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Mitigation of formation of chlorine rich deposits affecting on superheater corrosion under co-combustion conditions (CORBI)


Objectives and Problems to be solved:
Corrosion has been studied over several decades but still corrosion mechanisms in waste and especially in biomass combustion are not well understood due to the complex and variable ash behaviour and chemical nature of the fuel ashes. The overall object of the proposed work is to improve the understanding of corrosion mechanisms in cases of biomass and waste combustion. Due to materials constraints steam temperatures in biofueled boilers are currently around 480 °C or even lower with waste fuels. These relatively low temperatures lead to low power generation efficiency. By increasing the understanding of corrosion mechanisms new superheated materials with higher corrosion resistance could be designed/selected in order to permit steam temperatures up to 550 °C. This would result in about a 10% increase in power generation efficiency. In addition, significant savings in maintenance costs could be achieved due to longer durability of super heaters. Description of the work: The main focus of the work is on power plant and laboratory tests to characterise fuel and ash behaviour, deposit formation and corrosion mechanisms. Different heat exchanger materials are used under controlled combustion conditions.
· Laboratory tests include material testing with model deposits using advanced methods. The principal target of these tests is to understand the corrosion formation mechanism and chlorine transport inside the corrosion layers. As a result, more corrosion resistant materials for biofueled boilers could be developed.
· Pilot plant testing will be carried out supplementing power plant tests but using more controlled gas and temperature conditions and also using a higher proportion share of hard to burn fuels. The pilot plant process parameters can be more widely varied than in large-scale commercial power plants.
· Power plant tests will be carried out at several plants. Characterization includes obtaining detailed fuel and operational parameter data as well as collecting operational experience and plant availability data. Several fuels such as wood chips, logging and agricultural residues, and demolition and processed municipal waste will be used. Performed measurements will be deposit/corrosion using temperature-controlled probe, alkali concentration and flue gas emission. Furnace monitoring by gas and solid material sampling, temperature, pressure and gas flow measurements will be carried out to describe ash and particulate behaviour and deposit formation· Mathematical modelling will analyse ash and particulate behaviour and deposit formation during combustion. Phase stability calculations using F.A.C.T. software will be carried out to analyse particulate agglomeration. A kinetic model for determination of devolatilization and oxidation of alkalis, trace metals and chlorine will also be used. A deposit formation model will characterise deposit structure and formation mechanisms. Expected Results and Exploitation Plans: Wider range of waste and bio fuels would be used in existing and new boilers in Europe. Project results contribute to achieving the goals of the Kyoto Protocol as well as for higher operational reliability, cost savings, less shutdowns, higher boiler steam properties and efficiency of the power plants. Results will be utilized in practice for power plant operation, for boiler design, for defining limits for fuel mixture ratios, and for heat exchanger material selection.

Funding Scheme

CSC - Cost-sharing contracts


Max-planck-strasse 1
40237 Duesseldorf

Participants (3)

Westerduinweg 3
1755 ZG Petten
Via A. Pisano 120
56122 Pisa
Vattenfall Utveckling AB
814 26 Aelvkarleby