METHODOLOGY FOR VENT DISPERSION ANALYSIS STUDY
1. Proposed Methodology
1.1. Introduction
Vent is used for safe disposal of the vented gases to the atmosphere. Flammable or toxic gases are released from the vent. To ensure that the hazards of venting these gases are tolerable for the people near the site, a quantitative hazard analysis of gas venting is often required.
The Dispersion study is carried to estimate and identify the quantity of material release from the vents to atmosphere, potential hazards and its effects, occurrence of hazards during the process.
Gas dispersion is typically performed using specialized software such as PHAST/ Safeti which is in-built with complex dispersion and transport phenomena equation and Unified dispersion model (UDM) to assess all phases of the dispersion.
Some of the common key inputs are Vent orientation, Properties of the vented fluid like flow rate, duration of release, composition, pressure, temperature , Surrounding area , Weather / wind conditions etc.
1.2. Methodology
Dispersion study methodology involves a series of steps as follows:
Identification of release points (atmospheric vents/ flare stack)
Gathering of inputs required for initiating the study by reviewing project documents such as project scope definition, P&ID, PFD and Heat & Material Balance sheets
Source term definition and collection of process data of identified release points
Study of meteorological input data and selection of wind speed & stability class.
Source term modeling and consequence analysis using PHAST/ SAFETI software for the identified release points
Extraction of consequence results
Results analysis, study key findings & conclusions
Reporting & documentation
Figure 1:Vent Dispersion Analysis Methodology Flow sheet
Selection of Damage Criteria
As per the objective of the study to understand the impact of flammable and toxic impacts due to dispersion of material released from atmospheric vent and cold venting from flare, below mentioned concentration are analyzed for impact in downwind direction and on ground level:
For flammable gas dispersion - LFL, 0.5LFL and 0.1 LFL
For toxic gas dispersion – IDLH and 0.5 IDLH.
1.3. Project Deliverables
Table 1:Vent Dispersion Analysis Study
1.4. Guideline Used for Vent Dispersion Analysis Study
API-521, Pressure-relieving and Depressuring Systems
1.5. Software to be used
PHAST/Safeti software.
DISCLAIMER
HSE Risk Management Services Private Limited accepts no liability or responsibility whatsoever for it in respect of any use of or reliance upon this Methodology by any third party.
Copying this Methodology without the permission of HSE Risk Management Services Private Limited is not permitted.
