Structure and type of zirconia oxygen analyzer
The zirconia oxygen analyzer is composed of an oxygen Sensor (also known as an oxygen probe, an oxygen detector), an oxygen analyzer (also known as a transmitter, a transmission unit, a converter, an analyzer), a dustproof device, and a thermocouple. , heater, standard gas conduit, junction box and housing shell.
The dustproof device is composed of a dust cover and a filter, which can prevent dust in the flue gas from entering the inside of the zirconia zirconium tube, protect the zirconium tube component from pollution, and can act as a buffer gas sample.
The zirconia tube element is the core component of the oxygen probe, which produces an oxygen concentration potential signal. Zirconium oxide tubes are ceramic metal oxides that must be protected from violent vibrations to avoid damaging the zirconium tube components.
The thermocouple is used for constant temperature control of the built-in heater of the probe. It is also a component for measuring the temperature of the gas to be measured in the boiler and kiln flue, and provides a temperature signal for oxygen calculation. The function of the heater is to provide the temperature required for the zirconia solid electrolyte element to function properly, so that it can also function properly in a measured flue gas environment below 600 °C. The oxygen potential signal and the thermocouple temperature signal from the oxygen probe are amplified and sent to the A/D conversion circuit, and the data is processed together with the correction coefficient to obtain the percentage of the oxygen content. At the same time, the system can display the oxygen potential, probe temperature and correction coefficient value, and control the heating furnace of the zirconium tube with constant temperature control, supplemented by broken couple, over temperature protection and thermal couple reverse connection to ensure reliable operation of the system.
According to the different detection methods, zirconia oxygen probes are divided into two categories: sampling and detection oxygen probes and in-line oxygen probes.
Sampling and detecting oxygen probe
The sampling detection method is to introduce the gas to be measured into the zirconia detection chamber through the guiding tube, and then heat the zirconia to the working temperature (above 750 ° C) through the heating element. Zirconium oxide is generally tubular and the electrode is a porous platinum electrode. The advantage is that it is not affected by the temperature of the test gas, and the oxygen content in various temperature gases can be detected by using different draft tubes. This flexibility is used in many industrial online tests. The shortcoming is that the reaction time is slow; the structure is complicated, and the detection precision is easy to be affected; when the detected gas impurities are large, the sampling tube is easily blocked; the porous platinum electrode is easily damaged by corrosion of sulfur, arsenic, etc. in the gas and clogging of fine dust; The heater is generally heated by an electric furnace wire and has a short life.
When the temperature of the gas to be detected is low (0 ° C ~ 650 ° C), or when the gas to be tested is relatively clean, it is suitable for sampling type detection methods, such as nitrogen measurement by a nitrogen generator, and oxygen measurement in a laboratory.
Inline detection oxygen probe
In-line detection is to directly insert zirconia into the high-temperature gas to directly detect the oxygen content in the gas. This detection method is suitable for the temperature of the detected gas at 700 °C ~ 1150 °C (special structure can also be used for high temperature of 1400 °C) ), it uses the high temperature of the gas to be measured to bring the zirconia to the working temperature without the need for an additional heater. The key to the in-line oxygen probe is the high temperature sealing and electrode problems of ceramic materials.
Because the zirconia oxygen analyzer needs to be directly inserted into the detection gas, the length of the oxygen probe is high, and the effective length is about 500 mm to 1000 mm, and the special environmental length can reach 1500 mm. Moreover, the detection accuracy, working stability and service life have high requirements. Therefore, the in-line oxygen probe is difficult to adopt the integral zirconia tubular structure of the conventional zirconia oxygen probe, and more zirconia and oxidation are required. The structure of the aluminum tube connection. Sealing performance is one of the most critical technologies for this zirconia oxygen probe. At present, the most advanced connection method in the world is to permanently weld zirconia and alumina tubes. The sealing performance is excellent. Compared with the sampling type detection method, the in-line detection has obvious advantages: zirconia is in direct contact with gas. The detection precision is high, the reaction speed is fast, and the maintenance amount is small.
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