Carbon dioxide has long been recognized as a colorless, odorless gas. The molecular weight is 44.01, heavier than air, and its gas density is 1.9659/L under standard conditions. -78.5°C Solid carbon dioxide (called dry ice) sublimates into a gaseous state. Carbon dioxide gas is easily soluble in water. At 0°C, volumetric water can dissolve 1.7 volumes of carbon dioxide. At 20°C, I volume of water can dissolve 0.9 volume of carbon dioxide. Easily absorbed by alkali. Measurement of air samples by the CO2 meter showed that the volume of carbon dioxide in fresh air was maintained at 0.08%-0.04%. Carbon dioxide in the atmosphere comes from: fuel combustion, such as boilers, civil furnaces, etc., that use coal, oil, and diesel as fuel to produce carbon dioxide; engine exhaust contains high concentrations of carbon dioxide; biological respiration (including humans, animals, plants) produce carbon dioxide The amount of carbon dioxide in human exhaled breath is as high as 4%; biological fermentation, decomposition. Photosynthesis of greenery plants in the sun absorbs carbon dioxide in the air, thus maintaining the balance of carbon dioxide in the air of nature.
Through the auxiliary detection of air temperature and humidity recorders, the conditions and conditions for the presence of carbon dioxide have been different. For example, the atmospheric content is relatively constant and the concentration is low. Concentrations in the room vary depending on people's activity, generally. .3% or less. The concentration in the exhaled breath is relatively high. At the same time, the humidity in the higher engine exhaust is high and the temperature is also high. In the industrial production process, the concentration and coexisting gas will have a greater range of variation depending on the process conditions. Therefore, when selecting the measurement method, it must be comprehensively considered according to the characteristics of the application conditions and methods in order to achieve accurate results and convenient operation. There are several common methods for measuring carbon dioxide gas.
1. Volume measurement It is a method familiar to everyone and adopts a method. After a certain volume of air is absorbed by the potassium hydroxide solution to reduce carbon dioxide, the volume is reduced, and the amount of carbon dioxide is reduced. The Oxygen gas analyzer is the most commonly used analyzer. It uses different absorption solutions and can also determine the oxygen content in the air. This method does not require standard gas calibration and directly measures the volumetric content of carbon dioxide. When the concentration is low, accuracy is affected due to a large volume measurement error. The measurement takes time.
2. Titration This method is the recommended method for monitoring carbon dioxide in the ambient air. It uses a sand core absorber tube containing a barium hydroxide solution to collect carbon dioxide from the air to form barium carbonate precipitates. In order to increase the carbon dioxide gas absorption efficiency, a small amount of n-butanol is added as a blowing agent. After sampling, the remaining barium hydroxide was back titrated with an oxalic acid standard solution, and the barium hydroxide content in the absorbing solution was titrated as a blank value, and the carbon dioxide content was calculated based on the difference between the blank and the barium hydroxide content in the sample.
3. Infrared absorption method This method is the recommended method for monitoring carbon dioxide in the ambient air. Carbon dioxide has an absorption peak in the 4.3um infrared region. At this wavelength, there is no significant absorption of oxygen, nitrogen, carbon monoxide, and water vapor. Therefore, the infrared absorption method is an ideal method for measuring carbon dioxide in the air. Since the content of carbon dioxide in the air is at least 0.03%, the length of the absorption cell can be a few centimeters. Therefore, the use of infrared absorption principle, can be made into portable air carbon dioxide monitor. Commodity Infrared Absorption The carbon dioxide analyzer uses a wavelength of 4.3 μm as the measuring beam and a 3.9 μm wavelength as the reference beam. The structure of the instrument adopts the single optical path and time dual beam detection method to achieve the purpose of dual optical path. The instrument measurement range is. -1.5% CO2, with a lower detection limit of 0.01%. The instrument is equipped with a small electromagnetic pump that automatically sucks ambient air for measurement. This method is the most convenient and most commonly used method for measuring carbon dioxide in the ambient air. Place the instrument in the environment and measure the carbon dioxide content directly.
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