Faced with increased production demands, mine operator Compañía Minera Doña Inés de Collahuasi had the goal of increasing both the availability and performance of its vertical plate pressure filters (VPA) in Puerto Patache, Chile. In collaboration with Metso, Collahuasi developed an upgrade plan aimed at improving the performance of the equipment, as it was beginning to be outdated after more than 20 years of operation. With a plan based on using the very latest technology, the desired objectives were met and resulted in a 15% increase in filter availability.
The project was carried out at Collahuasi’s mine in northern Chile, about 180km southeast of the port of Iquique, at an altitude of 4,400m. This mining district has been in business since 1880 with the exportation of high-grade copper-silver vein systems. It is currently dedicated to the extraction and production of copper and molybdenum concentrate. During 2016, Collahuasi was the third-largest copper operation in the world and has one of the largest deposits of mineral resources of copper on the planet (9.964 million tonnes).
Collahuasi was facing the great challenge, common to many of the global mining groups, of optimising its operations to achieve the highest levels of efficiency. “To ensure productivity and profitability in the future, we decided to develop a preventive maintenance improvement programme, which is comprised of a master plan to maximise availability and minimise bottlenecks, through a long-term and sustainable approach. Its objective is to detect potential problems in advance and maximise the performance and availability of existing equipment,” explains Dalibor Dragicevic, vice president for processes at Collahuasi.
In addition to the VPA filters, Collahuasi also has other equipment from Metso, such as semi-autogenous (SAG) grinding mills, ball mills and and Vertimills.
Ageing equipment poses a challenge
Thanks to the collaborative relationship between Collahuasi and Metso, a joint diagnostic meeting was held to review the main needs and potential improvement to the filtrate-concentrate level, which was related to the requirements of its VPA vertical filters to increase their production capacity while also increasing the overall reliability of the system.
Due to the high productivity requirements and over 20 years of use since installation, the filters were showing a high degree of wear and misalignment, which reduced their availability due to the extra maintenance required by the filters and considerable unplanned downtime.
During the review stage of the overhaul, a joint decision was made to make improvements and upgrade the control systems, lubrication and structure of the equipment to achieve higher levels of availability.
The challenge for Metso resulted in upgrading the control systems to the latest technology, achieving values of over 92% availability and 100% of design capability. This involved reinstalling and upgrading equipment in less than 20 days to minimise lost production. The engineering coordination, parts procurement and planning activities began six months earlier to ensure the complete compatibility and successful outcome of this upgrade.
Comprehensive technological solution
The extensive upgrade of the equipment involved multiple steps. The Metso team first proposed improving the original design capacity by updating components and systems to produce some important benefits. For this, they focused on the main problems that were causing the structural misalignment of the filters. To solve the structural problems, the filter was completely disassembled and over 80% of its parts were replaced with new parts using a nanocoating technology for corrosive environments. Using this approach would double the lifespan of the key parts and components and reduce potential downtime.
To achieve the optimal selection of fabric, a pilot filter was implemented at the worksite to take samples of concentrate. The samples were then used to help define the proper fabric for the filtering process given the specific mineral conditions that Collahuasi was processing. In many situations, these types of tests involve using Metso laboratories located in Brazil and Finland. However, with the pilot filter on site, it was possible to perform all the tests in situ with the client, improving the selection and making it easier and quicker to get the results.
Another technological improvement introduced was the implementation OCS-4D, an advanced process control solution. This assisted in determining the optimal control modes through analysing the interplay between the selection of fabrics and maintenance events.
Finally, the chute was also examined for possible improvement opportunities. As the VPA filters discharge the filtered material (cake) into the chute, it was subjected to high rates of wear, causing a reduction in performance. Various designs and options were examined to improve ease of maintenance and thus reduce downtime.
“Searching for a design that improved maintainability, we implemented new, modular design upgrades to the chute so that it could receive maintenance section by section. Thus, when a specific part shows signs of wear, we can disassemble that part and change it quickly. This is also an improvement that was tailored for the client, given that with the original design we had to disassemble the entire equipment to be able to change some parts,” says Alejandro Bravo, manager of Minerals Process Equipment.
Expansion of the project to all VPA filters
Given the success of the project, Minera Doña Inés de Collahuasi is evaluating the implementation of the same upgrade concept in other VPA filters as part of its asset management plan.
“With this solution, we have been able to meet some of the availability goals we set for 2017. The filter works according to the plans drawn up with Metso, which helps us to continue
operating efficiently,” says Cristián Barros, senior engineer for Symptomatic Process at Collahuasi.