High Performance Retrofit

5/28/2018 High Performance Retrofit

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For: Pipeline & Gas Journal

A High Performance Retrofit

For the GE10 Gas Turbine

By Valter Quercioli, Mike Cocca, Massimiliano Alvino, Vittorio Olcese

GE Energy

The GE 10 gas turbine is a high-efficiency, heavy-duty machine developed for

power generation and mechanical drive applications. This 10-megawatt gas turbine is

being used in gas turbine transportation projects worldwide. A recent example is the San

Fernando Pipeline Project in northern Mexico, where GE 10-2 gas turbines are being

used to drive six compressor trains.

When the first PGT10 gas turbine (the forerunner of the GE 10) was developed, it

was designed for robust operation, with the flexibility to accommodate future

improvements in performance as gas turbine technologies evolved. These design margins

resulted in the introduction in 1999 of the newer model GE10. In 2004, the technology

has further advanced through an initiative called the GE10 Performance Improvement

Program (PIP)

Typically, the performance areas that are improved through technology upgrades

are output power, thermal efficiency and maintenance intervals. The current ISO ratings

for the GE10 PIP are the following:

Standard Combustor

Output Power 11982 kW

Heat Rate 10822 kJ/kWh Thermal Efficiency 33.27%

Maintenance Intervals each 8000 firing hrs


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DLE Combustor

Power 11615 kW

Heat Rate 11122 kJ/kWh Thermal Efficiency 32.37%

Maintenance Intervals each 8000 firing hrs

These figures represent an increase in excess of +12% on the output power and

+1.3 points of efficiency compared to the PGT10, as well as an increase of +3.6% on the

output power and +1.0 points of efficiency compared to the GE10-2. Clearly, the GE10

PIP is delivering on the promise to make the PGT10 promise the highest performing

heavy-duty gas turbine in the 10-megawatt class.

The GE10 PIP is available also as a retrofit kit to upgrade either PGT10s as well

as GE10s.Two types of retrofit can be done:

-- Minor Retrofit: this retrofit applies to both GE10-2s and PGT10s. Advanced, high

tech seals are embedded and selected components of the exhaust diffuser are changed.

The efficiency increase is 1.0 point while power increase is 3.6%).

-- Major Retrofit: this retrofit applies to PGT10s only. All the main gas turbine

components (i.e. axial compressor, first stage hot parts, etc.) are changed to deliver

the full 12% power increase. Advanced, high tech seals are embedded that contributes

to the 1.3 points of efficiency enhancement. A technical analysis of the current

configuration at the site is performed to determine the need to change other main

components such as the load gearbox, electrical generator, and inlet and/or exhaust

ducts.

GE10 PIP Technology


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The GE10 PIP embeds a number of advanced features:

Axial Compressor -- The compressor is a high-performance, 11-stage, axial-flow

design with a 15.4:1 pressure ratio and 46.9 kg/s mass flow at ISO conditions. The

design operating speed of the gas generator is 11,000 rpm. The rotor consists of a

combination of materials in order to address the different operating temperatures along

the compressor. Forward shaft and front disks/spacers are ASTM A471, while the after

shaft with the last four stages is a solid construction of CrMoV steel.

The rotor assembly is achieved with OD boltings and a low radius rabbet. The

first three blade rotor stages are made of 17-4-PH, while X22 CrMoV 12.1 and AM355

steel areused for the remaining three parts. The first three rows incorporate adjustablevanes, followed by five transonic rows. The axial compressor's high performance is

enabled by a reduced number of 11 stages compared to the 17 stages of the PGT10,

resulting in a higher-pressure ratio.

A new meridional flow path shape allows a higher average peripheral speed

which in turns means a lower stage work coefficient with a reduced number of stages.

Use of wide-chord airfoils, with a high mechanical strength, also contributed to the

reduction of stages. As a consequence, it has been possible to reduce the complexity (by

reducing the number of total parts) of the axial compressor and its external stator casing,

which facilitates maintenance and improves operational reliability.

Combustion System -- The GE10 model incorporates a reverse flow single can

combustion system (basically unaltered from the PGT10 version) consisting of a

combustion chamber assembly, fuel nozzle, spark plug, and flame detector. Main

characteristics are:


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Single combustion system/assembly configuration, enabling a wide fuel capability

Single composition for fuel injector/nozzle, spark plug and detector flame

Very low pressure drop

Readily accessible and easy to service

The combustion air, compressed in the axial flow compressor, enters the

combustion chamber through the holes made in the liner and flows along the liner itself

to keep it cool. After cooling, the hot air is mixed with combustion hot gases and is

expanded through the power turbine. Combustion of the fuel and air mixture is initiated

by a spark plug, with a retractile electrode. A flame detector is installed in the

combustion system to actuate the alarm in case a flame failure occurs. The combustion

chamber system for GE10 gas turbine is available in both standard and DLE (Dry Low

Emissions) options.

The standard configuration consists of single can reverse flow conventional

diffusion combustion. The fuel is injected through one nozzle with several injection

orifices to obtain an optimized distribution of the flame. Water or steam injection can be

used for emissions reduction; for power augmentation only, steam injection is currently

available.

The DLE system is based on the use of a special pre-mix combustion chamber.

The flame temperature is limited by the use of an air excess factor of 1.82 at full load.

This design permits a constant air/ fuel stoichiometric ratio at partial loads, to limit

pollutant emissions in all operating ranges. A rotating valve that changes the air passage

area toward the liner regulates the combustion air mass flow. Emissions levels achieved

are 25 ppmvd NOx@ 15 % O2and 20 ppmvd CO @ 15 % O2.


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The transition piece is the component that provides a homogeneous flow

distribution toward the first-stage turbine nozzle. For the GE10, it was redesigned to

provide higher reliability. With the latest commissioned PGT10 machines, the transition

piece, the combustor liner and the first stage nozzle are interchangeable. The materials

are Hastelloy Xfor the liner and Nimonic 263

for the transition piece.

Other relevant enhancements include reengineering of the combustion liner to

employ the slot-cooled technology developed for the large Frame MS9001E gas

turbine. This improves the cooling effect and therefore the operational ruggedness,

durability and reliability of the liner, which is subjected to high temperatures.

1stStage Nozzle -- Both first and second stage nozzle assemblies consist of airfoil

shaped segments made of FSX414

. Both nozzle assemblies are air cooled to increase the

life of the part. Air from the compressor discharge is directed through the body of the

individual nozzle partitions and out holes near the trailing edge. This not only cools the

metal but also blankets the trailing edge with a film of air.

HP Turbine Rotor -- The high-pressure turbine, directly coupled to the axial

compressor, is a two-stage reaction type unit designed to achieve very high expansion

efficiency. The rotor assembly, consisting of two Inconel 718forged turbine wheels,

inter-wheels spacer and buckets, is coupled by bolts to the axial compressor shaft end

flange. Turbine buckets are composed of high-temperature alloy investment castings

(GTD 111-DS) and incorporate long shanks and a three-tang dovetail. GT33 coating is

applied on the first stage while RT22 is applied on the second one. The HP rotor is

supported by two pressure-lubricated, tilting pad bearings. The thrust bearing, a directly

lubricated tilting pad type is located at the front end of the HP rotor.


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Advanced Seals -- The latest technology, advanced seals are incorporated in the

GE10 PIP project to reduce the undesirable effect of secondary flow. The new sealing

system consists of:

improved seals on the segment to segment stage one and two nozzles toreduce parasitic losses from leakage

replacing the busbars with new cloth seals between HPT hanger segments

(outer diaphragm)

introduction of four Omega seals at the interface of several components

use of bearing# 2 forward and aft labyrinth seals + brush seals

re-orientation of high pressure diaphragm wheel space cooling holes.

The advance sealing includes rub-tolerant brush seals, which are designed to

withstand rubs and maintain clearances in this critical sealing area. Metallic brush

material is used in place of one of the labyrinth teeth. Since the clearance between the

brush seal and the rotor is reduced relative to the design clearance used with labyrinth

tooth packing, there will be an increase in performance relative to a new labyrinth tooth

seal. The new advance sealing includes a new spline seal arrangement that is designed to

reduce leakage between shroud and nozzle segments.

Analysis and field rig testing has shown that changing from the labyrinth/bus bar

design to a flat side face with multiple cloth seals to reduce both axial and radial leakage

can significantly reduce inter-segmental leakage. In a cloth spline seal design, L605 metal

wire is woven into a cloth and then wrapped around and spot-welded to a strip of X750

metal. The L605 (or Haynes 25) material provides wear resistance and has been used in

floating seals and brush seals. X750 is the same material used in combustor hula seals.

The cloth spline design provide a more flexible, relatively compliant seal that can

conform to gap configuration changes between segments typically caused by thermal and

aerodynamic loading of the shroud. A seal on the forward side of the shroud


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segments provides improved sealing between the stage one nozzle retaining ring and the

shroud blocks. This is a thin metal strip with a cross-section that is inserted into a

groove on the shroud forward side. The retaining ring compresses the seal when the

nozzle is installed. It provides a positive sealing force and can comply with small

changes in the relative position of the nozzle and the shroud during operation.

Exhaust Diffuser -- To further improve performance, the exhaust diffuser was

redesigned to significantly improve the recovery factor. The old diffuser exhibited a poor

recovery factor with the higher GE10 swirl angle and a low area ratio. The new GE10 PIP

diffuser improves the recovery factor by increasing the length and area ratio and adding

turning vanes compared to old design.

GE10 PIP Maintenance Plan

The GE10 PIP maintenance can be carried out on-site or, due to its compact size,

the turbine can be swapped out with a rental unit while it is being serviced at an

authorized GE facility. Like all GE Energy heavy-duty gas turbines, the GE10 PIP

includes borescope holes to facilitate visual inspection, with a removal of the casings.

The GE10 PIP maintenance plan follows the standard GE10-2 plan: a combustion

inspection, hot gas path inspection, combustion inspection and major inspection for each

8,000 firing hours in a 32,000 firing hours cycle. During the major inspection, some

components are substituted (combustion liner, transition piece, first stage nozzle), and

first stage buckets could need repair. Other items (second stage nozzles and buckets, first

and second stage shrouds) are repaired depending on their condition.


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At a second major inspection (64,000 firing hours) all the following components

will be changed: combustion liners, transition pieces, first and second stage nozzles, first

and second stage buckets, first and second stage shrouds, inlet guide vanes, axial

compressor blades (stator and rotor), and bearings.

Conclusions

The use of new design techniques for the axial compressor and for the combustion

section and the introduction of advanced materials and coatings for the hot gas path

components result in a gas turbine that offers improved performance and increased

reliability. The GE 10 PIP is the latest example of GE's continuing efforts to update its

gas turbine fleet with the latest technology. It also represents the GE strategy of

introducing designs that can be retrofit into an existing gas turbine to significantly

improve its performance with a minimum impact on the layout of the unit.

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High Performance Retrofit

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