H2Tech - Q1 2021 - 18

SPECIAL FOCUS: ADVANCES IN HYDROGEN TECHNOLOGY

Advanced precooling for optimized
hydrogen liquefaction
G. W. HOWE and G. F. SKINNER, Gasconsult Ltd., London, UK;
and A. J. FINN, Costain, Manchester, UK

Meeting net carbon-neutral targets by
2050 requires new clean energy sources.
Hydrogen can be produced as a zero-carbon fuel and will be a major contributor
to meeting this objective. The significance
of H2 is illustrated by the formation of the
Hydrogen Council in Q1 2017; the preparation of " The future of hydrogen " report
by the IEA for the G20 meeting in Q2
2019; and the publication of " A hydrogen
strategy for a climate-neutral Europe " by
the European Commission in Q3 2020.
Zero-carbon H2 can be produced
through electrolysis of water using renewable electric power (green H2 ); or
through steam or autothermal reforming of natural gas, or gasification of coal
(blue H2 ). Blue H2 production processes
require carbon capture and storage to secure zero-carbon status.
Cost reductions will be needed for H2
to displace fossil fuels. While technology
advances in electrolyzers and lower-cost
renewable power will, over time, reduce
the cost of green H2 , the bulk of zerocarbon production will initially be blue
H2 , which, at present, can be produced at
greater scale and lower cost.
Demand for H2 will be impacted by
natural gas and carbon pricing. The latter
provides governments the leverage to impact the rate and extent of H2 's displace-

ment of fossil fuels and influence H2 's contribution to meeting the 2050 objectives.
Liquid H2 production. Producing liquid

H2 (LH2 ) reduces volumes by 800 and
reduces storage and distribution costs.
Liquefaction will, therefore, be central to
many H2 -based schemes. All existing LH2
plants are small (typically < 15,000 metric
tpy) and use a combination of liquid nitrogen evaporative precooling and Claude H2
expander cycle for final liquefaction. The
requirement for liquid nitrogen means that
larger LH2 plants require integration with,
or close proximity to, an air separation unit.
Aside from constrained supply logistics,
use of liquid nitrogen is thermodynamically inefficient, resulting in a liquefaction
power demand of 10 kWh/kg-15 kWh/kg
LH2 on existing plants, equivalent to 30%-
45% of the energy content of the H2 feed.
This level of power demand is unsustainable at the higher plant capacities required
to produce bulk LH2 .
This article describes a low equipment
count precooling concept integrated with
an H2 expander cycle for final cooling and
liquefaction. The dual-expander precooling configuration uses natural gas, a single, low-cost refrigerant, and avoids the
infrastructure needed to transfer, store
and blend conventional liquid refriger-

TABLE 1. Basis of design summary
Parameter

Value

Feed H2 composition, mol%

> 99.9

Feed H2 arrival temperature, °C

Feed H2 arrival pressure, bar

Target production rate, metric tpy

100,000

Cooled process streams temperature, °C

Cooling water supply temperature, °C

Seawater supply temperature, °C

18 Q1 2021 | H2-Tech.com

ants. For final cooling and liquefaction,
the cycle uses the H2 feed as refrigerant
and avoids external, high-cost refrigerants
such as neon and helium.
Overall, the scheme achieves a favorable balance between capital and operating costs by combining simplicity, less
equipment and low capital cost with a
competitive power demand.a
Basis of design. To provide a reference point for the data presented in this
article, the basis of design is provided in
TABLE 1. The basic premise is that the H2
feed derives from either a hydrocarbonbased production plant, such as a steam
reformer (blue H2 ) or from electrolyzers
(green H2 ).
In addressing the plant production
capacity and the desire to meet 2050 carbon targets, the authors have reflected
the need to make a significant impact
on consumption of liquid transportation
and industrial fuels, which are presently
used at an approximate rate of 4,000
metric MMtpy. To provide perspective, the Hydrogen Council1 projects
H2 consumption for transportation and
industrial fuel of 38 exajoules per year
in 2050 (1,050 metric MMtpy of oil
equivalent). This would require an additional installed H2 plant capacity of approximately 400 metric MMtpy. If only
10% of the H2 was required as LH2 , then
this would require approximately 400
liquefaction plants, each with a capacity
of 100,000 metric tpy.
Based on these challenging capacity parameters, the design capacity was
selected as 100,000 metric tpy, which
approximates the availability of maximum-sized electric-motor-driven H2
compression equipment.
The specified H2 arrival pressure of 25
bar is typical of the pressure of H2 supply

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