Corrosion |
exchangers. In particular, the research has contributed to quantifying and understanding the relationships between damage observed in different materials systems and the contaminants in the hot gas stream (from different sources and qualities of fuel and air), gas temperatures and pressures, component surface temperatures and deposits formed on surfaces (in terms of their compositions and fluxes).
Underpinning this approach has been work on investigating and quantifying the relationships between: the component operating conditions (gas temperatures, gas pressures, surface temperatures); the fuel/air compositions used in combustion; and, the component exposure conditions (gas compositions, deposit compositions and deposition fluxes, for example). Changes in these kinds of parameters, such as in deposition flux or in deposit composition arising from differences in fuel compositions (or fuel mixes), can have a significant effect on corrosion damage rates. A further factor that can also influence corrosion damage is the stress state of the components.
Changing fuels
Another strand of research has investigated the potential high temperature corrosion of candidate materials in future power systems — a UK collaboration co-ordinated by Cranfield and the US Department of Energy, with participants
from industry, laboratories and universities in both the US and the UK.
This has examined how corrosion varies depending on the operating environment, with a view to supporting the operation of gas turbines at higher gas temperatures and with novel fuels. Changing and optimising fuel specifications is one of the routes towards limiting high temperature corrosion damage in both gas turbines and solid fuel combustion plants.
Among power generation technologies considered are: integrated gasification combined cycle (IGCC) systems, employing biomass/ coal derived syngases, or hydrogen enriched syngases, to fire gas turbines; and pulverised fuel combustion systems using advanced ultra-supercritical steam conditions (A-USC) and thus requiring much higher temperature heat exchangers. Assessment of the exposure environments and operating conditions for components in these future systems have been used to guide experimental work and the development of system concepts to optimise the balance between potential efficiencies, fuel specifications and component lives. These activities have identified materials systems to be used for gas turbine blades/vanes (and materials systems to be avoided) for viable component lives.
For heat exchangers in solid fuel combustion plant, it is possible for specific biomass/coal
combinations to generate high damage rates at existing operating temperatures, with a corresponding reduction in heat exchanger lives. We have enabled much better understanding of the factors for assessing the potential for specific biomass/coal combinations to greatly accelerate fireside corrosion damage to superheater or reheater tubes. Quantitative models linking corrosion damage to the most important fuel and operating factors identified have been generated, with industrial partners for their use. The sheer scale of the value of existing plant, the importance of extending life over replacement, the challenges involved with making adaptations without disrupting operations, means new developments are always likely to be incremental. Innovations are piecemeal rather than revolutionary. But working with the balance between the need to preserve and the need for change, there continues to be progress towards more efficient, lower carbon technologies. For advanced power generation systems and fuel specification that can act as a bridge to a more sustainable energy infrastructure — the advanced fossil fuel/biomass fired power systems that are under development — full guidance is being provided for the development of power system concepts to optimise the balance between operating conditions, gas cleaning system requirements, fuel specifications and component lives.
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