Degradation of Components After Exposure in a Biomass Pyrolysis System

Abstract

X-ray diffraction, electron probe microanalysis, and scanning transmission electron microscopy with focused ion beam lift-out sample preparation techniques were used to study corrosion products in a 304L (UNS S30403) stainless steel fluidized-bed reactor segment from Iowa State University's Pyrolysis Process Development Unit Facility. This reactor segment is particularly valuable because a detailed history of operation time, temperature, and biomass feedstock was available. As previously reported for a range of stainless steel pyrolysis-related equipment, external scaling and internal attack along alloy grain boundaries were observed. The scaling was primarily associated with O, although S, Ca, K, Si, Mg, and P were also detected in the outer scale regions. However, unlike those other recent advanced characterization analyses, in this instance the internal alloy grain boundary attack was not directly related to S. Rather, only internal oxidation and localized nanoporosity were observed along the alloy grain boundaries, with associated local nanoscale Cr depletion and Ni enrichment. Mechanistic implications of this finding are discussed.

Performance of Structural Alloys in Bio-oil Production, Upgrading, and Storage Systems

“…A common feature of these exposed components, which are primarily 304L or 316L stainless steel, is a thicker corrosion product layer than would be expected for samples exposed in air. , Figure a shows a micrograph of a 316L stainless-steel sample oxidized in air at 550 °C for 500 h along with micrographs (panels b–e of Figure ) of typical samples exposed in operating fast pyrolysis systems under approximately equivalent time and temperature conditions. The samples from the operating systems, in addition to the considerably thicker corrosion product, sometimes display shallow intergranular attack, as shown in panels c–e of Figure . − …”

“…These micrographs, which show examples of intergranular attack, have been used in previous presentations. This figure was reproduced on the basis of the U.S. Government’s right to reproduce the published form of refs − .…”

“…These studies have utilized scanning electron microscopy (SEM), transmission electron microscopy (TEM), and scanning transmission electron microscopy (STEM), particularly of samples prepared using the focused ion beam system. Results of previously conducted studies have been reported in journal and conference publications. − These studies have shown that thick oxide scales often contain elements like Ca, K, P, S, and Si, which almost certainly originate in the biomass …”

“…37−40 These studies have shown that thick oxide scales often contain elements like Ca, K, P, S, and Si, which almost certainly originate in the biomass. 41 ■ RESULTS Thermochemical Processing Environments. Exposed samples have been returned to ORNL from several laboratories, including Iowa State University (ISU), NREL, Canmet ENERGY, PNNL, and Fortum Corporation, and exposed components have been provided by NREL, Technical Research Centre of Finland (VTT), PNNL, and ISU.…”

“…Our team was designated by the U.S. Department of Energy (DOE)’s Bioenergy Technologies Office (BETO) to conduct studies of the compatibility of structural materials with the many environments required for production, processing, storage, and transport of the bio-oil and then identify materials that are sufficiently corrosion-resistant so that commercialization of any of the technologies is not prevented because of deficiencies in structural materials. This has resulted in a significant number of additional publications on corrosion of materials in biomass-derived oils. − …”