Soot reduction in gas turbine combustors using oxidation catalyst additives

The combustion of viscous ash forming fuels generates soot and ash that collectively form the so called particulate matter (PM). In addition to existing SOx and NOx emission regulations, the World Bank has enacted a 50 mg/Nm(3) limit for the PM emissions of large combustion plants, creating a new challenge to power generators who use heavy fuel oils. LTL Holdings Ltd (Colombo, Sri Lanka) that own and operate a 300MW heavy-fueled gas turbine combined cycle (GTCC) at its Kerawalapitiya (Sri Lanka) power plant and GE Power & Water have embarked on a study intended to investigate the best PM abatement technique for heavy fueled gas turbines. This was done with TEKAT Ltd (London, UK) as the additive suppliers and the IRTES-LERMPS laboratory (Sevenans, France). In recent lab and field tests, the authors have thus evaluated the soot abatement capability of various combustion catalysts at different dosages. The results show that cerium proves an efficient oxidation catalyst in a real gas turbine, irrespective to its chemical form (Ce(III) or Ce(IV)), providing very substantial soot abatement rates. After briefly reviewing the different PM abatement techniques, the paper focuses on the lab and field tests performed and places emphasis on the performances of cerium in gas turbine combustors, along with the complex ash chemistry developed by heavy fuel oils.