 3 is a configuration diagram showing still another example of a batch-type evaporative concentration system used in the method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Supply tank 12 Supply pipe 14 Pump 16 Evaporator 18 Discharge pipe 20 Condenser 22 Condensate tank 24 Supply tank level gauge 26 Evaporator level gauge 28 Condensate tank level gauge 30 Arithmetic control unit 32 Flow control valve 34 Supply Liquid flow meter 36 Condensate flow meter

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hideaki Aikawa 4002 Narita-cho, Oarai-machi, Higashiibaraki-gun, Ibaraki Prefecture (72) Inventor Yoshio Sugano Yoshio Sugano 1 Tanabe Nitta, Kawasaki-ku, Kawasaki City, Kanagawa Prefecture No. 1 Fuji Electric Co., Ltd. F term (reference) 2F014 AC05 BA03 GA01 4D076 AA08 AA22 AA24 BA02 BB01 DA03 DA25 EA02Y EA04Y EA05Y EA08Y EA14Y EA15Y EA16Y EA32 FA31 HA06 HA13 JA02 JA03 JA05

Claims (4)

[Claims] 1. A processing liquid stored in a supply tank is supplied to an evaporator, and the processing liquid inside is evaporated by the evaporator.
The amount of processing liquid from the supply tank is controlled by a flow control valve so that the evaporator liquid level remains almost constant, and the generated steam is discharged to the condensate tank through the condenser and stored, and concentrated in the evaporator. In a batch processing system that discharges liquid when it reaches a predetermined concentration, the evaporator liquid level before operation, the total evaporator inflow and total evaporator outflow during operation are determined, and the evaporator liquid level during operation = operation The evaporator liquid level during operation is obtained by calculating the evaporator liquid level before start + (total evaporator inflow amount during operation−total evaporator outflow amount) / evaporator area. Position calculation method. 2. The total evaporator inflow during operation is obtained from a measured value of a supply tank level meter or a measured value of a supply liquid flow meter provided in a pipe connecting the supply tank and the evaporator.
The method for calculating the liquid level of the evaporator during operation as described in the above. 3. The total evaporator outflow during operation is obtained from a measured value of a condensate tank level meter or a measured value of a condensate flow meter provided in a pipe connecting the condenser and the condensate tank. 3. The method for calculating the liquid level of an in-operation evaporator according to 1 or 2. 4. The method for calculating the liquid level of an in-operation evaporator according to claim 1, wherein the volume of the condensate remaining in the condenser is corrected by adding it to the total amount of outflow of the evaporator.