Project Synopsis

Perform dispersion analyses to estimate atmospheric dispersion of ammonia from PRDs for an energy company at one of their electrical power generation stations.

Project Summary

The client, an independent energy company, is evaluating potential ammonia releases from pressure relief device (PRD) openings at one of their electrical power generating stations to help ensure their discharges are routed to safe locations.  The client has contracted Process Engineering Associates, LLC (PROCESS) to perform dispersion analyses to estimate atmospheric dispersion of ammonia from these PRDs.

The main objective of the analysis was to develop dispersion model outputs that will provide the estimated boundaries of defined hazardous concentrations.  That data will help the client to determine whether such reliefs are to a safe location or what modifications (whether procedural or physical plant changes) are necessary for compliance.

PROCESS utilized DNV’s Phast dispersion modelling software to estimate the atmospheric dispersion of anhydrous ammonia (NH3) released from PRD’s located on an anhydrous ammonia storage tank, associated evaporators, and related piping components (thermal expansion relief). In addition, a global relief was modeled, which included a global fire scenario during which the anhydrous ammonia tank and the vaporizer skid relieved simultaneously. The dispersion results were overlayed on the client’s site layout map for ease of interpretation.

This above work scope resulted in the following project deliverables:

  • Plan and elevation contour plots of defined concentrations of interest as defined by Occupational Safety and Health Administration (OSHA) and American Conference of Governmental Industrial Hygienists (ACGIH).
  • Project Presentation Report, including a discussion of the model’s design basis, methodology, and related atmospheric dispersion model outputs from DNV’s Phast dispersion modeling software.
  • Real-time relief animation video plots showing ammonia concentration gradient contours as the relief scenario unfolds

With safety at the forefront, the dispersion modeling results and reporting as provided by PROCESS in this study provided sufficient details for the client to make a data driven decision basis for plant modifications.

Industry Type

Electrical Power Generation


Utilized Skills

  • Pressure relief device modeling
  • Atmospheric dispersion modeling.

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