Abstract
Supercritical Water Gasification (SCWG) is a promising thermochemical conversion technology in which supercritical water (SCW) is used as a conversion medium to gasify wet biomass feedstocks, such as raw forest biomass, black liquor, crude bio-oils and biowastes, into syngas (a mixture of CO and H2). Despite that considerable studies have been done on the development of SCWG technology, the optimum SCWG conversion conditions have not yet been well defined due to the complexity of raw feedstocks and conversion chemistry. From the corrosion perspective, few information is available to determine which alloys are suitable for the construction of SCWG core components (e.g., reactor and gas lines) to avoid catastrophic disaster under harsh operating conditions, e.g., high temperature (>450°C) and high pressure (>22.1MPa). Thus, the corrosion of two candidate alloys with high Cr contents > 20% (UNS S31000 and UNS N06625), which exhibit high corrosion resistance in SCW environments, were investigated in a batch SCWG reactor containing supercritical water and a typical biomass model compound at 500 °C and 34.4 MPa. To obtain reliable results, a test of 12 SCWG cycles was completed, and the duration of each cycle was one hour. The gasification products were collected and analyzed to advance the fundamental understanding of how the organic compounds released during the conversion affect the corrosion performance of the alloys in the SCWG environments. CO2 was found to be the main gas product, along with certain amounts of H2 and CH4, and a trace contents of CO and C2H4. Acidic phenolic compounds are the major volatile compounds. Both alloys exhibited general and nodular oxidation. Furthermore, UNS N06625 alloy experienced more obvious localized oxide breakdown.
