Project Synopsis

Perform a pressure relief system review including relief valve sizing, flare header hydraulic debottlenecking, and develop recommended modifications for a major section of a petroleum refinery.

Project Summary


The client, an independent petroleum refinery, contracted Process Engineering Associates, LLC (PROCESS) to execute a refinery relief valve and flare system capacity evaluation for a major operating area of the refinery that encompassed multiple units.  The project included the following major tasks:

  • Conduct a comprehensive evaluation of the area’s approximately 100 process pressure relief valves for the purpose of determining relief valve capacities relative to current process throughput rates for units on the relevant flare
  • Conduct a comprehensive evaluation of the area’s relief (flare) system (including relief valve discharge piping, sub-headers, headers, and flare) for the purpose of determining relief system capacity for approximately 12 credible relief scenarios, which were identified by both PROCESS and the client.

The relief valve evaluation was initiated to update the capacity evaluation that PROCESS had performed for the refinery approximately 11 years prior to this project.  Additionally, PROCESS was tasked with sizing valves for retrofits associated with any existing units.  Using the process information as well as relevant engineering information, PROCESS utilized its proprietary, in-house relief valve capacity computer program to evaluate each process relief valve.  This program was used to evaluate the vapor and liquid relief capacities of each valve as well as relief requirements for all identified and credible relief scenarios.  For relief valves determined to be undersized, the same program was used to calculate new recommended sizes.

PROCESS used its licensed commercial computer process simulation software to calculate thermophysical properties for process streams, which were required as input to the relief valve program.  PROCESS also recorded the protecting relief device for every piece of equipment in the area for the client’s equipment database.

For the relief system evaluation task, PROCESS constructed detailed computer process simulations of the area’s relief system with the simulator’s hydraulics package that uses Node unit operations as points to balance pressure and flows for a given piping system.  The identified relief scenarios were then modeled for the purpose of determining the presence of excessive back-pressures (i.e., inadequate capacities).  For sections of the relief system identified as bottlenecks, PROCESS modeled modifications that would increase the system capacity.  In addition, where applicable, PROCESS developed additional recommendations to eliminate the bottlenecks, including pressure vessel pressure re-rating, process or operational changes to reduce the required relief loadings, and potential modifications to existing relief valves (e.g., decreasing set pressures, increasing orifice sizes, or replacing conventional relief valves with balanced-bellows relief valves).

Industry Type

  • Petroleum Refining

Utilized Skills

  • Release case scenario development
  • Relief valve sizing
  • Relief system debottlenecking

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