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Refinery Methane Analyzer Differential Safety Trip

A refinery required a third-party certified SIL 1 solution to calculate the differential between two analyzers that measure the methane content on the inlet and outlet of a reactor, which breaks down the hydrocarbon levels in the process stream.  The methane level is always higher on the outlet side of the reactor; however, should the differential with the input exceed a predefined setpoint, these higher methane levels could reach flashpoint with a sharp trend that could lead to an explosion. 

Refinery Methan Analyzer Moore Industries

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After a Hazard and Operability Analysis (HAZOP) of the existing installation was performed, it was determined the refinery needed to mitigate the risk and install an independent SIL1 safety trip solution. Moore Industries designed a methane differential trip Safety Instrumented Function (SIF) and provided the client with an independent Safety Integrity Level (SIL) verification report.

The two independent methane analyzer measurements are sent to the SST Signal Splitters, where one output is used for the differential calculation and the other is transmitted to the Basic Process Control System (BPCS). 

The methane differential is calculated by the STZ Transmitter and sent to the STA Logic Solver, where a differential between inlet and outlet  analyzers exceeding 10% MOL will trip the safety setpoint. In addition, the STA Logic Solver retransmits the calculated methane differential to the Basic Process Control System.

Key attributes:

  • STA, SST and STZ are all SIL2/3 capable and exida certified safety components
  • SST Signal Splitters provide independence between SIF and Basic Process Control System
  • Standard off the shelf hardware, user configurable for SIS solutions