New project of flue gas analyzer
How to Accurately Measure CO Concentration under High Concentration of CO2 Environment
The coal mill is the main auxiliary equipment of the pulverizing system of the coal-fired units in thermal power plant, which is the power machinery which grinds the raw coal to meet the fineness of the boiler suspension combustion. During the operation of the coal mill, the coal is exposed to air which will be oxidized to form CO gas and carbon, and the heat generated by the friction will first cause incomplete combustion of the pulverized coal, resulting in a large amount of CO gas. The concentration of CO gas increase in the internal spacer of coal mill, then reduce the ignition point of the combustible mixture in the coal mill and increases the risk of fire and explosion of the coal mill.
The main methods of CO gas detection are: infrared absorption, electrochemical, electrical (thermal conductivity and semi-conductive), chromatography, and currently, CO gas concentration online detection usually adopts infrared absorption and electrochemical.
Infrared absorption has more advantages than the electrochemical in both the detection technology and maintenance costs. In addition, the infrared gas analysis technology based on infrared absorption method has the advantages of wide measurement range, high sensitivity, high measurement precision, quick response, good selectivity and other advantages, but there are some problems in the infrared measurement process: water vapor and CO2 have interference on the CO gas.
CO absorption wavelength is near 4.6μm, CO2 in the vicinity of 4.3μm, water vapor in the 1 ~ 9μm wavelength range, almost continuous absorption zone. CO2 and water vapor have an overlapping part of the characteristic absorption wavelength range of CO, and the concentration of CO2 and water vapor is much larger than that of CO, which is obviously disturbed by the measurement of CO.
Therefore, it is necessary to carry out dehydration pretreatment of the sample gas with the cooling or desiccant before the measurement, or to remove the water gas in the gas analysis unit. At the same time, by selecting the filter unit, the infrared wavelength is selected, and the narrow band optical filter or the gas filter gas Room to limit the infrared radiation in the CO absorption of narrowband light range, in order to reduce the other components of the smoke on the measured value of the impact can be accurately measured in the flue gas CO concentration to ensure that the coal mill industry safety.
Therefore, it is necessary to perform the dehydration pretreatment of the sample gas with the cooling or desiccant, or have the special elimination measurement of the water gas in the gas analysis unit.
At the same time select the infrared wavelength by setting the filter unit with a narrow band optical filter or gas filter chamber to limit the infrared radiation in the CO absorption of narrowband light range, in order to reduce the other components of the smoke on the measurement value, then the concentration of CO in the flue gas can be measured accurately to ensure the safety of the coal mill industry.
Gasboard-3000Plus, a newly flue gas analyzer (low range online) developed by Hubei Cubic-Ruiyi Instrument Co., Ltd with a special sample pretreatment unit to eliminate moisture from the sample gas; the entire gas analysis unit is equipped with a thermostat to prevent condensation of gaseous water in the gas analysis unit in a low temperature environment, affecting the measurement results. The sensor is also equipped with moisture compensation adjustment device: the microfluidic infrared sensor on the use of mechanical structure design to change the ratio of space before and after expansion of the air chamber to increase the sensitivity of the sensor to the measured gas; by adjusting the blade and linear correction and adjust the signal so that the gas containing the non-condensed water is consistent with the signal of N2, then the influence of the water vapor on the front and rear expansion chambers of the sensor is canceled and the accuracy of the CO concentration measurement result is ensured.
For the effects of high concentration of CO2, the Gasboard-3000Plus gas analysis unit adopts a special CO2 interference reduction device, equipped with a filter chamber dedicated to absorb CO2 wavelengths, which can eliminate the effect of CO2 on CO absorption wavelength. At the same time, a narrow band optical filter with excellent filtering effect is adopted. Only infrared radiation with CO absorption wavelength can be used to effectively block the influence of CO2 radiation and ensure the accuracy of CO concentration measurement