Study of slagging and fouling mechanisms in a lignite-fired power plant

Abstract A significant proportion of the electrical power requirements of Greece are covered by lignite-fired power plants. Greek lignite is characterized by a high water and ash content and a low heating value. Slagging and fouling are common inside the power units and severely affect the performance of the power plants (reduced efficiency, steam leakage in the superheaters and water walls whereas the high temperature of the exhaust gases leads to the mal-functioning of the electrostatic filters). In addition excessive interior pollution cause the units to stop for cleaning resulting in a reduced production and increased maintenance costs. In this paper the results from a measurement campaign in a steam boiler affected by excessive deposits are presented and compared against the manufacturer's operating data. A number of differences were found between the two sets of data and were attributed to the particulars of excessive amount of deposits in the boiler. In addition, the present study investigates the chemical composition and behavior of the slagging and fouling deposits that occur in units of the Kardia power plant as well as of a bottom ash and a fly ash sampled from the same unit. The steam path of the unit was simulated using the DNA software in order to model the effect of the contamination on the global performance parameters of the power plant and the results were compared against the experienced operational performance parameters. In addition, a number of practices are proposed and assessed for reducing the levels of boiler contamination and extending the time between successive maintenance stoppages.