The fuel cost of gas turbines can be more than 80 percent of the total cost of electricity even for combined cycle plants. Generally, utilities, marine, and industrial plants are gradually looking for options to run lower cost alternative fuels. Consequently, new applications and technologies have been developed to meet the increasing demand for fuel flexibility.
The principal fuel for aeroderivative gas turbine is natural gas, that is clean fuel yet relatively inexpensive when compared to the majority of fossil fuel options like kerosene and diesel. A number of other liquid and gas fuels can also be burned with minimal modifications on the turbine and fuel cleaning.
Ultimately, the bulk replacement of fossil fuels is not going to happen anytime soon. Global power generation and commerce rely on fossil fuels. On the other hand, biofuels are on a growth path through mandates within the transportation sector even though they are only competitive in terms of pricing when subsidized.
Synthetic gas fuels have also gained popularity even though they are not accessible in volumes enough to support the energy needs of the world. Even then, there are fuels of opportunity that make both social and economic sense. Here is an exploration of those fuels as well as challenges and solutions associated with using them for the aeroderivative gas turbine power generation:
This is mainly derived from sugarcane in Brazil or corn in the US and is one of the biofuels that are most efficient in terms of carbon emissions and energy balance. About 80 percent of ethanol that is produced in the world is used as fuel, mostly by land based vehicles with less than 10 percent going into the beverage industry while another 10 percent goes into industrial products mainly solvents, medicines, and paints.
Two GE LM6000 PC aeroderivative have been converted to run on ethanol at a power plant in Brazil. This enhances the reliability and security of the plant by providing an alternative source of fuel that is valuable. The plant is the world’s first to use ethanol gas turbine system in the production of electricity on a commercial scale. While the performance of the turbine is the same, the ethanol flow needed is 1.6 times more compared to diesel.
Compatible components must be carefully selected when using biodiesel as it has detrimental effects on elastomers that are found in sealants and gaskets of a typical turbine engine package. Biodiesel has a heating value that is less than that of diesel by around 10 percent hence to get the same power; the output fuel flow needs to be increased. Among the main advantages of biodiesel is lubricity where it may be used to increase lubricity of fossil fuels like ultra-low sulfur diesel. In addition, it is clean when burnt and creates about 60 percent less net carbondioxide emissions compared to diesel engines.
- Synthetic gases
Tomorrow’s power generation technology demands fuel flexibility. Consequently, hydrogen-based fuels or biogas will be increasingly used in the mix of gas turbine simple and combined cycle power plant operations. Even then, this must be approached with caution, as high hydrogen fuels tend to pose ignition risks when initiating the flow of gas and following the termination of the flow of gas to the gas turbine.
- LNG Fuels
Owing to the fact that natural gas fuel reserves are usually remotely located from the major centres of demand, there is need for transportation. About a third of the natural gas internationally traded is transported in form of liquefied natural gas (LNG) 3. This is a mixture of gasses, predominantly methane that is liquefied at a temperature of -262°F (-163 °C).
- NGL fuels
Natural Gas Liquids may be burned in aeroderivative gas turbines depending on the ratios of hydrocarbon components. The major consideration is the hydrocarbon dew point and bubble point temperature as a function of pressure.
Aeroderivative gas turbines exhibit excellent performance on standard fuels like petrodiesel and natural gas. Consequently, there is a growing demand to burn alternative fuels of opportunity that would lower the cost of operating gas turbines while improving emissions. Contact us now for consultancy about efficiency and optimization of gas turbine fuel.