The solenoid valve of the mill’s pneumatic clutch is faulty; it is not possible to first stop the clutch and then the main motor in order to properly shut down the mill...
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Today I thought of an incident handling scenario from some time ago; I’d like to talk about it with everyone and hear your opinions. The situation is as follows: the operating rod mill needs to be stopped. When attempting to shut it down, it was found that the solenoid valve controlling the air supply for the pneumatic clutch was faulty; it was not possible to stop the mill either from the control room or on-site, yet the mill needed to be stopped as soon as possible. There were differing opinions regarding the on-site procedures: some wanted to disconnect the power supply to the air compressor on site in order to release the pressure in the air tank through the discharge outlet and thus disengage the pneumatic clutch, while others wanted to shut down the main motor directly to stop the grinder. Both methods carry their own risks. In the end, we stopped the main motor directly. As soon as the main motor stopped, the cylinder rotated forward for a few turns before starting to oscillate between forward and reverse rotation, forcing the main motor to rotate in reverse along with the cylinder. What do you all think? How would you handle this kind of problem if it came up again? Basis?
Many mills do not have clutches; instead, the main motor is simply turned off. After it stops, the drum does indeed swing back and forth a few times, which is normal. In such cases, the type of main motor used is different from those equipped with clutches – it is a longer-winding motor. If it is necessary to shut down the main motor in an emergency, I think it’s fine to simply turn off the motor; it won’t cause any damage ； The solenoid valve is faulty – why not replace it? Changing to another one won’t cause any delay.
To reiterate, the manufacturer claims that having a clutch will reduce the impact on the power grid, but that’s complete nonsense...
The first method is not recommended, as it takes too long to relieve pressure from the outlet and the pressure drop is also slow; it is advisable to shut down the main motor directly
Oh, I don’t know much about motors, especially the main motors of large mills; I always feel that it’s better to follow the rules to avoid damage. I’ll feel at ease if something similar happens again in the future. It seems that no replacement was made at the time because there were no spare parts; I can’t remember exactly.
The clutch in the mill functions as a soft starter; if the main motor of the mill is started directly, the torque required to rotate the drum can be too high, leading to easy motor overload. The main motors in mills are usually powered by 10-kilovolt high-voltage electricity, which can indeed cause disturbances in the power grid and result in voltage fluctuations. In addition to the mill, other high-voltage equipment in the gasification system includes high-pressure ash water pumps and cooling water pumps, and any problems with these devices can have serious consequences. Although such incidents are not inevitable, it is still necessary to take preventive measures. Additionally, both the intake and exhaust air on the air supply pipe for activating the clutch are controlled by solenoid valves. The failures of these solenoid valves, as mentioned by the poster, are usually caused by sudden issues with the power supply, such as power outages; in such cases the solenoid valves generally close, so it shouldn’t happen that the pneumatic clutch doesn’t disengage. In an emergency, the emergency stop button can be pressed directly or the main power supply to the motor can be cut off. During the stopping process, the pneumatic clutch hub is prone to burning due to inertia, which is a last resort.
The gauge should be replaced with a two-position three-way solenoid valve as soon as possible
Turning off the clutch air compressor and directly releasing the pressure in the clutch’s air reservoir helps to stop the clutch quite quickly as well
Have you done this before? Could it wear out the pneumatic clutch by being partially disengaged?
It’s fine, but it’s not recommended to do this.
Generally, the hub does not burn out; at most, it’s just the brake lining on the brake pads that gets burned