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Huntly Power Station leak

An example of Exergy Use from Huntly Power Station

Unit One Condenser Air Leakage Problem (A formal review)

Introduction

I have been asked to document the events surrounding the Unit 1 condenser air leakage problem that occurred between Aug 01 and Mar 03. This document details the sequence of events and provides conclusions and recommendations so the opportunity to learn from this experience is not lost. The primary purpose of this document is to prevent a future reoccurrence.

Aug 01: Problem Identified

The Operators point out unusual high back pressure on Unit 1 condenser. They suggest the condenser neck bellows as a possible source of leakage because of the history of problems with this component. It had already been patched on numerous occasions.

Aug 01: Leaks Repaired

The operators found leaks around the bellows during a visual inspection. These leaks are patched up but very little improvement in the back pressure is noted.

Aug 01: Process of elimination begins

Concerns over the air leak are discussed but no agreement on the source is reached. The air suction temperatures are running 4 degrees lower on Unit One than the other units. The air ejectors are identified as a possible cause and tests begin to investigate this.

Oct 01: Exergy alarms identify sudden air ingress

On the 14 of Oct at 02:43 an exergy alarm was emailed pointing to a heatrate excursion (appendix 1) valued at 73.6 $/hour at 50MW due to a 40mbar spike in the back pressure that lasted for one hour. I do not know whether it receded by itself with load increase, or the operator did something about it. It seems highly likely however, that the 14-OCT-2001 02:43 is the point of time when the first rupture took place at the condenser neck neck bellows.

The net result of this was a permanent increase in back-pressure from 76Mbar on October 12 to 82Mbar on October 16 (both at 233Mw).

Oct 01: More leaks identified in the bellows

On October the 17th Roy McPherson Finds two major leaks on the condenser neck bellows one on the top joint at the north east corner (behind the pillar) and another one on the bottom joint behind SW111 and 115, also a couple of minor leaks on the south side joint above the water boxes. It is possible that 2-shifting could of aggravated these leaks. The leaks are eventually patched and a high level leak check is recommended to trace other leaks that may not be obvious. Derek Krippner then takes an Ultra Probe to detect leaks around the Unit but he finds nothing significant.

Oct 01: Incongruity over temperature depression

There was disagreement about temperature depression as a suitable means to detect air leakage. A test had been conducted in 2000 to prove the theory but the results were inconclusive. Subsequent experience showed however that the method is valid and has a big part to play in air leakage detection.

The discussion and debate that took place proved to be detrimental to the Unit situation because it diverted attention away from the critical issues.

Nov 01: More concerns about the neck bellows

In late November a letter is circulated to identify Efficiency Issues prior to the outage as follows; (for clarity I am showing just the items that relate to the condenser)

  • Condenser bellows repair. Prior to the unit coming off we had persistent leakage around the bellows. Clearly, it cost big dollars in lost efficiency and should be made as perfect as possible before the RTS. If any doubt exits over the long term effectiveness of the repair we should consider replacement. This was also discussed.
  • Condenser high level check. Very important because the Unit has on-going leakage problems that may not be caused by the bellows alone. Other leaks might exist and should be identified/repaired before RTS.

Nov 01: Decision against replacement

It was decided not to replace the bellows during the outage due to high cost, lack of decisive evidence, and the lack of believable payback time.

Jan 02: Step change in back pressure noted

The outage took place during December and a high level leak check was carried out prior to RTS. The check revealed only a small leak at the neck bellows which was patched before RTS.
However, after only a few days in service, there was a major step change in the back pressure. The Unit ran with poor back pressure throughout that summer.

March 02: Analysis begins in earnest

In March (after river heating) investigations revealed the following; Condendser Exergetic efficiency down 10% when compared to the other Units, TTD running very high at 14 degrees and high heat rise across the condenser.

Further analysis showed the full extent of what had actually happened. The real disaster had taken place on January 12 2002. with two more "aftershocks". Exergy alarms had been raised for these events and gave the precise timing, cost and root cause of the problem. (appendix 2)

March 02: Exergy alarms pin point problems

It all began on January 12 2002 at 21:30. There were two alarms, one for $419 per hour the next for $465 per hour.
The alarms pointed clearly to an air-leak by way of temperature depression.

Another fact is that a huge rise in heatrate occurred, a step change, which was caused by a further 15Mbar rise in back pressure. This was all clear from the exergy email and some more analysis. What was not clear however is what the root cause actually was (bellows, glands or something else).

Dr (Eli) Yasni had also spotted this problem via remote access and suspected an LP turbine labyrinth gland was damaged or the ejectors did not cope with sudden air ingress for some reason.

April 02: Tracing air leaks

We commenced a process of trial and elimination to isolate the leaks by first working on the large plants items (heaters), finally, working our way down to the more difficult items. The results of these tests are attached.

April 02: Dr (Eli) Yasni arrives, we meet to discuss issues

In late April a meeting was held between Peter Stidolph, Dr Yasni and Tim Randall. Because of the slow progress to date and the mounting costs it was decided to call in Conco Systems Pty Ltd to search for the air leaks.

Dr Yasni gave an unconditional guarantee that the Exergy input data was correct and we definitely had major air leaks around the plant. This was definite beyond all doubt according to Dr Yasni who remained insistent on calling Conco Ltd.

May 02: Conco Systems arrive

Conco Systems arrived and tested both Unit 1 and Unit 2 for leaks over a two day period. They found major air leaks on Unit 1 at the Condenser Neck Bellows and LP turbine labyrinth glands which supported what Mr Yasni had said. Other leaks were found at the bursting discs and LP turbine top access doors (appendix 3).

We then sealed up as many leaks as possible during weekend outages which produced some improvement. We managed to seal all the door joints and seal three of the four bursting discs. The major leaks were repaired during the 02-03 cold survey with a subsequent 4% improvement in unit efficiency.

Conclusions

1. The exergy alarms are a useful tool for detecting plant problems like this. They pointed clearly to the leakage problem by utilising temperature depression theory and showed the exact time of the air ingress.

2. We lacked a formal process for dealing with air leakage problems at the basic level.

Recommendations

1. That we make exergy available to the Operators as an analysis tool as soon as possible.

2. The all exergy alarms are mailed to the appropriate unit desks for analysis and action.

3. That we draw up a formal document detailing the procedures to be adopted in the event of an air leak and place it in the QMS.

4. That all future identifiable efficiency risks are subject to a proper risk analysis and especially if they are identified prior to a significant outage.

5. That efficiency related items with the potential for significant loss are subject to a peer review before the decision becomes binding. This would apply when the decision has not been reached by a formal risk analysis.

Appendix 1

From: HPS1::EXERGY 14-OCT-2001 03:24:19.09
To: mx%"peter.stidolph@genesispower.co.nz"
CC: mx%"jorge.guerra@genesispower.co.nz", ELI,mx%"nick.lee@genesispower.co.nz
Subj: HUNTLY POWER STATION Unit 1

This is an alarm message from Unit 1
14-OCT-2001 03:23
Step change in efficiency occurred at time 14-OCT-2001 02:43
=====================================================
Cause-root(s) of loss in time interval
14-OCT-2001 02:08 to 14-OCT-2001 03:23:
COST OF HEATRATE EXCURSION= 73.6 $/Hour
Tags for drill-down, script 1:
Generator-unit TAG= D1900.LF
Main Turbine cycle TAG= D2800.LF
Lp Turbine area TAG= D3851.LF
Main condenser, CW+Condensate pumps, Air-Ejectors TAG= D4854.
LF Main condenser & condensate pumps TAG= D5864.LF

Main condenser & condensate pumps D5864.LF
At initial time14-OCT-2001 02:08
MAIN-CONDENSER "A" SHELL 03435.PR:3435 = 0.052BAR 51.75Mw
At mid time14-OCT-2001 02:43
MAIN-CONDENSER "A" SHELL 03435.PR:3435 = 0.072BAR 51.07Mw
At end time14-OCT-2001 03:23
MAIN-CONDENSER "A" SHELL 03435.PR:3435 = 0.095BAR 50.17Mw
_ _
At initial time14-OCT-2001 02:08
MAIN-CONDENSATE: EXT.PUMP SUCTION (HOT 05150.TP:6625 = 32.724OC. 51.75Mw
At mid time14-OCT-2001 02:43
MAIN-CONDENSATE: EXT.PUMP SUCTION (HOT 05150.TP:6625 = 37.722OC. 51.07Mw
At end time14-OCT-2001 03:23
MAIN-CONDENSATE: EXT.PUMP SUCTION (HOT 05150.TP:6625 = 41.791OC. 50.17Mw

Appendix 2

From: HPS1::EXERGY 12-JAN-2002 22:45:59.18
To: mx%"peter.stidolph@genesispower.co.nz"
CC: mx%"jorge.guerra@genesispower.co.nz",
ELI,mx%"nick.lee@genesispower.co.nz"
Subj: HUNTLY POWER STATION Unit 1

This is an alarm message from Unit 1
12-JAN-2002 22:45
Step change in efficiency occured at time 12-JAN-2002 22:05
=============================================
Cause-root(s) of loss in time interval
12-JAN-2002 21:30 to 12-JAN-2002 22:45:
COST OF HEATRATE EXCURSION= 418.9 $/Hour
Tags for drill-down, script 1:
Generator-unit TAG= D1900.LF
Main Turbine cycle TAG= D2800.LF
Lp Turbine area TAG= D3851.LF
Main condenser, CW+Condensate pumps, Air-Ejectors TAG= D4854.LF
Main condenser & condensate pumps TAG= D5864.LF

Main condenser & condensate pumps D5864.LF
At initial time12-JAN-2002 21:30
MAIN-CONDENSER A AIR AIR-COOLING AREA 06001.TP:6622 = 29.856OC. 99.99Mw
At mid time12-JAN-2002 22:05
MAIN-CONDENSER A AIR AIR-COOLING AREA 06001.TP:6622 = 29.015OC. 86.51Mw
At end time12-JAN-2002 22:45
MAIN-CONDENSER A AIR AIR-COOLING AREA 06001.TP:6622 = 28.786OC. 96.82Mw

From: HPS1::EXERGY 12-JAN-2002 22:50:58.71
To: mx%"peter.stidolph@genesispower.co.nz"
CC: mx%"jorge.guerra@genesispower.co.nz",
ELI,mx%"nick.lee@genesispower.co.nz"
Subj: HUNTLY POWER STATION Unit 1

This is an alarm message from Unit 1
12-JAN-2002 22:50
Step change in efficiency occured at time 12-JAN-2002 22:10
=====================================================
Cause-root(s) of loss in time interval
12-JAN-2002 21:35 to 12-JAN-2002 22:50:
COST OF HEATRATE EXCURSION= 465.4 $/Hour
Tags for drill-down, script 1:
Generator-unit TAG= D1900.LF
Main Turbine cycle TAG= D2800.LF
Lp Turbine area TAG= D3851.LF
Main condenser, CW+Condensate pumps, Air-Ejectors TAG= D4854.LF
Main condenser & condensate pumps TAG= D5864.LF

Main condenser & condensate pumps D5864.LF
At initial time12-JAN-2002 21:35
MAIN-CONDENSER A AIR AIR-COOLING AREA 06001.TP:6622 = 29.703OC. 96.86Mw
At mid time12-JAN-2002 22:10
MAIN-CONDENSER A AIR AIR-COOLING AREA 06001.TP:6622 = 28.882OC. 85.91Mw
At end time12-JAN-2002 22:50
MAIN-CONDENSER A AIR AIR-COOLING AREA 06001.TP:6622 = 28.796OC. 99.19Mw
_ _
At initial time12-JAN-2002 21:35
MAIN-CONDENSER A AIR AIR-COOLING AREA 06001.TP:6622 = 29.703OC. 96.86Mw
At mid time12-JAN-2002 22:10
MAIN-CONDENSER A AIR AIR-COOLING AREA 06001.TP:6622 = 28.882OC. 85.91Mw
At end time12-JAN-2002 22:50
MAIN-CONDENSER A AIR AIR-COOLING AREA 06001.TP:6622 = 28.796OC. 99.19Mw

Appendix 3

Conco FluorotracerTM Air In-Leakage Detection Service Report

Client: Genesis Power Limited, Huntly Power Station

Plant: Unit 1 and Unit 2 Turbo Generator
Purchase Order: 349774
Service Date: Monday 1 July 2002 to Wednesday 3 July 2002

A Conco FluortracerTM Leak Detection Service was carried out on Units 1 and 2 in an attempt to locate air ingress and vacuum loss points on the units. Both units were operating on demand load, and did not drop below 60% of full load during the leak detection.

The following Leak Points were found:

Huntly Power Station – Unit 1

ITEM DESCRIPTION DIGITAL READING
A L.P. Turbine Labyrinth Gland H.P. Turbine end 813
B L.P Turbine Labyrinth Gland Generator end 602
C The Expansion Joint was found to be leaking to some extent at most points around its entirety, it appears perished. The worst areas are a 1 metre section at the H.P. Turbine end 1 metre from the Auckland side, and A 1 metre section at the Hamilton side of the unit approximately 1 metre from the Generator end

855

827

D Manhole Cover H.P. Turbine end Auckland side 369
E Manhole Cover L.P. Turbine Generator end Auckland side 275
F Manhole Cover L.P. Turbine H.P. Turbine end Hamilton side 310
G Bursting Disc Generator end Auckland side 833
H Bursting Disc Generator end Hamilton side 832
I Bursting Disc H.P. Turbine end Auckland side 237
J Bursting Disc H.P. Turbine end Hamilton side 825
K H.P. Turbine Labyrinth Gland 158
Huntly Power Station – Unit 2
ITEM DESCRIPTION DIGITAL READING
L L.P. Turbine Labyrinth Gland H.P. Turbine end 740
M L.P Turbine Labyrinth Gland Generator end 591
N Expansion Joint Generator end Auckland side corner 875
O Manhole Cover H.P. Turbine end Auckland side 570
P Manhole Cover L.P. Turbine Generator end Hamilton side 240
Q Clear Tube to bottom of Condenser V/v not seating 910
R Bursting Disc Generator end Auckland side 857
S Bursting Disc Generator end Hamilton side 860
T Bursting Disc H.P. Turbine end Auckland side 833
U Bursting Disc H.P. Turbine end Hamilton side 847

Note 1:

Generating Stations already know what their total Air In-leakage is. To quantify each and every leak in our opinion Is not cost effective.

Due to variables of a condenser under vacuum, the quantifying of leaks would not add any information to what the plant personnel already know.

The analyser gives a digital millivolt reading which plant personnel can use to determine a plan of action to repair the leaks by comparing the millivolt readouts. These of course are relative values and are not calibrated in engineering units such as CFM.

What should be of most concern is the exact location of the leak and the subsequent repair and retest of it.

Note 2:

It is Conco’s considered opinion that items A, B, C, G, H, J, L, N, Q, R, S, T, and U are of considerable critical size.

Items D, F, M and O are of significant critical size.

Items E, I, K and P contribute to the Total Air Ingress in the turbine.

Note 3:

In repairing the turbine labyrinth gland leaks, it is suggested that the gland sealing steam drains to the drains cooler and the Main Condenser be checked as this may be the leak source.

As a rule of thumb for efficient running of a generating unit, air in-leakage levels should be held to 1CFM per 100MW of generating capacity.

Conco considers that, if these air in-leakage locations are rectified and eliminated, an increase in vacuum should be obtained resulting in lower running costs and improved efficiency of the units.

Conco Systems thanks you for using their Products and Services.

Yours faithfully

Neil McNickle
Technical Sales Manager
Conco Systems Pty Ltd

Contact us for more information.