Optimizing ventilation in medium- and short-term mine planning

Abstract

Mine planners utilize production schedules to determine when activities should be executed, e.g., blocks of ore should be extracted; a medium-term schedule maximizes net present value associated with activity execution while a short-term schedule reacts to unforeseen events. Both types of schedules conform to spatial precedence and resource restrictions. As a result of executing activities, heat accumulates and activities must be curtailed. Airflow flushes heat from the mining areas, but is limited to the capacity of the ventilation system and operational setup. We propose two large-scale production scheduling models: (i) that which prescribes the start dates of activities in a medium-term schedule while considering airspeed, in conjunction with ventilation and refrigeration; and, (ii) that which minimizes deviation between both medium- and short-term schedules, and production goals. We correspondingly present novel techniques to improve model tractability, and demonstrate the efficacy of these techniques on cases that yield short-term schedules congruent with medium-term plans while ensuring the safety of the work environment. We solve otherwise-intractable medium-term instances using an enumeration technique if the gaps are greater than 10%. Our short-term instances solve in 1,800 seconds, on average, to a 0.1% optimality gap, and suggest varying optimal airspeeds based on the maximum heat load on each level.