Project Synopsis

Conduct a relief valve and flare system capacity evaluation on a refiner’s recently revamped HDS Unit and Reformer Unit.

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.  The project included the following major tasks:

  • Conduct an evaluation of the revamped Hydrodesulfurizer (HDS) and Reformer Depentanizers’ two (2) process pressure safety valves (PSVs) for the purpose of determining relief valve capacities relative to revamp process throughput rates
  • Conduct a comprehensive evaluation of the HDS-Reformer relief (flare) system (including relief valve discharge piping, sub-headers, main flare headers, and flare) for the purpose of determining relief system capacity for four (4) credible relief scenarios:
    • Abnormal heat input
    • Blocked vapor outlet
    • External pool fire (multi-valve relief)
    • Gas blow-by.

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 licensed commercial computer process simulation software, as well as its in-house relief valve evaluation program, 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 relief system using the simulator’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 developed debottlenecking recommendations to eliminate them, 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).

During the course of the project, PROCESS simulated the Depentanizer towers for the purposes of determining more accurate abnormal heat input relieving rates.  The simulations were used to demonstrate that the existing system could actually handle the abnormal relieving rates, whereas conventional abnormal heat input calculations provided results that would have required a considerable change to the relief system to accommodate a flow rate that would, in reality, never be attained.

A project notebook was provided to the client that contained detailed calculations, a tabulated summary of each over-pressure scenario, and a working copy of the simulations.

Industry Type

  • Petroleum Refining

Utilized Skills

  • Pressure relief system analysis
  • Process debottlenecking

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