Carbon dioxide has long been recognized as a colorless, odorless gas. It is heavier than air and its gas density is 1.9659 / L under standard conditions. Carbon dioxide in the atmosphere comes from: fuel combustion, such as boilers, civilian furnaces and other coal, oil, wood fired when burning carbon dioxide; engine exhaust contains high concentrations of carbon dioxide; biological breathing (including humans, animals, plants) produces carbon dioxide Wait. The carbon dioxide content in human exhaled breath is as high as 4%, and the photosynthesis of green leaf plants in the sun can absorb carbon dioxide in the air, thereby maintaining the carbon dioxide concentration in the air in nature.
It has been seen through the auxiliary detection of the air temperature and humidity recorder that the places and conditions where carbon dioxide exists are different, for example: the content in the atmosphere is relatively constant and the concentration is very low. The indoor concentration varies depending on people’s activities and is generally below 0.3%. The concentration in the exhaled breath is relatively high, and at the same time, the concentration in the exhaust gas of the engine with high humidity is high, and the temperature is also high. In the industrial production process, with different process conditions, the concentration and coexisting gases will have a larger range of change. Therefore, when selecting a measurement method, it must be comprehensively considered according to the application conditions and the characteristics of the method to achieve accurate results and convenient operation. There are several common methods for measuring carbon dioxide gas.
- Volume measurement method
It is a method that is familiar and adopted by everyone. After a certain volume of air absorbs carbon dioxide through a potassium hydroxide solution, the volume decreases, and the reduction is the amount of carbon dioxide. Eyeless gas analysis and detection equipment is the most commonly used analyzer. It can also determine the oxygen content in the air at the same time by using different absorption solutions. This method does not require standard gas calibration and directly measures the volumetric content of carbon dioxide. When the concentration is low, the accuracy is affected due to the large volume measurement error.
This method is the recommended method for monitoring carbon dioxide in ambient air. It uses a sand core absorption tube filled with a barium hydroxide solution to collect carbon dioxide in the air and forms a barium carbonate precipitate. In order to increase the absorption efficiency of carbon dioxide gas, a small amount of n-butanol was added as a foaming agent. After sampling, the remaining barium hydroxide was titrated with an oxalic acid standard solution, and the barium hydroxide content in the absorption solution was titrated at the same time. The carbon dioxide content was calculated based on the difference between the blank and the barium hydroxide content in the sample.
- Infrared absorption method
This method is the recommended method for monitoring carbon dioxide in ambient air. Carbon dioxide has an absorption peak in the 4.3um infrared region. At this wavelength, oxygen, nitrogen, carbon monoxide, and water vapor have no obvious absorption. Therefore, the infrared absorption method is an ideal method for measuring carbon dioxide in the air. Because the content of carbon dioxide in the air is at least 0.03%, the length of the absorption tank can be a few centimeters. Therefore, using the infrared absorption principle, a portable carbon dioxide monitor can be made. The commercial infrared absorption method carbon dioxide analyzer uses a 4.3um wavelength as a measuring beam and a 3.9um wavelength as a reference beam. The structure of the instrument adopts the detection method of single optical path and time dual beams to achieve the purpose of dual optical paths. The measuring range of this instrument is. -1.5% carbon dioxide, the lower detection limit is 0.01%. The instrument is equipped with a small electromagnetic pump, which can automatically suck ambient air for measurement. This method is the most convenient and commonly used method for measuring carbon dioxide in ambient air. When the instrument is placed in the environment, the carbon dioxide content can be directly measured.
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