Low temperature corrosion in co-combustion of biomass and solid recovered fuels

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Publication Details

List of Authors: Emil Vainio, Hanna Kinnunen, Tor Laurén, Anders Brink, Patrik Yrjas, Nikolai DeMartini, Mikko Hupa
Publisher: Instituto Superior Técnico
Place: Lisbon
Publication year: 2015
Publisher: Instituto Superior Técnico
Book title: 12th International Conference on Energy for a Clean Environment
Number of pages: 8


In this work the risk of low temperature corrosion was studied in a full-scale bubbling fluidized bed boiler. The presence of sulfuric acid in the flue gases may lead to severe low temperature corrosion if the temperature of the pre-heaters and the flue gas duct parts are below the acid dew point. The risk of acid dew point corrosion was studied in the second pass and stack with a new SO3/H2SO4 measurement technique during the combustion of different biomass and solid recovered fuel mixtures. In this technique the SO3 or H2SO4 is captured in a KCl salt plug located in the tip of a sampling probe. Additionally, a short- and long-term corrosion probes were used. A carbon steel ring was placed on the tip of both corrosion probes and the temperature of the ring was maintained at 100°C. After exposure the corrosion products are washed away and the corrosion rate is determined gravimetrically and by calculating an average material loss. The windside, leeside, and side deposits on the ring were also collected and analyzed with SEM-EDX. Long-term corrosion probe deposits were analyzed by XRF and probe ring wall thinning was measured. Fly ash and fuel samples were also collected and analyzed. The work revealed that no risk for acid dew point corrosion existed and the SO2 in flue gases was fairly low. This implies that any SO3 and H2SO4 formed were captured by ash constituents such as calcium and alkalis. Interestingly, the deposits on the short- and long-term rings showed high CaCl2 contents. Calcium chloride is an extremely hygroscopic salt and absorbs water from the flue gas at a temperature higher than 40°C above the pure water dew point. Corrosion was seen when the flue gas water vapor concentration exceeded a critical level for CaCl2. The effect of hygroscopic salts present in combustion is discussed in the paper.

Last updated on 2019-19-06 at 04:48