H2Tech - Q3 2021 - 47

MEASUREMENT AND INSTRUMENTATION
In the final step, H2
is separated from the CO2
and other impurities
by pressure swing adsorption (PSA), a process that exploits
the differing tendencies of pressurized gases within a mixture to
adsorb to solid surfaces.
Measurement challenges in CCUS. Since the feedstock includes
a fossil fuel and the products include CO2
, enabling the use of H2
at the scale required is developed. The key question then is
how to deal with the CO2
, this process
is neither renewable nor carbon neutral. It is, however, a viable
route to producing vast amounts of H2
vehicles
and appliances while the infrastructure to produce green
H2
produced? Carbon capture, utilization
and storage (CCUS) can be used to create a net-zero emissions
process. The UK Government Clean Growth Strategy envisions
that 700 TWh of energy could be produced from H2
with most H2
in 2050,
to keep the process carbon neutral. The H2
route is known as " blue " H2
.
With CCUS, many potential measurement challenges are
expected due to both the physical properties of CO2
and the
processes involved in CCUS projects. Crucial to the implementation
of large-scale CCUS is the method by which it will be
monetized, with numerous different approaches being considered,
from taxation through to credit-based systems. Whichever
mechanism prevails, monetization requires accurate knowledge
of how much CO2
has been sequestered, much the same as custody
transfer metering in the oil and gas industry. For context,
the UK Oil and Gas Authority requires measurement uncertain120
140
20
40
60
80
100
120
140
20
40
60
80
100
5
FIG.
2. Phase envelopes for CO2
10
15
Temperature, °C
with impurities.
H2Tech | Q3 2021 47
20
25
30
5
30% CO
10
15
Temperature, °C
CO2 + CO
20% CO
10% CO
Critical point
Two-phase
liquid-gas
region
20
25
30
600
100
200
300
400
500
Gas
5
10
15
Temperature, °C
20
25
30
30% N2
CO2 + N2
20% N2
10% N2
Critical point
Two-phase
liquid-gas
region
20
40
60
80
100
5
10
15
Temperature, °C
CO2 + H2
Critical point
Two-phase
liquid-gas
region
30% H2
20% H2
10% H2
20
25
30
30% CH4
20% CH4
10% CH4
Critical point
Two-phase
liquid-gas
region
produced from reforming, coupled with CCUS
produced from this
ty of ±1% for fiscal metering of natural gas, while uncertainties
of ±2.5% or less for the total mass of CO2
measured are required
under the EU Emissions Trading System (EU ETS).
In addition to the pecuniary aspects, the ability to accurately
measure the flowrate of process streams at various points and
reconcile this data to provide a holistic mass balance across the
entire system will be important for two other reasons. The first
is reservoir management, which will require knowledge of the
amount of CO2
the geological formation. The second is safety; CO2
and other process stream components fed into
is a heavy,
asphyxiant gas that can readily pool upon leakage if conditions
are correct, and so any breach of system integrity will need to be
detected and located quickly.
CO2
is unusual because of the closeness of its triple point
and critical point to the temperatures and pressures commonly
found in industrial processes. Compared to other substances
that are transported by pipeline (e.g., oil, natural gas and water),
the critical point of CO2
lies close to ambient temperature. This
means that even small changes in pressure and temperature may
lead to rapid and substantial changes in the physical properties
of CO2
(e.g., phase, density, compressibility) (FIG. 1).
In CCUS applications, tightly regulating the temperature and
pressure can be a difficult undertaking, particularly over long
distances. Pipelines can span hundreds of miles and be subjected
to various climates and conditions that affect operating pressure
and temperature. When operating near a phase boundary
line, there is a risk that the fluid will change phases, or even that
multiphase flow conditions will arise. If this occurs at measure120
CO2
+ CH4
Pressure, bara
Pressure, bara
Pressure, bara
Pressure, bara
Liquid
Liquid
Gas
Gas
Liquid
Gas
Liquid
H2Tech - Q3 2021

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