Principles and characteristics of conventional industrial gas detection
Portable gas detection and alarm devices commonly used in petrochemical enterprises include single gas detection and alarm devices (such as those specifically designed to detect combustible gases, oxygen, hydrogen sulfide, etc.)
According to the hazards, we can divide toxic and harmful gases into two categories: combustible gases and toxic gases. Due to their different properties and hazards, their detection methods also differ. The key part of portable gas detectors is gas sensors, which can be divided into three categories based on their detection principles:
(1) Gas sensors utilizing physical and chemical properties, such as semiconductor, catalytic combustion, solid thermal conductivity, and other gas sensors.
(2) Gas sensors that utilize physical properties, such as thermal conductivity type, cross interference type, infrared absorption type, etc.
(3) Gas sensors utilizing electrochemical properties, such as constant potential electrolysis, Gavanni battery, membrane ion electrode, solid electrolyte, and other gas sensors.
Although there are various types of gas detection sensors, each type has its own advantages and limitations. Based on a comparison of years of on-site use in petroleum and petrochemical enterprises, it is believed that the most widely used and comprehensive gas detection method is catalytic combustion method for combustible gas detection, and electrochemical method for toxic gas and oxygen detection.
1 Catalytic combustion type
Catalytic combustion is a type of gas sensor that uses sensing elements to generate catalytic combustion when they come into contact with combustible gases, causing the temperature of the sensing element to rise. The gas concentration is measured by detecting changes in its resistance. The advantages of catalytic combustion gas sensors are high accuracy, good stability, good linear relationship between output signal and gas concentration, and little influence from environmental temperature and humidity. Its disadvantage is that the catalyst is prone to poisoning and failure.
2 Electrochemical sensors
Electrochemical sensors use electrochemical principles to detect gas concentration, which can be roughly divided into:
(1) By using gas to maintain a certain potential at the interface between the electrode and electrolyte in a device, direct oxidation reduction is achieved, and current changes are generated in the external circuit to achieve sensing.
(2) Gas dissolution and electrolysis in a solution form ionization of gaseous substances, which generate potential changes through electrode action to achieve sensing.
(3) The reaction between gas and electrolyte solution generates changes in electrolytic current to achieve sensing and other forms. In the chemical formula detection method, the constant potential electrolysis method (using the first principle) has been widely used, with the advantages of high sensitivity, high selectivity, small interference with gas, and the disadvantage of short lifespan.
