Considerations and Development of a Ventilation on Demand System in Konsuln Mine

Seth Gyamfi

Civil Engineering, master's level (120 credits) 2020

Luleå University of Technology Department of Civil, Environmental and Natural Resources Engineering

Master Programme in Civil Engineering, with specialization in Mining and Geotechnical Engineering

Considerations and Development of a Ventilation on Demand System in Konsuln Mine

Master thesis, 2020

Division of Mining and Geotechnical Engineering Department of Civil, Environmental and Natural Resources Engineering Luleå University of Technology SE-97187 Luleå Sweden ACKNOWLEDGEMENT

All glory and honor be to the Almighty God for seeing me through my studies successfully and for giving me strength throughout my time at LTU. I will like to thank my supervisors, Dr. Adrianus (Adrian) Halim and Dr. Anu Martikainen for their guidance, technical support, and editorial insight. I humbly express my profound gratitude to Mr. Michael Lowther (Manager for SUM project at Konsuln) for granting me the opportunity to carry out this study at the mine. I am also grateful to Dr. Matthias Wimmer (Manager, Mining Technology, LKAB - Kiruna) and Mr. Jordi Puig (Department Manager) for giving me the opportunity to be part of such a world class company like LKAB and to make a value-added contribution through this research.

A very special gratitude goes to all the wonderful people at the R&D department of LKAB. The teamwork and the love shown are well appreciated. To Mr. Michal Grynienko and Mr. Mikko Koivisto, thank you for the underground time and inputs.

To Ms. Stina Klemo (Ventilation engineer, NGM), I thank you for your contributions. I wish to thank Associate Professor David Siang, Dr. Musa Adebayo Idris, together with my fellow graduate students (Gloria, Adam and Rayan) at the Division of Mining and Geotechnical Engineering, LTU, for their support, discussion, and encouragement.

It gives me great pleasure to thank the many individuals for their cooperation and encouragement which have contributed directly or indirectly in preparing this report. To David Vojtech (production manager at Konsuln), Tomas Bolsöy (EOL Vent Mining AB) and the entire employees at Konsuln, I say thank you.

To my Pastor Dr. Stephen Mayowa Famurewa and family, Dr. Musah Salifu, Dr. Esi Sari, Miss Dorine Andreasson, Mr. Senzia Warema, and all the lovely friends in my life, I am grateful to everyone for making my stay at LTU a memorable one. To my family, I say thank you for your unwavering support and sacrifices throughout my studies in Sweden.

Seth Gyamfi September 2020 Luleå, Sweden.

ABSTRACT

Ventilation on demand (VOD) concept has earned significant worldwide attention by several mining companies in recent years. It is a concept where airflow is provided only to areas that require ventilation. The implementation of the concept has resulted in significant savings in annual energy consumption and cost for several companies globally. The research presented in this thesis sought to present the VOD system as an alternative solution and strategy to improve the ventilation system of Konsuln mine. The system is expected to cope with a planned increase in production rate and meet requirements in the new Swedish Occupational Health & Safety (OH&S) regulations, Arbetsmiljöverkets förtfattningssamling (AFS) 2018:1, which is based on the EU directive 2017/164 where Threshold Limit Value (TLV) for gases have been significantly reduced and provide safe work environment for workers in the mine.

The thesis work started with planning and execution of a PQ (Pressure – Quantity) survey to calibrate the existing ventilation model of Konsuln mine. This was to ensure that the model is reasonably accurate to give reliable simulation predictions of the performance of Konsuln ventilation system in its current state and for the future. The good correlation between the modelled and underground measured values validated the model for further ventilation planning.

The study further investigated and analyzed the current and future ventilation demand of LKAB test mine, Konsuln, to design a VOD system for its operations.The work outlined three main VOD design scenarios I, II, and III based on the proposed production plan, schedule, and the mining process that present the underground working conditions on the three main levels (436, 486 and 536) of Konsuln mine.

Diesel, battery-powered, heat, and blast simulations were carried out for all the scenarios in the calibrated ventilation model using VentSim Design simulation software. The model was again used to estimate the annual ventilation power cost for the VOD scenarios to highlight the benefit and cost savings advantage under the VOD design system to deliver enough airflow quantity compared to the conventional system of ventilation.

Simulation results showed that about 15.6% – 49.1% and 76.4% - 86.7% of significant cost savings will be achieved for diesel and battery-powered machineries respectively, while still supplying the needed amount of air to working areas to keep contaminants below their Threshold Limit Value -Time Weighted Average (TLV-TWA) and provide a good working environment.

For additional benefits and savings of the Ventilation on Demand (VOD) system implementation, some considerations for equipment, personnel positioning and identification, monitoring system, and stations have also been discussed in this work. These include; (i) Utilization of LKAB’s database system, Giron, in addition to mounting tags with unique IDs on machineries, to track the route of LHDs and trucks to deal with the challenge of airflow supply shortfall associated with auxiliary fans adjustment to affect target locations. (ii) Installation of temperature sensors, flow meters, gases and Diesel Particulate Matter (DPM) monitoring systems at specific, appropriate, and optimal locations in the mine for efficient implementation of the VOD system strategy.

The heat simulations for both diesel and battery-powered machineries were carried out for the month of July when the highest temperatures in Kiruna are often recorded for the summer. They predicted the highest temperatures in working areas to be well below the limit used in Australia, 28°C Wet Bulb (WB).

Four scenarios A, B, C and D were also considered for blast clearance time simulation using both the ramp and exhaust shaft. The blast simulation results indicated that the time to dilute and clear blast fumes through the exhaust shaft saves some clearance time compared to exhaustion through the ramp, although the shaft exhaustion will require additional financial commitment to purchase and install exhaust fans on each of the three main levels of the mine.

Nevertheless, major ventilation work and practices such as removal of regulator in front of primary fans, additional radon measurement, and good auxiliary ventilation practices have been recommended to improve and actualize the benefits outlined in this work.

iii

TABLE OF CONTENTS

ACKNOWLEDGEMENT ...... i ABSTRACT ...... ii TABLE OF CONTENTS ...... iv CHAPTER 1 ...... 1 Introduction ...... 1 1.1 Background and motivation ...... 2 1.2 Aims and objectives ...... 3 1.3 Methodology ...... 3 1.4 Thesis outline ...... 4 CHAPTER 2 ...... 5 Konsuln mine ...... 5 Introduction ...... 5 2.1 Ventilation system at Konsuln ...... 9 CHAPTER 3 ...... 12 3.1 Ventilation and its importance, airflow requirement and determination ...... 12 3.2 Ventilation surveys ...... 13 3.2.1 Air quantity survey ...... 13 3.2.2 Pressure survey ...... 14 3.3 Ventilation Control Devices ...... 14 3.4 Diesel and electric machineries and their effects on ventilation...... 15 3.4.1 Diesel machines ...... 15 3.4.2 Electric machines ...... 15 3.5 Mine environment conditions and monitoring ...... 18 3.6 Ventilation modelling and commercial software packages ...... 18 3.7 Ventilation system in Sweden...... 19 3.7.1 General system layout and practice ...... 19 3.7.2 Ventilation requirement is Sweden...... 20 3.7.3 Radon ...... 22 3.8 Introduction/concept to VOD system ...... 22 3.9 Levels/strategies of VOD implementation ...... 24 3.9.1 User control (manual control) ...... 24 3.9.2 Time of day scheduling ...... 25 3.9.3 Event-based ...... 25 3.9.4 Tagging ...... 25

3.9.5 Environmental ...... 25 3.10 The VOD system and its components/elements ...... 26 3.11 How the VOD system works ...... 26 3.12 Commercial VOD software ...... 29 3.13 VentSim control (formerly SmartExec) ...... 29 3.13.1 Manual ...... 29 3.13.2 Automatic schedules and events ...... 29 3.13.3 Automatic set points ...... 29 3.13.4 Dynamic requirements (VOD) ...... 29 3.13.5 Complete infrastructure optimization including main fans...... 30 3.14 ABB Ability Ventilation Optimizer (formerly SmartVentilation) ...... 30 3.14.1 Basic control ...... 30 3.14.2 Ventilation on Demand (VOD functionality) ...... 30 3.15 NRG1-ECO (Energy Consumption Optimization) ...... 30 CHAPTER 4 ...... 31 Model Calibration and Validation, VOD Consideration, Design and Simulation ...... 31 4.1 Model Calibration and Validation ...... 31 4.2 Pressure-Quantity survey ...... 31 4.3 Primary fan performance measurement ...... 33 4.4 Results of model calibration ...... 34 CHAPTER 5 ...... 35 Results and Discussion ...... 35 5.1 VOD considerations, system design and simulation...... 35 5.1.1 VOD system design criteria...... 35 5.2 Ventilation power cost for base case, scenario I, II and III...... 38 5.2.1 Fans power cost ...... 39 5.3 Diesel emissions and heat simulations ...... 40 5.3.1 Diesel emissions and Heat simulation results ...... 42 5.4 Blast fumes clearance simulation ...... 43 5.4.1 Blast fumes clearance simulation result ...... 45 5.5 Radon simulation ...... 47 5.5.1 Radon simulation result ...... 47 5.6 Some considerations to implement the VOD system ...... 47 5.6.1 Equipment and personnel positioning and identification ...... 47 5.6.2 Monitoring system and stations ...... 48 5.7 Ventilation modelling for the use of Battery-powered Machineries...... 50

5.7.1 Simulation with Battery-powered Machineries ...... 50 CHAPTER 6 ...... 52 Summary and conclusions, recommendations and future work...... 52 6.1 Summary and conclusions ...... 52 6.2 Recommendations ...... 53 6.3 Future work ...... 54 REFERENCES ...... 55 APPENDICES ...... 61

CHAPTER 1

Introduction

Underground mine ventilation plays an important role in the extraction of mineral resources at subsurface. As a matter of fact, no underground mine can operate effectively without a good ventilation system. With the gradual increase in mining at greater depth, the challenges of mine ventilation have become even more of a major concern to provide a safe working environment for mine workers. Ventilation is the primary means of supplying fresh air to dilute atmospheric contaminants from blasting and other mining activities in an underground mine operation. The utilization of diesel-powered machinery in underground metal mines produces toxic gases such as carbon monoxide (CO), oxides of nitrogen (NOx) and diesel particulate matter (DPM). Drilling and blasting, which is the primary means of fragmentation in underground hard rock mines for transportation and further processes, also produces toxic gases which also must be diluted and removed from the mine.

These contaminants have driven major mining countries such as Australia, Canada and the United States to set stringent regulations on mine air quantity, quality and diesel emissions over the years. To address these challenges and to make underground mining sustainable in the future, several ventilation optimization methods and techniques that minimize fan power cost, improve airflows, reduce energy consumption and optimize ventilation networks have been studied within the mining industry (Acuña et al., 2014; Acuña et al., 2010; Chen et al., 2015; De Souza, 2007; Pritchard, 2009). Implementing Ventilation on Demand (VOD) and replacing diesel machineries with battery-powered ones are measures that have been taken by some mines to make underground mining sustainable in the future. Studies on such sustainable solutions and transitions have proven and predicted to comply with mining regulations and generate significant ventilation cost savings (Paraszczak et al., 2013; Chadwick, 2008).

The mining environment is dynamic and sporadic. Mining operations therefore need a flexible and responsive system to accommodate this dynamic nature of the mining environment and stringent mining regulations (Skawina, 2019). An automated VOD system provides the ventilation engineer with the flexibility to adjust and modify the ventilation requirements at an active section of the mine based on the calculated demands of the system. However, to develop a VOD system, the mine ventilation model needs to be calibrated and validated to ensure that simulation results predicting the performance of the actual mine environment, based on the operational parameters and other factors, are reliable.

1.1 Background and motivation

The concept of VOD has earned significant worldwide attention by several mining companies in recent years. It is gradually being implemented by a lot of companies globally due to the system´s ability to cope with the increasing challenges of underground mine ventilation by supplying the required (quantity and quality) amount of fresh air to the mine area only at the very time it is needed. The implementation of the concept has seen several companies make significant savings in annual energy consumption and cost (Acuña et al., 2016; Acuña and Allen, 2017; Burman and Markström, 2016; Ge et al., 2019; Nensen and Lundkvist, 2005).

Konsuln mine is owned and operated by Luossavaara Kiirunavaara Aktiebolag (LKAB), a Swedish state-owned iron ore mining company. The mine was developed as a test mine for LKAB´s Sustainable Underground Mining (SUM) project (SUM, 2020b; SUM, 2020d), as well as to contribute additional production to the one from Kiruna operation. Currently the mine produces 0.8 million tonnes of iron ore per annum (mtpa) and planning to increase it to around 1.8 - 3 mtpa. This means that a lot of trucks and other vehicles will be in operation at the same time in the mine since truck haulage is the chosen method to transport ore from the mine to the processing plant. The increase in production rate will affect the mine ventilation requirements. The current fresh air capacity in Konsuln is about 100 m³/s. There is a concern whether this capacity will still be adequate for the planned increase in production rate. Another concern is whether this capacity will comply with the recent change in Sweden’s Occupational Health & Safety (OH&S) regulations. In Sweden, mines must comply with TLV of contaminants that are stated in Arbetsmiljöverkets förtfattningssamling (AFS) 2018:1, which follows directive from the European Union (EU) that was issued in 2017, Directive 2017/164. In this new regulation, TLV for gases are significantly reduced which means that it is likely that more airflow will be required to dilute the same amount of gases that are produced by mining activities. However, the EU advisory committee on workplace safety and health has raised concerns about the practicality of measuring the new TLVs and has granted a transition period until 21 August 2023 for underground mines and tunneling to take measures to adapt to these new TLVs. Until this date, the limits listed in previous regulation, AFS 2015:7 are still in force (Halim et al, 2020).

Therefore, LKAB seeks to consider and implement a VOD system in Konsuln mine. An investigation must be carried out to understand the current and future ventilation demand of Konsuln mine to ensure that the VOD system and consideration will provide an alternative

2 solution and strategy to meet the ventilation requirement, environmental regulations in Sweden and provide a safe work environment for workers.

The knowledge obtained from this research can further be used to potentially implement the VOD system to improve the ventilation system at Konsuln and ultimately increase safety, productivity and provide a safe work environment for workers while saving energy and cost.

1.2 Aims and objectives The objective of the work described in this thesis is to improve the ventilation system of Konsuln mine in order to cope with the planned increase in production rate and the new OH&S regulations based on the EU directive 2017/164.

To fulfill this objective, the following research questions were formulated:

• Will the existing capacity at Konsuln be enough to handle all the diesel emissions and requirements for the increased production rate? • How much airflow needs to be delivered in an energy-efficient way? o Do all areas in Konsuln mine need to be ventilated at the same time? o Do the areas require a constant airflow? o Are all auxiliary fans required at the same time? o Are there non-active areas that still needs ventilation? • Will the VOD system and battery-powered machineries be the solution for Konsuln mine to comply with Swedish OH&S regulation and to provide a safe work environment for workers?

1.3 Methodology To achieve the above objective, this work was carried out with the following steps:

i. Calibration of Konsuln mine ventilation model • Field work, continuation of previous work • Modelling work component with VentSim ii. Analysis of implementation of VOD in Konsuln mine • Planning of a ventilation on demand system from level 436 to 536 • Consideration of operational requirements • Equipment and their placement/location

iii. Investigate the impact of replacing diesel machineries with battery-powered ones on VOD system • Review of current regulations, future regulations and available machinery • How would switching to battery-powered machineries affect the VOD system in Konsuln mine (short description and example calculations)

1.4 Thesis outline The thesis will be structured as outlined below:

i. Chapter 1 gives an introduction, background and motivation for this work. The aims and objectives as well as the methodology used to achieve the project objective are also presented in this chapter. ii. Chapter 2 describes the study site and the ventilation activities at Konsuln that contribute/relate to this study. iii. Chapter 3 presents the literature available on general ventilation practices, ventilation system in Sweden and the concept of ventilation on demand (VOD) system. iv. Chapter 4 presents the methodology, field work, data collection, VentSim model calibration and validation, VOD system consideration and development for the mine and simulation of various VOD scenarios based on operational requirements and other factors. v. Chapter 5 discusses and evaluate the results. vi. Chapter 6 presents a summary and conclusions, recommendations and future work.

CHAPTER 2

Konsuln mine Introduction The company Luossavaara-Kiirunavaara AB (publ), abbreviated LKAB, is a high-tech international minerals group, world leading producer of processed iron ore products for steel making, and a growing supplier of mineral products for other industrial sectors.

LKAB mines one of the world's richest iron ore deposits in northern Sweden. The company was established in 1890 and has been fully state owned since 1976. It has been an important cog in Sweden's export industry and industrial development for more than a century. Currently, LKAB is operating two underground mines, Kiruna and Malmberget, and one open pit (Leveäniemi) in Svappavaara. Svappavaara is also the location of the Mertainen and Gruvberget open-pit mines, where there is currently no mining taking place (LKAB, n.d. “This is LKAB”). The company is the major producer of iron ore within the EU and produces three main product types: pellets, fines and special products. The operational areas and the integrated production structure of LKAB of the current and planned operating sites to produce its major products are presented in Figure 2.1. The products are sent to two harbors, Kiruna and Svappavaara products to Narvik harbor and Malmberget products to Luleå, where they are shipped to customers.

Figure 2.1 (a) LKAB operational areas (b) Integrated production structure of LKAB (courtesy LKAB)

Large-scale sublevel caving is the main method used in LKAB’s underground mines. The process consists of several phases as depicted in Figure 2.2.

Figure 2.2 Sublevel caving process in LKAB (courtesy LKAB)

Konsuln mine is located in the southern part of Kirunavaara and is a small, almost separate section of the Kiruna mine (see Figure 2.3). The mine currently produces approximately 0.8 million tonnes of iron ore annually (SUM, 2020a).

Figure 2.3 Location of Konsuln operating test mine

The mining operation in Konsuln is similar to that of Kiruna mine in terms of the utilized methods and techniques. The significant difference is the new layout in Konsuln on its levels 436, 486 and 536 as well as the utilization of trucks in Konsuln instead of trains in Kiruna to haul the ore. The objective of the Sustainable Underground Mining (SUM) project is to set a new global standard for sustainable mining at great depths, and the target is a future mine that is safe, carbon dioxide free, digitalized and autonomous. In the automation and digitisation of the whole mining process, Konsuln Mine Operations Control (MOC) room will mark a distributed way of working and not just a physical place. 3D visualisations of required data on positioning of people and assets, mine condition and mine plans will be monitored and updated in real-time. With the management system and integration with people at the centre, the right information will then be distributed in a transparent way. The information will then be made available to the right users at the right time to find new solutions in the test mine. Figure 2.4 shows the MOC room at Konsuln test mine.

Figure 2.4 Mine Operations Control room at Konsuln test mine

As LKAB continues to mine iron ore at greater depth, higher rock stresses are encountered. With this comes greater distances, high seismicity, and increasing costs. These new challenges need to be solved. For this reason, LKAB together with other innovative Swedish companies (ABB, Epiroc, Combitech and Volvo Group) have joined forces to design a future mining system with the goal of setting a new world standard for sustainable mining at great depths (LKAB annual report, 2019; Leonida, 2019). “We know that rock stresses increase with depth. In order to be able to continue working safely, we need to move our infrastructure further from the mining area, which increases development costs. If we increase the sublevel height from the current 29 to 50 meters, then we will reduce the number of meters we develop and thereby

7 reduce costs,” says Carlos Quinteiro, mining engineering specialist at LKAB and project manager of DP1 within SUM in an LKAB interview. In order to maintain LKAB’s competitiveness and to ensure the continuation of safe mining, the company decided to test the increased sublevel height and a new type of layout. Parts of new levels (436, 486 and 536) at Konsuln have therefore been designed with what is known as a “fork” layout (see Figure 2.5). Among other things, this type of layout is expected or anticipated, to make it possible to increase the total number of vehicles transporting ore from the production area, something that will increase the production capacity. “A fork layout allows the mine’s infrastructure to be moved further from the mining area, making it less susceptible to rock stress. We believe that this will improve stability; for example, in the rock excavation,” says Carlos Quinteiro (SUM, 2020a).

Figure 2.5 New layout illustration in Konsuln mine (courtesy LKAB - SUM)

These initiatives among others, have all been put within the framework of what is known as Sustainable Underground Mining (SUM). The SUM project has been split into four parts which includes; mine layout and technology, autonomous, intelligent CO2-free machines, management system and integration and the people at the center. Figure 2.6 presents a 3D- model of Konsuln where tests will be conducted in a virtual mine in parallel with live

8 experiments as part of the SUM project. All test data from SUM are expected to be collected by 2023 to be used as a basis to support decisions on future production systems at greater depths to mine iron ore deeper in LKAB’s mines in Kiruna and Malmberget (SUM, 2020d; SUM, 2020c).

Figure 2.6 3D-model of Konsuln, operating test mine in Kiruna

2.1 Ventilation system at Konsuln The Konsuln mine employs a combination of force and push-pull primary ventilation systems. The primary intake fans are two 75 kW EOL Vent system inline axial fans. Both fans are equipped with variable frequency drive (VFD) to vary their speed. These fans are located 254 m below surface and currently deliver about 100 m³/s of fresh air to the mine (Bolsöy, 2019). A direct-contact heating system, using electric coils, is installed on the top of the fan intake raise.

The push-pull system is only used during the clearance of production blasting fumes. After production blasting is done in a certain level, two 22 kW fans located in the connecting drive to the exhaust raise are turned on to suck the fumes from that level. After the fumes are cleared, these fans are turned off. Figure 2.7 shows a schematic of this system.

Figure 2.7 An example of schematic of primary ventilation system

Primary airflow on each level is provided by 30 kW auxiliary fans bolted to bulkhead located in the access to the intake raise/shaft. Each fan is connected to a 1000 mm diameter duct that extends to the level footwall drive. This air is then distributed to each crosscut (production drive) using a 11 kW auxiliary air fan connected to a 800 mm diameter duct installed in the access to each drive. Figure 2.8 shows a schematic to level ventilation in Konsuln mine.

Figure 2.8 An example of schematic of level ventilation

CHAPTER 3

3.1 Ventilation and its importance, airflow requirement and determination

Ventilation is the primary means of diluting contaminants in underground mines. As surface resources are being exploited and depleted, the mining industry in other to meet the increasing demand for minerals have mined ore bodies several kilometres below the earth to cut down mining cost while increasing production to its optimum. Providing a good ventilation system for a safe underground operation is therefore a key factor which cannot be neglected.

As a general fact, no underground mine can exist without providing a good working environment for the workforce (unless otherwise automation is employed). To some extent even in an automated mine, ventilation may be required to cool mine equipment (e.g. LHD, trucks etc).Diesel emissions, blast fumes and natural phenomenon such as gas burst in a rock renders the underground mine environment unsafe for employees, hence the need to provide fresh air to the mine. The primary objectives of an underground mine ventilation system are to; provide fresh air for mine personnel, provide oxygen for diesel equipment, remove mine atmospheric contaminants (gases, dust, DPM), provide comfortable working temperatures and cool mine equipment (Halim, 2018).

The ventilation system should however include both the quantity and quality of the airflow. Quantitatively, the airflow should be sufficient as required at all the areas of the mine where employees are required to work or travel. In terms of quality, the sufficient airflow should dilute all gases and contaminants to the acceptable level of concentration (exposure limit). In most cases the required airflow and acceptable level of contaminants concentrations have been stated in the mining regulations of a country or through a dedicated body set up to regulate such requirements (McPherson, 2009).

Theoretically, the above-mentioned concept of mine ventilation may seem very easy to achieve. However, as described by Wallace et al. (2015), the concept can be very challenging due to the expansion of mining projects which has resulted in deeper, hotter, gasier and more mechanized mines. It is therefore important for ventilation engineers to understand certain practices such as dust control, refrigeration and/or heating (in cold climates) and the economics of ventilating a mine in order to minimize the annual cost.

3.2 Ventilation surveys

Ventilation surveys play an important role in obtaining the frictional pressure drop and the corresponding airflow quantities needed for calibration and validation of a model. This minimizes the errors in the parameters used. It can also be used to generate historical data for planning purposes, routine monitoring and to track the ventilation system performance of the mine workings and carry out adjustment if necessary. The parameters measured includes the quantity, pressure, temperature and airflow quality (contaminants concentrations). From the surveyed data, other parameters such as friction factors, resistances, shock losses, efficiency etc. can also be determined. A guideline for survey execution to build and calibrate a given ventilation model has been presented by other researchers (Rowland, 2009; Rowland, 2010; Rowland, 2011).

3.2.1 Air quantity survey

The quantity of air Q, passing through any point in an underground mine airway or duct every second is expressed as; 푄 = 푉퐴 Where: V is the velocity of the air passing the given point (m/s) A is the area of the airway at that point (m2)

This basically means that to determine the quantity of air at any point in the mine, the velocity of the air and the cross-sectional area at the point of measurement must be known. There are two main types of airflow measurement. The first type is the spot check measurement which is done when one wants to know the airflow in a specific area underground by just spot checking the values to have a quick idea on the ventilation performance. The second type is what is termed as airflow quantity survey. This type of measurement follows a defined technique with the aid of calibrated instruments to minimize errors as well as easy comparison of results. Where applicable, the Davis anemometer, hot wire anemometer, Kestrel, digital vane anemometer or a smoke tube may be employed (Prosser, 2018).

Today due to advancement in technology, multifunction instruments have been developed for several measurement possibilities with the aid of various modules and probes for several parameters. For the accuracy of the measurement results, the cross-sectional area of the point or station must be determined. The most common and simple method is the use of tapes. This is very reliable for geometric shapes airways such as rectangle, square etc. However, due to mine airways having different form of shapes, several other methods such the offset method,

13 profilometer method and photographic method have been developed for the measure of mine airways cross-sectional areas (McPherson, 2009). The distance meter is commonly used in recent times.

3.2.2 Pressure survey As air flows through mine airways from an area of higher pressure to lower pressure, there is a gradual reduction of pressure (pressure drop) along the airway. The pressure losses are determined either directly by differential pressure measurements, or indirectly by calculating the pressure losses from the absolute pressure difference. The two common methods used to measure the differential pressure drop during a ventilation survey are the barometric method and the gauge and tube method. The choice of the method varies from mine to mine depending on the field of application (Prosser and Loomis, 2004, McPherson, 2009). Other factors may also include the extent of the mine workings, the accuracy required, portability of the instrument and the availability of time to carry out the survey.

The barometric method is easy to perform since it is limited to some distance between two measurement stations. On the other hand, the gauge and tube method gives much accurate results though the method seems to be very time consuming as a lot of work and effort is needed to carry and lay hoses from station to station. Figure 3.1 shows an illustration of the gauge and tube technique. The procedure, advantages, and disadvantages of both measurement techniques have been described in detail by Prosser and Loomis (2004).

Figure 3.1 Gauge and tube technique (Prosser and Loomis, 2004).

3.3 Ventilation Control Devices

As air moves in the mine workings, the air would always flow along the path of least resistance as is the case for fluids. However, the areas of less resistance might not necessarily need to be

14 ventilated (e.g. an abandoned area of the mine or old levels). Ventilation devices are therefore used to control airflow distribution to the mine workings where they are needed by workers or mine equipment to work. A range of ventilation control devices may be used, including self- closing or manual doors, walls, brattice cloth, regulators etc. The regulators usually have openings which can be adjusted with a sliding shutter to reduce or increase the airflow to a working area of the mine. An orifice also comes in different shapes, but the rectangular openings are common due to easy determination of the area of the opening. In certain cases, ventilation may not be required at certain areas of the mine, but workers and vehicle access may be needed. Doors are therefore used to prevent airflow to these areas but grant access for both workers and equipment. A wall is used when certain areas of the mine (e.g. old levels) will no longer be used again throughout the mine life.

3.4 Diesel and electric machineries and their effects on ventilation.

3.4.1 Diesel machines

Diesel machineries are the most widely used machinery in the mining sector over the years because they are very reliable and flexible to use. However, apart from the toxic exhaust gases (CO and NOx) and DPM they emit, they also produce a significant amount of both sensible and latent heat where the latent heat is a very important factor in mine ventilation because of its relationship with wetness factor and humidity. It also influences the determination of the mine effective temperature (Bascompta, 2016).

These exhaust emissions can be minimized through frequent maintenance, good engine design and the use of exhaust treatment units. The diesel particulate matter is regarded as the most hazardous component of the diesel exhaust to health (McPherson, 2009).

3.4.2 Electric machines

Electric-powered machineries do not produce exhaust gases and DPM, and emit significantly less heat than that emitted by an equivalent diesel-powered machine, about a third (Halim and Kerai, 2013; Stinnette et al., 2019). Replacing diesel machineries with electric ones has the potential to improve air quality, reduce airflow requirements and therefore ventilation power cost. Although some electric machineries (LHDs and trucks) have been manufactured by Sandvik, Epiroc (formerly Atlas Copco), and ABB, their application is still limited due to their inflexibility (they require a trailing cable or an overhead trolley line). This prevents them from being employed in many mines where working sites are spread across a large area and vehicles

15 are required to move from one site to another quickly. However, recent development in battery technology has allowed some reliable battery-powered mining machineries to be manufactured in the past five years such as Epiroc’s ST7 and ST14 LHDs and MT2010 and MT42 trucks, and Artisan’s (now is a part of Sandvik) A4 and A10 LHDs and Z50 truck. These machineries do not have flexibility issues encountered in cable-trailed and overhead trolleyed electric machineries and have a potential to match productivity and flexibility of diesel machineries.

Over the past decade, there has been an increased pressure on the mining industry to reduce the rate at which underground mine workers are exposed to diesel emissions. Major mining countries continue to tighten their emission standard limits on air pollutants. For instance, the European regulatory pathway for vehicle emissions control have implemented six stages of increasingly stringent emission control requirements which started in 1992 with Euro 1 and have significantly progressed through to Euro 6 in 2015 (Williams and Minjares, 2016). In Sweden, a new exposure limits based on the European Union (EU) regulation 2017/164 was put in force on August 1, 2018. This new exposure limits have significantly reduced TLV-

TWA and STEL of CO, NO and NO2, which is very challenging to comply with, even with Euro VI engines. With this continuous trend of stringent and reduced exposure limits, mining companies have been compelled to consider a transition from diesel to electric equipment as an alternative sustainable solution to eliminate air quality challenges that are associated with the use of diesel engine equipment. Studies to compare the economics of diesel and electric vehicles operating cost (wear parts, lubrication, maintenance and overhaul etc.) and economic benefits have been carried out to justify the above mentioned benefits (Jacobs, 2013; Paraszczak et al., 2013; Paraszczak et al., 2014; Varaschin and De Souza, 2015; Varaschin and De Souza, 2017.; Varaschin, 2016).

Even though electric machineries do not produce exhaust gases and DPM, it does not mean that airflow quantity can be reduced a lot. This is because electric machineries still produce heat, albeit significantly less than that produced by diesel vehicles. This heat must still be managed by the mine ventilation system. If it is not managed adequately, air temperatures at working areas can reach unsafe levels for the mine personnel.

However, there are other major heat sources in addition to machineries; surface air temperatures during summer, auto-compression, and temperature of rock and groundwater must also be managed by the mine ventilation system. The reduction of ventilation power cost

16 depends on these heat sources as well as machineries. The magnitude of each of these heat sources depends on two factors, which are the location of the mine and the depth of the mine.

1. Impact of the location of the mine

Location of the mine affects surface air temperatures during summer and temperature of rock and groundwater. Mines that are located in tropical and sub-tropical regions such as those in Australia and Southern USA have high surface air temperatures during summer and high rock and groundwater temperature. Conversely, mines that are located in cold regions such as those in Canada and Nordic countries do not have these conditions.

2. Impact of the depth of the mine

The depth of the mine affects auto-compression and temperature of rock and groundwater. Rock and groundwater temperature increase proportionally along with the depth of the mine because the ground becomes warmer closer to the core of the earth. Auto-compression is the increase of air temperatures as it travels down the intake ventilation shaft. Because the air is compressed, its temperature increases due to thermodynamic principle. The magnitude of auto- compression increases proportionally with the depth of the mine. So auto-compression is a major heat source in mines that are deeper than 1.5 km.

Therefore, the reduction of ventilation power cost is different in each mine, depending on the location and the depth of the mine. For example, a shallow mine in the Nordic region theoretically has higher reduction than a deep mine located in the same region because the deep mine has more heat coming from auto-compression, rock, and groundwater than the shallow mine. Another example is a deep mine in Nordic region theoretically has higher reduction than a deep mine in Australia because the mine in Australia has more heat coming from surface air temperature, rock, and groundwater than the mine in Nordic region.

In some cases, mines can encounter other issues such as the existence of radon. It is noted that these mines might not get significant reduction because their airflow requirement is dictated by the requirement to dilute radon instead of requirement to dilute diesel exhaust gases. Another aspect that must be considered is re-entry time after blasting. Reducing airflow quantity will extend the re-entry time. VOD system is a solution to make re-entry time as short as possible by temporarily increasing airflow into the areas where blasting has just been done.

3.5 Mine environment conditions and monitoring

The mine environment can be said to be one of the hardest working conditions. Unlike other work environment where contamination sources are contained and the ventilation system can be designed to isolate the contaminant source, all underground mine workings contain the potential for release of air contaminants such as blast fumes, strata gas, dust, and diesel exhaust (Hartman et al., 2012). Theoretically, fresh air supply from surface to underground mine workings is composed of 78% nitrogen, 21% oxygen and 1% of other gases. However, due do mine activities such as blasting and strata gases, this composition changes as air flows to the mine environment. It is therefore important to monitor the air quality in the mine to ensure that contaminant levels are well below their acceptable TLV-TWA and STEL as stipulated in a country’s mine legislation. Today, with the advancement in technology, several gas detection and monitoring systems have been developed to detect and measure gas concentrations in an underground mine environment.

3.6 Ventilation modelling and commercial software packages

The ventilation system of a mine may be too complex to be used in manual planning, analysis and monitoring. Several simulation programs have therefore been developed over the years to help ventilation engineers in planning. Although several of these programs were originally developed, very few have been updated to catch up with current technology (Hardy and Heasley, 2006).

Some of the simulation softwares available for commercial, educational and private industry use have proved to be of great benefit in the initial design of a mine ventilation circuit and airflow requirements. They have also played key roles is accident control system by simulating several scenarios to support decision-making process in the event of incident in the mine to address various issues such as gas or fire control problems underground (Wu et al., 2019).

The most common softwares available for mine ventilation system design are VentSim design, VumA, and VnetPC. These are capable mine ventilation softwares which have helped engineers to model the ventilation circuit of a mine, have a thorough understanding of how the airflow will behave, the fan pressures and effects when certain activities such as fan installation are carried out in the mine. They are also useful in modelling the spread of blast fumes, heat and contaminants in the mine on a real time basis. For instance, the VentSim design simulation

18 software enables ventilation engineers to carry out airflow, radon, pressure, heat, fire and several other simulations in a given mine ventilation model (VentSim Design, 2020).

3.7 Ventilation system in Sweden

3.7.1 General system layout and practice

In most countries, a requirement to operate an underground mine includes at least two openings, one for regular use and the other in case of an emergency. This is similar for a ventilation system which requires at least one intake airway and one exhaust. Depending on the method used, a fan is then placed on either airway to create a pressure difference.

In major mining countries such as Australia, Canada and USA, a ventilation system or circuit usually consist of a primary fan(s), control devices (e.g. regulators, doors etc.) to distribute air from the primary fans to main levels of the mine, booster fans (if allowed by regulation) to boost the air pressure and auxiliary fans that distribute air to crosscuts and dead-end workings of the mine through ducts. However, mines in Nordic countries such as Sweden and Finland, have quite different circuit or system. Auxiliary fans instead of regulators are used to control primary airflow distribution, as well as distributing airflow to dead-end workings. A schematic diagram of a typical ventilation system used in Swedish and Finnish mines have been presented by Franzen, Myran, Larsson, and Rustan from Stiftelsen bergteknik forskning (Swedish Rock Engineering Research Foundation).This is shown in Figure 3.2 with the English translation written next to the Swedish terminologies (Halim et al., 2020).

Figure 3.2 Schematic diagram of the Nordic ventilation system (Franzen, Myran, Larsson, and Rustan, 1984).

The primary airflow is circulated to levels by auxiliary fans that are bolted to a bulkhead located in the access to intake raise/shaft. These intake fans are attached to ventilation ducts that distribute airflow to all working faces.

3.7.2 Ventilation requirement is Sweden

In mining countries such as Australia, Canada and Germany, the airflow requirements for diesel machineries in underground mines are clearly specified in the country’s mining Occupational Health & Safety (OH&S) regulations. These airflow requirements are usually based on the engine power of diesel vehicles used in the mine, multiplied by unit airflow requirement, such

20 as 0.05 to 0.06 m3/s per kW engine power used in Australia or 0.047 to 0.092 m3/s per kW used in Canada (Halim, 2017).

Unlike the above-mentioned countries, Sweden currently has no specific airflow requirement specified in its Occupational Health & Safety (OH&S) regulations. The regulations only require that sufficient air quantity is provided to dilute contaminants at working places in the mine to levels that are below their TLV-TWA. Companies such as LKAB and Boliden determine their own airflow requirement based on the mine experiences. It may therefore be difficult for a new underground mine to determine its airflow requirements but contacting these already existing companies can be very helpful in the process.

The limits in Sweden are listed in AFS 2015:7 and AFS 2018:1 Hygieniska gränsvärden (occupational exposure limits), a regulation issued by Arbetsmiljöverket (Swedish Work Environment Authority). These limits are based on the European Union (EU) regulation

2017/164 that was issued on 31 January 2017. The TLV-TWA and STEL of CO, NO and NO2 have been significantly reduced in the AFS 2018:1 compared to the AFS 2015:7. This difference is presented in Table 3.1 below.

Table 3.1 Comparison of AFS 2015:7 and AFS 2018:1 exposure limit values (Arbetsmiljöverket 2015, 2018) Gases Exposure Limits NO CO NO2 TLV-TWA 25 ppm 35 ppm 2 ppm (AFS 2015:7) TLV-TWA 2 ppm 20 ppm 0.5 ppm (AFS 2018:1 STEL 50 ppm 100 ppm 5 ppm (AFS 2015:7) STEL - 100 ppm 1 ppm (AFS 2018:1)

The EU advisory committee on workplace safety and health has raised concerns about the practicality of measuring the new TLV-TWAs and STELs presented above. Due to this, the previous limits that are listed in AFS 2015:7 Hygieniska gränsvärden are still permitted to be

21 used. However, the committee has decided a transition period for underground mines and tunneling to take measures to adapt to the new TLV-TWAs and STELs until August 21, 2023 (European Union Commission, 2017). It must be noted DPM is not currently regulated in Sweden nor in the EU.

3.7.3 Radon

Radon is not an issue to most metal mines in the world as far as ventilation is concerned. However, it is a major ventilation challenge in some Swedish mines like LKAB’s Kiruna and Malmberget iron ore mines. The Swedish Work Environment Authority and the Swedish Radiation Safety Authority oversee radiation protection in Sweden. The former is responsible for radon concentration measurements with reports made to the later when radon concentration exceeds 200 Bq/m³. The exposure limits in Sweden are based on radon concentration in ventilating air instead of exposure to ionizing radiation. The radon exposure level for each person is calculated by multiplying measured radon level with working time. The exposure limits of radon in force in Sweden are 0.36 MBqhr/m3 in surface mines and 2.1 MBqhr/m3 in underground mines (Strålsäkerhetsmyndigheten, 2018).

3.8 Introduction/concept to VOD system

Ventilation on demand (VOD) is a concept where airflow is provided only to areas requiring ventilation. Historically, mine ventilation systems are designed for peak demand and are operated at this maximum level regardless of the true demand, i.e. Ventilation is provided to areas that are inactive, resulting in significant amounts of wasted airflow and air conditioning, and low ventilation-system efficiency. For example, a mine that has 15 ventilated working areas, even if only 10 of them are active at any one time would waste 33% of the airflow supplied. VOD improves the system efficiency and hence reduces the overall ventilation requirement in that mine, which subsequently reduces ventilation power consumption.

The concept has been successfully used in Kristineberg and Malmberget mines in Sweden (Isaksson et al., 2009; Nensen and Lundkvist, 2005), and Coleman, Creighton and Nickel Rim South mines in Canada (Allen and Keen, 2008; O’Connor, 2008; Bartsch et al., 2010). All of them are large and deep mines, producing more than 1 million tonnes of ore per year. The system automates the ventilation control devices such as auxiliary fans and regulators based on input from remote air quantity and quality monitoring systems, and a vehicle detection system.

Sensors installed at the entrance of an area detect gas concentrations and the number and type of vehicles or even people that are operating in that area. These sensors are linked to the fan and/or regulator that control the airflow in that area (airflow in an area can be controlled with both auxiliary fan and regulator, or by each of them independently). When a gas concentration exceeds a pre-set limit, the fan is started, and if a regulator is used, its opening is increased so that the air flows into the area until the concentration falls below the limit. Once the concentration falls low enough, the fan automatically stops, and the regulator automatically reduces its opening. Similarly, when a vehicle enters an area, the system identifies the type of vehicle and automatically adjusts itself according to pre-set values, allowing airflow into that area adequate for that vehicle’s heat creation and emissions. For example, auxiliary fans in Malmberget mine run at full capacity when a diesel loader is working in a particular area, and only run at 20% of the maximum capacity when an electric loader works in the same area (Nensen and Lundkvist, 2005).

Besides automatic control, the system can also be controlled manually from a control room. Several companies such as ABB (Switzerland), Bestech (Canada), and Simsmart (Canada) have developed control systems for VOD. Figure 3.3 shows a schematic of a VOD system developed by ABB, which is named OMVOD (Optimized Mine Ventilation on Demand).

Figure 3.3 Schematic of ABB’s Optimized Mine Ventilation on Demand (ABB, 2009)

In-mine trials show that VOD has reduced ventilation power consumption in these mines. For example, Malmberget mine reported a reduction of annual power consumption from 167 GWhr to 72 GWhr after the installation of their VOD system (Nensen and Lundkvist, 2005).

3.9 Levels/strategies of VOD implementation

The implementation of a VOD system does not necessarily require all essential components to be installed. The level of implementation varies from mine to mine depending on site specific requirements or as situations permit. According to Tran-Valade and Allen (2013), five main levels/strategies of VOD can be implemented. They include user control (manual control), time of day scheduling, event based, tagging and environmental. Tran-Valade and Allen (2013) again reveals that these levels/strategies of implementation can be used separately or in combination.

These strategies are incremental in benefits that can be delivered and the technology cost and the capabilities of hardware and software components available in the market, has improved significantly over the years which ensures that each strategy is worth considering if implemented properly in a given project according to Flores and Acuña (2016). Brief description of each strategy is presented below (Acuna et al., 2016; Wallace et al., 2015; Acuña and Allen, 2017; Pandey et al., 2015; Dicks and Clausen, 2017).

3.9.1 User control (manual control)

The manual control allows ventilation engineers to manually start or stop (on or off) mine fans and also vary doors and regulators openings to certain percentages. Operational points for the ventilation system components are set at this level. According to Acuna et al. (2016), these operational points can be divided into two subcategories, namely; fixed settings and proportional integral derivative (PID) control loop. The fixed settings involve the on/off (or VFD) to ensure the fan operates at a certain revolution per minute (RPM) to deliver the airflow needed. In the case of regulators and doors, they are also opened to some amount of percentage (0 – 100%) to also deliver the same amount of airflow required. The proportional integral derivative (PID) control loop is basically a feedback control system that is used to achieve the required set points using a measured process variable.

3.9.2 Time of day scheduling

In this strategy, there is room for automatic changes to the ventilation system using a daily on/off routine (time input). The time input then triggers the planned changes to be made in a way that the control devices are started/stopped or regulated to deliver the desired airflow base on the mine schedule (e.g. Shift change).

3.9.3 Event-based

The event-based strategy of a VOD system allows the changes to be made to the ventilation system of the mine base on certain activities in the mine. For example, auxiliary fans can be started after blasting in the mine to reduce the blast fumes clearance time and shorten re-entry times. Tran-Valade and Allen (2013), describes it as “an automatic trigger of prescribed actions in reaction to configured events”. These configured events may also include fire, strata gas outburst or other unexpected events.

3.9.4 Tagging

In this level/strategy, the local air demand is accomplished with tracking and identification system to transmit information for communication. This ensures the system responds to personnel and equipment location as well as the impact they introduce to deliver the given airflow (calculated regulatory demand for equipment and personnel) in the exact location of the mine.

3.9.5 Environmental

This level allows the ventilation system to respond to any changes in the mine environment. This is made possible in real time with the aid of monitoring devices or sensors for several parameters of interest such as airflow, relative humidity, wet and dry bulb temperatures, and gases (CO, NO, NOx etc.).This level/strategy is sometimes referred to as quality-based VOD though this is applicable to countries where the regulations permit its use to manage airflows base on the concentration and TLV-TWA of contaminants (DPM, dust and gases). This level is therefore usually used alongside the other control strategies as a failsafe system (in case contaminants exceed their allowable concentrations) according to Acuna et al. (2016). The ventilation system is therefore adjusted to supply an additional airflow until the contaminant concentrations are below their acceptable TLVs.

3.10 The VOD system and its components/elements

The VOD concept may seem theoretically easy enough, but in practice it requires good design and execution as well as financial commitment for components that suits the demands of each mine. Fully automated VOD system even places more responsibilities on ventilation engineers to fully understand the mine ventilation circuit not only to fully utilize the system´s benefits, but also to convert or translate these benefits into financial value (Pandey et al., 2015). The essential components for the implementation of any VOD system may include; data acquisition system, ventilation control system, central system process and control and a communication facility. This is illustrated in Figure 3.4

Central Data system Acquisition process and system ventilation control Eg. Sensors, system RTLS Eg. VOD software

Controlled devices Eg. Regulator, door

Figure 3.4 Essential components of a VOD system and their interaction (modified after Pandey et al., 2015)

3.11 How the VOD system works

A ventilation on demand (VOD) system uses a combination of advanced software and electronically controlled hardware coupled with mine environment monitoring system to continually monitor air quality and adjust the airflow as required (RAMJACK, 2015). The system ensures that the active mine workings where the workers are located benefit from better and more efficient ventilation.

A typical ventilation system consists of the main fan with motors equipped with variable frequency/speed drives, regulators and doors to change airflow to calculated demands through

26 the mine. Equipment and personnel are equipped with tracking and identification system which are connected together to a central control and communication system to transmit information from the data and triggering devices. There are also auxiliary fans with on/off system or VFD that are linked to the main fans by a pressure transmitter to ventilate local production areas.

Where the mine working environment is to be monitored, gas sensors (e.g. CO, NO, NOx, etc.) are installed. In summary, the system functions by interacting with the mine monitoring system, ventilation circuit and the ventilation simulation system. The integrated relationship is demonstrated in the Figure 3.5.

Ventilation Simulation

Mine design (ventilation circuit)

Mine VOD environment system monitoring

Figure 3.5 Diagram showing the relationship of a VOD system interaction

Figure 3.6 also presents a sample schematic diagram of a VOD control system and its working principle which combines a VOD software and a real time location system (RTLS) coupled with mine environment monitoring system to continually monitor air quality and adjust the airflow as required.

Fig 3.6 Schematic diagram of a VOD control system

Figure 3.7 also shows the ventilation of demand system for auxiliary fan controls where a transmitter has been installed in the vehicles with a receiver connected to a control system. Vehicles entering a zone are detected such that signals are sent to the fans to start and deliver the required quantity of air based on the pre-set ventilation demand for that type of vehicle.

Figure 3.7 Auxiliary fans control system (courtesy Gefa system)

3.12 Commercial VOD software

The execution of a VOD system requires a control software. Several of these softwares are available for commercial use. However, the three main and widely used among them includes; ABB Ability Ventilation Optimizer (formerly SmartVentilation), NRG1-ECO (BESTECH) – Energy consumption optimization and VentSim Control (formerly SmartExec), (ABB, 2020b; NRG1-ECO, 2020; VentSim CONTROL, 2020).

3.13 VentSim control (formerly SmartExec)

The VentSim control software provides ventilation design capabilities which can be used for control and optimization. The software features five levels of control that may be implemented (VentSim CONTROL, 2020):

3.13.1 Manual

With the manual level of control, ventilation engineers are able to use the software interface to remotely turn fans on or off, to modify their speed or to set the percentages of regulators. These settings then stay as they are until they are manually changed again.

3.13.2 Automatic schedules and events

This level of control allows underground fans and regulator settings to be automatically changed as part of a schedule such as shift changes or planned events such as blasting.

3.13.3 Automatic set points

This level of control also allows ventilation engineers to enter set points for airflow, gas levels, and/or temperature. Monitoring stations conditions are read in real time such that the software automatically adjusts fans and regulator settings to achieve the required airflow.

3.13.4 Dynamic requirements (VOD)

With the aid of tracking and identification system on personnel and mine equipment, the software determines the requirements for airflow, gas levels, and temperature at each location. VentSim control also communicates with data from monitoring stations conditions in real time such that the software automatically adjusts fans and regulators to achieve the required airflow.

3.13.5 Complete infrastructure optimization including main fans

This level enables the software to read real-time conditions from monitoring stations and automatically optimizes the underground fans and regulator settings, and also adjusts the main fan settings to realize the required airflow and maximize energy savings. This level of optimization controls the ventilation system as an entire unit using advanced control strategies designed for mine ventilation applications.

3.14 ABB Ability Ventilation Optimizer (formerly SmartVentilation)

The ABB Ability ventilation optimizer is a ventilation control system that provides ventilation on demand functionality. It is a modular system which can be fully integrated into the ABB ability system 800xA to offer three levels of implementation to fit different demands of operation. These include (ABB, 2020a);

3.14.1 Basic control

This level involves a remote starting and stopping of mine fans from a control room without the ventilation officer going down the mine to carry out the command.

3.14.2 Ventilation on Demand (VOD functionality)

This level ensures an automatic control of the ventilation equipment to deliver the desired airflow. The calculated airflow demands are based on information from mine schedules, events and equipment and personnel location to define the required air quantity.

In the third level of implementation, an algorithm, sensor feedback and advanced multivariable control technology are employed to run all the fans in an optimal operational mode and deliver the required airflow quantity in an efficient way to minimize energy consumption in real time.

3.15 NRG1-ECO (Energy Consumption Optimization)

The NRG1-ECO is an energy management system developed by Bestech that can be applied in mine ventilation to reduce energy consumption. It offers the five levels of ventilation on demand control strategy similar to that of VentSim control. The control strategy ranges from manually switching on/off of control devices to a fully automated system with environmental monitoring system (NRG1-ECO, 2020).

CHAPTER 4

Model Calibration and Validation, VOD Consideration, Design and Simulation

4.1 Model Calibration and Validation

The first step in this work was calibrating the existing ventilation model of Konsuln mine. This was to ensure that the model is reasonably accurate to give reliable simulation predictions of the performance of Konsuln ventilation system in its current state and future works.

The ventilation model of Konsuln mine as of 2 December 2019 was obtained as the base case model for calibration. The model was created using VentSim™ Design software, a popular ventilation simulation software created by Craig Stewart from Chasm Consulting in Australia, which is now a part of Howden Group, a global leading fan manufacturing company.

In mine ventilation model calibration process, some criteria need to be set to compare ventilation survey results with it to ensure good correlation between actual and modelled values. These criteria may include but not limited to the following; airflow, correct fan curve, primary fan duty point and other correlation parameters such as resistance, shock losses and friction factors.

In modelling of mine ventilation networks, the input parameters such as friction factor, shock loss, and resistance of control devices play a significant role in accurate simulation of the actual performance of the mine ventilation circuit. If these parameters are inaccurate, it will be difficult to precisely simulate the airflow circulation in the ventilation modelling software. A calibrated ventilation model ensures that the simulated airflow results is close to the actual (measured) airflow. The process therefore minimizes the variation in the simulated and measured values by controlling the errors of the input parameters within a minimum range. The calibration process verifies the accuracy of the model to improve and presents the model as good for further underground mine ventilation planning.

4.2 Pressure-Quantity survey

The calibration was done using barometer Pressure-Quantity (PQ) survey. The main purpose of this survey was to determine the actual friction factor of airways inside the mine. This is because the friction factors in the base case model are based on default values only, which were obtained from literatures. The model was then updated by using actual friction factors as the

31 input and then the airflow quantity predicted by the updated model was compared with the actual (measured) one.

In this survey, air pressure at two points within a uniform airway was measured simultaneously using a barometer, and airflow quantity within these two points was also measured using a vane anemometer. In addition to these measurements, distance between two measurement points, cross-sectional dimension of the airway between these two points, and air density between these two points were also measured.

The difference between the measured pressure includes pressure differential required to flow measured airflow quantity between these two points (pressure loss) and the weight of the air column between these two points if these two points are not at the same elevation, like inside a ramp. When the two points are not at the same elevation, a correction must be made to exclude the weight of the air column. After correction, the airway resistance and friction factor can be determined using the following equations:

푃 = 푅푄2 Where: P is the pressure loss between two points in an airway R is the resistance of the airway (Ns2/m8, nicknamed as Gaul) Q is the required air quantity inside the airway (m3/s) The resistance of the airway is calculated using the following equations: 푘퐶퐿 휌 푅 = × 퐴3 1.2 Where: k is airway friction factor, the factor that defines the roughness of the inner surface of the airway (Ns2/m4 or kg/m3). This factor is proportional to the inner surface roughness, i.e. rough surface has high value of k and smooth surface has a low value of k. For airways that have infrastructures inside them like belt conveyor and railway, “roughness” of the infrastructure is included in k factor of these airways C is the circumference (perimeter) of the cross-section of the airway (m) L is the length of the airway (m) or the distance between two measurement points A is the area of the cross-section of the airway (m2) ρ is the density of the air that flows inside the airway (kg/m3), calculated based on measured temperatures and barometric pressure 1.2 is the density of air at sea level. The unit is kg/m3

Due to practical reason, the survey was not done in all airways within the mine. Rather, it was done on some airways that represent airways that have the same characteristic, i.e. airways that have the same dimension and ground support. For example, on level 436 and 486 only some parts of the footwall drive that have the same dimension and ground support were surveyed at the same elevation, as shown in Appendices A and B. Some part of the ramp with similar dimension and ground support were also surveyed at different elevations in the mine.

4.3 Primary fan performance measurement

In addition to the PQ survey to determine actual airway resistance and friction factor, another PQ survey was done on the primary fans to determine their actual performance or duty point. Figures 4.1 and 4.2 show photo and layout of Konsuln’s primary fans. The photo presents the diffusers with the fan impellers not seen because they have been covered by the fan dampers when the fans were turned off. It can also be seen in Figure 4.2 that the airflow delivered by the primary fans encounters two 90° (approximately) bends after the regulator which should be changed to lower the system resistance. The fan quantity was measured using vane anemometer at the regulator in front of the fans outlet and Fan Total Pressure (FTP) was determined by measuring the pressure across fan bulkhead using digital manometer. It was then adjusted with shock loss caused by the expansion of the ejected air from the fan into the fan chamber.

2× EVS 160-56-06-75kW-37.5o N=1480rpm, 50Hz

Figure 4.1 Konsuln primary fan configuration

Figure 4.2 Plan view of the physical structure installation of primary fan.

4.4 Results of model calibration

Through the calibration process, the percentage of difference in airflow quantity on level 436 has been reduced from about 68.6% in the base case model to as low as 0.4% in the fine-tuned model. For level 486, the percentage of difference in airflow quantity is also reduced from about 44.1% in the base case model to 7.7% in the fine-tuned model. For the primary fans, the percentage of difference in airflow quantity is from 18% to 0.6% and in fan total pressure (FTP) from 29.2% to 21.3%.

These differences are considered low and reflects the accuracy of the updated model. The model can be said to be good for further underground mine ventilation planning and is therefore usable to give reliable predictions of the performance of Konsuln ventilation system in its current state and future works such as the consideration and design of a comprehensive VOD system which will be highlighted in the next chapter.

CHAPTER 5

Results and Discussion

5.1 VOD considerations, system design and simulation.

5.1.1 VOD system design criteria.

The production cycle; mainly loading and hauling activities, equipment and ventilation requirements were considered to understand the current and future needs for ventilation at Konsuln mine. With an annual production rate somewhere between 1.8 - 3 million tonnes per annum (mtpa), it is estimated that 1-3 Load-Haul-Dump (LHDs) and 7-12 trucks would be working at the same time in the mine. The proposed LHDs and trucks will be a mix of diesel and battery powered and might be replaced with electric powered in the sustainable mine of the future which LKAB aims to achieve. However, this VOD work still focuses on diesel powered equipment which will be employed in the initial stage of the SUM project. Consideration for the consequences of the transition to electric fleet on the ventilation requirements is presented later.

Diesel powered LHDs and trucks considered for the simulation studies are Scania R500 trucks (40 tonnes payload) and Epiroc ST18 LHD (18 tonnes payload), which are currently used in the development of Konsuln mine. These machines are proposed to be equipped with Euro VI engine rating, which plays a vital role in the simulation input parameters as well as the total mine airflow requirements.

Based on the proposed production plan and schedule of Konsuln mine, the mining process on the three main levels (436, 486 and 536) was divided into three scenarios that present the underground working conditions as illustrated in Table 5.1 and Figure 5.1. The scenarios were selected to reflect the start of the proposed production plan and schedule of the mine, the mining progression stage and the full production stage when all the levels are active with operating machineries.

Table 5.1 Scenarios for VOD system design and consideration

Level Scenario I (77 m3/s) Scenario II (99 m3/s) Scenario III (121 m3/s)

436 Two Scania R500 Two Scania R500 One Scania R500 trucks, trucks, one Epiroc ST18 trucks, one Epiroc ST18 one Epiroc ST18 LHD LHD LHD

486 Two Scania R500 Two Scania R500 Two Scania R500 trucks, trucks, one Epiroc ST18 trucks, one Epiroc ST18 two Epiroc ST18 LHD LHD LHD

536 No active Production One Scania R500 Two Scania R500 trucks, trucks, one Epiroc ST18 one Epiroc ST18 LHD LHD

Ramp Three Scania R500 trucks

Regulator

Figure 5.1 Schematic illustration of the three scenarios in Konsuln mine layout.

In all the three scenarios, three Scania R500 trucks were assumed to be located within the main ramp throughout the shift. For scenario I, it was assumed that there will be two Scania R500 trucks for one ST18 LHD in both level 436 and 486 with no ongoing active production at level 536. In scenario II, the same Scania R500 truck and ST18 LHD ratio for scenario I on level 436 and 486 applies, but with an added activity on level 536 where one ST18 LHD is paired to a Scania R500 truck. Scenario III considers the busiest case scenario where the number of ST18 LHDs increases from three to four with two in operation on level 486 each paired to a Scania R500 truck with level 436 and 536 having a one to one and two to one Scania truck-ST18 LHD ratios respectively. However, for levels with two Scania R500 trucks paired with one ST18 LHD, it was assumed that one truck will be in waiting while the other one is being loaded.

All the three scenarios were simulated in the updated ventilation model. This model was used to estimate the annual ventilation power cost based on the proposed production plan scenarios to deliver enough airflow quantity under the VOD design system. Enough airflow quantity in this case means that the airflow is adequate to keep gases concentration to be below the TLV- TWA in Swedish OH&S regulation AFS 2018:1, which are 20 ppm for CO and 0.5 ppm for 3 NO2 (Arbetsmiljöverket, 2018), to keep radon below the exposure limit of 2.1 MBqhr/m (Strålsäkerhetsmyndigheten, 2018), and also to check whether DPM concentration and temperature in working areas will be within safe limit. Currently there is no limit for DPM and temperature in working areas prescribed in Swedish OH&S regulation. Therefore, simulated results will be compared to the limit used in Australia, a major mining country. Australian TLV-TWA for DPM is 0.1 mg/m3 of Elemental Carbon (EC) and Australian limit for safe temperature in working areas is the 28°C Wet Bulb (Halim, 2020). This temperature is the temperature measurement of a mixture of air and water vapour. It is the temperature felt when wet skin is exposed to moving air. This is different from the temperature used in weather reports on public media (TV, radio, internet), which is Dry Bulb (DB). WB is widely used to assess risk of heat illnesses in underground mines worldwide. The reason why WB is used for this purpose instead of DB is that various studies that have been done in South Africa and Australia found that the risk of heat illnesses is highly influenced by the change in WB instead of DB. Many mines in these two countries have heat issue. Therefore, there have been many studies done in both countries to combat this issue.

To compare and highlight the benefit and cost savings advantage of the VOD system, a base case scenario which is a conventional way by which the main and auxiliary fans are always left on to operate continuously and at their maximum speed was carried out. The three scenarios

37 were also simulated by adjusting the main, auxiliary and crosscut fans speed to deliver the required airflow based on machinery requirements and also ensuring that contaminants are below their TLV-TWA and STELs.

5.2 Ventilation power cost for base case, scenario I, II and III.

This section describes an estimation of the economic savings the VOD system offers based on the proposed production scenarios while providing a safe work environment at the same time.

In the steady state operation of the mine, the ventilation of level 436, 486 and 536 consist of 30kW secondary fresh air fans with 1000mm duct extended to the end of each footwall drift. A minimum of three fans are planned to be used together with 11kW secondary fan in each crosscut (production drive) with 800mm duct for crosscuts with length greater than 40m. For easy tabulation of results, the three minimum 30kW fans on each level are named as auxiliary fan 1, 2 and 3 respectively. This is illustrated in Figure 5.2 below.

Figure 5.2 Auxiliary fans arrangement on each level

The total measured quantity for the primary fan was 84 m3/s. This is lower than the designed capacity of 100 m3/s due to the regulator in front of the fan outlet as shown in Figure 4.3 and 4.4. However, for easy and realistic results, it is assumed that the regulator will be removed to boost airflow to the mine, hence all simulations were carried out without the regulator in the model. When the regulator was removed, VentSim simulation estimates an airflow quantity of approximately 99.3 m3/s. This will be used in the diesel, heat, and blast fumes clearance simulations in this study.

In the base case scenario, the fans are assumed to run continuously throughout the year (24 hours per day, 365 days per year) at their maximum speed. In the case of scenario I, II and III, the speed of the main fan, secondary fresh air fans, crosscut fans (if applicable), and regulator on level 436 were adjusted (see Tables 5.2 – 5.4) to meet airflow requirements while ensuring that contaminants and DPM level are below their TLV-TWA. The simulation results and comparison are presented in Table 5.5.

5.2.1 Fans power cost

In the base case scenario, the electrical power cost for all fans was estimated to be 701 559 kr per year at a unit cost of 0.70 kr as a long-term estimate, although the average figures (unit cost per kWhr) may be a little below this value.

Table 5.2 Details of scenario I adjustments in model

Main fan Auxiliary fan 1 Auxiliary fan 2 Auxiliary fan 3 Crosscut fan Regulator Level Speed Quantity Speed Quantity Speed Quantity Speed Quantity Speed Quantity opening (%) (m3/s) (%) (m3/s) (%) (m3/s) (%) (m3/s) (%) (m3/s) (%) 436 100 13.4 50 7.0 40 3.3 65 5.1 50 486 80.0 79.8 100 13.4 40 6.0 50 6.6 None - None 536 40 5.5 40 5.9 40 5.4 None - None

Table 5.3 Details of scenario II adjustments in model Main fan Auxiliary fan 1 Auxiliary fan 2 Auxiliary fan 3 Crosscut fan Regulator Level Speed Quantity Speed Quantity Speed Quantity Speed Quantity Speed Quantity opening (%) (m3/s) (%) (m3/s) (%) (m3/s) (%) (m3/s) (%) (m3/s) (%) 436 100 13.4 50 7.0 40 3.3 None - 50 486 90.0 90.0 100 13.4 40 6.0 50 6.6 65 5.0 None 536 100 13.4 50 7.3 40 5.5 None - None

Table 5.4 Details of scenario III adjustments in model Main fan Auxiliary fan 1 Auxiliary fan 2 Auxiliary fan 3 Crosscut fan Regulator Level Speed Quantity Speed Quantity Speed Quantity Speed Quantity Speed Quantity opening (%) (m3/s) (%) (m3/s) (%) (m3/s) (%) (m3/s) (%) (m3/s) (%) 436 100 13.4 50 7.0 40 3.3 None - 50 486 95.0 95.5 100 13.4 40 6.0 100 12.9 None - None 536 100 13.4 40 6.0 50 6.8 65 5.1 None

Table 5.5 Comparison of simulation results for ventilation power cost Scenario Main fan (%speed) Annual power cost (kr) cost savings % cost savings Base case 100 701 559 - - Scenario I 80 357 182 344 377 49.1 Scenario II 90 506 922 194 637 27.7 Scenario III 95 592 268 109 291 15.6

From Table 5.5, it can be observed that the simulated VOD design scenario will account for about 15.6% – 49.1% of cost savings while still supplying the needed amount of air to working areas to ensure that contaminants are below their TLV-TWA and provide a good working environment. This estimation is based on the above scenarios and fan speed adjustment. It must be noted that where there is a differential pressure transmitter to provide intelligent adjustment of main and auxiliary fans speed based on the quantity changes and pressure at the bottom of the shaft, fans may even run at a lower speed than that illustrated in the scenarios above. This may translate into higher cost savings. Also, where real time data from radon sensors are significantly low, fans may be completely turned off instead of running as assumed in each scenario.

5.3 Diesel emissions and heat simulations For diesel emissions and heat simulations, additional input data are required, which are:

• Emission rate of toxic diesel exhaust contaminants (CO, NO2, and DPM) in gram per kilowatt-hour (g/kWhr). This data was obtained from Scania and Epiroc. Due to confidentiality, the values cannot be stated in this report. • Rated engine power of diesel machineries, in kilowatt (kW). This is input data for the heat emitted by diesel machineries and obtained from the machines’ specification brochure that

can be downloaded from Scania and Epiroc website. An example is https://www.epiroc.com/sv-se/products/loaders-and-trucks/diesel-loaders/scooptram-st18. • Surface climate during summer, which is average temperatures on the surface of the mine during summer. This is input data for the heat that comes from the atmosphere above the mine and is obtained from Sverige’s meteorologiska och hydrologiska institut (SMHI) website. It was found that average temperatures in Kiruna during summer are 12.6°C DB and 7.5°C WB. • Thermal parameters of the surrounding rock mass, which are surface Virgin Rock Temperature (VRT), geothermal gradient, rock thermal conductivity, rock thermal diffusivity, and rock specific heat. These are input data for heat that comes from the rock mass surrounding the mine. Table 5.6 shows the description of each of these parameters. These parameters are obtained by field and laboratory measurements because they are influenced by local climate and local geological features such as multiple rock types, joints, faults, and folds. Unfortunately, they are yet to be measured since the mine is yet to have heat issue. This is also the case in other Swedish mines.

Table 5.6 Description of rock mass thermal parameters input data Parameter Description Surface VRT Temperature of rock mass on the surface above the mine Geothermal gradient Rate of increase of rock mass temperature along with the increase of the depth of the rock mass. It is shown as °C per km depth or °C per 100m depth Rock thermal The ability of a rock mass to transmit heat through itself. It is shown as conductivity Watt per meter - degree C (W/m°C) Rock thermal The ability of rock to diffuse or transmit contained heat over a unit area per diffusivity unit of time. It is shown as m2 per second (m2/s) Rock specific heat The amount of heat required to change the temperature of a kilogram of rock mass by one degree. It is shown as Joule per kg – degree C (J/kg°C)

Therefore, thermal conductivity, diffusivity, and specific heat were assumed based on the laboratory measurement values of Quartzite, which is the dominant rock type in Konsuln (VentSim Design, 2020; Jokelainen, 2020; VentSim DESIGN™ user manual, 2020). Surface VRT and geothermal gradient were assumed based on field measurements in a mine in Canada, which has a similar climate with Sweden.

• Thermal conductivity: 3.0 W/m°C • Thermal diffusivity: 1.39 x 10-6 m2/s • Rock specific heat: 800 J/kg°C • Surface VRT: 1°C

• Geothermal gradient: 1°C per 100 m increase of depth

The average diesel power output of the trucks and LHD during a shift was assumed to be 45% (Bolsöy, 2020) of the rated engine power to ensure that DPM concentrations are not over predicted. This is because no typical diesel equipment will run at full engine power during an entire shift. The power output even become much less when trucks and LHDs are empty.

5.3.1 Diesel emissions and Heat simulation results

The diesel emission simulation was carried out and the highest concentration values on the levels and ramp for each simulated scenario are presented in Table 5.7 below. The theories behind the simulations are not presented in this thesis because they are complex. They can be read in book “Subsurface Ventilation Engineering” by M.J. McPherson (2009).

Table 5.7 Diesel emissions simulation results

3 Scenario CO (ppm) NO2 (ppm) DPM (mg/m of EC) I 5.4 0.1 0.020 II 6.1 0.1 0.023 III 7.0 0.1 0.026

CO: TLV-TWA is 20 ppm

NO2: TLV-TWA is 0.5 ppm DPM: Australian TLV-TWA is 0.1 mg/m3 of EC

From the above concentration levels, all contaminants are below their TLV-TWA. Also, it can be seen that levels of CO and DPM increases with increased fleet size. This observation therefore highlights the need for this study even if equipment with Euro VI engines have been proposed for use in the test mine. These machineries are rated to have better emission standards that improve air quality and comply with limit values for air pollution.

The heat simulation was done for the month of July where the highest temperatures in Kiruna are often recorded for the summer. From each scenario, the highest temperatures in Konsuln were predicted as 17.0°C, 18.3°C and 20.7°C WB for scenario I, II and III respectively. As discussed earlier, Swedish regulations currently have no requirements for heat (working temperature) but the simulated results indicate that the highest temperature in working areas in Konsuln will be less than the limit used in Australia, 28°C WB.

5.4 Blast fumes clearance simulation

The “blast fumes clearance time” simulation was done for production blasting only since it will be the largest blasting done in Konsuln. The planned design of production (ring) blasting in Konsuln is shown in Figure 5.3 (Nordqvist, 2020). It consists of 16 blastholes that contain approximately 5290 kg of emulsion type of explosive, Kimulux KR0500, with a total gas volume of around 4920 m3. Details of the studied ring and the technical data of the explosive used are presented in Tables 5.8 and 5.9. This estimate assumes that an ideal detonation will occur for the blast and might also depend on the possible reaction with the ground.

Table 5.8 Studied ring details for blast simulation Sublevel Cross-cut Blasthole Numer of Toe Side angle Burden Explosive Height (m) Spacing (m) Dia (mm) Holes Spacing (m) Side holes (°) (m) 50 25 115 16 3.2 45 3 KR0500

Table 5.9 Technical data of Kimulux KR0500 Property Unit Kimulux R 0500 (KR 0500) Density kg/m3 1200 Detonation speed m/s (ø = 40 mm) ~4800 Energy (theoretical) MJ / kg 3.8 Gas volume L/kg 930 Acid balance % -1.43

65 Charges in red 60

0 -15 -10 -5 0 5 10 15

Figure 5.3 Studied ring of 16 boreholes for new 50m sublevel height in Konsuln (courtesy Anders Nordqvist, LKAB)

Four blast simulation scenarios were considered as scenario A, B, C, and D. These four scenarios are illustrated in Figure 5.4.

Figure 5.4 Blast fumes clearance simulation scenarios

In scenario A, only one ring was considered to be blasted on level 436 whilst two rings were considered to be blasted on level 436 for scenario B. Scenario C considers two rings to be also blasted, but one on each level for both level 436 and 486. The last scenario D, factors a worse case where three rings will be blasted with one on each level 436,486 and 536. During blasting, the blast fumes are planned to be exhausted through an exhaust shaft. For this reason, 22kW,125mm diameter exhaust fans will be used to prevent blasting fumes from going up the ramp. In this simulation however, exhaustion of the blast fumes using the ramp as exhaust was also carried out and the results was compared with the use of the exhaust shaft for the blast fumes clearance. This was to investigate which of the two approaches saves some amount of clearance time for the blast fumes to reduce re-entry time. For easy comparison of results, all the blast scenarios were assumed to take place in the southern part of the mine with corresponding fresh air and crosscut fans turned on where applicable. Again, for levels where blasting is carried out, corresponding auxiliary, crosscut, and exhaust fans are turned on and operating at 100% speed. However, due to radon, fans on levels with no blast activity were not completely turned off but their speed were reduced and varied between 40-50% as it deemed fit to maintain low levels of concentration below the exposure limit. The primary fan speed was maintained for the same scenario used in the diesel simulation with blast scenario D assumed to run on the same speed as that of scenario C.

5.4.1 Blast fumes clearance simulation result

The time taken to clear blast fumes for each scenario through the exhaust shaft as planned are presented in Table 5.10. In the simulation, VentSim software assumes that all the fumes are

released by blasting and not contained within the muckpile. Though CO and NO2 contaminants were simulated, CO levels are presented to represent all contaminants since the simulation

show that it takes longer to clear CO than to clear NO2.

Table 5.10 Blast clearance time for each scenario, through shaft exhaust TLV-TWA time (Hrs:min) Simulated total clearance time (Hrs:min) Scenario Level 436 Level 486 Level 536 Level 436 Level 486 Level 536 A 01:18 02:20 - - - - B 01:44 03:20 C 1:24 2:02 - 2:30 3:55 - D 2:09 1:57 1:14 3:52 3:55 2:30

The blast clearance simulation using the shaft as the exhaust was then compared with the results of the blast fumes clearance through the ramp. Table 5.11 present this comparison. The top of the ramp near the mine entry was used as a monitoring station in the simulation.

Table 5.11 Ramp and exhaust shaft blast clearance simulation comparison Shaft exhaust Ramp exhaust TLV-TWA time Simulated total TLV-TWA time Simulated total Scenario (Hrs:min) clearance time (Hrs:min) clearance time (Hrs:min) (Hrs:min) A 01:18 02:20 01:27 02:30 B 01:44 03:20 01:50 03:30 C 02:02 03:55 02:04 04:00 D 02:09 03:55 02:24 04:15

From the results it can be seen that, under the conditions for each blast scenario, it will take approximately 2.30, 3.30, 4.00 and 4.15 hours to dilute and clear the blast fumes for scenario A, B, C, and D respectively if the ramp is used as exhaust. Again, the removal of the blast fumes through the exhaust shaft saves about 5–20 minutes of clearance time, which can be beneficial for reduced re-entry time compared to the use of the ramp. However, it can be said that there is not much difference in clearance time between the two considering the fact that exhaustion through the shaft comes with the purchase and installation of exhaust fans at each internal raisebored exhaust shaft. It is therefore ideal that the exhaustion through the shaft is carefully investigated for a possible room to improve clearance time to benefit from the economic factor that comes along with it.

The standard in Konsuln is that blasting is done at 1:15 am and it is expected that workers can re-enter the mine by 5:00 am. This amounts to about 3hours and 45minutes of acceptable clearance time. From the simulated results in Tables 5.10 and 5.11, exhaustion through the shaft approximately falls within this standard time for blast clearance. Exhaustion through the ramp indicates a clearance time slightly above expected. Since the shaft exhaust system will be used for blast clearance in Konsuln, it means that the simulated results will be acceptable by Konsuln standard and can even be improved under the VOD system. For example, auxiliary fans speed that were reduced for radon concentrations can be increased during production blast to temporarily increase airflow into the areas where blasting has been done to boost the clearance time and reduced again after the blast fumes are cleared.

5.5 Radon simulation

Radon is a major ventilation issue in both LKAB’s mines. Real-time fixed radon sensors are placed in the upper part of the ramp in Konsuln mine. These sensors have detected an average radon concentration of 245 Bq/m3 (0.245 Bq/l) and this value was used as an input data in this simulation.This concentration was placed as a fixed concentration in the production levels on both the northern and southern part of the mine in this simulation.

5.5.1 Radon simulation result

The exposure limits of radon in force in Sweden are 0.36 MBqhr/m3 in surface mines and 2.1 MBqhr/m3 in underground mines. Underground mine workers under the age of 18 are not allowed to be exposed to more than 0.72 MBqhr/m3. The limits are based on radon concentration in ventilating air instead of exposure to ionizing radiation. The radon exposure level for each person is calculated by multiplying the measured radon level by working time. If a person exceeds the annual exposure limit, he/she must do a physical examination and a report is sent to the Swedish Radiation Safety Authority. In addition, the person is not allowed to work within areas of the mine that contain radon for the rest of the year. The simulation results show a maximum radon concentration of 0.12 Bq/l (120 Bq/m3), which is far below the limits of 0.72 MBqhr/m3 and 2.1 MBqhr/m3. With annual underground working hours of approximately 1,804 hours for LKAB employees at Konsuln, the mine workers will be exposed to 0.22 MBqhr/m3 of radon for the whole year.

5.6 Some considerations to implement the VOD system

5.6.1 Equipment and personnel positioning and identification

Mounting of tags or transmitters with unique IDs on LHDs and trucks can be easily achieved for equipment identification and positioning system. Sensor technology may also allow for a quick response time to change auxiliary fan speed to supply the required airflow to a location where an LHD machine may be loading. However, airflow supply shortfall may occur from auxiliary fans adjustment to affect target locations of an LHD equipment and trucks in general if the response time is delayed. This challenge can be reduced if a mine can track the route of an LHD equipment and trucks. LKAB’s “Giron” system therefore provides an advantage in this case. Giron is LKAB’s database system which stores all the information about the mine geology, mine operations, development, production data, and schedules with relevance to place, location and time. The system can provide information on blasted locations in the mine

47 where loading of ore will be carried out. In this case, auxiliary fresh air fans and corresponding crosscut fans may be adjusted so that the system recognizes the intended route of the LHDs and trucks and apply the required changes just in time to dilute the diesel fumes. It may be hard to quantify the financial benefit of the use of the “Giron” system, but the best estimate is that the adoption of this system can save a lot of time in fixing ventilation problems.

5.6.2 Monitoring system and stations

Monitoring stations play a vital role in providing real time information of the mine environment. During the simulation scenarios, contaminants were monitored in the access to each level from the ramp (see Figure 5.5). The fresh air shaft at level 436 serves as the main fresh air intake point for all the three main levels in Konsuln. It is recommended that at least a flow meter is installed at such entry level to continuously monitor the air velocity.

Figure 5.5 Schematic diagram indication for monitoring stations

Again, from Figure 5.5, it can be seen that there are old mined out levels above level 436. A flow meter installed at this location as indicated in figure 5.5 will serve as an indicator to check the source of any leakages or airflow challenges either above or below the level. This will provide an easy means of trouble shooting in the event of airflow problems. For example, if a

48 flow meter is installed at level 436 as indicated in Figure 5.5, an airflow quantity of about 58.3 m3/s will be expected at that location. In the event of airflow challenge on level 486 or 536, this flow meter can be checked to verify the expected flow. Any significant change, say 25% decrease in airflow will probably mean that the old levels above level 436 should be surveyed to check and fix any leakage issue and vice versa.

Where applicable, CO and temperature sensors may be added to establish the base level of CO and temperature in the mine. A DPM monitoring system should be installed in the upper part of the ramp since simulated results shows that DPM concentration will be higher in the upper part of the ramp. This scenario and arrangement are illustrated on level 436 in Figure 5.6 below. Two to three flow meters can also be installed at appropriate locations in the ramp to monitor the direction and airflow quantity in the ramp during normal production activities. Again, pressure sensors should be installed at the bottom of the shaft to provide intelligent adjustment of main and auxiliary fans speed based on the quantity changes and pressure at the bottom of the shaft.

Figure 5.6 Monitoring system and station arrangement scenario on level 436

5.7 Ventilation modelling for the use of Battery-powered Machineries

5.7.1 Simulation with Battery-powered Machineries

The simulation of the battery-powered machineries was done for the same scenarios used to simulate diesel machineries. The only difference is that all machineries were replaced with their electric version. Battery-powered LHD and truck used are Epiroc’s MT42 truck (42 tonnes payload, which is almost the same as the payload of Scania R500) and ST18 LHD (18 tonnes payload). Since Epiroc is yet to release the battery version of its ST18, a motor power of 506.9 kW was estimated using the ratio of the ST14 battery motor’s power and ST14 diesel engine’s power.

The simulation was run for the same settings for the fans speed (primary, auxiliary, and crosscut) used in the diesel machineries simulation to keep the same airflow quantity. The results indicated the highest temperature of 13.8°C, 14.1°C, and 16.3°C WB inside the mine for scenario I, II and III respectively. This represents 18.8%, 23.0%, and 21.3% decrease in temperatures inside the mine for the respective scenarios I, II, and III compared to the diesel machineries heat simulation. The results also show zero emissions of gases and DPM which highlights the air quality advantage that electric machineries offer to the underground mine environment, especially in the active locations of the mine where loading and hauling may be taking place.

Again, the settings for the fans speed were further adjusted to ensure that the temperature in the mine is just below 28°C WB (limit used in Australia). The speed (%) of all primary, auxiliary and crosscut fans were adjusted to half (50%) of their maximum speed.

This further adjustment in the fans speed delivered a reduction in airflow quantity of 35.7%, 41.6% and 43.7% for scenario I, II and III respectively. The annual power cost, cost savings and percentage in cost savings for the electric machineries compared to that of diesel machineries is also presented in Table 5.12 for each scenario.

Table 5.12 Diesel and electric machineries annual power cost comparison Annual power cost (kr) Scenario cost savings % cost savings Diesel machineries Battery-powered machineries Scenario I 357 182 84 358 272 824 76.4 Scenario II 506 922 81 811 425 111 83.9 Scenario III 592 268) 78 918 513 350 86.7

From Table 5.12, it can be seen that the reduction in airflow quantity for electric machineries will further account for a significant cost savings of 76.4%, 83.9%, and 86.6% for scenario I, II and III respectively due to the cubic relationship between airflow quantity and fan power. The simulated highest temperatures inside the mine for these adjustments are 17.5°C, 17.3°C, and 19.2°C WB for scenario I, II and II respectively. These are still well below the limit used in Australia, 28°C WB for caution and 32°C WB for stop working.

CHAPTER 6

Summary and conclusions, recommendations and future work.

6.1 Summary and conclusions

In this study, three main VOD system scenarios were simulated, and four blast clearance simulations were also considered. The scenarios were based on the annual production plan and schedule of Konsuln mine with an estimation that 1-3 Load-Haul-Dump (LHDs) and 7-12 trucks would be working at the same time in the mine. The scenarios were simulated by adjusting the main, auxiliary and crosscut fans speed to deliver the required airflow based on machinery airflow requirements. Diesel machineries simulated were replaced with their electric version (battery-powered) to investigate the impact battery-powered machineries on the VOD system. From the diesel, battery-powered, heat and blast simulations carried out for all the scenarios outlined, the following conclusions were drawn;

• The VOD scenarios I, II and III will account for about 49.1%, 27.7% and 15.6% of cost savings respectively, compared to the conventional system of ventilation where fans are left to run continuously throughout the year (24 hours per day, 365 days per year) at their maximum speed.

• All the VOD system scenarios considered will supply the needed amount of air to working areas to ensure that contaminants are below their TLV-TWA and provide good working temperatures (17.0°C, 18.3°C, and 20.7°C WB) and environment.

• Blast fumes clearance through the exhaust shaft will save some amount of clearance time, which can be beneficial for a reduced re-entry time compared to the use of the ramp. However, the exhaustion through the shaft calls for financial commitment to achieve the savings.

• Battery-powered machineries will account for a reduction in airflow quantity of 35.7%, 41.6% and 43.7% for scenario I, II and III while delivering a significant cost savings of 76.4%, 83.9%, and 86.7% respectively compared to diesel machineries.

• Battery-powered machineries will also provide good working temperatures of 17.5°C, 17.3°C, and 19.2°C WB, for scenario I, II and II respectively, which are still well below the limit used in Australia, 28°C WB for caution and 32°C WB for stop working.

Overall, the VOD system scenarios considered and simulated indicated that the current airflow capacity will be sufficient to cover for the planned increase in production rate and machine fleet and handle all the diesel emissions, provide fresh air for the mine workers, and allow for safe work environment. Again, the current airflow capacity will comply with the new Swedish Occupational Health & Safety (OH&S) regulations based on the EU directive 2017/164 where TLV for gases have been significantly reduced.

Furthermore, the VOD system and battery-powered machinery will provide alternative solution for Konsuln mine to deliver the required airflow quantity to the mine working areas in an energy efficient way. This is because the old mined out levels in the mine will not require ventilation and all auxiliary fans in the mine will not be required at each point in time in the mine based on this study and the current practice of the mine. Nevertheless, some major ventilations changes are required (see section 6.2) to improve and actualize the benefits outlined in this work.

6.2 Recommendations

Although from this study, the increased production will require no changes to be made to the existing designed fresh air capacity in Konsuln, the following recommendations are required;

• The regulator in front of the primary fans should be removed to boost airflow to the mine as it significantly increases the resistance of the ventilation circuit.

• It is recommended that the considerations (utilization of Giron, installation of gases and DPM monitoring system, flow meters, and pressure sensors) discussed under section 5.6 are implemented as part of the VOD system strategy to improve and actualize the benefits and cost savings of the VOD system outlined in this work.

• The airflow delivered by the primary fans encounters two 90° (approximately) bends after the regulator. This should be reviewed for future modification and improvement to lower the system resistance.

• Additional radon measurement is recommended to support and validate the average value of radon concentration from real-time fixed radon sensors used as an input data in this simulation.

• Good auxiliary ventilation practices must be observed (fix leakages or replace duct when needed, maintain a uniform cross-sectional area for ventilation duct and remove any airway obstructions).

6.3 Future work

• The old mined out levels above level 436 should be surveyed to check and seal any form of leakages if any, to ensure that fresh air supply by the VOD system is adequate to meet the requirements discussed in this work.

• Studies on the VOD system installation should be conducted to ensure balance and avoid any delay or significant effect on the mine operations that could overcome the expected benefits.

• Evaluation of the overall financial which includes capital costs (monitoring stations (airflow, temperature, gas sensors), communication network, engineering, supply and installation etc.), maintenance cost, as well as the savings of power cost should be carried out before the VOD system installation.

• The gradual and complete utilization of battery-powered machinery that produce zero emissions calls for studies to be made on the theory of recirculation as a further strategy to improve airflow, save cost and energy, taking into consideration the legislation and existing routes that could be used for partial recirculation.

• Studies on power conservation in the charging of battery-powered machineries should be conducted to reflect the ventilation cost savings in the overall energy cost of the mine.

• Fire simulation studies should also be carried out to outline exhaust fans that should be started and their speed while looking at the potential fire source and shortest routes to refuge chamber scenarios in the mine.

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APPENDICES

APPENDIX A: Schematic layout of measurement locations on level 436 with flow measurements.

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APPENDIX B: Schematic layout of measurement locations on level 486 with flow measurements.

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