Toby Lockwood shares his highlights from our latest workshop on Advanced Ultrasupercritical Power Plant (AUSC3) in Rome on 13-14 December 2017.
Last week we held our 3rd workshop on advanced ultrasupercritical (AUSC3) power plant in Rome, where it was co-hosted by CSM (the Centre of Materials Development) at the headquarters of INAIL. Last held also in Rome in 2014, this workshop series may appear to have taken a bit of a hiatus, but we combined AUSC sessions with other high-efficiency coal research for the ‘HELE’ workshop in Tokyo last year. The return to a principal focus on AUSC materials research this time is largely thanks to ‘Demonstration Plant 700áµ’C’ (DP700) – a European research consortium which presented the findings of its first phase at the event. Representatives from AUSC research efforts in the US, India, China, and Japan also shared a stage with the European researchers on the first day, while the second day was devoted to major developments in state-of-the-art power plant.
For the last twenty years, researchers have targeted AUSC as the next stage in the evolution of coal plant, envisioning a power plant which uses the nickel superalloys originally developed for jet engines to harness steam at 700áµ’C – thus raising the efficiency of the steam cycle to 50%. The challenge has been to develop and test a spectrum of new and existing steels and nickel superalloys for roles throughout the plant, and build confidence and regulatory approval that they can operate safely throughout a power plant’s long lifetime. However, progress has not been as straight-forward as expected, and early European efforts encountered some problems with a few materials.
Led by Doosan Babcock, DP700 has been tasked with collating the data and knowledge of AUSC built up over this two decades of research to provide an open-source database of materials, as well as conducting new work on materials modelling and component manufacture and inspection. A central theme to its work is championing a move to a ‘design by analysis’ approach to power plant and component design, as opposed to the current ‘design by code’, based on the design rules laid out by the American Society of Mechanical Engineers (ASME) and related bodies. This has the potential to produce more economic and reliable results for power plant design, which would be particularly effective for making AUSC plant feasible. Dr Peter Barnard from Doosan Babcock proclaimed that an AUSC demonstration could be built in Europe today, but also that it may not last more than 12 years – materials should therefore be studied and replaced as needed. Among a variety of other presentations from the consortium, our hosts CSM detailed some fascinating work on how sensitive nickel alloy microstructure (and thus, mechanical properties) is to small changes in processing and fabrication. The DP700 materials database will go live in April 2018.
In the USA, AUSC research has also been ongoing since the early 2000s, and is currently working on establishing a test facility for large-scale components known as ComTest. This programme has the standout characteristic of aiming for steam temperatures of 760áµ’C – an effort to get the most possible out of nickel superalloys (and arguably also to hit a nice round number of 1400áµ’F). Technical lead on the project, the Electric Power Research Institute detailed how they have achieved ASME approval of key nickel alloys, and performed some of the largest ever nickel casting to produce a turbine valve body. An interesting development came of the 2015 merger between Alstom and GE, which brought Alstom’s intellectual property to the table and revealed that there was no need to run planned steam turbine testing. The programme now plans to take steam from a host power plant to test water walls, superheaters, steam piping, and two-stage steam attemperator; it should be up and running in 2019.
We were particularly pleased to have all three organisations from the Indian AUSC research consortium represented in Rome: power plant manufacturer BHEL, state power utility NTPC, and research institute IGCAR. With its enormous and still-growing coal fleet, India has enthusiastically taken up the baton of AUSC research, and has started a project in earnest this year. Talks from NTPC and BHEL outlined the unique challenges to India, such as the high-ash coal and need for a domestic supply chain, and warned that AUSC would need to mature faster, and would be given less margin for error than previous generations of coal technology. Now in the midst of a two and a half year project of materials development and testing, a second phase will involve construction of a 800 MW AUSC demonstration at NTPC’s Sipat plant.
Highlights of the second day came from GE and Shanghai Waigaoqiao Power Plant, both of which currently stake a claim to operate the most efficient coal plants in the world. Since acquiring Alstom, GE have sought to emphasise their status as a market leader in cleaner coal technologies, In November, the company announced it was making a significant step forward in commercial coal plant design with ‘SteamH’, which takes the pragmatic approach of going not all the way to 700áµ’C, but to 650áµ’C (with reheated steam at 670áµ’C) – promising a record-breaking efficiency of 49.1%. Relying on a wealth of experience and research with materials in USC plant, the new design only employs a nickel superalloy for the turbine valve, with the superheaters and main steam pipe instead using the lower cost high-nickel-content steel HR6W. GE have already received orders for this exciting new technology for a new power plant in Turkey, and (boiler only) the Pingshan II project in China. This ‘smaller-step’ approach echoed that of Dongfang Turbine Company, who had earlier presented their commercial 620áµ’C/633áµ’C plant, partly using metals developed in China.
The Pingshan II project was itself the subject of the presentation from the team at Waigaoqiao, and has already been touched on in my previous blog on the CCT2017 conference earlier this year. Essentially, it will demonstrate a novel approach conceived by Waigaoqiao’s Professor Weizhong Feng, to raise the high-pressure turbine to the level of the boiler’s superheaters. This dramatically reduces the length of steam pipe, cutting costs and gaining efficiency. Based on this and other energy-saving technologies developed at Waigaoqiao, Pingshan has a lofty design efficiency of 49.8%. As a double reheat unit, Pingshan is one of a wave of 15 new plants in China currently reviving this almost discarded HELE technology, which were informatively reviewed by EPPEI.
The incremental efficiency improvements made possible by these technologies may not seem hugely significant in the context of the 10 Gt of CO2 emitted by coal power plant each year. And yet, the extent of the global coal fleet is such that huge savings of over 2 Gt/year are possible if inefficient plant can be replaced by the state-of-the-art in HELE plant, and even more if efficiencies can be pushed to 50%. At the workshop, India’s NTPC called for greater international coordination on AUSC development, and to establish better linkages with global climate initiatives. We hope that this workshop series and other international projects of the IEA CCC are making significant strides in this direction.