Project Synopsis

Perform a plant wide relief valve and flare system evaluation at a lube oil refinery.

Project Summary


The client, an independent petroleum refinery, contracted Process Engineering Associates, LLC (PROCESS) to execute a relief valve and flare system capacity evaluation project for the four (4) units (Hydrotreater Unit, Hydrogen Plant, Amine Unit, and Sulfur Recovery Unit) that comprise a major complex at its lube oil refinery.  The project included the following major tasks:

  • Create computer process simulations for the Hydrotreater Unit, the Hydrogen Plant, and the Amine Unit to generate thermophysical properties of the relieving materials.
  • Conduct a comprehensive evaluation of the complex’s approximately 100 process pressure relief valves for the purpose of determining relief valve capacities relative to current process throughput rates.
  • Conduct a comprehensive evaluation of the complex’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 conjunctively by PROCESS and the client.

PROCESS utilized the refinery’s product specifications, operating data, and equipment engineering information to generate thermophysical properties of the relieving materials using PROCESS‘ licensed commercial computer process simulation software in an effort to support the relief valve sizing calculations.

The relief valve evaluation was initiated because the client did not possess complete engineering documentation for the sizing of the existing relief devices in the complex and required assistance in sizing new relief valves for equipment found to be unprotected during a recent process hazard analysis (PHA) of the complex.  At the initiation of this task, the PROCESS project team gathered the requisite process and engineering information at the client site.  Using the process information as well as engineering information relative to the existing relief valves, PROCESS utilized its proprietary in-house relief valve capacity computer program to evaluate each process relief valve.  PROCESS used the program to evaluate the vapor and liquid relief capacities of each valve as well as relief requirements for all identified credible relief scenarios.  For existing relief valves that were determined to be undersized, the same program was used to calculate new recommended sizes.  PROCESS used the simulation software’s thermodynamics package to calculate thermophysical properties for process streams, which were required as inputs to the relief valve program.  PROCESS also recorded the protecting relief device for every piece of equipment in the complex for the client’s equipment database.

For the relief system evaluation task, PROCESS constructed detailed computer process simulations of the relief system for the complex using the simulation software’s fluid flow (hydraulics) package.  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).

PROCESS followed up this project with another site visit to explain both the findings of the study and the recommendations that were generated to address the shortcomings found during the study.

Industry Type

  • Petroleum Refining

Utilized Skills

  • Relief case scenario development
  • Relief device sizing
  • Hydraulic modeling
  • Debottlenecking

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