Analyzing battery swapping of battery-electric load haul dump (LHD) machines in block cave mining using discrete event simulation (DES)

Transitioning from diesel-powered loading and hauling machinery to battery-electric vehicles (BEVs) responds to the need for deepening underground mines as regulations become tighter. When using BEVs, exhaust gases and diesel particulate matter (DPM) emissions can be eliminated, and the energy required for the machines is used more effectively. Unlike their diesel counterparts, which are refueled, BEV loading and hauling machines — specifically, load haul dump (LHD) machines — can use battery swapping. This brings additional aspects to the operation that need to be considered, which have not yet been studied extensively. This study used discrete event simulation (DES) to analyze how the different numbers of BEV LHDs affect queueing and productivity when using different numbers of batteries and different swapping times in an underground block cave mine. The results identified the formation of working groups, where the machines swapped their batteries concurrently within each group, and their relation to the queueing time. Additionally, the minimum number of batteries per machine was identified to maximize productivity while minimizing queueing time. This study demonstrates DES as a powerful tool to assess and analyze conceptual systems and identify their underlying structures, which can enhance the deployment of BEV LHDs in underground block cave mine operations. Background Loading and hauling operations conducted with LHDs are a central part of underground mining operations. As underground mining moves deeper, mines are facing more challenges in providing a healthy working environment for miners, as well as sustaining cost-effective operations because of ventilation requirements. Currently, several original equipment manufacturers (OEMs) provide LHDs powered primarily by three different power sources: diesel, electric (cable-tethered) and BEVs. Electric vehicles and BEVs do not emit exhaust gases or DPM. In terms of operation, diesel and BEV LHDs enable similarly flexible operations from the movement perspective, while the electric version can face logistical issues and limitations due to the trailing cable. To date, research on the operational aspects of underground mining LHDs has mainly focused on electric and diesel LHDs. Therefore, this study was initiated to analyze and evaluate how different numbers of BEV LHDs and different battery swapping times in underground block cave mine affect the efficiency of the machines when varying the number of available batteries. Fig. 1 Simulated layout with swapping station locations and LHDhauling directions. Fig. 2 Average daily amount hauled and queueing time for swapping station per LHD with 80 percent availability, using an unlimited number of batteriesand swap times of 3, 10, 20, 40 and 60 min. Methodology A DES model was built with Arena using a feasibility-study-stage layout of an underground block cave mine (Fig. 1). The layout consists of six extraction drives, where each drive has its battery swapping station. The loading and hauling operations are conducted using LHDs that operate in a circulative pattern, forming a clockwise loop between the drives (6-5, 4-3 and 2-1 when the exiting drive is available; otherwise, the LHD will perform a counterclockwise loop) and the crusher. In previous studies, it was found that a minimum number of eight LHDs was required to reach the set production target. To assess the effect of different numbers of LHDs on queueing, six and 12 LHDs were additionally simulated with different swapping times (the time it takes for a battery to be swapped). Simulations were initiated using an unlimited number of batteries with these three numbers of LHDs and five different battery swap times (Table 1) to identify the amount of time the LHDs spent queueing because another machine is already occupying the battery swapping station — as the LHD needs to wait until the LHD ahead of it has conducted its battery swap — and whether this amount increases as the number of LHDs increases or as the battery swap time changes. Subsequently, the simulations were continued using a limited number of batteries between eight and 20, with eight LHDs using the same five different battery swap times (Table 2). This was conducted to determine the amount of queueing due to a lack of batteries and how queueing and productivity were affected when using different battery swap times, and to identify the required number of batteries. Fig. 3 Yearly amount hauled and the sum of swapping and queueing time for an available battery per LHD with 80 percent availability, using a limited number of batteries and swap times of 3, 10, 20, 40 and 60 min. Results and discussion According to the simulation results, when using an unlimited number of batteries, even with a maximum number of 12 LHDs and a maximum duration of 60 min swap time, the queueing time will be very low: 40 s per day per LHD (Fig. 2). During these simulations, it was noted that when having four battery swap stations and a maximum of 12 LHDs, the queueing time will stay low as long as the number of working groups stays lower than the ratio of the operational time of the battery to battery swap time, when there are enough batteries within the system. A simplified explanation of the formation of these working groups is presented in Table 3. Results simulated using a limited number of batteries suggest that with 16 to 18 batteries, depending on the battery swap time, the eight LHDs reach the minimum queueing time and the maximum productivity (Fig. 3). The minimum queueing is reached as the average time used for swapping and queueing reduces close to the time that the machines used only for swapping when queueing is excluded (that is, the average time used for swapping when using an unlimited number of batteries — see Fig. 6 in the full paper). Conclusions In this study, the operational aspects of BEV LHDs with battery swapping were analyzed. A DES was used in a conceptual study to assess how battery swapping affects the overall efficiency and whether it introduces additional bottlenecks to the operation in the form of queueing. The results show that for this case with a feasibility-study-stage layout, when using four battery swapping stations, the accumulation of queueing was not observed even with 12 LHDs. During the simulations, the formation of the working groups was identified, and because the ratio of the operational time of the battery to the battery swapping time remained higher than the number of working groups (where working groups are the result of the ratio of the number of LHDs to number of battery swapping stations), as long as they had enough batteries to enable the required productivity, the amount of queueing remained low. References A list of all references is available in the full paper.

Analyzing battery swapping of battery-electric load haul dump (LHD) machines in block cave mining using discrete event simulation (DES)

Authored by: Jenni Hooli, Bartłomiej Skawina, Adrianus Halim and Fredrik Sundqvist

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