Project Synopsis

Perform a overpressure vapor cloud release Lower Explosion Limit (LEL) study for the distillation unit in an ethanol production facility.

Project Summary


Process Engineering Associates, LLC (PROCESS) was contracted by the client, an ethanol production facility, to model the Lower Explosion Limit (LEL) for eight (8) existing pressure safety valves (PSVs) in the distillation area at one of the client’s midwestern U.S. facilities at the highest ethanol mass flow release scenario.  The distillation PSV relief LEL modeling is follow-up work to a previous Safe Atmospheric Discharge PSVs Study performed by PROCESS, to identify relief risks due to atmospheric discharge. The steady state LEL dispersion estimate for each PSV was made via the ALOHA hazard modeling program published by the U.S. Environmental Protection Agency (EPA).

Project tasks included:

  • PSV relief scenarios preparation, which involved generating a tabular summary of the relief scenarios for each PSV, the required release rate, and mass rate of ethanol release.  The information was obtained from the Safe Atmospheric Discharge PSVs Study.
  • LEL modeling, which involved using the ALOHA program to generate threat zones for the largest ethanol release rate for each PSV.  The following three (3) threat zones were defined in ALOHA:
    • 60% LEL (Flame Pockets) – 19,800 ppm Ethanol
    • 25% LEL – 8,300 ppm Ethanol
    • 10% LEL – 3,300 ppm Ethanol

Threat zones generated by ALOHA were imported into MARPLOT and overlaid on a map of the facility to depict the area and direction of vapor cloud and highlight the flammable threat zone.  PROCESS generated a short summary report that includes relief device sizing information and all backup calculations and documentation.

Industry Type

Industry Type

  • Large Commercial Scale Ethanol Production

Utilized Skills

  • PSV release LEL modeling
  • Vapor cloud dispersion modeling