Balancing Diagram in the Planning of Dragline Workings
Introduction Draglines
have been abundantly used in coal mining for decades, either as stripper or stripper and coal extractor. High initial capital outlay for dragline makes effective and efficient operation imperative to obtain low costs of overburden striping . Constant supervision, good overburden preparation, and preventive maintenance of dragline and selecting proper bench height of overburden for suitably selected machine should ensure efficient and effective operation of a dragline. Improvement in dragline productivity can have a dramatic effect on overall mining operation.
What is a balancing diagram?
Balancing diagram can be defined as the graphical representation of the scheme to be adopted for determining the suitable seating position of the dragline in order to get maximum overburden
accommodation in de-coaled area with least re-handling for achieving high rate of coal exposure and ensuring slope stability.
Dragline balancing primarily means establishing relationship between the system capacity and its workload. High capital outlay for dragline requires efficient operation to obtain low cost of OB removal.
What is the purpose of drawing a balancing diagram? As
the namesuggests, the overburdento be removedby the dragline shallbebalanced inthe available void, of previouscut, such that the re-handlingpercentage isminimum, the internal dumpis safe andstable, andleast susceptible tofailure.
Adragline-balancingdiagram
isprepared incorporating
suitably selected machine, design and geotechnical parameters of quarry
. The processof preparingsuch a diagramishighly interactiveand time consuming. Ifadragline isdeployed asper the guidelinebalancingdiagram, better safety, higher productivityand greater productioncan beachieved.
Key points: The balancing diagram shows: The dragline cut sections – key cut, first dig and re-handled section. The dragline bench height, cut width taken by draglines, thickness of coal seam and gradient and various slope angles. The balancing diagram is used for calculation of: Rate of coal exposure. Workload distribution on each •
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Method of Drawing Balancing Diagram
Step 1 – Decide the Width of Cut Depends on no. of shovels to be deployed, o/p parameters of dragline and system of working of dragline to be adopted. Step 2 – Decide the Thickness of Dragline Bench •
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V = Capacity of dragline in solid and re-handling A = Width of cut H = Height of dragline bench K = Coefficient of re-handling P= Coal Production target h = Height of coal seam n = Coefficient of loss of coal
Step 3 – Assume different Angles for drawing balancing diagram. Depends upon past experience and records. Step 4 – Deduce seating position of dragline. Depends on the technological system of face operation and the boom length of dragline. Step 5 – Calculate volume of OB to be accommodated for upper dragline. Limit of cutting depth and radius of unloading by D/L should be kept in mind Step 6 – Calculate the volume of OB to be rehandled. Step 7 – Calculate the area to be excavated by lower dragline. Step 8 – Calculate the maximum capacity of dump accommodation. •
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Case Study •
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The following case study has been carried out in mine 1 of a major opencast coal mine of Northern Coalfields Ltd, Singrauli, India. In the mine 1, the dragline bench was divided into two vertical benches, ie, upper bench (top bench) and lower bench (main bench). The upper bench height was about 14 m and l ower bench height was about 28 m. A dragline (dragline1) seated on upper bench excavated the overburden and casted the spoil into the de-coaled area to form a level pad to be re-handled subsequently. When the upper bench was advanced sufficiently, it provided the seat to excavate the key cut for coal exposure. Thereafter, the lagging dragline (dragline 2) on lower bench excavated the first dig to fully expose the coal seam subsequent to which it marched towards the spoil side to sit on the previously formed level pad, from where it re-handled the spoil to a greater height and distance.
The balancing diagram for draglines operating in vertical tandem was prepared to the scale, by using the given field parameters as registered during the field study and tabulated in the following table:
Parameters
Details
Dragline make and operational make
One 15/90 Russian make and one 24/96 Rapier and Ransome make working in vertical tandem mode.
Bench Height, m
Approx. 42
Cut width, m
85
Strip length, m
2000
Highwall slope angle, degree
70
OB bench slope angle, degree
60
Angle of repose for loose material, degree
38
Coal bench slope angle, degree
80
Gradient of coal seam, degree
3
Key cut width at top, m
38
Key cut width at bottom, m
5
Fig. Balancing diagram as prepared for the case study
Fig. Sectional view of the draglines working in vertical tandem
Results from the Balancing Diagram Dragline
Excavation
Cut area
Dump area
Equivalent annual o/p , Mm3
15/90 leading dragline no.1
Top Cut
ABCDA (1190 m2)
IJKQPI
1.725
Key Cut
EFGHE (520 m2)
PQROP
0.755
First Dig
GHIJG (1860 m2)
VWNLKRSTU V
2.67
24/96 lagging dragline no.2
Re-handle IJLNI 1.11 Total annual output = (1.725 + 0.755 + 2.67 + 1.10) Mm3 = 6.26 Mm3 {+10%} (702 m2)
Where, B = bucket capacity of dragline (m3); C = overall cycle time of dragline (s); K = overall utilization factor (AU); S = Swell factor for loose easy digging sandstone (0.719); F = Fill factor for loose easy digging sandstone (0.933); M = Machine travelling and positioning factor (0.8); Nh = No. of hours in a shift (8h); Ns = No. of shifts in a day (3 shifts); and Nd = No. of days in a year (365 days). Where, CE is in Mt; PFD = annual output of the dragline from the first dig (Mm3); A = Area of first dig (m2); W = Cut width (m); T = Thickness of coal seam (m); D = Specific gravity of coal; and R = Recovery factor.
References •
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A Critical Case Study on Draglines Operating in Vertical Tandem in a Coal Mine - Dr P Rai Opencast mine planning, deployment of HEMM for optimum utilization, total technical parameters of HEMM including limitations, and haul roads and it’s maintenance. - P.D. Rathi Balancing diagram—a basic planning tool for dragline operation. – V.K.Rai
