Rechristened the Energy Science Lecture to reflect its broadening scope, the annual Coal Science Lecture was given this Tuesday by Professor Rachel Thomson of Loughborough University on ‘challenges for flexible operation of power plants: materials solutions’. The talk provided some great insight into the impact being made in the power industry by relatively new techniques in materials science – now not only used to help predict the behaviour of existing metals, but also to design new, ideal materials with better performances.
As the capacity of intermittent renewables on the UK grid grows, fossil fuel power plants are increasingly required to ramp their output up and down to balance electricity demand, placing their metal components under stresses they were never intended to endure. Part of Professor Thomson’s work has been to bring a sophisticated array of materials characterisation and modelling techniques to the challenge of better predicting the remaining lifetime of these metal parts, such as the martensitic steels used in steam pipes. The widely used metals derive their strength from microscopic particles of certain metal carbides and nitrides which attach to grain boundaries and prevent them from deforming under high temperature and stress. Using an imaging technique which bombards the metal surface with metal ions, the researchers were able to visualise these particles and even to distinguish beneficial particles from other kinds which have no strengthening properties. Certain parameters which were not strictly controlled previously, such as the aluminium content in the metal or the precise temperatures they experience during welding, were found to favour the formation of these detrimental particles and severely weaken the metals.
The efficiency of state-of-the-art fossil fuel power plants is limited by the steam temperatures which the metal components can withstand, so efforts to improve plant efficiency are centred around developing new, high-strength metals which allow higher steam temperatures of up to 700°C to be used. By modelling the behaviour of new martensitic steel compositions, the addition of boron was found to prevent the beneficial particles from growing in size over time and losing their effectiveness. This ‘designer material’ has now been made in a bulk quantity and is being tested under real power plant conditions.
A similar approach was also used to design new coatings for gas turbine blades which help protect them from high temperatures and corrosion they encounter, particularly when the fuel composition is varied. This task is rendered even more challenging by the complex interaction between the substrate metal and the coating, with can diffuse into each other and form new materials at the interface. Nevertheless, Professor Thomson’s team have managed to develop a new, high-performance multi-layered coating based on their models, which is now also being tested in a real gas turbine.
The solutions offered by materials science and advanced manufacturing currently seem to be developing faster than the power industry can keep pace with, and future fossil fuel power plants will surely draw on these new techniques more and more as they meet the growing demands for high efficiency and flexibility. This exciting field will be covered by a new IEA CCC workshop series on high efficiency, low emissions power plant or ‘HELE2016’, which will be held in Tokyo next May, http://hele.coalconferences.org.