Dependence of changes in pressure of superheated steam upon reducing heat drop in the throttling regulation of steam turbines

Transcription

1 Enginring Riw, Vol. 35, Issu 2, 25-2, Dpndnc of changs in prssur of suprhatd sta upon rducing hat drop in th throttling rgulation of sta turbins I. Jakoljić * M. Prčić 2 INA d.d., Milutina Barača 26, 5 Rijka, Rpublic of Croatia, 2 Faculty of Enginring, Unirsity of Rijka, Vukoarska 58, 5 Rijka, Rpublic of Croatia ARTICLE INFO Articl history: Rcid: Rcid in risd for: Accptd: Kywords: Sta turbin Rgulation Throttling Turbin powr Introduction Th sta turbin [-4], is a achin of high spd, so it is ncssary to stablish saf rgulation or both th quantity of sta supplid into th turbin and th rotor spd. Th ain turbin rgulation systs includ: - Powr rgulation, - Spd rgulation, - Safty rgulation. Rgulation of sta turbin powr is dfind as a controlld supply of sta ndd to aintain th turbin spd du to th load. Th sta turbin has a spd controllr which nsurs a constant spd whn changing th load and protcts th turbin fro potntial disastrs at an incrasing spd abo th noinal spd of rotation of th rotor. At full ratd powr, sta turbins oprat within iniu spds, and unloadd by th sta turbin rotor spd thy achi axiu oprating spd. Safty rgulation is installd in ry turbin, rgardlss of its application. Each turbin has a dsignd oprating spd of rotation, which is dtrind by th working conditions of th Abstract: Rgulation of th sta turbin can b achid by optial, rliabl and saf opration. Powr rgulation adjusts th opration of th sta turbin load currnt, i.., it changs th thral drop (throttling control) or quantity of sta (nozzl control group). An analysis of th throttling rgulation rals th turbin powr dpndnc on th prssur and th supplid aount of sta, and shows th losss du to a prssur drop in th aforntiond rgulation. turbin. In cas th spd incrass by or than % abo th oprating spd, safty rgulation acts within a tifra fro.2 to.3 sconds, idiatly closing th ain al of inlt sta, and with it also th control als for ach nozzl group. Bsids, safty rgulations protct th turbin fro disturbancs in th prssur and tpratur of th sta, prssur and tpratur of th oil and incrasing ibration. Powr rgulation of sta turbins is prford in following ways: - Changs in hat fall (throttling rgulation), - Changing supplid quantity of sta (rgulation by quantity of sta), - Cobining th first and scond typ. Th throttling rgulation is usd for turbins in th lowr powr rang, whil th rgulation of quantity of sta is usd for turbins with gratr powr loads. As th ost coon for of sta turbin powr rgulation, this articl prsnts a athatical odl of throttling rgulation. Prsntd athatical odl of sta turbin powr rgulation (throttling rgulation) can b usd for all typs of sta turbins (condnsing, backprssur). * Corrsponding author. E-ail addrss: ian.jakoljic@ina.hr

2 26 I. Jakoljić, M. Prčić: Dpndnc of changs in prssur 2 Rgulation of powr sta turbins Through rgulation of th powr turbins, [5-8], th ffct is obtaind by ans of adapting th currnt load. For opration and conoy, rgulation is of ajor iportanc. During an incras or dcras in load, th spd changs only slightly (spd control), or th turbin sustains constant prssur (prssur control sta which gos to th industrial ntwork). Th powr of th turbin is dfind by th xprssion: Pi h, () which dpnds on th quantity of sta, th thortical hat drop and th intrnal usability of th turbin. Sta turbin powr rgulation is diidd into sral typs by changing arious quantitis: h i. Changing th hat fall, i.., throttling, throttling rgulation 2. Changing th quantity of sta, i.., rgulation quantity of sta (rgulation group nozzl or filling nozzl) 3. Cobining th first and scond typ, i.., cobind rgulation 2. Throttling rgulation In th throttling rgulation, th total quantity of sta passs through a throttl al, in which th sta prssur attnuats (dcrass), thus rducing th hat drop in th turbin (Figur ). This rgulation is rarly usd in cass whn th turbin is always undr th sa load, or in cas that th construction of th turbin principl dos not allow anothr solution. Th raction turbin, as a rar xcption, can b rgulatd only by throttling du to full dosing, which is ndd by this typ of turbin. Hat loss drop % Gubitak toplinskog pada 3 bar 2 a Groups of nozzls Grupa sapnica Groups of nozzls 2 Grupa sapnica 2 Groups of nozzls 3 Grupa sapnica 3 d c Groups of nozzls 4 Grupa sapnica 4 b Quantity of sta, t/h Količina par Figur. Dcras in hat loss and prssur changs in th als; th control group of nozzls (solid lin), at throttling control (dashd lin); a and b dcras in hat loss, c prssur in th first stag, d and prssur in front of th nozzl.

3 Enginring Riw, Vol. 35, Issu 2, 25-2, Whil proiding quantitati rgulation with raction turbins, th first stag which is usd for rgulation is prforing lik an action stag. Mathatical xprssions for calculating hat drop in th turbin stag du to throttling ar shown as follows. At full load th adiabatic hat drop is: h h. (2) h kt Throttling to lin h = const. Th prssur p to p, Figur 2, with a lowr load, rducing th adiabatic hat drop to: Th loss aounts to: h h h. (3) kt hg h h hkt h, (4) h s. (5) g T k Th ratio of loss du to throttling and adiabatic initial hat drop is: hg hkt hkt. (6) h h h kt kt Hrin, it is assud that th prssur in th condnsr rains unchangd. Th loss can b isualizd graphically in a diagra as a function of load, or as a function of th prssur bhind th throttl al. To dtrin th rgulation of sta consuption at partial load, it is ncssary to know th distribution of th hat drop of th indiidual stags of th turbin with changs in th quantity of sta that passs through th turbin. According to sta consuption, and by knowing th dpndnc on th flow rat and sta prssur at th inlt of th first stag turbin (aftr th throttl), th lowr th backprssur, th bttr its cur fits to th cur of sta consuption, which rsults in linar charactristics. For a sufficintly strong acuu, it can b said that th aount of sta is approxiatly proportional to th prssur in front of th first guid an channls. Th prssur in th turbin stags is changd proportionally according to th inlt sta prssur and quantity of sta. Th initial throttl prssur rains h =const. If th quantity of sta is proportional to th prssur in front of th turbins, thn it is qual to th ratio Kp k p follows; whr K is constant; or whn T a p p x p h k h kt h k h kt h g T k s s s Figur 2. T-s and h-s diagra of th throttling rgulation.

4 28 I. Jakoljić, M. Prčić: Dpndnc of changs in prssur K k K konst. K. (7) With th throttl, th olu of sta passing through th turbin is constant, and it follows: and K p p K K 2 p p k p K 2 (8). (9) At a rducd load, axiu powr is proidd by th first stags of th turbin. Hat drops in ths stags undrgo alost no changs, whil thr ar significant dcrass in th last stag. Th olu of sta which runs at a rat of on scond through th turbin at all loads is qual to const. Th powr is proportional to th throttl prssur in front of th di first guid an whl. If th noinal load is alid for th quantity of sta and th prssur of sta p, thn for so othr load it is alid for th quantity of sta prssur of sta alus is as follows: p and. Th intrrlation of ths K p p p p. () With th knowldg of sta consuption for a axiu and on lss load, according to th xapl of 5 % or idl, w can apply sta consuption as a function of powr, roughly a straight lin (Figur 3). This has also gin th prssur ahad of th first guid an whl, which ust b throttld for ach load. In addition, using th h-s diagra, th aailabl hat drop can b dtrind for ach load, Figur 3. Oprating paratrs of sta as a function of turbin load for throttling rgulation: c-locity, -spcific olu of sta, p-inlt prssur, -ass flow, A-throttl ara.

5 Enginring Riw, Vol. 35, Issu 2, 25-2, Th following is an xapl of dtrining th cofficint K 2, th intrnal powr of sta turbins, dpnding on th chang in prssur in front of th guid an channl of th condnsing sta turbin with controlld xtraction of sta. Th input paratrs of th calculation ar as follows: p = 2 4 bar, t = 43 C, p k =.225 bar, = 3 36 t/h. K 2 Dpndnc cofficint K 2 on throttl prssur and th quantity of sta Oisnost koficijnta K 2 o tlaku prigušianja i količini sjž par,9,8,7,6,5,4,3,2, kg/s 4 bar 38 bar 36 bar 34 bar 32 bar 3 bar 28 bar 26 bar 24 bar 22 bar 2 bar Figur 4. Dpndnc of cofficint K 2, throttl prssur and th quantity of inlt sta. P, kw Dpndnc on prssur throttl powr and quantity of inlt sta Oisnost snag o tlaku prigušianja i količini ulazn par kg/s 4 bar 38 bar 36 bar 34 bar 32 bar 3 bar 28 bar 26 bar 24 bar 22 bar 2 bar Figur 5. Intrnal powr of th turbin in dpndnc of throttl prssur and quantity of inlt sta.

6 2 I. Jakoljić, M. Prčić: Dpndnc of changs in prssur Th ai of th calculation is to show th changs in th cofficint K 2, and th dpndnc upon th throttl prssur and changs of th inlt quantity of sta by rducing th prssur of 4 bar in intrals of 2 bar to a final prssur of 2 bar whil changing th inlt quantity of sta fro 3 t/h, with intrals of 3 t/h, to a axiu flow of 36 t/h. Th rsults ar shown graphically in Figur 4. Th loss du to throttl prssur fro 4 bar to 2 bar is shown in Tabl. Figur 5 prsnts th powr dpndnc on throttl prssur and th quantity of inlt sta. Fro th diagra, it is obious that th diation has gratr and gratr strngth with an incrasing quantity of sta. Tabl. Th losss du to throttl prssur Throttl prssur loss 38 bar,994,6% 36 bar,987,24% 34 bar,98,93% 32 bar,973 2,68% 3 bar,965 3,49% 28 bar,956 4,36% 26 bar,946 5,3% 24 bar,936 6,37% 22 bar,924 7,52% 2 bar,9 8,8% 3 Conclusion This papr instigatd rgulation by throttling th sta. W prsntd an oriw of th ipact of th cofficint K 2 on intrnal powr of a sta turbin, by changing th prssur in corrlation with th prssur and quantity of sta at th turbin inlt. Th rsults ga insight into ths rlationships which furthr show that with an incrasing sta prssur, th diation fro th initial sta prssur and th changd sta prssur is linarly incrasing. In addition, thr is a loss anifstd by throttling that aris in th rang fro.6 % to 8.8%. Th highr th throttl prssur is, th highr th loss, i.., th lowr th intrnal powr of th turbin. Rfrncs [] Milr; J.: Sta and Gas Turbins, Part II, Tchnical Books, Zagrb, 965. [2] Tirli, E., Martinoić, D.: Marin sta turbins, Mariti Collg in Rijka, Rijka, 2. [3] Zitann, C.: Dsign and construction of sta turbins, Scintific Book, Bograd, 95. [4] Traupl, W.: Thrisch Turboaschinn, 2 Aufl., Springr-Vrlag, Brlin/Hidlbrg/Nw York, 968. [5] Staniša, B., Prlc, Z., Jakoljić I.: Efficincy Analysis of a Sta Turbin Cognration Plant with Capacity of 5,7 MW l, Enginring Riw, Vol. 3, No., July 2, Pags: [6] Forsthoffr, W. E. B.: Forsthoffr s Roating Equipnt Handbooks, 23 Sta turbin inlt sta rgulation, Volu : Principls of Rotating Equipnt, Elsir 25. [7] Daiani, L., Pini Prato A.: Siulation of a Powr Rgulation Syst for Sta Powr Plants, Enrgy Procdia, Vol. 45, 24, Pags: [8] Dulau, M., Bica, D.: Siulation of Spd Sta Turbin Control Syst, Procdia Tchnology, Vol. 2, 24, Pags: