How to Liquefy Hydrogen
by Admin
Posted on 23-06-2023 04:51 PM
Hydrogen's boiling point is incredibly low – at just under 21 degrees kelvin (roughly -421 degrees fahrenheit), liquid hydrogen will turn into a gas. And because pure hydrogen is incredibly flammable, for safety's sake the first step to liquefying hydrogen is to bring it to its critical pressure – the point at which, even if hydrogen is at its critical temperature (the temperature at which pressure alone cannot turn a gas into a liquid), it will be forced to liquefy.
Hydrogen is pumped through a series of condensers, throttle valves and compressors to bring it to its pressure of 13 bar, or roughly 13 times the standard atmospheric pressure of earth.
Hydrogen energy has become a growing area of research due to its potential for clean and renewable power generation. Compressing hydrogen can help make it more efficient and accessible as a fuel source. By compressing the gas, higher concentrations can be achieved in smaller volumes, allowing for easier transportation and storage. This makes compressed hydrogen an ideal choice for fueling vehicles, powering reciprocating engines, or generating electricity through fuel cells. Compressed hydrogen is stored at pressures from 500-700 bar and temperatures ranging from -253 degrees centigrade to 20 degrees centigrade, depending on the type of compressor used. Ionic liquids are being explored as an alternative method to liquefy and store hydrogen, which could potentially reduce costs associated with process gases like nitrogen which are currently used during compression. https://www.sciencedirect.com/science/article/pii/S0925838821038755
How to Compress Hydrogen to Power an Engine
Hydrogen Advantages & Disadvantages
Another possibility is to take advantage of the current infrastructure available for liquid fuels and use ammonia as a hydrogen carrier. Ammonia has high volumetric and gravimetric hydrogen densities, can be stored as a liquid at moderate pressures and can be decomposed to release hydrogen in a catalytic reaction. The main disadvantages of using ammonia as a hydrogen carrier are related to its toxicity and reversibility, as trace amounts of ammonia are found in the hydrogen after it decomposes. The ammonia needs to be decomposed to release the hydrogen, which is usually done at high temperatures in the presence of a catalyst, with much recent research focussed on low temperature (<300°c) catalytic decomposition of ammonia.
Hydrogen in liquid form has a considerably higher energy density than in its gaseous form, making it an attractive storage medium (figure 1). This hydrogen storage technology is rather effective but has disadvantages, mainly the energy required to liquefy the gas and the strict control needed on the container temperature stability to avoid any risk of overpressure. It also requires cryogenic vessels and suffers from hydrogen losses through evaporation from the containers (boil-off). The cryogenic vessels used to store liquid hydrogen on-board vehicles, sometimes also called cryostats, are metallic double-walled vessels with a high vacuum or material insulation, sandwiched between the walls.