Sodium Sulfate in Gas Turbines★

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Abstract
Sodium sulfate forms when residual fuels are burned in gas turbines. Its presence in the deposits which may appear on the working surfaces has undesirable physical and chemical effects. The physical effects are discussed in terms of sintering and melting. The chemical effects considered are the various possible corrosion reactions. Although all of these reactions are complex, simplified mechanisms for them are proposed, which are consistent with the experimental results and with general experience. In particular, the violent destruction of a high temperature alloy by sodium sulfate in large excess is attributed to the triggering of an autocatalytic reaction involving this salt. Even with thin films of sodium sulfate, enhanced oxidation is observed when the atmosphere is alternately reducing and oxidizing. The following mechanism is suggested for this enhancement. Lower-valent sulfur produced in a reducing environment leads to the formation of a liquid metal-metal sulfide eutectic, which penetrates the alloy. The metal dissolved in this eutectic is more rapidly oxidized by atmospheric oxygen than is the sulfur-free alloy. Sodium sulfate itself appears to be innocuous so long as all lower-valent sulfur is absent. Because sodium sulfate will be formed from any sodium compound present in residual fuels, the General Electric Gas Turbine Department has undertaken large-scale measures to remove sodium compounds from the fuels before combustion. Results so far are promising.

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