Brief introduction of galvanized line process:
The core of galvanizing unit is annealing furnace, including horizontal and vertical continuous annealing furnace, which is heated indirectly by gas radiation pipe and uses nitrogen and hydrogen as protective gas, which not only prevents the oxidation of strip steel in the annealing process but also ensures the plasticity of strip steel.
The annealing furnace is successively composed of preheating section, radiant tube heating section, soaking section, injection cooling section, equalization section, outlet section and furnace nose. By heating and cooling the strip in the furnace, the rolling stress can be eliminated, the internal crystal structure can be improved, the temperature of the galvanized strip can be guaranteed, and the mechanical properties and heat treatment process requirements such as deep drawing can be met.

Gas composition in the process:
Reducing gas: Hydrogen, its main role is to form a reducing atmosphere, but also can infiltrate into the furnace trace oxygen reduction into water vapor, prevent oxygen accumulation and cause danger. The mixture of hydrogen (reduction) and nitrogen (protection) is generally referred to as the protection gas. The concentration of hydrogen according to the quality and safety needs to determine, galvanized line horizontal furnace is generally about 15 ~ 20%, vertical furnace 5 ~ l0 %, aluminum zinc line requirements of reducing some strong, horizontal furnace 30% ~ 40%, vertical furnace 15% ~ 25%.
Protective gas: nitrogen, its main role is to protect the steel strip, and do not contact with the oxidizing air, so as not to produce new oxidation.
Safety gas: After the maintenance of the annealing furnace or opening the operating hole of the furnace door, when the oxygen enters the furnace, nitrogen must be injected to replace the oxygen in the furnace. Only when the temperature exceeds 650℃ and the oxygen content in the furnace is less than 0.5%, can the protective gas be injected. After the annealing furnace is shut down in normal production, there is still some hydrogen in the furnace. Nitrogen must also be passed into the furnace to replace the hydrogen and ensure that the hydrogen concentration is less than 0.5%, before the furnace door can be opened and air can be entered. This kind of gas used for purging is called safety gas or purging gas.
Cooling gas: the plate temperature meter and other instruments of annealing furnace work at high temperature. Some production lines seal the motor of the fast cooling fan in the furnace, and the working temperature is very high. Therefore, nitrogen must be used as the cooling gas to cool down, so as to ensure the working environment of instruments and equipment.
Sealed gas: at the entrance of the furnace, because the pressure of the annealing furnace with full radiation tube is very low when working and stopping the furnace, and the pressure of the annealing furnace with or without oxygen furnace is also very low, the outside air is easy to enter the furnace, so it is necessary to use nitrogen to form an air curtain, to isolate the inside of the furnace gas from the outside air, referred to as nitrogen seal. When the observation and operation holes of the annealing furnace are opened, nitrogen sealing must be used even when the furnace is shut down to minimize the air entry into the furnace.

Galvanized gas analysis system industry application:
Through the gas analyzer, analysis system, the furnace trace oxygen, hydrogen, dew point real-time online analysis.
The dew point analysis of the protective gas mainly relies on the dew point instrument in the analysis system to complete the sampling analysis in the preheating section, heating section, cooling section and outlet section respectively. The monitored dew point value is uploaded to the central control room in real time.
At the same time, hydrogen and oxygen concentration analysis in the furnace is completed by hydrogen analyzer and oxygen analyzer, respectively in the preheating section, heating section, cooling section and outlet section real-time monitoring. The measured value and alarm value are linked to the control system and uploaded to the machine room. The gas analysis system adopts the inspection mode (manual control or automatic inspection), and the analysis system is completed by the sample gas pretreatment system, sampling pump, sampling manual valve or solenoid valve. Note that the instrument shall be checked regularly and all levels of preprocessing shall be cleaned regularly to ensure the normal operation of the analysis system.