📐 About the Hammerschmidt Equation
The Hammerschmidt equation is the industry-standard method for calculating thermodynamic inhibitor requirements for hydrate prevention in gas processing. Published in 1934 and refined in the GPSA Engineering Data Book, it relates temperature depression to inhibitor concentration.
Hammerschmidt Equation:
ΔT = (Kh × W) / (M × (100 - W))
Rearranged to solve for W:
W = (M × ΔT) / (Kh - (M × ΔT))
Where:
• W = weight % inhibitor in water phase
• ΔT = temperature depression (°F)
• Kh = Hammerschmidt constant (inhibitor specific)
• M = molecular weight of inhibitor (g/mol)
🧪 Inhibitor Properties Comparison
| Inhibitor |
Mol. Wt. (g/mol) |
Kh |
Sp. Gr. |
Best For |
| Methanol |
32.04 |
2335 |
0.791 |
Low cost, short-term |
| MEG |
62.07 |
2200 |
1.113 |
Recovery systems |
| DEG |
106.12 |
2200 |
1.118 |
Lower volatility |
| TEG |
150.17 |
2200 |
1.125 |
Lowest losses |
🎯 Typical Applications
- Well Flowlines: Prevent hydrate formation in cold wellhead conditions
- Gathering Systems: Protect uninsulated pipelines in winter operations
- Gas Processing: Turboexpander inlet protection, chilling systems
- Transmission: Pipeline hydrate prevention during startup/shutdown
- Offshore: Subsea flowlines and risers
⚙️ Design Considerations
- Injection Point: Must be upstream of the coldest point where hydrates can form
- Mixing: Ensure adequate turbulence for inhibitor-water contact (static mixers may be needed)
- Recovery: For glycols, recovery systems can reduce costs by 70-90%
- Overdose Prevention: Excess inhibitor can cause corrosion, foaming, and emulsion problems
- Pump Sizing: Account for viscosity increase at low temperatures
- Storage: Proper containment and secondary containment for environmental protection