Dynamic Simulation of Gas Turbine Fuel Gas Supply System During Transient Operations

Abstract

The primary purpose of this paper is to simulate the fuel gas supply system of a gas turbine unit. This simulation allows determination of supply gas flow properties such as flow rate and pressure as a function of time. The concentration is on transient processes of heavy duty gas turbine such as startup, shutdown, emergency stop and load following. In the past, it was common to use a quasi steady assumption allowed the simulation of the gas turbine system. In this work, a one dimensional dynamic model of the gas flow in a fixed area pipe with friction is developed. This development is based on McCormack finite difference method in straight pipes combined with the method of characteristic at branches. The McCormack technique is based on prediction-correction of steps. Such a procedure will allow one to take into account the time delays and response time of various devices associated with the transient processes of the gas turbine system. The most important device in the pipeline system of a gas turbine is the control valve that adjusts the fuel gas flow by precise control of its traveling piston. This particular element is modeled and simulated similar to a standard nozzle entrance section. Such a modeling scheme considers a chocked flow through the control valve. The considered hydraulic circuit is comprised of a combination of simple gas pipes, valves, and pressure loss components (e.g., junctions, bends, fittings, and injection nozzles). By specifying the boundary conditions and the control valve piston position, a method is developed that allows simulation of such hydraulic circuits. In continuation, the above mentioned hydraulic circuit is considered as a fuel gas supply system for a heavy duty gas turbine operating in a power plant. The circuit is simulated, and such disturbances during start, shutdown, piston travel of the control valve, and break in power generation are taken into account. Finally, fuel flow properties during mentioned processes would be obtained as a function of time and an analysis of the simulation results is performed.