Simulation-based improvement of bulk air heat exchanger efficiency in deep-level gold mines

Abstract

One of the primary concerns within deep-level mining is the mitigation of heat, which ensures the health, safety, and productivity of the miners. This is achieved through cooling and ventilation infrastructure which includes finned-tubbed bulk air coolers (BACs) that form part of the secondary cooling systems in mines where working/active levels are at depths that exceed 2 km. Due to "off-design" conditions, which include restricted air flow or water flow, increased inlet temperatures and fouling, the operational performance of the BACs decreases over time, as heat is being transferred between the working fluids. Previous methods relied on "pre-selected" operating variables, such as fouling, water flow, or geometry for analysing the performance of a BAC, which required extensive monitoring instrumentation or the assumption that the infrastructure had to operate within the design specifications. This resulted in the actual performance being significantly lower than the achievable performance under real mining conditions. The shortfall of the previous literature was then the lack of a systematic method to identify, quantify, and mitigate the influence of operating variables as the BAC operates within the mining conditions. This study, therefore, developed a simulation-based methodology for determining the achievable performance of the BACs, the limiting operating variable/s, and the recommended corrective measures to increase the actual operational performance and decrease the outlet Wet bulb (WB) temperatures. The method was applied to four BACs within a gold mine, and the results provided insight into the performance restrictions of BACs and potential improvements. After the corrective measures were implemented, the achievable performances were 1156.0 kW, 1157.3 kW, 503.3 kW, and 1423.0 kW for the respective Case Studies 1 through 4 where the re-audit results additionally indicated the following: ● Case Study 1: 44% operational performance increase and a 1.5 °C WB temperature decrease. ● Case Study 2: 26% operational performance increase and a 1.5 °C WB temperature decrease. ● Case Study 3: 28% operational performance increase and no decrease in WB temperature due to an increased thermal and relative humidity load. ● Case Study 4: 13% operational performance increase and a 6.5 °C WB temperature decrease. Therefore, the mine had increased the available cooling capacity and supplied the working areas with cooler air and was a direct benefit from the increased operational performance of the secondary cooling infrastructure in terms of the BACs on the working levels. The results of the simulations validated the methodology and the respective objectives, and the aim of the study was successfully achieved.