Refinery Crude Distillation Unit Relief Valve and Flare System Capacity Evaluation

Project Synopsis

Project Summary

REFINERY RELIEF VALVES AND FLARE SYSTEM CAPACITY EVALUATIONS

The client, an independent petroleum refinery, contracted Process Engineering Associates, LLC (PROCESS) to execute a refinery relief valves and flare system capacity evaluation project.  The project included the following major tasks:

• Create computer process simulation mass balances for a Crude Distillation Unit (CDU)
• Conduct a comprehensive evaluation of approximately 30 of the refinery’s process pressure relief valves for the purpose of determining relief valve capacities relative to current process throughput rates
• 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 for approximately 6 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 mass balances using PROCESS‘ licensed commercial computer process simulation software.

The relief valve evaluation was initiated due to the fact that the client did not possess the appropriate engineering documentation for the sizing of the refinery’s relief devices.  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 relief valves determined to be undersized, the same program was used to calculate new recommended sizes.  PROCESS used its process simulation software’s thermodynamics package 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 refinery for the client’s equipment database.

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 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

• Relief valve sizing
• Flare header evaluation