|
And, since there is no other route out of the process for the CO2
, the CO2 in the CO2 capture rate from
recompression closed Brayton cycle
the Allam–Fetvedt cycle is very high, about 100%. Supercritical CO2
Sandia National Laboratories, Albuquerque, has researched and demonstrated a supercritical
recompression Brayton cycle and dispatched around 10 kW of power to the Sandia–Kirtland Air Force Base electrical grid for 50 minutes during a test in August 2022.
At a larger scale, the US DOE-funded STEP Demo project will see the operation of a 10 MWe power plant using similar technology (see Modern Power Systems, Nov/Dec 2023, pp 14-18). This plant will be the world’s largest indirect-
power cycle test facility and will use a recompression closed Brayton cycle (RCBC) with sCO2
fired sCO2 as the working fluid.
Like the Allam–Fetvedt cycle, high efficiency heat exchangers and robust turbines are the key technology components in the indirect-fired sCO2
Supercritical CO2 based power cycles have
the potential for increased heat-to-electricity conversion efficiencies. As a power generation working fluid, sCO2
remains in the closed system and is not released as a
greenhouse gas. It is an advantage that sCO2 can operate at up to 700°C – a much high temperature than steam.
A large amount of energy is lost when steam turns back into water in the Rankine cycle. The implication is that only one third of the energy in the steam can be converted into electricity. In comparison, the sCO2
Brayton cycle has combines the best properties
of both a liquid and a gas because it has a high density and low viscosity. The sCO2
recompression Brayton cycle and these are two of the main research areas within the STEP programme.
Allam–Fetvedt cycle, natural gas application: oxy-fuel thermal power generation with integrated CO2
capture
Stream composition, referenced to combustor feed
Temperature (°C)
Oxy-fuel combustor feed Expansion turbine feed
Primary heat exchanger feed High pressure captured CO2
Direct contact chiller drain 700
1150 720 60 20
Pressure (bar)
300 300 30 80 30
(wt%) 94
CO2
97.25 97.25 100 0
Natural gas (wt%)
1.25 0 0 0 0
Oxygen (wt%)
4.75 0 0 0
0
(wt%) 0
H2
2.75 2.75 0
100 O
www.modernpowersystems.com | January/February 2024 |
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