Method for measuring concentration of CO2 and CH4 in water through bubbling

Abstract

According to the method for measuring the concentration of CO2 and CH4 in water through bubbling, a device gas outlet pipe is connected with a gas inlet end of a drying bottle, a gas outlet end of the drying bottle is connected with a gas inlet end of a gas detector, and a gas outlet end of the gas detector is connected with a gas inlet pipe of a water sample measuring bottle. And starting the gas detector, and recording the initial concentration value of the gas detector and the concentration curve of CO2 and CH4 in the gas from the initial state to the equilibrium state. The concentration of CO2 and CH4 in water is obtained by fitting the relationship between the concentration of CO2 and CH4 in the gas from the bubbling and the concentration of CO2 and CH4 in water when the concentration of CO2 and CH4 in water is balanced, the Henry constant at the measurement temperature and the concentration curve of CO2 and CH4 in the gas detector. The measuring method is used for calculating the concentration of CO2 and CH4 in water, the calculation process is simple, the calculation result is accurate, the concentration of CO2 and CH4 in a certain water sample can be continuously monitored and analyzed for a long time, a basic basis is provided for subsequent further treatment of the water sample to be measured, and the measuring method has great practical significance.

Description

Technical Field

[0001] The present invention relates to a nuclear radiation detection technology, in particular to a method for measuring the concentrations of CO2 and CH4 in water by bubbling. Background Art

[0002] Carbon dioxide (CO2) and methane (CH4) in water bodies are important sources of greenhouse gases. The greenhouse effect of methane is 21 - 23 times that of carbon dioxide. The contributions of CO2 and CH4 to the global greenhouse effect are significant. Accurately measuring the concentrations of these two gases in water helps to study the carbon cycle and estimate the budget of global greenhouse gases, thereby better understanding and addressing climate change. In addition, dissolved CO2 and CH4 in water can affect the acid-base balance and dissolved oxygen content of the water body, and further affect the living environment of aquatic organisms. Therefore, monitoring the concentrations of these two gases in water is also of great significance for evaluating the health status of water bodies, preventing water eutrophication and ecological disasters.

[0003] Common methods for measuring CO2 and CH4 include gas chromatography, mass spectrometry, and optical sensing technology measurement. Gas chromatography is one of the traditional methods for measuring the concentration of dissolved gases in water. This method releases the gas in the water sample through a gas-liquid equilibrium device and then uses a gas chromatograph for separation and detection. It has high sensitivity and accuracy, but the operation process is relatively complex and requires professional equipment and technical personnel. Mass spectrometry analyzes the gas components in the sample through techniques such as ionization and dispersion. A dissolved methane detector in water based on mass spectrometry technology has been commercialized, with the characteristics of high sensitivity and high resolution, and can detect gas concentrations at trace levels. Optical sensing technology includes tunable diode laser absorption spectroscopy, off-axis integrated cavity output spectroscopy, etc., which measures the gas concentration by utilizing the absorption characteristics of gas molecules for light of specific wavelengths, with high sensitivity and high stability, and can achieve high detection accuracy within a relatively short average time. However, the above methods all require relatively high costs and complex data processing. Therefore, how to achieve simple and low-cost measurement of the concentrations of CO2 and CH4 in water is very important and necessary. Summary of the Invention

[0004] The object of the present invention is to overcome the above-mentioned deficiencies of the prior art and provide a method for measuring the concentrations of CO2 and CH4 in water by bubbling.

[0005] The technical solution of the present invention is: a method for measuring the concentrations of CO2 and CH4 in water by bubbling. The method includes a measurement process and a calculation process. The bubbling measurement device includes a water sample measurement bottle, a bottle cap, an air inlet pipe sleeve, an air outlet pipe sleeve, an air inlet pipe, an air outlet pipe, a drying bottle, and a gas detector. The air inlet pipe sleeve and the air outlet pipe sleeve are respectively installed on the bottle cap. The air inlet pipe is inserted into the air inlet pipe sleeve, and the air outlet pipe is inserted into the air outlet pipe sleeve. The air outlet pipe is connected to the air inlet end of the drying bottle through a hose. The air outlet end of the drying bottle is connected to the air inlet end of the gas detector through a hose. The air outlet end of the gas detector is connected to the air inlet pipe of the water sample measurement bottle through a hose.

[0006] The specific steps of the measurement process and the calculation process are as follows: I. Measurement process Take a certain amount of water sample to be measured and pour it into the water sample measurement bottle, and tighten the bottle cap. Set the air outlet of the air inlet pipe in the water sample to be measured and close to the bottom of the water sample measurement bottle, and the air inlet of the air outlet pipe is located above the liquid level of the water sample to be measured.

[0007] Start the pump of the gas detector. Under the action of the pump, the air containing CO2 and CH4 in the water sample bubbles in the water sample measurement bottle. Thus, the air enters the drying bottle through the air outlet pipe for drying, and then enters the gas detector. Record the concentration value of the gas detector at this time. Assuming that the gas concentration in the water sample is uniform, when the reading of the gas detector tends to be stable, the concentrations of CO2 and CH4 in the bubbles coming out of the water sample measurement bottle reach equilibrium with the concentrations of CO2 and CH4 in the water in the water sample measurement bottle. Record the concentration curves of CO2 and CH4 in the gas measured by the gas detector from startup to the equilibrium state.

[0008] II. Calculation process Let the concentrations of CO2 and CH4 in the water in the water sample measurement bottle be C 1 (t) , the concentrations of CO2 and CH4 in the gas path of the device for measuring CO2 and CH4 in water by the bubbling method be C 2 (t) , and the concentrations of CO2 and CH4 in the bubbles coming out of the water sample measurement bottle be C(t) . When the concentrations of CO2 and CH4 in the bubbles coming out have reached equilibrium with the concentrations of CO2 and CH4 in the water, considering gas leakage and ignoring the water temperature change in a short time, there is the following calculation expression: (1) Where, V 1 is the volume of the water sample to be measured in the water sample measurement bottle, with the unit of m 3 ; V 2 is the volume of the gas path, with the unit of m 3 ; Lis the flow rate of the gas detector pump, fixed at 0.5 L / min; l is the leakage rate, with the unit of m / s; k are the concentrations of CO2 and CH4 coming out of the bubble under the equilibrium state C(t) and the concentrations of CO2 and CH4 in the device gas path C 1 (t) The ratio of them is a dimensionless quantity.

[0009] From the definition of Henry's constant H k and the gas partial pressure calculation formula, the following expression is obtained: (2) (3) Among them, P are the partial pressures of CO2 and CH4 gases in the mixed gas at the top of the water sample measurement bottle; P 总 is the total pressure of the mixed gas at the top of the water sample measurement bottle, generally 1 atm.

[0010] Substitute formula (3) into formula (2) and solve to obtain the following expression: (4) Therefore, from formula (4), it is known that the concentrations of CO2 and CH4 coming out of the bubble under the equilibrium state C(t) and the concentrations of CO2 and CH4 in the device gas path C 2 (t) The ratio of k is calculated through the following formula: (5) Among them, the Henry's constants of gases CO2 and CH4 H k are coefficients related to temperature. Substitute the temperature-related Henry's constant into formula (5) to solve for k value.

[0011] Let a be the initial concentrations of CO2 and CH4 in the gas path, with the unit of mol / m 3 ; b be the initial concentrations of CO2 and CH4 in the bubble of the water sample measurement bottle, with the unit of mol / m 3 ; Substitute the two initial values into formula (1) to obtain the solution of the equation as: (6) Among them, , .

[0012] Substitute the k value calculated by formula (5) into formula (6), and then fit the measured CO2 and CH4 concentration curves in the gas using formula (6), and the CO2 and CH4 concentrations in the water can be obtained.

[0013] A further technical solution of the present invention is that calcium chloride powder is placed in the drying bottle; the gas detector selects the JK40-M2-D detector.

[0014] The present invention has the following advantages compared with the prior art: 1. The device for measuring the CO2 and CH4 concentrations in water provided by the present invention has a simple and portable structure, is convenient to operate, and has a lower cost than the existing measurement methods.

[0015] 2. By calculating the CO2 and CH4 concentrations in water through the measurement method provided by the present invention, the calculation process is simple, the calculation results are accurate, and the CO2 and CH4 concentrations in different water samples can be monitored and analyzed continuously for a long time.

[0016] The following further describes the detailed structure of the present invention in conjunction with the drawings and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic structural diagram of the bubbling method for measuring the CO2 and CH4 concentrations in water of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0018] Example 1. As Figure 1 shown, a method for measuring the CO2 and CH4 concentrations in water by bubbling, the method includes a measurement process and a calculation process, and is based on the existing bubbling method measurement device.

[0019] The bubbling method measurement device includes a water sample measurement bottle 1, a bottle cap 2, an air inlet pipe sleeve 3, an air outlet pipe sleeve 4, an air inlet pipe 5, an air outlet pipe 6, a drying bottle 7 and a gas detector 8. Substances for drying gas, such as calcium chloride powder, etc., are placed in the drying bottle 7. The gas detector 8 selects the JK40-M2-D instrument. The air inlet pipe sleeve 3 and the air outlet pipe sleeve 4 are respectively installed on the bottle cap 2, the air inlet pipe 5 is inserted on the air inlet pipe sleeve 3, the air outlet pipe 6 is inserted on the air outlet pipe sleeve 4, the air outlet pipe 6 is connected to the air inlet end of the drying bottle 7 through a hose, the air outlet end of the drying bottle 7 is connected to the air inlet end of the gas detector 8 through a hose, and the air outlet end of the gas detector 8 is connected to the air inlet pipe 5 of the water sample measurement bottle 1 through a hose.

[0020] The specific steps of the measurement process and the calculation process are as follows: 1. Measurement process Pour a certain amount of the water sample to be measured into the water sample measuring bottle 1, and tightly close the bottle cap 2. Set the air outlet of the intake pipe 5 to be inside the water sample to be measured and close to the bottom of the water sample measuring bottle 1, and the air inlet of the outlet pipe 6 to be located above the liquid level of the water sample to be measured.

[0021] Start the pump of the gas detector 8. Under the action of the pump, the air containing CO2 and CH4 in the water sample bubbles in the water sample measuring bottle 1. Thus, the air enters the drying bottle 7 through the outlet pipe 6 for drying, and then enters the gas detector 8. Record the concentration value of the gas detector 8 at this time. Assuming that the gas concentration in the water sample is uniform, when the reading of the gas detector 8 tends to be stable, the concentrations of CO2 and CH4 in the bubbles coming out of the water sample measuring bottle 1 reach equilibrium with the concentrations of CO2 and CH4 in the water in the water sample measuring bottle 1. Record the concentration curves of CO2 and CH4 in the gas measured by the gas detector 8 from startup to the equilibrium state.

[0022] II. Calculation process Let the concentrations of CO2 and CH4 in the water in the water sample measuring bottle 1 be C 1 (t) , and the concentrations of CO2 and CH4 in the gas path of the device for measuring CO2 and CH4 in water by the bubbling method be C 2 (t) , and the concentrations of CO2 and CH4 in the bubbles coming out of the water sample measuring bottle 1 be C(t) . When the concentrations of CO2 and CH4 in the bubbles coming out have reached equilibrium with the concentrations of CO2 and CH4 in the water, considering gas leakage and ignoring the short-term water temperature change, there are the following calculation expressions: (1) Among them, V 1 is the volume of the water sample to be measured in the water sample measuring bottle 1, with the unit of m 3 ; V 2 is the volume of the gas path, with the unit of m 3 ; L is the flow rate of the pump of the gas detector 8, which is fixed at 0.5 L / min; l is the leakage rate, with the unit of m / s; k is the concentrations of CO2 and CH4 in the bubbles coming out at the equilibrium state C(t) and the concentrations of CO2 and CH4 in the gas path of the device C 1 (t) the ratio of, which is a dimensionless quantity.

[0023] From the definition of the Henry's constant H k and the gas partial pressure calculation formula, the following expression is obtained: (2) (3) Among them, P is the partial pressure of CO2 and CH4 in the mixed gas at the top of the water sample measurement bottle 1; P 总 is the total pressure of the mixed gas at the top of the water sample measurement bottle 1, generally 1 atm.

[0024] Substitute formula (3) into formula (2) and solve to obtain the following expression: (4) Therefore, from formula (4), it is known that the concentrations of CO2 and CH4 coming out of the bubbles under the equilibrium state C(t) and the concentrations of CO2 and CH4 in the device gas path C 2 (t) The ratio of k , is calculated by the following formula: (5) Among them, the Henry's constants of the gases CO2 and CH4 H k is a coefficient related to temperature. Specific data can be obtained by referring to relevant literature. For example, at room temperature of 25 °C, the theoretical value of the Henry's constant of carbon dioxide is 0.0345 - 0.0399 M atm -1 , substitute the temperature-related Henry's constant into formula (5) and solve for k value.

[0025] Let a be the initial concentrations of CO2 and CH4 in the gas path, that is C 2 (0) , with the unit of mol / m 3 , and is obtained by reading the data through the connected gas detector 8, that is, the data of the gas detector 8 recorded after startup; b is the initial concentration of CO2 and CH4 in the bubbles of the water sample measurement bottle 1, that is C1(0), with the unit of mol / m 3 . Substitute the two initial values into formula (1) to obtain the solution of the equation as: (6) Among them, , .

[0026] Substitute the k value calculated by formula (5) into formula (6), and then fit the measured concentration curves of CO2 and CH4 in the gas using formula (6), that is, the concentrations of CO2 and CH4 in the water are obtained.

Claims

1. A method for measuring the concentrations of CO2 and CH4 in water by bubbling. This method includes a measurement process and a calculation process. The bubbling measurement device includes a water sample measurement bottle, a bottle cap, an air inlet pipe sleeve, an air outlet pipe sleeve, an air inlet pipe, an air outlet pipe, a drying bottle, and a gas detector. The air inlet pipe sleeve and the air outlet pipe sleeve are respectively installed on the bottle cap. The air inlet pipe is inserted into the air inlet pipe sleeve, and the air outlet pipe is inserted into the air outlet pipe sleeve. The air outlet pipe is connected to the air inlet end of the drying bottle through a hose. The air outlet end of the drying bottle is connected to the air inlet end of the gas detector through a hose. The air outlet end of the gas detector is connected to the air inlet pipe of the water sample measurement bottle through a hose. The features are as follows: The specific steps of the measurement process and the calculation process are as follows: I. Measurement process Take a certain amount of the water sample to be measured and pour it into the water sample measurement bottle, and tighten the bottle cap. Set the air outlet of the air inlet pipe in the water sample to be measured and close to the bottom of the water sample measurement bottle, and the air inlet of the air outlet pipe is located above the liquid level of the water sample to be measured. Start the pump of the gas detector. Under the action of the pump, the air containing CO2 and CH4 in the water sample bubbles in the water sample measurement bottle. Thus, the air enters the drying bottle through the air outlet pipe for drying, and then enters the gas detector. Record the concentration value of the gas detector at this time. Assume that the gas concentration in the water sample is uniform. When the reading of the gas detector tends to be stable, the concentrations of CO2 and CH4 in the bubbles coming out of the water sample measurement bottle reach equilibrium with the concentrations of CO2 and CH4 in the water in the water sample measurement bottle. Record the concentration curves of CO2 and CH4 in the gas measured by the gas detector from startup to the equilibrium state. II. Calculation process Let the concentrations of CO2 and CH4 in the water in the water sample measurement bottle be C 1 (t) , and the concentrations of CO2 and CH4 in the gas path of the device for measuring CO2 and CH4 in water by the bubbling method be C 2 (t) , and the concentrations of CO2 and CH4 coming out of the bubbling in the water sample measurement bottle be C(t) . When the concentrations of CO2 and CH4 coming out of the bubbling have reached equilibrium with the concentrations of CO2 and CH4 in the water, considering gas leakage and ignoring the water temperature change in a short period of time, there is the following calculation expression: （1） Among them, V 1 is the volume of the water sample to be measured in the water sample measuring bottle, with the unit of m 3 ; V 2 is the gas path volume, with the unit of m 3 ; L is the flow rate of the gas detector pump, fixed at 0.5 L / min; l is the leakage rate, with the unit of m / s; k is the concentrations of CO2 and CH4 coming out of the bubble in the equilibrium state C(t) and the concentrations of CO2 and CH4 in the device gas path C 1 (t) The ratio of them is a dimensionless quantity; From Henry's constant H k and the gas partial pressure calculation formula, the following expression is obtained: （2） （3） wherein, P is the partial pressure of CO2 and CH4 gases in the mixed gas at the top of the water sample measuring bottle; P 总 is the total pressure of the mixed gas at the top of the water sample measuring bottle, generally 1 atm; Substitute formula (3) into formula (2) to solve and obtain the following expression: （4） Therefore, from Equation (4), the concentrations of CO2 and CH4 coming out of the bubble in the equilibrium state are known. C(t) The ratio of the concentrations of CO2 and CH4 in the gas circuit of the device C 2 (t) is k , and is calculated by the following formula: （5） Among them, the Henry's constants of gases CO2 and CH4 H k are coefficients related to temperature. Substitute the temperature-related Henry's constant into Equation (5) to solve for k the value; Let a be the initial concentrations of CO2 and CH4 in the gas path, with the unit of mol / m 3 ; b be the initial concentrations of CO2 and CH4 in the bubbling of the water sample measuring bottle, with the unit of mol / m 3 ; Substituting the two initial values into formula (1), the solution of the equation is obtained as follows: （6） Among them, , ； Substitute the k value calculated by formula (5) into formula (6), and then fit the measured concentration curves of CO2 and CH4 in the gas using formula (6), and the concentrations of CO2 and CH4 in the water can be obtained.

2. The method for measuring the concentrations of CO2 and CH4 in water by bubbling according to claim 1, wherein: Calcium chloride powder is placed in the drying bottle. The gas detector selects the JK40-M2-D detector.

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