The working principle of zirconia oxygen analyzer
A porous platinum (Pt) electrode was sintered on both sides of the zirconia electrolyte (ZrO2 tube), and the measurement battery body was divided into three layers: platinum (electrode)-zirconia (electrolyte)-platinum (electrode). The platinum electrode is porous. The flue gas passes through the filter or the calibration gas through the conducting tube to the side of the measured gas of the measuring cell, while the other side is the reference air (20.60% oxygen).
Two gases with different oxygen concentrations act on the measuring cell, producing a logarithmic potential (the greater the difference in oxygen concentration on both sides, the greater the potential signal). The millivolt signal is converted to a 0-10 mA or 4-20 mA standard current by an oxygen analyzer. This current is output from the oxygen analyzer terminals.
The operating temperature of the measuring battery is set to a constant temperature higher than 650 ° C. In order to keep the working temperature constant, the operating temperature of the battery is measured with a K-type thermocouple, and the heating voltage of the heater is adjusted by a temperature controller in the oxygen analyzer.
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Schematic diagram of zirconia oxygen sensor When measuring the temperature of the flue gas above 700 °C, the heater and temperature measuring thermocouple are omitted in the sensor composition.
Under ideal conditions, when the measured flue gas is the same as the reference gas concentration, its output potential E is 0 mV, but in practical applications, the actual conditions and field conditions of the zirconium tube are not ideal. Therefore, the actual zirconium tube deviates from this value. In fact, the potential of the output of the zirconium tube with a certain oxygen content is the sum of the theoretical value and the background potential. We call the potential value of the zirconium tube output without the concentration condition as the background potential or the zero potential, the magnitude of this value. It also has different values ​​at different temperatures and varies with the extended life of the zirconium tube. Therefore, failure to deal with this situation can seriously affect the accuracy of the entire oxygen analyzer and probe life.
Structure and type of zirconia oxygen analyzer
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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 purpose of the heater is to provide the temperature required for the zirconia solid electrolyte element to function properly, so that it will 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 protection 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. 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 impurity of the detected gas is 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 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.
In-line 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.
Since the zirconia 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 is up to 1500 mm. And 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 adopts the technically demanding zirconia and oxidation. 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 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. This article Source: electromagnetic flowmeter http:// orifice flowmeter http://
A porous platinum (Pt) electrode was sintered on both sides of the zirconia electrolyte (ZrO2 tube), and the measurement battery body was divided into three layers: platinum (electrode)-zirconia (electrolyte)-platinum (electrode). The platinum electrode is porous. The flue gas passes through the filter or the calibration gas through the conducting tube to the side of the measured gas of the measuring cell, while the other side is the reference air (20.60% oxygen).
Two gases with different oxygen concentrations act on the measuring cell, producing a logarithmic potential (the greater the difference in oxygen concentration on both sides, the greater the potential signal). The millivolt signal is converted to a 0-10 mA or 4-20 mA standard current by an oxygen analyzer. This current is output from the oxygen analyzer terminals.
The operating temperature of the measuring battery is set to a constant temperature higher than 650 ° C. In order to keep the working temperature constant, the operating temperature of the battery is measured with a K-type thermocouple, and the heating voltage of the heater is adjusted by a temperature controller in the oxygen analyzer.
Schematic diagram of zirconia oxygen sensor When measuring the temperature of the flue gas above 700 °C, the heater and temperature measuring thermocouple are omitted in the sensor composition.
Under ideal conditions, when the measured flue gas is the same as the reference gas concentration, its output potential E is 0 mV, but in practical applications, the actual conditions and field conditions of the zirconium tube are not ideal. Therefore, the actual zirconium tube deviates from this value. In fact, the potential of the output of the zirconium tube with a certain oxygen content is the sum of the theoretical value and the background potential. We call the potential value of the zirconium tube output without the concentration condition as the background potential or the zero potential, the magnitude of this value. It also has different values ​​at different temperatures and varies with the extended life of the zirconium tube. Therefore, failure to deal with this situation can seriously affect the accuracy of the entire oxygen analyzer and probe life.
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 purpose of the heater is to provide the temperature required for the zirconia solid electrolyte element to function properly, so that it will 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 protection 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. 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 impurity of the detected gas is 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 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.
In-line 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.
Since the zirconia 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 is up to 1500 mm. And 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 adopts the technically demanding zirconia and oxidation. 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 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. This article Source: electromagnetic flowmeter http:// orifice flowmeter http://
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