A. Agüero1, M. Gutiérrez1, A. Illana2, F.J. Pérez2, M. Benito3 and A. Bahillo3
1) Instituto Nacional de Técnica Aeroespacial, Área de Materiales Metálicos, Ctra. Ajalvir Km 4,
28850 Torrejón de Ardoz, Spain
2) Universidad Complutense de Madrid, Research Group of Surface Engineering and Nanostructured Materials, Av. Complutense S/N, 28040 Madrid, Spain
3) CIEMAT, Sustainable Thermochemical Valorization Unit, Avda. Complutense 40, 28040 Madrid, Spain
In order to increase the efficiency of biomass burning power plants, the operating temperature must be increased with a consequent increase in corrosion rates. New materials and/or coatings are required, and screening laboratory testing is needed to evaluate the high temperature corrosion resistance of these new materials under various and very complex atmospheres resulting from the different types of available biomass. However, there is no general agreement regarding the methodology to carry out biomass corrosion laboratory tests, which can allow realistic ranking of materials and coatings. A laboratory test procedure based on data obtained from a thistle/coal-burning pilot plant employing oxy-combustion conditions, was established and the corresponding rig implemented. A model atmosphere was established on the basis of the composition of gases measured in the pilot plant. The same composition of the deposits found on samples tested in the pilot plant was also used in the lab. Two alloys, P92 and T22 and slurry deposited aluminide coatings were tested both on the laboratory scale both at 600º C and 650º C and on the pilot rig at a nominal temperature of 600º C in order to compare the results.
The lab results at 600º C were similar to those obtained in the plant, in particular keeping in mind that the temperature control in the plant was not as stable and varied between 600º C and 620º C.Coated P92 does not show corrosive attack at 600º C in the lab, whereas at 650º C half of the initial coating thickness (~50 µm) corroded and coating-substrate interdiffusion had taken place. The sample tested in the pilot plant exhibited some degree of corrosion as compared with the 600º C tested sample, which can be due a higher average temperature in the plant due to the already mentioned variation between 600 and 620º C during the test. At 600º C in the lab, coated T22 exhibited corrosion likely due to a lower Cr content (Cr is known to improve the corrosion resistance of aluminide coatings). Again interdiffusion took place and 2/3 of the original coating thickness was corroded at 650º C in the lab, whereas in the pilot plant tested specimen the corrosion level was intermediate between the 600 and 650º C lab specimens.
This method of testing can therefore result in more realistic studies as well as a meaningful ranking of materials and coatings in the laboratory to obtain the best possible solution without more complex testing.