Experiences with high temperature corrosion at straw‐firing power plants in Denmark

Abstract

By the end of 2009, there will be eight biomass and five biomass co‐firing plants in Denmark. Due to the steep increase of corrosion rate with respect to temperature in biomass plants, it is not viable to have similar steam data as fossil fuel plants. Thus for the newer plants, Maribo Sakskøbing, Avedøre 2 biomass boiler, Fyn 8 and Amager 1 (Fyn 8 and Amager 1 are under commissioning), the steam temperature of the final superheaters are approximately 540 °C and the steel type used is an 18–10 stainless steel, (TP347H). However there is still a need to monitor corrosion rates, and to collate data to enable better lifetime prediction of vulnerable components in straw‐firing plants since the corrosion rates are so much faster than in coal firing plants. Therefore, there are continued investigations in recently commissioned plants with test tubes installed into actual superheaters. In addition temperature is measured on the specific tube loops where there are test tube sections. Thus a corrosion rate can be coupled to a temperature histogram. This is important since although a superheater has a defined steam outlet temperature, there is variation in the tube bundle due to variations of heat flux from the flue gas. This paper will describe the corrosion investigations for tube sections removed from Maribo Sakskøbing and Avedøre 2 biomass boiler which have been exposed for up to 30 000 h. In addition to monitoring the corrosion rates of actual components, there is a need to measure corrosion rates at higher temperatures to assess if there is a possibility to increase the outlet temperature of the plant, thus making the plant more cost effective. For this purpose Avedøre 2 biomass boiler has a test superheater loop fabricated in TP347H FG (the same material as the final superheaters). Some results from this test superheater will also be described. Effects of flue gas temperature and flue gas direction on corrosion rates are also discussed.

KCl‐induced high temperature corrosion of selected commercial alloys

“…This can be explained using reaction (1) showing that the original chromium-rich oxide reacts with potassium to form chromate [2]. Consequently all alloys relying on chromia for protection suffer from (at least an initial) corrosive attack by this mechanism.…”

KCl-Induced High-Temperature Corrosion Behavior of HVAF-Sprayed Ni-Based Coatings in Ambient Air

“…8 indicated presence of oxides and spinel structures, e.g., NiCr 2 O 4-that formed in a reaction between NiO and Cr 2 O 3 (Ref 38). Transition metal chlorides, e.g., NiCl 2 , NiCl 3 or CrCl x peaks, were not observed in XRD spectra in Fig. 8(a) and (b) probably due to higher amount of the stable and protective oxides, e.g., Cr 2 O 3 and Al 2 O 3 and XRD detection limit.…”

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

“…[4][5][6][7]. In particular, operation at lower steam temperatures (~ 540 o C) to control the rate of corrosion limits the electrical efficiency of biomass-fired power plants [8]. The development of corrosion resistant alloys and coatings relies on detailed understanding of the underlying corrosion mechanisms.…”

“…Some studies have attempted to characterize the corrosion products on plant exposed test superheaters or probes [8,[13][14][15][16][17][18]. In these studies, the complex morphology of corrosion products restricted the characterization to light optical and scanning electron microscopy as well as energy dispersive X-ray spectroscopy, mostly carried out on cross sections of samples.…”