Selecting the Optimised Pump Configuration and Drive...

Willem van der Westhuizen

Eskom Enterprises EngineeringJohannesburg, South Africa

Selecting the Optimised Pump Configuration and DriveOption for the Condensate Extraction and Boiler FeedPumps for the New Eskom Supercritical Power Stations

Orig i nal sci en tific paperUDC: 621.577.012:620.92

Eskom has em barked on a ma jor Cap i tal Ex pen di ture pro gram to ca ter for the grow ingde mand for power as a re sult of a rap idly de vel op ing South Af ri can econ omy. Fu ture de -vel op ments in clude elec tri cal power gen er a tion uti liz ing di verse tech nol o gies such as:fos sil, nu clear, peb ble bed mod u lar re ac tors, hy dro, open gas cy cle, com bined cy cle,wind, and so lar en ergy.The first two new super criti cal fos sil fired power sta tions, Medupi (6 units, each 650 MW)and Kusile (6 units, each 800 MW) are pres ently in the de sign and con struc tion phase.The con den sate ex trac tion pumps and boiler feed pumps are amongst the high est con -sum ers of aux il iary elec tri cal power within a power sta tion, it is there fore of ut most im -por tance that the cor rect op ti mized pump con fig u ra tions and drive op tions for each ofthese pumps is se lected.The pa per de scribes how the fi nal se lec tion of the con den sate ex trac tion pumps for thetwo new super criti cal power sta tions was made. The op tion of a ver ti cal vs. a hor i zon -tally po si tioned pump, uti liz ing an air cooled con denser was con sid ered. Each con den -sate ex trac tion pump is sized for 100% by pass op er a tion. The pa per dis cusses why two100% duty pumps were se lected with one be ing vari able speed elec tri cal mo tor drivenand the standby one fixed speed elec tri cal mo tor driven.In or der to achieve the re quired high plant avail abil ity, a 3 ́ 50% boiler feed pump con -fig u ra tion per unit will be uti lized at the two new super criti cal power sta tions.The pa per also dis cusses four dif fer ent vari able speed boiler feed pump drive op tionsthat were avail able for se lec tion.The de tails of each vari able speed drive op tion are in cluded and dis cussed. The fi nal de -ci sion in se lect ing the op ti mized boiler feed pump drive was based on an eco nomic eval -u a tion model that in cluded three dif fer ent modes of op er a tion, i. e. (base load, loadfol low ing, and two shift ing), ini tial cap i tal cost and aux il iary power con sump tion asbased on boiler feed pump set ef fi ciency over the ex pected 50 year life span of the powersta tion.

Key words: Eskom, super criti cal fos sil power sta tion, con den sate ex trac tion pump,boiler feed pump, vari able speed drive

van der Westhuizen, W.: Selecting the Optimised Pump Configuration and Drive ...TERMOTEHNIKA, 2009, XXXV, 2, 163–176

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IN TRO DUC TION

In South ern Af rica, the elec tric ity sup ply in dus try is dom i nated by South Af -rica’s state-owned util ity, Eskom*. It op er ates 17 coal-fired power sta tions in the coun tryand, in clud ing its hydropower, nu clear, and gas tur bine sta tions, has a gen er at ing ca pac ity of 39 000 MW. Eskom sup plies 90% of the elec tric ity used in South Af rica, gen er atesaround two-thirds of the elec tric ity pro duced in the whole of Af rica and is ex tend ing itstrans mis sion grid north into neigh bor ing sub-Sa ha ran coun tries [1].

The cur rent elec tric ity us age for South Af rica is 35 000 MW for morn ing peakand 36 000 MW for eve ning peak. The peak power de mand is dur ing the win ter months inSouth Af rica.

Eskom has em barked on a ma jor cap i tal ex pen di ture pro gram to ca ter for thegrow ing de mand for power as a re sult of a rap idly de vel op ing South Af ri can econ omy.Fu ture de vel op ments in clude elec tri cal power gen er a tion uti liz ing di verse tech nol o giessuch as: fos sil, nu clear, peb ble bed mod u lar re ac tors, hy dro, open gas cy cle, com bined cy -cle, wind, and so lar en ergy.

The first two new super criti cal fos sil fired power sta tions, Medupi (6 units, each650 MW) and Kusile (6 units, each 800 MW) are pres ently in the de sign and con struc tionphase.

The con den sate ex trac tion pumps and boiler feed pumps are amongst the high -est con sum ers of aux il iary elec tri cal power within a power sta tion, it is there fore of ut -most im por tance that the cor rect op ti mized pump con fig u ra tions and drive op tions foreach of these pumps is se lected.

The pa per dis cusses the se lect ing of the op ti mized pump con fig u ra tion and drive op tion for the con den sate ex trac tion and boiler feed pumps for the new Eskom super -criti cal power sta tions.

CON DEN SATE EX TRAC TION PUMPS

Con den sate ex trac tion pump con fig u ra tion

The fol low ing con den sate ex trac tion pump (CEP) con fig u ra tions were consid-ered:– 2 ́ 100% duty pumps, one in op er a tion and one 100% on standby (Eskom stan dard), and– 3 ´ 50% duty pumps, two in par al lel op er a tion and one 50% on standby.

When com par ing the two CEP con fig u ra tions the fol low ing was con sid ered:– ini tial cap i tal costs,– pip ing and in stru men ta tion, in clud ing valves,– elec tri cal ca bling and sys tems,– space re quired for in stal la tion,– re dun dancy, and– spares hold ing.

van der Westhuizen, W.: Se lect ing the Op ti mised Pump Con fig u ra tion and Drive ...TERMOTEHNIKA, 2009, XXXV, 2, 163–176

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* Eskom is the South Af ri can power util ity. It is the fifth larg est elec tri cal util ity in the world and sup plies 90%of South Af rica’s power and two thirds of the power gen er ated on the en tire Af ri can con ti nent

As de ter mined by an eco nomic eval u a tion us ing all fac tors as stated above, it was con cluded that a 2 ́ 100% duty CEP con fig u ra tion would be the op ti mal CEP con fig u ra -tion for the ex pected 50 year life span of the power sta tion.

Con den sate ex trac tion pumps in stal la tions insmaller and older Eskom power sta tions

All ex ist ing Eskom power sta tions uti lize a 2 ´ 100% CEP con fig u ra tion. Theolder type power sta tions that don’t have any main tur bine by pass sys tems uti lizes twofixed speed CEP’s with their de sign point the same as the tur bine max i mum con tin u ousrat ing (TMCR) duty point.

The con den sate flow of the CEP is con trolled by throt tling the main con den -sate con trol valve. The CEP’s in stalled at the power sta tions with an out put of less than350 MW are all fixed speed hor i zon tally ar ranged CEP’s. The pumps are hor i zon tallysplit cas ing de signs with a dou ble en try suc tion im pel ler. De pend ing on the flow andhead re quire ments, the pumps could be sin gle, two or three stage de sign. The pumps allrun at 6 pole speed (N = 980 rpm). The slow speed and dou ble suc tion im pel lers arespe cif i cally con sid ered in or der to sat isfy the NPSH re quire ments of the pumps and dueto the low NPSH avail able from the con denser hot-well.

Con den sate ex trac tion pumps in stal la tions innewer larger de sign power sta tions

On our newer larger plants with an out put of greater than 500 MW, where thecon dens ers are larger and the pump flow greater, the con den sate ex trac tion pumps arever ti cal mul ti stage with the pump el e ment mounted in a suc tion can which is con necteddi rectly to the hot-well of the con dens ers. In this way the first stage im pel ler is way downat the bot tom of the suc tion can. The length of the can is de ter mined by the NPSH re -quired by the first stage im pel ler of the pump. The ver ti cal CEP’s run at two pole speed(1500 rpm).

All the power sta tions, whose out puts are greater than 500 MW per unit, havemain tur bine by pass sys tems. In this case the de sign point “A” of the pumps are de signedand se lected/sized to ac com mo date the full low pres sure by pass flow dur ing a main tur -bine trip op er a tion. The to tal flow of the CEP will in clude the main for ward con den sateflow as well as the spray wa ter re quire ment to the LP tur bine by pass control valve station.

The tur bine MCR or duty point “C” will then be ob tained by throt tling the maincon den sate con trol valve, see fig. 1.

The con den sate flow of the CEP is also con trolled dur ing part load op er a tion bythrot tling the main con den sate con trol valve fur ther on the pump curve (ar ti fi cially in -creas ing the sys tem re sis tance). In the case of a LP tur bine by pass op er at ing con di tion,the main con den sate con trol valve will open fully and the pump will run at the de signpoint “A” of the pump, see fig. 1. The NPSH re quired and NPSH avail able needs to be sat -is fied at this de sign point and the mo tor power re quire ment also needs to be consideredfor this design point.


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With this pump se lec tion and op er at ingmode the best ef fi ciency point (BEP) of thepump is at the de sign point “A” and not thetur bine MCR duty point “C”.

To sum ma rize: The CEP will run at a re -duced ef fi ciency as well as a throt tled op er at -ing con di tion dur ing tur bine MCR op er at ing con di tion. This con di tion re sults in un nec es -sary aux il iary power us age or “wasted” en -ergy con sump tion over the life span of thepower sta tion.

Con den sate ex trac tion pumps forthe two new super criti cal power sta tions

Dur ing the fea si bil ity stud ies and thetech ni cal clar i fi ca tions meet ings for theequip ment to be sup plied for the two newsuper criti cal power sta tions, the fol low ingop tions for the CEP’s were con sid ered:– CEP con fig u ra tion, – ver ti cally ar ranged vs. hor i zon tally ar -

ranged CEP’s, and– vari able speed vs. fixed speed elec tri cal

mo tor driven CEP’s.

CEP con fig u ra tion

Based on an eco nomic eval u a tion and us ing all fac tors as listed in the sec tionCon den sate ex trac tion pump con fig u ra tion, it was con cluded that a 2 ´ 100% duty CEPcon fig u ra tion would be the op ti mal CEP con fig u ra tion for the ex pected 50 year life spanof a power sta tion.

Ver ti cally ar ranged vs. hor i zon tally ar ranged CEP’s

The two new super criti cal power sta tions Medupi and Kusile will be uti liz ing anair cooled con denser (ACC) for con dens ing the steam from the main tur bine. In this casethe CEP’s will not take suc tion from the hot-well of the con denser which is nor mally un -der vac uum for a wet cooled sys tem, hav ing low NPSH avail able. The air cooled con -denser con den sate tank (ACCCT) is in stalled at 15 m level above grade and wouldthere fore be able to sup ply suf fi cient NPSH avail able to the CEP’s to con sider a hor i zon -tally arranged CEP.


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Fig ure 1. Con den sate ex trac tion pump –fixed speed pump curve

Both ver ti cally ar ranged and hor i zon tally ar ranged CEP con fig u ra tions werecon sid ered.

The fol low ing ta ble with ar row cod ing was used to help de ter mine which CEPcon fig u ra tion would be op ti mal for the Medupi and Kusile power CEP’s.

Con clu sions

From tab. 1, con sid er ing all tech ni cal as pects as well as NPSH re quire ments forthe CEP’s the hor i zon tal CEP ar range ment was se lected for the two new super criti cal po-wer sta tions, Medupi and Kusile.

Vari able speed vs. fixedspeed elec tri cal mo tordriven CEP’s

As ex plained in thesec tion Con den sate ex trac -tion pumps in stal la tions innewer larger de sign powersta tions, the CEP's run at are duced ef fi ciency as wellas a throt tled op er at ingcon di tion dur ing tur bineMCR op er a tion con di -tions. With the aid of fig. 1, a vari able speed CEP op -tion was in ves ti gated andcon sid ered.

The re duced effi-ciency and throt tled op er -at ing con di tions results inun nec es sary aux il iary power us age or “wasted” en ergy consumption over the life span ofthe power sta tion.

It was there fore im por tant to con sider a vari able speed CEP for the two newsuper criti cal power sta tions, Medupi and Kusile.

By uti liz ing a vari able speed CEP on “A” CEP the fol low ing power sav ings areachieved at duty point “C” or tur bine MCR op er at ing point, see fig. 2 and tab 2.

From tab. 2 one can clearly see that there is a sig nif i cant sav ing in the power ab -sorbed by the CEP at tur bine MCR op er at ing con di tions, when the fixed speed unit iscom pared with the vari able speed unit. The vari able speed op tion will also give a powersav ing at loads be low tur bine MCR con di tions, i. e. part load (the flow is di rectly pro por -tional to the speed of the pump). The mo tors se lected for the fixed speed and vari ablespeed CEP’s are the same (they will be in ter change able). The only dif fer ence is the ac tual vari able speed con trol cou pled to “A” CEP mo tor.


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Ta ble 1. Tech ni cal con sid er ations used to eval u ate thever ti cally and hor i zon tally ar ranged CEP

Ver ti cal Hor i zon tal

Pump de sign ¯

In stal la tion weights and main te nance ¯

Pump duty points ¯

Pump ma te ri als

Elec tric mo tors

Spares hold ing ¯

Po si tion ing of CEP’s

Past Eskom P/S CEP’s ¯

Ref er ences

Lo cal man u fac ture

¯ in di cat ing a lower rat ing; in di cat ing higher rat ing

Dur ing nor mal op er a tion at tur bineMCR op er at ing con di tions, the “A” vari -able speed CEP will run at a re duced speedof N = 1377 rpm, with the main con den sate con trol valve in the fully open po si tion andthe ac tual pump dis charge pres sure lower(no throt tling across valve). As soon as theunit is op er ated in a main tur bine by passop er at ing con di tion the pump will in creasein speed to a speed of N = 1485 rpm withthe main con den sate valve still fully openand op er at ing at the re quired LP turbineby pass or de sign point “A” con di tion. Theload of the unit will also be con trolled bythe speed of the pump.

The power sav ing us ing a vari able speed CEP jus ti fied the cap i tal lay out in us ing aVSD on one of the CEP’s.

In the case of a trip on “A” CEP the fixed speed pump will start and the main con den -sate con trol valve will then con trol the re -quired con den sate de liv ered by the fixedspeed CEP by throt tling the pump to there quired flow on the fixed speed pumpcurve.

BOILER FEED PUMPS

Boiler feed pump con fig u ra tion

The fol low ing boiler feedpump (BFP) con fig u ra tionswere con sid ered:– 1 ´ 100% duty, steam tur bine

driven boiler feed pump, and2 ́ 50% duty standby elec tri cally driven boiler feed pumps com plete with geared vari -able speed fluid drive cou plings (Eskom stan dard on wet cooled con denser power sta -tions), and

– 3 ́ 50% duty, vari able speed elec tri cally driven boiler feed pumps, two in par al lel op er -a tion and one 50% on standby (Eskom stan dard on dry-cooled power sta tions).

When com par ing the two BFP con fig u ra tions the fol low ing was con sid ered:– ini tial cap i tal costs,– pip ing and in stru men ta tion, in clud ing valves,


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Ta ble 2. CEP power ab sorbed at tur bine MCR op er at ingcon di tion for the fixed speed and vari able speed pumps

Power ab sorbed at tur bine MCR op er at ing condition

Foxed speed CEP 1410.05 kW

Variable speed CEP 1082.80 kW

Saving in kW and % 327.25 kW and 30% saving

Fig ure 2. Con den sate ex trac tion pump– vari able speed pump curve

– elec tri cal ca bling and sys tems,– space re quired for in stal la tion,– re dun dancy,– spares hold ing, and– ef fect of BFP tur bine ex haust on cy cle ef fi ciency should a 100% duty, steam tur bine

driven boiler feed pump be in stalled on a dry cooled sta tion.As de ter mined by an eco nomic eval u a tion us ing all fac tors as stated above, it was

con cluded that a 3 ́ 50% duty vari able speed elec tri cally driven BFP con fig u ra tion would be the op ti mal con fig u ra tion for the ex pected 50 year life span of the power sta tion.

Boiler feed pump vari able speed drives

The BFPs for the 3 ́ 50% duty elec tri cally driven vari able speed pumps will con -sist of the fol low ing:– a booster pump,– a main pump, and– a vari able speed drive sit u ated be tween the booster and the main pumps.

Note: The boiler feed pumps and drives con sid ered will be sized and se lected to sat -isfy the de sign point of the power sta tion which is HP by pass op er a tion or de sign point “A”.

Pump vari able speed drive se lec tion

Four al ter na tive vari able speed drives were con sid ered, namely:– high speed VSD mo tor with speed re duc tion gear box,– low speed VSD mo tor with speed in crease gear box,– voith Vorecon vari able speed plan e tary gear fluid drive cou pling, and– voith vari able speed fluid drive cou pling.

Boiler feed pump drive op tion 1

With this drive op tion a high speed vari -able speed elec tric mo tor is di rectly con -nected to the main pump. A speed re duc tiongear box links the other side of the high speedmo tor shaft to the booster pump, see fig. 3.

This drive op tion will have the high estBFP set ef fi ciency of 81.2% (pumps, mo torand gear box com bined) with the low est power con sump tion (12.14 MW at tur bine MCR op -er at ing con di tion for one BFP set). An otherad van tage would be that the BFP set will alsorun at very high ef fi ciency and low power con -sump tion at part load con di tions.


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Fig ure 3. High speed VSD elec tri callydriven mo tor with a speed re duc tion

gear box

The big gest dis ad van tage would be the ini tial cap i tal cost of the vari able speeddrive and high speed elec tric mo tor.

Eskom has ex pe ri ence of this BFP lay out and drive op tion at our Matimba,Kendal, and Majuba power sta tions. It is proven tech nol ogy which con trib utes to highavail abil ity and re li abil ity of the com plete BFP train.


With this drive op tion a low speed vari ablespeed elec tric mo tor is di rectly con nected tothe booster pump. A speed in crease gear boxlinks the other side of the high speed mo torshaft to the booster pump, see fig. 4.

This drive op tion will also have a high BFPset ef fi ciency of 79.9% (pumps, mo tor andgear box com bined), with low power con sump -tion (12.34 MW at tur bine MCR op er at ing con -di tion for one BFP set). The BFP set ef fi ciencywill not be as high as that for op tion 1 due to thespeed in crease gear box losses (driv ing the main pump ~11.2 MW). An ad van tage would be thatthe BFP set will also run at very high ef fi ciencyand low power con sump tion at part load con di -tions.

As the cap i tal cost of a low speed vari able speed elec tric mo tor is lower than thatfor a high speed vari able speed elec tric mo tor, op tion 2 will be more cost ef fec tive thanop tion 1 but is still high when com pared to drive op tions 3 or 4.

Eskom has no ex pe ri ence with this driveop tion and Eskom would re quire ac cess toref er ence plant and de tailed tech ni cal in for -ma tion for this drive op tion be fore it wouldbe se ri ously con sid ered.


This BFP drive op tion uti lizes an ad -vanced fluid drive cou pling – Voith Voreconvari able speed plan e tary gear fluid drive cou -pling, see fig. 5.

In this op tion the booster pump will becon nected di rectly to an 19 MW – 4 pole dou -ble shaft ex ten sion, 6.6 kV in duc tion mo tor.


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Fig ure 5. Fixed speed elec tric mo tor withVoith Vorecon vari able speed plan e tary

geared fluid drive cou pling

Fig ure 4. Low speed VSD elec tri callydriven mo tor with a speed in crease

gear box

The Voith Vorecon vari able speed plan e tary gear fluid drive cou pling will con nect theother end of the mo tor shaft to the main pump.

The main pump flow will be reg u lated by in creas ing or de creas ing the speed ofthe Voith Vorecon vari able speed plan e tary gear fluid drive cou pling.

This drive op tion will have a lower BFP set ef fi ciency of 77.2% when com paredto op tions 1 or 2. It will also ab sorb more power (12.76 MW, at tur bine MCR op er at ingcon di tion for one BFP set), than op tions 1 or 2. This op tion does how ever have ad van -tages when com pared to op tion 4 where at part load con di tions the ef fi ciency of the BFPset will be lower than op tions 1 or 2 but higher than op tion 4 [2].

This BFP drive op tion will have a sub stan tially lower cap i tal cost than op tions 1or 2, but still greater than op tion 4.

Eskom has no ex pe ri ence with the Voith Vorecon vari able speed plan e tary gearfluid drive cou pling. A ref er ence list was made avail able by Voith list ing the in stal la tionswhere Voith Vorecon vari able speed plan e tary geared fluid drive cou plings are in use.The ref er ence list in cludes: boiler feed pumps, fans, com pres sors, coal mills, and ID fans[3].

The two high est power rat ing Vorecon’s built and sup plied for a BFP ap pli ca tion are:– 9.9 MW, 3 units in stalled 2004 (Flowserve, Weston, USA), and– 8.5 MW, 2 units in stalled 1989 (Mannheim, Grosskraftwerk, Ger many).

The two high est power rat ing Vorecon built and sup plied to in dus try are:– 28 MW, 1 unit in stalled 2005, com pres sor drive test stand (Shenyang Blower Works,

Shenyang, China), and– 14.8 MW, 1 unit in stalled 2004, Com pres sor drive (BHEL, Lekhwair Gas Iwection,

Oman).The 50% BFP unit con sid ered for Medupi and Kusile will ab sorb ~12.34 MW at

tur bine MCR and 17.2 MW at run-out duty point.


This BFP drive op tion uti lizes a Voithvari able speed fluid drive cou pling.

In this op tion the booster pump will becon nected di rectly to an 19 MW – 4 poledou ble shaft ex ten sion, 6.6 kV in duc tionmo tor. The Voith vari able speed fluid drivecou pling will con nect the other end of themo tor shaft to the main pump, see fig. 6.

The main pump speed will be reg u latedby in creas ing or de creas ing the speed of theVoith vari able speed fluid drive cou pling.

This drive op tion will have the low estBFP set ef fi ciency of 70.2% com pared to op -tions 1, 2, or 3. It will also ab sorb more power


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Fig ure 6. Fixed speed elec tric mo tor withVoith vari able speed fluid drive cou pling

(14.05 MW, at tur bine MCR op er at ing con di tion for one BFP set), than op tions 1, 2, or 3.This op tion has a fur ther dis ad van tage when com pared to op tion 3 where at part loadcon di tions the ef fi ciency of the BFP set will be re duced due to the high slip losses in thefluid drive coupling.

This BFP drive op tion will have the low est cap i tal cost when com pared to op -tions 1, 2, or 3. Eskom has ex pe ri ence with the Voith vari able speed fluid drive cou plingsat the Matla, Duvha, Lethabo, and Tutuka power sta tions. The BFP’s which are equippedwith the Voith vari able speed fluid drive cou plings at these power sta tions are only usedfor unit start up and shut down or used as standby BFP’s in the case of un avail abil ity of the 100% duty, steam tur bine driven boiler feed pump.

Sum mary of the BFP drives

Ta ble 3 sum ma rizes the BFP set ef fi cien cies, power con sump tion us ing two 50%BFP in par al lel at tur bine MCR op er at ing con di tion and ini tial capital costs.

Eco nomic eval u a tion of the boiler feed pump drive op tions

Al though all four BFP drives were tech ni cally ac cept able with em pha sis on BFPset ef fi ciency and power ab sorbed, the fi nal de ci sion is de pend ant on the eco nomic eval u -a tion results.

The new Eskom gen er a tion eco nomic eval u a tion model was used to cal cu latethe levelised costs of the four drive op tions over the ex pected 50 years life span of thepower station.

The eco nomic eval u a tion in cluded:– cap i tal costs,– ab sorbed power,– op er at ing phi los o phy of power sta tion,– avail abil ity and re li abil ity of plant,


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Ta ble 3. Boiler feed pump drive op tion, ef fi ciency, power ab sorbed, and cap i tal costs

BFP drive op tionBFP set ef fi ciency

[%]Power consumption

[kW]Cap i tal cost

[%]

High speed VSD electric motorwith speed reduction gearbox

81.2 24274.8 203

Low speed VSD electric motorwith speed increase gearbox

79.9 24685.2 161

Fixed speed motor with VoithVorecon variable speed planetarygeared fluid drive coupling

77.2 25520.84 133

Fixed speed motor with Voithvariable speed fluid drive coupling

70.2 28103.1 100

– aux il iary power costs, and– main te nance costs.

The re sults from the eco nomic eval u a tion model yielded the fol low ing or der of pref er ence:(1) fixed speed mo tor with Voith Vorecon vari able speed plan e tary gear fluid drive cou -

pling,(2) low speed VSD mo tor with speed in crease gear box,(3) fixed speed mo tor with Voith vari able speed fluid drive cou pling, and(4) high speed VSD mo tor with speed re duc tion gear box.

Con clu sions and rec om men da tion on the BFP drives

Based on the eco nomic eval u a tion re sults Eskom in ves ti gated the fixed speedmo tor with Voith Vorecon vari able speed plan e tary gear fluid drive cou pling fur ther byvis it ing Mannheim power sta tion in Ger many and SES Meliti power sta tion in Greeceboth of whom uti lize Vorecon BFP drives. The visit was spe cif i cally aimed at gain ing op -er a tional and main te nance ex pe ri ence from the two us ers [4]. The two Vorecon’s in -stalled in Mannheim Power Sta tion have been in ser vice for more than 100 000 op er at inghours since in stal la tion.

Based on the high re li abil ity and avail abil ity of the Voith Vorecon’s in stalled asBFP drives at Mannheim and SES Meliti Power Sta tions, it can be con cluded that thisBFP drive op tion is vi a ble and proven. The se lec tion of the Voith Vorecon BFP drive isthere fore the pre ferred and ac cepted boiler feed pump drive for Medupi and Kusilepower sta tion and should also be con sid ered for fu ture power stations.

It was there fore con cluded and rec om mended that the Medupi and Kusilepower sta tion boiler feed pump con fig u ra tion re mains as per the orig i nal spec i fi ca tion;i. e. 3 ́ 50% duty elec tric mo tor driven boiler feed pump sets in cowunction with a VoithVorecon hy drau lic drive cou pling.

The fi nal con tract signed with Alstom for the 3 ́ 50% boiler feed pump sets perunit for the six units at the Medupi power sta tion con sists of the fol low ing equip ment:– Sulzer booster pumps – HZB 303-720,– Sulzer main pumps – HPT 350-370-6S/29, and– ABB elec tric mo tor – squir rel cage in duc tion mo tor DQWGH 1000/4-274 and Voith

Vorecon – RW16-145 F 9.

AC KNOWL EDGE MENTS

The au thor wish to thank Eskom for the in for ma tion and the per mis sion to pub -lish the pa per.

No men cla ture

H – head, [m]N – ro ta tional speed, [rpm]NPSH – net pos i tive suc tion head, [m]


173

NPSHa – net pos i tive suc tion head avail able, [m]NPSHr – net pos i tive suc tion head re quired, [m]P – power, [kW]Q – flow, [m3/h]h – ef fi ciency, [%]

Accronimes

ACC – air cooled con denserACCCT – air cooled con denser con den sate tankBEP – best ef fi ciency pointBFP – boiler feed pumpCEP – con den sate ex trac tion pumpEE – eco nomic eval u a tionHP – high pres sureID – in duced draughtLP – low pres sureMCR – max i mum con tin u ous rat ingP/S – power sta tionST – steam tur bineTMCR – tur bine max i mum con tin u ous rat ingVSD – vari able speed drive

REF ER ENCES

[1] ***, Eskom An nual re port, Eskom, Jo han nes burg, South Af rica, 2008[2] Wahl, G., Suhari, L., Im prove ment of Ef fi ciency of Hy dro dy namic Vari able Speed Cou pling

Multi-Stage Vari able – Speed Drive – A New De vel op ment, Kraftwerkskomponente,STEAG, Essen, Ger many, 1986

[3] ***, Voith Vorecon, Ref er ence list, Voith, Crailsheim, Ger many, 2006[4] Cattaert, A. E., Pininski, E., Ngcobo, G., van der Westhuizen,W., Over seas Re port on Boiler

Feed Pump Re dun dancy and Voith Vorecon Me chan i cal Vari able Speed Drive, Re port No.N.RDZ-45-13, Eskom En ter prises En gi neer ing, Eskom, Jo han nes burg, South Af rica, 2007


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Apstrakt

Viqem van der VESTHOJZEN

Eskom Enterprajz InìweringJohanesburg, Ju`noafri~ka Republika

Izbor optimalne konfiguracije i na~ina radapumpi za ispumpavawe kondenzata i pumpiza snabdevawe napojnom vodom za nove Eskomtermoelektrane sa natkriti~nim parametrima

Kompanija Eskom je otpo~ela kapitalni investicioni pro gram da bi zadovo-

qila rastu}u potrebu za elektri~nom energijom u ekonomiji Ju`noafri~ke Repub-

like koja se intenzivno razvija zadwih godina. Budu}i razvoj podrazumeva proiz-

vodwu elektri~ne energije uz kori{}ewe razli~itih tehnologija, kao {to su:

sagorevawe fosilnih goriva, nuklearne energije, modularni reaktori sa fluidizo-

vanim slojem, gasnih ciklusa, energije vodenih tokova, kombinovana proizvodwa

toplotne i elektri~ne energije, energija iz vetra i sun~eva energija.

Prve dve, od planiranog ve}eg broja novih termoelektrana sa natkriti~-

nim parametrima, Medupi (6 blokova, svaki po 794 MW) i Kusile (6 blokova, svaki

po 798 MW) su u postupku projektovawa i izgradwe.

Pumpe za ispumpavawe kondenzata i snabdevawe napojnom vodom su me|u naj-

ve}im potro{a~ima elektri~ne energije u termoelektranama, tako da wihov izbor i

izbor odgovaraju}eg na~ina rada predstavqa primarni zadatak u procesu projekto-

vawa ovih sistema.

U radu su opisani na~ini kona~nog izbora pumpi za ispumpavawe kondenzata

na dve novoizgra|ene termoelektrane sa natkriti~nim parametrima u Ju`noafri~-

koj Republici. Razmatrana je opcija vertikalnog postavqawa sa vazdu{no hla|enim

kondenzatorom u odnosu na horizontalno postavqawe pumpi za ispumpavawe konden-

zata. Svaka od pumpi za ispumpavawe kondenzata je dimenzionisana za 100%-tno

optere}ewe u bajpasnom modu rada. U radu je obja{weno za{to je izabrana konfigu-

racija sa dve pumpe sa 100%-tnim optere}ewem od kojih je jedna sa elektromotorom sa

promenqivom brzinom i druga sa elektromotorom sa nepromenqivom brzinom

obrtawa.

Da bi se obezbedila visoka pouzdanost snabdevawa napojnom vodom, tri

pumpe sa 50% optere}ewa po bloku }e biti postavqene na dve nove termoelektrane sa

natkriti~nim parametrima.

U radu su, tako|e, opisana ~etiri razli~ita radna reìma pumpi za snabde-

vawe vodom koje su bile raspoloìve prilikom izbora.


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Detaqi svakog re`ima rada pumpi su opisani i diskutovani. Kona~na odluka

prilikom izbora pumpi napojne vode je zasnovana na ekonomskom modelu procene

koji je uzeo u razmatrawe tri razli~ita moda rada, po~etnu cenu izgradwe, potro{wu

elektri~ne energije u radu i zahtevanu efikasnost rada napojnih pumpi u predvi-

|enom pedesetogodi{wem `ivotnom veku rada termoelektrana.

*

* *

Eskom kompanija je elektroprivreda Ju`noafri~ke Republike. Eskom je

peta kompanija u svetskim razmerama u odnosu na proizvodwu elektri~ne energije,

pokriva 95% potreba Ju`noafri~ke Republike i 45% elektri~ne energije koja se

proizvede na Afri~kom kontinentu.

Kqu~ne re~i: Eskom, natkriti~ni parametri rada termoelektrana koje sagore-vaju fosilna goriva, pumpe za ispumpavawe kondenzata, napojnepumpe, elektromotor sa promenqivim brojem obrtaja

Au thor's e-mail:[email protected]


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Selecting the Optimised Pump Configuration and Drive...

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