Biomass-fired power plants with higher efficiency could generate more power but also reduce the emission of greenhouse gases, e.g. CO2. Biomass is the largest global contributor to renewable energy and offers no net contribution of CO2 to the atmosphere. To obtain greater efficiency of power plants one option is to increase the temperature and the pressure in the boiler section of the power plant. Raised temperature and pressure increase the demands of the operating materials of the future high-efficient biomass-fired power plants. This requires improved properties, such as higher yield strength, creep strength and high-temperature corrosion resistance as well as structural integrity and safety. Also, the number of start-and-stop cycles will increase, leading to demands on increased material performance under cyclic loading, both from thermal and mechanical loads.
High-temperature austenitic alloys, such as austenitic stainless steels and nickel-based alloys, possess excellent mechanical and chemical properties at the elevated temperatures and under the cyclic loading conditions of today’s biomass-fired power plants. However, today austenitic stainless steels are design to withstand temperatures up to 650 °C in tough environments. Nickel-based alloys are designed to withstand even higher temperatures in tough environments. Austenitic stainless steels are more cost effective than nickel-based alloys due to a lower amount of expensive alloying elements. However, the performance of austenitic stainless steels at the elevated temperatures of the future operation conditions in biomass-fired power plants is not yet fully understood.
Aims of the research
The research aims to increase the knowledge of the influence of long term high-temperature ageing on mechanical properties, the influence of very slow deformation rates at high-temperature on deformation, damage and fracture mechanisms, and the influence of high-temperature environment and cyclic operation conditions on the material behaviour. In the long term, this research can contribute to material development to achieve the transition to more sustainable power generation by biomass-fired power plants.
Mechanical testing such as impact toughness tests, uniaxial tensile tests at elevated temperatures using varies strain rates and creep and fatigue interaction tests are used in the research. Also, thermal testing such as long term ageing and thermal cycling in water vapour environment are used. Microscopy is used to analyse the microstructure of the mechanical and thermal tested materials.