| Corrosion
Why we need to understand it better
Adapting existing fossil fuelled power plants for operation on lower carbon fuels – and thereby helping protect the vast amount of capital investment the existing fleet represents – requires a deeper understanding of the mechanisms driving corrosion. This has been a focus for research carried out by Cranfield University in the UK. It has also collaborated with the US Department of Energy in assessing high temperature corrosion issues that could arise in the operating conditions envisaged for future power generation technologies
Nigel Simms Professor of Energy Materials, Centre for Energy Engineering, Cranfield University, UK (
www.cranfield.ac.uk)
Coal-fired power plants are billion-pound investments that businesses (as well as whole nations themselves) around the world can’t afford to simply discard. However, the combination of old plant, new fuels and new operating conditions leads to corrosion, faults, downtime and inefficiencies for plant operators and manufacturers.
But these kinds of bridging technologies — between the ‘black’ and the ‘green’ — need to be adopted as early as possible to minimise greenhouse emissions from power generation and ensure the sector can meet tightening emissions targets.
Adapting plants to enable them to be co-fired using lower or zero carbon emission fuels, such as biomass, natural gas or hydrogen, means an urgent need to better understand the forces driving corrosion. High temperature corrosion is one of the key factors in the degradation of critical components in thermal energy systems. It limits component lives and the efficiencies of thermal energy systems, as well as increasing maintenance costs, risks of failures and the levels of CO2
emissions.
There are several potential types of high temperature corrosion (such as various forms of hot corrosion and fireside corrosion) that can limit the lives of critical metallic components in thermal energy systems. To counter the range of challenges — and enable the improved selection of materials for critical components that can be more corrosion resistant — a systematic approach has been developed by Cranfield University since 2000 for high temperature corrosive degradation testing at 300-1100°C. This includes multiple types of corrosion exposures and the scale and location of the damage produced.
Setting a corrosion standard Establishing a standardised approach to testing is essential for industry. It means the power generation businesses — and the manufacturers of power generation plant — can have more confidence in their selection of materials, and access to more reliable datasets of materials damage distributions under real-life conditions for the purposes of maintenance and capital investment planning. The systematic assessment
methods have been, and continue to be, taken up and used by an increasing number of major industrial companies involved with power generation.
At Cranfield the research itself has been focused on exposing materials to specific targeted conditions in controlled atmosphere furnaces, using a ‘deposit recoat’ technique. Assessment of the materials damage has been carried out using dimensional metrology to quantify the damage generated in terms of distributions of metal losses (and any internal damage). This has enabled the research to be scaled up for use on components and probes in pilot and utility-scale plants.
In turn, the methods have facilitated research aimed at improving understanding of the different specific forms of high temperature corrosion that can be found on materials (alloys and coatings) used in gas turbines and heat
Below: Rig for testing coating technologies at high temperatures
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