Paper on

COMBINED CYCLE POWER

PLANT PERFORMANCE

DEGRADATION

at PowerGen 98

YONG VOON YUI

YONG VOON YEE

PARAMJIT SINGH

SDN. BHD.

(420420-D)
Title ; Combined Cycle Power Plant Performance Degradation - PowerGen Asia Sept 98

Company : VY Consult (Consulting Engineers), Malaysia [Email - yong@vycon.po.my,Fax : 603-7032687]

Combined Cycle Power Plant Performance Degradation

Paramjit Singh, Vy Consult Sdn Bhd

Yong Voon Yee, Vy Consult Sdn. Bhd.

Yong Voon Yui, Vy Consult Sdn Bhd

Abstract

This paper investigates the causes and the effect of performance degradation in a combined

cycle power plant. Performance degradation ultimately affects the power output and heatrate

which in turn reduces the revenue while increasing the expenditure of the power plant.

Degradation issues should be carefully considered in the design and operation of the plant.

Degradation of equipment such as gas turbine generators, steam turbine generators, heat

recovery steam generators and condensers are discussed.

Degradation due to the normal wear and tear of the equipment is predictable based on the

operating experiences of the installed plants. Normal wear and tear refers to the situation

when the plant is operated at its design conditions. Degradation can be aggravated by the use

of improperly treated fuel and feedwater which is fed into gas turbine and HRSG make-up

respectively. Severe ambient operating conditions such as the presence of fine sand and dust

particles in the air which may pass through the air inlet filters can also cause the deterioration

of the gas turbine compressor.

Industrial practice in ways of minimizing the effects of performance degradation is discussed.

This includes the proper treatment of fuel and water, regular GTG compressor washing,

condenser tube cleaning and others.

Degradation characteristics of a combined cycle plant on the whole is discussed. This

includes prediction of degradation between periods of major overhaul.

A case study is discussed to demonstrate the effect of performance degradation on a typical

100 MW combined cycle power plant. The case study estimates the loss of revenue due to the

following conditions:

• Inlet air filter clogging

• Gas turbine compressor and turbine fouling

• HRSG tube fouling and scaling

• Condenser tube fouling and scaling

The paper further presents the degradation parameters in relation to loss of revenue such that

the plant operator can take positive steps to minimise degradation. The understanding of

predominant degradation parameters would enable suitable monitoring system be built into

the plant and formulation of degradation models (or plant performance evaluation models) to

correlate the key parameters to the plant performance in both technical and financial terms.

SDN. BHD.

(420420-D)
POWERGEN ASIA 98 – Combined Cycles

 

Title ; Combined Cycle Power Plant Performance Degradation - PowerGen Asia Sept 98 1

Company : VY Consult (Consulting Engineers), Malaysia [Email - yong@vycon.po.my,Fax : 603-7032687]

SDN. BHD.

(420420-D)

Nomenclature

HRSG Heat Recovery Steam Generator k Thermal conductivity

GTG Gas Turbine Generator L Length of scale

STG Steam Turbine Generator T Temperature

CCPP Combined Cycle Power Plant DT Temperature differential

HP High Pressure fw Water-side Fouling factor

LP Low Pressure h Efficiency

IP Intermediate Pressure P Power output

HPB High Pressure Boiler m Mass flow of fluid

RH Relative Humidity rr Pressure ratio

SPE Solid Particle Erosion Uf Fin tube heat transfer coefficient

IPP Independent Power Producer Ub Bare tube heat transfer coefficient

TIT Turbine Inlet Temperature ­ Increasing

C Constant Ø Decreasing

Q Heat energy transfer

Introduction

A new power plant which is designed, constructed and commissioned properly shall be able

to operate at the plant’s declared power and heatrate as guaranteed by the contractor. This is

valid provided that the plant is operated within the equipment operating limits and when the

plant is in a new condition. The power plant’s overall performance would be gradually

reduced over time due to the degradation of the plant’s components. It is necessary for the

plant owner/operator to monitor and minimise the plant’s degradation to optimise the

revenue.

Degradation

Degradation is the loss of machine performance (Gas turbine, Steam Turbine, HRSG,

Condenser and other auxiliaries) over time due to the wear and tear during

operation/startup/shutdown and the presence of contaminants in fuel, water and air which is

ingressed into the system. Degradation can generally be divided into the following categories:

Type of Degradation Typical causes

Recoverable Degradation Clogging, scaling and build up of deposits on the working

surfaces that are in constant contact with the working fluids.

Non-Recoverable

Degradation

Wear and tear of machine components, aging, loss of working

surface, corrosion/oxidation, erosion and other damages to the

working parts. .
POWERGEN ASIA 98 – Combined Cycles

 

Title ; Combined Cycle Power Plant Performance Degradation - PowerGen Asia Sept 98 2

Company : VY Consult (Consulting Engineers), Malaysia [Email - yong@vycon.po.my,Fax : 603-7032687]

SDN. BHD.

(420420-D)

Typical contaminants

There are three paths in which contaminants can flow into the system and that is through the

air, fuel and water. A typical power plant configuration would include the inlet air filtration

system, fuel centrifuge/scrubber and water treatment system to reduce the level of

contaminants to an acceptable level within the equipment specification limits.

Typical contaminants Description

Air-borned contaminants Microscopic particles from industrial emission and

transportation, dust from vehicular and construction activity,

and natural sources

Fuel contaminants Traces of Sodium, Potassium, Calcium, Lead, Sulfur and other

metals for liquid fuel only.

Water contaminants Sodium, Potassium, Calcium, Silica, Carbonate, Sulphate,

Chloride, Suspended Solids especially from river & sea water

Gas Turbine Generator Degradation

Degradation causes Description

Erosion Small abrasive particles entering into the Gas Turbine via

air/fuel path and propelled by the compressor, combustion gas

through the hot section turbine at high velocity can cause

erosion. This results in damage to the compressor and turbine

blade surfaces and its protective coating. It depends on the

size of objects ingested into the GTG (i.e. objects with

sufficient mass and hardness to physically damage GTG

blades & components) and the period of exposure. This is a

non-recoverable degradation.

Corrosion / Oxidation The combustor and the hot section turbine blades are

subjected to high velocity gas with traces of contaminants at

high temperature. Furthermore microscopic pitting and

damage to the protective coating of the blades shall further

induce oxidation/corrosion process. The stage efficiency is

reduced by alteration of blade surface finish.

This is a non-recoverable degradation.

Deposition Air borned and fuel borned contaminants such as water

soluble constituents, insoluble dirt, etc. are deposited on the

rough surfaces of the combustion chamber and turbine blades.

Deposition on the blades would affect the blade surface

roughness.

This is a partially recoverable degradation and is dependent on

the effectiveness of the blade and combustor cleaning process.
POWERGEN ASIA 98 – Combined Cycles

 

Title ; Combined Cycle Power Plant Performance Degradation - PowerGen Asia Sept 98 3

Company : VY Consult (Consulting Engineers), Malaysia [Email - yong@vycon.po.my,Fax : 603-7032687]

SDN. BHD.

(420420-D)

HRSG Degradation

Degradation causes Description

Fouling Fouling in the HRSG is almost entirely due to scaling and

sludge buildup. Scale material in the form of dissolved solids

is deposited on the water side tube surfaces when evaporation

occurs. Scale material is a relatively hard and adherent

deposit, while sludge is softer and can be easily dislodged.

Scale buildup is associated with compounds whose solubility

decrease with increasing temperatures. Conversely, sludge is

precipitated directly from the boiler water when their

solubility are exceeded.

Oxidation Steam flowing through the superheater tubes, reacts with the

alloy constituents of the tube material (Fe, Cr, etc.) as given

by the following equation :

4H2O + 3 Fe → Fe3O4 + 4H2

The magnetite scale thus formed normally adheres to the tube

surface and limits the extent of further reaction. As such, the

oxidation rate is asymptotic in nature. As the oxide becomes

thicker, they become more brittle and when critical thickness

is reached, the protective layer is lost and thus becoming

susceptible to spalling which can cause tube blockage and

solid particle erosion (SPE)

Heat Transfer in Scaled

Tubes

Scale causes resistance to the heat transfer between the hot

exhaust gases and the boiler water. Heat transfer through the

scale can be represented by the following equation.

 Q = kDT/L = DT/fw (where fw = L/k)

The quantity of heat energy transferred is proportional to the

thermal conductivity of the scale and inversely proportional to

the scale thickness.

The tube side fouling factor (fw) affects duty and tube wall

temperatures. This impact is more significant in a finned tube

boiler as compared to a bare tube boiler. The thermal

conductivity of several substances which are characteristic of

boiler scale deposits are presented in the table below.

The table on the next page shows the Thermal conductivity of boiler scale deposits
POWERGEN ASIA 98 – Combined Cycles

 

Title ; Combined Cycle Power Plant Performance Degradation - PowerGen Asia Sept 98 4

Company : VY Consult (Consulting Engineers), Malaysia [Email - yong@vycon.po.my,Fax : 603-7032687]

SDN. BHD.

(420420-D)

Thermal conductivity of boiler scale deposits

Material Thermal Conductivity

W/(mK)

Material Thermal Conductivity

W/(mK)

Analcite 1.269 Magnetic Iron Oxide 2.884

Calcium Phosphate 3.605 Silicate scale 0.0865

Calcium Sulfate 2.307 Fire brick 1.010

Magnesium

Phosphate

2.163 Insulating brick 0.1010

STG Degradation

Degradation causes Description

Performance Loss Due to

Leakages

Rubbing of rotating stationary parts will result in increased

clearance and hence increased steam leakage occurring in the

stage, diaphragm and end seals.

Solid Particle Erosion Solid particle erosion occurs when iron oxide particles

(magnetite) in the form of scale (produced in the inner surface

of the HRSGs superheater tubes) are entrained in the steam

flow. This erodes the steam path. The damage is usually most

severe on the first HP, first IP, first reheat stages and nozzles

as well as the control valves.

Moisture Erosion (Water

Drop Erosion)

Moisture erosion in the STG is caused by water droplets that

form as the steam crosses the saturation line. Larger water

drops lag behind the steam flow and attack (cause erosion) the

tip region of the last stage blades where the circular velocity is

the highest.

Steam Path Chemical

Deposition

Chemical deposition is caused by the presence of impurities

in the steam attributed to the following factors :-

• Evaporation from boiler water

• Entrainment (carryover) of boiler water droplets into

superheater tubes and subsequently into the STG.

• Impurities present in feedwater for desuperheating sprays.

Foreign Object Damage This is caused by the inadvertent admission of foreign

material into the turbine steam path. Typical foreign materials

include , weld bead and slag that may have come loose from

upstream piping and components which may not have been

flushed clean before startup.
POWERGEN ASIA 98 – Combined Cycles

 

Title ; Combined Cycle Power Plant Performance Degradation - PowerGen Asia Sept 98 5

Company : VY Consult (Consulting Engineers), Malaysia [Email - yong@vycon.po.my,Fax : 603-7032687]

SDN. BHD.

(420420-D)

Condenser (Once through) Performance Degradation

Degradation causes Description

Condenser

Scaling/Fouling

As the temperature and concentration of the cooling water

increases, several types of ions which are initially soluble, are

precipitated on the surfaces of the condenser tubes. River

water usually contains significant quantities of Calcium

Carbonate. Scaling occurs under higher water temperatures

and aerated conditions. The following reversible equation

applies.

Ca(HCO3)2 ↔ Ca CO3 + CO2 + H2O

CO2 loss tends to shift the equation to the right and thus

increasing the scale formation.

Biological Fouling Micro-organisms present in cooling (river/sea) water tend to

form slime films on the heat transfer surfaces thus increasing

the water side fouling factor.

Degradation of Other CCPP Components

Diverter Dampers -. A tight gas seal after a period of time cannot be expected as damper

blade edges and seals deteriorate in service. Dampers can and do remain in one position for

months at a time while the HRSG is operating and thus sometimes fail to operate to their

design requirements.

Case Study of the Effect of CCPP Component Degradation on CCPP Performance

Method of Conducting Case Study

GTPro is used to calculate the plant configuration design performance. GTMaster is used to

calculate the off-design plant performance based on the various fouling and deration factors

which include :-

1. Inlet Filter Pressure drop

2. GTG turbine and compressor efficiency

3. Fouling factor at the HRSG

4. Fouling factor at the condenser

5. Diverter damper leakages

For analysis of degradation of individual CCPP components, it is assumed that all other

components are operating at design conditions.
POWERGEN ASIA 98 – Combined Cycles

 

Title ; Combined Cycle Power Plant Performance Degradation - PowerGen Asia Sept 98 6

Company : VY Consult (Consulting Engineers), Malaysia [Email - yong@vycon.po.my,Fax : 603-7032687]

SDN. BHD.

(420420-D)

A case study for a typical 100 MW CCPP is conducted to analyse the effects of degradation

of the various CCPP components. The plant is simulated based on an ambient temperature of

32 ° C/ 80%RH. The plant is made up of the following equipment.

Item Description

1. GE 6551 B GTG

2. Dual pressure HRSG

3. Once through cooling for condenser

4. Condensing STG

HP FEED

PUMP

CONDENSER

TO

DEAERATOR

GAS TURBINE

GENERATOR

Inlet Air

Natural Gas

HEAT RECOVERY 

STEAM GENERATOR

DEAERATOR

IP FEED

PUMP

FROM

CONDENSER

From

cooling

source

HP STEAM

IP STEAM

Intermediate

Pressure

Boiler

Low

Pressure

Boiler

HP

Economizer

IP

Superheater

IP

Economizer

HP

Superheater

STEAM TURBINE

GENERATOR

Generator

Generator

To

Cooling

source

Compressor Turbine

Combustor

From DeaeratorTo Deaerator

Inlet Air Filters

STG

Exhaust

High

Pressure

Boiler

Exhaust

Gases to

the

Atmosphere

.

Exhaust Gases from GTG to HRSG

Figure 1 : Schematic of a Typical CCPP

It is assumed for the case study that only a single component undergoes degradation at any

one time. This is to gauge the magnitude of the effect of these individual degradations on the

CCPP.
POWERGEN ASIA 98 – Combined Cycles

 

Title ; Combined Cycle Power Plant Performance Degradation - PowerGen Asia Sept 98 7

Company : VY Consult (Consulting Engineers), Malaysia [Email - yong@vycon.po.my,Fax : 603-7032687]

SDN. BHD.

(420420-D)

GTG Inlet Air Filter Clogging

The effect of GTG inlet air filter pressure drop is shown below.

Effect of GTG Inlet Air Filter Pressure Drop on CCPP Performance

98.0%

98.5%

99.0%

99.5%

100.0%

100.5%

101.0%

4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0

GTG Inlet Air Filter Pressure Drop (inches Wg)

% Performance

GTG Gross power

STG Gross Power

Total Plant Gross Power

GTG Gross Heatrate

Figure 2 : Effect of GTG Inlet Air Filter Pressure Drop on CCPP Performance

Texhaust = C

TIT = C

Tambient = C

Plant Power Output =  ̄

Plant Heatrate = -

Temperature

GTG 

Compressor

STG

P STG =  ̄

msteam =  ̄

Tstack = C

GTG 

Turbine

Pturb = C

h GTG =  ̄

PGTG =  ̄

mexhaust =  ̄

Qcombustor

QHRSG =  ̄

Figure 3 : Schematic of the effect of GTG inlet air filter pressure drop on CCPP performance

Effect of GTG inlet air pressure drop on revenues

GTG inlet air pressure drop 6” H2O 8” H2O

% loss of revenue 0.8% 1.6%
POWERGEN ASIA 98 – Combined Cycles

 

Title ; Combined Cycle Power Plant Performance Degradation - PowerGen Asia Sept 98 8

Company : VY Consult (Consulting Engineers), Malaysia [Email - yong@vycon.po.my,Fax : 603-7032687]

SDN. BHD.

(420420-D)

GTG Compressor Degradation

Effect of GTG Compressor Degradation on CCPP Performance

94%

95%

96%

97%

98%

99%

100%

101%

102%

103%

104%

105%

0 2.5 5 7.5 10 12.5 15

Compressor Exit Temperature Rise (°C)

% Performance

Total plant gross pow er

GTG Gross pow er

GTG Gross heatrate

Figure 4 : Effect of GTG compressor degradation on CCPP Performance

Texhaust = C

TIT = C

Tambient = C

Plant Power Output =  ̄

Plant Heatrate = -

Temperature

rrcompressor = C

Qcombustor

STG

h STG = C

P STG = C

msteam = C

GTG 

Compressor

m air = C

h comp =  ̄

P comp = -

GTG 

Turbine

hturb = C

Pturb = C

h GTG =  ̄

PGTG =  ̄

mexhaust = C

QHRSG = C

Tstack = C

Figure 5 :Schematic of the effect of GTG compressor degradation on CCPP performance

Effect of GTG compressor degradation on revenues

Compressor exit temperature rise 3 °C 8 °C 14 °C

% loss of revenue 0.8 % 2.6% 4.4%
POWERGEN ASIA 98 – Combined Cycles

 

Title ; Combined Cycle Power Plant Performance Degradation - PowerGen Asia Sept 98 9

Company : VY Consult (Consulting Engineers), Malaysia [Email - yong@vycon.po.my,Fax : 603-7032687]

SDN. BHD.

(420420-D)

GTG Turbine Degradation

Effect of GTG Turbine Degradation on CCPP Performance

94%

95%

96%

97%

98%

99%

100%

101%

102%

103%

104%

0 1 2 3 4 5 6 7 8 9 10 11 12

GTG Exhaust Temperature Rise (°C)

% Performance

GTG Gross Pow er

STG Gross Pow er

Total Plant Gross Pow er

Plant Gross Heatrate

Figure 6 : Effect of GTG turbine degradation on CCPP Performance

Texhaust = -

TIT = C

Tambient = C

Plant Power Output =  ̄

Plant Heatrate = -

Temperature

Qcombustor

STG

h STG = C

P STG = -

msteam = -

GTG 

Compressor

m air = C

hcomp = C

P comp = C

GTG 

Turbine

hturb =  ̄

Pturb =  ̄

h GTG =  ̄

PGTG =  ̄

mexhaust = C

Tstack =  ̄

QHRSG = 

-

Figure 7 : Schematic representation of the effect of GTG turbine degradation on CCPP performance

Effect of GTG turbine degradation on revenues

GTG Exhaust Temperature Rise 2.3 °C 7.1 °C 11.9 °C

% loss of revenue 0.4% 1.1% 1.9%
POWERGEN ASIA 98 – Combined Cycles

 

Title ; Combined Cycle Power Plant Performance Degradation - PowerGen Asia Sept 98 10

Company : VY Consult (Consulting Engineers), Malaysia [Email - yong@vycon.po.my,Fax : 603-7032687]

SDN. BHD.

(420420-D)

Heat Recovery Steam Generator Degradation

A brief investigation is carried out on the effect of degradation on the HP boiler of the HRSG

on the CCPP. Two conditions are considered where one case considers a Bare tube evaporator

while another case considers Finned tube evaporator

Degradation for High Pressure Boiler (Finned Tube and Bare Tube)

20%

30%

40%

50%

60%

70%

80%

90%

100%

0.00 0.05 0.10 0.15 0.20 0.25

Scale thickness on High pressure Evaporator Tube (mm)

 % Performance

0

50

100

150

200

250

300

350

400

450

500

Uf, F inned Tube Evaporato r

Ub, B a re T ube E v apo rato r

F in T ip Temp (F inned T ube)

Tube Surface Temp (B are Tube)

Figure 8: Effect of HRSG fouling on High Pressure Boiler Performance

Increase in the water-steam side fouling factor (fw) due to the formation of thick layer of scale

results in reduced duty and higher tube wall temperatures. The larger the fin surface area

(obtained by using high fin density) the higher the temperature of the tube wall and tip. In

cases of extreme degradation the tubes can be overheated and even result in tube failure. The

next investigation looks at how the HRSG degradation would affect the performance of the

entire combined cycle plant. Refer to Figure 9 .

Èffect of HRSG Degradation on CCPP performance

85%

90%

95%

100%

105%

110%

0 5 10 15 20 25 30 35 40 45 50

HRSG Exhaust Stack Temperature Rise (°C)

% Performance

Total Plant Gross Pow er

Plant Gross Heatrate

STG Gross Pow er

Figure 9 : Effect of HRSG degradation on CCPP Performance
POWERGEN ASIA 98 – Combined Cycles

 

Title ; Combined Cycle Power Plant Performance Degradation - PowerGen Asia Sept 98 11

Company : VY Consult (Consulting Engineers), Malaysia [Email - yong@vycon.po.my,Fax : 603-7032687]

SDN. BHD.

(420420-D)

Texhaust = C

TIT = C

Tambient = C

Plant Power Output =  ̄

Plant Heatrate = -

Temperature

GTG 

Compressor

m air = C

STG

P STG =  ̄

msteam =  ̄

Tstack = -

GTG 

Turbine

Pturb = C

h GTG = C

PGTG = C

mexhaust = C

Qcombustor

QHRSG =  ̄

Figure 10 :Schematic representation of the effect of HRSG degradation on CCPP performance

Effect of HRSG degradation on revenues

HRSG Exhaust Stack Temperature Rise 8.9 °C 28.4 °C 48.7 °C

% loss of revenue 1.1% 3.4% 5.6%
POWERGEN ASIA 98 – Combined Cycles

 

Title ; Combined Cycle Power Plant Performance Degradation - PowerGen Asia Sept 98 12

Company : VY Consult (Consulting Engineers), Malaysia [Email - yong@vycon.po.my,Fax : 603-7032687]

SDN. BHD.

(420420-D)

Condenser Degradation

Effect of Condenser Degradation on CCPP Performance

80%

85%

90%

95%

100%

105%

110%

0 2 4 6 8 10 12 14 16 18

Condensate Temperature Rise (°C)

% Performance

Total Plant Gross Pow er

Plant Gross Heatrate

STG Gross Pow er

Figure 11 : Effect of condenser degradation on CCPP Performance

Texhaust = C

TIT = C

Tambient = C

Plant Power Output =  ̄

Plant Heatrate = -

Temperature

Qcombustor

STG

hSTG = C

P STG =  ̄

msteam = C

GTG 

Compressor

m air = C

Tcond = -

GTG 

Turbine

hturb = C

Pturb = C

h GTG = C

PGTG = C

mexhaust = C

Tstack = C

QHRSG = C

Figure 12 :Schematic representation of the effect of condenser degradation on CCPP performance

Effect of condenser degradation on revenues

Condensate temperature rise 3 °C 9 °C 13.6 °C

% loss of revenue 0.7 % 2.7% 3.9%
POWERGEN ASIA 98 – Combined Cycles

 

Title ; Combined Cycle Power Plant Performance Degradation - PowerGen Asia Sept 98 13

Company : VY Consult (Consulting Engineers), Malaysia [Email - yong@vycon.po.my,Fax : 603-7032687]

SDN. BHD.

(420420-D)

Diverter Damper Leakage

Effect of Diverter Damper Leakage on CCPP Peformance

95.0%

95.5%

96.0%

96.5%

97.0%

97.5%

98.0%

98.5%

99.0%

99.5%

100.0%

100.5%

0.0% 0.5% 1.0% 1.5% 2.0% 2.5% 3.0% 3.5% 4.0% 4.5% 5.0%

Diverter Damper Leakage(%)

% Performance

GTG Gross Pow er Output

STG Gross Pow er Output

Total Plant Gross Pow er

Figure 13 : Effect of diverter damper leakage on CCPP Performance

Texhaust = C

TIT = C

Tambient = C

Plant Power Output =  ̄

Plant Heatrate = -

Temperature

GTG 

Compressor

m air = C

STG

P STG =  ̄

msteam =  ̄

Tstack = C

GTG 

Turbine

Pturb = C

h GTG = C

PGTG = -

(small)

mexhaust Qcombustor from GTG= C

QHRSG =  ̄

Figure 14 :Schematic representation of the effect of diverter damper leakage on CCPP performance

Effect of diverter damper leakage on revenues

Exhaust gas leakage (% of total GTG exhaust gas) 1% 3% 5%

% loss of revenue 0.3 % 0.9% 1.6%
POWERGEN ASIA 98 – Combined Cycles

 

Title ; Combined Cycle Power Plant Performance Degradation - PowerGen Asia Sept 98 14

Company : VY Consult (Consulting Engineers), Malaysia [Email - yong@vycon.po.my,Fax : 603-7032687]

SDN. BHD.

(420420-D)

Minimizing Performance Degradation

From the above, it can be seen that degradation on various plant components have a

significant impact on the plant performance and thus there is a need to minimize them.

Minimizing GTG Performance Degradation

Control / Remedial Description

Fuel Quality Control • Treatment/scrubbing of liquid and gas fuel at site as some

contamination may have occurred during transport

• Constantly monitoring of fuel quality to meet the

equipment specification limits.

Compressor / Turbine

Wash

Compressor/Turbine wash can remove the fouling deposits

and oil traces on the blades. The wash method include

• On-line liquid cleaning

• Off-line liquid cleaning

• Solid compound cleaning

Strict Adherence to

Manufacturer’s

Maintenance Program

The manufacturer’s maintenance program includes :-

• Scheduled servicing and parts replacement

• Continuous trending and monitoring of compressor and

turbine operational parameters

• Scheduled Borescope inspection

Blade Coating System There are options for blade coating which includes providing a

thin layer or protective coating (very hard and corrosion

resistant layer) or a sacrificial coating (coating which is

sacrificed as it reacts with corrosive elements).

Minimizing HRSG Performance Degradation

The most effective means of controlling performance degradation in HRSGs is by utilizing

good water treatment practices. Water chemistry is of the utmost importance to HRSG

operation as all fouling and operational problems originate from here. Poor feed water quality

is also detrimental to the operation of the STG.

An effective method for detecting fouling and performance degradation involves the trending

of the HRSG performance data such as steam flowrate and pressure. This data is then

compared against the base-line data to detect deterioration in performance.
POWERGEN ASIA 98 – Combined Cycles

 

Title ; Combined Cycle Power Plant Performance Degradation - PowerGen Asia Sept 98 15

Company : VY Consult (Consulting Engineers), Malaysia [Email - yong@vycon.po.my,Fax : 603-7032687]

SDN. BHD.

(420420-D)

Minimizing STG Performance Degradation

Control / Remedial Description

Leakages Improve tip leakage controls

Solid Particle Erosion Application of diffusion coating to the first stage and reheat

stage nozzles.

Moisture Erosion Blades operating in the wet region are protected at the tips

(either by hardening or with a protective coating). The

equipment design should include moisture separation feature

within the wet regions of the steam path to prevent erosion in

the Steam Turbine.

Steam Path Deposits Water used for attemperating sprays and exhaust hood sprays

could also be a potential source of steam contaminants and

thus mitigation measures must be taken accordingly.

Minimizing Condenser Performance Degradation

Control / Remedial Description

Continuous Mechanical

Cleaning of Condensers

This is a physical method of continuously cleaning condenser

tubes by circulation of sponge rubber balls in the cooling

water system. The frequent use of this system would reduce

the quantity of chlorination required.

Continuous Acid Dosing - Low cooling water pH almost reduces scales completely but

an acidic environment can cause corrosion problems in

virtually all components (i.e. steel and concrete) that make up

the cooling water system. As such, a great deal of care and

very tight control should be exercised when using this method

Chemical Additives Chemical additives modify the crystal structure of compounds

precipitating from supersaturated solutions such that scaling is

minimized. These chemicals are expensive and are used in

low dosage rates. Injection of these chemicals do not require

very strict monitoring as over-dosing is very unlikely to cause

attacks on concrete or metals.
POWERGEN ASIA 98 – Combined Cycles

 

Title ; Combined Cycle Power Plant Performance Degradation - PowerGen Asia Sept 98 16

Company : VY Consult (Consulting Engineers), Malaysia [Email - yong@vycon.po.my,Fax : 603-7032687]

SDN. BHD.

(420420-D)

Economics of CCPP Degradation

Case Study for Simultaneous Degradation

The examples discussed earlier consider the effect of degradation one component on the

CCPP while in real life, all components undergo simultaneous but varying degradation. The

case study below simulates this condition.

Design Conditions

The case study takes a simplified approach to show the effect of performance degradation on

the CCPP. The “New and Clean” condition is what would be expected when the power plant

has operated for less than 100 hours. Case 1 considers predominant GTG degradation while

Case 2 considers predominant HRSG and condenser degradation. Case 3 is a composite of

GTG, HRSG and condenser degradation.

Description Units New &

Clean

Case 1 Case 2 Case 3

Inlet air pressure drop in H2O 4 6 4 6

GTG compressor temperature rise °C 0 5 0 5

GTG turbine exhaust temperature rise °C 0 5.6 0 5.6

HRSG stack temperature rise °C 0 -1.2 5.7 5.1

Condensate temperature rise °C 0 0 6.18 6.34

Exhaust gas leakage at diverter damper % 0 1 1 1

Note : Temperature rise is defined as the change with reference to the Design Temperatures.

Results

Description Units New &

Clean

Case 1 Case 2 Case 3

Net plant power output MW 106.3 103.0 103.8 100.8

Net plant output kJ/kWh 7,620 7,768 7,802 7,937

Loss of revenue per day % NA 3.6 % 2.3% 5.6%

Considering Case 1, the IPP stands to lose 3.6% of revenue per day while in Case 2, there

would be a loss of 2.3 % a day. For the conditions of Case 3, there would be a loss of 5.6%

revenue per day.

Some of the steps that an IPP owner can take to minimize the effects of degradation apart

from those that have already been discussed include:

• Strictly follow maintenance procedures
POWERGEN ASIA 98 – Combined Cycles

 

Title ; Combined Cycle Power Plant Performance Degradation - PowerGen Asia Sept 98 17

Company : VY Consult (Consulting Engineers), Malaysia [Email - yong@vycon.po.my,Fax : 603-7032687]

SDN. BHD.

(420420-D)

• Ensure that degradation of the CCPP due its location has been considered at the design

stage. (i.e. use of marinized GTG blades for CCPP located in sea environment or use of

titanium tubes for once through condensers with sea water cooling)

• On-line monitoring of key parameters for early detection of plant equipment degradation.

Prediction of CCPP Degradation

Most manufacturers only provide typical degradation percentages for GTGs and CCPP from

existing plants operation experience. These data do not reveal the detailed aspects of

Combined Cycle Power Plant configuration and thus making the degradation estimates for a

proposed plant difficult. It is also not possible to depend only on the tenderer’s estimates or

manufacturer’s publication due to the lack of detailed information.

Since the characteristic of the Gas Turbine, HRSGs and STGs are well defined, it is possible

to model a specific CCPP configuration to analyse the impact of degradation and to design

the plant with the necessary mitigation measures to suit the specific conditions.

For example, it may be necessary to design and install suitable inlet air filtration system with

on line pulse cleaning facilities for a power plant located near a clinker plant whereby the air

pollutants are high. The loss of revenue due to pressure drop may be significant enough to

justify the initial investment in suitable mitigation measures against degradation losses.

In other cases, it may be necessary to design and install suitable heat exchanger system, on

line monitoring system, condenser cleaning system to cope with cooling (river/sea) water with

high Total Dissolved Solids and Total Suspended Solids with significant traces of heavy

metals. The impact of degradation on the revenue and Internal Rate of Return against capital

investments shall be used to determine the selection of power plant configuration and

mitigation infrastructure.

Conclusion

The largest contribution to CCPP performance deterioration is by GTG degradation. The

combined effect of compressor /turbine degradation and inlet air filter clogging can reduce the

performance of the CCPP rapidly. As such plant operators should ensure that the plant

degradation is minimized. Possible performance degradation should be analyzed at the design

stage such that proper counter-measures can be taken to reduce it.

From the above investigation, it could be seen that it is possible to;

• Provide useful real time data for plant performance diagnostics via trending and

correlation of key measurable parameters to the plant component actual degradation

physical effects.

• To develop on-line plant performance evaluation models to maximise the efficiency and

reliability. A set of parameters of the new plant (design) conditions will be used as the

baseline or benchmark and the calculated results from the real-time data, would be

presented in the form not only to highlight the problems and probable causes but also the

associated financial impact of the plant.

• Establish optimal plant performance inspection and overhaul schedules based on

performance
POWERGEN ASIA 98 – Combined Cycles

 

Title ; Combined Cycle Power Plant Performance Degradation - PowerGen Asia Sept 98 18

Company : VY Consult (Consulting Engineers), Malaysia [Email - yong@vycon.po.my,Fax : 603-7032687]

SDN. BHD.

(420420-D)

• Acquisition of data for plant engineering appraisals to improve reliability.

References

1. Ganapathy, V., “Waste Heat Recovery Boiler Deskbook”, The Fairmont Press

2. Leyzerovich,A., “Large Power Steam Turbines: Operations, Volume 2”, Penwell

Biographical Information

Name : Yong Voon Yee

Company : Vy Consult

Country : Malaysia

Yong Voon Yee received his degree in Electrical & Electronic Engineering from University

of Melbourne, Australia. He joined Foxboro in 1990 as a control system engineer and was

involved in the system & software design of Distributed Control System for offshore oil &

gas production platforms. In 1995, he joined Vy Consult to pursue a career in Electrical and

Power Generation. He was the site engineer for supervision of fast track installation, testing

and commissioning of 20MW Gas Turbine Power Plant. He has been involved in the

technical and economic feasibility study of a 100MW Combined Power Plant in the East

Malaysia for an IPP company. Vy Consult is taking the lead in promoting cogeneration

feasibility studies and applications in Malaysia.

Name : Paramjit Singh

Company : Vy Consult , Malaysia

Country : Malaysia

Paramjit obtained a degree in Mechanical Engineering from University of Malaya in 1996. He

joined Vy Consult and has been involved in the development of power generation and

cogeneration projects. He has been involved in the technical and economic feasibility study of

a 100MW Combined Power Plant in the East Malaysia for an IPP company. Vy Consult is

taking the lead in promoting cogeneration feasibility studies and applications in Malaysia.