The Cause And Solution For Scale Formation On Gas Turbine Blade
In some case, the gas turbine blade might have scale formation which is difficult to clean. The volume and quality of scale formation on gas turbine blade depends on many factors, such as the gas turbine load, burning temperature, the nebulization level of fuel oil, the quality of fuel oil, the cleaning method of turbine and so on. Under normal circumstances, vanadium corrosion inhibitor would react with metal compounds in fuel under high temperature, to form high-melting-point solid-state inorganic double salt. Most of the double salt will flow out with exhaust gas as solid ash, a small part would stick on blade surface and most of it can be washed off, but little residual could still remain especially on the root of stationary blade, which needs to be cleaned with machine during the outage maintenance. Here to provide the analysis of cause and advice of solution according to the fuel oil specification below as an example, any other on-site factors that could impact the blade scaling needs to be analyzed case by case.
According to above table, the fuel oil belongs to heavy and high sulfur content fuel, and it has high contents of colloid and asphaltene. If the fuel temperature is not high enough before getting into the jet nozzle, the fuel nebulization by nozzle is incomplete, which the combustion could probably be incomplete, and hence impact the fluffiness of ash. As for high sulfur content, the sulfur trioxide, which is a combustion product of sulfur, will accelerate the polymerization of hydrocarbons, and make the carbon deposition increased and hardened, hence impact the fluffiness of ash which to be easily stick on blade surface to build up scale. The specification didn’t indicate the calcium content, if the calcium content is high, it will also be one of the reasons of scale hardness. Here to provide below suggestions of improvement for reference:
- Add additive to vanadium corrosion inhibitor which helps the dispersion and combustion to asphaltene and colloid, to make the combustion more sufficient, hence the blade scale can be fluffier and easier to be washed off.
- Increase the dosage of vanadium corrosion inhibitor, which has the function of neutralization of sulfur oxides, to reduce the impact of sulfur on ash content, and also reduce the machine corrosion by acidic sulfide.
If the calcium content of fuel is high, suggest to add decalcifying agent during the washing process of fuel oil, to make the fuel calcium content less than 10 ppm before it goes into the gas turbine.
Comparison of the performance between TianChen (TC) vanadium inhibitor and other vanadium inhibitor:
