3.2.2.1 Introduction
The axial-flow compressor section consists of the compressor rotor and the compressor casing as showing in Fig. (3.8). Within The compressor casings are the variable inlet guide vanes, the various stages of rotor and stator balding, and the exit guide vanes. 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) airfoil-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.
3.2.2.2 Compressor Components
1. Inlet Guide Vanes
Inlet guide vanes used at compressor inlet to ensure the air enters the first stage rotor as desired angle .in addition to the stators, another diffuser at the exit of compressor further diffuse the fluids and controls its velocity entering the combustor, Variable inlet guide vanes are located at the aft end of the inlet casing and are mechanically positioned, by a control ring and pinion gear arrangement connected to a hydraulic actuator drive and linkage arm assembly. The position of these vanes has an effect on the quantity of compressor inlet air flow as shown in Figure (3.9)
2. Rotor
The compressor portion of the gas turbine rotor is an assembly of wheels; a speed ring, tie bolts, the compressor rotor blades, and a forward stub shaft (see Figure (3.10). Each wheel has slots broached around its periphery. The rotor blades and spacers are inserted into these slots and held in axial position by staking at each end of the slot. 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 forward stub shaft is machined to provide the thrust collar, which carries the forward and aft thrust loads. The stub shaft also provides 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 stage 17 wheel carries the rotor blades and also provides the sealing surface for the high-pressure air seal and the compressor-to-turbine marriage flange.
3. Stator
The casing area of the compressor section is composed of three major sections:
a. Inlet casing
b. Compressor casing
c. Compressor discharge casing
These casings, in conjunction with the turbine casing, form the primary
structure of the gas turbine. They support the rotor at the bearing points and
constitute the outer wall of the gas-path Annulus. All of these casings are split
horizontally to facilitate servicing.
4. Inlet Casing
The inlet casing (Figure 3.12) is located at the forward end of the gas turbine. Its prime function is to uniformly direct air into the compressor. The inlet casing also supports the No. 1 bearing assembly. The No. 1 bearing lower half housing is integrally cast with the inner bell mouth. The upper half bearing housing is a separate casting, flanged and bolted to the lower half. The inner bell mouth is positioned to the outer bell mouth by nine airfoil-shaped radial struts. The struts are cast into the bell mouth walls.
They also transfer the structural loads from the adjoining casing to the forward support which is bolted and doweled to this inlet casing. Variable inlet guide vanes are located at the aft end of the inlet casing and are mechanically positioned, by a control ring and pinion gear arrangement connected to a hydraulic actuator drive and linkage arm assembly. The position of these vanes has an effect on the quantity of compressor inlet air flow
5. Compressor Casing
The forward compressor casing contains the stage 0 through stage 4 compressor stator stages. The compressor casing lower half is equipped with two large integrally cast reunions which are used to lift the gas turbine when it is separated from its base. The aft compressor casing contains stage 5 through stage 12 compressor stator stages. Extraction ports in aft casing permit removal of 13th-stage compressor air. This air is used for cooling functions and is also used for pulsation control during startup and shutdown
.
6. Compressor Discharge Casing
The compressor discharge casing is the final portion of the compressor section as shown in fig(3.13). It is the longest single casting, is situated at midpoint - between the forward and aft supports - and is, in effect, the keystone of the gas turbine structure. The compressor discharge casing contains the final compressor stages, forms both the inner and outer walls of the compressor diffuser, and joins the compressor and turbine casings. The discharge casing also provides support for the combustion outer casings and the inner support of the first-stage turbine nozzle. The compressor discharge casing consists of two cylinders, one being a continuation of the compressor casing and the other being an inner cylinder that surrounds the compressor rotor. The two Cylinders are concentrically positioned by fourteen radial struts. A diffuser is formed by the tapered annulus between the outer cylinder and inner cylinder of the discharge casing. The diffuser converts some of the compressor exit velocity into added static pressure for the combustion air supply.
7. Bleeding
The compressor rotor and stator blades are airfoil shaped and designed to compress air efficiently at high blade tip velocities. The blades are attached to the compressor wheels by dovetail arrangements. The dovetail is very precise in size and position to maintain each blade in the desired position and location on the
wheel. The compressor stators blades are airfoil shaped and are mounted by similar dovetails into ring segments in the first five stages. The ring segments are inserted into circumferential grooves in the casing and are held in place with locking keys. The stator blades of the remaining stages have a square base dovetail and are inserted directly into circumferential grooves in the casing. Locking keys hold them in place.
The axial-flow compressor section consists of the compressor rotor and the compressor casing as showing in Fig. (3.8). Within The compressor casings are the variable inlet guide vanes, the various stages of rotor and stator balding, and the exit guide vanes. 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) airfoil-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.
3.2.2.2 Compressor Components
1. Inlet Guide Vanes
Inlet guide vanes used at compressor inlet to ensure the air enters the first stage rotor as desired angle .in addition to the stators, another diffuser at the exit of compressor further diffuse the fluids and controls its velocity entering the combustor, Variable inlet guide vanes are located at the aft end of the inlet casing and are mechanically positioned, by a control ring and pinion gear arrangement connected to a hydraulic actuator drive and linkage arm assembly. The position of these vanes has an effect on the quantity of compressor inlet air flow as shown in Figure (3.9)
2. Rotor
The compressor portion of the gas turbine rotor is an assembly of wheels; a speed ring, tie bolts, the compressor rotor blades, and a forward stub shaft (see Figure (3.10). Each wheel has slots broached around its periphery. The rotor blades and spacers are inserted into these slots and held in axial position by staking at each end of the slot. 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 forward stub shaft is machined to provide the thrust collar, which carries the forward and aft thrust loads. The stub shaft also provides 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 stage 17 wheel carries the rotor blades and also provides the sealing surface for the high-pressure air seal and the compressor-to-turbine marriage flange.
3. Stator
The casing area of the compressor section is composed of three major sections:
a. Inlet casing
b. Compressor casing
c. Compressor discharge casing
These casings, in conjunction with the turbine casing, form the primary
structure of the gas turbine. They support the rotor at the bearing points and
constitute the outer wall of the gas-path Annulus. All of these casings are split
horizontally to facilitate servicing.
4. Inlet Casing
The inlet casing (Figure 3.12) is located at the forward end of the gas turbine. Its prime function is to uniformly direct air into the compressor. The inlet casing also supports the No. 1 bearing assembly. The No. 1 bearing lower half housing is integrally cast with the inner bell mouth. The upper half bearing housing is a separate casting, flanged and bolted to the lower half. The inner bell mouth is positioned to the outer bell mouth by nine airfoil-shaped radial struts. The struts are cast into the bell mouth walls.
They also transfer the structural loads from the adjoining casing to the forward support which is bolted and doweled to this inlet casing. Variable inlet guide vanes are located at the aft end of the inlet casing and are mechanically positioned, by a control ring and pinion gear arrangement connected to a hydraulic actuator drive and linkage arm assembly. The position of these vanes has an effect on the quantity of compressor inlet air flow
5. Compressor Casing
The forward compressor casing contains the stage 0 through stage 4 compressor stator stages. The compressor casing lower half is equipped with two large integrally cast reunions which are used to lift the gas turbine when it is separated from its base. The aft compressor casing contains stage 5 through stage 12 compressor stator stages. Extraction ports in aft casing permit removal of 13th-stage compressor air. This air is used for cooling functions and is also used for pulsation control during startup and shutdown
.
6. Compressor Discharge Casing
The compressor discharge casing is the final portion of the compressor section as shown in fig(3.13). It is the longest single casting, is situated at midpoint - between the forward and aft supports - and is, in effect, the keystone of the gas turbine structure. The compressor discharge casing contains the final compressor stages, forms both the inner and outer walls of the compressor diffuser, and joins the compressor and turbine casings. The discharge casing also provides support for the combustion outer casings and the inner support of the first-stage turbine nozzle. The compressor discharge casing consists of two cylinders, one being a continuation of the compressor casing and the other being an inner cylinder that surrounds the compressor rotor. The two Cylinders are concentrically positioned by fourteen radial struts. A diffuser is formed by the tapered annulus between the outer cylinder and inner cylinder of the discharge casing. The diffuser converts some of the compressor exit velocity into added static pressure for the combustion air supply.
7. Bleeding
The compressor rotor and stator blades are airfoil shaped and designed to compress air efficiently at high blade tip velocities. The blades are attached to the compressor wheels by dovetail arrangements. The dovetail is very precise in size and position to maintain each blade in the desired position and location on the
wheel. The compressor stators blades are airfoil shaped and are mounted by similar dovetails into ring segments in the first five stages. The ring segments are inserted into circumferential grooves in the casing and are held in place with locking keys. The stator blades of the remaining stages have a square base dovetail and are inserted directly into circumferential grooves in the casing. Locking keys hold them in place.
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