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

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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

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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

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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. ToDavid 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.

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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.

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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.

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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.

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2 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

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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

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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.

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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.

a

b

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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

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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

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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

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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.

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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.

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Figure 2.8 An example of schematic of level ventilation

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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.

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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;

𝑄 = 𝑉𝐴

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,

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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

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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 alsoinfluences 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

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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

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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.

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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

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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).

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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

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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)

Exposure Limits

Gases

NO CO NO2

TLV-TWA

(AFS 2015:7) 25 ppm 35 ppm 2 ppm

TLV-TWA

(AFS 2018:1 2 ppm 20 ppm 0.5 ppm

STEL

(AFS 2015:7) 50 ppm 100 ppm 5 ppm

STEL

(AFS 2018:1) - 100 ppm 1 ppm

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

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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/m³in 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.

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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)

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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.

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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.

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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

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 doorsto change airflow to calculated demands through

Central system process and

ventilation control system Eg. VOD software

Controlled devices Eg. Regulator, door Data

Acquisition system Eg. Sensors,

RTLS

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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.

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.

Mine design (ventilation

circuit) Ventilation Simulation

Mine environment

monitoring VOD

system

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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)

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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.

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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).

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