Choice criteria in the composition of fuel applied in gas turbine installations with minor fuel system modifications

The present study is aimed at determining criteria for selecting the optimal composition of fuel applied in gas turbine installations while avoiding major alterations of the fuel system. During operation and commissioning of gas turbine units, all fuel parameters must meet quality re-quirements. Although the primary fuel used in gas turbine units included in combined-cycle plants is natural gas, it is possible to apply a wide range of gaseous fuels. Due to the content of the main components and impurities, the thermodynamic properties of each fuel can vary significantly, af-fecting the composition of the combustion products, as well as the integral parameters of the gas turbine installation. In this connection, since the automatic control system must reliably perform its functions within a certain limit of this characteristic, the flow rate of the fuel gas comprises a critical parameter. The Wobbe index is applicable in technical approaches for approving the use of a particular fuel gas for a given gas turbine with a certain accuracy and without reconfiguring the automatic control system. In the present study, a GE PG111 6FA gas turbine unit was used. A mathematical model was created to study the effect of fuel variant on turbine performance. In order to eliminate damage of the combustion chamber and hot gas path, it is necessary to fulfil the requirements for condensation of moisture and hydrocarbons in the fuel gas. Therefore, conden-sation dependences for hydrocarbons and moisture in the fuel gas are also presented. In cases of acceptable application of fuel gases satisfying the Wobbe index, the effect of these values on the performance of gas turbine fuel systems is shown. Out of four types of gas fuels considered in the study, only the gas obtained from the Stepanovskoye field met the requirements of the Wobbe index, allowing its substitution for the originally-intended fuel without necessitating alterations to the fuel system.

combined cycle gas turbine, gas turbine plant, fuel gas, fuel composition, Wobbe index, hydrocarbons