Improving the efficiency of heavy-fuelled gas turbines: The successful experience achieved at the Yugadanavi 300 MW CCGT in Sri Lanka

An important asset of heavy duty gas turbines (''GT'') is their ability to burn a large variety of hydrocarbons, including low grade ones such as ash-forming fuels, in a well-controlled manner while achieving fairly high energy conversion efficiency. In fact, there is still a considerable margin for improving the efficiency of gas turbines burning ash forming fuels if one succeeds in reducing the deposition of the ash in the turbine section which represents however a challenging technology lock. The main difficulty for achieving this ambitious objective lies in the additional fouling entailed by the ``inhibition process''. Indeed a magnesium-based corrosion inhibitor is injected into the GT combustors in order to suppress the corrosion threat placed by the highly fusible vanadium species coming from the fuel. This additive represents a substantial increase in the amount of ash crossing the machine whereby substantially accentuating the fouling of the hot gas path parts. Within a joint initiative, LTL Holdings Ltd, GE Power & Water and the UTBM University have successfully tested a novel family of vanadium inhibitors called ``bimetallic inhibitors'' that combines magnesium and iron and lead to a considerable reduction in ash deposition while keeping intact the anti-corrosion protection. This new inhibitor family brings a decisive improvement in GT efficiency as well as a significant increase in plant availability. Indeed it enables reducing the frequency of the machine shutdowns that are periodically required to remove the ash deposits through water wash. In addition, iron procures an interesting soot suppression effect. The paper outlines the development carried out in this project and sets out the successful field test performed in 2015 at the Yugadanavi 300 MW power plant in Sri Lanka.