1.3.2-GE 9 HA Compressor and Turbine Design

3.3 Casings of Compressor

The casing area of the compressor section is composed of three major sections. These are the:

·         Inlet casing

·         Compressor casing

·         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.

3.3.1 Inlet Casing

The inlet casing is located at the forward end of the gas turbine. its primary function is to uniformly direct air into the compressor. the inlet casing also support the No.1 bearing assembly. The No.1 bearing assembly housing is a separate component assembled into the inner bellmouth. The upper half bearing housing is flanged and bolted to the lower half bearing housing. The inner bellmouth is positioned to the outer bellmouth by nine air foil-shaped radial struts. The struts are cast into the support which is bolted and doweled to this inlet casing.

The inlet casing lower half is equipped with two large integrally cast trunnions which are used to lift the gas turbine.

Variable inlet guide vanes (VIGV) are located at the aft end of the inlet casing and are mechanically positioned, by a control ring and vane arm arrangement connected to an actuator drive and linkage arm assembly. The position of these vanes has a effect on the quantity of compressor inlet air flow.

3.3.2 Compressor Casing

The compressor casing contains the variable stator vane stage 1 through stage 3 and the fixed stator stage 4 through stage 8. Each stage of variable stator vanes is mechanically positioned, by a control ring and vane arm arrangement connected to an actuator drive through a torque tube and linkage arm assembly. The positioned of these vanes has an effect on the quantity and efficiency of the compressor air flow.

The aft end of the compressor casing contains extraction ports to permit removal of 8^th stage compressor air. This bleed air is used for turbine static hardware cooling functions and is also used for pulsation control during start up and shutdown.

3.3.3 Compressor Discharge Casing

The compressor discharge casing (CDC) is the final portion of the compressor section and is the longest single casting. The CDC is situated at the gas turbine midpoint, between the forward and aft supports, and is, in fact, is the keystone of the gas turbine structure. the CDC contains the final compressor stages 9-14, and contains extraction ports to permit removal of 11^th stage compressor air used for turbine static hardware cooling functions.

The CDC and its components form the flow path surfaces of the compressor diffuser, and join the compressor and turbine casings. The CDC also provides support for the combustion casings, transition piece support bracket 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 and the being an inner cylinder that surrounds the compressor rotor. The two cylinders are concentrically positioned by twelve radial struts.

A dual-path diffuser is formed by the tapered annulus between the outer cylinder and inner cylinder of the discharge casing and a third member which splits the compressor flow into two steams. The diffuser converts some of the compressor exit velocity into added static pressure for the combustion air supply.

3.3.4 Blading

The compressor rotor and stator blades are air foil shaped and designed to compress air efficiently at the high blade tip velocities. The blades are attached to the compressor wheels by dovetail arrangements. The dovetails are very precise in size and position to maintain each blade in the desired position and location on the wheel.
The compressor stator blades are air foil shaped and are mounted by similar dovetails into ring segments stage 4 through stage 14 stage 14 and exit guided vane. The ring segments are inserted into circumferential grooves in the casing and are held in place with locking keys. The variable inlet guide vane and variable stator vanes stage 1 through stage 3 are mounted through Trunnion holes in the casing walls and secured with a vane arm and nut assembly.