8. yazd-system description for auxiliary steam system_combined

MINISTRY OF ENERGY IRAN POWER DEVELOPMENT CO.

I P D C

PROJECT : 22 COMBINED CYCLE POWER PLANTS YAZD COMBINED CYCLE POWER PLANT

SYSTEM DESCRIPTION

FOR

AUXILIARY STEAM SYSTEM

B IN CORPORATED MOM DATED 27~31 AUG. AND 08~12 SEP.’04 Nov.09,’04 Y.K.LEE Nov.09,’04 H. C. YOO Nov.09,’04 W. Y. LEE Nov.09,’04

A FOR CONSTRUCTION July. 5,’04 Y.K.LEE July. 5,’04 H. C. YOO July. 5,’04 W. Y. LEE July. 5,’04

0 FIRST ISSUE Dec.5,’03 D.C.KIM Dec.5,’03 H. C. YOO Dec.5,’03 W. Y. LEE Dec.5,’03

REV DESIGNATION DATE DESIGN DATE CHKD DATE APPROVED DATE

DOCUMENT NO. : MP-YZC-GA-04-SA0-001 REV. C MAPNA C o . ( PRIVATE JOINT STOCK )

IRAN POWER PLANT PROJECTS MANAGEMENT Co. CONTRACT NO. : 22-0701/BA/TL PAGE 1 OF 8

ORIGINATOR NO. : YZC-A-SP-449-SDE-004 ORIGINATOR

DOOSAN HEAVY INDUSTRIES & CONSTRUCTION CO.,LTD. ORIG

LOC.ORIG. DEPT.

PROJ. NAME

DISC.

DOC. TYPE

AREA TYPE

SYS. FA.N

SEQ. N.

SH. N. REV. C

FOR CONSTRUCTION

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MINISTRY OF ENERGY IRAN POWER DEVELOPMENT CO.

I P D C

PROJECT : 22 COMBINED CYCLE POWER PLANTS YAZD COMBINED CYCLE POWER PLANT

REVISION REVISION

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DOCUMENT NO. : MP-YZC-GA-04-SA0-001 REV. C MAPNA C o . ( PRIVATE JOINT STOCK )

IRAN POWER PLANT PROJECTS MANAGEMENT Co. CONTRACT NO. : 22-0701/BA/TL PAGE 2 OF 7

ORIGINATOR NO. : YZC-A-SP-449-SDE-004 ORIGINATOR

DOOSAN HEAVY INDUSTRIES & CONSTRUCTION CO.,LTD. ORIG

LOC.ORIG. DEPT.

PROJ. NAME

DISC.

DOC. TYPE

AREA TYPE

SYS. FA.N

SEQ. N.

SH. N. REV. C

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YAZD Combined Cycle

SYSTEM DESCRIPTION AUXILIARY STEAM SYSTEM

DOOSAN Changwon, KOREA

Contract No. : 22-0701/BA/TL

Doc. No. : MP-YZC-GA-04-SA0-001 Originator No. : YZC-A-SP-449-SDE-004

Revision : C Date : Nov. 09, ‘04 Page: 3 OF 8

AUXILIARY STEAM SYSTEM

CONTENTS CLAUSE NO. DESCRIPTION PAGE NO. 1.0.0 REFERENCE DRAWINGS 4 2.0.0 INTRODUCTION 4 3.0.0 AUXILIARY STEAM SYSTEM CONFIGURATION 5 4.0.0 DESIGN BASIS 6 5.0.0 GENERAL CONTROL DESCRIPTION 8

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YAZD Combined Cycle






1.0.0 REFERENCE DRAWINGS

- Auxiliary Steam System P&I diagrams (MP-YZC-GA-02-SA0-001) - P&I diagram for Feed Water Storage Section (MP-YZC-GA-02-HL0-003)

2.0.0 INTRODUCTION

The auxiliary steam system consists of auxiliary boiler (supplied by Others) and auxiliary steam header(ALBG30BR001) with attemperator(ALBG20AZ001), pressure control valve (ALBG10AA151), temperature control valve(ALCE11AA151). Auxiliary steam header(ALBG30BR001) is connected to the main piping(ALBG70BR001) from auxiliary boiler. Each consumer for auxiliary steam is branched from the nearest tapping point of the main auxiliary steam lines (ALBG30BR001, ALBG70BR001). The auxiliary steam from auxiliary steam header is supplied to : - Steam turbine gland sealing - Hogging / holding ejector - Two (2) deaerators for two (2) HRSGs - H V A C - Water treatment plant - CPP regeneration plant The auxiliary steam is provided from HP steam common line by means of pressure control valve (ALBG10AA151) and attemperator (ALBG20AZ001) and also provided from the auxiliary boiler that can supply steam to the auxiliary steam headers. The source of attemperator spray water is provided from the condensate extraction pumps(ALCB11AP001/002).

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YAZD Combined Cycle






3.0.0 AUXILIARY STEAM SYSTEM CONFIGURATION

Auxiliary steam for the steam turbine gland seal steam system must be provided until the steam turbine becomes self-sealing. For normal operation of Plant, auxiliary boiler should be operated to supply its auxiliary steam as a backup while HP steam of plant is not available as auxiliary steam. Auxiliary steam for deaerators will be also supplied from the auxiliary steam header during plant start-up. A safety valve (ALBG30AA191) with relieving capacity of maximum steam flow of desuperheated HP steam provided on module auxiliary steam header to protect from over-pressure.

3.1.0 Auxiliary steam flow paths.

Auxiliary steam is supplied from the HP superheated steam common header(ALBA30BR004) via 2.5 inch line(ALBG10BR001) with a motorized isolation valve(ALBG10AA051) to the pressure control valve(ALBG10AA151). Pressure controlled HP steam is mixed with condensate water by means of an attemperator (ALBG20AZ001) to meet the auxiliary steam condition (15bar.a, 240℃). Mixed steam is supplied to the auxiliary steam header via 4 inch auxiliary steam header (ALBG30BR001). Auxiliary steam drain lines are provided to drain condensate water to blow down tank(1/2LCQ60BB001) or flash tank(ALCM30BB001) during start-up and normal operation. Each auxiliary steam drain line is provided with a drain leg with steam trap with bypass. The auxiliary steam for gland steam will be drained on the inlet side of gland steam control valve skid to avoid accumulation of water that can be injected into the seal system. Before start up operation of plant, the initial steam from auxiliary boiler will be flowed to flash tank through 1” pipe by opened MOV (ALCM91AA051) until the related lines are fully

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YAZD Combined Cycle






warmed-up. In this time, the small quantity of drain flow will be drained through orifice by the opened isolation valves. And, during normal operation, the MOV is being closed, and the aux. steam to gland steam control valve skid is drained continuously through the plug resistance orifice (ALCM91AZ001).

The auxiliary steam header(ALBG30BR001) supplies the following branches :

- 3 inch line(ALBG60BR001) for gland steam. - 2.5 inch line(ALBG50BR001) for hogging & holding ejector. - 3 inch lines(1/2LBG41BR001) for deaerators of two(2) HRSGs. - 6 inch line(ALBG70BR001) for HVAC, water treatment plant, CPP regeneration plant. The auxiliary steam will be supplied from the following steam source: - 4 inch line(ALBG30BR001) from outlet of auxiliary steam attemperator after pressure

control valve (ALBG21BR001). - 6 inch line(ALBG70BR001) from auxiliary steam boiler.

4.0.0 DESIGN BASIS

The auxiliary steam system is designed to satisfy the following requirements:

1. Auxiliary steam flow to consumers

(1) During start-up (Aux. steam shall be provided from Aux. boiler)

- Gland steam : 1.5 0.75 kg/s - Hogging ejector : 1.0 kg/s - 1st HRSG Deaerator : 1.8 1.0 kg/s - HRSG #2 Deaerator : 1.8 kg/s - HVAC : 0.694 0.7 kg/s - CPP regen. & Water treatment : N/A 0.6 kg/s - Water treatment : 0.37 kg/s - Chemical storage plant : 0.19 kg/s

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(2) During normal operation (Aux. steam shall be provided from HP steam header)

- Holding ejector : 0.153 kg/s (Continous mode) - HVAC : 0.694 0.7 kg/s (Intermittent mode) - CPP regen. & Water treatment : N/A 0.6 kg/s (Intermittent mode) - Water treatment : 0.37 kg/s (Intermittent mode) - Chemical storage plant : 0.19 kg/s (Intermittent mode) - Total coincident steam flow : 1.937 kg/s ※ If CPP regeneration and water treatment operate simultaneously, their total

steam consumption will be 0.9 0.6 kg/s. ※ HRSG #1 and HRSG #2 are not started simultaneously. And, when 2nd HRSG

start-up with normally operated 1st HRSG, the required steam for each consumer is provided from HP steam desuperheating system. But, the required steam for water treatment plant & CPP regeneration is not considered during this start-up time

2. Flow from sources for generating auxiliary steam

(1) Max. steam flow of aux. boiler during start-up : **

(2) Steam flow of de-superheated HP steam during normal operation

- Flow at guarantee condition : 0.14 kg/s - Maximum flow : 1.937 1.515 kg/s

(3) Spray water flow CEP discharge during normal operation

- Flow at guarantee condition : 0.03 kg/s - Maximum flow : 0.416 0.338 kg/s

3. Operating pressure : 15 bar.a

4. Operating temperature : 240 ℃

5. Design pressure : 20 bar.a

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YAZD Combined Cycle






6. Design temperature : 265 ℃

7. Safety valve

- Setting pressure : 20 bar.a - Relieving capacity : 2.0 kg/s

※ ** : To be finalised by MAPNA.

5.0.0 GENERAL CONTROL DESCRIPTION

5.1.0 Auxiliary Steam Header Pressure/Temperature Control The auxiliary steam is monitored on the auxiliary steam header by means of signals from pressure transmitters (ALBG30CP101/102) and temperature transmitters(ALBG30CT 101/102). The pressure and temperature signals generated by the pressure and temperature transmitters initiate an alarm from the DCS when either the steam temperature or the steam pressure is higher or lower than the corresponding set points for maximum or minimum values. The auxiliary steam is supplied from the HP steam system. The auxiliary steam control admits HP superheated steam, after pressure reduction and attemperation, to the auxiliary steam header. The auxiliary steam pressure control is achieved by the steam pressure control valve. The set point for the pressure control valve is the desired value (15 bar.a) in the auxiliary steam header. The auxiliary temperature control is achieved by the spray water control valve in the condensate discharge line. The set point for the spray water control valve is the desired value (240 ℃) in the auxiliary steam header.

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APPROVAL ISSUE

Module 234·4

Course 234 - Turbine and Auxiliaries - Module Four

NOTES & REFERENCES

AUXILIARY STEAMSYSTEMS

OBJECTIVES:After completing this module you will be able to:

4.1 a) For each of the two types of the reheat system. explain how the ~Pages 3-4flow of reheater heating stearn is regulated through the wholerange of turbine load.

b) Explain the reason why reheating must be limited during turbine <=>Page 4startup and operation at light loads.

c) State three reasons why reheaters should be valved in (out) ~Page5

slowly.

d) State the operating concern caused by exceeding the limit on the ~Page5

side-to-side stearn temperature difference at the LP turbine inlet

4.2 a) For each of the two types of the reheat system. describe how ~Page6

the Donna! drains level is controlled.

b) State the automatic actions triggered by improper reheater drains ~Pages 6-7level:

i) Too high a level (4);

il) Too Iowa level (2).

c) Describe the adverse consequences/operating concerns caused ~Pages 6-8by improper reheater drains level:

i) Too high • level (3);

il) Too Iowa level (2).

d) List two causes of each of the following reheater drains level ~ Pages 8-9upsets:

i) Too high a level;

il) Too Iowa level.

4.3 a) Describe three adverse consequences/operating concerns caused ~ Pages 9-10by a significant loss of reheat if no corrective action is taken.

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Course 234 - Turbine and Auxiliaries- Module Four APPROVAL ISSUE

NOTES & REFERENCESPages 10-11 ~ b) i) State two actions which minimize two of these consequences.

til Explain how these actions achieve it.

4.4 For a reheater tube leak:

Pages 12-13 ~ a) Describe four adverse consequences/operating concerns causedby a large leak;

Page 13 ~ b) State three operator actions to minimize or prevent these conse-quences;

Pages 13-14 ~ c) Describe one method of detecting a smail leak and two additionalindications of a large leak.

Page 14 ~

Pages 15-16 ~

Pages 17-18 ~

Pages 18-19 ~

Page 19 ~

Pages 19-20 ~

• In some stations, the nameof this system is slightlydifferent. Examples: theturbine Aland steam system, the gland steam system or the gland sealingsystem.

Page 2

4.5 State two operating practices used in the reheat system to preventwater hammer.

4.6 State three reasons why attemperating sprays· must be valved inwhen the gland exhaust condenser is unavailable.

4.7 a) Describe two adverse consequences/operating concerns causedby overheating of the LP turbine exhaust.

b) i) Ust four important operating parameters that should becarefully monitored while operating in a condition that promotes overheating of the LP turbine exhaust.

til Explain why each of these parameters should be monitored.

c) State two general operator actions that can be taken if heating ofthe LP turbine has reached a point such that lack of action couldresult in turbine damage.

d) State the operating concern caused by excessive use of the LPturbine exhaust hood sprays.

• • •

INSTRUCTIONAL TEXT

INTRODUCTIONIn this module. the following auxiliary stearn systems are discussed:

- The reheat system;- The gland stearn sealing system';- The LP turbine exhaust cooling system.

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APPROVAL ISSUE Course 234 - Turbine and Auxiiiaries - Module Four

The previous turbine courses describe the major functions and the layout ofthese systems. as well as the functions of their major components. Basedon this general knowledge, this module discusses operation of these systems. In the discussion. emphasis is placed on operational upsets.

For your convenience, simplified flowsheets of these systems are attachedto the module end. The appropriate flowsheet can be pulled out and kept insight for easy reference.

Due to inherent station specific differences. the information presented in thismodule is only generic and does not cover all variations.

THE REHEAT SYSTEM

Recall that two different types of this system are used in CANDU stations:

- Live steam reheat systems l"here boiler steam is the only heat input;

- Two-stage reheat systems where two different heat inputs are used: HPturbine extraction steam in the ftrst stage, and boiler steam in the secondstage.

The first pullout diagram (on page 29) shows both these systems. For simplicity. part a) of this diagram shows steam supply to only one reheater.Likewise. part b) illustrates only one two-stage rebeater with its steam supply and drainage equipment. The remaining reheaters are equipped identically.

In this module. you wilileam about the following aspects of reheater operation:

- Reheating steam flow control;- Drains level control;- Effects of loss of reheat on unit operation;- Reheater tube leak;- Water hammer.

Reheating steam flow control

In both types of reheat system. the reheating steam flow changes withturbine load.

1. In live steam rebeat systems and the second stage or the twostage reheat systems. this happens as follows.

At high turbine loads", the reheating steam flow is self-regulating.What it means is that the flow adjusts itself to turbine load. No control

NOTES & REFERENCES

~ Obj. 4.10)

'" Typically, above.50-60% FP.

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Course 234 - TurbiDe and Auxiliaries- Module Four APPROVAL ISSUE

NOTES & REFERENCES

.. Pressure losses in thepiping are only about3-5% of boiler pressureat full power, and lessat partial loads.

.. A more detailed description is given in module234-6.

Obj. 4.1 b) ~

• Typically, below20-30% FP.

• Details are on pages17-18.

... Usually, the controlvalves are fully closed atabout 20-30% FP, andfully open at 50-60% FP.

Page 4

valve takes part in this process, ie. all valves in the steam supply pipingstay fully open. Here is how this self-regulation happens.

At any steady load. only as much steam enters the reheater as condensesinside the tubes. The rate of condensation depends on. among other .factors, the turhine steam flow rate. In the extreme case, where nosteam flows through the turbine, the rate of condensation is, in principle, zero and hence no reheating steam is taken. When the turbine loadincreases, so does the rate of heat transfer through the reheater tubes because more turbine steam flows through this heat exchanger. If the rateof condensation exceeds the flow of incoming reheating steam. the pressure inside the reheater tubes drops. As a result, more steam is drawnthrough the reheater steam supply piping until a new equilibrium is established.

The pressure drop that is necessary to increase the reheating steam flowis very small" because the reheater steam piping has a very small resistance to flow. This is achieved by proper sizing of the piping such thatsteam velocity is kept reasonably low.

The opposite changes in the reheating steam flow occur when the turbine load decreases.

The above description is somewhat simplified". In reality, any factorthat influences heat transfer across the reheater tubes (eg. tube flooding), changes the rate of condensation of the reheating steam, and henceits flow. Note that some other heat exchangers (eg. feedbeaters) exhibitthis self-regulating feature, too.

At light turbine loads", the reheating steam flow is isolated (exceptfor startup, when a small flow of steam is admitted to prewarm the reheaters). This is done to prevent overheating of the LP turbine exhaust Recall from the previous turbine courses that during turbinestartop and at very light loads, the LP turbine exhaust steam can be superheated, even if no reheat is used. As steam wetness is not a problemduring these operating states, there is no need to use the reheat. Its usewould only aggravate the LP turbine exhaust overheating which, if excessive, could damage the turbine".

As to the reheat operation at medium turbine loads, the reheatingsteam flow Is throttled. The opening of the control valves graduallyincreases with rising load". During turbine unloading, the valves closeover a similar range of turbine load. Depending on the station, thevalves are controlled either by the operator or automatically. In the lattercase, a turbine steam pressure (eg. at the HP turbine exhaust) is used asa measure of turbine load.

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APPROVAL ISSUE Course 234 - Turbine aod Auxiliaries - Module Four

Because the control valve position is linked to turbine load - whose rateof changing is limited during turbine startup and power manoeuvres the reheaters are valved In/out gradually.

This has the following advantages:

- Thermal stresses in the reheaters and LP turbines are minimized:- Abrupt changes in rebeater drains flow are avoided, which facilitates

drains level control;- As the reheater steam and drains flows change gradually, their dis

turbing effect on boiler pressure and level control is minimized.

2. In the first stage of two.slage reheat systems, the reheatingsteam flow is self-regulating over the whole range of turbineload. Note that the stage is supplied with HP turbine extraction steamwhose pressure and temperature rise with turbine load. Therefore, thestage can be valved in at all turbine loads.

In both types of the reheat system, more than one reheater is used. As theyare not perfectly identical, the temperature of the superheated steamproduced by Individual reheaters Is not exaelly the same. Thiscreates a side-to-side temperature difference (11T) at the LP turbine inlet. If excessive, the I1T ean produce thermal deformations in the LPturbine easing sufficient to cause biade and/or seal rubbing as well asIncreased vibrations. To prevent this, a iimit is imposed on the I1T.Proper actions (eg. valving out of some reheater lUbe bundles), as specifiedin the appropriate operating manual, must be taken when this limit is approached or exceeded.

SUMMARY OF THE KEY CONCEPTS

• Typically, the reheating steam flow is isolated during turbine startup andoperation at light turbine loads, throttled at medium turbine loads, andself-regulating at high loads.

• During turbine startup and at light loads, reheating must be limited in order to prevent overheating of the LP turbine exhaust

• Rebeaters should be valved in (out) slowly to minimize thermal stressesin the reheaters and LP turbines. Also, gradual changes of the rebeatersteam and drains flow facilitates reheater drains level control and boilerpressure and level control.

• Exceeding the limit on slde-to-side I1T at the LP turbine inlet can resultin large thermal deformations of the LP turbine casing. The deformations can cause rubbing in the turbine, as well as increased vibration.

NOTES & REFERENCES

~ Obj. 4.1 c)

~ Obj. 4.1 d)

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NOTES & REFERENCES

Obi. 4.2 a) ~

Obi. 4.2 b) ~

Obi. 4.2 c) ~

Page 6

REHEATER DRAINS LEVEL CONTROL

Normal control

In both types of reheat system. condensate of the reheating steam is collected in one or more drain tanks. In live steam reheat systems (see Fig.4.5 a) on page 29), there is only one tank which is shared by both reheaters.Their drains are pumped to the boilers, and the drains level In the tank isnorrnaily maintained by a control valve whiclt adjusts the drains now tothe boliers. When the level rises, the valve opens more, increasing theoutflow from the tank. A recirculatinn line back to the tank is provided toprevent overheating of the drains pump due to too small a flow. The recircuiation line operates when the dntios flow to the boiler is below a certain limit. This happens when the control valve opening is small in response to alow level in the drains tank.

Note in Fig 4.5 a) that some water is supplied from the discharge of theboiler feed pumps to the suction of the reheater drains pumps. The purposeof this water - whose temperature is well below the drains temperature - isto subeool the dntios, thereby preventing pump cavitationlvapourlocking.If not isolated when necessary. this water may. however, flood the reheat-·ers and their steam piping. Such an incident has happened in a CANDUunit.

In two-stage reheat systems (see Fig. 4.5 b) on page 28), separatedrain tanks are used for each stage because of their different operating pressures and temperatures. Typically, each individual reheater has its own setof two drain tanks. The ftrst stage drains cascade to the HP feedheaters.whereas the second stage drains are pumped to the boilers. The drains levels are normally maintained in the same way as described above. ie. byadjusting the drains outflow.

Automatic actions in response to improper drains level

The above descrlption covers the normal control action performed when thelevel error is relatively small. When the error is too large, other actions arecarried out to protect the equipment. The most typical of these actions aredepicted in Fig. 4.1.

Adverse consequences and operating concerns caused byimproper drains level

Improper reheater dntios level can have serious operating implications. Letus fltst consider the adverse consequences/operating concerns caused bytoo high a drains level. They are.1isted below in order of rlsing level.

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APPROVAL ISSUE Course 134 ..:. Turbine and Auxiliaries - Module Four

NOTES & REFERENCESDrains Level

-..I:i. Steam Supply Isolated •• Applie~ only to some

stations .

...l:1 High Level AlarmStandby Pump (If any) Starts

LeV Dump \tIlve (if any) to Condenser OpensOpono

------------~~~~~~---

LCVCIooea

-v Low LevelAlarm

-v Orail'll Pump (if any) Tripe

Fig. 4.1. M8jor eutomltle re8pon... to reheeter drains level:

LeV. Level control valve.

I. Reduced overall thennal efficiency.

Even when the reheater tubes are still not flooded, the typical protectiveaction on too high a drains level is to dump the drains to the condenser.Usually, this action can quickly restore the nonnalleve!. However,dumping hot drains to the condenser reduces the overall thennal efficiency which can be of concern when such operation is continued.

2. Flooding of the reheater tubes would result in a partial or total lossof reheat. Its adverse consequences are described on page 10.

Once the reheater tubes are flooded with dntins, condensation of reheatingstearn in the flooded reheater(s) is stopped (for all practical purposes).Therefore, in the stations where no attemperating water is supplied from theboiler feed pump discharge to the reheater drains pump suction, the reheaterdrains level also stops rising. But in the stations where attemperating wateris used (see Fig. 4.5 a) on page 28), failure to isolate its supply on a veryhigh drains level may cause the additional adverse consequences describedbelow.

3. Flooding of the reheat steam piping could cause the following problems:

a) Large thermal stresses in the piping if the drains are much cooler than the piping.

Note that attemperating water temperature' is far below the reheatstearn piping temperature. When this water is allowed to reach the

• 12S-1S0'C, depending.on the station.

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NOTES & REFERENCES

Obj. 4.2 d) ~

Page 8

resultant quenching of the hot pipes could overstress them, possiblycausing their failure. Weids in the live steam piping are particularlysusceptible and, in the extreme case, could crack.

b) Water hammer In the piping.

For example, this can happen in the main steam lines to the HP tur

bine when the reheat drains have reached the main balance headerfrom where slugs of water can be driven by the main steam flow.The presence of large quantities of water in the reheater steam pipesalso promotes water hammer during system restartup if pipelinedrainage is inadequate.

c) Water Induction to the UP turbine.

This can bappen through the main steam lines after the drains bavereacbed the main balance heatier. The resultant damage can be veryserious.

Too Iowa reheater drains level is of much less concern. However, itcauses the following adverse consequences/operating concerns:

I. Possible cavltaUonlvapourlocklng of the reheater drains pump dueto an excessive reduction of their suction head.

In most installations, a drop in the drains level would have to be substantial (ie. the tank would have to be nearly completely drained) tocause these problems.

2. If the low level is caused by the dralns dump valve stuck open,the following consequences would occur:

a) The overall thermal emclency would be reduced due to dumping hot drains to the condenser;

b) Water hammer in the drain lines would occur if the level droppedenough for steam to enter the drain piping and drive slugs of water.

Causes of reheater drains level problems

Some of the possible causes of reheater drains level problems are as follows:

1. Too hlgh a drains level can be caused by:

a) Control or mechartical problems with the level control valve resulting in too small opening of the valve;

b) Tripping of the rehealer drains pump combined with failure of thestandby pump (if any) to start up.

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APPROVAL ISSUE Course 234 - Turbine and Auxiliaries - Module Four

NOTES & REFERENCES2. Too Iowa drains level can result from:

a) Control or mechanical problems with the level control valve or thedrains dump valve resulting in excessive opening of either one;

b) A large leak in the system (eg. a pipeline break).


• The normal drains level is controlled by adjusting the drains outllow.

• When reheater drains level is abnormally high, an alarm is given and thedump valve (if any) to the condenser opens. The standby drains pump(if applicable) starts up as well. In some stations, the steam supply isautomatically isolated when the drains level reaches a very high limit

• Too Iowa reheater drains level gives an alarm. When applicable, thedrains pump trips as well.

• Too high a reheater drains level can result in the following adverse consequences, listed in the order of rising level. First, the overall thermalefficiency is reduced when hot drains are dumped to the condenser.Second, flooding of the reheater tubes results in a partial or total loss ofreheat - with all attendant consequences. Finally, flooding of the reheater steam piping can damage the piping due to water hammer orquenching. Water induction to the HP turbine can also occur.

• Too Iowa reheater drains level can cause reheater drains pump cavitationlvapourlocking. The overall thermal efficiency would be reduced ifhot drains were dumped to the condenser due to the dump valve stuckopen. In the extreme case, water hammer in the drains piping can resultif the level has dropped enough to cause steam to drive slugs of waterthrough the piping.

• Typical causes of improper reheater drains level are controVmechanicalproblems with the drains LCV or the dump valve. A large leak in the reheat system and failure of the reheater drains pump are other causes.

You can now do assignment questions 1..9.

LOSS OF REHEAT

Adverse consequences/operating concerns

Any serious operational problem (eg. loss of drains level control or a largesteam leak) may require some or all of the reheater tube bundles W be isolated. This (orced action causes the following major adverse consequencesand operating concerns:

¢'> Pages 21-23

¢'> Obj. 4.3 a)

Page 9

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Course 234 - Turbine and Auxiliaries- Module Four

NOTES & REFERENCES1. Increased thermal stresses in:

APPROVAL ISSUE

... In the reactor leading mode,BPe raises the setpoint tothe turbine governing system. The GYs open more.If they can accommodate theextra flow, the MW outputincreases. But if they cannot, the small SRVs open,forcing a manual reductionin reactor power to conservemakeup water. This action,combined with decreased LPturbine effICiency, may reduce the generator MW output somewhat.

In the reactor lagging mode,BPC lowers the setpoint tothe reactor regulating system.. Reduced reactor power,combined with decreased LPturbine efficiency, leads tosome loss of the generatorMW oUlput. But because inthis mode of unit operationthe output is maintained automatically, the GVs openmore. This action tends toreduce boiler pressure, andBPC responds by adjustingreactor power. If the GVopening can be increasedenough, the normal oulputis restofC!l. Otherwise, theoulput is somewhat reduceddue to the limited flow capacity of the fully openGVs.

Page 10

a) Tlte LP turbine casing.

If the loss of reheat is rapid, the LP turbine inlet is subjected to fastcooling. and thus increased thermal stresses. The stresses can beparticularly high if the loss of reheat is asymmelrical with respect tothe turbine, ego when only ooe reheater is experiencing tube flooding. In such a case, an excessive side-to-side dT is produced at theLP turbine inleL The resultant thenna! deformation of the turbinecasing can cause high turbine vibration and possible blade and!or seal rubbing.

b) The affected reheater(s).

A rapid loss of the reheating steam subjects the reheater tubes to fastcooling by the turbine steam. The resultant thermal stresses, if repeated a sufficient number of times. can eventually cause a reheatertube or gasket failure.

2. Increased steam wetuess In the LP turbine.

Recall from module 234-1 that this results in accelerated erosion andcorrosion, increased overspeed potential and reduced LP turbine efficiency. Because of these consequences, and particularly due to drastically increased erosion rate in the latter stages of the turbine, prolongedoperation with no reheat should he avoided.

As for the reduced LP turbine efficiency, it decreases the additional MWoutput produced by the increased turbine steam flow. The latter happens because less boiler steam (or none. in the extreme case of a totalloss of reheat) is used for reheating. Note that the MW gain is conditional upon maintaining reactor power, and the avs heing able to accommodate the increased turbine steam flow (see also point 3 helow formore information),

3. DIsturbed boOer pressure and level control due to loss of reheatersteam and drains.

At full power, the reheaters take about 5-7% of the total boiler steamoutput, depending on the type of the reheat system. Loss of this flowdisturbs a thermal equilibrium in the boilers, causing their pressure torise. BPC counteracts it as descrihed in the preceding module and summarized in the sidenote*, Note that this action may result in someloss of the generator MW output.

In turn, loss of the reheater drains tends to lower the boiler level. If thelevel control is ineffective for whatever reason. a low boiler level- withits attendant adverse consequences as descrihed in module 234-2 - willresulL

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APPROVAL ISS1JE Course 234 - Turbine and Auxiliaries - Module Four

NOTES & REFERENCES

Mitigating actions

Some of the above consequences and concerns can be minimized if the operator takes proper actions. First, thermal stresses in the LP turbine can bekept at a safe level if the side-to-side aT at the turbine inlet is within its limit. To ensore this, loss of reheat on one side of the turbine must beaccompanied by vaIvlng out a proper number of reheater tube bundIes on the other side of the turbine.

Second, a snbstuntIaI loss of reheat should be followed by a proper reducllon In turbine load as specified in the appropriate opetating manual. Operation at full load can be continued only when absolutely necessary (to supply the grid load at the time when other sources of generation areunavailable), and then only over a limited period of time (usually, up to 12hours).

When the torbine is unloaded, following a substantialloas of reheat, the excessive steam wetness In the LP turbine Is reduced back to the acceptable level. This effect is shown in Fig. 4.2, where sample values ofsteam preasore, temperatore and wetneas are plotted, and torbine unloadingis aasorned to reduce load to about 60% W*.

2SO'C

10% StMm Wetnne

15% Steam WIt\neIIs

SpIc.1c EnII'OPY

Fig. 4.2. Effects of 1088 at reheat on • simplified turbine ....m expansion line:Operation at full poNef wtth fuY reheat available;

- - - - Operation at full power with reheat capacity SUbstantially reduced;- •- Operatlon at partial load with the same reduction In the reheat capacity.

<=> Obj. 4.3 b)

• Recall that turbine interstage pressures cbangeproportionally to turbineload. In this example,480 kPa I 800 kPa '" 0.6'" 60% FP.

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Course 234 - Turbine and Auxiliaries- Module Four

NOTES & REFERENCES

APPRUVAL 1:>:>U.I£

Notice in Fig. 4.2 that turbine unloading is effective in reducing the LP turbine exhaust steam wetness for two reasons:

1. Reduced LP turbine inlet pressure (and hence, the pressure ratio) causesthe turbine to extract less heat from the steam;

2. In the case of partial loss of reheat. the remaining reheat capacity can superheat the reduced flow of turbine steam to a higher temperature. Naturally, this effeCt does not apply to the total loss of reheat

REHEATER TUBE LEAK

Obj. 4.4 a) ~

• Recall from the 225 coursethat during throttling enthalpy is assumed to stayconstant. You can easilyverify the temperaturesquoted below in the text ifyou plot a line showingthis process in a Mollierdiagram. By the way, youare not required to memorize these temperatures they are quoted only tohelp you understand theproblem.

Page 12

Adverse consequences and operating concerns

During turbine operation, the reheating steam pressure is higher than the tur·bine steam pressure. In fact. during startup and at low loads. the pressuredifference can approach 4-S MFa Hence, a reheater internal leak (through afaulty tube or gasket) causes the reheating steam to leak into the reheatershell where it mixes with the turbIne steam.

The leak. if large enough, can raise the HP turbine exbaust pressureand iower the LP turbine Inlet steam temperature. The latter effect perhaps a bit surprising - stems from the throttling process that the leakingsteam undergoes·. During this process. steam temperature drops substantially: from about 2S0-25S'C (assuming that the leaking reheater is suppliedwith boiler steam) to about 170-180'C, depending on the station. Note thatthe latter temperature is well helow the normal LP turbine inlet steam temperature (22S-240'C at full power, dependi,ng on the station). This is whythe leak tends to lower this temperat)lre. Of course, the leak rate must belarge enough for this temperature reduction to be measurable.

This brings us to adverse consequences/operating concerns causedby a large Internal leak:

1. Reduced steam temperature on one side of the LP turbine (it isassumed here that a large tube leak appears only in one tube bundle at atime) may result In an excessive side-tn-slde ~T at the turbine inlet.

You will recall that the ~Tlimit would force valving out a similar tubebundle on the other side of the turbine in order to prevent damage due toexcessive deformations of the turbine casing.

2. Increased moisture content of the LP turbine steam due to reduced Inlet temperature.

Accelerated erosion and corrosion, reduced overall thennal efficiency.and increased overspeed potential result from it

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NOTES & REFERENCES3. Increased HP turbine exhaust pressure.

In the extreme case (which would require a very large leak), the following operational concerns could arise:

a) Overloading of the LP turbine stages due to an excessive steamflow.

Recall from module 234-1 that turbine load is essentially proportionalto the turbine inlet pressure. Hence, when a large reheater internalleak results in the LP turbine inlet pressure exceeding its full powerlevel, the load on the LP turbine stages exceeds its full power value.This can eventually lead to overstressing of some of the turbinecomponents.

b) Reduced overall thermal efficiency and loss of generator output dueto the following automatic protective actions which intend toprevent overpressure of the moisture separators. reheaters and interconnecting pIping:

Opening of the release valves· (if there are any);

Tripping the turbine - in early CANDU stations, this featuremay be absent;

Operation of the reheater safety valves or bursting discs (depending on the station) as the last line of defence.

c) Overpressure of the moiotore separators, reheaters andthelnlerconnecting pipelines if the protective actions listed inpoint b) above have failed.

4. Turbine speed control problems and possible overspeed If alarge rehealer lube leak occurred during while unsynchronlzed.

Operator actions

While a small tube leak creates no acute problem, a large leak requires thefollowing operator actions to prevent further equipment damage:

I. Identification and Isolation of the leaking lube bundle.

Note that in some stations equipped with a two-stage reheat system, isolation of the frrst stage bundle may force valving out the second stage.This action may be necessary to prevent excessive thennal stresses inthe second stage of the reheater.

2. Isolation of another tube bundle(s) on the other side of the turbine.

This action may be necessary to prevent an excessive side-to-side AT atthe LP turbine inlel

3. If necessary, turbine unloading as described on pages 11-12.

• In some stations, thisaction is not performed.

<=> Obj. 4.4 b)

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Course 234 - Tmbine and Auxiliaries- Module Four APPROVAL ISSUE

NOTES & REFERENCES

Obj. 4.4 c) <=>

Obj. 4.5 <=>

Page 14

Detection of a reheater internal leak

Recall that a large leak in one of the reheaters is indicated by reduced LPturbine inlet temperature and increased HP turbine exhaust pressure. What about detecting a leak which is too small to cause any measurabie change in these pllI1lllleters?

A classic method used for this purpose relies on isolating the suspectedtube bundle and monitoring the rate at which the pressure inside decays. Anexcessive rate indicates a leak. However, the leak mayor may not be located in the tube bundle; for example. an isolating valve may be leaking. Thisuncertainty about the leak location is the main drawback of this method.This testing can be performed both on load as well as during a shutdown; inthe latter case, instrument air - and not reheating steam - is used to pressurize the tube bundle.

In some stations. another method is used where dedicated reheater tubeleak detecting instmmentation measures the reheating steam flow rate to individual tube bundles. The measured flow is compared with its expectedvalue for a given turbine load. A sufficiently large difference between thetwo implies a tube leak. This method is believed to be capable of detecting asingie tube leak .

WATER HAMMER PREVENTION

To prevent water hammer in the reheat system, the following major generaloperating practices are necessary:

I. Proper drainage, particularly when prewarmlng the system during startup and at light loads.

Recall from module 234-3 that the above operating conditions cause increased rate of steam condensation in the piping. To prevent an excessive accumulation of condensate, that could lead to the fonnation of water slugs. the drain valves must be open during these operatingconditions. At medium and high turbine loads. drainage is provided bysteam traps.

2. After baving Isolated the faulty reheater(s) upon a very highdrains level, the reheat steam piping must he properly drainedprior to steam admission.

This precaution is taken because some drains might enter the steam piping during the drains level excursion. To remove this water, drainvalves in the piping must be open for a sufficiently long period of time.

You will recall that prevention of a very low drains level (such that steamcould enter the drains dump pipmg to the condenser and drive slugs of water) is also important to prevent water hammer in the reheat system.

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• A loss of reheat increases thermal stresses in the LP turbine and the affected reheater(s), raises the steam wetness in the LP turbine and disturbs boiler pressure and level control.

• To minimize thermal stresses in the LP turbine. the operator must ensurethat the loss of reheat is symmetrical with respect to the turbine such thatthe LP turbine inlet side-tn-side AT is within its limit

• A substantial loss of reheat should be followed bY an appropriate turbineunloading to avoid prolonged operation with excessive wetness of theLP turbine steam.

• A large internal leak in a reheater can result in an excessive side·to-sideAT at the turbine inlet, increased moisture content of the LP turbinesteam, and increased HP turbine exhaust pressure.

• Major indications of a large leak include reduced LP turbine inlet steamtemperature and increased HP turbine exhaust pressure.

• To prevent equipment damage in the event of a large interoaI.leak in a reheater, the leaking bundle, as well as another tube bundle on the otherside of the turbine, must be isolated. The turbine may have to be unloaded, depending on the extent of the loss of reheat

• Detection of a small internal leak requires isolating the suspected bundleand monitoring the rate of pressure decay. In the alternate method, noisolation is performed, and the actual reheating steam flow rate is measured and compared with the expected value for a given turbine load.

• To prevent.water hammer, the reheat steam piping must be properlydrained during system warming, at light loads, and after any reheaterhas been isolated on a very high drains level.

You can now do assignment questions 1()"13.

THE GLAND STEAM SEALING SYSTEMMost of the information about this system is provided in the previous turbine courses. The only topic that is left over is the use of attemperatingsprays. Fig. 4.3 on the next page shows the part of the system where thesprays are installed, whereas the whole system is shown in a pullout diagram at the module end (Fig. 4.6 on page 29).

NOTES & REFERENCES

~ Pages 23·25

~Obj. 4.6

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Steam and ai' from thegland exhaust manifold

ATTEMPEAATING SPRAYS **-------1", ..../........... .~_ From CEP

discharge

t"i:l atmosphere

GLANO* IEXHAUST~ ~__~

FANS \..J !10 LP feedhealers ....._~-J.- .,,/''''-

GLAND EXHAUST *CONDENSER L. DralnslD r'nain condenser

NOTES & REFERENCES

"Not installed in someunits.

... Other names of this equipment, that are used insome stations, are listedon page 29 (Fig. 4.6).

Flg.4.3. The exhllult part of the gland ."m..ling system:--Steam ----- Air _.- Condensate

... In the units where no attemperating sprays are fitted, the gland exhaustcondenser has an overflowsized to handle the con·densate from a tube leak.Therefore, the gland exhaust condenser with atube leak does not have tobe valved out, and operation can be continued.

.. The adverse consequencesof sucb leakage are out·lined in module 234·1.

• Also discussed in module234-6.

Normally inoperative, the attemperating sprays must be valved in whenevertemperature of the air flowing to the gland exhaust fans reaches an alarmlevel. The sprays must also be valved In before the gland exhaustcondenser Is isolated (eg. due to tube leaks)-, while steam supply to thegland steam sealing system is continued. The sprays condense the glaildsteam leakoff, thereby compensating for the loss of cooling in the gland exhaust condenser.

Failure to use the sprays in these clrcumstances would mean a totalloss of cooling of the steam leakoff from various seals. As a result, thesteam would flow through the gland exhaust fans which normally handleonly air evacuated from the seals. The following adverse consequences/operating concerns would result:

1. Possible damage to the gland exhaust fans due to overheating.

2. Release of steam from the turbine and steam valve gland sealswhich are connected to the gland exhaust condenser.

Note that the greatly increased flow rate would exceed the capacity ofthe fans, causing their suction pressure to rise. As a result. the pressurein the gland exhaust manifold would rise enough to cause steam outleakage from the glaild seals connected to this manifold-. Recall that themanifold pressure must be maintained a few kPa below abnospheric inorder for the gland seals to function properly.

3. Possible steam hammer in the condensate system.

The flow of hot steam through the gland exhaust condenser, combinedwith a loss of condensate flow. would cause the condensate inside thetubes to boil. The relief valve installed on the condensate line shouldopen, preventing overpressure of the tubes. But the steam pocketsformed inside the tubes would implode when the condensate flow is restored. The resultant collisions of water columns previously separatedby the pockets would produce steam hammer-.

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• The attemperating sprays in the gland steam sealing system must bevalved in to compensate for loss of normal cooling in the gland exhaustcondenser.

• Failure to do this would result in steam flowing through the gland exhaust fans which normally handle air only. The fans could suffer damage due to overheating. In addition, their suction pressure would risebecause the actual flow would greatly exceed their flow capacity. As aresult, steam egress from the turbine and steam valve gland seals wouldoccur. Finally, water hammer in the condensate system could occur dueto implosion of the steam pockets created (due to beat input from thegland leakoff steam) inside the gland exhaust condenser tubes.

THE LP TURBINE EXHAUST COOLING SYSTEM

In the previous turbine courses, the purpose, major components and operation of the LP turbine exhaust cooling system were described. In this module, you willieam about:

- Possible LP turbine damage due to overheating of its exhaust if the system failed to provide adequate cooling;

- Operating parameters that should be monitored to prevent such damage;- Operator actions that should be taken wben the turbine exhaust beating

is excessive;- Operating concern caused by excessive use of the LP turbine exhaust

hood cooling sprays.

For easy reference. the system is shown in a pullout diagram (Fig. 4.7) onpage 29.

LP turbine exhaust overbeating

You will recall that prolonged motoring" or operation at very light load promotes overheating of the LP turbine exhaust During these operating conditions, large windage losses occur in the turbioe last stage(s). and the smallstearn flow cannot provide adequate cooling. As a result, the moving bladesand (to a smaller extent) the shaft, diaphragms, casing and exhaust coverbecome hotter. The ttansient heating produces increased thermal sttesses.It also results in reduced radial and axial ciearances in the turbine due to therotating and statiooary components expanding at different rates.

If proper condenser vacuum is maintained and the LP turbine exhaust cooling system operates satisfactorily, LP turbine exhaust temperature - whileelevated as.compared with normal operation - stays at a safe level. Otherwise, overheating of the LP turbine exhaust may develop, causiog the following adverse consequences/operating concerns:

NOTES & REFERENCES

~ Db}. 4.7 a)

• Motoring is discussed indetail in module 234·13.

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NOTES & REFERENCES

• Turbine generator damage due to excessive vi·bration is described inmodule 234-14.

Obj. 4.7 b) ~

Page 18

I. If no protective action were taken. the turbine could suffer damagedue to:

- Rubbing of turbine internals. ego seals;

- Increased rotor vibration· caused by rubbing and/or increasedbearing misalignment due to the thermal distortion of the LP turbinecasing and exhaust cover;

- Permanent distortion (in the extreme case, cracking) nf turbineparts, ego the exhaust cover.

2. Forced turbine trip for turbine protection. As necessary as this actionis. it would cause loss of production for which poor condenser vacuumand/or malfunction oflbe LPturbine exbaustcooling system may be responsible.

Monitored parameters

To prevent turbine damage, the following paramelers must be carefullymonitored:

I. LP turbine exhaust temperatures.

Several temperature sensors are installed in the six LP turbine exhausts.The indicated temperatures should be checked against the operating limits (as specified in the appropriate operating manual) to make sure theturbine trip limit bas not been exceeded and that the cooling waler spraysin the LP turbine exhaust hood operate properly.

2. LP turbine bearing vibrations.

They are monitored to ensure that hearing of the LP turbine exhaust hasnot resulted in excessive bearing misalignment and/or internal rubbing inthe turbine.

3. LP turbine axial differential expansions.

These parameters (typically, one for each LP turbine) are monitored tomake sure that the axial clearances in the turbine have not been reducedexcessively.

4. Condenser vacuum.

Efforts should be made to keep condenser vacuum as high as possibleduring the turbine operating states when LP turbine exhaust overheatingis a potential problem. Note that high condenser vacuum results in alow density of the LP turbine exhaust steam, thereby reducing the windage losses in the turbine last stage(s).

In addition to these parameters, a proper supply of condensate to theLP turbine exhaust cooling sprays must be ensured by checking the

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status of the isolating valves (should be open) and the pressure drop acrossthe strainer (should not be excessively high). During motoring, similarchecks should be made to ensure proper supply of motoring coolingsteam and Its attemperatlng sprays (if installed).

Operator actions

If the LP turbine exhaust overheating has become excessive (as indicated by some of the monitored parameters), prevention of turbine damagerequires the opemtor to take either of the fonowing actions:

I. Load the turbine.

This action reduces the windage losses in the turbine last sfage(s) andimproves cooling of the turbine internals by the increased Steam flow.To minimize thermal stresses caused by the cooling, the initial loadingshould be performed slowly.

2. Trip the turbine (if loading is impossibie. ego due to reactor problems).

Excessive use of the LP turbine exhaust cooling sprays

The major operating concern caused by excessive use of the LP turbine exhaust cooling sprays is that it can result in erosion of the last stageblades. Recall that at nollight loads - not to mention motoring - intensivesteam recirculation occurs in the exhaust hood and the last stage biading.This was already described in module 234·1, but for your convenience isalso shown below in Fig. 4.4.

FIXEDBLADES

MOVINGBLADES

ROTOR

Fig. 4.4. Steem reclrculetlon In the la.t stage at nollightturbina load.

NOTES & REFERENCES

~ Obj. 4.7 c)

~ Obj. 4.7 d)

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NOTES & REFERENCES

Pag•• 25·27 ~

Page 20

Note in Fig. 4.4 that the recirculating steam enters the moving blades at theirtrailing edge close to the blade root The stearn carries the sprayed waterdroplets that have not been fuHy evaporated. Collisions between thesedroplets ood the trailing edge of the blades eventually cause blade erosion.To minimize this erosion. it is important not to use the sprays when they arenot necessary for turbine protection from overheating.


• If no action is taken. overheating of the LP turbine exhaust can result insevere damage to the torbine.

• LP turbine exhaust temperatures, bearing vibrations, axial differentialexpaosions ood condenser vacuum should be carefully monitored whlieoperating in acondition that promotes overheating of the LP turbine exhaust

• If ooy safe limit has been reached. turbine load sbouldbe slowly increased. When loading is impossible. the turbine should be tripped inorder to prevent damage.

• Excessive use of the LP turbine exhaust cooling sprays can result in erosion of the traliing edge of the moving blades in the last stage.

You coo now do assignment questions 14-17.

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APPROVAL ISSUE

ASSIGNMENT

Course 234 - Turbine and Auxiliaries - Module Four

NOTES & REFERENCES

I. a) In a typical live steam reheat system and the second stage of atwo-stage reheat system. the reheating stearn flow is controlledas follows:

i) At high turbine loads:

Ii) At medium turbine loads:

iii) At low turbine loads:

b) In the fIrSt stage of a two-stage reheat system, the reheating steam

flow is over the whole range of turbine

bine load.

2. a) Reheating must be limited during turbine startup and operation at

light loads in order to _

b) Valving out the reheat during turbine startup and operation at lightloads (does I does not) result in excessive steam webless in theLP turbine.

3. Reheaters should be valved inlout slowly in order tn:

a)

b)

c)

4. An excessive side-tn-side ~T at the LP turbine inlet can result in

5. The nonnal reheater dntins level is controlled by _

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NOTES & REFERENCES6. The following actions (other than the nonnal control) are canied out in

response to:

a) Too high a reheater drains level:

i)

ti)

iii)

iv)

b) Too Iowa reheater drains level:

i)

ti)

7. a) Even when the reheater tubes are still not flooded, too high adrains level reduces the overall thennal efficiency due to

b) Flooding of the reheater tubes results in _

c) Flooding of the reheat stearn piping could cause:

i)

ti)

iii)

8. Too Iowa .reheater drains level can cause the following adverse conse~

quencesloperating concerns:

a)

b)

9. a) Too high a reheater drains level can be caused by:

i)

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APPROVAL ISSUE

il)

Course 234 - Turbine and Auxiliaries - ModulI> Four

NOTES & REFERENCES

b) Too Iowa reheater drains level can be caused by:

i)

il)

10. a) Valving out some or all of the rebeatertube bundles while operating at a high load can cause the following adverse consequences!operating concerns:

i)

il)

iii)

b) Reducing turbine load can alleviate excessive wetness of the LPturbine steam due to the following two effects:

i)

il)

11. a) A rebeater internal leak causes the (reheating I turbine) steam toleak into the reheater (shell I tubes).

b) A large leak can (decrease I increase) the temperature of the superheated steam supplied to the LP turbines.

c) A reheater leak detection instrumentation enables detection of a

small leak by _

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NOTES & REFERENCESd) A classic method of leak detection relies on _

12. a) A large reheater internal leak is indicated by:

i)

il)

b) The adverse consequences/operating concerns caused by a largereheater intemalleak are:

i)

il)

iii)

iv)

c) When a large reheater internal leak results in increased HP turbine exhaust pressure, the following operating concerns arise:

i)

il)

iii)

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NOTES & REFERENCESd) A large rehealer intemalleak requires the following operator ac

tions to prevent further equipment damage:

i)

til

iii)

13. Water hammer in the reheat system is prevented by the following general operating practices:

a)

b)

14. a) Attemperating sprays in the gland sealing steam system must be

valved in when _

b) Fallure to do this would result in the following adverse consequences/operating concerns:

i)

til

iii)

15. a) Overhealing of the LP turbine exhaust is promoted during the following turbine operating states:

i)

til

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NOTES & RI;FERENCESb) Excessive heating of the turbine during these operating states

causes the following adverse consequences/operating concerns:

i)

il)

16. a) The fonowing parameters should be carefolly monitored whileoperating in a state that promotes overheating of the LP turbineexhaust:

i) Parameter: _

Reason Why it is monitored: _

il) Parameter. _


iii) Parameter: _


iv) Parameter: _


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APPROVAL ISSUE Course 234 - Turbine and Auxiliaries - Module Fow

b) In addition to the above, the following checks should also be

made: _

c) If any of the monitored parameters listed in point a) has reachedits safe limi~ the operator can take either of the following actions:

i)

ti)

17. The major operating concern caused by excessive use of the LP turbine

exhaust cooling sprays is _

Before you move on to the next module, review the objectlves and makesure that you can meet their requirements.

Prepared by: J. Jung, ENTD

Revised by: 1. Jung, ENID

Revision date: May, 1994

NOTES & REFERENCES

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APPROVAL ISSUE Course 234 - Turbin I Auxiliaries - Module Four

A) UVE STEAM REHEAT SYSTEM

Steam pressure correspondill\l *to turbine load

REHEATISOLATING

VALVE

Live st611,~--1t>lq.-...., ,k1....-_REHEAT *

CONTROLVALVE REHEATER

Frommoisture -separato~

_ ToLP- turbines

Drains fromother rehealer

From boilerfoodWaler pump

discharge

AEHEATEA DRAINSTANK

~=--~-;;p ~.,' =

.0' =." :.' .

OR~T~~tT~~(S) ,.f;_._._._..~~:?~F~..JL..,!f:"";.;,:;;;;;;:: 10 boilersl ....f REHEATER DRAINSLEVEL CONTROL VALVE(S)

To condenser

REHEATER DRAINS *DUMP VALVE

B) TWO-STAGE REHEAT SYSTEM

p ..j. ISZC()fld -'''II''

AEHE.od REHEATV

ISOLATli'll3 ",m"" REHEATER~" .P-" IA

"REHEAT Firsts!..;

STOPCHECI( t~'"II

From th. moistures8plvator in Ina

( AEHE!J"ER FIRST ( " ( EHEIUER SECON : \..same \/essel STAGE OFWNS"t'NK STAGE DRAINS TANK,;:..~... - - @ .. - - .

'....~"i".REHE.oJER -

o~" l..............o- FIRSTO~"DUMP ~~,

~""""~"'LEVEL DUMP

"" DAAlNS,~ VALVE PUMP

~'"

To condenser 10 HP feedheaters ,•••••.•.•-Q- REHE."JERSECONO sto.GE9- LEVEL CONTROl.

VALVE

To condense,

Steam pr_urecorrespondinglolu,birwload

HP turbineextraclio

steam

Live sleam

Tooolers

Fig. 4.5. Reheatsysterns in CANDU stations:______ Turbine process steam, Reheater steam and drains,_._.- Attemperating water, Control signals.

* Not in all stations.

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APPROVAL ISSUE Course 234 - Turbin Auxiliaries - Module Four

.. ofl'OfP/'lO'"

'- FromollomOltOOllf'l>Ot 1)I ol ••••''90111am

i PF\V

STJV,INEATURBINES~"IA

VAIYES

LP TURBINES

:...-_.- ~"" 10 mo,n condon..,

t" Iln'IOCpIItrll .lrTEMPEPATING SPRAYS 1)GLANDEXIi,o.USTFANS2)h At

\.J ---,_ "'", ./'......... P _ _ F"""CEP

llLPf.._..... ~,,, ...... ' ~ di~_'9'

GLAND EXHAUST3)CONDENSER

Flg.4,6. SImplified gl_nd steam s.allng system:Steam ------ Air --- Condensate ......•...• Control signalNotes:1) Not in all stalkms.2) AlsO /al<:>wn undsr othernal7l68 "",h as vapour 9Xlraction lans,

!uItJ.'MQJRtId 8J8wn VlIf'OiH ~r,idots. (ff gI.Mdsleam ax/Wtst foWs.3) A few otller n!ll!ll!l& III" <1180 in U!JJ9, £""mp/lls: the gland sream

OOndtlflS6f or rll8 srum paoking UhBUfI/tIf.

CEP~

OJdlachatQll

toEXHAUST HOOD SPI:l.AYSCONTROL VAlVE

'rom +.eheaters To .m

1 ."""".. --- --_..~ LP tUrb

OSPPtAY.

RING

I, , ~

XHAUST "'0'" LPTURBINE1'. ...'1'$ I", "

MOTOAING COOLING STEAM •CEsuPlOAHEIITING SPRI>oYS

ISOlATING VALVE

STRAINER

MOTORING STEAMISOLATINQ VALVE

;-~-_··i}-----,: PRESSURE" L_I f'.EOUClOO. II OR\F~E I

~1;1 ...._.~ ..L~......• t~~b7~ tESV GV To olher

L?turolnlljl

- Cooling BPraya waler E

- -- - Momnngcoollngste&m (_ nola bEllowl 51'

............ Turblna ataam

* Notina!!stmW/18.

Fig. 4.1. SImplified lP turbine exhaust cooling sy81em:CEP '" Condensate extraction pump; ESV '" Emergency stop valve.GV = Governorvll.lve.N0t9:In soms sfBtlons. motoring cooling steam;s not used at all or isSIJPP/isd to (fie HP turbine, bypassing m@cfos/JdGItS. In the lattercase. the steam follows the normal fIr:Nv path tllrough tfl9 tur/)ifle set.

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HOME ABOUT US PRODUCTS CO-GENERATION PHOTOGALLERY

MBT-6 Multi Stage Back Pressure

Steam Turbine with Bleed

• Upto 5 Stages for High Efficiency.

• Bleed Provision for different back pressure outlets.

• Programmable Control Panel for Synchronised and Stand alone

• Woodward Governor for accurate control.

• Robust and Sturdy turbine for continuous operation.

Constructional Features MBT - 6 Turbines

TURBINE CASING

The turbine casing of this MULTI-STAGE turbine is split on horizontal centre-line to facilitate easy inspection and assembly dur

Proper tightness of the mating surfaces is ensured through high-accuracy finish and using metal-to-metal contact without any sealin

bottom half high pressure end of casing is secured and supported by a kinematic support to allow controlled expansion between c

pedestal. Radial pins fitted between casing flange and bearing pedestal, permit radial expansion of casing maintaining its conc

pedestal which in turns ensures correct alignment during operation. A gap between the casing and the bearing pedestal allows for

air thus minimises the transfer of heat between from hot casing to the bearing pedestal.

IB Turbo Pvt. Ltd. http://www.ibturbo.com/multistage_back_pressure_steam_turbine.html

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TURBINE ROTOR AND BLADES

The rotor is a solid alloy steel forging and designed to be of stiff; i.e. the first critical speed is well above any operating speed or

soundness of the rotor is ensured using latest Ultrasonic testing techniques.

The blades are made of alloy steel. Each blade is machined in one piece with its spacer root and is fixed in the grooves on periph

The outer ends of blades are connected by short lengths of shrouds riveted on.

Each rotor is dynamically balanced to high degree of accuracy. This ensures the trouble free and smooth operation of rotor

bearings.

COMBINED STOP AND EMERGENCY VALVE, CONTROL VALVE

The stop-and-emergency valve is spring loaded. The whole steam flow to the turbine passes first through the single beat co

emergency valve, and then through the double seated control valve to the first stage nozzles of the turbine. The stop and em

mounted horizontally for ease of operation. The valve held fully open by the latch. Under the emergency conditions determined b

trip gear and solenoid valve, the trip latch is operated and the Valve is closed by the action of valve spring. The valve when trippe

the hand wheel clockwise moves the guide nut, compressing the valve spring and keeping the valve on its seat. As the guide nut r

its travel, the trip catch is automatically engaged and is locked. Turning the hand wheel in ANTI-CLOCK direction, valve may then b

The Combined stop and Emergency Valve incorporates a balanced main valve and a pilot valve to enable it to be freely opened or

full steam pressure, except when the valve is close, steam may pass through the holes in the main valve to equalize the pressure

the valve. However, when the Combined Stop and Emergency valve is shut, the pilot valve having a small sliding movement re

valve closes these holes.

The control valve is mounted in the steam chest, which is rigidly bolted to the bottom half of the turbine cylinder. Depending o

turbine, the control valve is opened by the linkage from the speed governor.

A steam strainer is provided on the inlet side of the valve to protect the turbine from the ingress of foreign matter.

BEARINGS

The rotor is supported at both ends with special designed white-metal lined journal bearings called OFF SET HALF type. The bearing

side is housed in the pedestal attached with the turbine cylinder with a special attachment.

A tilting pad type thrust bearing also contained in this bearing pedestal, which locates the rotor in its correct position and carries ax

during operation. The exhaust end bearing is fitted in a housing formed at the exhaust end of the turbine cylinder.

NOZZLES AND DIAPHRAGMS

The nozzle blades are secured to the steam belt formed at the steam end of the turbine cylinder and may be divided in Maximu

depending on the individual contract requirement.

Inter-stage diaphragms with nozzles are mounted in grooves in the casing. These diaphragms are supported on radial copper cru

are fitted to give the correct vertical location of the diaphragm. Transverse location of the diaphragm is maintained in a similar m

steel side pins in the upstream side of the diaphragm.

The top half diaphragms are further secured with help of Check screws at the horizontal face.

SPEED REDUCTION GEAR

Speed-reducing gear is generally mounted on the turbine base-plate. The high-speed gears are precision-machined, hardened and

long operating-life. Lubricating oil from the lubricating oil system is used for cooling of the gears. The main oil-pump is mounted o

the low-speed gear.

GLAND SEALS

Metallic LABYRINTH type glands seal the passage of the rotor shaft through the turbine cylinder. These are formed by group of k

loaded NICKEL LEADED BRONZE rings and mounted in segments in annular grooves in the gland housings and also inte

baffles are able to move radially on contact with the shaft to provide protection against rubs and bending of the rotor. These

clearances with the rotor shaft. These form series of multiple throttling, which reduces the pressure, and minimize the leakage o

shaft.

Spaces are arranged between the groups of baffle rings at the steam end and exhaust end of the turbine. The high-pressure end

to the exhaust branch. The remaining two H.P. leak offs and the two L. P. leak offs are led to terminal flanges, which also receive t

from the valve spindles of emergency and control valve.


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OIL BAFFLES

The turbine bearings adjacent to the steam glands are provided with oil baffles. In addition to preventing the escaping of lubric

bearing housing these baffles, in association with the steam ejector, also minimize the chances of any steam or moisture-laden

bearing housing thus avoiding contamination of oil. In this way, the greatest difficulty of turbine maintenance is avoided.

SPEED GOVERNOR

The speed governor is Hydro Mechanical type as standard scope of supply. This governor takes its drive from the turbine rotor sha

of worm and worm wheel. The link rod attaches the output of the governor to the steam control valve. The governor has a provisio

adjustment and motorized gear to operate from a remote position.

EMERGENCY OVERSPEED TRIP GEAR.

The eccentric ring is mounted on the rotor shaft within the steam end pedestal and is held in concentricity with the shaft axis by a

turbine speed reaches approximately 10% above the normal, the centrifugal unbalance overcome the spring force and the ring flie

trip lever, which de-latch the trip rod. The emergency valve is then closed by its spring.

The emergency trip gear may also be operated manually or by the solenoid trip valve, which is associated with the protection syste

LUBRICATING OIL SYSTEM

Lubricating main oil for the turbo set is provided from the geared type oil pump driven from the free end of bull gear shaft of the r

through a flexible coupling. An auxiliary A.C. motor driven geared oil pump is also provided for flooding the bearings before

maintaining an adequate supply of oil while running up and shutting down. The operation of A.C. motor driven pump is made autom

a pressure switch in the lubricating oil system. Non-return valves on the delivery lines of auxiliary pump and main oil pump preven

of auxiliary pump by the discharge of the main oil pump.

The lubricating oil is water cooled through the oil cooler. A fine filter is provided in the oil system to avoid any foreign mater

bearings.

LOW OIL PRESSURE TRIP

Its purpose is to protect the turbine from damage, which might be caused by low oil pressure.

The trip consists of a hydraulic piston and cylinder. In running conditions the lube oil pressure held the valve in position and if oil

value 0.5-0.7 kg/cm2 this pressure is incapable of holding the valve against the spring load, thus activating the tripping system.

BASEPLATE

This is of fabricated construction and has a built-in oil reservoir. An oil level indicator is fitted. The base-plate is secured with

special bolts.

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Patents

CLAIMS (7)

I claim:

1. A steam turbine gland seal control system for a steam turbine driving an

electrical generator which supplies power to a load after main circuit breakers

are closed, and in which the gland is self-sealing by steam in the turbine after

said closing, comprising:

(A) means for measuring turbine speed for providing an output signal

indicative of turbine speed;

(B) means for measuring turbine load for providing an output signal indicative

of load, when said circuit breakers are closed;

(C) a steam line in steam communication with said gland seal;

(D) a gland seal steam supply controllably connected to said steam line;

(E) means for measuring the temperature of steam within said steam line for

providing a temperature output signal;

(F) a control circuit responsive to (a) said temperature output signal and (b)

one of said speed or load output signals, depending upon whether said

turbine is on-line, to provide an output control signal which continuously

varies as said speed or load output signals vary; and

(G) heating means responsive to said output control signal to modify the

temperature of steam in said steam line.

2. Apparatus according to claim 1 wherein said heating means includes:

(A) a heater in heat transfer relationship with said steam line and

Steam turbine gland seal control systemUS 4541247 A

ABSTRACT

A high pressure steam turbine having a sealing gland where the turbine rotor

penetrates the casing of the turbine. Under certain conditions the gland is sealed

by an auxiliary steam supply, and under other conditions the gland is self sealed

by turbine inlet steam. A control system is provided to modify the temperature of

the auxiliary steam to be more compatible with the self sealing steam, so as to

eliminate thermal shock to the turbine rotor.

DESCRIPTION

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention in general relates to steam turbines, and particularly to a system

for maintaining proper temperature in the gland sealing system of the turbine.

2. Description of the Prior Art

A steam turbine ordinarily has a shaft, or rotor, resting in bearings and enclosed

in one or more casings, referred to as cylinders. At the point where the rotor

penetrates the outer cylinders some means is required in order to prevent

leakage of air into, or steam from, the cylinders. Members known as glands

having labyrinth-type seal rings in conjunction with a gland sealing steam system

are provided to perform this function.

During startup or at relatively low load conditions, sealing steam for the glands is

provided by a steam supply such as an auxiliary boiler designed for this purpose.

Once the turbine is running at higher load levels, the steam for sealing the gland

is provided from within the turbine itself such as by exhaust steam, during which

condition the system is self-sealing.

Some turbines are designed such that the turbine inlet steam is utilized to

self-seal a gland, in which case the steam temperature for sealing is much higher

than that provided by an auxiliary system. If the turbine is suddenly tripped, or if

the load drops below a predetermined level, sealing switches from self-seal back

to the auxiliary system at the much lower temperature. This subjects the rotor to

an objectionable thermal shock due to the difference in temperatures between

the sealing steam, and thus reduces the life of the rotor. Conversely, during

Find prior art Discuss this patent

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Patent US4541247 - Steam turbine gland seal control system - Google Patents http://www.google.com/patents/US4541247

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responsive to said control signal to modify the steam temperature

in said steam line.

3. Apparatus according to claim 2 wherein:

(A) said heater is an electric heater.


(A) said turbine is a high pressure single flow turbine, and

(B) said gland is disposed at the high pressure inlet end of said

turbine.

5. Apparatus according to claim 1 which includes:

(A) valving means connecting said steam supply to said steam line

and responsive to said output control signal to allow mixing of

steam from said supply with steam in said steam line.


(A) said steam supply includes at least first and second sources;

(B) said valving means includes first and second valves for

respectively controlling steam flow from said first and second

sources; and

(C) said control circuit provides first and second output control

signal for respectively controlling said first and second valves.


(A) said turbine is a high pressure single flow turbine, and

(B) said gland is disposed at the high pressure inlet end of said

turbine.

startup conditions sealing steam will switch from the relatively low temperature

auxiliary to the relatively higher temperature inlet steam again subjecting the

rotor to the objectionable thermal shock.

The present invention provides for an improved gland sealing system which

minimizes or eliminates the objectionable thermal shock and therefore increases

rotor life.

SUMMARY OF THE INVENTION

The improved steam turbine gland seal control system of the present invention

includes a steam line in steam communication with a gland seal of the turbine

and a gland seal steam supply is controllably connected to the steam line.

Means are provided for measuring the temperature in the steam line, for

generating a temperature output signal and a control means responsive to the

temperature output signal and a signal indicative of a predetermined operating

condition of the turbine functions to modify the temperature of the steam in the

steam line.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified block diagram of a steam turbine generator system;

FIGS. 2A and 2B are sectional views diagrammatically illustrating a gland sealing

arrangement;

FIG. 3 is a block diagram of a gland sealing steam system of the prior art;

FIGS. 4 and 5 are curves illustrating improved sealing operation provided by the

present invention;

FIG. 6 is one embodiment of the present invention as applied to a high pressure

turbine; and

FIG. 7 illustrates another embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a typical steam turbine system for a power plant and includes a

steam turbine arrangement 10 having a plurality of turbines in the form of high pressure turbine 12, intermediate pressure

turbine 14 and low pressure turbine 16. The turbines are coupled to a common shaft 18 to drive an electrical generator 20

which supplies power to a load 22, after main circuit breakers 23 are closed.

A power detector 24 is operable to provide an output signal (MW) indicative of load and a speed transducer system 25 is

operable to provide an output signal (RPM) indicative of turbine speed.

Steam to drive the turbines is supplied from a boiler system 26 which includes a reheater section 28. Boiler steam is

provided to the high pressure turbine 12 through input valving 30 and steam exiting the high pressure turbine 12 is reheated

in the reheater section 28 and provided to intermediate pressure turbine 14 through valving 32. Steam exiting the

intermediate pressure turbine 14 is provided by way of crossover piping 33 to the low pressure turbine 16 from which the

steam is exhausted into a conventional condenser 34 and thereafter circulated back to the boiler system.

As will be described, the turbines include glands which must be sealed under certain operating conditions by means of gland

seal steam. The steam supply for this can be one of a number of sources one of which is the steam input to reheater 28,

such steam also being known as the cold reheat steam, and controllably supplied by valve 35. The main steam, controlled

by valve 36, may also be used as a source as well as steam from an auxiliary boiler 37 controllably supplied by valve 38.

A typical rotor gland seal is illustrated in simplified form in FIG. 2A. The gland seal arrangement includes a plurality of gland

seal rings 40 to 42 each containing a respective number of seal strips 43 to 45 which encircle the rotor 48 at the ends of the

outer cylinder 50 and which clear the rotor surface just enough to prevent contact during operation.

The atmospheric environment outside of the turbine is represented by letter A while B represents the turbine interior. The

gland sealing arrangement defines two interior chambers X and Y each encircling the rotor 48. During startup or at relatively

low loads, the pressure at B is below the atmospheric pressure at A and sealing steam is supplied to chamber X via steam

line 60. The sealing steam thus supplied to chamber X leaks past the seals into the turbine, as indicated by arrow 62, and

into chamber Y as indicated by arrow 63. Chamber Y is maintained at a pressure slightly below atmospheric pressure by a

connection to a gland condenser via line 64. Since chamber Y is at subatmospheric pressure, air leaks past the outer seal

from the atmosphere to chamber Y, as indicated by arrow 66.


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When the pressure at B exceeds the pressure of chamber X, a reversal in flow occurs across the inner seal ring, as

indicated by arrow 62' in FIG. 2B. With increasing pressure, flow increases such that the gland becomes self-sealing and

steam is discharged from chamber X back to the gland's steam system where it will be supplied to the glands of the low

pressure turbine and any excess steam will be provided to the system condenser. The pressure at B may be the pressure

at the turbine exhaust and, for a single flow high pressure turbine, may be the pressure at the high pressure inlet end. (This

would be maintained at the same pressure as the high pressure exhaust.)

A typical prior art gland steam system is illustrated in FIG. 3. High pressure turbine 12 includes on respective ends thereof

glands 70 and 71, intermediate pressure turbine 14 includes glands 72 and 73 and low pressure turbine 16 includes glands

74 and 75. The glands of all three turbines are commonly connected to a gland condenser 80 which accepts leakage steam

and air and maintains one chamber (Y) of the gland seal at subatmospheric pressure. The glands of high and intermediate

pressure turbines 12 and 14 are additionally commonly connected to a steam header 82 the connection being made to

chamber X such as by steam line 60 illustrated in FIGS. 2A and 2B.

Discharge from chamber X is utilized for sealing the glands of low pressure turbine 16, after being cooled to a compatible

operating temperature by means of a desuperheater 84. Any excess steam flows to the main condenser via a valve 86

which serves to maintain the proper pressure in the header.

The steam supply for sealing the glands may include main steam which is controllably provided to header 82 by means of a

valve 88 as well as auxiliary steam from an auxiliary boiler or cold reheat steam controllably provided to header 82 by

means of valve 90.

If the high pressure turbine 12 is of a single flow design wherein gland 70 is self-sealed by inlet steam, a problem arises in

potential thermal shock to the turbine rotor due to the significant difference in temperature between the inlet steam and the

gland supply steam. To illustrate this, reference is made to FIG. 4 wherein the dot-dash curve 100 represents turbine load,

plotted on the right vertical scale. Curve 100 represents a decreasing load from 100% to about 10 percent at time t.sub.1

and during which decrease, gland 70 is self-sealing by the inlet steam; steam temperature is represented by solid curve

102. The temperature is plotted on the leftmost vertical axis and it is seen that the temperature of gland sealing steam is in

the 800 (426.7.degree.-482.2.degree. C.) range, provided by the inlet steam. At time t.sub.1 at the 10% load figure the self

sealing condition switches to the gland steam supply system such as provided by the auxiliary boiler, which, from practical

considerations, provides steam at a maximum temperature in the range of 500 (260 function at time t.sub.1. The abrupt

change in temperature is a thermal shock to the rotor and will potentially reduce rotor life. The present invention smooths

out this thermal shock by gradually reducing sealing steam temperature from the upper range to the lower range, and is

illustrated by the dotted curve 104 which portrays a gradual reduction in temperature from time t.sub.1 to time t.sub.2.

A similar problem exists when the turbine comes on line. For example, the dot-dash curve 106 of FIG. 5 represents

increasing turbine speed up to the rated speed, plotted on the rightmost vertical scale. After having achieved rated speed

from time T.sub.0 to T.sub.1 the unit thereafter will pick up load at time T.sub.2. Up until time T.sub.2 the gland is being

sealed by auxiliary steam in the lower temperature range as indicated by solid curve 108. At time T.sub.2 self-sealing

occurs with the higher temperature inlet steam resulting in a step function of temperature at time T.sub.2. The present

invention eliminates this step function shock by gradually increasing the sealing steam temperature from T.sub.0 to T.sub.2,

as illustrated by the dotted curve 110.

One embodiment of the present invention which accomplishes the elimination of thermal shock is illustrated in FIG. 6 which

reproduces portions of FIG. 3. For convenience the intermediate and low pressure turbines 14 and 16 as well as the gland

condenser system are not illustrated.

The arrangement of FIG. 6 includes a control means 120 having a control circuit 122 for regulating the heat provided by

heater 124 such as an electric heater in heat transfer relationship with steam pipe 60. A transducer 126 associated with

steam pipe 60 provides an output signal indicative of the steam temperature within the pipe and provides this indication to

the control circuit 122 which also receives signals indicative of speed (RPM) and load (MW).

When the unit is on line, the control circuit 122 is able to sense decreasing load such that when it attains a predetermined

value, such as the 10% level, the control system will be operative to initially impart a higher than normal temperature to the

auxiliary steam for sealing and to gradually decrease the heat energy supplied in accordance with curve 104 of FIG. 4.

Conversely, when coming on line, the temperature and speed indications will cause the control arrangement to gradually

increase the heat of the auxiliary steam used to seal gland 70 until it attains the temperature of inlet steam which will be

applied, in accordance with curve 110 of FIG. 5.

Although a similar control arrangement can be applied to the steam line for gland 71, it will generally be unnecessary since

the self-sealing steam for that gland is the turbine exhaust steam at a lower temperature more compatible with the auxiliary

steam, thereby resulting in a less severe and more acceptable thermal shock.

FIG. 7 illustrates an alternate embodiment wherein sealing steam temperature is controlled by steam mixing as opposed to


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electric heating. Higher temperature main steam, just prior to valve 88, can be supplied to steam line 60 by means of a

valve 131 and the lower temperature auxiliary steam, from ahead of valve 90 can be supplied by means of valve 132. The

opening and closing of these valves 131 and 132 is governed by the control circuit 122 which in response to the temperature

indication provided by transducer 126 and load or speed indication will regulate these valves to add or reduce heat, as the

case may be, as previously described. In the steam mixing embodiment, a nonreturn or one-way valve 134 is included in the

steam line 60.

Accordingly an arrangement has been described for reducing stress in the steam turbine gland area and prolonging rotor life

by eliminating thermal shock due to the different temperatures in sealing steam when switching from or to a self sealing

condition.

PATENT CITATIONS

Cited Patent Filing date Publication date Applicant Title

US3062553 * Apr 19, 1960 Nov 6, 1962 Sulzer Ag Method and means for producing sealing vapor

US4282708 * Aug 22, 1979 Aug 11, 1981 Hitachi, Ltd. Method for the shutdown and restarting of combined power plant

JP46034805A * Title not available

JPS54132001A * Title not available

* Cited by examiner

REFERENCED BY

Citing Patent Filing date Publication date Applicant Title

US6748742 * Nov 7, 2001 Jun 15, 2004 Capstone Turbine Corporation Microturbine combination systems

US7147427 Nov 18, 2004 Dec 12, 2006 Stp Nuclear Operating CompanyUtilization of spillover steam from a high pressure

steam turbine as sealing steam

US7461544 * Feb 24, 2006 Dec 9, 2008 General Electric CompanyMethods for detecting water induction in steam

turbines

US8161724 Dec 1, 2010 Apr 24, 2012Eif Nte Hybrid Intellectual Property

Holding Company, LlcHybrid biomass process with reheat cycle

US8495878 Aug 28, 2012 Jul 30, 2013Eif Nte Hybrid Intellectual Property

Holding Company, LlcFeedwater heating hybrid power generation

US8596034 Mar 31, 2010 Dec 3, 2013Eif Nte Hybrid Intellectual Property

Holding Company, Llc

Hybrid power generation cycle systems and

methods

US20120198845 * Feb 4, 2011 Aug 9, 2012 William Eric Maki Steam Seal Dump Re-Entry System

EP2369140A2 * Mar 21, 2011 Sep 28, 2011 General Electric Company Steam seal system

* Cited by examiner

CLASSIFICATIONS

U.S. Classification 60/660, 60/676, 60/657

International Classification F01D11/06

Cooperative Classification F01D11/06

European Classification F01D11/06

LEGAL EVENTS

Date Code Event Description

Dec 7, 1993 FPExpired due to failure to pay

maintenance feeEffective date: 19930919

Sep 19, 1993 LAPSLapse for failure to pay

maintenance fees

Nov 18, 1988 FPAY Fee payment Year of fee payment: 4

Jun 5, 1984 AS Assignment

Owner name: WESTINGHOUSE ELECTRIC CORPORATION, WESTINGHOUSE BL

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:MARTIN,

HARRY F.;REEL/FRAME:004270/0412

Effective date: 19840501

Google Home - Sitemap - USPTO Bulk Downloads - Privacy Policy - Terms of Service - About Google Patents - Send Feedback

Data provided by IFI CLAIMS Patent Services©2012 Google


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Saturday, January 10, 2009

Sealing Arangements for Casing

Gland seal systems are very important to main and auxiliary

turbines. Turbine shafts must exit their casings in order to couple

up or connect with the unit that the turbines drive (reduction

gears, pumps, etc.) The main and auxiliary gland seal systems

enable the turbine to be sealed where the shaft exits the casing; in

effect keeping "air out and steam in."

The purpose of gland seal system is to prevent the leakage of air

from the atmosphere into turbine casings and prevent the escape

of steam from turbine casings into the atmosphere (see Figure 1).

Operation Overview

1. The pressure differential between the atmosphere and inside

the main engine turbine casing will vary depending on ship's

speed. Similarly, the differential between the atmosphere and

inside the ship's service turbine generator (SSTG) turbine casing

will vary depending on electrical load.

2. Labyrinths- Sets of labyrinth packing are employed along the

turbine rotor where the rotor exits the turbine casing to maintain

this pressure differential.

a. The labyrinths create many little chambers causing pressure

drops along the shaft. The number of labyrinth sets depends

greatly on the steam pressure possible in that area. Labyrinth

packing alone will neither stop the flow of steam from the turbine

nor prevent air flow into the turbine.

3. Gland Sealing Steam

a. The gland sealing system provides low pressure steam to the

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Steam turbineA little information on steam Engineering as I understand it, using all the sources from Internet. It

proves that if you want to search , there are vast informations you can collect from the webs.

Steam turbine: Sealing Arangements for Casing http://amnrrr12.blogspot.ae/2009/01/sealing-arangements-for-casing.html

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turbine gland in the final sets of labyrinth packing. This assists the

labyrinth packing in sealing the turbine to prevent the entrance of

air into the turbine, which would reduce or destroy the vacuum in

the associated condenser. Excess pressure (excess gland seal) is

removed by the gland seal unloader.

4. Gland Exhaust

a. Since there are times when steam escapes from the seals, a

gland exhaust system is provided. The gland exhaust system

consists of low pressure piping connected to the gland area

between the last two outer sets of labyrinths which receives and

prevents steam from escaping to the atmosphere. This system

collects the steam and directs it to a condenser for further use in

the steam plant.

C. Main Engine Gland Seal System Components.

1. The gland seal regulator (see Figure 2)

a. Senses system pressure on the outlet side of the regulator. The

gland seal regulator valve reduces 150 psig auxiliary ("dry or wet"

steam depending on the ship type) steam to gland seal system

pressure of .5 to 2 psig. The valve begins to open at 2 psig and is

fully open at .5 psig. The bypass valve allows the operator to

maintain system pressure in the event the regulator valve is

inoperable. (see Figure 1)

2. The Gland seal unloader valve (see Figure 3)

a. This valve senses the pressure of the gland seal supply piping.


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The unloader piping is wider in diameter than the regulator piping.

The gland seal unloader "dumps" the excess gland seal piping

pressure to the LP turbine exhaust trunk. The unloader begins to

open at 2 psig, and is fully open at 3 psig. It has a handwheel to

permit manual operation of the unloader to control gland seal

system pressure during a loss of control air causality.

Piping system (see Figure 1)

a. The regulator supplies the gland seal header. This header has

branch lines to each turbine gland area and a branch line to the

unloader. The ahead throttle valve assembly and the astern

throttle valve also have a connection to receive gland sealing

steam. The reason is the same on the unloader- to prevent the

possible introduction of air into the system. Any air entering the

turbines or piping systems affect the vacuum in the main

condenser.

b. On some ships, spectacle flanges are installed in the supply

lines to the HP turbine glands to allow the gland seal and gland

exhaust system to be isolated when singling up with the LP turbine

operating.

c. Inputs to the gland seal system include the gland seal regulator,

astern throttle leak-off, ahead throttle lifting rod leak-off, HP

turbine forward and after gland leak-off, and main steam

emergency throttle leak-off (on ships with singling up capabilities).

4. Main engine gland exhaust system

a. Steam leaking from the gland seal section of the shaft packing is

drawn off by the gland exhaust system. Gland exhaust is drawn

into the gland exhaust condenser section of the Main Engine Air

Ejector.

b. The gland exhaust steam is then condensed and returned to the

fresh water drain collecting tank. The air and non-condensable

gases are drawn off by the gland exhaust fan.

5. Gland Seal steam system operation

a. The gland seal regulator supplies .5 to 2 psig steam to the

glands in varying degrees as bells change on the main engine.

When answering a low bell or all stop, the gland leak off is

minimal, causing the regulator to supply the total gland sealing

steam. As engine speed increases, the casing is pressurized and

the increased gland leak off, along with the regulator, supplies all

the gland sealing steam required by the system.

(1) As ship's speed increases, the main engine becomes self

sealing. The gland seal regulator is fully shut and the unloader is

functioning to maintain the system pressure between 2 3 psig,

dumping the excess gland seal steam to the LP turbine exhaust

trunk.

(2) As ship's speed slows, the gland seal system operates in

reverse sequence. (see Figure 4,5,6)


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D. SSTG Gland Seal System Components

1. These components are almost identical to the main engine

gland sealing components. The major difference between the main

and SSTG system is the size.

a. The Gland seal regulator

(1) Senses pressure on the drain pot (or manifold). The drain pot

or manifold is similar to a header and acts as "collection area" for

the system steam. This area allows for the sensing lines to

accurately measure the system pressure. The valve functions by

reducing 150 psig auxiliary steam to the system pressure of .5 2

psig.

2. The Gland seal unloading valve

a. Senses the pressure on the drain pot. The operating range is 2 3

psig, unloading excess gland seal pressure to the lower section of

the turbine exhaust casing.

3. The piping system (see Figure 7)

a. Consists of piping to the forward and after glands from the drain

pot or manifold. The inputs to the system are gland seal regulator,

and the forward turbine bearing. At a 60% load on the generator,

leakage from the forward end of the turbine (high pressure end)

supplies the system, the regulator is closed and the unloader

bleeds excess to the turbine exhaust trunk.

E. Gland Exhaust System

1. Steam leaking from the gland seal area of the shaft packing,

steam leak off from the steam chest lift rods, and steam leak off

from the trip throttle valve is drawn into the gland exhaust system

and into the air ejector condenser.

2. The steam is condensed in the SSTG air ejector condenser. Air


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and non condensable gases are discharged to the atmosphere via

the gland exhaust fan which maintains a slight vacuum on the

auxiliary air ejector condenser.

F. Causes of System Failure

1. Since most gland seal regulators are air operated reducing

valves, improper pressure settings on the air pilots for the

regulating and unloading valves can cause system pressure to be

too high or low, or both valves may be open at the same time.

Ruptured diaphragms may occur in these air pilot controllers and

air operated valves. Oil and water in the air lines to the pilots or

air operated valves can cause erratic operation and deterioration

of the rubber diaphragms. Upon loss of air pressure, both valves

fail open and the unloader valve must be operated with the

manual handwheel to control gland seal pressure.

2. Painted valve stems or improper packing installation can cause

binding of the stem, restricting valve operation.

3. Improperly calibrated gages can cause the system to be

improperly operated.

4. In the event of a jammed gland seal regulator, the operator

should take control of gland seal pressure by using the regulator

bypass valve.

G. Safety Precautions

1. Do not admit steam to the glands of an idle turbine, as varying

degrees of corrosion, erosion, or a bowed rotor may result.

2. Ensure the gland seal system is in operation on the main engine

before aligning the main engine air ejectors. This helps prevent

dirt and debris from being drawn into the turbine glands.

3. Adjustment of components shall be conducted by qualified and

knowledgeable personnel. When performing adjustments, careful

coordination of involved personnel will minmize confusion of gage

indication.

Posted by aza ni at 6:48 PMLabels: turbine

16 COMMENTS:

joseph19 February 25, 2010 at 3:57 AM

I have a steam turbine 330 mw which if i operate at

control valve set point of 345 mw causes the self sealing of

hp ip and lp glands to fail and the auxilary sealing valve

opens in auto. Why does this happen?

Reply

AZANI February 25, 2010 at 7:13 AM

dear joseph

the auxiliary steam is making up the gland sealing

steam...if the ammount of sealin steam in the pockets is

low, the aux steam will top up the required steam.

when you increase steam demand to the turbine,the


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ammount of steam tapped to accommodate aux steam will

be affected.normally aux steam is either supplied from its

own aux boiler or tapped from main steam,pressure

reduced, furthermore by adding etra steam to turbine,you

will heat up the turbine,cooling steam from aux steam is

required to redice the temperature difference between

blades and casing.The turbine is designed to run own its

manufactured range.By overloading it you tend to

overheat.

Reply

AZANI February 25, 2010 at 7:14 AM

to others please rephrase your question so that i can read

and understand

Reply

High Temperature Sealant March 19, 2010 at 2:51

AM

Thanks allot for this articles it was a nice articles about

steam seal, the promoter of silicon free high temperature

sealant, polyurethane adhesives, thread locker and steam

seals.

Reply

New And Used Catering Equipment June 24, 2010

at 6:50 AM

My cousin recommended this blog and she was totally right

keep up the fantastic work!

Reply

RR Scar August 2, 2010 at 1:52 PM

How far out (max time)before a plant start up should you

set seals? Why would you not want to set seals 10hrs

before a start?

Toshiba D11 Steam Turbine. GE 7H Gas Turbine.

Reply

Anonymous September 7, 2010 at 3:22 AM

Hello!

We have problem with vacuum in the steam system!We

checked almost all lines,retaided,retaped with special


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tape,main condenser is cleaned,vacuum pumps ok but sill

vacuum only 680mmHg!Water temperature is 26 after

Cel!Maybe it could bee a gland steam!On screen ir shows

0,1 bar, but on gland steam air regulator valve pressure ir

adjusted 0,2 bar............and spill valve more than 0.2 bar

but still is only 0.1 bar in the system!!What could be

wrong???Maybe no water in constant level pot?Or air

regulators have some error??!!

Reply

agrawalsatish September 12, 2010 at 12:03 AM

Application area, metal-to-metal joints

BIRKOSIT - Dichtungskitt ®

BIRKOSIT - Dichtungskitt ® Sealing Compound has been

used for 50 years on Siemens turbines (product

development 1952 with Siemens). Without the additional

sealing of individual pressure areas using BIRKOSIT -

Dichtungskitt ® the production imprecision or the

distortion under loads are no longer evened out, which

means that the turbine areas in the individual pressure

areas become permeable under pressure. This means the

turbine loses power, and can even lead to unplanned

reconditioning.

BIRKOSIT - Dichtungskitt ® is formulated to be practically

inert in its standard applications in steam and gas

turbines. It is, therefore, resistant to exposure to hot air,

steam, water, light fuel oils and lubricants. By implication,

it should be resistant to crude oil and natural gas.

For placing your orders, please contact

Project Sales Corporation, General Agency of A.I. Schulze,

for marketing BIRKOSIT - Dichtungskitt ® in India

28 Founta Plaza, Suryabagh, Visakhapatnam 530 020, AP,

India; phone: +918912564393; fax: +918912590482

http://india.birkosit.com

Ordering Instructions:

Product : BIRKOSIT DICHTUNGSKITT (SEALING

COMPOUND)

Make : AI SCHULZE, GERMANY

Pack Size: 1 kg

Price: Rs.4250 per KG

Taxes: CST 2% extra against form C, else 14.5% extra

Delivery FOR Destination through First Flight Courier/GATI

MOQ: 10 kgs

India Distributors: Project Sales Corporation,

Visakhapatnam


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Country of Origin: Germany

Reply

agrawalsatish October 23, 2010 at 11:58 PM

Sole manufacturer and Distributor A.I. Schulze

Chemotechnische Fabrik e.K.

Project Sales Corporation

General Agency of A.I. Schulze

for marketing BIRKOSIT - Dichtungskitt ®

in the India

---------------------------------------------------------------------------

-----

Product Data Sheet


for extreme conditions of temperature and pressure

Description:

BIRKOSIT is a single-component, paste luting agent /

sealing compound for industrial use wherever conditions of

temperature and pressure at smooth, plane sealing

surfaces (butt joints) make extreme demands on the

quality of the sealing compound.

Product data sheet This applies, in particular, to the

sealing

of metallic joints: steam and gas turbines, compressors,

pumps, housings, flange joints etc.

Technical data:

Temperature resistance:

hot steam and air, hot and cold water, light fuel oils and

lubricants, crude oil and natural gas at up to 900 °C.

Pressure resistance:

The excellent adhesion on sealing surfaces and butt joints

guarantees a perfect seal up to 250 bar. The pressure

resistance for flanges without sealing rings is up to 450 bar

and even up to 550 bar for screw joints.

Plastic deformation:

is unlimited in its plastic workability so that, even under

the most demanding conditions, the sealing film does not

break. cf. temperature and pressure resistance.

Application areas:

Steam and gas turbines, power plants, gasworks and

waterworks, oil refineries, smelting works, shipyards, paint


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and rubber manufacturing, chemical industry.

Working recommendations:

To be spread on the dry surfaces using a putty knife or

rubber spatula. As the product doesn’t cure but slightly

changes its consistence staying flexible and elastic,

application on butt joints without time pressure is possible.

And the product can be subjected immediately to working

loads!

A small amount of linseed oil varnish may be added to

improve the spreading properties.

Storage:

Unlimited storage life when correctly stored. Its properties

are stable and it is flexible in use. The tin should be

properly closed when only a part of the contents is used.

Packaging:

BIRKOSIT is packed and supplied in special 1-kg tins. Its

colour is reddish-brown. For further properties of the

product, see the materials safety data sheet 91/155/EEC,

changed 93/112/EC and the storage life certificate. State

of October 2009.

This issue of the product data sheet supersedes back

issues.

---------------------------------------------------------------------------

-----

Reply

agrawalsatish October 23, 2010 at 11:58 PM


BIRKOSIT - Dichtungskitt ® Sealing Compound has been

used for 50 years on turbines (product development 1952

with Siemens). Without the additional sealing of individual

pressure areas using BIRKOSIT - Dichtungskitt ® the

production imprecision or the distortion under loads are no

longer evened out, which means that the turbine areas in

the individual pressure areas become permeable under

pressure. This means the turbine loses power, and can

even lead to unplanned reconditioning.

BIRKOSIT - Dichtungskitt ® is formulated to be practically

inert in its standard applications in steam and gas

turbines. It is, therefore, resistant to exposure to hot air,

steam, water, light fuel oils and lubricants. By implication,

it should be resistant to crude oil and natural gas.


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[main application]

single-component, paste sealing compound for sealing

between machined surfaces (joints between parts) in

steam and gas turbines at temperatures up to 900 °C and

pressures up to 250 bar.

[other applications]

can also be used for sealing between smooth surfaces in

compressors, housings, pumps etc. and by extension, in

valve glands and screw joints.

[additional applications]

All kinds of screwed metal flange pipe connections

(independent of flange diameter and shape). Their

operating conditions are characterized by water, steam,

pressure, high temperature

Reply

Anonymous December 8, 2010 at 6:21 PM

what is a turbine steam pressure control?

Reply

Anonymous April 7, 2011 at 9:07 PM

what are the effect of overheating and overcooling of

turbine casing

Reply

Anonymous July 8, 2012 at 9:01 PM

Can anyone tell me the advantages of pressure balanced

gland segment please?

Reply

chittaranjan mohapatra September 8, 2012 at 7:52

PM

hi, can tell me why and how gland sealing of steam turbine

temp. increse keeping pr. const.,& also auxulary staem

team. const..And how control its temp.

Reply

enerzea power March 4, 2013 at 3:46 AM

The Steam turbine manufacturers company should be

known for manufacturing best quality of industry specific

and customized steam turbines.


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Steam turbine manufacturers - Kessels is a leading

Steam Turbine manufacturer in the range of 5 KW to 30

MW, providing the most reliable and efficient steam

turbine solutions for over 25 years.

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8. yazd-system description for auxiliary steam system_combined

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