Abstract
Vale’s Coleman mine has significant mineralization at depth, it is currently mining at 1850 m (6050 feet). At these depths, the effects of autocompression superimposed on summer climatic conditions can generate increasingly adverse thermal working conditions that require heat exposure management through work:recovery regimens. To offset production restrictions, Vale recognized they would need surface cooling, this resulted in the installation of a 10.3MW air cooling plant. This paper summarizes the preliminary studies, and then the design, engineering, procurement, and construction of a fit-for-purpose bespoke mine air-cooling plant.
Prior to opting for a conventional surface plant, studies investigated underground cooling options and the use of opportunistic seasonal coolth storage solutions using glycol pits. These studies found that the required services and infrastructure were not available and/or cost prohibitive for an underground solution; in addition, the unproven coolth storage option could be impractically large, and would likely fail to meet the desired cooling introduction timeline.
BBE were contracted to design and construct a turnkey refrigeration plant in December 2018, ground breaking began in October 2019, and cooling was provided July 2020. The many challenges to this project included: the short delivery timeline, lead-time on components, fitting the plant into the limited space available directly in front of the mine’s main intake fans without impacting their performance, power availability, and then the significant construction and supply-chain issues related to working through COVID-19. The latter resulted in site shutdowns and restrictive work practices, consequently the plant was only able to operate at 50%, construction continued through to September 2020 while the plant was operating.
The direct proximity of the plant to the primary mine intake fans was considered through computational flow dynamic modelling, this showed that the air coolers did not impact the existing intake fan system. However, it also indicated the potential loss of some cooled air, which is being addressed through the addition of side walls.
In the absence of timely available grid electrical supply, the plant is being powered by generators using the natural gas supply for the mine’s winter heating system.
Additional unexpected challenges included varying pressure availability in the mine’s make-up water supply and the cyclical nature of diurnal temperatures in the shoulder seasons affecting the evaporator circuit.
Regardless, from contract award to plant start-up, this project showed a surface cooling system can be designed and constructed within 9 months even with COVID-19.