Method and system for improving measurement accuracy and reliability of concentration of CO2 in raw flue gas

Abstract

The invention discloses a method and a system for improving the accuracy and reliability of measuring the concentration of CO2 in raw flue gas, and the method for improving the accuracy and reliability of measuring the concentration of CO2 in the raw flue gas comprises the following steps: utilizing the difference value between the oxygen concentration C4 in the atmosphere and the oxygen concentration C1 in the raw flue gas measured in a flue; calibrating the measured value C2 of the concentration of CO2 in the raw flue gas according to the difference between the oxygen concentration C4 in the atmosphere and the oxygen concentration C3, measured outside the flue, in the raw flue gas, so as to obtain the actual concentration C of CO2 in the raw flue gas; further, C = C2 * (C4-C1) / (C4-C3). According to the method, the wet oxygen concentration at the front end and the rear end of CEMS sampling is compared through homologous monitoring, and whether the CEMS sampling system leaks air or not is judged and calibrated online in real time, so that the CO2 monitoring accuracy is improved, and the technical problem of inaccurate calculation of the total carbon emission amount caused by air leakage in the process from sampling to measurement is solved; the method is simple, accurate, low in cost and easy to industrially popularize.

Description

Technical Field

[0001] This invention relates to a method and system for improving the accuracy and reliability of CO2 concentration measurement in raw flue gas, belonging to the field of industrial gas component sampling and measurement technology. Background Technology

[0002] In industrial production practices, pollutants are inevitably emitted or released into the atmosphere, and these emissions are often organized through flues, chimneys, or exhaust stacks. To calculate the total amount of pollutant emissions, devices for measuring flue gas flow rate and pollutant concentration are typically installed on the flues, chimneys, or exhaust stacks.

[0003] CEMS (Continuous Emission Monitoring System) can continuously collect, analyze, record, and transmit emission data 24 hours a day, providing a scientific basis for environmental supervision and corporate compliance. CEMS refers to a device that continuously monitors the concentration and total emissions of gaseous pollutants and particulate matter from air pollution sources and transmits the information to the relevant authorities in real time. It is also known as an "automatic flue gas monitoring system," "continuous emission monitoring system," or "online flue gas monitoring system." CEMS consists of a gaseous pollutant monitoring subsystem, a particulate matter monitoring subsystem, a flue gas parameter monitoring subsystem, and a data acquisition, processing, and communication subsystem. The gaseous pollutant monitoring subsystem is mainly used to monitor the concentration and total emissions of gaseous pollutants such as SO2, NOx, and CO2; the particulate matter monitoring subsystem is mainly used to monitor the concentration and total emissions of particulate matter; the flue gas parameter monitoring subsystem is mainly used to measure flue gas velocity, temperature, pressure, oxygen content, and humidity, for the purpose of total emission calculation and concentration conversion; the data acquisition, processing, and communication subsystem consists of a data acquisition unit and a computer system, which collects various parameters in real time, generates dry-basis, wet-basis, and converted concentrations for each concentration value, generates daily, monthly, and annual cumulative emissions, compensates for lost data, and transmits reports to the competent authority in real time. Particulate matter testing has evolved from cross-flue opacity dust meters and beta-ray dust meters to insertion-type backscattering infrared or laser dust meters, as well as forward-scattering, side-scattering, and electrostatic dust meters. Depending on the sampling method, CEMS is mainly divided into direct measurement, extraction measurement, and remote sensing measurement.

[0004] Currently, most CEMS used in actual operation to monitor the concentration of gaseous pollutants such as SO2, NOx, and CO2 are extraction-type measurements. Direct extraction CEMS refers to sampling and gas delivery systems where flue gas passes through a front-end filter and a sampling tube and gas delivery tube equipped with heating and insulation devices to prevent moisture in the flue gas from condensing in the pipeline. The overall temperature is controlled between 120 and 220°C, and a negative pressure sampling method is used. If air leaks during the sampling process, it will lead to lower than expected concentration values ​​of gaseous pollutants such as SO2, NOx, and CO2. Although this does not affect the specific concentration values ​​of pollutants under a certain baseline oxygen level, it will lead to an underestimation of the total pollutant count.

[0005] In the field of carbon emission monitoring technology, accurate measurement of flue gas flow rate and flue gas CO2 concentration is required. The product of these two values ​​represents the total carbon emissions. If air leakage in the CEMS sampling system leads to a lower measured CO2 concentration, it will further result in an underestimation of the total carbon emissions, thus affecting the fairness of carbon emission trading. For negative pressure sampling systems, air leakage can be common, and small leaks are difficult to detect. Therefore, there is an urgent need to develop a technology that can determine online in real time whether a CEMS sampling system is leaking even trace amounts of air.

[0006] In addition, CO2 emission monitoring from stationary sources is still in the pilot stage. When CO2 concentration meter data is abnormal, it is sometimes difficult for staff to identify the problem. They can only discover it afterward by comparing it with manually calculated data or with reference meters. This has affected the accuracy of carbon emission measurement for a period of time, causing great trouble for both the main body of carbon emission and the regulatory agencies. Summary of the Invention

[0007] This invention provides a method and system for improving the accuracy and reliability of CO2 concentration measurement in raw flue gas. By comparing the wet-based oxygen concentration at the front and back ends of the CEMS sampling system through homogeneous monitoring, the system can online real-time identify and calibrate whether the CEMS sampling system is leaking air. This overcomes the technical problem of inaccurate carbon emission calculation caused by air leakage during the sampling and measurement process. The method is real-time, efficient, highly accurate, and simple.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0009] A method for improving the accuracy and reliability of CO2 concentration measurement in raw flue gas involves calibrating the measured CO2 concentration C2 in the raw flue gas using the difference between atmospheric oxygen concentration C4 and the oxygen concentration C1 measured inside the flue, and the difference between atmospheric oxygen concentration C4 and the oxygen concentration C3 measured outside the flue. This calibrates the actual CO2 concentration C in the raw flue gas.

[0010] If C3 > C1, it indicates that there is a leak.

[0011] The above-mentioned method for improving the accuracy and reliability of CO2 concentration measurement in raw flue gas utilizes the in-situ oxygen correction method to enhance the reliability and accuracy of carbon dioxide concentration measurement in raw flue gas. It solves the technical problem of inaccurate calculation of total carbon emissions caused by gas leakage during the sampling and measurement process in carbon emission monitoring. The method is simple, accurate, and efficient.

[0012] This application can be combined with existing automation control technology to achieve online real-time automatic calibration.

[0013] To further improve the accuracy of carbon emission accounting, the measured CO2 concentration C2 in the raw flue gas is calibrated using the ratio of the difference between the atmospheric oxygen concentration C4 and the oxygen concentration C1 measured inside the flue gas to the difference between the atmospheric oxygen concentration C4 and the oxygen concentration C3 measured outside the flue gas. This calibrates the actual CO2 concentration C in the raw flue gas, i.e., C = C2 × (C4 - C1) / (C4 - C3). The aforementioned method is simple, efficient, and accurate.

[0014] To improve the accuracy of CO2 concentration calibration, the distance between the gas sampling location for measuring oxygen concentration C1 and the gas sampling location for measuring oxygen concentration C3 shall not exceed 1.0 meter.

[0015] To facilitate installation and improve the accuracy of CO2 concentration calibration, the angle between the gas sampling angle for measuring oxygen concentration C1 and the gas sampling angle for measuring oxygen concentration C3 is 30-60°. More preferably, the angle between the gas sampling angle for measuring oxygen concentration C1 and the gas sampling angle for measuring oxygen concentration C3 is 40-50°. More preferably, it is 45°.

[0016] A system for improving the accuracy and reliability of CO2 concentration measurement in raw flue gas includes at least one oxygen meter and one CO2 / O2 concentration meter; the oxygen meter and the CO2 / O2 concentration meter are respectively installed on the raw flue and both take samples in the raw flue;

[0017] The analysis chamber of the oxygen sensor element of the oxygen meter is located inside the flue or near the flue wall; when the analysis chamber of the oxygen sensor element of the oxygen meter is located near the flue wall, there is no leakage in the sampling gas path of the oxygen meter, that is, there are no leakable joints in the sampling gas path.

[0018] The analysis chamber of the CO2 / O2 concentration meter is located outside the flue, and the CO2 sensing element and the O2 sensing element share the same analysis chamber; the CO2 / O2 concentration meter is based on hot and wet sampling analysis;

[0019] The oxygen meter reading is recorded as C1, the CO2 concentration measured by the CO2 / O2 concentration meter is recorded as C2, the O2 concentration is recorded as C3, and the atmospheric oxygen concentration is recorded as C4. The difference between the atmospheric oxygen concentration C4 and the oxygen concentration C1 measured in the original flue gas inside the flue, and the difference between the atmospheric oxygen concentration C4 and the oxygen concentration C3 measured in the original flue gas outside the flue, is used to calibrate the CO2 concentration C2 in the original flue gas, thus obtaining the actual CO2 concentration C in the original flue gas.

[0020] The term "near the flue wall" refers to a location located outside the flue wall and at a distance of no more than 1.0m from the outer wall of the flue.

[0021] If C3 > C1, it indicates that there is a leak in the CO2 / O2 concentration meter sampling measurement.

[0022] To further simplify the operation and ensure the accuracy of the calibration test, the actual concentration of CO2 in the raw flue gas is C = C2 × (C4 - C1) / (C4 - C3).

[0023] To improve the accuracy of CO2 concentration calibration, the distance between the gas sampling point of the oxygen meter and the gas sampling point of the CO2 / O2 concentration meter should not exceed 1.0 meter.

[0024] To facilitate installation and improve the accuracy of CO2 concentration calibration, the angle between the gas sampling angle for measuring oxygen concentration C1 and the gas sampling angle for measuring oxygen concentration C3 is 30-60°. More preferably, the angle between the gas sampling angle for measuring oxygen concentration C1 and the gas sampling angle for measuring oxygen concentration C3 is 40-50°. More preferably, it is 45°.

[0025] To further improve the accuracy of CO2 concentration calibration, preferably, the analysis chamber of the oxygen sensor element of the oxygen meter is located inside the flue, with a range of 0-25%; and / or, preferably, both the CO2 and O2 concentration meters are based on the principle of tunable semiconductor laser absorption spectroscopy (TDLAS), with a CO2 concentration range of 0-20% and an O2 concentration range of 0-25%.

[0026] Any techniques not mentioned in this invention are based on existing technologies.

[0027] This invention provides a method and system for improving the accuracy and reliability of CO2 concentration measurement in raw flue gas. By comparing the wet-based oxygen concentration at the front and back ends of the CEMS sampling system through homogeneous monitoring, it enables online real-time identification and calibration of whether the CEMS sampling system is leaking air, thereby improving the accuracy of CO2 monitoring and overcoming the technical problem of inaccurate carbon emission calculation caused by air leakage during the sampling and measurement process. The method is simple, accurate, low-cost, and easy to promote in industry. Attached Figure Description

[0028] Figure 1This is a schematic diagram of the system (installed in a vertical flue) for improving the accuracy and reliability of CO2 concentration measurement in flue gas according to the present invention.

[0029] Figure 2 This is a schematic diagram of the system (installed in a horizontal flue) for improving the accuracy and reliability of CO2 concentration measurement in raw flue gas according to the present invention.

[0030] In the diagram, 1 represents the original flue, 2 represents the oxygen meter, and 3 represents the CO2 / O2 concentration meter. Detailed Implementation

[0031] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0032] Example 1

[0033] A method for improving the accuracy and reliability of CO2 concentration measurement in raw flue gas involves calibrating the measured CO2 concentration C2 in the raw flue gas using the difference between atmospheric oxygen concentration C4 and the oxygen concentration C1 measured inside the flue gas, and the difference between atmospheric oxygen concentration C4 and the oxygen concentration C3 measured outside the flue gas, to obtain the actual CO2 concentration C in the raw flue gas. Specifically, in this example, the ratio of the difference between atmospheric oxygen concentration C4 and the oxygen concentration C1 measured inside the flue gas to the difference between atmospheric oxygen concentration C4 and the oxygen concentration C3 measured outside the flue gas is used to calibrate the measured CO2 concentration C2 in the raw flue gas, thus obtaining the actual CO2 concentration C in the raw flue gas, i.e., C = C2 × (C4 - C1) / (C4 - C3).

[0034] In carbon emission monitoring technology, CO2 concentration measurement and oxygen concentration are negatively correlated, and their sum tends to a constant value. Therefore, by reliably and accurately monitoring oxygen levels, the accuracy of CO2 concentration monitoring can be verified, solving the technical problem of inaccurate calculation of total carbon emissions due to gas leakage. This method is simple, efficient, and accurate.

[0035] Example 2

[0036] Based on Example 1, the following improvements were made: To improve the accuracy of CO2 concentration calibration, the distance between the gas sampling positions for measuring oxygen concentration C1 and C3 does not exceed 1.0 meter. For ease of installation and to further improve the accuracy of CO2 concentration calibration, the angle between the gas sampling angles for measuring oxygen concentration C1 and C3 is 30-60°. In this example, the distance between the gas sampling positions for measuring oxygen concentration C1 and C3 is 30 cm, and the angle between the gas sampling angles for measuring oxygen concentration C1 and C3 is 45°.

[0037] Example 3

[0038] A system for improving the accuracy and reliability of CO2 concentration measurement in raw flue gas includes at least one oxygen meter and one CO2 / O2 concentration meter; the oxygen meter and CO2 / O2 concentration meter are respectively installed on the raw flue gas duct and both take samples in the raw flue gas duct; such as Figure 1-2 As shown, the oxygen meter and CO2 / O2 concentration meter can be installed in either the vertical or horizontal section of the original flue.

[0039] The analytical gas chamber of the oxygen sensor element of the oxygen meter is located inside or near the flue wall; when the analytical gas chamber of the oxygen sensor element of the oxygen meter is located near the flue wall, there is no leakage in the sampling gas path of the oxygen meter.

[0040] The analysis chamber of the CO2 / O2 concentration meter is located outside the flue, and the CO2 sensing element and the O2 sensing element share the same analysis chamber; the CO2 / O2 concentration meter is based on hot and wet sampling analysis;

[0041] The oxygen meter reading is recorded as C1, the CO2 concentration measured by the CO2 / O2 concentration meter is recorded as C2, the O2 concentration is recorded as C3, and the atmospheric oxygen concentration is recorded as C4. The difference between the atmospheric oxygen concentration C4 and the oxygen concentration C1 measured in the original flue gas inside the flue, and the difference between the atmospheric oxygen concentration C4 and the oxygen concentration C3 measured outside the flue gas, is used to calibrate the CO2 concentration C2 in the original flue gas to obtain the actual CO2 concentration C in the original flue gas. The actual CO2 concentration C in the original flue gas is C2 × (C4 - C1) / (C4 - C3).

[0042] Example 4

[0043] Based on Example 3, the following improvements were made: To improve the accuracy of CO2 concentration calibration, the distance between the gas sampling positions for measuring oxygen concentration C1 and oxygen concentration C3 does not exceed 1.0 meter. To facilitate installation and improve the accuracy of CO2 concentration calibration, the angle between the gas sampling angles for measuring oxygen concentration C1 and oxygen concentration C3 is 30-60°. In this example, the distance between the gas sampling positions for measuring oxygen concentration C1 and oxygen concentration C3 is 30 cm, and the angle between the gas sampling angles for measuring oxygen concentration C1 and oxygen concentration C3 is 45°.

[0044] To further improve the accuracy of CO2 concentration calibration, in this example, the oxygen sensor of the oxygen meter is located inside the flue, with a range of 0-25%. An S-2000 series zirconia oxygen analyzer was used, and the measured oxygen concentration in the original flue gas was 7.12%. Both the CO2 and O2 concentration meters are based on the Tunable Semiconductor Laser Absorption Spectroscopy (TDLAS) principle, with CO2 concentration ranges of 0-20% and O2 concentration ranges of 0-25%. The model used in this example is XH-C800. To improve reliability and maintainability, the measuring chamber of the CO2 / O2 concentration meter is located outside the flue. Due to a possible minor leak at the intermediate transition joint, the measured CO2 concentration was 12.89%, and the O2 concentration was 7.33%. The local atmospheric oxygen concentration is 20.69%. Under these conditions, the actual CO2 concentration in the flue is 12.89% × (20.69% - 7.12%) / (20.69% - 7.33%) = 13.09% (the actual measurement by a third-party testing agency using a calibrated handheld CO2 concentration meter is 13.07%, with a relative deviation of only 0.15%). If the actual value of the CO2 / O2 concentration meter is used to calculate carbon emissions, the carbon emissions will be underreported by 1.55% (without calibration, this is equivalent to illegally emitting greenhouse gases, affecting carbon trading fees by millions for a 600MW coal-fired unit). Therefore, using the method of this invention to measure CO2 concentration in the flue can maximize the authenticity and accuracy of the measurement data and significantly reduce the possibility of "cheating" during the measurement process.

Claims

1. A method for improving the accuracy and reliability of CO2 concentration measurement in raw flue gas, characterized in that: The measured CO2 concentration C2 in the original flue gas is calibrated by using the difference between the atmospheric oxygen concentration C4 and the oxygen concentration C1 in the original flue gas measured inside the flue, and the difference between the atmospheric oxygen concentration C4 and the oxygen concentration C3 in the original flue gas measured outside the flue, so as to obtain the actual CO2 concentration C in the original flue gas.

2. The method for improving the accuracy and reliability of CO2 concentration measurement in raw flue gas according to claim 1, characterized in that: The measured CO2 concentration C2 in the original flue gas is calibrated by using the ratio of the difference between the atmospheric oxygen concentration C4 and the oxygen concentration C1 in the original flue gas measured inside the flue gas to the difference between the atmospheric oxygen concentration C4 and the oxygen concentration C3 in the original flue gas measured outside the flue gas. The actual CO2 concentration C in the original flue gas is then obtained, i.e., C = C2 × (C4 - C1) / (C4 - C3).

3. The method for improving the accuracy and reliability of CO2 concentration measurement in raw flue gas according to claim 1 or 2, characterized in that: The distance between the gas sampling location for measuring oxygen concentration C1 and the gas sampling location for measuring oxygen concentration C3 shall not exceed 1.0 meter.

4. The method for improving the accuracy and reliability of CO2 concentration measurement in raw flue gas according to claim 1 or 2, characterized in that: The angle between the gas sampling angle for measuring oxygen concentration C1 and the gas sampling angle for measuring oxygen concentration C3 is 30-60°.

5. The method for improving the accuracy and reliability of CO2 concentration measurement in raw flue gas according to claim 4, characterized in that: The angle between the gas sampling angle for measuring oxygen concentration C1 and the gas sampling angle for measuring oxygen concentration C3 is 40-50°.

6. A system for improving the accuracy and reliability of CO2 concentration measurement in raw flue gas, characterized in that: It includes at least one set of oxygen meter and one set of CO2 / O2 concentration meter; the oxygen meter and CO2 / O2 concentration meter are installed on the original flue and samples are taken in the original flue. The analytical gas chamber of the oxygen sensor element of the oxygen meter is located inside the flue or near the flue wall; when the analytical gas chamber of the oxygen sensor element of the oxygen meter is located near the flue wall, there is no leakage in the sampling gas path of the oxygen meter. The analysis chamber of the CO2 / O2 concentration meter is located outside the flue, and the CO2 sensing element and the O2 sensing element share the same analysis chamber; the CO2 / O2 concentration meter is based on hot and wet sampling analysis; The oxygen meter reading is recorded as C1, the CO2 concentration measured by the CO2 / O2 concentration meter is recorded as C2, the O2 concentration is recorded as C3, and the atmospheric oxygen concentration is recorded as C4. The difference between the atmospheric oxygen concentration C4 and the oxygen concentration C1 measured in the original flue gas inside the flue, and the difference between the atmospheric oxygen concentration C4 and the oxygen concentration C3 measured in the original flue gas outside the flue, is used to calibrate the CO2 concentration C2 in the original flue gas, thus obtaining the actual CO2 concentration C in the original flue gas.

7. The system for improving the accuracy and reliability of CO2 concentration measurement in raw flue gas according to claim 6, characterized in that: The actual concentration of CO2 in the original flue gas is C = C2 × (C4 - C1) / (C4 - C3).

8. The system for improving the accuracy and reliability of CO2 concentration measurement in raw flue gas according to claim 6 or 7, characterized in that: The distance between the gas sampling point of the oxygen meter and the gas sampling point of the CO2 / O2 concentration meter shall not exceed 1.0 meter.

9. The system for improving the accuracy and reliability of CO2 concentration measurement in raw flue gas according to claim 6 or 7, characterized in that: The angle between the gas sampling angle for measuring oxygen concentration C1 and the gas sampling angle for measuring oxygen concentration C3 is 30-60°.

10. The system for improving the accuracy and reliability of CO2 concentration measurement in raw flue gas according to claim 6 or 7, characterized in that: The oxygen meter's oxygen sensing element has its analysis chamber located inside the flue, with a range of 0-25%; and / or, the CO2 / O2 concentration meters are based on the principle of tunable semiconductor laser absorption spectroscopy, with CO2 concentration ranges of 0-20% and O2 concentration ranges of 0-25%.

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