Automatic control design for safe operation of pellet plant

1. Roller and ring die automatic protection system
In order to prevent iron or other large and hard impurities from entering into the press roller and ring die of pellet plant and cause damages to the roller and ring die, a safety pin type or hydraulic hoop type safety protection agency is set on the spindle end. When the pellet plant is in serious overload, exceeding the shear force of safety pin or the friction of the friction plate in the hoop and the friction disc, then the safety pin would be cut or the friction disc rotates to touch the safety switch and send action signals to the control center. The stop instruction would be sent by the control center to protect of the roller and ring die of pellet plant.


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2. Pellet plant belt automatic speed control mechanism  
In order to prevent the belt from slipping that lowers the transmission efficiency and gets the belt burnt, a speed sensor can be installed on the driven pulley to sense the speed of the pulley. When the belt slips after getting loose, the speed of driven pulley would decrease. When it is lower than certain level of normal speed, generally 90% ~ 95% of the normal speed, the control center would give an alarm, and then cut the power of pellet plant in case the belt get burned.

3. Pellet plant by-pass door automatic unloading mechanism
Sometimes, periodical overload phenomenon of pellet plant would occur because of the change of feed raw materials, moisture or temperature, if not handled, the pellet plant may be blocked due to the overloading. In most cases, when the operator find the current overload, he would open the by-pass door control switch to make the incoming materials flow out from by-pass door, which would be closed when the current back to normal. The control principle of by-pass door automatic unloading mechanism is similar with the process mentioned above. When the control center detects that the actual current is higher than the set value, it would give an opening signal to the electromagnetic valve of the control cylinder in the by-pass door. Then, the by-pass door would be open by the cylinder to make the feed flow out and the current decreases as well. Then, the by-pass door would close automatically. The automatic control process avoids the blocking of pellet plant that might happen at any time, also the operating personnel is no longer need to watch the change of the current situation at the scene and reduces the workload of the operator.
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