The portable flue gas analyzer is a meter for measuring the oxygen content in flue gas. There are two types of commonly used portable flue gas analyzers: thermomagnetic and zirconia.
(1) Thermomagnetic oxygen analyzer for portable flue gas analyzer
The principle is to determine the oxygen content in the flue gas by using the physical property that the magnetic susceptibility of oxygen in the flue gas component is particularly high. Oxygen is a paramagnetic gas (the gas that can be attracted by a magnetic field is called a paramagnetic gas). It is attracted in an uneven magnetic field and flows to a stronger magnetic field. A heating wire is provided there, so that the temperature of oxygen increases and the magnetic susceptibility decreases, so the magnetic field attractive force is reduced, and the magnetic field is pushed out by the unheated oxygen molecules with a higher magnetic susceptibility, which causes the magnetic field to be discharged. “Thermomagnetic convection” or “magnetic wind” phenomenon. Under certain gas sample pressure, temperature and flow rate, the oxygen content in the gas sample can be measured by measuring the size of the magnetic wind. Because the thermal element (platinum wire) serves as both bridge arm resistance of the unbalanced bridge and heating resistance wire, a temperature gradient occurs under the action of magnetic wind, that is, the temperature of the intake side bridge arm is lower than that of the exit side bridge The temperature of the arm. The unbalanced bridge will output the corresponding voltage value according to the oxygen content in the gas sample.
Although the thermal magnetic oxygen analyzer has the advantages of simple structure and easy manufacture and adjustment, it has gradually been oxidized by zirconia due to its short reaction speed, large measurement error, prone to measurement ring chamber blockage and severe corrosion of thermal elements. Analyzer replaced.
(2) Portable flue gas analyzer zirconia sensor type oxygen analyzer
Zirconia (ZrO2) is a ceramic, a solid with ion-conducting properties. At room temperature, it is a monoclinic crystal. When the temperature rises to 1150 ° C, the crystal form changes to cubic crystals, and at the same time, it shrinks by about 7%. When the temperature decreases, it becomes monoclinic crystals. If heating and cooling are repeated, ZrO2 will break. 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 baked at high temperature, it will become a stable zirconia material. At this time, tetravalent zirconium is replaced by divalent calcium or Trivalent yttrium replacement, while generating oxygen ion holes, so ZrO2 belongs to anionic solid electrolyte. ZrO2 conducts electricity mainly through the movement of holes. When the temperature reaches above 600 ° C, ZrO2 becomes a good oxygen ion conductor.
A platinum electrode is sintered on each side of the zirconia electrolyte. When the oxygen partial pressures on the two sides of the zirconia are different, the oxygen on the side with the higher oxygen partial pressure migrates to the side with the lower oxygen partial pressure in the form of ions, resulting in the oxygen partial pressure. The high-side platinum electrode loses electrons and becomes positively charged, while the low-oxygen partial pressure side of the platinum electrode receives electrons and becomes negatively charged, thus generating an oxygen concentration 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 (for example, the oxygen content in the air is constant), the oxygen content on the other side (such as the oxygen content in the flue gas) can be expressed by the oxygen concentration potential, and the smoke concentration can be determined by measuring the oxygen concentration potential. The amount of oxygen in the gas.
The portable flue gas analyzer zirconia oxygen analyzer has the advantages of simple structure and sampling pretreatment system, high sensitivity and resolution, wide measurement range, and fast response speed.
