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GE 9 HA Compressor and Turbine Design
1.0 Introduction
1.1 General
The 9HA is a single-shaft gas turbine designed for operation
as simple cycle unit or in a combined steam and gas turbine cycle. The gas
turbine assembly contains six major section or groups
- Air Inlet
- Compressor
- Combustion system
- Turbine
- Exhaust gas system
- Support systems
This section briefly describes how the gas turbine operates
and the interrelationship of the major components.
1.2 Gas Path Description
The gas path is the path by which gases flow through the gas
turbine from the air inlet through the compressor, combustion section and
turbine, to the turbine exhaust.
When the turbine starting system is actuated, ambient air is
drawn through the air inlet plenum assembly, filtered and compressed in the
multi-stage, axial-flow compressor. For pulsation protection during startup,
compressor bleed valves are open and the variable inlet guide vanes (VIGV) and
variable stator vanes (VSV) are in the closed position. When the high-speed
relay actuates, the bleed valves begin operation automatically and VIGV and VSV
actuators energize to position the VIGV and VSV for normal Turbine operation.
Compressed air from the compressor flows into the e spaces between the outer
combustion casing and the combustion liners and enters the combustion zone
through metering holes in each of the combustion liners.
Fuel from an off-base source is provided to flow lines each
terminating at the primary and secondary fuel nozzles in the end cover of the
separate combustion chambers.
Options:
On liquid fuel machines, the fuel s controlled prior to
being distributed to the nozzles to provide an equal flow into each liquid fuel
distributor valve mounted on each end cover and each liquid fuel line on each
secondary nozzle assembly.
On gas-fuel machines the fuel nozzles are the metering
orifices which provide the proper flow into the combustion zones in the
chambers.
The nozzles introduce the fuel into the combustion zone
within each chamber where it mixes with the combustion air and is ignited by
one or more of the spark plugs. At the instant when fuel is ignited in the one
combustion chamber flame is propagated, through connecting crossfire tubes, to
all other combustion chambers where it is detected by four primary flame
detectors, each mounted on a flange provided on the combustion casings.
The combustion hot gases flow through the flow sleeves and
transition pieces and into the four-stage turbine section. Each stage consists
of a row of fixed nozzles and a row of turbine buckets.
In each nozzle row, the kinetic energy of the jet is
increased, with an associated pressure drop, which is absorbed as useful work
by the turbine rotor buckets, resulting in shaft rotation used to turn the
compressor and generator rotor to generate electrical power.
After passing through the fourth-stage buckets, the gases
are directed into the exhaust diffuser. The gases then pass into the exhaust
plenum and are introduced to atmosphere through the exhaust stack or go to HRSG
in combined cycle mode.
2.0 Base
and Supports
2.1
Turbine
Base
The base that support the gas
turbine is a structural steel fabrication of welded steel beams and plate. Its prime
function is to provide a support upon which to mount the gas turbine.
Lifting trunnions and support are
provided, two on each side of the base in line with the two structural cross
members of the base frame. Machines pads on each side on the bottom of the base
facilitate its mounting to the site foundation. Two machines pads, atop the
base frame are provided for mounting the aft supports
2.2
Turbine
Supports
The
9HA.01 has rigid leg-type supports at the compressor end and supports with top
and bottom pivots at the turbine end. The support legs maintain the axial and vertical
positions of the turbine, whole two gib keys coupled with the turbine supports
legs maintain its lateral position. One gib key is machined o the lower half of
with exhaust frame. The other gib key is machined on the lower half of the
compressor inlet casing. The key fit into guide block which are welded to the
cross beams of the turbine base. The keys are held securely in place in the
guide blocks with bolts that bear against the keys on each side. The key-and-block
arrangement prevents lateral or rotational movements of the turbine while
permitting axial and radial movement resulting from thermal expansion.
3.0 Compressor Section
3.1 General
The axial-flow compressor section consists of the compressor
rotor and the compressor casing. Within the compressor casing are the variable
inlet guide vanes, the variable stator vanes, the various stages of rotor and
stator blading, the exit guide vanes and the compressor exit diffuser.
In the compressor, air is confined to the space between the
rotor and stator where it is compressed in stages by a series of alternate rotating
(rotor) and stationary (stator) air-foil-shaped blades. The rotor blades supply
the force needed to compress the air in each stage and the stator blades guide
the air so that it enters the following rotor stage at the proper angle. The compressed
air exits through the compressor discharge casing to the combustion chambers.
Air is extracted from the compressor for turbine cooling and for pulsation
control during startup.
3.2 Rotor
The compressor portion of the gas turbine is an assembly of
wheels, a speed ring, a forward stub shaft (FSS), Tie bolts, the compressor
rotor blades, and a mid-shaft.
The first three wheels have slots broached around their periphery.
The rotor blades and spacers are inserted into these slots and held in axial position
by a ring on the forward side of each wheel. Wheels stages 4 through stage 14
have a circumferential position using blade-locks positioned at several
circumferential locations on each wheel. The wheels are assembled to each other
with mating rabbets for concentricity control and are held together with tie
bolts. Selective positioning of the wheels is made during assembly to reduce
balance correction. After assembly, the rotor is dynamically balanced.
The FSS is machined to provide the thrust collar, which
carries the forward and aft thrust loads. The FSS also provide the journal for
the NO. 1 Bearing, the sealing surface for the No.1 bearing Oil seals and the
compressor low pressure air seal.
The Mid shaft provides the sealing surface for several
high-pressure air seals, locations of balance weight grooves the
compressor-to-turbine marriage flange. Axial holes pass through the aft end of
the Mid Shaft to supply the first stage bucket cooling air compressor 14th
stage.
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