- Email: [email protected]
Study on Dragline-Bulldozer Operation with Variations in Coal Seam Thickness
Dec. 2007
Journal of China University of Mining & Technology
J China Univ Mining & Technol
Vol.17
No.4
2007, 17(4): 0464 – 0466
Study on Dragline-Bulldozer Operation with Variations in Coal Seam Thickness ZHOU Wei, CAI Qing-xiang, CHEN Shu-zhao School of Mining and Safety Engineering, China University of Mining &Technology, Xuzhou, Jiangsu 221008, China Abstract: The dragline is one of the most promising surface mining machines in China. This paper studies the interaction between the working bench advancing speed and the stripping volume with variation in coal seam thickness. Adjusting the bulldozing volume (depth) and/or changing the dragline bench height are proposed as means to ensure a smooth and economical mining operation. When the coal seam is getting thicker it is recommended to reduce the bulldozing volume (depth) for a higher dragline efficiency. When the coal seam is getting thinner it is recommended to increase the bulldozing volume (depth) to ensure the dragline can work at the proper bench height. Key words: open pit; coal thickness variation; dragline; adaptability; bulldozer CLC number: TP 39
1
Introduction
The dragline mining system is a combination of overburden removing, hauling and dumping. Due to simplicity of operation it is known as a low-cost process. Although the dragline has not yet been widely utilized in China as the world mining equipment market trends to larger and more centralized systems mines in China have been showing a strong interest in draglines[1–3]. Therefore, it is expected that both developing and operating mines will begin adopting the dragline stripping system[4–5]. To make full use of the dragline’s capability, the stripping bench height should be at the proper height and operation of the dragline and bulldozer is coordinated[6]. Assuming the stripping bench height is unchanged cooperation between the dragline and the bulldozer is a critical issue. In addition to these issues this study also discusses the issue of variations in coal seam thickness.
2
Annual Volumes of Dragline and Bulldozer
The dragline’s maximum production capability is determined once the specifications are selected. In
some cases the bulldozing volume (height) and dragline bench height must be adjusted to meet the machine’s production capacity. Suppose the designed annual production is M and the average length of the mining line is Lm. Then the annual advancing distance must be l=
M Lm h ρ
(1)
where h is annual average thickness of the coal seam in meters; H is the height of the stripping bench with dragline in meters; and ρ is the coal density in kg/m3. The annual stripping volume for the dragline is given by:
Vd = Kl ( H − H t ) Lp
(2)
The annual stripping volume for the bulldozer is given by: Vt = KlH t Lp
(3)
where Ht is the bulldozer operating depth in meters; K is a rock factor reflecting the looseness of the rock; and Lp is the average length of the stripping line in meters. The annual stripping volume for both the dragline
Received 09 January 2007; accepted 21 March 2007 Projects 50474069 supported by the National Natural Science Foundation of China and 2006BAB16B00 by the State Scientific and Technological Project of the 11th Five-Year Plan Corresponding author. Tel: +86-13815314985; E-mail address: [email protected]
ZHOU Wei et al
Study on Dragline-Bulldozer Operation with Variations in Coal Seam Thickness
and bulldozer is:
V = Vd + Vt
(4)
From equations (1), (2) and (3) it is clear that, over a period where Lm, ρ and Lp are unchanged, l and h have an inverse relationship. Adjusting Ht can satisfy the requirement for a required annual stripping volume. Given that dragline bench height and bulldozing depth remain unchanged the dragline stripping volume and bulldozing volume remain unchanged, too.
3
Coordinating Operating Height Between the Dragline and Bulldozer
1) Annual average thickness of coal seam Coal is the outcome of a long geological period so its thickness, ash content and heat value are regarded as random regionalized variables. Suppose the thickness of a coal seam is x; in a certain area the semi-variogram of the thickness is f(x),
( ) ∫ xf ( x )dx
E X =
(5)
dragline also increases, given that the dragline bench height is unchanged.
∆ Vb = KLp ⎡⎣ ( H − H t2 ) ls − ( H − H t1 ) l ⎤⎦
∆Vb = KLp ⎡⎣( H − H t1 ) l − ( H − H t2 ) l2 ⎤⎦
(6)
where l is the annual advance speed for the design coal seam thickness in m/a; l2 is the annual advance speed for a thicker coal seam (m/a); Ht1 is the bulldozing depth for the initially assumed coal seam (m); and Ht2 is the bulldozing depth for a thicker coal seam (m). To achieve higher dragline efficiency the production capacity of the dragline should be fully utilized. In other words, it is optimum to have ∆ Vb=0, or:
( H − H t1 ) l − ( H − H t2 ) l2 = 0
(7)
In equation (7) l and l2 are two fixed values. There are two options: ķ decrease the bulldozing depth Ht; ĸ increase the dragline bench height H. However, the actual annual average thickness of a coal seam is expected to vary to some extent and the increasing H may lead to changes in some primary operating parameters. This may result in an adverse impact. Therefore, typically the second measure is not adopted in strip mining but the first option is very common. 3) Optimization of the bulldozing depth and dragline bench height with a variation in coal seam thickness In this case as the annual advancing speed of the dragline increases the annual stripping volume of the
(8)
In a dragline stripping system there are up to three bulldozers that can be deployed along the working bench: Therefore, Vft is fixed. When ∆ Vb > Vf, simply increasing the annual operating volume of the dragline and bulldozer could meet the production demand. When Vf < ∆ VbİVf + Vft, increasing the annual operating volume of the bulldozer can meet the production demand, When ∆ Vb > Vf + Vft, the dragline bench height must be adjusted. The bench height after adjustment is:
Hh = H −
Vb − Vf − Vft KLp l
(9)
4) Maximum bulldozing depth The bulldozing depth is constrained by both the bulldozer production capacity and the bench geometry. The constraints are shown as follows:
S
2) Solving to meet production demand when the coal seam thickness is greater than initially supposed In this case the dragline’s annual advancing speed becomes slower. The dragline’s annual stripping volume is also reduced. The volume difference is given by:
465
nt İ 2 ht max lt l İ ntVt max
(10) (11)
where nt is the number of bulldozers; htmax is the maximum bulldozing depth (m); lt is the average working length of a bulldozer (m); l is the mining advancing speed (m); and Vtmax is the maximum production (m3/a). The relationship between the bulldozer operating efficiency and the bulldozing depth must also be considered. The greater the depth, the lower the operating efficiency will be. 5) Production reliability of the dragline given variations in coal seam thickness The production reliability of a dragline system means the probability for a dragline to achieve the production plan given a probability that the coal seam becomes either thicker or thinner. The reliability is:
Ms ×100% (12) M where Ms is the dragline realized production and M is the design annual production rate (Mt). It is shown from the reliability property 0 İ R İ1 : ķ When Ms ı M, R=1. In this case the dragline can achieve the production target; ĸ When 0İMsİM, 0İR˘1. In this case the dragline can not achieve the production target so that a larger value of R will provide higher system reliability. R=
466
4
Journal of China University of Mining & Technology
Vol.17 No.4
Table 1 Dragline and bulldozer operating parameters with variation in average coal seam thickness
Case Study[7]
The Haerwusu Surface Coal Mine uses a dragline with an operating radius of 94.5 m and a bucket capacity of 93.93 m3. assume that the casting rate of cast blasting is 0.243, the annual stripping capacity of the dragline is 16.67 Mm3, the annual target coal production is M=20 Mt, that two bulldozers are used (the annual capacity of the bulldozer is 2.41 Mm3), that the thickness of the coal seam is a constant; h =28 m, that the stripping bench height is H=50 m, that the designated bulldozing depth is Ht=6 m, that the length of the coal mining bench is Lm=2000 m and that the length of the stripping bench Lp=2030 m. Table 1 shows that if the average thickness of the coal seam becomes thinner then the annual advance speed becomes faster. Comparing the operating capacities of the bulldozer and the dragline if the annual average thickness of the coal seam is less than 28 m then the bulldozing depth should be increased. However, if the annual average thickness of the coal seam is less than 25 m then the bulldozer operating depth has reached the limit and the bench height must be reduced.
Average annual thickness of coal seam (m) 28
Advance speed (m) 249.75
Bulldozing depth (m) 6
Dragline production (Mm3) 16.15
Bulldozing production (Mm3) 3.04
27 26
259 268.96
8 8
15.69 16.3
4.2 4.37
25
279.7
8.48
16.67
4.81
5
Conclusions
1) A dragline mining system incorporated with cast blasting is widely used in stripping mining. In most cases the bulldozer prepares the floor for the dragline. By use of cast blasting techniques a large amount of overburden can be cast into the mined-out area thus making the dragline stripping method very cost-effective. 2) An equation, depending on the capacity and work efficiency of the bulldozer, was derived for the maximum bulldozing depth. A methodology for evaluating the production reliability of a cooperating dragline-bulldozer system was developed. 3) As the thickness of a coal seam varies the flexibility of a dragline-bulldozer system is higher than that of a pure dragline system. With the aid of the bulldozer the production capacity of the dragline can be fully utilized without adding significant extra cost.
References [1]
[2] [3] [4] [5] [6] [7]
Zhang Y D, Li K M, Shang T. Open cast method and its application prospect in surface mines in China—technical paper series for open cast method in surface mines. Journal of China University of Mining & Technology, 2002, 31(4): 331–334. (In Chinese) Zhang Y D, Guo S H, Yang Y H, et al. Selection of draglines for open cast mining. Journal of China University of Mining & Technology, 2002, 31(5): 341–343. (In Chinese) Shang T, Cai Q X, Zhang Y D, et al. Analysis of some technological problems for large surface coal mines in China. Journal of China University of Mining & Technology, 2005, 34(3): 138–142. (In Chinese) Guo S H. Application Research of Dragline Stripping System in Heidaigou Surface Mine [Ph.D. dissertation]. Fuxin: Liaoning Technical University, 2003. (In Chinese) Zhang Y D, Fu H X, Wang Q R, et al. Casting blast and analysis of mining parameters of stripping bench. Journal of China University of Mining & Technology, 2003, 32(1): 27–30. (In Chinese) Ma J, Li K M. Research on overcast blast and dragline stripping system. China Mining, 2003, 12(7): 44–46. (In Chinese) Ma J, Cai Q X, Zhou W, et al. Study on the adaptability of dragline to the variation of coal seam thickness during mining operation period of large surface coal mine. Journal of Liaoning Technical University, 2006, 25(5): 622–625. (In Chinese)
Journal of China University of Mining & Technology
J China Univ Mining & Technol
Vol.17
No.4
2007, 17(4): 0464 – 0466
Study on Dragline-Bulldozer Operation with Variations in Coal Seam Thickness ZHOU Wei, CAI Qing-xiang, CHEN Shu-zhao School of Mining and Safety Engineering, China University of Mining &Technology, Xuzhou, Jiangsu 221008, China Abstract: The dragline is one of the most promising surface mining machines in China. This paper studies the interaction between the working bench advancing speed and the stripping volume with variation in coal seam thickness. Adjusting the bulldozing volume (depth) and/or changing the dragline bench height are proposed as means to ensure a smooth and economical mining operation. When the coal seam is getting thicker it is recommended to reduce the bulldozing volume (depth) for a higher dragline efficiency. When the coal seam is getting thinner it is recommended to increase the bulldozing volume (depth) to ensure the dragline can work at the proper bench height. Key words: open pit; coal thickness variation; dragline; adaptability; bulldozer CLC number: TP 39
1
Introduction
The dragline mining system is a combination of overburden removing, hauling and dumping. Due to simplicity of operation it is known as a low-cost process. Although the dragline has not yet been widely utilized in China as the world mining equipment market trends to larger and more centralized systems mines in China have been showing a strong interest in draglines[1–3]. Therefore, it is expected that both developing and operating mines will begin adopting the dragline stripping system[4–5]. To make full use of the dragline’s capability, the stripping bench height should be at the proper height and operation of the dragline and bulldozer is coordinated[6]. Assuming the stripping bench height is unchanged cooperation between the dragline and the bulldozer is a critical issue. In addition to these issues this study also discusses the issue of variations in coal seam thickness.
2
Annual Volumes of Dragline and Bulldozer
The dragline’s maximum production capability is determined once the specifications are selected. In
some cases the bulldozing volume (height) and dragline bench height must be adjusted to meet the machine’s production capacity. Suppose the designed annual production is M and the average length of the mining line is Lm. Then the annual advancing distance must be l=
M Lm h ρ
(1)
where h is annual average thickness of the coal seam in meters; H is the height of the stripping bench with dragline in meters; and ρ is the coal density in kg/m3. The annual stripping volume for the dragline is given by:
Vd = Kl ( H − H t ) Lp
(2)
The annual stripping volume for the bulldozer is given by: Vt = KlH t Lp
(3)
where Ht is the bulldozer operating depth in meters; K is a rock factor reflecting the looseness of the rock; and Lp is the average length of the stripping line in meters. The annual stripping volume for both the dragline
Received 09 January 2007; accepted 21 March 2007 Projects 50474069 supported by the National Natural Science Foundation of China and 2006BAB16B00 by the State Scientific and Technological Project of the 11th Five-Year Plan Corresponding author. Tel: +86-13815314985; E-mail address: [email protected]
ZHOU Wei et al
Study on Dragline-Bulldozer Operation with Variations in Coal Seam Thickness
and bulldozer is:
V = Vd + Vt
(4)
From equations (1), (2) and (3) it is clear that, over a period where Lm, ρ and Lp are unchanged, l and h have an inverse relationship. Adjusting Ht can satisfy the requirement for a required annual stripping volume. Given that dragline bench height and bulldozing depth remain unchanged the dragline stripping volume and bulldozing volume remain unchanged, too.
3
Coordinating Operating Height Between the Dragline and Bulldozer
1) Annual average thickness of coal seam Coal is the outcome of a long geological period so its thickness, ash content and heat value are regarded as random regionalized variables. Suppose the thickness of a coal seam is x; in a certain area the semi-variogram of the thickness is f(x),
( ) ∫ xf ( x )dx
E X =
(5)
dragline also increases, given that the dragline bench height is unchanged.
∆ Vb = KLp ⎡⎣ ( H − H t2 ) ls − ( H − H t1 ) l ⎤⎦
∆Vb = KLp ⎡⎣( H − H t1 ) l − ( H − H t2 ) l2 ⎤⎦
(6)
where l is the annual advance speed for the design coal seam thickness in m/a; l2 is the annual advance speed for a thicker coal seam (m/a); Ht1 is the bulldozing depth for the initially assumed coal seam (m); and Ht2 is the bulldozing depth for a thicker coal seam (m). To achieve higher dragline efficiency the production capacity of the dragline should be fully utilized. In other words, it is optimum to have ∆ Vb=0, or:
( H − H t1 ) l − ( H − H t2 ) l2 = 0
(7)
In equation (7) l and l2 are two fixed values. There are two options: ķ decrease the bulldozing depth Ht; ĸ increase the dragline bench height H. However, the actual annual average thickness of a coal seam is expected to vary to some extent and the increasing H may lead to changes in some primary operating parameters. This may result in an adverse impact. Therefore, typically the second measure is not adopted in strip mining but the first option is very common. 3) Optimization of the bulldozing depth and dragline bench height with a variation in coal seam thickness In this case as the annual advancing speed of the dragline increases the annual stripping volume of the
(8)
In a dragline stripping system there are up to three bulldozers that can be deployed along the working bench: Therefore, Vft is fixed. When ∆ Vb > Vf, simply increasing the annual operating volume of the dragline and bulldozer could meet the production demand. When Vf < ∆ VbİVf + Vft, increasing the annual operating volume of the bulldozer can meet the production demand, When ∆ Vb > Vf + Vft, the dragline bench height must be adjusted. The bench height after adjustment is:
Hh = H −
Vb − Vf − Vft KLp l
(9)
4) Maximum bulldozing depth The bulldozing depth is constrained by both the bulldozer production capacity and the bench geometry. The constraints are shown as follows:
S
2) Solving to meet production demand when the coal seam thickness is greater than initially supposed In this case the dragline’s annual advancing speed becomes slower. The dragline’s annual stripping volume is also reduced. The volume difference is given by:
465
nt İ 2 ht max lt l İ ntVt max
(10) (11)
where nt is the number of bulldozers; htmax is the maximum bulldozing depth (m); lt is the average working length of a bulldozer (m); l is the mining advancing speed (m); and Vtmax is the maximum production (m3/a). The relationship between the bulldozer operating efficiency and the bulldozing depth must also be considered. The greater the depth, the lower the operating efficiency will be. 5) Production reliability of the dragline given variations in coal seam thickness The production reliability of a dragline system means the probability for a dragline to achieve the production plan given a probability that the coal seam becomes either thicker or thinner. The reliability is:
Ms ×100% (12) M where Ms is the dragline realized production and M is the design annual production rate (Mt). It is shown from the reliability property 0 İ R İ1 : ķ When Ms ı M, R=1. In this case the dragline can achieve the production target; ĸ When 0İMsİM, 0İR˘1. In this case the dragline can not achieve the production target so that a larger value of R will provide higher system reliability. R=
466
4
Journal of China University of Mining & Technology
Vol.17 No.4
Table 1 Dragline and bulldozer operating parameters with variation in average coal seam thickness
Case Study[7]
The Haerwusu Surface Coal Mine uses a dragline with an operating radius of 94.5 m and a bucket capacity of 93.93 m3. assume that the casting rate of cast blasting is 0.243, the annual stripping capacity of the dragline is 16.67 Mm3, the annual target coal production is M=20 Mt, that two bulldozers are used (the annual capacity of the bulldozer is 2.41 Mm3), that the thickness of the coal seam is a constant; h =28 m, that the stripping bench height is H=50 m, that the designated bulldozing depth is Ht=6 m, that the length of the coal mining bench is Lm=2000 m and that the length of the stripping bench Lp=2030 m. Table 1 shows that if the average thickness of the coal seam becomes thinner then the annual advance speed becomes faster. Comparing the operating capacities of the bulldozer and the dragline if the annual average thickness of the coal seam is less than 28 m then the bulldozing depth should be increased. However, if the annual average thickness of the coal seam is less than 25 m then the bulldozer operating depth has reached the limit and the bench height must be reduced.
Average annual thickness of coal seam (m) 28
Advance speed (m) 249.75
Bulldozing depth (m) 6
Dragline production (Mm3) 16.15
Bulldozing production (Mm3) 3.04
27 26
259 268.96
8 8
15.69 16.3
4.2 4.37
25
279.7
8.48
16.67
4.81
5
Conclusions
1) A dragline mining system incorporated with cast blasting is widely used in stripping mining. In most cases the bulldozer prepares the floor for the dragline. By use of cast blasting techniques a large amount of overburden can be cast into the mined-out area thus making the dragline stripping method very cost-effective. 2) An equation, depending on the capacity and work efficiency of the bulldozer, was derived for the maximum bulldozing depth. A methodology for evaluating the production reliability of a cooperating dragline-bulldozer system was developed. 3) As the thickness of a coal seam varies the flexibility of a dragline-bulldozer system is higher than that of a pure dragline system. With the aid of the bulldozer the production capacity of the dragline can be fully utilized without adding significant extra cost.
References [1]
[2] [3] [4] [5] [6] [7]
Zhang Y D, Li K M, Shang T. Open cast method and its application prospect in surface mines in China—technical paper series for open cast method in surface mines. Journal of China University of Mining & Technology, 2002, 31(4): 331–334. (In Chinese) Zhang Y D, Guo S H, Yang Y H, et al. Selection of draglines for open cast mining. Journal of China University of Mining & Technology, 2002, 31(5): 341–343. (In Chinese) Shang T, Cai Q X, Zhang Y D, et al. Analysis of some technological problems for large surface coal mines in China. Journal of China University of Mining & Technology, 2005, 34(3): 138–142. (In Chinese) Guo S H. Application Research of Dragline Stripping System in Heidaigou Surface Mine [Ph.D. dissertation]. Fuxin: Liaoning Technical University, 2003. (In Chinese) Zhang Y D, Fu H X, Wang Q R, et al. Casting blast and analysis of mining parameters of stripping bench. Journal of China University of Mining & Technology, 2003, 32(1): 27–30. (In Chinese) Ma J, Li K M. Research on overcast blast and dragline stripping system. China Mining, 2003, 12(7): 44–46. (In Chinese) Ma J, Cai Q X, Zhou W, et al. Study on the adaptability of dragline to the variation of coal seam thickness during mining operation period of large surface coal mine. Journal of Liaoning Technical University, 2006, 25(5): 622–625. (In Chinese)