Effect of flue gas composition on deposit induced high temperature corrosion under laboratory conditions mimicking biomass firing. Part I: Exposures in oxidizing and chlorinating atmospheres

Abstract

In biomass fired power plants, deposition of alkali chlorides on superheaters, as well as the presence of corrosive flue gas species, give rise to fast corrosion of superheaters. In order to understand the corrosion mechanism under this complex condition, the influence of the flue gas composition on high temperature corrosion of an austenitic superheater material under laboratory conditions mimicking biomass firing is investigated in this work. Exposures involving deposit (KCl)‐coated and deposit‐free austenitic stainless steel (TP 347H FG) samples were conducted isothermally at 560 °C for 72 h, under both oxidizing and oxidizing‐chlorinating atmospheres, and the resulting corrosion products were comprehensively studied with scanning electron microscopy (SEM), energy dispersive X‐ray spectroscopy (EDS), and X‐ray diffraction (XRD) techniques. The results show that deposit‐free samples suffer grain boundary attack only in an oxidizing‐chlorinating atmosphere, otherwise corrosion results in formation of a duplex oxide. Corrosion attack on deposit‐coated samples was higher than on deposit‐free samples irrespective of the gaseous atmosphere. Specifically, severe volatilization of alloying elements occurred on deposit‐coated samples under oxidizing‐chlorinating atmosphere due to enhanced impact of KCl and HCl.

Complementary Methods for the Characterization of Corrosion Products on a Plant-Exposed Superheater Tube

“…In particular, the identification of a Ni-rich austenite phase γ Ni from depth-resolved diffraction (Figure 4) can be explained by the thermodynamics on the chlorination reaction which results in selective attack of Cr and Fe. Similarly, the development of a Ni-rich austenite phase on the same steel due to selective Fe and Cr attack was also observed under controlled laboratory conditions [33]. The variation in the diffraction line positions of γ Ni (Figure 5d) within the corrosion product hints at a non-linear dependence of its lattice parameter on the Ni concentration.…”

Effect of flue gas composition on deposit induced high temperature corrosion under laboratory conditions mimicking biomass firing. Part II: Exposures in SO2 containing atmospheres

“…The detailed results from cross‐section and plan view characterization of corrosion products from this exposure have been previously reported by the present authors , where the effect of the water content in the corrosive gas mixture was addressed. In the present paper, a summary of results is presented to aid comparison with both experimental conditions IIIa in the present work, that is, without HCl in the gas mixture, and experimental condition IIa in Part I of this work , without SO 2 present in the gas mixture.…”

“…In Part I of this work, the effect of a KCl deposit on corrosion of samples exposed under oxidizing conditions was discussed . Potassium from the deposits was suggested to disrupt the initial protective layer (Cr 2 O 3 ) causing the formation of a non‐protective Fe‐rich layer instead .…”

“…This paper is the second part of the study addressing the effect of flue gas composition on the corrosion of superheaters in biomass‐fired boilers using laboratory scaled investigations. Part I reports on the effect of Cl containing species (in both the deposit and the gas phase) on the corrosion of a superheater material (TP 347H FG). The present paper (Part II) focusses on the influence of SO 2 in the gas phase during corrosion of the same superheater material.…”

“…The present paper (Part II) focusses on the influence of SO 2 in the gas phase during corrosion of the same superheater material. In analogy to Part I of this study , the present investigation considers both deposit‐free and KCl‐deposited samples, and it also addresses the influence of additional HCl in the gas phase, to clarify the effect of the interaction between SO 2 and deposit particles on corrosion.…”