The hot corrosion of Ni-based ternary alloys and superalloys for application in gas turbines employing residual fuels

Decreasing quality and stricter environmental regulations impose potential limitations to the use of heavy fuel oils in combustion. Because of their low cost they are economical alternatives for power generation. However, they contain large amounts of nitrogen and sulphur, which form NOx and Sox during combustion and cause undesirable pollution. Additionally they often produce carbonaceous particulates. A knowledge of the formation and interaction of nitrogen and sulphur compounds in combustion is necessary to establish pollution abatement strategies. In this thesis a study of those processes was performed using a number of heavy petroleum-based fuels. An extensive literature review on relevant aspects of heavy fuel combustion was carried out, with particular emphasis on the formation of NOx, SOx, particulates and ash. In the first stage of the experimental work, the ignition characteristics of the fuels were determined by means of the single suspended droplet technique. They were found to comply with most of the correlations for heavy fuel combustion established by Taylor and Burgess, relating the combustion characteristics of a fuel droplet to its dimensions. The formation of NOx and SO2 was studied in a drop-tube furnace as a function of the stoichiometry, flame temperature and residence time. Additional information about other species formed was also obtained, as well as about the formation of thermal-NOx. In a further stage, a numerical model was used to simulate mathematically the experimental results and study the mechanisms of interaction between N and S species. These calculations were aided by measurements of the flame temperature in the drop-tube furnace. In the last stage of the experimental work, the interaction of sulphur species with NOx (ie NO and NO2) was studied experimentally by adding SO2-gas to the combustion system in the drop-tube furnace. Sulphur was found to influence the formation and emission of NO and NO2 in different ways according to the equivalence ratio. Nitrogen-sulphur interactions were also studied as a function of the residence time.

Pollutant formation and interaction in the combustion of heavy liquid fuels.

Effects of SO2/SO2 on the efficiency with which MgO inhibits vanadic corrosion in residual fuel fired gas turbines

Reaction chemistry of plutonium with vanadium pentoxide in molten salts

Many alloys used at high temperature in industrial processes are Ni-based and many others contain it in appreciable quantities, so it is of interest to evaluate the performance of pure nickel in order to determine the behavior of its alloys once the elements responsible for their protection have been depleted due to accelerated corrosion processes in the presence of vanadium-rich molten salts. Due to this, this work presents the study of Ni behavior in NaVO3-V2O5 mixtures at different temperatures. The behavior of pure nickel was determined by both electrochemical and mass loss measurements. The results show that the aggressiveness of the vanadium salts is increased by increasing both the V2O5 content and temperature. V2O5 addition considerably increases the current densities of the anodic and cathodic reactions. The corrosion process of Ni is modified due to the presence of its corrosion products, and its presence increases the activation energy by at least one order of magnitude. Although nickel shows a high reactivity in vanadium-rich salts, its reaction products are highly stable and protect it from the corrosive medium because the corrosion reactions trap the vanadium and block the migration of nickel ions.

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J. R. Wilson

Papers

Corrosion of Metals by Liquid Vanadium Pentoxide and the Sodium Vanadates

The Corrosion of a 50Cr-50Ni Alloy in Liquid Vanadate Systems in the Temperature Range 750–950°C