Working principle of the dilution fan

The interlock connected to the dilution fan is the circulating air dew point interlock. Generally, when the dew point of the recirculated air reaches 65°C (corresponding to a moisture content of 189 g/m3), the dilution fan starts automatically as part of a interlock mechanism, and at the same time the outlet solenoid valve opens ； When it drops to 55°C (corresponding to a moisture content of 148 g/M3), the chain shuts off. It is usually also possible to operate by switching on and off periodically. Of course, if atmospheric pressure nitrogen is used as the medium for the dilution fan, the oxygen content in some parts of the system can be reduced after startup. It must be clear, however, that the oxygen level control interlock of the recirculation air system does not include the fan section; it relies on the fire suppression nitrogen system.

These two pipelines are designed for carbon dioxide in one case and low-pressure nitrogen in the other. Additionally, carbon dioxide is added before the hot air furnace; the purpose of this design is mainly to lower the dew point temperature. However, in actual production, it is not used in most cases. The low-pressure nitrogen line, which is located between the hot blast stove and the coal grinder, is controlled via a control valve based on the oxygen content; it can be operated in automatic cascade control, but manual control is generally used. The explosion-proof nitrogen system mentioned upstairs likely refers to the two low-pressure nitrogen supply lines connected to the grinder and the bag filter; this interlock mechanism is linked to the carbon monoxide detection device at the outlet of the bag filter – if an abnormally high level of carbon monoxide is detected, the control valves for these two low-pressure nitrogen supply lines automatically open.

I’m extremely grateful to my senior. Our control system indicates that the oxygen level at the exit of the hot blast furnace is high, which triggers the shutdown of the dilution fan. Could it be that the nitrogen supplied by the dilution fan at atmospheric pressure leads to incomplete combustion of oxygen inside the hot blast furnace, thereby increasing the oxygen level at its exit?