COD (Chemical Oxygen Demand) water quality online analyzer

Abstract

The COD water quality online analyzer comprises a controller, a water sample pretreatment unit, a sampling unit and an analysis unit, the sampling unit comprises a sample tank, a pure water tank, a pretreatment reagent tank and a standard liquid tank, the analysis unit comprises a reaction tank, a heating wire, a first photoelectric detector and a light source, the top and the bottom of the reaction tank are respectively provided with an upper port and a lower port, and the upper port and the lower port are communicated with each other. An upper high-pressure electromagnetic valve and a lower high-pressure electromagnetic valve are respectively arranged at two ports, the first photoelectric detector and the light source are respectively arranged on two opposite sides of the reaction tank, and the heating wire is arranged on the outer side of the reaction tank; the water sample pretreatment unit comprises two chloride ion filters, the input end of a first-stage chloride ion filter is connected with a water sample, the output end of the first-stage chloride ion filter is connected with the input end of a second-stage chloride ion filter, and the output end of the second-stage chloride ion filter is connected with a sample tank; the sample tank, the pure water tank, the pretreatment reagent tank and the standard liquid tank are respectively connected with the lower port of the reaction tank through the metering unit. According to the utility model, the detection efficiency and accuracy can be improved.

Description

Technical Field

[0001] This utility model relates to the field of water quality analysis and detection technology, specifically to an online COD water quality analyzer. Background Technology

[0002] In today's petrochemical industry, water quality is of paramount importance to industrial water safety. Water quality monitoring allows for the timely detection of water quality problems and provides a scientific basis for water quality optimization, ensuring that water quality meets national standards. In the petrochemical industry, high concentrations of chemical oxygen demand (COD) in water primarily originate from processes such as petroleum refining and chemical production. Excessive COD levels severely disrupt the aquatic ecosystem, leading to eutrophication, decreased dissolved oxygen, and other environmental problems, which in turn cause significant harm to the industrial water systems of the petrochemical industry. Therefore, it is urgent to monitor COD levels in industrial water to enable timely and effective measures to ensure water safety and environmental sustainability in petrochemical production processes.

[0003] Currently, the main methods for COD detection include potassium dichromate titration, coulometric method, absorption spectroscopy, and rapid digestion spectrophotometry. Among these, potassium dichromate titration has a long detection time and is not suitable for online detection; coulometric measurement is easily affected by chloride ions and other interferences, and the electrodes require regular maintenance, resulting in high maintenance costs; absorption spectroscopy requires expensive spectrometers, and the post-processing of detection data is complex; rapid digestion spectrophotometry, by using heating to shorten the digestion time and using less reagent, is suitable for online detection and is currently the most commonly used detection method in online equipment.

[0004] The principle of rapid digestion spectrophotometry is based on the redox reaction between reducing organic matter in water and excess potassium dichromate under high-temperature acidic medium (concentrated sulfuric acid) and silver sulfate catalysis, resulting in the oxidation of hexavalent chromium (Cr). 6+ It is reduced to trivalent chromium (Cr). 3+ The solution changes color, and the absorbance of the solution at a specific wavelength is measured spectrophotometrically to calculate the COD value. When using rapid digestion spectrophotometry to detect COD, chloride ions (Cl-) in the water sample... - Chloride ions are a key factor affecting the accuracy of test results. In strongly acidic media, chloride ions readily undergo redox reactions with the oxidant potassium dichromate, increasing oxidant consumption and leading to falsely high COD readings. Therefore, current water quality testing methods require the addition of a masking agent to water samples containing chloride ions to reduce interference with test results. However, the masking agents used in traditional national standard methods can only block chloride ions at certain concentrations. For water in petrochemical industry circulating water systems, the concentration of chloride ions is often too high due to the presence of chloride in the water source itself, the addition of chlorine-containing reagents, and atmospheric deposition. Simply adding a chloride ion masking agent during testing is insufficient to completely remove chloride ions from the water sample, thus affecting the accuracy of the test results.

[0005] Existing COD water quality testing equipment still generally uses the addition of shielding agents to remove chloride ions, which makes it difficult to guarantee accurate detection of water samples with high chloride ion concentrations. In addition, existing COD water quality testing equipment also has the following shortcomings: First, existing instruments generally use a two-point calibration method, which leads to distortion of the standard curve and low detection accuracy; second, when performing color development according to national standard methods, the color development time requires continuous heating for 15 minutes, followed by cooling to room temperature, but existing equipment has slow heating and cooling rates, resulting in a long color development cycle; third, existing testing equipment has a complex structure and cumbersome testing procedures, leading to a long overall testing cycle. Utility Model Content

[0006] To address the problems in the background technology, this utility model proposes an online COD water quality analyzer, including a controller, a water sample pretreatment unit, a sampling unit, and an analysis unit. The sampling unit includes a sample tank, a pure water tank, a pretreatment reagent tank, and a standard solution tank. The analysis unit includes a reaction cell, a heating wire, a first photodetector, and a light source. The top and bottom of the reaction cell are respectively provided with an upper port and a lower port, and an upper high-pressure solenoid valve and a lower high-pressure solenoid valve are respectively provided at the upper port and the lower port. The first photodetector and the light source are respectively located on opposite sides of the reaction cell, and the heating wire is located on the outside of the reaction cell.

[0007] The water sample pretreatment unit includes a primary chloride ion filter and a secondary chloride ion filter. The input end of the primary chloride ion filter is connected to the water sample, and the output end of the primary chloride ion filter is connected to the input end of the secondary chloride ion filter. The output end of the secondary chloride ion filter is connected to the sample tank. The sample tank, pure water tank, pretreatment reagent tank, and standard solution tank are respectively connected to the lower port of the reaction cell through a metering unit.

[0008] The controller is connected to the metering unit, the light source, the first photodetector, the heating wire, the upper high-pressure solenoid valve, and the lower high-pressure solenoid valve, respectively.

[0009] Preferably, the metering unit includes a multi-channel selection valve and a metering pump. The input end of the metering pump is connected to air, the sample container, the pure water container, the pretreatment reagent container, and the standard solution container respectively through the multi-channel selection valve. The output end of the metering pump is connected to the lower port of the reaction cell. The controller is connected to the multi-channel selection valve and the metering pump respectively.

[0010] Preferably, the output end of the metering pump is connected to the lower port of the reaction tank via a three-way valve. The three-way valve is also connected to the input end of a waste discharge pump. The output end of the waste discharge pump is connected to a waste liquid tank. Both the waste discharge pump and the three-way valve are connected to a controller.

[0011] Preferably, a second photodetector is provided below the light source, the second photodetector is located on the same side of the reaction tank as the light source, and the second photodetector is connected to the controller.

[0012] Preferably, the reaction tank is equipped with a temperature sensor for detecting the temperature inside the reaction tank, and the temperature sensor is connected to the controller.

[0013] Preferably, a fan is provided on one side of the reaction tank, and the fan is connected to a controller.

[0014] Preferably, the controller is also connected to a human-machine interface unit and an alarm device.

[0015] Preferably, the human-computer interaction unit is a resistive touch screen, and the alarm device is an alarm light.

[0016] Preferably, both the primary chloride ion filter and the secondary chloride ion filter are ion exchange resin filters.

[0017] Preferably, there are four standard solution containers, each containing a different COD standard solution, and the concentrations of the standard solutions in the four standard solution containers are different.

[0018] The beneficial effects of this utility model are as follows:

[0019] 1. This utility model is equipped with a water sample pretreatment unit, which uses two chloride ion filters connected in series to pretreat the water sample for testing in two stages, which can effectively reduce the chloride ion content in the water sample. Then, a chloride ion shielding agent is added in the detection process to improve the accuracy and reliability of the detection.

[0020] 2. This utility model uses a heating wire and a high-pressure solenoid valve. The heating wire heats the reaction tank. During heating, the upper and lower high-pressure solenoid valves are closed, which can form a sealed space inside the reaction tank to achieve a rapid temperature increase, accelerate the reaction time, and thus shorten the color development cycle.

[0021] 3. This utility model is equipped with a fan to dissipate heat from the reaction tank, thereby achieving rapid cooling, accelerating the cooling of the solution after the reaction, and shortening the detection time.

[0022] 4. This invention employs a four-point calibration method, setting four standard solutions. During detection, the four standard solutions are sequentially sampled to obtain the correspondence between absorbance y and concentration x. A standard curve of four-point calibration, y=Kx+B, is plotted, and the values ​​of K (standard curve slope) and B (standard curve intercept) of the standard curve are saved. The standard curve of four-point calibration has higher linearity, thus ensuring high detection accuracy. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the overall structure of this utility model.

[0024] The diagram is labeled as follows: 1. Primary chloride ion filter; 2. Secondary chloride ion filter; 3. Sample container; 4. Pretreatment reagent container; 5. Standard solution container; 6. Pure water container; 7. Multi-channel selector valve; 8. Metering pump; 9. Reaction cell; 10. Upper high-pressure solenoid valve; 11. Lower high-pressure solenoid valve; 12. Light source; 13. First photodetector; 14. Second photodetector; 15. Temperature sensor; 16. Three-way valve; 17. Waste pump; 18. Alarm light; 19. Controller; 20. Heating wire; 21. Human-machine interface unit; 22. Waste liquid tank. Detailed Implementation

[0025] To make this utility model clearer and more understandable, the technical solution of this utility model will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the given embodiments are only one of the implementation methods and do not represent all embodiments.

[0026] In this article, terms such as "inner," "outer," "upper," and "lower" are established based on the positional relationships shown in the attached drawings. Depending on the attached drawings, the corresponding positional relationships may also change. Therefore, they should not be interpreted as an absolute limitation on the scope of protection.

[0027] Combined with appendix Figure 1 An online COD water quality analyzer includes a controller 19, a water sample pretreatment unit, a sampling unit, and an analysis unit. The sampling unit includes a sample tank 3, a pure water tank 6, a pretreatment reagent tank 4, and a standard solution tank 5. The analysis unit includes a reaction cell 9, a heating wire 20, a first photodetector 13, and a light source 12. The top and bottom of the reaction cell 9 are respectively provided with an upper port and a lower port. An upper high-pressure solenoid valve 10 and a lower high-pressure solenoid valve 11 are respectively provided at the upper port and the lower port. The first photodetector 13 and the light source 12 are respectively arranged on opposite sides of the reaction cell 9. The heating wire 20 is arranged on the outside of the reaction cell 9.

[0028] The water sample pretreatment unit includes a primary chloride ion filter 1 and a secondary chloride ion filter 2. Both the primary chloride ion filter 1 and the secondary chloride ion filter 2 are ion exchange resin filters. The input end of the primary chloride ion filter 1 is connected to the water sample, and the output end of the primary chloride ion filter 1 is connected to the input end of the secondary chloride ion filter 2. The output end of the secondary chloride ion filter 2 is connected to the sample container 3. The sample container 3, the pure water container 6, the pretreatment reagent container 4, and the standard solution container 5 are respectively connected to the lower port of the reaction cell 9 through a metering unit.

[0029] The controller 19 is connected to the metering unit, the light source 12, the first photodetector 13, the heating wire 20, the upper high-pressure solenoid valve 10, and the lower high-pressure solenoid valve 11, respectively.

[0030] Specifically, the heating wire 20 is wound around the outside of the reaction tank 9, so that the entire reaction tank 9 can be heated. More specifically, the heating wire 20 has two sections: one section is wound around the upper part of the reaction tank 9, and the other section is wound around the lower part of the reaction tank 9. The heating wire 20 located at the lower part of the reaction tank 9 is a high-resistance heating wire 20 with a power of up to 100W, which can improve the heating speed and thus shorten the detection cycle.

[0031] In the chloride ion filter, negatively charged ions in the micropores can exchange with chloride ions, adsorbing and retaining them within the filter, thus filtering out chloride ions. Before testing, the water sample enters the primary chloride ion filter 1 from the circulating water system for preliminary filtration. Then, it enters the secondary chloride ion filter 2 for further chloride ion removal. After two stages of filtration, most of the chloride ions are removed. The filtered water sample then enters the sample tank 3 and is pumped to the reaction tank 9 via a metering unit for testing. Mercuric sulfate is added during the testing process as a chloride ion shielding agent to ensure that COD detection is not interfered with by residual chloride ions, thereby improving the accuracy and reliability of the test results.

[0032] Specifically, the light source 12 is an LED light source 12; the first photodetector 13 is a transmission photodetector that receives the emitted light from the light source 12 through the reaction tank 9. More specifically, a second photodetector 14 is located below the light source 12, on the same side of the reaction tank 9 as the light source 12, and is connected to the controller 19; the second photodetector 14 is a reference detector used to receive the scattered light from the light source 12. When setting the photodetectors, the positions of the first photodetector 13 and the second photodetector 14 are adjusted to ensure that the emitted light from the light source 12, after refraction by the solution in the reaction tank 9, can be received by the first photodetector 13, and that the second photodetector 14 can receive the scattered light from the light source 12.

[0033] Specifically, there are four standard solution containers 5, each containing a different COD standard solution, and the concentrations of the standard solutions in the four containers are different. There are three pretreatment reagent containers 4, each containing a different pretreatment reagent, and the types of pretreatment reagents in the three pretreatment reagent containers are different. The pure water container 6 contains pure water. The three reagent containers contain reagent one, reagent two, and reagent three, respectively. Reagent one is a potassium dichromate standard solution, reagent two is a silver sulfate-sulfuric acid solution, and reagent three is a mercuric sulfate solution and a shielding agent. The standard solution is a COD standard solution prepared from potassium hydrogen phthalate.

[0034] Specifically, the metering unit includes a multi-channel selection valve 7 and a metering pump 8. The input end of the metering pump 8 is connected to air, the sample container 3, the pure water container 6, the pretreatment reagent container 4, and the standard solution container 5 through the multi-channel selection valve 7. The output end of the metering pump 8 is connected to the lower port of the reaction cell 9. The controller 19 is connected to the multi-channel selection valve 7 and the metering pump 8.

[0035] Specifically, the output of the metering pump 8 is connected to the lower port of the reaction tank 9 via a three-way valve 16. The three-way valve 16 is also connected to the input of the waste discharge pump 17, and the output of the waste discharge pump 17 is connected to a waste liquid tank 22. Both the waste discharge pump 17 and the three-way valve 16 are connected to the controller 19. The three-way valve 16 switches the connection status of the reaction tank 9, allowing the reaction tank 9 to be connected to either the metering pump 8 or the waste discharge pump 17. When the reaction tank 9 is connected to the metering pump 8, the metering pump 8 can pump the solution from the sampling unit, such as the pretreatment reagent, into the reaction tank 9. When the reaction tank 9 is connected to the waste discharge pump 17, the waste discharge pump 17 can discharge the solution from the reaction tank 9 to remove waste liquid, which is then stored in the waste liquid tank 22.

[0036] Specifically, the reaction tank 9 is equipped with a temperature sensor 15 for detecting the temperature inside the reaction tank 9, and the temperature sensor 15 is connected to the controller 19. A fan is installed on one side of the reaction tank 9, and the fan is connected to the controller 19. During testing, the temperature inside the reaction tank 9 is detected by the temperature sensor 15, which helps the testing personnel determine whether the temperature inside the reaction tank 9 has reached the required reaction temperature. The fan is used to dissipate heat from the reaction tank 9, enabling the reaction tank 9 to cool down more quickly and shortening the testing time.

[0037] Specifically, the controller 19 is also connected to a human-machine interface unit 21 and an alarm device. The human-machine interface unit 21 is a resistive touchscreen, and the alarm device is an alarm light 18. The controller 19 controls the overall detection process and transmits the detection signals to the human-machine interface unit 21. The human-machine interface unit 21 is used to issue control commands, display the reaction status, reaction progress, and historical data. The alarm device is used to sound an alarm. The controller 19 judges whether the detection result is abnormal based on the detection status of the photoelectric detector. If the detection result does not meet the detection requirements, the controller 19 controls the alarm to sound. More specifically, the sample tank 3, pure water tank 6, pretreatment reagent tank 4, and standard solution tank 5 are all equipped with liquid level sensors. The liquid level sensors are connected to the controller 19. When the liquid level sensor detects that the liquid in the tank is insufficient, it transmits the liquid level information to the controller 19. The controller 19 controls the alarm device to sound an alarm, reminding the testing personnel to replenish the corresponding reagents.

[0038] Testing process:

[0039] S1. Water sample pretreatment: The water sample is filtered through a primary chloride ion filter 1 and a secondary chloride ion filter 2 to remove most of the chloride ions. The filtered water sample is then placed into a water sample tank.

[0040] S2, Blank absorbance calibration: Pure water in pure water tank 6 enters reaction tank 9 through metering pump 8. LED light source 12 emits light of a specific wavelength. Part of the scattered light is received by second photodetector 14, and the other part of the light is received by first photodetector 13.

[0041] S3. Blank absorbance measurement: The first photodetector 13 and the second photodetector 14 respectively detect the energy values ​​of transmitted light and reference light, and calculate the current blank absorbance y1;

[0042] S4. Transmission absorbance measurement: The standard solution is metered into the reaction cell 9 through metering pump 8 for rinsing, and this process is repeated multiple times. After rinsing, reagent 1, reagent 2, reagent 3, and pure water are added sequentially to the reaction cell 9 through metering pump 8 for pretreatment. Then, air is introduced into the reaction cell 9 through metering pump 8 to stir the solution in the reaction cell 9. At the same time, heating wire 20 heats the solution to 165°C and maintains a constant temperature for color development for 15 minutes. After color development, the fan is turned on to dissipate heat and rapidly cool the solution in the reaction cell 9 to room temperature. After cooling, the first photodetector 13 and the second photodetector 14 detect the current transmitted light and reference light energy values, respectively, and calculate the current transmission absorbance y2.

[0043] S5. Standard curve plotting: The difference between the transmitted absorbance and the blank absorbance is the absorbance of the solution, y, i.e., y = y2 - y1; Repeat step S4 using standard solutions of different concentrations, record the data of four sets of solution absorbance y and corresponding COD concentration x, and plot the standard curve of COD y = Kx + B.

[0044] S6. Sample concentration determination: Pure water enters the reaction tank 9 through metering pump 8, and the current blank absorbance Y1 is calculated; the water sample is processed according to the processing method in step S4, and the current transmission absorbance Y2 of the water sample is calculated. The absorbance Y of the water sample solution is then Y = Y2 - Y1; based on the four-point standard curve y = Kx + B, the COD concentration X of the water sample is calculated from the absorbance Y of the solution.

[0045] Although embodiments of the present invention have been shown and described, those skilled in the art will be able to make various changes, modifications, substitutions and alterations to these embodiments without departing from the principles and spirit of the present invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A COD water quality on-line analyzer characterized by comprising: The system includes a controller (19), a water sample pretreatment unit, a sampling unit, and an analysis unit. The sampling unit includes a sample tank (3), a pure water tank (6), a pretreatment reagent tank (4), and a standard solution tank (5). The analysis unit includes a reaction cell (9), a heating wire (20), a first photodetector (13), and a light source (12). The reaction cell (9) has an upper port and a lower port at its top and bottom, respectively. The upper port and the lower port are respectively equipped with an upper high-pressure solenoid valve (10) and a lower high-pressure solenoid valve (11). The first photodetector (13) and the light source (12) are respectively located on opposite sides of the reaction cell (9). The heating wire (20) is located on the outside of the reaction cell (9). The water sample pretreatment unit includes a primary chloride ion filter (1) and a secondary chloride ion filter (2). The input end of the primary chloride ion filter (1) is connected to the water sample, and the output end of the primary chloride ion filter (1) is connected to the input end of the secondary chloride ion filter (2). The output end of the secondary chloride ion filter (2) is connected to the sample container (3). The sample container (3), the pure water container (6), the pretreatment reagent container (4), and the standard solution container (5) are respectively connected to the lower port of the reaction cell (9) through a metering unit. The controller (19) is connected to the metering unit, the light source (12), the first photodetector (13), the heating wire (20), the upper high-pressure solenoid valve (10), and the lower high-pressure solenoid valve (11), respectively.

2. The COD water quality on-line analyzer according to claim 1, characterized in that: The metering unit includes a multi-channel selection valve (7) and a metering pump (8). The input end of the metering pump (8) is connected to air, the sample container (3), the pure water container (6), the pretreatment reagent container (4), and the standard solution container (5) through the multi-channel selection valve (7). The output end of the metering pump (8) is connected to the lower port of the reaction cell (9). The controller (19) is connected to the multi-channel selection valve (7) and the metering pump (8) respectively.

3. The COD water quality on-line analyzer according to claim 2, characterized in that: The output end of the metering pump (8) is connected to the lower port of the reaction tank (9) through a three-way valve (16). The three-way valve (16) is also connected to the input end of the waste discharge pump (17). The output end of the waste discharge pump (17) is connected to the waste liquid tank (22). The waste discharge pump (17) and the three-way valve (16) are both connected to the controller (19).

4. The COD water quality on-line analyzer according to claim 1, characterized in that: A second photodetector (14) is provided below the light source (12). The second photodetector (14) and the light source (12) are located on the same side of the reaction tank (9). The second photodetector (14) is connected to the controller (19).

5. The COD water quality on-line analyzer according to claim 1, characterized in that: The reaction tank (9) is equipped with a temperature sensor (15) for detecting the temperature inside the reaction tank (9), and the temperature sensor (15) is connected to the controller (19).

6. The COD water quality on-line analyzer according to claim 5, characterized in that: A fan is provided on one side of the reaction tank (9), and the fan is connected to the controller (19).

7. The COD water quality on-line analyzer according to claim 1, characterized in that: The controller (19) is also connected to a human-machine interaction unit (21) and an alarm device.

8. The COD water quality online analyzer according to claim 7, characterized in that: The human-computer interaction unit (21) is a resistive touch screen, and the alarm device is an alarm light (18).

9. The COD water quality on-line analyzer according to claim 1, characterized in that: Both the primary chloride ion filter (1) and the secondary chloride ion filter (2) are ion exchange resin filters.

10. The COD water quality on-line analyzer according to claim 1, characterized in that: There are four standard solution tanks (5), each containing a COD standard solution. The standard solution concentrations in the four standard solution tanks (5) are different. There are three pretreatment reagent tanks (4), each containing a reagent.

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