Deposition of Corrosive Alkali Salt Vapors on the Blades of Gas Turbines Fueled by Coal-Derived Syngases

Abstract

Many proposed clean coal technologies for power generation couple a gasification process with a gas turbine combined cycle unit. In the gasifier, the coat is converted into a syngas which is then cleaned and fired before entering the turbine. A problem is that coat-derived syngases may contain alkali metal impurities that combine with the sulfur and chlorine from the coal to form salts that deposit on the turbine blades, causing corrosion. This paper describes a new model, applicable to most types of coal, for predicting the dewpoint temperatures and deposition rates of these sodium and potassium salts. When chtorine is present the main atkati species in the mainstream gas flow are the chtorides; but when chlorine is absent, the Superoxides dominate. However, because the high-pressure turbine blades are film-cooled, they are at much lower temperatures than the mainstream gas flow and analysis then shows that the deposit is composed almost entirely of the sulfates in either liquid or solid form. This is true whether or not chlorine is present. Detailed calcutations using the new model to predict the alkali salt deposition rates on three stages of an example utility turbine are presented. The calculations show how the dewpoint temperatures and deposition rates vary with the gas-phase chlorine and sulfur levels as well as with the concentrations of sodium and potassium. It is shown that the locations where corrosion is to be expected vary considerably with the type of coal and the levets of impurities present.

Evaluation of the potential for hybridization of gas turbine power plants with renewable energy in South Africa

“…However, it has been shown that the combustion of this gas has adverse effect on the turbine blades due to the presence of inherent chemicals in the gas despite its cleaning before firing. The problem is that coal-derived syngases may contain alkali metal impurities that combine with the sulphur and chlorine elements from coal to form salts that are deposited on the turbine blades, causing corrosion [24]. A model developed by Young et al [24] for predicting dew point temperatures and deposition rates of sodium and potassium salts on turbine blades showed that when chlorine is present the main alkali species in the mainstream gas flow are the chlorides; but when chlorine is absent, the superoxides dominate.…”

“…The problem is that coal-derived syngases may contain alkali metal impurities that combine with the sulphur and chlorine elements from coal to form salts that are deposited on the turbine blades, causing corrosion [24]. A model developed by Young et al [24] for predicting dew point temperatures and deposition rates of sodium and potassium salts on turbine blades showed that when chlorine is present the main alkali species in the mainstream gas flow are the chlorides; but when chlorine is absent, the superoxides dominate. On the contrary, synthesis gases from biomass conversion do not contain alkali metals, hence their combustion has no significant effect on the turbine blades.…”

Hot corrosion of TBC‐coated components upon combustion of low‐sulfur fuels

“…[ 34 ] Müller and Escobar [ 35–38 ] used equilibrium calculations to analyze the dew points of released alkali metal species upon coal gasification and subsequent combustion in gas turbines to identify the risk of hot corrosion. Young et al [ 39 ] modeled the deposition of alkali sulfates on blade surfaces by performing thermodynamic equilibrium calculations utilizing JANAF data. Subsequently, they solved boundary layer equations for the diffusion of alkali species.…”