Enter Operating Conditions and Gas Composition
Use absolute pressure. Composition is treated as mole percent and normalized automatically if the total differs from 100.
Example Data Table
The following sample case uses the same internal method as the calculator. Your exact result changes with pressure, composition, and heavy-end content.
| Case | Pressure, bar(a) | Operating temp, °C | Total composition, mol% | Estimated dew point, °C | Margin, °C | Risk |
|---|---|---|---|---|---|---|
| Example mixture | 20.00 | 30.00 | 100.00 | 39.42 | -9.42 | Condensation likely |
| Component | Example feed, mol% |
|---|---|
| Nitrogen (N₂) | 1.00 |
| Carbon Dioxide (CO₂) | 1.30 |
| Methane (C₁) | 78.00 |
| Ethane (C₂) | 8.00 |
| Propane (C₃) | 5.00 |
| i-Butane (i-C₄) | 2.00 |
| n-Butane (n-C₄) | 2.00 |
| i-Pentane (i-C₅) | 1.00 |
| n-Pentane (n-C₅) | 1.00 |
| n-Hexane (n-C₆) | 0.70 |
Formula Used
This calculator applies a vapor-liquid equilibrium screening method. At a fixed pressure, the dew point temperature is the temperature where the dew criterion becomes exactly satisfied.
∑ ( zi / Ki(T, P) ) = 1
Ki = ( Pc,i / P ) × exp[ 5.373 × (1 + ωi) × (1 − Tc,i / T) ]
xi = ( zi / Ki ) / ∑ ( zj / Kj )
Where:
- zi = feed gas mole fraction of component i
- xi = first condensed liquid mole fraction of component i
- Ki = equilibrium ratio for component i
- P = absolute system pressure
- Pc,i = critical pressure of component i
- T = absolute temperature in kelvin
- Tc,i = critical temperature of component i
- ωi = acentric factor of component i
This is a practical screening correlation. It is useful for engineering checks, trending, and sensitivity review, but it is not a substitute for a rigorous equation-of-state package in critical design work.
How to Use This Calculator
- Enter the process pressure as absolute pressure in bar(a).
- Optionally enter the operating temperature to assess margin to condensation.
- Enter the gas composition in mole percent for each listed component.
- Set the minimum pressure, maximum pressure, and graph points for the sensitivity plot.
- Click Calculate Dew Point to solve the dew point temperature.
- Review the result cards, risk note, graph, and incipient liquid composition table.
- Download CSV for spreadsheet work or PDF for reports and handoff.
- Use the example button when you want a quick validation case.
Frequently Asked Questions
1. What is hydrocarbon dew point?
It is the temperature at which the first liquid hydrocarbon droplets form from a gas mixture at a fixed pressure. Above it, the gas remains fully vapor. Below it, condensation begins.
2. Why must I use absolute pressure?
Equilibrium calculations depend on true thermodynamic pressure. Gauge pressure excludes atmospheric pressure and would shift K-values incorrectly, causing the predicted dew point to be biased.
3. Does this replace a rigorous process simulator?
No. It is a screening calculator based on Wilson K-values. For final design, sales gas compliance, or disputes involving heavy ends, validate with a rigorous equation-of-state model.
4. What happens if my composition does not total 100?
The calculator automatically normalizes the entered values before solving. This helps with rounding differences, but large input errors should still be corrected before relying on the result.
5. Why do heavy components raise dew point?
Heavier hydrocarbons are less volatile. As propane, butanes, pentanes, and hexane increase, the mixture condenses at higher temperatures, so the dew point usually rises.
6. How should I interpret the temperature margin?
Margin equals operating temperature minus dew point. Negative values mean condensation is likely. Small positive margins suggest caution. Larger margins provide more operating robustness against variations.
7. Why does the plot use multiple pressures?
The plot shows how sensitive dew point is to pressure. This is helpful when reviewing compression, throttling, transportation, separator changes, or seasonal operating scenarios.
8. Can I use this for export or pipeline specification checks?
You can use it for early screening and troubleshooting. For contractual acceptance or formal compliance, verify results with the project’s approved analytical and simulation method.