Issues with the interlocked shutdown mechanism in the coal grinding system?
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In vertical coal grinding mills with grinding rollers, logical interlock shutdown is used; why is an interlock shutdown also required for the dilution fan? What is it mainly to prevent?
The dilution fan is used to reduce the humidity in the system; it draws in air, and if it stops operating, the oxygen level can become too high, which is unsafe.
If nitrogen is used, can we choose to keep it running continuously?
The mill has stopped; there’s no point in keeping it running.
The oxygen content is high; introducing nitrogen helps to reduce the oxygen level in the system. Isn’t that good?
The system oxygen content is adjusted using nitrogen. Furthermore, after the mill is shut down, the volume of circulating air should be reduced promptly to minimize emissions.
:) It’s actually quite simple: in the original design, the medium entering the dilution fan was air. Once the coal grinder stopped operating, the circulating air system also stopped functioning. If too much air were introduced, spontaneous combustion of the coal powder inside could occur. Therefore, the shutdown sequence for the coal grinder in the original design included a corresponding shutdown sequence for the dilution fan as well； If the inlet of the dilution fan has been changed to nitrogen, then this interlock is no longer relevant. The dilution fan is started and stopped as needed; its purpose is to lower the dew point. However, it is also effective for replacing the air in the system when the system is shut down, as the outlet pressure is lower in that case. As long as you understand the principle, you can handle it flexibly during the process.
Hehe, it’s clear that the person above has a pretty good understanding of the process flow and interlock mechanisms related to pulverized coal. The use of such dilution fans was part of the original design, but later on, various manufacturers opted to use nitrogen instead for practical reasons. Here, we newly installed a low-nitrogen gas supply line; during normal production, a butterfly valve is installed at the fan outlet to shut off the dilution fan. During shutdown for maintenance, a dilution fan is activated to cut off low-pressure nitrogen and ventilate the interior of the mill for replacement.