To prevent shafts from freezing at LKAB’s Malmberget and Kiruna underground mines, intake air is heated for more than half of a given year. In comparison, extensive cooling during the summers has so far been unnecessary. With the planned extension of the mines, need for cooling may become more prevalent. The extent of heating and cooling potentially required at both mines is to be given by setting up and conducting heat simulations using Ventsim mine ventilation software.
Background information is provided about both mines, and important factors in the total heat loads are introduced. Temperature measurements to define geothermal gradients were performed in both mines in the area where the extension is to take place. In Malmberget, temperature sensors were installed in purpose-drilled, short boreholes and a commercial temperature logger was lowered down long exploration boreholes. Only the second method was applied in Kiruna. Additionally, the main lithologies were identified for both mines using drill core database information and samples were collected for thermal parameter analysis and later calculation of a synthetic host rock.

For the heat simulations, a conservative approach was taken. Base models of a possible extension scenario were provided focusing on the lowest levels of the extension. The models were populated evenly with equipment as heat sources, which for both mines were assumed to be battery-electric based on previous studies at LKAB. The number of equipment was calculated using the planned production figures for the extension. Other mine-specific parameters were defined and justified through background research. Finally, winter and summer scenarios were established, and a threshold temperature limit was set based on Swedish workplace regulations to determine heating and cooling requirements for both mines.
While heating requirements will not change substantially, cooling is likely to become necessary during the summer months. Auto-compression is the single most important heat load factor at both mines. Several sustainable possibilities to provide heating and cooling are presented that are amenable to the goal of CO2-free production. Further research items are suggested to refine the simulations and improve insights with regards to heating and cooling.