CN107677699A - It is a kind of under high conditions in mirror surface dew point method detection gas micro-water content method - Google Patents

Abstract

The invention discloses it is a kind of under high conditions in mirror surface dew point method detection gas micro-water content method, comprise the following steps, (1) test equipment temperature T₁, the atmospheric pressure P of test site₁；(2) start dew point hygrometer, be passed through nitrogen gas drying system, (3) test sample gas, obtain dew point T₂, measure at least 3 times, untill numerical value is basicly stable；(4) the saturated vapor pressure table of ice is used, checks in dew point T₂Corresponding water vapour pressure P₂；(5) pressure correction of water vapor pressure and sulfur hexafluoride is returned 20 DEG C, under conditions of 1 atmospheric pressure using updating formula, tries to achieve the micro-water content X in the SF6 of standard state after correction of a final proof₁.The present invention is corrected the test result of dew point hygrometer using the updating formula provided, makes test result more accurate according to the temperature of test equipment and the atmospheric pressure of testing location.

Description

A method for detecting micro-water content in gas by mirror surface dew point method under plateau conditions

technical field

The invention belongs to the technical field of dew point measurement and correction, and in particular relates to a method for detecting micro-water content in gas by mirror surface dew point method under plateau conditions.

Background technique

Dew point meter is an important humidity measurement equipment, widely used in power system SF ₆ dew point detection, air purification and clean room, compressed air drying, steam turbine anti-icing, drying industry, food processing, plastic substrate drying, ammonia production and Purity maintenance and other aspects are currently widely used in high-altitude areas, but the test results of dew point meters in high-altitude areas and low-altitude areas have a large deviation. The method for testing water content with a dew point meter is to divide the vapor pressure of water corresponding to the dew point value by the corresponding atmospheric pressure at 20°C and 1 atmospheric pressure to obtain the water content. But in the plateau environment, the atmospheric pressure decreases, the dew point value decreases, and the partial pressure of water also decreases. However, according to the old calculation method, it is still divided by 1 atmospheric pressure, and the test results will be greatly deviated. If the atmospheric pressure Down to 0.65, the deviation can be as high as 40%. However, there is no literature report on how to detect the true value of the micro-water content in the gas by the mirror dew point method under plateau conditions.

Contents of the invention

Aiming at the deficiencies of the prior art, the invention provides a method for detecting the micro-water content in the gas by the specular dew point method under plateau conditions. The correction calculation method provided by the invention mainly solves the pressure change brought by the plateau environment and the temperature change brought by the environment, and corrects the test deviation when the mirror surface dew point method is used to test the micro-water content. The invention simultaneously corrects the temperature and pressure in the plateau environment, and obtains more accurate results.

The technical scheme of the present invention is as follows: a method for detecting micro-water content in gas by mirror surface dew point method under plateau conditions, comprising the following steps:

Step (1) Test the temperature T ₁ of the equipment under plateau conditions, and test the atmospheric pressure P ₁ of the field environment;

Step (2) start the dew point meter, feed nitrogen drying system;

Step (3) Test the sample gas to obtain the dew point temperature T ₂ ; query the saturated vapor pressure table of ice to obtain the water vapor pressure P _{2 corresponding to the dew point T 2 ;}

Step (4) Correct the water vapor pressure and the pressure of the sample gas under the plateau condition to 20° C. and 1 atmospheric pressure through the correction formula, that is, the micro-water content X ₁ in the sample gas under the standard state;

The correction formula is as follows:

In the formula: X ₁ is the micro-water content in SF6 in the standard state after final correction; P ₂ is the water vapor pressure corresponding to the dew point; R is the ideal gas constant; T ₁ is the equipment temperature; P ₁ is the on-site atmospheric pressure; T ₃ The temperature in the standard state is generally taken as 293.15K.

Further, the equipment temperature T1 in step ( ₁ ) is the surface temperature of the equipment.

Further, in step (2), the dew point is tested more than ₃ times until the dew point temperature T2 is stable, and when calculating the value, the last measured value shall prevail.

Further, the sample gas is SF6 gas.

The features of the present invention are as follows: Since the temperature and pressure of plateau conditions deviate from the conditions of 20°C and 1 atmospheric pressure marked in the industry standard, according to the formula X ₁ =P _{water vapor pressure/} P _{mixed gas} , but the test result of the dew point meter is still water When the vapor pressure is divided by 1 atmosphere, since the value of the denominator changes, the numerator does not change, so a large deviation needs to be corrected. According to the requirements of industry standards, the present invention adopts the correction formula provided by the present invention to simultaneously correct the water vapor pressure and atmospheric pressure to 20°C, and divide them under the condition of 1 atmospheric pressure to obtain the corrected standard water content.

The derivation process of the correction formula is roughly as follows:

Suppose SF6 gas is a mixture of SF6 and water, according to the fitting of a large number of experimental data,

The equation of state for the mixed gas is as follows:

V ₁ is the specific volume of the mixed gas, and the specific volume does not change because the specific volume changes. P ₃ is the pressure value of SF6 gas under standard conditions (20°C) after temperature and pressure correction.

The equation of state for SF6 gas at atmospheric pressure and temperature in the field

The equation of state for SF6 gas at 1 atmosphere and 20°C

Connect the upper and lower formulas together, and calculate the pressure value (P ₃ ) of the SF6 gas under the standard condition (20°C) after temperature and pressure correction.

Finally, divide the water vapor pressure by the corrected pressure of SF6 gas to get the final water content.

Using this correction formula can obtain a more accurate test result of the micro-water content in the sample gas.

Compared with the prior art, the present invention has the following beneficial effects: according to the temperature of the test equipment and the atmospheric pressure of the test site, the present invention uses the given correction formula to correct the test results of the dew point meter, so that the test results are more accurate and the test process is simple , which is convenient for promotion and use.

detailed description

The technical solutions of the present invention will be described in further detail below in conjunction with specific embodiments, but the present invention is not limited to the following technical solutions.

Example 1

Step (1) Test the equipment temperature T ₁ (303.15K) in the Kunming plateau environment, and the atmospheric pressure P ₁ (0.08MPa) at the test site;

Step (2) start the dew point meter, and ventilate the nitrogen drying system;

Step (3) Test the sulfur hexafluoride (SF6) gas sample to obtain the dew point T ₂ (-20.2°C), and measure it at least 3 times until the value is basically stable; check the saturated vapor pressure table of ice to obtain the dew point T ₂ ( -20.2℃) corresponds to the water vapor pressure P ₂ (101.296Pa).

Step (4) Use the correction formula to correct the water vapor pressure and the pressure of sulfur hexafluoride back to 20°C under the condition of 1 atmosphere, and calculate the micro-water content X ₁ in SF6,

The correction formula is as follows, the calculation result of the correction formula is in ppm:

Putting in P ₂ P ₁ T ₁ T ₃ R to calculate the result, the calculated water content should be: 1267.23ppm. The standard water content of this sample is 1260ppm, and the deviation between the calculated value of the present invention and the standard water content is within the range. But now the water content displayed by the equipment is still 1000ppm, the measured value of the instrument is far less than the standard value, and the test method result provided by the present invention is more accurate.

Claims (4)

1. A method of specular dew point method detection of micro-water content in gas under plateau conditions, is characterized in that, comprises the following steps: Step (1) Test the temperature T ₁ of the equipment under plateau conditions, and test the atmospheric pressure P ₁ of the field environment; Step (2) start the dew point meter, feed nitrogen drying system; Step (3) Test the sample gas to obtain the dew point temperature T ₂ ; query the saturated vapor pressure table of ice to obtain the water vapor pressure P _{2 corresponding to the dew point T 2 ;} Step (4) Correct the water vapor pressure and the pressure of the sample gas under the plateau condition to 20° C. and 1 atmospheric pressure through the correction formula, that is, the micro-water content X ₁ in the sample gas under the standard state; The correction formula is as follows: <mrow><msub><mi>X</mi><mn>1</mn></msub><mo>=</mo><mfrac><mrow><msub><mi>P</mi><mn>2</mn></msub><mo>&amp;times;</mo><mrow><mo>(</mo><mfrac><mrow><msub><mi>RT</mo>mi><mn>1</mn></msub></mrow><msub><mi>P</mi><mn>1</mn></msub></mfrac><mo>-</mo><mn>0.0007972</mn><mo>&amp;times;</mo><mo>(</mo><mrow><mfrac><mn>4268</mn><msubsup><mi>T</mi><mn>3</mn><mn>1.6</mn></msubsup></mfrac><mo>+</mo><mfrac><mrow><mn>1.2264</mn><mo>&amp;times;</mo><msup><mn>10</mn><mn>9</mn></msup></mrow><msubsup><mi>T</mi><mn>3</mn><mn>4.2</mn></msubsup></mfrac><mo>-</mo><mfrac><mn>4268</mn><msubsup><mi>T</mi><mn>1</mn><mn>1.6</mn></msubsup></mfrac><mo>-</mo><mfrac><mrow><mn>1.2264</mn><mo>&amp;times;</mo><msup><mn>10</mn><mn>9</mn></msup></mrow><msubsup><mi>T</mi><mn>1</mn><mn>4.2</mn></msubsup></mfrac></mrow><mo>)</mo><mo>)</mo></mrow></mrow><mrow><msub><mi>RT</mi><mn>3</mn></msub></mrow></mfrac><mo>;</mo></mrow> In the formula: X ₁ is the micromoisture content in the SF6 of the standard state after final calibration; P ₂ is the water vapor pressure corresponding to the point; R is the desired gas constant; T ₁ is the equipment temperature; P ₁ is the on-site atmospheric pressure; T ₃ The temperature of the quasi-state is generally taken as 293.15K. 2. the method for micromoisture content in the specular surface dew point method detection gas under plateau conditions as claimed in claim 1, is characterized in that, described equipment temperature T in step (1) ₁ is equipment surface temperature. 3. as claimed in claim 1, under plateau conditions, the mirror surface dew point method detects the method of micromoisture content in the gas, it is characterized in that, in the step (2), the dew point test is more than 3 times, until the dew point temperature T ₂ is stable, calculate the value , the last measured value shall prevail. 4. The method for detecting micro-water content in gas by mirror surface dew point method under plateau conditions as described in any one of claims 1 to 3, wherein the sample gas is SF6 gas.