The IEA Clean Coal Centre’s second Workshop on Upgrading and efficiency improvements in coal-fired power plants was held at E-ON’s Ratcliffe-on-Soar power station near Nottingham, UK on 20-21 March. A diverse group of delegates from twelve different countries representing both industry and academia were welcomed, with an equally varied programme of talks touching on a range of state-of-the-art upgrades, including materials for advanced steam conditions, analysis tools, flue gas scrubbing and ash handling.
Proceedings on both days were initiated with presentations on the remarkable growth of high efficiency coal power currently taking place in China, given by the Electric Power Planning and Engineering Institute and the China Power Engineering Consulting Group Corporation. China’s generating capacity has almost trebled in the last ten years, and coal power has remained dominant in the energy mix. Since 2006, policy has encouraged the replacement of small and inefficient plant with supercritical and ultra-supercritical units, which now represent nearly a third of the total capacity. Last year, attention was turned to upgrading existing plant, with a range of economic incentives implemented to reward gains in efficiency. Areas identified for energy savings included steam-drying of lignite, reducing condenser pressures, and streamlining flue gas ducts, as well as more efficient scrubbing technologies needed to meet China’s strict new emissions regulations.
International efforts to develop materials suitable for operating coal plant with higher steam temperatures were well-represented by speakers from Italy, Poland, and the UK. Results presented from the international Macplus research programme included refractory materials enhanced by surface modification, protective metal alloy coatings for boiler tubing, and the performance of MARBN steel in pipework welds. More detail on this promising metal was provided by a speaker from E-ON, whose research has shown that significant strength gains over P92 steel can be achieved at less rigid compositional specifications than previously thought.
A session on the application of new analysis tools covered thermo-optical measurements for assessing materials at high temperature, and a laser-based system for real-time optimisation of combustion conditions. A grid of lasers placed across a boiler cross-section can perform absorption spectrometry to accurately map the temperature and concentrations of oxygen, CO and CO2. Feedback of this information to burners and overfire air allows continuous optimisation of combustion efficiency and reduction of NOx emissions. Effective NOx reduction strategies were touched on throughout, including a presentation on the implementation of SNCR for large coal boilers. Optimisation of urea injection and use of temperature measurements and CFD modelling is enabling this technology to rival the more capital intensive SCR in many cases, particularly for biomass cofiring projects.
Efficiency gains from equipment upgrades were represented by talks on dry bottom ash handling systems and steam turbine upgrades. Advances in computer modelling and blade fabrication have allowed new steam turbines to increase plant output by 2% whichm in the case of a 600 MW boiler, can be strikingly compared to ten wind turbines; providing the same carbon emissions reduction at a fraction of the cost. The great potential of turbine upgrading was also highlighted in a review of notable upgrade projects around the world by Dr Colin Henderson of the IEA CCC, who provided a useful perspective on how some of the technologies discussed have been implemented in practice.
The workshop was concluded by an informative tour of E-ON’s combustion test rig at the Ratcliffe site, constructed in 1993 principally to study the combustion and slagging behaviour of imported coals. The 1 MWt rig was also one of the first installations to be equipped for oxy-combustion, and has more recently been employed to study mercury scrubbing and combustion of various types of biomass.
Helped in part by the compact group of attendees, discussion sessions between talks were lively and enlightening, and continued late into the night during the workshop dinner held at the Crowne Plaza Hotel in Nottingham. A prevailing theme of the workshop was the powerful and perhaps underestimated means of reducing global carbon emissions provided by even small efficiency gains for coal plant, given its global prevalence and rapid growth in developing economies. Furthermore, the most significant improvements can only come from the cumulative effect of optimising all aspects of plant operation. This workshop has aimed to provide a forum for coordinating the correspondingly diverse range of technologies and research which this process must draw upon.