Superheater material test of the compound tubes in a 65 MW(sub th) PYROFLOW CFB boiler. (Testning av kompoundtuber som oeverhettarmaterial i en 65 MW(sub v) Pyroflow CFB-panna)

摘要

A one-year test on four seamless composite tubes was carried out in a 65 MW(sub th) Ahlstrom PYROFLOW boiler. The composite tubes of SANDVIK FECRAL/HT8 were installed in the hot end of the final superheater (SH III). The clad metal FECRAL on the base metal 10CrMo910 has two different Si contents; FECRAL0 0.29 w-% and FECRAL1 1.04 w-%. These samples of the two similar kinds of composite tubes were installed for parallel tests. Besides, the reference test tubes 13CrMo44 and 10CrMo910 were welded into SH III. The boiler is a Circulating Fluidized Bed (CFB) boiler. The steam is used for electricity generation, and in the paper mill. During the test the main daily steam generation varied between 8 and 19 kg/s. The mean temperature of the steam was 470 degrees C and the mean pressure was 80 bar. The co-combustion of Refuse Derived Fuel (RDF) started in September 1993. The main fuels used in the boiler were peat and coal. Approximately 30 tons of RDF was co-combusted daily until June 1994. The total test time in hot flue gas conditions was 7900 hours. The RDF proportion of the thermal energy input into the boiler was 10%, (i.e. 15 w-% of wet fuels) on a monthly basis. The actual combustion time of one truck load was from 10 to 12 hours. Consequently, the estimated continuous test time in RDF combustion for the tubes was 2500 hours, i.e. 25 to 30% of the thermal energy input. According to the measurements the corrosion rate was not significantly increased by the RDF co-combustion. Also the fouling tendency of the boiler was quite normal. In the basis of the test, the FeCrAl compounds tubes are more resistant to hot corrosion than the reference tubes. Figs, tabs