Classification of on-line analytical instruments

Commonly used are: ① thermal analysis instruments, such as thermal conductivity gas analyzer and thermochemical gas analyzer; ② Electrochemical analytical instruments, such as pH meter, conductivity meter, salt meter, electromagnetic concentration meter, galvanic cell type, polarographic type, zirconia oxygen analyzer, etc. ③ Magnetic analytical instruments, such as thermomagnetic and magnetomechanical oxygen analyzers; ④ Optical analysis instruments, such as infrared gas analyzer, uv analyzer, process photoelectric colorimeter, etc. ⑤ Chromatographic analyzers, such as process gas chromatograph and process liquid chromatograph; In addition, there are densitometers, hygrometers, hygrometers and viscometers.

On-line analytical instruments commonly used in typical instrument chemical industry are as follows:

① Thermal conductivity gas analyzer is based on the physical characteristics related to the thermal conductivity of gas and its component content. The content of each component can be known by detecting the change of the resistance of the hot wire in the thermal conductivity cell when the measured gas passes through the thermal conductivity cell. It is mainly used to analyze the content of hydrogen, sulfur dioxide or carbon dioxide in mixed gas.

(2) Based on the electrochemical characteristics that the concentration of hydrogen ions in the aqueous solution is related to the electromotive force generated by a pair of electrodes inserted into the solution, the pH value of the measured solution can be known by measuring the electromotive force. It is often used in oil refining industry, pharmaceutical industry and food industry, especially in sewage treatment engineering.

③ Zirconia oxygen analyzer Zirconia is conductive at high temperature due to the existence of oxygen ions. If platinum electrodes are attached to the inside and outside of the zirconia tube, when the oxygen content of the gas on both sides of the electrode is different, the electrode will produce electromotive force. If the oxygen concentration on one side (reference side) is fixed, the oxygen concentration on the other side (measurement side) has a corresponding relationship with electromotive force. By measuring the electromotive force, the oxygen content in the measured gas can be known. The analyzer has the advantages of fast response, simple structure, convenient use and installation, and small maintenance workload. It is often used to measure and control the oxygen content in the flue gas of industrial furnaces to improve the combustion thermal efficiency.

(4) The infrared gas analyzer is based on the selective absorption of infrared radiation energy by various gases. After infrared radiation is absorbed by a component in the gas, the radiant energy is partially converted into heat energy, which raises the temperature of the gas. By measuring the change of gas temperature or gas pressure in a certain volume, we can know the content of this component in the gas. It can analyze a wide range of objects (such as carbon monoxide, carbon dioxide, methane, acetylene, various hydrocarbons, ethanol and steam). ), high sensitivity, wide measuring range and fast response.

⑤ Online chromatographic analyzer includes gas chromatographic analyzer and liquid chromatographic analyzer. Using the characteristics that different substances have different distribution coefficients in different phases. When the two phases move relatively in the chromatographic column, these substances are repeatedly distributed between the two phases, so that the components with different distribution coefficients are separated and determined one by one in the detector, and the signals and concentrations of each component are automatically recorded to form a chromatogram. According to this diagram, the composition and content of the tested substance can be obtained qualitatively and quantitatively. In a chromatographic column, two relatively moving phases are stationary phase and mobile phase. Gas chromatograph using gas as mobile phase to carry samples; Liquid chromatograph with liquid as mobile phase. Chromatographic analyzer can perform multi-point and multi-component periodic automatic analysis with good selectivity, high sensitivity and fast response. Mainly used for multi-component analysis of gas or liquid mixtures in petroleum, fertilizer and other industries.