Identify and document refinery-wide flare loading scenarios.
REFINERY FLARE LOADING SCENARIOS IDENTIFICATION
Process Engineering Associates, LLC (PROCESS) was contracted by the client to perform a Phase I flare system capacity evaluation project for a U.S. petroleum refinery. The purpose of this project was to identify 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 main and secondary flare systems. Scenario classes reviewed during this Phase I study included:
- External pool fire
- Loss of electric power
- Loss of cooling water
- Loss of instrument air.
PROCESS utilized existing refinery information including process and utilities piping and instrumentation diagrams (P&IDs), process unit plot plans, flare system isometric piping drawings, and electrical substation equipment service lists in executing this project, as well as individual process relief valve capacity and relief requirement calculations previously completed by a separate contractor. With this information and PROCESS’ knowledge of, and experience with similar projects, PROCESS was able to semi-quantitatively identify the worst case flare loading scenarios. A total of 12 scenarios were identified for Phase II evaluation: 9 external fire scenarios, 1 loss of electric power scenario, and 2 loss of instrument air scenarios. In addition to these overpressure flare loading scenarios, PROCESS identified two “rapid dump” flare loading scenarios, resulting from compressor failure, that qualified for further evaluation during Phase II. No significant loss of cooling water scenarios were identified for further evaluation due to redundancy within and between cooling tower systems and significant air cooler capacity present within most refinery units.
During the course of this project, PROCESS also discovered significant technical problems associated with the individual relief valve calculations that were done for the client prior to PROCESS’ involvement. As such, it is expected at this point that the client will authorize PROCESS to execute a separate project to calculate individual relief capacities and requirements for all process relief valves in the refinery. In addition, PROCESS anticipates award of the Phase II flare capacity study subsequent to completion of the individual relief valves evaluation project.
The following refinery units were included in this Phase I study:
- FCC / Gas Con
- Naphtha Unifiner
- Mid-Distillate Unifiner
- #1/#2 Crude
- Tail Gas
- Propane/Butane Storage.
- Petroleum Refining
- Process Engineering
- Process Safety
- Pressure relief valve (PRV) or pressure safety valve (PSV) sizing