Temperature stratification is normal in distillation columns. However, in some chemical or refinery processes too much temperature differential between layers within the column can yield poor quality product or create a dangerous condition that could lead to a column rupture or explosion.
The SLA can help mitigate this situation by accepting up to six temperature inputs, in this case thermocouples, and performing an absolute differential calculation between any temperature sections to ensure that temperature stratification levels within critical zones in each column never differ by too much. The SLA can implement up to 16 alarms based on any input, equation, or combination of inputs/equations. This Figure shows the SLA installed in a temperature alarm Safety Instrumented System (SIS) application.
In this application, three separate alarms, one for each zone, are configured to alarm if more than a 50degC temperature differential exists between the zone’s lower and upper temperature points. The temperature differential for each zone is calculated with an absolute differential equation via SLA’s advanced configuration settings. An alarm voting architecture is put in place where relay outputs will be activated to trigger an alert (1oo3 voting), warning (2oo3 voting), or shutdown (3oo3 voting) situation. A contact closure wired to one of the SLA’s four available Discrete I/O channels is used to release latching alarms and/or relays.
The BPCS (Basic Process Control System) monitors each zone’s temperature differential via the SLA’s three analog outputs. All inputs, outputs, alarms, faults, and various other parameters from the SLA are transmitted via MODBUS/TCP over Ethernet to the BPCS.
The SLA’s built-in web server also provides quick and easy read-only viewing of inputs, alarms, outputs, internal variables, faults, warnings, and more via any standard web browser. Prebuilt web pages include simple to navigate menus and tables that neatly lay out all of the SLA’s parameters.
Key attributes:
- SIL 2/3 capable exida® approved to IEC 61508:2010 standard
- Easy to use equation editor allows for quick absolute value temperature calculations
- Voting architecture alarms of 1oo3, 2oo3 and 3oo3 simple to configure with checkboxes
- -40 to 85 degrees Celsius ambient temperature operating range
- Standard MODBUS/TCP protocol sends all process and diagnostic data to BPCS
If you’d like to talk to sales or request a quote, call us at 1 (800) 999-2900 in the US and Canada or +1 (818) 894-7111 and select 1 for Sales, or send us an email via our online form.
