Refinery Increases Production with Modern DCS. The fourth largest zinc producer in the world was experiencing costly unplanned downtimes, which led to over $ 1,000,000 100 per hour and operational and financial risks.
Initially, the extraction of zinc ore is not an easy task to separate from other minerals and materials, but it is much more difficult if your old control system lacks spare parts, technical expertise and communication capabilities are limited.
These were some of the technical challenges faced by NexaResources at the zinc refinery near Lima, Peru. Many of the process control and automation technologies were 15-20 years old and lacked support for many spare parts or many older components that needed expertise, even if they were very costly.
According to Daniel Izarra, senior automation engineer at NexaResources, it was determined that the provision of some of the spare parts would be close to 50 percent of the total cost of a project.
Nexa used a hybrid control system with 50 percent RockwellAutomation and percent 50 from another DCS manufacturer. In addition to the aging threat, they had connection servers for every control system that could not communicate with each other, and over a thousand 700, the signal allowed 60 to be displayed on an HMI with different operator graphics.
Nexa's use of two different types of engineering stations posed difficulties in training users, maintaining expertise for both stations, and finding spare parts. This meant that preventive maintenance was not an option.
For Nexa, which faced these challenges, the need to replace incompatible control systems with modern technology was very clear and had to be done without affecting production. The closure time was limited to only two hours per week and four hours per month to complete the transition.
In this narrow period of time, they had to continue with old system drawings and limited technical expertise. The operations team and refinery personnel knew the old controls and were concerned that changes to system cabling and programming could cause processes to fail.
Izarra reports that Nexa has decided to design the old ControlLogix® and CompactLogix ™ additions and integrate the rest of the process controls into a unified PlantPAx® distributed control system.
The scope of the project will now include upgrading the communication network with an Ethernet; renewal of workstations and servers; it included installing two remote I / O (RIO) enclosures and upgrading CPUs. They could use the existing ControlNet protocol.
In order to realize this two-month transition project with minimum risk and optimum programming, Izarra explains that he and his team are preparing the refinery signals, wiring and terminal blocks in advance, and precisely scheduling factory downtime in two and four hour blocks that can be used.
He added that they trained in the existing control room, performed factory acceptance tests with Nexa technicians, established initial connections with the new RockwellAutomation platform, and passed control loops for each functional area.
The old and new control systems used the 2-3 month in parallel, so people could get used to the new solution and the feedback could be shared. They started with non-critical loops and signals and switched from pump to pump. By pre-defining signals and cables, they could do most of the transition while the factory was running, and they didn't have to wait only for downtimes.
With the control system migration and upgrade, Nexa has achieved numerous improvements, including:
• Control system reliability of hydrometallurgy application reaches 100 percent
• Security incidents caused by DCS shutdown have dropped to zero
• Technical support available
• Refinery owns its own spare parts
• Low cost due to gradual integration of transition
Nexa believes that the following important lessons have been learned to make a transition project in use successful:
• Precision programming
• Operators and maintenance personnel should be involved from the beginning of the project and continue to communicate and coordinate areas critical to the development of planning, control and execution of these projects.
• Approval of technical documents required to avoid delays in response processes
• An emergency plan should be prepared and sent to all areas before the transition begins