The Power Generator for GTP runs only on Fuel gas system. The schematic sketch of the Gas Turbine is given below:
Fig. 7 – Schematic sketch of a Gas Turbine
The various systems of a Gas Turbine Unit are described below:
Lubrication Oil
The lubrication oil system has three pumps (Auxiliary, main and emergency) to
circulate oil to provide cooling and lubrication of the turbine, gearbox and driven unit bearings. The control system will operate the auxiliary pump when the main gearbox pump is unable to deliver sufficient lubrication oil pressure (during turbine run up and run down). The Emergency Oil Pump is used to supply lubrication oil to the hot section bearings and will be operated when the auxiliary pump has failed to deliver sufficient pressure. Oil pressure is monitored by a low pressure transmitter and will initiate a turbine shutdown when the oil pressure is insufficient to maintain safe turbine
operation. Lubricating oil temperature, monitored using a thermocouple, is maintained within operating limits by the use of a tank heater and a thermostatically controlled cooler. The lubrication oil tank is fitted with level and temperature monitoring, and
heater control to ensure there is sufficient oil at the required temperature for turbine operation.
Up to 2 additional oil tank heaters for cold ambient
Triple oil cooler fans with vibration switches
Oil supply temperature high trip transmitterGas Fuel
Gas fuel is supplied to the engine burners via an off-skid block and vent system, an on- skid double block and vent system, and metering valves. The control system positions and monitors the block and vent valves dependant upon the operating requirements. During a start the integrity of the on-skid block and vent valves is proved by pressure rise and fall tests. In cold climates the control system can be configured to flow gas to vent (for a short period) to ensure it is above a minimum temperature that is safe to run the engine. The fuel metering valves are positioned by an independent integrated gas fuel valve controller depending on current fuel demand from the turbine governor, and local gas fuel pressure and temperature. There is also provision for the operator to initiate a Controlled change from gas fuel running to liquid fuel running.
Liquid Fuel and Purge
Control is provided for an off-skid fuel forwarding pump (customer supply), an off-skid block valve, an on-skid boost pump, metering valves, and block valves. Prior to the block valves there are prime valves which are operated to ensure that the liquid fuel system is full. A prime is initiated during a liquid fuel start, prior to a change to liquid fuel and periodically while running on gas fuel. During the liquid fuel prime a small amount of liquid fuel is pumped into the turbine drains tank. The controller sequences the pumps and valves and positions the metering valve to obtain light-up, stable running, fuel changeover and turbine shutdown.
The liquid burner system is purged using process air or air from the turbine compressor. The valves that control the purge and air selection are operated automatically by the control system on a shutdown or after a changeover from liquid fuel in order to minimise carbon build up on the burners.
There is also provision for the operator to initiate a controlled change from running liquid fuel to running gas fuel. The liquid fuel system is often used as a standby fuel in case of a problem with gas fuel supply. As such the controller is capable of
automatically changing to liquid fuel if such condition arises. An automatic change from gas fuel to liquid fuel will be initiated should a rapid reduction in gas pressure be detected or the differential pressure across the gas throttle fall below 1.9 bar.
Elements
Gas assisted liquid starting
Propane assisted liquid startingGovernor
The turbine governor controls gas turbine speed by varying fuel demand to the fuel system metering valves. The fuel demand is calculated using turbine shaft speed, gas
path temperatures, gas path pressures, and turbine load. The turbine gas path
temperatures (Gas exhaust temperatures are used to optimise the turbine performance and keep it within operating limits. Deviation from the limits is protected by initiating a turbine shutdown. The turbine gas path pressures (gas generator inlet, compressor delivery, and interduct) are measured to ensure that the gas turbine is running within its operating envelope. Any deviation from the operating envelope will initiate turbine shutdowns.
The turbine shaft speeds (gas generator and power turbine) are measured to ensure that the turbine is not approaching or in an over speed condition. The turbine bearing temperatures are measured to protect the bearings from over-temperature. The radial movement of the turbine shafts is monitored to detect high levels of vibration.
Ventilation System
The turbine enclosure is fitted with a ventilation system to provide cooling for the gas turbine and enclosure mounted equipment and a gas free environment in which to operate the turbine.
The control system will operate the ventilation fan to maintain a purged enclosure while the unit is operating and afterwards during the cooling period. While the fan is running the enclosure air flow is monitored to ensure it is sufficient to supply adequate cooling and maintain a fully purged enclosure.
Elements
Dual vent fans operating as duty/standby where the operator has the ability to select the duty fan.
Differential pressure monitoring of the ventilation inlet filter to indicate to the operator that the filters are blocking and require servicing.
An inlet filter scavenge fan which runs when the enclosure ventilation system is running.Combustion Inlet and Exhaust
The combustion inlet is fitted with a filter across which the differential pressure is monitored to advise the operator that servicing is required. If this does not happen, the increasing differential pressure will eventually cause the turbine to be
automatically shutdown Elements
A scavenge fan fitted to the combustion inlet filter.
Fire and Gas Monitoring System
The turbine controller (PLC) monitors the fire and gas detection system. If the fire controller detects a fire it signals the PLC to initiate a turbine shutdown, the gas fuel system will be isolated/vented, enclosure ventilation fans are inhibited, enclosure dampers will close and the emergency lubricating oil pump will run.
The level of gas present at the turbine enclosure ventilation exit is measured and if the level detected is too high then a turbine shutdown is initiated and the gas fuel system is isolated and vented. The enclosure ventilation fan will continue to run to extract the gas. The level of gas present at the turbine enclosure
ventilation/combustion inlet is measured and if the level detected is too high then a turbine shutdown is initiated and the gas fuel system is isolated and vented. The enclosure ventilation fan will be isolated to prevent gas being drawn into the enclosure.
Turbine Compressor Washing System
The turbine has connections for a compressor washing system. Washing can be initiated with the turbine stopped (cold wash) or with the turbine running (hot wash). The operator connects the wash module to the turbine and initiates a wash sequence which comprises of a wash cycle followed by a rinse cycle.
Seal Air System
The turbine uses process air and P2 air from the compressor (when the shaft is rotating at speed where sufficient pressure is being developed) to provide a seal which
prevents oil carry over from the bearings. The controller operates a valve to supply the process air to the seals during turbine run up and shutdown. The pressure of the sealing air is measured to ensure it is within turbine operational limits.
Fluid Drains System
The off package drains tanks (Supplied by Siemens for hydrocarbons, water wash, oil, etc) are monitored by high level warning and shutdown transmitters respectively. Control is provided for an automatic drain valve to ensure that any remaining fluids are drained from the turbine into the drains system prior to running.
Starter System
Control is provided for a hydraulic starter system. The control system drives the starter system to spin the gas turbine during start up and shutdown, and accelerate it during the start sequence. The windings of the electric motor are monitored to prevent damage by overheating.
Air Flow Control
The air flow through the engine is controlled by modulating the variable guide vanes and blow off valve, and operating the interstage bleed valves. The interstage bleed valves are used to prevent a compressor surge during the run up. The variable guide vanes are used during a turbine start to control the air flow into the compressor to prevent engine surge. They can also be used for emissions control while running. The blow off valves are operated to prevent the engine from over speeding during a load reduction. Control of these devices will keep the engine within its operating envelope and prevent events such as surge and over speed.
Driven Unit Generator
The generator windings, bearings and cooling air are all monitored to protect
components against over temperature. Control of dual cooling fans and monitoring of a filter’s differential pressure is provided.