There are many field and laboratory studies [1–16] which investigate the mechanics of corrosion due to straw burning, and some corrosion models based on chlorination have been suggested. Also, the use of chemical additives has been proposed to minimize this problem [17–21] in combination with mathematical models used to simulate the deposition behavior based on computational fluids dynamics [22].
To understand the corrosion mechanism of corrosion that superheaters tubes suffer it is necessary to know more about chemical reactions that happen in the biomass boiler. To do so, a valid tool is the realization of thermodynamic calculations [23–25].
The focus of this work is the realization of thermodynamic calculations starting from the reactions that take place among the metals of the superheaters with the combustion atmosphere and the deposits that are formed on the tubes.
We have also carried out field tests. The Sangüesa Power Station belongs to Acciona Energia and is located in Navarra (Spain). It has a grate-fire boiler with a power of 25 MWth.
The most corrosive conditions in the plant happen in the third superheater which is in the third pass and has an outlet steam temperature of 540°C. The temperature of the metal is calculated to be at 570°C. The gas temperature at this point was 850–900°C. The fuel used in the power station was only straw; straws studied will cause high temperature superheater corrosion when fired alone in power plants (with steam temperature higher than 420°C). Fly ash from straw firing on grate was rich in the volatile elements K, Cl, and S [4].
To complete the thermodynamic calculations, the deposits formed on the superheaters tubes as well as the oxides formed on the tubes have been characterized. The final objective of this work is to contribute to the knowledge of the corrosion that superheaters tubes suffer in the biomass plants and, in this way, contribute to the development of the biomass as industrial fuel for...