Tests were run on four inter-cooled regenerative high-temperature gas turbines of like design to measure the effect of burning several different residual fuels. Some of the tests were made with the help and co-operation of the Central Vermont Public Service Corporation on two of their units at Rutland, Vermont. Other tests were made at Bangor, Maine, with the help and co-operation of The Esso Research and Engineering Company, and the Bangor Hydroelectric Company, on the two units in the Graham Station. The results of the tests can be summarized as follows:
1. After a few hundred hours of intermittent operation, the first-stage nozzle area reaches a steady-state condition wherein it oscillates between zero and a maximum of about 8 percent reduction in area due to oil ash. The maximum reduction varies from 4 percent to 8 percent, depending on the fuel;
2. With continuous operation the first-stage nozzle area does not reach a steady-state value in 100 hours but plugs more or less continuously at rates varying from 5 to 24 percent per hundred hours, depending on the fuel. The load decreases also at rates varying from one to twenty percent in the same period;
3. Increasing the magnesium content of the fuel with respect to its vanadium content increases the deposition rate, but increasing the aluminum with respect to the vanadium content has the opposite effect;
4. Substantial temperature changes due to load variations and changes of firing temperature have little or no effect on dislodging the ash, but shutdowns in excess of two hours duration cause recoveries of over 70 percent in the area and over 50 percent in the load;
5. Introducing about 15 pounds of spent refinery catalyst into the low-pressure compressor inlet results in more than 40 percent recovery in the nozzle area and about the same recovery in the load. This cleaning operation, followed by a shutdown, results in practically complete recovery in both load and area during subsequent operation.
A test was run for 2400 hours with a single residual fuel containing about 360 ppm of vanadium following 2700 hours operation on distillate fuel. Comparisons of the gas-path parts with those of two other units of the same design, one using a residual oil having 80 ppm of vanadium and the other using natural gas, lead to the following conclusions:
1. The life of the gas-path parts is no different whether a high vanadium or a low vanadium residual fuel is used;
2. The corrosion of the nozzles and buckets is not much greater with treated residual oil than with natural gas.