full paper fp a.5 clp ccgt upgrade - cepsi 2016 … crossover pipework lp cylinder lp cylinder...

FULL PAPER

FP_A.5_CLP_CCGT Upgrade

Major 9FA Combined Cycle Upgrade Works at Black Point Power Station for Improved

Efficiency and Lower Emissions

David Yip, Senior Project Manager, Generation Business Group, CLP Power Hong Kong Limited

(Telephone: +852 2678 4156, email: [email protected])

ABSTRACT

Black Point Power Station is one of the largest combined cycle gas turbine (CCGT) power stations in the world

consisting of 8 units of 9FA single-shaft generating units with a total capacity of 2500MW. To further improve

thermal efficiency and reduce nitrogen oxides (NOx) emission from the CCGT, a Gas Turbine Upgrade Project

was put forward commencing in 2014. Besides these performance improvements, the Project could also reduce

maintenance costs and contribute to the reliability of the units in the longer term.

This Paper is written to

describe changes to the thermodynamic cycle and the new design features that account for the upgrade

performance in efficiency, NOx emission and generating output

outline the approach and process to define the scope of works and boundary conditions based on the

examination of physical parameters, operating conditions and cycle performance parameters

present a summary of the execution pathway of the Project and the initial performance results

[Key Word] Combined cycle gas turbine, gas turbine, compressor, efficiency, NOx Emission, thermodynamic cycle,

combustion system

1. INTRODUCTION

Black Point Power Station (BPPS) is one of the largest combined cycle gas turbine (CCGT) power stations in

the world consisting of 8 units of 9FA single-shaft generating units with a total capacity of 2500MW. To

further improve thermal efficiency and reduce nitrogen oxides (NOx) emission from the CCGT, a Gas

Turbine Upgrade Project was put forward commencing in 2014.

The major scope of works in the Project includes the complete replacement of the gas turbine and

compressor, hot gas path components, combustion system, etc., and the associated modifications to other

plants including the heat recovery steam generator (HRSG) and generator transformer in the same single-

shaft configuration that are necessary to cope with the changes in operating conditions from the gas turbine.

2. PROJECT DESCRIPTIONS

2.1 DESIGN CHANGES TO THE THERMAL CYCLE

2.1.1 Configuration at Black Point Power Station (BPPS)

Each of the combined cycle units (CCGT) at BPPS is an identical configuration, where the Frame 9FA

gas turbine and the two-cylinder steam turbine drive one single generator, in a single-shaft line

arrangement. The HRSG is located at the axial exhaust of the gas turbine, in a “vertical” arrangement,

i.e. flue gas flows in a vertical direction through the HRSG, perpendicular to the arrangement of most

of the pressure piping in the HRSG.

Figure 2.1.1 - Descriptions of the Steam Cycle in the BPPS CCGT Arrangement

The gas turbine inlet duct connects the air filters located on the turbine hall roof to the compressor inlet

plenum and incorporates a silencer. The generating shaft line is supported on an elevated reinforced

concrete foundation. The shaft line auxiliaries are located either in the turbine hall (below the

generating shaft line) or in the mechanical annex alongside the unit.

The gas turbine shaft line comprises the following major equipment:-

Air inlet

Inlet guide vanes

Compressor (rotor and casing)

Combustor

Turbine (rotor and casing)

Exhaust frame

Exhaust diffuser

Load coupling

Bearings – journal and thrust

Support frame

Instrumentation

“On-base” pipe-works

The Unit electrical and control equipment is located in an electrical annex within the turbine hall

alongside the generator.

The physical space and footprint below the HRSG are fully utilized to accommodate the feed-water

pumps, chemical dosing, and sampling equipment and the condensate polishing plant.

2.1.2 Thermal Cycle Descriptions

The gas turbine operates in a thermal cycle that could be categorized by the Brayton cycle of which the

ideal cycle could be described in typical P-V & T-S diagrams.

Efficiency

η brayton = Ideal Brayton Cycle (thermal) efficiency

Rp = pressure ratio =

k = specific heat ratio

and Maximum WorkNET

when Rp

where Tmax (i.e. T3 limited by metallurgy) and

Tmin (i.e. T1 set by air temperature at inlet)

Figure 2.1.2 - Description of Ideal Brayton Cycle for the Gas Turbine

To produce higher cycle efficiency and generation output from the gas turbine, increasing the

compressor compression ratio and the turbine firing temperature are the typical approaches adopted

which are obvious from the Brayton cycle. But due to thermal fixation process, a higher turbine firing

temperature would favor the formation of nitrogen oxides (NOx) which is the key control emission

parameter from gas turbine of today. Therefore the selection of the new combustion system that would

provide a higher turbine temperature will have to strike a delicate balance between output, efficiency,

combustion dynamics, carbon monoxide, and NOx emission.

Finally a new type of dry low-NOx combustion system is adopted which is designed to offer the dual

benefits of higher turbine firing temperature and lower NOx emission. The extended use of pre-mix

fuel combustion was an important design and operation principle of the new dry-NOx combustion

system which would reduce the overall formation of NOx.

2.2 ENGINEERNIG

2.2.1 Holistic Engineering Approach

An overall holistic engineering approach was taken and is depicted in Figure 2.2.1 for illustration. This

comprises the following elements and objectives.

a) Thermal loading to the HRSG and Steam Turbine should be within the original design margin of

the installed equipment as modifications to these existing equipment could make the project more

costly and not commercial viable, and impose additional project execution risks

b) The above approach also applied to electrical loading on other equipment, including the Generator

and the Generator Transformer.

c) Capacity assessments were to be carried out on all the equipment to make sure that there is no

bottom-neck and cost of modifications, if any, were factored in the overall cost-benefit evaluation

of the Project

d) All new equipment and modifications had to be fitted into the existing “footprint” of the CCGT,

and constructability review was to be carried out together with engineering

e) Potential exchangeability of new equipment for use in other CCGT units in the same BPPS was

required to be evaluated.

Figure 2.2.1 – Overall Holistic Engineering Approach

2.2.2 Front-end Engineering

Gas Turbine Engineering

Gas turbine unit rotor, compressor discharge casing and turbine casing will be engineered by the gas

turbine supplier.

The existing compressor will be redesigned for robustness, increased pressure ratio and improved surge

margin. The new compressor rotor upgrade involves an incremental increase in rotor wheel diameters

in the heavy pressure stages with a corresponding decrease in the length of the rotor blades and the

stator vanes on these stages.

The turbine rotor will be of a new design that has the special cooling slot design on the wheels.

Gas Turbine Auxiliary Systems Engineering

The major change involves the conversion of the existing dry low-NOx combustion system to a new

type combustion system. The new dry low-NOx combustion system will provide improved combustor

operability, reduced emissions levels, extended turndown capability and extended interval hardware.

This new dry low-NOx system has more number of nozzles that improve flame stability and involve

changes in mode transition.

Generator and Generator Auxiliary Systems Engineering

The equipment supplier has conducted a review on the engineering and design changes required on the

generator and generator auxiliary systems. As the original generator capacity is adequate to cover the

increase in unit output after the gas turbine upgrade, no change is required for the generator and

generator auxiliary systems.

HRSG Engineering

The equipment supplier was engaged to identify necessary enhancement required on the HRSG to cope

with the increase in exhaust energy from the gas turbine exhaust. The following areas/issues were

reviewed by the equipment supplier:

Flow induced tube vibration

Attemperator

Flow accelerated corrosion

Inlet duct casing

HRSG casing

Expansion joint

Pressure parts

Sling system

Steam Turbine Engineering

The equipment supplier was engaged to identify necessary enhancement required on the steam turbines

and associated equipment to cope with the increase in steam flow. The following equipment were

reviewed by the equipment supplier to identify design modifications:

High Pressure (HP) steam chests

HP turbine pipework

HP valve actuators

HP rotor

HP inner and outer cylinders

HP inlet and cylinder bolting

HP blading

HP diaphragms

Low Pressure (LP) rotor

HP-LP crossover pipework

LP cylinder

LP cylinder bolting

LP blading

LP diaphragms

LP steam supply

HP & LP bypass systems

LP spray cooling system

Gland steam system

Turbine drains

Control fluid system

Lube oil system

Balance of Plant Engineering

The equipment supplier was engaged to identify necessary enhancement required on the BOP

equipment to cope with the increase in system demand. The following equipment were reviewed by the

equipment supplier to identify design modifications:

Condenser

Condensate extraction pump

HP boiler feed pump

LP boiler feed pump

Main cooling water pump

Condensate line to deaerator

Deaerator and feed water tank

Main control valves

Electrical System Engineering

The equipment supplier was engaged to identify necessary enhancement on the Load Commutated

Inverter (LCI) equipment to cope with the Project. As a result of the higher LCI torque required after

the upgrade, the maximum current rating of the LCI needs to be increased. The existing AC reactor and

heat exchanger will be replaced.

Engineering review and design changes required on the 415V system to cope with increase in electrical

loading of the equipment after the Project were carried out.

The Generator supplier was engaged to identify necessary enhancement required on the generator

transformer cooling system to cope with the increase in unit output.

Civil Engineering

The potential civil work includes:

Furnish and construct fuel gas module support structure.

Modify gas turbine pedestals, if necessary.

Flash and weatherproof penetrations (pipe, structural steel, equipment, duct, and other

miscellaneous) in Turbine Hall, if any.

Control Philosophy

All systems shall be designed such that no single failure of any control component will cause a trip of

the unit. All transmitters and plant sensors which could directly leading to tripping of a unit shall be

triplicated and their signals shall be used in a 2 out of 3 voting logic.

2.3 SCOPE DEFINITION AND DESIGN BASIS

By adopting this holistic engineering approach, the following definition of scope of work was defined at the

closure of front-end engineering as the design basis:-

i. Replace the existing compressor rotor with a new more robust design with a slight increase in

compression ratio

ii. Complete the upgrade of all hot-gas path components (i.e. stationary and rotating blades, etc) to

the new and robust design

iii. Replace the existing dry low-NOx combustion system to a new design that promote pre-mix

combustion and enable a higher firing temperature

iv. Complete the full replacement of fuel gas control system

v. Complete necessary upgrade of all GT auxiliary systems (more than 10 systems are required to be

upgraded or modified)

vi. Complete necessary upgrade of the Load Commutated Inverter (part of the excitation system)

vii. Complete some flow measuring and control devices in the fuel quality management system

viii. Complete some modifications of steam turbine (mostly on low-pressure steam turbine cylinder)

ix. Complete some minor modifications on the HRSG (mostly some flow control devices)

x. Complete some modifications of the Generator Transformer (mostly on the cooling system and

control)

Also as part of the design basis, the upgrade unit should be able to run on gas fuels with a wider range of

composition (and Modified Wobbe Index) without the need of hardware changes. The following table is a

typical requirement of potential variability of gas fuels.

Table 2.3 – Typical Requirement of Potential Variability of Gas Fuels

Potential Gas Fuel Gas Fuel 1 Gas Fuel 2

Composition

Methane mol% ~85 ~93

Carbon Dioxide mol% ~10 ~2

Nitrogen mol% ~1 ~1

Air mol% 0 0

Total 100 100

LHV (60oF, 1 atm.) Btu/scf 858 929

MWI at 55oC Btu/scf.R

1/2 42.7 49.1

MWI at 120oC Btu/scf.R

1/2 39.0 44.9

2.4 BOUNDARY LIMITS AND CONDITIONS

The Front-end Engineering had identified all the boundary limits and conditions for the Project. In particular

to boundary limits, the techniques of 3-D laser scanning and modeling were used extensively. This

technique had provided numerous inputs for physical dimensional analysis and general arrangement design

of various systems. As a specific application of this technique, physical clash and interference of new

equipment with the existing equipment had been effectively avoided.

3-D design model with laser scanning input

Existing equipment

Figure 2.4 – Application of 3-D Modeling, Laser Scanning and Constructability Review to avoid

interference both during installation and for permanent use

2.5 FINAL DETAILED DESIGN AND ENGINEERING

To meet the stringent reliability requirement of CLP, some rigorous studies were also carried out as part of

the final detailed design and engineering. These include the following studies:-

- Tuning of the Power System Stabilizer (PSS) of the upgrade CCGT unit

- Final bearing stress analysis based on the definitive design of the new gas turbine

- Structural and bearing capacity analysis of all new and modified plant and equipment

The PSS is a supplementary control that acts through the Automatic Voltage Regulator (AVR) of the

excitation system, and provides positive damping to generator rotor angle swings. These swings are in a

broad range of frequencies in a power system. Single-shaft CCGT such as the BPPS units have low

frequency torsional modes, which would more likely to interact with the PSS. This interaction was therefore

required to be assessed to determine whether there exists the need for torsional filters in the PSS to mitigate

the level of interaction to acceptable levels.

3. PROJECT EXECUTION

3-D design

iterative

modeling

Laser scan of existing

equipment to avoid

interference for permanent

use

Constructability review to

devise installation sequence and

fine-tune final assembly part

design

3.1 ENGINEERING MANAGEMENT

Site engineering reports were used to provide feedback from the Project Team to the respective Contractor of

engineering problems, suggested improvements, defects and omissions which are found during construction

and commissioning. The formal reports were issued by CLP and the Contractor would have to reply by a

formal response within a short period. These report will cover though not necessarily be limited to the

following types of problems:

Interfaces

Incompatibility of Equipment and civil works

Inappropriate Equipment supplied for a required duty

Omissions and shortfalls in the design and extent of supply

Inadequacies in shipping, packing and protection

Equipment failing to fulfill design requirements

Equipment failing during construction or commissioning tests

Where CLP wishes to make modifications to the Equipment as supplied which require comment from

the Contractor or which need to be incorporated in the Contractor’s drawings.

3.2 DOCUMENT MANAGEMENT

A specific document and drawing management software system was used to manage all the technical

submissions and correspondences between the Project Team, the equipment suppliers and contractors. This

software system served as a hub with security features to control the incoming and outgoing information,

tracked changes and version control of documents, and as a central database.

3.3 MATERIAL MANAGEMENT

Discrepancy reports were used to notify the Contractor of items were damaged in transit or short shipped.

Following receipting a discrepancy report, the Contractor shall supply replacement parts or make good the

omission as soon as possible.

3.4 CONSRUCTION PLANNING AND EXECUTION

All the Contractors were required to submit their site execution programme. The programme had to indicate

the erection and commissioning logic and duration of all activities and had to be coordinated with the

delivery programme and the design submission programme. The site execution programme was required to

be expanded to a level of details that could reasonably be used by CLP to control the relevant activities on

Site. CLP developed an overall Project’s schedule that integrated all Contractor’s site execution programmes

altogether.

“Technical Advisors” are personnel and specialists supplied by the Contractor to support the execution of the

Project on Site, including but not limited to equipment transportation, equipment preservation, engineering,

materials coordination, quality management, installation, cold commissioning, hot commissioning, tuning,

testing, start-up and tests on completion.

In this Project, technical advisors were required to ensure ‘Technical Compliance’ during the execution of

work on Site, including provision of services in areas including site handling, quality assurance, quality

compliance during installation, cold commissioning, hot commissioning start-up, tuning and testing work. In

addition, Technical Advisors shall prepare, validate and counter-sign completion statements during

installation, and prior to cold and hot commissioning.

CLP also required the contractor to make the Technical Advisors available promptly at CLP’s request.

Technical Advisors with valid work permits shall be nominated a few months prior to the start of

mobilization for confirmation by CLP.

Figure 3.4.1 – A Bird-eye View of the Site Showing Ongoing Major Construction Activities

Aerial view showing gas turbine systems installation

Internal view showing the installation of new

combustion system

Installation of “spaghetti-like” pipe-work / piping

serving each of the dual-fuel combustor

Modification works on the Fuel Gas Supply

Associated works on the Steam Turbine

Associated works on the Generator Transformer

Figure 3.4.2 – Photos Showing Other Construction Activities

3.5 COMMISSIONING PLANNING AND EXECUTION

A clear stage-by-stage commissioning programme covering construction completion, cold commissioning,

hot commissioning until handover of the facilities’ custodianship from project execution to operations was

developed. Check-sheets, transfer of project document custodianship, and facility walk-down were typically

used to signify the completion of different stages of commissioning. Figure 3.5.1 depicts the overall process

of this stage-by-stage commissioning programme.

Figure 3.5.1 – Overall Stage-by-Stage Commissioning Programme

Also a clear division of responsibility was agreed between CLP and Contractors through the respective

contracts.

Table 3.5.1 - Example of Division of Responsibility between CLP and Contractors

Contractor Activity / Responsibility (Examples only) CLP Activity (Examples only)

1. Mechanical Acceptance Package

Provide CLP with the Turnover Certification

Package for each system

Review – issue comments back to the

Contractor and distribute to other

parties.

2. Tie-Ins at Battery Limits (Interface Points)

Provide complete tie-in list, including the location

and method of each tie-in.

Review / Verify / Approve /

Coordinate

Provide a method statement for each tie-in point. Approve

Coordinate schedule of tie-in work with CLP Coordinate

3.6 TRAINING PRIOR TO OPERATION

The equipment suppliers were required to make available training services for CLP’s staff for any item of

Equipment supplied under the Contract, prior to commencement of operation. A training needs analysis was

carried out to match the overall operation and maintenance (O&M) needs as well as the competency

requirement of individual O&M personnel.

Venue of classroom and simulator training sessions were arranged local in Hong Kong to facilitate

involvement and participation of O&M personnel. More than 200 training man-days were recorded prior to

O&M personnel took over the facilities.

4. RESULTS AND DISCUSSIONS

The first CCGT generating unit upgrade was completed in early 2016, in a safety manner and ahead of

schedule. More about 250,000 man-hours were recorded for the first unit upgrade from project inception to

close-out without a lost-time injury, medical case or environmental incident.

The post-upgrade machine performance was satisfactory with test results generally better than the plan. For

example, the emission levels of NOx were consistently maintained to below 15 ppm (parts per million) with

an extended turndown ratio, hence allows a wider operability range for the upgraded CCGT unit to suit

system demand. Moreover, a higher level of adaptability to gas fuel with different Modified Wobbe Index

(MWI) has also been successfully tested, without any need for hardware and software changes.

Notes: Due to commercially sensitive information, only indicative figures on a

comparative basis were shown. Figures > 100% depict actual results better than planned

(i.e. 100%).

Figure 4 – Overview of the Project Performance and Benefits Realization

50%60%70%80%90%

100%110%120%130%140%150%

Safety

Schedule

Efficiency

Output

NOx Emission

Turndown

Project Performance and Benefits Realization

Plan

Actual

5. CONCLUSIONS The Project has been successfully implemented in one of the CCGT generating unit in the Black Point Power

Station in a safe manner, slightly ahead of original schedule and with good machine performance results after

upgrade. Hence upgrading existing CCGT generating units provides a feasible and sustainable way to uprate

thermal and emission performance of the entire combined cycle fleet.

REFERENCE

Nil

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