H2Tech - Q1 2021 - 21

ADVANCES IN HYDROGEN TECHNOLOGY
with a sub-ambient inlet
temperature increases the inlet
density. As an example, at -120°C
the inlet density is approximately
twice the density at ambient
temperature, facilitating the future
use of lower-cost centrifugal
compression in H2 liquefaction.
Process performance. A realistic expected specific power of the H2 liquefaction process is in the range of 6.7 kWh/
kg-7.5 kWh/kg LH2 , depending significantly on the LH2 delivery pressure and
the efficiencies of the compressors and
expanders. Other factors affecting the
specific power include the disposition
of the ortho-para conversion catalyst (in
the heat exchangers, or external) and the
selected precooling refrigerant (methane, nitrogen or combinations of these).
Relative process performance and
configuration issues. Recognizing the

inadequacies of present LH2 technology
for the scale required to support the H2
economy, various configurations have
been investigated by a number of parties.
The IDEALHY consortium published
data4 on a survey of various configurations of existing operating LH2 facilities
and new concepts. An extract from the
consortium's data is provided in TABLE 2,
which shows a drive to improvement in
both the precooling and liquefaction circuits. A measure of caution is required
in interpreting this data, as the bases of
design for the various processes are not
identical and predicted machine efficiencies vary significantly.
In terms of power demand, the most
promising schemes indicate a move towards single mixed-refrigerant (SMR)
precooling and use of efficient, though
expensive refrigerants, neon and helium,
for the liquefaction stage. Other work5
indicates that SMR precooling combined
with a high-pressure Claude H2 cycle
achieves power demand in the range of
6 kWh/kg-7 kWh/kg.
The authors sought to improve on
these configurations with the following
objectives:
*	 Simplify the plant and its operation
*	 Reduce capital cost
*	 Achieve a competitive power
demand.
The described scheme achieves these
objectives:

SPECIAL FOCUS

than triple-expander nitrogen
processes and > 20% lower than
dual-expander nitrogen processes
*	 Operations are simplified as
precooling refrigerant composition
adjustments are not required;
the methane precooling system
is self-adjusting
*	 Both the precooling and
liquefaction refrigeration cycles
utilize low-cost, readily available
refrigerants that do not require
storage or handling facilities

*	 The major equipment count
for methane precooling (19 items)
is > 25% lower than SMR processes
(26 items), as refrigerant storage,
blending and transfer facilities
are not required
*	 Experience from the LNG
industry indicates the power
demand of dual-methane expander
refrigeration incorporating partial
liquefaction in the low-temperature
expander is up to 10% lower than a
typical SMR process, > 10% lower

TABLE 2. Current technology and proposed new developments
Technology

Status

Precooling
cycle

Cryo-cooling and
liquefaction cycle

Power demand,
kWh/kg

Linde-Ingolstadt

Operating

LN2

H2--Claude

13.6

Linde-Leuna

Operating

LN2

H2--Claude

11.9

Air Products

6 × operating

LN2

H2--Claude

12-15

Praxair

4 × operating

LN2

H2--Claude

12.5-15

Air Liquide

5 × operating

LN2

H2--Claude

12-15

WE-NET

Study

LN2

H2--Claude

8.53

WE-NET

Study

LN2

He-Reverse Brayton

8.69

WE-NET

Study

LN2

Ne-Reverse Brayton

8.58

Quack

Study

Propane

Ne/He-
Reverse Brayton

6.93

Valenti and Macchi

Study

None

He-Reverse Brayton

5.29

Sintef

Study

Mixed
refrigerant

Ne/He-
Reverse Brayton

6.2-6.5

Shimko

Study

None

He-Reverse Brayton

8.73

IDEALHY

Study

Mixed
refrigerant

Ne/He-
Reverse Brayton

6.4

AD2
Ortho-para catalyst

Cold box
H2 feed gas

AD1

LH2
CP2

CP1

CP3

SP1
EC1

EC2

EH1

EH2

Flash to low
pressure

Liquefying expander

FIG. 4. Low-temperature H2 compression.
H2Tech | Q1 2021 21
H2Tech - Q1 2021

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