In a metals refinery, precise acid concentration management is critical to ensuring that various processes such as leaching and metal extraction go smoothly and efficiently. An imbalance, particularly as it relates to acid levels, can result in decreased productivity, product quality difficulties, equipment damage, and even personnel danger.
In this application, to mitigate high-risk conditions due to out-of-specification acid concentration levels, a Safety Integrity Level 2 (SIL 2) Safety Instrumented Function (SIF) is implemented using the SLA Safety Logic Solver and Alarm. Redundant flow and acid concentration transmitters are monitored by the SLA, along with the status of acid pumps and demineralized shutoff valves. To ensure proper safety coverage, continuous monitoring of several variables and advanced alarming and logic is required.
The SLA has several inputs and 16 internal alarms which can be configured to monitor flow and acid concentration levels from the redundant transmitters. Additionally, a total of six digital inputs are fed into the SLA which report acid pump run status and demineralized water shutoff valve status. The SLA’s internal alarm statuses or outputs, along with the digital inputs, are then used to create internal logic equations using simple to configure Excel-like formulas to generate more advanced alarm scenarios. The SLA then uses these advanced internal alarms to create a 1oo2 voting logic strategy to determine when it is necessary to trigger the shutoff valves via its relay outputs. In addition, all inputs, outputs and internal variables and alarms can be monitored via the SLA’s read only web server or communicated to a remote host by MODBUS/TCP or MODBUS RTU.
Key attributes:
- 16 internal alarms and 16 internal logic equations aid in advanced shutdown strategy
- Simple to configure 1oo2 voting alarm logic with check boxes and pill-down menus
- SLA is SIL 2/3 capable and exida® approved to IEC 61508:2010 standard
- Accepts six Digital Inputs to monitor pump run status and open/closed status of valves
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