Abstract
Sodium in gas-turbine fuel causes rapid deposit formation as well as corrosion. Besides naturally contained sodium, sea-water contamination during transportation introduces additional amounts. In order to obtain the benefits of a low-sodium fuel, 90 per cent or more of the sodium is washed out of the fuel by a scheme described. The results of the desalting show that calcium also can be reduced substantially. Turbine tests of 50 to 1500 hr duration using these desalted fuels show that deposit can be almost eliminated by keeping both the sodium and the calcium below 10 parts per million. The steady-stage decrease in turbine efficiency resulting from burning these low-sodium, low-calcium fuels is shown to be about 2 per cent and the reduction in regenerator effectiveness about 5 points. A specification is proposed, defining a fuel which can be obtained at the point of use by means of the desalting method described and by adding a water solution of magnesium sulphate to the fuel just before it is burned. Treating vanadium-containing fuels with calcium or magnesium shows that, below 1650 F, magnesium is a better inhibitor than calcium and, since magnesium does not cause deposit, it is used. Lead in the fuel in sufficient quantities is shown to spoil, somewhat, the inhibition of vanadium by means of magnesium. There now appear to be at least two methods available for modifying residual fuel to make it suitable for long-life gas turbines, one of which is described herein.
