Trapezoidal stockpile Vs Trapezoidal stockpile

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Trapezoidal stockpile can be formed in the following two methods,
1.   Without compensating the travel length of the machine.
2.   By compensating the travel length of the machine.
Each method has its own advantage and disadvantage. Before comparing the advantages and disadvantages, let us discuss how a trapezoidal stockpile is formed.
Without compensating the travel length of the machine:


The above figure shows a trapezoidal stockpile formed without compensating the travel length of the machine.
By compensating the travel length of the machine:


The above figure shows a trapezoidal stockpile formed by compensating the travel length of the machine.
Travel length compensation:
To understand travel length compensation, first let us discuss how a triangular stockpile is formed with the help of a stacking mode drawing.
(Stacking mode drawing: Is the drawing which defines the slewing angle, luffing angle and the travel position of the stacker machine to form a desired stockpile. This drawing is the vital input for doing PLC programming. How to prepare this drawing shall be discussed separately)

From the above stacking mode drawing it is clear that to form this triangular stockpile, there is no need to change the starting point ‘S’ (and the end point ‘E’) of the long travel motion (‘End cone correction’ is not taken into account in this case. End cone correction shall be discussed separately).

If we form a trapezoidal stockpile without changing the starting point ‘S’ (and the end point ‘E’) of the long travel motion, the plan view of the stockpile shall be as shown in the below sketch.


If we form a trapezoidal stockpile by changing the starting points ‘S’ (and the end points ‘E’) of the long travel motion, the plan view of the stockpile shall be rectangular in shape as shown in the below sketch.


CASE STUDY:
         Machine              - Bucket wheel stacker reclaimer (BWSR)
         Boom length        - 41m (machine axis to bucket-wheel centre)
         Bucketwheel dia   - 8m
         Rail gauge           - 8.2m
         Rail to Stockpile   - 2.5m
         Tripper length     - Approx. 60 m (machine axis to tripper end)
         Stockpile length   - 300m
         Stockpile height   - 10m 
         Stockpile width    - 40m
         Material              - Coal
         Repose angle      - 37°
Form stockpiles (by chevron method)
a.   without compensating the travel length
b.   by compensating the travel length
and discuss these stacking methods.
(In both the cases assume that the entire stockyard length is available for forming the stockpile of 300m length and there are no restrictions by the yard conveyor profile at feeding and discharge points)



Case 1 – Without compensating the travel length

Case 2 – By compensating the travel length


Comparing the above methods:
Capacity: Capacity of the stockpile formed by compensating the travel length is slightly more than the capacity of the stockpile formed without compensating the travel length. But this statement is true ONLY WHEN the entire stockyard length is available for forming the stockpile of desired length and there are no restrictions by the yard conveyor profile at feeding point and at discharge point. 




Starting (& End) point: Starting (& End) points of stacking are different when the stockpile is formed by compensating the travel length and the starting (& end) points are same when the stockpile is formed without compensating the travel length. Due to this reason the PLC programming will be simple and easy when the stockpile is formed without compensating the travel length.
Rail length: Rail length required to form the stockpile by compensating the travel length is more. Also, the rail length required to reclaim the material from the stockpile which is formed by compensating the travel length is more.
Space utilisation: Maximum space in the stockyard shall be utilised when the stockpile is formed without compensating the travel length.
Reclaim capacity: Effective reclaim capacity shall be achieved when the material is reclaimed from the stockpile which is formed by compensating the travel length (due to less number of change in slew motion from positive to negative). 
Due to the above-mentioned reasons, in coal power-plants the coal stockpiles are formed without compensating the travel length of the machine.

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Comments

  1. Unknown28 December 2017 at 07:30

    Sir your showing only the stockpile forming. Your not showing the reclaiming position. For reclaiming the travel length will be vary from stacking. So which length we have to take for estimation. Either stacking length or reclaiming length.

    ReplyDelete
    Replies
    1. Basics in Stacker Reclaimer28 December 2017 at 09:24

      Dear Richy, please refer the reclaim mode drawing which clearly shows the positions of the machine during reclaiming operation. Comparing the reclaim mode drawing with the stacking mode drawing, you can notice that the travel length of the machine is more during reclaiming operation.
      For rail length estimation purpose you have to consider travel length during reclaiming + tripper length (also take care of the parking position of the machine)

      Delete
  2. Unknown28 December 2017 at 07:34

    In the blog you mentioned that wheel diameter is eight. In which capacity it will 8m.any thumb rule for this or its a example from yours experience.

    ReplyDelete
    Replies
    1. Basics in Stacker Reclaimer28 December 2017 at 09:13

      Dear Richy, wheel diameter is not based on any thumb rule and this is based on the capacity calculation which decides the capacity and the number of buckets. Accordingly the bucket wheel diameter is fixed.

      Delete

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