Supercritical CO2
|
Above: Figure 6. Temperature–entropy (T–s) diagram of the sCO2
Rankine) cycle pushes technology to the limits in turbo machinery, heat exchangers, seals, and bearings.
In addition to already mentioned R&D activities under the aegis of the US DOE (eg, the STEP facility), OEMs such as GE, Siemens, Hanwha, and others are also active in product development. Offices and national laboratories of the US Department of Energy are active in investigating applications of the sCO2
cycle
to CSP and nuclear energy. Fundamental research is being conducted in university labs on combustion, aerodynamics, and heat transfer areas pertinent to sCO2
cycle with recuperation and intercooled compression
welding, 3D printing, electrochemical machining (ECM), and electro discharge machining (EDM). (Note that the STEP turbine rotor is fabricated using a 5-axis EDM machine.)
A particular concern is maintaining the integrity of parts under thermal stresses caused by normal operating transients such as startup, shutdown, and load ramps. This will be one of the key focus areas in the STEP programme (with PCHE recuperators designed and manufactured by Heatric).
A novel technology under development by GE cycle components. As an
example, one can cite the falling particle central receiver concept investigated by the Sandia National Laboratories. The goal is to achieve high turbine inlet temperature (up to 1000°C) in CSP applications, for higher cycle efficiency. (When using the molten salt as heat transfer and energy storage medium, the upper temperature limit is about 560°C.)
To achieve the highest possible cycle efficiency, effective heat transfer with low pressure loss in the recuperator is a must (ie, higher than 95% effectiveness with less than 2% pressure loss in hot and cold legs). This requires complex heat exchanger designs, ie, printed circuit (PCHE) or plate-and-frame (PFHE), with parts made from nickel-based alloys or other materials (aluminium or stainless steel). Construction of such complex components requires advanced subtractive or additive manufacturing techniques such as laser cutting/
40% 45% 50% 55% 60% 65% 70% 75% 80%
is trifurcating heat exchangers manufactured via direct metal laser melting (DMLM) using GE AM303 superalloy or binder jet 3D printing (employing SS316L). The trifurcating geometry is claimed to achieve twice the power density of conventional designs. DMLM technology (at a TRL of 4) with superalloy materials enables up to 900°C turbine inlet temperature at 250 bar with less than 0.5% pressure loss.
Accurate property calculation, especially with the presence of impurities in the sCO2
working fluid, is of prime importance for performance
PR = 6.7:1 PR = 10:1 AFC (Ultimate)
AFC (Introductory) CSP, WHR, Nuclear
400 500 600 700 800 900 1000 1100 1200 1300 TIT, °C
Above: Figure 7. Ideal and mature sCO2 14 | January/February 2023|
www.modernpowersystems.com cycle efficiency
Efficiency
Heat Addition
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