CLASSIFICATION OF STEAM TURBINES

Steam turbines may be classified in the following ways:

a) way of energy conversion

1) impulse turbines

· simple, or single-stage

· velocity-stage, Curtis

· pressure-stage, Rateau

· combination pressure- and velocity-stage

2) reaction turbines, Parsons

3) Impulse and reaction combined

 

b) flow direction

1) Axial.

Single axial flow simply means the steam flows in only one direction parallel to the axis of the turbine rotor. Steam enters the forward end of the turbine and exhausts through the after end of the turbine. On a dual flow turbine the steam enters in the center of the turbine rotor and flows both forward and aft simultaneously.

2) Radial.

In a radial-flow turbine, steam flows outward from the shaft to the casing. The unit is usually a reaction unit, having both fixed and moving blades. They are used for special jobs and are more common to European manufacturers, such as de Laval (now ABB).

3) Mixed.

Steam flows along the axis of turbine over blades. These axial flow turbines are well suited for large turbo generators and very commonly used presently.

4) Tangential.

The steam in the nozzle directs steam tangentially into buckets at the periphery of single wheel and steam reverses back and re-enters other bucket at its’ periphery. This is repeated several times as steam follows the helical path. Tangential flow turbines are very robust but less efficient.

5) Helical.

A steam turbine in which the steam is directed tangentially and radially inward by nozzles against buckets milled in the wheel rim; the steam flows in a helical path, reentering the buckets one or more times. Also known as tangential helical-flow turbine.

6) Reentry.

Single Pass, and Re-entry or Repeated Flow. — Practically all turbines are single pass, except the tangential-flow type just described and the re-entry turbine. The blades are set radially, and the steam after passing through them once, following its discharge from the nozzle, is returned by a reversing chamber and again sent through them. Re-entry turbines also fall into the velocity-stage classification.

c) According to number of cylinders

1) Single cylinder turbine

Single casing units are the most basic style where a single casing and shaft are coupled to a generator.

2) Compound

§ tandem- compound

Tandem compound are used where two or more casings are directly coupled together to drive a single generator.

§ cross-compound

A cross compound turbine arrangement features two or more shafts not in line driving two or more generators that often operate at different speeds. A cross compound turbine is typically used for many large applications.

 

d) Number of stages

1) Single stage.

It is also called the de Laval turbine after its inventor. In this type a single rotor is used to which impulse blades are attached. The steam is fed through one or several nozzles which don’t extend completely around the circumference of the rotor, so only part of the blades are impinge at any one time. The pressuredrop in this type occurs mainly in the nozzle and the velocity drops on the blades.

2) Multi-stage.

In multi cylinder turbines the stages are accommodated in more than one cylinder, say two or three. Flow in these can be single flow, double flow, cross flow or reversed flow.

3) Whether there is one or more revolving vanes separated by stationary reversing vanes.

 

e) Rotational speed

 

lowspecific speed	8.5 to 30 range	Pelton turbine
medium specific speed	50-340 range	Francis turbine
highspecific speed	255-860 range	Kaplan turbine

 

f) Inlet steam pressure

- high pressure (p> 6, 5MPa)

- intermediate pressure(2, 5MPa < p< 6, 5MPa)

- low-pressure (p< 2, 5MPa)

 

g) Way of energy utilization

1) condensing

Condensing turbines are most commonly found in electrical power plants. These turbines exhaust steam in a partially condensed state, typically of a quality near 90%, at a pressure well below atmospheric to a condenser.

2) non-condensing

Non-condensing or back pressure turbines are most widely used for process steam applications. The exhaust pressure is controlled by a regulating valve to suit the needs of the process steam pressure. These are commonly found where large amounts of low pressure process steam are available. There is no condenser in such a turbine unit. The steam at the required pressure is fed from the turbine and used for processes and for domestic needs.

3) reheat

Reheat turbines are also used almost exclusively in electrical power plants. In a reheat turbine, steam flow exits from a high pressure section of the turbine and is returned to the boiler where additional superheat is added. The steam then goes back into an intermediate pressure section of the turbine and continues its expansion.

4) extraction

Extracting type turbines are common in all applications. In an extracting type turbine, steam is released from various stages of the turbine, and used for industrial process needs or sent to boiler feedwater heaters to improve overall cycle efficiency. Extraction flows may be controlled with a valve, or left uncontrolled.

5) induction

Induction turbines introduce low pressure steam at an intermediate stage to produce additional power.

 

h) According to method of governing:

    1) Throttle governing turbine.

    2) Nozzle governing turbine.

    3) By pass governing turbine.

 

i) Application

1)power station

2)industrial

3)transport

 

j) Named turbine types

A number of famous names are associated with certain turbine types.

1) Parsons. (Парсонс)A reaction turbine where steam expansion takes place in the fixed and moving blades. A stage is made up of one of each blade type. Half of the stage heat drop occurs in each blade type, therefore providing 50% reaction per stage.

2) Curtis. ( Кертис )An impulse turbine with more than one row of blades to each row of nozzles, i.e. velocity compounded.

3) De Laval. (Лавал ь ).A high-speed impulse turbine which has only one row of nozzles and one row of blades.

4) Rateau.( Рато ) An impulse turbine with several stages, each stage being a row of nozzles and a row of blades, i.e. pressure compounded.

 

 

VOCABULARY

1. turbinewheel – диск турбины

2. turbine - турбина

· action (impulse)-активная турбина

· aft (astern) (back-up) -турбиназаднегохода

· ahead -турбинапереднего хода

· axial(-flow) –осеваятурбина

· back-pressure – турбина с противодавлением

· bucketwheel –турбина с тангенциальным потоком рабочего тела

· combined –комбинированнаятурбина

· compound –двухкорпусная турбина

· cross-compound –   двухвальная (турбина)

· doublereductiongear – турбоагрегат с двухступенчатым редуктором

· double-stage(d) – двухступенчатаятурбина

· dual-flow – двухпоточнаятурбина

· geared – турбина с зубчатой (редукторной) передачей

· low-pressure –турбина низкого давления

· multistage(d) – многоступенчатая турбина

· output – силовая турбина

· pressure (reaction) - реактивнаятурбина

· radialflow - радиально-проточная турбина

· single-cylinder –однокорпуснаятурбина

· tandem-compound–одновальная (турбина)

· twin-shaft – двухвальная турбина

3. blade, vane - лопатка

· movingblades - рабочие лопатки

· fixedblades – неподвижные (направляющие) лопатки

· stationaryblades -неподвижные (направляющие) лопатки

4. heatengine - тепловой двигатель

5. torevolve - вращаться

6. stationarynozzle - неподвижное сопло

7. gland - уплотнение

8. bearing - подшипник

9. usefulwork - полезная работа

10. toconvert - превращать

11. steamjet - паровая струя

12. toderivefrom - произвести от

13. rotation - вращение

14. shippropulsion - движение судна

15. drive - привод

16. increaseinvelocity - увеличение скорости пара

17. gearedunit - турбозубчатый агрегат

18. turbo-electricinstallation - турбоэлектрическая установка

19. nozzle ring -аппаратсопловой

20. dynamic balancing - балансировкадинамическая

21. intake duct - воздухозаборник

22. diaphragm - диафрагма

23. unbalance - дисбаланс

24. diffuser - диффузор

25. combustion chamber – камерасгорания

26. throttle valve - клапандроссельный

27. casing, housing - корпус

28. stage, step -stage, step

29. maneuveringgear - устройство маневренное

30. bladeroot - хвост лопатки 

31. velocity of steam entering - скоростьвходящегопара

32. velocity of steam leaving - скоростьвыходящегопара

33. clearance - зазор

34. exhaust - выход

EXERCISES

1. Find in the text English equivalents for the following:

· активная/реактивная турбина

· одновальная/двухвальная/многовальная турбина,

· многокорпусная/ двухкорпусная /однокорпусная турбина

· однопоточная/двухпоточная турбина

· многоступенчатая /одноступенчатая турбина

· турбина со ступенями давления/со ступенями скорости/комбинированная (со ступенями скорости и давления)

· паровая/газовая турбина

· осевая/радиальная/тангенциальная турбина

· турбина высокого/ среднего/низкого давления

· турбина двойного давления

· турбина переднего/ заднего хода

· турбина с противодавлением /конденсационная /теплофикационная

· предвключенная /приключенная турбина

· турбина осевая/ радиальная/ радиально-осевая

· одноцилиндровая/двухцилиндровая/многоцилиндровая турбина

 

 

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