Analysis of Uncertainty in Measurement of Oxygen Content in Exhaust Smoke

Abstract: Uncertainty analysis information in the measurement of oxygen content in exhaust gas is provided by excellent flowmeter and flowmeter manufacturers. 1. The importance of correct measurement and control of oxygen content in flue gas In the fields of thermal power generation, petroleum, chemical industry, iron and steel industry, glass manufacturing, metallurgy, light industry, etc. Kiln, cement kiln, soaking furnace. More flowmeter manufacturers choose models and price quotations. You are welcome to inquire. The following is the details of the uncertainty analysis article in the measurement of oxygen content in exhaust gas. 1. The importance of correct measurement and control of oxygen content in flue gas In the fields of thermal power generation, petroleum, chemical industry, iron and steel industry, glass manufacturing, metallurgy, light industry, etc. Accurate measurement and control of oxygen content in flue gas of kilns, cement kilns, soaking furnaces, carburizing heat treatment furnaces, annealing furnaces, etc., can save energy, reduce environmental pollution and prolong furnace life. When the oxygen content is high, the oxygen easily reacts chemically with the sulfur in the fuel and nitrogen in the air at high temperature, resulting in SOx and NOx that have adverse effects on the heat exchange equipment and the environment; when the oxygen content is low, the fuel combustion is insufficient, reducing the combustion economy. Therefore, it is necessary to accurately and reliably measure and control the oxygen in the flue gas to ensure that the oxygen content is within a reasonable range. The automatic control of oxygen content in boiler operation is to achieve the optimization of combustion to the greatest extent, and to adjust the air-coal ratio reasonably. Among them, the realization of reliable and accurate online measurement of flue gas oxygen content is a necessary premise to realize this process. At present, there are many methods for measuring oxygen content in flue gas, and most of them are zirconia oxygen content measurement systems for online real-time measurement. The analysis is now carried out for an oxygen measurement system consisting of zirconia. 2. The influence of oxygen measurement deviation on the operation economy The correctness of the oxygen measurement of exhaust gas has a great influence on the efficiency of the boiler unit and the energy consumption of auxiliary machines. For the current level of oxygen measurement technology, the basic error of the zirconia oxygen meter used in the online detection of oxygen content:±2%～±3%FS (full scale); Repeatability:±1%FS; Stability:±1% to 2% FS/month; response time (up to 90%) is less than 5s; measurement system uncertainty is about 4%. From the on-site calibration results [1], the absolute error caused by sampling during single-point sampling measurement is about 1% to 2% O2, and the comprehensive measurement error is calculated as 2% O2. The inaccurate oxygen measurement will have the following effects on the unit (Take a 460t/h boiler as an example): (1) the air supply volume increases by 81221m3/h; (2) the induced air volume increases by 89537m3//h (the air leakage rate is calculated as 10%); (3) the exhaust gas temperature increases by 5℃ ; Boiler efficiency is reduced by about 1. 3. Uncertainty of oxygen measurement system The oxygen measurement system consists of a sampling system, an oxygen sensor and a secondary instrument (or transmitter). There are many factors that affect the reliability of oxygen detection results in online real-time measurement. In addition to the accuracy of sensors and secondary instruments, the reliability of measurement results largely depends on the rationality of the sampling system, which is analyzed as follows. 3.1 Basic error in measurement In the detection and evaluation of the measurement system itself, the error shown by the system is the basic error. The error is caused by the error of the sensor and the secondary instrument itself, which depends on the respective manufacturing methods and manufacturing processes, and is closely related to the development level of microelectronics technology and sensor production technology. From the point of view of the use process, the measurement system can generally reach the specified error range. 3.2 Additional errors in measurement 3.2.1 Among the many reasons for the influence of repeatability and stability errors on oxygen measurement, the stability of the temperature field of the atmosphere where the sensor probe is located, the contamination of the probe surface and the degree of internal poisoning are the causes of the measurement results. The direct cause of repeatability and stability errors, but also another important indicator of the measurement system——Response time has a negative impact. Repeatability and stability errors are part of the additional measurement error. 3.2.2 Gas atmosphere on both sides of the probe From the current probe installation and sampling methods, the gas on both sides of the zirconium tube is in a non-flowing state. Figure 1 shows the installation method of the zirconia probe in actual measurement. During the measurement process, the oxygen molecules in the reference gas continuously diffuse into the sample gas through the wall of the zirconium tube. On both sides of the zirconium tube, oxygen is generated from the reference gas to the surface of the zirconium tube and from the sample gas to the surface of the zirconium tube. The concentration gradient, that is, the oxygen field on both sides is not uniform. Since the gas on both sides is basically in a non-obvious flow state, the mass transfer process is mainly realized by diffusion, which forms a relatively stable oxygen field on both sides of the zirconium tube, which is extremely unfavorable for real-time measurement.

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