This paper aims to determine the impact of load flexible operations on heating surface depositions. Therefore, measurements along the flue gas channel during full and partial load in a lignite fired power plant with an electrical output of 600 megawatts were made. For this purpose, the particle wire mesh method and the temperature-range-probe were used along the flue gas path in the burner area, the radiation section, the superheater area and the air preheater. With the aid of the particle wire mesh method, the fly ash particles contained in the flue gas were characterized with respect to particle morphology and chemical composition. As result, no impact of the load-flexible mode on the fly ash particles could be detected. The chemical composition of the particles found corresponded to the fuel ash composition. The temperature-range-probes were used over short and long term periods within the flue gas to examine the deposition amount and composition near the burner area. Results showed more depositions and the deposition of ferrous sulphides during full load in the burner area. Long term temperature-range-probes showed different layers of deposition and a limited growth possibly due to load flexible operation. The results of the practical investigations in real power plant operation indicate that the changes in the fouling behaviour are caused by thermochemical processes in the area close to the wall or directly on the heating surfaces. In addition, however, changes in the mill operation also play an important role, which affect the flame shape and position, temperature and flow velocity distribution, etc., which are not part of this work.

In addition to the short term and long term measurements and calculations, an online deposit identification method is presented, which allows the in-process monitoring of the local cleanliness of the heating surfaces in the radiation section and the burner area of the steam generator and the cleaning efficiency of existing water blowers. With the help of an algorithm, the two key figures “local cleanliness” and “cleaning efficiency” are determined from the measurement signals, which are used to evaluate the local fouling situation and the cleaning efficiency of the water blowers. Through the combination of so called heat flux sensors and the evaluation of large amounts of signal data, it is possible to monitor the fouling of the heating surfaces by means of a non-invasive, simple and cheap technology. This allows the online optimization of the local heating surface cleaning which is demonstrated for a lignite-fired power plant in Germany.