Fundamental of Gas Turbine FUEL 4 c = compressor b = burners 2 b t = turbine c t GENERATOR 3 AIR 1When the Brayton Cycle is worked out for a steady flowprocess, we have a simple gas turbine cycle.In a simple gas turbine cycle, combustion & exhaust occurat constant pressure and compression & expansion occurcontinuously.
General Description of GE 9001E• The Model Series 9001E gas turbine is a 3000 rpm, single shaft with a 14 combustor, reverse- flow combustion system, simple-cycle power package that basically requires only fuel & fuel connections, generator breaker and AC power source for turbine start-up.• The MS9001E is also available in a combined- cycle configuration for application utilizing a Heat Recovery Generator or similar device
Gas Turbine Unit• The gas turbine unit consists of a 17-stage axial flow compressor and a 3-stage power turbine.• Each section, compressor rotor & turbine rotor is assembled separately and joined together through bolt construction.• The assembled rotor is a three bearing design utilizing pressure-feed elliptical & tilt-pad journal bearings. This design assures that rotor-critical speed are above the operating speed for optimum turbine bucket/turbine shell clearances.
Gas turbine Components• The MS9001E gas turbine assembly consists of six major section or groups : 1. Air inlet 2. Compressor 3. Combustion system 4. Turbine 5. Exhaust 6. Support system
Gas Path DescriptionStarting system actuated - ambient air drawn in through inlet plenum -compress in 17 stages axial compressor - compressed air flow intoannular space surrouding 14 combustion chambers - flows into linersthrough metering holes.Fuel from off-base source divide into 14 equal flows lines - fuel isequally controlled into 14 nozzles - ignition by spark plugs - flamepropagate through crossfire tubes - combustion chamber pressurecauses spark plug retract from hot flame zone at operating speed.Hot gas from combustion chamber expand into 14 separate transitionpiece - flow through 3-stage turbine section (rows of fixed nozzles &rotating buckets) - In fixed nozzles (kinetic energy increased &pressure drop) - In moving buckets (kinetic energy turn to rotorrotation to generate electrical power)
Gas Path Description - continueAfter 3rd. Stage buckets - gases directed into exhaust hood& diffuser (a series of turning vanes to turn the gases fromaxial to radial direction, minimizing exhaust hood losses) -Gases pass into exhaust plenum - introduced to atmospherethrough exhaust stack.
Accessory Compartment• Several system involved in turbine operation located in this section : 1. Starting Mean 2. Fuel System 3. Lubrication & Seal Oil System 4. Hydraulic System 5. Cooling Water System 6. Atomizing Air System Major components - starting motor, torque converter & accessory drive gear.
Turbine Base & Support• Turbine base - supports the gas turbine & is a structural steel fabrication of welded steel beam & plates.• Turbine supports - gas turbine is mounted to its base by vertical supports at three locations : 1. Forward support 2. Two Aft supports (with cooling jacket) - on either side of exhaust frame• Gib key & Guide Block - Gib key is machined on lower half of turbine shell & fit into the guide block which is welded to the aft cross beam of turbine base (prevent lateral & rotational movement & permitting axial & radial movement for thermal expansion)
Compressor Section• The Axial flow Compressor section consists of : 1. Compressor Rotor 2. Enclosing Casing Within the compressor casing are Inlet guide Vanes (IGV), 17 stages of rotor & stator airfoil-shaped blades and exit guide vanes. The stator (casing) for compressor composed of four major sections : 1. Inlet casing 2. Forward Compressor casing 3. Aft Compressor casing 4. Compressor discharge casing
Combustion System• The combustion system is a reverse-flow type with 14 combustion chambers arranged around the periphery of the compressor discharge casing.• The major components consists of : 1. Fuel nozzles 2. Spark plug ignition system 3. Ultraviolet flame detector 4. Combustion wrapper 5. Combustion chamber - comb. liners & transition piece 6. Crossfire tubes
Turbine Section• The three-stage turbine section is the area where energy, in the form of high temperature pressurized gas produced by the compressor & combustion sections, is converted to mechanical energy.• Major components in the turbine section are : 1. Turbine rotor - consists of two wheel shafts, the 1st., 2nd. & 3rd. Stage turbine wheel with buckets & two turbine spacers. 2. Turbine stator - consists of turbine shell and exhaust frame. Turbine stationary nozzles, diaphragm, shroud, bearing no. 3 & exhaust diffuser are internally supported from these components.
Bearings• The MS9000 gas turbine unit contain three main journal bearings used to support the gas turbine rotor & thrust bearing to maintain rotor to stator axial position & support thrust load developed on the rotor. No. Class Type 1 Loaded Tilting pad -thrust equalizing 1 Unloaded Tilting pad - non thrust equalizing 1 Journal Elliptical 2 Journal elliptical 3 Journal Tilting pad.
Lubrication Oil System• The lubricating requirements for the gas turbine are furnished by a common forced-feed lubrication system. Lubricating fluid is circulated to the three main turbine bearings, generator bearings, reducing gear, accessory gear, as hydraulic oil in torque converter and also as control, trip oil, high pressure hydraulic oil & generator seal oil.
Lub. Oil System - continue• Such a system must supply cool, clean and pressurized oil to bearing. This lub. system includes the following : 1. Lub. oil reservoir in the accessory base (12,490 liter) 2. Main lub. oil pump (shaft driven from accessory gear). 3. Auxiliary lub. oil pump 4. Emergency lub. oil pump 5. Auxiliary & emergency seal oil pump 6. Lub. oil heat exchangers 7. Lub. oil filters. 8. Pressure relief valve VR1 in main pump discharge header (6.9) 9. Bearing header pressure regulator VPR2-1 (1.7 bars) 10. Mist Eliminator
Lub. oil system - control components• Some important operating parameters monitored by Speedtronic Mark V control system : 1. Oil Level Detection 71 QH = Level detector switch, Alarm when level is high (254 mm) 71 QL = Level detector switch, alarm when level is low ( 432 mm) 2. Pressure & Temperature Protective Devices 63QT-2A & 2B = Pressure switch in lub. oil feed piping to generator bearings. Trip turbine when < 0.55 bar 63QT-1A & 1B = Temperature switch in lub. oil header. Trip the turbine if temperature > 79.4o C 63 QQ-1 = Differential pressure switch alarm when pressure across oil filters of 1.03 bar (15 psi)
Lubricating oil Pumps• Main Oil Pump - positive displacement pump mounted on & driven by the accessory gear, rated 2725 lpm & 7 bar.• Auxiliary Oil Pump - submerged centrifugal pump driven by AC motor (88QA-1), rated 2460 lpm & 7.5 bar. Higher pressure for torque converter during slow roll & start-up. Starts when speed drop below 14HS (90% rated speed) stop when turbine attains 95% rated speed. Also when 63QA-1 sense a drop below 4.83 bar.• Emergency Lub. Oil Pump - submerged centrifugal pump driven by a DC motor (88QE-1). Rated at 1590 lpm & 1.4 bar. Back-up for AOP when 63QT-2A & 2B below 0.55 bar.
Seal Oil Pump• The seal oil to the generator bearings is normally supplied by the main lub. system through a separate line directly to the seal oil control unit of the generator. This line is plumbed into the system upstream of VPR2-1. The seal oil control unit will regulate the seal oil pressure to maintain it a nominal 0.32 bar above hydrogen gas pressure.• The seal oil pump is driven by two motors : AC motor - 88QS-1 DC motor - 88ES-1
Hydraulic Supply System• Hydraulic supply system provides fluid power required for operating the control components of the gas turbine fuel system. The fluid furnished the means for opening or resetting the fuel stop valves, in addition to the variable turbine inlet guide vanes and the hydraulic control & trip devices of the gas turbine.• Major system components includes the main hydraulic pump, an auxiliary supply pump, the system filters, an accumulator assembly and the hydraulic supply manifold assemblies.
Trip Oil System• The hydraulic trip oil system is the primary interface between the turbine protection system circuits of the Speedtronic Mark V Control System and the the components on the turbine which open the IGVs and allow fuel flow to turbine.• The trip oil system contains devices which are eletrically operated by Speedtronic control signals as well as completely mechanical devices that operate directly on trip oil system independent of the turbine control panel.• The trip oil system ensures that fuel flow is halted & the IGVs close at a unit trip.
Variable Inlet Guide Vanes (IGVs)• IGVs are used to control the airflow through the compressor, in turn controlling the airflow through the entire machine.• The IGVs modulate during the start-up and acceleration of the gas turbine to rated speed, loading & unloading of the generator and deceleration of the gas turbine during shutdown.• This modulation maintains proper flows & pressure, and thus stresses in the compressor during part-speed operation, maintains a minimum pressure drop across fuel nozzles while operating at 100% speed & also maintains high exhaust temperatures at low generator load level.
Starting System• Like other internal combustion engines, a gas turbine cannot produce torque at zero speed.• The starting mean system is used to start the gas turbine rolling, crank it to firing speed and assist the fired turbine to self-sustaining speed.• This is accomplished by an induction motor starting device operating through a torque converter coupled to the accessory gear.• This arrangement provides the cranking torque for turbine start-up. For shutdown, this continues to rotate the turbine rotor at slow speed for cool down purposes.
Dual Fuel System• This gas turbine has duel fuel capability. It supplied with both a natural gas & a liquid fuel (distillate) system.• While operating on gas fuel, if the gas fuel pressure should drop below a pre-set value, the control system will automatically transfer to liquid fuel operation.• There is no automatic transfer from liquid to gas, that transfer must be initiated by operator.• Mechanical fuel handling & electrical control components are incorporated in the design of capable of burning either two fuel individually or both fuels simultaneously.
Gas Fuel• The gas fuel system is designed to deliver gas fuel to the turbine combustion chambers at the proper pressures & flow rates to meet all of the starting, accelerating, loading requirements of gas turbine operation. Major components are : 1. Pneumatic block valve VA27-1 2. Y-type strainer 3. Gas stop/speed ratio (VSR) & control (VGC) valve 4. Fuel gas low pressure alarm switch 63FG 5. Gas pressure gauges & vent valves 6. Gas fuel hydraulic trip relay VH5 7. Valve control servo-valves 8. Valve control LVDTs 9. Gas manifolds to Comb. chambers. 10. Fuel metering system
Liquid Fuel• The liquid fuel system pumps and distributes fuel supplied from off- base fuel forwarding system to the fourteen fuel nozzles of the combustion system.• The fuel system filters the fuel & divides the fuel flow into 14 equal parts for distribution to the combustion chamber at the required pressure & flow rates.• Fuel pump bypass VC3 regulates the amount of fuel input to the turbine combustion chamber by varying amount of bypassed fuel. If valve closes, less fuel is circulated around the pump and more fuel goes to the combustors & vice versa.• The position of the bypass valve is a linear function of the Fuel Stroke Reference (FSR) generated by the Speedtronic Mark V Control.
Cooling & Sealing Air system• The cooling & sealing air system provides the necessary air flow from the compressor to the other parts of the gas turbine rotor & stator to prevent excessive temperature buildup in these parts during normal operation and sealing of the turbine bearings. Atmospheric air from external centrifugal blowers is also used cool the turbine exhaust frame.• Cooling & sealing function provided by the system are : 1. Sealing of turbine bearings 2. Cooling the internal turbine parts subjected to high temperature 3. Cooling of the turbine outer shell & exhaust frame 4. Providing an operating air supply for air operated valves 5. Compressor pulsation protection
Atomizing Air System• The atomizing air system provides high pressure air to atomize the liquid fuel as it enters the combustors. Atomization is necessary to ensure complete and proper combustion. The ration of atomizing air to compresor discharge pressure approx. 1.2 or greater. Major components : 1. Main atomizing air compressor (driven by accessory gear) 2. Starting atomizing air compressor 3. Atomizing air heat exchanger
Cooling Water System• The cooling water system is a closed system designed to accommodate the heat-dissipation requirements of the turbine & generator lub. oil system, the atomizing air precooler, the water cooled flame detector and turbine support legs.• On-based components includes lub. oil heat exchanger in accessory base, turbine aft support legs, atomizing air heat exchanger& heat exchanger of generator’s air cooling system.• The hot water of the cooling water system is then cooled by off-base industrial type water cooling module.
Fire Protection System• The carbon dioxide fire protection system extinguished fires by reducing the oxygen content of the air in the compartment from an atmospheric normal of 21% to less than 15%, an insufficient concentration to support combustion.• To reduce the oxygen content, a quantity of carbon dioxide equal or > than 34% of the compartment volume is discharge into the compartment in one minute and recognizing the reflash potential of combustibles exposed to high temperature metal, it provides an extended discharge to maintain an extinguishing concentration for a prolong period to minimize likelihood of reflash condition.
Compressor Water Wash System• Gas turbine can experience a loss of performance during operation as result of deposits of contaminants on internal components. The deposits of atmospheric contaminants on the compressor parts occur with the ingestion of air. This contaminants can be removed by washing with water-detergent solution followed by a water rinse.• Major components for Compressor Water Wash System : 1. On- base Equipment 2. Off-base Equipment• Two type of water wash procedures : 1. Off-line Compressor Wash 2. On-line compressor Wash
Gas Turbine Maintenance• Classification Gas Turbine Maintenance ; 1. Standby Inspection 2. Running Inspection 3. Dis-assembly Inspection Dis-assembly Inspection can be classified into : 1. Combustion Inspection 2. Hot Gas Path Inspection 3. Major Inspection