Effect of flue gas composition on deposit induced high temperature corrosion under laboratory conditions mimicking biomass firing. Part II: Exposures in SO<sub>2</sub> containing atmospheres

et al. 2016

Materials & Corrosion

Self Cite

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.

Section: Introductionmentioning

confidence: 99%

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

Okoro

Kiamehr

et al. 2016

Materials & Corrosion

Self Cite

“…A series of investigations were conducted in a gaseous environment (6 %O 2 , 12 %CO 2 , 82 %N 2 , 400 ppm HCl, 60 ppm SO 2 ) and varying amounts of H 2 O with the use of KCl deposit to mimic the biomass corrosion 56,57,58 . A deposit of KCl was applied as a slurry according to EU guidelines, which after drying was characterized as a compact layer.…”

Section: Results From Laboratory Studies Flue Gas Parametersmentioning

confidence: 99%

“…Another interesting observation was that increased water vapor content decreased the amount of attack measured 57 . In addition, when HCl gas was not in the gas mixture, a thick potassium sulfate layer was present, and underneath there was deep pitting reminiscent of reducing conditions observed in coal gasifiers 58 . Earlier results in the same equipment but where the deposit was applied as a powder did not reveal deep sulfidation pitting.…”

Section: Results From Laboratory Studies Flue Gas Parametersmentioning

confidence: 99%

Danish Experiences in Biomass Corrosion and Recent Areas of Research

Malede

et al. 2018

CORROSION

In Denmark, biomass has been implemented in the majority of power plants either by firing biomass alone or co-firing of biomass and fossil fuels/additives. This has resulted in an accumulation of experience over the past two decades both from corrosion testing and also the assessment of failures which has given understanding with respect to alloy selection and corrosion rates at various temperatures. Many laboratory investigations focusing on specific aspects of corrosion in controlled atmospheres have also been undertaken to give improved understanding of corrosion mechanisms. However, there are still areas where further investigations are underway, with respect to both laboratory and field testing. The present focus areas of research include: a) Use of coatings in biomass power plants where the coatings perform differently in different biomass plants depending on fuel mix and temperature b) Importance of understanding the microstructure of component materials and how microstructure evolution with time and temperature can influence corrosion. This paper will recap past experience and highlight some of the results from the new research. Based on the brief review of research in the field, and the research described in detail in this paper, critical unresolved issues and a way forward for the industry is presented.

“…Upon dissociation of HCl via the Deacon process [47][48][49], Cl2 is generated and can propagate the corrosion attack by chlorination of the alloying elements at the corrosion front, where the oxygen partial pressure is relatively low. Although the HCl originally present in the gas mixture also has the tendency of inducing chlorination attack by itself, previous studies [50,51] have shown that this has a lower influence on the degree of corrosion attack, compared to corrosion attack in the presence of KCl deposits.…”

Section: Discussionmentioning

confidence: 97%

Influence of preoxidation on high temperature corrosion of a Ni-based alloy under conditions relevant to biomass firing

Okoro

Surface and Coatings Technology

Frandsen

et al. 2017

Development of corrosion resistant materials in biomass fired power plants demands specific attention since the condensation of deposits rich in KCl on heat exchanger surfaces induces severe corrosion attack, which is different from corrosion in traditional coal fired plants. Therefore, the ability of preoxidized layers formed on a commercial Cr-Ti-Al-containing Ni-based alloy (Nimonic 80A) to withstand biomass-induced corrosion was investigated. Preoxidation treatments at 900 o C in O2 and O2 + 10 vol % H2O, respectively, were conducted before samples were exposed to conditions that mimicked biomass firing. Complementary characterization methods were employed to study samples after preoxidation as well as after corrosion exposure. The oxides obtained by the preoxidation treatments protected the alloy during corrosion exposure at 560 o C for a period of 168 h. In contrast, non-preoxidized samples suffered corrosion attack and formed porous non-protective oxides containing the alloying elements, Ni, Cr, Ti and Al. The influence of the preoxidation layers on the corrosion mechanism is discussed.