Optimization of productivity with surface miner using conveyor loading and truck dispatch system
3 likes277 views
The paper discusses optimizing productivity at a limestone mine using a surface miner with a conveyor loading and dump-truck dispatch system. A simulation model developed in MATLAB indicates that an optimal number of trucks for efficient operation is approximately five, with a confidence interval of 2.3 to 7.4. The study emphasizes the importance of face length and truck availability in enhancing productivity while minimizing downtime.
![IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
__________________________________________________________________________________________
Volume: 02 Issue: 09 | Aug-2013, Available @ http://www.ijret.org 393
OPTIMIZATION OF PRODUCTIVITY WITH SURFACE MINER USING
CONVEYOR LOADING AND TRUCK DISPATCH SYSTEM
S. K. Palei1
, N. C. Karmakar2
, P. Paliwal3
, B. Schimm4
1
Assistant Professor, 2
Professor, Department of Mining Engineering, Indian Institute of Technology (Banaras Hindu
University), Varanasi 221005, U.P., India, skpalei.min@iitbhu.ac.in
3
Assistant Manager, Chhatarpur I Mine, Pathkhera Area, WCL, Coal India Limited
4
Manager, Mining Division, Wirtgen GmbH, Windhagen, Germany
Abstract
This paper aims at optimizing the productivity at the surface miner’s face with conveyor loading and dump-truck dispatch system to
minimize the down times of surface miner as well as trucks. The surface miner was working in opencut method in a limestone mine
located in the Southern part of India. Time study was carried out during three working shifts (each of eight-hour duration) for
productivity analysis. A model has been developed and simulated in MATLAB for the productivity of surface miner considering the
impact of two major parameters – number of trucks and available face length. The number of trucks for optimum production was
found to be five. However, the 5% and 95% confidence interval for the number of trucks was 2.3 and 7.4 respectively for the case
study face. It was also observed that the face of 330 m length was sufficient for the surface miner to work efficiently.
Index Terms: Opencast mine, Surface miner, Mining machinery, Truck dispatch system, Productivity analysis
-----------------------------------------------------------------------***-----------------------------------------------------------------------
1. INTRODUCTION
Surface miner is a crawler mounted machine generally used
for selective mining of coal and useful minerals. Though the
first surface miner was introduced to the South African
gypsum mine in 1983, now-a-days about 300 machines are
working worldwide. The application of rock cutting
technology has been extended with the mechanization process
to increase the productivity of mines. Surface miners play an
important role in getting the desired production in opencast
mines. The site-specific problems still exist in some of the
mines to get the desired output from the opencast mines.
The present work is based on time-study data collected for a
surface miner with conveyor loading and dump-truck
(henceforth called truck) dispatch system in a limestone mine.
The major parameters influencing the productivity of the
surface miner are strength of rock mass, area available for
mining operation, availability of trucks and their capacity,
cutting tools used, and production planning. Mining industry
emphasizes on the best possible utilization of its resources to
increase the productivity. This paper aims at optimizing two
important parameters like face length and availability of
dump-trucks through a developed simulation model to
increase the productivity of the mine.
2. BACKGROUND
It is the requirement of mining industry to produce good
quality minerals with the available techniques. Surface miners
are generally deployed for selective mining of minerals for
efficient exploitation of the deposit. It eliminates the multiple
operations such as drilling, blasting and primary crushing.
Surface miner drastically reduces whole body vibration of
operator. There are also environmental gains in terms of noise
levels and air-borne dust concentrations [1]. The surface
miners are used in opencast mines for mining the soft
sedimentary deposits layer by layer, and dispatching the mined
out material onto the truck traveling alongside, or side-casting,
or windrowing the material [2]. The mineral is cut into small
lumps/chips and can be transported through in-built conveyor
belts [3]. It works on the principle of the central drum cutting
technology. The cutting drum has cutting tool holders welded
to its body in the form of helix. Cutting tool holders are
specially designed, replaceable, and picks are fitted to these
tool holders. The drum is driven mechanically by a diesel
engine of adequate power by a shifting clutch and power belts
acting on the drum gear. The first surface miner was deployed
in the Indian mineral sector in 1994 to a limestone mine of
Gujarat Ambuja Cements Limited, Gujarat [3]. Since then
Wirtgen surface miners have gained popularity in India for
mining soft to medium hard limestone and coal deposits.
Currently, in various mining companies, multiple units of
surface miners are in operation e.g., Gujurat Ambuja (7 unit),
Madras Cements (5 units), India Cement (3 units) and MPL (2
units) [4]. Surface miners have already proved their strength
as a profitable alternative to conventional mining methods.
The use of surface miner is also an alternative, where blasting
is prohibited or use of explosives is a crucial issue.](https://image.slidesharecdn.com/optimizationofproductivitywithsurfaceminerusingconveyorloadingandtruckdispatchsystem-160802125846/85/Optimization-of-productivity-with-surface-miner-using-conveyor-loading-and-truck-dispatch-system-1-320.jpg)
![IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
__________________________________________________________________________________________
Volume: 02 Issue: 09 | Aug-2013, Available @ http://www.ijret.org 394
3. METHODOLOGY
The time study was carried out to increase the productivity of
the surface miner with conveyor loading and truck dispatch
system. A model has been developed to minimize the idle time
of surface miner and trucks, and to estimate the optimum face
length desired for a surface miner to work effectively.
3.1 Mine Description and Data Collection
The opencast limestone mine is located in the Southern part of
India, where the surface miner was working in the opencut
method (as shown in Fig. 1) during time study. Opencut is a
method in which surface miner cuts the material along the
face-length and returns to the starting place simultaneously
cutting the adjacent slice [3]. Time-study was carried out for
three shifts, consisting of two II Shifts (working hours
between 2 p.m. to 10 p.m.) and one III Shift (working hours
between 10 p.m. to 6 a.m.). The changes in engine ‘hourly
machine rate’ (HMR) for each eight-hour shift were 5.1, 6.3
and 5.2 hours respectively. The surface miner, SM 2200
(Wirtgen make), was working at the same face for all the
shifts during the time study. The SM 2200 used had a
maximum cutting depth of 300 mm with cutting width of
2200 mm. The surface miner was working in a face of length
about 330 m and width 50 m. The average production rate was
288.3 tonnes per hour from the case study face. The mean
capacity of the trucks used during the study period was 23.3
tonnes with variance of 2.4.
Fig1. Cutting sequence of a Surface Miner in Opencut method
(Source: Wirtgen Surface Mining manual, 2002).
3.2 Development of Simulation Model
The independent variables are loading time of trucks, the
cutting time of surface miner to load a truck, truck positioning
time, truck hauling time, truck waiting time at the face, and
the cycle time of a truck. The response variables were the
number of trucks and length of the face. The schematic
diagram of the conveyor loading-truck dispatch system is
depicted in Fig. 2.
Unloaded
Truc k
S urfac e Miner
with C onveyor
L oading
L oaded
Truc k
Weig h
B ridg e
C rus her
L oaded
Truc k
Unloaded
Truc k
S urfac e Miner
with C onveyor
L oading
L oaded
Truc k
Weig h
B ridg e
C rus her
L oaded
Truc k
Fig2. Schematic diagram of Surface miner’s conveyor loading
and truck dispatch system
The following notations have been used:
Cs : Cycle time of the SM
Ct : Cutting time of SM to load a truck
St : Positioning time of SM in opencut method of working
after turning
Is : Idle time i.e. down-time of SM
Tt : Turning time of SM
Ac : Actual cutting time of SM in a single cycle
Cd : Cycle time of truck
Hd : Hauling time of trucks
Ul : Unloading time of trucks
Tw : Truck waiting time in the queue at the face
Ts : Truck positioning time
Ld : Loading time of truck = Ct + Ts
Ac′ : Average cutting time of a surface miner to load a single
truck
Nd : Number of trucks required in a single cycle of SM
The cycle time of surface miner (Cs) and that of the truck (Cd)
are obtained from the following relationships:
Cd = Ct + Ts + Hd + Ul + Tw … (1)
Cs = Ct + Ts + St + Tt + Is … (2)
The number of trucks (N) can be related to the time
parameters for developing the model. The number of trucks
for efficient exploitation of the deposit for increasing the
productivity of the surface miner face can be calculated as
outlined below:
Average cutting time to load a truck
c
Cycle time of SM
A '
Number of trucks in single cycle of SM
… (3)
No. of trucks required in a single cycle of SM
d
Actual cutting time of SM in a cycle
N
Loading time of a truck
… (4)](https://image.slidesharecdn.com/optimizationofproductivitywithsurfaceminerusingconveyorloadingandtruckdispatchsystem-160802125846/85/Optimization-of-productivity-with-surface-miner-using-conveyor-loading-and-truck-dispatch-system-2-320.jpg)
![IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
__________________________________________________________________________________________
Volume: 02 Issue: 09 | Aug-2013, Available @ http://www.ijret.org 395
Total no. of trucks required for the SM face (N)
Cycle time of a truck Actual cutting time of SM in a single cycle
Cycle time of SM Loading time of a single truck
d c
s d
C
C L
(C +H +U +T +T )
(C +T +T +S +I ) + C )
l
t
t w s cd
t s t st s
… (5)
Actual cutting time of surface miner in a cycle is the time
during which a surface miner cuts and loads the material onto
the trucks. It is the cycle time of surface miner excluding idle
time, turning time and truck waiting time. The collected data
are processed to fit to the suitable statistical distribution for
simulation. The independent and response variables were
modeled by fitting to suitable probability density functions. A
model was developed to maximize the production
simultaneously optimizing system utilization at the surface
miner face to increase the overall work efficiency of the
system.
3.3 Modeling of Independent Variables
The independent variables in this study are truck positioning
time, cutting time of surface miner, hauling time of truck,
truck waiting time, turning time of surface miner and idle time
of surface miner. The modeling of independent variables from
the collected time study data were fitted to suitable probability
density functions. For fitting the data to probability
distributions, SIMULINK of MATLAB 7.0.1 was used [5].
The observed data as well as the fitted curves are depicted in
Fig. 3 for the independent variables.
Before surface miner starts cutting and simultaneously loading
onto the truck, the truck should be positioned properly so that
spillage of material is minimum. This time is called the truck
positioning time (Ts in min). This truck positioning time is
fitted to a single parameter exponential distribution with β =
0.17 min as shown in Fig. 3(a). Hauling time of truck (Hd) is
the time taken by truck from the face to the unloading point
(may be dump yard or crusher) and coming back to the face,
excluding time of loading and truck waiting time for loading.
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
0
1
2
3
4
5
6
Dump-truck setting time (min)
ProbabilityDensity
Dump-truck setting time, Ts
fitted curve
10 12 14 16 18 20 22 24 26
0
0.02
0.04
0.06
0.08
0.1
0.12
Hauling time of dump-trucks (minutes)
ProbabilityDensity
Hauling time of
dump-trucks, Hd
Fitting curves
1.5 2 2.5 3 3.5 4 4.5
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Cutting time of SM (min)
ProbabilityDensity
Cutting time of SM, Ct
fitted curve
0 1 2 3 4 5
0
0.5
1
1.5
2
2.5
3
3.5
4
Ideal time of SM (min)
ProbabailityDensity
Ideal time of SM, Is
fitted curve
0 2 4 6 8 10 12
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0.2
Turning time of Surface Miner (min)
ProbabilityDensity
Turning time of SM, Tt
fitted curve
Figure 3 (a). Exponential distribution for Truck setting time Figure 3 (b). Log-normal distribution for hauling time of truck
Figure 3 (c). Log-normal distribution for cutting time of surface miner
Figure 3 (e). Log-normal distribution for turning time of Surface Miner
Figure 3 (d). Exponential distribution for idle time of surface miner
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
0
1
2
3
4
5
6
Dump-truck setting time (min)
ProbabilityDensity
Dump-truck setting time, Ts
fitted curve
10 12 14 16 18 20 22 24 26
0
0.02
0.04
0.06
0.08
0.1
0.12
Hauling time of dump-trucks (minutes)
ProbabilityDensity
Hauling time of
dump-trucks, Hd
Fitting curves
1.5 2 2.5 3 3.5 4 4.5
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Cutting time of SM (min)
ProbabilityDensity
Cutting time of SM, Ct
fitted curve
0 1 2 3 4 5
0
0.5
1
1.5
2
2.5
3
3.5
4
Ideal time of SM (min)
ProbabailityDensity
Ideal time of SM, Is
fitted curve
0 2 4 6 8 10 12
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0.2
Turning time of Surface Miner (min)
ProbabilityDensity
Turning time of SM, Tt
fitted curve
Figure 3 (a). Exponential distribution for Truck setting time Figure 3 (b). Log-normal distribution for hauling time of truck
Figure 3 (c). Log-normal distribution for cutting time of surface miner
Figure 3 (e). Log-normal distribution for turning time of Surface Miner
Figure 3 (d). Exponential distribution for idle time of surface miner
Fig3. Observed as well as fitted distributions of various time
variables
The observed as well as fitted curves for hauling time of
trucks (Hd, in min) is presented in Fig. 3(b). The hauling time
is fitted to a log-normal distribution with µ=2.88 and σ = 0.19.
Cutting time of surface miner to load a truck (Ct) is time taken
by a surface miner to cut the mineral and load a single truck.
The observed as well as fitted curves for cutting time of
surface miner to load a single truck (Ct) are presented in Fig.
3(c). The cutting time of surface miner to load a single truck is
fitted to a log-normal distribution with µ=1.01 and σ = 0.19.
Down time of surface miner (Is) is the time during which the
surface miner was not cutting and loading. The observed as
well as the fitted curves for down time of surface miner (Is) is
presented in Fig. 3(d). The data is fitted to an exponential
distribution with mean value of 0.63 min. Turning time (Tt) is
the time taken by the surface miner to take a turn and enter in
another line of cutting and loading. The turning time of
surface miner is fitted to a log-normal distribution with
parameters µ=1.42 and σ =0.56 as depicted in Fig. 3(e).
4. ANALYSIS AND RESULTS
Random samples are selected for the response variable,
number of trucks and length of face based on the modeled
independent parameters. The developed model was simulated
with a program written in MATLAB. The number of trucks
was estimated in surface miner face to optimize the conveyor
loading-truck dispatch system by collecting 10,000 samples.
The mean number of trucks required was found to be 4.7 with
standard deviation of 1.2 (as shown in Fig. 4). Hence, the
number of trucks based on the results of simulation model](https://image.slidesharecdn.com/optimizationofproductivitywithsurfaceminerusingconveyorloadingandtruckdispatchsystem-160802125846/85/Optimization-of-productivity-with-surface-miner-using-conveyor-loading-and-truck-dispatch-system-3-320.jpg)
![IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
__________________________________________________________________________________________
Volume: 02 Issue: 09 | Aug-2013, Available @ http://www.ijret.org 396
would be 5 (taking integer approximation of 4.7). However,
the 5% and 95% confidence interval for the number of trucks
was found to be 2.3 and 7.4 respectively. The effect of face
length on productivity of surface miner was estimated from
the available time study data as shown in Fig. 5. It
demonstrates that with increase in face length, say up to 330m,
the hourly production of surface miner increases, beyond
which there’s only marginal improvement in productivity.
2 3 4 5 6 7 8 9 10
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
Number of dump-trucks
ProbabilityDensity
Number of dump-trucks, N
Fitting curve
Fig4. Simulation results for number of dump-trucks
Fig5. Hourly productivity of SM vs. face length
CONCLUSIONS
This paper explains how to optimize the production in a
surface miner face with conveyor loading to minimize idle
time of both surface miner and trucks. Two parameters
namely, face length and the availability of number of trucks at
the surface miner face are considered for the study. The idle
times (such as unavailability of trucks, turning and
repositioning of surface miner, jamming of material in
conveyor belt and its clearance, break for operator change),
and truck positioning are always associated with the surface
miner. A simulation model was developed and the time study
data of a limestone mine was used to optimize the area
availability and to assign desired number of trucks. The
surface miner was working in opencut method with direct
conveyor directly loading onto trucks. The number of trucks
and area availability (e.g., face length) has been estimated to
efficiently increase the productivity of the system. The
parameters of the time study data were modeled to suitable
‘probability density functions’ by SIMULINK of MATLAB
7.0.1 and a program was written to simulate the developed
model. The number of trucks based on the simulation results
would be five. The mean truck capacity used during the time
study was 23.3 tonnes with the variance of 2.4. It is also
observed 33o m face length was optimum from productivity
pointy of view.
The objective of this paper was to optimize the idle time of
both surface miner and trucks to increase work efficiency and
productivity. During modeling of idle time of surface miner,
major breaks continuing for more than 20 min were excluded
for the sake of simplicity in calculation. This study can be
extended to consider the cutting speed of surface miner and
hauling speed of surface miner to estimate the number of
trucks for efficient operation. Any change in truck capacity,
face length, surface miner’s model, make and productivity,
and rock characteristics may affect the results of the developed
model. The developed methodology can well be extended to
other mines having similar conveyor loading–truck dispatch
arrangement.
ACKNOWLEDGEMENTS
The authors are grateful to Wirtgen India Private Limited,
Bangalore for their permission to use the time-study data. The
authors are also grateful to the mine management for their
cooperation.
REFERENCES
[1] . Dey, K and Bhattacharya, J.: Operation of Surface
Miner: Retrospect of a Decade Journey in India.
Procedia Engineering, 2012, Vol. 46, pp. 97 – 104.
[2] . B. Schimm: Economic mining of thin seams in flat
deposits with surface miners, Mining Technology,
1996, 78(895), pp.89-92.
[3] . Wirtgen surface mining manual, Wirtgen group,
Windhagen, Germany, p.52, 2002.
[4] . Prakash, A., Murthy, V. M. S. R. and Singh, K. B.:
Rock excavation using surface miners: An overview of
some design and operational aspects. International
Journal of Mining Science and Technology 2013, Vol.
23, pp. 33–40.
[5] . MATLAB 7.0.1: Matlab software package.](https://image.slidesharecdn.com/optimizationofproductivitywithsurfaceminerusingconveyorloadingandtruckdispatchsystem-160802125846/85/Optimization-of-productivity-with-surface-miner-using-conveyor-loading-and-truck-dispatch-system-4-320.jpg)
Optimization of productivity with surface miner using conveyor loading and truck dispatch system
- 1. IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308 __________________________________________________________________________________________ Volume: 02 Issue: 09 | Aug-2013, Available @ http://www.ijret.org 393 OPTIMIZATION OF PRODUCTIVITY WITH SURFACE MINER USING CONVEYOR LOADING AND TRUCK DISPATCH SYSTEM S. K. Palei1 , N. C. Karmakar2 , P. Paliwal3 , B. Schimm4 1 Assistant Professor, 2 Professor, Department of Mining Engineering, Indian Institute of Technology (Banaras Hindu University), Varanasi 221005, U.P., India, skpalei.min@iitbhu.ac.in 3 Assistant Manager, Chhatarpur I Mine, Pathkhera Area, WCL, Coal India Limited 4 Manager, Mining Division, Wirtgen GmbH, Windhagen, Germany Abstract This paper aims at optimizing the productivity at the surface miner’s face with conveyor loading and dump-truck dispatch system to minimize the down times of surface miner as well as trucks. The surface miner was working in opencut method in a limestone mine located in the Southern part of India. Time study was carried out during three working shifts (each of eight-hour duration) for productivity analysis. A model has been developed and simulated in MATLAB for the productivity of surface miner considering the impact of two major parameters – number of trucks and available face length. The number of trucks for optimum production was found to be five. However, the 5% and 95% confidence interval for the number of trucks was 2.3 and 7.4 respectively for the case study face. It was also observed that the face of 330 m length was sufficient for the surface miner to work efficiently. Index Terms: Opencast mine, Surface miner, Mining machinery, Truck dispatch system, Productivity analysis -----------------------------------------------------------------------***----------------------------------------------------------------------- 1. INTRODUCTION Surface miner is a crawler mounted machine generally used for selective mining of coal and useful minerals. Though the first surface miner was introduced to the South African gypsum mine in 1983, now-a-days about 300 machines are working worldwide. The application of rock cutting technology has been extended with the mechanization process to increase the productivity of mines. Surface miners play an important role in getting the desired production in opencast mines. The site-specific problems still exist in some of the mines to get the desired output from the opencast mines. The present work is based on time-study data collected for a surface miner with conveyor loading and dump-truck (henceforth called truck) dispatch system in a limestone mine. The major parameters influencing the productivity of the surface miner are strength of rock mass, area available for mining operation, availability of trucks and their capacity, cutting tools used, and production planning. Mining industry emphasizes on the best possible utilization of its resources to increase the productivity. This paper aims at optimizing two important parameters like face length and availability of dump-trucks through a developed simulation model to increase the productivity of the mine. 2. BACKGROUND It is the requirement of mining industry to produce good quality minerals with the available techniques. Surface miners are generally deployed for selective mining of minerals for efficient exploitation of the deposit. It eliminates the multiple operations such as drilling, blasting and primary crushing. Surface miner drastically reduces whole body vibration of operator. There are also environmental gains in terms of noise levels and air-borne dust concentrations [1]. The surface miners are used in opencast mines for mining the soft sedimentary deposits layer by layer, and dispatching the mined out material onto the truck traveling alongside, or side-casting, or windrowing the material [2]. The mineral is cut into small lumps/chips and can be transported through in-built conveyor belts [3]. It works on the principle of the central drum cutting technology. The cutting drum has cutting tool holders welded to its body in the form of helix. Cutting tool holders are specially designed, replaceable, and picks are fitted to these tool holders. The drum is driven mechanically by a diesel engine of adequate power by a shifting clutch and power belts acting on the drum gear. The first surface miner was deployed in the Indian mineral sector in 1994 to a limestone mine of Gujarat Ambuja Cements Limited, Gujarat [3]. Since then Wirtgen surface miners have gained popularity in India for mining soft to medium hard limestone and coal deposits. Currently, in various mining companies, multiple units of surface miners are in operation e.g., Gujurat Ambuja (7 unit), Madras Cements (5 units), India Cement (3 units) and MPL (2 units) [4]. Surface miners have already proved their strength as a profitable alternative to conventional mining methods. The use of surface miner is also an alternative, where blasting is prohibited or use of explosives is a crucial issue.
- 2. IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308 __________________________________________________________________________________________ Volume: 02 Issue: 09 | Aug-2013, Available @ http://www.ijret.org 394 3. METHODOLOGY The time study was carried out to increase the productivity of the surface miner with conveyor loading and truck dispatch system. A model has been developed to minimize the idle time of surface miner and trucks, and to estimate the optimum face length desired for a surface miner to work effectively. 3.1 Mine Description and Data Collection The opencast limestone mine is located in the Southern part of India, where the surface miner was working in the opencut method (as shown in Fig. 1) during time study. Opencut is a method in which surface miner cuts the material along the face-length and returns to the starting place simultaneously cutting the adjacent slice [3]. Time-study was carried out for three shifts, consisting of two II Shifts (working hours between 2 p.m. to 10 p.m.) and one III Shift (working hours between 10 p.m. to 6 a.m.). The changes in engine ‘hourly machine rate’ (HMR) for each eight-hour shift were 5.1, 6.3 and 5.2 hours respectively. The surface miner, SM 2200 (Wirtgen make), was working at the same face for all the shifts during the time study. The SM 2200 used had a maximum cutting depth of 300 mm with cutting width of 2200 mm. The surface miner was working in a face of length about 330 m and width 50 m. The average production rate was 288.3 tonnes per hour from the case study face. The mean capacity of the trucks used during the study period was 23.3 tonnes with variance of 2.4. Fig1. Cutting sequence of a Surface Miner in Opencut method (Source: Wirtgen Surface Mining manual, 2002). 3.2 Development of Simulation Model The independent variables are loading time of trucks, the cutting time of surface miner to load a truck, truck positioning time, truck hauling time, truck waiting time at the face, and the cycle time of a truck. The response variables were the number of trucks and length of the face. The schematic diagram of the conveyor loading-truck dispatch system is depicted in Fig. 2. Unloaded Truc k S urfac e Miner with C onveyor L oading L oaded Truc k Weig h B ridg e C rus her L oaded Truc k Unloaded Truc k S urfac e Miner with C onveyor L oading L oaded Truc k Weig h B ridg e C rus her L oaded Truc k Fig2. Schematic diagram of Surface miner’s conveyor loading and truck dispatch system The following notations have been used: Cs : Cycle time of the SM Ct : Cutting time of SM to load a truck St : Positioning time of SM in opencut method of working after turning Is : Idle time i.e. down-time of SM Tt : Turning time of SM Ac : Actual cutting time of SM in a single cycle Cd : Cycle time of truck Hd : Hauling time of trucks Ul : Unloading time of trucks Tw : Truck waiting time in the queue at the face Ts : Truck positioning time Ld : Loading time of truck = Ct + Ts Ac′ : Average cutting time of a surface miner to load a single truck Nd : Number of trucks required in a single cycle of SM The cycle time of surface miner (Cs) and that of the truck (Cd) are obtained from the following relationships: Cd = Ct + Ts + Hd + Ul + Tw … (1) Cs = Ct + Ts + St + Tt + Is … (2) The number of trucks (N) can be related to the time parameters for developing the model. The number of trucks for efficient exploitation of the deposit for increasing the productivity of the surface miner face can be calculated as outlined below: Average cutting time to load a truck c Cycle time of SM A ' Number of trucks in single cycle of SM … (3) No. of trucks required in a single cycle of SM d Actual cutting time of SM in a cycle N Loading time of a truck … (4)
- 3. IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308 __________________________________________________________________________________________ Volume: 02 Issue: 09 | Aug-2013, Available @ http://www.ijret.org 395 Total no. of trucks required for the SM face (N) Cycle time of a truck Actual cutting time of SM in a single cycle Cycle time of SM Loading time of a single truck d c s d C C L (C +H +U +T +T ) (C +T +T +S +I ) + C ) l t t w s cd t s t st s … (5) Actual cutting time of surface miner in a cycle is the time during which a surface miner cuts and loads the material onto the trucks. It is the cycle time of surface miner excluding idle time, turning time and truck waiting time. The collected data are processed to fit to the suitable statistical distribution for simulation. The independent and response variables were modeled by fitting to suitable probability density functions. A model was developed to maximize the production simultaneously optimizing system utilization at the surface miner face to increase the overall work efficiency of the system. 3.3 Modeling of Independent Variables The independent variables in this study are truck positioning time, cutting time of surface miner, hauling time of truck, truck waiting time, turning time of surface miner and idle time of surface miner. The modeling of independent variables from the collected time study data were fitted to suitable probability density functions. For fitting the data to probability distributions, SIMULINK of MATLAB 7.0.1 was used [5]. The observed data as well as the fitted curves are depicted in Fig. 3 for the independent variables. Before surface miner starts cutting and simultaneously loading onto the truck, the truck should be positioned properly so that spillage of material is minimum. This time is called the truck positioning time (Ts in min). This truck positioning time is fitted to a single parameter exponential distribution with β = 0.17 min as shown in Fig. 3(a). Hauling time of truck (Hd) is the time taken by truck from the face to the unloading point (may be dump yard or crusher) and coming back to the face, excluding time of loading and truck waiting time for loading. 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 0 1 2 3 4 5 6 Dump-truck setting time (min) ProbabilityDensity Dump-truck setting time, Ts fitted curve 10 12 14 16 18 20 22 24 26 0 0.02 0.04 0.06 0.08 0.1 0.12 Hauling time of dump-trucks (minutes) ProbabilityDensity Hauling time of dump-trucks, Hd Fitting curves 1.5 2 2.5 3 3.5 4 4.5 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Cutting time of SM (min) ProbabilityDensity Cutting time of SM, Ct fitted curve 0 1 2 3 4 5 0 0.5 1 1.5 2 2.5 3 3.5 4 Ideal time of SM (min) ProbabailityDensity Ideal time of SM, Is fitted curve 0 2 4 6 8 10 12 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 Turning time of Surface Miner (min) ProbabilityDensity Turning time of SM, Tt fitted curve Figure 3 (a). Exponential distribution for Truck setting time Figure 3 (b). Log-normal distribution for hauling time of truck Figure 3 (c). Log-normal distribution for cutting time of surface miner Figure 3 (e). Log-normal distribution for turning time of Surface Miner Figure 3 (d). Exponential distribution for idle time of surface miner 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 0 1 2 3 4 5 6 Dump-truck setting time (min) ProbabilityDensity Dump-truck setting time, Ts fitted curve 10 12 14 16 18 20 22 24 26 0 0.02 0.04 0.06 0.08 0.1 0.12 Hauling time of dump-trucks (minutes) ProbabilityDensity Hauling time of dump-trucks, Hd Fitting curves 1.5 2 2.5 3 3.5 4 4.5 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Cutting time of SM (min) ProbabilityDensity Cutting time of SM, Ct fitted curve 0 1 2 3 4 5 0 0.5 1 1.5 2 2.5 3 3.5 4 Ideal time of SM (min) ProbabailityDensity Ideal time of SM, Is fitted curve 0 2 4 6 8 10 12 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 Turning time of Surface Miner (min) ProbabilityDensity Turning time of SM, Tt fitted curve Figure 3 (a). Exponential distribution for Truck setting time Figure 3 (b). Log-normal distribution for hauling time of truck Figure 3 (c). Log-normal distribution for cutting time of surface miner Figure 3 (e). Log-normal distribution for turning time of Surface Miner Figure 3 (d). Exponential distribution for idle time of surface miner Fig3. Observed as well as fitted distributions of various time variables The observed as well as fitted curves for hauling time of trucks (Hd, in min) is presented in Fig. 3(b). The hauling time is fitted to a log-normal distribution with µ=2.88 and σ = 0.19. Cutting time of surface miner to load a truck (Ct) is time taken by a surface miner to cut the mineral and load a single truck. The observed as well as fitted curves for cutting time of surface miner to load a single truck (Ct) are presented in Fig. 3(c). The cutting time of surface miner to load a single truck is fitted to a log-normal distribution with µ=1.01 and σ = 0.19. Down time of surface miner (Is) is the time during which the surface miner was not cutting and loading. The observed as well as the fitted curves for down time of surface miner (Is) is presented in Fig. 3(d). The data is fitted to an exponential distribution with mean value of 0.63 min. Turning time (Tt) is the time taken by the surface miner to take a turn and enter in another line of cutting and loading. The turning time of surface miner is fitted to a log-normal distribution with parameters µ=1.42 and σ =0.56 as depicted in Fig. 3(e). 4. ANALYSIS AND RESULTS Random samples are selected for the response variable, number of trucks and length of face based on the modeled independent parameters. The developed model was simulated with a program written in MATLAB. The number of trucks was estimated in surface miner face to optimize the conveyor loading-truck dispatch system by collecting 10,000 samples. The mean number of trucks required was found to be 4.7 with standard deviation of 1.2 (as shown in Fig. 4). Hence, the number of trucks based on the results of simulation model
- 4. IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308 __________________________________________________________________________________________ Volume: 02 Issue: 09 | Aug-2013, Available @ http://www.ijret.org 396 would be 5 (taking integer approximation of 4.7). However, the 5% and 95% confidence interval for the number of trucks was found to be 2.3 and 7.4 respectively. The effect of face length on productivity of surface miner was estimated from the available time study data as shown in Fig. 5. It demonstrates that with increase in face length, say up to 330m, the hourly production of surface miner increases, beyond which there’s only marginal improvement in productivity. 2 3 4 5 6 7 8 9 10 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 Number of dump-trucks ProbabilityDensity Number of dump-trucks, N Fitting curve Fig4. Simulation results for number of dump-trucks Fig5. Hourly productivity of SM vs. face length CONCLUSIONS This paper explains how to optimize the production in a surface miner face with conveyor loading to minimize idle time of both surface miner and trucks. Two parameters namely, face length and the availability of number of trucks at the surface miner face are considered for the study. The idle times (such as unavailability of trucks, turning and repositioning of surface miner, jamming of material in conveyor belt and its clearance, break for operator change), and truck positioning are always associated with the surface miner. A simulation model was developed and the time study data of a limestone mine was used to optimize the area availability and to assign desired number of trucks. The surface miner was working in opencut method with direct conveyor directly loading onto trucks. The number of trucks and area availability (e.g., face length) has been estimated to efficiently increase the productivity of the system. The parameters of the time study data were modeled to suitable ‘probability density functions’ by SIMULINK of MATLAB 7.0.1 and a program was written to simulate the developed model. The number of trucks based on the simulation results would be five. The mean truck capacity used during the time study was 23.3 tonnes with the variance of 2.4. It is also observed 33o m face length was optimum from productivity pointy of view. The objective of this paper was to optimize the idle time of both surface miner and trucks to increase work efficiency and productivity. During modeling of idle time of surface miner, major breaks continuing for more than 20 min were excluded for the sake of simplicity in calculation. This study can be extended to consider the cutting speed of surface miner and hauling speed of surface miner to estimate the number of trucks for efficient operation. Any change in truck capacity, face length, surface miner’s model, make and productivity, and rock characteristics may affect the results of the developed model. The developed methodology can well be extended to other mines having similar conveyor loading–truck dispatch arrangement. ACKNOWLEDGEMENTS The authors are grateful to Wirtgen India Private Limited, Bangalore for their permission to use the time-study data. The authors are also grateful to the mine management for their cooperation. REFERENCES [1] . Dey, K and Bhattacharya, J.: Operation of Surface Miner: Retrospect of a Decade Journey in India. Procedia Engineering, 2012, Vol. 46, pp. 97 – 104. [2] . B. Schimm: Economic mining of thin seams in flat deposits with surface miners, Mining Technology, 1996, 78(895), pp.89-92. [3] . Wirtgen surface mining manual, Wirtgen group, Windhagen, Germany, p.52, 2002. [4] . Prakash, A., Murthy, V. M. S. R. and Singh, K. B.: Rock excavation using surface miners: An overview of some design and operational aspects. International Journal of Mining Science and Technology 2013, Vol. 23, pp. 33–40. [5] . MATLAB 7.0.1: Matlab software package.