Technical Market Support » Thermal Coal
Research and development has been undertaken worldwide to realise coal fired power plants that are capable of operating at higher steam temperatures and pressures to achieve higher plant efficiencies. These efficient units use low-NOx coal burners and are fitted with state-of-the-art technologies for pollutant capture to control environmental emissions. These are commonly referred to as HELE (high-efficiency low-emissions) coal-fired power plants, and the best examples can meet the emission limits for gas-fired power plants.
This project reviewed the HELE technology development renovation roadmap in three components:
- Steam cycle side;
- Fire side featured with low NOx burning; and
- Flue gas treatments (including PM capture and deSOx/deNOx).
This report aims to provide a comprehensive overview on the HELE pulverised coal power generation side where most Australian thermal coals are and will be used, and covers both the technical R&D and the modelling efforts in the literature for the first two components. The increases in the steam pressure and temperature represents the roadmap to HELE coal boiler technology R&D over the past decades, from subcritical to supercritical through to ultra-supercritical and advanced ultra-supercritical boilers. The increases in the plant efficiency, the drop in coal consumption and the carbon emissions, and lower NOx formation are regarded as the main advantageous features of the HELE coal combustion technologies. The achievements in reaching higher steam pressures and temperatures have been made possible owing to the use of advanced materials that can withstand such conditions.
Extensive numerical modelling efforts have been made in the past several decades, which has improved our understanding of the technical issues associated with HELE boilers, including combustion and boiler performance optimisation, ash deposition, and materials issues at higher operating temperatures. The current modelling research in the open literature has been overviewed in this report, which has improved our understanding of the technical issues in coal fired boilers under HELE conditions, including boiler performance optimisation, ash deposition, and materials issues. The effects of changes in the configuration and operating conditions are discussed with a focus on the optimisation of boiler performance, such as unburnt carbon and NOx emissions. The retrofit and optimisation of burner geometry and operating conditions in low-NOx coal combustion technology, which is necessary to operate HELE power plants, are also overviewed.
In terms of ash deposition, the development of sub-models, including particle sticking and impacting behaviour and its impact on the prediction of ash deposit growth under different temperatures have been discussed. The numerical models for material oxidation and creep of austenitic and nickel-based alloys used under HELE conditions have been developed based on the finite element method to predict the availability of advanced alloys and creep life and the actual service time of the boiler parts. The prediction of oxide scale growth and exfoliation in both steam-side and fire-side as well as creep strength, have also been analysed and reviewed.
The project also identifies further research needs on numerical modelling that are required to further optimise the coal combustion processes and to address the technical issues associated with the advanced HELE power plant operations.
The literature data demonstrate that coal quality seems to be responsible for various issues during coal combustion, especially, slagging and fouling in both subcritical and advanced coal-fired boilers. Coal quality data that influence such issues have been collected from the open literature, based on which we have developed the thermal coal database, currently including 34 Australian and 26 international thermal coals, ranging from subbituminous to bituminous coals. Various slagging/fouling empirical and experimental indices have been included in the database to evaluate the slagging/founding propensity.