Cryogenic equipment built for sea-level sites rarely performs the same way on a mountain. High-altitude cryogenic installations face thin air, and thin air changes how machines cool. This article shows which units lose output at height and what to state in the RFQ.
Vaporizers, air-cooled units, compressors and motors all feel it. Therefore, teams should treat altitude as a design input from day one.
Why air density drops at high-altitude cryogenic installations
Air pressure falls as you climb. Each cubic metre of air then holds less mass. In plain terms, the air is thinner.
That matters for any machine that uses open air for heat transfer or cooling. For example, gear sized for sea-level air may need a derating on a mountain site.
Ambient vaporizers can lose capacity
Air vaporizers take heat from the air to boil LNG, LIN, LOX or LAR. Their fins rely on free air flow. Thin air past each fin carries less heat, so the unit makes less gas.
Air temperature, humidity, wind, run time and ice still matter most. However, altitude adds one more check. A unit picked for sea level needs a review before it serves at 3,000 m.
Air-cooled equipment is also affected
The same rule applies to machines that dump heat into air. Air-cooled exchangers, radiators and cooling skids push air across their surfaces. Thin air moves less mass past each surface for the same fan speed.
The fix may be a larger surface, more air flow or a different fan. The point turns critical when thin air meets a hot day, because the cooling load stays the same.
Compressor performance requires attention
Altitude also affects compressors. How much depends on the type and where it takes suction. A compressor that draws open air takes in less mass at low inlet pressure. Its capacity then falls below the sea-level figure.
A process compressor held at fixed suction pressure behaves in another way. Its capacity does not drop just because the site is high. However, its fans and motors may still need a check. In addition, the cooling loop around it often needs a fix.
Motors and electrical equipment may need derating
Electrical gear also uses air for cooling and insulation. Thin air cools it less well. Depending on the type and rating, motors may need a derating or a pick made for high sites.
Most makers publish altitude limits. Ignore them and the machine runs hot, with no margin left.
Define altitude in the RFQ
Site height is easy to miss early in a project. However, it belongs with the other site data: heat, cold, humidity, wind, seismic loads and hazardous-area class. Suppliers can then apply the right factors in design.
For high-altitude cryogenic installations, the datasheet should state:
- Site height and air pressure
- Minimum and maximum ambient temperature
- Vaporizer duty at site conditions
- Air-cooling requirements
- Compressor suction conditions
- Motor and electrical derating rules
- Any maker altitude factors
Conclusion
Thinner air changes the working world of high-altitude cryogenic installations. It hits air flow, vaporizer output, cooling, compressor suction and electrical gear.
Each machine reacts in its own way, so one blanket altitude factor for a whole plant would be wrong. Instead, state the site height early and let each supplier check its own machine. For more on equipment data, see our guide to the cryogenic equipment datasheet and our article on cryogenic compressors.
In cryogenic engineering, altitude is one line on a site datasheet, but it can move the performance of the whole plant.
References and further reading
- Density of air: how it changes with pressure and temperature
- Altitude and its effect on pressure and density
- EIGA publications on industrial gas equipment