MINE VENTILATION
Almost carbon-neutral ventilation
Sweden-based mining major Boliden is evaluating many solutions in its quest to achieve its goal of reducing its carbon intensity by 40 % by 2030 , with underground ventilation being one developing area .
The recent installation of a heat exchanger in the Kankberg gold and tellurium mine , in northern Sweden , marks a giant step toward carbonneutral ventilation at the operation , according to Andreas Markström , Mine Engineer at Boliden .
Heat exchangers are already used for ventilation purposes at Boliden ’ s Garpenberg mine , south of Kankberg , but , after extending Kankberg ’ s ventilation system , the right conditions have recently been met to incorporate this at the gold and tellurium mine .
At Kankberg , in the winter , ventilated air must be heated using LPG to prevent the shaft freezing . The exhaust air from the mine is heated further , both by geothermal heat in the rock and the vehicles used in the mine . Using the heat exchanger , Boliden can lead the warmer exhaust air past the inlet air on either side of plates such that the heat is transferred . This process allows the reduction of Kankberg ’ s LPG consumption by 85 %. Since this is the first time the technology has been used in such a cold climate , the Swedish EPA ’ s Climate Leap is subsidising 28 % of the circa- SEK20 million ($ 2 million ) investment .
IM put some questions to Markström to find out more about this coldclimate first .
IM : How does this system differ to the one at Garpenberg ? What different systems / components have been put in place to deal with the extreme cold climate experienced in the Boliden area where Kankberg is located ? AM : Garpenberg has several intake and exhaust shafts , which create the opportunity to draw the ventilation through several different paths in the mine .
Boliden have two heat exchangers ( HE ) running from the same supplier in Garpenberg . In Garpenberg , we can , for instance , increase the exhaust airflow at the shafts connected to HEs to get sufficient heat to avoid the need for other heat sources . The external heat needed is added at the other shafts where we don ’ t have HEs .
The main difference with the HE in Kankberg compared with the one installed in Garpenberg is the distance between the intake and exhaust shaft . The distance between the shafts is a maximum of 50 m in those installations at Garpenberg . The HE in Kankberg proves that this technology will be suitable even where there is a medium distance ( 230 m ) between the intake and exhaust shaft .
The energy lost over the duct system is very small ; the main disadvantage is the increase in capital expenditure .
Another difference is the balance of airflow between the intake and exhaust over the HE at Kankberg . Two kilometres from the HE , exhaust air reaches the surface from the main ramp . Some air will always be controlled to go to this path to have plus-zero temperatures in all ramps and avoid icy roads underground .
A third difference is that since there is only an exhaust and intake shaft at Kankberg , we have installed valves after the HE and at the intake station to be able to turn off all airflow from the HE to the mine in case of a fire .
IM : How much of the required heat for the exchanger comes from vehicle heat and how much from the geothermal heat from the rock ? With the transition towards battery-electric equipment , for instance , how will you compensate for the heat loss ? AM : Approximately 3 % of the total heat exchanged comes from diesel vehicles and the rest from other sources ( eg geothermal , blasts and heat from electrical motors ).
With a transition towards battery-electric equipment , the total heat will indeed decrease , but the airflow needed to dilute contaminants from diesel will decrease to a larger degree .
By the time we use such equipment , the mine will be even deeper , which will compensate for the loss of heat from diesel equipment .
The propane gas burners used to heat the air before the HE was installed is still in place to heat the air on very cold days and has more than enough capacity to heat the air if battery-electric equipment is used .
It is , of course , also possible to electrify this source of heat , but for the time being the incoming power line does not have enough capacity to add this load to the mine .
A new power line will be constructed at Kankberg by 2024 .
IM : Do you also have a VoD system installed at Kankberg ? Does this further improve the efficiency of the operation ? AM : We have had a VoD system installed in Kankberg since 2015 , which is position based . It is supplied by ABB ( 800xA ), with vehicle positioning based off the closest access point within the Mobilaris platform .
A geofence of all access points in each production area is created in Mobilaris and an external ID is created for the corresponding fan in the ABB system . When a machine enters the production area , information about the activity type and which fan requires activation is transferred from Mobilaris to the ABB system .
When connection is lost , the fan runs for a pre-set time to ventilate the contaminants from the activity performed .
When the VoD system was installed , it decreased the Kankberg electrical energy input for the ventilation system by 50 %, as well as reduced the propane gas use by 20 %. The total energy reduction was 30 %.
This new gas monitoring drone , which will integrate critical gas sensors onto the ExynAero™ and ExynPak™ platforms , is , effectively , the “ quickest and safest mobile gas monitor on the planet ”, Gribbons says . “ The drone is able to automatically launch and log targeted gases directly on the point cloud in any confined area without deploying mine rescue personal with Scott Air-Paks .”
This , in turn , improves worker safety and accelerates the time to obtain accurate data in emergency conditions or for more granular data at the headings for reducing blast re-entry times , he added .
Powered by ExynAI ’ s multi-sensor fusion capabilities , gas sensor readings are captured while the robot is in flight and displayed in real time via a ruggedised tablet , Exyn explained . These sensor readings are saved with precise coordinates in a high-fidelity point cloud that can be exported and examined in a variety of mining software .
Performance across the fan curve
Maestro is also involved with ventilation
developments at the Odyssey Mine in Quebec , Canada , which will develop the continuity of the
deposit of the Canadian Malartic Mine , managed by the Canadian Malartic Partnership ( CMP ).
This mine , owned and operated by the CMP through a 50:50 joint venture between Yamana Gold Inc and Agnico Eagle Mines Ltd , will see an underground mine developed near the existing Canadian Malartic Mine open pit . The Odyssey Mine will be accessed by a ramp and a shaft estimated to be 1,800 m deep .
The owners of the mine have already gone on record to say that Odyssey Mine will feature an LTE mobile communication network , an automated fleet of 65 t trucks operated from the surface and on-demand ventilation .
Maestro is set to provide 4 x 4 m MaestroFlex™ regulators to the mine , which will be used as backdraft dampers on the two underground booster fans from Spain-based Zitrón .
60 International Mining | JULY 2022