2.2 TURBINE BASE AND SUPPORTS

2.2.1. TURBINE BASE

Description :
The base upon which the gas turbine is mounted is a structural-steel fabrication of welded  steel beams and plate. It forms a single platform which provides support upon which to mount  the gas turbine.

In addition, the base supports the gas turbine inlet and exhaust plenums. Lifting trunnions and supports are provided, two on each side of the base in line with the structural cross members of the base frame. Machined pads, three on each side of the bottom of the base, facilitate its mounting to the side foundation. Two machined pads, atop the base frame are provided for mounting the aft turbine support.


2.2.2. TURBINE SUPPORTS

Description :

The gas turbine is mounted to its base by vertical supports. The forward support is located at the lower half of the vertical flanges of the forward compressor casing, and the aft two support-legs are located on either side of the turbine exhaust frame.

The forward support is a flexible plate that is bolted and doweled to the turbine base, at the forward base cross frame beam, and bolted and doweled to the forward flanges of the forward compressor casing.

The aft supports are leg-type supports, located one on each side of the turbine exhaust frame. Both vertical support legs rest on machined pads on the base and attach snugly to the turbine exhaust-frame-mounted support pads. The legs provide center-line support to supply casing alignment.

Fabricated to the outer surface of each aft support leg is a water jacket. Cooling water is circulated through the jackets to minimize thermal expansion of the support legs and assist in maintaining alignment between the turbine and the generator. The support legs maintain the axial and vertical positions of the turbine, while a gib key coupled with the turbine support legs maintains its lateral position.

 

Drawings of the turbine supports.

 

Forward Turbine Support

 Aft Turbine Support Leg 

(one on each side)

2.2.3. GIB KEY AND GUIDE BLOCK

Description :
A gib key is machined on the lower half of the turbine shell. The key fits into a guide block which is welded to the turbine base aft cross beam. The key is held securely in place in the guide block with bolts that bear against the key on each side.

This key-and-block arrangement prevents lateral or rotational movement of the turbine while permitting axial and radial movement resulting from thermal expansion.

2.1. GENERAL, FUNCTIONAL DESCRIPTION

2.1.1. GENERAL ABOUT GAS TURBINE UNITS
A package power plant, as furnished for most installations, is comprised of the single-shaft, simple cycle, heavy duty gas turbine unit driving a generator. Fuel and air are used by the gas turbine unit to produce the shaft horsepower necessary to drive certain accessories and ultimately the driven load generator.

The turbine unit is composed of a starting device, support systems, an axial-flow compressor, combustion system components, a three-stage turbine. Both compressor and turbine are directly connected with an in-line, single-shaft rotor supported by two pressure lubricated bearings. The inlet end of the rotor shaft is coupled to an accessory gear having integral shafts that drive the fuel pump, lubrication pump, and other system components.

2.1.2. GENERAL ABOUT GAS TURBINE UNITS
(Figure at the end of paragraph 2)
When the turbine starting system is actuated and the clutch is engaged, ambient air is drawn through the inlet plenum assembly, filtered, then compressed in the 17th stage, axial flow compressor. For pulsation protection during start-up, the 11th stage extraction valves are open and the variable inlet guide vanes are in the closed position.

When the speed relay corresponding to 95 per cent speed actuates, the 11th stage extraction bleed valves close automatically and the variable inlet guide vane actuator energizes to open the inlet guide vanes (I.G.V.) to the normal turbine operating position.

Compressed air from the compressor flows into the annular space surrounding the fourteen combustion chambers, from which it flows into the spaces between the outer combustion casings and the combustion liners.

The fuel nozzles introduce the fuel into each of the fourteen combustion chambers where it mixes with the combustion air and is ignited by both (or one, which is sufficient) of the two spark plugs.

At the instant one or both of the two spark plugs equipped combustion chambers is ignited, the remaining combustion chambers are also ignited by crossfire tubes that connect the reaction zones of the combustion chambers. After the turbine rotor approximates operating speed, combustion chamber pressure causes the spark plugs to retract to remove their electrodes from the hot flame zone.

The hot gases from the combustion chambers expand into the fourteen separate transition pieces attached to the aft end of the combustion chamber liners and flow towards the three stage turbine section of the machine. Each stage consists of a row of fixed nozzles followed by a row of rotatable turbine buckets. In each nozzle row, the kinetic energy of the jet is increased, with an associated pressure drop, and in each following row of moving buckets, a portion of the kinetic energy of the jet is absorbed as useful work on the turbine rotor. After passing through the 3rd stage buckets, the exhaust gases are directed into the exhaust hood and diffuser which contains a series of turning vanes to turn the gases from the axial direction to a radial direction, thereby minimizing exhaust hood losses. Then, the gases pass into the exhaust plenum.

The resultant shaft rotation is used to turn the generator rotor, and drive certain accessories.

NOTE :

Throughout this manual, reference is made to the FORWARD and AFT ends, and the RIGHT and LEFT sides of the gas turbine and its components.
By definition, the air inlet of the gas turbine is the forward end, while the exhaust end is the aft end. The forward and aft ends of each component are determined in like manner with respect to its orientation within the complete unit.
The RIGHT and LEFT sides of the turbine or of a particular component are determined by standing forward and looking aft.

 

Simple Cycle Gas Turbine Flow Diagram

2. GAS TURBINE SUMMARY CONTENTS

2.1. GENERAL, FUNCTIONAL DESCRIPTION

            2.1.1. GENERAL ABOUT GAS TURBINE UNITS

            2.1.2. GAS TURBINE FUNCTIONAL DESCRIPTION

2.2. TURBINE BASE AND SUPPORTS

            2.2.1. TURBINE BASE

            2.2.2. TURBINE SUPPORTS

            2.2.3. GIB KEY AND GUIDE BLOCK

2.3. COMPRESSOR SECTION

            2.3.1. GENERAL

            2.3.2. COMPRESSOR ROTOR

            2.3.3. COMPRESSOR STATOR

2.4. COMBUSTION SECTION

            2.4.1. GENERAL

            2.4.2. COMBUSTION WRAPPER, COMBUSTION CHAMBERS AND CROSSFIRE TUBES

            2.4.3. SPARK PLUGS AND FLAME DETECTORS

            2.4.4. FUEL NOZZLES WITH DUAL CAPABILITIES (GAS)

            2.4.5. TRANSITION PIECES

            2.4.6. FALSE START DRAIN

2.5. TURBINE SECTION

            2.5.1. GENERAL

            2.5.2. TURBINE ROTOR

            2.5.3. TURBINE STATOR

            2.5.4. EXHAUST FRAME AND DIFFUSER

2.6. BEARINGS

            2.6.1. GENERAL

            2.6.2. DESCRIPTION

2.7. COUPLINGS

            2.7.1. GENERAL

            2.7.2. ACCESSORY GEAR AND LOAD COUPLING

2.8. ENCLOSURES

            2.8.1. GENERAL

2.9. INLET AND EXHAUST SECTIONS

            2.9.1. AIR INLET SYSTEM

            2.9.2. EXHAUST SYSTEM

1. EQUIPMENT DATA

1.1. GAS TURBINE DESIGN DATA

            TYPE : PG 9171 E

            GAS TURBINE APPLICATION : GENERATOR DRIVE

            CYCLE : COMBINED CYCLE

            TYPE OF OPERATION : BASE

           

            COMPRESSOR : STAGE : 17 SPEED : 3000 R.P.M.

            TURBINE : STAGE : 3 SPEED : 3000 R.P.M.

 

1.2. GAS TURBINE EQUIPMENT DATA SUMMARY

            COMPRESSOR SECTION

                        Number of compressor stages - Seventeen (17)

                        Compressor type -  Axial flow, heavy duty

                        Casing split  - Horizontal flange

                        Inlet guide vanes type - Modulated

            TURBINE SECTION

                        Number of turbine stages - Three (3) single shaft

                        Casing splits - Horizontal

                        Nozzles - Fixed area

            COMBUSTION SECTION

                        Type - Fourteen (14) multiple combustors, reverse flow design

                        Fuel nozzles - One (1) per combustion chamber

                        Spark plugs - Two (2), electrode type. Spring-injected self-retracting

                        Flame detectors

                                    Eight (8), ultra-violet type

                                    Four (4) primary

                                    Four (4) secondary

            BEARING ASSEMBLIES

                        Quantity - Three (3)

                        Lubrication - Pressure lubricated

                        N° 1 bearing assembly (located in inlet casing assembly)

                                    - Active and inactive thrust and journal, all contained in one assembly

                        Journal - Elliptical

                        Active thrust - Tilting pad, self-equalizing

                        Inactive thrust - Tapered land

                        N° 2 bearing assembly (located in the compressor discharge casing)

                                    - Elliptical journal

                        N° 3 bearing assembly (located in the Exhaust frame)

                                    - Journal, tilting pad

            FUEL SYSTEM

                        Operating type - Natural gas DLN

                        Fuel control signal - SPEEDTRONIC control system

                        Gas stop/ratio and control - Electro-hydraulic servo-control valves 

            LUBRICATION SYSTEM

                        Lubricant - Petroleum base

                        Total capacity - 3,300 gallons (approx.) i.e. 12,491 liters (approx.)

                        Main lube pump - Shaft-driven, integral with accessory gear

                        Auxiliary lube pump - A.C. motor-driven, vertical, submerged, centrifugal type

                        Emergency lube pump - D.C. motor-driven, vertical, submerged, centrifugal type

                        Heat exchanger(s) :

                                    Type - Oil heat to fresh water

                                    Quantity - Two in parallel

                        Filter(s) :

                                    Type - Full flow with transfer valve     

                                    Quantity - One (1)

                                    Cartridge - type Five micron filtration pleated paper

            COOLING WATER SYSTEM (in closed loop)

                        Pumps - Two (2) water pumps located on the water skid outside of the G.T. building

            CONTROL - SPEEDTRONIC MARK VI control system

            PROTECTION - Over temperature, vibration, flame detection

            BLEED HEATING SYSTEM