#3811 Extracting Nitrogen from Air to Cool Data Centers
#3811 Extracting Nitrogen from Air to Cool Data Centers
Amazon strategised about keeping its datacentres’ full water use secret, leaked document shows
https://www.theguardian.com/technology/2025/oct/25/amazon-datacentres-water-use-disclosure
#3811 Data center require cooling, usually in the form of water. Could pure oxygen be used in place of water to cool the datacenters just as effectively?
No, pure oxygen could not be used in place of water to cool data centers just as effectively.
Water is a vastly superior coolant to oxygen due to fundamental differences in their thermal properties, particularly its much higher specific heat capacity and density.
Why Water is a Superior Coolant
The effectiveness of a coolant is determined by how much heat it can absorb and transfer. Water excels because of its:
High Specific Heat Capacity (Cp): Water has one of the highest specific heat capacities of common substances.
1 This means it requires a large amount of energy (heat) to raise its temperature by a small amount.2 Water (liquid): ~ 4.184 Joules per gram per Kelvin (J/g x K).
Oxygen ($\text{gas}$): ~ 1.005 J/g x K.
In simple terms, a mass of water can absorb about four times more heat than the same mass of oxygen gas for the same temperature change.
Much Higher Density: Water is a liquid and is significantly denser than gaseous oxygen.
Standard data center cooling systems circulate a high volume of coolant. Liquid cooling systems often move 10 times the mass of coolant (water) per unit volume compared to air (which is mostly nitrogen and oxygen) circulating in a gas cooling system.
When you combine the higher mass flow with the higher specific heat capacity, the difference in total heat transfer capability is enormous. A unit volume of water can transport tens of times more heat than the same volume of oxygen gas.
Practical Considerations
Beyond the physics, using pure oxygen would introduce severe practical and safety issues:
Cost: Oxygen gas production (especially pure oxygen) and circulation on the massive scale required for a data center would be exponentially more expensive than using water.
Flammability/Fire Risk: Pure oxygen is a powerful oxidizer. While it is not flammable itself, it significantly accelerates combustion. Introducing a large volume of pure oxygen into a building full of electronic equipment and wiring would create an extreme fire hazard, making any small spark or electrical failure potentially catastrophic.
Efficiency: Liquid cooling, whether with water or a specialized dielectric fluid (for immersion cooling), is up to 3,500 times more effective at heat transfer than air cooling because liquids are far better thermal conductors than gases.
3 Replacing water with a gas, even pure oxygen, would dramatically decrease cooling efficiency.
Is there any component of air that could be used in place of water?
While gaseous components of air are poor coolants, the liquid form of the most abundant component of air—Nitrogen—can be used for cooling, but its application in a data center is very different from that of water.
The component is Nitrogen ($\text{N}_2$), which makes up about 78% of the atmosphere.
Liquid Nitrogen (LN2) as a Coolant
Liquid Nitrogen is an extremely cold, non-flammable, and inert (non-reactive) liquid that boils at
Cooling Power:
5 LN2 provides exceptionally rapid cooling, primarily due to its extremely low temperature and its high heat of vaporization (the energy it absorbs when turning from liquid back into a gas).6 This makes it very effective for removing heat quickly.Application: LN2 is generally not used for continuous, primary data center cooling because it's a consumable that constantly boils off and requires continuous replenishment. It is mainly considered for:
Cryogenic Cooling/Backup: In specialized, high-performance computing (HPC) environments or for emergency backup cooling systems where rapid, high-capacity heat removal is needed to prevent catastrophic hardware failure.
7 Superconducting Applications: Cooling components to cryogenic temperatures to achieve enhanced electrical efficiency or enable superconducting systems.
Why Water is Still the Standard
Despite the incredible cold of liquid nitrogen, water remains the standard for continuous data center cooling due to several overwhelming practical and thermodynamic reasons:
| Feature | Water (H2O) | Liquid Nitrogen (LN2) |
| Coolant Type | Circulating, re-chilled liquid | Consumable (boils off), non-recirculating |
| Primary Mechanism | High Cp (absorbs heat) | Very low temperature / High Heat of Vaporization |
| Specific Heat Capacity | ~ 4.184 J/g x K (High) | Lower (but is extremely cold) |
| Safety/Logistics | Safe, easy to pipe/store, closed-loop | Cryogenic hazard, requires specialized, insulated storage (Dewars) |
| Operating Cost | Low (only energy for pumping/chilling) | High (requires continuous manufacturing/delivery/storage) |
| Major Risk | Liquid leaks (electrical hazard) | Condensation (water forming on cold surfaces) & Asphyxiation |
In short, while liquid nitrogen is an incredibly powerful coolant, the logistical and cost challenges of constantly supplying and safely managing a cryogenic fluid make it impractical for the scale and continuous operation of a typical data center.
Consider the cost and burden of supplying water for datacenter cooling. Describe a method to extract nitrogen from air to be use for cooling.
A key strategy to mitigate the cost and burden of supplying water for data center cooling is to implement on-site systems to extract Nitrogen (N2) from the air.
This nitrogen can then be used in its gaseous form for fire suppression or, in its liquid form (LN2), for cryogenic backup cooling or specialized high-density cooling, which avoids the water supply chain entirely.
Methods for Extracting Nitrogen from Air
There are three primary industrial methods for separating nitrogen from the air:
1. Pressure Swing Adsorption (PSA)2
This is the most common and cost-effective method for generating pure nitrogen gas on-site.
Process: Ambient air is compressed and forced into vessels (tanks) filled with a material called a Carbon Molecular Sieve (CMS).
3 The CMS selectively adsorbs (sticks to the surface of) oxygen (
4 O2) and other trace gases, while allowing the less-adsorbed nitrogen (5 N2) to pass through and be collected at a desired purity (typically 95% to 99.999%).6 Once the CMS bed is saturated, the pressure is released, and the adsorbed gases are vented, regenerating the sieve for the next cycle.
Application for Data Centers: PSA generates N2 gas, which is excellent for inerting environments. In data centers, this gas is often used in fire suppression systems because it displaces oxygen, suffocating any potential fire without damaging sensitive electronics (unlike water).
2. Membrane Separation
This method is simpler and quieter, though it typically yields lower purity nitrogen than PSA.
Process: Compressed, clean air is passed through a bundle of hollow polymer fibers.
7 Oxygen, water vapor, and Argon permeate (pass through) the fiber walls faster than Nitrogen.
The high-purity Nitrogen is collected at the outlet, while the other gases are vented.
8
Application for Data Centers: Suitable for applications requiring lower nitrogen purity, such as general inerting or purging tasks.
3. Cryogenic Distillation
This is the process used to create Liquid Nitrogen (LN2).
Process: Air is cleaned, compressed, and intensely cooled to cryogenic temperatures (around
9 -196 degrees C or10 -321 degrees F).11 The air liquefies and is then piped into a distillation column.
The liquefied components are separated by carefully raising the temperature, leveraging the different boiling points of Nitrogen (-196 degrees C) and Oxygen (-183 degrees C). Nitrogen boils off first and is collected as a liquid.
Application for Data Centers: The produced LN2 can be stored for use in extremely high-density or specialized cryogenic cooling systems, where its intense cooling power is critical.
Cost Advantage of On-Site Nitrogen Generation
For continuous use, generating nitrogen on-site using PSA or Membrane technology is generally much more economical than purchasing and receiving deliveries of bulk gas or liquid nitrogen.
| Cost Factor | Bulk Delivery (Purchased) | On-Site Generation (PSA/Membrane) |
| Operational Cost | High (gas cost + delivery fees + tank rental) | Low (primarily electricity for compression) |
| Hidden Costs | Gas wastage through boil-off/venting, emergency delivery surcharges | Maintenance of generator and compressor |
| Control | Low (dependent on supplier) | High (can produce desired volume/purity on demand) |
| ROI | None (ongoing expense) | Typical ROI is 6 to 24 months for high-volume users |
You can see an experiment to produce liquid nitrogen at home in this video:
Seems like the data center heat should be useable to help extract and liquify the nitrogen
That's an insightful idea! You're pointing out a potential circular economy for energy, where the waste from one process (data center heat) could power another process (nitrogen liquefaction).
However, due to the extreme temperatures required for nitrogen liquefaction, data center waste heat is generally not suitable for this purpose on its own because it's considered "low-grade heat."
Here's why, and a look at potential integration:
The Mismatch in Heat Quality
Nitrogen liquefaction uses a process called cryogenic distillation, which requires cooling air to below -196 degrees C (-321 degrees F). This process is highly energy-intensive, and the vast majority of that energy is used for compression and cryogenic refrigeration—not for adding heat.
Low-Grade Waste Heat: Data center waste heat is typically a low-temperature heat, usually captured in water loops between 30 degrees C and 60 degrees C (86 degrees F and 140 degrees F).
High-Grade Energy Input: Cryogenic separation units require high-grade energy input, primarily in the form of electricity to run powerful air compressors.
1 The major energy consumption for cryogenic distillation is2 ~ 2.56 kWh/kg of liquid nitrogen.3
The waste heat's temperature is too low to directly power the refrigeration cycle that produces liquid nitrogen efficiently.
How Waste Heat Could Be Used (Indirectly)
While the data center heat can't perform the liquefaction itself, it could be used for other parts of the nitrogen generation process, improving the overall efficiency of an integrated system:
1. Powering Ancillary Systems
Waste heat could be converted back into electricity to run a portion of the nitrogen plant using technologies like:
Organic Rankine Cycle (ORC): This system uses low-temperature heat to boil an organic fluid, whose vapor then drives a turbine to generate electricity.
4 This reclaimed electricity could offset the power drawn by the compressors in the nitrogen separation unit.Absorption Chillers: Data center heat could power absorption chillers to help pre-cool the air stream entering the cryogenic unit. By cooling the air from ambient temperature to a lower temperature before the main, high-energy cryogenic refrigeration takes over, you reduce the load and energy consumption of the most expensive part of the process.
2. Regenerating Separation Media
For Pressure Swing Adsorption (PSA) systems (which produce nitrogen gas, not liquid), the waste heat could be used to:
Heat the air intake during regeneration cycles to help efficiently remove the adsorbed oxygen from the carbon molecular sieves, reducing the electrical energy otherwise needed for this step.
In summary, integrating a liquid nitrogen plant with a data center is primarily about managing extreme thermal differences. The data center provides low-temperature heat that can be converted back into high-value electricity or used for pre-cooling, making the energy-hungry process of nitrogen liquefaction more efficient.
Think innovatively. Is this nitrogen extraction and liquification process for the purpose of datacenter cooling even feasible and practical?
That's an excellent question that pushes the boundaries of traditional data center design. While using on-site generated and liquefied nitrogen (LN2) for continuous cooling is not currently feasible or practical for most large data centers, it is becoming a niche solution for very specific, extreme scenarios.
Here is a breakdown of the feasibility and practicality:
Feasibility and Practicality Challenges (The "Why Not")
The main obstacles are the fundamental physics of the process and the colossal energy requirements.
1. Energy Cost Dominates
The most significant barrier is the energy required to produce Liquid Nitrogen via cryogenic distillation.
Massive Electrical Input: Even with the most efficient processes, the energy required to run the compressors and refrigeration cycles to cool air to -196 degrees C is huge (~2.56 kWh/kg of LN2). This electricity demand would offset, or even exceed, the cooling energy savings.
Low-Grade Heat Mismatch: As discussed, data center waste heat is too low-temperature (30 degrees C to 60 degrees C) to drive the necessary cryogenic refrigeration directly. The gains from waste heat recovery via technologies like the Organic Rankine Cycle are minimal compared to the main energy input needed for liquefaction.
2. The Consumable Model
Water cooling works because it is a closed-loop system; the water is recirculated and re-chilled. LN2 works by being a consumable; it absorbs heat by turning from a liquid to a gas (boiling).
Continuous Loss: The nitrogen gas must be constantly vented from the cooling system after absorbing heat. This necessitates a continuous, large-scale nitrogen generation plant on-site, effectively replacing a recirculating cooling system with a continual production factory.
Infrastructure Complexity: This requires massive, specialized cryogenic storage tanks, complex heat exchangers built to withstand extreme cold, and dedicated facilities for the cryogenic air separation unit (ASU).
3. Safety Risks
Introducing high volumes of cryogenic liquid significantly raises operational safety risks.
Asphyxiation Risk: Nitrogen is non-toxic, but it displaces oxygen. A leak could quickly create an oxygen-deprived environment, posing a severe and silent asphyxiation risk to personnel.
Condensation: Extreme cold causes moisture in the surrounding air to freeze or condense instantly, which can lead to ice buildup and potential damage or malfunctions in non-cryogenic equipment.
Innovative Feasibility (The Niche "Why Yes")
Despite these challenges, LN2 is feasible for non-traditional applications where extreme performance or space savings are critical.
1. Emergency and Peak Cooling
The most practical application is as an emergency backup system or for peak load shedding in high-density racks.
LN2 can instantly and rapidly absorb heat to prevent equipment damage during a primary cooling system failure. This avoids the use of energy-hungry backup generators and chillers for a short-term crisis.
2. Cryogenic Computing
For next-generation hardware like superconducting processors or quantum computing components, extremely low temperatures are mandatory for the IT to function.
In these specific, niche data centers, LN2 is the only option, making its generation a non-negotiable part of the operation, regardless of the energy cost.
3. Energy Storage and Power Generation
Innovative proposals suggest using LN2 less for continuous cooling and more for Combined Cooling and Power (CCP):
Cryogenic Energy Storage: Excess electricity (e.g., from an intermittent renewable source) could be used to liquefy air/nitrogen. When power is needed later, the liquid is regasified, driving a turbine to generate electricity (a "liquid air engine"), providing a clean backup power source that also offers intense cooling during the regasification process.
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