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Friday, 12 December 2014

Classification of Steam Turbines

Classification of Steam Turbines Points : Classification of Steam Turbines Steam turbines can be classified into unusual categories base on various point as given below. (a) Based on the blade flow passage In steam turbine thermal energy presented by steam is changed into kinetic energy which in turn produces driving thrust on shaft. Base upon rotor blades the blade flow way can be of (i) constant cross section area type as of blade inlet to outlet, or, (ii) varying cross section area type as of blade inlet to outlet. Turbines have former type blading are call impulse turbines as later type are in reaction turbines. (b) Based on cylinder flow arrangement Steam turbines can be classify based upon flow arrangement into following types.
(i) Single flow single casing turbine
(ii) Double flow single casing turbine
(iii) Cross flow compound turbine by single flow
(iv) Cross flow compound turbine by double flow
(v) Triple cross flow compound turbine by double flow

Single cylinder turbines are one which contain all stages enclosed in one cylinder as in multi cylinder turbines the stages are contain in more than one cylinders, say two or three. Flow in these can single flow, double flow, cross flow or reversed flow.
(c) Based on direction of flow The radial flow turbines developed through B.F. Ljungstorm of Sweden and this turbine incorporate two shafts end to end and can be of correctly small sizes. Radial flow turbines can be start rapidly and so well suitable for peak load and use as stand by turbine or peak load turbines. These are too termed as Ljungstrom turbines. The radial flow turbines steam is inserting in middle by shaft and steam flows radially outwards through the consecutive moving blades positioned concentrically. In radial flow turbines there are no fixed blades so pressure drop occur in moving blade passage. Concentric moving blades rings are planned to move in opposed directions.

In tangential flow turbines nozzle direct steam imaginatively into buckets at edge of single wheel and steam reverses back and re-enters other bucket at its edge. This is recurring some times as steam follows the helical path. Tangential flow turbines are extremely robust but fewer efficient.

In axial flow turbines steam flows along axis of turbine more blades. These axial flow turbines are well suitable for large turbo generators and extremely usually use currently.
(d) Based on number of stages Steam turbines can too be classify base upon number of stages in steam turbines that is depending upon the amount of heat drop. It can be:
(i) Single stage turbine
(ii) Multi stage turbine.

The single stage turbines contain expansion occurring in single stage as in multi stage turbines the expansion occurs in extra than one stages of turbine. As expansion occur in two stages it is call double stage turbine and through expansion occurring in three stages it is call triple stage turbine.
(e) Based on the application of turbine Depending upon purpose the steam turbine can be classify as under:
(i) Condensing turbine
(ii) Non-condensing turbine
(iii) Back pressure turbine
(iv) Pass out turbine

The condensing steam turbines are those in which steam exit turbine enters into condenser. Such type of steam turbines allow for recirculation of condensate leaving condenser. Also the pressure at end of extension can be lowered a lot under atmospheric pressure as expanded steam is discarded into condenser where vacuum can be maintained. Condensing turbines are commonly use in thermal power plants.

Non-condensing steam turbines are those in which steam exit turbine is discarded to atmosphere and not to condenser as in case of condense turbine.

Back pressure turbines refuse steam at a pressure greatly over the atmospheric pressure and steam exit turbine by considerably high pressure can be use for some other purpose for example heating or running small condense turbines.

Pass out turbines are those in which definite amount of steam is always extracted for purpose of heating and allowing remain steam to pass during pressure control valve into low pressure section of turbine. Pressure control valve and control gear is necessary so as to keep speeds of turbine and pressure of steam stable irrespective of variations of power and heating loads.
(f) Based on speed of turbine Steam turbines can be classify base upon steam turbine as low down speed, normal speed and high speed turbines as particular under.
(i) Low speed steam turbine.
(ii) Normal speed steam turbine.
(iii) High speed steam turbine.

The low speed turbines are these steam turbines which run at speed under 3000 rpm. Normal speed steam turbines are these turbines which run at speed of on 3000 rpm as high speed steam turbines are the one which run at over 3000 rpm.
(g) Based on pressure in steam turbines Steam turbines can also be classify based upon the inlet pressure of steam turbine as follows:
(i) Low pressure steam turbine
(ii) Medium pressure steam turbine
(iii) High pressure steam turbine
(iv) Super pressure steam turbine

Low pressure steam turbines contain pressure of inlet steam below 20 kg/cm2 as medium pressure steam turbines contain steam inlet pressure among 20 kg/cm2 near 40 kg/cm2. High pressure steam turbines contain steam inlet pressure lying between 40 kg/cm2 to 170 kg/cm2 while turbines having inlet steam pressure more than 170 kg/cm2 are call super pressure steam turbines.

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