Thermomagnetic oxygen analyzer and zirconia sensor principle

Oxygen Analyzer Principle

Commonly used oxygen analyzers are mainly thermal magnetic and zirconia types.

Oxygen analyzer, dew point meter, hydrogen analyzer, infrared analyzer, alarm, coke oven gas oxygen analyzer, cement kiln gas analyzer, calcium carbide furnace tail gas analyzer, blast furnace coal injection system, semi-water gas analyzer.

(1) Thermomagnetic oxygen analyzer

　　Its principle is to use the physical property of the particularly high magnetic susceptibility of oxygen in the flue gas components to determine the oxygen content in the flue gas. Oxygen is a paramagnetic gas (a gas that can be attracted by a magnetic field is called a paramagnetic gas). In an uneven magnetic field, it is attracted and flows to a place with a stronger magnetic field. A heating wire is provided at this place, so that the temperature of the oxygen here increases and the magnetic susceptibility decreases, thereby reducing the magnetic field attraction. It is pushed out of the magnetic field by the unheated oxygen molecules with higher magnetic susceptibility at the back, thereby causing "thermomagnetic convection" or "magnetic wind" phenomenon. Under certain gas sample pressure, temperature and flow, the oxygen content in the gas sample can be measured by measuring the size of the magnetic wind. Since the thermistor (platinum wire) serves as both the two arm resistors of the unbalanced bridge and the heating resistor wire, a temperature gradient appears under the action of the magnetic wind, that is, the temperature of the inlet arm is lower than that of the outlet arm. The unbalanced bridge will output a corresponding voltage value depending on the oxygen content in the gas sample.

(2) Zirconia sensor oxygen analyzer

　　Zirconia (ZrO2) is a ceramic, a solid with ion conductive properties. It is a monoclinic crystal at room temperature. When the temperature rises to 1150°C, the crystal form changes to a cubic crystal, and the volume shrinks by about 7%; when the temperature drops, it changes back to a monoclinic crystal. If heated and cooled repeatedly, ZrO2 will crack. Therefore, pure ZrO2 cannot be used as a measuring element. If a certain amount of calcium oxide (CaO) or yttrium oxide (Y2O3) is added to ZrO2 as a stabilizer and then calcined at high temperature, it will become a stable zirconium oxide material. At this time, the tetravalent zirconium is replaced by divalent calcium or trivalent yttrium, and oxygen ion holes are generated at the same time, so ZrO2 belongs to anionic solid electrolyte. ZrO2 conducts electricity mainly through the movement of holes. When the temperature reaches above 600℃, ZrO2 becomes a good oxygen ion conductor.

　　A platinum electrode is sintered on each side of the zirconium oxide electrolyte. When the oxygen partial pressure on both sides of the zirconium oxide is different, the oxygen on the side with high oxygen partial pressure migrates to the side with low oxygen partial pressure in the form of ions. As a result, the platinum electrode on the side with high oxygen partial pressure loses electrons and shows positive electricity, while the platinum electrode on the side with low oxygen partial pressure gains electrons and shows negative electricity, thus generating an oxygen concentration difference potential between the two platinum electrodes. This potential is only related to the difference in oxygen content (oxygen concentration difference) in the gas on both sides when the temperature is constant. If the oxygen content on one side is known (such as the oxygen content in the air is a constant), the oxygen content on the other side (such as the oxygen content in the flue gas) can be expressed by the oxygen concentration difference potential. By measuring the oxygen concentration difference potential, the oxygen content in the flue gas can be known.