Investigation of the corrosion behaviour of 13CrMo4–5 for biomass fired boilers with coupled online corrosion and deposit probe measurements

High-temperature corrosion in biomass fired boilers is still an insufficiently explored phenomenon whichcauses unscheduled plant shutdowns and hence, economical problems. To investigate the high-temper-ature corrosion and deposit formation behaviour of superheater tube bundles, online corrosion probe aswell as deposit probe measurements have been carried out in a specially designed fixed bed/drop tubereactor in order to simulate a superheater boiler tube under well-controlled conditions. The investigatedboiler steel 13CrMo4–5 is commonly used as steel for superheater tube bundles in biomass fired boilers.Forest wood chips and quality sorted waste wood (A1–A2 according to German standards) as relevantfuels have been selected to investigate the influence on the deposit formation and corrosion behaviour.The following influencing parameter variations have been performed during the test campaigns: flue gastemperature between 650 and 880C, steel temperature between 450 and 550C and flue gas velocitybetween 2 and 8 m/s. One focus of the work presented is the detailed investigation of the structureand the chemical composition of the deposits formed as well as of the corrosion products. A further goalof the work presented was the development of an empirical model which can be used within CFD sim-ulations of flow and heat transfer to calculate and evaluate the local corrosion potential of biomass firedplants already at the planning stage. The corrosion probe measurements show a clear dependency on theparameters investigated and the empirical function developed reproduces the measured corrosionbehaviour sufficiently accurate. Since the additional calculation time within the CFD simulation is negli-gible the model represents a helpful tool for plant designers to estimate whether high-temperature cor-rosion is of relevance for a certain plant or not, when using fuels with similar compositions and the steel13CrMo4–5.