The effect of CO2 on the corrosion rate in simulated combustion atmospheres

摘要

The aim of the study is to improve the understanding of the corrosion mechanism in biomass andrnwaste combustion processes. Laboratory, pilot and full scale testing of materials are performed.rnThe obtained results are discussed, e.g., with reference to thermodynamic modelling calculations.rnThe laboratory experiments in JRC Plant Simulation Test Laboratory are focused mainly onrncommon ferritic and austenitic steels (X10, X20, 2.25Cr1Mo, AC66, Sanicro28, Esshette 1250rnetc), which are used as superheater steel tube materials in such applications. The main aim of thisrnpart of the project is to understand the effect of deposition as well as the CO2 or/and CO/CO2rncontent in combustion atmospheres on corrosion rate and mechanism of studied materials.rnLaboratory tests include the thermogravimetric studies using Cahn thermobalances and longrnexposure tests in horizontal/autoclave multi-sample furnaces. Post experimental analyses arernmade using SEM/EDS + XRD techniques and optical microscopy. The experiments are carriedrnout at isothermal temperature – 535℃ n various simulated combustion atmospheres (22%H2O+rn5%O2 +xCO2 + N2) with different CO2 content vary from 0 to 25 vol. % for the samples withoutrndeposit and with filter/cyclone ash deposition (long exposure tests). In this stage, followingrnconclusions can be made:rn- Corrosion rate, for the alloys with and without the deposit, increase with increasing CO2rncontent, especially for the ferritic steelsrn- Corrosion rate for samples with the deposit increase significantly and in this case therninternal oxidation of the studied samples was observedrn- Thermodynamic model calculations performed resulted, a.o., to the following propositionsrnstill of preliminary naturern- Various carbides of metallic alloying elements become less stable at oxide scale-metallicrnalloy phase boundary with increasing partial pressure of carbon dioxidern- Carbides and oxides of various alloying elements (Fe, Cr, Mo, Mn…) are unstable in theirrnmixtures with alkali metal carbonates or model ashrn- However, some of the mixed alkali oxide-transition metal oxides that are predicted to bernformed as reaction products, may dissociate under atmospheres with appreciable carbonrndioxide and/or water vapour content.