1.4.0 DLN-2.6 + Combustion System

4.0 DLN-2.6 + Combustion System

The combustion system is a reverse-flow design with 16 combustion chambers arranged around the periphery of the compressor discharge casing. Combustion chambers are numbered counter-clockwise starting with the chamber just left of the chamber at top dead center when looking aft end. This system also includes the fuel nozzles, a spark plug ignition system, flame detectors, and crossfire tubes.

High pressure air from the compressor discharge is directed around the aft end of the transition piece. Most of the compressor discharge air enters the holes in the aft end of the transition piece to cool the transition piece and for annulus between the flow sleeve and liner, through holes in the aft end of the flow sleeve. This air passes through the quaternary fuel ring and then enters the combustion zone through the cap assembly for proper fuel combustion. Fuel is supplied to each combustion chamber through six nozzles designed to disperse and mix the fuel with the proper amount of combustion air (and to the quaternary ring at during baseload operation). Hot gases, generated from burning fuel in the combustion chambers, flow through the impingement cooled flow sleeve and transition piece to the turbine.

4.1 Combustor Configurations for Fuel Type:

Dual Fuel
This configuration is capable of operation on either natural gas or liquid fuel. The fuel type can be changed gas to liquid to gas while the GT is operating.

Gas Fuel Only
The fuel nozzles feed only natural gas to the combustion system, with no provision for liquid fuel operation.

Liquid fuel only
The fuel nozzles feed only liquid fuel and water into the combustion system, with no provision for gas fuel.

·         On gas fuel, the combustor operates on 6 fuel nozzles per combustor, where the number of fuel nozzles fueled increases as the GT load increases. One nozzle is fueled from FSNL to low load; three nozzles are fueled from low load to intermediate load; and six nozzles are fueled plus the quaternary fuel circuit from intermediate load to baseload. Emissions complaint operation required all fuel circuit to be fueled and GT firing temperature to be above a threshold temperature.

·         On oil operation, this combustor operated in diffusion amide across the entire load range, with only the outer 5 fuel nozzles fueled. Water injection is also injected by the fuel nozzles into the combustor for NOx reduction.

4.3 Outer Combustion chambers and Flow Sleeves

The outer combustion chamber, or casing, acts as the pressure vessel for the combustor. They also provide flanges for the fuel nozzle-end cover assemblies, crossfire tube flanges, spark plugs, flame detectors and false start drains. The flow sleeve forms an annular space around the cap and transition piece assemblies that directs the combustion and cooling into the forward end of the combustor fuel nozzle jet.

4.4 Cap, Flow Sleeve, and Transition Piece Assemblies

The combustion flow sleeves and transition pieces are passively cooled on their outside with air directed by the impingement sleeve to the forward end of the combustor and fuel nozzle inlet. Ridges on the liner outer surface augment the cooling effectiveness. The inner surfaces of the transition piece and flow sleeve have thermal barrier coating to reduce metal temperatures and thermal gradients. The aft end of the transition piece transforms the combustor annular flow into  flow profile to be fed into the Stage 1 Turbine Nozzle. The Cap has six burner tubes that engages each of the six fuel nozzles. The cap is cooled by effusion cooling passages.

4.5 Fuel Nozzle End Covers

There are six fuel nozzles assemblies in each combustor. They arranged with 1 located in the center and five arranged around the outer edge. Each fuel nozzle premixes the inlet air and gas fuel, and then forwards this mixture to the combustor reaction zone for burning. The outer fuel nozzles contain a liquid fuel and water passage down the center of the fuel nozzle for operation on oil, where oil and water is injected directly into the combustor. Water is injected into the reaction zone when the combustor is to be operated within emissions compliance on oil fuel.

4.6 Quaternary Fuel Ring

Each combustion chamber contain a Quaternary fuel ring located between the combustion casing and the CDC. Fuel is instructed at intermediate load and above.

4.7 Crossfire Tubes

All combustion chambers are interconnected by crossfire tubes to provide means for ignition of the chambers without ignitors. The outer chambers are connected with an outer crossfire tube and the combustion liners are connected by the inner crossfire tubes.

4.8 Spark Plugs

The combustor is ignited with two spark plugs that are positioned within the combustor downstream of a fuel nozzle. Once the combustor is ignited, the pressure from the combustor forces the ignitor tip to retract from the combustor for continous operation. These spark plugs receive their energy from high energy-capacitor discharge power supplies. Once the combustor chamber is ignited with the spark plug, the remaining chambers are ignited by the flame passing through the crossfire tubes that interconnect the reaction zone of the remaining chambers.

4.3 Flame Detectors

A flame monitoring system is used consisting of 4 flame detectors. The signals from the flame detectors are sent to the control system which uses an internal logic system to confirm whether the combustors are ignited or extinguished.

 

 

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.

1.3.1-GE 9 HA Compressor and Turbine Design

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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

1. Air Inlet
2. Compressor
3. Combustion system
4. Turbine
5.  Exhaust gas system
6.   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 14^th stage.

1.2.2- 9HA GE Gas Turbine Lubrication Oil System

9 HA GE Gas Turbine Lubrication Oil System

2.4 Heat Exchanger and Filters:

The lubricant oil heat exchangers(LOHX-1 and LOHX-2) connect o the parallel lubricant filters(LF3-1 and LF3-2) This design is provided so that filters not in service can be changed without taking the turbine out of service.

Filter housings and heat exchangers are self-venting. A sight glass is located in the vent line from e filter and heat exchanger. When the heat exhanger and filter housing are full, oil will be visible in this sight glass.

By means of the manually-operated three-way transfer valve, one filter can be put into service as the second is taken out, without interrupting the oil flow to the main lube oil header. The transfer of operation from one filter to the other should be accomplished as follows:

1.           Close the drain valve of the filter. Open the filter valve and fill the standby filter until a solid oil flow can be seen in the flow sight in filter vent pipe. This will indicate a “filled” condition.
2.            Operate the transfer valve to bring the standby filter into service.
3.          Close the filler valve.                                                                                                                   

This procedure simultaneously brings the reserve heat exchanger into service.

Note

Only one heat exchanger is intended to be in service at one time. After transfer, the operator must verify that the cooling water isolation butterfly valves to/from the heat exchanger not in service are closed. Do not leave all four cooling water isolation valves open.

2.5 Seal Oil

The seal oil to the generator bearing is normally supplied by the lubricating system by the lubricating system through a separate line directly to the generator in the event of low lube system pressure or lube system shutdown for service one of two seal oil pumps supply the oil required to seal in the generator hydrogen. Under normal circumstances the AC motor driven pump would serve this function however if this AC motor should fail or if AC power is lost the emergency DC motor is activated and drives the seal oil pump in piggyback AC/DC motor configuration separated AC and DC pumps). The AC motor includes a heater to prevent condensation in the motor. The seal oil pumps circulate oil through filter. Differential pressure switch provides a high differential pressure alarm signal across the filter. The filter element should be replaced near or at the alarm set point.

2.6 Optional Devices

Pressure transmitters

The lubrication module may include the following additional pressure transmitters (indication only) when selected by a customer as an option;

1.      Differential pressure transmitters which provide remote monitoring capability of differential pressure across oil filters.

2.       Pressure transmitter which provides remote monitoring capability of bearing header pressure.

3.       Pressure which provides remote monitoring capability of tank oil level.

These transmitters are indication only devices. They do not alarm or trio the machine in case of failure, low pressure, level etc.

Lube Oil Conditioner

The lube oil system may also include a lube oil conditioner when selected by a customer as an option. The lube oil conditioner is a stand-alone, kidney-loop lube oil conditioning skid designed specifically to remove particulate contamination (from 0.2 to 2 microns in size). Particulate contamination in this size range is the precursor to varnish formation and accumulation. The implementation of lube oil condition together with monitoring and maintenance of the lubrication oil additive package will help prevent the formation and accumulation of varnish and therefore varnish related turbine trips due to sticking hydraulic servo valves etc.) The lube oil condition skid is a standalone customer located skid with all function controlled by an onboard PLC there is no interface to MK VI control system.

Oil entering the Lube oil conditioner skid is monitored for temperature via thermocouple LT-LC. The oil then passes through the pump and into the pre-filter which is monitored for pressure by transducer. The oil then passes into the charging/mixing vessel, which is monitored for pressure by a transducer. Next, the oil moves to the final canister, containing the post-filter which is monitored for pressure by transducer. Finally, oil exiting the skid is monitored for pressure by transducer. All of these devices communicate solely with the PLC onboard the Lube Oil Conditioner Skid.