PGE/REWE 2015

Sessions Speakers Exhibitors Products Press Releases Show Specials Floor Plan

Improving Flexibility of Lignite Boilers Through Firing System Optimisation and Retrofit (Room G104, Auditorium Centre, First Floor)

Utilization of low rank coals such as lignite is gaining increasing importance in Europe and worldwide. More specific, in several European countries like Germany, Spain and Greece, a drastic decrease of the average electricity market price is observed in the last years, caused by the increasing share of renewables and the “merit order” effect. Modern, highly efficient NGCC power plants are no more competitive according to the current market conditions and are being mothballed. Hard coal and lignite power plants shall stay available, as the backbone of the electricity system, and shall cover the increasing fluctuations of the residual load and provide increased ancillary services towards grid stabilization. Lignite power plants are usually the least flexible plants, due to their restrictions in the mill-drying and firing system caused by the higher water and ash content of lignite. Therefore limitations of minimum load to more than 50% for existing lignite power plants and to more than 40% for new builds are currently foreseen. What is more, flame stabilitiy issues - usually observed in aged lignite units firing low quality lignites - hinder the flexible operation of the plants and impose the utilisation of expensive supporting fuels like oil or natural gas for a long time period just to keep stable operation. Retrofitting concepts for three different lignite boilers having different firing configurations are presented in the present paper. Pre-drying of lignite and 100% indirect firing, as well as “hybrid firing”, i.e. co-firing of pre-dried and raw lignite, are some of the solutions proposed towards minimum load decrease in the different cases examined. Lowering minimum load down to 20% is then possible with such optimized firing systems, which is equal with the current state of the art of hard coal power plants operating in Germany today.