MS5001 PA Complete Maintenance MANUAL

g GE Power Systems Oil & Gas Technical Training

MS5001 PA GAS TURBINE Operation and Maintenance

Training Manual

Customer: AGIP GAS BV LYBIAN BRANCH Plant location: WAFA COAST- LYBIA

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Nuovo Pignone INDEX CHAP. 1 Page 1.

INTRODUCTION................................................................................................1-1 1.1

STATIONARY APPLICATIONS .............................................................1-1

1.2

MOBILE APPLICATIONS........................................................................1-2

1.3

HISTORICAL NOTES ...............................................................................1-2

1.4

NUOVO PIGNONE GAS TURBINE MANUFACTURING PLANT ......1-3

09-98-E MOD. ARGE 2/S

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Nuovo Pignone 1.

INTRODUCTION A gas turbine is an internal combustion motive machine. From all points of view, it can be considered as a self-sufficient system: in fact, it is capable to aspirate and compress ambient air via its own compressor, to enrich the energetic power of air in its own combustion chamber and to convert this power into useful mechanical energy during the expanding process that takes place in its own turbine section. The resulting mechanical energy is transmitted via a coupling to a driven operating machine, which produces work useful for the industrial process in which the gas turbine belongs.

1.1

STATIONARY APPLICATIONS These applications are the subject of this traning course. They are intended for the following industrial uses:


•

Generator drive, in order to produce electric energy by an open cycle.

•

Generator drive, to produce electric energy by a combined cycle.

•

Generator drive, to produce electric energy by co-generation.

•

Compressor drive

•

Pump drive

•

Pipeline compressor drive

•

Pipeline pump drive

•

Particular industrial processes

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Nuovo Pignone 1.2

MOBILE APPLICATIONS These applications were the first ones to be introduced in terms of time. They include the following fields:

1.3

•

railways

•

marine propulsion

•

aviation

•

road traction

HISTORICAL NOTES The first gas turbines to be used in operating applications appeared on the market at the end of the Forties; they were generally used in railways and presented the advantage of burning liquid fuel, even of poor quality. In this regard, we will mention the MS3001 turbine built by General Electric, with a power of 4500 HP, which was used just for this purpose. Successive achievements in material technology and extensive research into combustion resulted in rapid improvements in performance, in terms of specific power and efficiency, obtained by increasing maximum temperatures in the thermodynamic cycle. In this matter, three generations of evolution can be defined, distinguished by the maximum temperature (°C) ranges of gases entering the first rotor stage of the turbine:

First generation Second generation Third generation

760
Obviously, to an increase in temperature there corresponded an increase in thermodynamic efficiency, which passed from values lower than 20% on the first machines to current values higher than 40% (LM6000 gas turbine).


P. 1-2

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Nuovo Pignone 1.4

NUOVO PIGNONE GAS TURBINE MANUFACTURING PLANT Nuovo Pignone has built gas turbines of “heavy duty” type for industrial applications since 1961. These are made in the Florence workshop under a Manufacturing Agreement with General Electric, Schenectady - N.Y. - USA, which, in time, has led to the acquisition of complete licences (MS5002 gas turbine) and to the complete execution of some gas turbine models (turbines of the PGT range), starting from engineering and on to all construction phases. As a complement to their main activities, Nuovo Pignone converts gas turbines intended originally for the aircraft industry into packages for industrial applications which use the originary gas generator in conjunction with power turbines made by General Electric (LM range), or by Nuovo Pignone (PGT16 and PGT25 ranges). Since 1962 up to the present time, Nuovo Pignone has built about 1000 turbines, complete with all auxiliaries required for their operation; of these, a good deal are part of turnkey plants for all application purposes listed at para. 1.1.


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Nuovo Pignone In the following tables, gas turbines currently produced by Nuovo Pignone are divided by model and by type of application. TABLE 1.1 GAS TURBINES FOR MECHANICAL DRIVE APPLICATIONS (1)

Model

Continuous duty Power KW

Heat Rate

RPM on the load side

PGT 2

2180

13360

22500

PGT 5

5500

13680

10290

PGT 5 R

4850

10530

10290

PGT 10

10440

10590

7900

MS 3002

10890

13480

6500

MS 3002 R

10440

10480

6500

PGT 16

14260

9935

7900

PGT 25

23270

9565

6500

H.S.P.T

29980

8935

6100

LM 2500

22670

9720

3600

MS 5002(D)

32600

11890

4670

LM 5000

34450

9960

3600

MS 6001

41010

10780

5100

LM 6000

44850

8435

3600

MS 7001

86280

10750

3600

Kj/Kwh

_____________________________ The values in the table refer to the turbine loading flange, under ISO conditions and the use of natural gas.

(1)


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Nuovo Pignone

TABLE 1.2 TURBINE S FOR GENERATOR DRIVE APPLICATIONS (1)

Model

Continuous duty Power KW

Heat Rate

Hz on load side

PGT 2

2150

13536

60/50

PGT 5

5500

12852

60/50

PGT 10

10700

11052

60/50

PGT 16

13760

10295

60/50

PGT 25

22450

9910

60/50

H.S.P.T

28930

9260

60/50

LM 2500

22330

10110

60/50

MS 5001

26300/27830

12650/12640

60/50

LM 5000

33060

10270

60/50

MS 6001

38340/41400

10780

60/50

LM 6000

43450

8710/

60/50

MS 6001 FA

70140

10530

60/50

MS 7001 EA

83500/90200

11060

60

MS 9001 E

123400/133000

10850

50

MS 9001 EC

169200

10300

50

MS 9001 FA

226500

10090

50

Kj/Kwh

_____________________________ (1) The values in the table refer to the turbine loading flange, under ISO conditions and

the

use of natural gas. 09-98-E MOD. ARGE 2/S

P. 1-5

GE 2 (PGT 2) Overview The GE2 is a 2MW single shaft machine for base load power generation. Thanks to the high exhaust temperature, the GE2 is perfectly suited for cogeneration in industrial and civil applications (over 5MW of thermal power) and emergency electric power generation. The single combustion chamber can operate with a wide variety of liquid and gaseous fuels (or dual fuels) and it is designed to reduce environmental impact to a minimum, thus satisfying the most restrictive environmental regulations. The load reduction gear is integrated with the gas turbine and provides output speeds suitable for power generation (1500/1800 RPM). A microprocessor system for regulation, control and protection has been designed to render the management and operation of the GE2 gas turbine completely automatic.

Design Info Compressor • • Combustion • Turbine • • Package • • • • • Emissions • •

Two stage centrifugal compressor Pressure ratio 12.5:1 Single, combustion chamber Two stage turbine Investment cast blades, forged discs

The complete Gen Set ismounted on a single baseplate The enclosure is integral with the baseplate providing maximum accessibility for gas turbine and auxiliaries maintenance; noise level < 85dB (A) at 1m In outdoor applications the filter plenum is flanged on top of the enclosure The package design is standardized for quick delivery; custom applications can be provided Package dimensions (including generators and filters) LxWxH = 5.5mx3.8mx2.3m; Weight = 12t Control Steam or water injection for standard combustion chamber Dry Low Emission configuration available to satisfy the most stringent environmental regulations

Performance Info Generator Drive (Expected Performance at ISO Conditions with fuel natural gas) Model GE2

Output 2000 kWe

Heat Rate 14400 kJ/kWh

Exhaust Flow 10.7 kg/s

Exhaust Temperature 525 C° P. 1-4

INTRODUCTION

GE 5 (PGT 5) Overview The PGT5 heavy-duty gas turbine has been designed with modular concepts to facilitate accessibility and maintainability. The gas generator consists of a 15-stage, high efficiency, axial-flow compressor directly coupled to a single stage turbine. The low pressure shaft (two-shaft version) is a single-stage, high-energy turbine, with variable second stage nozzles which grant maximum flexibility for mechanical drive service. The PGT5 has a single combustion chamber system which is rugged, reliable and able to burn a wide range of fuels, from liquid distillates and residuals to all gaseous fuels, including low BTU gas. Typical applications include pump drive for oil pipelines and compressor drive for gas pipelines.

Design Info Compressor • Axial flow compressor, 15 stages • Pressure ratio 9.1:1 Combustion • Single, reverse flow combustion can Turbine Two shafts • High Pressure turbine one reaction stage • Low Pressure turbine one reaction stage Package • The gas turbine module on a single baseplate includes the engine, starting system, auxiliaries and acoustic enclosure • Std. Configuration (excluding inlet/exhaust ducts/system): • size 8mLxWxH = 8.5mx2.5mx3.0m • weight 28 t Emissions Control • DLE combustion system • Steam and water injection system

Performance Info Generator Drive: Single Shaft version(Expected Performance at ISO Conditions with fuel natural gas) Model Output Heat Rate Exhaust Flow Exhaust Temperature PGT5 5220 kWe 13422 kJ/kWh 24.6 kg/s 524 °C Mechanical Drive:Two Shafts version (Expected Performance at ISO Conditions with fuel natural gas) Model Output Heat Rate Exhaust Flow Exhaust Temperature PGT5 5450 kW 13450 kJ/kWh 25.8 kg/s 533 °C

P. 1-5 INTRODUCTIONS

GE 5B (PGT 5B) Overview The GE5B series is a 6 MW range industrial duty gas turbine designed in two configurations: A single shaft configuration for power generation and a two shaft configuration for mechanical drive applications. The completely new design of the GE5B combines the technology of aircraft engine design with the ruggedness of the heavy duty PGT class of turbines. The flexibility, simplicity and compactness of the GE5B make it ideal for industrial power generation, including steam production, Oil & Gas applications in remote areas and Offshore installations. The control system is configured for fully automatic operation and has provisions for connection to Remote Monitoring and Diagnostics. The GE5B is ideally suited for applications, which require a continuous supply of electrical power with high availability and reliability. The exhaust energy is enough to provide a substantial quantity of steam at various pressures and temperatures when coupled to a Heat Recovery Steam Generator.

Design Info Compressor • • • Combustion • Turbine • • Package • • • • • • Emissions •

Axial flow compressor, 11 stages First three stator stages are variable geometry Pressure ratio 15:1 Annular combustion chamber, 18 fuel nozzles Two reaction stages First stage cooled

The gas turbine module on a single baseplate includes engine, starting system, load gear, auxiliaries and acoustic enclosure The off-base equipment is limited to the lube oil coolers and electric generator The inlet filtration module is designed for mounting above the gas turbine enclosure The enclosure has wide double-joined doors allowing for ease of access to all turbine components and auxiliaries or engine removal The package design is standardized for quick delivery; custom applications can be provided Package dimensions (including filters on top of the enclosure) LxWxH = 5.9mx2.5mx5.7m;Weight = 30t Control The standard unit is configured with a DLE combustion system

Performance Info Generator Drive (Expected Performance at ISO Conditions with fuel natural gas) Model GE5

Output 5500 kWe



Exhaust Temperature 571 °C P. 1-6

INTRODUCTION

PGT 10A (two shaft) Overview The PGT10 is a high efficiency gas turbine designed and developed by Nuovo Pignone for shaft outputs ranging between 9,500 and 15,000 HP at ISO conditions. Since first introduced to the market in 1988, the PGT10 has met its design goals by providing customers with high performance and high reliability and availability while keeping its design simplicity and easy maintenance concepts. To achieve high efficiencies over an extended spectrum of power range, an uncommon combination of features has been incorporated into the design: High pressure ratio, firing temperature level in line with second generation gas turbines, variable axial compressor stator vanes and power turbine nozzles. The PGT10 combustion system consists of a single combustion chamber designed for low NOx emissions and is suitable for a large variety of gaseous and liquid fuels. Typical applications for PGT10 two-shaft gas turbines are not only natural gas compression, centrifugal pump drive and process application, but also power generation as well as Cogeneration and Offshore applications.

Design Info Compressor • Axial flow compressor, 17 stages • Pressure ratio 14.1:1 Combustion • Single combustion chamber Turbine (Two shafts) • High Pressure turbine two stages • Low Pressure turbine two reaction stages Package • The gas turbine module on a single baseplate includes the engine and a load gear; the auxiliaries are installed on a separate baseplate joined to that of the gas turbine to form a single lift on which the sound-insulated enclosure is mounted • The electric generator is installed on a concrete foundation to limit overall shipping dimension • The package design is standardized for quick delivery, but custom applications can be provided • Package dimensions (excluding generator and filters) 9.1mx2.5mx3.0m; Weight: 32t Emissions Control • The combustion system is available both in conventional and DLE configuration to satisfy the most stringent environmental regulations • Steam and water injection systems are available for NOx reduction and power augmentation

Performance Info Generator Drive: Two Shaft version(Expected Performance at ISO Conditions with fuel natural gas) Model Output Heat Rate Exhaust Flow Exhaust Temperature PGT10 10220 kWe 11540 kJ/kWh 42.1 kg/s 484 °C Mechanical Drive:Two Shafts version (Expected Performance at ISO Conditions with fuel natural gas) Model Output Heat Rate Exhaust Flow Exhaust Temperature PGT10 10660 kW 11250 kJ/kWh 42.3 kg/s 493 °C P. 1-7 INTRODUCTIONS

GE 10B (single/two shaft) (PGT 10B 1/2) Overview The GE10 is a high efficiency and environmental friendly Heavy Duty Gas Turbine designed and developed by Nuovo Pignone for Power Generation (including industrial co-generation) and Mechanical Drive applications. Since it was first introduced to the market in 1988, the model PGT10A has been providing high performance, reliability and availability to worldwide customers while keeping with easy maintenance concepts. From this starting point, in 1998 Nuovo Pignone launched on the market the high performance version of this model with two different configurations: Two shafts for mechanical drive and single shaft for power generation and cogeneration applications. The GE10 Gas Turbine, with its ability to burn different fuels (natural gas, distillate oil, low BTU fuel), can be installed in many countries with different environmental conditions: continental, tropical, offshore and desert. Continuous improvement of the model is carried out with reference to performance and emissions reduction capability. In this context particular emphasis has been placed on the design of a DLN system for Nitrogen Oxides (NOx) reduction in order to meet present and future standards for pollutant emissions.

Design Info Compressor • Axial flow compressor, 11 stages • First three stages of stator are variable geometry • Pressure ratio 15.5:1 Combustion • Single combustion chamber Turbine Single shaft GE10/1 Two shaft GE10/2 • Three reaction stages • High Pressure turbine two reaction stages (cooled) • First two stages cooled • Low Pressure turbine two reaction stages Package • The gas turbine module on a single baseplate includes the engine and the load gear; the auxiliaries are installed on a separate baseplate joined to that of the gas turbine to form a single lift on which the sound-insulated enclosure is mounted • The electric generator is installed on a concrete foundation to limit overall shipping dimensions • The package design is standardized for quick delivery; but custom applications can be provided • Package dimensions (excluding generator and filters) LxWxH = 9mx2.5mx3; Weight = 40t Emissions Control • The combustion system is available both in conventional and DLN configuration to satisfy stringent environmental regulations • Steam and water injection systems are available for NOx reduction and power augmentation

Performance Info Generator Drive: Single Shaft version(Expected Performance at ISO Conditions with fuel natural gas) Model Output Heat Rate Exhaust Flow Exhaust Temperature GE10 11250kW 11467 kJ/kWh 47.3 kg/s 490 °C Mechanical Drive:Two Shafts version (Expected Performance at ISO Conditions with fuel natural gas) Model Output Heat Rate Exhaust Flow Exhaust Temperature GE10 11690 kW 11060 kJ/kWh 46.9 kg/s 487 °C P. 1-8 INTRODUCTION

PGT 16 Overview The PGT16 gas turbine is composed of the twin spool GE Aeroderivative LM1600 Gas Generator coupled with a rugged, industrial power turbine designed by Nuovo Pignone. The LM1600 Gas Generator is derived from the F404 turbofan aircraft engine, while the power turbine of the PGT16 gas turbine is identical to the power turbine of the PGT10 Nuovo Pignone Heavy Duty, high efficiency gas turbine, which has been in operation for more than half a million hours. The power turbine shaft speed (7900 RPM) is optimized for direct coupling to pipelines and injection and process centrifugal compressors with speed ranges that suit all operating conditions. High efficiency and reliability are just two of a large number of benefits contributing to LM2500+ customer value. For generator drive applications the LM1600, coupled to its synchronous generator with a speed reduction gear, is a highly flexible turbogenerator that can also cover combined cycle/cogeneration applications with an electrical efficiency close to 50%.

Design Info Compressor • • Combustion • Turbine • • Package • • •

Emissions • •

Twin spool axial compressor (3 stages LP compressor, 7 stages HP compressor) Pressure ratio 20.1:1 Annular combustion chamber (18 fuel nozzles) Twin Spool Gas Generator turbine (1 stage HP turbine, 1 stage LP turbine) Two stages Power turbine (7900 RPM) with variable angle first stage nozzles

The complete gas turbine module is mounted on a single baseplate The enclosure is integrated with the baseplate providing maximum accessibility for gas turbine and auxiliaries maintenance Standard Configuration (excluding inlet/exhaust ducts/system): • Size LxWxH = 8.1mx2.5mx3.8m • Weight 19t Control Steam or water injection systems for NOx abatement Dry Low Emission (DLE) combustion system

Performance Info Generator Drive: (Expected Performance at ISO Conditions with fuel natural gas) Model Output Heat Rate Exhaust Flow Exhaust Temperature PGT16 13735 kWe 10314 kJ/kWh 47.4 Kg/s 493 °C Mechanical Drive: (Expected Performance at ISO Conditions with fuel natural gas) Model Output Heat Rate Exhaust Flow Exhaust Temperature PGT16 14252 kW 9756 kJ/kWh 47.4 kg/s 493 °C P. 1-9 INTRODUCTIONS

PGT 25 Overview The PGT25 gas turbine consists of the GE Aeroderivative LM2500 Gas Generator coupled with a rugged, industrial power turbine designed by Nuovo Pignone. The LM2500 gas generator and the PGT25 power turbine demonstrated the best overall performances to cover the 17,000-31,000 HP range with maximum efficiency above 37%. The speed of the output shaft, 6500 rpm, as well as the high capacity and simplicity of maintenance have made the PGT25 highly suitable for driving direct coupled centrifugal compressors for pipeline service or natural gas reinjection plants. Its light weight and high efficiency makes it well suitable for offshore and industrial power generation. The modular design, extended to all accessory equipment, takes into account the special requirements of platform applications (minimum weights and overall dimensions), as well as drastically reduces erection time and costs. The gas generator can be easily dismantled with a simple translation within the package space, thus reducing the time required for maintenance. Simplicity of construction and the high quality of the materials employed allow for long intervals between overhauls and reduced maintenance costs.

Design Info Compressor • • Combustion • Turbine • • Package • • • Emissions • •

Sixteen stages axial compressor Pressure ratio 17.9:1 Annular combustion chamber (30 fuel nozzles) Two stages Gas Generator turbine Two stages Power turbine (6500 RPM)

The complete gas turbine module comes mounted on a single baseplate The enclosure is integrated with the baseplate providing for maximum accessibility for gas turbine and its auxiliaries maintenance Standard Configuration (excluding inlet/exhaust ducts/system): • LxWxH = 9.1mx3.5mx3.7m ,Weight 38t Control Steam or water injection systems for NOx abatement Dry Low Emission (DLE) combustion system

Performance Info Generator Drive: (Expected Performance at ISO Conditions with fuel natural gas) Model Output Heat Rate Exhaust Flow Exhaust Temperature PGT25 22417 kWe 9919 kJ/kWh 68.9 Kg/s 525 °C Mechanical Drive: (Expected Performance at ISO Conditions with fuel natural gas) Model Output Heat Rate Exhaust Flow Exhaust Temperature PGT25 23260 kW 9560 kJ/kWh 68.9 kg/s 525 °C P. 1-10 INTRODUCTION

MS 5001 Overview The MS5001 single shaft turbine is a compact heavy-duty turbine designed for long life and easy maintenance. The MS5001 gas turbine is the ideal solution for industrial power generation where low maintenance, reliability and economy of fuel utilization are required. Low investment costs make the MS5001 package power plant an economically attractive system for peak load generation. The MS5001 is ideally suited for cogeneration achieving very high fuel utilization indexes and allowing for considerable fuel savings. Typical applications are industrial plants for cogeneration of power and process steam or in district heating systems.


Emissions • •

Axial flow compressor, 17 stages Pressure ratio 10.5:1 Can-annular combustion, 10 chambers 2 stages First stage nozzles cooled

Complete turbine package mounted on a single baseplate Enclosure integrated with the baseplate providing maximum accessibility for gas turbine and auxiliaries maintenance Standard configuration (excluding inlet/exhaust ducts/system): • size LxWxH = 11.6mx3.2mx3.7m; • weight 87.5t Control Steam or water injection systems for NOx abatement Dry Low NOx (DLN) combustion system

Performance Info Generator Drive (Expected Performance at ISO Conditions with fuel natural gas) Model Output MS5001 26300 kWe



Exhaust Temperature 487 °C


MS 5002 Overview The MS5002 gas turbine was launched in the 1970s and it has been updated and up-rated along the years to match the higher power demand. Presently two versions are available: MS5002C - 38000 HP at ISO condition MS5002D - 43700 HP at ISO condition. The MS5002 is a gas turbine specifically designed for mechanical drive applications with a wide operating speed range to meet operating conditions of the most common driven equipment, centrifugal compressors and pumps. It also has the capability to burn a large variety of gaseous and liquid fuels. Almost 500 units (more than 300 of which were manufactured by Nuovo Pignone) have been installed world-wide in all possible environments including arctic, desert, offshore, etc., always demonstrating easy operability as well as very high reliability and availability. The simple design and robustness of the machine allow for complete maintenance to be performed on site without the need for special tools or service shop assistance. Typical applications include Gas Boosting, Gas Injection/Reinjection, Oil & Gas Pipelines, LNG plants and Gas Storage

Design Info Compressor MS5002C • Sixteen stages axial compressor • Pressure ratio 8.9:1 MS5002D • Seventeen stages axial compressor • Pressure ratio 10.8:1 Combustion • Reverse flow, multi chamber (can-annular) combustion system (12 chambers) Turbine • Single stage Gas Generator turbine • Single stage power turbine (4670 RPM rated speed) with variable angle nozzles. Package • Two baseplates configuration (gas turbine flange to flange unit and auxiliary system. • Enclosures integrated with the baseplates providing maximum accessibility for gas turbine and auxiliaries maintenance • Standard configuration (excluding inlet/exhaust ducts/system): • size LxWxH = 15.0mx3.2mx3.8m • weight 110t Emissions Control • Steam or water injection systems for NOx abatement • Dry Low NOx (DLN) combustion system

Performance Info Mechanica Drive (Expected Performance at ISO Conditions with fuel natural gas) Model Output Heat Rate Exhaust Flow Exhaust Temperature MS5002C 28340 kW 12310 kJ/kWh 126.0 kg/s 515 °C MS5002D 32590 kW 11900 kJ/kWh 141.3 kg/s 510 °C P. 1-12 INTRODUCTION

PGT 25+ Overview The PGT25+ gas turbine has been developed for 30 MW ISO shaft power service with the highest thermal efficiency level (approx. 40%). The PGT25+ gas turbine consists of the GE Aeroderivative LM2500+ Gas Generator (updated version of LM2500 gas generator with the addition of zero stage to axial compressor) coupled with a 6100 RPM Power Turbine. Built on the LM2500 heritage and with demonstrated 99.6% reliability, the PGT25+ incorporates proven technology improvements and a large percentage of parts in common with LM2500 in order to deliver the same outstanding level of reliability. Designed for its ease of maintenance, the PGT25+ also provides a high level of availability. High efficiency and reliability are just two of large number of benefits contributing to PGT25+ customer value. Application flexibility makes the PGT25+ ideal for a range of mechanical drive (gas pipeline etc.), power generation, industrial cogeneration and offshore platform applications in any environment.


Emissions • •

Seventeen stages axial compressor Pressure ratio 21.5:1 Annular combustion chamber (30 fuel nozzles) Two stage Gas Generator turbine Two stage Power turbine (6100 RPM)

Gas Generator, Power Turbine and auxiliary System mounted on a single baseplate The enclosure is integrated with the baseplate providing maximum accessibility for gas turbine and auxiliaries maintenance Standard Configuration (excluding inlet/exhaust ducts/system): • size LxWxH = 6.5mx3.6mx3.9m (gas turbine and auxiliary baseplate) • weight 38t (gas turbine and auxiliary baseplate) Control Steam or water injection systems for NOx abatement Dry Low Emission (DLE) combustion system

Performance Info Generator Drive: (Expected Performance at ISO Conditions with fuel natural gas) Model Output Heat Rate Exhaust Flow Exhaust Temperature PGT25+ 30226 kWe 9084 kJ/kWH 84.3 Kg/s 500 °C Mechanical Drive: (Expected Performance at ISO Conditions with fuel natural gas) Model Output Heat Rate Exhaust Flow Exhaust Temperature PGT25+ 31360 kW 8754 kJ/kWh 84.3 kg/s 500 °C P. 1-13 INTRODUCTIONS

MS 6001 Overview The MS6001 is a single shaft heavy-duty gas turbine. Its design was based on the well proven mechanical features of the MS5001 in order to achieve a compact, high efficency unit. The MS6001 is widely applied in power generation applications for base, mid-range and peak load service. Other typical applications include driving of process machines, such as compressors, in LNG plants. Combined cycle plants based on MS6001 achieve very high efficiencies with higher availability and reliability than conventional thermal plants.

Design Info Compressor • • Combustion • • Turbine • • Package • • •

Emissions • •

Axial flow compressor, 17 stages Pressure ratio 11.9:1 Can-annular combustion, 10 chambers Dual fuel capability 3 stages, first two cooled buckets First 2 stage nozzles cooled

Complete turbine package mounted on a single baseplate Enclosure integrated with the baseplate providing for maximum accessibility for gas turbine and its auxiliaries maintenance Standard configuration (excluding inlet/exhaust ducts/system): • size LxWxH = 15.9mx3.2mx3.8m; • weight 96t Control Steam or water injection systems for NOx abatement Dry Low NOx (DLN) combustion system

Performance Info Generator Drive: (Expected Performance at ISO Conditions with fuel natural gas) Model Output Heat Rate Exhaust Flow MS6001B 42100 kWe 11230 kJ/kWh 145.8 kg/s


Mechanical Drive: (Expected Performance at ISO Conditions with fuel natural gas) Model Output Heat Rate Exhaust Flow Exhaust Temperature MS6001B 43530 kW 10825 kJ/kWh 145 kg/s 544 °C

Experiences •

More than 46 units sold

P. 1-14 INTRODUCTION

LM 6000 Overview The GE LM6000 delivers more than 44.8 MW of power at over 42.7% thermal efficiency. It is the world’s most fuel-efficient, simple-cycle gas turbine. High efficiency, low cost and easy installation make the LM6000 the perfect modular building block for electrical power applications such as industrial cogeneration of utility peaking, both midrange and base-load operations. As an aircraft engine aboard the Boeing 747, the LM6000 has logged more than 10 million flight hours, with the lowest shop visit rate of any jet engine. Continuing the tradition of GE’s LM6000 established record, the LM6000 is ideal as a source of drivepower for pipeline compression, offshore platforms, gas reinjection and LNG compressors. The LM6000 has been GE’s first aeroderivative gas turbine to employ the new Dry-Low Emission premixed combustion system; this system is retrofittable on LM6000’s already in operation. Water or steam injection can also be used to achieve low NOx emissions.

Design Info Compressor • • • Combustion • Turbine • • Package • • •

Emissions • •

Low pressure compressor 5 stages High pressure compressor 14 stages Pressure ratio 30:1 Annular combustion chamber High Pressure turbine 2 stages Low Pressure turbine 5 stages

Gas Generator, Power Turbine and auxiliary system mounted on a single baseplate The enclosure is integrated with the baseplate providing maximum accessibility for gas turbine and auxiliaries maintenance Standard configuration (excluding inlet/exhaust ducts/system): • size LxWxH = 9.3mx4.2mx4.4m • weight 31t Control Steam or water injection system for NOx abatement Dry Low Emission (DLE) combustion system

Performance Info Generator Drive: (Expected Performance at ISO Conditions with fuel natural gas) Model Output Heat Rate Exhaust Flow LM6000 43076 kWe 8707 kJ/kWh 131 Kg/s


Mechanical Drive: (Expected Performance at ISO Conditions with fuel natural gas) Model Output Heat Rate Exhaust Flow Exhaust Temperature LM6000 44740 kW 8455 kJ/kWh 127 kg/s 456 °C


MS 7001 Overview The MS7001EA is a single shaft heavy-duty gas turbine for power generation and industrial applications requiring the maximum reliability and availability. With design emphasis placed on energy efficiency, availability, performance and maintainability, the MS7001EA is a proven technology machine with more than 500 units of its class in service. Typical applications in addition to the 60Hz power generation service are large compressor train drives for LNG plants.

Design Info Compressor • • Combustion • Turbine • Package • • •

Emissions • •

Seventeen stages axial compressor Pressure ratio 12.5:1 Reverse flow, multi chamber (can-annular) combustion system (10 chambers) Three stages turbine (3600 RPM)

Two baseplates configuration (gas turbine flange to flange unit and auxiliary system) Enclosures integrated with the baseplates providing maximum accessibility for gas turbine and auxiliaries maintenance Standard configuration (excluding inlet/exhaust ducts/system): • size LxWxH = 11.6mx3.3mx3.8m • weight 121t Control Steam or water injection systems for NOx abatement Dry Low NOx (DLN) combustion system

Performance Info Generator Drive: (Expected Performance at ISO Conditions with fuel natural gas) Model Output Heat Rate Exhaust Flow MS7001EA 85100 kWe 11000 kJ/kWh 300 kg/s


Mechanical Drive: (Expected Performance at ISO Conditions with fuel natural gas) Model Output Heat Rate Exhaust Flow Exhaust Temperature MS7001EA 81590 kW 11020 kJ/kWh 278 kg/s 546 °C

P. 1-16 INTRODUCTION

MS 9001 Overview The MS9001E is a single shaft heavy-duty gas turbine. It was developed for generator drive service in the 50 Hertz market. The MS9001E is widely applied in power generation for base, mid-range and peak load service. Combined cycle plants based on MS9001E achieve very high efficiencies with higher availability and reliability than conventional thermal plants.

Design Info Compressor • • Combustion • • Turbine • • Package • • • •

Axial flow compressor, 17 stages Pressure ratio 12.6:1 Can-annular combustion, 14 chambers Dual fuel capability 3 stages, first two cooled buckets First 2 stage nozzles cooled Two baseplates configuration (gas turbine flange to flange unit and auxiliary system) Enclosures integrated with the baseplates providing maximum accessibility for gas turbine and auxiliaries maintenance Standard configuration (excluding inlet/exhaust ducts/system): • size LxWxH = 22.1mx4.5mx6.3m • weight 217.5 Emissions Control • Steam or water injection systems for NOx abatement • Dry Low NOx (DLN) combustion system

Performance Info Generator Drive: (Expected Performance at ISO Conditions with fuel natural gas) Model Output Heat Rate Exhaust Flow MS9001E 123400 kWe 10650 kJ/kWh 412.8 kg/s


Experiences •

44 Units sold


TYPE

POWER

MAX EFFiCIENCY

GE 2

2,0MW

25 %

GE 5 (1/2 shaft)

5,2 - 5,4 MW

26,9 %

GE 5 B

5,9 - 6,2 MW

32 %

PGT 10

10,5 MW

32,6 %

GE 10 B(1/2 shaft) 11,7 MW

33 %

PGT 16

14,2 MW

36,9 %

PGT 25

23,2 MW

37,7 %

MS 5001

26,3 MW

28,5 %

MS 5002 C-D

28,3 -32,5 MW

29,2 - 30,3%

PGT 25+

29,9 MW

40, 3 %

MS 6001 B

42 MW

32,5 %

LM 6000

44,8 MW

41,1 %

MS 7001 EA

81,5 MW

32,7 %

MS 9001 E

123,4 MW

33,8 % P. 1-18

INTRODUCTION

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Nuovo Pignone INDEX CHAP. 2 Page 2.

THEORETICAL OPERATING SCHEME .........................................................2-1 2.1

OPERATING PRINCIPLE ........................................................................2-2

2.2

MAIN COMPONENT PARTS OF A GAS TURBINE .............................2-4 2.2.1 2.2.2 2.2.3

2.3

BRAYTON CYCLE ...................................................................................2-7

2.4

INFLUENCE OF EXTERNAL FACTORS ON GAS TURBINE PERFORMANCE .........................................................2-14

2.5

INFLUENCE OF INTERNAL FACTORS ON GAS TURBINE PERFORMANCE .........................................................2-16


Compressor .....................................................................................2-5 Combustion section ........................................................................2-6 Turbine section ...............................................................................2-7

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THEORETICAL OPERATING SCHEME Fig. 2.1 shows an example of a gas turbine (in this specific case, it is our MS6001 gas turbine) with a sectional view of the machine properly said. This figure has the purpose to highlight the main component parts involved in the operating cycle.

AUSILIARI AUXILIARIES

FLANGIA-FLANGIA FLANGE TO FLANGE

BASAMENTO BASEPLATE

Fig. 2.1 - Example of a simple cycle gas turbine (single shaft) The main component parts illustrated in Fig. 2.1 are: •

machine, generally called flange - flange

•

auxiliary equipment

•

baseplate

The above systems are completed by the suction, exhaust and control systems, which, like the auxiliary equipment and the baseplate, are dealt with in the relevant chapters, whereas here only details about their arrangement and interface with the flange-flange assembly (Fig. 2.1) are described. In fact, this chapter deals exclusively with the operating principles of a flangeflange.


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Nuovo Pignone 2.1

OPERATING PRINCIPLE A gas turbine works in the following way: •

it aspirates air from the surrounding environment;

•

it compresses it to a higher pressure;

•

it increases the energy level of compressed air by the addition of fuel gas which undergoes combustion in a combustion chamber;

•

it directs high pressure and high temperature air to a turbine section, which converts thermal energy into mechanical energy that makes the shaft revolve; this serves, on the one hand, to supply useful energy to the driven machine, coupled to the machine by means of a coupling and, on the other hand, to supply energy necessary for air compression, which takes place in a compressor connected directly with the turbine section itself;

•

it expels low pressure and low temperature gases resulting from the abovementioned converting process into the atmosphere.

Fig. 2.2 overleaf shows the behavioral pattern of pressures and temperatures, in terms of quality, inside the different machine sections corresponding to the abovementioned operating phases.


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Fig. 2.2


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Nuovo Pignone Fig. 2.2 enhances the fact that combustion takes place under almost constant pressure conditions. Unlike alternative motors, compression and expansion take place on a continual basis, as happens for power generation. On the contrary, in an alternative motor (for ex., a four-stroke, eight cycle motor), though power is generated in the expansion phase, like in a turbine, this process takes only 1/4 of the complete cycle, whereas in a gas turbine expansion takes place continually all through the cycle. The same applies to compression. For the same reason, along with the fact that there are no masses in alternate motion, the degree of regularity of the running cycle of a gas turbine is incomparably greater than that of an alternative motor (eight or Diesel cycle).

2.2

MAIN COMPONENT PARTS OF A GAS TURBINE

Fig. 2.3 - A sectional View of a Gas Turbine

A gas turbine (Fig. 2.3) is composed of three main sections, described in the following paragraphs. As concerns design and construction features, these are extensively dealt with in Chapter 3.


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Nuovo Pignone 2.2.1 Compressor The compressor shall be of the axial type (Fig. 2.3). The choice of this type of compressor depends on the fact that this compressor is capable to deliver high air output ratings, necessary to obtain high values of useful power in a reduced size. This concept will be resumed later, when the main thermodynamic ratios in the operating cycle of a gas turbine are described. A compressor consists of a series of stages of rotating blades, which increase air speed in terms of kinetic energy, followed alternately by stages of stator blades, which convert kinetic energy into higher pressure. The number of compression stages is related to the structure of the gas turbine and, above all, to the compression ratio to be obtained. At the compressor inlet side, there are Inlet Guide Vanes (or, IGV), whose primary purpose is to direct air, delivered by the suction system, towards the first stage of rotating blades. Another important function of IGVs is to ensure a correct behaviour by the compressor, in terms of fluid dynamics, under different transient operating conditions (for example, during start-up and shut down) when, due to different running speeds as apposed to normal operating speed, the opening angle of IGVs is changed: this serves to vary the air delivery rate and to restore ideal speed triangles in transient phases. Finally, in combined cycles and in the co-generation process, the capability to change the geometrical position of IGVs permits to optimise temperatures at the turbine exhaust side and, thus, to increase the efficiency of the recovery cycle by varying the flow rate of the air entering the compressor. At the compressor output side there are a few stages of Exit Guide Vanes or EGV, necessary to obtain maximum pressure recovery before air enters the combustion chamber. The compressor serves also to supply a source of air needed to cool the walls of nozzles, buckets and turbine disks, which are reached via channels inside the gas turbine, and via external connecting pipings. Additionally, the compressor supplies sealing air to bearing labyrinth seals.


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Nuovo Pignone 2.2.2 Combustion Section In the case of "heavy duty" gas turbines as the one shown in Fig. 2.3, the combustion section consists of a system of one or more tubular combustion chambers (in this specific case there are ten combustion chambers) arranged symmetrically and evenly in a circumference; these chambers receive and burn fuel by means of an equal number of burners (one per combustion chamber). Air enters each chamber with a flow direction inverse to that of the hot gases inside (for this reason, this method of air distribution is called "reverse flow"). This external flow, which marginally touches the various chambers, serves to cool them. In addition, the part of air that does not take part in the combustion process is used for cooling the combustion products; in fact, it is introduced into the chambers through “diluition” holes until optimal temperature conditions are established to allow the gas and air mixture into the turbine section. Air passage from the combustion section properly said to the gas turbine inlet takes place inside manifolds called “transition pieces”; here, the gases flowing out of the single combustion chambers are led to form a continuous annular profile, equal to the one that leads into the first stage nozzles ring. Initially, the combustion process is ignited by one or more spark plugs. Once ignited, combustion proceeds in a self-sufficient way without the help of spark plugs, as long as the delivery conditions of fuel and combustion air are fulfilled. In the case of gas turbines built for the aviation industry (LM , PGT16 and 25 range), the combustion section consists of a single chamber of toroidal shape, with direct and not "reverse flow" cooling; in fact, this helped reduce external diametral sizes, since a smaller frontal section was needed in order to offer as little resistance as possible to aircraft motion. For the same reason, this combustion chamber does not need any separate transition pieces. The other operating principles are the same as those described for tubular chambers.


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Nuovo Pignone 2.2.3 Turbine Section In the case of "heavy duty" turbines, as shown in Fig. 2.1, the turbine section comprises a certain number of stages (in this specific case, three stages), each one of them consisting of one stator stage (distributor nozzle); in this stage, high temperature and high pressure gases delivered by the transition piece described beforehand are accelerated and directed towards the rotor stage of buckets mounted on a disk connected with the power shaft. As mentioned before (para. 2.1), the conversion of thermal energy and pressure into kinetic energy takes place in the stator stage. The rotor stage completes this conversion, as here kinetic energy is transformed into energy that drives the shaft, thus generating the power required to drive the compressor (internal compression work, cannot be used as externally useful work) and to operate the driven machine (generator, compressor, etc.) connected to the gas turbine by means of a coupling. The energy of gases supplied by the combustion system can be varied by changing the delivery rate of fuel. In this way you can regulate the useful power values needed for the technological process of which the gas turbine is the motor. 2.3

BRAYTON CYCLE The thermodynamic cycle according to which a gas turbine works is known as the Brayton cycle. Fig. 2.4 illustrates a diagram of a gas turbine (in this specific case, an MS6001 single shaft turbine). This diagram is useful to understand the meaning of the thermodynamic cycle more easily.

Fig. 2.4 - Gas Turbine Operating Diagram Air enters the compressor at point (1), which represents ambient air conditions. These conditions are classified according to pressure, temperature and relative humidity values.


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Nuovo Pignone It was agreed that standard design conditions be classified as ISO Conditions, to which there correspond the following reference values:

ISO CONDITIONS Ambient temperature (°C) Ambient pressure (mbar) Relative humidity (%)

15 1013 60

Afterwards, air is compressed inside the compressor, and exits in the condition indicated at point (2). During the converting process from (1) to (2), no heat is released outside. However, air temperature increases, due to polytropic compression, up to a value variable depending on gas turbine model and ambient temperature. After leaving the compressor, air enters the combustion area, practically under the same pressure and temperature conditions as at point (2) (except for losses undergone on the way from the compressor delivery side to the combustion chamber inlet, which amount to about 3 to 4% of the absolute value of delivery pressure). Fuel is injected into the combustion chamber via a burner, and combustion takes place at practically constant pressure. Conversion between points(2) and (3) represents not only combustion. In fact, the temperature of the combustion process properly said, which takes place under virtually stechiometric conditions, reaches excessively high values (around 2000 °C) locally in the combustion area next to the burner, due to the resistance of materials downstream. Therefore, the conversion final temperature, relative to point (3), is lower, as it is the result of primary gases mixing with cooling and dilution air as described previously. In this regard, it is useful to give some definitions of temperature at point (3), which is the maximum cycle temperature or firing temperature (see Fig. 2.5).


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Fig. 2.5 - Firing temperature Section A refers to the so-called "turbine inlet temperature", which is the average temperature of gases in plane A. Section B refers to the so-called “firing temperature”, which is the average gas temperature in plane B. Section C refers to the so-called “ISO firing temperature", which is the average gas temperature in plane C, calculated as a function of the air and fuel flow rates via a thermal balance of combustion according to the ISO 2314 procedure. The difference in the interpretation of temperatures in sections A and B consists in the fact that, on gas turbines like those which we are dealing with in this training course, in section B we take into account the mixture of 1st stage nozzle cooling air, which was not involved in the combustion process, but mixes with burnt gases after cooling the surface of the nozzle. According to the Nuovo Pignone - General Electric standard, the temperature that best represents point (3) is the one in section B.


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Nuovo Pignone The following transformation, comprised between points (3) and (4), represents the expansion of gases through the turbine section, which, as mentioned before, converts therma energy and pressure into kinetic energy and, thanks to the revolutions of the power shaft, into work used for compression (internal, not useable) and external useful work, thanks to the connection with an operating machine. Over 50% of the energy developed by expansion in the gas turbine is absorbed by the axial compressor for its compressing work. Downstream of section (4), gases are exhausted into the atmosphere. The thermodynamic representation of the events described so far is visible in Fig. 2.6 (pressure diagrams - volume P-V and temperature - entropy T-S).

Fig. 2.6 - Brayton Cycle In the cycle illustrated in the above figure, the 4 points correspond to the same described before. In particolar, note the compression and expansion transformations, obviously these are not isoentropic. In this respect, please remember that: the specific compression work Wc , from (1) to (2), is expressed with good approximation by the following ratio: Wc = Cpm(T2-T1) • (T2-T1)

(Kj/Kgasp. air)

the specific expansion work Wt , from (3) through (4), is expressed by: Wt = Cpm(T3-T4) • (T3-T4)

(Kj/Kggas.)

Heat Q1, supplied to the combustion chamber from (2) to (3), is expressed by: Q1 = Cpm(T3-T2) • (T3-T2)


(Kj/Kggas.)

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Nuovo Pignone The gas turbine cycle "closes" ideally with the transformation from (4) to (1), which corresponds to the cooling of exhaust gases, in that heat Q2 is aspirated out into the atmosphere, as though the latter were a refrigerant of infinite capability. The thermodynamic ratio that describes the cooling process of exhaust gases is the following: Q2 = Cpm(T4-T1) • (T4-T1) (Kj/Kggas.) The various values for Cpm, expressed in the preceding ratios, represent the average specific heat at constant pressure between the extreme temperature values in the interval examined. For a more rigorous evaluation, it would be necessary to proceed by means of integral calculation. Once Q1, Q2, Wc and Wt, are known, you can obtain the valuesforthe following significant parameters: Thermodynamic efficiency η = (Q1 - Q2)/Q1 This ratio means that, by parity of heat Q1, introduced into the combustion chamber by fuel, efficiency will increase as heat Q2 decreases, “dissipated” into the atmosphere. We will see in Chap. 8 how to recover this heat partially in combined cycles and in the regenerative cycle. Useful work Nu supplied to the driven machine = GgasWt - GariaWc In the latter ratio, Ggas and Garia correspond respectively the weight of gases delivered to the turbine inlet section, and to the air aspirated by te compressor, necessary to pass from specific to global values. So far, all descriptions and examples refer to a single shaft turbine like MS 6001. In fact, in the diagram illustrated in Fig. 2.4, the entire turbine section is connected mechanically witht the axial compressor. Such types of single shaft turbines are suitable for driving operating machines that run at constant speed, such as alternators and, for this reason, are used typically in the generation of electric energy. In applications, in which power regulation is achieved by means of speed variation in the driven machine, two-shaft gas turbines are usually employed (see diagram in Fig. 2.7); in this case, the turbine is divided into two mechanically separate sections: • •


A high pressure section, which runs at constant speed within a wide range of powers, and drives exclusively an axial compressor. A low pressure section, connected with the operating machine via a coupling; this section can vary its running speed independent of the high pressure turbine section.

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Nuovo Pignone This configuration, with the addition of other elements which will be described in Chapter 4, serves to regulate the driven machine speed without the need to vary the speed of the axial compressor; thus, the latter may continue to run at its design speed, with optimal efficiency.

Fig. 2.7 - Two Shaft Gas Turbine Diagram The ratios described so far apply in general to all machine types. The classical concepts of thermodynamics permit to give a correct evaluation to the Brayton cycle and to the influence by parameters such as pressures, temperatures, specific heats, polytropic exponents, etc. A diagram in Fig. 2.8 expresses the ratios among the following parameters: • • • •


Firing temperature T3 (°C) Compression ratio Thermal efficiency Specific power (KW/(Kg/sec.))

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Fig. 2.8 - Relations between significant thermodynamic quantities This diagram indicates that: a)

b)

c) d)


under equal temperature T3, maximum efficiency is reached by increasing the compression ratio. The maximum efficiency value does not corresponds to the maximum specific power. The higher the increase in the compression ratio, the greater the benefit provided by increased firing temperature T3 for specific power and efficiency values. However, it is not possible to exceed certain values for T3, because of limitations imposed by the resistance of the materials currently available. The increase in temperature T3 represents therefore a very important parameter that requires vast and constant efforts in the research about materials, blade cooling technology, etc., in order to achieve reliable and efficient products capable to meet ever growing demands by the market. Specific power is important, because, to a higher specific power there corresponds a gas turbine of smaller size, though of equal power output. Efficiency is important, because the higher the efficiency, the lower the consumption and operating costs.

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Nuovo Pignone 2.4

INFLUENCE OF EXTERNAL FACTORS ON GAS TURBINE PERFORMANCE A gas turbine uses ambient air, therefore, its performance is greatly affected by all factors that influence the flow rate of air delivered to the compressor, in terms of weight. These factors are: • • •

Temperature Pressure Relative humidity

In this regard, we remind you that reference conditions for the three abovementioned factors are, by convention, ISO standards (para. 2.3). As the compressor inlet temperature increases, there increases the specific compression work, while the weight of the air delivered decreases (because of a decrease in specific weight γ). Consequently, the turbine efficiency and useful work (and, therefore, power) diminish as well. If temperature decreases, the reverse occurs. This dependence of temperature on the air aspirated by the compressor and power and efficiency varies from turbine to turbine, according to cycle parameters, compression and expansion output and air delivery rate. Fig. 2.9 shows an example of how power, specific consumption (heat rate) and the delivery rate of exhaust gases depend on ambient temperature.

Fig. 2.9 - Influence of ambient temperature on turbine performance


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Nuovo Pignone Specific consumption, dimensionally represented in figure 2.9 as HEAT RATE, is the inverse of efficiency, in that it indicates the ratio between thermal energy, resulting from the combustion process, and mechanical energy, supplied to the power shaft (or to the generator terminals, if we consider the performance of a load gear and generator, if present). To summarise, we call Q1 the energy resulting from combustion and Nu the external useful work: thus, specific consumption or Heat Rate is defined as:

HR = Q1/Nu and is generally expressed as Kj/Kwh.

If the atmospheric pressure decrases in comparison with the ISO reference pressure, there decreases the weight of air delivered (because of a reduction in its specific weight) and, proportionally, there decreases the useful power, which is proportional to the weight of the gas delivered. On the contrary, the other parameters of the thermodynamic cycle (HR, etc.) are left uninfluenced. Fig. 2.10 shows the percentage pattern of the useful power of a gas turbine in relation to its installation altitude.

CORRECTION FACTOR

ATMOSPHERIC PRESSURE

CORRECTION FACTOR ATMOSPHERIC PRESSURE

ALTITUDE - 1000 FEET

Fig. 2.10


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Nuovo Pignone Relative humidity influences the specific weight of air aspirated by the compressor. In fact, humid air is less dense than dry air, so if the relative humidity increases,there decreases the power output and there increases specific consumption (HR) (Fig. 2.11). In the past, such an effect used to be neglected. Nowadays, as ever more powerful gas turbines are made and humidity is added in the form of water or steam by reduction of NOx, this effect must be taken into consideration.

Fig. 2.11 2.5

INFLUENCE OF INTERNAL FACTORS ON GAS TURBINE PERFORMANCE Next to the three “external” factors described in the preceding paragraph, there are other factors which notably affect the performance of a gas turbine. These may be called “internal” factors, because they are related to the auxiliary systems of the gas turbine. They are the following: • • • • • • •


Pressure drop in the compressor inlet section Pressure drop in the turbine exhaust system Fuel type Air extraction from the axial compressor Steam injection Water injection Evaporative cooling P. 2-16

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Nuovo Pignone Pressure drops in the compressor inlet section Pressure drops are caused by the gas turbine suction system, composed of an airfiler, a silencer, a length of duct, pipe section regulators, etc., installed upstream of the compressor suction flange. When air flows through this system, it is subjected to friction, which reduces its pressure and thus its specific weight. These drops cause a reduction in useful power and an increase in specific consumption or "heat rate", as mentioned previously in the case of the influence exerted by ambient pressure. Pressure drops in the turbine exhaust system These are caused by the exhaust system of the gas turbine, composed of one or more silencers, a length of duct, a recovery boiler (in the case of combined cycles or co-generation), diverters, shutters, etc., through which exhaust gases are expelled into the atmosphere. Exhaust gases flowing through this system are subjected to friction, which increases the value of back pressure as opposed to the value of external, atmospheric pressure. This reduces the amount of turbine expansion, as the latter terminates one isobar higher than the reference one, which results in reduced useful power and increased specific consumption (heat rate). Table 2.1 reports the typical values by which performance is dependent on pressure drops at the compressor inlet section and at the turbine exhaust section. For the reasons explained above, this dependance is proportional to the values of pressure drop. TABLE 2.1 EFFECTS OF PRESSURE DROPS Every 100 mm H2O at suction : 1.42 % power loss 0.45 % increase in Heat Rate 1 °C increase in exhaust temperature

Every 100 mm H2O at exhaust : 0.42 % power loss 0.42 % increase in Heat Rate 1 °C increase in exhaust temperature

Fuel gas influence Best performance is achieved if natural gas rather than diesel oil is used. In fact, output power under base load power and under equal conditions (environmental, pressure drops , etc.) will be about 2% greater and specific consumption (Heat Rate) between 0.7 and 1% lower, depending on gas turbine model. These differences will become all the more remarkable if we compare performances obtained with natural gas and with progressively "heavier"fuel types, such as residuals, Bunker C, etc. This behavior is due to the higher heating power of products originated by the combustion of natural gas, as the latter has a higher content of water vapour, resulting from a higher ratio between hydrogen and carbon, which is typical of methane, the main component part of natural gas.


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Nuovo Pignone Gaseous fuels with a lower calorific value than natural gas (commonly called "low btu gases") can greatly influence the performance of a gas turbine. In fact, if the calorific value diminishes (Kj/Nm3), the weight of fuel delivered to the combustion chamber must increase to provide the necessary amount of energy (Kj/h). This addition in the weight of the fluid, which is not even compressed by the compressor, provokes an increase in power (see the definition of useful work at para. 2.3) and a reduction in specific consumption. In this case, the power absorbed by the compressor is left substantially unvaried. However, in the case of combustion of “low btu gases”, the following side effects must be taken into consideration: •

•

•

An increase in the weight of fluid delivered to the turbine increases the compression ratio in the compressor, which must not come too near the surging limit. An increase in the fuel delivered often requires larger diameters of tubings and control valves (and, consequently, higher costs). This effect is all the more conspicuous in the case in which also the temperature of a gas and, therefore, its specific volume, are higher (for example, gases produced by coal gassing). Gases with a low calorific value are frequently enough saturated with water vapour upstream of the gas turbine combustion system. This provokes an increase in the coefficients of heat transmission by combustion products, and an increase in metal temperature on hot parts of the turbine.

Air extraction from the axial compressor On some gas turbine applications (chemical processes, pipe blowing during the commissioning stage, etc.) it may become necessary to extract compressed air from the compressor delivery side. As a general rule, and unless prescribed otherwise in the case of machines originally built for the aviation industry, it is possible to extract as much as 5% of the air delivered by the compressor without the need to alter the turbine layout at all. It is possible to achieve extraction values ranging between 6 and 20 % , depending on the machine and combustion chamber configuration, if alterations are made to casings, pipings and the control system. Fig. 2.12 shows how percentages of air extraction influence output power and specific consumption (heat rate), taking into consideration also ambient temperature.


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HEAT RATE (%)

HEAT RATE (%)

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Fig. 2.12

Steam injection and water injection Steam or water injection may have the following two purposes: • •

a reduction in nitrogen oxide (NOx) level. an increase in output power.

Reducing the nitrogen oxide (NOx) level The method of steam or water injection was introduced in the early 70s to limit and control the presence of nitrogen oxides or NOX. Injection is usually performed in the area where the combustion chamber cap is present. The injection system is built in a way to set a limit to the amount of injectable steam or water, in order to safeguard stability and continuity in the combustion process. Anyway, the amount of steam and water injected is sufficient to guarantee a massive reduction in the level of NOx. According to the amount of steam or water injected into the combustion chamber, which the turbine control system automatically monitors in relation to the NOx level desired, output power will increase consequently to an increase in the mass of fluid delivered through the gas turbine. In the case of steam injection, the Heat Rate or specific consumption will also decrease for the same reasons that apply to fuel gases with a low calorific value. On the contrary, the latter advantage does not exist in the case of water injection, as here a higher quantity of fuel is needed to vaporize water to the condition that allows it to be injected into the combustion chamber.


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Nuovo Pignone In condition of peak duty, with a maximum of 1250 hours/year, it is possible to increase the water delivered through the combustion chamber cap area in order to increase the gas turbine power output. Obviously, this calls for shorter maintenance intervals. As concerns the maximum water flow rates and maintenance procedures, these must be evaluated case by case, depending on the machine model and its combustion system. Output power increase Steam injection for increasing the gas turbine output power has been available and warranted by over 30 years' experience. Unlike water, steam is injected into the compressor exhaust casing, thus eliminating all limitations imposed in order to safeguard stability in the combustion process. For this reason, the maximum amount of injectable steam is limited to percentage values of the weight of air aspirated by the compressor. Steam must be overheated, and there must be at least 25 °C difference with respect to the compressor delivery temperature; steam supply limit pressure must be at least 4 bar(g) greater than maximum pressure in the combustion chamber. In the case of steam or water injection, the amount of steam injected in conditin of partial load must be equal to the amount required to abate NOx. Once the load base value is reached, the control system gives the OK to inject the additional steam needed to increase the turbine output power.


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Nuovo Pignone Fig. 2.13 shows the typical effects of steam injection on the output power of a gas turbine (in this case, an MS 5002 gas turbine) as a function of ambient temperature.

Fig. 2.13 - Effects of steam injection on output power (MS5002 Gas Turbine)


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Nuovo Pignone Evaporative cooling Curves in fig. 2.9 show clearly how power and efficiency increase as the compressor inlet temperature decreases. The latter can be reduced artificially by using an evaporative cooler located upstream of the suction filter. Water, fractioned into drops or in the form of a liquid film, cools the air by evaporating in the cooler as it flows in contrary direction, thus originating an adiabatic-isoenthalpic exchange (see fig. 2.14).

CELLE AD EVAPORAZIONE EVAPORATION CELLS

H20 HEADER COLLETTORE H2O COALESCER/DEMISTER COALESCER/DEMISTER

ARIA CALDA AMBIENTE

COOLED AIRREFRIGERATA ARIA VERSOAIR IL FILTRO TOWARD

AMBIENT HOT AIR

DELL’ARIA

FILTER

POMPA DI CIRCOLAZIONEPUMP H2O H 0 CIRCULATING 2

SUMP TANK SUMP TANK

Fig. 2.14 Evaporative cooler In order to prevent water from being drawn towards the compressor and fouling it, downstreams of the cooler there are one or more stages of drop separators (demisters), which, by inertia, separate any water drops that might be carried away downstream of the cooler by the flow of air aspirated by the turbine. Fig. 2.15 shows the effects of evaporative cooling on the gas turbine output power and specific consumption. As can be noted, benefits increase as relative humidity decreases and ambient temperature increases. Unfortunately, the above requirements are met in environments (for example, deserts), in which water is not always available in the amounts needed by the cooler.


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Fig. 2.15 Effects of Evaporative Cooling on Performance

Inlet chilling In environments in which a high degree of average relative humidity is present (higher than 60%) and ambient temperatures are not excessively high, it is advisable to cool air with a different method, commonly called "inlet chilling"; according to this method, air is cooled during a refrigerating cycle (based generally on absorption) carried out in a closed circuit. In this way, the restrictions imposed by relative humidity and by ambient temperature, described in the preceding system, can be eliminated. The minimum temperature reached by air at the end of the cooling process is strictly dependent on the capability of the refrigerating cycle to produce cold liquid and on the efficiency of the thermal exchange that takes place in the water - air exchanger. Figure 2.16 shows an operating diagram of this system (in this example, steam is used for the absorption cycle), composed of a chiller, water connecting pipings and a water - air exchanger, installed downstream of the gas turbine suction filter. Same as in evaporative cooling, also in this case it is necessary to install a coalescer/demister downstream of the system, in order to prevent humidity from reaching the compressor inlet section.


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Nuovo Pignone DEMISTER/COALESCER

DEMISTER/COALESCER

SCAMBIATORE

HEAT EXCHANGER

ARIA AMBIENTE AMBIENT AIR

CAMERA FILTRI

ARIA FREDDA COOLED AIR VERSO IL COMPRESSORE TOWARD COMPRESSOR

FILTERS CHAMBER

DRAIN DRENAGGIO

COOLING WATER INLET

INGRESSO ACQUA FREDDA CHILLER CHILLER

RITORNO ACQUA DA RAFFREDDARE

STEAM INLET VAPORE INGRESSO

ALLA TORRE DI RAFFREDDAMENTO TO COOLING

TOWER

Fig. 2.16 Air "chilling cooling" system, based on absorption

Figure 2.17 shows a comparison between the cooling powers of the two systems.

% RH const. lines

Saturation line

d PSYCHROMETRIC CHART

a b

constant moisture content line Kgwater/Kgair

c constant enthalpy line

Tc Tb

Td

Ta

Fig. 2.17 Comparison psychometric chart


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Nuovo Pignone Line a - d represents air cooling in the case of evaporative cooling. As mentioned before, this line follows the constant enthalpy line, resulting in a progressive increase in relative humidity. The restriction imposed by this cooling method consists in the fact that there remains a minimum distance from the saturation curve, compatibly with realistic exchange surfaces, considered from the point of view of construction. Normal values indicate around 90% relative humidity, that is, there still remains a 10% margin before the saturation line is reached. Under these conditions, the final air temperature is equal to Td. In the case of the chilling process, the cooling line has a constant moisture content along segment a - b. If the potential of the refrigerating cycle and the efficiency of the exchanger allow it, cooling can reach the saturation line and follow it along segment b - c, in which heat is removed to form condensate (H2O). In this second segment, there is a smaller temperature reduction, because most of the cooling energy serves for the condensing process and only a small part of it participates in lowering temperature. In the chilling system, the air final temperature will be equal to Tb or Tc, according to the chosen degree of cooling.


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MS5001 PA Complete Maintenance MANUAL

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