Powerful partnership - a UK-US collaboration on energy
Derek Allen from international company Alstom Power reports on the joint UK-US project to assist development of energy materials and processes.
Further development and understanding of advanced materials is needed if the targets of any future energy policies are to be achieved and stringent environmental and efficiency targets are to be met.
These challenges are global and will not be solved by one country or organisation, so there is a positive incentive for international collaboration in pre-competitive technologies. This has led to a materials R&D programme being carried out between organisations and laboratories from the UK and USA under the auspices of the UK-US Memorandum of Understanding for Fossil Energy Research and Technology Development, signed under the Bush-Blair administration.
Nearly 20 organisations participated in a five-year collaboration, supported by the UK Department of Energy and Climate Change and the US Department of Energy.
The key objective was sharing and developing the partners’ knowledge in the key area of high-temperature materials for advanced fossil energy power plant applications where there is a need to understand the impact of changes in fuel type, plant operating cycles/environments and the introduction of CO2 capture technology, which will place severe demands on the materials and components used.
This UK-US effort involved sharing test facilities, expertise and best practices, developing common tools and methods, and industrial secondments. It also provided a significant opportunity to develop long-term co-operation.
Specific technical objectives related to:
• Optimised test methods, data analysis and storage.
• Development of lifetime prediction tools.
• Materials evaluation techniques and ranking methodologies.
• Joining and thermomechanical processing.
These were delivered through five technical tasks covering steam oxidation, boiler corrosion, gas turbines fired on syngas, standards and databases, and oxide dispersion strengthened (ODS) alloys. These tasks were deemed the most appropriate for equitable collaboration, where both UK and US partners could maximise the value and benefits to their organisations.
Materials for high efficiency ultrasupercritical (USC) steam power plant, which are capable of operating at higher temperatures (up to 760ºC) and pressures, need to be developed and qualified. The programme comprised three discrete areas – a state-of-the-art review of steam oxidation data, steam oxidation testing to fill gaps and extend data coverage, and development of models to simulate oxide growth and exfoliation.
This has resulted in over one million hours of new steam oxidation data generated for 30 alloys and two new high-pressure steam test facilities commissioned and fully operational, as well as improved oxide growth and exfoliation models for use in life prediction methodologies and power plant design.
The driver for this was gaining a better understanding of the mechanisms and the monitoring of fireside corrosion, which is a key life-limiting factor in power plant boilers. Boiler corrosion is increasing in importance as a result of the more arduous operating conditions associated with current and future developments, such as NOx emission control, co-firing, USC steam technology and oxy-fuel firing. This programme focused on two main areas – representative laboratory-scale boiler corrosion tests and evaluation of the results, and the development, implementation and assessment of fireside corrosion probes to measure corrosion rates online.
As a result, comprehensive high temperature corrosion data generation and analysis allowed the performance of boiler materials in a variety of atmospheres to be ranked. Also, effects on corrosion of more novel technologies such as oxy-fuel and co-firing have been measured and corrosion probe technologies have been evaluated and demonstrated under real operating conditions, providing important indicators for commercial probe development.
By moving towards higher efficiency power generation systems, gasification-based combined cycle technologies have become more attractive. These produce fuel gases derived from a range of feedstocks including coal, biomass and waste. All such fuel gases contain contaminants detrimental to the turbine system, compared to natural gas, and these effects needed to be quantified to identify the best operating conditions and aid materials selection. This task focused on two areas:
• Assessment of future fuels and their effects on the operating environments of hot gas path components.
• Ranking of candidate alloys and coating systems through high velocity burner rig testing, simulating a range of operating conditions.
Damage and degradation mechanisms have been identified and measured, and these can be used in lifetime modelling of hot gas path components. Also, by combining high-velocity, high-temperature burner rig tests under simulated operating environments with advanced analytical techniques, the team has ranked various alloy and coating systems. This will assist in materials selection for future components.
The drive for new and improved materials and the optimum use of existing materials in a cost effective manner requires the amalgamation of data from different sources. It is essential that such shared results and test methods are comparable and meaningful. To achieve this, the methods used and the results from each source were evaluated, shared, stored and analysed using agreed standard methods.
Activities were undertaken to explore the comparability of data, including a review of existing standards and test methods, and the development of a data exchange and storage tool that was accessible by all partners.
This led to a standard method of data collection, exchange, analysis and storage (including microstructural). Inter-laboratory tests have demonstrated the need for improved standardisation of high-temperature corrosion and oxidation testing.
Due to their excellent high temperature properties, ODS alloys could be used in the next-generation of high-temperature power plant, where good creep strength and oxidation resistance are required. However, due to the nature of the materials, their use depends on overcoming challenges such as the low creep strength of joints fabricated by conventional fusion welding and optimisation of secondary recrystallisation to produce microstructures where large grains can be custom-oriented to withstand maximum stress in service.
The aim was to overcome some of these challenges by evaluating different joining techniques such as friction stir and diffusion bonding, and addressing how to manipulate and customise secondary recrystallisation by cross-rolling and flow forming to modify the microstructure of the material.
This has revealed the feasibility of producing joints with creep strengths comparable to the parent material. Thermo-mechanical methods for improving the microstructural evolution of ODS alloys have also been successfully developed, allowing optimum strength to be aligned with the direction of maximum operating stress.
The benefits of the collaboration can be seen from:
• Shared data, facilities and experience, leading to reduced cost and effort.
• The combination of the partners’ experience to obtain better understanding of materials behaviour and degradation mechanisms.
• Identifying and resolving problems when comparing data from different sources and recognising the importance of standardisation.
• Developing combined analysis and predictive tools (and hardware) to improve future component development and lifetime prediction methods.
• Establishing a solid platform for collaborations with agreed equitable programmes.
Continued UK-US collaboration on advanced materials is planned. This will help accelerate the development of competitive low-emission power plant solutions with significantly reduced development costs and technical risk. Additional programmes in the area of plant asset management are also being considered.
Further information: https://us-uk.fossil.energy.gov