A Tracer Study on sCO2 Corrosion with Multiple Oxygen-Bearing Impurities

Juho Lehmusto,Ercan Cakmak,James R. Keiser,Anton V. Ievlev,Bruce A. Pint

doi:10.1007/s11085-021-10071-6

Juho Lehmusto, Ercan Cakmak + Show 3 more

Open Access

https://doi.org/10.1007/s11085-021-10071-6

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Abstract

Several modern power production systems utilize supercritical CO2 (sCO2), which can contain O2 and H2O as impurities. These impurities may degrade the compatibility of structural alloys through accelerated oxidation. However, it remains unclear which of these impurities plays a bigger role in high-temperature reactions taking place in sCO2. In this study, various model and commercial Fe‐ and Ni‐based alloys were exposed in 300 bar sCO2 at 750 °C to low levels (50 ppm) of O2 and H2O for 1,000 h. 18O-enriched water was used to enable the identification of the oxygen source in the post-exposure characterization of the samples. However, oxygen from the water did not accumulate in the scale, which consisted of Cr2O3 in the cases where a protective oxide formed. A 2wt.% Ti addition to a Ni-22%Cr model alloy resulted in the formation of thicker oxides in sCO2, while a 1wt.% Al addition reduced the scale thickness. A synergistic effect of both Al and Ti additions resulted in an even thicker oxide than what was formed solely by Ti, similar to observations for Ni-based alloy 282.

Highlights

Increasing electricity demand and reductions in CO2 emissions are key considerations when designing new power plants with higher production efficiencies
The Brayton cycle can be used with supercritical carbon dioxide (sCO2) as a working fluid in modern power production systems regarding nuclear energy, concentrated solar power (CSP), and emission-free fossil energy [1,2,3]
The mass gains from exposure in industrial grade (IG) sCO2 are shown for several alloys

Summary

Introduction

Increasing electricity demand and reductions in CO2 emissions are key considerations when designing new power plants with higher production efficiencies. The use of sCO2 could enable efficiencies over 50% with a sCO2 Brayton cycle operating above 700 °C and 200–300 bar (20–30 MPa) [7]. Especially higher-alloyed ones, perform satisfactorily in RG sCO2, it has been reported to initiate breakaway corrosion of Crrich stainless steel through the growth of an Fe-rich oxide and rapid precipitation of internal Cr carbides [14] due to C ingress into the alloy [15]. It was reported that an amorphous carbon layer together with Cr-rich carbides (M23C6) was found below the oxide, indicating that the chromia scale might be, to some extent, permeable to carbon. The low oxygen partial pressure p(O2) at the scale/alloy interface enables the following reactions to occur: CO2(g) → CO(g) + 1∕2 O2(g)

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