Simulation of an Underground Haulage System, Renström Mine, Boliden Mineral

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MASTER'S THESIS

Simulation of an Underground Haulage System, Renström Mine, Boliden Mineral

Nurnihal Fjellström

Master of Science Civil Engineering

Luleå University of Technology

Department o Civil, Environmental and Natural Resources Engineering

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Title: Simulation of an underground haulage system, Renström Mine, Boliden Mineral

Date 7 Juni 2011

Level and category Master’s Thesis, Engineering, 30ECTS

Key words Haulage simulation, mine truck, highway truck, Renström, Renströmsgruvan, cost, transportation, underground mine

Author Nurnihal Fjellström, Mining Engineer,

Boliden Mineral AB

Telephone: +46 910 77 41 36

E-post: Nurnihal.Fjellstrom@boliden.com

School Lulea University of Technology (LTU)

Mining and Geotechnical Engineering

Company Boliden Mineral AB, SWEDEN

E-post: boliden.info@boliden.com

Supervisor Arne Renström (Boliden Mineral AB) E-post: Arne.Renström@boliden.com

Examiner: Jenny Greberg (Lulea University of Technology) E-post: Jenny.Greberg@ltu.se

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PREFACE

This report has been written as a Master’s Thesis and the study has been carried out at Technology Department, Boliden Mineral AB, and Sweden. The thesis is a part of a simulation project of Renström mine which is the second step of time studies conducted by TG section in Boliden Mineral AB in Renström mine.

In the thesis, transportation cost of ore and waste material to the crusher and backfilling rooms in the underground Renström mine are determined by using the software package called AutoMod simulation program.

I first would like to thank to my manager, Craig Griffiths for giving me support both during my master studies and master thesis.

I also would like to thank Arne Renström for all support he has given me since we have met and worked together.

I would like to thank my supervisor Jenny Greberg for the interest she has shown to this study and all the guidance.

The contribution, help and support of Linus Bördin and Niels Glahamheden from ÅF is gratefully acknowledged.

I want to thank my friend Nils Johansson for his kindness, help and support.

Finally, I would like to thank my dear husband, Peter Fjellström, for all the support and encouragement he has given me during all these years.

Skellefteå, 7 Juni 2011

Nurnihal Fjellström

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ABSTRACT

The scope of the simulation project is to simulate different alternatives for the transport of ore and waste rock to the backfilling room and to the crusher in the mine and then determine the transportation cost for respective alternatives and finally choose the best option with the lowest transportation cost.

In Renström mine, the truck fleet consists of 3 highway trucks with an addition of 1 mine truck due to test driving reasons before purchase. Renström mine has a demand for a decrease in transportation costs and the number of break downs of the trucks. By simulating different transportation alternatives and comparing the costs, it is easy and fast to make decisions about the production system.

In order to achieve this goal, a literature study on simulation and the application of simulation on mining industry has been conducted. All the necessary input data were collected in activity studies in Renström mine in September and October period, 2010.

With the support and help of ÅF consult, a simulation model of Renström mine was created using AutoMod software. AutoMod is a simulation program which can simulate all the processes not only in the mine but also in other industries. The reason why AutoMod software was selected as a simulation program was because it was used for short term scheduling in Boliden Mineral AB in 1999 - 2000.

Major findings from the model are that the mine truck is 23% more effective than the highway trucks, the usage of only highway trucks are 34% more expensive than the usage of only mine trucks and for combination alternatives, if most of the transportation is done by mine trucks instead of highway trucks, the transportation cost per tonne is decreasing by 10-20%.

In conclusion, after all analyses were done, 3 mine trucks with one reserve truck have been selected as the cheapest feasible alternative for the mine. To sum up, it is possible to build a simulation model of an underground mine for transportation system to determine the most productive and the cheapest option. Moreover, the simulation model of the underground haulage system of Renström mine can also be used to analyse the influence of different transportation strategies on mine production in the future.

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SAMMANFATTNING

Den här rapporten är baserad på resultaten från en simulering av transport i Boliden Mineral ABs Renströmsgruva.

Omfattningen av examensarbetet är att simulera gråberg och malm transport till återfyllningsrum och till krossen och sedan beräkna transportkostnader för att slutligen välja det bästa alternativet med lägst transportkostnader.

I Renströmsgruvan används 3 lastbilar tillsammans med en extra bergtruck som används för provkörning innan inköp. Renström har krav på en minskning av transportkostnader och störningar i produktionen. Genom att simulera olika transport alternativ och jämföra kostnaderna, är det lätt och snabbt att fatta beslut om produktionssystemet.

En litteraturstudie om simulering och tillämpning av simulering gruvindustrin har genomförts. Alla nödvändiga indata har samlats in vid aktivitetsstudier i Renström under september och oktober period, 2010. Med stöd och hjälp av ÅF konsult, skapades en simuleringsmodell av Renström i AutoMod programvara. AutoMod är ett simuleringsprogram som kan används för att simulera alla processer inte bara i gruvan men även i andra branscher. Anledningen varför AutoMod valdes ut är på grund av det användes för kortsiktiga planering i Boliden Mineral AB mellan 1999 och 2000.

Viktiga resultat från modellen är att bergtruckar är 23 % mer effektiva än lastbilar, användningen av endast lastbilar är 34 % dyrare än användning av bara bergtruckar och för kombinations alternativ, om större delen av transporten sker med bergtruckar i stället för lastbilar minskar transportkostnaderna per ton från 10 till 20 %.

Sammanfattningsvis, efter alla analyser genomförts, har 3 bergtruckar med en reserv bil valts ut som det billigaste alternativet för gruvan. Det är möjligt att bygga en simulerings modell för en underjordsgruva för att bestämma det mest produktiva och billigaste alternativet för transport. Dessutom kan simuleringsmodellen över transport systemet för Renströmsgruvan också användas för att se inverkan av olika transport strategier på gruvproduktion i framtiden.

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LIST OF FIGURES

Figure 1: The view over Skellefte field ... 13

Figure 2: The view over Renström mine ... 15

Figure 3: The sequence of activities in the mine ... 17

Figure 4: The life cycle of a simulation study (Balci, O., 1990) ... 26

Figure 5: Steps in a Simulation study (Groumpos, P. & Merkuryev, Y.) ... 27

Figure 6: Sensitivity analysis for Highway truck (20% over and under estimations) ... 32

Figure 7: Sensitivity analysis for Mine truck (20% over and under estimations) ... 33

Figure 8: Different activities during working hours (source: Caterpillar) ... 51

Figure 9: The view over loading activity ... 56

Figure 10: The view over activities displayed in a Gantt chart (Gantt Browser) ... 70

Figure 11: Vehicles sheet in excel ... 71

Figure 12: Scheduled and Actual blasting dates for each blast (Cyclelog sheet) ... 72

Figure 13: The vehicles sheet in excel (the values are not representative) ... 73

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LIST OF TABLES

Table 1: The amount of probable, indicated and inferred resources in Renström ... 14

Table 2: The grade of the ore for reserve, indicated resource and inferred resource in Renström ... 14

Table 3: The usage of each mining methods according to the years in Renström mine .... 15

Table 4: Parameters and their influence on cost calculation for Highway and Mine trucks ... 31

Table 5: Simulation runs with only highway trucks ... 35

Table 6: Simulation runs with only mine trucks ... 36

Table 7: Simulation of combination (both mine trucks and highway trucks) without reserve truck ... 37

Table 8: Simulation runs of combination with reserve truck ... 38

Table 9: Simulation runs with productions higher than 76 500 tonne and transportation cost ratios for each option ... 39

Table 10: Risky options ... 41

Table 11: Transportation options that meet the production target of 76 500 tonnes ... 42

Table 12: Calculation table for the cost of transported ore ... 43

Table 13: The corresponding start points of the machines ... 53

Table 14: The list of activities in the mine ... 60

Table 15: Working hours in the mine for early, late and night shift ... 61

Table 16: Blasting and Ventilation hours for each shift team ... 61

Table 17: Different cycle types and their durations (Cycles sheet in excel) ... 62

Table 18: The example view over machine properties table in excel for AutoMod (Machines sheet in excel) ... 63

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Table 19: Amount of machines in reality and in AutoMod ... 64 Table 20: Detailed activity times in Renström mine (Shift sheet in excel) ... 65 Table 21: Average activity duration for haulage by Highway truck and Mine truck... 66 Table 22: Ore and waste transportation schedule according to date and room (Blasting sheet in excel) ... 66 Table 23: Backfilling rooms (Backfilling sheet in excel) ... 67 Table 24: Loading, dumping and meeting duration for haulage vehicle (General Input sheet in excel) ... 68

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1. INTRODUCTION

1.1 Introduction and scope of work

In recent years, there has been an increasing demand for minerals and metals in the world.

Many mining companies are trying to find new innovative equipment which can increase the productivity by reducing labour costs and supplying safer and cleaner working conditions.

The scope of the simulation project is to simulate different alternatives for the transport of ore and waste rock to the backfilling room and to the crusher in the mine and then determine the transportation cost for respective alternatives and finally choose the best option with the lowest transportation cost.

In this thesis work, transportation cost of ore and waste material to the crusher and backfilling rooms in the underground Renström mine are determined using the software package called AutoMod simulation program. A simulation model of haulage transportation system of Renström Mine is described. With the help of the software, maintenance and repair costs, fuel consumption cost and tire wear of the trucks etc. in a certain wished period for different haulage system alternatives can be determined by the user.

Today in Renström mine, highway trucks are being used for the haulage transportation of ore and waste material in combination with one mine truck. Mine trucks are not usually being used in Renström so most of the transportation is done with highway trucks.

However, there is only one mine truck for test driving before purchase. The main consideration in Renström mine is to take a decision about how many and which type of trucks that should be used for the transportation of ore and waste rock in order to decrease the transportation cost as much as possible.

An activity study was conducted in Renström mine in September and October 2010 regarding the same issue (highway truck versus mine truck). This study only aimed at investigating the transportation cost of the existing system.

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However, the management of Renström mine wants to identify other possible transportation options and to evaluate them in order to choose the best and the cheapest option that can handle the planned production.

The management of Renström mine wants to know the lowest transportation costs according to the following scenarios:

If only highway trucks are used If only mine trucks are used

If a combination of both types are used.

In addition, the best option is the one that can handle the existing planned production for a given period at the lowest cost.

Renström mine has been simulated in 1999 using AutoMod simulation program but the same model could not be used due to the many changes since 1999 in the layout of mine such as backfilling rooms, new levels, new production rooms and transportation style.

Therefore, a new layout model of the mine has been built by using Microstation computer aided design (CAD) program. In Microstation, the transportation route between stopes and crusher/backfilling room and meeting points have been drawn and each stope for ore and waste, crusher and backfilling rooms are shown as stations according to the production plan valid between 1^st September and 31^st October. In this period, activity studies were conducted to gather the input data for the model, thus, the same period is also selected as a simulation period to ease the verification and validation stages. In order to verify that the simulation model is working properly and reflecting the reality, the results obtained by the simulation model and the results from the activity study have been compared. Due to the reason that AutoMod program already exists in Boliden Mineral, the new model is again created in AutoMod.

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1.2 Boliden Mineral AB 1.2.1 Background

Boliden Mineral AB started its activities in 1931 and has grown to be a mining, smelting and recycling company focusing on firstly copper and zinc and secondly gold, lead and silver production. The company has 4400 employees and the turnover amounts to 28 billion SEK annually. Boliden Mineral AB has its mines in Sweden and Ireland and smelters are located in Norway, Sweden and Finland.

Boliden has the third rank on the largest copper metals and zinc metals supplier in Europe.

In addition, the company shares are listed on the Stockholm (Sweden) stock exchange and Toronto (Canada) stock exchange.

For more information please visit: www.boliden.com

1.2.2 Skellefte field

In Skellefte field, Boliden Mineral AB owns and operates 3 mines (see Figure 1); two underground mines (Renström and Kristineberg mine) and one open pit mine (Maurliden).

Beside this, there is also a concentrator and a gold leaching plant. The mines located at this region have sulphide ores which contains copper, zinc, lead, gold and silver.

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Source: Boliden Mineral AB Figure 1: The view over Skellefte field

1.2.3 Renström Mine

The production in Renström Mine started in 1952 and complex ore containing zinc, copper, lead, gold and silver has been mined. Renström mine is the deepest mine in Sweden (1300 m below surface in January 2010). The yearly ore production in the mine is approximately 250 000 tonnes and 10, 3 million tonnes of ore has been mined (by the end of 2008). There are 105 employees working in Renström mine (2009). The mining method is cut and fill mining method.

Renström mine is combined to Petiknas mine with a 2.5 km long drift at 800 level (see Figure 2). Mineralization continues down to 1700 meter and the mine has a good future potential (see Table 1 and 2).

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Ore bodies Probable ore Indicated and inferred resource

Main ore 288 ktonnes 511 ktonnes

Simon 550 ktonnes 1717 ktonnes

Vilma 235 ktonnes 195 ktonnes

Julia 180 ktonnes 410 ktonnes

Fingal 180 ktonnes

Aina 170 ktonnes

Source: Boliden Mineral AB

Table 1: The amount of probable, indicated and inferred resources in Renström

In Renström mine, 1060 ktonnes has already been mined out.

Au (g/t) Ag (g/t) Cu % Zn % Pb % S %

Reserves 2.6 161 0.5 7.6 1.5 12

Indicated resource 2.6 285 0.5 8,2 2.1 18

Inferred resource 2.2 155 0.8 5.7 1.4 12

Sill pillars 3.0 161 1 8 2 14

Table 2: The grade of the ore for reserve, indicated resource and inferred resource in Renström

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Source: Boliden Mineral AB Figure 2: The view over Renström mine

1.2.4 Mining Methods

Most of the ore is mined using the cut and fill method, with 5m slices (see Table 3).

Mined out stopes are backfilled with waste from the development.

The sill pillars between the stopes are mined using a vertical retreat method, locally known as opping.

METHOD 2006 2007 2008 2009 2010 2011

Cut and fill 96% 96% 96% 99% 100% 94%

Vertical retreat (opping)

4% - 1% - - 5%

Benching - 4% 4% 1% - 1%

Table 3: The usage of each mining methods according to the years in Renström mine

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1.2.5 The Mining Sequence for Ore Extraction and Backfilling

According to Figure 3, the first step to extract ore begins with diamond drilling. The sample rock obtained is sent to the laboratories to be analysed by geologist in order to decide the direction of the highest mineral concentration of the mineralization. The mine planning department decides how the ore body will be mined according to the information from the geology department. The face to be blasted is drilled by drilling machines according to the production plan.

The face which has been drilled is charged with explosives and blasting caps are placed into the boreholes. The blasting is done using a surface remote firing system after all the workers have left the mine during shift change. During blasting all staff must leave the mine. After each blasting, ventilation is done to remove the harmful gases and dust and to supply fresh air to the workers. After ventilation is completed the blasted rock is watered before the loading operation starts in order to depress the dust and the unexploded explosives in the blast. The ore is loaded onto the trucks by front end loader and transported to the crusher located at 800 m level. The waste rock is used as backfilling material together with sand.

After all the blasted ore has been loaded onto the trucks and sent to the crusher, scaling machine checks the roof and the walls to prevent loose rock fall. After scaling, primary cleaning is done to remove the rocks that have been removed by the scaler from the roof and the walls. In order to reinforce the walls and the roof of the stope, shotcreting is performed. In the concrete, there are small thin metal pieces to make the concrete capture the surface better and to increase the toughness of the concrete. After the concrete has dried, in other words when the shotcrete has settled down, the roof and the wall is ready to be drilled for the cement or resin bolting. The stopes that have already been mined out are backfilled with waste rock or sand. The sand used as backfilling material comes from the enrichment plant in Boliden.

After the crushed ore is sent to the skip by the conveyor belts it is hoisted to the surface / headframe by the skip (capacity of 4.5 ton per skip and 90 ton per hour). The trucks transport the ore to the process plant in Boliden for the further handling.

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17 Figure 3: The sequence of activities in the mine

1.2.6 Transport of ore and waste

The ore is transported with trucks to the crusher at 800m level. In 2008, the distance between the ore stopes and the crusher was 2.4 km (from room H1110) and 3.3 km (from rooms S946 and H1255).

The type of crusher is AR 150 jaw crusher and it has been in operation since 2003. The crushed ore is transported and dumped by conveyors into the shaft which has a capacity of 2500 tonnes. The shaft is located between 800m and 900m level.

The ore is transported with conveyors to the skip. This process is fully automated. The second conveyor in the series has a scale which makes sure that a certain tonnage is loaded onto the skip (capacity of 4. 5 ton per skip and 90 ton per hour). The skip can be monitored from the surface station. The headframe holds about 600 tonnes. The ore is loaded onto the trucks with 48 tonnes capacity and carried to the concentrator located in Boliden (17 km away).

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Most of the waste rock is used as backfilling material in mined out areas of the mine.

Waste from the upper levels is transported through the Petiknas drift or with the skip. The waste that is hoisted is not crushed and it is dumped outside of the headframe.

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2 METHODOLOGY

Before the simulation model of Renström mine was created, a literature study on simulation was done. The literature study comprised previous technical reports, articles and books which were written about simulation, Automod and mine transportation systems.

Secondly, an activity time study in Renström mine was done in order to gather input data for the simulation model. The activity time study was done only on the highway trucks and the mine truck. For the time period of the activity study, production planning reports of Renström mine were used to register the ore stopes and backfilling rooms into the model.

According to information and drawings from the mine planning section, a new layout of the mine was prepared in Microstation computer aided design (cad) program.

The new layout with stations, stopes, backfilling rooms, and crusher and meeting points was sent to ÅF consult to transfer it to AutoMod. After this stage, ÅF started to write the basic code in order to create the transportation between these points. The main code which will execute the model was written by Linus Bördin, ÅF, with a continuous and intense communication between the author and him about the logic behind the transportation system and the parameters affecting the system. The verification - validation stages were done by the author by comparing the results with the earlier activity study results and the necessary corrections in the code was done Linus Bördin, ÅF.

After the model accuracy was judged acceptable, the experimental design stage started and a large number of runs were simulated. The result of each transportation alternative in terms of production amount and engine hours were written down in a list and finally after all the runs finished, the lowest cost transportation model which handled the planned production was selected.

The results were presented in Renström mine as a recommendation to show the best transportation system alternative in terms of low transportation cost according to planned production amount, existing trucks and the mine design.

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3 SIMULATION THEORY

Simulation is the imitation of real life in another controlled environment. For example, while children play with their toys, they execute a simulation. The other examples can be Chess and Go which are the simulations of warfare.

According to Cochrane J, “Computer simulation is a tool that is commonly used in operations research to study the way in which a system works, and to look for ways in which the system can be improved”.

Simulation study is a quite challenging job and requires both quantitative and qualitative skills together and a suitable tool. The results coming from a simulation model can be used to support the decisions regarding a system.

3.1 Simulation in the mining industry

In recent years, mining companies are using simulation models in order to improve, modify, analyse or/and plan their existing systems. In addition, simulation models that are working properly can help us to make critical decision by looking into the future and (more or less) predicting the issues about our system.

Due to the reason that traditional methods such as manual calculations, flow diagrams etc.

is not enough to solve the complex problems, there is a requirement for better methods and tools for the production planning and the design of the mine.

Many simulation programs have been built and used for different purposes in the mining industry. There are some examples below:

Simulation of a continuous surface mining system (Aguoutantis and Stratakis, 1998)

Underground Ore handling systems (Bailey, Olsson and Glassock) Simulation of Pillara’s haulage system (Bradstreet, 2001)

Simulation of Truck/shovel system at Tuncbilek Coal Mine (Cetin, Erarslan and Okuducu, 2001)

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Simulation of battery powered coal haulers ( Cochrane, 1998) Autonomous vs Manual haulage trucks (Parreira and Meech, 2010)

Development of a short term scheduling tool for the Aitik open pit mine using simulation (Wageningen, 2001)

Simulation studies for truck dispatching (Wilke and Keck, 1982) Additional examples (from Zhou, 2010):

Studying the performance of surface mining equipment including production subsystems, waste material , conveyor subsystems and dumping system

Minimizing truck haulage cost which involves determining the optimum fleet haul size, organization of haul system, the best dispatching scheme and reliable maintenance and servicing system

Dispatch controlling in surface mines

Planning and analysing the truck/shovel operations in opencast mines and quarries Studying the truck transportation system consisting of traffic patterns, truck

utilization and operation costs

Selection of dragline and stripping method in surface coal mines Mine transportation systems analyse of costs

Benchmarking of existing operations

Scheduling maintenance for both production and ground handling system.

Comparison of timing and efficiency between drill – blast method and high speed continuous mining for new block cave development.

Different logistic options and their logistic consequence on transport from mine dumps to the proposed new treatment plant

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3.2 Simulation benefits and disadvantages

According to Banks (2000), the user can through simulation apply different type of rules, policies, procedures etc. without disturbing the real ongoing real system operation and different types of design, layout, and transportation systems and understand the modification availabilities in the system. In addition, the interaction between variables and their importance on system performance can also be understood within expanded or compressed time. By showing the information on work and materials, bottlenecks in the mine can be found or helping new system designs by answering “What if” questions.

In short, simulation helps us to understand how the system operates rather than how individuals think the system operates (Banks and al. , 1996)

On the other hand, simulation requires experience and special training to be able to build the model of the existing system. The results taken from a simulation model may be difficult to understand due to random variable outputs. In addition, analysis and building the model can be time consuming and expensive (Banks and al., 1996).

However, today, many packages on the market require only input data and give easily readable output data. Simulation can be performed faster due to computer hardware advances. Finally, complex systems are very difficult to be analysed by analytical method.

3.3 Simulation Tools

Simulation tools are consisting of three basic classes; general purpose simulation languages, simulation front ends and simulation packages. The last one, simulation software package is more advanced than the other ones. There are several simulation softwares such as AutoMod, Arena, Witness, SimCad, SimMine, Flexsim, SLAM on the market.

Arena is used from forestry to mining and it is an extendible and popular simulation/animation package. (www.arenasimulation.com)

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Witness is a user-friendly simulation system but it is not so common for mining applications. (www.lanner.com/en/witness.cfm)

SimMine is another simulation package which has been developed solely for mining activities and for conducting complete mining simulation projects. Due to the reason that the staff has a good knowledge and wide experience both in programming and mining activities, it is possible to obtain accurate simulation models with this package.

(www.simmine.com)

AutoMod is an industrial simulation modelling package but it can be adapted to mining systems. In this thesis work, simulation model of Renström mine has been built by AutoMod due to previous use of the software within Boliden. (www.automod.se)

3.4 AutoMod

AutoMod has both the features of a general-purpose simulation language and a special purpose material-handling simulator. With AutoMod, it is possible to simulate some advanced features such as robots, machine tool transfer system and special machinery.

Movement systems are divided into manually and automated equipment systems.

Material movement systems are as follows:

Path Mover Conveyors

Automated Storage and Retrieval Systems (ASRS) Robots

Bridge Cranes

Power and Free Chain conveyors etc

For the material movement systems, paths and stations must be created and then input data to define the operation is created. The logic which corresponds to the movement system and the 3D animation which can be observed from any angle is created automatically.

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Spreadsheets and CAD (computer aided design) packages can easily be imported into AutoMod (www.automod.se)

On the other hand, AutoMod has some limitations for mine simulations. Firstly, it requires good command of programming skill and special training is required for model building.

However, model building is learned over time by training and gaining experience of the programme. Secondly, its implementation over mining transportation systems is very complicated in terms of programming code.

3.5 The Simulation Process

Computer simulation has several steps which communicate with each other all the time.

Due to this reason, it is a continuous and dynamic process.

The simulation model of Renström mine is discrete event simulation. The transportation system has a sequence of events and all these events are in order. These events occur at a specific time in discrete event simulation (Robinsson, 2004).

Discrete event simulation is used to model and evaluate real systems over time. A system can be static or dynamic. The model used for discrete event simulation is dynamic because the system changes by time (Banks et al.,2000).

“Discrete event simulation utilizes a mathematical/logical model of a physical system that portrays state changes at precise points in simulated time. Both the nature of the state change and the time at which the change occurs mandate precise description. Customers waiting for service, the management of parts inventory or military combat are typical domains of discrete event simulation” (Nance 1993, cited from www.albrechts.com) The first step in the simulation process begins with identifying the goals for the simulation and understanding the system which will be modelled (see Figure 4 and 5). Secondly, the problem is formulated in terms of mathematic. Then, the formulated problem is transferred into the simulation software. After the model is transferred and created, the next step is the verification step. In this step, the model is verified by controlling that reasonable output is given from inputs which are collected from real operation. The

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question “Is the model/program performing properly?” must be asked. In the fifth step, the validation step, the conceptual model is checked to understand and to decide if it represents the real system or not. In the following step, the experimental design step, the simulated alternatives, critical performance measures, number of runs, simulation length is determined. The seventh step is the analysis of the results. In order to evaluate the outcomes of the results one must get insight of the results by analysing the results. In the final step, documentation of the work is done and includes findings and recommendations in it.

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Figure 4: The life cycle of a simulation study (Balci, O., 1990)

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Figure 5: Steps in a Simulation study (Groumpos, P. & Merkuryev, Y.)

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4 DEVELOPMENT OF the SIMULATION MODEL

The computer model of Renström mine was built by using the software package AutoMod. It is possible to see the interaction between the loading machine and transportation vehicles in the model. The logic behind the model is written into AutoMod by using programming language and an excel interface is created and combined with the model in order to run different scenarios of the haulage process. In the excel interface, there are different categories of input data and output data.

4.1 Excel Interface

The excel interface consists of two sections; Input data and Output data section. Prior to simulation runs, the output data section is completely empty. The output data section presents only for gathering the results of each run. The input data section is filled with required data in order to be able to extract results from the model.

The sheets in the input data section are:

General input Blasting plan Backfilling Cycles Machines Shifts

For details see Appendix II.

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The sheets in output data section are:

General output Log

Vehicles Haulers Cycle log Vehicles table

For details see Appendix III.

4.2 Verification

In verification stage, the model is tested and evaluated as to whether the model is an accurate representation of the formulated problem or not. It is very important to verify that the program is performing properly and the conceptual model is an accurate representation of the real system (Koivisto, 2001). The reasons for the model not being accurate can be concerning the logic or the code behind the model. The necessary corrections are made after the analysis of the results.

In Automod, the corrections in the programming code and logic must be done continuously until the model is judged as reasonable. Therefore, the communication between the user (and someone who knows the real system very well) and the programmer is very important to be able to build a good model that is working properly.

During the verification of the model, it is important to judge if the results are reasonable and reflecting the reality or not. As it is mentioned before, mistakes can be due to programming code and logic. In order to understand if it is due to the programming code a log file where all the activities are being logged after every activity for each machine is useful. By going through the log file, analysing the activities in the list, the simulation model of Renström has been verified.

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4.3 Validation

The validation step was done according to the activity study which was conducted in September to October (2010). This activity study was done in order to gather input data for simulation and to calculate and determine the transportation cost of existing transportation system in Renström. Due to the model already being built according to the existing plan of September to October period; the results of this period from activity study and the model have been compared.

Firstly, the existing transportation scenario, one mine truck and three highway trucks, has been entered to the model input section and the output generated by the model has been compared with the real production data. All parameters such as production amount, MTBF (mean time between failure), MTTR (mean time to repair); engine hours, costs etc. are more or less matching with the results from the activity study. Small difference in values is due to availability of machines and utilization of shift and the other assumed values for the calculation of costs. Some values have to be assumed due to no available data on maintenance services and costs in Renström.

4.4 Sensitivity of the simulation model

The calculation of the ore transportation cost for mine truck and highway truck is consisting of many parameters. The effect of making error with the estimation of these parameters is varying. Due to this reason a sensitivity analysis has been conducted on the input and output parameters of the model.

The sensitivity analyses are done on the following parameters:

Production per period (tonne) Required engine hours Availability

Shift utilization

Number of drivers per shift

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Total man hours per period Driver salaries (SEK/hour)

Maintenance cost (SEK/motor hour) Diesel cost (SEK/m³)

Tire cost (SEK/tonne)

Life length of trucks (engine hours) Purchase price

Depreciation per period

In the table below, the results from the sensitivity analysis; the influence of each parameter on the cost is shown.

RANK Highway truck & Mine truck

HIGH Influence

LOW influence

1 Production (tonne/period*)

2 Required engine hours

3 Availability, shift utilization and available working hours

4 Number of driver per shift, salary and required man hours

5 Life length of trucks (motor hour)

6 Purchase price and depreciation per period

7 Maintenance cost (SEK/motor hour)

8 Diesel cost (SEK/m³)

9 Tire cost (SEK/tonne)

Table 4: Parameters and their influence on cost calculation for Highway and Mine trucks

*period = 8 weeks

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Figure 6: Sensitivity analysis for Highway truck (20% over and under estimations)

In figure 6 and 7, the most sensitive parameters in the cost calculation are required engine hours and production amount. Moreover, the tire and diesel cost are the least sensitive parameters in the cost calculation. In other words, any mistake in the calculation of tire and diesel cost will not lead big deviations in the result.

The sensitivity analysis shows the same results for both highway truck and mine truck (see Figure 6 and 7). The transportation cost is very sensitive to required engine hours and the planned production amount. Any small mistake that will be done in the calculation of these parameters leads to large changes in cost calculation. Therefore, this is another reason why Renström mine is simulated in order to estimate the cost instead of the cost being calculated manually.

If the required engine hours are overestimated or underestimated by 20% the difference is 13.29 SEK/tonne. According to Renström production plans, the amount of production for

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8 weeks is 76 500 tonne. The difference in transportation cost becomes 1 016 685 SEK for 8 weeks and 6 100 110 SEK per year.

However, if the sensitivity of the tire cost is observed, then the difference is only 0.91 SEK. This becomes 69 615 SEK for 8 weeks and 417 690 SEK per year. Thus, it is not as sensitive as required engine hours.

Figure 7: Sensitivity analysis for Mine truck (20% over and under estimations)

To sum up, production amount and engine hours are the most sensitive two parameters in transportation cost calculation. In other words, any mistake that will be done in the calculation of these parameters will cause large diversions in transportation cost as mentioned above.

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5 SIMULATION RUNS AND RESULTS

52 different transportation alternatives have been simulated in order to find the cheapest option for ore and waste transportation in Renström. Some transportation alternatives include both mine trucks and highway trucks (Table 7 and 8) and some alternatives contain only highway trucks (Table 5) or mine trucks (Table 6). The number of trucks has been changed between runs in order to find the effect of truck type and quantity on transportation cost for the ore to the crusher by including maintenance, tyre, fuel, driver etc. costs. In addition, the number of loaders has also been changed to see how the production is being effected by the loaders (Table 5, 6, 7 and 8).

16 runs with only highway trucks and 12 runs with only mine trucks have been simulated.

For mine truck-highway truck combinations, two groups have been created; one with a reserve truck (12 runs) and one without a reserve truck (12 runs). When the target production amount 76 500 tonnes is reached, there is no longer need for more runs. For some options, production amount is more than 76 500 tonnes. The reason behind this is the last blasts which are blasted at the end of the period are still being transported on some additional days. Thus, the maximum production amount of the mine in 9* weeks is 79 566 tonnes. However, the transportation in 8 weeks is 76 500 tonnes.

For the simulation runs, all the parameters have been fixed stable according to the real system in Renström mine in terms of capacity of trucks and cycle times. The only changed parameters are the number of trucks and loaders in the model.

*(8 weeks + some additional days = 9 weeks)

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35 Runs Total production

(tonne) Number of loader Number of highway trucks

1 21163 1 1

2 22998 2 1

3 27668 1 1+reserve

4 32579 2 1+reserve

5 32666 1 2

6 42603 2 2

7 33496 1 2+reserve

8 64243 2 2+reserve

9 33845 1 3

10 63276 2 3

11 33845 1 3+reserve

12 76245 2 3+reserve

13 33695 1 4

14 75115 2 4

15 33695 1 4+reserve

16 77114 2 4+reserve

Table 5: Simulation runs with only highway trucks

*Reserve truck is used in case of failure and service time of a production truck. It is also a highway truck

According to Table 5, the alternatives with only 1 loader cannot cope with a planned production amount of 76 500 tonne. There is only one alternative that can handle more than the planned production; run 16, 4 highway trucks with one reserve truck.

According to Table 6, there is no alternative that can handle the planned production with 1 loader. Thus, if only 2 loader alternatives are focused on, then there is again only one alternative that can handle the production; run 28, 3 mine trucks with reserve truck. The reserve truck is also a 36 tonne mine truck.

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36 Runs Total production

(tonne) Number of loader Number of mine trucks

17 28136 1 1

18 33525 2 1

19 29258 1 1+reserve

20 36208 2 1+reserve

21 33198 1 2

22 66831 2 2

23 33695 1 2+reserve

24 70042 2 2+reserve

25 33270 1 3

26 75292 2 3

27 33270 1 3+reserve

28 76663 2 3+reserve

Table 6: Simulation runs with only mine trucks

Beside these two types of runs, only highway truck and only mine truck, the combination type alternatives are simulated. The combination types are the combined usage of mine trucks and highway trucks in the mine. However, this combination alternatives are also divided into two subgroups; trucks with and without a reserve truck.

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Runs Total

production (tonne)

Number of loader Number of highway trucks

Number of mine trucks

29 33695 1 1 1

30 52782 2 1 1

31 33695 1 1 2

32 74228 2 1 2

33 33844 1 2 1

34 72226 2 2 1

35 33696 1 2 2

36 76664 2 2 2

37 33643 1 3 1

38 76936 2 3 1

39 33398 1 1 3

40 77113 2 1 3

Table 7: Simulation of combination (both mine trucks and highway trucks) without reserve truck

According to Table 7, simulation runs with 1 loader cannot meet the production target but run 36, 38 and 40 have higher productions than 76 500 tonne. The first feasible combination is 2 highway trucks with 2 mine trucks, the second alternative is 3 highway trucks with 1 mine truck and the last alternative is 1 highway truck with 3 mine trucks.

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Runs Total

production (tonne)

Number of loader Number of highway trucks

Number of mine trucks

41 33696 1 1+reserve 1+reserve

Table 8: Simulation runs of combination with reserve truck

In Table 8, runs with 1 loader does not meet the production target but Run 44, 46, 48, 50 and 52 have higher production than 76 500 tonnes.

In Table 9 below, the alternatives that can meet the planned production target are shown in summary.

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Options Ratio Total

production** Number of loader Number of highway

trucks Engine hours Number of mine

trucks Engine hours

16 1.34 77114 2 4+reserve 1565 - -

28 1.00 76663 2 - - 3+reserve 1469

36 1.21 76664 2 2 633 2 895

38 1.32 76936 2 3 1060 1 481

40 1.10 77113 2 1 227 3 1285

44 1.10 76664 2 1+reserve 469 2+reserve 1029

48 1.17 77113 2 2+reserve 766 2+reserve 791

50 1.10 77113 2 1+reserve 362 3+reserve 1173

52 1.25 78281 2 3+reserve 1168 1+reserve 409

Table 9: Simulation runs with productions higher than 76 500 tonne and transportation cost ratios for each option

*Ratio is the price difference between the alternatives according to the cheapest option. For instance, option 1 is 34% more expensive than option 2 (the cheapest option)

**Production = Total transported amount of waste + ore production

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The production target of waste and ore in total is about 76 500 tonnes according to production plans of Renström mine. The corresponding engine hour for this amount of production is approximately 1500 truck engine hours.

According to Table 9,

All the options can transport more than 76 500 tonnes in 8 weeks.

If only highway trucks are in operation without a reserve truck, then the availability is 77%. However, if the highway trucks work together with a reserve highway truck then the availability increases from 77% to 95 %. Similarly, the availability of mine truck also increases from 95% to 99 % with the existence of 1 reserve mine truck. The reason why the availability cannot reach up to 100% is due to small failures during operation time.

The options simulated in run 36 2+2 (2 highway trucks + 2 mine trucks), Run 38 3+1 (3 highways+1 mine truck) and Run 40, 1+3 (1 highway+3 mine truck) are not recommended because they do not have any reserve truck and in case of failure of a truck, these options cannot meet the production requirement of 76 500 tonnes. In case of failure, for example, Run 38 becomes like Run 34, 2 highway trucks + 1 mine truck with a production of 72 226 tonnes or like Run 10 only 3 highway trucks with a production of 63 276. Thus, these three risky options (Table 10) must be discarded from the best option table (Table 9).

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Risky options Run 36 (2 + 2 )

Run 38 Run 40

If 1 truck breaks down

Run 36 becomes like Run 34 with 2+1 or Run 32 with 1+2.

None of them can reach the target production.

Run 38 becomes like Run 10 with 3 highway trucks or Run 34 with 2+1.

None of them can reach the target production

Run 40 becomes like Run 26 with 3 mine trucks or Run 32 with 1+2. None of them can reach the target production

Table 10: Risky options

If the production amounts are grouped within the Table 6, 3 production groups;

77 113-77 114 tonnes, 76 663-76 664 tonnes and 78 281 tonnes are created. The reason why costs are being compared according to production amount instead of number of trucks is as mentioned before. Transportation costs are calculated according to corresponding motor hours to each production amount.

According to Table 11, the most expensive option is Run 16. Four highway trucks are being used in the mine with reserve truck. The next most expensive options are Run 52 and Run 48.

In table 11, the cheapest options of each group are Run 28, Run 50 and Run 52.

Due to the reason that Run 52 cannot be compared with any other option in its own group one more extra simulation has been done. After comparison, the extra run is selected instead of Run 52 as the cheapest option of the third group. The reason why 4 mine trucks are selected is that only 4 mine trucks with one reserve truck can reach the production amount of 78 280 tonnes.

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42 Production (tonnes) Cost

(SEK/tonne)

Options

Runs Highway truck Mine truck

76 663-76 664 tonnes

26.44 - 3+reserve Run 28

29.00 1+reserve 2+reserve Run 44

77 113-77 114 tonnes

35.50 4+reserve - Run 16

78 280-78 281 tonnes

27.14 - 4+reserve Extra

Table 11: Transportation options that meet the production target of 76 500 tonnes

According to the results,

o For 76 663 tonnes production, 3 mine trucks with a reserve truck with a cost of 26.44 SEK/tonne is the cheapest option.

o For 78 280 tonnes production, 4 mine trucks with reserve truck with a cost of 27.14 SEK/tonne is the most effective and productive option. However, the required amount of production is only 76 500 tonnes for 8 weeks. This option is producing 1 780 tonnes more so it can be used in the future if the production amount will be increased.

An example on calculation of transportation cost is shown in the table below but some values are confidential such as purchase prices, salaries etc.

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Highway truck Mine truck

Period (weeks) 8 8

Weeks in a year 48 48

Production (tonnes) 77114 76663

Average gradient 1:8 1:8

Average Lift height 371 m 371 m

Cycle time 28 min 40 min

Tonnage of truck 25 tonnes 36 tonnes

Required engine hours acc. tonnes 1565 1469

Amount of shifts 3 3

Working hours exc. holidays 360 360

Total shift hours 1080 1080

Availability (Ratio) 1 1.23*

Shift utilization

Required amount of trucks 4 3

Amount of driver per shift 3.1 3

Extra truck 1 1

Total man hours

Maintenance cost (SEK / motor hour) Diesel price (SEK / m3)

Diesel consumption (lt / hr) 24 35

Tire cost (SEK/tonnes) Total sum salary (SEK/period) Life length motor hour Depreciation year Purchase price

Depreciation per period

Total cost per ton (Ratio) 1.34** 1

Table 12: Calculation table for the cost of transported ore

*The availability of the mine truck is 23% more than the availability of the highway truck.

**The transportation of same amount of material is 34% more expensive with highway trucks than with mine trucks.

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6 DISCUSSION AND CONCLUSION

The scope of the simulation project is to compare the effect of usage and number of highway trucks and mine trucks on the costs for transport of ore and waste rock in Renström mine. The main consideration in the mine is to decide how many and what type of truck that is the best option to be used for the transportation of ore and waste rock with respect to operation cost per tonne.

AutoMod simulation software has been very helpful for the determination of engine hours, total production amount, shift utilization, availability of trucks and has also showed how the selection of trucks affects the costs and the production. If the calculations had been done manually instead of using simulation with AutoMod, it would have taken very long time and the results would not have been a good reflection of reality due to Renström mine being a complex system containing many factors that cannot be handled manually that is affecting the transportation. However, the model has been build neither as complicated as reality nor too simple and it is possible to test different transportation strategies by using it.

On the other hand, due to the reason that AutoMod is designed for industries such as manufacturing, automotive, airport baggage handling etc., both the graphics and the logic of the program is not so suitable for the mining industry. For the users who are not familiar with programming, AutoMod can initially be difficult to use. Moreover, while the excel interface is giving opportunities to make changes in input data, it can also cause some mistakes due to the reason that some input parameters must not be changed such as speed, tonnage of the truck and the activity durations.

As an advice, when using the AutoMod program, the programmer and the person who knows the mine very well should build the model together, especially in the model building and verification stages.

A mine truck can be 2-3 times more expensive than a highway truck. Instead of using only mine trucks in the mine if highway trucks are bought due to their lower purchase prices then the transportation cost per tonnes increases approximately 34%.

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In addition, in the combination alternatives, if the mine truck does most of the job and carries more than the highway truck the transportation cost per tonne is sinking approximately with 10 to 20%.

The availability of the mine trucks is 23% more than the availability of the highway trucks.

It is very important that the reserve truck is able to transport the required amount of production material in a given period. In case of failure and service time for a production truck, one reserve truck must always be ready to replace the production truck and continue to transport material to the crusher and the backfilling rooms.

The results taken from this study are an input to the discussions about ore & waste transportation trucks in Renström mine. Due to the reason that highway trucks are designed for normal highway conditions, they are faster and easier to manoeuvre. On the other hand, mine trucks are designed according to mine environment. They are tough and relatively slow moving machines in comparison to highway trucks. It is sometimes hard to convince the mine workers about the effectiveness of these two different kinds of trucks.

Most of the workers believe that highway trucks are the most effective due to their cycle time. However, these trucks are not designed according to tough mine environment and their mean time between failure (MTBF) is very short and the vehicles are wearing out very quickly in comparison to the other highway trucks that are driven on normal city roads and to the mine trucks. Therefore, the availability of the highway are lower than the availability of the mine trucks.

In conclusion, the cheapest alternative for Renström mine in order to reach the required production target and to obtain a relatively cheap transportation cost is to use 3 mine trucks with a capacity of 36 tonnes (corresponding to 16 m³) and 1 reserve truck.

Simulation of an Underground Haulage System, Renström Mine, Boliden Mineral

MASTER'S THESIS