Operation of Gas Turbines in Heavy Fuel Oils
The continuing development of the gas turbine has resulted in its increased use for power generation throughout the world, especially in high efficiency combined cycle stations. Today there are gas turbines available which are capable of burning a wide range of fuels, even the lowest and cheapest grades of commercial fuel oil, and this flexibility has often been a crucial factor in its selection. Alfa Laval have developed and proved a range of fuel treatment systems which keep pace with the gas turbine technology. In addition to proven separation systems for cleaning fuel oil, the Alfa Laval equipment range has been extended to include fuel conditioning systems.
They now offer power stations a fully integrated fuel treatment system, from the fuel oil settling tanks to the gas turbine. For equipment suppliers and owners, this means a single supplier that can assume total responsibility, including service and spare parts, for the entire fuel treatment system - cleaning and conditioning. Fuel Conditioning Systems for gas turbine fuel oils are the systems which control the supply of fuel from the day tanks to the gas turbines. The functions of the Fuel Conditioning System will depend on the type of fuel oil and the specific conditions required at the gas turbine. A high content of filterable dirt in these oils usually means that self-cleaning filters must be employed in the fuel train otherwise cartridge filters would require frequent filter changes. Normally gas turbines burning heavy fuel oils crudes will have a backup supply of distillate required during start-up and shutdown operations. An important function of the Fuel Conditioning System is to select the desired fuel and precisely control the changeover in response to signals from the gas turbine operator. For low viscosity crude oils, some gas turbine manufacturers have units which can start up and close down directly on this type of fuel.
In such cases a fuel selection function will be unnecessary. Vanadium can cause high temperature corrosion in a gas turbine. It is present in fuel oils in a complex oil soluble form and cannot be removed by mechanical separation. When vanadium levels in the fuel oil exceed gas turbine manufacturers recommendations, it will be necessary to inhibit the vanadium to prevent high temperature vanadic corrosion. However, the use of magnesium-based additives has provided a commercially acceptable and practical solution to the problem.
In the presence of magnesium, vanadium forms non-corrosive compounds with high melting points during combustion. …