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

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1 van der Westhuizen, W.: Selecting the Optimised Pump Configuration and Drive... Willem van der Westhuizen Eskom Enterprises Engineering Johannesburg, South Africa Selecting the Optimised Pump Configuration and Drive Option for the Condensate Extraction and Boiler Feed Pumps for the New Eskom Supercritical Power Stations Original scientific paper UDC: : Eskom has em barked on a ma jor Cap i tal Ex pen di ture pro gram to ca ter for the grow 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 - velopments include electrical power generation utilizing diverse technologies 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 supercritical 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 of these 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 the two 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 two 100% duty pumps were se lected with one be ing vari able speed elec tri cal mo tor driven and 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 tions that 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, load fol low ing, and two shift ing), ini tial cap i tal cost and aux il iary power con sump tion as based on boiler feed pump set ef fi ciency over the ex pected 50 year life span of the power station. Key words: Eskom, super criti cal fossil power station, condensate extraction pump, boiler feed pump, vari able speed drive 163

2 van der Westhuizen, W.: Se lect ing the Op ti mised Pump Con fig u ra tion and Drive... INTRODUCTION 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 try and, in clud ing its hydropower, nu clear, and gas tur bine sta tions, has a gen er at ing ca pac ity of MW. Eskom sup plies 90% of the elec tric ity used in South Af rica, gen er ates around two-thirds of the elec tric ity pro duced in the whole of Af rica and is ex tend ing its transmission grid north into neighboring sub-saharan countries [1]. The cur rent elec tric ity us age for South Af rica is MW for morn ing peak and MW for eve ning peak. The peak power de mand is dur ing the win ter months in South Af rica. Eskom has em barked on a ma jor cap i tal ex pen di ture pro gram to ca ter for the grow 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 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 supercritical 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 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 - critical power sta tions. CONDENSATE EXTRACTION PUMPS Con den sate ex trac tion pump con fig u ra tion The following condensate extraction pump (CEP) con fig u ra tions were considered: 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: initial capital costs, piping and instrumentation, including valves, electrical cabling and systems, space required for installation, redundancy, and spares hold ing. * 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 164

3 van der Westhuizen, W.: Selecting the Optimised Pump Configuration and Drive... 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 configuration would be the optimal 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 in smaller and older Eskom power sta tions All existing Eskom power sta tions uti lize a 2 100% CEP con fig u ra tion. The older type power sta tions that don t have any main tur bine by pass sys tems uti lizes two fixed speed CEP s with their de sign point the same as the tur bine max i mum con tin u ous rating (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 than 350 MW are all fixed speed hor i zon tally ar ranged CEP s. The pumps are hor i zon tally split cas ing de signs with a dou ble en try suc tion im pel ler. De pend ing on the flow and head re quire ments, the pumps could be sin gle, two or three stage de sign. The pumps all run at 6 pole speed (N = 980 rpm). The slow speed and dou ble suc tion im pel lers are spe cif i cally con sid ered in or der to sat isfy the NPSH re quire ments of the pumps and due to the low NPSH avail able from the con denser hot-well. Con den sate ex trac tion pumps in stal la tions in newer larger de sign power sta tions On our newer larger plants with an out put of greater than 500 MW, where the con dens ers are larger and the pump flow greater, the con den sate ex trac tion pumps are ver ti cal mul ti stage with the pump el e ment mounted in a suc tion can which is con nected di rectly to the hot-well of the con dens ers. In this way the first stage im pel ler is way down at 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, have main tur bine by pass sys tems. In this case the de sign point A of the pumps are de signed and 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 sate flow 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 main con 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 by throt 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 sign point 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 considered for this design point. 165

4 van der Westhuizen, W.: Selecting the Op ti mised Pump Con fig u ra tion and Drive... With this pump se lec tion and op er at ing mode the best ef fi ciency point (BEP) of the pump is at the de sign point A and not the tur 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 condition during turbine MCR operating 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 the power sta tion. Con den sate ex trac tion pumps for the two new super criti cal power sta tions Figure 1. Condensate extraction pump fixed speed pump curve Dur ing the fea si bil ity stud ies and the tech ni cal clar i fi ca tions meet ings for the equip ment to be sup plied for the two new supercritical power sta tions, the fol low ing op tions for the CEP s were con sid ered: CEP con fig u ra tion, vertically arranged vs. horizontally ar - ranged CEP s, and variable speed vs. fixed speed elec tri cal motor driven CEP s. CEP configuration Based on an eco nomic eval u a tion and us ing all fac tors as listed in the sec tion Con den sate ex trac tion pump con fig u ra tion, it was con cluded that a 2 100% duty CEP configuration would be the optimal CEP con fig u ra tion for the ex pected 50 year life span of a power sta tion. Vertically arranged vs. horizontally arranged CEP s The two new supercritical power sta tions Medupi and Kusile will be uti liz ing an air cooled con denser (ACC) for con dens ing the steam from the main tur bine. In this case the 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 would there 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. 166

5 van der Westhuizen, W.: Selecting the Optimised Pump Configuration and Drive... Both vertically arranged and horizontally arranged CEP con fig u ra tions were considered. The fol low ing ta ble with ar row cod ing was used to help de ter mine which CEP configuration would be optimal 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 for the CEP s the horizontal CEP ar range ment was se lected for the two new supercritical power sta tions, Medupi and Kusile. Vari able speed vs. fixed speed electrical motor driven CEP s Table 1. Technical considerations used to evaluate the vertically and horizontally arranged CEP Ver ti cal Horizontal As ex plained in the Pump de sign sec tion Con den sate ex trac - Installation weights and maintenance tion pumps in stal la tions in newer larger de sign power Pump duty points stations, the CEP's run at a Pump ma te ri als reduced efficiency as well Elec tric mo tors as a throttled operating Spares hold ing condition during turbine MCR operation condi - Positioning of CEP s tions. With the aid of fig. 1, Past Eskom P/S CEP s a vari able speed CEP op - References tion was in ves ti gated and Lo cal man u fac ture considered. The re duced efficiency and throt tled op er - in di cat ing a lower rat ing; in di cat ing higher rat ing at ing con di tions results in un nec es sary aux il iary power us age or wasted en ergy consumption over the life span of the power sta tion. It was there fore im por tant to con sider a vari able speed CEP for the two new supercritical 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 are achieved 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 is com pared with the vari able speed unit. The vari able speed op tion will also give a power sav 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 able speed 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. 167

6 van der Westhuizen, W.: Selecting the Op ti mised Pump Con fig u ra tion and Drive... Fig ure 2. Con den sate ex trac tion pump vari able speed pump curve During normal operation at turbine MCR op er at ing con di tions, the A vari - able speed CEP will run at a re duced speed of N = 1377 rpm, with the main con den sate con trol valve in the fully open po si tion and the ac tual pump dis charge pres sure lower (no throt tling across valve). As soon as the unit is op er ated in a main tur bine by pass operating condition the pump will increase in speed to a speed of N = 1485 rpm with the main con den sate valve still fully open and op er at ing at the re quired LP turbine by pass or de sign point A con di tion. The load of the unit will also be con trolled by the 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 a VSD 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 fixed speed CEP by throt tling the pump to the re quired flow on the fixed speed pump curve. Ta ble 2. CEP power ab sorbed at tur bine MCR operating con di tion for the fixed speed and vari able speed pumps BOILER FEED PUMPS Boiler feed pump con fig u ra tion Foxed speed CEP kw The fol low ing boiler feed Variable speed CEP kw pump (BFP) con fig u ra tions Saving in kw and % kw and 30% saving were con sid ered: 1 100% duty, steam tur bine driven boiler feed pump, and 2 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: initial capital costs, piping and instrumentation, including valves, 168 Power ab sorbed at tur bine MCR op er at ing condition

7 van der Westhuizen, W.: Selecting the Optimised Pump Configuration and Drive... electrical cabling and systems, space required for installation, redundancy, 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 tion gear box links the other side of the high speed mo tor shaft to the booster pump, see fig. 3. This drive op tion will have the high est BFP set ef fi ciency of 81.2% (pumps, mo tor and gear box com bined) with the low est power con sump tion (12.14 MW at tur bine MCR op - erating condition for one BFP set). An other ad van tage would be that the BFP set will also run at very high ef fi ciency and low power con - sump tion at part load con di tions. Fig ure 3. High speed VSD elec tri cally driven mo tor with a speed re duc tion gearbox 169

8 van der Westhuizen, W.: Selecting the Op ti mised Pump Con fig u ra tion and Drive... The big gest dis ad van tage would be the ini tial cap i tal cost of the vari able speed drive 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 high availability and reliability of the complete BFP train. Fig ure 4. Low speed VSD electrically driven mo tor with a speed in crease gearbox Boiler feed pump drive op tion 2 With this drive op tion a low speed vari able speed elec tric mo tor is di rectly con nected to the booster pump. A speed in crease gear box links the other side of the high speed mo tor shaft to the booster pump, see fig. 4. This drive op tion will also have a high BFP set ef fi ciency of 79.9% (pumps, mo tor and gear box com bined), with low power con sump - tion (12.34 MW at tur bine MCR operating condi tion for one BFP set). The BFP set ef fi ciency will not be as high as that for op tion 1 due to the speed in crease gear box losses (driv ing the main pump ~11.2 MW). An ad van tage would be that the BFP set will also run at very high ef fi ciency and 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 that for a high speed vari able speed elec tric mo tor, op tion 2 will be more cost ef fec tive than op 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 drive option and Eskom would re quire ac cess to reference plant and detailed technical infor - ma tion for this drive op tion be fore it would be se ri ously con sid ered. Boiler feed pump drive op tion 3 Fig ure 5. Fixed speed elec tric mo tor with Voith Vorecon vari able speed plan e tary geared fluid drive cou pling This BFP drive op tion uti lizes an ad - vanced fluid drive cou pling Voith Vorecon vari able speed plan e tary gear fluid drive cou - pling, see fig. 5. In this op tion the booster pump will be con nected di rectly to an 19 MW 4 pole dou - ble shaft ex ten sion, 6.6 kv in duc tion mo tor. 170

9 van der Westhuizen, W.: Selecting the Optimised Pump Configuration and Drive... The Voith Vorecon vari able speed plan e tary gear fluid drive cou pling will con nect the other 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 of the 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 pared to op tions 1 or 2. It will also ab sorb more power (12.76 MW, at tur bine MCR operating condition 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 BFP set 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 1 or 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 gear fluid drive cou pling. A ref er ence list was made avail able by Voith listing the installations where 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 application 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 MW at tur bine MCR and 17.2 MW at run-out duty point. Boiler feed pump drive op tion 4 This BFP drive op tion uti lizes a Voith vari able speed fluid drive cou pling. In this op tion the booster pump will be con nected di rectly to an 19 MW 4 pole dou ble shaft ex ten sion, 6.6 kv in duc tion motor. The Voith vari able speed fluid drive cou pling will con nect the other end of the mo tor shaft to the main pump, see fig. 6. The main pump speed will be reg u lated by in creas ing or de creas ing the speed of the Voith vari able speed fluid drive cou pling. This drive op tion will have the low est BFP set ef fi ciency of 70.2% com pared to op - tions 1, 2, or 3. It will also ab sorb more power Fig ure 6. Fixed speed elec tric mo tor with Voith vari able speed fluid drive cou pling 171

10 van der Westhuizen, W.: Selecting the Op ti mised Pump Con fig u ra tion and Drive... (14.05 MW, at tur bine MCR operating condition 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 load con di tions the ef fi ciency of the BFP set will be re duced due to the high slip losses in the fluid 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 plings at the Matla, Duvha, Lethabo, and Tutuka power sta tions. The BFP s which are equipped with the Voith vari able speed fluid drive cou plings at these power sta tions are only used for 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 operating condition and initial capital costs. Ta ble 3. Boiler feed pump drive op tion, ef fi ciency, power ab sorbed, and cap i tal costs BFP drive op tion High speed VSD electric motor with speed reduction gearbox Low speed VSD electric motor with speed increase gearbox Fixed speed motor with Voith Vorecon variable speed planetary geared fluid drive coupling Fixed speed motor with Voith variable speed fluid drive coupling BFP set ef fi ciency [%] Power consumption [kw] Cap i tal cost [%] 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 BFP set ef fi ciency and power ab sorbed, the fi nal de ci sion is de pend ant on the eco nomic eval u - ation results. The new Eskom generation economic evaluation model was used to calculate the levelised costs of the four drive op tions over the ex pected 50 years life span of the power station. The economic evaluation included: capital costs, absorbed power, operating philosophy of power station, availability and reliability of plant, 172

11 van der Westhuizen, W.: Selecting the Optimised Pump Configuration and Drive... aux il iary power costs, and maintenance 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 speed motor with Voith Vorecon vari able speed plan e tary gear fluid drive cou pling fur ther by vis it ing Mannheim power sta tion in Ger many and SES Meliti power sta tion in Greece both of whom uti lize Vorecon BFP drives. The visit was spe cif i cally aimed at gain ing op - erational and maintenance experience from the two users [4]. The two Vorecon s in - stalled in Mannheim Power Sta tion have been in ser vice for more than op er at ing hours since in stal la tion. Based on the high re li abil ity and avail abil ity of the Voith Vorecon s in stalled as BFP drives at Mannheim and SES Meliti Power Sta tions, it can be con cluded that this BFP drive op tion is vi a ble and proven. The se lec tion of the Voith Vorecon BFP drive is there fore the pre ferred and ac cepted boiler feed pump drive for Medupi and Kusile power 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 Kusile power 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 Voith Vorecon hy drau lic drive cou pling. The fi nal con tract signed with Alstom for the 3 50% boiler feed pump sets per unit for the six units at the Medupi power sta tion con sists of the fol low ing equip ment: Sulzer booster pumps HZB , Sulzer main pumps HPT S/29, and ABB elec tric mo tor squir rel cage in duc tion mo tor DQWGH 1000/4-274 and Voith Vorecon RW F 9. ACKNOWLEDGEMENTS 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 rotational speed, [rpm] NPSH net positive suction head, [m] 173

12 van der Westhuizen, W.: Selecting the Op ti mised Pump Con fig u ra tion and Drive... NPSH a net pos i tive suc tion head avail able, [m] NPSH r net pos i tive suc tion head re quired, [m] P power, [kw] Q h flow, [m 3 /h] efficiency, [%] Accronimes ACC air cooled con denser ACCCT air cooled con denser con den sate tank BEP best efficiency point BFP boiler feed pump CEP con den sate ex trac tion pump EE economic evaluation HP high pres sure ID induced draught LP low pres sure MCR maximum continuous rating P/S power sta tion ST steam tur bine TMCR turbine maximum continuous rating VSD vari able speed drive REFERENCES [1] ***, Eskom An nual re port, Eskom, Johannesburg, South Africa, 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, Reference 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 Enterprises Engineering, Eskom, Johannesburg, South Africa,

13 van der Westhuizen, W.: Selecting the Optimised Pump Configuration and Drive... Apstrakt Viqem van der VESTHOJZEN Eskom Enterprajz In`iwering Johanesburg, Ju`noafri~ka Republika Izbor optimalne konfiguracije i na~ina rada pumpi za ispumpavawe kondenzata i pumpi za snabdevawe napojnom vodom za nove Eskom termoelektrane sa natkriti~nim parametrima Kompanija Eskom je otpo~ela kapitalni investicioni pro gram da bi zadovoqila rastu}u potrebu za elektri~nom energijom u ekonomiji Ju`noafri~ke Republike koja se intenzivno razvija zadwih godina. Budu}i razvoj podrazumeva proizvodwu elektri~ne energije uz kori{}ewe razli~itih tehnologija, kao {to su: sagorevawe fosilnih goriva, nuklearne energije, modularni reaktori sa fluidizovanim 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 najve}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 projektovawa 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 kondenzata. 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 konfiguracija 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 re`ima pumpi za snabdevawe vodom koje su bile raspolo`ive prilikom izbora. 175

14 van der Westhuizen, W.: Selecting the Op ti mised Pump Con fig u ra tion and Drive... 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 sagorevaju fosilna goriva, pumpe za ispumpavawe kondenzata, napojne pumpe, elektromotor sa promenqivim brojem obrtaja Author's willem.vdwesthuizen@eskom.co.za 176