Fuel Gas is normally supplied from the Compressor discharge with back-up take-off from MP separator gas outlet header. At start-up, the gas wells should be run first to provide fuel gas. Alternatively, gas may be sourced from Separator.
The gas will initially pas through the HP fuel gas scrubber for removal of any entrained liquids, prior treatment to ensure the fuel gas specification of the turbine is satisfied. The liquid in the suction scrubber is drained to the HP flare system under level control via level controller. The operating pressure is controlled by pressure controller.
HP Fuel gas will be heated in the HP fuel gas treater to a temperature of at least 27 degC above the dew point of the fuel gas by Differential temperature controller prior to delivery to the compressor or gas turbine generator. The heater is provided with a warm up line located at the common heater outlet header. The line shall be opened during start up to warm up the gas to achieve the required differential temperature before feeding gas to the turbines.
Control loop description
Pressure controller
The controller maintains a constant pressure in the fuel gas scrubber at desired pressure by actuating control valve. If the pressure continues to fall, the pressure controller will actuate control valve. The control valve is fail closed type. The controller input signal shall be reverse acting and the control valve OPDIR is direct. As the pressure falls below the setpoint, the controller shall open the control valve to increase the pressure.
Level controller
The level control is performed by opening and closing the level control valve between ON and OFF levels using GAP control configuration.
Control valve is fail closed type. As the level reaches the ON set point, the controller will open the control valve to decrease the liquid level and close the control valve when the level reaches the OFF setpoint,
Differential temperature controller
The differential temperature controller maintans constant superheated to the fuel gas by regulating the operating heater control panel. The heater is equipped with thyristor control to provide the various heat loads required to maintain the fuel gas superheat, When the high and low differential temperature threshold is reached. The alarms shall be displayed on the HMI.
A remote star and stop command is provided such that the heater can be manually started from Control room by using pulsed signal.
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