[ gas cooling ]
Hydrogen gas distribution in bulk also requires a large quantity of hydrogen to be stored on the trailer . If more hydrogen can be transported in one journey , then fewer journeys , vehicles , and drivers are required . Therefore , high-pressure hydrogen storage favours economical compressed hydrogen distribution operations .
The highest-pressure storage in current operation is offered by Type 4 carbon-fibre composite cylinders . However , this is also the most expensive type of storage tank in common use .
Hydrogen storage tanks on cars , trains , and trucks should not overheat during refuelling . High temperatures can overpressurise the tank or cause damage to sensitive materials . Pre-cooling the hydrogen gas is therefore safety critical .
Science is behind the need for hydrogen gas cooling
When ammonia as a refrigerant gas expands from 14 bar to atmospheric pressure , it cools to around -33 ° C . This principle is used to cool carbon dioxide ( CO 2
) and liquefy it for distribution and storage . Similarly , when propane acting as a refrigerant gas is expanded from 10 to 1 bar , it cools from 30 ° C to -30 ° C .
In the above cases , the temperature and pressure range in which the gases are expanding means that they become cold as the pressure reduces . This is because the Joule-Thomson coefficient of these gases under these conditions is greater than zero . However , under different conditions of temperature or pressure , the Joule-Thomson coefficient could be less than zero , meaning the gases would increase their temperature as they expand .
Joule-Thomson Effect for Heating and Cooling of Gases as They Expand
Joule-Thomson Inversion Curve µ JT
– Joule-Thomson coefficient ( K / bar ) and� inversion temperatures at atmospheric pressure
|
1200 |
|
|
0.4 |
|
|
|
|
|
1000 |
Heating zone |
|
0.3 |
|
|
|
|
Temperature ( K ) |
800
600
400
200
|
Cooling zone
µ JT
= 0
N 2
Air
Lines of isenthalpic expansion , shown for air
H 2
µ JT
= 0
|
CH 4 |
µ JT
0.2
0.1
0
|
H 2 |
N 2 |
Ar |
CO 2 |
|
|
|
|
|
He |
|
|
|
0 |
0 |
100 200 300 400 500 600 |
- 0.1
0 100 200
|
300 400 500 600 700 800 |
|
|
Pressure ( bar ) |
|
Temperature ( K ) |
H 2
N 2
Hydrogen Nitrogen
CH 4
Methane He Helium Ar Argon
CO 2
Carbon dioxide µ JT
> 0 means the gas will cool down during expansion
µ JT
< 0 means the gas will warm up during expansion
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Hydrogen Tech World | Issue 16 | June 2024 45