Corrosion in Supercritical Water Oxidation Systems: A Phenomenological Analysis

Abstract

Pronounced corrosion damage occurs in supercritical water oxidation reactors, and few materials are immune to attack. In this paper, we describe a phenomenological mode] for the corrosion process, and we discuss the effect of electrolyte dissociation and water density, as influenced by temperature and pressure, upon the kinetics of corrosion of metals and alloys in supercritical.water. The corrosion process at near-critical temperatures is believed to involve acid attack, with the concentration of H § being a function of the dissociation constant of HC1, which is a major product of the oxidation of chlorinated organic waste, and of the density of the solution. We show that the competing effects of temperature on the heterogeneous rate constant and on the concentrations of H § and 02 leads to a pressure (and hence density)-dependent maximum in the corrosion rate in the vicinity of the critical temperature. This result is in general agreement with experimental data on corrosion in aqueous solutions at near-critical temperatures.

Supercritical water oxidation: A technical review

“…95 The main ones are elevated temperatures and high concentrations of dissolved oxygen, along with the extreme pH values, high concentrations of ionic species (at subcritical conditions), and sharp pressure changes.…”

“…Corrosion experiments in supercritical aqueous solutions show that the corrosion at supercritical temperatures of 500°C was lower by orders of magnitude than at subcritical temperatures of 300°C. 95,[97][98][99] This fact is explained by the sharp change of the thermophysical properties of water in the surroundings of the critical point such as density and dielectric constant.…”

Development of advanced in-situ techniques for chemistry monitoring and corrosion mitigation in SCWO environments. 1998 annual progress report

“…Electrochemical noise measurements will be employed to monitor corrosion processes that occur on metallic materials exposed to super critical water (SCW) [15,16]. A schematic of the electrochemical noise sensor is shown in Figure 11.…”

“…In the case of localized corrosion, the noise frequently arises from discrete events that can be related to the development of damage. In previous work in this laboratory, Macdonald et al [15] and Kriksunov and Macdonald [16] developed an ENS system based on a zero resistance ammeter (ZRA) coupled to a bandpass-filter/RMS (root-mean-squares) integrated circuit to monitor electrochemical noise on carbon steel and stainless steels in aqueous solutions at temperatures ranging from 200°C to 550°C. These studies demonstrated the viability of ENS for monitoring corrosion phenomena in high subcritical and supercritical aqueous systems, and confirmed the previous& observed maximal corrosion rate within the neighborhood of the critical temperature (350-400°C).…”

Catalytic effect of different reactor materials under subcritical water conditions: decarboxylation of cysteic acid into taurine

“…Alternatively, supercritical CO2 has been used for various purposes, such as the recycling of precious metals [15], leaf oil extraction and quinone analysis, among others [16]. As SFT simultaneously uses extreme temperatures and pressures, consequently, chemical corrosion increases [17,18]. The corrosion of various types of materials under high temperature and pressure conditions has been investigated intensively [19][20][21][22].…”