Thesis (PhD)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: The steam-side side operation of a practical air-cooled steam condenser is
investigated using a combination of CFD, numerical, analytical and experimental
methods. Particular attention is directed towards the vapor flow distribution in the
primary condensers and dephlegmator performance.
Analysis of the vapor flow in the distributing manifold, connecting the steam
turbine exhaust to the air-cooled heat exchangers, highlights the importance of
careful design of the guide vanes in the manifold bends and junctions. Improved
guide vane design and configuration can reduce the steam-side pressure drop over
the manifold and improve the vapor flow distribution, which may be beneficial to
condenser operation.
The vapor flow in the primary condensers is shown to exhibit a non-uniform
distribution amongst the heat exchanger tubes. The vapor flow distribution is
strongly linked to the distribution of tube inlet loss coefficients through the heat
exchanger bundles. The non-uniform flow distribution places an additional
demand on dephlegmator performance, over and above the demands of row
effects in the case of multi-row primary condenser bundles. Row effects are
shown to account for as much as 70 % of available dephlegmator capacity in this
case. Simultaneously, inlet loss coefficient distributions can account for up to
30 % of dephlegmator capacity. In some situations then, the dephlegmator is fully
utilized under ideal operating conditions and there is no margin of safety to cope
with non-ideal operation of the primary condensers. The upstream regions of the
primary condensers are therefore exposed to a high risk of undesirable noncondensable
gas accumulation. Reduced dephlegmator capacity due to insufficient
ejector performance may further compound this problem. Single-row primary
condenser bundles eliminate row effects and thereby significantly reduce the
demands on dephlegmator performance. The use of such bundles in the
dephlegmator would also measurably reduce ejector loading. In light of the
findings of this study, it is recommended that single-row bundles be considered as
the primary option for future air-cooled condenser applications. A hybrid (dry/wet) dephlegmator concept is analysed and shown to be able to
provide measurably enhanced dephlegmator performance when operating in wet
mode, while consuming only a small amount of water. The enhanced
dephlegmator cooling translates to an increase in total air-cooled condenser
capacity of up to 30 % at high ambient temperatures in this case. The benefit of
this enhanced cooling capacity to steam turbine output may be significant. The
hybrid dephlegmator concept therefore offers a simple, cost-effective and
sustainable solution to the issue of reduced air-cooled condenser performance
during hot periods. Careful design of the first and second stage bundle
configurations in the hybrid dephlegmator is necessary to avoid flooding in the
first stage during wet operation of the second. Furthermore, the slightly poorer
dry-operation performance of the hybrid dephlegmator results in increased risk of
non-condensable gas accumulation in multi-row primary condensers. Again,
single-row primary condenser bundles would lay rest to such concerns. / AFRIKAANSE OPSOMMING: Die bedryf aan die stoom-kant van ʼn praktiese lugverkoelde-stoomkondensor
word ondersoek met behulp van 'n kombinasie van berekeningsvloeimeganika,
numeriese, analitiese en eksperimentele metodes. ʼn Spesifieke fokus word geplaas
op die dampvloeiverspreiding in die primêre kondensors asook die deflegmatorwerksverrigting.
Ontleding van die damp vloei in die verdeelspruitstuk, wat die uitlaat van die
stoomturbine aan die lugverkoelde-stoomkondensor koppel, beklemtoon die
belangrikheid van noukeurige ontwerp van die leilemme in die spruitstukdraaie en
aansluitings. Verbeterde leilemontwerp en opstelling kan die drukval aan die
stoom-kant van die draaie en aansluitings verminder en die
dampvloeiverspreiding verbeter. Dit kan gevolglik lei tot verbeterde
werksverrigting van die kondensor.
Die studie toon dat ʼn nie-eenvormige dampvloeiverspreiding in die
warmteruilerbuise van die primêre kondensors bestaan. Die verspreiding van
buisinlaat-verlieskoëffisiënte deur die bundels van die warmteruiler is sterk
afhanklik van die voorgenome dampvloeiverspreiding. Die nie-eenvormige
vloeiverspreiding veroorsaak 'n groter aanvraag na deflegmator-werksverrigting,
bo-en-behalwe nog vereistes van ry-effekte in die geval waar multi-ry-bundels vir
primêre kondensors gebruik word. Ry-effekte is verantwoordelik vir so veel as
70 % van die beskikbare deflegmator kapasiteit. Terselfdertyd kan die
verspreiding van inlaat-verlieskoëffisiënte verantwoordelik wees vir tot 30 % van
die deflegmator kapasiteit. In sommige gevalle is die deflegmator dus ten volle
aangewend onder ideale bedryfstoestande, en bestaan daar geen band van
veiligheid om nie-ideale werksverrigting van die primêre kondensor te hanteer
nie. Sekere dele van die stroom-op primêre kondensors word dus blootgestel aan
'n hoë risiko vir die opbou van ongewenste nie-kondenseerbare gasse. Verder kan
‘n vermindering in deflegmator kapasiteit, weens onvoldoende werksverrigting
van die vakuumpompe, dié probleem vererger. Enkel-ry-bundels vir primêre
kondensors vermy ry-effekte en lei sodoende tot ʼn aansienlike vermindering in die aanvraag na deflegmator-werksverrigting. Die gebruik van sulke bundels in die
deflegmator sou die vakuumpomplas ook meetbaar verminder. Uit die bevindinge
van hierdie studie word dit aanbeveel dat enkel-ry bundels beskou word as die
primêre opsie vir toekomstige lugverkoelde-kondensor aansoeke.
’n Konsep vir ’n hibriede-deflegmator (droog/nat) word ontleed. Die studie toon
dat, deur hierdie konsep in die nat-modus te gebruik, ’n meetbare verbetering in
deflegmator-werksverrigting gesien kan word, ten koste van net ʼn klein
hoeveelheid waterverbruik. Die verbetering in verkoelingsvermoë van die
deflegmator beteken ʼn toename van tot 30 % in die totale verkoelingsvermoë van
die lugverkoelde-kondensor gedurende periodes wanneer hoë
omgewingstemperature heersend is. Die voordeel van hierdie verbeterde
verkoelingsvermoë op die werksuitset van die stoomturbine kan beduidend wees.
Die konsep vir ’n hibriede-deflegmator bied dus 'n eenvoudige, koste-effektiewe
en volhoubare oplossing vir warm atmosferiese periodes, wanneer die
lugverkoelde-kondensor se verkoelingsvermoë afneem. Noukeurige ontwerp van
die eerste en tweede fase bundelkonfigurasies in die hibriede-deflegmator is nodig
om oorstroming in die eerste fase, tydens nat werking van die tweede fase, te
verhoed. Verder veroorsaak die effens swakker werksverrigting, gedurende die
bedryf van die hibriede-deflegmator in die droog-modus, ʼn verhoogde risiko vir
die opbou van nie-kondenseerbare gasse in multi-ry primêre kondensors.
Weereens sal enkel-ry-bundels in primêre kondensors hierdie probleem oplos.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/85731 |
| Date | 12 1900 |
| Creators | Owen, Michael Trevor Foxwell |
| Contributors | Kroger, D. G., Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | xxi, multiple numbered pages : ill. |
| Rights | Stellenbosch University |
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