An online dissolved oxygen meter zero point calibration system and method

Abstract

The present invention provides an online dissolved oxygen meter zero point calibration system and method, including a circulation pool and a standard solution pool; a dissolved oxygen sensor is arranged in the circulation pool, the circulation pool is connected to a water sample valve through a water sample tube, and a sample discharge valve is arranged on the circulation pool; the outlet of the standard solution pool is connected to one end of a standard solution pipeline, an exhaust valve is arranged at the other end of the standard solution pipeline, the standard solution pipeline is connected to the water sample tube through a connecting pipe, and a standard solution valve is arranged on the connecting pipe; when the online dissolved oxygen meter is zero-calibrated using this method, the dissolved oxygen sensor is prevented from contacting with the air, and the polarization time of the sensor in the zero point standard solution is shortened. There is no air accumulation in the circulation pool, the polarization time of the sensor is shortened, and the sensor is in a sealed state during polarization, and the zero point standard solution is always kept in an oxygen-free state, and it is also ensured that the background oxygen concentration of the electrolyte in the sensor reaches the lowest point when calibrating the zero point. The accuracy of the online dissolved oxygen meter is improved and the time for zero point calibration is shortened.

Description

Technical Field

[0001] The invention relates to the field of online chemical instrument measurement and calibration of a water vapor circulation system in a power plant, and in particular to an online dissolved oxygen meter zero point calibration system and method. Background Art

[0002] Accurate control of dissolved oxygen is an important means to prevent corrosion, scaling and salt accumulation of thermal equipment in power plants. For units with fully volatilized feed water, the dissolved oxygen in the feed water is generally controlled to be less than 10μg / L, otherwise it will cause metal corrosion; for units with oxygenated feed water, the dissolved oxygen must be controlled within a certain range to achieve the expected anti-corrosion effect. To achieve the above purpose, the concentration of dissolved oxygen in the water vapor system must be accurately measured. Therefore, accurate measurement of dissolved oxygen in the water vapor system is of great significance to the safe operation of the unit.

[0003] At present, the monitoring of dissolved oxygen in power plants mainly relies on online dissolved oxygen meters. To accurately measure dissolved oxygen, the working error of the dissolved oxygen meter must comply with the provisions of the power industry standard DL / T 677-2018 "Testing Procedures for Online Chemical Instruments in Power Plants". The necessary condition for its working error to be within the prescribed range is the accuracy of the zero point of the dissolved oxygen meter.

[0004] When calibrating the zero point of the dissolved oxygen meter, the traditional calibration method can easily cause the zero point to be too high, reduce the accuracy of the instrument zero point, make the measured value too low, or even cause the measured value to be zero. This is mainly caused by the following reasons: When the online dissolved oxygen meter measures low dissolved oxygen water samples, the background oxygen content of the electrolyte in the dissolved oxygen sensor is extremely low. The traditional calibration method is to remove the dissolved oxygen sensor from the circulation pool, and a large number of oxygen molecules quickly pass through the breathable membrane into the sensor room, so that the background oxygen concentration of the electrolyte increases to more than 5000μg / L. After the dissolved oxygen sensor is placed in the zero point standard solution, the polarization time of the electrolyte background oxygen will be very long, which will extend the time of zero point calibration, generally more than 24 hours, which will seriously affect the instrument zero point calibration. In the traditional calibration method, the sealing between the calibration container and the dissolved oxygen sensor is poor; when the dissolved oxygen sensor is installed in the calibration container, it is difficult to exhaust the air, causing air to gather in the calibration container. Due to the long polarization time of the sensor consuming the background oxygen in the electrolyte, the poor sealing between the calibration container and the dissolved oxygen sensor, and the accumulation of air in the circulation pool, it is difficult to ensure that the zero standard solution is oxygen-free when the dissolved oxygen sensor is polarized in the zero standard solution. At this time, calibrating the zero point will cause the zero point to be too high; due to the long polarization time of the sensor consuming the background oxygen, the poor sealing between the calibration container and the dissolved oxygen sensor, and the accumulation of air in the circulation pool, it is also difficult to ensure that the background oxygen concentration of the electrolyte in the sensor reaches the lowest point when calibrating the zero point. At this time, zero calibration will also cause the zero point to be too high. Therefore, the traditional online dissolved oxygen meter zero point calibration method has a long calibration time and poor accuracy. Summary of the invention

[0005] In view of the problems existing in the prior art, the present invention provides an online dissolved oxygen meter zero point calibration system and method, which avoids the dissolved oxygen sensor from contacting with the air and avoids the air from gathering in the circulation pool. The dissolved oxygen sensor is sealed in the circulation pool, and the polarization time of the sensor consuming the background oxygen of the electrolyte in the zero point standard solution is shortened, thereby realizing fast and accurate zero point calibration of the online dissolved oxygen meter.

[0006] The present invention is achieved through the following technical solutions:

[0007] An online dissolved oxygen meter zero point calibration system comprises a circulation pool and a standard solution pool;

[0008] The circulation pool is provided with a dissolved oxygen sensor, the circulation pool is connected to a water sample valve through a water sample tube, and a sample discharge valve is provided on the circulation pool;

[0009] The outlet of the standard solution pool is connected to one end of a standard solution pipeline, an exhaust valve is arranged at the other end of the standard solution pipeline, the standard solution pipeline is connected to the water sample tube through a connecting pipe, and a standard solution valve is arranged on the connecting pipe;

[0010] When calibrating the dissolved oxygen meter, the exhaust valve is used to exhaust the gas in the connecting pipe and the standard solution pipeline, and to inject the standard solution in the standard solution pool into the circulation pool through the connecting pipe.

[0011] Preferably, the dissolved oxygen sensor is sealed and disposed in a circulation pool.

[0012] Preferably, a one-way valve is provided on the standard solution pipeline and is located on the standard solution pipeline between the connecting pipe and the standard solution pool.

[0013] Preferably, the height of the standard solution pool is greater than the height of the circulation pool.

[0014] Preferably, the minimum height difference between the standard solution pool and the circulation pool is 0.2 m.

[0015] Preferably, the volume of the standard solution pool is 5-10 times greater than the sum of the volumes of the circulation pool, the water sample tube and the connecting tube.

[0016] A calibration method for an online dissolved oxygen meter zero point calibration system comprises the following steps:

[0017] Step 1, close the sample discharge valve, open the water sample valve, standard solution valve and exhaust valve, squeeze the gas in the connecting pipe and the standard solution pipe through the water sample and the zero point standard solution in the standard solution pool, and discharge the gas from the exhaust valve until the gas is completely discharged, and then close the water sample valve, standard solution valve and exhaust valve;

[0018] Step 2: Close the water sample valve and the exhaust valve, open the sample discharge valve and the standard solution valve, and allow the zero point standard solution to flow into the circulation pool under the action of the pressure difference until the water sample in the circulation pool is completely replaced;

[0019] Step 3: Close the sample valve and the standard solution valve. The dissolved oxygen sensor begins to polarize. When the displayed value of the dissolved oxygen transmitter connected to the dissolved oxygen sensor drops to the minimum value, calibrate the zero point of the dissolved oxygen meter.

[0020] Preferably, in step 1, when the liquid flows out of the exhaust valve for a predetermined time, it is determined that the gas is completely exhausted.

[0021] Preferably, in step 2, the liquid discharged from the sample discharge valve is collected, and when the volume of the liquid is greater than 5 times the sum of the volumes of the circulation pool, the water sample tube and the flow tube, it is determined that the zero-point standard solution completely replaces the water sample.

[0022] Preferably, in step 2, when the liquid flows out of the sample discharge valve for a predetermined time, it is determined that the zero-point standard solution completely replaces the water sample.

[0023] Compared with the prior art, the present invention has the following beneficial technical effects:

[0024] The invention provides an online dissolved oxygen meter zero point calibration system. Since the dissolved oxygen meter is in an online working state, the dissolved oxygen sensor is always sealed and immersed in the water sample. The difficulty of the dissolved oxygen meter calibration lies in the sealed switching of the water sample and the zero point standard solution in the circulation pool to prevent oxygen from entering the circulation pool. During calibration, the calibration system of the invention uses the zero point standard solution in the online water sample and the standard solution pool to discharge the gas in the connecting pipe and the standard solution pipeline from the exhaust valve to ensure that the pipeline of the entire calibration system is in an oxygen-free environment, and then the zero point standard solution is added to the circulation pool through the standard solution pipe and the connecting pipe to replace the water sample in the circulation pool, so as to achieve the replacement of the water sample and the zero point standard solution in the circulation pool in an oxygen-free environment, avoid the dissolved oxygen sensor from contacting with the air, and also avoid the oxygen in the air from entering the sensor chamber through the breathable membrane, and avoid the gathering of air in the circulation pool, shorten the sensor polarization time, shorten the calibration time to less than one hour, and ensure that the background oxygen concentration in the electrolyte in the sensor reaches the lowest point when calibrating the zero point, thereby improving the accuracy of the zero point calibration. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a structural schematic diagram of the calibration system of the present invention.

[0026] In the figure: 1. dissolved oxygen transmitter, 2. dissolved oxygen sensor, 3. circulation pool, 4. sample discharge valve, 5. water sample valve, 6. standard solution valve, 7. standard solution pool, 8. one-way valve, 9. exhaust valve. DETAILED DESCRIPTION

[0027] The present invention will be further described in detail below in conjunction with the accompanying drawings, which are intended to explain the present invention rather than to limit it.

[0028] See also Figure 1 An online dissolved oxygen meter zero point calibration system includes a circulation pool 3 filled with water samples, a sample discharge valve 4, a water sample valve 5, a standard solution pool 7, an exhaust valve 9 and a standard solution valve 6.

[0029] A dissolved oxygen sensor 2 is sealed in the circulation pool 3, the circulation pool 3 is connected to the water sample valve 5 through a water sample tube, the discharge valve 4 is arranged at the upper part of the circulation pool 3, the standard solution pool 7 is connected to the standard solution pipeline, the standard solution pipeline and the water sample tube are connected through a connecting pipe, the standard solution valve 6 is arranged on the connecting pipe, and the exhaust valve 9 is arranged at the end of the standard solution pipeline.

[0030] When calibrating the dissolved oxygen meter, the exhaust valve 9 is used to exhaust the air in the connecting pipe and the standard solution pipeline, and to inject the standard solution in the standard solution pool 7 into the circulation pool 3 through the standard solution pipe and the connecting pipe.

[0031] In the zero point calibration system of the online dissolved oxygen meter, since the dissolved oxygen meter is in an online working state, the dissolved oxygen sensor is always sealed and immersed in the water sample. The difficulty of the calibration of the dissolved oxygen meter lies in the sealed switching of the water sample and the zero point standard solution in the circulation pool 3 to prevent oxygen from entering the circulation pool 3. During calibration, the calibration system of the present invention uses the zero point standard solution in the online water sample and the standard solution pool 7 to discharge the gas in the connecting pipe and the standard solution pipeline from the exhaust valve 9 to ensure that the pipeline of the entire calibration system is in an oxygen-free environment, and then the zero point standard solution is added to the circulation pool 3 through the standard solution pipe and the connecting pipe to replace the water sample in the circulation pool 3, so as to achieve the replacement of the water sample and the zero point standard solution in the circulation pool 3 in an oxygen-free environment, avoid the dissolved oxygen sensor 2 from contacting with the air, and also avoid the oxygen in the air from entering the sensor 2 chamber through the breathable membrane, shorten the polarization time of the sensor 2, and achieve the oxygen-free calibration of the dissolved oxygen meter. When calibrating the zero point, it can ensure that the background oxygen concentration in the electrolyte in the sensor 2 reaches the lowest point, and improve the accuracy of the zero point calibration.

[0032] The dissolved oxygen meter includes a dissolved oxygen transmitter 1 and a dissolved oxygen sensor 2. The circulation pool 3 is a sealed pool. The dissolved oxygen sensor 2 is sealed in the circulation pool 3, and the dissolved oxygen transmitter 1 is located outside the circulation pool 3. The existing calibration container has poor sealing performance with the dissolved oxygen sensor 2, and when the dissolved oxygen sensor 2 is installed in the calibration container, it is difficult to exhaust the air in the calibration container, causing air to gather in the calibration container. During calibration, the oxygen in the air dissolves into the zero-point standard solution, resulting in inaccurate calibration of the dissolved oxygen meter. In the present invention, a sealed circulation pool 3 is used to avoid air from gathering in the circulation pool 3, and to avoid oxygen in the air from dissolving into the zero-point standard solution, so that the calibration of the dissolved oxygen meter is in a completely oxygen-free environment, thereby improving the accuracy of the calibration.

[0033] The three-way joints at both ends of the connecting pipe are respectively connected to the water sample tube and the standard liquid pipeline, and the connecting pipe, the standard liquid pipeline and the exhaust valve 9 are respectively connected to one interface of the three-way joint; the other end of the water sample valve 5, the water sample tube and the connecting pipe are respectively connected to one interface of another three-way joint.

[0034] A one-way valve 8 is provided on the pipeline between the standard solution pool 7 and the three-way valve. When the gas in the connecting pipe is discharged, the water sample is used to squeeze the gas in the pipeline, and the one-way valve 8 is used to unidirectionally close the standard solution pool 7 to prevent the water sample from entering the standard solution pool 7. At the same time, the standard solution in the standard solution pool 7 can be used to discharge the air in the standard solution pipeline to ensure that the pipeline of the entire calibration system is in an oxygen-free state.

[0035] The standard solution pool 7 is funnel-shaped. The height of the standard solution pool 7 is greater than the height of the circulation pool 3. The zero-point standard solution in the standard solution pool 7 is displaced into the circulation pool 3 by the pressure difference. The zero-point standard solution is injected by the pressure difference method without the need for an external pressurizing tool, and the structure is simple and easy to operate.

[0036] In order to enable the zero-point standard solution to quickly replace the water sample in the circulation pool 3 and to avoid reducing the concentration of the zero-point standard solution to the greatest extent, the minimum height difference between the standard solution pool 7 and the circulation pool 3 is 0.2 m.

[0037] Furthermore, the volume of the standard solution pool 7 is 5-10 times greater than the sum of the volumes of the circulation pool 3, the water sample tube and the connecting tube, so that the zero point standard solution can completely replace the water samples in the circulation pool 3, the water sample tube and the connecting tube, and ensure the concentration of the zero point standard solution.

[0038] The following is a detailed description of a calibration method for an online dissolved oxygen meter zero point calibration system provided by the present invention, which specifically includes the following steps:

[0039] Step 1: Close the standard solution valve 6 and the exhaust valve 9, and add the zero point standard solution into the standard solution pool 7. At this time, air accumulates in the pipeline between the standard solution valve 6, the one-way valve 8 and the exhaust valve 9.

[0040] Step 2, close the sample discharge valve 4, open the water sample valve 5, the standard liquid valve 6 and the exhaust valve 9, the water sample is discharged from the exhaust valve 9 through the connecting pipe, and the zero point standard solution is discharged from the exhaust valve 9 through the standard liquid pipeline, so that the air in the pipeline between the standard liquid valve 6, the one-way valve 8 and the exhaust valve 9 is discharged from the exhaust valve 9.

[0041] When liquid flows out of the exhaust valve 9, or after the liquid flows out for a predetermined time, it can be determined that there is no gas in the pipeline.

[0042] Step 3, close the water sample valve 5 and the exhaust valve 9, open the sample discharge valve 4 and the standard solution valve 6, and the zero point standard solution flows into the circulation pool 3 under the action of the pressure difference until the water sample in the circulation pool 3 is completely replaced.

[0043] Step 4: Close the sample valve 4 and the standard solution valve 6, the dissolved oxygen sensor 2 begins to polarize, and when the displayed value of the dissolved oxygen transmitter 1 drops to the minimum value, calibrate the zero point of the dissolved oxygen meter.

[0044] Collect the liquid discharged from the discharge valve 4. When the volume of the liquid is greater than 5 times the sum of the volumes of the circulation pool 3, the water sample tube and the flow tube, mutual dissolution is inevitable when the water sample in the circulation pool 3 is replaced by the zero-point standard solution. However, by controlling the injection pressure and injection volume, the concentration of the zero-point standard solution can be avoided to the greatest extent. At the same time, since the zero-point standard solution is in an oversaturated state, a small amount of dilution can be ignored and will not affect the zero-point calibration of the dissolved oxygen meter.

[0045] Taking the dissolved oxygen meter at the economizer inlet of a 600MW supercritical direct current furnace unit in a power plant as an example, the effects of different calibration methods are shown in Table 1.

[0046] Table 1 Effects of different calibration methods

[0047] Calibration Method Calibration time Instrument display value Standard instrument indication value Working error conventional 24h 0μg / L 3.1 μg / L -3.1 The present invention 1h 3.2 μg / L 3.0μg / L 0.2

[0048] The power industry standard DL / T 677-2018 "Online Chemical Instrument Inspection Procedure for Power Plants" stipulates that when the oxygen concentration of the water sample measured by the inspected meter is no more than 10μg / L, the working error is -1<δ G <1, obviously, after the conventional calibration method calibrates the zero point of the dissolved oxygen meter at the economizer inlet, the meter is in an unqualified state. After calibration using the method of the present invention, the meter error is qualified.

[0049] The calibration method of the online dissolved oxygen meter zero point calibration system is as follows: during the calibration process, the dissolved oxygen sensor 2 is sealed in the circulation pool 3, the dissolved oxygen sensor 2 has no contact with the air, and the polarization time of the dissolved oxygen sensor 2 consuming background oxygen in the zero point standard solution is greatly shortened; meanwhile, there is no air accumulation in the circulation pool 3, and the zero point standard solution is always kept in an oxygen-free state, which further shortens the polarization time of the sensor 2, and also ensures that the background oxygen concentration of the electrolyte in the dissolved oxygen sensor 2 reaches the lowest point when calibrating the zero point, thereby improving the accuracy of the zero point calibration, thereby reducing the instrument working error and increasing the accuracy of the instrument; shortening the time of the zero point calibration can realize accurate calibration of the online dissolved oxygen meter in a short time.

[0050] The above contents are only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. An online dissolved oxygen meter zero point calibration system, characterized in that: It includes a circulation pool (3) and a standard solution pool (7); The circulation pool (3) is provided with a dissolved oxygen sensor (2), the circulation pool (3) is connected to a water sample valve (5) via a water sample tube, and a sample discharge valve (4) is provided on the circulation pool (3); The outlet of the standard solution pool (7) is connected to one end of the standard solution pipeline, and an exhaust valve (9) is provided at the other end of the standard solution pipeline. The standard solution pipeline is connected to the water sample tube through a connecting pipe, and the standard solution valve (6) is provided on the connecting pipe. When calibrating the dissolved oxygen meter, the exhaust valve (9) is used to exhaust the gas in the connecting pipe and the standard solution pipeline, and inject the standard solution in the standard solution pool (7) into the circulation pool (3) through the connecting pipe. The dissolved oxygen sensor (2) is sealed and arranged in the circulation pool (3), and the height difference between the standard solution pool (7) and the circulation pool (3) is at least 0.2 m; A one-way valve (8) is provided on the standard solution pipeline and is located on the standard solution pipeline between the connecting pipe and the standard solution tank (7); The height of the standard solution pool (7) is greater than the height of the circulation pool (3).

2. An online dissolved oxygen meter zero point calibration system according to claim 1, characterized in that: The volume of the standard solution pool (7) is 5-10 times greater than the sum of the volumes of the circulation pool (3), the water sample tube and the connecting tube.

3. A calibration method for an online dissolved oxygen meter zero point calibration system according to claim 1 or 2, characterized in that: The following steps are involved: Step 1, close the sample discharge valve (4), open the water sample valve (5), the standard solution valve (6) and the exhaust valve (9), squeeze the gas in the connecting pipe and the standard solution pipe through the water sample and the zero point standard solution in the standard solution pool (7), and discharge the gas from the exhaust valve (9). After the gas is completely discharged, close the water sample valve (5), the standard solution valve (6) and the exhaust valve (9); Step 2, close the water sample valve (5) and the exhaust valve (9), open the sample discharge valve (4) and the standard solution valve (6), and allow the zero point standard solution to flow into the circulation pool (3) under the action of the pressure difference until the water sample in the circulation pool (3) is completely replaced; Step 3: Close the sample discharge valve (4) and the standard solution valve (6), the dissolved oxygen sensor (2) begins to polarize, and when the displayed value of the dissolved oxygen transmitter (1) connected to the dissolved oxygen sensor (2) drops to the minimum value, calibrate the zero point of the dissolved oxygen meter.

4. The calibration method of an online dissolved oxygen meter zero point calibration system according to claim 3, characterized in that: In step 1, when the liquid flows out of the exhaust valve (9) for a predetermined time, it is determined that the gas is completely exhausted.

5. The calibration method of an online dissolved oxygen meter zero point calibration system according to claim 3, characterized in that: In step 2, the liquid discharged from the sample discharge valve (4) is collected. When the volume of the liquid is greater than 5 times the sum of the volumes of the circulation pool (3), the water sample tube and the flow tube, it is determined that the zero point standard solution completely replaces the water sample.

6. The calibration method of an online dissolved oxygen meter zero point calibration system according to claim 3, characterized in that: In step 2, when the liquid flows out of the sample discharge valve (4) for a predetermined time, it is determined that the zero point standard solution completely replaces the water sample.

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