Procedures for Systematic Start up and Stoppage of Ball Mill

Hi Friends,

In earlier post, we have developed the Design and motor rating calculations for Ball mill. In present post, we will discuss the systematic procedure for starting a Ball mill for taking into operation as well as stopping the Ball mill for taking out of circuit in Alumina refinery. Ball mill is one of the very critical equipment installed in Alumina refinery. Since the mass of the rotating cylinder with liners and balls is very high, thus the starting torque for the mill is enormously high. The drive motor for the Ball mill ranges fro 0.5 MW to 2.5 MW depending on the hardness of Bauxite, feed size and operating capacity of the mill for meeting the hourly alumina production requirement as described in earlier post. Generally squirrel cage induction motors are installed as drive motor for the Ball mill.  The mill is also provided with hydraulic pumps for lifting the Ball mill to provide a jerk to swing so that inertia of rest of the mill is broken for its rotation. The hydraulic pumps of Ball mills in Alumina refinery are popularly known as inching device for the mill. Since the drive motor rating of the mill is the highest among all the high tension (HT) motors of Alumina refinery, so it is connected with high voltage electrical supply line at about 6.60 kV. Hence all precautionary measures are taken to start the Ball mill for normal operation. Sudden start of the mill by direct power supply to its drive motor may cause serious damage to the equipment and power supply system as well.

Ball mill start up procedure: The systematic start up procedures for Ball mill are briefly outlined here under-

1. Check the readiness of upstream and down stream equipment in the process circuit,
2. Inform the turbine house of Co-generation plant to ensure the stable operation of Turbo-Generators (TGs) and connected boilers. During steam pressure fluctuations in boilers, the ball mill should not be started.
3. Check hydraulic oil level in oil tank,
4. Start hydraulic pumps for lifting the mill to swing,
5. When hydraulic oil pressure reached to around 2 kg/cm2, start the drive motor of the mill. The temperature of hydraulic oil should remain less than 40 degree centigrade,
6. Keep close watch on voltage, amperage, temperature and sound of drive motor,
7. Open aluminate liquor to the mill at controlled rate,
8. Start the ground slurry pump,
9. Start bauxite weigh feeder with low feeding rate to Ball mill,
10. If everything is normal, put the operation of grinding circuit in auto mode with normal grinding rate.

Ball mill stoppage procedure: The sequence of operation for stopping the Ball mill from normal running condition are given below-

1. Stop the bauxite feeder for stopping the feed to Ball mill first,
2. Continue flow of digestion liquor to mill for a few minutes to ensure flushing of slurry from the Ball mill,
3. Stop the Ball mill,
4. Stop the slurry pump,
5. Drain the slurry from pump including its suction and delivery lines.

Broadly, the above sequence of operations are followed for starting and stoppage of ball mills. Grinding section operators must be provided with written down procedures in order to avoid any confusion and thereby mishaps. Also, while starting the mill, presence of Area supervisor is considered essential as any small lapse during start up may cause serious damage to equipment as well as unsafe to the working personnel. Sudden start up may also cause damage to mill foundation and its alignment creating acute crisis for Alumina refinery. 

Hope, all major points have been covered under the topic. Please put your views / suggestions / remarks / comments, if any. We will always welcome your suggestions and recommendations.

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Thanks and regards.

Kunwar Rajendra