Process for Producing Liquefied Hydrogen
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Solution Overview
Problem
Current hydrogen liquefaction processes rely on expensive helium as a refrigerant and face logistical challenges, and using hydrogen as a refrigerant requires close temperature approaches in heat exchangers, making it difficult to produce liquid hydrogen at near-atmospheric pressures.
Innovation Solution
A process utilizing a partially-liquefying expander machine or turbine for hydrogen liquefaction, where the outlet stream is separated into liquid and vapor, with the vapor being re-compressed and recycled at cryogenic temperatures to minimize para-hydrogen conversion back to ortho-hydrogen, and a catalyst is used to convert residual ortho-hydrogen, eliminating the need for low-temperature heat exchangers with small temperature approaches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If hydrogen is used as the colder fluid in the final heat exchange stages, then the economic and practical objections to helium are avoided, but very small temperature differences are necessary in the coldest heat exchangers
Solution Approach 1:
The invention changes the pressure parameter of the hydrogen refrigerant from near-atmospheric to elevated pressures (10-50 bar). This pressure increase raises the saturation temperature of hydrogen, creating larger temperature differences in the heat exchangers that are sufficient for effective heat transfer without requiring extremely close temperature approaches.
Solution Approach 2:
Instead of using hydrogen as a refrigerant in a traditional heat exchanger configuration where it would require very small temperature differences, the invention inverts the approach by using an expander machine. The expander produces cold hydrogen directly through adiabatic expansion, and this cold hydrogen is then used to refrigerate the feed hydrogen in heat exchangers, eliminating the need for small temperature differences in the coldest heat exchangers.
2Reliability
If a final condensing heat exchanger with close temperature approaches is used, then hydrogen can be condensed, but it is difficult to produce liquid hydrogen at near-atmospheric pressures
Solution Approach 1:
The invention changes the pressure parameter of the system by operating the expander at elevated inlet pressures (10-50 bar) rather than near-atmospheric pressures. This allows the expansion process to produce liquid hydrogen that can then be pressure-reduced to near-atmospheric pressures for storage, avoiding the difficulties of producing liquid hydrogen directly at near-atmospheric pressures.
Solution Approach 2:
The invention segments the liquefaction process into distinct stages: (1) pre-cooling and ortho-para conversion of feed hydrogen, (2) expansion in the expander machine to produce cold hydrogen and liquid hydrogen, (3) separation of liquid and vapor phases, and (4) pressure reduction of the liquid product to near-atmospheric pressures. This segmentation allows each stage to be optimized independently.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces the need for low-temperature heat exchangers, decreases power required for hydrogen recycle compression, and facilitates the use of a centrifugal compressor, enabling efficient production of liquid hydrogen at near-atmospheric pressures while minimizing hydrogen loss.
Implementation Method 1
an expander machine or turbine, having an outlet stream consisting of vapour and liquid
Implementation Method 2
one or more stages of catalytic conversion at low temperatures in the range of −200deg C. to −250deg C. approximately, in which the ortho-hydrogen content of the incoming feed hydrogen is exothermically converted into para-hydrogen
Implementation Method 3
the ortho-hydrogen content of the incoming feed hydrogen is exothermically converted into para-hydrogen
Implementation Method 4
liquefaction of the resulting para-hydrogen gas or vapour by means of indirect heat exchange with a colder fluid
Implementation Method 5
The expander outlet stream flows to a vapour-liquid separator, in which the liquid fraction is separated to form the liquefied hydrogen product of the process
Data Source
AI summary
A process for liquefying hydrogen gas comprising:cooling hydrogen gas to a temperature suitable for substantially complete conversion of its ortho-hydrogen content to para-hydrogen,passing the said cooled hydrogen over a catalyst which facilitates said substantially complete conversion of its ortho-hydrogen content to para-hydrogen, with provision of further cooling to remove the heat of reaction evolved,passing the resulting stream, essentially comprising para-hydrogen, in the form of a gas or vapour to an expander machine or turbine having an outlet stream consisting of vapor and liquid,separating the said outlet stream into vapor and liquid fractions, the liquid fraction constituting the liquefied hydrogen product of the process, andrecycling the vapor fraction by means of one or more compressors having cryogenic inlet temperatures.