Nitrogen Purging Flow Rate Calculator
Calculate the required nitrogen flow rate for dilution purging of vessels and piping.
Calculation Results
Number of Volume Exchanges (N):
Total Nitrogen Required: ft³
Required Flow Rate: SCFM
Understanding Nitrogen Dilution Purging
Nitrogen purging is a critical safety procedure used in industrial processing to remove hazardous gases, moisture, or oxygen from vessels and piping systems. By introducing nitrogen—an inert gas—into the system, we reduce the concentration of oxygen to a level below the Limiting Oxygen Concentration (LOC), effectively preventing combustion or oxidation.
The Dilution Purging Formula
For dilution purging (where nitrogen mixes with the existing gas), the calculation follows a logarithmic decay. The number of volume exchanges (N) required to reach a target concentration is calculated as:
N = ln(Cinitial / Ctarget)
Once you know the number of volume exchanges, the total nitrogen volume required is V × N. To find the flow rate (Q), we divide that total volume by the time (t) allocated for the purge operation.
Example Calculation
Suppose you have a storage tank with a volume of 1,000 cubic feet. It is currently filled with air (20.9% Oxygen), and you need to reduce the oxygen level to 0.5% within 60 minutes.
- Step 1: N = ln(20.9 / 0.5) = ln(41.8) ≈ 3.73 exchanges.
- Step 2: Total N2 Volume = 1,000 ft³ × 3.73 = 3,730 ft³.
- Step 3: Flow Rate = 3,730 ft³ / 60 min = 62.17 SCFM.
Safety Considerations
Always ensure that the vessel is properly vented during the purging process to prevent over-pressurization. This calculator assumes ideal mixing (dilution purging). If the vessel geometry promotes "short-circuiting" (where nitrogen flows directly from inlet to outlet without mixing), a higher safety factor or more volume exchanges may be necessary.