Online measurement device and method for carbonate in continuous flowing water body

Abstract

The invention discloses a continuous flowing water carbonate online measurement device and method, and relates to the technical field of fresh water and seawater carbon monitoring. The device comprises a water body sample injector, a three-way valve, a constant flow pump, an acidification mixer, a water vapor balancer, a gas mass flow meter, a carbonate non-contact conductivity detector, an absorption tube, a data acquisition and control device and the like. A water body sample and a standard sample pass through an electric three-way valve and enter an acidification mixer through a constant flow pump, the acidified sample continuously enters a water vapor balancer, the bottom of the water vapor balancer is connected with high-purity nitrogen, the high-purity nitrogen enters the water vapor balancer after passing through a flow meter, CO2 in the acidified sample is purged out by using the high-purity nitrogen as carrier gas, and CO2 in the water vapor balancer is discharged from the water vapor balancer. The swept CO2 enters an absorption tube and is absorbed by alkali liquor in the absorption tube, and the alkali liquor absorbing the CO2 continuously enters a non-contact conductivity detector for continuous measurement. The device is simple in structure, high in detection precision and high in time resolution, and realizes real-time on-line automatic detection of carbonate in a water body.

Description

Technical Field

[0001] The present invention relates to the technical field of freshwater and seawater carbon monitoring, and in particular to a device and method for real-time continuous online measurement of carbonate in water bodies with high precision and high time resolution. Background Art

[0002] Carbonate is the main form of carbon in water and a key parameter for studying carbon cycle and climate change. It is the sum of carbon concentrations of various inorganic carbonates, bicarbonates, carbonic acid and carbon dioxide gases in water. Carbonate in water has become a basic parameter for studying water acidification and carbon cycle, and is an important parameter for understanding the biological production process in water. Accurate, rapid and convenient determination of the spatiotemporal distribution and variability of carbonate concentration in water with high spatiotemporal resolution is crucial for understanding water acidification and the absorption, transformation and migration of CO2 in water.

[0003] At present, the commonly used water carbonate measurement technologies mainly include coulometric titration, non-dispersive infrared CO2 analysis and conductivity detection. These methods have the characteristics of high precision and good stability, but due to the complexity of the device, large size and inconvenient operation, they can only be used for laboratory analysis and are difficult to be used for on-site shipborne cruise observation. Recently, with the development of technology, the detection device of dissolved inorganic carbon in water has also tended to be miniaturized and more suitable for on-site observation. Chinese patent CN101806789B discloses a dissolved inorganic carbon concentration analyzer in water, and Chinese patent CN103913553A discloses a seawater dissolved inorganic carbon cruise measurement device. These two public technologies use the method of converting dissolved inorganic carbon (DIC) in the water into CO2 first, and then analyzing the CO2 concentration through a CO2 detector. This method converts DIC into CO2, which requires a gas stripping process. The process of adding carrier gas makes the operation of the device complicated. Since the gas is greatly affected by temperature, humidity and pressure, the stability of the device is difficult to guarantee when applied on site, and the detection accuracy is also affected. Chinese patent CN102042981A discloses an in-situ dissolved inorganic carbon measuring instrument, which measures the DIC concentration in water samples by colorimetric method. Although this method overcomes the problems of CO2 gas stripping and detection, the colorimetric method requires the addition of a colorimetric agent, and the spectrophotometric method is greatly affected by temperature, and the measurement accuracy is difficult to guarantee. Both CO2 detection and colorimetric measurement of DIC require sufficient sample volume to measure, so a large sample volume is required, and the acid solution required for water sample acidification, the standard sample for measurement, and the added reagents are consumed in large quantities, which brings great difficulties to long-term on-site observation. Chinese patent CN104198538A discloses a ship-borne observation device for dissolved inorganic carbon in seawater. The device converts dissolved inorganic carbon in seawater into CO2 by acidification, dissolves CO2 in pure water by membrane exchange, and then measures dissolved inorganic carbon in water by conductivity detection. This method realizes online monitoring of dissolved inorganic carbon. However, since the detection method adopts an intermittent sampling method, the time for a single sample measurement is relatively long, and it cannot truly realize real-time online monitoring of dissolved inorganic carbon in seawater. At the same time, since a membrane separation and absorption method is adopted, the detection results and accuracy are significantly affected by the efficiency of membrane separation. In particular, when detecting seawater, the separation membrane is easily affected by impurities, resulting in a decrease in separation efficiency, which affects the accuracy and stability of the detection, and brings great difficulties to long-term continuous monitoring in the field. Summary of the invention

[0004] The purpose of the present invention is to provide a high-precision, high-time resolution measurement device and method suitable for real-time online and laboratory analysis of carbonate in water bodies in order to address the problems of existing on-site real-time online monitoring technology for carbonate systems in water bodies, such as complex equipment, low measurement accuracy, troublesome CO2 gas lift and measurement, large consumption of added reagents and great influence of on-site observation environment, insufficient measurement time resolution, and difficulty in long-term stable operation.

[0005] In order to achieve the above object, the present invention adopts the following technical scheme:

[0006] A continuous-flow water body carbonate online measuring device, comprising a sample constant flow pump, an acid mixer, a water vapor balancer, an absorption tube, a carbonate non-contact conductivity detector, a control and data acquisition device and a computer;

[0007] The sample continuously enters the acidification mixer through the sample constant flow pump to react with the acid. The sample after the reaction passes through the water vapor balancer and enters the absorption tube. The CO2 purged by the carrier gas is absorbed by the alkali solution in the absorption tube. The alkali solution after absorbing CO2 enters the carbonate non-contact conductivity detector to measure the change in conductivity.

[0008] The control and data acquisition device is connected to a computer and is used to control the startup and operation sequence of each component to realize remote control, data acquisition and processing.

[0009] The present invention also comprises an electric three-way valve connected to the sample constant flow pump, and the seawater inlet and the standard sample inlet are connected to the sample constant flow pump through the electric three-way valve, so as to switch the injection of water samples and standard samples.

[0010] The water vapor balance is connected to the acidification mixer and the water vapor balance. A carrier gas interface is provided at the bottom of the water vapor balance, which is used to purge CO2 in the acidified sample through the carrier gas; it also includes a gas mass flowmeter for controlling and monitoring the carrier gas flow entering the water vapor balance.

[0011] In the present invention, the carrier gas is high-purity nitrogen.

[0012] The invention also comprises an acid storage tank and an acid constant flow pump, wherein the acid storage tank is connected with the acidification mixer via the acid constant flow pump and is used for continuously conveying the acid to the acidification mixer.

[0013] The invention also comprises an alkali constant flow pump and an alkali solution storage tank, wherein the alkali solution storage tank is connected with the absorption pipe through the alkali constant flow pump and is used for continuously conveying the alkali solution to the absorption pipe.

[0014] The carbonate non-contact conductivity detector is connected to the absorption tube and is used to measure the conductivity change of the alkali solution after absorbing carbon dioxide, so as to determine the concentration of carbonate in the water body.

[0015] The continuous flow water body carbonate online measurement method of the present invention realizes the real-time online measurement of water body carbonate through a continuous flow sampling mode combined with purge capture and non-contact conductivity detection.

[0016] During the measurement process, samples, acids and alkali solutions all flow continuously through constant flow pumps, achieving long-term automated continuous operation.

[0017] The single measurement time of the measurement method reaches the millisecond level, and the number of measurements per minute is not less than 120 times.

[0018] The method for online measurement of carbonate in a continuously flowing water body comprises the following steps:

[0019] 1) Parameter setting through computer;

[0020] 2) Start the acid constant flow pump and the alkali constant flow pump, connect the carrier gas, and collect the background signal after the system stabilizes;

[0021] 3) Switch the valve position of the electric three-way valve to the water sample inlet, and start the sample constant flow pump to start sampling measurement;

[0022] 4) The sample reacts with acid in the acidification mixer to generate CO2. The sample after the reaction enters the water vapor balancer, where the CO2 is purged out by the carrier gas and enters the absorption tube to be absorbed by the alkali solution;

[0023] 5) The alkali solution after absorbing CO2 enters the carbonate non-contact conductivity detector to measure the conductivity;

[0024] 6) Compare the measured signal with the background signal to obtain the carbonate concentration in the water in real time;

[0025] 7) When it is necessary to measure the standard sample, switch the valve position of the electric three-way valve to the standard sample inlet and perform the measurement according to the same steps as the sample measurement.

[0026] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0027] The continuous flow water carbonate online measuring device disclosed by the present invention adopts a continuous flow sampling mode, and combines purge capture and non-conductivity detection technology at the same time. It has the characteristics of high sensitivity, short detection time, high precision and good stability, and especially realizes real-time online detection of water carbonate. A single measurement can reach the millisecond level, and the number of measurements per minute is higher than 120 times, which solves the problem of insufficient time resolution caused by the intermittent sampling measurement of water carbonate. At the same time, the present invention adopts the purge capture and contact exchange absorption mode to solve the problem of decreased measurement accuracy caused by the separation efficiency decreased due to the contamination or aging of the separation membrane, and the instrument is difficult to operate stably for a long time, and the separation membrane needs to be replaced frequently. The purge capture and contact absorption have higher absorption efficiency and more stability, which is suitable for long-term continuous field observation. In addition, the present invention combines purge capture with non-conductivity detection, which not only solves the problems caused by gas detection, but also solves the problems of membrane separation, and is particularly suitable for continuous online monitoring of field water carbonate with high time resolution and high-precision detection of water carbonate in the laboratory. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a structural schematic diagram of the present invention;

[0029] Figure 2 To continuously test the dissolved inorganic carbon in the waters in the coastal waters in the field monitoring data and the standard curve determined in the laboratory;

[0030] Figure 3 The data results of the surface seawater cruise observation carried out by the device of the present invention;

[0031] Figure 4 The present invention is a practical application in which the device is installed on an environmental monitoring ship.

[0032] Figure numerals: electric three-way valve 1, sample constant flow pump 2, acid constant flow pump 3, acid storage tank 4, acidification mixer 5, water vapor balance 6, carbonate non-contact conductivity detector 7, gas mass flow meter 8, control and data acquisition device 9, absorption tube 10, alkali constant flow pump 11, alkali solution storage tank 12, computer 13. DETAILED DESCRIPTION

[0033] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer and more understandable, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0034] Example 1

[0035] See also Figure 1 The continuous flow water carbonate online measuring device of the present invention connects the seawater inlet A and the standard sample inlet B to the electric three-way valve 1, the water sample is connected to the acidification mixer 5 through the sample constant flow pump 2, the acid solution of the acid storage tank 4 is connected to the acidification mixer 5 through the acid constant flow pump 3, the outlet of the acidification mixer 5 is connected to the water vapor balance 6, the high-purity compressed nitrogen bottle is connected to the water vapor balance 6 through the gas mass flow meter 8, the gas outlet of the water vapor balance 6 is connected to the absorption tube 10, the alkali liquid storage tank 12 is connected to the absorption tube 10 through the alkali constant flow pump 11, and the alkali liquid outlet of the absorption tube 10 is connected to the carbonate non-contact conductivity detector 7. The constant flow pump, the electric three-way valve, the gas mass flow meter, and the carbonate non-contact conductivity detector are controlled by the control and data acquisition device 9, and the control and data acquisition device 9 is connected to the computer 13 through the RS-485 interface to perform remote control, data acquisition, processing and storage, and real-time monitoring of the device. In this embodiment, the alkali liquid and CO2 are reversely absorbed.

[0036] When measuring a water sample, first start the carbonate non-contact conductivity detector 7 and the control and data acquisition device 9, preheat them, and turn on the computer 13 to set the parameters. After the settings are completed, start the acid constant current pump 3 and the alkali constant current pump 11, open the high-purity nitrogen interface, and after the absorption liquid stably passes through the carbonate non-contact conductivity detector 7, open the data acquisition software and start collecting data, which is recorded as the measurement background value. When the measurement is stable, adjust the valve position of the electric three-way valve 1 to the injection port, and start the sample constant current pump 2 at the same time. At this time, the sample enters the acidification mixer 5 through the sample constant current pump 2, and reacts with the acid in the acidification mixer 5 to generate CO2. In this process, the amount of acid added is controlled to be excessive to the total amount of carbonate in the sample to be measured, ensuring that all the carbonic acid in the sample is completely removed. The CO2 in the sample in the water vapor balance 6 is purged out by high-purity nitrogen. The purged CO2 continuously passes through the absorption tube 10 in reverse and is absorbed by the alkaline solution in the absorption tube 10. The absorbed liquid continuously flows into the carbonate non-contact conductivity detector 7 to measure the change in conductivity in the absorption liquid. The change in conductivity is the concentration change of the carbonate system in the sample. The sample is continuously injected during the detection process. The detection time can reach the millisecond level. More than 120 detection data are obtained per minute, and the concentration of carbonate in the water body can be obtained in real time.

[0037] When measuring the standard sample, you only need to switch the valve position of the electric three-way valve 1 to the standard sample port. The rest of the detection process is exactly the same as the sample detection process. When the electric three-way valve 1 is switched to the standard sample port, the system automatically records the start and end time of the standard sample measurement and stores the standard sample measurement data separately. When measuring the sample, you can switch to the standard sample measurement as needed to achieve automatic detection and calibration of the standard sample.

[0038] After the measurement is completed, the sample collection is completed first, the high-purity nitrogen is turned off, the sample constant current pump 2, the acid constant current pump 3 and the alkali constant current pump 11 are turned off, the carbonate non-contact conductivity detector 7 is turned off, and finally the system power is turned off.

[0039] During the operation of the device of the present invention, the sample and the acid and alkali solutions all flow continuously through the constant flow pump, thereby realizing long-term automatic continuous operation.

[0040] Figure 2 (a) shows the field monitoring data of continuous testing of dissolved inorganic carbon in water bodies in nearshore waters, indicating that the device of the present invention has a short time and high resolution for detecting dissolved inorganic carbon; Figure 2 (b) shows the standard curve of the device of the present invention measured in the laboratory. The concentrations of inorganic carbon dissolved in the standard solution are 0.2, 0.5, 1.0, 2.0, 3.0, 4.0 and 5.0 Mmol, respectively. The standard curve is prepared by averaging three measurements, indicating that the linearity of the standard curve of the device of the present invention is good within the range of 0-5 Mmol (R2 =0.999), the test accuracy is high.

[0041] Figure 3 The data results of surface seawater cruise observations carried out using the device of the present invention during a shared voyage with the Natural Science Foundation of China in July 2022 are given. Figure 3 (a) shows the spatial distribution data of dissolved inorganic carbon in surface seawater measured by the device of the present invention during the voyage. The voyage lasted for 7 days, with 24-hour continuous monitoring. The whole process ran well and high-resolution dissolved inorganic carbon data in the sea area were obtained, indicating that the device of the present invention has good stability and reliability. Figure 3 (b) shows the seawater samples collected at different stations during the voyage using a water sampler, and the dissolved inorganic carbon in the surface water was measured using the titration analysis method in the laboratory; Figure 3 (c) shows the dissolved inorganic carbon data of seawater measured by the device of the present invention and the sampling titration analysis method at the same time and station, indicating that the two have good consistency; Figure 3 (d) shows the correlation analysis between the device of the present invention and the sampled observation data, indicating that the results of the two tests have a good correlation (R 2 =0.96), which proves that the device of the present invention has high precision and accuracy and is suitable for high-resolution monitoring of dissolved inorganic carbon in water.

[0042] Figure 4 (a) is a diagram showing the installation of the device of the present invention on the environmental monitoring vessel "China Environmental Monitoring Su 001" of Jiangsu Provincial Environmental Monitoring Center; Figure 4 (b) is the on-site monitoring and commissioning installation diagram on the monitoring vessel; Figure 4 The one in the middle (c) is the environmental monitoring ship “China Environmental Monitoring Su 001” of Jiangsu Provincial Environmental Monitoring Center.

Claims

1. On-line carbonate measuring device for continuous flowing water, characterized by: It includes a sample constant flow pump, an acid mixer, a water vapor balancer, an absorption tube, a carbonate non-contact conductivity detector, a control and data acquisition device and a computer; The sample continuously enters the acidification mixer through the sample constant flow pump to react with the acid. The sample after the reaction passes through the water vapor balancer and enters the absorption tube. The CO2 purged by the carrier gas is absorbed by the alkali solution in the absorption tube. The alkali solution after absorbing CO2 enters the carbonate non-contact conductivity detector to measure the change in conductivity. The control and data acquisition device is connected to a computer and is used to control the startup and operation sequence of each component to realize remote control, data acquisition and processing.

2. The online carbonate measuring device for a continuously flowing water body according to claim 1, characterized in that: It also includes an electric three-way valve connected to the sample constant flow pump, which is used for switching the injection of water samples and standard samples.

3. The online carbonate measuring device for a continuously flowing water body according to claim 1, characterized in that: The water vapor balance is connected to the acidification mixer and the water vapor balance. A carrier gas interface is provided at the bottom of the water vapor balance, which is used to purge CO2 in the acidified sample through the carrier gas; it also includes a gas mass flowmeter for controlling and monitoring the carrier gas flow entering the water vapor balance.

4. The online carbonate measuring device for a continuously flowing water body according to claim 1, characterized in that: It also includes an acid storage tank and an acid constant flow pump. The acid storage tank is connected to the acidification mixer through the acid constant flow pump to continuously transport the acid to the acidification mixer.

5. The online carbonate measuring device for a continuously flowing water body according to claim 1, characterized in that: It also includes an alkali constant flow pump and an alkali solution storage tank. The alkali solution storage tank is connected to the absorption pipe through the alkali constant flow pump and is used for continuously conveying the alkali solution to the absorption pipe.

6. The online carbonate measuring device for a continuously flowing water body according to claim 1, characterized in that: The carbonate non-contact conductivity detector is connected to the absorption tube and is used to measure the conductivity change of the alkali solution after absorbing carbon dioxide, so as to determine the concentration of carbonate in the water body.

7. A method for measuring carbonate in a continuous flowing water body online, characterized in that: The device of any one of claims 1 to 6 is used to measure the carbonate in water in real time online through continuous flow sampling combined with purge capture and non-contact conductivity detection.

8. The method for online measurement of carbonate in a continuously flowing water body according to claim 7, characterized in that: During the measurement process, samples, acids and alkali solutions all flow continuously through constant flow pumps, achieving long-term automated continuous operation.

9. The method for online measurement of carbonate in a continuously flowing water body according to claim 7, characterized in that: The single measurement time of the measurement method reaches the millisecond level, and the number of measurements per minute is not less than 120 times.

10. The method for online measurement of carbonate in a continuously flowing water body according to claim 7, characterized in that: The following steps are involved: 1) Parameter setting through computer; 2) Start the acid constant flow pump and the alkali constant flow pump, connect the carrier gas, and collect the background signal after the system stabilizes; 3) Switch the valve position of the electric three-way valve to the water sample inlet, and start the sample constant flow pump to start sampling measurement; 4) The sample reacts with acid in the acidification mixer to generate CO2. The sample after the reaction enters the water vapor balancer, where the CO2 is purged out by the carrier gas and enters the absorption tube to be absorbed by the alkali solution; 5) The alkali solution after absorbing CO2 enters the carbonate non-contact conductivity detector to measure the conductivity; 6) Compare the measured signal with the background signal to obtain the carbonate concentration in the water in real time; 7) When it is necessary to measure the standard sample, switch the valve position of the electric three-way valve to the standard sample inlet and perform the measurement according to the same steps as the sample measurement.

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