Underground mining activities can be dated back to before 3000 B.C. (1). First subsurface systems were only of shallow depth and were built with basic tools such as hammer and pick. Over the time, new technologies allowed deeper and more complex mines and ventilation was recognised as a requirement for a safe mine environment (2). In the book “De Re Metallica” (3), Georgius Agricola (1494 – 1555) stated: “[…] if a drift is too long and there is no connections to other shafts, air can’t be diluted and thickens, making it difficult for miners to breathe. Sometimes they actually strangle and their lights go off. Hence machines are needed to ensure miners can breathe and fulfil their work.” Agricola also sketched first automated machinery, e. g. Airscoops, that was used for supplying fresh air in underground mines. By around 1700, depths of 300 m and more were documented (2).
The need for ventilation increased further with the introduction of blasting operations and the ongoing industrialisation from the 17th century. Using the stack-effect, fires were used in surface ovens to increase the airflow from the 18th century. Animals, like the canary and rodents, as well as safety lamps were used as first gas detection systems. After around 1800, control devices were used to better direct airflow inside the mines. Scientific awareness on fluid mechanics and thermodynamics increased the understanding of interdependencies (2).
Today, depths of more than 1,000 m are common and diesel equipment is accounting as one of the main pollutants since its introduction in the 1970s. New technologies – pneumatic and electric motors – have yet allowed to install large mine fans that would provide huge amounts of air. Also, smaller fans are in use since around 1900 to allow better flow control in the underground systems. The development of ventilation software (from about 1950) has made it comparably simple to plan a mine ventilation system even before starting the mining projects (2).
Mining has been the driving motor for new technologies in a various number of cases. Though, optimisation in the ventilation systems is not commonly conducted, leading to a “set-and-forget-mentality” (4). Existing systems are remaining untouched and only topped up with additional volumes as new sections are developed, resulting in a loss of overall efficiency.
With rising energy prices and consequently stricter occupational exposure limits regarding gases and dust, mining companies are recently facing the question of how to face these changing demands in the future. Among economic reasons, social acceptance is also a factor motivating companies to optimise their systems, as today’s society is conscious of environmental concerns.
A possible solution can be the adequate introduction of ventilation on demand (VOD) systems. Ventilation on demand means supplying required amounts of fresh air to individual mining areas only at times they are needed. This leads from a static to a dynamic and intelligent air supply which will lead to a reduction of the total required airflow within a mine. By reducing the total airflow, energy can be saved in disproportionately high amounts due to the cubic relationship between volume flow and fan power as shown with the following formulas:
P = ∆p · V‘ and ∆p = R · V‘2 result in P = R · V‘3
E. g.: A mine requires an increase of airflow (V’) by 20 %. This will lead to an increase of pressure drop (∆p) by 44 % which then leads to a power (P) increase of 73 %. By using VOD with intelligent air management, it is possible that no additional volumes will be required. On average, ventilation accounts for up to 50 % of a mine’s energy costs, and up to 15 % of a mine’s total costs. Thus, VOD can hold immense saving potentials (5, 6).
With intelligent air supply, quality demands will also be easier to meet. By this, VOD can also lead to a generally cleaner and safer mine environment. Also, other improvements such as new motors can lead to cleaner mine air and air flow demands may decrease, but such do not rely on controlling the airflow itself and, therefore, are not involved with VOD. In this case, the general concept of “Mine Ventilation Optimization” applies, of which VOD is a part of, too (7).
2 Today’s solutions and future challenges in mine ventilation
Mining companies have a range of available options to ventilate their mines. Depending on the individual requirements, ventilation can be arranged accordingly, such as with a pull or push, U-tube or flow-through, or split, perimeter or unit ventilation system. Necessary infrastructure can be installed easily as power and material supply is no more a subject to various uncertainties. Also, separate ventilation shafts and roads can be used to improve ventilation networks, e. g. Kirunavaara Mine, Sweden (8). Roads used for ventilation only are usually designed with smooth walls and do not hold any mining equipment in order to keep the overall resistance low.
The trend to deeper and more complex mines is still ongoing. Both results in longer airways, meaning higher heat transfer from strata and higher shock and friction losses, and deeper mines mean higher rates of auto-compression. Therefore, cooling is also in the centre of attention.
Assuming increasing numbers of diesel equipment, demanded air volumes will also increase to dilute diesel emissions and heat (Figure 1). In the case of diesel changing to electricity as an energy source for motors, heat will still be of relevance.
With rising electricity, investment and maintenance costs, optimisation is more and more a requirement for economic underground resource extraction. Without optimisation, additional volumes would lead to a significantly high increase in energy costs in mines. Automation, as it is often named in this context, is an available solution for reducing the risk that miners are exposed to. Oxygen levels down to 17 % (minimum for diesel equipment) are acceptable and air can be recirculated within a mine, meaning lesser amounts of input air. However, ventilation will still be required, and it is assumed that required volumes might even increase depending on the depth of the mine, as heat must be exhausted. Therefore, automation cannot stand as a solution alone (9).
3 Ventilation on demand: diversity of possible solutions
The overall goals of ventilation on demand (Figure 2) and the involved optimisation of the ventilation network are increasing production and saving energy by effectively controlling the flow of air within regulatory demands Production can be increased, e. g., by controlled ventilation after blasting to shorten re-entry times (10).
The new ventilation system will be beyond the ‘set-and-forget-mentality’ and operate dynamically. The following questions are of major concern (11):
- Do all areas need to be ventilated?
- Do these areas require a constant volume?
- Are all auxiliary systems required at the same time?
- Have the original system design criteria been exceeded?
- Is ventilation needed in non-active periods?
By optimising the schedules of single processes (blasting, extraction, haulage), efficiency can be further increased. Smart load management can lead to lower costs, e. g. by scheduling processes of high energy demands into times of low tariffs (12).
3.2 Elements of VOD-systems
Answering the questions above is of organisational nature. Applying a VOD system requests complete and detailed knowledge of the mine ventilation network, the ongoing processes, and regulatory demands.
To precisely define local air demands, all machinery with their properties and positions must be known. Furthermore, personnel should be localised. With no personnel in any area, flow rates can be decreased to allowed minima. For both, localising personnel and machinery, a tracking and identifying system will be required.
Information on machinery and personnel then must be analysed to define needed volume flows and adequate reactions. Analysing data and triggering commands can either be conducted by a central control system or decentral. In both cases, adequate infrastructure is required to transmit information.
Furthermore, ventilation infrastructure is to be installed to change the airflows to the calculated needs. It should be remote controlled to guarantee short reaction times. Among regulators and doors, especially fans can be subject to variable settings. More details can be found in the corresponding paper about controllable fans, also found in this publication (pp. 342 to 355).
To meet regulatory demands, only calculating static demands based on e. g. diesel-powered equipment will not be sufficient. Especially large mines hold an enormous hazard regarding unexpected events, such as gas outbursts. Monitoring the network with gas detection sensors and measuring devices can be used to analyse air qualities and react e. g. with higher flow rates if certain regulatory demands are not yet met.
Using a monitoring system instead of applying calculated quantities will finally make the system a quality-based VOD rather than a quantity-based system, which is unable to react on spontaneous events.
3.3 Hierarchy of different VOD systems
Not all the named elements have to be installed to make a system a VOD based system. It is recognised though, that with a higher grade of implementation, higher savings can be achieved.
Five levels of implementation can be differentiated (13):
- Level 1: Manual Control. The first step towards an efficient VOD is any control after all. Ventilation officials can manually turn on and off fans and vary regulators and doors. Fans may also be fitted with variable frequency drives (VFD) and adjusted in speed.
- Level 2: Time of Day Scheduling. Planned changes in the network are no longer enforced manually, but on a pre-set daily on/off pattern.
- Level 3: Event-based. Ventilation is changed depending on certain activities within the mine. E. g.: an auxiliary fan is turned on after blasting to shorten clearance time. In an event-based system, adequate reaction can also be given in case of fires and other unexpected events.
- Level 4: Tagging. As described under the aspect of quantity-control, tagging implies the knowledge of position and type of vehicles and other pollutants to define ventilation needs.
- Level 5: Environmental. Environmentally controlled networks respond automatically to any changes of the in-time underground condition. This is considered as quality-control.
Other than VOD systems of level 1, the execution of any control is based on software. The following are currently available on the market:
- SmartVentilation (ABB, new.abb.com). ABB, the Swiss developer of SmartVentilation , developed this software for mines from its initial version designed for buildings. It is available in three options that are of different complexity. SmartBasic only provides tools for manual control, SmartMid holds options to automatically control ventilation equipment, and SmartPerfect provides full quality-controlled ventilation optimisation.
- NRG1-ECO® (BESTECH, www.bestech.com). NRG1-ECO® was developed by a committee of experts in the field of mine ventilation which makes this programme ideal for mine environments. It works decentral, meaning communication with a surface control centre is not required to trigger certain actions. Reaction times are shortened and hazards from communication losses are minimised.
- SmartExec™ (Howden Simsmart, www.howden.com). The Canadian company Simsmart developed SmartExec™ from software used in submarine ventilation. Its structures are similar to ABB’s SmartVentilation which derives from the companies’ partnership in the past. It holds tools for full tracking of vehicles and personnel and takes control from a central control room.
As a general concern, VOD is introduced to mines to save energy and/or increase productivity. A good example is Barrick Gold’s Bousquet Mine in Canada. The ventilation system was designed for 188 m3/s in 1990 with an expected extraction of 1,800 t/d at a maximum of twelve faces. In fact, it was only ten in advance at one time. However, by 1999, production had increased to some 2,100 t/d and an additional 110 m3/s were required. With the implementation of VOD, the system could remain with its infrastructure and providing 188 m3/s (5).
Using VOD simulation software for a complex room and pillar mine with 110 auxiliary fans, a saving potential of 20,000 MWh/a was calculated (14). Both examples show the tremendous potential using intelligent directing of air volumes.
Other examples are given in the following report on adjustable fans (Engler, Kegenhoff, Papesch).
4 Open questions
With the above descriptions, VOD has been defined as the supply of air at certain places in the amount and time needed. With the elements of ventilation systems and VOD software, it is possible to provide the required amounts and with monitoring systems, qualities can be validated. However, some open questions remain and higher saving potentials can be achieved with further implementation.
If loaders are not running at full load, e. g. diesel emissions are reduced. By transmitting not only location and vehicle characteristics, but also actual status, air volume supply can be further adjusted.
With any adjustment of ventilation equipment, it is clear that changes will not affect the target locations immediately due to inertia. This means, that diesel fumes of a loader entering a section will not be diluted immediately, although the local ventilation system is adjusted in that very moment. This can lead to a supply shortfall. To avoid such shortages, routing should be available, meaning that the system will recognise the intended routes of machinery to adjust its elements just in time before the requirements actually apply.
The same principle applies to sensors that can be out of range, affected by cross-sensitivity and a subject to inertia.
Finally, emergency situations can lead to fatal system downtimes. Attempts of increasing ventilation to a maximum seems a good reaction to be on the safe side, but could be the wrong response, e. g. in case of mine fires. In this field, more research will be required to develop feasible and safe solutions.
Ventilation on demand is the conceptual name of any optimisation in mine ventilation systems that targets the intelligent and controlled supply of individual mine sites with the required quantities of air in the time they are needed. For the implementation of a VOD systems, the following matters can be respected:
- Concerning defining the demand knowing emission sources, consumers and regulatory guidelines.
- Concerning knowing consumers and emission sources, vehicle tracking, vehicle identification and personnel tracking.
- Concerning adjusting the system by adjustable main fans, auxiliary fans, regulators and ventilation doors.
- Concerning validation of airflow measuring devices, gas concentration measuring devices and dust measuring devices.
- Concerning network communication with tracking hardware, network infrastructure (connecting wires etc), control units and software.
Using VOD can not only lead to a reduction of energy consumption, but can also be used to increase production or to expand the mine network with the available ventilation utilities.
For a maximum benefit from VOD, further research is to be conducted. An example for a closer investigation of auxiliary system optimisation can be read in the following article on adjustable mine fans.
References / Quellenverzeichnis
References / Quellenverzeichnis
1) Jahn, M.: Der älteste Bergbau in Europa. Berlin: Akademischer Verlag, 1960.
(2) Die Geschichte der Grubenbewetterung. Online. Available: http://www.grubenbewetterung.de.
(3) Agricola, G.: De re metallica libri XII. 1556.
(4) Lagowski, K.: Air Supply on Demand – New Ventilation Technology Provides Airflow When and Where It Is Needed. 2013.
(5) Hardcastle, S. G.; Gangal, M. K.; Schreer M.; Gauthier, P.: Ventilation-on-Demand – Quantity or Quality – A Pilot Trial at Barrick Gold’s Bousquet Mine. In: Proceedings of the 8th US Mine Ventilation Symposium, Rolla, 1999.
(6) Katary, S.: Ventilation on Demand – CAF (Community Adjustment Fund). CEMI, 2012.
(7) Basu, A. J.; Andersen, M. M.; Godsey, A. J.: A Framework for Integrating Mine Ventilation Optimization (MVO) with Ventilation on Demand (VOD). 2013.
(8) Mukka, L.; Blomgren, C.: Extension of the main ventilation system at LKABs Kiruna Mine for the new main haulage level 1365 m. 12th U.S./North American Mine Ventilation Symposium, 2008.
(9) Kocsis, C. K.; Hardcastle, S. G.; Hall, R.: The Benefit of Using Mine Process Simulators to Design a “Life-Cycle” Mine Ventilation System. In: SME Annual Meeting, Denver, 2004.
(10) Gillies, A. D. S.; Wu, H. W.; Shires, D.: Development of an Assessmet Tool to Minimize Safe After Blast Re-Entry Time to Improve the Mining Cycle. In: Proceedings, 10th US Mine Ventilation Symposium, Anchorage, Balkema, 2004.
(11) Hardcastle, S. G.; Kocsis, C. K.: The Ventilation Challenge – A Canadian Perspective On Maintaining a Good Working Environment in Deep Mines. 2002.
(12) Chatterjee, A.; Zhang, L. Xia, X.: Optimization of Mine Ventilation Fan Speeds According to Ventilation on Demand and Time of Use Tariff. Department of Electrical, Electronic and Computer Engineering, University of Pretoria, Pretoria, 2014.
(13) Tran-Valade, T.; Allen: Ventilation-On-Demand key consideration for the business case”, in Canadian Institute of Mining (CIM) Convention: Proceedings of the Toronto 2013 CIM Conference, Toronto, Canada, 2013.
(14) Howden Simsmart: Ventilation on Demand brings substantial energy and cost savings. 2016.