Unitek: The Crane People
SKIP WINCH SYSTEMS IN LIME PLANTS
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While every engineering component plays an important role in the smooth functioning of a Lime kiln, there are a few key components that are so vital, that the non functioning of these key components would make the lime kiln inoperable, leading to long downtimes and ultimate waste of resources. One of these critical key components, is the skip winch system.
The skip winch system is the lifeline feeder mechanism for the entire lime kiln, feeding the lime kiln, sized lime stone, at pre determined intervals. Depending upon the capacity of the plant and the hourly requirement of lime, the working load, size and speeds of the skip winch system are determined.
The Skip winch systems consist of the following:
- Skip winch and rope guiding pulleys
- The Skip Bucket
- The Skip Track
- The VFD Control Panel/PLC / SCADA/ Instrumentation (automated control system)
The Skip Winch, essentially designed for a 24x7 operation, is in effect a simple winch mechanism that needs to be carefully designed to suit the type of kiln, the complicated layout of the kiln, the process feed rates, the location of the guide pulley mechanisms and the harsh environment that the winch operates under.
Skip winch design/ layouts need to be determined at the initial kiln design stage. Depending on the layout, skip winches could be single drum type, double drum type, long drum type, high speed type, single rope design, multiple rope design and so on.
Considering the continuous operational cycles, skip winch elements are required to be proportioned by checking that they have adequate safety against becoming unserviceable as a result of extreme loading conditions coupled with fatigue, overheating and deflection. High service factors in design of winch components selection, is a must.
The broad elements of a skip winch system are a motorised drive comprising of a motor, brake and gearbox that ultimately drives a rope drum on which the ropes hauling the skip bucket, are wound. Bearing housings, load monitoring system, rope slack detection, brake liner wear checking system, the ropes and its connection gear, form part of the winching mechanism.
The Guide Pulley Mechanisms are also designed with precision and the location of these pulleys and their connection to the kiln structure, is very critical. Guide pulley mechanisms which are not aligned and designed well, lead to high failure rate of the ropes as well as the pulleys themselves. Great care needs to be attributed to placement of these guiding mechanisms. Pulleys with higher radii are used to ensure extended life of ropes being guided. The use of sealed bearings and solid oil bearings go a long way in improving the operating life of the guide pulleys.
The Skip Bucket is basically the container carrying the sized lime stone to the top. It is this bucket along with the lime stones that is raised/lowered by the winch along an inclined track. The volume of the bucket, its shape and size need to be carefully designed considering the track inclination, volumetric efficiency, and tilting geometry at the top of the track.
The rollers of the buckets and arm hinge points need to be carefully designed and equipped with sealed bearings / solid oil bearings for long life. The alignment of the rollers on the bucket is critical and needs to be executed with care.
The Skip Track is essentially the structure along which the skip bucket is hauled and further allows the bucket to tilt at the upper levels of the track. The design of the track structure is done with careful checks for horizontal, vertical and wind loads. Skip Tracks can also come covered throughout most of their length so that weather doesn’t influence the raw material inside the bucket.
The Automated Control system along with the feedback field devices are an intricate part of the skip winch system and contribute to the seamless operation of the whole system, ensuring repeatability of operations with precision. The automation also helps in overall safety and prevention of accidents.
The VFD control panel is normally mounted within an air conditioned control room and houses the VFD and switchgear meant for operation of the winch. The PLC panel is also housed here and communication links between the VFD panel and PLC system is based on Ethernet or Profibus platforms. The SCADA , with its intelligent graphics, through feedback obtained from the various instrumentation and the PLC, gives the control room operator a clear picture of the skip system and the problems and failures and so on.
Sensors, counters, encoders mounted on the winch and along the track, give continuous feedback to the VFD and mostly the PLC system, to closely monitor the status of operation. The automated control system provides a good process control and optimization for the lime plant, ensuring maximum efficiency and higher profitability.
Automated control of the Skip winch system helps stabilize the loading cycles, optimizes production, manages and corrects process disruptions and minimizes wear on the skip winch system components. This ensures optimum equipment performance and hence decreases operational and maintenance costs.
The author of the above article is the Technical Director of Unitek Engineers Pvt. Ltd. , 235F, Bommasandra Industrial Area, Hosur Road, Bangalore 560099, INDIA , e mail : sa@unitekcranes.com
Unitek is a manufacturer of High speed Mineral winches for Lime and Steel Plants and its accessories like winch automated control systems, Skip buckets, Guiding pulley mechanisms and so on.
Unitek manufactures Mineral winches for many Lime plant Technology providers and manufacturers like QUALICAL, CIMPROGETTI, MAERZ, FL SMIDTH, NUBERG ENGG, etc.
