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GER
GE Power Syste
Steam Turbine Thermal Evaluation and Assessment Paul Albert GE Power Systems Schenectady, NY Sign up to vote on this title
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Steam Turbine Thermal Evaluation and Assessment Contents
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Baseline and Periodic Performance Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ASME PTC 6S Report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Capacity Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Enthalpy Drop Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Evaluation of Performance Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Assessment of Turbine Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Turbine Steam Path Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Advanced Method for Assessing Stage Efficiency Losses. . . . . . . . . . . . . . . . . . . . . . . . . . Loss Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Leakage Losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Friction Losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Aerodynamic Losses. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Losses Due to Changes in Flow Passage Areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Steam Path Audit Reporting . . . You're . . . . . .Reading . . . . . . .a. Preview .. ......... ......... .......... Advancements in the Evaluation and Data UnlockAssessment full access with aof free trial. . . . . . . . . . . . . . . . . . . . . . . . . Performance Monitoring. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Plant Evaluations . . . . . . . . . . . Download . . . . . . . . .With . . . .Free . . . .Trial .......... ......... ........ Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....... List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sign up to vote on this title
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Steam Turbine Thermal Evaluation and Assessment
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Steam Turbine Thermal Evaluation and Assessment Introduction
This data, with its associated results, will lish accurate trends of various perform characteristics. The basic theory of the tu steam path flow, pressure, and tempe relationships is reviewed to improve u standing of how these trends can be interp and used to locate and identify the cause turbine deterioration. Some common cau turbine deterioration include deposits, particle erosion, increased clearances in ings and tip spill strips, and foreign object age.
For a steam turbine-generator to operate at its optimum level of thermal performance, it must achieve a high initial level of performance and must be able to sustain thermal performance over time. This is best achieved by an ongoing program of evaluation and assessment of thermal performance data. This program has a three-fold purpose. The first is to detect deterioration in the thermal performance by trending changes in various performance parameters. The second is to identify the cause of perThis paper also reviews the value of condu formance degradation by proper data evaluaa turbine steam path evaluation to identi tion and interpretation. The third is to develop specific components contributing to the l cost-effective solutions to correct operational thermal performance. In addition, this in and equipment problems, which are contributtion can be used to verify the predictions o ing to the degradation in thermal performance. bine conditions from the monitoring pro To meet these objectives, a thermal performReading Technological a Preview advancements of ance program should include the You're following Performance Evaluation Services is als essential factors: Unlock full access with a free trial. cussed. s Obtain baseline performance data on individual turbines and cycle Download With Free Trial Baseline and Periodic Performanc components during initial operation Testing and after a maintenance outage to establish a base for identifying specific A performance test conducted in accor areas of performance losses with the ANSI/ASME PTC 6-1996 “ Turbine” Code (Reference 1) is an acc s Periodic acquisition of repeatable Sign up to vote on this title method of establishing the performance performance data Useful Not useful turbine-generator unit. The test require s Proper evaluation and assessment of use of highly accurate calibrated instrum performance data so that
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Steam Turbine Thermal Evaluation and Assessment The value of the analysis of performance test data greatly depends on the quality of the data. The use of “Acceptance” test procedures to obtain periodic performance results yields the most accurate test data for analysis and evaluation. Fortunately, performance monitoring does not necessarily require absolute accuracy, but it demands repeatable data for establishing accurate trends of various performance characteristics so simplified procedures can be used.
pressure transducer on the primary flo ment should be calibrated prior to the te addition, mechanical station watthour m usually have to be read by counting disk r tions to obtain a precise reading of kilowa put. Temperatures and pressures at the and outlet of the HP and IP sections shou made with instruments capable of prod high repeatability.
The repeatable determination of the tu cycle heat rate also depends on cycle isol ASME PTC 6S Report Since primary flow is measured in the feed The ANSI/ASME PTC 6S Report “Simplified line, any leakage between the flow me Procedures for Routine Performance Tests of ment and the turbine stop valve must be Steam Turbines” (Reference 2) provides guidance nated or the test results adjusted accord in developing procedures to monitor performOtherwise, an erroneous measurement o ance. This procedure provides the necessary rate will be obtained. Steam and water lea data to determine turbine cycle heat rate, kilo within the turbine cycle do not affect the watt capacity, HP and IP section efficiencies, You're Reading urement a Previewof heat rate, but these leakage and turbine stage pressures and flow capacities. cause a significant loss in the actual hea Unlock full access with a free trial. The essential measurements for ASME PTC 6S and kilowatt capacity. Report tests are shown in Figure 1. For this test, Free TrialTest like other heat rate tests, the most Download important WithCapacity measurements are electrical load and primary When a repeatable measurement of p flow, which is usually measured in the feedwater flow cannot be obtained, another pra line. To assure repeatability, the differential effective method of trending the perform Sign up toP.T. vote3 on this title V
W
Power
Useful Transf.
From Reheater From Superheater T T
T
P
P
T T P
T T P
w w
Phases
Not useful C.T. A
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Steam Turbine Thermal Evaluation and Assessment of the turbine-generator unit is to make periodic measurements with the turbine control valves wide open (VWO). This test, usually referred to as a Capacity Test, determines the generator output capacity, HP and IP enthalpy drop efficiency, and turbine stage pressures. In rare cases, when steam generator capacity may be inadequate to drive the unit to a VWO position at rated pressure, one alternative is to reduce pressure to permit opening all inlet control valves. This procedure is preferred over the more demanding method of accurately reproducing positions of partially opened control valves or for correcting results for valve position.
HP Section
AE
Y P L A H T N E
Efficiency
l e t t r o T P h
t a h e R e l d o P C
UE
t a h e e R t H o
P
l w
P B o
IP Se
UE =
AE
LP Sectio S a t u r a t i o n L i n e g 3 ” H = P
The Capacity Test, like the simplified heat rate ENTROPY test, depends on repeatable measurements of Figure 2. Enthalpy Drop Test electrical output and the pressures and temperYou're Reading a Preview atures at the inlet and outlet of the HP and IP couple wells should be located ahead of th turbine sections. Isolation of the turbine cycle is Unlock full access with a free trial.valve, ahead of the intercept va bine stop also important because it can significantly affect each cold reheat pipe, and in the crossov the electrical output of the unit. Download Withlow-pressure Free Trial section bowl. In the cold r
Enthalpy Drop Test The Enthalpy Drop Test is used frequently for monitoring steam turbines. This test involves a minimum number of instruments, but establishes the efficiency of those turbine sections most susceptible to deterioration. An Enthalpy Drop Test can be conducted on any turbine section operating entirely in the superheat region,
pipes, the pressure taps should be near th section exhaust connection, and the th couple wells should be in the horizontal after the first elbow to ensure good m beforeSign measuring up to votethe on temperature. this title
useful Useful Not instrumentation Duplicate temperature s be used to conduct an Enthalpy Drop Test will not only improve the accuracy of the
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Steam Turbine Thermal Evaluation and Assessment Main Reheat Steam
Main Steam
T T
P
P
T
T
T
T
Stop Valves
T P
P
T
Stop & Intercept Valves
Control Valve Chest
Intermediate Pressure Turbine
P
Cold Reheat Steam
P T T
LP Turbine P T
T
P
P
High Pressure Turbine T
T
Extraction Steam
Extraction Steam
Figure 3. HP & IP efficiency measurement locations
many individual equipment components. If the s Reheat temperature You're Reading a Preview test results indicate that heat rate has deterios Reheater pressure drop rated or the maximum electrical capacity of the Unlock full access with a free trial. s Condenser vacuum unit has changed, any of the following condirate and generator electrical output tions could be contributing factors: Download WithHeat Free Trial be corrected for these operating cond s Turbine steam flow using correction factor curves normally p s Efficiency of the turbine steam path ed in the unit's thermal kit. Figure 4 is a s of a correction curve. Variations in th s Available energy of the turbine (i.e., pressure and temperature alsochange steam conditions) Signtouptheir to vote on this flow due effect ontitle the specific vo s Performance and operation of the useful Useful Not of steam. This effect is typically combined balance of plant components the available energy effect in the relevan rection factors. Keep in mind that these c To assess the turbine condition and its contri-
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Steam Turbine Thermal Evaluation and Assessment 6
% change kilowatt load
1/4 Load 1/2 Load Rated Load
% increase 5
4
Method of Using Correction Curves
3
These correction factors assume constant control valve opening and are to be applied to heat rates and kilowatt load at specified steam conditions.
2
1 -5
-4
-3
-2
-1
+1
+2
+3
+4
+5
(1) The heat rate at the specified condition can be found by dividing the heat rate at test condition by the following:
% change in pressure 1
2
3
1+
% change in gross heat rate 100
4
(2) The kilowatt load at the specified condition can be found by dividing the kilowatt load at test conditions by the following:
5
% decrease 6
% change in heat rate
2
1
-4
+3
-2
-1
% change in kW load 100
% change in pressure +1
-5
1+
% increase
+2
0
1
+3
+4
+5
Rated Load 1/2 Load 1/4 Load
GT 25649
% decrease
Figure 4. Throttle pressure correction for single reheat units
The generic correction curves from the ASME trend in heat rate and/or generator outpu You're Reading a Preview PTC 6S Report test code for the more signifibe used to assess the turbine condition. S cant cycle changes are listed below: Unlock full access with flowa free andtrial. steam turbine efficiency are the relevant factors which must now be consid s Final feedwater temperature the Trial efficiencies of the superheated tur Download WithIf Free s Auxiliary extractions s
Main steam attemperation
.8
s
Reheat steam attemperation
.7
s
Condensate sub-cooling
s
Condenser make-up
Load Correction Reheat Steam Desuperheat
A sample correction curve is presented in Figure 5 .
.6
Sign up to vote on this title w o l F g n i t a e h r e p u s e D
% 1 r o
.5
Useful .4
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Steam Turbine Thermal Evaluation and Assessment sections have been established, a change in efficiency can be expressed in terms of a change in heat rate and generator output. Some typical values for the percent change in heat rate for a one-percent change in section efficiencies for a single reheat unit are: HP turbine
= 0.17
IP turbine
= 0.12 to 0.25
IP and LP turbine = 0.72 For non-reheat and industrial turbines with more than one turbine section, the effect on overall performance due to a change in the efficiency of one section can be estimated by multiplying that change by the proportion of total unit power produced in that section.
wide-open flow (at rated throttle pressur temperature) or a pressure ratio, such a stage pressure divided by throttle pressure upper curve represents a partial arc or p admission unit with the first stage nozzles ed into four separate nozzle arcs, each supplied with steam from its own control The lower curve represents full arc or admission with all control valves connecte a common chamber ahead of the first stag zles. Both curves demonstrate the signi effect of valve position on HP efficiency an need for testing at valve positions, which c set repeatedly and held constant for the t
Assessment of Turbine Conditions
The proper interpretation of test result The turbine efficiency characteristics must be lead to an assessment of the internal con understood in order to compare test results to of the turbine which can assist in priori Reading a Preview design or to previous test results. ForYou're example, maintenance activities. There may be i Figure 6 illustrates the efficiency characteristics Unlock full access with a freeoftrial. tions mechanical damage in a turbin of an HP turbine section in a fossil unit application, deposits or solid particle ero tion. Download WithKnowledge Free Trial of the turbine characteristics i An HP turbine achieves its best efficiency with essary to understand why the performanc all control valves wide open (VWO) and, as the changed. control valves are closed (or throttled), the effiMaximum generator output is directly af ciency decreases. The parameters usually used by changes in the efficiencies of the variou to represent valve position are a percent of valve Sign up to votechanges on this title bine sections and in the flow ca of the first three or stages of the high Useful Not useful four Locus of Valve sure turbine. Changes in the flow capacity Best Points lowing stages may indicate a physical chan
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Steam Turbine Thermal Evaluation and Assessment W = KACq √ P / v
(1)
where: W
= Flow to the following stage
K
= A constant
A
= Nozzle area
Cq
= Coefficient of discharge
P
= Inlet stage pressure
v
= Specific volume at stage inlet
The equation can be rearranged as: W / √ P / v = KACq
(2)
From the equation of state of an ideal gas (Pv = RT) the equation can be arranged as:
the stage. However, the flow function is no portional to the area change as implied i equation. It is important to note that the vation of the flow function equation is bas a constant pressure ratio across the stage. the effective flow area of a stage change stage pressure ratio also changes. Thus th tionship of the flow capacity to nozzle a somewhat more complex. Figure 7 show flow capacity change that can be expected change in nozzle area of an impulse-typ bine. For example, a 10% reduction in th zle area of the first stage would reduce the imum capacity of the unit by about 3%.
Since the Capacity Test does not prov repeatable measure of the primary steam W / P √ 1/R * T = KACq (3) the flow function cannot be calculated option is to trend turbine stage pressur You're Reading shown a Preview by equation 1, the steam flow divid where: the absolute pressure ahead of a stage i Unlock R = Universal gas constant full access with a free trial. portional to the effective area of the foll T = Inlet stage temperature stage, provided that the temperature re Download With Free Trial This equation states that the flow function constant. For a constant valve position and stant inlet steam conditions, a change in (W / √ P/v) is related to the flow passage area of the stage (A) and the design and condition bine stage pressure indicates either a chan the effective area downstream of the stag of the stage passage (C q). In more general terms, the flow function relates to the steam change in the flow capacity of theunit. Sign up to vote on this title path condition. If a particular stage flow funcTo use the trend of turbine stage pressu Useful Not useful tion has changed, then the downstream condipredict the internal condition of the tu tion of the turbine steam path must have the stage pressures during the test must b changed. This is a powerful diagnostic tool in
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Steam Turbine Thermal Evaluation and Assessment
STG 1
2
STG2 STG3 STG4
1
2 -10
-8
-6
-4
-2
4
6
8
10
CHANGE IN NOZZLE AREA (PERCENT)
-1 STG 4 STG 3
-2
STG 2 STG 1
-3 CHANGE IN CAPACITY (PERCENT)
GT 25687
Figure 7. Effect of change in nozzle area on flow capacity for impulse-type turbines
Pt
=
Test throttle pressure
where: You're Reading a v Preview= Design, or reference throttle Pd = Design, or reference, throttle pressure d Unlock full access with a free trial. specific volume When an extraction for feedwater heating is v t = Test throttle specific volume taken from an intermediate stage in the HP turDownload With Free Trial bine section, the measured stage or shell pres v tr = Specific volume at test temper sure should also be corrected using the same and test pressure at inlet to equation. Although not theoretically accurate, intercept valves this correction is a very close approximation. v dr = Specific volume at design rehe For stage or shell test pressures at or following temperature and Sign up to vote on this titletest pressure the inlet to the reheat section of the turbine, at inlet intercept useful valves Useful toNot and for the exit from the last stage of the HP Wrhs = Reheat spray flow to the boiler section, additional corrections must be made
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Steam Turbine Thermal Evaluation and Assessment
e c s n l u e r P e f e R m 0 o r f e r u s t r u a i n p M e D %
Initial Test Date
Test Dates
GT 2
Figure 8. Pressure or capability curve vs. chronological test dates
The steam path evaluation should cate the identified stage performance losses in The interpretation of the results of performcomponents: excess diaphragm packing ance monitoring activities can be used to idenloss, excess radial tip spill strip leakag You're Reading age a Preview tify turbine internal problems causing a deterinozzle recoverable and unrecoverable l oration in performance, and assist in planning Unlock full access with a free trial. recoverable and unrecoverabl and bucket maintenance required to address the problems. es. Recoverable losses are defined as thos However, to restore performance during a turDownload Withcan FreebeTrial recovered by cleaning, dressing, bine maintenance outage, the turbine compoof the components, or replacement of nents contributing to the performance loss ance controls. The unrecoverable loss i need to be identified. This can best be done by part of the performance loss that can on conducting a turbine steam path evaluation. recovered by replacement with new co A steam path evaluation should include a nents, Sign suchupastonew votediaphragms on this title or bucket detailed visual inspection of the steam path Useful Not Advanced Method foruseful Assessing Stag components and clearance measurements of Efficiency Losses the packings; and tip spill strips. The visual
Turbine Steam Path Evaluation
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Steam Turbine Thermal Evaluation and Assessment not only the effect of the observed component losses on the steam path efficiency, but also the interaction between these complex loss mechanisms. In other words, the feedback effect of the observed losses can now be calculated in greater detail and with greater accuracy.
Loss Mechanisms
Stage efficiency losses may be caused by a ber of reasons, such as deposits, solid pa erosion (SPE); foreign object damage (F rubbed or damaged packings, or rubb damaged spill strips. Regardless of the c leading to losses, stage efficiency losses m quantified by sorting the losses into one o following four categories:
GE has introduced a new tool for assessing the loss mechanisms that are evaluated during a Steam Path Audit. This new tool is called SPA 2000, and is a PC-based program that uses a s Leakage loss stage-by-stage calculation to analyze the pers Friction loss formance of a turbine section. This program, s Aerodynamic loss which is a user-friendly version of the same analysis program used by GE design engineers, s Loss caused by changes in flow pass is calibrated based on many years of field test areas data and GE lab test data. It is the most accurate These losses prevent the efficient transfer tool available to the auditor for the prediction energy into shaft work as the steam is expa of turbine section performance and flow capacthrough a turbine stage. ity. SPA 2000 is used for obtaining input of You're Reading a Preview Leakage Losses design data and inspection data, as well as for Unlock full access with free trial. reporting stage and turbine performance outIn aorder for a turbine to produce shaft p put data. Additional input parameters have steam must pass through both the nozzl Download Free Trial been added to allow the auditor to input specif- Withbucket flow passages. Steam bypassing ic component losses observed on the nozzle the nozzles and/or buckets due to diaph and bucket profiles. interstage packing leakage, bucket root le SPA 2000 is a FORTRAN-based program that uses a closed system for making comprehensive performance calculations, including the following: s
Nozzle and bucket efficiency
or bucket tip radial spill strip leakage, w produce kilowatts. It may also disrupt the through the and in such Sign up nozzles to vote on thisbuckets title as to further turbine shaft o Useful decrease Not useful Leakage losses are caused by increased ances between the rotating and stationary
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Steam Turbine Thermal Evaluation and Assessment
does not account for the effect of the increased side), the orientation, the size, and the g leakage on the energy distribution on the stage try of the projections on the airfoil surfac or the consequence of it on the downstream customary when evaluating friction lo stage. For example, if there is excess root cleardivide the airfoil into three regions: le ance on a diaphragm spill strip, there will be an edge, suction side trailing edge, and pr increase in the flow entering or leaving the side trailing edge. Nozzle suction side r steam path, which, in turn, affects the root reacness affects stage efficiency approximately tion of the stage and the amount of flow which times more than pressure side roughness passes through the bucket dovetail hole or the leading edge roughness will have the gr wheel hole. Similarly, if additional leakage flow contribution to stage efficiency loss occu is calculated over the tip spill strip of a bucket, on the bucket. Bucket leading edge suctio the tip reaction of the stage will also be affected, roughness affects stage efficiency approx which affects the energy distribution on the ly two times more than pressure side roug stage as well as on the stage immediately down Also, because of the higher-pressure stream. The stage-by-stage analysis program utithrough the nozzles relative to the bucke an impulse design stage, approximately 7 lized by SPA 2000 calculates the various leakage flows in the steam path based on all of the measa stage efficiency loss caused by surface r ured clearances during the audit. Furthermore, ness is attributed to the nozzles. Figure 9 the complex interplay of the increase or the approximate loss in stage efficiency You're Reading a Preview decrease in any of these flows relative to the function of surface finish for GE steam Unlock full access with a free trial. design case for each stage is determined. bines. This information is separated by section. Since higher Reynolds Number Download Withfound Free Trial Friction Losses in the High-Pressure section (sm Stage efficiency losses due to an increase in the boundary layer), the smaller the proje measurable roughness of a nozzle partition or have to be in order to avoid an increase i bucket vane surface will be a function of the tion loss. This plot assumes a 63 micro-inc ratio of the height of the projections to the ish for the as-built surface finish of the thickness of the boundary layer, and whether up to votecauses on this title tions. Sign Common for friction this flow is laminar or turbulent (Reynolds include and Useful Notforeign useful object da deposits Number). The thinner the boundary layer Although the Steam Path Audit insp (higher Reynolds Number), the more signifirequires an evaluation of the surface roug
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Steam Turbine Thermal Evaluation and Assessment 0 L.P. Turbine 2 ) t n e c r e P ( y c n e i c i f f E e g a t S n i s s o L
I.P. Turbine
4 500 Mw Unit H.P. Turbine
200 Mw Unit
6
8
8
16
32
63
125
250
500
Surface Finish, Micro-Inches C.L.A. (Flow Across Cut) 16
32
63
125
250
500
1000
Surface Finish, Micro-Inches C.L.A. (Flow With Cut) 900
10
0.01
600
400
240
Emery Grade 0.05
0.1
0.2
0.4
0.6 0.8 1.0
2.0
4.0 4.0
6.0 8.0 10.0 6.0 8.0 10.0
Equivalent Sand Grain Size (Mils)
Figure 9. Approximate loss in stage efficiency as a function of surface roughness
the roughness is applied as discrete loss in stage zle throat widths. HP and IP turbine se efficiency relative to the stage in a new and diaphragms are designed with nozzle tr You're Reading a Preview clean condition with all other geometrical edge thickness in the range of 15 to 25 parameters equivalent to their designUnlock values. depending full access with a free trial. on the stage. The most com causes of off-angle losses are due to erosi Aerodynamic Losses trailing edges and poor quality re Download Withnozzle Free Trial As previously mentioned, turbine nozzle and When nozzle trailing edges become erode bucket profiles and geometry are designed so nozzle trailing edges decrease until, that steam accelerating through nozzle passages enough material is lost, pieces of trailing can be redirected onto the buckets at optimum begin to break off. When this occurs the tr entrance angles and velocities. Any changes to edge thickness will increase andthe off Sign up to vote on this title nozzle and/or bucket profiles will change the losses will increase. Diaphragm repairs Useful Not useful entrance and/or exit steam angles, increasing increase nozzle trailing edge thickness the aerodynamic losses within a stage. These the design thickness will also increas
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Steam Turbine Thermal Evaluation and Assessment Nozzle Trailing Edge Thickness Loss Percent of Nozzle Efficiency
stant valve position. Deposits in the n throat area will decrease the efficiency as w the flow passing capability (and therefore watt capability) of the unit, while erosion o zle flow passages will decrease the efficien increase the turbine's flow passing capabil
Percent Nozzle Efficiency Loss
10
0.045
9 8
0.035
7 6
0.25
5 4 3
0.015
2 1 0
0
0.1
0.2
0.3
0.4
0.5
Nozzle Throat - Inches
0.6
0.7
0.8
However, with the introduction of the SPA program, the geometry specific to the path is used to calculate the flow pa through the turbine stages and a more acc prediction of the flow capacity of the un be determined. This analysis also include effect of the change in the stage flow cients due to the presence of the observe mechanisms, such as steam path erosio deposits on the turbine stages.
SPE damage to the turbine steam path ca
Figure 10. Estimated loss in stage efficiency for result in secondary cycle losses cause different trailing edge thickness You're Reading a Preview
changes in section efficiencies and stage sures. a free For trial. example, higher-than-design Losses Due to Changes in Flow Unlock full access with reheat temperatures (caused by erosion i Passage Areas section) Download WithHP Free Trial may necessitate the need for r If the flow passage area of a stage changes, the attemperation. First reheat stage erosio initial pressure into that stage must change in reduce cold reheat pressure, resulting order to pass a constant steam flow. This change lower pressure to the final feedwater heate in the initial pressure will change the amount of thus a reduced final feedwater tempe available energy to the stage, which in turn will when the turbine extraction to the top he Sign up to vote on this title affect the efficiency of the stage. Changes to at the reheat point. First reheat stage er Useful Not useful flow passage areas are commonly caused by will also reduce the reheat bowl pressure deposits (area reduction), erosion (area increasing the velocity through the reh increase), or mechanical damage (area reduc-
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Steam Turbine Thermal Evaluation and Assessment Path Audit report, using SPA 2000, will include the following information: s
Background information on unit inspected
s
Efficiency appraisal evaluation summary
s
Tabular breakdown of losses 1. End shaft packings and snout rings. 2. Recoverable losses for each section showing losses by component (on each stage inspected). 3. Unrecoverable losses for each section showing losses by component (on each stage inspected). (See Figure 11.)
s
s
Color photographs of steam path
Photos of the major components and each which is inspected are made using either tional photography or employing the lat digital camera technology. Digital photog (see Figure 12) allows the auditor to make a review of the quality of the photographs format makes the photos easily available mail to GE turbine experts who are not pr at the site. This enhances the compreh analysis that is presented to the custome report-out at the conclusion of the audit.
Advancements in the Evaluation an Assessment of Data
The prior section explained the value Advanced Steam Path Audit (SPA 2000) d 1. Recovered losses for each turbine You're Reading aa Preview steam turbine maintenance ou section inspected (pie charts). Advancements are also ongoing for acqu Unlock full access with a free trial. 2. Summary of losses by stage and type evaluating, and assessing thermal perform (bar charts). of operating power plants. To deliver mor Download With Free Trial tomer value, the focus of advancement 3. Summary of losses by stage for each automation, remote access for timely diag major component, i.e., bucket, assistance, and expansion of expertise to nozzle, tip leakage, root leakage the entire power plant. (bar charts).
Graphical presentation of results
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Figure 12. Digital photography
mize overall plant profitability at any given and operating conditions. The On Performance Monitoring is an ongoing diagOptimizer uses real time data, allowing o Reading a Preview nostic activity coupled with software You're tools that tors to determine how best to adjust co allow the collection and presentation of data. Unlock full access with a free trial. lable parameters to maximize profit. Th Preliminary interpretation of the data can be Line Module simulates the plant perform performed automatically. A detailed review and Download Withbased Free Trial upon specific user inputs to the he determination of data requires periodic review ance model. by an engineer and/or plant operator. GE now The Data Module consists of an embe offers performance monitoring products for Plant Information (PI™) System by steam turbines / gas turbines / combined cycle Software, Inc., which communicates mea plants which have a suite of related modules Sign up to vote this title tag values from theonplant DCS and ser that provide on-line plant performance moniEfficiencyMaps’ Useful historian. Not useful toring. The performance monitor powered by Plant diagnostic assistance, remote sof GE Enter Software’s EfficiencyMap and Gate support and consulting services are pro Cycle software provide real-time guidance to
Performance Monitoring
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Steam Turbine Thermal Evaluation and Assessment ance expertise to deliver a Total Plant Evaluation Service. This service enables the customer to make cost-effective business decisions to improve plant efficiency or increase plant electrical output capacity. This service begins by gathering plant design data to understand the expected performance and operating constraints of a plant. Next, performance engineers visit the plant to gather performance data and to gain a first-hand understanding of the operating requirements and limitations. A detailed assessment is completed to identify loss performance and recommend about operational changes or maintenance actions to recover performance. The study can also include a thermal model study of equipment uprates/upgrades or cycle modifications for improving plant efficiency or kilowatt capacity.
ing methods for periodic data acquisition, pretation of performance data, inspecti the turbine steam path, monitoring the formance of your steam turbine and evalu the total plant. These programs are essen order to achieve and maintain the highes of thermal performance of a turbine-gene unit.
GE continues to look for better ways to s customers by improving the thermal effic and kilowatt capacity of power plants. T internet and e-Business technology is development to better compare unit per ance with fleet data and quickly assess per information.
References
1. ANSI/ASME PTC 6-1996, “Steam Turb Reading a Preview * EER Energy and Environmental You're Research 2. ANSI/ASME PTC 6S Report Corporation, a wholly owned subsidiary of Unlock full access with a free trial. “Simplified Procedures for Ro General Electric Company Performance Tests of Steam Turbines” Download With Free Trial Summary 3. Forster, V.T., “Performance Loss of M Over the next few years, becoming the “lowSteam Turbine Plant Due to Su cost” power producer will be increasingly Roughness”, The Institution of Mech important. Power plant owners can make a sigEngineers Proceedings, 1966-67, vol. nificant contribution toward achieving this goal PartSign I, Number up to vote17, on England. this title by implementing a well-organized perform Useful Not useful ance-diagnostic program, which will reduce fuel Acknowledgements costs and facilitate cost-effective maintenance. Marriner, Brian W., “Advanced Metho
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Steam Turbine Thermal Evaluation and Assessment List of Figures Figure 1.
Test instrumentation location for a PTC 6S Test - fossil unit
Figure 2.
Enthalpy Drop Test
Figure 3.
HP & IP efficiency measurement locations
Figure 4.
Throttle pressure correction for single reheat units
Figure 5.
Correction for main steam and reheat steam desuperheating flow
Figure 6.
HP turbine efficiency
Figure 7.
Effect of change in nozzle area on flow capacity for impulse-type turbines
Figure 8.
Pressure or capability curve vs. chronological test dates
Figure 9.
Approximate loss in stage efficiency as a function of surface roughness
Figure 10.
Estimated loss in stage efficiency for different trailing edge thickness
Figure 11.
Overall summary of losses
Figure 12.
Digital photography
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