Project Synopsis

Perform an evaluation of the safety pressure relief system and flare system capacity at a petroleum refinery.

Project Summary


The repeat client contracted Process Engineering Associates, LLC (PROCESS) to perform a Phase II flare system capacity evaluation.  During Phase I, PROCESS identified worst-case multiple relief valve flare system loading scenarios throughout the refinery to be used during the Phase II study to determine the adequacy of the refinery flare system.  A total of 16 scenarios were identified for four different scenario classes:

  • Five (5) fire scenarios
  • Four (4) loss of instrument air scenarios
  • Four (4) loss of electrical power scenarios
  • Three (3) rapid dump hydraulic analyses.

Phase II comprised of following major tasks:

  • Conduct a comprehensive evaluation of the refinery’s relief (flare) system (including relief valve discharge piping, sub-headers, headers, and flare) for the purpose of determining relief system capacity
  • In addition to the relief header hydraulic analysis, perform an evaluation of the flare thermal radiation, flare tip velocity, and flare knockout drum.

At the initiation of this project, 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 licensed commercial computer process simulation software, as well as its in-house relief valve evaluation program, to evaluate any missing or outdated pressure safety valve (PSV) capacity information.  PROCESS used the programs to evaluate the vapor and liquid relief capacities of each valve as well as relief requirements for all identified credible relief scenarios.

For the relief system evaluation task, PROCESS constructed detailed computer process simulations of the refinery relief system 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 debottlenecking recommendations, 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).

A project notebook was provided to the client that contained detailed calculations, a tabulated summary of each over-pressure scenario, a tabulated summary of the flare thermal radiation and tip velocity for three worst-case over-pressure scenarios, calculation of the flare knockout drum capacity, and a working copy of the simulations.

As a result of the flare system evaluation, PROCESS identified excessive built-up back pressure in a relief header for a unit wide external pool fire scenario.  Fire proof insulation was recommended for the unit charge drum in order to reduce the total fire relief load in the header.

Industry Type

  • Petroleum Refining

Utilized Skills

  • Hydraulics analysis
  • Debottlenecking

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